Nana-Maria Heida

Leptin Enhances the Potency of Circulating Angiogenic Cells Via Src Kinase and Integrin αvβ5. Implications for Angiogenesis in Human Obesity

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 &agr;v&bgr;5 integrins, which depended on the interaction of leptin with its receptor ObR, and on Janus kinase (JAK) 2– and phospholipase C (PLC) &ggr;-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 [mean±SD] 30±15 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. Conclusion—Our results point to the ObR–Src kinase–&agr;v&bgr;5 cross talk as a distinct novel component of the network of specific interactions between integrins and cytokine receptors in angiogenesis.

Effects of Obesity and Weight Loss on the Functional Properties of Early Outgrowth Endothelial Progenitor Cells

OBJECTIVES The purpose of this study was to examine the impact of obesity and weight loss on the angiogenic and regenerative capacity of endothelial progenitor cells (EPCs). BACKGROUND EPCs participate in angiogenesis and tissue repair. Several cardiovascular risk factors are associated with EPC dysfunction. METHODS Early outgrowth EPCs were isolated from 49 obese (age 42 +/- 14 years; body mass index 42 +/- 7 kg/m(2)) normoglycemic participants in a professional weight reduction program and compared with those from 49 age-matched lean controls. EPC function was tested both in vitro and in vivo. RESULTS EPCs expanded from the obese possessed reduced adhesive, migratory, and angiogenic capacity, and mice treated with obese EPCs exhibited reduced EPC homing in ischemic hind limbs in vivo. EPCs from the obese subjects failed to respond to conditioned medium of lean controls or to potent angiogenic factors such as vascular endothelial growth factor. Although no differences existed between lean and obese EPCs regarding the surface expression of vascular endothelial growth factor or chemokine receptors, basal p38 mitogen-activated protein kinase (MAPK) phosphorylation was elevated in obese EPCs (3.7 +/- 2.1-fold increase; p = 0.006). These cells also showed reduced secretion of the angiogenic chemokines interleukin-8 (p = 0.047) and monocyte chemoattractant protein-1 (p = 0.012). By inhibiting p38 MAPK, we could restore chemokine levels to those of lean control EPCs and also improve the angiogenic properties of obese EPCs. Accordingly, 6-month follow-up of 26 obese persons who achieved significant weight reduction revealed normalization of p38 MAPK phosphorylation levels and improved EPC function. CONCLUSIONS 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.

Leptin promotes the mobilization of vascular progenitor cells and neovascularization by NOX2-mediated activation of MMP9

AIMS Bone marrow (BM) progenitors participate in new vessel formation and endothelial repair. The leptin receptor (ObR) is expressed on hematopoietic cells; however, the effects of leptin on BM progenitor cells and their angiogenic potential are unknown. METHODS AND RESULTS In the present study, we show that the short-term administration of leptin (over five consecutive days) into wild-type mice increased the number of circulating, BM-derived sca-1(+), flk-1(+) vascular progenitors, 95 ± 1.7% of which also expressed ObR. Ex vivo stimulation of BM cells with leptin enhanced the expression of NADPH oxidase isoform 2 (NOX2), and the leptin-induced increase in reactive oxygen species production, matrix metalloproteinase-9 (MMP9) expression and circulating soluble KitL levels was absent in mice lacking NOX2. Furthermore, intraperitoneal injections of leptin improved perfusion and increased the number of BM-derived, CD31-positive endothelial cells in ischaemic hindlimbs after femoral artery ligation. The effects of leptin on the mobilization of sca-1(+), flk-1(+) cells and neovascularization were abolished in mice transplanted with BM from ObR-deficient and in NOX2(-/-) mice. CONCLUSION 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.

Overexpression of Integrin β5 Enhances the Paracrine Properties of Circulating Angiogenic Cells via Src Kinase–Mediated Activation of STAT3

Objective—To determine the intracellular mechanisms mediating the angiogenic effects of integrin &agr;v&bgr;5 overexpression in circulating angiogenic cells (CACs). Methods and Results—Integrin &agr;v&bgr;5 is expressed on angiogenic endothelial cells, and integrin &agr;v&bgr;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 &bgr;5 (CAC-ITGB5) or control-vector (CAC-vector). Integrin &bgr;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 &agr;v&bgr;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. Conclusion—Src kinase–mediated activation of STAT3 and subsequent angiogenic gene expression mediate the effects of integrin &agr;v&bgr;5 and may be exploited to enhance the paracrine activities of CACs.

Prolactin as a modulator of platelet function and thrombosis: The end of the story, or a new beginning?

Prolactin as a modulator of platelet function and thrombosis: The end of the story, or a new beginning? -