Valproate protects dopaminergic neurons in midbrain neuron/glia cultures by stimulating the release of neurotrophic factors from astrocytes

Overexpression of heme oxygenase-1 protects dopaminergic neurons against 1-methyl-4-phenylpyridinium-induced neurotoxicity

Heme oxygenase-1 (HO-1) is up-regulated in response to oxidative stress and catalyzes the degradation of pro-oxidant heme to carbon monoxide (CO), iron, and bilirubin. Intense HO-1 immunostaining in the Parkinsonian brain is demonstrated, indicating that HO-1 may be involved in the pathogenesis of Parkinsonism. We here locally injected adenovirus containing human HO-1 gene (Ad-HO-1) into rat substantia nigra concomitantly with 1-methyl-4-phenylpyridinium (MPP(+)). Seven days after injection of MPP(+) and Ad-HO-1, the brain was isolated for immunostaining and for measurement of dopamine content and inflammatory cytokines. It was found that overexpression of HO-1 significantly increased the survival rate of dopaminergic neurons; reduced the production of tumor necrosis factor alpha (TNF-alpha) and interleukin-1beta (IL-1beta) in substantia nigra; antagonized the reduction of striatal dopamine content induced by MPP(+); and also up-regulated brain-derived neurotrophic factor (BDNF) and glial cell line-derived neurotrophic factor (GDNF) expression in substantia nigra. Apomorphine-induced rotation after MPP(+) treatment was also inhibited by Ad-HO-1. On the other hand, inhibition of HO enzymatic activity by zinc protoporphyrin-IX facilitated the MPP(+)-induced rotatory behavior and enhanced the reduction of dopamine content. HO-1 overexpression also protected dopaminergic neurons against MPP(+)-induced neurotoxicity in midbrain neuron-glia cocultures. Overexpression of HO-1 increased the expression of BDNF and GDNF in astrocytes and BDNF in neurons. Our results indicate that HO-1 induction exerts neuroprotection both in vitro and in vivo. Pharmacological or genetic approaches targeting HO-1 may represent a promising and novel therapeutic strategy in treating Parkinsonism.

Histone deacetylase inhibitors up-regulate astrocyte GDNF and BDNF gene transcription and protect dopaminergic neurons

Parkinson's disease (PD) is characterized by the selective and progressive loss of dopaminergic (DA) neurons in the midbrain substantia nigra. Currently, available treatment is unable to alter PD progression. Previously, we demonstrated that valproic acid (VPA), a mood stabilizer, anticonvulsant and histone deacetylase (HDAC) inhibitor, increases the expression of glial cell line-derived neurotrophic factor (GDNF) and brain-derived neurotrophic factor (BDNF) in astrocytes to protect DA neurons in midbrain neuron-glia cultures. The present study investigated whether these effects are due to HDAC inhibition and histone acetylation. Here, we show that two additional HDAC inhibitors, sodium butyrate (SB) and trichostatin A (TSA), mimic the survival-promoting and protective effects of VPA on DA neurons in neuron-glia cultures. Similar to VPA, both SB and TSA increased GDNF and BDNF transcripts in astrocytes in a time-dependent manner. Furthermore, marked increases in GDNF promoter activity and promoter-associated histone H3 acetylation were noted in astrocytes treated with all three compounds, where the time-course for acetylation was similar to that for gene transcription. Taken together, our results indicate that HDAC inhibitors up-regulate GDNF and BDNF expression in astrocytes and protect DA neurons, at least in part, through HDAC inhibition. This study indicates that astrocytes may be a critical neuroprotective mechanism of HDAC inhibitors, revealing a novel target for the treatment of psychiatric and neurodegenerative diseases.

