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Loss of serotonin transporter function alters ADP‐mediated αIIbβ3 activation through disregulation of 5HT 2A receptor
Author(s) -
Oliver Kendra H,
Hamm Heidi,
Carneiro Ana M. D.
Publication year - 2016
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.30.1_supplement.943.10
Subject(s) - serotonergic , ketanserin , serotonin , platelet , serotonin transporter , 5 ht receptor , citalopram , platelet activation , medicine , endocrinology , receptor , serotonin plasma membrane transport proteins , chemistry , pharmacology , biology
Clinical observations indicate that patients taking selective serotonin reuptake inhibitors (SSRIs) have an increased risk of bleeding. However it remains unclear how SSRIs, which inhibit the serotonin transporter (SERT), modulate hemostasis, particularly platelet activation. 5HT (serotonin, 5‐hydroxytryptamine) is taken up by platelets via SERT and activates the 5HT 2A receptor, the only serotonergic receptor found on platelets. αIIbβ3 is an integrin that binds fibrinogen and plays a critical role in platelet aggregation, which is central to hemostasis and thrombosis. Futhermore, it is known that αIIbβ3 and SERT interact genetically, physically, and functionally. To gain a clearer understanding of how SERT function regulates platelet activity we examined two independent models of SERT inhibition – constitutive genetic deletion (SERT −/− ) and 6‐day water citalopram administration. As observed in clinical populations, whole blood 5HT was drastically reduced in SERT −/− and 6‐day water citalopram‐treated mice. This suggests that, through SERT, platelets are the major storage site for 5HT in whole blood. In this model of altered serotonergic peripheral tone, SERT −/− platelets respond normally to PAR4‐AP activation, but ADP‐mediated αIIbβ3 activation is decreased as assessed by JON/a binding. Additionally while 5HT alone does not cause any platelet activation in SERT +/+ , 5HT synergizes with submaximal ADP to potentiate αIIbβ3 activation. We next tested if the 5HT‐ADP synergy remained intact in SERT −/− platelets by adding exogenous 5HT. Strikingly, we found that 5HT was unable to potentiate ADP‐mediated αIIbβ3 activation in SERT −/− platelets. Blocking 5HT 2A receptor with an antagonist, ketanserin (50nM), inhibited ADP‐mediated αIIbβ3 activation, suggesting that 5HT‐ADP synergy could be mediated through activation of the 5HT 2A receptor. We hypothesized that SERT −/− platelets may not respond to 5HT due to an alteration in 5HT 2A receptor and found that surface expression of 5HT 2A receptor was reduced in SERT −/− platelets. SERT −/− platelet membranes incubated with a 5HT 2A agonist, DOI, also exhibited reduced 35S GTPys incorporation as compared to SERT +/+ . These findings suggest that long‐term inhibition of SERT leads to reduced 5HT 2A receptor‐dependent potentiation of αIIbβ3 activation. Additional experiments are required to investigate the mechanism governing altered surface expression of 5HT 2A receptor and ADP‐receptor status in SERT −/− platelets. However, these findings suggest a novel mechanism central to the increased bleeding observed in patients taking SSRIs and support the continued investigation of 5HT 2A receptor inhibitor as anti‐platelet drugs for treatment of cardiovascular diseases. Support or Funding Information 14PRE19640007 AHA Pre‐doctoral Fellowship