雄激素受体在周期性机械牵拉调控成肌细胞增殖与分化中的作用和机制

Proliferation and differentiation of myoblast are major factors that determine the mass and strength of skeletal muscle. Our previous study found that 15% and 20% cyclic mechanical stretch promoted and inhibited the proliferation of myoblast C2C12, respectively. The effects of stretch on the proliferation of myoblast C2C12 were associated with androgen receptor (AR), which was likely to be mediated by insulin-like growth factor (IGF-1) and its downstream pathway phosphoinositide 3-kinase (PI3K)/Akt as well as two members of mitogen-activated protein kinases (p38 MAPK and ERK1/2). However, the effects of AR on myoblast differentiation and its mechanisms are still unclear. The present proposal will determine and compare between myoblast C2C12 (stable expression of AR) and myoblast L6 (undetected AR expression) the stretch-induced proliferation and differentiation, especial differentiation including onset of myogenic differentiation, myotube fusion, myotube number, myotube diameter, sarcomere structure and the ratio of fast and slow myofibers. Furthermore, using AR antagonist, transfection with AR overexpression plasmid, IGF-1 neutralizing antibody, recombinant IGF-1, and specific inhibitors of p38, ERK1/2 and PI3K, we will demonstrate the roles of AR in regulating proliferation and differentiation of myoblast are related to IGF-1-PI3K/Akt, p38 and ERK1/2 pathways, and AR target genes such as myogenic differentiation antigen (MyoD), myogenin, MyoG、myostatin、forkhead box O1 (FOXO1) are also involved in the differentiation of stretched myoblast. The proposal provides a new theoretical explanation for stretch-induced proliferation and differentiation of myoblast, which is beneficial to clarify the mechanism of exercise-induced alterations in mass and strength of skeletal muscle.

成肌细胞增殖与分化是决定骨骼肌质量和力量的主要因素。前期研究发现，15%和20%周期性机械牵拉分别促进和抑制成肌细胞C2C12增殖，这与雄激素受体(AR)有关，且通过AR相关信号通路(IGF-1、PI3K/Akt、p38、ERK1/2)介导。但AR在牵拉调控成肌细胞分化中的作用及机制尚不明确。本课题拟研究牵拉对C2C12(表达AR)和L6(不表达AR)两种成肌细胞增殖、分化(分化延迟、肌管融合、肌管数目和大小等)的影响及差异，并利用AR阻断剂、AR质粒转染、IGF-1中和抗体和重组多肽以及PI3K、p38、ERK1/2抑制剂证实AR在牵拉调控成肌细胞增殖和分化中的作用与上述AR相关信号通路有关，而AR靶基因MyoD, myogenin, MyoG、myostatin、FOXO1也调控牵拉成肌细胞分化。这为牵拉调控成肌细胞增殖和分化提供新的理论解释，也有利于阐明运动改变肌肉质量和力量的机制。

雄激素受体(AR)在运动增加骨骼肌质量和力量中的作用与AR促进成肌细胞的增殖与分化密切相关，但其作用机制仍未阐明。本课题研究了15%和20%的机械牵拉对C2C12（表达AR）和L6（不表达AR）两种成肌细胞增殖、分化（分化延迟、肌管融合、肌管数目和大小等）的影响及差异，并利用AR阻断剂、AR质粒转染、IGF-1中和抗体和重组多肽以及PI3K、p38、ERK1/2抑制剂证实了AR在牵拉调控成肌细胞增殖和分化中的作用与上述AR相关信号通路有关，而AR靶基因MyoD, myogenin, myostatin、FOXO1还调控牵拉成肌细胞的分化。此外，本研究还证实雄激素/AR能调控骨髓干细胞的成肌、成脂分化方向和糖脂代谢，在肥胖发生发展中起重要作用；进一步用敲除小鼠发现雄激素合成依赖脂肪因子chemerin、反过来chemerin作用也是通过雄激素/AR调控糖脂代谢酶和线粒体实现。这有利于阐明适宜和过度运动分别增加和降低肌肉质量和力量、并调控脂肪量和糖脂代谢的机制。