TRIM24 suppresses development of spontaneous hepatic lipid accumulation and hepatocellular carcinoma in mice

Purpose: aberrantly high expression of TRIM24 occurs in human cancers, including hepatocellular carcinoma. In contrast, TRIM24 in the mouse is reportedly a liver-specific tumor suppressor. To address this dichotomy and uncover direct regulatory functions of TRIM24 in vivo, we developed a new mouse model that lacks expression of all Trim24 isoforms, as the previous model expresses normal levels of Trim24 lacking only exon 4. Methods: To produce germline-deleted Trim24dlE1 mice, deletion of the promoter and exon 1 of Trim24 was induced in Trim24LoxP mice by crossing with a zona pellucida 3-Cre line for global deletion. Liver-specific deletion (Trim24hep) was achieved by crossing with an Albumin-Cre line. Phenotypic analyses were complemented by protein, gene-specific and global RNA expression analyses and quantitative chromatin immunoprecipitation. Results:Global loss of Trim24 disrupted hepatic homeostasis in 100% of mice with highly significant, decreased expression of oxidation/reduction, steroid, fatty acid and lipid metabolism genes, as well as increased expression of genes in unfolded protein, endoplasmic reticulum stress and cell cycle pathways. Trim24dlE1/dlE1 mice have markedly depleted visceral fat and, like Trim24hep/hep mice, spontaneously develop hepatic lipid-filled lesions, steatosis, hepatic injury, fibrosis and hepatocellular carcinoma. Conclusions: TRIM24, an epigenetic co-regulator of transcription, directly and indirectly represses hepatic lipid accumulation, inflammation, fibrosis and damage in the murine liver. Complete loss of Trim24 offers a model of human nonalcoholic fatty liver disease, steatosis, fibrosis and development of hepatocellular carcinoma in the absence of high-fat diet or obesity. mRNA profiles of 8 weeks wild type (WT) and Trim24-/- mice were generated by deep sequencing, in triplicate, using Illumina HiSeq 2000研究目的：TRIM24（TRIM24）的异常高表达可见于包括肝细胞癌（hepatocellular carcinoma）在内的多种人类恶性肿瘤。与之相反，已有研究表明小鼠体内的TRIM24是一种肝脏特异性肿瘤抑制因子。为阐明这一矛盾现象并揭示TRIM24在体内的直接调控功能，我们构建了一种可敲除所有Trim24亚型的全新小鼠模型——此前的模型仅缺失外显子4，但仍可正常表达Trim24。 研究方法：为构建生殖系敲除型Trim24dlE1小鼠，我们将Trim24LoxP小鼠与透明带蛋白3-Cre（zona pellucida 3-Cre）转基因品系杂交，实现Trim24启动子与外显子1的全局敲除。通过与白蛋白-Cre（Albumin-Cre）转基因品系杂交，可获得肝脏特异性敲除小鼠（Trim24hep）。表型分析辅以蛋白质检测、基因特异性及全转录组RNA表达分析，以及定量染色质免疫沉淀。 研究结果：100%的全局Trim24敲除小鼠均出现肝脏稳态紊乱，其氧化还原、类固醇、脂肪酸及脂质代谢相关基因的表达显著下调，而未折叠蛋白反应、内质网应激及细胞周期通路相关基因的表达显著上调。Trim24dlE1/dlE1小鼠表现为内脏脂肪显著耗竭，且与Trim24hep/hep小鼠类似，可自发形成肝脏脂质沉积病变、脂肪变性、肝损伤、纤维化及肝细胞癌。 研究结论：TRIM24作为一种转录表观遗传共调控因子，可直接或间接抑制小鼠肝脏内的脂质沉积、炎症反应、纤维化及肝损伤。在无需高脂饮食或肥胖造模的前提下，全局Trim24敲除可作为人类非酒精性脂肪性肝病、脂肪变性、纤维化及肝细胞癌发生的理想动物模型。本研究采用Illumina HiSeq 2000测序平台，对8周龄野生型（wild type, WT）及Trim24-/-小鼠进行了三次生物学重复的深度测序，以获取其mRNA表达谱。