Abstract 525: Reduced Ability of Endothelial Progenitor Cells to Inhibit Smooth Muscle Cell Proliferation and Migration Compared to Aortic Endothelial Cells Under Flow

Early endothelial restoration at sites of vascular intervention is one of the recognized important potential treatment strategies that can be exploited to limit arterial restenosis associated with intimal smooth muscle cell hyperplasia. In recent years, much attention has been focused on the potential of circulating bone marrow derived cells named endothelial progenitor cells (EPC) to differentiate into mature endothelial cells upon attachment at injured vascular sites and, thereby, potentially limit intimal hyperplasia. Our objective was to compare the influence of isolated porcine blood EPC and aortic endothelial cells (HAEC) on the proliferation and migration of underlying aortic smooth muscle (SMC) cells using a novel arterial wall model system exposed to arterial flow patterns. An in vitro arterial wall model co-culture system was constructed as the bottom plate within a parallel plate flow chamber. A 2mm thick collagen gel containing porcine SMC was overlayed by a porous (5μm) polyester mesh. After 2 days, either porcine aortic EC or CD34+ EPC or no cells (control) were seeded on the surface and allowed to attain confluence. These constructs were then placed into a flow chamber and exposed to arterial flow (12 dynes/cm 2 ) for 48h using circulating culture medium. After the flow regimen, SMC that had migrated through the mesh were immunologically identified and counted. The mesh was removed and the percent proliferating cells in the underlying gel were identified by PCNA staining.EC coverage resulted in an almost 7-fold inhibition of SMC migration compared to control (127±33 vs 840±193 SMC/cm 2 ) and more than 4- fold more than observed with EPC coverage (553±7 SMC/cm 2 ). Similarly, EC coverage resulted in reducing SMC proliferation to 3.2% compared to 8.5% in EPC covered SMC and 14% PCNA positive SMC in the control underlying SMC. These result indicate that blood-derived CD34+ EPC are less effective in limiting adjacent SMC proliferation and migration than native arterial endothelial cells. This may have important implications for strategies designed to employ or attract these cells as a means to limit restenosis at stented interventional sites.