Circadian clock and temporal control in nutrient metabolism

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Project Summary The circadian clock confers temporal control to metabolic pathways, and its disruption leads to insulin resistance and obesity. Skeletal muscle plays a critical role in nutrient metabolism and protein homeostasis. We and others demonstrated that the muscle-intrinsic clock regulates skeletal muscle development, growth, and metabolism. Despite the extensive studies of circadian regulation in glucose and lipid metabolism, there is a current knowledge gap regarding clock function in protein metabolism that determines muscle mass. In addition, although circadian misalignment is prevalent in a modern lifestyle, potential circadian etiologies underlying muscle wasting and impaired metabolic capacity remains unknown. We have identified a novel clock-driven temporal control of PI3K-Akt-mTORC1 signaling in skeletal muscle that is independent of feeding-induced activation. Surprisingly, clock disruption mimicking shiftwork resulted in progressive muscle atrophy accompanied with impaired PI3K-Akt signaling and elevated protein turnover. Furthermore, mechanistic studies revealed circadian clock transcriptional control of the Insulin/Igf-1-PI3K-Akt-mTOR signaling cascade. These findings, together with prior research support a hypothesis that that the muscle-intrinsic clock confers temporal control in PI3K-Akt-mTOR cascade to drive protein metabolism and insulin sensitivity, and this mechanism underlies circadian disruption-induced muscle atrophy and insulin resistance. The overarching goal of this project is to comprehensively define this newly discovered clock-PI3K-Akt-mTOR regulatory axis in muscle nutrient homeostasis and muscle mass regulation. Specifically, we will leverage our unique clock modulation models with multi-omics approaches to comprehensively define the molecular mechanisms responsible for and the physiological significance of the clock-Akt-mTOR regulatory axis in protein metabolism, insulin sensitivity and muscle mass maintenance. More importantly, we propose to test genetic and pharmacological clock-augmenting interventions to counteract muscle anabolic and metabolic deficits induced by clock disruption. The outcome of this proposal may uncover a circadian etiology underlying impaired metabolic capacity in sarcopenia and provide the mechanistic basis for clock-targeting interventions.