Receptor activator of the NFκB ligand system protects renal function during experimental renal ischemia-reperfusion in mice

Abstract

Renal ischemia-reperfusion (I/R) injury is closely associated with delayed graft function and poor long-term graft survival following transplantation. Various pathophysiologies can cause the deterioration of renal function; however, the immune system plays important roles in promoting and protecting renal tissues. Receptor activator of NFκB ligand (RANKL) is a member of the TNF superfamily and is produced by bone-forming osteoblasts; the receptor for RANKL is called RANK. In bone biology, RANKL-RANK signaling has been extensively studied, but its roles in the immune system are still obscure. We investigated the role of the RANK system in I/R injury of the kidney using an experimental mouse I/R model. The left renal pedicles of 10-week-old male mice were clamped for 60 min, and reperfusion and right nephrectomy were simultaneously performed. Separate groups were administered an anti-RANKL antibody and recombinant RANKL (rRANKL) 24 h prior to I/R. After reperfusion for a set period of time, the serum creatinine level was measured, and the left kidney was removed for histological examination and western blotting to evaluate the expression and localization of RANK-associated molecules and cytokines. The serum creatinine levels were significantly elevated after I/R injury. A time-dependent increase in RANKL was observed up to 24 h, whereas RANK was induced for 12 h after reperfusion. RANK was expressed in infiltrating inflammatory cells, which were positive for CD68, a marker of monocytes/macrophages. The pre-treatment with the anti-RANKL antibody significantly impaired renal function and increased the induction of inflammatory cytokines (TNFα and IL-6), Toll-like receptor (TLR4) and MyD88 (all p < .05) compared to the levels in the I/R group. However, rRANKL significantly improved renal function and decreased the levels of inflammatory cytokines (TNFα and IL-6), TLR4 and MyD88 (p < .05) compared to those in the I/R group. The present study is the first to evaluate the role of the RANK system in renal I/R injury. RANKL-RANK signaling affects macrophage function and results in the downregulation of TLR4 and reduction in TNFα and IL-6, leading to improved renal function following I/R injury.