Platelet ADP Receptor P2Y12 Stabilizes Atherosclerosis Plaques by Regulating Alpha Granule Release and Inflammatory Cell Recruitment

Atherosclerosis, a major cause of cardiovascular disease, is a complicated chronic inflammatory process. A variety of data demonstrate that platelets are crucial players in this pathological process. Platelet activation results in a-granule secretion and the secreted materials include adhesive proteins, chemokines and growth factors, which attract and mediate continuous inflammatory cell attachment to, and infiltration of dysfunctional endothelium and atherosclerotic plaques. Here, we show that the ablation of P2Y12, an ADP receptor highly expressed in platelets and smooth muscle cells, can significantly decrease monocyte infiltration of the aortic root, and thereby negatively affect enlargement of the atherosclerotic lesion in ApoE−/− mice fed on a high fat diet for 5 months. Ablation of P2Y12 in ApoE−/− mice also stabilizes the atherosclerotic plaques that do form in the double knockout mice. Plaque stability was demonstrated by Immunohistochemistry studies that revealed greater fibrous and diminished macrophage content in the atherosclerotic plaques. Bone marrow transplantation experiments confirmed that platelet P2Y12, but not smooth muscle P2Y12, is the key factor responsible for atherosclerosis formation. Further work demonstrated that P2Y12, through inhibition of the cAMP/PKA signaling pathway, critically regulates platelet expression of p-selectin and the release of PF4. This demonstration is crucial because PF4 is a chemokine documented to be important for atherosclerosis development. The results of in vitro assays demonstrated that under standard conditions, P2Y12+/+ platelets, but not P2Y12−/− platelets, released their a-granule contents during platelet activation and thereby enhanced monocyte migration. Compared to results obtained using P2Y12+/+ApoE−/− mice under the same conditions, the basal levels of PF4 and SDF-1a in platelet-poor plasma were significantly lower in P2Y12−/−ApoE−/− double knockout mice fed a high-fat diet, thereby providing in vivo support for our thesis that P2Y12 affects atherogenesis by regulating a-granule secretion. Our results point out that platelet P2Y12 modulates atherogenesis primarily through regulation of a-granule release, and secondarily by the resulting inflammatory cell recruitment, and therefore serves as a potential drug target for atherosclerosis prevention, in addition to being the target for prevention of thrombus formation in response to plaque rupture.

No relevant conflicts of interest to declare.