Abstract Body (Do not enter title and authors here): Introduction Pulmonary arterial hypertension (PAH) is characterized by a fibroproliferative vasculopathy that narrows distal lung arterioles due to pulmonary artery endothelial and smooth muscle cell proliferation and increased extracellular matrix deposition. The resulting loss of vessel wall elasticity and increased stiffening present a challenge to current pharmacotherapeutics which are predominantly pulmonary vasodilators and do not induce a sustained improvement in pulmonary hypertension. Protein NEDD9 is increased in blood and regulates fibrotic remodeling in pulmonary vasculature of PAH patients, whereas its inhibition or knockdown prevents experimental PAH.
Hypothesis. Inhibition of NEDD9 reverses fibroproliferative remodeling of distal pulmonary arterioles in PAH.
Methods Sprague Dawley rats were administered Sugen-5416 (20 mg/kg) and exposed to hypoxia (10% O₂) for 3 weeks and then normoxia for 10 days (SU-5416-Hyp-Norm). siRNA against NEDD9 (siNEDD9) or vehicle (V) control non-targeting siRNA (1mg/kg of body weight) was administered by intratracheal injection on days 14, 19 and 25. On day 32, right ventricular systolic pressure (RVSP) and right ventricle (RV) mass (Fulton index) were measured. Lungs were analyzed by histological and immunohistochemical staining for fibroproliferative remodeling.

Results Compared to controls, SU-5416-Hyp-Norm rats (N=8/condition) at day 14 developed extensive pulmonary arterial remodeling, defined by increased vascular hypertrophy (30±7 vs. 8.3±2.4 lumen:vessel ratio, P<0.001) and collagen III deposition detected by immunostaining (2.8±0.2 vs. 4.2±0.1 arb. units, P<0.001), which increased RVSP (19±1.9 vs. 73±8.6 mmHg, P<0.001) and RV mass (0.22±0.03 vs. 0.51±0.05 Fulton index, P<0.001). Compared to V-treated rats, SU-5416-Hyp-Norm rats treated with si-NEDD9 had significantly improved lumen:vessel ratio (2.7±0.4 vs. 16±3.8, P<0.001), decreased collagen III deposition (5.09±0.79 vs. 2.83±0.6 arb. units, P<0.001), RVSP (102±19 vs. 53±12 mmHg, P<0.001) and RV remodeling (0.59±0.08 vs. 0.37±0.05 Fulton index, P<0.001) on day 32. In addition, all those values were significantly improved compared to SU-5416-Hyp-Norm rats at day 14.
Conclusion NEDD9 inhibition reversed fibroproliferative remodeling in SU-5416-Hyp-Norm model of PAH. These results suggest NEDD9 is a potential therapeutic target by which to modulate sustained improvement in pulmonary hypertension.