肝源因子Betatrophin重设肝脏生物时钟的分子机制研究

Mammalian circadian clocks precisely control the rhythms of behavior and physiology, and can be reset by various environmental signals. A master clock is reset by the light-dark cycle, while timed food intake is a potent synchronizer of peripheral clocks. As the largest metabolic organ, the liver sensitively responds to the food signals and secrets hepatokines, which regulate metabolic and clock processes. However, it remains unknown whether any hepatokines function as the Zeitgebers independent of the central clock. In our preliminary study, we found that intraperitoneal injection of Betatrophin, a specific hepatokine, led to the advance of rhythmic phases of hepatic clock gene expression. In addition, Betatrophin “shock” induced the rhythmic expression of clock genes in vitro. Based on these findings, we will use classic molecular and cellular approaches in the present study, to elucidate the mechanism through which Betatrophin responds to nutritional stimuli and resets hepatic circadian clock by transiently activating the clock gene Per1. We hope this study will identify the significance of Betatrophin in simultaneously regulating clock and metabolism, and will provide novel experimental evidences and potential drug targets for the therapy of metabolic diseases through the view of chronobiology.

哺乳动物生物时钟系统精准控制着行为和生理活动节律性，并可被各种环境信号所重设。光线的明暗循环，对于中枢性时钟而言，是最重要的授时因子；而进食时间可重设外周性生物时钟。作为机体最大的代谢器官，肝脏能迅速响应进食信号，分泌肝源因子调控代谢和时钟进程。然而，有哪些肝源因子，能独立于中枢性时钟，行使授时因子的功能，目前还不清楚。我们前期的研究发现，腹腔注射肝源因子Betatrophin使得小鼠肝脏中时钟基因的表达相位提前。Betatrophin“休克”刺激能引起时钟基因产生节律性表达。据此，在本项目中，我们拟运用经典的分子和细胞生物学实验手段，从体内体外两个层次，阐明Betatrophin应答营养信号，通过瞬时激活时钟基因Per1，重设肝脏生物时钟的分子机制。我们希望通过本研究，发掘Betatrophin作为时钟和代谢双重调控节点的价值，为防治时钟紊乱所致的代谢异常提供新的实验依据及药物调控靶点。

哺乳动物生物时钟系统精准控制着行为和生理活动节律性，并可被各种环境信号所重设。光线的明暗循环，对于中枢性时钟而言，是最重要的授时因子；而进食时间可重设外周性生物时钟。作为机体最大的代谢器官，肝脏能迅速响应进食信号，分泌肝源因子调控代谢和时钟进程。然而，有哪些肝源因子，能独立于中枢性时钟，行使授时因子的功能，目前还不清楚。我们的研究利用高通量RNA-Seq手段结合生物信息学分析方法，最终筛选到既能响应食物信号，又能应答时钟信号的肝源性因子Angptl8。腹腔注射Angptl8能提前小鼠肝脏中时钟基因的表达相位。“Angptl8休克”刺激能引起小鼠肝癌细胞Hepa1c1c-7中时钟基因产生节律性表达。分子层面上，Angptl8能通过结合细胞膜上受体蛋白PirB，调控该受体酪氨酸磷酸化水平，进而调节SHP1/2的活化水平，影响下游激酶（如Akt、P38）和转录因子（NF-κB）的磷酸化，通过瞬时激活时钟基因Per1的表达重设肝脏生物时钟。更重要地是，肝脏特异性干扰Angptl8表达或利用Angptl8中和性抗体能部分拮抗食物信号对于小鼠肝脏时钟表达的重设过程。该研究工作将Angptl8定义为响应食物信号的重要肝脏生物时钟调节因子，揭示了Angptl8作为时钟和代谢双重调控节点的价值，为防治时钟紊乱所致的代谢异常提供新的实验依据及药物调控靶点。