<p>Original data.</p>

Non-alcoholic fatty liver disease (NAFLD) is a type of metabolic stress-induced liver injury that is closely related to type 2 diabetes mellitus (T2DM). Ursolic acid (UA), a natural pentacyclic triterpenoid compound, has anti-inflammatory, hypoglycemic and liver-protective effects. However, its role in regulating liver injury through the NLRP3 inflammasome pathway in a T2DM combined with NAFLD model has not been systematically elucidated. This study systematically evaluated the protective effect of UA on NAFLD and its molecular mechanism through in vivo (STZ + high-fat diet-induced NAFLD mouse model) and in vitro (high glucose + palmitic acid-induced LO2 cell oxidative stress model) experiments. The results showed that UA significantly improved hepatic lipid deposition, reduced serum ALT/AST levels, and effectively alleviated oxidative stress, as indicated by decreased malondialdehyde (MDA) content and increased activities of superoxide dismutase (SOD), catalase (CAT), and glutathione peroxidase (GSH-Px) in liver tissues. Further mechanism studies revealed that UA could significantly down-regulate the expression levels of pro-inflammatory factor IL-1β and pro-fibrotic factor TGF-β1 by inhibiting NLRP3 inflammasome activation, and simultaneously reduce the deposition of type IV collagen. This study demonstrated that ursolic acid (UA) has a protective effect on T2DM combined with NAFLD, and its mechanism of action may be related to the regulation of the NLRP3 signaling pathway by UA, which inhibits oxidative stress, inflammation and fibrosis.