Progenitor cells and Abdominal Aortic Aneurysms

Abdominal aortic aneurysms (AAAs) are characterised by progressive, degenerative changes in the wall of the aorta leading to a structurally weaker vessel which is at risk of potentially fatal rupture. The incidence of fatal rupture is 10,000 per year in the UK alone (only 50% survival after surgical repair), and the number is increasing. Current treatment of AAA involves surgical intervention as there are no drugs to stabilise it, induce regression or prevent rupture. Understanding events leading to rupture are key targets for stabilisation and management of aneurysmal disease.

Bone marrow derived progenitor cells have been implicated in the modulation and repair of various vascular disease processes. Progenitor cells are mobilised from the bone marrow, move by chemotaxis to specific sites, adhere, transmigrate and differentiate becoming incorporated into the vasculature.

Recently, we have shown in human AAA samples an increased number of neocapillaries adjacent to the rupture site when compared to tissue sampled from the rest of the aneurysmal sac.

Consistent with this, we have shown that the number of circulating EPCs is increased in aneurysm patients in comparison to age-matched controls. We hypothesise that there is functional impairment of mobilised progenitor cells from AAA patients either due to intrinsic phenotypic differences or as a consequence of key changes in the extrinsic AAA environment resulting in altered ability to repair/stabilise the aneurysm contributing to progression and rupture. Changes in the local AAA environment which would influence progenitor cell plasticity include chemokine release, altered ECM, and upregulation of metalloproteinases (MMPs). Changes in ECM and matrix enzymes (MMPs etc) could influence progenitor cell repair by altering cell adherence, migration and differentiation.

Experimental outline:

This project will investigate in vitro progenitor cell transmigration, and differentiation in response to chemokine treatment. Blood will be collected from patients undergoing aortic aneurysm repair. Mononuclear cells will be isolated by density gradient separation, followed by selection of CD133+ cells by incubating with anti-CD133 labelled magnetic beads and subsequent cell sorting. These cells will be cultured for the following functional assays.

1)Chemotaxis and transmigration: cells will be placed in transwells and the ability to migrate across the chamber assessed in response to chemokines

2)Differentiation: to determine ability to differentiate cells will be cultured +/- chemokines and the expression of mature EC markers determined by immunofluorescence staining

References:

1. Thompson MM, Bell PR. ABC of arterial and venous disease. Arterial aneurysms. BMJ. Apr 29 2000;320(7423):1193-1196
2. Xu Y, Arai H, Zhuge X, et al. Role of bone marrow-derived progenitor cells in cuff-induced vascular injury in mice. Arterioscler Thromb Vasc Biol. Mar 2004;24(3):477-482
3. Choke E, Thompson MM, Dawson J, et al. Abdominal aortic aneurysm rupture is associated with increased medial neovascularisation and overexpression of proangiogenic cytokines. Arterioscler Thromb Vasc Biol. Jun 29 2006;26(9):2077-82
4. Dawson J, Tooze J, Cockerill G, et al. Endothelial progenitor cells and abdominal aortic aneurysms. Ann N Y Acad Sci. 2006 Nov;1085:327-30