Thyroid hormone receptor beta (THRB) dependent regulation of diurnal hepatic lipid metabolism in adult male mice

Thyroid hormones (THs) are critical regulators of systemic energy metabolism and homeostasis. In the liver, high TH action protects against steatosis by enhancing cholesterol and triglyceride turnover, with thyroid hormone receptor beta (THRB) signaling playing a pivotal role. This study probed the potential interaction between THRB action and another critical regulator of liver energy metabolism, the circadian clock. Liver transcriptome analysis of THRB deficient (THRBKO) mice under normal chow conditions revealed a markedly modest impact of THRB deletion. Temporal transcriptome and lipidome profiling uncovered significant alterations in diurnal metabolic rhythms attributable to THRB deficiency pointing to a pro-steatotic state with elevated levels of cholesterol, tri- and diacylglycerides, and fatty acids. These findings were confirmed by THRB agonization in hepatocytes under steatosis-promoting conditions in vitro. Integration of transcriptome profiles from THRBKO mice and mice with induced high or low TH action identified a subset of TH responsive but THRB insensitive genes implicated in immune processes. In summary, our study reveals a complex time-of-day dependent interaction of different TH-related signals in the regulation of liver physiology indicating an opportunity for chronopharmacological approaches to TH/THR(B) manipulation in fatty liver diseases. Two to three-months-old male wild type (THRB+/-) and knockout (THRB-/-) were group-housed under 12h/12h light/dark conditions (LD, 200 400 lux) at 22 2C with food and water provided ad libitum (normal chow, 5 % fat, 1314, Altromin, Germany). Mice were culled by cervical dislocation at 4-hour intervals, tissues were kept in dry ice, and stored at -80C甲状腺激素（Thyroid hormones, THs）是全身能量代谢与稳态的关键调控因子。在肝脏中，高水平甲状腺激素信号通过增强胆固醇与甘油三酯周转来抵御肝脂肪变性，其中甲状腺激素受体β（thyroid hormone receptor beta, THRB）信号通路发挥核心作用。本研究探究了THRB信号与另一种肝脏能量代谢关键调控因子——生物钟之间的潜在相互作用。正常饮食条件下对THRB敲除（THRBKO）小鼠的肝脏转录组分析显示，THRB缺失的影响相对温和。时序转录组与脂质组学分析揭示，THRB缺失会显著改变昼夜代谢节律，进而导致促脂肪变性状态，表现为胆固醇、三酰甘油、二酰甘油及脂肪酸水平升高。上述发现于体外脂肪变性诱导条件下的肝细胞THRB激动实验中得到验证。整合THRBKO小鼠与甲状腺激素高低水平诱导小鼠的转录组数据，筛选出一类受甲状腺激素调控但不依赖THRB的基因，这类基因与免疫过程相关。综上，本研究揭示了不同甲状腺激素相关信号在调控肝脏生理功能时存在复杂的昼夜依赖性相互作用，这为针对甲状腺激素/甲状腺激素受体β的时辰药理学干预策略治疗脂肪肝病提供了潜在方向。本研究使用2~3月龄雄性野生型（THRB+/-）与敲除型（THRB-/-）小鼠，将其以组群饲养于12h/12h明暗循环环境（光照强度200~400 lux，温度22±2℃），自由进食饮水（正常饲料：脂肪含量5%，货号1314，德国Altromin公司生产）。小鼠每隔4小时通过颈椎脱臼法处死，组织样本置于干冰保存，并于-80℃冰箱存储。