S100A8/A9-TMEM24 axis drives podocyte injury by impairing autophagy: a novel theranostic target for early diabetic nephropathy.

OBJECTIVE: To establish a comprehensive theranostic framework for early-stage diabetic kidney disease (DKD) by validating serum S100A8/A9 as a highly sensitive diagnostic biomarker and exploring therapeutic strategies targeting the S100A9/transmembrane protein 24 (TMEM24) signaling axis to restore podocyte autophagy. METHODS: A clinical cohort and machine learning algorithms (Random Forest/Neural Networks) were employed to evaluate the diagnostic performance of S100A8/A9. In vivo (db/db mice) and in vitro (HG-stimulated podocytes) models were used to investigate the molecular mechanisms. Co-IP-LC/MS and protein truncation assays identified S100A9-interacting partners. Structure-based virtual screening was utilized to identify Shikonin as a novel TMEM24-targeting ligand, and its renoprotective effects were rigorously validated. RESULTS: Serum S100A8/A9 levels were significantly elevated in early DKD, outperforming conventional markers in machine learning models (AUC up to 0.978). Mechanistically, S100A9 interacts with Transmembrane Protein 24 (TMEM24) through its SMP and C2 domains, hyperactivating the PI3K/AKT/mTOR pathway and impairing podocyte autophagy. Shikonin, identified through virtual screening, demonstrated a strong binding affinity for TMEM24. Administration of Shikonin dose-dependently inhibited the TMEM24-mediated PI3K/AKT/mTORC1 signaling, thereby restoring autophagic flux and ameliorating podocyte injury, glomerular basement membrane thickening, and renal fibrosis. CONCLUSIONS: This study defines S100A8/A9 as a pivotal biomarker and therapeutic target, offering a theranostic strategy where Shikonin serves as a potent agent to ameliorate DKD progression by targeting the TMEM24-autophagy axis.