Platelets Protect Cardiomyocytes from Ischaemic Damage

Platelets are classically known for their roles in bleeding control and occlusive thrombus formation causing ischaemic tissue damage. Recently non-classical roles for platelets have been described, many of which may be mediated by the heterogeneous cargo that platelets secrete from granular stores upon activation. Using an in vitro model of ischaemic injury to ventricular cardiomyocytes, we observed that platelets, through secreted factors, delayed the rate of cardiomyocyte death during ischaemia. This protective effect appeared independent of platelet dense granule cargo, but required α-granule components stromal cell-derived factor (SDF)-1α and transforming growth factor (TGF) β1. Protein kinase C (PKC) activity within cardiomyocytes was responsible for mediating the protective signals initiated by the released platelet cargo. Importantly, pretreating platelets with a P2Y₁₂ antagonist, but not the cyclooxygenase inhibitor aspirin, substantially attenuated this protective effect. These findings therefore reveal a paradoxically protective role for platelet activation during cardiac ischaemia and could have important implications for the use of anti-platelet therapeutics in the management of myocardial infarction.