The complex and multifactorial pathogenesis of pulmonary hypertension (PH) involves constriction, remodeling, and in situ thrombosis of pulmonary vessels. Both serotonin (5-HT) and Rho kinase signaling may contribute to these alterations.Objectives:
To investigate possible links between the 5-HT transporter (5-HTT) and RhoA/Rho kinase pathways, as well as their involvement in the progression of human and experimental PH.Methods:
Biochemical and functional analyses of lungs, platelets, and pulmonary artery smooth muscle cells (PA-SMCs) from patients with idiopathic PH (iPH) and 5-HTT overexpressing mice.Measurements and Main Results:
Lungs, platelets, and PA-SMCs from patients with iPH were characterized by marked elevation in RhoA and Rho kinase activities and a strong increase in 5-HT binding to RhoA indicating RhoA serotonylation. The 5-HTT inhibitor fluoxetine and the type 2 transglutaminase inhibitor monodansylcadaverin prevented 5-HT–induced RhoA serotonylation and RhoA/Rho kinase activation, as well as 5-HT–induced proliferation of PA-SMCs from iPH patients that was also inhibited by the Rho kinase inhibitor fasudil. Increased Rho kinase activity, RhoA activation, and RhoA serotonylation were also observed in lungs from SM22–5-HTT+mice, which overexpress 5-HTT in smooth muscle and spontaneously develop PH. Treatment of SM22–5-HTT+ mice with either fasudil or fluoxetine limited PH progression and RhoA/Rho kinase activation.Conclusions:
RhoA and Rho kinase activities are increased in iPH, in association with enhanced RhoA serotonylation. Direct involvement of the 5-HTT/RhoA/Rho kinase signaling pathway in 5-HT–mediated PA-SMC proliferation and platelet activation during PH progression identify RhoA/Rho kinase signaling as a promising target for new treatments against PH.