Hughes M A, Downs R M, Webb G W, Crocker C L, Kinsey S T, Baumgarner Bradley L
Division of Natural Sciences and Engineering, University of South Carolina Upstate, Spartanburg, SC, 29303, USA.
Department of Biology and Marine Biology, University of North Carolina Wilmington, Wilmington, NC, 28403-5915, USA.
J Muscle Res Cell Motil. 2017 Apr;38(2):201-214. doi: 10.1007/s10974-017-9473-9. Epub 2017 Jun 20.
Caffeine is a highly catabolic dietary stimulant. High caffeine concentrations (1-10 mM) have previously been shown to inhibit protein synthesis and increase protein degradation in various mammalian cell lines. The purpose of this study was to examine the effect of short-term caffeine exposure on cell signaling pathways that regulate protein metabolism in mammalian skeletal muscle cells. Fully differentiated C2C12 skeletal myotubes either received vehicle (DMSO) or 5 mM caffeine for 6 h. Our analysis revealed that caffeine promoted a 40% increase in autolysosome formation and a 25% increase in autophagic flux. In contrast, caffeine treatment did not significantly increase the expression of the skeletal muscle specific ubiquitin ligases MAFbx and MuRF1 or 20S proteasome activity. Caffeine treatment significantly reduced mTORC1 signaling, total protein synthesis and myotube diameter in a CaMKKβ/AMPK-dependent manner. Further, caffeine promoted a CaMKII-dependent increase in myostatin mRNA expression that did not significantly contribute to the caffeine-dependent reduction in protein synthesis. Our results indicate that short-term caffeine exposure significantly reduced skeletal myotube diameter by increasing autophagic flux and promoting a CaMKKβ/AMPK-dependent reduction in protein synthesis.
咖啡因是一种具有高度分解代谢作用的膳食兴奋剂。先前已表明，高浓度咖啡因（1-10 mM）可抑制多种哺乳动物细胞系中的蛋白质合成并增加蛋白质降解。本研究的目的是检测短期接触咖啡因对调节哺乳动物骨骼肌细胞蛋白质代谢的细胞信号通路的影响。完全分化的C2C12骨骼肌肌管分别接受载体（二甲基亚砜）或5 mM咖啡因处理6小时。我们的分析表明，咖啡因使自溶酶体形成增加40%，自噬通量增加25%。相比之下，咖啡因处理并未显著增加骨骼肌特异性泛素连接酶MAFbx和MuRF1的表达或20S蛋白酶体活性。咖啡因处理以CaMKKβ/AMPK依赖的方式显著降低mTORC1信号传导、总蛋白质合成和肌管直径。此外，咖啡因促进了肌生成抑制素mRNA表达以CaMKII依赖的方式增加，这对咖啡因依赖的蛋白质合成减少没有显著贡献。我们的结果表明，短期接触咖啡因通过增加自噬通量并促进CaMKKβ/AMPK依赖的蛋白质合成减少，显著减小了骨骼肌肌管直径。
