Serotonin stimulates platelet receptor shedding by tumor necrosis factor-alpha-converting enzyme (ADAM17).
BACKGROUND
Peripheral serotonin (5-hydroxytryptamine, 5-HT) is transported by platelets and released upon stimulation. In the platelet cytoplasm, 5-HT is transamidated to small GTPases, promoting alpha-granule release and primary hemostasis.


OBJECTIVE
We hypothesized that 5-HT could also stimulate platelet receptor shedding after binding to the membrane 5-HT receptor (5-HT2AR).


METHODS
Western blot and flow cytometry were used to determine levels of the adhesion receptor glycoprotein (GP)Ibalpha on platelets or its shed fragment glycocalicin in plasma and serum from wild-type mice, Tph1(-/-) mice lacking peripheral 5-HT, and mice lacking functional tumor necrosis factor-alpha-converting enzyme (TACE, ADAM17). Flow chamber experiments and intravital microscopy were used to examine the adhesive properties of platelets after stimulation of 5-HT2AR.


RESULTS
Glycocalicin was significantly reduced in Tph1(-/-) plasma and serum. In isolated platelets, 5-HT induced shedding of GPIbalpha, which was increased to 60% when 5-HT uptake was inhibited by the selective serotonin reuptake inhibitor fluoxetine. Specific 5-HT2AR agonism and antagonism suggested activation of this receptor. The shedding could not be induced in TACE(DeltaZn/DeltaZn) platelets, suggesting that activated TACE mediated the shedding of GPIbalpha. Intracellular signaling involved phosphorylation of p38 mitogen-activated protein kinase rather than G-protein signaling. 5-HT2AR stimulation decreased platelet adhesion to collagen-bound von Willebrand factor under arterial shear (1500 s(-1)) and incorporation into FeCl3-induced thrombi in mesenteric arterioles.


CONCLUSIONS
Stimulation of 5-HT2AR on platelets induces TACE-mediated shedding of GPIbalpha, the key adhesion molecule under high shear conditions. Our observations demonstrate a new pathway through which 5-HT could modulate cardiovascular disease.
Duerschmied
D
D
Immune Disease Institute, Harvard Medical School, Boston, MA 02115, USA.
Canault
M
M
Lievens
D
D
Brill
A
A
Cifuni
S M
SM
Bader
M
M
Wagner
D D
DD
D051722:ADAM Proteins / Q000502:physiology*; D000072198:ADAM17 Protein; D000818:Animals; D001792:Blood Platelets / Q000378:metabolism*; D015153:Blotting, Western; D005434:Flow Cytometry; D051379:Mice; D008810:Mice, Inbred C57BL; D010766:Phosphorylation; D044348:Receptors, Serotonin, 5-HT2 / Q000378:metabolism*; D012701:Serotonin / Q000378:metabolism / Q000502:physiology*; D048051:p38 Mitogen-Activated Protein Kinases / Q000378:metabolism
D044348:Receptors, Serotonin, 5-HT2; D012701:Serotonin; D048051:p38 Mitogen-Activated Protein Kinases; D051722:ADAM Proteins; D000072198:ADAM17 Protein; C000606463:Adam17 protein, mouse