Stress-induced gene expression and behavior are controlled by DNA methylation and methyl donor availability in the dentate gyrus

Abstract

Stressful events evoke long-term changes in behavioral responses; however, the underlying mechanisms in the brain are not well understood. Previous work has shown that epigenetic changes and immediate-early gene (IEG) induction in stress-activated dentate gyrus (DG) granule neurons play a crucial role in these behavioral responses. Here, we show that an acute stressful challenge [i.e., forced swimming (FS)] results in DNA demethylation at specific CpG (5′-cytosine-phosphateguanine-3′) sites close to the c-Fos (FBJ murine osteosarcoma viral oncogene homolog) transcriptional start site and within the gene promoter region of Egr-1 (early growth response protein 1) specifically in the DG. Administration of the (endogenous) methyl donor S-adenosyl methionine (SAM) did not affect CpG methylation and IEG gene expression at baseline. However, administration of SAM before the FS challenge resulted in an enhanced CpG methylation at the IEG loci and suppression of IEG induction specifically in the DG and an impaired behavioral immobility response 24 h later. The stressor also specifically increased the expression of the de novo DNA methyltransferase Dnmt3a [DNA (cytosine-5-)-methyltransferase 3 alpha] in this hippocampus region. Moreover, stress resulted in an increased association of Dnmt3a enzyme with the affected CpG loci within the IEG genes. No effects of SAM were observed on stress-evoked histone modifications, including H3S10p-K14ac (histone H3, phosphorylated serine 10 and acetylated lysine-14), H3K4me3 (histone H3, trimethylated lysine-4), H3K9me3 (histone H3, trimethylated lysine-9), and H3K27me3 (histone H3, trimethylated lysine-27). We conclude that the DNA methylation status of IEGs plays a crucial role in FS-induced IEG induction in DG granule neurons and associated behavioral responses. In addition, the concentration of available methyl donor, possibly in conjunction with Dnmt3a, is critical for the responsiveness of dentate neurons to environmental stimuli in terms of gene expression and behavior.stress | behavior | DNA methylation | immediate-early gene | hippocampus A daptation to stressful challenges is crucial for maintaining health and well-being. These events induce physiological and behavioral responses that enable the individual to cope with the challenge. In the brain, molecular mechanisms are initiated that facilitate learning of adaptive behavioral responses and the consolidation of memories of the event. Inappropriate responses to stress have been linked with psychiatric disorders, such as major depression and anxiety (1-3).Glucocorticoid hormones, secreted in response to a stressful challenge, in conjunction with activated intracellular signaling pathways in neurons of the hippocampus, play a key role in consolidating behavioral responses to stress (4, 5). The hippocampal extracellular signal-regulated kinase mitogen-activated protein kinase (ERK MAPK) pathway, activated through N-methyl D-aspartate receptors (NMDA-Rs) and other membrane receptors, is involved in behavioral responses seen in Mo...

Molecular and Epigenetic Mechanisms Underlying Cognitive and Adaptive Responses to Stress

“…We found, serendipitously, that forced swimming raises histone H3 phosphorylation (H3S10p) selectively in sparsely distributed, mature dentate granule neurons in rats and mice [26,27]. It appeared that this histone mark exists in combination with an acetylation mark at lysine14 (i.e., H3S10p-K14ac; and lysine9 H3K9ac-S10p; [12]), indicating that this combinatorial epigenetic mark could be involved in transcriptional activation [27,28]. Subsequent studies showed that the formation of H3S10p-K14ac in DG neurons was dependent on signaling through GRs and NMDA-Rs [13,27,28].…”

“…Hence, pre-treatment with SAM before forced swimming resulted in an increased DNA methylation of the gene promoters/5 -UTR of Fos and Egr1 and decreased expression of these IEGs specifically within the DG. SAM administration also interfered with the memory consolidation process post-forced swimming, because the rats presented significantly less behavioral immobility than the vehicle-treated animals during the FS re-test 24 h later [12]. Importantly, SAM exerted no effects on the forced swimming-induced formation of H3S10p-K14ac in DG neurons; thus, the methyl donor did not affect the FS-activated signaling pathway required for IEG induction in these neurons [12].…”

“…Forced swimming resulted in a decrease in DNA methylation at certain 5 -cytosine-phosphate-guanine-3 (CpGs) within the c-Fos and Egr-1 gene promoters and 5 -untranslated regions specifically in DG neurons; there was no effect in the CA regions of the hippocampus [12]. Furthermore, administration of the endogenous methyl donor S-adenosyl methionine (SAM) before the FS challenge reversed the effect of the stressor on the DNA methylation level of the IEGs.…”

“…These IEGs are involved in long-term memory paradigms like the MWM [35]. Based on a series of pharmacological, gene deletion, immunohistochemical, and chromatin immunoprecipitation (ChIP) studies, it was indeed found that the formation of H3S10p-K14ac is associated with the induction of FOS and EGR1 in DG neurons [12,13,27,28]. Moreover, the induction of these IEGs in DG neurons was also found to be dependent of signaling through GRs [13].…”

Neurophysiological Changes Induced by Chronic <em>Toxoplasma gondii</em> Infection

“…This suggests that T. gondii is able to co-op host mechanisms of chromatin regulation. Advances in epigenetics have demonstrated that DNA methylation within cells is not as restricted to development as it was once considered; DNA methylation is a dynamic process [94][95][96]. Epigenetic modifications are essential for neurological functions such as memory, hormonal, and behavioral responses.…”