Drug-induced activation of dopamine D(1) receptor signaling and inhibition of class I/II histone deacetylase induce chromatin remodeling in reward circuitry and modulate cocaine-related behaviors

Chromatin remodeling, including histone modification, is involved in stimulant-induced gene expression and addiction behavior. To further explore the role of dopamine D(1) receptor signaling, we measured cocaine-related locomotor activity and place preference in mice pretreated for up to 10 days with the D(1) agonist SKF82958 and/or the histone deacetylase inhibitor (HDACi), sodium butyrate. Cotreatment with D(1) agonist and HDACi significantly enhanced cocaine-induced locomotor activity and place preference, in comparison to single-drug regimens. However, butyrate-mediated reward effects were transient and only apparent within 2 days after the last HDACi treatment. These behavioral changes were associated with histone modification changes in striatum and ventral midbrain: (1) a generalized increase in H3 phosphoacetylation in striatal neurons was dependent on activation of D(1) receptors; (2) H3 deacetylation at promoter sequences of tyrosine hydroxylase (Th) and brain-derived neurotrophic factor (Bdnf) in ventral midbrain, together with upregulation of the corresponding gene transcripts after cotreatment with D(1) agonist and HDACi. Collectively, these findings imply that D(1) receptor-regulated histone (phospho)acetylation and gene expression in reward circuitry is differentially regulated in a region-specific manner. Given that the combination of D(1) agonist and HDACi enhances cocaine-related sensitization and reward, the therapeutic benefits of D(1) receptor antagonists and histone acetyl-transferase inhibitors (HATi) warrant further investigation in experimental models of stimulant abuse.

Epigenetic targets for melatonin: induction of histone H3 hyperacetylation and gene expression in C17.2 neural stem cells

We have reported the induction of glial cell line-derived neurotrophic factor, a potent survival factor for dopaminergic neurons, in the C17.2 neural stem cell line following in vitro treatment with melatonin. Furthermore, we have detected the melatonin MT(1) receptor in these cells. Given these findings and recent evidence that melatonin may play a role in cellular differentiation, we examined whether this indoleamine induces morphological and transcriptional changes suggestive of a neuronal phenotype in C17.2 cells. Moreover, in order to extend preliminary evidence of a potential role for melatonin in epigenetic modulation, its effects on the mRNA expression of several histone deacetylase (HDAC) isoforms and on histone acetylation were examined. Physiological concentrations of melatonin (nanomolar range) increased neurite-like extensions and induced mRNA expression of the neural stem cell marker, nestin, the early neuronal marker beta-III-tubulin and the orphan nuclear receptor nurr1 in C17.2 cells. The indoleamine also significantly increased mRNA expression for various HDAC isoforms, including HDAC3, HDAC5, and HDAC7. Importantly, treatment with melatonin for 24 hr caused a significant increase in histone H3 acetylation, which is associated with chromatin remodeling and gene transcription. Since the melatonin MT(2) receptor was not detected in C17.2 cells, it is likely that the MT(1) receptor is involved in mediating these physiological effects of melatonin. These findings suggest novel roles for melatonin in stem cell differentiation and epigenetic modulation of gene transcription.

Enhancement of glutamate uptake in 1-methyl-4-phenylpyridinium-treated astrocytes by trichostatin A

Histone deacetylases (HDAC) inhibitors have been emerging as neuroprotective agents by acting on neurons and microglia. In this study, we found trichostatin A (TSA), a HDAC inhibitor, could inhibit the elevation of glutamate in 150 microM 1-methyl-4-phenylpyridinium (MPP+)-treated primary cultured astrocytes medium when its concentration reached 132 nM. TSA of 132 nM or more could promote the uptake of [3H]-D, L-glutamate by astrocytes. Further study showed the downregulation of glutamate transporter 1 and glutamate/aspartate transporter induced by MPP+ were prevented by TSA. Therefore, these findings suggested TSA could alleviate MPP+-induced impairment of astrocytic glutamate uptake, which might be a novel mechanism contributing to neuroprotection by HDAC inhibitors.

