Longitudinal follow-up of the asthma status in a French-Canadian cohort.

Asthma affects 340 million people worldwide and varies in time. Twenty years ago, in Canada, the Saguenay-Lac-Saint-Jean asthma family cohort was created to study the genetic and environmental components of asthma. This study is a follow-up of 125 participants of this cohort to explore the appearance, persistence, and progression of asthma over 10-20 years. Participants answered a clinical standardized questionnaire. Lung function was assessed (forced expiratory volume in 1 s, forced vital capacity, bronchial reversibility, and methacholine bronchoprovocation), skin allergy testing was performed, blood samples were obtained (immunoglobulin E, white blood cell counts) and phenotypes were compared between recruitment and follow-up. From the participants without asthma at recruitment, 12% developed a phenotype of adult-onset asthma with the presence of risk factors, such as atopy, high body mass index, and exposure to smoking. A decrease of PC20 values in this group was observed and a decrease in the FEV1/FVC ratio in all groups. Also, 7% of individuals with asthma at recruitment developed chronic obstructive pulmonary disease, presenting risk factors at recruitment, such as moderate-to-severe bronchial hyperresponsiveness, exposure to smoking, and asthma. This study allowed a better interpretation of the evolution of asthma. Fine phenotypic characterization is the first step for meaningful genetic and epigenetic studies.

PIM1 (Moloney Murine Leukemia Provirus Integration Site) Inhibition Decreases the Nonhomologous End-Joining DNA Damage Repair Signaling Pathway in Pulmonary Hypertension.

OBJECTIVE: Pulmonary arterial hypertension (PAH) is a fatal disease characterized by the narrowing of pulmonary arteries (PAs). It is now established that this phenotype is associated with enhanced PA smooth muscle cells (PASMCs) proliferation and suppressed apoptosis. This phenotype is sustained in part by the activation of several DNA repair pathways allowing PASMCs to survive despite the unfavorable environmental conditions. PIM1 (Moloney murine leukemia provirus integration site) is an oncoprotein upregulated in PAH and involved in many prosurvival pathways, including DNA repair. The objective of this study was to demonstrate the implication of PIM1 in the DNA damage response and the beneficial effect of its inhibition by pharmacological inhibitors in human PAH-PASMCs and in rat PAH models. Approach and Results: We found in vitro that PIM1 inhibition by either SGI-1776, TP-3654, siRNA (silencer RNA) decreased the phosphorylation of its newly identified direct target KU70 (lupus Ku autoantigen protein p70) resulting in the inhibition of double-strand break repair (Comet Assay) by the nonhomologous end-joining as well as reduction of PAH-PASMCs proliferation (Ki67-positive cells) and resistance to apoptosis (Annexin V positive cells) of PAH-PASMCs. In vivo, SGI-1776 and TP-3654 given 3× a week, improved significantly pulmonary hemodynamics (right heart catheterization) and vascular remodeling (Elastica van Gieson) in monocrotaline and Fawn-Hooded rat models of PAH. CONCLUSIONS: We demonstrated that PIM1 phosphorylates KU70 and initiates DNA repair signaling in PAH-PASMCs and that PIM1 inhibitors represent a therapeutic option for patients with PAH.

Exome sequencing study of partial agenesis of the corpus callosum in men with developmental delay, epilepsy, and microcephaly.

BACKGROUND: This study reports the genetic features of four Caucasian males from the Saguenay-Lac-St-Jean region affected by partial agenesis of the corpus callosum (ACC) with hypotonia, epilepsy, developmental delay, microcephaly, hypoplasia, and autistic behavior. METHODS: We performed whole exome sequencing (WES) to identify new genes involved in this pathological phenotype. The regions of interest were subsequently sequenced for family members. RESULTS: Single-nucleotide variations (SNVs) and insertions or deletions were detected in genes potentially implicated in brain defects observed in these patients. One patient did not have mutations in genes related to ACC, but carried a de novo pathogenic mutation in Mucolipin-1 (MCOLN1) and was diagnosed with mucolipidosis type IV. Among the other probands, missense SNVs were observed in DCLK2 (Doublecortin Like Kinase 2), HERC2 (HECT And RLD Domain Containing E3 Ubiquitin Protein Ligase 2), and KCNH3 (Potassium channel, voltage-gated, subfamily H, member 3). One patient also carried a non-frameshift insertion in CACNA1A (Cav2.1(P/Q-type) calcium channels). CONCLUSION: Although no common genetic defect was observed in this study, we provide evidence for new avenues of investigation for ACC, such as molecular pathways involving HERC2, CACNA1A, KCNH3, and more importantly DCLK2. We also allowed to diagnose an individual with mucolipidosis type IV.

