Functional characterization of cryptochromes CRY1 and CRY2 as metabolic sensors in the circadian regulation of mammalian physiology

生物钟通过基因表达的激活因子和抑制因子的交替作用来协调昼夜周期的行为和生理过程。转录调节因子BMAL1和CLOCK激活许多基因的表达，包括它们自己的抑制剂周期（PER1-3）和隐色素（CRY1&2），导致靶基因的表达振荡。很长一段时间以来，哺乳动物的生物钟被认为局限于下丘脑的一个小区域，这个区域控制着与光刺激有关的运动活动的昼夜节律。然而，在过去的十年里，研究表明生物钟在哺乳动物组织中广泛分布。研究表明，进食时间表决定了外周时钟的时间，以及昼夜节律失调可能导致肥胖和糖尿病的新证据表明，昼夜节律调节与代谢稳态密切相关。最近的研究表明，代谢信号的中心介质AMPK磷酸化，从而破坏CRY1的稳定，提供了一种代谢信号可以重置生物钟时间的分子机制。此外，这一发现表明，除了它们在时钟功能中的作用，CRYs可能是重要的代谢调节因子。这一发现进一步支持了CRYs与PPARs的物理相互作用，PPARs是一个调节各种基本代谢过程的核激素受体家族。在本研究中，我将验证ampk介导的CRY1磷酸化在骨骼肌代谢的转录调节中发挥作用，并且CRYs与PPARs的相互作用参与了这些过程的假设。这些分析具有进一步阐明CRYs调节代谢信号转录的分子机制的潜力，并将揭示其对骨骼肌生理学的影响，骨骼肌生理学在哺乳动物代谢稳态中起着核心作用。

Circadian clocks coordinate behavioral and physiological processes with day-night cycles through alternating actions of activators and repressors of gene expression. The transcriptional regulators BMAL1 and CLOCK activate expression of many genes including their own inhibitors period (PER1-3) and cryptochrome (CRY1&2), resulting in oscillating expression of target genes. For a long time mammalian clocks were thought to be confined to a small area of the hypothalamus that controls circadian rhythms in locomotor activity in relation to light stimuli. However, within the last decade, it has been shown that circadian clocks are widely distributed in mammalian tissues. The demonstration that feeding schedules determine the timing of peripheral clocks and the emerging evidence that dysregulation of circadian rhythms can contribute to obesity and diabetes, suggest that circadian regulation is intimately linked to metabolic homeostasis. The recent demonstration that AMPK, a central mediator of metabolic signaling, phosphorylates and thereby destabilizes CRY1 provides a molecular mechanism by which metabolic signals can reset the timing of circadian clocks. Moreover this finding suggests that, in addition to their role in clock function, CRYs may be important regulators of metabolism. This is further supported by the finding that CRYs physically interact with PPARs, a family of nuclear hormone receptors that regulates various essential metabolic processes.In the proposed study I will test the hypothesis that AMPK-mediated CRY1 phosphorylation plays a role in the transcriptional regulation of skeletal muscle metabolism and that CRYs interaction with PPARs is involved in these processes. These analyses hold the potential to further elucidate the molecular mechanisms by which CRYs regulate transcription in response to metabolic signals and will unravel their impact on skeletal muscle physiology, which plays a central role in mammalian metabolic homeostasis.