Transcriptional programming of lipid and amino acid metabolism by the skeletal muscle circadian clock

Circadian clocks are fundamental physiological regulators of energy homeostasis, but direct transcriptional targets of the muscle clock machinery are unknown. To understand how the muscle clock directs rhythmic metabolism, we determined genome-wide binding of the master clock regulators brain and muscle ARNT-like protein 1 (BMAL1) and REV-ERBα in murine muscles. Integrating occupancy with 24-hr gene expression and metabolomics after muscle-specific loss of BMAL1 and REV-ERBα, here we unravel novel molecular mechanisms connecting muscle clock function to daily cycles of lipid and protein metabolism. Validating BMAL1 and REV-ERBα targets using luciferase assays and in vivo rescue, we demonstrate how a major role of the muscle clock is to promote diurnal cycles of neutral lipid storage while coordinately inhibiting lipid and protein catabolism prior to awakening. This occurs by BMAL1-dependent activation of Dgat2 and REV-ERBα-dependent repression of major targets involved in lipid metabolism and protein turnover (MuRF-1, Atrogin-1). Accordingly, muscle-specific loss of BMAL1 is associated with metabolic inefficiency, impaired muscle triglyceride biosynthesis, and accumulation of bioactive lipids and amino acids. Taken together, our data provide a comprehensive overview of how genomic binding of BMAL1 and REV-ERBα is related to temporal changes in gene expression and metabolite fluctuations.

生物钟（Circadian Clock）是能量稳态的核心生理调控因子，但目前尚不明确肌肉生物钟系统的直接转录靶标。为阐明肌肉生物钟如何调控节律性代谢，我们在小鼠肌肉组织中检测了核心生物钟调控因子脑和肌肉ARNT样蛋白1（brain and muscle ARNT-like protein 1, BMAL1）与REV-ERBα的全基因组结合位点。我们整合了全基因组结合占有率数据、24小时基因表达谱与代谢组学数据，并结合肌肉特异性BMAL1与REV-ERBα缺失后的实验结果进行分析，揭示了将肌肉生物钟功能与脂质、蛋白质代谢昼夜周期相关联的新型分子机制。我们通过荧光素酶报告基因实验与体内挽救实验验证了BMAL1与REV-ERBα的靶标基因，证实肌肉生物钟的核心功能之一是促进中性脂质储存的昼夜节律，同时在觉醒前协同抑制脂质与蛋白质分解代谢。该调控过程通过BMAL1依赖性激活二酰甘油酰基转移酶2（Dgat2），以及REV-ERBα依赖性抑制脂质代谢与蛋白质周转相关的核心靶标（MuRF-1、Atrogin-1）实现。据此，肌肉特异性BMAL1缺失会导致代谢效率降低、肌肉甘油三酯生物合成受损，以及生物活性脂质与氨基酸异常积累。综上，本研究数据全面阐明了BMAL1与REV-ERBα的基因组结合如何与基因表达的时间动态变化及代谢物波动相关联。