Loss-of-function mutations in bone morphogenetic protein receptor II (BMP-RII) are linked to pulmonary arterial hypertension (PAH); the ligand for BMP-RII, BMP-2, is a negative regulator of SMC growth. Here, we report an interplay between PPARγ and its transcriptional target apoE downstream of BMP-2 signaling. BMP-2/BMP-RII signaling prevented PDGF-BB-induced proliferation of human and murine pulmonary artery SMCs (PASMCs) by decreasing nuclear phospho-ERK and inducing DNA binding of PPARγ that is independent of Smad1/5/8 phosphorylation. Both BMP-2 and a PPARγ agonist stimulated production and secretion of apoE by SMCs. Using a variety of methods, including short hairpin RNAi in human PASMCs, PAH patient-derived BMP-RII mutant PASMCs, a PPARγ antagonist, and PASMCs isolated from PPARγ-and apoE-deficient mice, we demonstrated that the antiproliferative effect of BMP-2 was BMP-RII, PPARγ, and apoE dependent. Furthermore, we created mice with targeted deletion of PPARγ in SMCs and showed that they spontaneously developed PAH, as indicated by elevated RV systolic pressure, RV hypertrophy, and increased muscularization of the distal pulmonary arteries. Thus, PPARγ-mediated events could protect against PAH, and PPARγ agonists may reverse PAH in patients with or without BMP-RII dysfunction.

Abstract-Our previous studies have demonstrated that inhaled nitric oxide (NO) decreases nitric oxide synthase (NOS) activity in vivo and that this inhibition is associated with rebound pulmonary hypertension upon acute withdrawal of inhaled NO. We have also demonstrated that inhaled NO elevates plasma endothelin-1 (ET-1) levels and that pretreatment with PD156707, an ETA receptor antagonist, blocks the rebound hypertension. The objectives of this study were to further elucidate the role of ET-1 in the rebound pulmonary hypertension upon acute withdrawal of inhaled NO. Inhaled NO (40 ppm) delivered to thirteen 4-week-old lambs decreased NOS activity by 36.2% in control lambs (PϽ0.05), whereas NOS activity was preserved in PD156707-treated lambs. When primary cultures of pulmonary artery smooth muscle cells were exposed to ET-1, superoxide production increased by 33% (PϽ0.05). This increase was blocked by a preincubation with PD156707. Furthermore, cotreatment of cells with ET-1 and NO increased peroxynitrite levels by 26% (PϽ0.05), whereas preincubation of purified human endothelial nitric oxide synthase (eNOS) protein with peroxynitrite generated a nitrated enzyme with 50% activity relative to control (PϽ0.05). Western blot analysis of peripheral lung extracts obtained after 24 hours of inhaled NO revealed a 90% reduction in 3-nitrotyrosine residues (PϽ0.05) in PD156707-treated lambs. The nitration of eNOS was also reduced by 40% in PD156707-treated lambs (PϽ0.05). These data suggest that the reduction of NOS activity associated with inhaled NO therapy may involve ETA receptor-mediated superoxide production. ETA receptor antagonists may prevent rebound pulmonary hypertension by protecting endogenous eNOS activity during inhaled NO therapy. Key Words: nitric oxide Ⅲ rebound pulmonary hypertension Ⅲ receptor blockade Ⅲ superoxide Ⅲ peroxynitrite I nhaled nitric oxide (NO) is a selective, potent pulmonary vasodilator that is currently used as an adjunct therapy for a number of pulmonary vasculature disease states. 1 However, a number of studies have observed an acute and potentially life-threatening increase in pulmonary vascular resistance (PVR) upon acute withdrawal of inhaled NO. In children with congenital heart disease, this is manifested by an increase in PVR that may compromise cardiac output. 2,3 In newborns with persistent pulmonary hypertension, this is manifested by a sudden decrease in systemic arterial oxygen saturation. 4 This rebound pulmonary hypertension can occur after only hours of therapy and is independent of the initial response; patients with no initial pulmonary vasodilatory response can have life-threatening pulmonary vasoconstriction upon withdrawal. These manifestations of acute NO withdrawal suggest that inhaled NO may alter endogenous endothelial function, but its mechanisms are unclear.In vitro and in vivo studies indicate that exogenous NO decreases endothelial nitric oxide synthase (eNOS) activity, an effect mediated, in part, by superoxide production. 5,6 eNOS is responsible for ...

Clinically significant increases in pulmonary vascular resistance have been noted on acute withdrawal of inhaled nitric oxide (NO). Endothelin (ET)-1 is a vasoactive peptide produced by the vascular endothelium that may participate in the pathophysiology of pulmonary hypertension. The objectives of this study were to determine the effects of inhaled NO on endogenous ET-1 production in vivo in the intact lamb and to determine the potential role of ET-1 in the rebound pulmonary hypertension associated with the withdrawal of inhaled NO. Seven 1-mo-old vehicle-treated control lambs and six PD-156707 (an ET(A) receptor antagonist)-treated lambs were mechanically ventilated. Inhaled NO (40 parts per million) was administered for 24 h and then acutely withdrawn. After 24 h of inhaled NO, plasma ET-1 levels increased by 119.5 +/- 42.2% (P < 0.05). Western blot analysis revealed that protein levels of preproET-1, endothelin-converting enzyme-1alpha, and ET(A) and ET(B) receptors were unchanged. On acute withdrawal of NO, pulmonary vascular resistance (PVR) increased by 77.8% (P < 0.05) in control lambs but was unchanged (-5.5%) in PD-156707-treated lambs. Inhaled NO increased plasma ET-1 concentrations but not gene expression in the intact lamb, and ET(A) receptor blockade prevented the increase in PVR after NO withdrawal. These data suggest a role for ET-1 in the rebound pulmonary hypertension noted on acute withdrawal of inhaled NO.

Life-threatening increases in pulmonary vascular resistance have been noted on acute withdrawal of inhaled nitric oxide (NO), although the mechanisms remain unknown. In vitro data suggest that exogenous NO exposure inhibits endothelial NO synthase (NOS) activity. Thus the objectives of this study were to determine the effects of inhaled NO therapy and its acute withdrawal on endogenous NOS activity and gene expression in vivo in the intact lamb. Six 1-mo-old lambs were mechanically ventilated and instrumented to measure vascular pressures and left pulmonary blood flow. Inhaled NO (40 ppm) acutely decreased left pulmonary vascular resistance by 27. 5 +/- 4.7% (P < 0.05). This was associated with a 207% increase in plasma cGMP concentrations (P < 0.05). After 6 h of inhaled NO, NOS activity was reduced to 44.3 +/- 5.9% of pre-NO values (P < 0.05). After acute withdrawal of NO, pulmonary vascular resistance increased by 52.1 +/- 11.6% (P < 0.05) and cGMP concentrations decreased. Both returned to pre-NO values within 60 min. One hour after NO withdrawal, NOS activity increased by 48.4 +/- 19.1% to 70% of pre-NO values (P < 0.05). Western blot analysis revealed that endothelial NOS protein levels remained unchanged throughout the study period. These data suggest a role for decreased endogenous NOS activity in the rebound pulmonary hypertension noted after acute withdrawal of inhaled NO.