Valproate protects cells from ER stress-induced lipid accumulation and apoptosis by inhibiting glycogen synthase kinase-3

Activated microglia decrease histone acetylation and Nrf2-inducible anti-oxidant defence in astrocytes: restoring effects of inhibitors of HDACs, p38 MAPK and GSK3β

Histone deacetylase (HDAC) inhibitors have promising neuroprotective and anti-inflammatory properties although the exact mechanisms are unclear. We have earlier showed that factors from lipopolysaccharide (LPS)-activated microglia can down-regulate the astroglial nuclear factor-erythroid 2-related factor 2 (Nrf2)-inducible anti-oxidant defence. Here we have evaluated whether histone modification and activation of GSK3β are involved in these negative effects of microglia. Microglia were cultured for 24 h in serum-free culture medium to achieve microglia-conditioned medium from non-activated cells (MCM(0)) or activated with 10 ng/mL of LPS to produce MCM(10). Astrocyte-rich cultures treated with MCM(10) showed a time-dependent (0-72 h) increase in astroglial HDAC activity that correlated with lower levels of acetylation of histones H3 and H4 and decreased levels of the transcription factor Nrf2 and γ-glutamyl cysteine ligase modulatory subunit (γGCL-M) protein levels. The HDAC inhibitors valproic acid (VPA) and trichostatin-A (TSA) elevated the histone acetylation levels, restored the Nrf2-inducible anti-oxidant defence and conferred protection from oxidative stress-induced (H(2)O(2)) death in astrocyte-rich cultures exposed to MCM(10). Inhibitors of GSK3β (lithium) and p38 MAPK (SB203580) signaling pathways restored the depressed histone acetylation and Nrf2-related transcription whereas an inhibitor of Akt (Ly294002) caused a further decrease in Nrf2-related transcription. In conclusion, the study shows that well tolerated drugs such as VPA and lithium can restore an inflammatory induced depression in the Nrf2-inducible antioxidant defence, possibly via normalised histone acetylation levels.

The impact of glycogen synthase kinase 3β gene on psychotic mania in bipolar disorder patients

OBJECTIVE

The aim of this study was to examine the relationships between glycogen synthase 3β gene polymorphisms and bipolar I disorder, manic in a Korean sample.

METHODS

Patients with bipolar disorder (n=118) and a control group (n=158) were assessed by genotyping for GSK3β single nucleotide polymorphisms (SNPs) -1727A/T and -50C/T. The patients were divided into two groups according to the presence of psychotic symptoms (psychotic mania, n=92; non-psychotic mania, n=26) and also divided based on gender and age of onset. The severity of symptoms was measured using the Young Mania Rating Scale (YMRS) and the Brief Psychiatric Rating Scale (BPRS).

RESULTS

There were no significant differences in the genotype distributions or allelic frequencies of GSK3β polymorphisms and gender between patients with bipolar disorder and a normal control group. According to haplotype analysis, there was no association between these two groups. However, analysis of the age of onset of bipolar disorder revealed significant differences in genotype and allele distributions among the patients. Patients who were homozygous for the wild-type variant (TT) had an older age of onset than carriers of the mutant allele (A/A: 27.4±9.1; A/T: 30.1±11.8; T/T: 42.3±19.9; p=0.034). We detected differences in allele frequencies of the GSK3β -1727A/T polymorphism between the psychotic mania group and the non-psychotic mania group.

CONCLUSION

This study suggests that GSK3β polymorphisms are not associated with bipolar disorder. However, the GSK3β SNP -1727A/T is associated with age of onset and presence of psychotic symptoms in bipolar disorder.

Apoptotic cell death in the fission yeast Schizosaccharomyces pombe induced by valproic acid and its extreme susceptibility to pH change

Schizosaccharomyces pombe treated with valproic acid died with apoptotic markers such as DNA fragmentation, loss of a mitochondrial electrochemical gradient and chromatin condensation, independently of metacaspase, a yeast homolog of metazoan caspase. Sensitivity to valproic acid was strongly dependent on growth phase. Cells in a later growth phase were much more sensitive to valproic acid than those in an earlier one. Altering the pH of the medium with HCl and with NaOH also caused remarkable changes in sensitivity. Cells in an acidic medium were more sensitive to valproic acid. This pH-dependent change in sensitivity did not require de novo protein synthesis, and a change in pH 60 min after the administration of valproic acid affected sensitivity. These results suggest that the intracellular cell death process was susceptible to extracellular pH. Although a sir2 mutant of Saccharomyces cerevisiae has been reported to be resistant to valproic acid, mutations in sir2 did not affect the sensitivity to valproic acid of S. pombe.

Chronic ethanol consumption in mice alters hepatocyte lipid droplet properties

BACKGROUND

Hepatosteatosis is a common pathological feature of impaired hepatic metabolism following chronic alcohol consumption. Although often benign and reversible, it is widely believed that steatosis is a risk factor for development of advanced liver pathologies, including steatohepatitis and fibrosis. The hepatocyte alterations accompanying the initiation of steatosis are not yet clearly defined.

METHODS

Induction of hepatosteatosis by chronic ethanol consumption was investigated using the Lieber-DeCarli (LD) high fat diet model. Effects were assessed by immunohistochemistry and blood and tissue enzymatic assays. Cell culture models were employed for mechanistic studies.

RESULTS

Pair feeding mice ethanol (LD-Et) or isocaloric control (LD-Co) diets for 6 weeks progressively increased hepatocyte triglyceride accumulation in morphological, biochemical, and zonally distinct cytoplasmic lipid droplets (CLD). The LD-Et diet induced zone 2-specific triglyceride accumulation in large CLD coated with perilipin, adipophilin (ADPH), and TIP47. In LD-Co-fed mice, CLD were significantly smaller than those in LD-Et-fed mice and lacked perilipin. A direct role of perilipin in formation of large CLD was further suggested by cell culture studies showing that perilipin-coated CLD were significantly larger than those coated with ADPH or TIP47. LD-Co- and LD-Et-fed animals also differed in hepatic metabolic stress responses. In LD-Et but not LD-Co-fed mice, inductions were observed in the following: microsomal ethanol-oxidizing system [cytochrome P-4502E1 (CYP2E1)], hypoxia response pathway (hypoxia-inducible factor 1 alpha, HIF1α), endoplasmic reticulum stress pathway (calreticulin), and synthesis of lipid peroxidation products [4-hydroxynonenal (4-HNE)]. CYP2E1 and HIF1 α immunostaining localized to zone 3 and did not correlate with accumulation of large CLD. In contrast, calreticulin and 4-HNE immunostaining closely correlated with large CLD accumulation. Importantly, 4-HNE staining significantly colocalized with ADPH and perilipin on the CLD surface.

