Swietenine Enhances Autophagy to Improve Renal Fibrosis via AMPK/mTOR/ULK1 Signaling Pathway in Diabetic Nephropathy

Diabetic nephropathy (DN) is a major complication of diabetes. Swietenine (Swi), a natural compound derived from the fruit of Swietenia macrophylla , has shown beneficial effects in alleviating diabetic complications. However, its underlying mechanism for treating DN remains unclear. This study aimed to elucidate the therapeutic effects and molecular mechanisms of Swi against DN through in vitro and in vivo experiments. A model of streptozotocin/high-fat diet (STZ/HFD)-induced Sprague-Dawley (SD) rats was employed to evaluate the effects of Swi on improving DN renal fibrosis and enhancing autophagy in vivo. Followed based on the results of proteomics, network pharmacology, and molecular docking, the potential mechanism of Swi in treating DN was predicted, and subsequently the cell model of high glucose induced human renal tubular epithelial cells (HK-2) was established in vitro, and the potential mechanism of Swi's therapeutic effect was further validated through Western blot analysis, immunofluorescence, immunohistochemistry, and flow cytometry. After Swi treatment, levels of urinary protein, uric acid, creatinine, and urea nitrogen were significantly reduced in DN rats. Pathological improvements included decreased thickness of the tubular basement membrane, reduced PAS-positive deposits, less glycogen accumulation, and alleviated fibrosis. The number of autolysosomes increased significantly, especially with high-dose Swi. Immunofluorescence of renal tissue showed enhanced LC3B fluorescence intensity, suggesting restored autophagy levels. Western blot analysis revealed upregulation of LC3B and Beclin-1 and downregulation of p62 after Swi treatment. Immunohistochemistry indicated reduced expression of fibronectin (Fn) and collagen I (COI-I), indicating decreased extracellular matrix accumulation and renal injury. In high glucose-induced human renal tubular epithelial cells (HK-2), similar trends were observed. Swi treatment upregulated p-AMPK and p-ULK1 expression and downregulated p-mTOR. Overall, Swi significantly improved renal function and pathological damage in DN rats by activating the AMPK/mTOR/ULK1 signaling pathway, enhancing autophagy, reducing ROS production, and ameliorating mitochondrial injury, thereby delaying renal fibrosis progression. In conclusion, Swi exerts protective effects against DN by promoting autophagy and mitigating oxidative stress, suggesting its potential as a therapeutic agent for DN.