RNA-Seq of Myf6-knockout versus Wild-type satellite cells. RNA-Seq of Myf6-knockout versus Wild-type satellite cells

In metazoans, skeletal muscle evolved to contract and produce force. Recent experimental evidence, however, suggests that skeletal muscle has also acquired endocrine functions and produces a vast array of muscle-derived cytokines and growth factors, collectively called myokines. The mechanisms that regulate myokine production and their effect on the resident stem cell population inskeletal muscle remain unknown. Here, we report that in adult skeletal muscle, Myf6/MRF4 is a major regulator of myokine expression. Genetic deletion of Myf6 in skeletal muscle leads to reduction of the muscle stem cell (MuSCs) pool in adult mice in a myokine-dependent manner but, surprisingly, does not disrupt muscle differentiation. Using ChIP-Seq and gene expression analyses of myogenic factors, we show that Myf6/MRF4 is a direct regulator of many myokines and muscle-secreted proteins, including ligands for canonical signaling pathways such as EGFR and VEGFR. Consequently, in Myf6-deficient animals,MuSCs increasingly break quiescence, but can nevertheless undergo differentiation. Lastly, we show that Myf6 and its gene network rapidly respondto aerobic and anaerobic exercise. Together, these findings indicate that control of myokine signaling by Myf6 is critical to maintain muscle stem cell pool and skeletal muscle function via myokine signaling. Overall design: Satellite cells from two 10 month-old female wild-type mice, two 10 month-old female Myf6-knockout mice and three 4 week-old male wild-type mice were analyzed.

在后生动物中，骨骼肌演化而来的核心功能为收缩并产生机械力。然而近年的实验证据表明，骨骼肌还额外获得了内分泌功能，可分泌大量肌源性细胞因子与生长因子，这类物质被统称为肌因子（myokines）。调控肌因子生成的具体机制，以及肌因子对骨骼肌内驻留干细胞群体的作用，目前仍未明晰。本研究发现，在成体骨骼肌中，Myf6/MRF4是肌因子表达的关键调控因子。通过在骨骼肌中特异性敲除Myf6，会以肌因子依赖的方式减少成体小鼠的肌肉干细胞（MuSCs）库，但令人意外的是，这并未干扰肌肉的正常分化过程。借助对肌源性因子的染色质免疫沉淀测序（ChIP-Seq）与基因表达分析，本研究证实Myf6/MRF4可直接调控大量肌因子与骨骼肌分泌蛋白的表达，涵盖表皮生长因子受体（EGFR）与血管内皮生长因子受体（VEGFR）等经典信号通路的配体。因此，在Myf6缺陷型动物体内，肌肉干细胞（MuSCs）会愈发频繁地脱离静息状态，但仍可正常完成分化程序。此外，本研究还证实Myf6及其基因调控网络可快速响应有氧与无氧运动。综上，本研究结果表明，Myf6对肌因子信号通路的调控，对于通过肌因子信号维持肌肉干细胞库与骨骼肌功能具有关键作用。实验设计概述：本研究分析了2只10月龄雌性野生型小鼠、2只10月龄雌性Myf6敲除小鼠，以及3只4周龄雄性野生型小鼠的卫星细胞。