CONCLUSIONS

These data suggest that ethanol contributes to macrosteatosis by both altering CLD protein composition and inducing lipid peroxide adduction of CLD-associated proteins.

The teratogenic potencies of valproic acid derivatives and their effects on biological end-points are related to changes in histone deacetylase and Erk1/2 activities

Valproic acid (VPA) is a known teratogen. In the present study, the effects of VPA and seven VPA derivatives with different teratogenic potencies (isobutyl-, 5-methyl-, ethyl-, propyl-, butyl-, pentyl- and hexyl-4-yn-VPA) were investigated in L929 cells in vitro. Evaluated end-points included changes in cell proliferation, growth, cell cycle distribution, morphology, speed, glycogen synthase kinase-3β (GSK-3β) and Erk1/2 phosphorylation, and histone H3 acetylation. Changes in proliferation, growth, speed, Erk1/2 and GSK-3β-Tyr216 phosphorylation, and H3 acetylation were significantly associated with the teratogenic potencies of the VPA derivatives. However, in contrast to changes in Erk1/2 phosphorylation and H3 acetylation, significant changes in GSK-3β phosphorylation could only be obtained in response to prolonged incubation at high drug concentration. There was an association between changes in H3 acetylation and GSK-3β-Tyr216 phosphorylation, whereas none of these end-points were associated with changes in Erk1/2 phosphorylation. These results suggest that the teratogenic potencies of VPA and VPA derivatives are related to effects on both Erk1/2 and histone deacetylase activities, whereas changes in GSK-3β activity are possibly a secondary effect.

Glycogen synthase kinase-3 (GSK-3) inhibition attenuates hepatocyte lipoapoptosis

BACKGROUNDS & AIMS

Saturated free fatty acids induce hepatocyte lipoapoptosis, a key pathologic feature of non-alcoholic steatohepatitis. The saturated free fatty acid palmitate induces hepatocyte lipoapoptosis via an endoplasmic reticulum stress pathway resulting in c-Jun-N-terminal (JNK) activation. Glycogen synthase kinase (GSK)-3 is a serine/threonine kinase which may also promote JNK activation. Thus, our aim was to determine if GSK-3 inhibition suppresses palmitate induced JNK activation and lipoapoptosis.

METHODS

For these studies, we employed mouse primary hepatocytes, Huh-7 and Hep3B cell lines.

RESULTS

Palmitate-induced GSK-3 activation was identified by phosphorylation of its substrate glycogen synthase. GSK-3 pharmacologic inhibition, by GSK-3 inhibitor IX and enzastaurin, significantly reduced PA-mediated lipoapoptosis. More importantly, Huh-7 cells, in which either GSK-3α or GSK-3β isoforms were stably and selectively knocked down by shRNA, displayed resistance to palmitate-induced cytotoxicity. GSK-3 pharmacological inhibitors and shRNA-targeted knockdown of GSK-3α or GSK-3β also suppressed JNK activation by palmitate. JNK activation, in part, promotes lipoapotosis by inducing expression of the pro-apoptotic effector p53-upregulated modulator of apoptosis (PUMA). Consistent with this concept, GSK-3 pharmacologic inhibition also reduced PUMA cellular protein levels during exposure to palmitate. On the other hand, the GSK-3 inhibitors did not prevent PA induction of ER stress.

CONCLUSIONS

Our results suggest that GSK-3 activation promotes a JNK-dependent cytotoxic signaling cascade culminating in lipoapoptosis.

Reversion of the human calreticulin gene promoter to the ancestral type as a result of a novel psychosis-associated mutation

Development-dependent, tissue-specific expression of the calreticulin (CALR) gene in the gray matter coincides with the expression of psychoses phenotypes. We have recently reported instances of mutations within the core promoter sequence of the gene in schizoaffective disorder. In view of the mounting evidence on the genetic overlap in the psychiatric spectrum, we investigated this gene in a spectrum of patients afflicted with schizophrenia, schizoaffective disorder and major affective disorder. We found that a unique mutation at nucleotide -220 from the transcription start site, located at a conserved genomic block in the promoter region of the gene, co-occurs with the spectrum of psychoses (p<0.005). This mutation reverts the human promoter sequence to the ancestral type observed in chimpanzee, mouse, and several other species, implying that the genomic block harboring nucleotide -220 may be involved in the evolution of human-specific higher-order functions of the brain (e.g. language, conceptual thinking, and judgment), that are ubiquitously impaired in psychoses. We propose that CALR is not only a promising candidate in the spectrum of psychoses, but also, a gene that may be important in the human-unique brain processes.

Interaction networks of lithium and valproate molecular targets reveal a striking enrichment of apoptosis functional clusters and neurotrophin signaling

The overall neurobiological mechanisms by which lithium and valproate stabilize mood in bipolar disorder patients have yet to be fully defined. The therapeutic efficacy and dissimilar chemical structures of these medications suggest that they perturb both shared and disparate cellular processes. To investigate key pathways and functional clusters involved in the global action of lithium and valproate, we generated interaction networks formed by well-supported drug targets. Striking functional similarities emerged. Intersecting nodes in lithium and valproate networks highlighted a strong enrichment of apoptosis clusters and neurotrophin signaling. Other enriched pathways included MAPK, ErbB, insulin, VEGF, Wnt and long-term potentiation indicating a widespread effect of both drugs on diverse signaling systems. MAPK1/3 and AKT1/2 were the most preponderant nodes across pathways suggesting a central role in mediating pathway interactions. The convergence of biological responses unveils a functional signature for lithium and valproate that could be key modulators of their therapeutic efficacy.