Driving GDNF expression: the green and the red traffic lights

Glial cell line-derived neurotrophic factor (GDNF) is widely recognized as a potent survival factor for dopaminergic neurons of the nigrostriatal pathway that degenerate in Parkinson's disease (PD). In animal models of PD, GDNF delivery to the striatum or the substantia nigra protects dopaminergic neurons against subsequent toxin-induced injury and rescues previously damaged neurons, promoting recovery of the motor function. Thus, GDNF was proposed as a potential therapy to PD aimed at slowing down, halting or reversing neurodegeneration, an issue addressed in previous reviews. However, the use of GDNF as a therapeutic agent for PD is hampered by the difficulty in delivering it to the brain. Another potential strategy is to stimulate the endogenous expression of GDNF, but in order to do that we need to understand how GDNF expression is regulated. The aim of this review is to do a comprehensive analysis of the state of the art on the control of endogenous GDNF expression in the nervous system, focusing mainly on the nigrostriatal pathway. We address the control of GDNF expression during development, in the adult brain and after injury, and how damaged neurons signal glial cells to up-regulate GDNF. Pharmacological agents or natural molecules that increase GDNF expression and show neuroprotective activity in animal models of PD are reviewed. We also provide an integrated overview of the signalling pathways linking receptors for these molecules to the induction of GDNF gene, which might also become targets for neuroprotective therapies in PD.

Why neurodegenerative diseases are progressive: uncontrolled inflammation drives disease progression

Neurodegenerative diseases are a group of chronic, progressive disorders characterized by the gradual loss of neurons in discrete areas of the central nervous system (CNS). The mechanism(s) underlying their progressive nature remains unknown but a timely and well-controlled inflammatory reaction is essential for the integrity and proper function of the CNS. Substantial evidence has documented a common inflammatory mechanism in various neurodegenerative diseases. We hypothesize that in the diseased CNS, interactions between damaged neurons and dysregulated, overactivated microglia create a vicious self-propagating cycle causing uncontrolled, prolonged inflammation that drives the chronic progression of neurodegenerative diseases. We further propose that dynamic modulation of this inflammatory reaction by interrupting the vicious cycle might become a disease-modifying therapeutic strategy for neurodegenerative diseases.

Early intervention in bipolar disorder, part II: therapeutics

Recent evidence has shown that early pharmacological and psychosocial treatment dramatically ameliorates poor prognosis and outcome for individuals with psychotic disorders, reducing conversion rates to full-blown illness and decreasing symptom severity. In a companion paper, we discussed methodological issues pertaining to early intervention in bipolar disorder (BPD), reviewed clinical studies that focus on high-risk subjects as well as first-episode patients, and reviewed findings from brain imaging studies in the offspring of individuals with BPD as well as in first-episode patients. In this paper, we discuss how drugs that modulate cellular and neural plasticity cascades are likely to benefit patients in the very early stages of BPD, because they target some of the core pathophysiological mechanisms of this devastating illness. Cellular and molecular mechanisms of action of agents with neurotrophic and neuroplastic properties are discussed, with a particular emphasis on lithium and valproate. We also discuss their potential use as early intervention strategies for improving symptoms and functioning in patients in the earliest stages of BPD, as well as high-risk individuals.

HDAC4 inhibits cell-cycle progression and protects neurons from cell death

HDAC4 is a Class II histone deacetylase (HDAC) that is highly expressed in the brain, but whose functional significance in the brain is not known. We show that forced expression of HDAC4 in cerebellar granule neurons protects them against low potassium-induced apoptosis. HDAC4 also protects HT22 neuroblastoma cells from death induced by oxidative stress. HDAC4-mediated neuroprotection does not require its HDAC catalytic domain and cannot be inhibited by chemical inhibitors of HDACs. Neuroprotection by HDAC4 also does not require the Raf-MEK-ERK or the PI-3 kinase-Akt signaling pathways and occurs despite the activation of c-jun, an event that is generally believed to condemn neurons to die. The protective action of HDAC4 occurs in the nucleus and is mediated by a region that contains the nuclear localization signal. HDAC4 inhibits the activity of cyclin-dependent kinase-1 (CDK1) and the progression of proliferating HEK293T and HT22 cells through the cell cycle. Mice-lacking HDAC4 have elevated CDK1 activity and display cerebellar abnormalities including a progressive loss of Purkinje neurons postnatally in posterior lobes. Surviving Purkinje neurons in these lobes have duplicated soma. Furthermore, large numbers of cells within these affected lobes incorporate BrdU, indicating cell-cycle progression. These abnormalities along with the ability of HDAC4 to inhibit CDK1 and cell-cycle progression in cultured cells suggest that neuroprotection by HDAC4 is mediated by preventing abortive cell-cycle progression.

