PDK1 Determines Collagen-Dependent Platelet Ca2+ Signaling and Is Critical to Development of Ischemic Stroke In Vivo

Objective—Activation of platelets by subendothelial collagen results in an increase of cytosolic Ca2+ concentration ([Ca2+]i) and is followed by platelet activation and thrombus formation that may lead to vascular occlusion. The present study determined the role of phosphoinositide-dependent protein kinase 1 (PDK1) in collagen-dependent platelet Ca2+ signaling and ischemic stroke in vivo. Approach and Results—Platelet activation with collagen receptor glycoprotein VI agonists collagen-related peptide or convulxin resulted in a significant increase in PDK1 activity independent of second-wave signaling. PDK1 deficiency was associated with reduced platelet phospholipase Cγ2–dependent inositol-1,4,5-trisphosphate production and intracellular [Ca2+]i in response to stimulation with collagen-related peptide or convulxin. The defective increase of [Ca2+]i resulted in a substantial defect in activation-dependent platelet secretion and aggregation on collagen-related peptide stimulation. Furthermore, Rac1 activati...