Glycogen synthase kinase-3 regulates endoplasmic reticulum (ER) stress-induced CHOP expression in neuronal cells

Endoplasmic reticulum (ER) stress, often resulting from cellular accumulation of misfolded proteins, occurs in many neurodegenerative disorders, in part because of the relatively long lifetime of neurons. Excessive accumulation of misfolded proteins activates the unfolded protein response (UPR) that dampens protein synthesis and promotes removal of misfolded proteins to support survival of ER-stressed cells. However, the UPR also initiates apoptotic signaling to kill cells if recovery is not achieved. Thus, there is much interest in identifying determinants of the life-death switch and interventions that promote recovery and survival. One intervention that has consistently been shown to protect cells from ER stress-induced apoptosis is application of inhibitors of glycogen synthase kinase-3 (GSK3). Therefore, we examined where in the UPR pathway GSK3 inhibitors intercede to impede signaling towards apoptosis. Apoptosis following UPR activation can be mediated by activation of two transcription factors, ATF4 and ATF6, that activate expression of the death-inducing transcription factor C/EBP homologous protein (CHOP/GADD153) following ER stress. We found that ER stress activated ATF6 and ATF4, but these responses were not inhibited by pretreatment with GSK3 inhibitors. However, inhibition of GSK3 effectively reduced the expression of CHOP, and this was apparent in several types of neural-related cells and was evident after application of several structurally diverse GSK3 inhibitors. Therefore, reduction of CHOP activation provides one mechanism by which inhibitors of GSK3 are capable of shifting cell fate towards survival instead of apoptosis following ER stress.

Modulation of acetylation: creating a pro-survival and anti-inflammatory phenotype in lethal hemorrhagic and septic shock

Histone deacetylases (HDACs) play a key role in homeostasis of protein acetylation in histone and nonhistone proteins and in regulating fundamental cellular activities. In this paper we review and discuss intriguing recent developments in the use of histone deacetylase inhibitors (HDACIs) to combat some critical conditions in an animal model of hemorrhagic and septic shock. HDACIs have neuroprotective, cardioprotective, renal-protective, and anti-inflammatory properties; survival improvements have been significantly shown in these models. We discuss the targets and mechanisms underlying these effects of HDACIs and comment on the potential new clinical applications for these agents in the future. This paper highlights the emerging roles of HDACIs as acetylation modulators in models of hemorrhagic and septic shock and explains some contradictions encountered in previous studies.

Endoplasmic reticulum stress and lipid dysregulation

Cellular cholesterol homeostasis is a fundamental and highly regulated process. Transcription factors known as sterol regulatory element binding proteins (SREBPs) coordinate the expression of many genes involved in the biosynthesis and uptake of cholesterol. Dysregulation of SREBP activation and cellular lipid accumulation has been associated with endoplasmic reticulum (ER) stress and activation of the unfolded protein response (UPR). This review will provide an overview of ER stress and the UPR as well as cholesterol homeostasis and SREBP regulation, with an emphasis on their interaction and biological relevance.

High fluence low-power laser irradiation induces apoptosis via inactivation of Akt/GSK3β signaling pathway

High fluence low-power laser irradiation (HF-LPLI) is a newly discovered stimulus through generating reactive oxygen species (ROS) to trigger cell apoptosis. Activation of glycogen synthase kinase 3β (GSK3β) is proved to be involved in intrinsic apoptotic pathways under various stimuli. However, whether the proapoptotic factor GSK3β participates in HF-LPLI-induced apoptosis has not been elucidated. Therefore, in the present study, we investigated the involvement of GSK3β in apoptosis under HF-LPLI treatment (120 J/cm2, 633 nm). We found that GSK3β activation could promote HF-LPLI-induced apoptosis, which could be prevented by lithium chloride (a selective inhibitor of GSK3β) exposure or by GSK3β-KD (a dominant-negative GSK3β) overexpression. We also found that the activation of GSK3β by HF-LPLI was due to the inactivation of protein kinase B (Akt), a widely reported and important upstream negative regulator of GSK3β, indicating the existence and inactivation of Akt/GSK3β signaling pathway. Moreover, the inactivation of Akt/GSK3β pathway depended on the fluence of HF-LPLI treatment. Furthermore, vitamin c, a ROS scavenger, completely prevented the inactivation of Akt/GSK3β pathway, indicating ROS generation was crucial for the inactivation. In addition, GSK3β promoted Bax activation by down-regulating Mcl-1 upon HF-LPLI treatment. Taken together, we have identified a new and important proapoptotic signaling pathway that is consisted of Akt/GSK3β inactivation for HF-LPLI stimulation. Our research will extend the knowledge into the biological mechanisms induced by LPLI.

Effect of S-adenosylmethionine on neointimal formation after balloon injury in obese diabetic rats

AIMS

The association between hyperhomocysteinaemia and cardiovascular disease has been attributed to low levels of S-adenosylmethionine (SAM), a metabolic intermediate of homocysteine. However, the role of SAM in the development of restenosis has not been explored. Therefore, we investigated the effects of SAM on neointimal formation after balloon injury in obese diabetic rats and cultured cells.

METHODS AND RESULTS

Otsuka Long-Evans Tokushima fatty rats were divided into the following three groups: control (normal saline); SAM15; and SAM30 (15 and 30 mg/kg per day, respectively; n = 10 per group). SAM was administered orally from 1 week before carotid injury to 2 weeks thereafter. SAM treatment for 3 weeks caused a significant dose-dependent reduction in the intima-to-media ratio. SAM treatment significantly reduced the proliferation of vascular smooth muscle cells (VSMCs) and induced more apoptosis than was observed in the control group. This effect was accompanied by reduced circulating levels of high-sensitivity C-reactive protein and monocyte chemoattractant protein-1, reduced urine 8-hydroxy-2'-deoxyguanosine (8-OHdG), and increased adiponectin. Intima-to-media ratio correlated significantly with the levels of inflammatory markers, adiponectin, and 8-OHdG. In vitro experiments demonstrated that VSMC proliferation and migration and the adhesion of monocytes decreased in response to SAM. SAM treatment also reduced tumour necrosis factor-α-induced reactive oxygen species and tunicamycin-induced GRP78 expression in VSMCs.

CONCLUSION

These findings suggest that SAM exerts protective effects against restenosis after balloon injury in a rat model of type 2 diabetes by reducing the proliferation and inducing the apoptosis of VSMCs, modifying the inflammatory processes and reducing oxidative and endoplasmic reticulum stresses.

