Protein disulfide isomerase (PDI) catalyzes the reversible formation and isomerization of disulfide bonds in proteins. This proposal focuses on two members of the PDI family-the traditional PDI, and a more recently discovered member of the PDI family, ERp57. We found that PDI mediates platelet aggregation, and intravascular PDI has been shown to be required for thrombus formation. We recently showed that ERp57 mediates platelet aggregation, hemostasis and thrombosis. ERp57 and PDI are involved in conversion of IIb3 to its high affinity state; however, the mechanisms by which they regulate IIb3 and platelet aggregation are unknown. Furthermore, there are now up to 20 different members of the PDI family, and a number of these are found in platelets. How these enzymes function together remains a mystery. Previous approaches have generally used non-specific inhibitors of PDI to document a role for PDI in platelet function and thrombosis. Newer approaches are therefore required to define the molecular roles of each enzyme, as well as the intravascular sources of these enzymes. We have generated targeted knockout mice with platelets specific deficiencies in ERp57 and in PDI, and transgenic mice with a mutant PDI. We have also generated an antibody to ERp57 that despite the high homology between ERp57 and PDI does not inhibit PDI. Our current goal is to characterize the role of intravascular and platelet-derived ERp57 in platelet function and thrombus formation. We will also characterize the role of platelet-derived PDI in platelet function and thrombosis. We hypothesize that platelets provide an essential source of these enzymes for hemostasis and thrombosis.
The specific aims are to: 1. Characterize the role of intravascular and platelet-derived ERp57 in platelet accumulation and fibrin generation, and the role of platelet-derived ERp57 in platelet function; 2. Characterize the role of platelet-derived PDI in platelet function, thrombosis, platelt accumulation, and fibrin generation; and 3. Characterize the mechanism of activation of IIb3 by ERp57 and PDI. A principal technique used will be the laser-induced injury model of thrombosis. To determine the mechanisms by which ERp57 and PDI work, we will employ a thiol labeling strategy with mass spectrometry identification of the labeled thiols. We will determine the role of platelet-derived ERp57 and PDI in platelet function and thrombosis, and begin to unravel the mechanisms by which these enzymes work. Determining the extracellular redox mechanisms required for the final steps in the activation of IIb3 is a highly significant aspect of platelet function and thrombus formation that could lead to novel types of inhibitors or ways to regulate platelet aggregation.

Public Health Relevance

Platelets are small circulating blood cells that are important in bleeding cessation after injury and in formation of blood clots that cause heart attacks and strokes. Thrombotic disorders involving platelets are a leading cause of morbidity and mortality in the United States. This project focuses on defining the mechanisms by which platelets form clots. Insight into the specific mechanisms could lead to novel ways to regulate her inhibit platelet aggregation for the prevention of thrombotic disorders.

National Institute of Health (NIH)
National Heart, Lung, and Blood Institute (NHLBI)
Research Project (R01)
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Special Emphasis Panel (ZRG1)
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Sarkar, Rita
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Temple University
Internal Medicine/Medicine
Schools of Medicine
United States
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Chen, Fengwu; Zhao, Zhenzhen; Zhou, Junsong et al. (2018) Protein disulfide isomerase enhances tissue factor-dependent thrombin generation. Biochem Biophys Res Commun 501:172-177
Zhou, Junsong; Wu, Yi; Chen, Fengwu et al. (2017) The disulfide isomerase ERp72 supports arterial thrombosis in mice. Blood 130:817-828
Wang, L; Essex, D W (2017) A new antithrombotic strategy: inhibition of the C-terminal active site of protein disulfide isomerase. J Thromb Haemost 15:770-773
Zhou, Junsong; Wu, Yi; Wang, Lu et al. (2015) The C-terminal CGHC motif of protein disulfide isomerase supports thrombosis. J Clin Invest 125:4391-406
Zhou, J; Wu, Y; Wang, L et al. (2014) The disulfide isomerase ERp57 is required for fibrin deposition in vivo. J Thromb Haemost 12:1890-7
Wang, Lu; Wu, Yi; Zhou, Junsong et al. (2013) Platelet-derived ERp57 mediates platelet incorporation into a growing thrombus by regulation of the ?IIb?3 integrin. Blood 122:3642-50