Rajiv P. Sharma

An epigenetic mouse model for molecular and behavioral neuropathologies related to schizophrenia vulnerability

Reelin and glutamic acid decarboxylase (GAD)67 expressed by cortical γ-aminobutyric acid-ergic interneurons are down-regulated in schizophrenia. Because epidemiological studies of schizophrenia fail to support candidate gene haploinsufficiency of Mendelian origin, we hypothesize that epigenetic mechanisms (i.e., cytosine hypermethylation of CpG islands present in the promoter of these genes) may be responsible for this down-regulation. Protracted l-methionine (6.6 mmol/kg for 15 days, twice a day) treatment in mice elicited in brain an increase of S-adenosyl-homocysteine, the processing product of the methyl donor S-adenosyl-methionine, and a marked decrease of reelin and GAD67 mRNAs in both WT and heterozygous reeler mice. This effect of l-methionine was associated with an increase in the number of methylated cytosines in the CpG island of the reelin promoter region. This effect was not observed for GAD65 or neuronal-specific enolase and was not replicated by glycine doses 2-fold greater than those of l-methionine. Prepulse inhibition of startle declined at a faster rate as the prepulse/startle interval increased in mice receiving l-methionine. Valproic acid (2 mmol/kg for 15 days, twice a day) reverted l-methionine-induced down-regulation of reelin and GAD67 in both WT and heterozygous reeler mice, suggesting an epigenetic action through the inhibition of histone deacetylases. The same dose of valproate increased acetylation of histone H3 in mouse brain nearly 4-fold. This epigenetic mouse model may be useful in evaluating drug efficacy on schizophrenia vulnerability. Hence the inhibition of histone deacetylases could represent a pharmacological intervention mitigating epigenetically induced vulnerability to schizophrenia in individuals at risk.

Repetitive transcranial magnetic stimulation versus electroconvulsive therapy for major depression: preliminary results of a randomized trial.

BACKGROUND Many severely depressed patients do not benefit from or tolerate existing treatments. Repetitive transcranial magnetic stimulation (rTMS) has been reported to benefit depression. We compared rTMS to electroconvulsive therapy (ECT) in severely ill, depressed patients. METHODS Twenty-five patients with a major depression (unipolar or bipolar) deemed clinically appropriate for ECT were randomly assigned to rTMS (10-20 treatments, 10 Hz, 110% motor threshold applied to the left dorsolateral prefrontal cortex for a total of 10,000-20,000 stimulations) or a course of bitemporal ECT (4-12 treatments). The primary outcome measure was the 24-item Hamilton Depression Rating Scale (HDRS). The Brief Psychiatric Rating Scale (BPRS), Young Mania Rating Scale (YMS), and Clinical Global Impression scale (CGI) were secondary measures. Minimal rescue medications were utilized. RESULTS Mean percent improvement on the baseline HDRS score did not significantly differ between the two treatments (i.e., 55% for the rTMS group vs. 64% for the ECT group [p = ns]). With response defined as a 50% reduction from baseline and a final score < or = 8 on the HDRS, there was also no significant difference between the two groups. We did not observe any differences between groups on the secondary measures. CONCLUSIONS A 2-4 week randomized, prospective trial comparing rTMS to ECT produced comparable therapeutic effects in severely depressed patients.

Is There a Future for Histone Deacetylase Inhibitors in the Pharmacotherapy of Psychiatric Disorders

In recent years, it has become widely recognized that a comprehensive understanding of chromatin biology is necessary to better appreciate its role in a wide range of diseases. The histone code has developed as a new layer of our appreciation of transcription factor-based mechanisms of gene expression. Although epigenetic regulation refers to a host of chromatin modifications that occur at the level of DNA, histones, and histone-associated proteins, how this regulation is orchestrated is still incompletely understood. Of those processes that comprise the epigenetic regulatory machinery, DNA methylation and histone acetylation/deacetylation have been the most thoroughly studied. Compounds that act as inhibitors of DNA methyltransferases or histone deacetylases (HDACs) activate a variety of intracellular signaling pathways that ultimately affect the coordinated expression of multiple genes. The altered patterns of mRNA and protein expression collectively converge on pathways linked to apoptosis and cell cycle arrest, among others. This has prompted a widespread search for epigenetic inhibitors that could be used as chemotherapeutic agents, and several are undergoing clinical evaluation. More recently, there has been interest in the use of HDAC inhibitors to activate the expression of mRNAs that are down-regulated in various neurological and psychiatric conditions. Considerably less is known regarding the effect these drugs have on postmitotic cells such as neurons. Before we consider the clinical use of additional HDAC inhibitors to treat schizophrenia or unipolar depression, there are a number of key issues that need to be resolved.

