Journal of Neurochemistry - Aktuelle Forschungsartikel
Aktuelle Forschungsartikel: Neurochemie
Die Urheberrechte und Veröffentlichungsrechte der in der nachfolgenden Liste aufgeführten Fachartikel liegen bei den jeweiligen Verlagen, die am Ende des jeweiligen Artikels als Quelle genannt werden. Diese sind auch für die Inhalte verantwortlich.
Weitere aktuelle Fachartikel von Chemiezeitschriften ähnlicher Thematik finden Sie im Navigationsmenue links.
Hinweise zur Veröffentlichung Ihrer Pressemitteilung unter Internetchemie.Info entnehmen Sie bitte der entsprechenden Info-Seite.
Diese Seite können Sie mit folgender Tastenkombination nach Stichwörtern durchsuchen: <STRG> und <F>.
Hier aufgeführte Forschungsartikel:
Journal of Neurochemistry - Herausgeber: Wiley
JNC ist eine führende Quelle für die Forschung zu allen Aspekte der Neurowissenschaften, mit besonderem Schwerpunkt auf die molekularen und zellulären Aspekte des Nervensystems, der Pathogenese von neurologischen Erkrankungen und die Entwicklung der Krankheit spezifischer Biomarker.
J. Neurochem. (2012) 120, 795–805.AbstractAmyloid-? peptide (A?), which is generated by the ?- and ?-secretase-mediated proteolysis of ?-amyloid precursor protein (APP), plays an important role in the pathogenesis of Alzheimer’s disease (AD). We recently reported that prostaglandin E2 (PGE2) stimulates the production of A? through both EP2 and EP4 receptors and that activation of the EP4 receptor stimulates A? production through endocytosis and activation of ?-secretase. We here found that transgenic mice expressing mutant APP (APP23) mice showed a greater or lesser apparent cognitive deficit when they were crossed with mice lacking EP2 or EP4 receptors, respectively. Mice lacking the EP4 receptor also displayed lower levels of A? plaque deposition and less neuronal and synaptic loss than control mice. Oral administration of a specific EP4 receptor antagonist, AE3-208 to APP23 mice, improved their cognitive performance, as well as decreasing brain levels of A? and suppressing endocytosis and activation of ?-secretase. Taken together, these results suggest that inhibition of the EP4 receptor improves the cognitive function of APP23 mice by suppressing A? production and reducing neuronal and synaptic loss. We therefore propose that EP4 receptor antagonists, such as AE3-208, could be therapeutically beneficial for the prevention and treatment of AD.The purpose of this study is to know the role of EP2 and EP4 receptors in cognitive performance in APP23 mice, model mice for Alzheimer’s disease. Results suggest that inhibition of the EP4 receptor improves the cognitive function of APP23 mice and that EP4 receptor antagonists, such as AE3-208, are therapeutically beneficial for the prevention and treatment of AD.
J. Neurochem. (2012) 120, 721–731.AbstractNogo-66 is a 66-amino-acid-residue extracellular domain of Nogo-A, which plays a key role in inhibition neurite outgrowth of central nervous system through binding to the Nogo-66 receptor (NgR) expressed on the neuron. Recent studies have confirmed that NgR is also expressed on the surface of macrophages/microglia in multiple sclerosis, but its biological effects remain unknown. In the present study, our results demonstrated that Nogo-66 triggered microglia anti-adhesion and inhibited their migration in vitro, which was mediated by NgR. We also assessed the roles of small GTP (glycosyl phosphatidylinositol)-binding proteins of the Rho family as the downstream signal transducers on the microglia adhesion and mobility induced by Nogo-66. The results showed that Nogo-66 activated RhoA and reduced the activity of Cdc42 in the meanwhile, which further triggered the anti-adhesion and migration inhibition effects to microglia. Nogo-66 inhibited microglia polarization and membrane protrusion formation, thus might eventually contribute to the decreasing capability of cell mobility. Taken together, the Nogo-66/NgR pathway may modulate neuroinflammation via mediating microglia adhesion and migration in addition to its role in neurons. Better understanding the relationship between Nogo-66/NgR and neuroinflammation may help targeting NgR for treating central nervous system diseases related with inflammation.This article explores the role of NgR expressed on microglia in the regulation of microglia behavior. Results demonstrated that Nogo-66 triggered microglia anti-adhesion and inhibited their migration in vitro, which was mediated by NgR and its downstream signal transducers RhoA and Cdc42. The finding revealed the Nogo-66/NgR pathway may modulate neuroinflammation via mediating microglia adhesion and migration, and blocking NgR may be beneficial to promote microglia migrating out injury site. This may help targeting NgR for treating central nervous system diseases related with inflammation.
J. Neurochem. (2012) 120, 741–751.AbstractSynaptic remodeling has been postulated as a mechanism underlying synaptic plasticity and cell adhesion molecules are thought to contribute to this process. We examined the role of nectin-1 ectodomain shedding on synaptogenesis in cultured rat hippocampal neurons. Nectins are Ca2+-independent immunoglobulin-like adhesion molecules, involved in cell-cell adherens junctions. Herein, we show that the processing of nectin-1 occurs by multiple endoproteolytic steps both in vivo and in vitro. We identified regions containing two distinct cleavage sites within the ectodomain of nectin-1. By alanine scanning mutagenesis, two point mutations that disrupt nectin-1 ectodomain cleavage events were identified. Expression of these mutants significantly alters the density of dendritic spines. These findings suggest that ectodomain shedding of nectin-1 regulates dendritic spine density and related synaptic functions.Ectodomain shedding of nectin-1 regulates the maintenance of dendritic spine density What is the role of secretase-mediated ectodomain shedding of synaptic cell adhesion molecules in synaptogenesis? The expression of shedding refractory nectin-1 mutants dramatically increased the density of dendritic spines. Our data suggest that ectodomain shedding of synaptic adhesion molecules by sheddases is a regulator of synaptic plasticity through its modulation of synaptic connections.
J. Neurochem. (2012) 120, 842–849.AbstractEndocannabinoids are neuromodulatory lipids that mediate the central and peripheral neural functions. Endocannabinoids have demonstrated their anti-proliferative, anti-angiogenic and pro-apoptotic properties in a series of studies. In the present study, we investigated the levels of two major endocannabinoids, anandamide and 2-arachidonylglycerol (2-AG), and their receptors, CB1 and CB2, in human low grade glioma (WHO grade I-II) tissues, high grade glioma (WHO grade III-IV) tissues, and non-tumor brain tissue controls. We also measured the expressions and activities of the enzymes responsible for anandamide and 2-AG biosynthesis and degradation, that is, N-acylphosphatidylethanolamine-hydrolysing phospholipase D (NAPE-PLD), fatty acid amide hydrolase (FAAH), monoacylglycerol lipase (MGL), and diacylglycerol lipase-alpha (DGL), in the same samples. Liquid chromatography–mass spectometry analysis showed that the levels of anandamide decreased, whereas the levels of 2-AG increased in glioma tissues, comparing to the non-tumor controls. The expression levels and activities of NAPE-PLD, FAAH and MGL also decreased in glioma tissues. Furthermore, quantitative-PCR analysis and western-blot analysis revealed that the expression levels of cananbinoid receptors, CB1 and CB2, were elevated in human glioma tissues. The changes of anandamide and 2-AG contents in different stages of gliomas may qualify them as the potential endogenous biomarkers for glial tumor malignancy.Endocannabinoids are neuromodulatory lipids mediating anti-proliferation, anti-angiogenesis and pro-apoptosis processes. To understand the role of endocannabinoid system in tumorigenesis, we demonstrated that endocananbinoid signals, CB1 and CB2, were elevated in human gliomas. We concluded that the changes of anandamide and 2-AG contents in different stages of gliomas might serve as the potential biomarkers for glial tumor malignancy.
J. Neurochem. (2012) 120, 710–720.AbstractAstrocytes respond to trauma by stimulating inflammatory signaling. In studies of cerebral ischemia and spinal cord injury, astrocytic signaling is mediated by the cytokine receptor glycoprotein 130 (gp130) and Janus kinase (Jak) which phosphorylates the transcription factor signal transducer and activator of transcription-3 (STAT3). To determine if STAT3 is activated after traumatic brain injury (TBI), adult male Sprague–Dawley rats received moderate parasagittal fluid-percussion brain injury or sham surgery, and then the ipsilateral cortex and hippocampus were analyzed at various post-traumatic time periods for up to 7 days. Western blot analyses indicated that STAT3 phosphorylation significantly increased at 30 min and lasted for 24 h post-TBI. A significant increase in gp130 and Jak2 phosphorylation was also observed. Confocal microscopy revealed that STAT3 was localized primarily within astrocytic nuclei. At 6 and 24 h post-TBI, there was also an increased expression of STAT3 pathway-related genes: suppressor of cytokine signaling 3, nitric oxide synthase 2, colony stimulating factor 2 receptor ?, oncostatin M, matrix metalloproteinase 3, cyclin-dependent kinase inhibitor 1A, CCAAT/enhancer-binding protein ?, interleukin-2 receptor ?, interleukin-4 receptor ?, and ?-2-macroglobulin. These results clarify some of the signaling pathways operative in astrocytes after TBI and demonstrate that the gp130-Jak2-STAT3 signaling pathway is activated after TBI in astrocytes.Is STAT3 activation during traumatic brain injury pro- or anti-inflammatory? STAT3 activation can either worsen or improve recovery after spinal cord injury or ischemia, depending upon the cell type and signaling pathways involved. Here, we used fluid-percussion brain injury, a clinically relevant model of traumatic brain injury, and found that STAT3 was rapidly activated and translocated to nuclei within astrocytes. This resulted in a stimulation of both pro- and anti-inflammatory gene expression.
J. Neurochem. (2012) 120, 732–740.AbstractSeveral prior investigations of Alzheimer’s disease (AD) patients have indicated naturally occurring autoantibodies against amyloid-? (A?) species are produced. Although many studies have focused on the relative concentrations or binding affinities of autoantibodies against A?-related proteins in AD and aging, data regarding their functional properties are limited. It is generally believed that these antibodies act to aid in clearance of A?. However, as antibodies which bind to A? also typically bind to the parent amyloid precursor protein (APP), we reasoned that certain A?-targeting autoantibodies may bind to APP thereby altering its conformation and processing. Here we show for the first time, that naturally occurring A?-reactive autoantibodies isolated from AD patients, but not from healthy controls, promote ?-secretase activity in cultured cells. Furthermore, using monoclonal antibodies to various regions of A?, we found that antibodies generated against the N-terminal region, especially A?1-17, dose dependently promoted amyloidogenic processing of APP via?-secretase activation. Thus, this property of certain autoantibodies in driving A? generation could be of etiological importance in the development of sporadic forms of AD. Furthermore, future passive or active anti-A? immunotherapies must consider potential off-target effects resulting from antibodies targeting the N-terminus of A?, as co-binding to the corresponding region of APP may actually enhance A? generation.Autoreactive A? may be deleteriousAlthough many studies have focused on the relative concentrations or binding affinities of autoantibodies against A?-related proteins in AD and aging, data regarding their functional properties are limited. We show that naturally occurring A?-reactive autoantibodies isolated from AD patients, but not from healthy age-matched controls, promote amyloidogenic APP processing. Such results suggest a novel etiology for sporadic AD because antibodies binding to N-terminal A? regions, such as (a) A?17-26 or (b) A?1-17, also bind extracellular corresponding regions of the parent (APP) molecule and demonstrate a functional capacity to alter APP processing in a manner promoting A? generation.
J. Neurochem. (2012) 120, 818–829.AbstractIn a retinal ischemic ex vivo model, we have reported protective effects of somatostatin (SRIF) receptor 2 (sst2). As an ischemic condition not only causes cell death but also induces a vascular response, we asked whether vascular endothelial growth factor (VEGF) is altered in this model and whether its expression, release or localization are affected by sst2 activation. Ex vivo retinas of wild-type (WT) and sst1 KO mice (which over-express sst2) were incubated in ischemic conditions with SRIF, octreotide (OCT) or a VEGF trap. Ischemia in WT retinas caused increase of VEGF release and decrease of VEGF mRNA. Both effects were counteracted by SRIF or OCT. VEGF immunoreactivity was in retinal neurons and scarcely in vessels. Ischemia caused a significant shift of VEGF immunoreactivity from neurons to vessels. The increase of vascular VEGF was reduced in sst1 KO retinas and in WT retinas treated with SRIF or OCT. VEGF trap also limited this increase, demonstrating that vascular VEGF was of extracellular origin. Together, the data show a VEGF response to ischemia, in which VEGF released by damaged neurons reaches the retinal capillaries. The activation of sst2 protects neurons from ischemic damage, thereby limiting VEGF release and the VEGF response.In retinal disease, ischemia causes cell death. We investigated whether ischemia may also initiate pathological angiogenesis mediated by vascular endothelial growth factor (VEGF). This study identified a rapid VEGF response to ischemia, in which VEGF is released by damaged neurons and is taken up by endothelial cells of retinal capillaries. Activation of somatostatin subtype 2 receptor (sst2) is known to reduce cell death. Similarly, we found that the VEGF response is also limited by sst2.
J. Neurochem (2012) 120, 699–709.AbstractL1 cell adhesion molecule (L1CAM), an adhesion/signaling protein encoded by a gene target of the transcription repressor RE-1-Silencing Transcription factor (REST), is expressed in two alternatively spliced isoforms. The full-length isoform, typical of low-REST neural cells, plays key roles in survival/migration, outgrowth/fasciculation/regeneration of axons, synaptic plasticity; the isoform missing two mini-exons, abundant in a few high-REST non-neural cells, maintains some effect on migration and proliferation. To investigate whether and how L1CAM alternative splicing depends on REST we used neural cell models expressing low or high levels of REST (PC12, SH-SY5Y, differentiated NT2/D1 and primary neurons transduced or not with REST). The short isoform was found to rise when the low-REST levels of neural cells were experimentally increased, while the full-length isoform increased in high-REST cells when the repressor tone was attenuated. These results were due to Nova2, a neural cell-specific splicing factor shown here to be repressed by REST. REST control of L1CAM occurs therefore by two mechanisms, transcription and alternative splicing. The splicing mechanism, affecting not only L1CAM but all Nova2 targets (?7% of brain-specific splicing, including the mRNAs of other adhesion and synaptic proteins) is expected to be critical during development and important also for the structure and function of mature neural cells.Neural mRNA splicing, a new function of REST. Differential mRNA splicing is a key mechanism of brain specificity. Here, we show that REST, the master factor of neural cells, controls the transcription of the Nova2 gene and thus the splicing, whether neural and highly effective or non-neural, of the adhesion protein L1CAM. Most likely the same mechanism operates on many other spliced products specific of the brain.
