Fu Shaoting, Lin Xiaojing, Yin Lijun, Wang Xiaohui
Department of Exercise Physiology, School of Kinesiology, Shanghai University of Sport, 188 Hengren Road, Yangpu District, Shanghai, 200438, China.
Department of Kinesiology, College of Physical Education, Shanghai Normal University, Shanghai, 200234, China.
Nutr Metab (Lond). 2021 Sep 15;18(1):85. doi: 10.1186/s12986-021-00610-y.
Androgen receptor (AR) exerts important roles in exercise-induced alterations of muscle mass, in which the proliferation and differentiation of satellite cells or myoblasts are crucial. Our previous study in C2C12 myoblasts demonstrated that 15% (mimic appropriate exercise) and 20% (mimic excessive exercise) stretches promoted and inhibited the proliferation respectively; and AR played a crucial role in 15% stretch-induced pro-proliferation through IGF-1-modulated PI3K/Akt, p38 and ERK1/2 pathways, but AR's role in stretches-modulated proliferation of general myoblasts, especially 20% stretch, remains unclear, and the mechanisms need to be further clarified.
Firstly, the discrepancy in proliferation and the above indicators between L6 (without AR) and C2C12 (with AR) myoblasts were compared under 15% or 20% stretch. Then the influences of transfection AR or exogenous IGF-1 treatment on proliferation and these indicators were detected in stretched L6 myoblasts.
(1) Under un-stretched state, the proliferation of L6 was slower than C2C12 cells. Furthermore, AR knockdown in C2C12 myoblasts repressed, while AR overexpression in L6 myoblasts promoted the proliferation. (2) 15% stretch-induced increases in the proliferation and activities of p38 and ERK1/2 were lower in L6 than C2C12 cells; AR overexpression enhanced the proliferation of 15% stretched L6 cells accompanied with the increases of p38 and ERK1/2 activities. (3) 20% stretch-induced anti-proliferation and inhibition of p38 activity were severer in L6 than C2C12 myoblasts; AR overexpression reversed the anti-proliferation of 20% stretch and enhanced p38 activity in L6 myoblasts. (4) In stretched L6 myoblasts, AR overexpression increased IGF-1R level despite no detectable IGF-1; and recombinant IGF-1 increased the proliferation, the level of IGF-1R, and the activities of p38 and ERK1/2 in 15% stretched L6 myoblasts.
The study demonstrated AR's crucial roles in stretches-regulated proliferation of myoblasts, and increased AR fulfilled 15% stretch's pro-proliferation via activating IGF-1R- p38 and ERK1/2 pathways while decreased AR achieved 20% stretch's anti-proliferation via inhibiting IGF-1R- p38 pathway, which is useful to understand in depth the role and mechanisms of AR in appropriate exercise increasing while excessive exercise decreasing muscle mass.
雄激素受体（AR）在运动诱导的肌肉量改变中发挥重要作用，其中卫星细胞或成肌细胞的增殖和分化至关重要。我们之前在C2C12成肌细胞中的研究表明，15%（模拟适度运动）和20%（模拟过度运动）拉伸分别促进和抑制增殖；AR通过IGF-1调节的PI3K/Akt、p38和ERK1/2途径在15%拉伸诱导的促增殖中起关键作用，但AR在一般成肌细胞拉伸调节的增殖中的作用，尤其是20%拉伸的作用仍不清楚，其机制有待进一步阐明。
首先，比较15%或20%拉伸下L6（无AR）和成肌细胞C2C12（有AR）在增殖及上述指标上的差异。然后在拉伸的L6成肌细胞中检测转染AR或外源性IGF-1处理对增殖及这些指标的影响。
（1）在未拉伸状态下，L6的增殖比C2C12细胞慢。此外，C2C12成肌细胞中AR敲低会抑制增殖，而L6成肌细胞中AR过表达则促进增殖。（2）15%拉伸诱导的L6细胞增殖增加以及p38和ERK1/2活性增加低于C2C12细胞；AR过表达增强了15%拉伸的L6细胞的增殖，并伴随着p38和ERK1/2活性的增加。（3）20%拉伸诱导的L6成肌细胞抗增殖和p38活性抑制比C2C12成肌细胞更严重；AR过表达逆转了20%拉伸的抗增殖作用，并增强了L6成肌细胞中的p38活性。（4）在拉伸的L6成肌细胞中，尽管未检测到IGF-1，但AR过表达增加了IGF-1R水平；重组IGF-1增加了15%拉伸的L6成肌细胞的增殖、IGF-1R水平以及p38和ERK1/2的活性。
该研究证明了AR在成肌细胞拉伸调节的增殖中起关键作用，AR增加通过激活IGF-1R-p38和ERK1/2途径实现15%拉伸的促增殖，而AR减少通过抑制IGF-1R-p38途径实现20%拉伸的抗增殖，这有助于深入理解AR在适度运动增加而过度运动减少肌肉量中的作用和机制。
