Heterotrimeric G-protein subunit Gα_i2 contributes to agonist-sensitive apoptosis and degranulation in murine...

Gα_i2 , a heterotrimeric G-protein subunit, regulates various cell functions including ion channel activity, cell differentiation, proliferation and apoptosis. Platelet-expressed Gα_i2 is decisive for the extent of tissue injury following ischemia/reperfusion. However, it is not known whether Gα_i2 plays a role in the regulation of platelet apoptosis, which is characterized by caspase activation, cell shrinkage and cell membrane scrambling with phosphatidylserine (PS) translocation to the platelet surface. Stimulators of platelet apoptosis include thrombin and collagen-related peptide (CoRP), which are further known to enhance degranulation and activation of α_IIb β3-integrin and caspases. Using FACS analysis, we examined the impact of agonist treatment on activation and apoptosis in platelets drawn from mice lacking Gα_i2 and their wild-type (WT) littermates. As a result, treatment with either thrombin (0.01 U/mL) or CoRP (2 μg/mL or 5 μg/mL) significantly upregulated PS-exposure and significantly decreased forward scatter, reflecting cell size, in both genotypes. Exposure to CoRP triggered a significant increase in active caspase 3, ceramide formation, surface P-selectin, and α_IIb β3-integrin activation. These molecular alterations were significantly less pronounced in Gα_i2 -deficient platelets as compared to WT platelets. In conclusion, our data highlight a previously unreported role of Gα_i2 signaling in governing platelet activation and apoptosis.