Hemodynamic Regulation of Endothelial Cell Gene Expression: Effects of p65 Expression Level on Constitutive and TNFα Induced NF-κB Signalling

Atherosclerosis is a chronic inflammatory disease of arterial blood vessels, characterized by deposition of lipoproteins in the arterial wall. Atherosclerotic plaques form preferentially in distinct regions of the vasculature such as branch points, curvatures and bifurcations, suggesting that local hemodynamic forces may contribute to disease susceptibility. Shear stress imparted on endothelial cells (ECs) by the flowing blood has been shown to modulate gene expression and remodelling of the artery.\nIn this thesis, an in vitro model was established to recreate the contrasting environments found in atherosclerosis-prone and atherosclerosis-resistant regions of the vasculature to demonstrate a direct causal-relationship between shear stress and expression of endothelial nitric oxide synthase (eNOS) and p65 in ECs. In vitro assessment of cell shape and expression patterns of these anti- and atherogenic genes demonstrated that shear stress can induce cell morphology and gene expression patterns that are similar to ECs in atherosclerosis-prone and atherosclerosis-resistant regions of the mouse vasculature. Regulation of eNOS transcription by shear stress was demonstrated using a transgenic mouse model and in vitro heterogeneous nuclear RNA (hnRNA) quantification.\nSimilar to ECs in atherosclerosis-prone regions, epithelial cells lining the small intestine lumen express high levels of p65. To investigate the effects of p65 expression levels on constitutive and tumour necrosis factor α (TNFα)-induced nuclear factor-κB (NF-κB) signalling, p65 expression was suppressed in HeLa cells by RNA interference. Lower p65 expression resulted in reduced TNFα-induced expression of NF-κB target genes, including many subunits of inhibitor of nuclear factor κB (IκB), demonstrating modulation of NF-κB priming by p65 expression levels. Suppression of p65 also affected constitutive expression levels of IκB, and resulted in re-setting of the NF-κB/IκB equilibrium. Experiments using inhibitors of canonical NF-κB signalling found that basal expression of NF-κB components is independent of nuclear factor κB kinase β (IKKβ) activity and proteasome-mediated degradation of IκBα. Together, these studies elucidate the mechanism of flow-mediated gene regulation and the effect of resulting changes in p65 expression on NF-κB signalling.

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