SPARC Upregulation Mediates Podocyte Injury in Alport Syndrome Mice

Alport syndrome (AS) is a hereditary kidney disease with no curative treatment, which characterized by hematuria, proteinuria, and progressive kidney failure. Podocyte injury has been observed in AS, whereases, the mechanism is still unclear. Reported studies showed the expression level of secreted protein acidic and rich in cysteine (SPARC) correlated with podocyte injury in chronic kidney diseases, yet its mechanism still unknown. Especially, its role in AS-related podocyte injury is unclear. Therefore, the kidney of Col4a3-/- AS mice was used to detect SPARC expression, location, and podocyte injury, and mouse podocyte cell line (MPC5) was used to explore the mechanism of SPARC-induced podocyte injury. Besides, SPARC expression in both urine and kidney samples from AS patients were analyzed. The results showed, SPARC upregulated and located in podocytes were detected in Col4a3-/- AS mice, and increased inflammatory cytokines, impaired podocyte structure and function were identified in SPARC-overexpression MPC5, importantly, knockdown adhesion G protein-coupled receptor B1 (ADGRB1) exerted a protective effect. In AS patients, urinary increased level of SPARC was detected, SPARC deposition in glomeruli of kidney sections was identified. Our findings identified SPARC as a key mediator of podocyte injury in AS, with ADGRB1 acting as its downstream effector.