Abstract 5114: Leptin Promotes Mobilization of Flk1-positive Vascular Progenitor Cells From the Bone Marrow and Enhances Neovascularization After Peripheral Ischemia
Experimental evidence suggests that bone marrow-derived progenitor cells participate in the formation of new blood vessels and endothelial repair. We have previously shown that leptin enhances the recruitment and incorporation of human, culture-expanded endothelial progenitor cells (EPC) into neointimal lesions after vascular injury and promotes re-endothelialization. The aim of the present study was to examine the potential of circulating leptin to promote ischemia-induced neovascularization in vivo, and to determine the contribution of bone marrow-derived (endothelial) progenitor cells to this process. In wild-type mice, daily intraperitoneal injection of leptin over five days promoted neovascularization after hindlimb ischemia, as determined by the quantification of CD31-immunopositive capillary endothelial cells (P<0.01 vs. control). In vitro studies demonstrated that systemic administration of leptin increased the number of cultured, spleen-derived acLDL+, lectin+ EPC (P<0.01 vs. vehicle), and enhanced their potential to integrate into endothelial cell networks (P<0.001) or to adhere to endothelial cell sprouts (P<0.001). Analysis of mice after sublethal irradiation and transplantation of GFP-positive bone marrow revealed that bone marrow-derived cells are recruited to ischemic muscles and incorporate into CD31-positive capillaries. Although flow cytometry analysis revealed that leptin did not alter the number of sca1+, c-kit+ cells within the bone marrow or peripheral blood, leptin increased the number of circulating sca1+ or GFP+, Flk1+ cells, in contrast to vehicle or GCSF (P<0.05 for both). PCR analysis confirmed mRNA expression of the leptin receptor in bone marrow cells. Ongoing studies focussing on potential mechanisms mediating the effects of leptin on bone marrow cells indicate increased protein kinase B phosphorylation and MMP9 expression in response to leptin. Taken together, our studies suggest that the proangiogenic effects of leptin may involve the interaction with leptin receptor-positive cells within the bone marrow resulting in enhanced mobilization of Flk1+ vascular progenitors and neovascularization in response to ischemia.