Saunderson Emily A, Spiers Helen, Mifsud Karen R, Gutierrez-Mecinas Maria, Trollope Alexandra F, Shaikh Abeera, Mill Jonathan, Reul Johannes M H M
Neuro-Epigenetics Research Group, University of Bristol, Bristol BS1 3NY, United Kingdom;
Institute of Psychiatry, King's College London, London SE5 8AF, United Kingdom;
Proc Natl Acad Sci U S A. 2016 Apr 26;113(17):4830-5. doi: 10.1073/pnas.1524857113. Epub 2016 Apr 12.
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-phosphate-guanine-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.
应激事件会引发行为反应的长期变化；然而，大脑中的潜在机制尚未完全明确。先前的研究表明，应激激活的齿状回（DG）颗粒神经元中的表观遗传变化和即刻早期基因（IEG）诱导在这些行为反应中起关键作用。在此，我们表明，急性应激挑战[即强迫游泳（FS）]会导致靠近c-Fos（FBJ小鼠骨肉瘤病毒癌基因同源物）转录起始位点以及Egr-1（早期生长反应蛋白1）基因启动子区域内特定CpG（5'-胞嘧啶-磷酸-鸟嘌呤-3'）位点的DNA去甲基化，且这种去甲基化特异性地发生在DG中。给予（内源性）甲基供体S-腺苷甲硫氨酸（SAM）在基线时并不影响CpG甲基化和IEG基因表达。然而，在FS挑战前给予SAM会导致IEG基因座处的CpG甲基化增强，特异性地抑制DG中的IEG诱导，并在24小时后损害行为不动反应。应激源还特异性地增加了该海马区域中从头DNA甲基转移酶Dnmt3a[DNA（胞嘧啶-5-）-甲基转移酶3α]的表达。此外，应激导致Dnmt3a酶与IEG基因内受影响的CpG位点的结合增加。未观察到SAM对应激诱发的组蛋白修饰有影响，包括H3S10p-K14ac（组蛋白H3，磷酸化丝氨酸10和乙酰化赖氨酸-14）、H3K4me3（组蛋白H3，三甲基化赖氨酸-4）、H-K9me3（组蛋白H3，三甲基化赖氨酸-9）和H3K27me3（组蛋白H3，三甲基化赖氨酸-27）。我们得出结论，IEG的DNA甲基化状态在FS诱导的DG颗粒神经元IEG诱导及相关行为反应中起关键作用。此外，就基因表达和行为而言，可用甲基供体的浓度，可能与Dnmt3a共同作用，对于齿状神经元对环境刺激的反应性至关重要。
