Recent neuroimaging and postmortem studies have reported abnormalities in white matter of schizophrenic brains, suggesting the involvement of oligodendrocytes in the etiopathology of schizophrenia. This view is being supported by gene microarray studies showing the downregulation of genes related to oligodendrocyte function and myelination in schizophrenic brain compared to control subjects. However, there is currently little information available on the response of oligodendrocytes to antipsychotic drugs (APDs), which could be invaluable for corroborating the oligodendrocyte hypothesis. In this study we found: (1) quetiapine (QUE, an atypical APD) treatment in conjunction with addition of growth factors increased the proliferation of neural progenitors isolated from the cerebral cortex of embryonic rats; (2) QUE directed the differentiation of neural progenitors to oligodendrocyte lineage through extracellular signal-related kinases; (3) addition of QUE increased the synthesis of myelin basic protein and facilitated myelination in rat embryonic cortical aggregate cultures; (4) chronic administration of QUE to C57BL/6 mice prevented cortical demyelination and concomitant spatial working memory impairment induced by cuprizone, a neurotoxin. These findings suggest a new neural mechanism of antipsychotic action of QUE, and help to establish a role for oligodendrocytes in the etiopathology and treatment of schizophrenia.

These findings establish a role for Notch signaling in modulating the microglia innate response and suggest that inhibition of Notch might represent a complementary therapeutic approach to prevent reactive gliosis in stroke and neuroinflammation-related degenerative disorders.

The present study examined the effects of the atypical antipsychotic drugs clozapine, olanzapine, quetiapine and risperidone, on N-methyl-4-phenylpyridinium ion-induced apoptosis and DNA damage in PC12 cells, and explored the molecular mechanisms underlying these effects. Haloperidol, a typical antipsychotic drug, was used for comparison. Exposure of PC12 cells to 50 micro m N-methyl-4-phenylpyridinium ion for 24 h resulted in a 35-45% loss of cells in culture. Pretreatment with the aforementioned atypical antipsychotic drugs significantly reduced the N-methyl-4-phenylpyridinium ion-induced cell loss, whereas haloperidol (10-100 micro m) did not have this protective effect. Hoechst 33258 staining revealed the apoptotic nuclear features of the N-methyl-4-phenylpyridinium ion-induced cell death, and showed that the atypical antipsychotic drugs, but not haloperidol, effectively prevented PC12 cells from this N-methyl-4-phenylpyridinium ion-induced apoptosis. DNA fragmentation assays further confirmed the N-methyl-4-phenylpyridinium ion-induced nuclear fragmentation. Pretreatment with the atypical antipsychotic drugs completely prevented this nuclear fragmentation, whereas haloperidol only partially prevented it. In vitro oligonucleotide assays indicated an activation of a specific glycosylase that recognizes and cleaves bases (at the 8-hydroxyl-2-deoxyguanine site) that were damaged by N-methyl-4-phenylpyridinium ion. Pretreatment with the atypical antipsychotic drugs more effectively attenuated this N-methyl-4-phenylpyridinium ion-induced activation than did haloperidol. Northern blot analyses showed that the atypical antipsychotic drugs, but not haloperidol, blocked the N-methyl-4-phenylpyridinium ion-induced substantial increase of copper/zinc superoxide dismutase mRNA in PC12 cells. Atypical antipsychotic drugs slightly up-regulated the expression of copper/zinc superoxide dismutase mRNA, whereas haloperidol strongly increased the expression of copper/zinc superoxide dismutase mRNA. These data may account for the different therapeutic effects and side-effect profiles of typical and atypical antipsychotic drugs in schizophrenia.