Mitochondrial HSP90 Accumulation Promotes Vascular Remodeling in Pulmonary Arterial Hypertension.

RATIONALE: Pulmonary arterial hypertension (PAH) is a vascular remodeling disease with a poor prognosis and limited therapeutic options. Although the mechanisms contributing to vascular remodeling in PAH are still unclear, several features, including hyperproliferation and resistance to apoptosis of pulmonary artery smooth muscle cells (PASMCs), have led to the emergence of the cancer-like concept. The molecular chaperone HSP90 (heat shock protein 90) is directly associated with malignant growth and proliferation under stress conditions. In addition to being highly expressed in the cytosol, HSP90 exists in a subcellular pool compartmentalized in the mitochondria (mtHSP90) of tumor cells, but not in normal cells, where it promotes cell survival. OBJECTIVES: We hypothesized that mtHSP90 in PAH-PASMCs represents a protective mechanism against stress, promoting their proliferation and resistance to apoptosis. METHODS: Expression and localization of HSP90 were analyzed by Western blot, immunofluorescence, and immunogold electron microscopy. In vitro, effects of mtHSP90 inhibition on mitochondrial DNA integrity, bioenergetics, cell proliferation and resistance to apoptosis were assessed. In vivo, the therapeutic potential of Gamitrinib, a mitochondria-targeted HSP90 inhibitor, was tested in fawn-hooded and monocrotaline rats. MEASUREMENTS AND MAIN RESULTS: We demonstrated that, in response to stress, HSP90 preferentially accumulates in PAH-PASMC mitochondria (dual immunostaining, immunoblot, and immunogold electron microscopy) to ensure cell survival by preserving mitochondrial DNA integrity and bioenergetic functions. Whereas cytosolic HSP90 inhibition displays a lack of absolute specificity for PAH-PASMCs, Gamitrinib decreased mitochondrial DNA content and repair capacity and bioenergetic functions, thus repressing PAH-PASMC proliferation (Ki67 labeling) and resistance to apoptosis (Annexin V assay) without affecting control cells. In vivo, Gamitrinib improves PAH in two experimental rat models (monocrotaline and fawn-hooded rat). CONCLUSIONS: Our data show for the first time that accumulation of mtHSP90 is a feature of PAH-PASMCs and a key regulator of mitochondrial homeostasis contributing to vascular remodeling in PAH.

Implication of Inflammation and Epigenetic Readers in Coronary Artery Remodeling in Patients With Pulmonary Arterial Hypertension.

OBJECTIVE: Pulmonary arterial hypertension (PAH) is a vascular disease not restricted to the lungs. Many signaling pathways described in PAH are also of importance in other vascular remodeling diseases, such as coronary artery disease (CAD). Intriguingly, CAD is 4× more prevalent in PAH compared with the global population, suggesting a link between these 2 diseases. Both PAH and CAD are associated with sustained inflammation and smooth muscle cell proliferation/apoptosis imbalance and we demonstrated in PAH that this phenotype is, in part, because of the miR-223/DNA damage/Poly[ADP-ribose] polymerase 1/miR-204 axis activation and subsequent bromodomain protein 4 (BRD4) overexpression. Interestingly, BRD4 is also a trigger for calcification and remodeling processes, both of which are important in CAD. Thus, we hypothesize that BRD4 activation in PAH influences the development of CAD. APPROACH AND RESULTS: PAH was associated with significant remodeling of the coronary arteries in both human and experimental models of the disease. As observed in PAH distal pulmonary arteries, coronary arteries of patients with PAH also exhibited increased DNA damage, inflammation, and BRD4 overexpression. In vitro, using human coronary artery smooth muscle cells from PAH, CAD and non-PAH-non-CAD patients, we showed that both PAH and CAD smooth muscle cells exhibited increased proliferation and suppressed apoptosis in a BRD4-dependent manner. In vivo, improvement of PAH by BRD4 inhibitor was associated with a reduction in coronary remodeling and interleukin-6 expression. CONCLUSIONS: Overall, this study demonstrates that increased BRD4 expression in coronary arteries of patient with PAH contributes to vascular remodeling and comorbidity development.

