非酒精性脂肪性肝病（NAFLD）始于肝脏中甘油三酯的过度积累，而过度严重的肝脂变性则会发展成非酒精性脂肪性肝炎（NASH），其特征为脂质过氧化、炎症和纤维化。泛素特异性蛋白酶14（USP14）调节炎症、肝细胞癌和病毒感染，但其对NAFLD的作用尚不清楚。本研究旨在揭示USP14在NAFLD进展中的作用和其潜在机制。我们证明了在NAFLD患者和小鼠中，肝脏中USP14的表达显著增加。肝脏中USP14过表达加剧了饮食诱导的肝脂变性、炎症和纤维化，与肝脏中USP14敲除的结果相反。此外，过表达USP14会明显增加棕榈酸/油酸诱导的肝细胞脂质过氧化和炎症，而USP14敲除则会减少这些效应。值得注意的是，体内或体外数据显示，USP14以细胞色素p4502E1（CYP2E1）为依赖因子促进NAFLD的进展，进一步加剧了肝细胞的氧化应激、干扰了线粒体呼吸链和炎症，通过促进CYP2E1的蛋白水平。在机制上，我们通过免疫沉淀和泛素化分析证明，USP14通过降低其赖氨酸48键结合泛素化作用抑制热休克蛋白90α家族A成员1（HSP90AA1）的降解。与此同时，高表达HAP90AA1蛋白会增加CYP2E1蛋白的积累。总之，我们的数据表明一个未知的USP14-HSP90AA1-CYP2E1轴对NAFLD的进展起到贡献作用，我们提出抑制USP14可能是治疗NASH的有效策略。© 2023. 作者。

Nonalcoholic fatty liver disease (NAFLD) begins with excessive triglyceride accumulation in the liver, and overly severe hepatic steatosis progresses to nonalcoholic steatohepatitis (NASH), which is characterized by lipid peroxidation, inflammation, and fibrosis. Ubiquitin-specific proteinase 14 (USP14) regulates inflammation, hepatocellular carcinoma and viral infection, but the effect of USP14 on NAFLD is unknown. The aim of this study was to reveal the role of USP14 in the progression of NAFLD and its underlying mechanism. We demonstrated that hepatic USP14 expression was significantly increased in NAFLD in both humans and mice. Hepatic USP14 overexpression exacerbated diet-induced hepatic steatosis, inflammation and fibrosis in mice, in contrast to the results of hepatic USP14 knockdown. Furthermore, palmitic/oleic acid-induced lipid peroxidation and inflammation in hepatocytes were markedly increased by USP14 overexpression but decreased by USP14 knockdown. Notably, in vivo or in vitro data show that USP14 promotes NAFLD progression in a cytochrome p4502E1 (CYP2E1)-dependent manner, which exacerbates hepatocyte oxidative stress, impairs the mitochondrial respiratory chain and inflammation by promoting CYP2E1 protein levels. Mechanistically, we demonstrated by immunoprecipitation and ubiquitination analysis that USP14 inhibits the degradation of heat shock protein 90 alpha family class A member 1 (HSP90AA1) by decreasing its lysine 48-linkage ubiquitination. Meanwhile, upregulation of HAP90AA1 protein promotes CYP2E1 protein accumulation. Collectively, our data indicate that an unknown USP14-HSP90AA1-CYP2E1 axis contributes to NAFLD progression, and we propose that inhibition of USP14 may be an effective strategy for NASH treatment.© 2023. The Author(s).