Abstract
BACKGROUND: Although the role of thrombin in atherothrombosis is well studied, its role in the pathogenesis of diet-induced atherosclerosis is not known. METHODS: Using a mouse model of diet-induced atherosclerosis and molecular biological approaches, here we have explored the role of thrombin and its G protein-coupled receptor signaling in diet-induced atherosclerosis. RESULTS: In exploring the role of G protein-coupled receptor signaling in atherogenesis, we found that thrombin triggers foam cell formation via inducing CD36 expression, and these events require Par1-mediated Gα12-Pyk2-Gab1-protein kinase C (PKC)θ-dependent ATF2 activation. Genetic deletion of PKCθ in apolipoprotein E (ApoE)(-/-) mice reduced Western diet-induced plaque formation. Furthermore, thrombin induced Pyk2, Gab1, PKCθ, and ATF2 phosphorylation, CD36 expression, and foam cell formation in peritoneal macrophages of ApoE(-/-) mice. In contrast, thrombin only stimulated Pyk2 and Gab1 but not ATF2 phosphorylation or its target gene CD36 expression in the peritoneal macrophages of ApoE(-/-):PKCθ(-/-) mice, and it had no effect on foam cell formation. In addition, the aortic root cross-sections of Western diet-fed ApoE(-/-) mice showed increased Pyk2, Gab1, PKCθ, and ATF2 phosphorylation and CD36 expression as compared with ApoE(-/-):PKCθ(-/-) mice. Furthermore, although the monocytes from peripheral blood and the aorta of Western diet-fed ApoE(-/-) mice were found to contain more of Ly6C(hi) cells than Ly6C(lo) cells, the monocytes from Western diet-fed ApoE(-/-):PKCθ(-/-) mice were found to contain more Ly6C(lo) cells than Ly6C(hi) cells. It is interesting to note that the Ly6C(hi) cells showed higher CD36 expression with enhanced capacity to form foam cells as compared with Ly6C(lo) cells. CONCLUSIONS: These findings reveal for the first time that thrombin-mediated Par1-Gα12 signaling via targeting Pyk2-Gab1-PKCθ-ATF2-dependent CD36 expression might be playing a crucial role in diet-induced atherogenesis.