Doctor of Philosophy
Microbiology and Immunology
Renal transplantation is a life-saving procedure for patients with end-stage renal disease. Persistent graft inflammation and fibrosis due to injury from repeated insults - both alloantigen-dependent and -independent - lead to chronic allograft dysfunction and long-term graft loss. Ischemia-reperfusion injury (IRI) to the graft is an inescapable consequence of transplantation and can result in significant delayed graft function (DGF). Tissue damage and graft dysfunction resulting from transplant-associated IRI have been correlated with acute rejection and long-term graft loss. During IRI, dying renal proximal tubular epithelial cells (TECs) release pro-inflammatory mediators, worsening tissue damage and further potentiating injury by initiating an auto-amplification loop of inflammation and cell death. Therefore, therapies that curtail this auto-amplification loop may mitigate graft dysfunction and extend the lifespan of grafts. Kidney injury molecule-1 (KIM-1) is a phagocytic receptor specifically upregulated on TECs during renal injury, enabling them to engulf apoptotic and necrotic cells during acute kidney injury. While KIM-1 can directly bind to apoptotic cells via phosphatidylserine, the clearance of necrotic cells is enhanced by the opsonin, Apoptosis Inhibitor of Macrophage (AIM) protein. The extent to which KIM-1 in the donor kidney contributes to renal transplantation has not been well-studied. In this thesis, we studied the role of KIM-1 in the donor kidney on graft outcomes following renal transplantation. We assessed the therapeutic potential of exogenous recombinant AIM (rAIM) in mitigating transplant-associated IRI. Finally, we explored the association between polymorphisms of the KIM-1 gene and DGF. Using a syngeneic murine renal transplant model, we found that KIM-1 in the donor kidney protects against renal dysfunction, inflammation, graft damage and death. Moreover, the protective effect of KIM-1 was further enhanced with the administration of rAIM. Finally, we found that common genetic variations of the coding region of human KIM-1 gene suppressed the phagocytic ability in vitro compared to wild-type KIM-1. However, none of the variations were associated with increased risk of DGF in our patient cohort. In summary, the findings reported in this thesis provide further evidence of the protective properties of KIM-1 in transplant-related IRI and the viable therapeutic potential of rAIM in renal transplantation.
Summary for Lay Audience
A kidney transplant has the potential to prolong the life of patients with kidney failure and immensely improve their quality of life. A major limitation of transplantation is the limited lifespan of the organs in the host. This is mainly due to cumulative damage sustained by the organ during procurement/surgery (lack of blood flow to the organ) and the host immune system (i.e. rejection). At the molecular level, this is caused by dying kidney cells which “explode”, releasing their inflammatory cellular contents into the body which can serve to activate the rejection process. Thus, the clearance of these dangerous remains is necessary. In this thesis, I have characterized a protein called Kidney injury molecule-1 (KIM-1), which help the remaining healthy kidney cells within the transplant to “eat” the surrounding dying cells, thereby preventing the abovementioned inflammatory cascade and help repair the damaged organ. In addition, I have documented the use of a potential therapeutic agent, “AIM”, which when administered intravenously immediately following transplantation, can compound the positive effect of KIM-1, to promote even faster and more effective clearance. Finally, I translated my findings into humans and investigated whether different versions of KIM-1 in the human population would affect the primary role of KIM-1, which could have undesirable effects on its function during transplant resulting in patients requiring dialysis within the first week- a problem known as delayed graft function (DGF). I uncovered that different versions of KIM-1 protein found in the human population decreased its ability to clear dying cells compared to normal KIM-1. However, the variation of KIM-1 was not associated with increased risk of DGF. Taken together, these findings uncover a new therapeutic target (KIM-1 and AIM) that may prolong kidney transplant survival.
Lee, Ji Yun, "Kidney Injury Molecule-1 Mediated Phagocytosis and Its Therapeutic Application in Ameliorating Renal Transplant Ischemia Reperfusion Injury" (2020). Electronic Thesis and Dissertation Repository. 7557.