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P ulmonary arterial hypertension (PAH) is a rapidly progressive disease characterized by obstructive remodeling of distal pulmonary arteries (<500 μm), leading to a progressive elevation in pulmonary vascular resistance and subsequent right heart failure and death. There is currently no cure for PAH, which has a very poor prognosis (mean survival of 2.8 years).1 It is well known that pulmonary arteries display complex structural and functional changes in PAH and that pulmonary endothelial cell (EC) dysfunction plays a crucial role in the disease progression. Despite an increased knowledge in the past years about PAH pathobiological cellular and molecular mechanisms, we still do not know what initiates this disease and its characteristic pulmonary vascular remodeling. Editorial see p 1545 Clinical Perspective on p 1597Pericytes are central regulators of vascular development, stabilization, maturation, and remodeling, modulating EC Background-Pericytes and their crosstalk with endothelial cells are critical for the development of a functional microvasculature and vascular remodeling. It is also known that pulmonary endothelial dysfunction is intertwined with the initiation and progression of pulmonary arterial hypertension (PAH). We hypothesized that pulmonary endothelial dysfunction, characterized by abnormal fibroblast growth factor-2 and interleukin-6 signaling, leads to abnormal microvascular pericyte coverage causing pulmonary arterial medial thickening. Methods and Results-In human lung tissues, numbers of pericytes are substantially increased (up to 2-fold) in distal PAH pulmonary arteries compared with controls. Interestingly, human pulmonary pericytes exhibit, in vitro, an accentuated proliferative and migratory response to conditioned media from human idiopathic PAH endothelial cells compared with conditioned media from control cells. Importantly, by using an anti-fibroblast growth factor-2 neutralizing antibody, we attenuated these proliferative and migratory responses, whereas by using an anti-interleukin-6 neutralizing antibody, we decreased the migratory response without affecting the proliferative response. Furthermore, in our murine retinal angiogenesis model, both fibroblast growth factor-2 and interleukin-6 administration increased pericyte coverage. Finally, using idiopathic PAH human and NG2DsRedBAC mouse lung tissues, we demonstrated that this increased pericyte coverage contributes to pulmonary vascular remodeling as a source of smooth muscle-like cells. Furthermore, we found that transforming growth factor-β, in contrast to fibroblast growth factor-2 and interleukin-6, promotes human pulmonary pericyte differentiation into contractile smooth muscle-like cells. Conclusions-To the best of our knowledge, this is the first report of excessive pericyte coverage in distal pulmonary arteries in human PAH. We also show that this phenomenon is directly linked with pulmonary endothelial dysfunction. 10 In particular, pericytes that are found along arterioles and capillaries express different degrees...

Delayed shear adaptation, which promotes shear-induced endothelial injury, is a newly identified dysfunction specific to the microvascular endothelium in PAH. The shear response is normalized on stabilization of PECAM-1, which reverses intimal remodeling in vivo.

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Background: Mutations in bone morphogenetic protein receptor type II (BMPR2) are leading to the development of hereditary pulmonary arterial hypertension (PAH). In non-hereditary forms of PAH, perturbations in the transforming growth factor-β (TGF-β)/BMP-axis are believed to cause deficient BMPR2 signaling by changes in receptor expression, the activity of the receptor and/or downstream signaling. To date, BMPR2 expression and its activity in the lungs of patients with non-hereditary PAH is poorly characterized. In recent decades, different animal models have been used to understand the role of BMPR2 signaling in PAH pathophysiology. Specifically, the monocrotaline (MCT) and Sugen–Hypoxia (SuHx) models are extensively used in interventional studies to examine if restoring BMPR2 signaling results in PAH disease reversal. While PAH is assumed to develop in patients over months or years, pulmonary hypertension in experimental animal models develops in days or weeks. It is therefore likely that modifications in BMP and TGF-β signaling in these models do not fully recapitulate those in patients. In order to determine the translational potential of the MCT and SuHx models, we analyzed the BMPR2 expression and activity in the lungs of rats with experimentally induced PAH and compared this to the BMPR2 expression and activity in the lungs of PAH patients. Methods: the BMPR2 expression was analyzed by Western blot analysis and immunofluorescence (IF) microscopy to determine the quantity and localization of the receptor in the lung tissue from normal control subjects and patients with hereditary or idiopathic PAH, as well as in the lungs of control rats and rats with MCT or SuHx-induced PAH. The activation of the BMP pathway was analyzed by determining the level and localization of phosphorylated Smad1/5/8 (pSmad 1/5/8), a downstream mediator of canonical BMPR2 signaling. Results: While BMPR2 and pSmad 1/5/8 expression levels were unaltered in whole lung lysates/homogenates from patients with hereditary and idiopathic PAH, IF analysis showed that BMPR2 and pSmad 1/5/8 levels were markedly decreased in the pulmonary vessels of both PAH patient groups. Whole lung BMPR2 expression was variable in the two PAH rat models, while in both experimental models the expression of BMPR2 in the lung vasculature was increased. However, in the human PAH lungs, the expression of pSmad 1/5/8 was downregulated in the lung vasculature of both experimental models. Conclusion: BMPR2 receptor expression and downstream signaling is reduced in the lung vasculature of patients with idiopathic and hereditary PAH, which cannot be appreciated when using human whole lung lysates. Despite increased BMPR2 expression in the lung vasculature, the MCT and SuHx rat models did develop PAH and impaired downstream BMPR2-Smad signaling similar to our findings in the human lung.