J. Neurochem. (2012) 120, 684–698.AbstractcAMP induces neurite outgrowth in the rat pheochromocytoma cell line 12 (PC12). In particular, di-butyric cAMP (db-cAMP) induces a greater number of primary processes with shorter length than the number induced by nerve growth factor (NGF). db-cAMP up- and down-regulates GTP-RhoA levels in PC12 cells in a time-dependent manner. Tat-C3 toxin stimulates neurite outgrowth, whereas lysophosphatidic acid (LPA) and constitutively active (CA)-RhoA reduce neurite outgrowth, suggesting that RhoA inactivation is essential for the neurite outgrowth from PC12 cells stimulated by cAMP. In this study, the mechanism by which RhoA is inactivated in response to cAMP was examined. db-cAMP induces phosphorylation of RhoA and augments the binding of RhoA with Rho guanine nucleotide dissociation inhibitor (GDI). Moreover, RhoA (S188D) mimicking phosphorylated RhoA induces greater neurite outgrowth than RhoA (S188A) mimicking dephosphorylated form does. Additionally, db-cAMP increases GTP-Rap1 levels, and dominant negative (DN)-Rap1 and DN-Rap-dependent RhoGAP (ARAP3) block neurite outgrowth induced by db-cAMP. DN-p190RhoGAP and the Src inhibitor PP2 suppress neurite outgrowth, whereas transfection of c-Src and p190RhoGAP cDNAs synergistically stimulate neurite outgrowth. Taken together, RhoA is inactivated by phosphorylation of itself, by p190RhoGAP which is activated by Src, and by ARAP3 which is activated by Rap1 during neurite outgrowth from PC12 cells in response to db-cAMP.RhoA inactivation is required for neurite outgrowth of PC12 cells in response to cAMP. Hereby, we elucidated the mechanism of RhoA inactivation by cAMP: the phosphorylation of RhoA and the activation of p190RhoGAP and Rap1/ARAP3 participate in RhoA inactivation. Because neuronal regeneration is induced by RhoA inactivation, Rho inhibitors are emerging as the therapeutic reagents to promote neuronal regeneration.
J. Neurochem. (2012) 120, 752–764.AbstractObesity can be associated with systemic low-grade inflammation that contributes to obesity-related metabolic disorders. Recent studies raise the possibility that hypothalamic inflammation contributes to the pathogenesis of diet-induced obesity (DIO), while another study reported that obesity decreases the expression of pro-inflammatory cytokines in spleen. The following study examines the hypothesis that obesity suppresses the splenic synthesis of the anti-inflammatory cytokine, interleukin (IL)-10, thereby resulting in chronic hypothalamic inflammation. The results showed that due to oxidative stress or apoptosis, the synthesis of splenic IL-10 was decreased in DIO when compared with non-obesity rats. Splenectomy (SPX) accelerated DIO-induced inflammatory responses in the hypothalamus. Interestingly, SPX suppressed the DIO-induced increases in food intake and body weight and led to a hypothalamic pro-inflammatory state that was similar to that produced by DIO, indicating that hypothalamic inflammation exerts a dual effect on energy metabolism. These SPX-induced changes were inhibited by the systemic administration of IL-10. Moreover, SPX had no effect on hypothalamic inflammatory responses in IL-10-deficient mice. These data suggest that spleen-derived IL-10 plays an important role in the prevention of hypothalamic inflammation and may be a therapeutic target for the treatment of obesity and hypothalamic inflammation.Obesity may be associated with a systemic low-grade inflammation that affects obesity-related metabolic disorders. Splenectomy (SPX)-induced inflammatory changes in the hypothalamus were inhibited by the systemic administration of IL-10 and SPX had no effect on hypothalamic inflammatory responses in the IL-10-deficient mice. Thus, spleen-derived IL-10 may be a key to treat the pathogenesis of obesity including hypothalamic inflammation.
J. Neurochem. (2012) 120, 644–659.AbstractS100B is a calcium-binding protein concentrated in glial cells, although it has also been detected in definite extra-neural cell types. Its biological role is still debated. When secreted, S100B is believed to have paracrine/autocrine trophic effects at physiological concentrations, but toxic effects at higher concentrations. Elevated S100B levels in biological fluids (CSF, blood, urine, saliva, amniotic fluid) are thus regarded as a biomarker of pathological conditions, including perinatal brain distress, acute brain injury, brain tumors, neuroinflammatory/neurodegenerative disorders, psychiatric disorders. In the majority of these conditions, high S100B levels offer an indicator of cell damage when standard diagnostic procedures are still silent. The key question remains as to whether S100B is merely leaked from injured cells or is released in concomitance with both physiological and pathological conditions, participating at high concentrations in the events leading to cell injury. In this respect, S100B levels in biological fluids have been shown to increase in physiological conditions characterized by stressful physical and mental activity, suggesting that it may be physiologically regulated and raised during conditions of stress, with a putatively active role. This possibility makes this protein a candidate not only for a biomarker but also for a potential therapeutic target.
J. Neurochem. (2012) 120, 765–778.AbstractExposure to psychostimulants results in neuroadaptive changes of the mesencephalic dopaminergic system including morphological reorganization of dopaminergic neurons. Increased dendrite arborization and soma area were previously observed in primary cultures of mesencephalic dopaminergic neurons after 3-day exposure to dopamine agonists via activation of D3 autoreceptors (D3R). In this work, we showed that cocaine significantly increased dendritic arborization and soma area of dopaminergic neurons from E12.5 mouse embryos by activating phosphorylation of extracellular signal-regulated kinase (ERK) and thymoma viral proto-oncogene (Akt). These effects were dependent on functional D3R expression because cocaine did not produce morphological changes or ERK/Akt phosphorylation neither in primary cultures of D3R mutant mice nor following pharmacologic blockade with D3R antagonists SB-277011-A and S-33084. Cocaine effects on morphology and ERK/Akt phosphorylation were inhibited by pre-incubation with the phosphatidylinositol 3-kinase inhibitor LY294002. These observations were corroborated in vivo by morphometrical assessment of mesencephalic dopaminergic neurons of P1 newborns exposed to cocaine from E12.5 to E16.5. Cocaine increased the soma area of wild-type but not of D3R mutant mice, supporting the translational value of primary culture. These findings indicate a direct involvement of D3R and ERK/Akt pathways as critical mediators of cocaine-induced structural plasticity, suggesting their involvement in psychostimulant addiction.Psychostimulants promote structural plasticity in neurons of the terminal fields of the mesocorticolimbic dopaminergic system, but it is unclear if morphological reorganization occurs also in the neurons that originate these projections. When primary cultures of mesencephalic dopaminergic neurons from the mouse embryos were exposed to cocaine, a dopamine D3 autoreceptor (D3R)-dependent activation of ERK and PI3K-Akt pathways occurred, leading to a later expansion of dendrite arborization and soma size. In utero exposure to cocaine also increased the soma area of dopaminergic neurons, but only in newborns of wild-type mice, not in D3KO. Our results indicate that D3R is a necessary mediator of the cocaine-dependent structural remodeling of dopaminergic neurons via ERK and PI3K-Akt activation, suggesting a possible mechanism of action for the anti-addictive behavioral effects of D3 antagonists.
J. Neurochem (2012) 120, 667–683.AbstractcAMP-dependent protein kinase (PKA) plays a critical role in nervous system development by modulating sonic hedgehog and bone morphogenetic protein signaling. In the current studies, P19 embryonic carcinoma cells were neuronally differentiated by expression of the proneural basic helix-loop-helix transcription factor Ascl1. After expression of Ascl1, but prior to expression of neuronal markers such as microtubule associated protein 2 and neuronal ?-tubulin, P19 cells demonstrated a large, transient increase in both mRNA and protein for the endogenous protein kinase inhibitor (PKI)?. PKI?-targeted shRNA constructs both reduced the levels of PKI? expression and blocked the neuronal differentiation of P19 cells. This inhibition of differentiation was rescued by transfection of a shRNA-resistant expression vector for the PKI? protein, and this rescue required the PKA-specific inhibitory sequence of the PKI? protein. PKI? played a very specific role in the Ascl1-mediated differentiation process as other PKI isoforms were unable to rescue the deficit conferred by shRNA-mediated knockdown of PKI?. Our results define a novel requirement for PKI? and its inhibition of PKA during neuronal differentiation of P19 cells.
J. Neurochem (2012) 120, 806–817.AbstractRecent studies suggest that l-3,4 dihydroxyphenylalanine (l-DOPA)-induced dyskinesia (LID), a severe complication of conventional l-DOPA therapy of Parkinson’s disease, may be caused by dopamine (DA) release originating in serotonergic neurons. To evaluate the in vivo effect of a 5-HT1A agonist [(±)-8-hydroxy-2-(dipropylamino) tetralin hydrobromide, 8-OHDPAT] on the l-DOPA-induced increase in extracellular DA and decrease in [11C]raclopride binding in an animal model of advanced Parkinson’s disease and LID, we measured extracellular DA in response to l-DOPA or a combination of l-DOPA and the 5-HT1A agonist, 8-OHDPAT, with microdialysis, and determined [11C]raclopride binding to DA receptors, with micro-positron emission tomography, as the surrogate marker of DA release. Rats with unilateral 6-hydroxydopamine lesions had micro-positron emission tomography scans with [11C]raclopride at baseline and after two pharmacological challenges with l-DOPA + benserazide with or without 8-OHDPAT co-treatment. Identical challenge regimens were used with the subsequent microdialysis concomitant with ratings of LID severity. The baseline increase of [11C]raclopride-binding potential (BPND) in lesioned striatum was eliminated by the l-DOPA challenge, while the concurrent administration of 8-OHDPAT prevented this l-DOPA-induced displacement of [11C]raclopride significantly in lesioned ventral striatum and near significantly in the dorsal striatum. With microdialysis, the l-DOPA challenge raised the extracellular DA in parallel with the emergence of strong LID. Co-treatment with 8-OHDPAT significantly attenuated the release of extracellular DA and LID. The 8-OHDPAT co-treatment reversed the l-DOPA-induced decrease of [11C]raclopride binding and increase of extracellular DA and reduced the severity of LID. The reversal of the effect of l-DOPA on [11C]raclopride binding, extracellular DA and LID by 5-HT agonist administration is consistent with the notion that part of the DA increase associated with LID originates in serotonergic neurons.l-DOPA induced dopamine release from serotonergic neurons activate dopamine D2 receptors in Parkinson’s disease The effect of a 5-HT1A agonist on the l-DOPA induced decrease in [11C]raclopride binding was evaluated in an unilateral lesioned animal model of Parkinson’s disease (PD). The baseline increase of [11C]raclopride binding in lesioned striatum was eliminated by the l-DOPA challenge, while the concurrent administration of 8-OHDPAT prevented this. This study concludes that evaluating the effect(s) of pharmacological challenges by one or multiple drugs may be a feasible goal in human subjects with PD.
J. Neurochem. (2012) 120, 660–666.AbstractDeposition of the amyloid-? (A?) peptide in senile plaques and cerebral A? angiopathy (CAA) can be stimulated in A?-precursor protein (APP)-transgenic mice by the intracerebral injection of dilute brain extracts containing aggregated A? seeds. Growing evidence implicates a prion-like mechanism of corruptive protein templating in this phenomenon, in which aggregated A? itself is the seed. Unlike prion disease, which can be induced de novo in animals that are unlikely to spontaneously develop the disease, previous experiments with A? seeding have employed animal models that, as they age, eventually will generate A? lesions in the absence of seeding. In the present study, we first established that a transgenic rat model expressing human APP (APP21 line) does not manifest endogenous deposits of A? within the course of its median lifespan (30 months). Next, we injected 3-month-old APP21 rats intrahippocampally with dilute Alzheimer brain extracts containing aggregated A?. After a 9-month incubation period, these rats had developed senile plaques and CAA in the injected hippocampus, whereas control rats remained free of such lesions. These findings underscore the co-dependence of agent and host in governing seeded protein aggregation, and show that cerebral A?-amyloidosis can be induced even in animals that are relatively refractory to the spontaneous origination of parenchymal and vascular deposits of A?.Jump-starting amyloid in resistant brains. Cerebral amyloid-? (A?) deposition can be seeded in the brains of susceptible animals by brain extracts containing aggregated A?, but whether A? aggregation can be seeded in resistant models is uncertain. Using Alzheimer brain extracts, we induced A? deposition in the hippocampal formation of A?-precursor protein-transgenic rats that do not normally generate senile plaques. Our findings highlight the role of corruptive protein templating in the initiation of A? amyloidosis, and show that this process can be actuated even in a relatively resistant animal model.
J. Neurochem. (2012) 120, 830–841.AbstractWe previously reported the involvement of conventional protein kinase C (cPKC) ?II, ?, novel PKC (nPKC) ? and their interacting proteins in hypoxic pre-conditioning (HPC)-induced neuroprotection. In this study, the large-scale miRNA microarrays and bioinformatics analysis were used to determine the differentially expressed miRNAs and their PKC-isoform specific gene network in mouse brain after HPC and 6 h middle cerebral artery occlusion (MCAO). We found 4 up-regulated and 13 down-regulated miRNAs in the cortex of HPC mice, 26 increased and 39 decreased gene expressions of miRNAs in the peri-infarct region of 6 h MCAO mice, and 11 up-regulated and 22 down-regulated miRNAs in the peri-infarct region of HPC and 6 h MCAO mice. Based on Diff Score, 19 differentially expressed miRNAs were identified in HPC and 6 h MCAO mouse brain. Then the miRNA-gene-network of 19 specified miRNAs target genes of cPKC?II, ? and nPKC?-interacting protein was predicted by using bioinformatics analysis of genome databases. Furthermore, the down-regulated miR-615-3p during HPC had a detrimental effect on the oxygen-glucose deprivation (OGD)-induced N2A cell injury. These results suggested that the identified 19 miRNAs, notably miR-615-3p, might target these genes of cPKC?II, ? and nPKC?-interacting proteins involved in HPC-induced neuroprotection.Differentially expressed miRNAs in cerebral cortex of mice following hypoxic pre-conditioning (HPC) and middle cerebral artery occlusion (MCAO)-induced focal cerebral ischemia Differentially expressed miRNAs were identified in cerebral cortex of mice following HPC and MCAO. The miRNA-gene-network of these 19 specified miRNAs target genes of cPKC?II, ? and nPKC?-interacting proteins involved in HPC-induced neuroprotection was predicted using bioinformatics analyses of genome databases. Furthermore, the down-regulated miR-615-3p during HPC had a detrimental effect on the oxygen-glucose deprivation (OGD)-induced N2A cell injury.