Effects of mood stabilizers on adult dentate gyrus-derived neural precursor cells

Neurogenesis in the adult dentate gyrus (DG) is considered to be partly involved in the action of mood stabilizers. However, it remains unclear how mood stabilizers affect neural precursor cells in adult DG. We have established a culture system of adult rat DG-derived neural precursor cells (ADP) and have shown that lithium, a mood stabilizer, and dexamethasone, an agonist of glucocorticoid receptor, reciprocally regulate ADP proliferation. Neurogenesis constitutes not only proliferation of neural precursor cells but also apoptosis and differentiation. To develop further understanding of mood stabilizer effects on neural precursor cells in adult DG, we investigated and compared the effects of four common mood stabilizers-lithium, valproate, carbamazepine, and lamotrigine-on ADP proliferation, apoptosis, and differentiation. ADP proliferation, decreased by dexamethasone, was examined using Alamar Blue assay. Using TUNEL assay, ADP apoptosis induced by staurosporine was examined. The differentiated ADP induced by retinoic acid was characterized by immunostaining with anti-GFAP or anti-Tuj1 antibody. Lithium and valproate, but not carbamazepine and lamotrigine, recovered ADP proliferation decreased by dexamethasone. All four mood stabilizers decreased ADP apoptosis. Retinoic acid differentiated ADP into both neurons and astrocytes. Lithium and carbamazepine increased the ratio of neurons and decreased that of astrocytes. However, valproate and lamotrigine increased the ratio of astrocytes and decreased that of neurons. Therefore, these four stabilizers exhibited both common and differential effects on ADP proliferation, apoptosis, and differentiation.

Valproate attenuates the risk of myocardial infarction in patients with epilepsy: a nationwide cohort study

PURPOSE

Patients with epilepsy have increased risk of myocardial infarction (MI). Valproate can exert anti-atherosclerotic effects. We therefore examined the risk of MI in patients with epilepsy receiving valproate.

METHODS

Two cohorts of patients with valproate-treated epilepsy and sex- and age-matched individuals (controls) from the general Danish population were identified by individual-level-linkage of nationwide registries and followed for 10 years. The two cohorts comprised patients treated with valproate at baseline and valproate-naïve patients initiating treatment in the study period, respectively. The hazard ratios (HR) of MI and all-cause death were estimated by two different Cox proportional-hazard models; valproate treatment was analysed as a baseline categorical covariate in the first cohort and as a time-dependent exposure covariate in the second cohort.

RESULTS

The two cohorts comprised 53,086 and 102,003 individuals, respectively. In the first cohort, the risk of MI was decreased (HR 0.75, 95% confidence interval 0.59-0.97) while the risk of all-cause death was increased (HR 2.11, 95% confidence interval 1.95-2.28), compared to the controls. In the second cohort, the risk of MI was decreased (HR 0.62, 95% confidence interval 0.53-0.73) while the risk of all-cause death was similar to the controls (HR 1.02, 95% confidence interval 0.97-1.07).

CONCLUSIONS

In this nationwide pharmacoepidemiological study, we found a consistent association between valproate treatment and a reduced risk of MI in patients with epilepsy.

Is glycogen synthase kinase-3 a central modulator in mood regulation?

Little is known regarding the mechanisms underlying the complex etiology of mood disorders, represented mainly by major depressive disorder and bipolar disorder. The 1996 discovery that lithium inhibits glycogen synthase kinase-3 (GSK3) raised the possibility that impaired inhibition of GSK3 is associated with mood disorders. This is now supported by evidence from animal biochemical, pharmacological, molecular, and behavioral studies and from human post-mortem brain, peripheral tissue, and genetic studies that are reviewed here. Mood disorders may result in part from impairments in mechanisms controlling the activity of GSK3 or GSK3-regulated functions, and disruptions of these regulating systems at different signaling sites may contribute to the heterogeneity of mood disorders. This substantial evidence supports the conclusion that bolstering the inhibitory control of GSK3 is an important component of the therapeutic actions of drugs used to treat mood disorders and that GSK3 is a valid target for developing new therapeutic interventions.

Atherosclerosis induced by a high-fat diet is alleviated by lithium chloride via reduction of VCAM expression in ApoE-deficient mice

Endothelial cell dysfunction may play an important role in the development of various vascular diseases, including atherosclerosis. Here we investigated whether lithium chloride (LiCl), an inhibitor of glycogen synthase kinase-3β (GSK-3β), could counteract atherosclerosis induced by a high-fat diet in ApoE⁻/⁻ mice. Ten-week-old male mice were randomly divided into four groups: normal chow diet, high-fat diet (i.e., 20% fat and 0.5% cholesterol), high-fat diet with LiCl treatment for 6 weeks and high-fat diet with LiCl treatment for 14 weeks. Examination of plasma profiles indicated that blood glucose levels were significantly decreased by LiCl treatment. Supplementation with LiCl dramatically reduced atherosclerotic lesion formation in the aorta and aortic root. LiCl treatment also decreased vascular cell adhesion molecule (VCAM)-1 expression and macrophage infiltration into atherosclerotic lesion areas within the aortic valve. In addition, inhibition of GSK-3β by TDZD-8, SB216763, and LiCl, as well as adenoviral transduction with a catalytically inactive GSK-3β, reduced palmitate-induced VCAM-1 expression through inhibition of JNK activity and degradation of Iκ-Bα in human umbilical vein endothelial cells (HUVECs). The results of the present study suggest that LiCl alleviates palmitate-induced cell adhesion molecule expression in HUVECs and decreases atherosclerosis induced by a high-fat diet in ApoE⁻/⁻ mice. Thus, GSK-3β may be involved in the development of atherosclerosis induced by a high-fat diet in ApoE⁻/⁻ mice.

The mood stabilizers valproic acid and lithium enhance mesenchymal stem cell migration via distinct mechanisms

Mesenchymal stem cells (MSCs) show high potential for the therapy of several human diseases; however, the effectiveness of MSC transplantation has been hampered by the relatively poor migratory capacity of these cells toward disease target sites. This study investigated whether treatment of MSCs with two mood stabilizers-valproic acid (VPA) and lithium-would enhance cell migration and, if so, to explore the mechanisms underlying their effects. Short-term (3 h) exposure of MSCs to a relatively high concentration (2.5 mM) of VPA markedly increased the transcript and protein levels of CXC chemokine receptor 4 (CXCR4). VPA-induced CXCR4 expression required inhibition of histone deacetylases (HDACs), including the HDAC1 isoform, and involved histone hyperacetylation at the promoter region of the CXCR4 gene. Notably, VPA treatment enhanced stromal cell-derived factor-1α (SDF-1α)-mediated MSC migration, which was completely blocked by AMD3100, a CXCR4 antagonist. Treatment of MSCs with lithium (2.5 mM for 1 day) selectively elevated the transcript and protein levels of matrix metalloproteinase-9 (MMP-9) and its enzymatic activity; these effects were mimicked by inhibition or gene silencing of glycogen synthase kinase-3β (GSK-3β). Lithium treatment also potentiated SDF-1α-dependent MSC migration across the extracellular matrix, which was suppressed by two MMP-9 inhibitors, doxycycline and GM6001. Combining VPA and lithium treatment further increased MSC migration. Overall, VPA and lithium stimulated MSC migration through distinct targets and mediators: HDAC-CXCR4 and GSK-3β-MMP-9, respectively.

