DNA Methylation in the PFC in response to peripheral neuropathic pain and therapeutic treatment with s-adenosylmethionine. DNA Methylation in the PFC in response to peripheral neuropathic pain and therapeutic treatment with s-adenosylmethionine

Chronic pain is associated with persistent but reversible structural and functional changes in prefrontal cortex (PFC). This stable yet malleable plasticity implicates epigenetic mechanisms, including DNA methylation, as a potential mediator of chronic pain-induced changes. We have previously demonstrated that chronic oral administration of the methyl donor S-adenosyl methionine (SAM) is capable of attenuating long-term peripheral neuropathic pain and affecting global PFC DNA methylation. However, there was no evidence as of yet that alterations in DNA methylation underlie SAM-mediated pain attenuation. To elucidate these mechanisms, we performed epigenome-wide analysis of mouse PFC after 4 months of SAM treatment initiated 3 months following induction of peripheral nerve injury. Over injury triggered chronic pain was associated with 4000 differentially methylated genomic regions which were enriched in intracellular signaling, cell locomotion and migration, cytoskeletal structure, and cell adhesion pathways. A third of the regions that were differentially methylated in chronic pain mice (1415 regions representing 1030 genes) were reversed by SAM treatment. 100 genes with known pain-related function were differentially methylated following nerve injury; several of which were reversed by SAM treatment. These results demonstrate that DNA methylation alterations in the PFC caused by chronic pain and reversed by SAM treatment providing at least partially a mechanism of action. These data point to the possibility of epigenetic modulators such as SAM as novel approach to treat chronic pain. Overall design: Comparison of DNA Methylation between Sham-Vehicle, Sham-SAM Treated, Injury-vehicle, and injury-SAM treated animals

慢性疼痛与前额叶皮层（Prefrontal Cortex, PFC）持续但可逆的结构与功能变化密切相关。这种稳定却具备可塑性的脑区重塑，提示表观遗传机制（包括DNA甲基化（DNA Methylation））可能作为慢性疼痛诱导脑内变化的潜在介导因子。我们此前的研究已证实，长期口服给予甲基供体S-腺苷甲硫氨酸（S-adenosyl Methionine, SAM），能够缓解长期外周神经性疼痛，并改变前额叶皮层的全基因组DNA甲基化水平。但截至彼时，尚无证据表明DNA甲基化改变是SAM介导疼痛缓解的核心机制。为阐明此类作用机制，我们在外周神经损伤造模3个月后启动SAM给药治疗，持续4个月后，对小鼠前额叶皮层开展了表观基因组范围的分析。结果显示，神经损伤诱发的慢性疼痛与4000个差异甲基化基因组区域相关，这些区域显著富集于细胞内信号传导、细胞运动与迁移、细胞骨架结构以及细胞黏附通路中。慢性疼痛小鼠中出现差异甲基化的区域有三分之一（共1415个区域，对应1030个基因）可被SAM治疗逆转。另有100个已知与疼痛调控功能相关的基因在神经损伤后出现差异甲基化，其中多个基因的甲基化异常可被SAM治疗矫正。上述结果表明，慢性疼痛诱导的前额叶皮层DNA甲基化改变可被SAM逆转，这至少部分揭示了SAM缓解慢性疼痛的作用机制。本研究数据提示，诸如SAM这类表观遗传调控剂有望成为治疗慢性疼痛的全新策略。整体实验设计：对比假手术-溶剂处理组、假手术-SAM处理组、神经损伤-溶剂处理组以及神经损伤-SAM处理组动物的DNA甲基化水平。