J. Neurochem. (2012) 120, 779–794.AbstractMu opioid receptors are densely expressed in the patch compartment of striatum and contribute to methamphetamine-induced patch-enhanced gene expression and stereotypy. To further elucidate the role of mu opioid receptor activation in these phenomena, we examined whether activation of mu opioid receptors would enhance methamphetamine-induced stereotypy and prodynorphin, c-fos, arc and zif/268 expression in the patch and/or matrix compartments of striatum, as well as the impact of mu opioid receptor activation on the relationship between patch-enhanced gene expression and stereotypy. Male Sprague–Dawley rats were intrastriatally infused with d-Ala(2)-N-Me-Phe(4),Gly(5)-ol]enkephalin (DAMGO; 1 ?g/?L), treated with methamphetamine (0.5 mg/kg) and killed at 45 min or 2 h later. DAMGO augmented methamphetamine-induced zif/268 mRNA expression in the patch and matrix compartments, while prodynorphin expression was increased in the dorsolateral patch compartment. DAMGO pre-treatment did not affect methamphetamine-induced arc and c-fos expression. DAMGO enhanced methamphetamine-induced stereotypy and resulted in greater patch versus matrix expression of prodynorphin in the dorsolateral striatum, leading to a negative correlation between the two. These findings indicate that mu opioid receptors contribute to methamphetamine-induced stereotypy, but can differentially influence the genomic responses to methamphetamine. These data also suggest that prodynorphin may offset the overstimulation of striatal neurons by methamphetamine.Think twice before mixing your psychostimulants with opiates. Mu opioid receptors are densely expressed in the striatum, a major target nucleus for the actions of methamphetamine. We examined whether activation of these receptors would alter methamphetamine-induced behaviour and gene expression. Mu opioid receptor activation intensified methamphetamine-induced stereotypy and gene expression in the striatum, indicating that the mu opioid system can enhance the behavioural and genomic responses to methamphetamine.
J. Neurochem. (2012) 10.1111/j.1471-4159.2012.07671.xAbstractImpairment of cognitive functions including hippocampus-dependent spatial learning and memory affects nearly half of the aged population. Age-related cognitive decline is associated with synaptic dysfunction that occurs in the absence of neuronal cell loss, suggesting that impaired neuronal signaling and plasticity may underlie age-related deficits of cognitive function. Expression of myelin-associated inhibitors (MAIs) of synaptic plasticity, including the ligands myelin-associated glycoprotein, neurite outgrowth inhibitor A, and oligodendrocyte myelin glycoprotein, and their common receptor, Nogo-66 receptor, was examined in hippocampal synaptosomes and Cornu ammonis area (CA)1, CA3 and dentate gyrus subregions derived from adult (12–13 months) and aged (26–28 months) Fischer 344 × Brown Norway rats. Rats were behaviorally phenotyped by Morris water maze testing and classified as aged cognitively intact (n = 7–8) or aged cognitively impaired (n = 7–10) relative to adults (n = 5–7). MAI protein expression was induced in cognitively impaired, but not cognitively intact, aged rats and correlated with cognitive performance in individual rats. Immunohistochemical experiments demonstrated that up-regulation of MAIs occurs, in part, in hippocampal neuronal axons and somata. While a number of pathways and processes are altered with brain aging, we report a coordinated induction of myelin-associated inhibitors of functional and structural plasticity only in cognitively impaired aged rats. Induction of MAIs may decrease stimulus-induced synaptic strengthening and structural remodeling, ultimately impairing synaptic mechanisms of spatial learning and memory and resulting in cognitive decline.Aged rats with impaired spatial learning and memory over-express myelin-associated inhibitors (MAIs). MAIs suppress neuronal plasticity, which is dysregulated with age-related cognitive decline. We demonstrate that expression of MAG, Nogo-A, OMgp and the NgR1 receptor is up-regulated in the hippocampus of aged rats with impaired spatial learning and memory, but not in their age-matched cognitively intact counterparts. Increased MAI signaling may underlie age-related deficits of hippocampal cognition by inhibiting structural and functional synaptic plasticity throughout the hippocampus.
J. Neurochem. (2012) 10.1111/j.1471-4159.2012.07670.xAbstractSeizures that are resistant to standard medications remain a major clinical problem. One underutilized option for patients with medication-resistant seizures is the high-fat, low-carbohydrate ketogenic diet. The diet received its name based on the observation that patients consuming this diet produce ketone bodies (e.g., acetoacetate, ?-hydroxybutyrate, and acetone). Although the exact mechanisms of the diet are unknown, ketone bodies have been hypothesized to contribute to the anticonvulsant and antiepileptic effects. In this review, anticonvulsant properties of ketone bodies and the ketogenic diet are discussed (including GABAergic and glutamatergic effects). Because of the importance of ketone body metabolism in the early stages of life, the effects of ketone bodies on developing neurons in vitro also are discussed. Understanding how ketone bodies exert their effects will help optimize their use in treating epilepsy and other neurological disorders.
J. Neurochem. (2012) 10.1111/j.1471-4159.2012.07667.xAbstractIn this study, we report that spiro[imidazo[1,2-a]pyridine-3,2-indan]-2(3H)-one (ST101; previously coded as ZSET1446) targets T-type voltage-gated calcium channels in mediating improved cognition in the CNS. We prepared rat somatosensory cortical and hippocampal slices, treated them with 0.01 to 100 nM ST101, and performed immunoblotting and electrophysiological analyses using various voltage-gated calcium channel (VGCC) inhibitors. Treatment of rat cortical slices with a range of ST101 concentrations significantly increased calcium/calmodulin-dependent protein kinase II (CaMKII) autophosphorylation following a bell-shaped dose–response curve, with 0.1 nM ST101 representing the maximally effective concentration. protein kinase C? autophosphorylation was also significantly increased by 0.1 nM ST101 treatment. ST101 treatment had a moderate effect on CaMKII autophosphorylation but no effect on hippocampal protein kinase C? autophosphorylation in slice preparations. Consistent with increased cortical CaMKII autophosphorylation, AMPA-type glutamate receptor subunit 1 (Ser-831) phosphorylation as a CaMKII post-synaptic substrate was significantly increased by treatment with 0.1–1 nM ST101, whereas phosphorylation of the pre-synaptic substrate synapsin I (Ser-603) remained unchanged. Notably, enhanced CaMKII autophosphorylation seen following 0.1 nM ST101 treatment was significantly inhibited by pre-treatment with 1 ?M mibefradil, a T-type VGCC inhibitor, but not with N-type (?-conotoxin), P/Q-type (?-agatoxin) or L-type (nifedipine) VGCC inhibitors. Similarly, 0.1 nM ST101 significantly potentiated long-term potentiation in cortical but not hippocampal slices. Enhanced long-term potentiation in cortical slices was totally inhibited by 1 ?M mibefadil treatment. Finally, whole-cell patch-clamp analysis of Neuro2A cells over-expressing recombinant human CaV3.1 (?1G) T-channels and treated with 0.1 nM ST101 showed significant increases in T-type VGCC currents. These results indicate that T-type VGCCs are direct molecular targets for the novel cognitive enhancer ST101, a potential Alzheimer disease therapeutic.Novel Alzheimer disease therapeutics targeting for T-type voltage-gated Ca2+ channels We successfully developed novel cognitive enhancer, ST101. ST101 is under investigation of clinical trial phase 2 as Alzheimer disease therapeutics. We firstly discovered that ST101 stimulates Ca2+ current through T-type voltage-gated calcium channels, thereby promoting Ca2+/clmodulin-dependent protein kinase II (CaMKII) activity in the cortical and hippocampal neurons. Therefore, T-type voltage-gated calcium channels are unique and crucial targets for Alzheimer disease therapeutics.
J. Neurochem. (2012) 10.1111/j.1471-4159.2012.07666.xAbstract20-Hydroxyeicosatetraenoic acid (20-HETE) is a cytochrome P450 metabolite of arachidonic acid that that contributes to infarct size following focal cerebral ischemia. However, little is known about the role of 20-HETE in global cerebral ischemia or neonatal hypoxia-ischemia (H-I). The present study examined the effects of blockade of the synthesis of 20-HETE with N-hydroxy-N?-(4-n-butyl-2-methylphenyl) formamidine (HET0016) in neonatal piglets after H-I to determine if it protects highly vulnerable striatal neurons. Administration of HET0016 after H-I improved early neurological recovery and protected neurons in putamen after 4 days of recovery. HET0016 had no significant effect on cerebral blood flow. cytochrome P450 4A immunoreactivity was detected in putamen neurons, and direct infusion of 20-HETE in the putamen increased phosphorylation of Na+,K+-ATPase and NMDA receptor NR1 subunit selectively at protein kinase C-sensitive sites but not at protein kinase A-sensitive sites. HET0016 selectively inhibited the H-I induced phosphorylation at these same sites at 3 h of recovery and improved Na+,K+-ATPase activity. At 3 h, HET0016 also suppressed H-I induced extracellular signal-regulated kinase 1/2 activation and protein markers of nitrosative and oxidative stress. Thus, 20-HETE can exert direct effects on key proteins involved in neuronal excitotoxicity in vivo and contributes to neurodegeneration after global cerebral ischemia in immature brain.Little is known about the role of 20-HETE in neonatal hypoxia-ischemia. Here, blockade of 20-HETE synthesis with HET0016 in newborn piglets after H-I had no significant effect on cerebral blood flow. However, it inhibited the PKC-dependent NMDA receptor and Na, K-ATPase phosphorylation, and improved Na, K-ATPase activity. Thus, 20-HETE can exert direct effects on proteins involved in neuronal excitotoxicity in immature brain.
J. Neurochem. (2012) 10.1111/j.1471-4159.2012.07664.xAbstractNeuroglial cells define brain homeostasis and mount defense against pathological insults. Astroglia regulate neurogenesis and development of brain circuits. In the adult brain, astrocytes enter into intimate dynamic relationship with neurons, especially at synaptic sites where they functionally form the tripartite synapse. At these sites, astrocytes regulate ion and neurotransmitter homeostasis, metabolically support neurons and monitor synaptic activity; one of the readouts of the latter manifests in astrocytic intracellular Ca2+ signals. This form of astrocytic excitability can lead to release of chemical transmitters via Ca2+-dependent exocytosis. Once in the extracellular space, gliotransmitters can modulate synaptic plasticity and cause changes in behavior. Besides these physiological tasks, astrocytes are fundamental for progression and outcome of neurological diseases. In Alzheimer’s disease, for example, astrocytes may contribute to the etiology of this disorder. Highly lethal glial-derived tumors use signaling trickery to coerce normal brain cells to assist tumor invasiveness. This review not only sheds new light on the brain operation in health and disease, but also points to many unknowns.
J. Neurochem. (2012) 10.1111/j.1471-4159.2012.07665.xAbstractKainate receptors (KARs) have been described as modulators of synaptic transmission at different synapses. However, this role of KARs has not been well characterized in the amygdala. We have explored the effect of kainate receptor activation at the synapse established between fibers originating at medial geniculate nucleus and the principal cells in the lateral amygdala. We have observed an inhibition of evoked excitatory postsynaptic currents (eEPSCs) amplitude after a brief application of KARs agonists KA and ATPA. Paired-pulse recordings showed a clear pair pulse facilitation that was enhanced after KA or ATPA application. When postsynaptic cells were loaded with BAPTA, the depression of eEPSC amplitude observed after the perfusion of KAR agonists was not prevented. We have also observed that the inhibition of the eEPSCs by KARs agonists was prevented by protein kinase A but not by protein kinase C inhibitors. Taken together our results indicate that KARs present at this synapse are pre-synaptic and their activation mediate the inhibition of glutamate release through a mechanism that involves the activation of protein kinase A.Presynaptic kainate receptor-mediated modulation of glutamate release in the lateral nucleus of the amygdala We wanted to determine the role of kainate receptors at thalamo-lateral amygdala synapses. The activation of presynaptic kainate receptors at these synapses inhibits glutamate release through a mechanism that involves the activation of protein kinase A. This action of kainate receptors could be involved in fear conditioning learning.
J. Neurochem. (2012) 10.1111/j.1471-4159.2012.07661.xAbstractChronic nicotine and oral contraceptive (NOC) exposure caused significant loss of hippocampal membrane-bound estrogen receptor-beta (ER-?) in female rats compared with exposure to nicotine alone. Mitochondrial ER-? regulates estrogen-mediated mitochondrial structure and function; therefore, investigating the impact of NOC on mitochondrial ER-? and its function could help delineate the harmful synergism between nicotine and OC. In this study, we tested the hypothesis that NOC-induced loss of mitochondrial ER-? alters the oxidative phosphorylation system protein levels and mitochondrial respiratory function. This hypothesis was tested in hippocampal mitochondria isolated from female rats exposed to saline, nicotine, OC or NOC for 16 days. NOC decreased the mitochondrial ER-? protein levels and reduced oxygen consumption and complex IV (CIV) activity by 34% and 26% compared with saline- or nicotine-administered groups, respectively. We also observed significantly low protein levels of all mitochondrial-encoded CIV subunits after NOC as compared with the nicotine or saline groups. Similarly, the silencing of ER-? reduced the phosphorylation of cyclic-AMP response element binding protein, and also reduced levels of CIV mitochondrial-encoded subunits after estrogen stimulation. Overall, these results suggest that mitochondrial ER-? loss is responsible for mitochondrial malfunction after NOC.The severity of ischemic brain damage is greater in females simultaneously exposed to nicotine and oral contraceptives (NOC) than to nicotine alone. NOC inhibits mitochondrial estrogen receptor-beta signaling and mitochondrial functions in the brain. These findings distinguish the effects of nicotine from its combination with oral contraceptives in the female brain.
