RHOA and pulmonary arterial hypertension: RhoA serotonylation, following SERT-mediated cellular internalization of serotonin has been described in platelets.25 RhoA and Rho kinase activities are increased in idiopathic PAH (iPAH), in association with enhanced RhoA serotonylation and this may involve platelet activation.26 Serotonin-induced fibrosis may also play a role in PAH.