Department of Rehabilitation Medicine, Hokkaido University Graduate School of Medicine, Kita 15, Nishi 7, Kitaku, Sapporo-shi, Hokkaido, 060-8638, Japan.
Department of Rehabilitation Medicine, Hokkaido University Hospital, Kita 14, Nishi 5, Kitaku, Sapporo-shi, Hokkaido, 060-8648, Japan.
J Muscle Res Cell Motil. 2021 Dec;42(3-4):443-451. doi: 10.1007/s10974-021-09609-7. Epub 2021 Oct 18.
Skeletal muscles undergo adaptations in response to mechanical stimuli such as stretching. However, there is limited evidence regarding the hypertrophic effects of passive repetitive stretching in vivo. We examined the effect of passive repetitive stretching on skeletal muscle myofiber morphology, satellite cell content, and messenger RNA expression of myogenic regulatory factors and signaling molecules involved in muscle protein synthesis and degradation. The gastrocnemius muscles of mice were stretched 15 times/min by manual ankle dorsiflexion for 15 min, 5 days a week for 2 weeks. We found that passive repetitive stretching significantly increased myofiber cross-sectional area. In stretched gastrocnemius muscles, the messenger RNA expression of p70S6K and myogenin was upregulated, whereas MuRF1, MAFbx, myostatin, and 4E-BP1 were downregulated. The phosphorylation level of p70S6K was significantly increased in stretched muscles. The number of Pax7+ cells was unaffected. Passive repetitive stretching induces muscle hypertrophy by regulating signaling pathways involved in muscle protein turnover. These findings are applicable to clinical muscle strengthening and for the maintenance of skeletal muscle mass and function in patients who are unconscious or paralyzed.
骨骼肌会对拉伸等机械刺激做出适应性改变。然而，关于体内被动重复拉伸的肥大效应，目前相关证据有限。我们研究了被动重复拉伸对骨骼肌肌纤维形态、卫星细胞含量，以及参与肌肉蛋白合成和降解的肌生成调节因子和信号分子的信使 RNA 表达的影响。通过手动踝关节背屈，每周 5 天，每天 15 分钟，将小鼠的比目鱼肌拉伸 15 次/分钟，持续 2 周。我们发现，被动重复拉伸显著增加了肌纤维横截面积。在拉伸的比目鱼肌中，p70S6K 和肌生成素的信使 RNA 表达上调，而 MuRF1、MAFbx、肌肉生长抑制素和 4E-BP1 表达下调。p70S6K 的磷酸化水平在拉伸肌肉中显著增加。Pax7+细胞数量不受影响。被动重复拉伸通过调节参与肌肉蛋白周转的信号通路来诱导肌肉肥大。这些发现适用于临床肌肉强化，以及用于维持无意识或瘫痪患者的骨骼肌质量和功能。