J. Neurochem. (2012) 10.1111/j.1471-4159.2012.07660.xAbstractThis study describes the effects of long-chain fatty acids on inflammatory signaling in cultured astrocytes. Data show that the saturated fatty acid palmitic acid, as well as lauric acid and stearic acid, trigger the release of TNF? and IL-6 from astrocytes. Unsaturated fatty acids were unable to induce cytokine release from cultured astrocytes. Furthermore, the effects of palmitic acid on cytokine release require Toll-like receptor 4 rather than CD36 or Toll-like receptor 2, and do not depend on palmitic acid metabolism to palmitoyl-CoA. Inhibitor studies revealed that pharmacologic inhibition of p38 or p42/44 MAPK pathways prevents the pro-inflammatory effects of palmitic acid, whereas JNK and PI3K inhibition does not affect cytokine release. Depletion of microglia from primary astrocyte cultures using the lysosomotropic agent l-leucine methyl ester revealed that the ability of palmitic acid to trigger cytokine release is not dependent on the presence of microglia. Finally, data show that the essential ?-3 fatty acid docosahexaenoic acid acts in a dose-dependent manner to prevent the actions of palmitic acid on inflammatory signaling in astrocytes. Collectively, these data demonstrate the ability of saturated fatty acids to induce astrocyte inflammation in vitro. These data thus raise the possibility that high levels of circulating saturated fatty acids could cause reactive gliosis and brain inflammation in vivo, and could potentially participate in the reported adverse neurologic consequences of obesity and metabolic syndrome.The good fat, the bad fat, and the brain Obesity and metabolic syndrome detrimentally affect the brain through unknown mechanisms. This paper demonstrates the ability of saturated fatty acids to trigger cytokine release from cultured astrocytes, and the ability of ?-3 unsaturated fatty acids to block cytokine release. These data suggest that circulating saturated fatty acids could cause brain inflammation and thus participate in the adverse neurologic consequences of metabolic syndrome
J. Neurochem. (2012) 10.1111/j.1471-4159.2012.07658.xAbstractCell adhesion molecules of the immunoglobulin superfamily (IgCAMs) have been shown to modulate growth factor signaling and follow complex trafficking pathways in neurons. Similarly, several growth factors, including members of the neurotrophin family, undergo axonal retrograde transport that is required to elicit their full signaling potential in neurons. We sought to determine whether IgCAMs that enter the axonal retrograde transport route co-operate with neurotrophin signaling. We identified activated leukocyte cell adhesion molecule (ALCAM), a protein involved in axon pathfinding and development of the neuromuscular junction, to be associated with an axonal endocytic compartment that contains neurotrophins and their receptors. Although ALCAM enters carriers that are transported bidirectionally in motor neuron axons, it is predominantly co-transported with the neurotrophin receptor p75NTR toward the cell body. ALCAM was found to specifically potentiate nerve growth factor (NGF)-induced differentiation and signaling. The extracellular domain of ALCAM is both necessary and sufficient to potentiate NGF-induced neurite outgrowth, and its homodimerization is required for this novel role. Our findings indicate that ALCAM synergizes with NGF to induce neuronal differentiation, raising the possibility that it functions not only as an adhesion molecule but also in the modulation of growth factor signaling in the nervous system.ALCAM: a seasoned traveller in neuronsNeurons rely on a network of long-range trafficking pathways for their differentiation and survival, and neurotrophin-containing signaling endosomes play a fundament role in this process. Unexpectedly, these signaling endosomes contain unusual cargoes, such as several cell adhesion molecules, including ALCAM. By studying this process, we found a novel role for ALCAM in the nervous system, where its extracellular domain can modulate the strength of neurotrophin signaling. This discovery not only contributes to the body of evidence on the interplay between neurotrophin signaling and cell adhesion, but may also have implications in neurodegenerative pathologies where trophic signaling is attenuated, or in cancer where trophic signaling is enhanced.
J. Neurochem. (2012) 10.1111/j.1471-4159.2012.07657.xAbstractC3 ADP-ribosyltransferase is a valuable tool to study Rho-dependent cellular processes. In the current study we investigated the impact of enzyme-deficient peptides derived from Clostridium botulinum C3 transferase in the context of neuronal process elongation and branching, synaptic connectivity, and putative beneficial effects on functional outcome following traumatic injury to the CNS. By screening a range of peptidic fragments, we identified three short peptides from C3bot that promoted axon and dendrite outgrowth in cultivated hippocampal neurons. Furthermore, one of these fragments, a 26-amino acid peptide covering the residues 156–181 enhanced synaptic connectivity in primary hippocampal culture. This peptide was also effective to foster axon outgrowth and re-innervation in organotypical brain slice culture. To evaluate the potential of the 26mer to foster repair mechanisms after CNS injury we applied this peptide to mice subjected to spinal cord injury by either compression impact or hemisection. A single local administration at the site of the lesion improved locomotor recovery. In addition, histological analysis revealed an increased serotonergic input to lumbar motoneurons in treated compared with control mice. Pull-down assays showed that lesion-induced up-regulation of RhoA activity within the spinal cord was largely blocked by C3bot peptides despite the lack of enzymatic activity.Short cut to regeneration: small C3bot peptides help neurons to regrow The current study was undertaken to determine the shortest peptide fragment derived from Clostridium botulinum C3 transferase to foster neuronal regenerative growth. Here, we show that short enzyme-deficient C3 peptides, especially a 26 amino acid fragment, can act to improve neuronal outgrowth and to enhance motor regeneration after spinal cord injury. Therefore, we consider treatment with C3 peptides as a very promising strategy for future goals to improve recovery from devastating neuronal injuries including damage to the spinal cord. This seems to be all the more important since no specific neuronal treatment regimes exist so far. Cross-section of mouse spinal cord at darkfield illumination. Graph shows results of C3bot 26mer on motor recovery following spinal cord injury. Small micrograph depicts serotonergic boutons contacting spinal motoneurons.
J. Neurochem. (2012) 10.1111/j.1471-4159.2012.07653.xAbstractIn the mammalian brain, the ?7 nicotinic and NMDA receptor antagonist kynurenic acid is synthesized by irreversible enzymatic transamination of the tryptophan metabolite l-kynurenine. d-kynurenine, too, serves as a bioprecursor of kynurenic acid in several organs including the brain, but the conversion is reportedly catalyzed through oxidative deamination by d-aminoacid oxidase. Using brain and liver tissue homogenates from rats and humans, and conventional incubation conditions for kynurenine aminotransferases, we show here that kynurenic acid production from d-kynurenine, like the more efficient kynurenic acid synthesis from l-kynurenine, is blocked by the aminotransferase inhibitor amino-oxyacetic acid. In vivo, focal application of 100 ?M d-kynurenine by reverse microdialysis led to a steady rise in extracellular kynurenic acid in the rat striatum, causing a 4-fold elevation after 2 h. Attesting to functional significance, this increase was accompanied by a 36% reduction in extracellular dopamine. Both of these effects were duplicated by perfusion of 2 ?M l-kynurenine. Co-infusion of amino-oxyacetic acid (2 mM) significantly attenuated the in vivo effects of d-kynurenine and essentially eliminated the effects of l-kynurenine. Thus, enzymatic transamination accounts in part for kynurenic acid synthesis from d-kynurenine in the brain. These results are discussed with regard to implications for brain physiology and pathology.Transamination of D-kynurenine generates kynurenic acid in rat and human brainLike the natural tryptophan metabolite l-kynurenine, d-kynurenine might be transaminated to kynurenic acid (KYNA), an astrocyte-derived neuromodulator with possible links to human brain diseases. This KYNA synthesis route was demonstrated using brain and liver tissue homogenate from rats and humans, and confirmed in the rat striatum in vivo. Endogenous d-kynurenine, perhaps stemming from microorganisms, might constitute an alternate source of KYNA in the mammalian brain.
J. Neurochem. (2012) 10.1111/j.1471-4159.2012.07652.xAbstractAquaporin-4, a predominant water channel in the brain, is specifically expressed in astrocyte endfeet and plays a central role in water homeostasis, neuronal activity, and cell migration in the brain. It has two dominant isoforms called M1 and M23, whose mRNA is driven by distinct promoters located upstream of exons 0 and 1 of the aquaporin-4 gene, respectively. To identify cis-acting elements responsible for the astrocyte-specific transcription of M1 mRNA, the promoter activity of the 5?-flanking region upstream of exon 0 in primary cultured mouse astrocytes was examined by luciferase assay, and sequences, where nuclear factors bind, were identified by electrophoretic mobility shift assay. An astrocyte-specific activity enhancing transcription from the M1 promoter was observed within ?2 kb from the transcriptional start sites of M1 mRNA. At least five elements clustered within the 286-bp region were found to function as a novel astrocyte-specific enhancer. Among the five elements, a consensus sequence of Pit-1/Oct/Unc-86 (POU) transcription factors was indispensable to the astrocyte-specific enhancer since disruption of the POU motif completely abolished the enhancer activity in astrocytes. However, the POU motif alone had little activity, indicating the requirement for cooperation with other upstream elements to exert full enhancer activity.Aquaporin-4 is a water channel specifically expressed in astrocytes in the brain. In this study, a 286-bp region in the 5?-flanking region of the mouse aquaporin-4 gene was found to enhance promoter activity specifically in astrocytes. Clustered five cis-elements, including a consensus sequence of POU transcription factors, are cooperatively involved in the transcription. This study demonstrates a novel mechanism for transcriptional regulation in astrocytes.
J. Neurochem. (2012) 10.1111/j.1471-4159.2012.07651.xAbstractThe repellent semaphorin 3A (Sema3A) causes growth cone turning or collapse by triggering cytoskeletal rearrangements and detachment of adhesion sites. Growth cone detachment is dependent on eicosanoid activation of protein kinase C epsilon (PKC?), but the characterization of the phospholipase A2 (PLA2) that releases arachidonic acid (AA) for eicosanoid synthesis has remained elusive. Here, we show, in rat dorsal root ganglion (DRG) neurons, that Sema3A stimulates PLA2 activity, that Sema3A-induced growth cone turning and collapse are dependent on the release of AA, and that the primary PLA2 involved is the group IV ? isoform (GIVA). Silencing GIVA expression renders growth cones resistant to Sema3A-induced collapse, and GIVA inhibition reverses Sema3A-induced repulsion into attraction. These studies identify a novel, early step in Sema3A-signaling and a PLA2 necessary for growth cone repulsion and collapse.Critical Role for Phospholipase A2 in Growth Cone Repulsion. The goal is to advance our understanding of the molecular mechanism that triggers growth cone detachment during repellent-induced turning and collapse. We report that semaphorin 3A stimulation of Group IVA phospholipase A2 (GIVA PLA2) is necessary for growth cone turning and collapse. The data introduce GIVA PLA2 and the generation of arachidonic acid into the semaphorin 3A-activated signaling pathway that regulates growth cone adhesion.
J. Neurochem. (2012) 10.1111/j.1471-4159.2012.07649.xAbstractChronic intake of high-fat (HF) diet is known to alter brain neurotransmitter systems that participate in the central regulation of food intake. Dopamine (DA) system changes in response to HF diet have been observed in the hypothalamus, important in the homeostatic control of food intake, as well as within the central reward circuitry [ventral tegmental area (VTA), nucleus accumbens (NAc), and pre-frontal cortex (PFC)], critical for coding the rewarding properties of palatable food and important in hedonically driven feeding behavior. Using a mouse model of diet-induced obesity (DIO), significant alterations in the expression of DA-related genes were documented in adult animals, and the general pattern of gene expression changes was opposite within the hypothalamus versus the reward circuitry (increased vs. decreased, respectively). Differential DNA methylation was identified within the promoter regions of tyrosine hydroxylase (TH) and dopamine transporter (DAT), and the pattern of this response was consistent with the pattern of gene expression. Behaviors consistent with increased hypothalamic DA and decreased reward circuitry DA were observed. These data identify differential DNA methylation as an epigenetic mechanism linking the chronic intake of HF diet with altered DA-related gene expression, and this response varies by brain region and DNA sequence.Chronic consumption of a high-fat diet can alter the expression of dopamine-related genes; however, the mechanism that drives this response remains unclear. This work identifies differential DNA methylation as a potential link between high-fat diet and altered gene expression in the brain. A better understanding of the CNS adaptations that occur during the development of obesity will prove critical in designing both better behavioral and pharmacological therapeutics for obesity.
J. Neurochem. (2012) 10.1111/j.1471-4159.2012.07648.xAbstractCerebellin precursor protein (Cbln1) is essential for synapse integrity in cerebellum through assembly into complexes that bridge pre-synaptic ?-neurexins (Nrxn) to post-synaptic GluR?2. However, GluR?2 is largely cerebellum-specific, yet Cbln1 and its little studied family members, Cbln2 and Cbln4, are expressed throughout brain. Therefore, we investigated whether additional proteins mediate Cbln family actions. Whereas Cbln1 and Cbln2 bound to GluR?2 and Nrxns1-3, Cbln4 bound weakly or not at all, suggesting it has distinct binding partners. In a candidate receptor-screening assay, Cbln4 (but not Cbln1 or Cbln2) bound selectively to the netrin receptor, (deleted in colorectal cancer (DCC) in a netrin-displaceable fashion. To determine whether Cbln4 had a netrin-like function, Cbln4-null mice were generated. Cbln4-null mice did not phenocopy netrin-null mice. Cbln1 and Cbln4 were likely co-localized in neurons thought to be responsible for synaptic changes in striatum of Cbln1-null mice. Furthermore, complexes containing Cbln1 and Cbln4 had greatly reduced affinity to DCC but increased affinity to Nrxns, suggesting a functional interaction. However, Cbln4-null mice lacked the striatal synaptic changes seen in Cbln null mice. Thus, Cbln family members interact with multiple receptors/signaling pathways in a subunit composition-dependent manner and have independent functions with Cbln4 potentially involved in the less well-characterized role of netrin/DCC in adult brain.Cbln1 binds to neurexins and GluR?2 on pre- and post-synaptic membranes, respectively to stabilize synapses. We show that another family member, Cbln4 binds weakly or not at all to these receptors and cbln4-null mice lack the synaptic defects seen in cbln1-knockout mice. However, Cbln4 binds uniquely to DCC in a netrin-displaceable manner suggesting it functions via this receptor in brain.
