Division of Human Genetics, Center for Molecular Medicine, Jichi Medical University, 3311-1 Yakushiji, Shimotsuke, Tochigi, 329-0498, Japan.
Division of Genetic Therapeutics, Center for Molecular Medicine, Jichi Medical School, Tochigi, Japan.
Sci Rep. 2023 Feb 1;13(1):1843. doi: 10.1038/s41598-023-29135-5.
Our previous genome-wide association study to explore genetic loci associated with lean nonalcoholic fatty liver disease (NAFLD) in Japan suggested four candidate loci, which were mapped to chr6, chr7, chr12 and chr13. The present study aimed to identify the locus involved functionally in NAFLD around the association signal observed in chr13. Chromosome conformation capture assay and a database survey suggested the intermolecular interaction among DNA fragments in association signals with the adjacent four coding gene promoters. The four genes were further screened by knockdown (KD) in mice using shRNA delivered by an adeno-associated virus vector (AAV8), and KD of G protein-coupled receptor 180 (Gpr180) showed amelioration of hepatic lipid storage. Gpr180 knockout (KO) mice also showed ameliorated hepatic and plasma lipid levels without influencing glucose metabolism after high-fat diet intake. Transcriptome analyses showed downregulation of mTORC1 signaling and cholesterol homeostasis, which was confirmed by weakened phosphorylation of mTOR and decreased activated SREBP1 in Gpr180KO mice and a human hepatoma cell line (Huh7). AAV8-mediated hepatic rescue of GPR180 expression in KO mice showed recovery of plasma and hepatic lipid levels. In conclusion, ablation of GPR180 ameliorated plasma and hepatic lipid levels, which was mediated by downregulation of mTORC1 signaling.
我们之前的全基因组关联研究探索了与日本瘦型非酒精性脂肪性肝病（NAFLD）相关的遗传位点，发现了四个候选位点，这些位点映射到 6 号、7 号、12 号和 13 号染色体上。本研究旨在鉴定与 13 号染色体上观察到的关联信号相关的 NAFLD 功能相关基因座。染色体构象捕获分析和数据库调查表明，与邻近四个编码基因启动子相关的关联信号中的 DNA 片段之间存在分子间相互作用。通过腺相关病毒载体（AAV8）递送的 shRNA 在小鼠中进一步筛选了这四个基因，发现 G 蛋白偶联受体 180（Gpr180）的敲低（KD）可改善肝脂质储存。高脂饮食摄入后，Gpr180 敲除（KO）小鼠的肝脏和血浆脂质水平也得到改善，而葡萄糖代谢不受影响。转录组分析显示 mTORC1 信号和胆固醇稳态下调，这在 Gpr180KO 小鼠和人肝癌细胞系（Huh7）中 mTOR 的磷酸化减弱和激活 SREBP1 减少得到证实。在 KO 小鼠中，AAV8 介导的 GPR180 表达肝拯救显示出血浆和肝脂质水平的恢复。总之，GPR180 的缺失改善了血浆和肝脏脂质水平，这是通过 mTORC1 信号的下调介导的。
