Overexpression of the 5-hydroxytryptamine transporter gene - Effect on pulmonary hemodynamics and hypoxia-induced pulmonary hypertension

Background - Increased serotonin (5-hydroxytryptamine, 5-HT) transporter activity has been observed in human familial pulmonary hypertension. Methods and Results - We investigated pulmonary hemodynamics and the development of hypoxia-induced pulmonary hypertension and pulmonary vascular remodeling in mice overexpressing the gene for the 5-HT transporter (5-HTT + mice). Right ventricular pressure was elevated 3-fold in normoxic 5-HTT + mice compared with their wild-type controls. Hypoxia-induced increases in right ventricular hypertrophy and pulmonary vascular remodeling were also potentiated in the 5-HTT+ mice. 5-HTT - like immunoreactivity, protein, and binding sites were markedly increased in the lungs from the 5-HTT+ mice. Hypoxia, however, decreased 5-HT transporter immunoreactivity, mRNA transcription, protein, and binding sites in both wild-type and 5-HTT + mice. Conclusions - Increased 5-HT transporter expression causes elevated right ventricular pressures, and this occurs before the onset of right ventricular hypertrophy or pulmonary arterial remodeling. Hypoxia-induced remodeling is, however, increased in 5-HTT + mice, whereas hypoxia inhibits 5-HTT expression. This provides a unique model that demonstrates differential mechanisms for familial pulmonary arterial hypertension and pulmonary arterial hypertension with hypoxemia.