Central to the pathogenesis of Alzheimer disease is the aberrant processing of the amyloid precursor protein (APP) to generate amyloid ␤-peptide (A␤), the principle component of amyloid plaques. The cell fate determinant Numb is a phosphotyrosine binding domain (PTB)-containing endocytic adapter protein that interacts with the carboxyl-terminal domain of APP. The physiological relevance of this interaction is unknown. Mammals produce four alternatively spliced variants of Numb that differ in the length of their PTB and proline-rich region. In the current study, we determined the influence of the four human Numb isoforms on the intracellular trafficking and processing of APP. Stable expression of Numb isoforms that differ in the PTB but not in the proline-rich region results in marked differences in the sorting of APP to the recycling and degradative pathways. Neural cells expressing Numb isoforms that lack the insert in the PTB (short PTB (SPTB)) exhibited marked accumulation of APP in Rab5A-labeled early endosomal and recycling compartments, whereas those expressing isoforms with the insertion in the PTB (long PTB (LPTB)) exhibited reduced amounts of cellular APP and its proteolytic derivatives relative to parental control cells. Neither the activities of the ␤-and ␥-secretases nor the expression of APP mRNA were significantly different in the stably transfected cells, suggesting that the differential effects of the Numb proteins on APP metabolism is likely to be secondary to altered APP trafficking. In addition, the expression of SPTB-Numb increases at the expense of LPTB-Numb in neuronal cultures subjected to stress, suggesting a role for Numb in stress-induced A␤ production. Taken together, these results suggest distinct roles for the human Numb isoforms in APP metabolism and may provide a novel potential link between altered Numb isoform expression and increased A␤ generation. The amyloid precursor protein (APP)2 is an integral transmembrane glycoprotein that is highly expressed in the brain and plays an important role in neuronal function (1). The abnormal processing of APP to generate the amyloid ␤-peptide (A␤) leads to the extracellular neuritic plaques characteristic of Alzheimer disease (AD) (1-3). The rate of A␤ production is believed to be a key determinant of the onset and progression of AD. Although proteolytic processing of APP and characterization of the APP-cleaving enzymes (␣-, ␤-, and ␥-secretases) have revealed important targets for drug discovery, the regulation of APP trafficking is less well understood. Several recent findings support the idea that the intracellular transport and subcellular localization of APP are crucial determinants of APP processing and A␤ generation (4, 5). One pathway for A␤ generation involves the reinternalization of membrane-bound full-length APP (4, 5). Endosomes have been shown to be intracellular compartments, where the sequential action of ␤-and ␥-secretases generates amyloidogenic COOH-terminal fragments of APP (APP-CTFs) and A␤ (1-3). APP is also targeted to...

Neuroanatomical studies suggest that neuronal atrophy and destruction occur over the course of many years in neurodegenerative conditions such as schizophrenia and Alzheimer's disease. In schizophrenia, early intervention with atypical neuroleptics such as olanzapine has been shown to prevent development of some of the more serious and debilitating symptoms in many patients. The mechanisms whereby olanzapine slows or prevents symptom progression in schizophrenia remain unclear. A previous study found that olanzapine increased mRNA for the copper/zinc isoform of the superoxide dismutase enzyme (SOD-1). We investigated the effects of olanzapine in PC12 cells exposed to hydrogen peroxide. We measured cell viability, observed evidence of necrosis and apoptosis, checked the SOD-1 mRNA by Northern blot analyses, and determined SOD-1 enzyme activity. We found that: (1) the decrease in cell viability induced by hydrogen peroxide was attenuated in PC12 cells pretreated with olanzapine; (2) olanzapine increased SOD enzyme activity in PC12 cells; (3) inhibiting SOD activity with diethyldithiocarbamic acid prevented the cytoprotective actions of olanzapine; and (4) the decrease in SOD-1 mRNA level induced by hydrogen peroxide was blocked by pretreatment with olanzapine. These data indicate that the neuroprotective action of olanzapine includes the upregulation of SOD.

Atypical antipsychotic drugs are widely used in the treatment of schizophrenia, and clinical evidence has shown that early and prolonged intervention with these drugs will improve the long-term outcome. It is still unclear, however, whether the atypical antipsychotic drugs are also neuroprotective. To clarify this matter, we used PC12 cell cultures and the MTT assay for cell viability to determine whether various concentrations of the atypical antipsychotics clozapine, quetiapine, and risperidone are neuroprotective after serum withdrawal. In addition, to explore the drugs' actions, Northern blot was used to examine the gene expression of SOD1 (Cu/Zn superoxide dismutase) and p75NTR (p75 neurotrophin receptor). The results demonstrated that 1) the antipsychotic drugs can protect PC12 cells from death after serum withdrawal; cell viability in these drug treatment groups is significantly different from that in the groups without serum in the medium (P < 0.01); and 2) these drugs up-regulated the SOD1 gene expression to more than 120% (P < 0.05) and also down-regulated p75NTR mRNA levels to less than 65% of their respective control values (P < 0.05). These findings suggest that the atypical antipsychotics clozapine, quetiapine, and risperidone may exert a neuroprotective function through the modulation of SOD1 and p75NTR expression.

