Ongoing angiogenesis in blood vessels of the abdominal aortic aneurysm

Abstract

Pathogenesis of the abdominal aortic aneurysm has been attributed to neovascularization of the aortic wall. However, it is not clear whether angiogenesis persists in the aneurysm. In sections of aneurysms, we determined the immunohistochemical distributions of the α_vβ₃ integrin, tenascin and endothelial nitric oxide synthase (eNOS), which are markers respectively, of angiogenesis, matrix remodeling and vasoregulatory function. In addition, we used reverse transcription followed by in situ PCR, to determine the distribution of α_v mRNA. All aneurysm specimens exhibited extensive increases of wall vascularization as compared with the control aortic wall, and showed the presence of perivascular inflammatory exudates containing macrophages and lymphocytes. The neovascularization consisted of thick-walled vessels in the media and adventitia, and capillaries in the subintima. The majority of vessels stained positively for the α_vβ₃ antigen and eNOS. Tenascin was deposited as bands that circumscribed thick-walled vessels. The distribution of av mRNA was extensive and was positive even in those vessels that failed to stain for the α_vβ₃ protein. No staining was evident in control aortas for the α_vβ₃ antigen, tenascin or α_v mRNA. The upregulation of av mRNA and the α_vβ₃ integrin in blood vessels surrounded by a matrix expressing tenascin, indicates that angiogenesis is an ongoing process in the mature aortic aneurysm.