Clinically relevant concentrations of valproic acid modulate melatonin MT(1) receptor, HDAC and MeCP2 mRNA expression in C6 glioma cells

C6 glioma cells were treated with clinically relevant concentrations of valproic acid (0.5 or 1.0 mM) for 1-7 days and RT-PCR used to examine expression of the melatonin MT(1) receptor and selected epigenetic modulators. Valproic acid caused significant time-dependent changes in the mRNA expression of the melatonin MT(1) receptor, histone deacetylase (HDAC) 1, 2 and 3, and methyl CpG binding protein 2 (MeCP2). A structurally distinct HDAC inhibitor, trichostatin A, also caused a significant concentration-dependent induction of melatonin MT(1) receptor mRNA expression, suggesting involvement of an epigenetic mechanism. The ability of clinical concentrations of valproic acid to significantly alter melatonin MT(1) receptor expression, suggests a role for this receptor in the diverse neuropharmacological and oncostatic effects of this agent.

Prevention of hypoxia-induced neuronal apoptosis through histone deacetylase inhibition

BACKGROUND

We have recently discovered that administration of valproic acid (VPA), a histone deacetylase inhibitor, enhances nuclear histone acetylation and improves survival after lethal hemorrhage in rats. In the present study, neurons were subjected to severe hypoxic condition in vitro to test whether VPA would prevent hypoxia-induced apoptosis, and to explore the possible mechanisms.

METHODS

Primary hippocampal and cortical cultures dissociated from E18 rat embryos were plated in quadruplicate at a density of 2 x 10/well in neurobasal medium supplemented with B-27 on glass cover-slips coated with poly-l-lysine. On the 10th day after plating, cells were incubated in a hypoxia chamber (0.5% O2, 10% CO2, 89.5% N2) at 37 degrees C for 6 hour and 16 hour in the presence or absence of VPA (1 mmol/L). The cells were then fixed, stained with antiactivated caspase-3 and antiacetyl histone H3 lysine 9 (Ac H3 K9) antibodies and visualized under confocal microscope. The caspase-3 positive cells were counted as apoptotic. Ratio of the apoptotic to total cells stained with 4',6-diamidino-2-phenylindole was determined. Numerical data were subjected to t test analysis. p < 0.05 was considered statistically significant. Western blot was performed to determine the level of acetylation of nuclear factor-kappa B (NF-kappaB) and phospho-JNK (c-Jun N-terminal kinase) in cells treated with or without VPA. Luciferase report assay was employed to analyze the activation of NF-kappaB after the cells were transfected with NF-kBLuc with or without VPA treatment.

RESULTS

Exposure of neurons to VPA prevented apoptotic cell death under hypoxic conditions (20% apoptosis). In contrast, about 95% cells underwent apoptosis at the same level of hypoxia. VPA treatment induced acetylation of histone H3 K9 and NF-kappaB lysine 310. NF-kappaB was activated at the same time as the protein acetylation. Moreover, JNK phosphorylation was inhibited after the cells were treated with VPA under hypoxia condition.

CONCLUSION

VPA enhances acetylation of histone 3 at lysine 9 and NF-kappaB at 310, induces NF-kappaB activation, reduces JNK activation, and protects the neurons from hypoxia-induced apoptosis in vitro.

