Abstract 053: The Role of Adventitial Sca-1+ Progenitor Cells in Angiotensin II-induced Aortic Stiffening

Abstract

The aortic adventitia contains progenitor cells that express the surface marker stem cell antigen-1 (Sca-1). Sca-1+ cells have been reported to transform into smooth muscle cells and promote neo-intimal formation. We have previously found that hypertension is associated with striking adventitial collagen deposition that contributes to aortic stiffening. We hypothesized that Sca-1+ progenitor cells serve as a source of adventitial collagen. Using confocal microscopy we found that Sca-1+ cells represent approximately one fourth of total adventitial cells and that chronic angiotensin II infusion increases their presence by approximately 3-fold. Flow cytometry confirmed that aortic Sca-1+CD31- cells are tripled in angiotensin II-induced hypertension (5.6±1.6 х103 vs. 15.9±2.4 х103 cells/per aorta). We isolated aortic Sca-1+ cells using magnetic-activated cell sorting and found collagen 1a1, 3a1, 5a1 and fibronectin-1 genes were significantly upregulated from 2.7 to 5.4-fold in these cells in angiotensin II-induced hypertension. These fibrotic genes were also upregulated by 2-3 fold in CD31+ cells suggesting endothelial to mesenchymal transition. Immunofluorescence staining demonstrated colocalization of Sca-1 and markers of fibroblasts such as vimentin, fibroblast specific protein-1 (FSP-1) and collagen I, indicating differentiation of these progenitor cells into fibroblasts during the onset of hypertension. Using bone marrow transplantation of EGFP+ cells, we find that angiotensin II stimulates mobilization of these cells from the marrow, and that they home to the vascular adventitia, where they shed Sca-1 and c-kit markers as they begin to produce collagen I. In conclusion, aortic Sca-1+ progenitor cells, both resident and bone marrow-derived, differentiate into fibroblasts and contribute to adventitial collagen deposition and promote aortic stiffening in response to hypertensive stimuli like angiotensin II. Our data also show that the bone marrow is responsive to angiotensin II through mechanisms that remain to be defined.