Abstract 5661: Akt/mTOR is an Essential Downstream Pathway of Platelet-Derived Growth Factor Signaling in Pulmonary Artery Smooth Muscle Cells
Background: Platelet-derived growth factor (PDGF) is known to be a potent mitogen involved in the development and progression of pulmonary vascular remodeling. Recently, PDGF has attracted attention due to the inhibition of its receptor having a positive effect on hemodynamics, remodeling, and survival. Indeed, a PDGF receptor inhibitor is now undergoing clinical trials. It is, however, unclear which downstream pathway is important in pulmonary vascular remodeling. The Akt/mTOR pathway is central to many biological responses including cell growth, proliferation, survival, and metabolism. The involvement of the Akt/mTOR pathway in PDGF signaling was evaluated, in addition to a potential role in store-operated Ca2+ entry (SOCE), which we previously reported to be important in cell proliferation and vascular remodeling in idiopathic and thromboembolic pulmonary hypertension.
Methods and Results: In human pulmonary artery smooth muscle cells (PASMC) and fibroblasts, PDGF transiently phosphorylated Akt, mTOR and p70S6K (24.8-, 3.6-, 8.1-fold increase in 15 minutes, P<0.01, 0.001, 0.01, respectively). Interestingly, PDGF failed to induce Akt phosphorylation in pulmonary artery endothelial cells. Chronic treatment with PDGF (10 ng/ml) significantly enhanced the increase in cytosolic Ca2+ due to cyclopiazonic acid (10 microM)-induced Ca2+ mobilization (from 0.75±0.02 to 0.88±0.03 arbitrary unit (a.u.), P<0.001) and SOCE (from 1.03±0.02 to 1.51±0.05 a.u., P<0.001). When treated with rapamycin (10 nM), an inhibitor of mTOR, or Akt inhibitor (1 microM), SOCE was significantly reduced (to 1.28±0.05, 0.60±0.02 a.u., respectively, P <0.001).
Conclusions: The data suggest that Akt/mTOR signaling is an important pathway in the regulation of SOCE in PASMC. A greater understanding of this pathway may enable the development of novel therapeutic approaches in patients with pulmonary vascular disease.