HEMOSTASIS, THROMBOSIS, AND VASCULAR BIOLOGY Insulin-like growth factor-1 regulates platelet activation through PI3-K isoform

Platelets release insulin-like growth factor-1 (IGF-1) from granules upon activation. We have investigated the regulation of IGF-1 in Gi-dependent pathways leading to Akt activation and the role of IGF-1 in platelet activation. IGF-1 alone failed to induce platelet aggregation, but IGF-1 potentiated 2-MeSADP–induced platelet aggregation in a concentrationdependent manner. IGF-1 triggered platelet aggregation in combination with selective P2Y1 receptor activation. IGF-1 also caused platelet aggregation without shape change when combined with selective Gz stimulation by epinephrine, suggesting the role of IGF-1 in platelet aggregation by supplementing Gi pathways. The potentiating effect of IGF-1 was not affected by intracellular calcium chelation. Importantly, IGF-1 was unable to potentiate platelet aggregation by the phosphatidylinositol 3-kinase (PI3-K) inhibitor wortmannin, suggesting a critical regulation by PI3-K. Moreover, the potentiating effect of IGF-1 was abolished by the presence of PI3-K p110 inhibitor PIK-75. Stimulation of platelets with IGF-1 resulted in phosphorylation of Akt, a downstream effector of PI3-K, which was completely inhibited by wortmannin. IGF-1induced Akt phosphorylation was abolished by PIK-75 suggesting the contribution of PI3-K p110 for activation of Akt by IGF-1. These results demonstrate that IGF-1 plays a role in potentiating platelet aggregation by complementing Gibut not Gq-signaling pathways via PI3-K p110 . (Blood. 2007;110:4206-4213)