Department of Geriatrics, the Second Xiangya Hospital of Central South University, Changsha 410011, Hunan, China.
Department of Emergency, the Third Xiangya Hospital of Central South University, Changsha 410013, Hunan, China.
Biochim Biophys Acta Mol Cell Res. 2024 Oct;1871(7):119765. doi: 10.1016/j.bbamcr.2024.119765. Epub 2024 May 28.
Metabolic-associated fatty liver disease (MAFLD) is a leading cause of chronic liver disease worldwide. Autophagy plays a pivotal role in lipid metabolism; however, the mechanism underlying the reduced autophagic activity in MAFLD remains elusive.
Autophagy was monitored by TUNEL assay and immunofluorescence staining of LC3. The expression of autophagy-related proteins, PPARα, HDAC2, and HRD1 was detected by Western blot. The association between HDAC2 and PPARα promoter was assessed by chromatin immunoprecipitation (ChIP) and dual-luciferase assays, and the HRD1-mediated ubiquitin-proteasomal degradation of HDAC2 was detected by co-immunoprecipitation (co-IP). The in vitro findings were validated in a hypoxia-induced MAFLD mouse model. Histological changes, fibrosis, and apoptosis in liver tissues were detected by hematoxylin and eosin staining, Masson's trichrome staining, and TUNEL assay. The immunoreactivities of key molecules were examined by IHC analysis.
Hypoxia-suppressed autophagy in hepatocytes. Hypoxic exposure downregulated HRD1 and PPARα, while upregulating HDAC2 in hepatocytes. Overexpression of PPARα promoted hepatic autophagy, while knocking down HDAC2 or overexpressing HRD1 reduced hypoxia-suppressed autophagy in hepatocytes. Mechanistically, HDAC2 acted as a transcriptional repressor of PPARα, and HRD1 mediated the degradation of HDAC2 through the ubiquitin-proteasome pathway. Functional studies further showed that hypoxia-suppressed hepatic autophagy via the HRD1/HDAC2/PPARα axis in vitro and in vivo.
HRD1-mediated ubiquitination of HDAC2 regulates PPARα-mediated autophagy and ameliorates hypoxia-induced MAFLD.
代谢相关脂肪性肝病（MAFLD）是全球慢性肝病的主要原因。自噬在脂质代谢中起着关键作用；然而，MAFLD 中自噬活性降低的机制仍不清楚。
通过 TUNEL 检测和 LC3 的免疫荧光染色监测自噬。通过 Western blot 检测自噬相关蛋白 PPARα、HDAC2 和 HRD1 的表达。通过染色质免疫沉淀（ChIP）和双荧光素酶测定评估 HDAC2 与 PPARα 启动子的关联，通过共免疫沉淀（co-IP）检测 HRD1 介导的 HDAC2 泛素蛋白酶体降解。在缺氧诱导的 MAFLD 小鼠模型中验证了体外研究结果。通过苏木精和伊红染色、马松三色染色和 TUNEL 检测检测肝组织的组织学变化、纤维化和细胞凋亡。通过免疫组化分析检测关键分子的免疫反应性。
缺氧抑制肝细胞中的自噬。缺氧暴露下调 HRD1 和 PPARα，同时上调肝细胞中的 HDAC2。过表达 PPARα 可促进肝自噬，而敲低 HDAC2 或过表达 HRD1 可减少肝细胞中缺氧抑制的自噬。机制上，HDAC2 作为 PPARα 的转录抑制剂，HRD1 通过泛素蛋白酶体途径介导 HDAC2 的降解。功能研究进一步表明，HRD1/HDAC2/PPARα 轴在体外和体内抑制了缺氧诱导的肝自噬。
HRD1 介导的 HDAC2 泛素化调节 PPARα 介导的自噬，改善缺氧诱导的 MAFLD。