Neurons derived from transplanted neural stem cells restore disrupted neuronal circuitry in a mouse model of spinal cord injury

The body's capacity to restore damaged neural networks in the injured CNS is severely limited. Although various treatment regimens can partially alleviate spinal cord injury (SCI), the mechanisms responsible for symptomatic improvement remain elusive. Here, using a mouse model of SCI, we have shown that transplantation of neural stem cells (NSCs) together with administration of valproic acid (VPA), a known antiepileptic and histone deacetylase inhibitor, dramatically enhanced the restoration of hind limb function. VPA treatment promoted the differentiation of transplanted NSCs into neurons rather than glial cells. Transsynaptic anterograde corticospinal tract tracing revealed that transplant-derived neurons reconstructed broken neuronal circuits, and electron microscopic analysis revealed that the transplant-derived neurons both received and sent synaptic connections to endogenous neurons. Ablation of the transplanted cells abolished the recovery of hind limb motor function, confirming that NSC transplantation directly contributed to restored motor function. These findings raise the possibility that epigenetic status in transplanted NSCs can be manipulated to provide effective treatment for SCI.

Persistent organic pollutants, mitochondrial dysfunction, and metabolic syndrome

The number of individuals with metabolic syndrome is increasing worldwide, constituting a major social problem in many countries. Recently, epidemiological and experimental studies have associated insulin resistance or type 2 diabetes with elevated body burdens of persistent organic pollutants (POPs). It has been proposed that mitochondrial dysfunction plays a key role in this association. Mitochondrial DNA abnormalities are known to cause pancreas beta cell damage, insulin resistance, and diabetes mellitus. Recently, much evidence has emerged showing that environmental toxins, including POPs, affect mitochondrial function and subsequently induce insulin resistance. In this review, we present a novel concept in which metabolic syndrome is the result of mitochondrial dysfunction, which in turn is caused by exposure to POPs. The potential mechanism including POPs for mitochondrial dysfunction on metabolic syndrome is also discussed. We propose that the mitochondrial paradigm for the etiology of metabolic syndrome will facilitate the prevention and treatment of this major health problem.

Activation of PERK signaling attenuates Abeta-mediated ER stress

Alzheimer's disease (AD) is characterized by the deposition of aggregated beta-amyloid (Abeta), which triggers a cellular stress response called the unfolded protein response (UPR). The UPR signaling pathway is a cellular defense system for dealing with the accumulation of misfolded proteins but switches to apoptosis when endoplasmic reticulum (ER) stress is prolonged. ER stress is involved in neurodegenerative diseases including AD, but the molecular mechanisms of ER stress-mediated Abeta neurotoxicity still remain unknown. Here, we show that treatment of Abeta triggers the UPR in the SK-N-SH human neuroblastoma cells. Abeta mediated UPR pathway accompanies the activation of protective pathways such as Grp78/Bip and PERK-eIF2alpha pathway, as well as the apoptotic pathways of the UPR such as CHOP and caspase-4. Knockdown of PERK enhances Abeta neurotoxicity through reducing the activation of eIF2alpha and Grp8/Bip in neurons. Salubrinal, an activator of the eIF2alpha pathway, significantly increased the Grp78/Bip ER chaperone resulted in attenuating caspase-4 dependent apoptosis in Abeta treated neurons. These results indicate that PERK-eIF2alpha pathway is a potential target for therapeutic applications in neurodegenerative diseases including AD.

Depression research: where are we now?

Extensive studies have led to a variety of hypotheses for the molecular basis of depression and related mood disorders, but a definite pathogenic mechanism has yet to be defined. The monoamine hypothesis, in conjunction with the efficacy of antidepressants targeting monoamine systems, has long been the central topic of depression research. While it is widely embraced that the initiation of antidepressant efficacy may involve acute changes in monoamine systems, apparently, the focus of current research is moving toward molecular mechanisms that underlie long-lasting downstream changes in the brain after chronic antidepressant treatment, thereby reaching for a detailed view of the pathophysiology of depression and related mood disorders. In this minireview, we briefly summarize major themes in current approaches to understanding mood disorders focusing on molecular views of depression and antidepressant action.

Novel mutations in the calreticulin gene core promoter and coding sequence in schizoaffective disorder

We have recently reported the first case of mutation in the core promoter sequence of the human calreticulin gene in a family case of schizoaffective disorder. Remarkably, this gene coincides with a region of suggested linkage at 19p13.2, identified in a whole genome scan [Hamshere et al. (2005); Arch Gen Psychiatry 62;1081-1088]. The identified mutation was located at the conserved position -48 from the transcription start site, and was shown to be of functional effect, resulting in the aberrant expression of the gene. Following screening of the gene in 60 independent cases of schizoaffective disorder, we report novel germ-line mutations at positions -205 C > T and the conserved exon 5 (c: 682 C > T, pro228ser) in two unrelated cases of schizoaffective disorder. These mutations were disease-specific, and as for the -48 G > C mutation, neither was detected in a control population of 370 individuals, indicating a contribution of 3.17% in this sample series. To our knowledge, this is the first instance of disease-specific mutations in schizoaffective disorder, which warrants systematic screening of the regulatory and coding regions of the calreticulin gene in this disorder.

Hexosamine biosynthesis pathway flux promotes endoplasmic reticulum stress, lipid accumulation, and inflammatory gene expression in hepatic cells

There is increasing evidence that endoplasmic reticulum (ER) stress contributes to the development of atherosclerosis in diabetes mellitus. The purpose of this study was to determine the effects of increased hexosamine biosynthesis pathway (HBP) flux on ER stress levels and the complications of ER stress associated with diabetes and atherosclerosis in hepatic cells. Glutamine:fructose-6-phosphate amidotransferase (GFAT), the rate-limiting enzyme of the HBP, was overexpressed in HepG2 cells by use of an adenoviral expression system. The ER stress response and downstream effects, including activation of lipid and inflammatory pathways, were determined using real-time PCR, immunoblot analysis, and cell staining techniques. GFAT overexpression resulted in increased expression of ER stress markers, including Grp78, Grp94, calreticulin, and GADD153, relative to cells infected with an empty adenoviral vector. In addition, GFAT overexpression promoted lipid, but not cholesterol, accumulation in hepatic cells as well as inflammatory pathway activation. Treatment with 6-diazo-5-oxo-norleucine, a GFAT antagonist, blocked the effects of GFAT overexpression. Consistent with our in vitro data, hyperglycemic mice presented with elevated markers of hepatic ER stress, glucosamine and lipid accumulation. Together, these data suggest that HBP flux-induced ER stress plays a role in the development of hepatic steatosis and atherosclerosis under conditions of hyperglycemia.

