Pulmonary Arterial Hypertension Lung Research Articles

MiR‐223 a new signaling hub accounting for DNA damage signaling and STAT3 activation in pulmonary arterial hypertension (406.6)

Background: We reported that pulmonary arterial hypertension (PAH) is associated with an increased activation of Poly(ADP‐ribose) polymerase‐1 (PARP‐1) and the transcription factor STAT3 within the pulmonary arterial smooth muscle cells (PASMC). PARP‐1/STAT3 are common denominators to numerous pathways implicated in PAH including inflammation, Warburg effect; DNA repair; proliferation and apoptosis; thus PARP‐1/STAT3 activation can eventually leads to PAH. Despite extensive research PARP‐1/STAT3 activation mechanism remains elusive. Micro‐RNAs are non‐coding small RNA implicated in PAH etiology, in sillico analysis revealed that an interaction between the transcription factor CEBPα and miR‐233 is likely implicated in PARP‐1/STAT3 activation. We hypothesized that miR‐223 is downregulated in PAH contributing to PARP‐1/STAT3 activation.Methods and results: Using qRT‐PCR, we demonstrated that miR‐223 is significantly downregulated in Human PAH lungs, distal pulmonary arteries (<800μm) and cultured PAH‐PASMCs compare to control donors (n=3 to 5 patients). Downregulation of miR‐223 was associated with a significant downregulation at both mRNA (qRT‐PCR) and protein levels (immunoblot and immunofluorescence) of CEBPα, a transcription factor known to regulate miR‐223. Interestingly, the CEBPα‐dependent downregulation of miR‐223 was associated with PARP‐1 and STAT3 activation in PAH‐PASMC contributing to their prolifération.Conclusion: We provide preliminary evidences of the implication of a CEBPα/miR‐223 axis in the etiology of PAH, and its likely implication in the activation of PARP‐1/STAT3 signaling known to regulates PASMC proliferation and resistance to apoptosis. Therefore, CEBPα/miR‐223 represents a new avenue of investigation and a putative new therapeutic target for PAH.

Modulation of endothelin receptors in the failing right ventricle of the heart and vasculature of the lung in human pulmonary arterial hypertension

AimsIn pulmonary arterial hypertension (PAH), increases in endothelin-1 (ET-1) contribute to elevated pulmonary vascular resistance which ultimately causes death by right ventricular (RV) heart failure. ET antagonists are effective in treating PAH but lack efficacy in treating left ventricular (LV) heart failure, where ETA receptors are significantly increased. The aim was to quantify the density of ETA and ETB receptors in cardiopulmonary tissue from PAH patients and the monocrotaline (MCT) rat, which recapitulates some of the pathophysiological features, including increased RV pressure. Main methodsRadioligand binding assays were used to quantify affinity, density and ratio of ET receptors. Key findingsIn RV from human PAH hearts, there was a significant increase in the ratio of ETA to ETB receptors compared with normal hearts. In the RV of the MCT rat, the ratio also changed but was reversed. In both human and rat, there was no change in LV. In human PAH lungs, ETA receptors were significantly increased in the medial layer of small pulmonary arteries with no change detectable in MCT rat vessels. SignificanceCurrent treatments for PAH focus mainly on pulmonary vasodilatation. The increase in ETA receptors in arteries provides a mechanism for the beneficial vasodilator actions of ET antagonists. The increase in the ratio of ETA in RV also implicates changes to ET signalling although it is unclear if ET antagonism is beneficial but the results emphasise the unexploited potential for therapies that target the RV, to improve survival in patients with PAH.

