Notoginsenoside R2 Antagonizes Renal Interstitial Fibrosis by Regulating Fatty Acid Oxidation via the CASP2 / ALDH3A1 Axis

Renal interstitial fibrosis (RIF) is a major driver of chronic kidney disease (CKD) progression, yet effective therapies remain limited. The Shen-Yan-Fang-Shuai formula (SYFSF) exhibits clinical renoprotective effects; however, its active components and mechanisms remain unclear. This study identifies notoginsenoside R2 (NGR2) as a core active compound of SYFSF that directly binds to caspase-2 (CASP2). Integrative multi-omics analyses in unilateral ureteral obstruction (UUO) rats and transforming growth factor-β1 (TGF-β1)-induced NRK-52E cells demonstrate that NGR2 upregulates CASP2, enhances the CASP2-aldehyde dehydrogenase 3 family member A1 (ALDH3A1) interaction, and promotes ALDH3A1 deubiquitination, thereby stabilizing ALDH3A1. This stabilization restores the integrity of mitochondria-associated endoplasmic reticulum membranes (MAMs) and improves fatty acid oxidation (FAO) by upregulating carnitine palmitoyltransferase 1A (CPT1A), acyl-CoA dehydrogenase long chain (ACADL), and peroxisome proliferator-activated receptor α (PPARα). It also reduces lipid accumulation, oxidative stress, epithelial-mesenchymal transition (EMT), inflammation, and collagen deposition. In vivo, NGR2 ameliorates renal dysfunction and fibrosis. Mechanistically, NGR2 binds the caspase activation and recruitment domain (CARD) of CASP2 without occluding the ubiquitin-interacting motif-like (UIML) region required for its deubiquitinase function, thereby increasing CASP2 abundance and stability rather than activating its apoptotic protease activity, and facilitating ubiquitin chain removal from ALDH3A1. These findings demonstrate that SYFSF and NGR2 antagonize RIF by targeting the CASP2/ALDH3A1 axis to restore MAM function and FAO, providing a molecular basis for traditional Chinese medicine in CKD therapy.