PAI-1 deficiency drives pulmonary vascular smooth muscle remodeling and pulmonary hypertension.

Pulmonary arterial hypertension (PAH) is a progressive disease characterized by vasoconstriction and remodeling of small pulmonary arteries (PAs). Central to the remodeling process is a switch of pulmonary vascular cells to a proliferative, apoptosis-resistant phenotype. Plasminogen activator inhibitors-1 and -2 (PAI-1 and PAI-2) are the primary physiological inhibitors of urokinase-type and tissue-type plasminogen activators (uPA and tPA), but their roles in PAH are unsettled. Here, we report that: 1) PAI-1, but not PAI-2, is deficient in remodeled small PAs and in early-passage PA smooth muscle and endothelial cells (PASMCs and PAECs) from subjects with PAH compared with controls; 2) PAI-1-/- mice spontaneously develop pulmonary vascular remodeling associated with upregulation of mTORC1 signaling, pulmonary hypertension (PH), and right ventricle (RV) hypertrophy; and 3) pharmacological inhibition of uPA in human PAH PASMCs suppresses proproliferative mTORC1 and SMAD3 signaling, restores PAI-1 levels, reduces proliferation, and induces apoptosis in vitro, and prevents the development of SU5416/hypoxia-induced PH and RV hypertrophy in vivo in mice. These data strongly suggest that downregulation of PAI-1 in small PAs promotes vascular remodeling and PH due to unopposed activation of uPA and consequent upregulation of mTOR and transforming growth factor-ß (TGF-ß) signaling in PASMCs, and call for further studies to determine the potential benefits of targeting the PAI-1/uPA imbalance to attenuate and/or reverse pulmonary vascular remodeling and PH.NEW & NOTEWORTHY This study identifies a novel role for the deficiency of plasminogen activator inhibitor (PAI)-1 and resultant unrestricted uPA activity in PASMC remodeling and PH in vitro and in vivo, provides novel mechanistic link from PAI-1 loss through uPA-induced Akt/mTOR and TGFß-Smad3 upregulation to pulmonary vascular remodeling in PH, and suggests that inhibition of uPA to rebalance the uPA-PAI-1 tandem might provide a novel approach to complement current therapies used to mitigate this pulmonary vascular disease.

PAI-1 Deficiency Drives Pulmonary Vascular Smooth Muscle Remodeling and Pulmonary Hypertension.

Pulmonary arterial hypertension (PAH) is a progressive and potentially a rapidly fatal disease characterized by vasoconstriction and remodeling of small pulmonary arteries (PA) leading to increased pulmonary vascular resistance and right heart failure. Central to the remodeling process is a switch of the smooth muscle cells in small PAs (PASMC) to a proliferative, apoptosis-resistant phenotype. There is reason to suspect that the plasminogen activator system may play an important role in the remodeling program in PAH based on its roles in vascular post-injury restenosis, fibrosis, angiogenesis and tumorigenesis. Plasminogen activator inhibitor-1 (PAI-1) is the primary physiological inhibitor of the plasminogen activators - urokinase-type and tissue-type (uPA and tPA, respectively). Immunohisto- chemical and immunoblot analyses revealed that PAI-1 was deficient in smooth muscle areas of small remodeled PAs and early-passage PASMC from subjects with PAH compared to non-PAH controls. PAI1-/- male and female mice developed spontaneous pulmonary vascular remodeling and pulmonary hypertension (PH) as evidenced by significant increase in PA medial thickness, systolic right ventricular pressure, and right ventricular hypertrophy. Lastly, the uPA inhibitors upamostat (WX-671) and amiloride analog BB2-30F down-regulated mTORC1 and SMAD3, restored PAI-1 levels, reduced proliferation, and induced apoptosis in human PAH PASMC. We examined the effect of inhibition of uPA catalytic activity by BB2-30F on the development of SU5416/Hypoxia (SuHx)-induced PH in mice. Vehicletreated SuHx-exposed mice had up-regulated mTORC1 in small PAs, developed pulmonary vascular remodeling and PH, as evidenced by significant increase of PA MT, sRVP, RV hypertrophy, and a significant decrease in the pulmonary artery acceleration time/pulmonary ejection time (PAAT/PET) ratio compared to age- and sex-matched normoxia controls, whereas BB2-30F-treated group was protected from all these pathological changes. Taken together, our data strongly suggest that PAI-1 down- regulation in PASMC from human PAH lungs promotes PASMC hyper-proliferation, remodeling, and spontaneous PH due to unopposed uPA activation. Further studies are needed to determine the potential benefits of targeting the PAI-1/uPA imbalance to attenuate the progression and/or reverse pulmonary vascular remodeling and PH.

Analysis of pulmonary hypertension patient survival after treatment in referral center (data of first Ukrainian register).

The aims of the study were: (1) to evaluate the Ukrainian reality of survival in patients with pulmonary arterial hypertension (PAH) and chronic thromboembolic pulmonary hypertension (CTEPH); and (2) to determine predictors of death. A total of 281 patients were enrolled (52 [18.5%] with CTEPH, 229 [81.5%] with PAH). Long-term survival (Kaplan-Meier) and its predictors (Stepwise binary logistic regression and Cox's proportional hazards analyses) were evaluated in adult patients with PH (diagnosed by right heart catheterization [RHC]) within a prospective registry at a single referral center in Kyiv, Ukraine. Follow-up period was up to 51 months. The Kaplan-Meier survival rate for the total cohort was 93.3%, 86.8%, and 81.5% at one, two, and three years, respectively. Survival was better in patients with congenital heart diseases (CHD) in comparison with idiopathic PAH (long rank P = 0.002), connective tissue diseases (CTD; long rank P = 0.001) and CTEPH (long rank P = 0.04). Univariate Cox's predictors of death were: functional class IV (odds ratio [OR] = 4.94; 95% confidence interval [CI] = 2.12-11.48), presence of ascites (OR = 4.52; 95% CI = 2.21-9.24), PAH-CTD (OR = 3.07; 95% CI = 1.07-8.87), PAH-CHD (OR = 0.28; 95% CI = 0.11-0.68), HR on treatment > 105 beats per min (OR = 7.85; 95% CI = 1.83-33.69), office systolic BP < 100 mmHg (OR = 2.78; 95% CI = 1.26-6.1), 6MWT on treatment < 340 m (OR = 3.47; 95% CI = 1.01-12.35), NT-proBNP > 300 pg/mL (OR = 4.98; 95% CI = 1.49-16.6), right atrium square > 22 cm2 (OR = 14.2; 95% CI = 1.92-104.89), right ventricular square in diastole (OR = 1.08; 95% CI = 1.03-1.14), right ventricular square in systole (OR = 1.08; 95% CI = 1.02-1.11), mean pressure in right atrium per each 1-mmHg increase (OR = 1.02; 95% CI = 1.02-1.19). In multivariate Cox regression analyses only presence of ascites, office systolic BP < 100 mmHg, CHD etiology of PH, and NT-proBNP > 300 pg/mL were associated with survival.