title: Mice Expressing Low Levels of CalDAG-GEFI Exhibit Markedly Impaired Platelet Activation With Minor Impact on Hemostasis.
abstract: The tight regulation of platelet adhesiveness, mediated by the αIIbβ3 integrin, is critical for hemostasis and prevention of thrombosis. We recently demonstrated that integrin affinity in platelets is controlled by the guanine nucleotide exchange factor, CalDAG-GEFI (CD-GEFI), and its target, RAP1. In this study, we investigated whether low-level expression of CD-GEFI leads to protection from thrombosis without pathological bleeding in mice.
  
  
  
  Cdg1(low) mice were generated by knockin of human CD-GEFI cDNA into the mouse Cdg1 locus. CD-GEFI expression in platelets from Cdg1(low) mice was reduced by ≈90% when compared with controls. Activation of RAP1 and αIIbβ3 was abolished at low agonist concentrations and partially inhibited at high agonist concentrations in Cdg1(low) platelets. Consistently, the aggregation response of Cdg1(low) platelets was weaker than that of wild-type platelets, but more efficient than that observed in Cdg1(-/-) platelets. Importantly, Cdg1(low) mice were strongly protected from arterial and immune complex-mediated thrombosis, with only minimal impact on primary hemostasis.
  
  
  
  Together, our studies suggest the partial inhibition of CD-GEFI function as a powerful new approach to safely prevent thrombotic complications.
authors.affiliation: From the McAllister Heart Institute, University of North Carolina, Chapel Hill (R.P., D.S.P., R.H.L., W.B.); Cardeza Foundation for Hematological Research, Department of Medicine, Thomas Jefferson University, Philadelphia, PA (S.E.M.); Department of Biochemistry and Biophysics (L.V.P., W.B.), Animal Models Core (D.O.C.), and Rodent Advanced Surgical Core (B.C.C.), University of North Carolina at Chapel Hill.
authors.forename: Raymond
authors.initials: R
authors.lastname: Piatt
authors.affiliation: From the McAllister Heart Institute, University of North Carolina, Chapel Hill (R.P., D.S.P., R.H.L., W.B.); Cardeza Foundation for Hematological Research, Department of Medicine, Thomas Jefferson University, Philadelphia, PA (S.E.M.); Department of Biochemistry and Biophysics (L.V.P., W.B.), Animal Models Core (D.O.C.), and Rodent Advanced Surgical Core (B.C.C.), University of North Carolina at Chapel Hill.
authors.forename: David S
authors.initials: DS
authors.lastname: Paul
authors.affiliation: From the McAllister Heart Institute, University of North Carolina, Chapel Hill (R.P., D.S.P., R.H.L., W.B.); Cardeza Foundation for Hematological Research, Department of Medicine, Thomas Jefferson University, Philadelphia, PA (S.E.M.); Department of Biochemistry and Biophysics (L.V.P., W.B.), Animal Models Core (D.O.C.), and Rodent Advanced Surgical Core (B.C.C.), University of North Carolina at Chapel Hill.
authors.forename: Robert H
authors.initials: RH
authors.lastname: Lee
authors.affiliation: From the McAllister Heart Institute, University of North Carolina, Chapel Hill (R.P., D.S.P., R.H.L., W.B.); Cardeza Foundation for Hematological Research, Department of Medicine, Thomas Jefferson University, Philadelphia, PA (S.E.M.); Department of Biochemistry and Biophysics (L.V.P., W.B.), Animal Models Core (D.O.C.), and Rodent Advanced Surgical Core (B.C.C.), University of North Carolina at Chapel Hill.
authors.forename: Steven E
authors.initials: SE
authors.lastname: McKenzie
authors.affiliation: From the McAllister Heart Institute, University of North Carolina, Chapel Hill (R.P., D.S.P., R.H.L., W.B.); Cardeza Foundation for Hematological Research, Department of Medicine, Thomas Jefferson University, Philadelphia, PA (S.E.M.); Department of Biochemistry and Biophysics (L.V.P., W.B.), Animal Models Core (D.O.C.), and Rodent Advanced Surgical Core (B.C.C.), University of North Carolina at Chapel Hill.
authors.forename: Leslie V
authors.initials: LV
authors.lastname: Parise
authors.affiliation: From the McAllister Heart Institute, University of North Carolina, Chapel Hill (R.P., D.S.P., R.H.L., W.B.); Cardeza Foundation for Hematological Research, Department of Medicine, Thomas Jefferson University, Philadelphia, PA (S.E.M.); Department of Biochemistry and Biophysics (L.V.P., W.B.), Animal Models Core (D.O.C.), and Rodent Advanced Surgical Core (B.C.C.), University of North Carolina at Chapel Hill.
authors.forename: Dale O
authors.initials: DO
authors.lastname: Cowley
authors.affiliation: From the McAllister Heart Institute, University of North Carolina, Chapel Hill (R.P., D.S.P., R.H.L., W.B.); Cardeza Foundation for Hematological Research, Department of Medicine, Thomas Jefferson University, Philadelphia, PA (S.E.M.); Department of Biochemistry and Biophysics (L.V.P., W.B.), Animal Models Core (D.O.C.), and Rodent Advanced Surgical Core (B.C.C.), University of North Carolina at Chapel Hill.
authors.forename: Brian C
authors.initials: BC
authors.lastname: Cooley
authors.affiliation: From the McAllister Heart Institute, University of North Carolina, Chapel Hill (R.P., D.S.P., R.H.L., W.B.); Cardeza Foundation for Hematological Research, Department of Medicine, Thomas Jefferson University, Philadelphia, PA (S.E.M.); Department of Biochemistry and Biophysics (L.V.P., W.B.), Animal Models Core (D.O.C.), and Rodent Advanced Surgical Core (B.C.C.), University of North Carolina at Chapel Hill. bergmeie@email.unc.edu.
authors.forename: Wolfgang
authors.initials: W
authors.lastname: Bergmeier
mesh_terms: D000818:Animals; D001792:Blood Platelets / Q000378:metabolism*; D004195:Disease Models, Animal; D005838:Genotype; D020662:Guanine Nucleotide Exchange Factors / Q000097:blood / Q000172:deficiency* / Q000235:genetics; D006487:Hemostasis; D006801:Humans; D008822:Mice, Transgenic; D009154:Mutation; D010641:Phenotype; D015539:Platelet Activation; D010974:Platelet Aggregation; D019039:Platelet Glycoprotein GPIIb-IIIa Complex / Q000378:metabolism; D015398:Signal Transduction; D013927:Thrombosis / Q000097:blood / Q000235:genetics / Q000517:prevention & control*; D013997:Time Factors; D020827:rap1 GTP-Binding Proteins / Q000097:blood
chemical_list: D020662:Guanine Nucleotide Exchange Factors; D019039:Platelet Glycoprotein GPIIb-IIIa Complex; C415483:RASGRP2 protein, human; D020827:rap1 GTP-Binding Proteins
keywords: hemostasis; mouse; platelet; signal transduction; small GTPase; thrombosis