Abstract
Vascular remodelling in arterial disease is characterised by vascular smooth muscle cell and adventitial fibroblast (AF) proliferation and migration due to mechanical and oxidative stresses within the vessel wall, leading to enhanced growth factor signalling. Transforming growth factor β-1 (TGF-β1) is a pleiotropic growth factor that mediates vascular remodelling through eliciting phenotypic changes in AF, which may result from the generation of reactive oxygen species (ROS). Nrf2 is a key transcription factor that co-ordinates expression of endogenous antioxidant defense genes such as heme oxygenase-1 (HO-1) and plays an important role in cellular defense against the deleterious effects of ROS. This thesis has investigated whether TGF-β1 modulates redox-related signalling pathways, gene expression, cell phenotype and motility in AF derived from human aortas.Results from this study have demonstrated that TGF-β1 treatment resulted in an increase in HO-1 protein expression in AF, an effect that was partially diminished in cells where Nrf2 had been knocked-down using siRNA. In addition, TGF-β1 also enhanced AF migration, measured using time-lapse video microscopy. In the presence of superoxide dismutase (SOD), migration of AF was significantly abrogated suggesting that TGF-β1-mediated AF migration may be mediated by the generation of superoxide. Measurement of ROS generation revealed an increase in AF treated with TGF-β1, an effect that was partially attenuated in the presence of a NAD(P)H oxidase inhibitor or SOD.
The ability of the dietary isothiocyanate, sulforaphane (SFN) to activate the Nrf2 pathway in AF was also investigated. Results revealed that SFN treatment increased HO-1 protein expression which was diminished in cells where Nrf2 had been silenced using siRNA, suggesting that HO-1 induction was Nrf2-dependent. SFN also caused increased nuclear accumulation of Nrf2 and binding to the antioxidant response element (ARE), suggesting the involvement of Nrf2 in ARE-mediated antioxidant gene expression. The ability of SFN to activate endogenous antioxidant defenses may be a potential therapeutic strategy to counteract pathophysiological processes following vascular injury and in the pathogenesis of atherosclerosis.
Findings from this study provide novel insights in to the mechanisms underlying the contribution of redox signaling in AF that lead to vascular diseases and for interventions to modulate TGF-β1-induced adventitial oxidative stress.
| Date of Award | 2014 |
|---|---|
| Original language | English |
| Awarding Institution |
|
| Supervisor | Richard Siow (Supervisor) & Madeline Parsons (Supervisor) |