An aneurysm is a localised dilatation of the arterial wall, characterised by thinning of the medial layer and degeneration of the internal elastic lamina. The formation and the rupture of an aneurysm is a significant cause of premature mortality in UK, accounting for 2% of all deaths. Aneurysms are usually asymptomatic until their rupture, and diagnosis is usually incidental in unrelated medical complaints. The sudden rupture of aortic aneurysms commonly results in haemorrhagic shock and death. There are currently no treatments for patients with non-ruptured aneurysms therefore novel treatments to prevent rupture, or biomarkers to identify vulnerability to aneurysm rupture, would represent major scientific breakthroughs. To gain insight into the pathogenesis of aortic aneurysms, several mouse models have been developed which rely upon Angiotensin II (Ang II) or calcium chloride (CaCl2) as inducers of aortic dilatation. However at least 15% of animals suffer aortic dissection and sudden death. The aim of this project is to develop and characterise a reproducible ex-vivo human model of aneurysm, to be used alongside or instead of mouse models. To mimic current in vivo animal models, a suitable replacement should harbour similar cellular and morphological features such as vessel dilatation, elastin loss and vascular smooth muscle cell (VSMC) apoptosis. In this study, arteries were isolated from human umbilical cords, placed within a bio-reactor and exposed to laminar flow (6.5 dynes/cm2) for 72 hours with and without Ang II or CaCl2. CaCl2 pre-treatment of umbilical arteries reduced medial thickness, medial elastin content, and medial cell density, despite no change in vessel area. Ang II stimulation significantly increased total vessel area and medial cell density, compared to untreated arteries. Moreover, Ang II significantly decreased medial thickness, and medial elastin content suggesting aneurysm formation. Considering the association of dysregulated MMP-directed elastinolytic activity with aneurysm progression, introduction of exogenous tissue inhibitor of metalloproteinases 3 (TIMP-3), a transforming growth factor beta neutralising antibody (TGFβ NAb) or a matrix metalloproteinase-12 (MMP-12)-specific inhibitor into the ex vivo model prevented aneurysm formation, mimicking effects observed in the Ang II-infused mouse model and providing robust validation of the ex vivo aneurysm model. Interestingly, Ang II or CaCl2 treatment of VSMC regulated the expression of a number of metalloproteinases (MMPs) and tissue inhibitors of MMPs (TIMPs), alongside differences in phenotypic markers. In addition, Ang II-induced marked haemodynamic effects on endothelial cells (ECs) which could be reversed by addition of exogenous TIMP-3 or the angiotensin receptor inhibitor Losartan. This study highlights the applicability of the ex vivo model for future aneurysm studies, providing a potential replacement for ethically contentious animal models.
|Date of Award||1 Oct 2019|
- The University of Bristol
|Supervisor||Jason L Johnson (Supervisor) & Sarah J George (Supervisor)|