Urocortin modulates dopaminergic neuronal survival via inhibition of glycogen synthase kinase-3β and histone deacetylase

Urocortin (UCN) is a member of the corticotropin-releasing hormone (CRH) family of neuropeptides that regulates stress responses. Although UCN is principally expressed in dopaminergic neurons in rat substantia nigra (SN), the function of UCN in modulating dopaminergic neuronal survival remains unclear. Using primary mesencephalic cultures, we demonstrated that dopaminergic neurons underwent spontaneous cell death when their age increased in culture. Treatment of mesencephalic cultures with UCN markedly prolonged the survival of dopaminergic neurons, whereas neutralization of UCN with anti-UCN antibody accelerated dopaminergic neurons degeneration. UCN increased intracellular cAMP levels followed by phosphorylating glycogen synthase kinase-3β (GSK-3β) on Ser9. Moreover, UCN directly inhibited the histone deacetylase (HDAC) activity and induced a robust increase in histone H3 acetylation levels. Using pharmacological approaches, we further demonstrated that inhibition of GSK-3β and HDAC contributes to UCN-mediated neuroprotection. These results suggest that dopaminergic neuron-derived UCN might be involved in an autocrine protective signaling mechanism.

Evidence supporting a role for endoplasmic reticulum stress in the development of atherosclerosis in a hyperglycaemic mouse model

We previously observed a correlation between elevated levels of vascular endoplasmic reticulum (ER) stress and accelerated atherosclerotic plaque development in chronically hyperglycemic apolipoprotein-deficient (ApoE(-/-)) mice. We hypothesize that ER stress plays a causative role in diabetic atherogenesis. Here we examine the temporal relation between the onset of hyperglycemia, glucosamine accumulation in the vessel wall, ER stress, and the development of atherosclerosis. We demonstrate, by using streptozotocin-induced hyperglycemic ApoE(-/-) mice, that conditions of hyperglycemia increase intracellular glucosamine levels and endothelial ER stress levels in the endothelium before the onset of atherosclerosis. At 15 weeks of age, hyperglycemic mice have significantly larger atherosclerotic lesions (0.120 +/- 0.023 vs. 0.065 +/- 0.021 mm2; p = 0.001) relative to normoglycemic mice. Significantly, hyperglycemia-associated accelerated atherosclerosis is observed before the onset of dyslipidemias, suggesting that leveled glucose is sufficient to promote atherogenesis independently. Diagnostic markers of elevated ER-stress levels are increased in macrophage-derived foam cells in early and advanced atherosclerotic lesions. Dietary supplementation with valproate, a small branched-chain fatty acid that interferes with ER-stress signaling, significantly attenuates accelerated atherogenesis in this model. Together, these data are consistent with a causative role for hyperglycemia-associated ER stress in the development and progression of diabetic atherosclerosis.

Phenylbutyrate ameliorates cognitive deficit and reduces tau pathology in an Alzheimer's disease mouse model

Chromatin modification through histone acetylation is a molecular pathway involved in the regulation of transcription underlying memory storage. Sodium 4-phenylbutyrate (4-PBA) is a well-known histone deacetylase inhibitor, which increases gene transcription of a number of genes, and also exerts neuroprotective effects. In this study, we report that administration of 4-PBA reversed spatial learning and memory deficits in an established mouse model of Alzheimer's disease (AD) without altering beta-amyloid burden. We also observed that the phosphorylated form of tau was decreased in the AD mouse brain after 4-PBA treatment, an effect probably due to an increase in the inactive form of the glycogen synthase kinase 3beta (GSK3beta). Interestingly, we found a dramatic decrease in brain histone acetylation in the transgenic mice that may reflect an indirect transcriptional repression underlying memory impairment. The administration of 4-PBA restored brain histone acetylation levels and, as a most likely consequence, activated the transcription of synaptic plasticity markers such as the GluR1 subunit of the AMPA receptor, PSD95, and microtubule-associated protein-2. The results suggest that 4-PBA, a drug already approved for clinical use, may provide a novel approach for the treatment of AD.

Sigma-1 receptor knockout mice display a depressive-like phenotype

Activation of sigma-1 receptors (Sig-1R) reportedly has antidepressant-like action. Limited data suggest that Sig-1Rs also modulate anxiety-related behaviors. The present experiments measured depressive-like, anxiety-like and motor behavior in Sig-1R knockout mice and their wildtype littermates. Sig-1R knockout mutants showed increased immobility in the forced swimming test, a depressive-like phenotype, but normal anxiety-like behavior in the elevated plus-maze and light/dark box tests and normal locomotor activity. The results further suggest that Sig-1Rs inversely modulate depressive-like behavior.

The unfolded protein response is activated in pretangle neurons in Alzheimer's disease hippocampus

Accumulation of misfolded proteins in the endoplasmic reticulum triggers a cellular stress response called the unfolded protein response (UPR) that protects the cell against the toxic buildup of misfolded proteins. Previously, we reported that UPR activation is increased in Alzheimer's disease (AD) patients. How the UPR relates to the pathological hallmarks of AD is still elusive. In the present study, the involvement of UPR activation in neurofibrillary degeneration in AD was investigated. Immunoreactivity for the phosphorylated UPR activation markers pancreatic ER kinase (pPERK), eukaryotic initiation factor 2alpha, and inositol-requiring enzyme 1alpha was observed in hippocampal neurons associated with granulovacuolar degeneration. The percentage of pPERK-immunoreactive neurons was increased in AD cases compared with nondemented control cases and with the Braak stage for neurofibrillary changes. Although absent from neurofibrillary tangles, pPERK immunoreactivity was most abundant in neurons with diffuse localization of phosphorylated tau protein. Additional analyses showed that pPERK immunoreactivity was associated with ubiquitin and the ubiquitin binding protein p62. A strong co-occurrence of immunoreactivity for both pPERK and glycogen synthase kinase 3beta in neurons was also observed. Together, these data indicate that UPR activation in AD neurons occurs at an early stage of neurofibrillary degeneration and suggest that the prolonged activation of the UPR is involved in both tau phosphorylation and neurodegeneration in AD pathogenesis.