DNA Damage and Pulmonary Hypertension.

Pulmonary hypertension (PH) is defined by a mean pulmonary arterial pressure over 25 mmHg at rest and is diagnosed by right heart catheterization. Among the different groups of PH, pulmonary arterial hypertension (PAH) is characterized by a progressive obstruction of distal pulmonary arteries, related to endothelial cell dysfunction and vascular cell proliferation, which leads to an increased pulmonary vascular resistance, right ventricular hypertrophy, and right heart failure. Although the primary trigger of PAH remains unknown, oxidative stress and inflammation have been shown to play a key role in the development and progression of vascular remodeling. These factors are known to increase DNA damage that might favor the emergence of the proliferative and apoptosis-resistant phenotype observed in PAH vascular cells. High levels of DNA damage were reported to occur in PAH lungs and remodeled arteries as well as in animal models of PH. Moreover, recent studies have demonstrated that impaired DNA-response mechanisms may lead to an increased mutagen sensitivity in PAH patients. Finally, PAH was linked with decreased breast cancer 1 protein (BRCA1) and DNA topoisomerase 2-binding protein 1 (TopBP1) expression, both involved in maintaining genome integrity. This review aims to provide an overview of recent evidence of DNA damage and DNA repair deficiency and their implication in PAH pathogenesis.

Role for Runt-related Transcription Factor 2 in Proliferative and Calcified Vascular Lesions in Pulmonary Arterial Hypertension.

RATIONALE: Pulmonary arterial hypertension (PAH) is characterized by excessive proliferation of pulmonary artery smooth muscle cells (PASMCs). This is sustained in time by the down-regulation of microRNA (miR)-204. In systemic vascular diseases, reduced miR-204 expression promotes vascular biomineralization by augmenting the expression of the transcription factor Runt-related transcription factor 2 (RUNX2). Implication of RUNX2 in PAH-related vascular remodeling and presence of calcified lesions in PAH remain unexplored. OBJECTIVES: We hypothesized that RUNX2 is up-regulated in lungs of patients with PAH, contributing to vascular remodeling and calcium-related biomineralization. METHODS: We harvested human lung tissues in which we assessed calcification lesions and RUNX2 expression. We also isolated PASMCs from these tissues for in vitro analyses. Using a bidirectional approach, we investigated the role for RUNX2 in cell proliferation, apoptosis, and calcification capacity. Ectopic delivery of small interfering RNA against RUNX2 was used in an animal model of PAH to evaluate the therapeutic potential of RUNX2 inhibition in this disease. MEASUREMENTS AND MAIN RESULTS: Patients with PAH display features of calcified lesions within the distal pulmonary arteries (PAs). We show that RUNX2 is up-regulated in lungs, distal PAs, and primary cultured human PASMCs isolated from PAH and compared with patients without PAH. RUNX2 expression histologically correlates with vascular remodeling and calcification. Using in vitro gain- and loss-of-function approaches, we mechanistically demonstrate that miR-204 diminution promotes RUNX2 up-regulation and that sustained RUNX2 expression activates hypoxia-inducible factor-1α, leading to aberrant proliferation, resistance to apoptosis, and subsequent transdifferentiation of PAH-PASMCs into osteoblast-like cells. In the PAH Sugen/hypoxia rat model, molecular RUNX2 inhibition reduces PA remodeling and prevents calcification, thus improving pulmonary hemodynamic parameters and right ventricular function. CONCLUSIONS: RUNX2 plays a pivotal role in the pathogenesis of PAH, contributing to the development of proliferative and calcified PA lesions. Inhibition of RUNX2 may therefore represent an attractive therapeutic strategy for PAH.

Potassium Channel Subfamily K Member 3 (KCNK3) Contributes to the Development of Pulmonary Arterial Hypertension.

