Although the role of thrombin in atherothrombosis is well studied, its role in the pathogenesis of diet-induced atherosclerosis is not known.

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.

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.

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.