SPARC Drives Podocyte Mitochondrial Damage and Ferroptosis in Diabetic Kidney Disease Following Klotho Deficiency

Diabetic kidney disease (DKD) is a leading cause of end-stage renal disease, with podocyte injury driving disease progression. Mitochondrial dysfunction and ferroptosis contribute to podocyte loss, yet the underlying molecular mechanisms remain incompletely understood. The anti-aging protein Klotho protects podocytes, but how Klotho deficiency links to mitochondrial dysfunction and ferroptosis is unclear. Here, we identify SPARC, a matricellular protein upregulated in podocytes, as a key mediator linking Klotho deficiency to mitochondrial injury and ferroptosis. In human DKD biopsies and genetically modified mice, including Klotho-deficient, Klotho-overexpressing, and SPARC knockout mice, reduced Klotho expression correlated with ferroptosis markers (GPX4, SLC7A11, P53, 4-HNE, and ACSL4) and mitochondrial abnormalities. Mechanistically, Klotho deficiency activated PKCα, leading to ubiquitination-mediated degradation of the transcription factor CUX1. Loss of CUX1 derepressed SPARC, which activated TGFβ-RII/Smad signaling, leading to mitochondrial dysfunction and ferroptosis. In vitro, SPARC knockdown or CUX1 overexpression preserved mitochondrial structure and ferroptosis defenses under high glucose, whereas SPARC overexpression alone induced ferroptosis even in normoglycemic conditions. These findings establish a Klotho/PKCα/CUX1/SPARC/TGFβ-RII axis as a critical regulator of podocyte mitochondrial dysfunction and ferroptosis. Beyond DKD, SPARC knockout also protected podocytes in ischemia-reperfusion injury and unilateral ureteral obstruction models, suggesting that SPARC may have broader implications in kidney injury and the progression toward chronic kidney disease.