Histone deactylase 1 expression is increased in the prefrontal cortex of schizophrenia subjects: analysis of the National Brain Databank microarray collection.

Histone deactylase enzymes are responsible for the deacetylation of histone tails, and consequently influence gene regulation through their ability to modify chromatin structure surrounding promoter regions. We analyzed the microarray collection of the National Brain Databank to investigate differential expression of these enzymes in the prefrontal cortices of control, schizophrenia and bipolar subjects. HDAC1 expression levels were significantly higher in schizophrenia versus normal subjects. The mRNA expression level of an epigenetically regulated schizophrenia candidate gene GAD67 was strongly and negatively correlated with the mRNA expression levels of HDAC1, HDAC3 and HDAC4 levels. These findings provide additional support for the proposal that epigenetic factors are operative in the brain pathology of patients with schizophrenia.

Proton magnetic resonance spectroscopy of the brain in schizophrenic and affective patients

Water-suppressed 1H magnetic resonance spectra were recorded from two brain regions of psychiatric patients and normal volunteers. The two regions studied were (a) the basal ganglia structures surrounding the anterior horn of the lateral ventricle and (b) the occipital cortex. N-Acetylaspartate (NAA), phosphocreatine-creatine (PCr-Cr), choline and inositol resonances were seen in both regions. Ratios of metabolite peak integrals to PCr-Cr peak integral were calculated for each spectrum. To control for partial volume effects, comparisons between patients and controls were made only from identical regions i.e. basal ganglia vs basal ganglia, and likewise for occipital cortex. Metabolite ratios from the occipital region of patients were similar to those from the occipital region of normal subjects. Bipolar patients being treated with lithium had elevated NAA/PCr-Cr in the basal ganglia region when compared to normals. These patients also demonstrated elevated choline/PCr-Cr and inositol/PCr-Cr ratios in the basal ganglia region.

Neurocognitive effects of repetitive transcranial magnetic stimulation in severe major depression.

OBJECTIVE Repetitive transcranial magnetic stimulation (rTMS) is being investigated as a potential treatment for depression. Few studies have addressed the neurocognitive effects of a course of rTMS in severely depressed patients. We evaluated neurocognitive effects of a 1-4 week course (mean 3 weeks) of rTMS using an aggressive set of parameters, in 15 severely depressed subjects. METHODS A battery of neurocognitive tests relevant to attention, working memory-executive function, objective memory and motor speed were administered to 15 subjects with treatment-resistant major depression (unipolar and bipolar), before and after a course of rTMS. Mean z scores were computed for each of 4 cognitive domains and analyzed using repeated measures multivariate analysis of covariance. Significant interactions were further clarified using univariate analysis of variance. RESULTS There was no worsening of performance on any of the cognitive domains over the baseline-post rTMS period. On the contrary, evidence of modest but statistically significant improvement in performance was noted in working memory-executive function, objective memory and fine motor speed domains over the rTMS treatment period. CONCLUSIONS There was no evidence of adverse neurocognitive changes over the baseline-post rTMS period in 15 treatment-resistant depressed subjects undergoing a 3 week (mean) trial of rTMS. Significant improvements in several domains observed over the rTMS treatment period could not be explained by improved mood. Practice effects as well as other factors potentially contributing to these findings are discussed. SIGNIFICANCE rTMS is being increasingly studied as a neurophysiological probe as well as for its potential antidepressive effects. The effects on neuronal function raise appropriate questions of safety of its use at varying stimulus parameters and durations. This study contributes to the small body of evidence of the cognitive effects of rTMS in severely depressed patients.

Schizophrenia, epigenetics and ligand-activated nuclear receptors: a framework for chromatin therapeutics

Covalent modifications of DNA and its surrounding chromatin constitute an essential and powerful regulatory mechanism for gene transcription. Epigenetics is the study of this regulatory system. There is now strong albeit indirect evidence that epigenetic mechanisms contribute to the pathophysiology of schizophrenia. Furthermore, the discovery that valproic acid, a widely used psychotropic, has powerful epigenetic effects in clinically relevant concentrations suggests new therapeutic possibilities, i.e., drugs that act on chromatin structure. Fortunately, many proteins engaged in these processes, particularly chromatin remodeling, are accessible to pharmacological agents that have a high likelihood of crossing the blood brain barrier. This review will first summarize the essentials of the epigenetic regulatory system, then address the molecular evidence for altered epigenetic mechanisms in schizophrenia, and finally focus on the retinoic acid family of ligand-activated nuclear transcription factors as a likely system for new drug development in the management of schizophrenia-related symptoms.