The endoplasmic reticulum (ER) is a key organelle regulating intracellular Ca 2؉ homeostasis. Oxidants and mitochondria-derived free radicals can target ER-based Ca 2؉ regulatory proteins and cause uncontrolled Ca 2؉ release that may contribute to protracted ER stress and apoptosis. Several ER stress proteins have been suggested to counteract the deregulation of ER Ca 2؉ homeostasis and ER stress. Here we showed that knockdown of Herp, an ubiquitin-like domain containing ER stress protein, renders PC12 and MN9D cells vulnerable to 1-methyl-4-phenylpyridinium-induced cytotoxic cell death by a mechanism involving up-regulation of CHOP expression and ER Ca 2؉ depletion. Conversely, Herp overexpression confers protection by blocking 1-methyl-4-phenylpyridinium-induced CHOP upregulation, ER Ca 2؉ store depletion, and mitochondrial Ca 2؉ accumulation in a manner dependent on a functional ubiquitinproteasomal protein degradation pathway. Deletion of the ubiquitin-like domain of Herp or treatment with a proteasomal inhibitor abolished the central function of Herp in ER Ca 2؉ homeostasis. Thus, elucidating the underlying molecular mechanism(s) whereby Herp counteracts Ca 2؉ disturbances will provide insights into the molecular cascade of cell death in dopaminergic neurons and may uncover novel therapeutic strategies to prevent and ameliorate Parkinson disease progression.Parkinson disease (PD) 2 is the second most common agerelated neurodegenerative disorder that results in the selective degeneration of dopaminergic neurons of the substantia nigra pars compacta (1, 2). The proximate cause of selective degeneration of dopaminergic neurons in PD has not been clearly elucidated. Several mechanisms are inferred to play a role in the pathogenesis of PD based on studies from animals or in vitro studies using dopaminergic neurotoxins. These include mitochondrial dysfunction, oxidative stress, and impairment of the ubiquitin-proteasomal pathway (UPP) (1-3). It has been shown that several genes that are mutated in familial PD encode for proteins that have functions linked to UPP and mitochondria (1-3). The UPP plays a critical role in ER-associated protein degradation (ERAD), a protein quality control system of the ER that eliminates misfolded proteins in the ER lumen (4). UPP dysfunction results in the accumulation of misfolded or unfolded proteins within the ER, which induces ER stress (5).Important roles for ER stress and ER stress-induced cell death have been reported in a broad spectrum of pathological conditions (6). To alleviate ER stress and enhances cell survival, cells launch the unfolded protein response (UPR), an adaptive response to minimize accumulation of misfolded proteins that would otherwise be toxic to the cell (7). The biological objectives of the UPR are to reduce the overall protein translation, increase the production of ER localized chaperones, and increase the clearance of unfolded proteins by UPP (7). Although short time UPR activation serves to reduce the unfolded protein load, a protracted activation o...

We have demonstrated recently that atypical antipsychotics possess neuroprotective actions in H2O2-mediated and serum-withdrawal models of cell death. In the present study, we compared the ability of atypical and typical antipsychotics to protect against an insult mediated by Abeta(25-35), an apoptogenic fragment of the Alzheimer's disease-related beta-amyloid (Abeta) peptide. Treatment of PC12 cell cultures with Abeta(25-35) did not significantly alter total cellular expression levels of Bax, a proapoptotic Bcl-2 family member, or levels of Bcl-XL, an antiapoptotic analogue. Treatment with Abeta(25-35), however, did result in mitochondrial translocation of Bax, which effectively increased the mitochondrial ratio of Bax to Bcl-X(L). This relative increase in proapoptotic molecules was reduced by pretreatment with atypical (quetiapine and olanzapine) and typical (haloperidol) antipsychotics. We also observed a selective increase in proapoptotic Bcl-XS immunodetection in haloperidol-treated cells, which was evident particularly in the mitochondrial compartment. This increase in proapoptotic molecules may account for the lower neuroprotective potential of haloperidol, as determined by the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium (MTT) reduction assay. The disparate neuroprotective effects of atypical and typical antipsychotics/neuroleptics may be due to their respective abilities to regulate pro- and anti-apoptotic protein translocation and expression.