The overall goal of the White lab is to understand the signaling pathways that mediate the hemostatic responses of blood platelets. Understanding these responses at a molecular level permits the development of methods to selectively and precisely manipulate those pathways, thereby controlling vascular diseases like heart attacks and strokes. A current focus is the role of rap1b, a low molecular weight GTP binding protein member of the ras superfamily, which is present in high concentrations in platelets and plays a role in the activation in platelets, including platelet aggregation, the integrin-mediated interaction of one platelet with another to form a platelet hemostatic plug. Rap1b also plays a role in the inhibition of platelets by cyclic AMP. Thus, rap1b appears to be positioned as a unique and critical bi-directional modulator of platelet activation. Using knock-out and transgenic mice combined with proteomic and genetic approaches like yeast two-hybrid screening, we are exploring the pathway(s) by which rap1b and other proteins mediate signals from G-protein coupled receptors such as P2Y12 to integrins like αIIbβ3 that mediate platelet aggregation. We are also exploring the pathway(s) that link cyclic AMP and rap1b. Understanding the rap1b-dependent pathways that are involved in mediating platelet responses will provide new ways to control platelet in vascular diseases.
Montage of platelet responses. Starting with the upper left panel, platelet low molecular weight G proteins rac and rho are involved in cytoskeletal rearrangements; rap1b knockout platelets (-/-) have an impaired response to collagen; signal transduction pathway from P2Y12 to aIIbb3 integrin; GDP/GTP exchange cycle for rap1b
Video microscopy of platelets adhering to fibrinogen. Rap1b deficient (left, -/-) and normal (right, +/+) platelets were exposed to glass microscope slides coated with fibrinogen for five minutes. Normal platelets extend pseudopods and spread on the fibrinogen. Rap1b deficient platelets attach normally but do not spread normally on the fibrinogen.
NIH: R01 (NHLBI) “Role of Carboxyterminal Hypervariable Region in Rap1b Function”, 2009- 2012
NIH: T32 (NHLBI) “Research Training in Transfusion Medicine”, 2008-2013
NIH: UL1 (NCRR), “Clinical and Translational Science Award”, Co-PI, 2010-2015
NIH: C06 (NCRR), “Initiative in Stem Cell Biology”, 2010-2015
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