代谢功能障碍相关脂肪肝病（MASLD）是一种以肝脂肪变性为特征的慢性肝病。泛素特异性蛋白酶 29 (USP29) 在肝缺血再灌注损伤和肝细胞癌中发挥着关键作用，但其在 MASLD 中的作用尚未被探索。因此，本研究的目的是揭示 USP29 在 MASLD 进展中的作用和潜在机制。在 MASLD 患者和小鼠的肝脏样本中评估了 USP29 的表达。在高脂肪饮食喂养和高脂肪/高胆固醇饮食喂养的小鼠以及棕榈酸和油酸处理的肝细胞中评估了 USP29 在 MASLD 中的作用和分子机制。USP29 蛋白水平在小鼠和人类中显着降低MASLD。 USP29 缺失显着加剧肝脏脂肪变性、炎症和纤维化，USP29 过表达则减轻肝脏脂肪变性、炎症和纤维化。从机制上讲，USP29在代谢刺激下显着激活与脂肪酸β-氧化（FAO）相关的基因表达，直接与酰基辅酶A合成酶长链家族成员5（ACSL5）相互作用，并通过增加ACSL5 K48连接的去泛素化来抑制ACSL5降解。此外，USP29对肝细胞脂质积累和MASLD的影响依赖于ACSL5。USP29通过稳定ACSL5来促进FAO，作为MASLD的新型负调节因子。 USP29-ACSL5 轴的激活可能代表 MASLD 的潜在治疗策略。

Metabolic dysfunction-associated fatty liver disease (MASLD) is a chronic liver disease characterized by hepatic steatosis. Ubiquitin-specific proteinase 29 (USP29) plays pivotal roles in hepatic ischemia‒reperfusion injury and hepatocellular carcinoma, but its role in MASLD remains unexplored. Therefore, the aim of this study was to reveal the effects and underlying mechanisms of USP29 in MASLD progression.USP29 expression was assessed in liver samples from MASLD patients and mice. The role and molecular mechanism of USP29 in MASLD were assessed in high-fat diet-fed and high-fat/high-cholesterol diet-fed mice and palmitic acid and oleic acid treated hepatocytes.USP29 protein levels were significantly reduced in mice and humans with MASLD. Hepatic steatosis, inflammation and fibrosis were significantly exacerbated by USP29 deletion and relieved by USP29 overexpression. Mechanistically, USP29 significantly activated the expression of genes related to fatty acid β-oxidation (FAO) under metabolic stimulation, directly interacted with Acyl-CoA synthetase long chain family member 5 (ACSL5) and repressed ACSL5 degradation by increasing ACSL5 K48-linked deubiquitination. Moreover, the effect of USP29 on hepatocyte lipid accumulation and MASLD was dependent on ACSL5.USP29 functions as a novel negative regulator of MASLD by stabilizing ACSL5 to promote FAO. The activation of the USP29-ACSL5 axis may represent a potential therapeutic strategy for MASLD.