Electronic Thesis and Dissertation Repository

Thesis Format

Monograph

Degree

Master of Science

Program

Pathology and Laboratory Medicine

Supervisor

Dr. Xiufen Zheng

2nd Supervisor

Dr. Dave Nagpal

Affiliation

London Heath Sciences Centre

Co-Supervisor

Abstract

There are currently ~600,000 Canadians with end stage heart failure. Although medications are effective, the ideal treatment would be heart transplantation. Loss of blood (ischemia) to the organ during preservation and restoration of blood flow (reperfusion) leads to ischemia reperfusion injury (IRI) which can lead to cell death. Circular RNA is a new type of non-coding RNA forming a covalently closed loop single stranded RNA. Evidence suggests circular RNA Hipk3 (circHIPK3) generated from exon 2 of the Hipk3 gene is involved in many pathologies. However, the role of circHIPK3 in IRI has not been investigated. Using our in vitro IRI model, we showed that CircHIPK3 expression is increased during IRI and knockdown increased cell death. In addition, circHIPK3 knockdown exacerbated pro-apoptotic Bax mRNA levels, caspase 3 activation and MLKL phosphorylation. We also observed no significant changes in inflammatory response following circHIPK3 knockdown and IRI. In conclusion, the loss of circHIPK3 expression exacerbates apoptosis and necroptosis during IRI and is crucial to cell survival.

Summary for Lay Audience

Heart diseases is a leading cause of death world-wide and the second leading cause of death in Canadians. Although we have developed many successful treatments for end-stage heart failure, the best treatment would be to replace the organ with a heart transplantation. However, loss of blood flow (ischemia) for long periods and restoring of blood (reperfusion) can leading to ischemia reperfusion injury (IRI) and cause the cells and the organ to die or exert extra damage in the recipient. IRI is a large barrier that prevents many hearts being viable from donors, with only 24% of donors having a viable heart. Therefore, the need to help the success rate of transplant surgeries and increase the availability of donors is immense. A new molecule known as circular RNA (circRNA) involvement in human disease is becoming increasingly important. CircRNA can act as a regulator by effecting other types of RNA or proteins involved in many diseases. Circular RNA Hipk3 (circHIPK3), has been identified as a key centre point in cell survival. However, circHIPK3s role in IRI has not been studied. Our research shows that circHIPK3 expression can directly influence the outcome of successful preservation. Our results showed that decreases in circHIPK3 leads to increased death during reperfusion and provides worse outcomes. This suggests that circHIPK3 plays a vital role in IRI and that its levels may be useful to determine the difference between successful and unsuccessful organ preservation. Success of this research will provide insight into previously unknown targets for IRI treatment and help develop new therapies. This in turn will allow us to increase the availability of heart donors and decrease the number of patients on the waiting list.

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