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

Abstract

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.

The importance of being rhythmic: Living in harmony with your body clocks

“…103 An additional metabolic sensor in the body is the oxygen level. 121 In the liver, REV-ERBα couples glucocorticoid signalling to energy metabolism via binding of the hepatocyte nuclear transcription factors HNF4A/HNF6. [104][105][106] Studies in genetic mouse models that lack a functional clock due to a whole-body or tissue-specific knockout of essential core clock components reveal that a proper circadian oscillator function is indispensable for glucose, lipid and protein metabolism.…”

“…Indeed, muscle-specific loss of BMAL1 directly leads to metabolic inefficiency, impairs muscle triglyceride biosynthesis, and causes accumulation of bioactive lipids and amino acids in mice. 121 In the liver, REV-ERBα couples glucocorticoid signalling to energy metabolism via binding of the hepatocyte nuclear transcription factors HNF4A/HNF6. 122 Liver-specific Bmal1KO leads to reduced lipid accumulation in hepatic cells via increased mRNA methylation, in particular of PPARα.…”

Circadian regulation of muscle growth independent of locomotor activity

“…Several genes are known to regulate catabolism in muscle tissue by activating proteasomal proteolysis of sarcomeric proteins and this is thought to regulate muscle size (Bodine et al, 2001;Witt et al, 2008). Among such genes are those encoding the Muscle RING Finger (Murf) family of Tripartite Motif (Trim) proteins that have been reported to undergo circadian changes in mRNA level in muscle (Amaral and Johnston, 2012;Dyar et al, 2018Dyar et al, , 2015McCarthy et al, 2007). Analysis of murf1/trim63a and murf2/trim55b mRNA levels in 3-5 dpf larvae by qRT-PCR suggested that these genes undergo circadian cycling, such that they peak in every dark phase at ZT15 (Fig.…”

“…In adult muscle, mass maintenance is also thought to be controlled by protein turnover, which is suggested to be regulated by the circadian clock. Previous studies, generally performed on adult rodent limb muscle, indicated that protein synthesis, as reflected by either p70S6K and ERK1/2 phosphorylation (Chang et al, 2016) or puromycin incorporation (Dyar et al, 2018), display a day/night variation in skeletal muscle. In addition, the expression of atrogenes, such as atrogin1 and murf1, were shown to undergo rhythmic circadian changes in skeletal muscle (Dyar et al, 2018(Dyar et al, , 2015McCarthy et al, 2007;Perrin et al, 2018).…”

“…Previous studies, generally performed on adult rodent limb muscle, indicated that protein synthesis, as reflected by either p70S6K and ERK1/2 phosphorylation (Chang et al, 2016) or puromycin incorporation (Dyar et al, 2018), display a day/night variation in skeletal muscle. In addition, the expression of atrogenes, such as atrogin1 and murf1, were shown to undergo rhythmic circadian changes in skeletal muscle (Dyar et al, 2018(Dyar et al, , 2015McCarthy et al, 2007;Perrin et al, 2018). Some of these circadian differences were shown to be abolished by loss-of-function of core clock genes (Dyar et al, 2018(Dyar et al, , 2015, indicating the critical requirement of the molecular clock in regulating muscle metabolism.…”