Hepatocyte nuclear factor 4a and glucocorticoid receptor coordinately regulate lipid metabolism in mice fed a high-fat-high-sugar diet

ABSTRACTHepatocyte nuclear factor 4α (HNF4α) and glucocorticoid receptor (GR), master regulators of liver metabolism, are down-regulated in fatty liver diseases. The present study was aimed to elucidate the role of down-regulation of HNF4α and GR in fatty liver and hyperlipidemia. Adult mice with liver-specific heterozygote and knockout (knockout) of HNF4α were fed a low-fat diet (LFD) or a high-fat-high-sugar diet (HFHS) for 15 days. Compared to LFD-fed mice, HFHS-fed wildtype mice had hepatic induction of lipid catabolic genes and down-regulation of lipogenic genes. Compared to HFHS-fed wildtype mice, HNF4α heterozygote mice had down-regulation of lipid catabolic genes, induction of lipogenic genes, and increased hepatic and blood levels of lipids, whereas HNF4α knockout mice had mild hypolipidemia, down-regulation of lipid-efflux genes, but induction of genes for uptake/storage of lipids. Sterol-regulatory-element-binding protein-1c (SREBP-1C), a master lipogenic regulator, was induced in HFHS-fed HNF4α heterozygote mice. In reporter assays, HNF4α potently inhibited the transactivation of mouse and human SREBP-1C promoter by liver X receptor. Surprisingly, nuclear GR proteins were gene-dosage-dependently decreased in HNF4α heterozygote and knockout mice. HFHS-fed mice with liver-specific knockout of GR had increased hepatic lipids and induction of SREBP-1C and PPARγ. In reporter assays, GR and HNF4α synergistically/additively induced lipid catabolic genes. Phosphorylation of AMP-activated protein kinase (AMPK), a key GR modulator, was dramatically decreased in HNF4α knockout mice. Thus, cooperative induction of lipid catabolic genes and suppression of lipogenic genes by HNF4α and GR, modulated by AMPK, may mediate the early resistance to HFHS-induced fatty liver and hyperlipidemia.