Role of TGF-β signaling for coupling of circadian oscillators in peripheral tissues

众所周知，视交叉上核的昼夜节律振荡器细胞之间的耦合是凝聚、强健和高幅度节律所必需的。然而，外围细胞时钟之间是否也存在耦合存在争议，可能的机制尚不清楚。最近，Schibler实验室能够明确地表明，活着的小鼠体内也有外周振荡器细胞(肝细胞)偶联。同时，我们发现转化生长因子-β信号通路是细胞生物钟在外周细胞中正常耦合所必需的途径。在这里，我们假设规范的转化生长因子-β信号有助于活体肝细胞间的偶联，从而在昼夜生理学中发挥重要作用。为了验证这一假说，我们建议研究以下两个目标：目标1：表征规范的转化生长因子-β信号在体内肝细胞偶联中的作用。周围组织内偶联的损害被预测会影响凝聚力、幅度、阶段以及对分子的反应。我们将创建典型的转化生长因子-β信号的组织特异性遗传功能丧失小鼠模型，并测试(I)时钟基因和时钟控制基因的昼夜节律幅度和相位是否受到影响；(Ii)摄食逆转时相移的动力学是否发生改变。目的：研究规范的转化生长因子-β信号在肝脏转录组节律中的作用，因为外周组织中的基因表达节律依赖于局部的昼夜节律振荡器和节律性的系统节律，耦合的扰动可能由于对系统输入的潜在改变而影响基因表达的昼夜节律。我们将利用肝细胞中典型的转化生长因子-β信号，分析小鼠肝脏的昼夜基因表达节律，并确定潜在的受影响的生理途径。

It has long been known that coupling among circadian oscillator cells in the suprachiasmatic nucleus is required for cohesive, robust and high amplitude rhythms. However, whether coupling also exists between cellular clocks in the periphery was controversial, and a possible mechanism was unknown. Recently, the Schibler laboratory was able to show unequivocally that peripheral oscillator cells (hepatocytes) are also coupled in living mice. At the same time, we have identified canonical TGF-β signaling as a pathway required for normal coupling of cellular circadian clocks in peripheral cells. Here, we hypothesize that canonical TGF-β signaling contributes to intercellular coupling of hepatocytes in vivo thereby playing an important role for circadian physiology. To test this hypothesis, we propose to study the following two objectives: Objective 1: Characterize the role of canonical TGF-β signaling for coupling of hepatocytes in vivo Impairment of coupling within peripheral tissues is predicted to affect cohesiveness, amplitudes, phases as well as responses to zeitgebers. We will create tissue-specific genetic loss-of-function mouse models of canonical TGF-β signaling and test (i) whether circadian amplitudes and phases of clock genes and clock-controlled genes are affected; (ii) whether the kinetics of phase shifting upon feeding reversal is altered. Objective 2: Study the role of canonical TGF-β signaling for liver transcriptome rhythms As gene expression rhythms in peripheral tissues depend on both the local circadian oscillator and rhythmic systemic zeitgebers, a perturbation of coupling likely affects circadian dynamics of gene expression due to a potentially altered response to systemic inputs. We will analyze circadian gene expression rhythms in murine liver with perturbed canonical TGF-β signalling in hepatocytes and identify potentially affected physiological pathways.