Abstract 231: Role of SDF-1α-induced Double Reciprocal E-Selectin/Ligand Pairs in Mediating Recruitment of Endothelial Progenitor Cells to Ischemic Wounds

Abstract

Introduction: We previously reported that stromal cell-derived factor-1α (SDF-1α)-induced endothelial progenitor cells (EPC) homing is enhanced by up-regulation of E-selectin (E-sel) on luminal endothelial cells (EC) lining capillaries, locally within wound tissues. We now investigate how elevated SDF-1α in wounds achieves a remote effect on bone marrow-derived (BMD) circulating EPC. Methods: SDF-1α-induced cell adhesion molecules in human EPC and human microvascular endothelial cells (HMVEC) were profiled using PCR-Array and validated by immunoblot. Induction of E-sel expression on murine BMD- and circulating EPC by SDF-1α was examined by flow cytometry. The involvement of E-sel/ligand in mediating SDF-1α-induced EPC-EC interaction and EPC transendothelial migration was studied using in vitro EPC-EC binding assay. The role of SDF-1α-induced E-sel in regulating EPC homing, wound neovascularization and healing were furthered studied by testing EPC from ROSA26-LacZ+/E-sel -/- versus ROSA26-LacZ+/E-sel +/+ mice in an ischemic wound model. Results: SDF-1α enhanced EPC-EC interaction by upregulating expression of E-sel/ligand in human EPC and HMVEC. Administration of SDF-1α in wound also increased E-sel expression on BMD- and circulating EPC in mice. The effects of SDF-1α on EPC-EC interaction and EPC transendothelial migration were specifically mediated by E-sel, as E-sel antagonists could inhibit these processes. E-sel was required for SDF-1α-induced EPC homing, wound neovascularization and healing in vivo (n=6, P<0.05). Conclusions: EPC-EC interaction is an essential process for EPC homing. SDF-1α induces both local luminal EC lining capillaries in wound tissue and remote BMD- and circulating EPC to express E-sel and its ligands. Up-regulated E-sel/ligand pairs reciprocally on EC and EPC serve as “Double-Lock” to secure targeted EPC-EC interactions selectively occurring within wound endothelium. These findings uncover a novel mechanism underlying the pro-angiogenic effect of SDF-1α on EPC homing and point to E-sel/ligand pairs reciprocally induced on circulating EPC and local endothelium as effective targets for ex vivo manipulation and therapeutic neovascularization.