Imaging analysis of phosphatidylserine-evoked initiation of coagulation cascade on activated platelets surface.

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(1) Analyses of the regulatory mechanisms on PS exposure on platelets' surface and its contribution to micro-particle bearing TF-evoked activation of coagulation cascade.Exposure of PS on platelets' surface plays essential role in thrombus formation. Based on our recent finding in in-vivo study that platelets expose PS only when they exist in the center of the thrombus, we analyzed the factors to regulate PS exposure on platelets surface. To elucidate how PS exposure is regulated within the thrombus, we analyzed PS exposure on platelets existing in fibrin network using diluted platelet-rich plasma by Confocal Laser Scanning Microscopy. Almost all platelets bound to fibrin scaffold and exposed PS after treatment with TF, thrombin or ionomycin. An attenuation of fibrin mesh formation by several pharmacological methods suppressed PS exposure. FK633, a GPIIb/IIIa antagonist, entirely inhibited fibrin(ogen) binding abrogated fibrin network formation, but also reduced PS exposure without suppressing fibrin(ogen) binding. Cytochalasin B impaired both platelets' binding to fibrin(ogen) and PS exposure. These results suggest that GPIIb/IIIa-mediated outside-in signals in platelets generated by the binding to fibrin scaffold and the associated mechanical foci, appear to be essential for PS exposure. Such regulation of platelet PS exposure may play an important role in the control of hemostasis.(submitted)U937 cells were treated by calcium ionophore, and TF bearing microparticles were obtained. Supplementation of the TF-bearing microparticle to the system mentioned above, successfully generated fibrin network. We stared to analyze the space-and time-dependent interaction between TF bared on microparticle and PS exposed on activated platelets both of which are essential to activate coagulation cascade.