BACKGROUND: Mutations in the KCNK3 gene have been identified in some patients suffering from heritable pulmonary arterial hypertension (PAH). KCNK3 encodes an outward rectifier K(+) channel, and each identified mutation leads to a loss of function. However, the pathophysiological role of potassium channel subfamily K member 3 (KCNK3) in PAH is unclear. We hypothesized that loss of function of KCNK3 is a hallmark of idiopathic and heritable PAH and contributes to dysfunction of pulmonary artery smooth muscle cells and pulmonary artery endothelial cells, leading to pulmonary artery remodeling: consequently, restoring KCNK3 function could alleviate experimental pulmonary hypertension (PH). METHODS AND RESULTS: We demonstrated that KCNK3 expression and function were reduced in human PAH and in monocrotaline-induced PH in rats. Using a patch-clamp technique in freshly isolated (not cultured) pulmonary artery smooth muscle cells and pulmonary artery endothelial cells, we found that KCNK3 current decreased progressively during the development of monocrotaline-induced PH and correlated with plasma-membrane depolarization. We demonstrated that KCNK3 modulated pulmonary arterial tone. Long-term inhibition of KCNK3 in rats induced distal neomuscularization and early hemodynamic signs of PH, which were related to exaggerated proliferation of pulmonary artery endothelial cells, pulmonary artery smooth muscle cell, adventitial fibroblasts, and pulmonary and systemic inflammation. Lastly, in vivo pharmacological activation of KCNK3 significantly reversed monocrotaline-induced PH in rats. CONCLUSIONS: In PAH and experimental PH, KCNK3 expression and activity are strongly reduced in pulmonary artery smooth muscle cells and endothelial cells. KCNK3 inhibition promoted increased proliferation, vasoconstriction, and inflammation. In vivo pharmacological activation of KCNK3 alleviated monocrotaline-induced PH, thus demonstrating that loss of KCNK3 is a key event in PAH pathogenesis and thus could be therapeutically targeted.

Bromodomain-Containing Protein 4: The Epigenetic Origin of Pulmonary Arterial Hypertension.

RATIONALE: Pulmonary arterial hypertension (PAH) is a vasculopathy characterized by enhanced pulmonary artery (PA) smooth muscle cell (PASMC) proliferation and suppressed apoptosis. Decreased expression of microRNA-204 has been associated to this phenotype. By a still elusive mechanism, microRNA-204 downregulation promotes the expression of oncogenes, including nuclear factor of activated T cells, B-cell lymphoma 2, and Survivin. In cancer, increased expression of the epigenetic reader bromodomain-containing protein 4 (BRD4) sustains cell survival and proliferation. Interestingly, BRD4 is a predicted target of microRNA-204 and has binding sites on the nuclear factor of activated T cells promoter region. OBJECTIVE: To investigate the role of BRD4 in PAH pathogenesis. METHODS AND RESULTS: BRD4 is upregulated in lungs, distal PAs, and PASMCs of patients with PAH compared with controls. With mechanistic in vitro experiments, we demonstrated that BRD4 expression in PAH is microRNA-204 dependent. We further studied the molecular downstream targets of BRD4 by inhibiting its activity in PAH-PASMCs using a clinically available inhibitor JQ1. JQ1 treatment in PAH-PASMCs increased p21 expression, thus triggering cell cycle arrest. Furthermore, BRD4 inhibition, by JQ1 or siBRD4, decreased the expression of 3 major oncogenes, which are overexpressed in PAH: nuclear factor of activated T cells, B-cell lymphoma 2, and Survivin. Blocking this oncogenic signature led to decreased PAH-PASMC proliferation and increased apoptosis in a BRD4-dependent manner. Indeed, pharmacological JQ1 or molecular (siRNA) inhibition of BRD4 reversed this pathological phenotype in addition to restoring mitochondrial membrane potential and to increasing cells spare respiratory capacity. Moreover, BRD4 inhibition in vivo reversed established PAH in the Sugen/hypoxia rat model. CONCLUSIONS: BRD4 plays a key role in the pathological phenotype in PAH, which could offer new therapeutic perspectives for patients with PAH.

miR-223 reverses experimental pulmonary arterial hypertension.

Pulmonary arterial hypertension (PAH) is a devastating disease affecting lung vasculature. The pulmonary arteries become occluded due to increased proliferation and suppressed apoptosis of the pulmonary artery smooth muscle cells (PASMCs) within the vascular wall. It was recently shown that DNA damage could trigger this phenotype by upregulating poly(ADP-ribose)polymerase 1 (PARP-1) expression, although the exact mechanism remains unclear. In silico analyses and studies in cancer demonstrated that microRNA miR-223 targets PARP-1. We thus hypothesized that miR-223 downregulation triggers PARP-1 overexpression, as well as the proliferation/apoptosis imbalance observed in PAH. We provide evidence that miR-223 is downregulated in human PAH lungs, distal PAs, and isolated PASMCs. Furthermore, using a gain and loss of function approach, we showed that increased hypoxia-inducible factor 1α, which is observed in PAH, triggers this decrease in miR-223 expression and subsequent overexpression of PARP-1 allowing PAH-PASMC proliferation and resistance to apoptosis. Finally, we demonstrated that restoring the expression of miR-223 in lungs of rats with monocrotaline-induced PAH reversed established PAH and provided beneficial effects on vascular remodeling, pulmonary resistance, right ventricle hypertrophy, and survival. We provide evidence that miR-223 downregulation in PAH plays an important role in numerous pathways implicated in the disease and restoring its expression is able to reverse PAH.

