Pulmonary hypertension (PH) is a disease which manifests itself in the lungs of both adults and children. Vascular proliferation and remodeling are the hallmarks of PH and are found mainly in the pulmonary arterial smooth muscle cells (PASMC). The cause of PASMC proliferation and vascular remodeling in PH is poorly understood. Hypoxia, or low oxygen content, underlies many forms of PH. Hypoxia results in alterations in the redox balance of the PASMC. Therefore, the aim of this study was to examine the role of the thioredoxin system, an antioxidant system in the cell, in hypoxia-induced proliferation in PASMC. Protein was isolated from human PASMC which were exposed to either hypoxia (1% O2, 5% CO2, balance N2) or normoxia (21% O2, 5% CO2 and balance N2) to determine the protein levels of thioredoxin 1 and 2 (Trx1 and Trx2), thioredoxin reductase (TrxR), and thioredoxin interacting protein (Txnip), by Western blotting. Proliferation studies were also done by seeding 6 well plates with 10,000 PASMC per well, incubating in either normoxia or hypoxia for 5 days and counting viable cells using trypan blue exclusion. We found that in hypoxia the Trx1 protein levels were significantly greater after 48 and 72 hours of exposure than in PASMC grown in normoxia. We also found that PASMC proliferate more in hypoxia than in normoxia. To determine if Trx1 had a role in hypoxia-induced PASMC proliferation we knocked down Trx1 protein in the PASMC using specific siRNA, and treatment with the Trx1 siRNA completely prevented hypoxia-induced proliferation in PASMC. These findings demonstrate that Trx1 protein is necessary for the hypoxia-induced proliferation of ii PASMC. We speculate that Trx1 may represent a novel therapeutic target for the vascular remodeling that underlies PH
