Clock genes regulate skeletal muscle energy metabolism through NAMPT/NAD⁺/SIRT1 following heavy-load exercise

The biological clock is an invisible "clock" in the organism, which can regulate behavior, physiology, and biochemical reactions. However, the relationship between clock genes and energy metabolism in postexercise skeletal muscle is not well known. The purpose of this study was to determine the mechanisms through which peripheral clock genes regulate energy metabolism in skeletal muscle. We analyzed the rhythm of mRNA expression of the clock genes Bmal1 and Clock in skeletal muscle following heavy-load exercise and measured related indicators of mitochondrial structure and function. We obtained the following experimental results. First, heavy-load exercise induced loss of circadian rhythm of Bmal1 between ZT0 and ZT24, and the circadian rhythm of Clock was not restored between ZT0 and ZT72. Second, analysis of mitochondrial morphology in group E showed abnormal swelling and ridge structure damage at ZT0, which recovered somewhat at ZT24 and ZT48, and the damage had essentially disappeared by ZT72. Third, the expression of NAMPT/NAD⁺/SIRT1 signaling axis proteins in group E was abnormal at ZT0, the content of NAMPT and the activity of SIRT1 significantly increased, and the content of NAD⁺ significantly decreased. Fourth, the expression of BMAL1 and PGC-1α in group E significantly increased, whereas the ATP and ADP content, as well as the activities of COXII and COXIV, were significantly changed. Finally, the colocalization of BMAL1 and SIRT1 in group E was significantly upregulated at ZT0. These results suggest that the skeletal muscle clock gene Bmal1 may regulate the energy metabolism level of skeletal muscle after exercise through the NAMPT/NAD⁺/SIRT1 signaling pathway.