Department of Nutritional Sciences, School of Environmental and Biological Sciences, Rutgers University, New Brunswick, New Jersey, United States.
Department of Animal Sciences, School of Environmental and Biological Sciences, Rutgers University, New Brunswick, New Jersey, United States.
Am J Physiol Endocrinol Metab. 2024 Oct 1;327(4):E563-E576. doi: 10.1152/ajpendo.00129.2024. Epub 2024 Aug 28.
Disruptions in circadian rhythms are associated with an increased risk of developing metabolic diseases. General control nonderepressible 2 (GCN2), a primary sensor of amino acid insufficiency and activator of the integrated stress response (ISR), has emerged as a conserved regulator of the circadian clock in multiple organisms. The objective of this study was to examine diurnal patterns in hepatic ISR activation in the liver and whole body rhythms in metabolism. We hypothesized that GCN2 activation cues hepatic ISR signaling over a natural 24-h feeding-fasting cycle. To address our objective, wild-type (WT) and whole body knockout (GCN2 KO) mice were housed in metabolic cages and provided free access to either a control or leucine-devoid diet (LeuD) for 8 days in total darkness. On the last day, blood and livers were collected at (CT = circadian time) and . In livers of WT mice, GCN2 phosphorylation followed a diurnal pattern that was guided by intracellular branched-chain amino acid concentrations ( = 0.93). Feeding LeuD to WT mice increased hepatic ISR activation at only. Diurnal oscillations in hepatic ISR signaling, the hepatic transcriptome including lipid metabolic genes, and triglyceride concentrations were substantially reduced or absent in GCN2 KO mice. Furthermore, mice lacking GCN2 were unable to maintain circadian rhythms in whole body energy expenditure, respiratory exchange ratio, and physical activity when fed LeuD. In conclusion, GCN2 activation functions to maintain diurnal ISR activation in the liver and has a vital role in the mechanisms by which nutrient stress affects whole body metabolism. This work reveals that the eIF2 kinase GCN2 functions to support diurnal patterns in the hepatic integrated stress response during natural feeding and is necessary to maintain circadian rhythms in energy expenditure, respiratory exchange ratio, and physical activity during amino acid stress.
昼夜节律紊乱与代谢性疾病风险增加有关。一般控制非抑制物 2（GCN2）是氨基酸不足的主要传感器，也是整合应激反应（ISR）的激活剂，它已成为多种生物体生物钟的保守调节因子。本研究旨在研究肝脏中 ISR 激活的昼夜节律和整个身体代谢的节律。我们假设 GCN2 激活会提示肝脏在自然的 24 小时禁食-进食周期中进行 ISR 信号传递。为了实现我们的目标，野生型（WT）和全身敲除（GCN2 KO）小鼠被安置在代谢笼中，并在完全黑暗的条件下总共 8 天内自由选择对照或缺乏亮氨酸的饮食（LeuD）。在最后一天，在 CT（生物钟时间）和 时收集血液和肝脏。在 WT 小鼠的肝脏中，GCN2 磷酸化遵循昼夜节律模式，该模式由细胞内支链氨基酸浓度指导（ = 0.93）。给 WT 小鼠喂食 LeuD 仅在 时增加肝脏 ISR 激活。肝脏 ISR 信号的昼夜波动、包括脂质代谢基因在内的肝脏转录组以及甘油三酯浓度在 GCN2 KO 小鼠中大大减少或不存在。此外，当喂食 LeuD 时，缺乏 GCN2 的小鼠无法维持全身能量消耗、呼吸交换率和体力活动的昼夜节律。总之，GCN2 激活有助于维持肝脏的昼夜 ISR 激活，并且在营养应激影响全身代谢的机制中起着至关重要的作用。这项工作表明，eIF2 激酶 GCN2 可用于在自然进食期间支持肝脏中昼夜节律模式的 ISR 激活，并且在氨基酸应激期间维持能量消耗、呼吸交换率和体力活动的昼夜节律是必需的。
