Laboratory of Physiology, School of Health Sciences, Toyohashi SOZO University, Toyohashi, Japan.
Department of Physiology, Graduate School of Health Sciences, Toyohashi SOZO University, Toyohashi, Japan.
Acta Physiol (Oxf). 2018 Jun;223(2):e13042. doi: 10.1111/apha.13042. Epub 2018 Feb 9.
Lactate is produced in and released from skeletal muscle cells. Lactate receptor, G-protein-coupled receptor 81 (GPR81), is expressed in skeletal muscle cells. However, a physiological role of extracellular lactate on skeletal muscle is not fully clarified. The purpose of this study was to investigate extracellular lactate-associated morphological changes and intracellular signals in C2C12 skeletal muscle cells.
Mouse myoblast C2C12 cells were differentiated for 5 days to form myotubes. Sodium lactate (lactate) or GPR81 agonist, 3,5-dihydroxybenzoic acid (3,5-DHBA), was administered to the differentiation medium.
Lactate administration increased the diameter of C2C12 myotubes in a dose-dependent manner. Administration of 3,5-DHBA also increased myotube diameter. Not only lactate but also 3,5-DHBA upregulated the phosphorylation level of mitogen-activated protein kinase kinase 1/2 (MEK1/2), p42/44 extracellular signal-regulated kinase-1/2 (ERK1/2) and p90 ribosomal S6 kinase (p90RSK). MEK inhibitor U0126 depressed the phosphorylation of ERK-p90RSK and increase in myotube diameter induced by lactate. On the other hand, both lactate and 3,5-DHBA failed to induce significant responses in the phosphorylation level of Akt, mammalian target of rapamycin, p70 S6 kinase and protein degradation-related signals.
These observations suggest that lactate-associated increase in the diameter of C2C12 myotubes is induced via activation of GRP81-mediated MEK/ERK pathway. Extracellular lactate might have a positive effect on skeletal muscle size.
乳酸在骨骼肌细胞中产生并释放。G 蛋白偶联受体 81（GPR81）是一种存在于骨骼肌细胞中的乳酸受体。然而，细胞外乳酸对骨骼肌的生理作用尚未完全阐明。本研究旨在探讨细胞外乳酸对 C2C12 骨骼肌细胞形态变化和细胞内信号的影响。
将小鼠成肌细胞 C2C12 分化 5 天形成肌管。在分化培养基中加入乳酸钠（乳酸）或 GPR81 激动剂 3,5-二羟基苯甲酸（3,5-DHBA）。
乳酸的给药剂量依赖性地增加 C2C12 肌管的直径。3,5-DHBA 的给药也增加了肌管的直径。不仅是乳酸，3,5-DHBA 还上调了丝裂原活化蛋白激酶激酶 1/2（MEK1/2）、p42/44 细胞外信号调节激酶 1/2（ERK1/2）和 p90 核糖体 S6 激酶（p90RSK）的磷酸化水平。MEK 抑制剂 U0126 抑制了由乳酸诱导的 ERK-p90RSK 的磷酸化和肌管直径的增加。另一方面，乳酸和 3,5-DHBA 均不能诱导 Akt、雷帕霉素哺乳动物靶蛋白、p70 S6 激酶和蛋白降解相关信号的磷酸化水平发生显著变化。
这些观察结果表明，乳酸诱导的 C2C12 肌管直径增加是通过激活 GPR81 介导的 MEK/ERK 通路引起的。细胞外乳酸可能对骨骼肌大小有积极影响。
