Podrini Christine, Koffas Apostolos, Chokshi Shilpa, Vinciguerra Manlio, Lelliott Christopher J, White Jacqueline K, Adissu Hibret A, Williams Roger, Greco Azzura
*Foundation for Liver Research, Institute of Hepatology, London, United Kingdom; University College London (UCL)--Institute for Liver & Digestive Health, UCL Medical School, London, United Kingdom, Mouse Genetics Project, Wellcome Trust Sanger Institute, Wellcome Trust Genome Campus, Cambridge, United Kingdom; and Physiology and Experimental Medicine Research Program, The Hospital for Sick Children, University of Toronto, Toronto, Ontario, Canada.
*Foundation for Liver Research, Institute of Hepatology, London, United Kingdom; University College London (UCL)--Institute for Liver & Digestive Health, UCL Medical School, London, United Kingdom, Mouse Genetics Project, Wellcome Trust Sanger Institute, Wellcome Trust Genome Campus, Cambridge, United Kingdom; and Physiology and Experimental Medicine Research Program, The Hospital for Sick Children, University of Toronto, Toronto, Ontario, Canada
FASEB J. 2015 May;29(5):1676-87. doi: 10.1096/fj.14-262717. Epub 2014 Dec 19.
The importance of epigenetic changes in the development of hepatic steatosis is largely unknown. The histone variant macroH2A1 under alternative splicing gives rise to macroH2A1.1 and macroH2A1.2. In this study, we show that the macroH2A1 isoforms play an important role in the regulation of lipid accumulation in hepatocytes. Hepatoma cell line and immortalized human hepatocytes transiently transfected or knocked down with macroH2A1 isoforms were used as in vitro model of fat-induced steatosis. Gene expressions were analyzed by quantitative PCR array and Western blot. Chromatin immunoprecipitation analysis was performed to check the association of histone H3 lysine 27 trimethylation (H3K27me3) and histone H3 lysine 4 trimethylation (H3K4me3) with the promoter of lipogenic genes. Livers from knockout mice that are resistant to lipid deposition despite a high-fat diet were used for histopathology. We found that macroH2A1.2 is regulated by fat uptake and that its overexpression caused an increase in lipid uptake, triglycerides, and lipogenic genes compared with macroH2A1.1. This suggests that macroH2A1.2 is important for lipid uptake, whereas macroH2A1.1 was found to be protective. The result was supported by a high positivity for macroH2A1.1 in knockout mice for genes targeted by macroH2A1 (Atp5a1 and Fam73b), that under a high-fat diet presented minimal lipidosis. Moreover, macroH2A1 isoforms differentially regulate the expression of lipogenic genes by modulating the association of the active (H3K4me3) and repressive (H3K27me3) histone marks on their promoters. This study underlines the importance of the replacement of noncanonical histones in the regulation of genes involved in lipid metabolism in the progression of steatosis.
表观遗传变化在肝脂肪变性发展过程中的重要性在很大程度上尚不清楚。组蛋白变体macroH2A1经可变剪接产生macroH2A1.1和macroH2A1.2。在本研究中，我们表明macroH2A1亚型在肝细胞脂质积累的调节中起重要作用。用macroH2A1亚型瞬时转染或敲低的肝癌细胞系和永生化人肝细胞作为脂肪诱导性脂肪变性的体外模型。通过定量PCR阵列和蛋白质印迹分析基因表达。进行染色质免疫沉淀分析以检查组蛋白H3赖氨酸27三甲基化（H3K27me3）和组蛋白H3赖氨酸4三甲基化（H3K4me3）与脂肪生成基因启动子的关联。使用尽管高脂饮食但仍对脂质沉积有抗性的基因敲除小鼠的肝脏进行组织病理学检查。我们发现macroH2A1.2受脂肪摄取调节，与macroH2A1.1相比，其过表达导致脂质摄取、甘油三酯和脂肪生成基因增加。这表明macroH2A1.2对脂质摄取很重要，而macroH2A1.1具有保护作用。在macroH2A1靶向基因（Atp5a1和Fam73b）的基因敲除小鼠中，macroH2A1.1呈高阳性，在高脂饮食下脂质osis最小，这一结果支持了上述结论。此外，macroH2A1亚型通过调节其启动子上活性（H3K4me3）和抑制性（H3K27me3）组蛋白标记的关联来差异调节脂肪生成基因的表达。本研究强调了非经典组蛋白替代在脂肪变性进展过程中参与脂质代谢的基因调节中的重要性。