J. Neurochem. (2012) 10.1111/j.1471-4159.2012.07647.xAbstractAll-trans-retinal and its condensation-products can cause retinal degeneration in a light-dependent manner and contribute to the pathogenesis of human macular diseases such as Stargardt’s disease and age-related macular degeneration. Although these toxic retinoid by-products originate from rod and cone photoreceptor cells, the contribution of each cell type to light-induced retinal degeneration is unknown. In this study, the primary objective was to learn whether rods or cones are more susceptible to light-induced, all-trans-retinal-mediated damage. Previously, we reported that mice lacking enzymes that clear all-trans-retinal from the retina, ATP-binding cassette transporter 4 and retinol dehydrogenase 8, manifested light-induced retinal dystrophy. We first examined early-stage age-related macular degeneration patients and found retinal degenerative changes in rod-rich rather than cone-rich regions of the macula. We then evaluated transgenic mice with rod-only and cone-like-only retinas in addition to progenies of such mice inbred with Rdh8?/?Abca4?/? mice. Of all these strains, Rdh8?/?Abca4?/?mice with a mixed rod–cone population showed the most severe retinal degeneration under regular cyclic light conditions. Intense light exposure induced acute retinal damage in Rdh8?/?Abca4?/? and rod-only mice but not cone-like-only mice. These findings suggest that progression of retinal degeneration in Rdh8?/?Abca4?/? mice is affected by differential vulnerability of rods and cones to light.Rods are more susceptible than cones to light-induced damage: implications for human macular diseases We asked whether rods or cones are more susceptible to light-induced, all-trans-retinal-dependent damage and how any difference of susceptibility could affect the pathology of human macular diseases. Rods are more susceptible than cones to light-induced cell death; similar pathological changes were observed in patients with human macular disease. This finding can partially explain initial pathological events of human macular diseases and add to our understanding of these pathologies.
J. Neurochem. (2012) 10.1111/j.1471-4159.2012.07646.xAbstractSerine hydroxymethyltransferase (SHMT) catalyzes the transfer of a ?-carbon from serine to tetrahydrofolate to form glycine and 5,10-methylene-tetrahydrofolate. This reaction plays an important role in neurotransmitter synthesis and metabolism. We set out to resequence SHMT1 and SHMT2, followed by functional genomic studies. We identified 87 and 60 polymorphisms in SHMT1 and SHMT2, respectively. We observed no significant functional effect of the 13 non-synonymous single-nucleotide polymorphism (SNPs) in these genes, either on catalytic activity or protein quantity. We imputed additional variants across the two genes using ‘1000 Genomes’ data, and identified 14 variants that were significantly associated (p < 1.0E?10) with SHMT1 messenger RNA expression in lymphoblastoid cell lines. Many of these SNPs were also significantly correlated with basal SHMT1 protein expression in 268 human liver biopsy samples. Reporter gene assays suggested that the SHMT1 promoter SNP, rs669340, contributed to this variation. Finally, SHMT1 and SHMT2 expression were significantly correlated with those of other Folate and Methionine Cycle genes at both the messenger RNA and protein levels. These experiments represent a comprehensive study of SHMT1 and SHMT2 gene sequence variation and its functional implications. In addition, we obtained preliminary indications that these genes may be co-regulated with other Folate and Methionine Cycle genes.Serine hydroxymethyltransferase (SHMT) genomics and functional genomics. SHMT1 and SHMT2 are enzymes in the ‘Folate Cycle’– a cycle that plays an important role in neural development and function. In this study, we resequenced the SHMT1 and SHMT2 genes and performed functional genomic studies which identified SNPs that were highly correlated with expression of both mRNA and protein.
J. Neurochem. (2012) 10.1111/j.1471-4159.2012.07645.xAbstractAstrocytes are important glial cells in the brain providing metabolic support to neurons as well as contributing to brain signaling. These different functional levels have to be highly coordinated to allow for proper cell and brain function. In this study, we show that in astrocytes the NAD+/NADH redox state modulates dopamine-induced Ca2+ signals thereby connecting metabolism and Ca2+ signaling. Application of dopamine induced a dose-dependent increase in Ca2+ signal frequency in these cells, which was dependent on D1-receptor signaling, glycolytic activity, an increase in cytosolic NADH and inositol 1,4,5-triphosphate receptor operated intracellular Ca2+ stores. Application of dopamine at a low concentration (1 ?M) did not induce an increase in Ca2+ signal frequency by itself. However, simultaneously increasing cytosolic NADH content either by direct application of NADH or by application of lactate resulted in a pronounced increase in Ca2+ signal frequency. This increase could be blocked by co-application of pyruvate, suggesting that indeed the NAD+/NADH redox state is regulating Ca2+ signals. We conclude that at the NAD+/NADH redox state metabolic and signaling information is integrated in astrocytes, thereby most likely contributing to precisely coordinate these different tasks of astrocytes.The adjustment of signaling and energy metabolism is a crucial task for the brain and the NAD+/NADH redox state is of central importance for cellular energy metabolism. Here, we show that the NAD+/NADH redox state modulates dopamine-induced Ca2+-signals in cortical astrocytes. This modulation most likely contributes to coordinating the metabolic status and Ca2+-signals in the context of cortical dopaminergic signaling.
J. Neurochem. (2012) 10.1111/j.1471-4159.2012.07644.xAbstractDeposition of amyloid ? protein (A?) in the brain is the hallmark of Alzheimer’s disease (AD) pathogenesis. Beta-site amyloid precursor protein (APP) cleaving enzyme 1 (BACE1) is the ?-secretase in vivo essential for generation of A?. Previously we demonstrated that BACE1 is ubiquitinated and the degradation of BACE1 is mediated by the ubiquitin-proteasome pathway (UPP). However the mechanism underlying regulation of BACE1 degradation by UPP remains elusive. Ubiquitin carboxyl-terminal hydrolase L1 (UCHL1) is a deubiquitinating enzyme highly specific to neuron, catalyzing the hydrolysis of ubiquitin conjugates from ubiquitinated substrates. UCHL1 regulates ubiquitin-dependent protein degradation. However, whether UCHL1 is particularly involved in the proteasomal degradation of BACE1 and what is the role of UCHL1 in AD pathogenesis remain elusive. To investigate the effect of UCHL1 on BACE1 degradation, HUCH cells, a UCHL1 stably over-expressed HEK293 cell line, was established. We found that inhibition of UCHL1 significantly increased BACE1 protein level in a time-dependent manner. Half life of BACE1 was reduced in HUCH cells compared with HEK. Over-expression of UCHL1 decreased APP C-terminal fragment C99 and A? levels in HUCH cells. Moreover, disruption of Uchl1 gene significantly elevated levels of endogenous BACE1, C99 and A? in the Uchl1-null gad mice. These results demonstrated that UCHL1 accelerates BACE1 degradation and affects APP processing and A? production. This study suggests that potentiation of UCHL1 might be able to reduce the level of BACE1 and A? in brain, which makes it a novel target for AD drug development.BACE1 is essential for generating A?, a central component of neuritic plaques in AD brains. Previously we demonstrated that BACE1 is ubiquitinated and the degradation of BACE1 is mediated by the ubiquitin-proteasome pathway. Ubiquitin carboxyl-terminal hydrolase L1 (UCHL1) is a deubiquitinating enzyme that regulates ubiquitin-dependent protein degradation. This study aimed to define the role of UCHL1 in the proteasomal degradation of BACE1. We found that overexpression of UCHL1 accelerates BACE1degradation and decreases APP C99 and A? generation in the stable cells, and disruption of Uchl1 gene significantly elevates levels of endogenous BACE1, C99 and A? in the Uchl1-null gad mice. The study demonstrated that UCHL1 affects BACE1 degradation, APP processing and A? production both in vitro and in vivo. The results suggest that potentiation of UCHL1 might be able to reduce the level of BACE1 and A? in brains, which makes it a novel target for AD drug development.BACE1 is essential for generating A?, a central component of neuritic plaques in AD brains. Previously we demonstrated that BACE1 is ubiquitinated and the degradation of BACE1 is mediated by the ubiquitin-proteasome pathway. Ubiquitin carboxyl-terminal hydrolase L1 (UCHL1) is a deubiquitinating enzyme that regulates ubiquitin-dependent protein degradation. This study aimed to define the role of UCHL1 in the proteasomal degradation of BACE1. We found that overexpression of UCHL1 accelerates BACE1degradation and decreases APP C99 and A? generation in the stable cells, and disruption of Uchl1 gene significantly elevates levels of endogenous BACE1, C99 and A? in the Uchl1-null gad mice. The study demonstrated that UCHL1 affects BACE1 degradation, APP processing and A? production both in vitro and in vivo. The results suggest that potentiation of UCHL1 might be able to reduce the level of BACE1 and A? in brains, which makes it a novel target for AD drug development.
J. Neurochem. (2012) 10.1111/j.1471-4159.2012.07642.xAbstractEtiology of Alzheimer’s disease (AD) is obscure, but neuroinflammation and accumulation of ?-amyloid (A?) are implicated in pathogenesis of AD. We have shown anti-inflammatory and neurotrophic properties of obovatol, a biphenolic compound isolated from Magnolia obovata. In this study, we examined the effect of obovatol on cognitive deficits in two separate AD models: (i) mice that received intracerebroventricular (i.c.v.) infusion of A?1–42 (2.0 ?g/mouse) and (ii) Tg2576 mice-expressing mutant human amyloid precursor protein (K670N, M671L). Injection of A?1–42 into lateral ventricle caused memory impairments in the Morris water maze and passive avoidance tasks, being associated with neuroinflammation. A?1–42-induced abnormality was significantly attenuated by administration of obovatol. When we analyzed with Tg2576 mice, long-term treatment of obovatol (1 mg/kg/day for 3 months) significantly improved cognitive function. In parallel with the improvement, treatment suppressed astroglial activation, BACE1 expression and NF-?B activity in the transgenic mice. Furthermore, obovatol potently inhibited fibrillation of A?in vitro in a dose-dependent manner, as determined by Thioflavin T fluorescence and electron microscopic analysis. In conclusion, our data demonstrated that obovatol prevented memory impairments in experimental AD models, which could be attributable to amelioration of neuroinflammation and amyloidogenesis by inhibition of NF-?B signaling pathway and anti-fibrillogenic activity of obovatol.Anti-neuroinflammation and improved cognitive function by obovatol. Neuroinflammation and deposition of amyloid-beta are implicated in pathogenesis of Alzheimer’s disease. Here, we demonstrated that obovatol, a natural anti-neuroinflammatory compound attenuated cognitive impairments in Alzheimer’s disease model and the effects were related to suppression of NF-?B pathway. These results suggest that obovatol could be a therapeutic intervention of Alzheimer’s disease pathogenesisAnti-neuroinflammation and improved cognitive function by obovatol. Neuroinflammation and deposition of amyloid-beta are implicated in pathogenesis of Alzheimer’s disease. Here, we demonstrated that obovatol, a natural anti-neuroinflammatory compound attenuated cognitive impairments in Alzheimer’s disease model and the effects were related to suppression of NF-?B pathway. These results suggest that obovatol could be a therapeutic intervention of Alzheimer’s disease pathogenesis.
J. Neurochem. (2012) 10.1111/j.1471-4159.2011.07631.xAbstractGlutamate receptor (GluR) ?1 is widely expressed in the developing forebrain, whereas GluR?2 is selectively expressed in cerebellar Purkinje cells. Recently, we found that trans-synaptic interaction of postsynaptic GluR?2 and pre-synaptic neurexins (NRXNs) through cerebellin precursor protein (Cbln) 1 mediates excitatory synapse formation in the cerebellum. Thus, a question arises whether GluR?1 regulates synapse formation in the forebrain. In this study, we showed that the N-terminal domain of GluR?1 induced inhibitory presynaptic differentiation of some populations of cultured cortical neurons. When Cbln1 or Cbln2 was added to cultures, GluR?1 expressed in HEK293T cells induced preferentially inhibitory presynaptic differentiation of cultured cortical neurons. The synaptogenic activity of GluR?1 was suppressed by the addition of the extracellular domain of NRXN1? or NRXN1? containing splice segment 4. Cbln subtypes directly bound to the N-terminal domain of GluR?1. The synaptogenic activity of GluR?1 in the presence of Cbln subtypes correlated well with their binding affinities. When transfected to cortical neurons, GluR?1 stimulated inhibitory synapse formation in the presence of Cbln1 or Cbln2. These results together with differential interactions of Cbln subtypes with NRXN variants suggest that GluR?1 induces preferentially inhibitory presynaptic differentiation of cortical neurons by interacting with NRXNs containing splice segment 4 through Cbln subtypes.Precise synaptic connections between neurons in the brain provide the basis of perception, learning, memory and cognition. Trans-synaptic interaction of glutamate receptor (GluR) ?2 and neurexins (NRXNs) through cerebellin precursor protein (Cbln) 1 mediates excitatory synapse formation in the cerebellum. Here, we show that GluR?1 preferentially induces inhibitory pre-synaptic differentiation of some populations of cortical neurons by interacting with NRXNs through Cblns.
J. Neurochem. (2012) 10.1111/j.1471-4159.2011.07639.xAbstractNeuroserpin is a brain-specific serine protease inhibitor that is expressed in the developing and adult nervous system. Its expression profile led to suggestions that it played roles in neuronal growth and connectivity. In this study, we provide direct evidence to support a role for neuroserpin in axon and dendritic growth. We report that axon growth is enhanced while axon and dendrite diameter are reduced following neuroserpin treatment of hippocampal neurons. More complex effects are seen on dendritic growth and branching with neuroserpin-stimulating dendritic growth and branching in young neurons but switching to an inhibitory response in older neurons. The protease inhibitory activity of neuroserpin is not required to activate changes in neuronal morphology and a proportion of responses are modulated by an antagonist to the LRP1 receptor. Collectively, these findings support a key role for neuroserpin as a regulator of neuronal development through a non-inhibitory mechanism and suggest a basis for neuroserpin’s effects on complex emotional behaviours and recent link to schizophrenia.Serine protease inhibitor neuroserpin has complex effects on axon and dendritic growth. A central issue in neurobiology is how the refinement of neural circuits is controlled during development to establish, maintain and modify synaptic plasticity. In this study, we report that the serine protease inhibitor neuroserpin has complex effects on axon and dendritic growth, through a mechanism that does not involve protease inhibition. Our results support roles for neuroserpin during neuronal development and suggest a mechanistic framework for neuroserpin’s function in regulating complex emotional behaviours and recent link to schizophrenia.
J. Neurochem. (2012) 10.1111/j.1471-4159.2011.07638.xAbstractChondroitin sulfate proteoglycans (CSPGs) are major components of the extracellular matrix in the CNS that inhibit axonal regeneration after CNS injury. Signaling pathways in neurons triggered by CSPGs are still largely unknown. In this study, using well-characterized in vitro assays for neurite outgrowth and neurite guidance, we demonstrate a major role for myosin II in the response of neurons to CSPGs. We found that the phosphorylation of myosin II regulatory light chains is increased by CSPGs. Specific inhibition of myosin II activity with blebbistatin allows growing neurites to cross onto CSPG-rich areas and increases the length of neurites of neurons growing on CSPGs. Using specific gene knockdown, we demonstrate selective roles for myosin IIA and IIB in these processes. Time lapse microscopy and immunocytochemistry demonstrated that CSPGs also inhibit cell adhesion and cell spreading. Inhibition of myosin II selectively accelerated neurite initiation without altering cell adhesion and spreading on CSPGs.Chondroitin sulfate proteoglycans (CSPGs) play a negative role in axon guidance and regeneration. We demonstrate that these actions of CSPGs are dependent upon myosin II activity as CSPGs increase the phosphorylation of myosin light chains and inhibition of myosin II activity promotes growth on CSPGs. These results extend our knowledge of the role of cytoskeletal motor proteins in response to inhibitory axon guidance molecules.
