Electronic Thesis and Dissertation Repository

Thesis Format

Monograph

Degree

Master of Science

Program

Pathology and Laboratory Medicine

Supervisor

Zhang, Zhu-Xu

Abstract

Cardiac transplantations are the golden standard treatment for end-stage heart failure but issues like ischemia-reperfusion injury (IRI) and graft rejection persist. Prolonged ischemia induces anaerobic metabolism, lactic acid accumulation, and intracellular acidosis. IRI is associated with programmed cell death, of which necroptosis is significant. We have shown that in hypoxia-reoxygenation, targeting necroptosis prevents murine microvascular endothelial cell (MVEC) death through cyclophilin D inhibition in vitro and apoptosis-inducing factor (AIF) is implicated in DNA damage. Here, we investigated AIF and the impact of acidic pH on cell death. Acidic pH conditions altered MVEC necroptosis to an apoptosis-like pattern. AIF nuclear translocation and DNA fragmentation increased. Endonuclease G did not translocate into the nucleus, suggesting other nucleases may be involved in DNA fragmentation. PARP-1 regulates AIF translocation and DNA fragmentation. Clarifying the mechanisms underlying ischemia and the acidic cellular environment may lead to therapeutic strategies preventing IRI and cardiac transplant graft rejection.

Summary for Lay Audience

Organ transplantation is an important treatment for patients with end-stage organ disease, including people with heart failure. However, transplantations can cause organ damage through limiting blood supply. This reduction in blood oxygen can cause the organ environment to be acidic. Despite advances in organ storage and transportation, there has been a lack of strategies that look to reduce cell death in ischemic injury. Thus, it is important to understand the pathways of cell death that are involved in ischemia in acidic conditions. Necroptosis is a form of cell death that has been found to be involved in transplantations and is believed to promote inflammatory injury, triggering an immune response against the transplanted organ. The specific mechanisms of necroptosis in the context of ischemia and transplantation are unclear, but current research has implicated the mitochondria and related molecules. This includes the focus of this project, apoptosis-inducing factor (AIF), which has been shown to move from the mitochondria to the nucleus facilitating DNA damage under conditions of ischemic stress. The goal of this project was to determine the role of AIF in a cardiac transplantation model. Chemical reagents and genetic inhibition were used to stimulate cell death and prevent AIF from performing its role within the cell. Cell death was reduced in acidic conditions, but the action of AIF was not blocked. It is hoped that by better understanding these cell death pathways, potential clinical targets can be studied to improve the organ transplantation process and long-term success.

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