Caspase-3 Is a Pivotal Regulator of Microvascular Rarefaction and Renal Fibrosis after Ischemia-Reperfusion Injury

Abstract

Background Ischemia-reperfusion injury (IRI) is a major risk factor for chronic renal failure. Here, we characterize the different modes of programmed cell death in the tubular and microvascular compartments during the various stages of IRI-induced AKI, and their relative importance to renal fibrogenesis. Methods We performed unilateral renal artery clamping for 30 minutes and contralateral nephrectomy in wild-type mice (C57BL/6) or caspase-32/2 mice. Results Compared with their wild-type counterparts, caspase-32/2 mice in the early stage of AKI had high urine cystatin C levels, tubular injury scores, and serum creatinine levels. Electron microscopy revealed evidence of tubular epithelial cell necrosis in caspase-32/2 mice, and immunohistochemistry showed upregulation of the necroptosis marker receptor-interacting serine/threonine-protein kinase 3 (RIPK3) in renal cortical sections. Western blot analysis further demonstrated enhanced levels of phosphorylated RIPK3 in the kidneys of caspase-32/2 mice. In contrast, caspase-32/2 mice had less microvascular congestion and activation in the early and extension phases of AKI. In the long term (3 weeks after IRI), caspase-32/2 mice had reduced microvascular rarefaction and renal fibrosis, as well as decreased expression of a-smooth muscle actin and reduced collagen deposition within peritubular capillaries. Moreover, caspase-32/2 mice exhibited signs of reduced tubular ischemia, including lower tubular expression of hypoxia-inducible factor-1a and improved tubular injury scores. Conclusions These results establish the pivotal importance of caspase-3 in regulating microvascular endothelial cell apoptosis and renal fibrosis after IRI. These findings also demonstrate the predominant role of microvascular over tubular injury as a driver of progressive renal damage and fibrosis after IRI.