Abstract 494: Proinflammatory Role of Stem Cells in Abdominal Aortic Aneurysms

Abstract

Background: The pathogenesis of abdominal aortic aneurysm (AAA) formation includes inflammation, vascular smooth muscle cell apoptosis, extracellular matrix degradation and oxidative stress. It is well established that multi-potent stem cells have an important role in cardiovascular health and disease but the role of stem cells in AAA formation remains controversial. We sought to describe the presence of stem cells in human AAA tissue. Additionally, we investigated the differentiation of stem cells within the aneurysmal aorta. Methods: Infra-renal aortic wall specimens (8 AAA patients; 5 males and 3 females; ages ranging from 55 to 78 years) were collected from patients undergoing AAA repair operations. Non-aneurysmal infra-renal aortic control samples were collected at autopsies (N=5; 3 males and 2 females; donor ages ranging from 53 to 78 years). Using immunohistochemistry, we compared the abundance of STRO1+, cKit+, and CD34+ cells in aortic tissue. Using double immunofluorescence staining, we evaluated stem cell differentiation into smooth muscle cells (SM22), fibroblasts (FSP1), and macrophages (CD68). Results: Both the media and adventitia of infra-renal AAA samples demonstrated a significantly greater number of STRO1+, c-Kit+ and CD34+ cells when compared with matched non-aneurysmal control aortic tissues. Furthermore, double immunofluorescence staining identified that AAA stem cells express the macrophage marker CD68 but not the smooth muscle cell marker SM22 or the fibroblast marker FSP1. Conclusions: Stem cells are significantly elevated in infra-renal AAA tissue compared to matched control aortic tissue. Our data also demonstrate that AAA stem cells express macrophage surface antigens but not smooth muscle cell or fibroblast markers. These finding suggest an inflammatory/immune role of stem cells during AAA pathogenesis.