Effect of complement 3/5 knockout on renal proteomics landscape after ischemia and reperfusion injury in rats.

Ischemia-reperfusion injury (IRI) is a major driver of acute kidney injury and development of chronic kidney disease. Although complement activation worsens IRI, the roles of upstream (C3) versus downstream (C5) components remain unclear. Renal IRI was surgically induced in C3 knockout (C3-/-) and C5 knockout (C5-/-) Lewis rats, and the renal function as well as histopathology were systematically assessed. Further, quantitative proteomics coupled with pathway enrichment analysis was performed to define complement-dependent mechanisms. C3 and C5 deficiency conferred strong protection against renal IRI with improved renal function, reduced tubular necrosis, and lower expression of injury markers (KIM-1, NGAL). Post-IRI, C3-/- enhanced mitochondrial, metabolic, and purine pathways while suppressing immune and extra-cellular matrix programs. C5-/- affected extracellular matrix remodeling and structural pathways with modest immune suppression. We demonstrate for the first time that upstream C3-/- impacts a diverse range of renal injury and repair mechanisms compared to C5-/- alone, although both interventions successfully reduced IRI-mediated injury. Together, these findings highlight strategies for future complement-based therapies targeting the upstream or downstream cascade.