*Purpose: Ischemia-reperfusion injury (IRI) is inevitable during organ transplantation. Clusterin (CLU) has shown to be protective in IRI. Supplementation of storage solution with recombinant CLU improved cardiac graft survival in preclinical transplantation model. Loss of CLU expression worsen IRI induced by renal clamping in CLU-deficient mice. To define the mechanism of CLU-mediated protection in a more physiologically relevant condition, we examined IRI in murine kidney transplantation.

*Methods: A/J (H-2^a) kidneys were perfused with UW solution and subjected to a clinically relevant 4 hours of cold-ischemia prior to transplantation to bilaterally nephrectomized C57BL/6 (H-2^b) and congenic CLU-deficient (H-2^b) recipients. Urine samples were collected at post-transplantation day 1 and 2. Mice were sacrificed at day 2 after transplantation and blood was collected by cardiac puncture to examine a marker of renal tubular injury, lipocalin 2 (LCN2) in urine and serum.

*Results: We found that CLU protein was increased in A/J (H-2^a) kidneys transplanted to CLU-deficient (H-2^b) mice compared to wild type C57BL/6 (H-2^b) recipients. CLU was strongly induced in renal tubular cells of CLU-deficient recipients. Urinary LCN2, a noninvasive tubular injury marker was significantly increased in CLU-deficient recipients compared to that in wild type mice at posttransplantation day 1 (6,380 ng/ml vs 2,561 ng/ml) and day 2 (4,299 ng/ml vs 775.8 ng/ml) in parallel with renal LCN2 expression. Glomerular and tubulointerstitial infiltration of (Gr1⁺) neutrophils were increased in grafts from CLU-deficient recipients. Cytokine array demonstrated that CXCL1, a strong neutrophil chemoattractant, was highly induced in kidneys transplanted to CLU-deficient mice and confirmed by quantification with ELISA. ICAM-1 and MMP-9 in kidney grafts were increased in CLU-deficient recipients determined by western blot. Exogenous CLU restored renal protection in CLU-deficient recipients attenuating upregulation of renal LCN2.

*Conclusions: These data indicate that CLU in circulation protects kidney transplants by regulating neutrophil migration during transplantation-related IRI.

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