Dissecting the autonomy of the liver circadian clock

摘要/摘要 哺乳动物依靠生物钟系统来协调日常的全身代谢和生理。内 这个系统，视交叉上核（SCN）中的中央时钟或起搏器，每天通过光同步 并且被认为在外围的“从属”组织时钟上具有等级优势。而SCN 生物钟对光有反应，外周组织中的生物钟在很大程度上受营养提示（例如进食- 禁食），并且可以同步到倒置的进食时间表，即使它与基于光的时间表相反 SCN的信号。组织特异性时钟缺陷的小鼠模型进一步表明， 大脑和周围的局部生物钟对于特定组织的完整昼夜节律是必要的， 概念在肝脏中体现。因此，生物钟系统似乎是一个联合网络， 相互依赖的组织时钟协同工作以实现生物体内平衡。虽然我们知道 这种生物钟之间的相互作用是存在的，生物钟通过这种机制进行交流， 这种串扰局部集成的调节是未知的。这一概念提出了一些重要的问题。是 外围组织时钟真正自主，这意味着它们可以在不受其他时钟影响的情况下振荡吗？到 它们的功能在多大程度上依赖于外在的节律信号，如定时代谢线索？回答这些 问题，我们已经产生了小鼠，除了肝脏外，所有组织中都没有时钟， 重建（肝脏重建[RE]小鼠）。我们的初步数据显示，Liver-RE小鼠的肝脏时钟 在光暗条件下自主振荡，仅再现正常节律的~10%。 转录输出，但在暗-暗条件下停止振荡。因此，在具体目标1中， 确定肝脏生物钟对光的自主反应，并识别潜在的光响应分子 调解员在具体目标2中，我们将确定是否有时间限制的喂养，同步器和驱动器的 在肝脏中的节律性转录物，可以恢复一部分缺失的~90%的正常节律性转录物， 输出.此外，我们将测试这是否是通过NAD+向生物钟发出代谢信号来实现的。整体 该提案的目标是确定自主肝脏时钟与两者之间的相互作用 驱动昼夜节律系统的主要因素，光线和食物。这样做，我们将揭示的内在能力， 肝脏生物钟和开始梳理它与其他生物钟和系统生理学的相互作用。鉴于 生物钟紊乱与代谢疾病之间的关系，以及 光和食物在日常生活中的普遍性，这些发现将提高我们对时钟的理解- 代谢交叉点和人体健康信息。

Summary/Abstract Mammals rely on the circadian clock system to orchestrate daily systemic metabolism and physiology. Within this system, the central clock or pacemaker in the suprachiasmatic nucleus (SCN) is synchronized daily by light and is considered hierarchically dominant over “subordinate” tissue clocks in the periphery. Whereas the SCN clock is responsive to light, clocks in peripheral tissues are largely influenced by nutritional cues (e.g. feeding- fasting) and can be synchronized to an inverted feeding schedule even when it opposes the light-based timing signals of the SCN. Mouse models of tissue-specific clock deficiency indicate further that both central clocks in the brain and local clocks in the periphery are necessary for full circadian rhythmicity in a particular tissue, a notion exemplified in the liver. Thus, the circadian clock system is a seemingly federated network of interdependent tissue clocks that work in concert to achieve organismal homeostasis. Although we know that this interplay between body clocks exists, the mechanisms through which clocks communicate and the levels of regulation where this cross talk integrates locally are not known. This notion raises important questions. Are peripheral tissue clocks truly autonomous, meaning can they oscillate without influence from other clocks? To what extent does their function depend on extrinsic rhythmic signals like timed metabolic cues? To answer these questions, we have generated mice which are devoid of clocks in all tissues except for the liver, where the clock is reconstituted (Liver-Reconstituted [RE] mice). Our preliminary data show that the liver clock of Liver-RE mice oscillates autonomously under light-dark conditions, recapitulating only ~10% of the normally rhythmic transcriptional output, but ceases to oscillate under dark-dark conditions. Therefore, in Specific Aim 1 we will determine the liver clock's autonomous response to light and identify potential light-responsive molecular mediators. In Specific Aim 2 we will determine whether time-restricted feeding, a synchronizer and driver of rhythmic transcripts in the liver, can reinstate a portion of the missing ~90% of normally rhythmic transcriptional output. Moreover, we will test if this is achieved through metabolic signaling to the clock via NAD+. The overall goal of this proposal is to identify the interactions between specifically the autonomous liver clock and the two main factors that drive the circadian system, light and food. In doing so, we will reveal the intrinsic capacity of the liver clock and begin to tease apart its interactions with other clocks and systemic physiology. Given the established relationship between disruption of the circadian clock and metabolic disease, as well as the pervasiveness of light and food in every day life, these findings will improve our understanding of the clock- metabolism intersection and inform on human health.