J. Neurochem. (2012) 10.1111/j.1471-4159.2011.07637.xAbstractEvidence accumulating during the past few years points to a significant role of matrix metalloproteinase 9 (MMP9) enzymatic activity in synaptic plasticity and cognitive processes. We have previously demonstrated that MMP9 is involved in receptor-mediated ?-secretase-like cleavage of APP in vitro, resulting in increased secretion of sAPP?, the soluble N-terminal product of the non-amyloidogenic pathway known to be involved in neuronal plasticity and memory formation. To study the in vivo role of MMP9, we have generated transgenic mice over-expressing MMP9 in the brain. Herein, we demonstrate that MMP9 transgenic animals display enhanced performance in the non-spatial novel object recognition and the spatial water-maze task and that their enhanced performance was accompanied by increased dendritic spine density in the hippocampus and cortex following behavioural testing. Consistent with the above observations, the electrophysiological analysis revealed prolonged maintenance of long-term synaptic potentiation in hippocampal slices from MMP9 transgenic mice. Moreover, elevated sAPP? levels in the hippocampus and cortex of MPP9 transgenic animals were also observed. Overall, our results extend previous findings on the physiological role of MMP9 in neuronal plasticity and furthermore reveal that, APP may be one of the physiological proteolytic targets of MMP9 in vivo.
J. Neurochem. (2012) 10.1111/j.1471-4159.2011.07636.xAbstractTacrine is an acetylcholinesterase (AChE) inhibitor used as a cognitive enhancer in the treatment of Alzheimer’s disease (AD). However, its low therapeutic efficiency and a high incidence of side effects have limited its clinical use. In this study, the molecular mechanisms underlying the impact on brain activity of tacrine and two novel tacrine analogues (T1, T2) were approached by focusing on three aspects: (i) their effects on brain cholinesterase activity; (ii) perturbations on electron transport chain enzymes activities of non-synaptic brain mitochondria; and (iii) the role of mitochondrial lipidome changes induced by these compounds on mitochondrial bioenergetics. Brain effects were evaluated 18 h after the administration of a single dose (75.6 ?mol/kg) of tacrine or tacrine analogues. The three compounds promoted a significant reduction in brain AChE and butyrylcholinesterase (BuChE) activities. Additionally, tacrine was shown to be more efficient in brain AChE inhibition than T2 tacrine analogue and less active than T1 tacrine analogue, whereas BuChE inhibition followed the order: T1 > T2 > tacrine. The studies using non-synaptic brain mitochondria show that all the compounds studied disturbed brain mitochondrial bioenergetics mainly via the inhibition of complex I activity. Furthermore, the activity of complex IV is also affected by tacrine and T1 treatments while FoF1-ATPase is only affected by tacrine. Therefore, the compounds’ toxicity as regards brain mitochondria, which follows the order: tacrine >> T1 > T2, does not correlate with their ability to inhibit brain cholinesterase enzymes. Lipidomics approaches show that phosphatidylethanolamine (PE) is the most abundant phospholipids (PL) class in non-synaptic brain mitochondria and cardiolipin (CL) present the greatest diversity of molecular species. Tacrine induced significant perturbations in the mitochondrial PL profile, which were detected by means of changes in the relative abundance of phosphatidylcholine (PC), PE, phosphatidylinositol (PI) and CL and by the presence of oxidized phosphatidylserines. Additionally, in both the T1 and T2 groups, the lipid content and molecular composition of brain mitochondria PL are perturbed to a lesser extent than in the tacrine group. Abnormalities in CL content and the amount of oxidized phosphatidylserines were associated with significant reductions in mitochondrial enzymes activities, mainly complex I. These results indicate that tacrine and its analogues impair mitochondrial function and bioenergetics, thus compromising the activity of brain cells.Understanding the brain activity of tacrine and related compounds is important to design drugs that improve their therapeutic efficiency for Alzheimer’s disease. We report that tacrine and two tacrine analogues decrease mitochondrial cardiolipin content and increase phosphatidylserines oxidation, which are linked with the loss of respiratory energy control. Although their inhibition on acetylcholinesterase activity might be considered therapeutic, they could also worsen the disease by damaging neural cell respiration.Understanding the brain activity of tacrine and related compounds is important to design drugs that improve their therapeutic efficiency for Alzheimer’s disease. We report that tacrine and two tacrine analogues decrease mitochondrial cardiolipin content and increase phosphatidylserines oxidation, which are linked with the loss of respiratory energy control. Although their inhibition on acetylcholinesterase activity might be considered therapeutic, they could also worsen the disease by damaging neural cell respiration.
J. Neurochem. (2012) 10.1111/j.1471-4159.2011.07635.xAbstractParkinson’s disease is a chronic neurodegenerative movement disorder characterized by the loss of dopaminergic neurons in the substantia nigra pars compacta. New therapeutic approaches aiming at delaying or reversing the neurodegenerative process are under active investigations. In this work, we found that harpagoside, an iridoid purified from the Chinese medicinal herb Scrophularia ningpoensis, could not only prevent but also rescue the dopaminergic neurodegeneration in MPTP/MPP+ intoxication with promising efficacy. Firstly, in cultured mesencephalic neurons, harpagoside significantly attenuated the loss of TH-positive neuron numbers and the shortening of axonal length. Secondly, in a chronic MPTP mouse model, harpagoside dose-dependently improved the loco-motor ability (rotarod test), increased the TH-positive neuron numbers in the substantia nigra pars compacta (unbiased stereological counting) and increased the striatal DAT density (125I-FP-CIT autoradiography). Thirdly, harpagoside markedly elevated the GDNF mRNA and GDNF protein levels in MPTP/MPP+ lesioned models. However, the protecting effect of harpagoside on the dopaminergic degeneration disappeared when the intrinsic GDNF action was blocked by either the Ret inhibitor PP1 or the neutralizing anti-GDNF antibody. Taken together, we conclude that harpagoside attenuates the dopaminergic neurodegeneration and movement disorder mainly through elevating glial cell line-derived neurotrophic factor.Harpagoside attenuates dopaminergic degeneration via elevating glial cell line-derived neurotrophic factorNew therapeutic approaches targeting the dopaminergic neurodegenerative process are under active investigations. In this study, we report that harpagoside, an iridoid purified from the Chinese medicinal herb Scrophularia ningpoensis, significantly prevents and rescues the MPP+/MPTP-induced dopaminergic neurodegeneration and movement disorder, mainly through elevating glial cell line-derived neurotrophic factor (GDNF). Thus, we provide brand-new basic evidence for clinical researches.
J. Neurochem. (2012) 10.1111/j.1471-4159.2011.07634.xAbstractDuring pregnancy, activation of the maternal immune system results in inflammation in the foetal nervous system. The causative agents are pro-inflammatory cytokines like interleukin-1? (IL-1?), produced by the foetus. In this study, we examine the effect of IL-1? on the proliferation and differentiation of neural progenitor cells (NPCs) to better understand its potential effects on the developing brain. We find that the IL-1? receptor (IL-1R1) is expressed in the ventral mesencephalon of the developing brain. Furthermore, IL-1R1 is expressed on Nestin-positive, Sox-2-positive NPCs. IL-1? treatment reduced the numbers of proliferating NPCs, an effect prevented by the IL-1R1 receptor antagonist. LDH and MTT assays, and western blot analysis for cleaved caspase 3 and poly(ADP-ribose) polymerase, confirmed that this was not due to an increase in cell death but rather an induction of differentiation. To further study the effects of IL-1? on cell fate determination, we differentiated NPCs in the presence and absence of IL-1?. Il-1? promoted gliogenesis and inhibited neurogenesis, an effect that required p38-MAPK kinase signalling. In summary, these data show that exposure of NPCs to IL-1? affects their development. This necessitates an examination of the consequences that maternal immune system activation during pregnancy has on the cellular architecture of the developing brain.A role for maternal inflammation in neural progenitor cell development? Inflammatory cytokines have the potential to affect the developing brain. Here, we report that IL-1? can inhibit the growth and alter the differentiation of foetal neural progenitor cells. This study necessitates an examination of the consequences that maternal immune system activation during pregnancy has on the cellular architecture of the developing brain
J. Neurochem. (2012) 10.1111/j.1471-4159.2011.07633.xAbstractCorticosterone-releasing hormone (CRH) and arginine vasopressin (AVP) are crucial components of the hypothalamic–pituitary–adrenal axis that stimulates the release of adrenocorticotropic hormone from the pituitary and mediate the stress response. CRH binds to two subtypes of CRH receptors (CRH-R1 and CRH-R2) that are present in both central and peripheral tissues. We used the CRH-R1-specific antagonist, antalarmin (ANT), the CRH-R1 and CRH-R2 peptide antagonist, astressin (AST), and the CRH-R2-specific peptide antagonist, astressin2b (AST2b), to determine which CRH receptor is involved in the nicotine-stimulated secretion of corticosterone. Male C57BL/6 mice were administered ANT (20 mg/kg, i.p.), AST (0.3 mg/kg, i.p.), AST2b (0.3 mg/kg, i.p.) or vehicle prior to administration of nicotine (1.0 mg/kg, s.c.), CRH (10 ?g/kg, s.c.), AVP (10 ?g/kg, s.c.) or saline (s.c.), killed 15 min later and trunk blood collected and assayed for corticosterone plasma levels. We found that CRH enhanced corticosterone release, and this response was blocked by both AST and ANT. Nicotine also increased corticosterone secretion, but this effect persisted in the presence of either CRH antagonist. Furthermore, AST but not ANT or AST2b decreased corticosterone levels associated with stress of handling and injection. We also assessed the role of AVP V1b-specific receptor antagonist, SSR149415 alone and in combination with AST and AST2b. Although the AVP antagonist did not alter basal or nicotine-stimulated corticosterone secretion, it attenuated the AVP-induced stimulation of corticosterone and its combination with AST but not AST2b completely abolished nicotine-mediated stimulation of corticosterone secretion. Our results demonstrate that the nicotine-induced stimulation of the hypothalamic–pituitary–adrenal axis is mediated by both the CRH-R and the AVP V1b receptor and when the CRH receptor is blocked, nicotine may utilize the AVP V1b receptor to mediate secretion of corticosterone. These results argue in favor of the development of specific antagonists that block both AVP and CRH receptors to decrease the pleasurable component of nicotine, which may be mediated by corticosterone.How does nicotine activate the stress response? The study was performed to determine which CRH receptor is involved in the nicotine-stimulated secretion of corticosterone. The nicotine-induced stimulation of the hypothalamic-pituitary adrenal axis (HPA) is mediated by both the CRH-R and the AVP V1b receptor and when the CRH receptor is blocked, nicotine may utilize the AVP V1b receptor to mediate secretion of corticosterone. The use of specific antagonists that block both AVP and CRH receptors may be needed to decrease the pleasurable component of nicotine, which may be mediated by corticosterone.
J. Neurochem. (2012) 10.1111/j.1471-4159.2011.07632.xAbstractMephedrone (4-methylmethcathinone) is a ?-ketoamphetamine with close structural analogy to substituted amphetamines and cathinone derivatives. Abuse of mephedrone has increased dramatically in recent years and has become a significant public health problem in the United States and Europe. Unfortunately, very little information is available on the pharmacological and neurochemical actions of mephedrone. In light of the proven abuse potential of mephedrone and considering its similarity to methamphetamine and methcathinone, it is particularly important to know if mephedrone shares with these agents an ability to cause damage to dopamine nerve endings of the striatum. Accordingly, we treated mice with a binge-like regimen of mephedrone (4 × 20 or 40 mg/kg) and examined the striatum for evidence of neurotoxicity 2 or 7 days after treatment. While mephedrone caused hyperthermia and locomotor stimulation, it did not lower striatal levels of dopamine, tyrosine hydroxylase or the dopamine transporter under any of the treatment conditions used presently. Furthermore, mephedrone did not cause microglial activation in striatum nor did it increase glial fibrillary acidic protein levels. Taken together, these surprising results suggest that mephedrone, despite its numerous mechanistic overlaps with methamphetamine and the cathinone derivatives, does not cause neurotoxicity to dopamine nerve endings of the striatum.“Meow meow” turns out to be a kitten and not a lion Mephedrone, a psychoactive component of “bath salts”, is being abused increasingly throughout the US and Europe but it is not known if this agent is neurotoxic like its close structural congener methamphetamine. Mice treated with a binge-like dosing regimen of mephedrone did not show signs of damage to dopamine nerve terminals despite developing significant hyperthermia and hyper-locomotion, indices of increased synaptic dopamine. It appears that the addition to methamphetamine of a ?-keto group and a 4-methyl substituent on the ring to yield mephedrone obviates the neurotoxicity caused by methamphetamine ingestion.
J. Neurochem. (2012) 10.1111/j.1471-4159.2011.07630.xAbstractMicroglia are the resident immune cells within the brain and their production of immune molecules such as cytokines and chemokines is critical for the processes of normal brain development including neurogenesis, axonal migration, synapse formation, and programmed cell death. Notably, sex differences exist in many of these processes throughout brain development; however, it is unknown whether a sex difference concurrently exists in the colonization, number, or morphology of microglia within the developing brain. We demonstrate for the first time that the number and morphology of microglia throughout development is dependent upon the sex and age of the individual, as well as the brain region of interest. Males have overall more microglia early in postnatal development [postnatal day (P) 4], whereas females have more microglia with an activated/amoeboid morphology later in development, as juveniles and adults (P30–60). Finally, gene expression of a large number of cytokines, chemokines and their receptors shifts dramatically over development, and is highly dependent upon sex. Taken together, these data warrant further research into the role that sex-dependent mechanisms may play in microglial colonization, number, and function, and their potential contribution to neural development, function, or potential dysfunction.Colonization of Microglia in Cognitive Brain Regions: Sex Differences Neonatal male rats have significantly more amoeboid microglia than females within the hippocampus, cortex and amygdala. Before adolescence and into adulthood, females have significantly more microglia with long, branched processes than males in these same brain regions. These data may lend valuable insight into distinct windows of vulnerability between the sexes following an immune challenge.
