Schisandrin B Attenuates Renal Fibrotic Remodeling in Association with Restoration of a PPARα-Related Tubular Fatty-Acid Oxidation Program

Background: Renal ischemia–reperfusion injury (RIRI) is a major cause of acute kidney injury (AKI) and contributes to delayed graft function and progression toward chronic kidney disease. In addition to oxidative stress and inflammation, RIRI induces profound metabolic derangements, particularly suppression of tubular fatty-acid β-oxidation (FAO), leading to energetic stress, lipid accumulation, and maladaptive repair. Peroxisome proliferator–activated receptor-α (PPARα) is a key regulator of tubular FAO, but whether Schisandrin B (Sch B) mitigates RIRI through restoration of a PPARα-associated metabolic program remains unclear. Objective: To determine whether Sch B alleviates RIRI in association with restoration of tubular FAO and attenuation of lipid accumulation and fibrotic remodeling. Methods: A unilateral murine renal I/R model and an HK-2 hypoxia/reoxygenation (H/R) model were used. Mice received Sch B (20 or 40 mg/kg/day) before I/R, and a subset was co-treated with the PPARα antagonist GW6471. Renal function, tubular injury, fibrosis, lipid accumulation, and FAO-related proteins were assessed by serum biochemistry, histopathology, Oil Red O staining, transmission electron microscopy, immunohistochemistry, immunofluorescence, and Western blotting. Bulk RNA-seq and public single-cell RNA-seq datasets were integrated to characterize metabolic pathway remodeling and cell-type-associated PPARα changes. Molecular docking and molecular dynamics simulations were performed to explore the potential interaction between Sch B and PPARα. Results: Sch B significantly improved renal function, reduced tubular injury, and attenuated interstitial collagen deposition after I/R. Sch B also reduced lipid droplet accumulation, preserved mitochondrial ultrastructure, and restored the expression of FAO-related proteins, including CPT1A, CPT2, and ACADM. In vivo and in vitro, Sch B decreased α-SMA, COL1A1, and vimentin expression, indicating attenuation of EMT-associated/profibrotic remodeling. Integrated transcriptomic analyses supported marked metabolic reprogramming after I/R, with enrichment of FAO- and PPAR-related pathways and reduced PPARα expression predominantly in tubular compartments. Sch B was associated with restoration of tubular PPARα expression, while docking and molecular dynamics analyses supported a plausible Sch B–PPARα interaction in silico. GW6471 blunted the beneficial effects of Sch B on fibrosis-related and FAO-related readouts. Conclusions: Sch B alleviates RIRI and limits subsequent fibrotic remodeling in association with restoration of a PPARα-related tubular FAO program, reduced lipid accumulation, and preservation of tubular metabolic homeostasis. These findings identify metabolic reprogramming as an important component of Sch B-mediated renoprotection, although the precise mode by which Sch B regulates PPARα requires further investigation.