Impact of SPAK Deficiency on Glomerular Injury and Mitochondrial Homeostasis in Adriamycin-Induced FSGS

BACKGROUND/AIM: Focal segmental glomerulosclerosis (FSGS) is characterized by podocyte injury, mitochondrial dysfunction, oxidative stress, and metabolic remodeling. STE20/SPS1-related proline-alanine-rich kinase (SPAK), a downstream component of WNK signaling, regulates renal ion transport and has been implicated in inflammatory and stress responses. This study examined the impact of SPAK deficiency on renal injury and mitochondrial homeostasis in Adriamycin-induced FSGS. MATERIALS AND METHODS: Eight-week-old male wild-type and global SPAK knockout C57BL/6 mice received a single intravenous injection of Adriamycin (18 mg/kg) or saline and were followed for four weeks. Renal function, proteinuria, glomerular histology, podocyte markers, mitochondrial dynamics, oxidative stress, apoptosis, and targeted metabolic profiles were assessed using biochemical assays, histology, immunohistochemistry, TUNEL staining, western blotting, quantitative PCR, and LC-MS-based metabolomics. RESULTS: Adriamycin induced proteinuria, serum creatinine elevation, glomerulosclerosis, and reduced nephrin and podocin expression in both wild-type and SPAK knockout mice. The severity of renal functional and histological injury was comparable between the two FSGS groups. SPAK deficiency was associated with baseline mitochondrial and apoptotic abnormalities, including reduced ATP5A1 expression and increased TUNEL-positive cells. In FSGS kidneys, SPAK deficiency did not restore ATP5A1, OPA1, PGC-1α, redox balance, or glycolytic remodeling, and SPAK-knockout FSGS mice exhibited greater apoptosis than wild-type FSGS mice. CONCLUSION: SPAK deficiency modifies mitochondrial and apoptotic responses but does not attenuate Adriamycin-induced glomerular injury. These findings suggest that SPAK contributes to glomerular homeostasis and that its role in kidney injury is context-dependent.