ER stress and unfolded protein response in amyotrophic lateral sclerosis

Several theories on the pathomechanism of amyotrophic lateral sclerosis (ALS) have been proposed: misfolded protein aggregates, mitochondrial dysfunction, increased glutamate toxicity, increased oxidative stress, disturbance of intracellular trafficking, and so on. In parallel, a number of drugs that have been developed to alleviate the putative key pathomechanism of ALS have been under clinical trials. Unfortunately, however, almost all studies have finished unsuccessfully. This fact indicates that the key ALS pathomechanism still remains a tough enigma. Recent studies with autopsied ALS patients and studies using mutant SOD1 (mSOD1) transgenic mice have suggested that endoplasmic reticulum (ER) stress-related toxicity may be a relevant ALS pathomechanism. Levels of ER stress-related proteins were upregulated in motor neurons in the spinal cords of ALS patients. It was also shown that mSOD1, translocated to the ER, caused ER stress in neurons in the spinal cord of mSOD1 transgenic mice. We recently reported that the newly identified ALS-causative gene, vesicle-associated membrane protein-associated protein B (VAPB), plays a pivotal role in unfolded protein response (UPR), a physiological reaction against ER stress. The ALS-linked P56S mutation in VAPB nullifies the function of VAPB, resulting in motoneuronal vulnerability to ER stress. In this review, we summarize recent advances in research on the ALS pathomechanism especially addressing the putative involvement of ER stress and UPR dysfunction.

Roles of endoplasmic reticulum stress in liver steatosis of type 2 diabetic mice

AIM: To investigate the roles of endoplasmic reticulum stress (ERS) in development of liver steatosis.

METHODS: The differential expressions of ERS and lipid metabolism related genes in the liver of T2DM and non-T2DM mice were analyzed using real-time quantitative RT-PCR. Serum total cholesterol (TC), triglyceride (TG), low-density lipoprotein cholesterol (LDL-C), free fatty acid (FFA), alanine amino transferase (ALT) and aspartate amino transferase (AST) levels were determined. The liver TG, FFA content and morphology were also analyzed.

RESULTS: Compared with non-T2DM, T2DM mice had manifestations: (1) Insulin Resistance, increased fasting blood glucose (increased 30.76 ± 4.52 vs 12.80 ± 2.13, 14.73 ± 2.74 vs 4.61 ± 1.12); (2) obviously elevated liver TG and FFA levels (P < 0.01); marked lesion of fatty liver was observed. (3) Up-regulated liver glucose regulated protein 78 (GRP78), X-box binding protein 1 (XBP1), C/EBP homologous protein (CHOP), mannosidase alpha-like 1 (EDEM1), glycogen synthase kinase3β (GSK3β), apolipoprotein100 (apoB100), sterol regulatory element binding proteins1c (SREBP1c), acetyl CoA carboxylase α (ACCα) and fatty acid synthase (FAS) mRNA levels (P < 0.05). (4) Significantly increased serum TG, TC, LDL-C, FFA, ALT and AST (P < 0.01). Serum apoB100 was first increased and then decreased (P < 0.05).

CONCLUSION: ERS plays a central role in the development of liver steatosis in the T2DM mouse through increased lipogenesis and decreased secretion of apoB100.

Challenges and new opportunities in the investigation of new drug therapies to treat frontotemporal dementia

BACKGROUND

Frontotemporal dementia spectrum disorders are a set of neurodegenerative disorders affecting the frontal and anterior temporal lobes. They are often fatal, and currently no medications have been shown to slow their progression. Recent developments in understanding these disorders may aid in developing treatments.

OBJECTIVE

To discuss the development of drug therapies for frontotemporal dementia spectrum disorders, both those under current investigation and those that could be targets for future investigation.

METHODS

This review is divided into four sections: First, a brief review of frontotemporal dementia spectrum disorders; second, a discussion of the challenges in the development of drug therapies third, a review of the current clinical trials; and finally a discussion of some recent discoveries, which have sparked new areas of investigation.

CONCLUSIONS

Hopefully, advances in understanding of frontotemporal dementia spectrum disorders and clinical trial design will aid the development of new treatments.

Inhibition of arachidonic acid and iron-induced mitochondrial dysfunction and apoptosis by oltipraz and novel 1,2-dithiole-3-thione congeners

4-Methyl-5-(2-pyrazinyl)-1,2-dithiole-3-thione (oltipraz), a prototype drug candidate containing a 1,2-dithiole-3-thione moiety, has been widely studied as a cancer chemopreventive agent. Oltipraz and other novel 1,2-dithiole-3-thione congeners have the capability to prevent insulin resistance via AMP-activated protein kinase (AMPK) activation. Arachidonic acid (AA, a proinflammatory fatty acid) exerts a deleterious effect on mitochondria and promotes reactive oxygen species (ROS) production. This study investigated whether AA alone or in combination with iron (catalyst of autooxidation) causes ROS-mediated mitochondrial impairment, and if so, whether oltipraz and synthetic 1,2-dithiole-3-thiones protect mitochondria and cells against excess ROS produced by AA + iron. Oltipraz treatment effectively inhibited mitochondrial permeability transition promoted by AA + iron in HepG2 cells, thereby protecting cells from ROS-induced apoptosis. Oltipraz was found to attenuate apoptosis induced by rotenone (complex I inhibitor), but not that by antimycin A (complex III inhibitor), suggesting that the inhibition of AA-induced apoptosis by oltipraz might be associated with the electron transport system. AMPK activation by oltipraz contributed to cell survival, which was supported by the reversal of oltipraz's restoration of mitochondrial membrane potential by concomitant treatment of compound C. By the same token, an AMPK activator inhibited AA + iron-induced mitochondrial permeability transition with an increase in cell viability. Moreover, new 1,2-dithiole-3-thiones with the capability of AMPK activation protected cells from mitochondrial permeability transition and ROS overproduction induced by AA + iron. Our results demonstrate that oltipraz and new 1,2-dithiole-3-thiones are capable of protecting cells from AA + iron-induced ROS production and mitochondrial dysfunction, which may be associated with AMPK activation.

