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.

Cigarette smoke exposure promotes arterial thrombosis and vessel remodeling after vascular injury in apolipoprotein E-deficient mice.

BACKGROUND: Cigarette smoking is a major risk factor for the development of cardiovascular disease. However, in terms of the vessel wall, the underlying pathomechanisms of cigarette smoking are incompletely understood, partly due to a lack of adequate in vivo models. METHODS: Apolipoprotein E-deficient mice were exposed to filtered air (sham) or to cigarette mainstream smoke at a total particulate matter (TPM) concentration of 600 microg/l for 1, 2, 3, or 4 h, for 5 days/week. After exposure for 10 +/- 1 weeks, arterial thrombosis and neointima formation at the carotid artery were induced using 10% ferric chloride. RESULTS: Mice exposed to mainstream smoke exhibited shortened time to thrombotic occlusion (p < 0.01) and lower vascular patency rates (p < 0.001). Morphometric and immunohistochemical analysis of neointimal lesions demonstrated that mainstream smoke exposure increased the amount of alpha-actin-positive smooth muscle cells (p < 0.05) and dose-dependently increased the intima-to-media ratio (p < 0.05). Additional analysis of smooth muscle cells in vitro suggested that 10 microg TPM/ml increased cell proliferation without affecting viability or apoptosis, whereas higher concentrations (100 and 500 microg TPM/ml) appeared to be cytotoxic. CONCLUSIONS: Taken together, these findings suggest that cigarette smoking promotes arterial thrombosis and modulates the size and composition of neointimal lesions after arterial injury in apolipoprotein E-deficient mice.

Leptin signalling and leptin-mediated activation of human platelets: importance of JAK2 and the phospholipases Cgamma2 and A2.

Leptin enhances agonist-induced platelet aggregation, and human platelets have been reported to express the leptin receptor. However, the pathways and mediators lying downstream of leptin binding to platelets remain, with few exceptions, unknown. In the present study, we sought to gain further insight into the possible role of leptin as a platelet agonist. Stimulation of platelets with leptin promoted thromboxane generation and activation of alpha(IIb)beta(3), as demonstrated by PAC-1 binding. Furthermore, it increased the adhesion to immobilised fibrinogen (p<0.001) and induced cytoskeletal rearrangement of both platelets and Meg01 cells. Leptin time- and dose-dependently phosphorylated the intracellular signalling molecules JAK2 and STAT3, although the importance of STAT3 for leptin-induced platelet activation remains to be determined. Important intracellular mediators and pathways activated by leptin downstream of JAK2 were found to include phosphatidylinositol-3 kinase, phospholipase Cgamma2 and protein kinase C, as well as the p38 MAP kinase-phospholipase A(2) axis. Accordingly, incubation with the specific inhibitors AG490, Ly294002, U73122, and SB203580 prevented leptin-mediated platelet activation. These results help delineate biologically relevant leptin signalling pathways in platelets and may improve our understanding of the mechanisms linking hyperleptinaemia to the increased thrombosis risk in human obesity.