Adaptation and remodelling of the pulmonary circulation in pulmonary hypertension.

Pulmonary arterial hypertension (PAH) is characterized by remodelling of pulmonary arteries caused by a proliferation/apoptosis imbalance within the vascular wall. This pathological phenotype seems to be triggered by different environmental stress and injury events such as increased inflammation, DNA damage, and epigenetic deregulation. It appears that one of the first hit to occur is endothelial cells (ECs) injury and apoptosis, which leads to paracrine signalling to other ECs, pulmonary artery smooth muscle cells (PASMCs), and fibroblasts. These signals promote a phenotypic change of surviving ECs by disturbing different signalling pathways leading to sustained vasoconstriction, proproliferative and antiapoptotic phenotype, deregulated angiogenesis, and formation of plexiform lesions. EC signalling also recruits proinflammatory cells, leading to pulmonary infiltration of lymphocytes, macrophages, and dendritic cells, sustaining the inflammatory environment and autoimmune response. Finally, EC signalling promotes proliferative and antiapoptotic PAH-PASMC phenotypes, which acquire migratory capacities, resulting in increased vascular wall thickness and muscularization of small pulmonary arterioles. Adaptation and remodelling of pulmonary circulation also involves epigenetic components, such as microRNA deregulation, DNA methylation, and histone modification. This review will focus on the different cellular and epigenetic aspects including EC stress response, molecular mechanisms contributing to PAH-PASMC and PAEC proliferation and resistance to apoptosis, as well as epigenetic control involved in adaptation and remodelling of the pulmonary circulation in PAH.

Therapeutic Potential of microRNA Modulation in Pulmonary Arterial Hypertension.

MicroRNAs have emerged as key players of gene regulation during development and disease states like cancer and cardiovascular diseases. Pulmonary arterial hypertension (PAH), a vascular disease characterized by pulmonary resistance and vessel occlusion, is not spared by microRNA implication. This is not surprising since PAH shares common aberrantly activated pathways with cancers that lead to proliferation and survival of pulmonary arterial smooth muscle cells, among others, within the artery wall and narrowing the lumen. Recent studies demonstrated the role of miR-204 and miR- 206 in pulmonary artery smooth muscle cell (PASMC) proliferation. Other microRNAs, such as miR-145, miR-21 and the miR17/92 cluster, have been associated with the disrupted BMPR2 pathway. During the last couple of years, the number of studies on the role of microRNA in PAH has broadened, defining it clearly as a HOT TOPIC. This current review presents an overview of the most recent knowledge as well as future possibilities. The use of microRNA therapies is still uncertain and poorly applied in the clinical setting yet. It is still critical to increase the knowledge and the translational potential of this HOT TOPIC to make it become a HOPE TOPIC.

miRNAs in PAH: biomarker, therapeutic target or both?

Pulmonary arterial hypertension (PAH) is characterized by progressive increase in pulmonary vascular resistance leading to right ventricular hypertrophy and failure. There is a need to find new biomarkers to detect PAH at its early stages and also for new, more effective treatments for this disease. miRNAs have emerged as key players in cardiovascular diseases and cancer development and progression and, more recently, in PAH pathogenesis. In this review, we focus on the potential of miRNAs as biomarkers and new therapeutic targets for PAH.

Role for DNA damage signaling in pulmonary arterial hypertension.

