HMGB1 preconditioning attenuates kidney ischemia reperfusion injury via TLR4 with involvement of the negative regulator Siglec-10

Chronic kidney transplantation failure is caused by both immunologic and non-immunologic factors. Non-immunologic factors include renal ischemia reperfusion injury (IRI), which is an inevitable consequence of the procedure of kidney transplantation, and which negatively impacts both short- and long-term graft survival. By researching the mechanisms underlying IRI, possible novel treatments can be discovered, which will result in improved initial allograft quality in patients and consequent enhanced graft survival. A potential method to attenuate IRI is through preconditioning with high-mobility group box 1 (HMGB1), a nuclear factor which is also released extracellularly as an inflammatory cytokine. This approach has been validated in hepatic and cardiac IRI models. HMGB1 is an endogenous ligand for Toll-like receptor (TLR4), a chief receptor which is involved in the underlying pathogenesis of IRI and is produced within the kidney. The aims of this study were to determine: 1) if HMGB1 preconditioning desensitises the kidney to endogenous HMGB1; 2) whether this is through TLR-mediated innate immunity; 3) whether this involves down-regulation of TLR signaling. To elucidate these hypotheses, wild-type (WT) and TLR4-/- mice were randomised to receive rHMGB1 (20μg per animal) or appropriate controls by i.p. injection 2h before ischemia. Kidney ischemia was induced for 20.5 min followed by reperfusion. Samples were collected at days 1 and 5 after reperfusion and analysed for serum creatinine, tubular damage, macrophage, neutrophil, CD4+ T cell and CD8+ T cell infiltration, and expression of various negative regulators of TLR signalling (Tollip, SIGIRR and Siglec-10). rHMGB1-pretreated WT mice were significantly protected against kidney IRI, with lower serum creatinine, less tubular damage and tubular epithelial cell apoptosis versus control mice. Tubule-interstitial neutrophil, macrophage and CD4+ T cell infiltration were markedly less in rHMGB1-pretreated mice versus controls. TLR4-/- mice were protected against kidney IRI, with no additional protection gained by rHMGB1 pretreatment. The expression of Siglec-10, a negative regulator of HMGB1-TLR4, was significantly increased after rHMGB1 preconditioning, indicating that HMGB1 preconditioning negatively regulates TLR4 signalling. In this study, rHMGB1 preconditioning affords protection against kidney IRI by negative regulation of TLR4 signalling with involvement of Siglec-10, demonstrating therapeutic potential to improve short- and long-term outcomes for kidney transplant patients.