J. Neurochem. (2012) 10.1111/j.1471-4159.2011.07628.xAbstractTo examine mechanisms underlying substance P (SP) release from primary sensory neurons in response to activation of the non-selective cation channel transient receptor potential ankyrin 1 (TRPA1), SP release from cultured rat dorsal root ganglion neurons was measured, using radioimmunoassay, by stimulating TRPA1 with allyl isothiocyanate (AITC), a TRPA1 agonist. AITC-evoked SP release occurred in a concentration- and time-dependent manner. Interestingly, p38 mitogen-activated protein kinase (p38) inhibitor SB203580 significantly attenuated AITC-evoked SP release. The in vivo effect of AITC-evoked SP release from primary sensory neurons in mice was evaluated. Hind paw intraplantar injection of AITC induced nociceptive behaviors and inflammation (edema, thermal hyperalgesia). AITC-induced thermal hyperalgesia and edema were inhibited by intraplantar pre-treatment with either SB203580 or neurokinin-1 receptor antagonist CP96345. Moreover, intrathecal pre-treatment with either CP96345 or SB203580 inhibited AITC-induced nociceptive behaviors and thermal hyperalgesia. Immunohistochemical studies demonstrated that intraplantar AITC injection induced the phosphorylation of p38 in mouse dorsal root ganglion neurons containing SP. These findings suggest that activation of TRPA1 evokes SP release from the primary sensory neurons through phosphorylation of p38, subsequent nociceptive behaviors and inflammatory responses. Furthermore, the data also indicate that blocking the effects of TRPA1 activation at the periphery leads to significant antinociception.How does activation of TRPA1 induce nociceptive behaviors and inflammatory responses? Activation of peripheral TRPA1 leads to phosphorylation of intracellular p38 MAP kinase and substance P release from both central and peripheral terminals of primary sensory neurons. Hence, substance P mediates TRPA1-induced responses and modulation of TRPA1 could be a potent therapeutic approach.
J. Neurochem. (2012) 10.1111/j.1471-4159.2011.07623.xAbstract?-Site APP-cleaving enzyme (BACE1) cleaves the amyloid precursor protein (APP) at the ?-secretase site to initiate the production of A? peptides. These accumulate to form toxic oligomers and the amyloid plaques associated with Alzheimer’s disease (AD). An increase of BACE1 levels in the brain of AD patients has been mostly attributed to alterations of its intracellular trafficking. Golgi-associated adaptor proteins, GGA sort BACE1 for export to the endosomal compartment, which is the major cellular site of BACE1 activity. BACE1 undergoes recycling between endosome, trans-Golgi network (TGN), and the plasma membrane, from where it is endocytosed and either further recycled or retrieved to the endosome. Phosphorylation of Ser498 facilitates BACE1 recognition by GGA1 for retrieval to the endosome. Ubiquitination of BACE1 C-terminal Lys501 signals GGA3 for exporting BACE1 to the lysosome for degradation. In addition, the retromer mediates the retrograde transport of BACE1 from endosome to TGN. Decreased levels of GGA proteins and increased levels of retromer-associated sortilin have been associated with AD. Both would promote the co-localization of BACE1 and the amyloid precursor protein in the TGN and endosomes. Decreased levels of GGA3 also impair BACE1 degradation. Further understanding of BACE1 trafficking and its regulation may offer new therapeutic approaches for the treatment of Alzheimer’s disease.
J. Neurochem. (2012) 10.1111/j.1471-4159.2011.07622.xAbstractGABAergic transmission in the neostriatum plays a central role in motor coordination, in which a plethora of GABA-A receptor subunits combine to modulate neural inhibition. GABA? receptors were originally described in the mammalian retina. These receptors possess special electrophysiological and pharmacological properties, forming a characteristic class of ionotropic receptors. In previous studies, we suggested that GABA? receptors are expressed in the neostriatum, and in this report we show that they are indeed present in all the calretinin-positive interneurons of the neostriatum. In addition, they are located in calbindin-positive interneurons and projection neurons that express the dopamine D2 receptor. GABA? receptors were also located in 30% of the glial fibrillary acidic protein-positive cells, and may therefore also contribute to gliotransmission. Quantitative reverse transcription-PCR suggested that the mRNAs of this receptor do not express as much as in the retina, and that GABA?2 is more abundant than GABA?1. Electrophysiological recordings in brain slices provided evidence of neurons expressing a cis-4-aminocrotonic acid-activated, 1,2,5,6-tetrahydropyridine-4-yl methylphosphinic acid-sensitive ionotropic GABA receptor, indicating the presence of functional GABA? receptors in the neostriatum. Finally, electron-microscopy and immunogold located the receptors mainly in perisynaptic as well as in extrasynaptic sites. All these observations reinforce the importance of GABA? receptors in the neostriatum and contribute to the diversity of inhibitory regulation in this area.GABA? receptors in neurons and astrocytes of striatum GABA transmission plays a central role in the interneurons of the striatum. We aimed to investigate whether GABA? receptors, which are bicuculline-resistant and do not desensitize are expressed in this area. We found that GABA? are present in calretinin neurons and astrocyes, and although the receptors are sensitive to TPMPA, they most likely form heteromeric complexes with other GABA subunits.
J. Neurochem. (2012) 10.1111/j.1471-4159.2011.07615.xAbstractThe microtubule-associated Stable Tubulie Only Polypeptide (STOP; also known as MAP6) protein plays a key role in neuron architecture and synaptic plasticity, the dysfunctions of which are thought to be implicated in the pathophysiology of psychiatric diseases. The deletion of STOP in mice leads to severe disorders reminiscent of several schizophrenia-like symptoms, which are also associated with differential alterations of the serotonergic tone in somas versus terminals. In STOP knockout (KO) compared with wild-type mice, serotonin (5-HT) markers are found to be markedly accumulated in the raphe nuclei and, in contrast, deeply depleted in all serotonergic projection areas. In the present study, we carefully examined whether the 5-HT imbalance would lead to behavioral consequences evocative of mood and/or cognitive disorders. We showed that STOP KO mice exhibited depression-like behavior, associated with a decreased anxiety-status in validated paradigms. In addition, although STOP KO mice had a preserved very short-term memory, they failed to perform well in all other learning and memory tasks. We also showed that STOP KO mice exhibited regional imbalance of the norepinephrine tone as observed for 5-HT. As a consequence, mutant mice were hypersensitive to acute antidepressants with different selectivity. Altogether, these data indicate that the deletion of STOP protein in mice caused deep alterations in mood and cognitive performances and that STOP protein might have a crucial role in the 5-HT and norepinephrine networks development.The deletion of MAP6/STOP protein triggers high imbalance in the serotonin and norepinephrine neurotransmissions between somas and terminals with functional consequences. STOP KO mice are depressed, less anxious and failed to perform in learning and memory tasks. Altogether, these data indicate that MAP6/STOP protein might have a crucial role in the serotonin and norepinephrine networks development.
The physiological function of the cellular prion protein (PrPC) and its conversion into its infectious form (PrPSc) are central issues to understanding the pathogenesis of prion diseases. The N-terminal moiety of PrPC (NH2-PrPC) is an unstructured region with the characteristic of interacting with a broad range of partners. These interactions endow PrPC with multifunctional and sometimes contrasting capabilities, including neuroprotection and neurotoxicity. Recently, binding of ?-sheet rich conformers to NH2-PrPC demonstrated a probable neurotoxic function for PrPC in Alzheimer’s disease. NH2-PrPC also enhances the propagation of prions in vivo and is the target of the most potent antiprion compounds. Another level of complexity is provided by endoproteolysis and release of most of NH2-PrPC into the extracellular space. Further studies will be necessary to understand how NH2-PrPC regulates the physiological function of PrPC and how it is involved in the corruption of its normal function in diseases.
J. Neurochem. (2012) 10.1111/j.1471-4159.2011.07597.xAbstractDietary n-6 polyunsaturated fatty acid (PUFA) deprivation in rodents reduces brain arachidonic acid (20:4n-6) concentration and 20:4n-6-preferring cytosolic phospholipase A2 (cPLA2-IVA) and cyclooxygenase (COX)-2 expression, while increasing brain docosahexaenoic acid (DHA, 22:6n-3) concentration and DHA-selective calcium-independent phospholipase A2 (iPLA2)-VIA expression. We hypothesized that these changes are accompanied by up-regulated brain DHA metabolic rates. Using a fatty acid model, brain DHA concentrations and kinetics were measured in unanesthetized male rats fed, for 15 weeks post-weaning, an n-6 PUFA ‘adequate’ (31.4 wt% linoleic acid) or ‘deficient’ (2.7 wt% linoleic acid) diet, each lacking 20:4n-6 and DHA. [1-14C]DHA was infused intravenously, arterial blood was sampled, and the brain was microwaved at 5 min and analyzed. Rats fed the n-6 PUFA deficient compared with adequate diet had significantly reduced n-6 PUFA concentrations in brain phospholipids but increased eicosapentaenoic acid (EPA, 20:5n-3), docosapentaenoic acid n-3 (DPAn-3, 22:5n-3), and DHA (by 9.4%) concentrations, particularly in ethanolamine glycerophospholipid (EtnGpl). Incorporation rates of unesterified DHA from plasma, which represent DHA metabolic loss from brain, were increased 45% in brain phospholipids, as was DHA turnover. Increased DHA metabolism following dietary n-6 PUFA deprivation may increase brain concentrations of antiinflammatory DHA metabolites, which with a reduced brain n-6 PUFA content, likely promotes neuroprotection and alters neurotransmission.Dietary n-6 polyunsaturated fatty acid (PUFA) deprivation increases docosahexaenoic acid (DHA) content and DHA-selective Ca2+-independent iPLA2 expression in rat brain. In this study, we report that these changes are accompanied by up-regulated DHA incorporation from plasma and DHA turnover in brain phospholipids. Increased DHA metabolism following dietary n-6 PUFA deprivation may increase antiinflammatory DHA metabolites in brain and promote neuroprotection.
J. Neurochem. (2011) 10.1111/j.1471-4159.2011.07600.xAbstractDuring central nervous system (CNS) development, individual oligodendrocytes myelinate multiple axons, thus requiring the outgrowth and extensive branching of oligodendroglial processes. Laminin (Lm)-deficient mice have a lower percentage of myelinated axons, which may indicate a defect in the ability to properly extend and branch processes. It remains unclear, however, to what extent extracellular matrix (ECM) receptors contribute to oligodendroglial process remodeling itself. In the current study, we report that the ECM receptor dystroglycan is necessary for Lm enhancement of filopodial formation, process outgrowth, and process branching in differentiating oligodendroglia. During early oligodendroglial differentiation, the disruption of dystroglycan–Lm interactions, via blocking antibodies or dystroglycan small interfering RNA (siRNA), resulted in decreased filopodial number and length, decreased process length, and decreased numbers of primary and secondary processes. Later in oligodendrocyte differentiation, dystroglycan-deficient cells developed fewer branches, thus producing less complex networks of processes as determined by Sholl analysis. In newly differentiating oligodendroglia, dystroglycan was localized in filopodial tips, whereas, in more mature oligodendrocytes, dystroglycan was enriched in focal adhesion kinase (FAK)-positive focal adhesion structures. These results suggest that dystroglycan–Lm interactions influence oligodendroglial process dynamics and therefore may regulate the myelination capacity of individual oligodendroglia.Legend: Dystroglycan (green) and F-actin (red) enriched filopodia extending from the leading edge of an oligodendroglial process. Methods: Oligodendrocyte precursor cells were transfected (Amaxa) with a full-length dystroglycan construct expressing GFP (DG-GFP), differentiated for 48 h, and fixed with 4% PFA. Cells were incubated with rabbit anti-GFP (Molecular Probes, Eugene, OR, USA) in 1% BSA, followed by DyLight 488 anti-rabbit secondary (Jackson Immuno-Research). Cells were co-stained with Texas Red phalloidin (Invitrogen) to visualize F-actin. Non-muscle dystroglycan: how oligodendroglia “shape” up We report that the extracellular matrix receptor dystroglycan is necessary for laminin enhancement of filopodial formation, process outgrowth, and process branching in differentiating oligodendroglia. Dystroglycan-blocking antibodies reduced filopodia formation in newly differentiating oligodendroglia, whereas dystroglycan depletion via siRNA decreased the process branching complexity of pre-myelinating oligodendroglia. These results suggest that dystroglycan–laminin interactions influence oligodendroglia process dynamics and may regulate the myelination capacity of individual oligodendroglia.
J. Neurochem. (2011) 10.1111/j.1471-4159.2011.07587.xAbstractThe choroid plexus (CP) epithelium develops from the ependyma that lines the ventricular system, and plays a critical role in the development and function of the brain. In addition to being the primary site of CSF production, the CP maintains the blood–CSF barrier via apical tight junctions between epithelial cells. Here we show that the 22-member ?-protocadherin (?-Pcdh) family of cell adhesion molecules, which we have implicated previously in synaptogenesis and neuronal survival, is highly expressed by both CP epithelial and ependymal cells, in which ?-Pcdh protein localization is, surprisingly, tightly restricted to the apical membrane. Multi-label immunostaining demonstrates that ?-Pcdhs are excluded from tight junctions, basolateral adherens junctions, and apical cilia tufts. RT-PCR analysis indicates that, as a whole, the CP expresses most members of the Pcdh-? gene family. Immunostaining using novel monoclonal antibodies specific for single ?-Pcdh proteins shows that individual epithelial cells differ in their apically localized ?-Pcdh repertoire. Restricted mutation of the Pcdh-? locus in the choroid plexus and ependyma leads to significant reductions in ventricular volume, without obvious disruptions of epithelial apical-basal polarity. Together, these results suggest an unsuspected role for the ?-Pcdhs in CSF production and demonstrate a surprising molecular heterogeneity in the CP epithelium.Not just for neurons anymore: brain epithelial cells show protocadherin specificity tooThe ?-protocadherins (?-Pcdhs) are a family of 22 cadherin-like adhesion molecules, differentially expressed among neurons, that are critical for neural circuit formation and neuronal survival. We found that these proteins are highly expressed in the choroid plexus (CP), epithelial cells that produce cerebrospinal fluid (CSF), suggesting a role in this tissue.We found that, like neurons, each CP epithelial cell expresses distinct subsets of ?-Pcdhs, and localizes the proteins to their apical surface. Mice lacking the ?-Pcdhs only in the CP exhibit small ventricles, suggesting a role for this protein family in CSF dynamics.This work uncovers a surprising molecular diversity of CP epithelial cells, and implicates this diversity in the control of brain metabolism.
