Alterations in GABAergic mRNA expression play a key role for prefrontal dysfunction in schizophrenia and other neurodevelopmental disease. Here, we show that histone H3-lysine 4 methylation, a chromatin mark associated with the transcriptional process, progressively increased at GAD1 and other GABAergic gene promoters (GAD2, NPY, SST) in human prefrontal cortex (PFC) from prenatal to peripubertal ages and throughout adulthood. Alterations in schizophrenia included decreased GAD1 expression and H3K4-trimethylation, predominantly in females and in conjunction with a risk haplotype at the 5Ј end of GAD1. Heterozygosity for a truncated, lacZ knock-in allele of mixed-lineage leukemia 1 (Mll1), a histone methyltransferase expressed in GABAergic and other cortical neurons, resulted in decreased H3K4 methylation at GABAergic gene promoters. In contrast, Gad1 H3K4 (tri)methylation and Mll1 occupancy was increased in cerebral cortex of mice after treatment with the atypical antipsychotic, clozapine. These effects were not mimicked by haloperidol or genetic ablation of dopamine D 2 and D 3 receptors, suggesting that blockade of D 2 -like signaling is not sufficient for clozapine-induced histone methylation. Therefore, chromatin remodeling mechanisms at GABAergic gene promoters, including MLL1-mediated histone methylation, operate throughout an extended period of normal human PFC development and play a role in the neurobiology of schizophrenia.
Little is known about the regulation of neuronal and other cell-type specific epigenomes from the brain. Here, we map the genomewide distribution of trimethylated histone H3K4 (H3K4me3), a mark associated with transcriptional regulation, in neuronal and nonneuronal nuclei collected from prefrontal cortex (PFC) of 11 individuals ranging in age from 0.5 to 69 years. Massively parallel sequencing identified 12,704 H3K4me3 enriched regions (peaks), the majority located proximal to (within 2 kb of) the transcription start site (TSS) of annotated genes. These included peaks shared by neurons in comparison with three control (lymphocyte) cell types, as well as peaks specific to individual subjects. We identified 6,213 genes that show highly enriched H3K4me3 in neurons versus control. At least 1,370 loci, including annotated genes and novel transcripts, were selectively tagged with H3K4me3 in neuronal but not in nonneuronal PFC chromatin. Our results reveal agecorrelated neuronal epigenome reorganization, including decreased H3K4me3 at approximately 600 genes (many function in developmental processes) during the first year after birth. In comparison, the epigenome of aging (>60 years) PFC neurons showed less extensive changes, including increased H3K4me3 at 100 genes. These findings demonstrate that H3K4me3 in human PFC is highly regulated in a cell type-and subject-specific manner and highlight the importance of early childhood for developmentally regulated chromatin remodeling in prefrontal neurons.D evelopmentally regulated changes in histone modifications and DNA methylation, shaping gene expression patterns and genome organization, are critical intermediates for numerous genetic and environmental factors affecting neuronal functions in healthy and diseased brains (1). For example, there is increasing evidence that epigenetic alterations in the cerebral cortex and hippocampus play an important role in the etiology of schizophrenia and other neurodevelopmental disease (2, 3). Cortical neurons permanently exit from the cell cycle during the fetal period, before the dramatic changes in functional connectivity, both on a micro-(e.g., synapse) and macroscale (e.g., network activity, cortical gray matter volumes), that extend into early childhood years and continue throughout adolescence and even beyond (4, 5). To date, however, comprehensive and genomewide maps of neuronal epigenomes, and their developmental trajectories, do not exist. This critical deficiency in epigenetic information, as it pertains to the human-and more generally animal-brain, finally can be addressed because recently it became possible to efficiently separate neuronal chromatin from other chromatin in tissue, thereby avoiding potential confounds such as the highly dynamic changes in glia cell densities during cortical ontogenesis and maturation (6). Here, we employ ChIP-Seq (7) to study the genome-wide distribution of histone H3K4 trimethylation (H3K4me3)-an epigenetic mark highly enriched at start sites of actual or potential transcription (8)-in n...
Background: DNA-protein interactions in mature brain are increasingly recognized as key regulators for behavioral plasticity and neuronal dysfunction in chronic neuropsychiatric disease. However, chromatin assays typically lack single cell resolution, and therefore little is known about chromatin regulation of differentiated neuronal nuclei that reside in brain parenchyma intermingled with various types of non-neuronal cells.
ObjectiveAdipose tissue (AT) inflammation is associated with systemic insulin resistance and hyperinsulinemia in obese rodents and humans. A longstanding concept is that hyperinsulinemia may promote systemic insulin resistance through downregulation of its receptor on target tissues. Here we tested the novel hypothesis that insulin also impairs systemic insulin sensitivity by specifically enhancing adipose inflammation.MethodsCirculating insulin levels were reduced by about 50% in diet-induced and genetically obese mice by treatments with diazoxide or streptozotocin, respectively. We then examined AT crown-like structures, macrophage markers and pro-inflammatory cytokine expression in AT. AT lipogenesis and systemic insulin sensitivity was also monitored. Conversely, insulin was infused into lean mice to determine its affects on the above parameters.ResultsLowering circulating insulin levels in obese mice by streptozotocin treatment decreased macrophage content in AT, enhancing insulin stimulated Akt phosphorylation and de novo lipogenesis (DNL). Moreover, responsiveness of blood glucose levels to injected insulin was improved by streptozotocin and diazoxide treatments of obese mice without changes in body weight. Remarkably, even in lean mice, infusion of insulin under constant euglycemic conditions stimulated expression of cytokines in AT. Consistent with these findings, insulin treatment of 3T3-L1 adipocytes caused a 10-fold increase in CCL2 mRNA levels within 6 h, which was blocked by the ERK inhibitor PD98059.ConclusionTaken together, these results indicate that obesity-associated hyperinsulinemia unexpectedly drives AT inflammation in obese mice, which in turn contributes to factors that suppress insulin-stimulated adipocyte DNL and systemic insulin sensitivity.
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