Activation of the platelet Fc receptor, Fc?RIIA, is central to the pathogenesis of several immune- mediated thrombocytopenia and thrombosis (ITT) syndromes, including heparin-induced thrombocytopenia/thrombosis. One of the barriers to successful treatment of these thrombotic syndromes is that therapeutic targeting of platelet activation pathways to prevent thrombosis is either not effective or comes with an inherent risk of bleeding complications. The purpose of this proposal is a) to identify critical signaling molecules, which preferentially contribute to Fc?RIIA- mediated platelet activation and b) to develop therapeutic anti-platelet strategies to prevent pathologic thrombosis in ITT while minimizing bleeding complications. Our preliminary studies identify the tyrosine kinase Syk, the Ser/Thr kinase Akt, and the Ca2+ sensor CalDAG-GEFI as promising new targets for antiplatelet therapy in the setting of ITT. Downstream of ITAM-coupled receptors like Fc?RIIA, Syk is important for the activation of phospholipase C?2 and thus the generation of the second messengers Ca2+ and diacylglycerol. CalDAG-GEFI links an increase in intracellular Ca2+ to the signaling pathways regulating integrin activation, thromboxane generation, and granule release. Preliminary studies on Akt demonstrate that it is important for Fc?RIIA-induced calcium flux and integrin activation, thus linking it to Syk and CalDAG-GEFI. Preliminary results as well as work by us and others further demonstrate that Syk, CalDAG- GEFI, and Akt are particularly important for Fc?RIIA/ITAM-mediated platelet activation. With the proposed studies, we will improve our understanding of the molecular mechanisms by which CalDAG-GEFI (aim 1) and Akt (aim 2) contribute to Fc?RIIA-mediated platelet activation.
In aim 3, we will validate Syk and Akt and explore CalDAG-GEFI as therapeutic targets in ITT. The safety and efficacy of pharmacologic inhibition of Syk and Akt for the treatment and prevention of ITT will be tested in our established mouse models. The utility of CalDAG-GEFI or Akt2 as therapeutic targets for the treatment of ITT will be evaluated in crosses between mice transgenic for the human Fc?RIIA and mice knockout for CalDAG-GEFI or Akt2. The successful completion of this proposal will accelerate the rational design of novel therapeutics for immune-mediated platelet disorders.

Public Health Relevance

The human platelet Fc receptor, Fc?RIIA, has been implicated in several hematological disorders characterized by immune-mediated thrombocytopenia and/or thrombosis (ITT). We have identified 3 signaling molecules, which preferentially mediate Fc?RIIA- dependent platelet activation and thus may make effective targets for the treatment or prevention of ITT. The successful completion of this proposal will accelerate the rational design of novel therapeutics for immune-mediated platelet disorders.

Agency
National Institute of Health (NIH)
Type
Research Project (R01)
Project #
5R01HL106009-04
Application #
8693003
Study Section
Hemostasis and Thrombosis Study Section (HT)
Program Officer
Kindzelski, Andrei L
Project Start
Project End
Budget Start
Budget End
Support Year
4
Fiscal Year
2014
Total Cost
Indirect Cost
Name
University of North Carolina Chapel Hill
Department
Biochemistry
Type
Schools of Medicine
DUNS #
City
Chapel Hill
State
NC
Country
United States
Zip Code
27599
Bergmeier, Wolfgang; Boulaftali, Yacine (2014) Adoptive transfer method to study platelet function in mouse models of disease. Thromb Res 133 Suppl 1:S3-5
Boulaftali, Yacine; Hess, Paul R; Kahn, Mark L et al. (2014) Platelet immunoreceptor tyrosine-based activation motif (ITAM) signaling and vascular integrity. Circ Res 114:1174-84
McKenzie, Steven E; Sachais, Bruce S (2014) Advances in the pathophysiology and treatment of heparin-induced thrombocytopenia. Curr Opin Hematol 21:380-7
Amirkhosravi, A; Boulaftali, Y; Robles-Carrillo, L et al. (2014) CalDAG-GEFI deficiency protects mice from Fc?RIIa-mediated thrombotic thrombocytopenia induced by CD40L and ?2GPI immune complexes. J Thromb Haemost 12:2113-9
Stefanini, Lucia; Ye, Feng; Snider, Adam K et al. (2014) A talin mutant that impairs talin-integrin binding in platelets decelerates ?IIb?3 activation without pathological bleeding. Blood 123:2722-31
Bergmeier, Wolfgang; Stefanini, Lucia (2013) Platelet ITAM signaling. Curr Opin Hematol 20:445-50
Boulaftali, Yacine; Hess, Paul R; Getz, Todd M et al. (2013) Platelet ITAM signaling is critical for vascular integrity in inflammation. J Clin Invest 123:908-16
Stolla, M C; Li, D; Lu, L et al. (2013) Enhanced platelet activity and thrombosis in a murine model of type I diabetes are partially insulin-like growth factor 1-dependent and phosphoinositide 3-kinase-dependent. J Thromb Haemost 11:919-29
Holly, Stephen P; Chang, Jae Won; Li, Weiwei et al. (2013) Chemoproteomic discovery of AADACL1 as a regulator of human platelet activation. Chem Biol 20:1125-34