Targeting SMPDL3B to Ameliorate Radiation- and Cisplatin-Induced Renal Toxicity.

Kidney toxicity remains a major dose-limiting complication of radiation therapy and platinum-based chemotherapy, yet the molecular determinants of renal susceptibility and resilience to these genotoxic treatments are incompletely understood. Podocytes are particularly vulnerable to such insults, and emerging evidence implicates lipid dysregulation in podocyte injury. This study investigated the role of sphingomyelin phosphodiesterase acid-like 3B (SMPDL3B), a podocyte-enriched lipid-modulating enzyme, in radiation- and cisplatin-induced nephrotoxicity. Using a doxycycline-inducible, podocyte-specific SMPDL3B transgenic mouse model, renal injury was assessed following focal kidney irradiation, cisplatin administration, or their combination through functional assays, histopathology, ultrastructural analysis, immunofluorescence, and targeted lipidomics. Combined radiation and cisplatin exposure markedly reduced podocyte SMPDL3B expression, accompanied by podocyte depletion, glomerular basement membrane remodeling, proteinuria, and impaired renal function. These structural and functional abnormalities were associated with the selective accumulation of long-chain ceramide-1-phosphate species. In contrast, podocyte-specific induction of SMPDL3B preserved glomerular architecture, maintained renal function, and prevented pathological ceramide-1-phosphate elevation. Collectively, these findings identify SMPDL3B as a key regulator of podocyte stability and lipid homeostasis during chemoradiation stress. Enhancing SMPDL3B activity may represent a mechanistically grounded strategy to mitigate treatment-induced kidney injury while preserving anticancer efficacy.