a Department of Biochemistry and Genetics , Chiba University Graduate School of Medicine , Chiba , Japan.
b Department of Endocrinology, Hematology, and Gerontology , Chiba University Graduate School of Medicine , Chiba , Japan.
Chronobiol Int. 2019 May;36(5):591-615. doi: 10.1080/07420528.2019.1570246. Epub 2019 Feb 3.
Gluconeogenesis is de novo glucose synthesis from substrates such as amino acids and is vital when glucose is lacking in the diurnal nutritional fluctuation. Accordingly, genes for hepatic gluconeogenic enzymes exhibit daily expression rhythms, whose detailed regulations under nutritional variations remain elusive. As a first step, we performed general systematic characterization of daily expression profiles of gluconeogenic enzyme genes for phosphoenolpyruvate carboxykinase (PEPCK), cytosolic form (Pck1), glucose-6-phosphatase (G6Pase), catalytic subunit (G6pc), and tyrosine aminotransferase (TAT) (Tat) in the mouse liver. On a standard diet fed ad libitum, mRNA levels of these genes showed robust daily rhythms with a peak or an elevation phase during the late sleep-fasting period in the diurnal feeding/fasting (wake/sleep) cycle. The rhythmicity was preserved in constant darkness, modulated with prolonged fasting, attenuated by Clock mutation, and entrained to varied photoperiods and time-restricted feedings. These results are concordant with the notion that gluconeogenic enzyme genes are under the control of the intrinsic circadian oscillator, which is entrained by the light/dark cycle, and which in turn entrains the feeding/fasting cycle and also drives systemic signaling pathways such as the hypothalamic-pituitary-adrenal axis. On the other hand, time-restricted feedings also showed that the ingestion schedule, when separated from the light/dark cycle, can serve as an independent entrainer to daily expression rhythms of gluconeogenic enzyme genes. Moreover, nutritional changes dramatically modified expression profiles of the genes. In addition to prolonged fasting, a high-fat diet and a high-carbohydrate (no-protein) diet caused modification of daily expression rhythms of the genes, with characteristic changes in profiles of glucoregulatory hormones such as corticosterone, glucagon, and insulin, as well as their modulators including ghrelin, leptin, resistin, glucose-dependent insulinotropic polypeptide (GIP), and glucagon-like peptide-1 (GLP-1). Remarkably, high-protein (60% casein or soy-protein) diets activated the gluconeogenic enzyme genes atypically during the wake-feeding period, with paradoxical up-regulation of glucagon, which frequently formed correlation networks with other humoral factors. Based on these results, we propose that daily expression rhythms of gluconeogenic enzyme genes are under the control of systemic oscillator-driven and nutrient-responsive hormones.
糖异生是指从氨基酸等底物重新合成葡萄糖，在昼夜营养波动中葡萄糖缺乏时至关重要。因此，肝糖异生酶的基因表现出每日表达节律，但其在营养变化下的详细调控仍不清楚。作为第一步，我们对磷酸烯醇丙酮酸羧激酶（PEPCK）、胞质形式（Pck1）、葡萄糖-6-磷酸酶（G6Pase）、催化亚基（G6pc）和酪氨酸转氨酶（TAT）（Tat）的肝糖异生酶基因的每日表达谱进行了全面系统的表征。在自由进食的标准饮食中，这些基因的 mRNA 水平表现出强烈的昼夜节律，在昼夜喂食/禁食（清醒/睡眠）周期的晚期睡眠-禁食期出现峰值或升高阶段。在持续黑暗中保持节律性，延长禁食时间会调节节律性，Clock 突变会减弱节律性，并且可以适应不同的光周期和限时喂养。这些结果与以下观点一致，即糖异生酶基因受内在生物钟振荡器的控制，该振荡器受光/暗周期的调节，进而调节喂食/禁食周期，并驱动系统信号通路，如下丘脑-垂体-肾上腺轴。另一方面，限时喂养也表明，当与光/暗周期分离时，摄食时间表可以作为糖异生酶基因每日表达节律的独立调节剂。此外，营养变化极大地改变了基因的表达谱。除了长时间禁食外，高脂肪饮食和高碳水化合物（无蛋白质）饮食还导致基因的昼夜表达节律发生变化，伴随着皮质酮、胰高血糖素和胰岛素等糖调节激素以及它们的调节剂如 ghrelin、瘦素、抵抗素、葡萄糖依赖性胰岛素释放肽 (GIP) 和胰高血糖素样肽-1 (GLP-1) 的特征性变化。值得注意的是，高蛋白（60%乳清蛋白或大豆蛋白）饮食在清醒-进食期异常激活糖异生酶基因，胰高血糖素反常上调，这常常与其他体液因素形成相关网络。基于这些结果，我们提出糖异生酶基因的每日表达节律受系统振荡器驱动和营养响应激素的控制。
