RhoA and Rho kinase activation in human pulmonary hypertension: role of 5-HT signaling.

RATIONALE 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.