The macrophage-TCRαß is a cholesterol-responsive combinatorial immune receptor and implicated in atherosclerosis.

Recent evidence indicates constitutive expression of a recombinatorial TCRαß immune receptor in mammalian monocytes and macrophages. Here, we demonstrate in vitro that macrophage-TCRß repertoires are modulated by atherogenic low density cholesterol (LDL) and high-density cholesterol (HDL). In vivo, analysis of freshly obtained artery specimens from patients with severe carotid atherosclerosis reveals massive abundance of TCRαß(+) macrophages within the atherosclerotic lesions. Experimental atherosclerosis in mouse carotids induces accumulation of TCR bearing macrophages in the vascular wall and TCR deficient rag(-/-) mice have an altered macrophage-dependent inflammatory response. We find that the majority of TCRαß bearing macrophages are localized in the hot spot regions of the atherosclerotic lesions. Advanced carotid artery lesions express highly restricted TCRαß repertoires that are characterized by a striking usage of the Vß22 and Vß16 chains. This together with a significant degree of interindividual lesion repertoire sharing suggests the existence of atherosclerosis-associated TCRαß signatures. Our results implicate the macrophage-TCRαß combinatorial immunoreceptor in atherosclerosis and thus identify an as yet unknown adaptive component in the innate response-to-injury process that underlies this macrophage-driven disease.

Overexpression of integrin beta 5 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 alpha v beta 5 overexpression in circulating angiogenic cells (CACs). METHODS AND RESULTS: Integrin alpha v beta 5 is expressed on angiogenic endothelial cells, and integrin alpha v beta 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 beta 5 (CAC-ITGB5) or control-vector (CAC-vector). Integrin beta 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 alpha v beta 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. CONCLUSIONS: Src kinase-mediated activation of STAT3 and subsequent angiogenic gene expression mediate the effects of integrin alpha v beta 5 and may be exploited to enhance the paracrine activities of CACs.

Leptin enhances the potency of circulating angiogenic cells via src kinase and integrin (alpha)vbeta5: 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 alphavbeta5 integrins, which depended on the interaction of leptin with its receptor ObR, and on Janus kinase (JAK) 2- and phospholipase C (PLC) gamma-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 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. CONCLUSIONS: Our results point to the ObR-Src kinase-alphavbeta5 cross talk as a distinct novel component of the network of specific interactions between integrins and cytokine receptors in angiogenesis.

Leptin enhances the recruitment of endothelial progenitor cells into neointimal lesions after vascular injury by promoting integrin-mediated adhesion.

The adipocytokine leptin modulates vascular remodeling and neointima formation. Because endothelial progenitor cells (EPCs) participate in vascular repair, we analyzed the effects of leptin on human EPC function in vitro and in vivo. After 7 days in culture, EPCs expressed the leptin receptor and responded to leptin stimulation with increased STAT3 phosphorylation. Incubation of EPCs with leptin (at concentrations between 1 and 100 ng/mL) increased the number of EPCs adhering to vitronectin and fibronectin in a receptor-specific manner. It also enhanced the capacity of EPCs to incorporate into a monolayer of human endothelial cells and the adherence of these cells to activated platelets. Leptin upregulated alphavbeta5 and alpha4 integrin expression in EPCs, and the effects of leptin on EPC function could be prevented, at least in part, by RGD peptides and function-blocking antibodies. Intravenous injection of fluorescently labeled human EPCs into athymic nude mice shortly after vascular injury revealed that preincubation of EPCs with leptin augmented their accumulation within intimal lesions, accelerating reendothelialization and decreasing neointima formation in an alphavbeta5 and alpha4 integrin-dependent manner. Our findings suggest that leptin specifically modulates the adhesive properties and the homing potential of EPCs and may thus enhance their capacity to promote vascular regeneration in vivo.

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.

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.