BACKGROUND: Pulmonary arterial hypertension (PAH) is associated with sustained inflammation known to promote DNA damage. Despite these unfavorable environmental conditions, PAH pulmonary arterial smooth muscle cells (PASMCs) exhibit, in contrast to healthy PASMCs, a pro-proliferative and anti-apoptotic phenotype, sustained in time by the activation of miR-204, nuclear factor of activated T cells, and hypoxia-inducible factor 1-α. We hypothesized that PAH-PASMCs have increased the activation of poly(ADP-ribose) polymerase-1 (PARP-1), a critical enzyme implicated in DNA repair, allowing proliferation despite the presence of DNA-damaging insults, eventually leading to PAH. METHODS AND RESULTS: Human PAH distal pulmonary arteries and cultured PAH-PASMCs exhibit increased DNA damage markers (53BP1 and γ-H2AX) and an overexpression of PARP-1 (immunoblot and activity assay), in comparison with healthy tissues/cells. Healthy PASMCs treated with a clinically relevant dose of tumor necrosis factor-α harbored a similar phenotype, suggesting that inflammation induces DNA damage and PARP-1 activation in PAH. We also showed that PARP-1 activation accounts for miR-204 downregulation (quantitative reverse transcription polymerase chain reaction) and the subsequent activation of the transcription factors nuclear factor of activated T cells and hypoxia-inducible factor 1-α in PAH-PASMCs, previously shown to be critical for PAH in several models. These effects resulted in PASMC proliferation (Ki67, proliferating cell nuclear antigen, and WST1 assays) and resistance to apoptosis (terminal deoxynucleotidyl transferase dUTP nick end labeling and Annexin V assays). In vivo, the clinically available PARP inhibitor ABT-888 reversed PAH in 2 experimental rat models (Sugen/hypoxia and monocrotaline). CONCLUSIONS: These results show for the first time that the DNA damage/PARP-1 signaling pathway is important for PAH development and provide a new therapeutic target for this deadly disease with high translational potential.

Targeting cell motility in pulmonary arterial hypertension.

Pulmonary artery smooth muscle cells (PASMC), in pulmonary arterial hypertension (PAH), contribute to obliterative vascular remodelling and are characterised by enhanced proliferation, suppressed apoptosis and, a much less studied, increased migration potential. One of the major proteins that regulate cell migration is focal adhesion kinase (FAK), but its role in PAH is not fully understood. We hypothesised that targeting cell migration by FAK inhibition may be a new therapeutic strategy in PAH. In vivo, inhalation of FAK-siRNA (n=5) or oral delivery of PF-228 (FAK inhibitor PF-573 228; n=5) inhibited rat monocrotaline induced PAH, improving the haemodynamics, vascular remodelling (media thickness), and right ventricular hypertrophy. In vitro, FAK was activated in PAH human lungs (n=8) or PASMC when compared to those form healthy subjects (Western blot, n=5), in a Src-dependent manner, as it was reversed by the specific Src inhibitor PP2. The degree of FAK phosphorylation at Y576 correlated positively with pulmonary vascular resistance in PAH patients. FAK inhibition (siRNA, PF-228 and PP2) in PAH-PASMCs induced a fivefold increase in apoptosis (percentage of terminal deoxynucleotidyl transferase dUTP nick end labelling), a 2.5-fold decrease in proliferation (%Ki67), an 18% decrease in cell migration (colorimetric assay) and a 50% decrease in cell invasion (wound healing). Suppressing PASMC migration by FAK inhibition inhibits PAH progression and may open a new therapeutic window in PAH.

Anti-inflammatory and immunosuppressive agents in PAH.

Pulmonary arterial hypertension (PAH) pathobiology involves a remodeling process in distal pulmonary arteries, as well as vasoconstriction and in situ thrombosis, leading to enhanced pulmonary vascular resistance and pressure, to right heart failure and death. The exact mechanisms accounting for PAH development remain unknown, but growing evidence demonstrate that inflammation plays a key role in triggering and maintaining pulmonary vascular remodeling. Not surprisingly, PAH is often associated with diverse inflammatory disorders. Furthermore, pathologic specimens from PAH patients reveal an accumulation of inflammatory cells in and around vascular lesions, including macrophages, T and B cells, dendritic cells, and mast cells. Circulating levels of autoantibodies, chemokines, and cytokines are also increased in PAH patients and some of these correlate with disease severity and patients' outcome. Moreover, preclinical experiments demonstrated the key role of inflammation in PAH pathobiology. Immunosuppressive agents have also demonstrated beneficial effects in animal PAH models. In humans, observational studies suggested that immunosuppressive drugs may be effective in treating some PAH subtypes associated with marked inflammation. The present chapter reviews experimental and clinical evidence suggesting that inflammation is involved in the pathogenesis of PAH, as well the therapeutic potential of immunosuppressive agents in PAH.

Signal transduction in the development of pulmonary arterial hypertension.

