title: PPARγ agonists negatively regulate αIIbβ3 integrin outside-in signaling and platelet function through up-regulation of protein kinase A activity.
abstract: Essentials peroxisome proliferator-activated receptor γ (PPARγ) agonists inhibit platelet function. PPARγ agonists negatively regulate outside-in signaling via integrin αIIbβ3. PPARγ agonists disrupt the interaction of Gα13 with integrin β3. This is attributed to an upregulation of protein kinase A activity.
  
  
  
  Background Agonists for the peroxisome proliferator-activated receptor (PPARγ) have been shown to have inhibitory effects on platelet activity following stimulation by GPVI and GPCR agonists. Objectives Profound effects on thrombus formation led us to suspect a role for PPARγ agonists in the regulation of integrin αIIbβ3 mediated signaling. Both GPVI and GPCR signaling pathways lead to αIIbβ3 activation, and signaling through αIIbβ3 plays a critical role in platelet function and normal hemostasis. Methods The effects of PPARγ agonists on the regulation of αIIbβ3 outside-in signaling was determined by monitoring the ability of platelets to adhere and spread on fibrinogen and undergo clot retraction. Effects on signaling components downstream of αIIbβ3 activation were also determined following adhesion to fibrinogen by Western blotting. Results Treatment of platelets with PPARγ agonists inhibited platelet adhesion and spreading on fibrinogen and diminished clot retraction. A reduction in phosphorylation of several components of αIIbβ3 signaling, including the integrin β3 subunit, Syk, PLCγ2, focal adhesion kinase (FAK) and Akt, was also observed as a result of reduced interaction of the integrin β3 subunit with Gα13. Studies of VASP phosphorylation revealed that this was because of an increase in PKA activity following treatment with PPARγ receptor agonists. Conclusions This study provides further evidence for antiplatelet actions of PPARγ agonists, identifies a negative regulatory role for PPARγ agonists in the control of integrin αIIbβ3 outside-in signaling, and provides a molecular basis by which the PPARγ agonists negatively regulate platelet activation and thrombus formation.
authors.affiliation: Institute for Cardiovascular and Metabolic Research, School of Biological Sciences, University of Reading, Reading, UK.
authors.forename: A J
authors.initials: AJ
authors.lastname: Unsworth
authors.affiliation: Institute for Cardiovascular and Metabolic Research, School of Biological Sciences, University of Reading, Reading, UK.
authors.forename: N
authors.initials: N
authors.lastname: Kriek
authors.affiliation: Institute for Cardiovascular and Metabolic Research, School of Biological Sciences, University of Reading, Reading, UK.
authors.forename: A P
authors.initials: AP
authors.lastname: Bye
authors.affiliation: Institute for Cardiovascular and Metabolic Research, School of Biological Sciences, University of Reading, Reading, UK.
authors.forename: K
authors.initials: K
authors.lastname: Naran
authors.affiliation: Institute for Cardiovascular and Metabolic Research, School of Biological Sciences, University of Reading, Reading, UK.
authors.forename: T
authors.initials: T
authors.lastname: Sage
authors.affiliation: Institute for Cardiovascular and Metabolic Research, School of Biological Sciences, University of Reading, Reading, UK.
authors.forename: G D
authors.initials: GD
authors.lastname: Flora
authors.affiliation: Institute for Cardiovascular and Metabolic Research, School of Biological Sciences, University of Reading, Reading, UK.
authors.forename: J M
authors.initials: JM
authors.lastname: Gibbins
mesh_terms: D000818:Animals; D001792:Blood Platelets / Q000378:metabolism*; D002417:Cattle; D002448:Cell Adhesion; D003018:Clot Retraction; D003094:Collagen / Q000737:chemistry; D017868:Cyclic AMP-Dependent Protein Kinases / Q000378:metabolism*; D005340:Fibrinogen / Q000737:chemistry; D044365:GTP-Binding Protein alpha Subunits, G12-G13 / Q000378:metabolism; D006487:Hemostasis; D006801:Humans; D039661:Integrin beta3 / Q000378:metabolism; D047495:PPAR gamma / Q000819:agonists*; D010766:Phosphorylation; D015539:Platelet Activation / Q000187:drug effects; D010973:Platelet Adhesiveness; D010974:Platelet Aggregation / Q000187:drug effects; D010979:Platelet Function Tests; D019039:Platelet Glycoprotein GPIIb-IIIa Complex / Q000378:metabolism*; D010980:Platelet Membrane Glycoproteins / Q000378:metabolism; D015398:Signal Transduction; D015854:Up-Regulation
chemical_list: D039661:Integrin beta3; D047495:PPAR gamma; D019039:Platelet Glycoprotein GPIIb-IIIa Complex; D010980:Platelet Membrane Glycoproteins; D005340:Fibrinogen; D003094:Collagen; D017868:Cyclic AMP-Dependent Protein Kinases; D044365:GTP-Binding Protein alpha Subunits, G12-G13
keywords: PPAR gamma; blood platelets; platelet activation; platelet glycoprotein GPIIb-IIIa complex; protein kinase A