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PAR1, but not PAR4, regulates human platelet activation through PLD
Author(s) -
Holinstat Michael,
Voss Bryan,
Bilodeau Matthew L,
Hamm Heidi E
Publication year - 2006
Publication title -
the faseb journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.709
H-Index - 277
eISSN - 1530-6860
pISSN - 0892-6638
DOI - 10.1096/fasebj.20.4.a695-d
Subject(s) - platelet activation , thrombin , platelet , chemistry , signal transduction , microbiology and biotechnology , p2y12 , pharmacology , propranolol , endocrinology , medicine , platelet aggregation , biochemistry , biology
Thrombin induces platelet activation in humans through two receptors, PAR1 and PAR4. Current anti‐platelet therapies result in excessive bleeding as a common side effect. A better understanding of thrombin regulation of platelet activation will aid in future development of anti‐platelet therapeutics with a better side effect profile. To address how thrombin regulates platelet activation, we have investigated the differential signaling pathways activated by the PARs in human platelets. Our findings establish a unique role for PAR1 and PAR4 in thrombin‐mediated platelet activation. In order to investigate PAR1 versus PAR4 signaling, we have utilized assays for Rap1 activation, flow cytometry, platelet aggregation and secretion. We observed that inhibiting the PLD‐induced formation of diacyglycerol with Propranolol, 1‐Butanol or Ethanol caused a reversal of PAR1‐mediated platelet activation, whereas these inhibitors had minimal effect on thrombin or PAR4‐mediated aggregation. Nadolol, a non‐specific β‐adrenergic inhibitor, had no effect on PAR1‐induced platelet aggregation confirming the effect of Propranolol on PAR1 was not caused by inhibition of β‐agrenergic receptors. Likewise, tertiary Butanol, a negative control for 1‐Butanol, had no inhibitory effect on PAR1‐mediated aggregation. Further, PAR1‐induced Rap1 activation appears to be altered following Propranolol, whereas no effect was observed with thrombin or PAR4. These findings indicate that PAR1 signals through PLD whereas PAR4‐mediated platelet activation appears to be PLD independent. A testable model of PAR1 versus PAR4 mediated platelet activation will allow for the identification of new targets for anti‐platelet drug intervention without the classical side effects of excessive bleeding.