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Objective-To investigate the capacity of the adipokine leptin to promote angiogenesis by modulating the function of circulating angiogenic cells (CACs). Methods and Results-In vitro, leptin specifically promoted CAC adhesion to tubular endothelial structures and migration along outgrowing sprouts of endothelial cells. In vivo, stimulation of CACs with leptin increased their capacity to promote new vessel formation in the chorioallantoic membrane of chicken embryos and to improve neovascularization of ischemic murine hind limbs. These effects required the phosphorylation of ␣v␤5 integrins, which depended on the interaction of leptin with its receptor ObR, and on Janus kinase (JAK) 2-and phospholipase C (PLC) ␥-mediated activation of Src kinase. Protein tyrosine phosphatase 1B, a negative regulator of leptin signaling, was overexpressed in CACs from obese, hyperleptinemic individuals, and this was associated with insensitivity of CACs to the angiogenic effects of leptin. Weight loss (by [meanϮSD] 30Ϯ15 kg) normalized protein tyrosine phosphatase 1B expression in CACs and restored their responsiveness to leptin. A similar dose-dependent response was found after incubation of CACs from obese subjects with a protein tyrosine phosphatase 1B inhibitor ex vivo. Key Words: angiogenesis Ⅲ circulating angiogenic cells Ⅲ leptin Ⅲ obesity Ⅲ PTP1B Ⅲ Src kinase A ngiogenesis, the formation of new blood vessels from the existing vasculature, is a complex multistep process involving the proliferation, migration, and remodeling of endothelial cells in response to growth factors and cytokines. The adipose tissue-derived cytokine leptin has been shown to exert proangiogenic effects on endothelial cells 1,2 and leptinstimulated corneal neovascularization in rats and in leptindeficient ob/ob mice. 3 On the other hand, the prevention of leptin binding to its receptor inhibited angiogenesis, 4 and leptin receptor (ObR)-deficient mice exhibited reduced basal capillary density and defective revascularization of ischemic muscles. 5 Conclusion-Our See accompanying article on page 135Angiogenesis requires the interplay of various cell types, among which circulating angiogenic cells (CACs) appear to be of particular interest. These cells, formerly considered to represent a subpopulation of endothelial progenitor cells 6 and now regarded as a distinct (progenitor) cell type, 7 are derived from the peripheral blood after expansion in culture. They have been shown to augment neovascularization after tissue ischemia 8 and promote endothelial repair after vascular injury. 9 The vasculoprotective properties of CACs and other progenitor cells are defined by their ability to adhere to molecules released from injured tissues, allowing them to home and transmigrate at sites of injury or ischemia. 10 These steps are regulated by integrins, the transmembrane receptor heterodimers connecting the extracellular matrix to cytoskeletal and signaling molecules. More important, the activation status of integrins appears to be modulated by soluble growth fact...

Obesity is associated with a reversible functional impairment of EPCs. This involves reduced secretion of angiogenic chemokines and increased basal phosphorylation of signaling molecules, notably p38 MAPK.

Our findings suggest that the angiogenic effects of leptin involve sca-1(+), flk-1(+) vascular progenitor cells mobilized from the BM in response to ObR-mediated activation of NOX2, increased MMP9 expression, and sKitL release.

Objective-To determine the intracellular mechanisms mediating the angiogenic effects of integrin ␣v␤5 overexpression in circulating angiogenic cells (CACs). Methods and Results-Integrin ␣v␤5 is expressed on angiogenic endothelial cells, and integrin ␣v␤5 activation was shown to improve the reparative functions of endothelial progenitors within the cardiovascular system. CACs were transiently transfected with the full-length cDNA of human integrin ␤5 (CAC-ITGB5) or control-vector (CAC-vector). Integrin ␤5 overexpression was confirmed using flow cytometry, Western blot, and PCR analysis; it enhanced the angiogenic capacities of CACs in vitro (spheroid and Matrigel angiogenesis assay) and stimulated new vessel formation in vivo (murine hind limb ischemia model). Overexpression of ITGB5 resulted in integrin ␣v␤5 phosphorylation and activation of Src kinase and signal transducer and activator of transcription (STAT) 3. Furthermore, elevated mRNA and protein expression of the CXC chemokine CXCL8 and the CC chemokine CCL2 was detected in CAC-ITGB5, and conditioned medium from CAC-ITGB5 enhanced the sprouting of coincubated human endothelial cells in a STAT3-, CXCL8-, and CCL2-dependent manner. A ngiogenesis is a hallmark of diverse physiological and pathological processes, including wound healing, inflammation, and tumor growth. The formation of new blood vessels from the existing vasculature involves the proliferation, migration, and morphogenesis of endothelial cells in response to growth factors and cytokines; and cross talk between growth factor and integrin receptors, both direct and indirect, via adaptor proteins or nonreceptor protein tyrosine kinases has been shown to modulate angiogenic signaling. 1 In addition to repair mechanisms provided by local cells, endothelial progenitor cells (EPCs) mobilized from the bone marrow into the circulation in response to tissue injury signals have been shown to contribute to neovascularization or reendothelialization after ischemia or endothelial denudation. 2,3 At least 2 types of EPCs need to be distinguished depending on the isolation protocol and their phenotypic and functional behavior in culture: endothelial colony unit-forming cells (late-outgrowth EPCs) and circulating angiogenic cells (CACs; early-outgrowth EPCs). 4,5 Although both cell types have been demonstrated to promote endothelial repair, their distinct functional characteristics may explain why EPCs structurally contributed to tissue repair in some studies, 6,7 whereas other studies 8,9 could not demonstrate incorporation, but rather secretion of paracrine factors acting on neighboring cells to stimulate proliferation, migration, and angiogenesis. Conclusion-SrcVitronectin receptors (ie, the integrins ␣v␤3 and ␣v␤5) are expressed on angiogenic endothelial cells. 10 Regarding their exact function during angiogenic processes, discrepant findings in gene-deleted mice as opposed to data obtained after integrin function blockade have left some uncertainties. 11-14 Previous findings 15,16 suggest that upregula...