Oyakawa Shun, Yamaguchi Yu, Kadowaki Tomoko, Sakai Eiko, Noguromi Mayuko, Tanimoto Ayuko, Ono Yusuke, Murata Hiroshi, Tsukuba Takayuki
Department of Dental Pharmacology, Graduate School of Biomedical Sciences, Nagasaki University, Nagasaki, Japan.
Department of Prosthetic Dentistry, Graduate School of Biomedical Sciences, Nagasaki University, Nagasaki, Japan.
J Cell Physiol. 2023 Oct;238(10):2253-2266. doi: 10.1002/jcp.31082. Epub 2023 Aug 10.
The skeletal muscle is a tissue that shows remarkable plasticity to adapt to various stimuli. The development and regeneration of skeletal muscles are regulated by numerous molecules. Among these, we focused on Rab44, a large Rab GTPase, that has been recently identified in immune cells and osteoclasts. Recently, bioinformatics data has revealed that Rab44 is upregulated during the myogenic differentiation of myoblasts into myotubes in C2C12 cells. Thus, Rab44 may be involved in myogenesis. Here, we have investigated the effects of Rab44 deficiency on the development and regeneration of skeletal muscle in Rab44 knockout (KO) mice. Although KO mice exhibited body and muscle weights similar to those of wild-type (WT) mice, the histochemical analysis showed that the myofiber cross-sectional area (CSA) of KO mice was significantly smaller than that of WT mice. Importantly, the results of muscle regeneration experiments using cardiotoxin revealed that the CSA of KO mice was significantly larger than that of WT mice, suggesting that Rab44 deficiency promotes muscle regeneration. Consistent with the in vivo results, in vitro experiments indicated that satellite cells derived from KO mice displayed enhanced proliferation and differentiation. Mechanistically, KO satellite cells exhibited an increased mechanistic target of rapamycin complex 1 (mTORC1) signaling compared to WT cells. Additionally, enhanced cell surface transport of myomaker and myomixer, which are essential membrane proteins for myoblast fusion, was observed in KO satellite cells compared to WT cells. Therefore, Rab44 deficiency enhances muscle regeneration by modulating the mTORC1 signaling pathway and transport of fusogenic regulators.
骨骼肌是一种对各种刺激具有显著可塑性以适应的组织。骨骼肌的发育和再生受众多分子调控。其中，我们聚焦于Rab44，一种大型Rab GTP酶，它最近在免疫细胞和破骨细胞中被发现。最近，生物信息学数据显示，在C2C12细胞中，成肌细胞向肌管的肌源性分化过程中Rab44表达上调。因此，Rab44可能参与肌生成。在此，我们研究了Rab44基因敲除（KO）小鼠中Rab44缺失对骨骼肌发育和再生的影响。尽管KO小鼠的体重和肌肉重量与野生型（WT）小鼠相似，但组织化学分析表明，KO小鼠的肌纤维横截面积（CSA）明显小于WT小鼠。重要的是，使用心肌毒素进行的肌肉再生实验结果显示，KO小鼠的CSA明显大于WT小鼠，这表明Rab44缺失促进肌肉再生。与体内结果一致，体外实验表明，源自KO小鼠的卫星细胞增殖和分化增强。从机制上讲，与WT细胞相比，KO卫星细胞表现出雷帕霉素复合物1（mTORC1）信号通路增强。此外，与WT细胞相比，在KO卫星细胞中观察到成肌细胞融合所必需的膜蛋白肌生成素和肌融合素的细胞表面转运增强。因此，Rab44缺失通过调节mTORC1信号通路和融合调节因子的转运来增强肌肉再生。
