Rudolf-Schönheimer-Institute of Biochemistry, Faculty of Medicine, Leipzig University, Leipzig, Germany; Institute of Biochemistry, Charité - Universitätsmedizin Berlin, Corporate Member of Freie Universität Berlin, Humboldt-Universität zu Berlin, and Berlin Institute of Health, Germany.
Rudolf-Schönheimer-Institute of Biochemistry, Faculty of Medicine, Leipzig University, Leipzig, Germany.
J Hepatol. 2019 Jun;70(6):1192-1202. doi: 10.1016/j.jhep.2019.01.022. Epub 2019 Feb 1.
BACKGROUND & AIMS: The mammalian circadian clock controls various aspects of liver metabolism and integrates nutritional signals. Recently, we described Hedgehog (Hh) signaling as a novel regulator of liver lipid metabolism. Herein, we investigated crosstalk between hepatic Hh signaling and circadian rhythm.
Diurnal rhythms of Hh signaling were investigated in liver and hepatocytes from mice with ablation of Smoothened (SAC-KO) and crossbreeds with PER2::LUC reporter mice. By using genome-wide screening, qPCR, immunostaining, ELISA and RNAi experiments in vitro we identified relevant transcriptional regulatory steps. Shotgun lipidomics and metabolic cages were used for analysis of metabolic alterations and behavior.
Hh signaling showed diurnal oscillations in liver and hepatocytes in vitro. Correspondingly, the level of Indian Hh, oscillated in serum. Depletion of the clock gene Bmal1 in hepatocytes resulted in significant alterations in the expression of Hh genes. Conversely, SAC-KO mice showed altered expression of clock genes, confirmed by RNAi against Gli1 and Gli3. Genome-wide screening revealed that SAC-KO hepatocytes showed time-dependent alterations in various genes, particularly those associated with lipid metabolism. The clock/hedgehog module further plays a role in rhythmicity of steatosis, and in the response of the liver to a high-fat diet or to differently timed starvation.
For the first time, Hh signaling in hepatocytes was found to be time-of-day dependent and to feed back on the circadian clock. Our findings suggest an integrative role of Hh signaling, mediated mainly by GLI factors, in maintaining homeostasis of hepatic lipid metabolism by balancing the circadian clock.
The results of our investigation show for the first time that the Hh signaling in hepatocytes is time-of-day dependent, leading to differences not only in transcript levels but also in the amount of Hh ligands in peripheral blood. Conversely, Hh signaling is able to feed back to the circadian clock.
哺乳动物的生物钟控制着肝脏代谢的各个方面，并整合营养信号。最近，我们描述了 Hedgehog（Hh）信号作为肝脏脂质代谢的新调节因子。在此，我们研究了肝 Hh 信号与昼夜节律之间的串扰。
通过对 Smoothened（SAC-KO）消融的小鼠肝脏和肝细胞以及 PER2::LUC 报告小鼠的杂交种进行昼夜节律的 Hh 信号研究。通过使用全基因组筛选、qPCR、免疫染色、ELISA 和体外 RNAi 实验，我们确定了相关的转录调节步骤。利用 shotgun 脂质组学和代谢笼分析代谢改变和行为。
Hh 信号在肝脏和体外肝细胞中表现出昼夜节律波动。相应地，印度 Hh 的水平在血清中波动。肝细胞中时钟基因 Bmal1 的耗竭导致 Hh 基因的表达发生显著改变。相反，SAC-KO 小鼠表现出时钟基因表达的改变，这通过针对 Gli1 和 Gli3 的 RNAi 得到证实。全基因组筛选显示，SAC-KO 肝细胞在各种基因的表达上表现出时间依赖性改变，特别是那些与脂质代谢相关的基因。时钟/ Hedgehog 模块在脂肪变性的节律性和肝脏对高脂肪饮食或不同时间饥饿的反应中进一步发挥作用。
首次发现肝细胞中的 Hh 信号依赖于一天中的时间，并反馈到生物钟。我们的研究结果表明，Hh 信号通过主要由 GLI 因子介导，在通过平衡生物钟来维持肝脏脂质代谢的内稳态方面发挥着整合作用。
我们的研究结果首次表明，肝细胞中的 Hh 信号依赖于一天中的时间，这不仅导致转录水平的差异，还导致外周血液中 Hh 配体的量的差异。相反，Hh 信号能够反馈到生物钟。
