Human Muscle Posses Epigenetic Memory. Human Muscle Posses Epigenetic Memory

It is unknown if adult human skeletal muscle has an epigenetic memory of earlier encounters with growth. We report, for the first time in humans, genome-wide DNA methylation (850,000CpGs) and gene expression analysis after muscle hypertrophy (loading), return of muscle mass to baseline (unloading), followed by later hypertrophy (reloading). We discovered increased frequency of hypomethylation across the genome after reloading (18,816 CpGs) versus earlier loading (9,153 CpG sites). We also identified AXIN1, GRIK2, CAMK4, TRAF1 as hypomethylated genes with enhanced expression after loading that maintained their hypomethylated status even during unloading where muscle mass returned to control levels, indicating a memory of these genes methylation signatures following earlier hypertrophy. Further, UBR5, RPL35a, HEG1, PLA2G16, SETD3 displayed hypomethylation and enhanced gene expression following loading, and demonstrated the largest increases in hypomethylation, gene expression and muscle mass after later reloading, indicating an epigenetic memory in these genes. Finally, genes; GRIK2, TRAF1, BICC1, STAG1 were epigenetically sensitive genes demonstrating hypomethylation after a single bout of resistance exercise that was maintained 22 weeks later with the largest increase in gene expression and muscle mass after reloading. Overall, we identify an important epigenetic role for a number of largely unstudied genes in muscle hypertrophy/ memory. Overall design: Using a within-subjects design, skeletal muscle samples from the vastus lateralis were analsyed at baseline ((control; N=9; subject 1 has a duplicate(rep2) all other subjects are in single (rep1)), immediately (30-mins) following one single bout of acute resistance exercise (N=8; where this session was the first session of the subsequent 7-week training intervention) after 7 weeks of chronic resistance exercise loading (N=8), following a further 7 weeks of unloading (N=8) and finally, following 7 weeks of chronic resistance exercise reloading (N=7). All samples are run in single unless otherwise stated.

目前尚不清楚成人人体骨骼肌是否留存有此前生长过程的表观遗传记忆（epigenetic memory）。本研究首次在人类中报道了骨骼肌肥大（loading，负荷刺激）、肌肉质量恢复至基线水平（unloading，去负荷）以及后续再次肥大（reloading，复负荷）过程中的全基因组DNA甲基化（genome-wide DNA methylation，覆盖850,000个CpG位点（CpG sites））与基因表达分析结果。
本研究发现，相较于首次负荷刺激阶段（涉及9,153个CpG位点），复负荷后全基因组范围内低甲基化事件的发生频率显著升高，共计18,816个CpG位点出现低甲基化。
研究团队还鉴定出AXIN1、GRIK2、CAMK4、TRAF1为低甲基化基因：这些基因在首次负荷刺激后表达水平上调，且在肌肉质量恢复至对照水平的去负荷阶段仍维持低甲基化状态，表明其甲基化特征留存了此前肌肉肥大的记忆。
此外，UBR5、RPL35a、HEG1、PLA2G16、SETD3在首次负荷刺激后同样呈现低甲基化且表达上调，并在后续复负荷阶段展现出最为显著的低甲基化程度提升、基因表达上调以及肌肉质量增加，提示这些基因存在表观遗传记忆。
最后，GRIK2、TRAF1、BICC1、STAG1这四个基因表现出表观遗传敏感性：单次阻力运动后即出现低甲基化，且该低甲基化状态可持续至22周后；在复负荷阶段，这些基因的表达上调幅度与肌肉质量增加幅度均为最大。
综上，本研究明确了一批此前鲜有研究的基因在肌肉肥大/记忆过程中的重要表观遗传调控作用。
整体实验设计：采用受试者内实验设计，对股外侧肌的骨骼肌样本进行多时间点采集与分析，具体时间点包括：基线状态（对照组；N=9，其中1名受试者设置2个生物学重复（rep2），其余受试者均为1个重复（rep1））、单次急性阻力运动后即刻（30分钟，N=8，该训练周期为后续7周训练干预的首次训练）、7周慢性阻力负荷训练后（N=8）、再经过7周去负荷阶段后（N=8）以及最终7周慢性阻力复负荷训练后（N=7）。除另有说明外，所有样本均进行单次检测分析。