Abstract 376: A Potential Role for TRAIL in the Pathogenesis of Pulmonary Arterial Hypertension
Pulmonary arterial hypertension (PAH) is a life threatening disease characterised by the narrowing and occlusion of small pulmonary arteries. Endothelial cell (EC) loss, and increased proliferation and migration of pulmonary artery smooth muscle cells (PA-SMC) are strongly implicated in disease pathogenesis. Tumor necrosis factor (TNF)-Related Apoptosis-Inducing Ligand (TRAIL) induces EC apoptosis and SMC migration, consistent with an important role in vascular biology. TRAIL is a type II TNF family transmembrane protein, whose extracellular domain can be proteolytically cleaved from the cell surface to act as a soluble cytokine (sTRAIL) capable of binding to five TRAIL receptors, (TRAIL-R1– 4) and osteoprotegerin (OPG). We hypothesised that TRAIL expression is increased in PAH and that this contributes to the excessive migration of PA-SMC that characterises this condition. TRAIL gene expression was studied in microarrays of PA-SMC RNA isolated from idiopathic PAH (IPAH) patients, and from the lungs of monocrotaline-treated (Mct) rats. Immunohistochemistry was performed to localise TRAIL in both human and rat lung sections. To investigate the functional effects of TRAIL in PA-SMC, human PA-SMC were incubated with recombinant human TRAIL (1–50 ng/ml) for 5h and migration assessed by transwell assay. TRAIL gene expression was 10-fold higher in PA-SMC from IPAH patients compared to controls. Moreover, strong TRAIL immunoreactivity was observed in pulmonary vascular lesions from IPAH patients but not in vessels from patients undergoing lobectomy for lung carcinoma. In the Mct-rat model of PAH we found a 20-fold increase in TRAIL gene expression and a 2-fold increase in protein from whole lung extracts. Immunohistochemistry revealed strong TRAIL immunoreactivity within the muscularised pulmonary arteries of Mct-treated but not saline-treated control rats. Recombinant TRAIL was found to induce a dose dependent (maximum 3 fold) increase in migration of human PA-SMC compared with cells incubated with 0.1% serum alone. These data suggest that TRAIL may be an important molecule in the pathogenesis of PAH. Further studies to elucidate the regulation and function of this molecule in PAH are warranted.