The goal of this proposal is to define the intracellular signaling pathways that contribute to the synthesis of phosphorylated phosphatidylinositols (phosphoinositides) in platelets, and to understand the role of phosphoinositides in platelet biology. Our recent research has focused on the synthesis of two phosphatidylinositol bisphosphates, PtdIns(4,5)P2 and PtdIns(3,5)P2. The hypotheses underlying this proposal are that the synthesis of PtdIns(4,5)P2 and PtdIns(3,5)P2 occurs within unique microdomains in platelets, and that PtdIns(4,5)P2 and PtdIns(3,5)P2 are each responsible for discrete aspects of platelet signaling and in vivo thrombus formation. We have studied the synthesis of PtdIns(4,5)P2 by the ?, ?, and ? isoforms of phosphatidylinositol phosphate 5-kinase I (PIP5KI), and found clear evidence that spatially distinct pools of PtdIns(4,5)P2 exist in platelets and in megakaryocytes. Moreover, the loss of either PIP5KI? or PIP5KI? leads to impaired in vivo thrombosis, but for different reasons. The pool of PtdIns(4,5)P2 that is synthesized by PIP5KI? is required to form second messengers and to extend lamellipodia. In contrast, PtdIns(4,5)P2 synthesized by PIP5KI? is vital for the membranecytoskeletal dynamics and allows for stable adhesion that is resistant to shear forces. We have also found that PtdIns(3,5)P2, which is synthesized by PIKFyve, regulates the biogenesis of platelet lysosomes. Deletion of PIKFyve specifically in murine platelets leads to a platelet lysosome disorder, which remarkably is associated with inflammation and accelerated thrombus formation in vivo. Taken together, these results support the hypothesis that the synthesis of particular phosphoinositides within discrete platelet subcellular microdomains regulates specific spatially distinct intracellular signaling pathways. The proposed experiments are designed to comprehensively and systematically study how PtdIns(4,5)P2 and PtdIns(3,5)P2 production regulates the platelet cytoskeleton and lysosomes. We will also study their effect on stable platelet adhesion in vivo.
In Aim 1, we will determine how PtdIns(4,5)P2 regulates platelet membrane-cytoskeletal dynamics.
In Aim 2, we will examine the spatial regulation of PtdIns(4,5)P2 synthesis. In the final Aim, we will formally analyze how PtdIns(3,5)P2 regulates the biology of the platelet lysosome and its contribution to in vivo thrombus formation.
PROJECT 5 - NARRATIVE Platelets and macrophages both play key roles in the pathogenesis of atherosclerosis as well as arterial thrombosis that lead to acute myocardial infarctions and strokes. This proposal will analyze a previously unrecognized link between platelet secretion and macrophage activation. A better understanding of this process will identify novel therapeutic targets that could be used to treat arterial thrombosis, the most common cause of morbidity and mortality in the US.
|Fong, Karen P; Zhu, Hua; Span, Lisa M et al. (2016) Directly Activating the Integrin Î±IIbÎ²3 Initiates Outside-In Signaling by Causing Î±IIbÎ²3 Clustering. J Biol Chem 291:11706-16|
|Lee, R H; Bergmeier, W (2016) Platelet immunoreceptor tyrosine-based activation motif (ITAM) and hemITAM signaling and vascular integrity in inflammation and development. J Thromb Haemost 14:645-54|
|Stefanini, Lucia; Bergmeier, Wolfgang (2016) RAP1-GTPase signaling and platelet function. J Mol Med (Berl) 94:13-9|
|Lozano, MarÃa Luisa; Cook, Aaron; Bastida, JosÃ© MarÃa et al. (2016) Novel mutations in RASGRP2, which encodes CalDAG-GEFI, abrogate Rap1 activation, causing platelet dysfunction. Blood 128:1282-9|
|Zhou, Zinan; Tang, Alan T; Wong, Weng-Yew et al. (2016) Cerebral cavernous malformations arise from endothelial gain of MEKK3-KLF2/4 signalling. Nature 532:122-6|
|Welsh, John D; Muthard, Ryan W; Stalker, Timothy J et al. (2016) A systems approach to hemostasis: 4. How hemostatic thrombi limit the loss of plasma-borne molecules from the microvasculature. Blood 127:1598-605|
|Geddings, J E; Hisada, Y; Boulaftali, Y et al. (2016) Tissue factor-positive tumor microvesicles activate platelets and enhance thrombosis in mice. J Thromb Haemost 14:153-66|
|Piatt, Raymond; Paul, David S; Lee, Robert H et al. (2016) Mice Expressing Low Levels of CalDAG-GEFI Exhibit Markedly Impaired Platelet Activation With Minor Impact on Hemostasis. Arterioscler Thromb Vasc Biol 36:1838-46|
|Ivanciu, L; Stalker, T J (2015) Spatiotemporal regulation of coagulation and platelet activation during the hemostatic response inÂ vivo. J Thromb Haemost 13:1949-59|
|Sayani, Farzana A; Abrams, Charles S (2015) How I treat refractory thrombotic thrombocytopenic purpura. Blood 125:3860-7|
Showing the most recent 10 out of 28 publications