Department of Pharmacology, SUNY Upstate Medical University, Syracuse, NY, 13210, USA.
Department of Medicine, SUNY Upstate Medical University, Syracuse, NY, 13210, USA.
Lipids Health Dis. 2022 May 25;21(1):46. doi: 10.1186/s12944-022-01654-6.
Hepatocyte nuclear factor 4α (HNF4α) and glucocorticoid receptor (GR), master regulators of liver metabolism, are down-regulated in fatty liver diseases. The present study aimed to elucidate the role of down-regulation of HNF4α and GR in fatty liver and hyperlipidemia.
Adult mice with liver-specific heterozygote (HET) and knockout (KO) of HNF4α or GR were fed a high-fat-high-sugar diet (HFHS) for 15 days. Alterations in hepatic and circulating lipids were determined with analytical kits, and changes in hepatic mRNA and protein expression in these mice were quantified by real-time PCR and Western blotting. Serum and hepatic levels of bile acids were quantified by LC-MS/MS. The roles of HNF4α and GR in regulating hepatic gene expression were determined using luciferase reporter assays.
Compared to HFHS-fed wildtype mice, HNF4α HET mice had down-regulation of lipid catabolic genes, induction of lipogenic genes, and increased hepatic and blood levels of lipids, whereas HNF4α KO mice had fatty liver but mild hypolipidemia, down-regulation of lipid-efflux genes, and induction of genes for uptake, synthesis, and storage of lipids. Serum levels of chenodeoxycholic acid and deoxycholic acid tended to be decreased in the HNF4α HET mice but dramatically increased in the HNF4α KO mice, which was associated with marked down-regulation of cytochrome P450 7a1, the rate-limiting enzyme for bile acid synthesis. Hepatic mRNA and protein expression of sterol-regulatory-element-binding protein-1 (SREBP-1), a master lipogenic regulator, was induced in HFHS-fed HNF4α HET mice. In reporter assays, HNF4α cooperated with the corepressor small heterodimer partner to potently inhibit the transactivation of mouse and human SREBP-1C promoter by liver X receptor. Hepatic nuclear GR proteins tended to be decreased in the HNF4α KO mice. HFHS-fed mice with liver-specific KO of GR had increased hepatic lipids and induction of SREBP-1C and PPARγ, which was associated with a marked decrease in hepatic levels of HNF4α proteins in these mice. In reporter assays, GR and HNF4α synergistically/additively induced lipid catabolic genes.
induction of lipid catabolic genes and suppression of lipogenic genes by HNF4α and GR may mediate the early resistance to HFHS-induced fatty liver and hyperlipidemia.
肝细胞核因子 4α（HNF4α）和糖皮质激素受体（GR）是肝脏代谢的主要调节因子，在脂肪性肝病中下调。本研究旨在阐明 HNF4α 和 GR 下调在脂肪肝和高脂血症中的作用。
采用肝特异性杂合子（HET）和敲除（KO）HNF4α 或 GR 的成年小鼠，给予高脂肪高糖饮食（HFHS）喂养 15 天。用分析试剂盒测定肝和循环脂质的变化，实时 PCR 和 Western 印迹法定量检测这些小鼠肝内 mRNA 和蛋白表达的变化。用 LC-MS/MS 定量血清和肝内胆汁酸水平。用荧光素酶报告基因检测法确定 HNF4α 和 GR 在调节肝基因表达中的作用。
与 HFHS 喂养的野生型小鼠相比，HNF4α HET 小鼠的脂质分解代谢基因下调，脂质生成基因诱导，肝和血液中脂质水平升高，而 HNF4α KO 小鼠则出现脂肪肝但血脂轻度降低，脂质外排基因下调，摄取、合成和储存脂质的基因诱导。HNF4α HET 小鼠血清中鹅脱氧胆酸和脱氧胆酸水平趋于降低，但 HNF4α KO 小鼠显著升高，这与胆汁酸合成限速酶细胞色素 P450 7a1 的显著下调有关。HFHS 喂养的 HNF4α HET 小鼠肝内甾醇调节元件结合蛋白-1（SREBP-1）mRNA 和蛋白表达诱导，SREBP-1 是主要的脂质生成调节因子。在报告基因检测中，HNF4α 与共抑制子小异二聚体伴侣协同作用，强烈抑制肝 X 受体对小鼠和人 SREBP-1C 启动子的转录激活。HNF4α KO 小鼠肝内核 GR 蛋白水平趋于降低。肝特异性 GR KO 的 HFHS 喂养小鼠肝内脂质增加，SREBP-1C 和 PPARγ 诱导，这些小鼠肝内 HNF4α 蛋白水平明显降低。在报告基因检测中，GR 和 HNF4α 协同/累加诱导脂质分解代谢基因。
HNF4α 和 GR 诱导脂质分解代谢基因和抑制脂质生成基因可能介导对 HFHS 诱导的脂肪肝和高脂血症的早期抵抗。