Metabolomic Heterogeneity of Pulmonary Arterial Hypertension

Although multiple gene and protein expression have been extensively profiled in human pulmonary arterial hypertension (PAH), the mechanism for the development and progression of pulmonary hypertension remains elusive. Analysis of the global metabolomic heterogeneity within the pulmonary vascular system leads to a better understanding of disease progression. Using a combination of high-throughput liquid-and-gas-chromatography-based mass spectrometry, we showed unbiased metabolomic profiles of disrupted glycolysis, increased TCA cycle, and fatty acid metabolites with altered oxidation pathways in the human PAH lung. The results suggest that PAH has specific metabolic pathways contributing to increased ATP synthesis for the vascular remodeling process in severe pulmonary hypertension. These identified metabolites may serve as potential biomarkers for the diagnosis of PAH. By profiling metabolomic alterations of the PAH lung, we reveal new pathogenic mechanisms of PAH, opening an avenue of exploration for therapeutics that target metabolic pathway alterations in the progression of PAH.

A Novel Vascular Homing Peptide Strategy to Selectively Enhance Pulmonary Drug Efficacy in Pulmonary Arterial Hypertension

A major limitation in the pharmacological treatment of pulmonary arterial hypertension (PAH) is the lack of pulmonary vascular selectivity. Recent studies have identified a tissue-penetrating homing peptide, CARSKNKDC (CAR), which specifically homes to hypertensive pulmonary arteries but not to normal pulmonary vessels or other tissues. Some tissue-penetrating vascular homing peptides have a unique ability to facilitate transport of co-administered drugs into the targeted cells/tissues without requiring physical conjugation of the drug to the peptide (bystander effect). We tested the hypothesis that co-administered CAR would selectively enhance the pulmonary vascular effects of i.v. vasodilators in Sugen5416/hypoxia/normoxia-exposed PAH rats. Systemically administered CAR was predominantly detected in cells of remodeled pulmonary arteries. Intravenously co-administered CAR enhanced pulmonary, but not systemic, effects of the vasodilators, fasudil and imatinib, in PAH rats. CAR increased lung tissue imatinib concentration in isolated PAH lungs without increasing pulmonary vascular permeability. Sublingual CAR was also effective in selectively enhancing the pulmonary vasodilation by imatinib and sildenafil. Our results suggest a new paradigm in the treatment of PAH, using an i.v./sublingual tissue-penetrating homing peptide to selectively augment pulmonary vascular effects of nonselective drugs without the potentially problematic conjugation process. CAR may be particularly useful as an add-on therapy to selectively enhance the pulmonary vascular efficacy of any ongoing drug treatment in patients with PAH.

Evidence for the Involvement of Type I Interferon in Pulmonary Arterial Hypertension

Evidence is increasing of a link between interferon (IFN) and pulmonary arterial hypertension (PAH). Conditions with chronically elevated endogenous IFNs such as systemic sclerosis are strongly associated with PAH. Furthermore, therapeutic use of type I IFN is associated with PAH. This was recognized at the 2013 World Symposium on Pulmonary Hypertension where the urgent need for research into this was highlighted. To explore the role of type I IFN in PAH. Cells were cultured using standard approaches. Cytokines were measured by ELISA. Gene and protein expression were measured using reverse transcriptase polymerase chain reaction, Western blotting, and immunohistochemistry. The role of type I IFN in PAH in vivo was determined using type I IFN receptor knockout (IFNAR1(-/-)) mice. Human lung cells responded to types I and II but not III IFN correlating with relevant receptor expression. Type I, II, and III IFN levels were elevated in serum of patients with systemic sclerosis associated PAH. Serum interferon γ inducible protein 10 (IP10; CXCL10) and endothelin 1 were raised and strongly correlated together. IP10 correlated positively with pulmonary hemodynamics and serum brain natriuretic peptide and negatively with 6-minute walk test and cardiac index. Endothelial cells grown out of the blood of PAH patients were more sensitive to the effects of type I IFN than cells from healthy donors. PAH lung demonstrated increased IFNAR1 protein levels. IFNAR1(-/-) mice were protected from the effects of hypoxia on the right heart, vascular remodeling, and raised serum endothelin 1 levels. These data indicate that type I IFN, via an action of IFNAR1, mediates PAH.

