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Title: Investigation into the mechanism of Nox2 NADPH oxidase-dependent signalling in doxorubicin cardiotoxicity
Author: McLaughlin, D.
Awarding Body: Queen's University Belfast
Current Institution: Queen's University Belfast
Date of Award: 2014
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Doxorubicin (DOX) is a widely used first-line treatment for cancers. However it induces cardiotoxicity, which is associated with increased production of myocardial reactive oxygen species (ROS). Recent work has suggested that ROS generated specifically from Nox2 NADPH oxidase, contributes to this cardiotoxicity. The aim of this study was (1) to characterise the role of Nox2-derived ROS in DOX-induced cardiotoxicity, (2) identify Nox2-regulated genes and signalling pathways in the development of DOX-induced cardiotoxicity, and (3) investigate detailed Nox2-dependent signalling mechanisms in vitro. Wild type (WT) and Nox2·/· mice were treated with or without DOX and studied after 4 weeks. DOX-induced contractile dysfunction and cardiomyocyte remodelling was attenuated in Nox2-/- but not WT mice, with Nox2 mRNA expression increased in WT, but not Nox2-1 - animals. Inhibitor studies confirmed the observed effects were mediated by ROS. These data suggest that Nox2-derived ROS make a significant contribution to DOX-induced cardiotoxicity. A whole-genome gene expression array was performed on ventricular tissue in order to identify Nox2-regulated pathways which may protect against DOX cardiotoxicity. Pathway analysis found 'Cell Death and Survival' as the network of most significance to the dataset with emphasis on 5 genes associated with cardiomyocyte apoptosis. Of these genes, PGCla. and Mfn2 were selected as candidates for further investigation. HL-l cardiomyocytes were used to investigate potential DOX-induced Nox2-mediated apoptosis signalling. DOX treatment for 24 hours increased expression of Nox2, Mfn2 and superoxide production. Targeted siRNA knockdown of Nox2 and Mfn2 produced significant downregulation of protein expression and exhibited a protective effect against DOX-induced apoptosis. Pharmacological inhibition of NADPH oxidase significantly reduced DOX-induced apoptosis and cytotoxicity. The findings of this study add further support to a key role for Nox2-derived ROS in DOX cardiotoxicity, and suggest that apoptosis may represent a central mechanism, which may involve mitochondrial fusion, thereby contributing to the associated contractile dysfunction.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available