Abstract 9906: Aldosterone Targets Raptor to Promote Pulmonary Smooth Muscle Cell Proliferation and Modulate Pulmonary Arterial Hypertension
In pulmonary arterial hypertension (PAH), elevated levels of aldosterone (ALDO) induce pulmonary smooth muscle cell (PSMC) proliferation and hypertrophy of distal arterioles. Raptor, part of the mammalian target of rapamycin (mTOR) complex 1, modulates PSMC growth; however, the role of ALDO-raptor signaling in PAH is not known. We hypothesized that stimulation of raptor by ALDO increases PSMC proliferation to promote vascular dysfunction in PAH. To test our hypothesis, human PSMCs were treated with vehicle control (V) or ALDO (10-7 mol/l) for 15, 30, or 60 min. Compared to V-treated cells, ALDO for 60 min increased protein levels of P-mTOR(Ser2448) (26.1 ± 12.8 vs. 61.4 ± 17.8 units, p<0.05) and P-raptor(Ser792) (19.4 ± 7.1 vs. 32.1 ± 2.2 units, p<0.05) without affecting total mTOR/raptor levels. We next explored the effect of ALDO on Akt, which is an upstream mediator of raptor activation. ALDO increased the P-Akt(Ser473)/Akt ratio at 15 and 30 min by 56% (P<0.02) and 80% (P<0.02), respectively. ALDO also induced a time-dependent (0, 15, 30, 60 min) increase in levels of the raptor target P-p70S6k (Thr389) (56.8 ± 3.1 vs. 75.6 ± 3.6 vs. 79.0 ± 2.8 vs. 84.6 ± 4.8 units, P<0.01), and increased cell proliferation by 29% (P<0.02) as assessed by the tetrazolium assay. Next, we investigated the effect of ALDO-raptor signaling on vascular remodeling in PAH in vivo. Compared to controls, immunohistochemistry of pulmonary arterioles from rats with monocrotaline (MCT)-PAH demonstrated increased P-p70S6k(Thr389) (114 ± 16 vs. 188 ± 25 units, P<0.02). In turn, inhibition of ALDO with eplerenone (10 μM) decreased P-p70S6k levels in ALDO-treated cells in vitro (33.6 ± 1.9 vs. 27.5 ± 2.2 units, P<0.03), and spironolactone (25 mg/kg/d) decreased P-p70S6k levels in pulmonary arterioles of MCT-PAH rats in vivo (188 ± 25 vs. 96 ± 27 units, P<0.02). Attenuation of P-p70S6k expression in MCT-PAH by spironolactone was associated with a decrease in indexed pulmonary vascular resistance (35.9 ± 3.2 vs. 21.5 ± 3.2 mmHg*min*g/ml, P<0.05) and the number of muscularized arterioles by 54% (P<0.05). These data demonstrate that Akt/raptor/p70S6k activation by ALDO promotes PSMC proliferation, and may represent a novel mechanism by which to account for pulmonary vascular remodeling in PAH.
- © 2013 by American Heart Association, Inc.