Abstract 12714: Aldosterone Activates Raptor to Promote Pulmonary Artery Smooth Muscle Cell Proliferation and Pulmonary Arterial Hypertension

Abstract

In pulmonary arterial hypertension (PAH), elevated levels of aldosterone (ALDO) induce a vasculopathy that is characterized by dysregulated pulmonary artery smooth muscle cell (PSMC) growth. Upregulation of the mammalian target of rapamycin complex 1 subunit Raptor induces PSMC growth; however, the factors regulating Raptor in PAH are not known. We hypothesized that Raptor activation by ALDO induces PSMC proliferation, hypertrophic vascular remodeling, and PAH. To test this hypothesis, PSMCs were exposed to vehicle (V) control or ALDO (10 -7 mol/l) for 1 h. Compared to V-treated cells, ALDO increased expression of P-Raptor(Ser792) and the Raptor target P-p70S6K(Thr389) by 68% (P<0.01) and 50% (P<0.01), respectively, without affecting total Raptor/p70S6K levels. Raptor upregulation in ALDO-treated cells also increased PSMC proliferation by 19% (P<0.01), assessed by BrdU incorporation. To explore the relevance of ALDO-Raptor signaling in vivo , we studied the monocrotaline (MCT) model of PAH, which is characterized by hyperALDO. In a prevention protocol, MCT-PAH rats were treated with spironolactone (SP)(25 mg/kg/d) in the drinking water to inhibit ALDO and/or intravenous Staramine-mPEG labeled with Raptor-siRNA (2 mg/kg dose x4)(si-Raptor). Anti-Raptor and anti-α-SM actin immunohistochemistry showed that compared to controls (N=4), Raptor expression and vessel thickness was increased in MCT-PAH rats (N=5) by 87% (P<0.01) and 5.8-fold (P<0.01), respectively, and pulmonary artery systolic pressure (PASP) was increased significantly (25 ± 4 vs. 77 ± 12 mmHg, P<0.01) as assessed by catheterization. Compared to MCT-PAH, MCT-si-Raptor (N=5) decreased Raptor levels by 31% (P<0.05), arteriole thickness by 41% (P<0.05), and PASP (77 ± 12 vs. 46 ± 5 mmHg, P<0.05) without affecting central blood pressure significantly. A further benefit was observed in MCT-si-Raptor+SP rats (N=5) for arterial thickness (-57%, P<0.01) and PASP (46 ± 5 vs. 39 ± 5 mmHg, P<0.05) compared to MCT-si-Raptor. Taken together, Raptor activation by ALDO induces PSMC proliferation in vitro to promote PAH in vivo . Identifying ALDO-Raptor signaling as a pathobiological mechanism underlying pulmonary vascular remodeling may have novel therapeutic implications for PAH patients.