SummaryLeptin 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 αIIbβ3, 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 Cγ2 and protein kinase C, as well as the p38 MAP kinase-phospholipase A2 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.
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 µg/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 α-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 cellsin vitro suggested that 10 µg TPM/ml increased cell proliferation without affecting viability or apoptosis, whereas higher concentrations (100 and 500 µg 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.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.