Inflammatory priming of the substantia nigra influences the impact of later paraquat exposure: Neuroimmune sensitization of neurodegeneration

Activation of microglia along with the release of inflammatory cytokines and oxidative factors often accompanies toxin-induced degeneration of substantia nigra pars compacta (SNc) dopamine (DA) neurons. Multiple toxin exposure may synergistically influence microglial-dependent DA neuronal loss and, in fact, pre-treatment with one toxin may sensitize DA neurons to the impact of subsequent insults. Thus, we assessed whether priming SNc neurons with the inflammatory agent, lipopolysaccharide (LPS), influenced the impact of later exposure to the pesticide, paraquat, which has been reported to provoke DA loss. Indeed, LPS infusion into the SNc sensitized DA neurons to the neurodegenerative effects of a series of paraquat injections commencing 2 days later. In contrast, LPS pre-treatment actually protected against some of neurodegenerative effects of paraquat when the pesticide was administered 7 days after the endotoxin. These sensitization and de-sensitization effects were associated with altered expression of reactive microglia expressing inducible immunoproteasome subunits, as well as variations of fibroblast growth factor and a time-dependent infiltration of peripheral immune cells. Circulating levels of the inflammatory cytokines, interleukin (IL)-6, IL-2, tumor necrosis factor-alpha and interferon-gamma were also time-dependently elevated following intra-SNc LPS infusion. These data suggest that inflammatory priming may influence DA neuronal sensitivity to subsequent environmental toxins by modulating the state of glial and immune factors, and these findings may be important for neurodegenerative conditions, such as Parkinson's disease (PD).

Class IIA HDACs in the regulation of neurodegeneration

Neurodegenerative diseases affect millions of patients annually and are a significant burden on the health care systems around the world. While there are symptomatic remedies for patients suffering from various neurodegenerative diseases, there are no cures as of today. Cell death by apoptosis is a common hallmark of neurodegeneration. Therefore, deciphering the molecular pathways regulating this process is of significant value to scientists' endeavor to understand neurodegenerative disorders. Efforts along these lines have uncovered a number of molecular pathways that regulate neuronal apoptosis. Recently, a family of proteins known as histone deacetylases (HDACs) has been linked to regulation of cell survival as well as death. The focus of this review is to summarize our current understanding of the role of HDACs and in particular a subgroup of proteins in this family classified as class IIa HDACs in the regulation of neuronal cell death. It is apparent based on the information presented in this review that although very similar in their primary sequence, members of this family of proteins often have distinct roles in orchestrating apoptotic cell death in the brain.

The effectiveness of anticonvulsants in psychiatric disorders

Anticonvulsant drugs are widely used in psychiatric indications. These include mainly alcohol and benzodiazepine withdrawal syndromes, panic and anxiety disorders, dementia, schizophrenia, affective disorders, bipolar affective disorders in particular, and, to some extent, personality disorders. A further area in which neurology and psychiatry overlap is pain conditions, in which some anticonvulsants, and also typical psychiatric medications such as antidepressants, are helpful. From the beginning of their psychiatric use, anticonvulsants have also been used to ameliorate specific symptoms of psychiatric disorders independently of their causality and underlying illness, eg, aggression, and, more recently, cognitive impairment, as seen in affective disorders and schizophrenia. With new anticonvulsants currently under development, it is likely that their use in psychiatry will further increase, and that psychiatrists need to learn about their differential efficacy and safety profiles to the same extent as do neurologists.

Valproic acid and other histone deacetylase inhibitors induce microglial apoptosis and attenuate lipopolysaccharide-induced dopaminergic neurotoxicity