Valproic acid and chromatin remodeling in schizophrenia and bipolar disorder: Preliminary results from a clinical population

Levels of acetylated Histone 3 and 4 proteins are strongly predictive of a chromatin structure that is conducive to gene expression. In cell and animal studies, valproic acid is a potent inhibitor of histone deactylating enzymes, and consequently results in increased levels of acetylated Histone 3 (acH3) and acetylated Histone 4 proteins (acH4). To examine this effect in a clinical setting, 14 schizophrenic and bipolar patients were treated with valproic acid (Depakote ER), either as monotherapy or in combination with antipsychotics, over a period of 4 weeks. AcH3 and acH4 levels from lymphocyte nuclear protein extracts were measured by Western Blot. Treatment with Depakote ER resulted in a significant increase of acH3 and a trend-level increase of acH4. Levels of valproic acid were positively and significantly correlated with percent increase in acH3 but not acH4. Schizophrenia patients were significantly less likely to increase their acH3 and acH4 levels after 4 weeks on Depakote ER. The authors consider these results in the context of future application of HDAC inhibitors to the treatment of psychiatric disorders.

Growth Arrest and DNA-Damage-Inducible, Beta (GADD45b)-Mediated DNA Demethylation in Major Psychosis

Aberrant neocortical DNA methylation has been suggested to be a pathophysiological contributor to psychotic disorders. Recently, a growth arrest and DNA-damage-inducible, beta (GADD45b) protein-coordinated DNA demethylation pathway, utilizing cytidine deaminases and thymidine glycosylases, has been identified in the brain. We measured expression of several members of this pathway in parietal cortical samples from the Stanley Foundation Neuropathology Consortium (SFNC) cohort. We find an increase in GADD45b mRNA and protein in patients with psychosis. In immunohistochemistry experiments using samples from the Harvard Brain Tissue Resource Center, we report an increased number of GADD45b-stained cells in prefrontal cortical layers II, III, and V in psychotic patients. Brain-derived neurotrophic factor IX (BDNF IXabcd) was selected as a readout gene to determine the effects of GADD45b expression and promoter binding. We find that there is less GADD45b binding to the BDNF IXabcd promoter in psychotic subjects. Further, there is reduced BDNF IXabcd mRNA expression, and an increase in 5-methylcytosine and 5-hydroxymethylcytosine at its promoter. On the basis of these results, we conclude that GADD45b may be increased in psychosis compensatory to its inability to access gene promoter regions.

Histone deacetylase inhibitors and candidate gene expression: An in vivo and in vitro approach to studying chromatin remodeling in a clinical population

OBJECTIVE The emerging field of psychiatric epigenetics is constrained by the dearth of research methods feasible in living patients. With this focus, we report on two separate approaches, one in vitro and one in vivo, developed in our laboratory. METHOD In the first approach, we isolated lymphocytes from 12 subjects and cultured their cells with either 0.7 mM valproic acid (VPA), 100 nM Trichostatin A (TSA), or DMSO (control) for 24h based upon previous dose response experiments. We then measured GAD67 mRNA expression using realtime RT-PCR, total acetylated histone 3 (H3K9,K14ac) levels using Western blot analysis, and attachment of H3K9,K14ac to the GAD67 promoter using ChIP. In the second approach, we measured GAD67 mRNA and total H3K9,K14ac levels in lymphocytes from 11 schizophrenia and 7 bipolar patients before and after 4 weeks of clinical treatment with Depakote ER (VPA). RESULTS In the first approach, VPA induced a 383% increase in GAD67 mRNA, an 89% increase in total H3K9,K14ac levels, and a 482% increase in H3K9,K14ac attachment to the GAD67 promoter. TSA induced comparable changes on all measures. In the second approach, bipolar subjects had significantly higher baseline levels of H3K9,K14ac compared to subjects with schizophrenia. Subjects with clinically relevant serum levels of VPA (> or = 65 microg/mL) showed a significant increase in GAD67 mRNA expression. CONCLUSIONS Our results utilizing two separate approaches for examining chromatin remodeling in real clinical time provide possible means to investigate epigenetic events in living patients.