Pulmonary arterial hypertension (PAH) is a unique disease. Properly speaking, it is not a disease of the lung. It can be seen more as a microvascular disease occurring mainly in the lungs and affecting the heart. At the cellular level, the PAH paradigm is characterized by inflammation, vascular tone imbalance, pulmonary arterial smooth muscle cell proliferation and resistance to apoptosis and the presence of in situ thrombosis. At a clinical level, the aforementioned abnormal vascular properties alter physically the pulmonary circulation and ventilation, which greatly influence the right ventricle function as it highly correlates with disease severity. Consequently, right heart failure remains the principal cause of death within this cohort of patients. While current treatment modestly improve patients' conditions, none of them are curative and, as of today, new therapies are lacking. However, the future holds potential new therapies that might have positive influence on the quality of life of the patient. This article will first review the clinical presentation of the disease and the different molecular pathways implicated in the pathobiology of PAH. The second part will review tomorrow's future putative therapies for PAH.

Critical role for the advanced glycation end-products receptor in pulmonary arterial hypertension etiology.

BACKGROUND: Pulmonary arterial hypertension (PAH) is a vasculopathy characterized by enhanced pulmonary artery smooth muscle cell (PASMC) proliferation and suppressed apoptosis. This results in both increase in pulmonary arterial pressure and pulmonary vascular resistance. Recent studies have shown the implication of the signal transducer and activator of transcription 3 (STAT3)/bone morphogenetic protein receptor 2 (BMPR2)/peroxisome proliferator-activated receptor gamma (PPARγ) in PAH. STAT3 activation induces BMPR2 downregulation, decreasing PPARγ, which both contribute to the proproliferative and antiapoptotic phenotype seen in PAH. In chondrocytes, activation of this axis has been attributed to the advanced glycation end-products receptor (RAGE). As RAGE is one of the most upregulated proteins in PAH patients' lungs and a strong STAT3 activator, we hypothesized that by activating STAT3, RAGE induces BMPR2 and PPARγ downregulation, promoting PAH-PASMC proliferation and resistance to apoptosis. METHODS AND RESULTS: In vitro, using PASMCs isolated from PAH and healthy patients, we demonstrated that RAGE is overexpressed in PAH-PASMC (6-fold increase), thus inducing STAT3 activation (from 10% to 40% positive cells) and decrease in BMPR2 and PPARγ levels (>50% decrease). Pharmacological activation of RAGE in control cells by S100A4 recapitulates the PAH phenotype (increasing RAGE by 6-fold, thus activating STAT3 and decreasing BMPR2 and PPARγ). In both conditions, this phenotype is totally reversed on RAGE inhibition. In vivo, RAGE inhibition in monocrotaline- and Sugen-induced PAH demonstrates therapeutic effects characterized by PA pressure and right ventricular hypertrophy decrease (control rats have an mPAP around 15 mm Hg, PAH rats have an mPAP >40 mm Hg, and with RAGE inhibition, mPAP decreases to 20 and 28 mm Hg, respectively, in MCT and Sugen models). This was associated with significant improvement in lung perfusion and vascular remodeling due to decrease in proliferation (>50% decrease) and BMPR2/PPARγ axis restoration (increased by ≥60%). CONCLUSION: We have demonstrated the implications of RAGE in PAH etiology. Thus, RAGE constitutes a new attractive therapeutic target for PAH.

Today's and tomorrow's imaging and circulating biomarkers for pulmonary arterial hypertension.

The pathobiology of pulmonary arterial hypertension (PAH) involves a remodeling process in distal pulmonary arteries, as well as vasoconstriction and in situ thrombosis, leading to an increase in pulmonary vascular resistance, right heart failure and death. Its etiology may be idiopathic, but PAH is also frequently associated with underlying conditions such as connective tissue diseases. During the past decade, more than welcome novel therapies have been developed and are in development, including those increasingly targeting the remodeling process. These therapeutic options modestly increase the patients' long-term survival, now approaching 60% at 5 years. However, non-invasive tools for confirming PAH diagnosis, and assessing disease severity and response to therapy, are tragically lacking and would help to select the best treatment. After exclusion of other causes of pulmonary hypertension, a final diagnosis still relies on right heart catheterization, an invasive technique which cannot be repeated as often as an optimal follow-up might require. Similarly, other techniques and biomarkers used for assessing disease severity and response to treatment generally lack specificity and have significant limitations. In this review, imaging as well as current and future circulating biomarkers for diagnosis, prognosis, and follow-up are discussed.