Park Jung Eun, Lee Mikang, Kim Seong-Chul, Zhang Yanqiao, Hardwick James P, Lee Yoon Kwang
Department of Integrative Medical Sciences Northeast Ohio Medical University Rootstown Ohio.
Hepatol Commun. 2017 Nov 8;1(10):1085-1098. doi: 10.1002/hep4.1120. eCollection 2017 Dec.
Peroxisome proliferator-activated receptor gamma (PPARγ) is a master regulator for white adipocyte differentiation and lipid storage. The increased level of hepatic PPARγ2 isoform reprograms liver for lipid storage and causes abnormal fat accumulation in certain pathophysiologic conditions. The current study aimed to investigate a role of transcriptional repressor hairy and enhancer of split 6 (HES6) in the regulation of expression and hepatic steatosis induced by diet. Liver-specific overexpression of using adenovirus reduced messenger RNA levels by 90% and hepatic triglyceride accumulation by 22% compared to the levels in mice injected with an adenoviral empty vector with Western diet feeding. In sharp contrast, silencing gene expression using short hairpin RNA increased hepatic lipid accumulation and messenger RNA levels by 70% and 4-fold, respectively. To locate hepatocyte nuclear factor 4 alpha (HNF4α) binding site(s), through which repressional activity of HES6 is mediated, a 2.5-kb promoter-driven luciferase reporter was constructed for transient transfection assays. Subsequently, chromatin immunoprecipitation and electrophoretic mobility shift assays were performed. An HNF4α binding consensus sequence was identified at 903 base pairs upstream from the transcription start site of . Deletion or point mutation of the sequence in a luciferase reporter containing the promoter abolished HNF4α-mediated activation in HeLa cells. Chromatin immunoprecipitation and electrophoretic mobility shift assays further confirmed direct recruitment and binding of HNF4α to the site. Gene expression analysis with liver samples from subjects with nonalcoholic steatohepatitis suggested that the axis of the Hes6-Hnf4a-Pparg2 transcriptional cascade is also responsible for hepatic fat accumulation in humans. : HES6 represses gene expression, thereby preventing hepatic lipid accumulation induced by chronic Western diet feeding or pathophysiologic conditions. ( 2017;1:1085-1098).
过氧化物酶体增殖物激活受体γ（PPARγ）是白色脂肪细胞分化和脂质储存的主要调节因子。在某些病理生理条件下，肝脏中PPARγ2亚型水平的升高会使肝脏重新编程以进行脂质储存，并导致异常脂肪堆积。当前研究旨在探究转录抑制因子毛状体和分裂增强子6（HES6）在饮食诱导的肝脏脂肪酸结合蛋白4（FABP4）表达调控及肝脂肪变性中的作用。与喂食西方饮食并注射腺病毒空载体的小鼠相比，利用腺病毒在肝脏中特异性过表达HES6可使FABP4信使核糖核酸水平降低90%，肝甘油三酯蓄积减少22%。形成鲜明对比的是，使用短发夹RNA沉默HES6基因表达可使肝脏脂质蓄积增加70%，FABP4信使核糖核酸水平增加4倍。为定位介导HES6抑制活性的肝细胞核因子4α（HNF4α）结合位点，构建了一个由2.5千碱基对FABP4启动子驱动的荧光素酶报告基因用于瞬时转染实验。随后，进行了染色质免疫沉淀和电泳迁移率变动分析。在FABP4转录起始位点上游903个碱基对处鉴定出一个HNF4α结合共有序列。在含有FABP4启动子的荧光素酶报告基因中删除或点突变该序列可消除HNF4α在人宫颈癌细胞系（HeLa细胞）中介导的激活作用。染色质免疫沉淀和电泳迁移率变动分析进一步证实HNF4α可直接募集并结合至该位点。对非酒精性脂肪性肝炎患者肝脏样本进行的基因表达分析表明，Hes6-Hnf4a-Pparg2转录级联轴也与人类肝脏脂肪蓄积有关。结论：HES6抑制FABP4基因表达，从而预防慢性西方饮食喂养或病理生理条件诱导的肝脏脂质蓄积。（《肝脏病学通讯》2017年；1:1085 - 1098）