Valproic acid (VPA), a widely prescribed drug for seizures and bipolar disorder, has been shown to be an inhibitor of histone deacetylase (HDAC). Our previous study has demonstrated that VPA pretreatment reduces lipopolysaccharide (LPS)-induced dopaminergic (DA) neurotoxicity through the inhibition of microglia over-activation. The aim of this study was to determine the mechanism underlying VPA-induced attenuation of microglia over-activation using rodent primary neuron/glia or enriched glia cultures. Other histone deacetylase inhibitors (HDACIs) were compared with VPA for their effects on microglial activity. We found that VPA induced apoptosis of microglia cells in a time- and concentration-dependent manner. VPA-treated microglial cells showed typical apoptotic hallmarks including phosphatidylserine externalization, chromatin condensation and DNA fragmentation. Further studies revealed that trichostatin A (TSA) and sodium butyrate (SB), two structurally dissimilar HDACIs, also induced microglial apoptosis. The apoptosis of microglia was accompanied by the disruption of mitochondrial membrane potential and the enhancement of acetylation levels of the histone H3 protein. Moreover, pretreatment with SB or TSA caused a robust decrease in LPS-induced pro-inflammatory responses and protected DA neurons from damage in mesencephalic neuron-glia cultures. Taken together, our results shed light on a novel mechanism whereby HDACIs induce neuroprotection and underscore the potential utility of HDACIs in preventing inflammation-related neurodegenerative disorders such as Parkinson's disease.

Histone deacetylase inhibitors exhibit anti-inflammatory and neuroprotective effects in a rat permanent ischemic model of stroke: multiple mechanisms of action

The pathophysiology of cerebral ischemia involves multiple mechanisms including neuroinflammation mediated by activated microglia and infiltrating macrophages/monocytes. The present study employed a rat permanent middle cerebral artery occlusion (pMCAO) model to study effects of histone deacetylase (HDAC) inhibition on ischemia-induced brain infarction, neuroinflammation, gene expression, and neurological deficits. We found that post-pMCAO injections with HDAC inhibitors, valproic acid (VPA), sodium butyrate (SB), or trichostatin A (TSA), decreased brain infarct volume. Postinsult treatment with VPA or SB also suppressed microglial activation, reduced the number of microglia, and inhibited other inflammatory markers in the ischemic brain. The reduction in levels of acetylated histone H3 in the ischemic brain was prevented by treatment with VPA, SB, or TSA. Moreover, injections with HDAC inhibitors superinduced heat-shock protein 70 and blocked pMCAO-induced down-regulation of phospho-Akt, as well as ischemia-elicited up-regulation of p53, inducible nitric oxide synthase, and cyclooxygenase-2. The motor, sensory, and reflex performance of pMCAO rats was improved by VPA, SB, or TSA treatment. The beneficial effects of SB and VPA in reducing brain infarct volume and neurological deficits occurred when either drug was administrated at least 3 h after ischemic onset, and the behavioral improvement was long-lasting. Together, our results demonstrate robust neuroprotective effects of HDAC inhibitors against cerebral ischemia-induced brain injury. The neuroprotection probably involves multiple mechanisms including suppression of ischemia-induced cerebral inflammation. Given that there is no effective treatment for stroke, HDAC inhibitors, such as VPA, SB, and TSA, should be evaluated for their potential use for clinical trials in stroke patients.

GSK-3 is a viable potential target for therapeutic intervention in bipolar disorder

Bipolar disorder is a serious psychiatric condition that has been treated for over 50 years with lithium. Lithium is a well established glycogen synthase kinase-3 (GSK-3) inhibitor, suggesting that manipulating GSK-3 may have therapeutic value in treating bipolar disorder. GSK-3 is regulated by a wide variety of mechanisms including phosphorylation, binding with protein complexes, phosphorylation state of its substrates, cellular localization and autoregulation, thus providing a wide number of potential therapeutic mechanisms. Mounting evidence suggests that GSK-3 regulation can be used to manage bipolar disorder symptoms. Although GSK-3 mutations have not been detected amongst the general bipolar population, they have been correlated with females with bipolar II and most of the drugs used for successful bipolar disorder treatment regulate GSK-3. These drugs produce a weak anti-depressant-like and a strong anti-mania-like effect in a wide range of animal models tested, mirroring their utility in treating bipolar disorder symptoms. Taken together, the evidence suggests that targeting GSK-3 may be a means to control the symptoms of bipolar disorder.