Background: Pulmonary hypertension (PH) is a common complication of idiopathic pulmonary fibrosis (IPF) that significantly contributes to morbidity and mortality. Macrophage migration inhibitory factor (MIF) is a critical factor in vascular remodeling of the pulmonary circulation. Objectives: We tested the effects of two small molecules targeting MIF on bleomycin (BLM)-induced collagen deposition, PH, and vascular remodeling in mouse lungs. Methods: We examined the distribution pattern of MIF, CD74, and CXCR4 in the lungs of patients with IPF-PH and the lungs of BLM-injected mice. Then, treatments were realized with (S,R)-3-(4-hydroxyphenyl)-4,5-dihydro-5-isoxazole acetic acid methyl ester (ISO-1) and N-(3-hydroxy-4-fluorobenzyl)-5 trifluoromethylbenzoxazol-2-thione 31 (20 mg/kg/day per os for 3 weeks) started 24 h after an intratracheal BLM administration. Results: More intense immunoreactivity was noted for MIF, CD74, and CXCR4 in lungs from IPF-PH patients and BLM-injected mice. Furthermore, we found that treatments of BLM-injected mice with ISO-1 or compound 31 attenuated lung collagen deposition and right ventricular systolic pressure increase. Additionally, reduced pulmonary inflammatory infiltration and pulmonary arterial muscularization were observed in the lungs of BLM-injected mice treated with ISO-1 or compound 31. Conclusions: Treatments with ISO-1 or compound 31 attenuates BLM-induced inflammation and fibrosis in lung, and prevents PH development in mice, suggesting that MIF is an important factor for IPF-PH development.

The combination of pulmonary vasoconstriction, in situ thrombosis, and pulmonary arterial wall remodeling is largely responsible for the rise in pulmonary vascular resistance (PVR) and pulmonary arterial pressure (PAP) in patients with pulmonary arterial hypertension (PAH). Even though several drugs have been developed over the past decades, at this time there is no cure for PAH. The overriding goals of the current therapeutic options seek to compensate for the defects in the relative balance of competing vasoconstrictor and vasodilator influences. Because the past decade has seen great strides in our understanding of the pathogenesis of PAH, interest has been growing in the potential use of anti-proliferative approaches in PAH. Indeed anti-proliferative strategies could offer ways not only to reinstate the homeostatic balance between cell proliferation and apoptosis but also to reverse the progressive pulmonary vascular obstruction in PAH. However, further efforts still need to be made in order to establish the long-term safety and efficacy of those anti-proliferative approaches in PAH and their potential additive benefit with other drugs.

IntroductionRisk stratification and assessment of disease progression in patients with pulmonary arterial hypertension (PAH) are challenged by the lack of accurate disease-specific and prognostic biomarkers. To date, B-type natriuretic peptide (BNP) and/or its N-terminal fragment (NT-proBNP) are the only marker for right ventricular dysfunction used in clinical practice, in association with echocardiographic and invasive hemodymamic variables to predict outcome in patients with PAH.MethodsThis study was designed to identify an easily measurable biomarker panel in the serum of 80 well-phenotyped PAH patients with idiopathic, heritable, or drug-induced PAH at baseline and first follow-up. The prognostic value of identified cytokines of interest was secondly analysed in an external validation cohort of 125 PAH patients.ResultsAmong the 20 biomarkers studied with the multiplex EllaTMplatform, we identified a 3-biomarker panel composed of ß-NGF, CXCL9 and TRAIL that were independently associated with prognosis both at the time of PAH diagnosis and at the first follow-up after initiation of PAH therapy. β-NGF and CXCL9 were predictors of death or transplantation, whereas high levels of TRAIL were associated with a better prognosis. Furthermore, prognostic value of the three cytokines was more powerful for predicting survival than usual non-invasive variables (functional class, 6-minute walking distance and BNP/NT-proBNP). The results were validated in a fully independent external validation cohort.ConclusionThe monitoring of ß-NGF, CXCL9 and TRAIL levels in serum should be considered in the management and treatment of patients with PAH to objectively guide therapeutic options.