Abstract 710: The Adipokine Leptin Promotes Integrin-Mediated Adhesion of Endothelial Progenitor Cells
Endothelial progenitor cells (EPC) appear to provide an intrinsic repair mechanism within the cardiovascular system. To examine the effects of the adipokine leptin, a hormone with pleiotropic cardiovascular effects, on EPC function, human peripheral blood monocytes were isolated from healthy volunteers and expanded ex vivo for 7 days. PCR analysis, flow cytometry and fluorescence microscopy confirmed that cells expressed surface markers consistent with the endothelial cell lineage. EPC expressed the leptin receptor at the mRNA and protein level, and binding of FITC-labeled leptin was inhibited by addition of soluble leptin receptor. Preincubation of cultured EPC with recombinant leptin (10 and 100 ng/mL) significantly enhanced their adherence to vitronectin-coated culture plates in a time- and dose-dependent manner without affecting adherence to fibronectin, collagen, or plastic. Leptin also enhanced the capacity of EPC to adhere to mature endothelial cells (243 ± 45% vs. control; P = 0.03), and transendothelial EPC migration (199 ± 33% vs. control; P = 0.01). Flow cytometry revealed that stimulation of EPC with 10 or 100 ng/mL leptin resulted in upregulation of αvβ5 integrins (198 ± 45%, P = 0.048; and 155 ± 19%, P = 0.02, respectively), while αvβ3, β1 and β2 integrins were unchanged. These effects could be completely blocked by addition of leptin-neutralizing antibodies, RGD peptides, or leptin receptor siRNA. Coincubation with specific signaling pathway inhibitors followed by Western blot analysis indicated that phosphatidylinositol 3-kinase-mediated pathways are involved in leptin-mediated EPC adhesion. Finally, intravenous injection of leptin-treated human EPC in athymic nude mice after ferric chloride-induced carotid artery injury resulted in strong accumulation of labeled EPCs in intimal lesions as detected by fluorescence microscopy. Morphometric analysis 3 weeks after injury revealed a significant decrease in neointima formation in mice injected with leptin-treated EPC (P = 0.018 vs. control). Thus, our in vitro and in vivo studies suggest that leptin specifically modulates the function of EPC. It promotes their adhesion, transmigration, and homing in neointimal lesions, possibly by modulating αvβ5 integrin expression.