Targeting the SMOX/ATP5F1A Axis Ameliorates Mitochondrial Dysfunction in Diabetic Kidney Disease

Background: Diabetic kidney disease (DKD), the predominant etiology of end-stage renal disease, progresses through renal tubular epithelial cell (RTEC) injury and subsequent fibrosis. Although tubular pathology drives DKD progression, early drivers remain unclear. Transcriptomic analysis of human DKD biopsies revealed tubular spermine oxidase (SMOX) upregulation inversely correlating with eGFR, suggesting its pathogenic involvement. Methods: Multi-model validation included: (1) DKD patient biopsies, (2) streptozotocin-induced Smox-/- mice, (3) high glucose/AGEs-stimulated RTEC, and (4) human kidney organoids. Mechanistic studies integrated MS-proteomics, Co-IP, and RNA-seq. Results: We revealed significant SMOX upregulation in RTEC from DKD patients, STZ-induced mice, and kidney organoids, independent of spermine level alterations. Genetic SMOX ablation substantially ameliorated renal tubulointerstitial fibrosis in DKD models. Compared to wild-type DKD mice, Smox-/- STZ mice exhibited comparable blood glucose but 31% lower serum BUN levels (p<0.01). Histopathological analysis of Smox-/- STZ mice revealed attenuated tubular basement membrane thickening and preserved brush border integrity (PAS staining), with Sirius red staining demonstrating significantly reduced interstitial collagen deposition. Mechanistically, RNA sequencing implicated mitochondrial metabolic dysfunction in SMOX-mediated injury. Mitochondrial translocation of SMOX was confirmed via immunofluorescence colocalization and mitochondrial isolation assays. Subsequent MS-based proteomics and Co-IP techniques identified SMOX could interact with ATP5F1A (independent of its canonical polyamine catabolic function), leading to dysfunction of mitochondrial respiratory chain complex V, reduced ATP synthesis, and increased ROS production. Conclusion: Our study identifies a non-catalytic role of SMOX in promoting DKD progression through direct mitochondrial targeting. By coupling with ATP5F1A to disrupt complex V function, SMOX drives RTEC metabolic crisis and fibrotic transformation, proposing the SMOX-ATP5F1A axis as a novel therapeutic target for DKD. Funding: Government Support – Non-U.S.