Muscle injury causes long-term changes in stem cell DNA methylation [RRBS]

Injury to muscle brings about the activation of stem cells, which then generate new myocytes to replace the damaged tissue. We now demonstrate that this activation causes a dramatic change in the stem cell methylation pattern that prepares them epigenetically for terminal myocyte differentiation. These demethylation and de novo methylation events occur at regulatory elements associated with genes involved in myogenesis. Local injury of one muscle brings about an almost identical epigenetic change in satellite cells from other muscles in the body, as well. Furthermore, this same methylation state is also generated in muscle stem cells of female animals following full-term pregnancy, even in the absence of any injury. In all of these cases, which appear to be mediated by circulating factors, the new methylation profile is then stably maintained in resident muscle stem cells and thus represents a molecular memory of previous physiological events that is probably programmed to provide a mechanism for adapting to the environment. Muscle injury was carried out on hind-limb muscles from 8.5-9 month old mice, virgin and pregnant, by piercing multiple times with a 23-gauge needle. Satellite cells were isolated from the injured or contralateral muscles according to specific markers and subjected to methylation studies using the RRBS protocol. At least 4 mice in each group.

肌肉损伤会激活干细胞，随后干细胞会生成新的肌细胞以替代受损组织。本研究证实，该激活过程会使干细胞的甲基化模式发生显著改变，从表观遗传层面为干细胞向终末肌细胞分化做好准备。这类去甲基化与从头甲基化事件，均发生在与肌发生相关基因的调控元件区域。单处肌肉的局部损伤，还会使机体其他肌肉来源的肌卫星细胞（satellite cell）发生几乎完全一致的表观遗传改变。此外，雌性动物在足月妊娠后，其肌肉干细胞中也会出现相同的甲基化状态，即便未发生任何肌肉损伤。上述所有过程似乎均由循环因子介导，新的甲基化谱会在驻留肌肉干细胞中稳定维持，进而成为既往生理事件的分子记忆，该机制大概率是为机体适应环境而演化形成的。本研究对8.5~9月龄的未生育及妊娠雌鼠的后肢肌肉实施损伤：使用23号针头多次穿刺肌肉组织。研究人员根据特异性标记物从损伤肌肉及对侧肌肉中分离肌卫星细胞，并采用RRBS技术开展甲基化分析。每组实验至少使用4只小鼠。