Date of Award

2020

Document Type

Thesis - MUSC Only

Degree Name

Master of Biomedical Science

Department

Microbiology and Immunology

College

College of Graduate Studies

First Advisor

Carl Atkinson

Second Advisor

Laura Kasman

Third Advisor

Satish Nadig

Fourth Advisor

Stephen Tomlinson

Abstract

Lung transplantation (LTx) is an accepted therapy for patients with end-stage lung disease. While LTx significantly improves survival and quality of life for recipients, the overall success of LTx continues to lag behind that of any other solid organ. There are several pathophysiological reasons for these poorer outcomes, including the lung’s exquisite sensitivity to cold storage and reperfusion injury. It is thought that these early insults play a significant role in the long-term outcome of the lung graft. Primary graft dysfunction (PGD) causes early mortality after LTx and contributes to late graft failure. Although the pathogenesis of PGD is multifactorial, clear associations have been made between PGD and the severity of ischemia-reperfusion injury (IRI). The complement system plays a central role in IRI and has been associated with PGD. Elevated C5a and C3a levels in LTx recipients early post-LTx are predictive of PGD development, and in the case of C3a, mortality. While complement’s pro-inflammatory functions are well described, recent studies have proposed a role for complement in cellular metabolic and mitochondrial injury. Previous studies from our group have also shown that injury to mitochondria because of cold organ preservation leads to heightened immune priming. Given these findings, here we explored the role of complement, specifically C3a, in mitochondrial injury. Using immortalized bronchial epithelial cells (BEAS-2B), we analyzed the impact of C3a on cellular oxidative phosphorylation using Seahorse XFe analysis and the release of mitochondrial DNA (mtDNA) from cells as a marker of mitochondrial injury. We demonstrate that C3a dose-dependently induces mitochondrial injury, a process that was blocked by C3a receptor antagonism. Recent studies have shown that intracellular complement activation plays key roles in metabolism and cellular inflammation. We therefore determined the extent to which BEAS-2B ischemic injury was associated with intracellular complement activity. We were unable to demonstrate C3 activation intracellularly. Taken together, our data demonstrates a novel role for extracellular complement activation-induced respiratory epithelial cell mitochondrial damage. In conclusion, inhibition of C3a signaling in vivo may inhibit complement-induced inflammation and provide protection from mitochondria injury, preserving epithelial cell function and integrity, which are important for recovery from ischemic injury.

Rights

All rights reserved. Copyright is held by the author.

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