RENALASE PROTECTS AGAINST SALT-INDUCED RENAL INJURY BY REGULATING NECROPTOSIS

Abstract

Objective: Renalase, an enzyme that can metabolize catecholamine, was recently reported to attenuate ischaemic and toxic renal injury. The aim of the study was to investigate the functions and regulation mechanisms of renalase in protection against salt-induced renal injury. Design and method: 1. A total of 515 Chinese participants from 124 families were eligible for this study in 2004. We followed up this cohort in 2009, 2012 and 2018, respectively. 30 tagging SNPs from necroptosis-related genes (RIPK1, RIPK3 and MLKL) were genotyped to investigate the associations with necroptosis and the incidence of subclinical renal damage (SRD). 2. To investigate the role of necroptosis in the development of salt-induced renal injury and the protective effects of renalase on salt-induced renal injury, cultured HK-2 cells, renalase knockout (KO) mice and SS rats were treated with high salt and recombinant renalase exogenously. Necroptosis related to key regulators, apoptosis, inflammation, reactive oxygen species production were analyzed. Results: 1. During 14 years of follow-up, 38 (11.8%) participants developed SRD. RIPK1 SNP rs3736724, MLKL SNPs rs11640974 and rs12924203 were significantly associated with SRD incidence over 14 years. Gene-based analysis found that MLKL was significantly associated with SRD incidence over 14-year follow-up (P = 0.036) after adjustment for multiple testing. 2. High salt significantly increased the proportions of apoptotic and necrotic cells, and the expressions of related necroptosis (RIPK1, RIPK3 and MLKL) in a dose-dependent manner. Besides, high salt increased MDA, NADPH content and suppressed SOD; and increased TNF-alpha, IL-6, and MCP-1 levels. Knockdown of RIPK1, RIPK3 or MLKL with small interfering RNA (siRNA) significantly abrogated the aforementioned effects. Consistent with in vitro findings, high salt diet significantly increased necroptosis in SS rats. Recombinant renalase significantly decreased apoptosis and necroptosis in high salt-treated HK2 cells and SS rats. Similarly, renalase KO mice exacerbated kidney injury in animals subjected to high-salt intake, and administering renalase inhibited necroptosis and reduced salt-induced renal injury. Conclusions: Our results suggest that necroptosis plays an important role in salt-induced renal injury, and renalase protects against renal injury by inhibiting necroptosis.