Glucagon-like peptide-1 (GLP-1) stimulates insulin secretion and suppresses food intake. Recent studies indicate that the hepatic vagal afferent nerve is involved in this response. Dipeptidyl peptidase-IV (DPP-IV) inhibitor extends the half-life of endogenous GLP-1 by preventing its degradation. The present study aimed to determine whether DPP-IV inhibitor-induced elevation of portal GLP-1 levels affect insulin secretion and feeding behavior via the vagal afferent nerve and hypothalamus. The effect of DPP-IV inhibitor infusion into the portal vein or peritoneum on portal and peripheral GLP-1 levels, food intake, and plasma insulin and glucose was examined in sham-operated and vagotomized male Sprague–Dawley rats. Analyses of neuronal histamine turnover and immunohistochemistry were used to identify the central nervous system pathway that mediated the response. Intraportal administration of the DPP-IV inhibitor significantly increased portal (but not peripheral) GLP-1 levels, increased insulin levels, and decreased glucose levels. The DPP-IV inhibitor suppressed 1- and 12- but not 24-h cumulative food intake. Intraportal infusion of the DPP-IV inhibitor increased hypothalamic neuronal histamine turnover and increased c-fos expression in several areas of the brain. These responses were blocked by vagotomy. Our results indicate that DPP-IV inhibitor-induced changes in portal but not systemic GLP-1 levels affect insulin secretion and food intake. Furthermore, our findings suggest that a neuronal pathway that includes the hepatic vagal afferent nerve and hypothalamic neuronal histamine plays an important role in the pharmacological actions of DPP-IV inhibitor.
?-secretase inhibitors (GSIs) have been developed to reduce A? production for the treatment of Alzheimer’s disease (AD) by inhibiting the cleavage of amyloid precursor protein (APP). However, cross inhibitory activity on the processing of Notch can cause adverse reactions. In order to avoid these undesirable effects, ?-secretase modulators (GSMs) are being developed to selectively reduce toxic A? production without perturbing Notch signaling. Since it is also known that GSIs can cause a paradoxical increase of plasma A? over the baseline after a transient reduction (known as A?-rebound), we asked if GSMs would cause a similar rebound and what the potential mechanism might be. Our studies were performed with one GSI (LY-450139) and two chemically distinct GSMs. Although LY-450139 caused A?-rebound as expected in rat plasma, the two GSMs did not. Inhibition of APP processing by LY-450139 induced an accumulation of ?-secretase substrates, ?- and ?-C-terminal fragments of APP, but neither GSM caused such an accumulation. In conclusion, we discover that GSMs, unlike GSIs, do not cause A?-rebound, possibly due to the lack of accumulation of ?-CTFs. GSMs may be superior to GSIs in the treatment of AD not only by sparing Notch signaling but also by avoiding A?-rebound.
J. Neurochem. (2011) 10.1111/j.1471-4159.2011.07524.xAbstractFOXP2, a forkhead box-containing transcription factor, forms homo- or hetero-dimers with FOXP family members and localizes to the nucleus, while FOXP2(R553H), which contains a mutation related to speech/language disorders, features reduced DNA binding activity and both cytoplasmic and nuclear localization. In addition to being a loss-of-function mutation, it is possible that FOXP2(R553H) also may act as a gain-of-function mutation to inhibit the functions of FOXP2 isoforms including FOXP2Ex10+ lacking forkhead domain. Foxp2(R552H) knock-in mouse pups exhibit impaired ultrasonic vocalization and poor dendritic development in Purkinje cells. However, expressions of Foxp2 isoforms in the developing Purkinje are unclear. The appearance of ‘apical cytoplasmic swelling’ (mitochondria-rich regions that are the source of budding processes) correlates with dendritic development of Purkinje cells. In the present study, we focused on Foxp2 isoforms localizing to the apical cytoplasmic swelling and identified two isoforms lacking forkhead domain: Foxp2Ex12+ and Foxp2Ex15. They partly localized to the membrane fraction that includes mitochondria. Foxp2Ex12+ mainly localized to the apical cytoplasmic swelling in early developing Purkinje cells at the stellate stage (P2–P4). Mitochondrial localization of Foxp2Ex12+ in Purkinje cells was confirmed by immune-electron microscopic analysis. Foxp2Ex12+ may play a role in dendritic development in Purkinje cells.Foxp2 isoform lacking the forkhead domain are important for developing Purkinje cells Expressions of Foxp2 isoforms in developing Purkinje cells are unclear. Here, two isoforms lacking forkhead domain, Foxp2Ex12+ and Foxp2Ex15+, were identified. Foxp2Ex12+ localized to perisomatic protrusions in early developing Purkinje cells and to the apical cytoplasmic swelling, mitochondria-rich regions that are the source of budding processes. These findings suggest that Foxp2Ex12+ may play a role in dendritic development in Purkinje cells.
J. Neurochem. (2012) 10.1111/j.1471-4159.2011.07489.xAbstractAlthough the pathological role of presenilin-1 mutation in early onset familial Alzheimer’s disease has been widely studied, few focused on how the presenilin-1 mutations result in memory impairment and tau hyperphosphorylation. In the present study, we expressed human Val97Leu mutant presenilin-1, which is reported in Chinese pedigrees by our group, in transgenic mice and found that the mutant presenilin-1 induced spatial memory deficit and tau hyperphosphorylation at PHF-1, pS199/202, pT231 and pS396 epitopes, but not at pS214 and pS422 epitopes. Pearson analysis showed that the memory deficit was only significantly correlated with tau phosphorylation level at PHF-1, pS199/202, pT231 and pS396 epitopes. Additionally, the hyperphosphorylated tau and tangle-like argentophilic structures were detected at CA3 and CA4, but not CA1, region of hippocampus, and we also found tangle-like structure and wizened degenerative neurons in frontal cortex. We demonstrated the tau hyperphosphorylation at the same epitopes in N2a cells expressing the mutant presenilin-1, which is caused by inhibition of phosphoinositol-3 kinase/Akt and activation of glycogen synthase kinase-3 specifically. Our data demonstrated that human Val97Leu mutant presenilin-1 causes spatial memory deficit in mice and increases tau phosphorylation level in glycogen synthase kinase-3-dependent manner.A novel Val97Leu mutation of presenilin-1 impaired spatial memory and induced neuronal degeneration in mouse: We found a novel missense mutation of presenilin-1, Val97Leu, in members of a Chinese family that had early onset Alzheimer disease from a Chinese pedigree. The Val97Leu transgenic mice manifested a spatial memory deficit and neuronal degeneration, which was caused by GSK-3-dependent tau hyperphosphorylation. We concluded that a single point Val97Leu mutation of presenilin-1 is sufficient to cause deficit in brain memory.
J. Neurochem. (2011) 10.1111/j.1471-4159.2011.07393.xAbstractHomeostasis of the brain is dependent on the blood–brain barrier (BBB). This barrier tightly regulates the exchange of essential nutrients and limits the free flow of immune cells into the CNS. Perturbations of BBB function and the loss of its immune quiescence are hallmarks of a variety of brain diseases, including multiple sclerosis (MS), vascular dementia, and stroke. In particular, diapedesis of monocytes and subsequent trafficking of monocyte-derived macrophages into the brain are key mediators of demyelination and axonal damage in MS. Endothelin-1 (ET-1) is considered as a potent pro-inflammatory peptide and has been implicated in the development of cardiovascular diseases. Here, we studied the role of different components of the endothelin system, i.e., ET-1, its type B receptor (ETB) and endothelin-converting enzyme-1 (ECE-1) in monocyte diapedesis of a human brain endothelial cell barrier. Our pharmacological inhibitory and specific gene knockdown studies point to a regulatory function of these proteins in transendothelial passage of monocytes. Results from this study suggest that the endothelin system is a putative target within the brain for anti-inflammatory treatment in neurological diseases.
J. Neurochem. (2011) 10.1111/j.1471-4159.2011.07363.xAbstractCyclooxygenases (COX)-1 and -2 are key enzymes required for the conversion of arachidonic acid to eicosanoids, potent mediators of inflammation. In patients with multiple sclerosis, COX-2 derived prostaglandins (PGs) are elevated in the CSF and COX-2 is up-regulated in demyelinating plaques. However, it is not known whether COX-2 activity contributes to oligodendrocyte death. In cuprizone-induced demyelination, oligodendrocyte apoptosis and a concomitant increase in the gene expression of COX-2 and PGE2-EP2 receptor precede histological demyelination. COX-2 and EP2 receptor were expressed by oligodendrocytes, suggesting a causative role for the COX-2/EP2 pathway in the initiation of oligodendrocyte death and demyelination. COX-2 gene deletion, chronic treatment with the COX-2 selective inhibitor celecoxib, or with the EP2 receptor antagonist AH6809 reduced cuprizone-induced oligodendrocyte apoptosis, the degree of demyelination and motor dysfunction. These data indicate that the PGE2 EP2 receptor contributes to oligodendrocyte apoptosis and open possible new therapeutic approaches for multiple sclerosis.
J. Neurochem. (2011) 10.1111/j.1471-4159.2011.07348.x.AbstractWe developed 1-(2-[18F]fluoro-3-pyridyl)-4-(2-isopropyl-1-oxo-isoindoline-5-yl)-5-methyl-1H-1,2,3-triazole ([18F]FPIT) as a promising positron emission tomography (PET) ligand for in vitro and in vivo imaging of metabotropic glutamate receptor type 1 (mGluR1) in rat and monkey brains. In vitro autoradiography with [18F]FPIT was used to determine the distribution of radioactivity in rat and monkey brains. In vivo experiments were performed using dissection and small-animal PET on rats, and PET on monkey. Metabolite analysis was performed on rat plasma and brain, and monkey plasma. Autoradiography of rat and monkey brains showed that [18F]FPIT binding is aligned with the reported distribution of mGluR1 with high specific binding in the cerebellum and thalamus. PET study on rat and monkey showed high brain uptake and distribution patterns consistent with those seen in the autoradiographic studies. The radioactivity in the brain was significantly decreased by pre-treatment with unlabeled FPIT, indicative of a specific signal for mGluR1 that was inhibited by mGluR1-selective ligand JNJ-16259865 in the brain. Metabolite analysis showed that the percentage of unchanged [18F]FPIT was 89% in the brain homogenate of rat at 90 min after injection. In the monkey plasma, the percentage of unchanged form was 50% at 90 min. [18F]FPIT produced in vitro and in vivo signals to visualize mGluR1 expression in rat and monkey brains, suggesting the usefulness of [18F]FPIT for imaging mGluR1 in human brain.
We have developed a thin layer chromatography (TLC)-Blot system that makes possible the direct analysis of blotted glycosphingolipids on a PVDF membrane from a high-performance TLC (HPTLC) plate by immunological staining, chemical staining, enzymatic treatment and mass spectrometric (MS) analysis. An ion trap type matrix-assisted laser desorption/ionization-time of flight (MALDI-QIT-TOF) MS apparatus improved not only the molecular identification but also the analysis of molecular species of lipids on the PVDF membrane. A new approach for glyco- and lipidomics, molecular scanning technology by a combination of TLC-Blot and MALDI-QIT-TOF MS, was developed and applied to human brain gangliosides separated from the tissues of patients with neural diseases and control patients. The results clearly showed a change of ganglioside composition, in addition to identifying individual ganglioside molecular species, in the hippocampus gray matter of patients with Alzheimer’s disease. The results strongly suggested that metabolic changes of gangliosides played an important role in the progression of this disease. The present technology with molecular imaging should provide valuable information for elucidating the significance of molecular species in neuronal functions such as neural transmission, memory, and learning.
Lysophosphatidic acid receptor (LPA1) signaling initiates neuropathic pain through demyelination of the dorsal root (DR). Although LPA is found to cause down-regulation of myelin proteins underlying demyelination, the detailed mechanism remains to be determined. In the present study, we found that a single intrathecal (i.t.) injection of LPA evoked a dose- and time-dependent down-regulation of myelin-associated glycoprotein (MAG) in the DR through LPA1 receptor. A similar event was also observed in ex vivo DR cultures. Interestingly, LPA-induced down-regulation of MAG was significantly inhibited by calpain inhibitors (calpain inhibitor X, E-64 and E-64d) and LPA markedly induced calpain activation in the DR. The pre-treatment with calpain inhibitors attenuated LPA-induced neuropathic pain behaviors such as hyperalgesia and allodynia. Moreover, we found that sciatic nerve injury activates calpain activity in the DR in a LPA1 receptor-dependent manner. The E-64d treatments significantly blocked nerve injury-induced MAG down-regulation and neuropathic pain. However, there was no significant calpain activation in the DR by complete Freund’s adjuvant treatment, and E-64d failed to show anti-hyperalgesic effects in this inflammation model. The present study provides strong evidence that LPA-induced calpain activation plays a crucial role in the manifestation of neuropathic pain through MAG down-regulation in the DR.
Nicotinic acetylcholine receptors (nAChRs) transmit the agonist signal to the channel gate through a number of extracellular domains. We have previously shown that particular details of the process of coupling binding to gating could be quantitative and qualitatively different in muscle and neuronal type nAChRs. We have extended previous studies on homomeric ?7 nAChRs to heteromeric ?3?4 nAChRs, by mutating residues located at loops 2 and 7, and M2-M3 linker of both ?3 and ?4 subunits which, in order to monitor surface expression, were modified to bind ?-bungarotoxin, and expressed in Xenopus oocytes. We show that, in general, mutations in these domains of both ?3 and ?4 subunits affect the gating function, although the effects are slightly larger if they are inserted in the ?3 subunit. However, the involvement of a previously reported intrasubunit interaction in coupling (Gln48-Ile130) seems to be restricted to the ?4 subunit. We also show that mutations at these domains, particularly loop 2 of the ?3 subunit, change the pharmacological profile of ?3?4 nAChRs, decreasing nicotine’s and increasing cytisine’s effectiveness relative to ACh. It is concluded that, unlike muscle nAChRs, the non-? subunits play a relevant role in the coupling process of neuronal ?3?4 nAChRs.
Die Urheberrechte sowie die Verantwortung fuer den Inhalt der verlinkten Artikel hat der in der Quelle genannte Anbieter.
Sie möchten Ihre überwiegend mit fachlichen Inhalten zur Chemie, Biochemie etc. ausgestattete Internetseite hier aufgeführt sehen: eMail genügt! Nach Prüfung des Inhalts Ihrer
Chemieseite entscheiden wir über eine eventuelle Aufnahme (kostenlos, ohne Bedingungen). Für einfache Einträge nutzen Sie bitte das Registrierungsformular!