Isolation stress for 30 days alters hepatic gene expression profiles, especially with reference to lipid metabolism in mice

To elucidate the physiological responses to a social stressor, we exposed mice to an isolation stress and analyzed their hepatic gene expression profiles using a DNA microarray. Male BALB/c mice were exposed to isolation stress for 30 days, and then hepatic RNA was sampled and subjected to DNA microarray analysis. The isolation stress altered the expression of 420 genes (after considering the false discovery rate). Gene Ontology analysis of these differentially expressed genes indicated that the stress remarkably downregulated the lipid metabolism-related pathway through peroxisome proliferator-activated receptor-alpha, while the lipid biosynthesis pathway controlled by sterol regulatory element binding factor 1, Golgi vesicle transport, and secretory pathway-related genes were significantly upregulated. These results suggest that isolation for 30 days with a mild and consecutive social stress regulates the systems for lipid metabolism and also causes endoplasmic reticulum stress in mouse liver.

Valproate attenuates accelerated atherosclerosis in hyperglycemic apoE-deficient mice: evidence in support of a role for endoplasmic reticulum stress and glycogen synthase kinase-3 in lesion development and hepatic steatosis

We have previously shown that glucosamine promotes endoplasmic reticulum (ER) stress in vascular cells leading to both inflammation and lipid accumulation--the hallmark features of atherosclerosis. Pretreatment with glycogen synthase kinase (GSK)-3 inhibitors protects cultured cells from ER stress-induced dysfunction. Here we evaluate the potential role of GSK-3 on the pro-atherogenic effects of hyperglycemia and ER stress. We show that GSK-3-deficient mouse embryonic fibroblasts do not accumulate unesterified cholesterol under conditions of ER stress. Furthermore, GSK-3 inhibitors, including valproate, attenuate ER stress-induced unesterified cholesterol accumulation in wild-type mouse embryonic fibroblasts. In vivo we show that hyperglycemic apoE-deficient mice have accelerated atherogenesis at the aortic root compared with normoglycemic control mice. Mice fed a diet supplemented with 625 mg/kg valproate have significantly reduced lesion volume relative to nonsupplemented controls. Valproate supplementation has no apparent effect on the plasma levels of either glucose or lipids or on the expression of diagnostic markers of ER stress in the lesion. Significant reductions were observed in total hepatic lipids (>50.4%) and hepatic GSK-3beta activity (>55.8%) in mice fed the valproate diet. In conclusion, dietary supplementation with low levels of valproate significantly attenuates atherogenesis in hyperglycemic apoE-deficient mice. The in vivo anti-atherogenic effects of valproate are consistent with its ability to inhibit GSK-3 and interfere with pro-atherogenic ER stress signaling pathways in vitro.

Targeting histone deacetylases for the treatment of disease

The ‘histone code’ is a well-established hypothesis describing the idea that specific patterns of post-translational modifications to histones act like a molecular ‘code’ recognized and used by non-histone proteins to regulate specific chromatin functions. One modification, which has received significant attention, is that of histone acetylation. The enzymes that regulate this modification are described as lysine acetyltransferases or KATs, and histone deacetylases or HDACs. Due to their conserved catalytic domain HDACs have been actively targeted as a therapeutic target. The pro-inflammatory environment is increasingly being recognized as a critical element for both degenerative diseases and cancer. The present review will discuss the current knowledge surrounding the clinical potential and current development of histone deacetylases for the treatment of diseases for which a pro-inflammatory environment plays important roles, and the molecular mechanisms by which such inhibitors may play important functions in modulating the pro-inflammatory environment.

Valproic acid inhibits Abeta production, neuritic plaque formation, and behavioral deficits in Alzheimer's disease mouse models

Neuritic plaques in the brains are one of the pathological hallmarks of Alzheimer's disease (AD). Amyloid β-protein (Aβ), the central component of neuritic plaques, is derived from β-amyloid precursor protein (APP) after β- and γ-secretase cleavage. The molecular mechanism underlying the pathogenesis of AD is not yet well defined, and there has been no effective treatment for AD. Valproic acid (VPA) is one of the most widely used anticonvulsant and mood-stabilizing agents for treating epilepsy and bipolar disorder. We found that VPA decreased Aβ production by inhibiting GSK-3β–mediated γ-secretase cleavage of APP both in vitro and in vivo. VPA treatment significantly reduced neuritic plaque formation and improved memory deficits in transgenic AD model mice. We also found that early application of VPA was important for alleviating memory deficits of AD model mice. Our study suggests that VPA may be beneficial in the prevention and treatment of AD.

Immortalized cortical neurons expressing caspase-cleaved tau are sensitized to endoplasmic reticulum stress induced cell death

It has been previously reported that an Asp421 cleaved form of tau is toxic when expressed in cells. The purpose of this study was to understand if, and in what manner, the presence of Asp421 cleaved tau in neurons, which is generated by caspase cleavage, might facilitate neuronal death in Alzheimer's disease (AD). For these studies we used immortalized cortical neurons that inducibly express either a full-length tau isoform (T4) or an isoform that has been pseudo-truncated at Asp421 (T4C3), to mimic caspase-3 cleavage. Neurons expressing either T4 or T4C3 were treated with thapsigargin, a drug, which has been shown to induce endoplasmic reticulum (ER) stress. Following long-term treatment with thapsigargin, cells expressing T4C3 presented with a marked increase in cell toxicity, underscored by differential activation of caspase-3 in comparison with cells expressing T4. Furthermore, we found that an inhibitor of the ERK1/2 signaling pathway, which is upregulated to different extents in each cell type, significantly reduced toxicity in both T4 and T4C3 cells. Our results suggest that the presence of Asp421 cleaved tau may sensitize neurons to ER stressors and possibly potentiate cell death processes during AD progression.

Mechanisms of action of the mood stabilizer valproate: a focus on GSK-3 inhibition

Valproate is the most widely prescribed antiepileptic drug worldwide, and it is also used in the treatment of bipolar affective disorder, migraine headache and cancer. However, the therapeutic mechanism of action of valproate in these illness states is not understood. This article reviews the pharmacological effects of valproate that may explain its therapeutic efficacy. It focuses on the hypothesis that inhibition of glycogen synthase kinase-3 by valproate is a crucial therapeutic mechanism of this drug in the treatment of bipolar affective disorder. Other cellular pathways and signaling molecules that are targets of valproate (such as inositol de novo biosynthesis, histone deacetylase, protein kinase C, γ-aminobutyric acid, the extracellular signal-regulated kinase pathway and others) are also discussed.