Unanticipated role of apelin: regulation of miRNA generation

Recently, a paper by Kim et al. [1] in Nature Medicine magazine in January, 2013 showed that apelin (also known as APLN) inhibits fibroblast growth factor 2 (FGF2) and FGF receptor 1 (FGFR1) expression to ameliorate pulmonary hypertension by regulating the expression of miR-424 and miR-503. This study revealed the molecular mechanism of apelin in inhibiting the process of pulmonary arterial hypertension (PAH) and discovered the role of apelin in regulating miRNA generation for the first time. miRNA functions in the transcriptional regulation of gene expression to control cellular processes. miRNA is a key regulatory factor of protein expression, but the generation and regulation mechanism of miRNA is still unclear. These novel findings bring us inspiration for further research, especially on the mechanism of miRNA generation. Experiments on revealing endogenous active substance, which regulates the generation of miRNAs or revealing miRNAs that regulate the expression of apelin, may bring more breakthroughs in the future. PAH is characterized by vascular remodeling associated with obliteration of pulmonary arterioles and formation of plexiform lesions composed of hyperproliferative endothelial and vascular smooth muscle cells. Recent studies have suggested that apelin is a novel PAH endothelial function homeostasis-related factor. Alastalo et al. [2] found that apelin expression is decreased in endothelial cells of the pulmonary hypertension. However, the exact mechanism remains poorly understood. FGF2 is highly expressed in PAH and plays an important role in the progress of PAH by promoting proliferation [3] and inhibiting apoptosis [4] in endothelial cells and smooth muscle cells. miRNA is a fundamental factor of numerous cellular events by regulating RNA modification, transcription, and translation. Current studies of miRNA showed its critical function in the development of PAH. Morphological changes of plexiform vasculopathy in the end-stage PAH lung are reflected by alterations at the miRNA level [5]. Kim et al. [1] integrated these isolated observations into a mechanism and identified the miRNA-FGF signaling axis that is apelin-dependent in the maintenance of pulmonary vascular homeostasis. Previous studies found that hypoxia induces endothelial function injury. Accumulating evidence revealed that hypoxia also induces the expression of apelin [6,7],which is reduced in PAH. Actually, apelin expression and secretion, which are strongly induced under hypoxic conditions, are the early response [7]. Mechanisms that maintain sustained expression of apelin may contribute to preventing injuries caused by hypoxia and restoring the function of endothelial cells in PAH. These findings supported the development of novel therapeutic strategies to augment apelin, as well as to inhibit FGF2 signaling. In portal vein hypertension, another vascular disease, apelin/APJ presents a novel therapeutic target. APJ antagonist F13A effectively decreased the formation of portosystemic collateral vessels [8]. In atherosclerosis (AS), increasing evidence tends to prove that apelin is a novel therapeutic target for AS [9]. Although no effective treatment for PAH is available at present, certain medicines are available to mitigate disease progression. Considering its protective effect on vasodilatory and endothelial cells, apelin may be a more efficacious target for PAH therapy. In past decades, apelin was suggested to involve in numerous physiological processes, including vasodilation, systole, salt and water balance, as well as pathophysiological processes such as high blood pressure, cancer, and so on. There must be many other undiscovered functions of apelin. The findings of the intimate relationship between apelin and miRNA provide much fresh thinking for the study of apelin. The study on miR-424 and miR-503 will help to discover additional features of apelin. Park et al. [10] found that the high expression of miR-424 and miR-503 is significantly implicated in chemoresistance and tumor progression in ovarian cancer, which probably regulates cancer stem cell processes. These results indicated that apelin probably plays a vital role in epithelial mesenchymal transition in cancers. A recent study revealed that miR-503 makes women predispose to lupus [11]. The relationship between apelin and lupus has not been explored. More evidence is required to confirm whether apelin controls the effects of miR-424 and miR-503 in the above process. There are some controversial reports of apelin/APJ effects on AS. Chun et al. [12] found that apelin decreases AS formation by blocking AngII actions in ApoE-KO mice. But Hashimoto et al. [13] Acta Biochim Biophys Sin 2013, 45: 896–898 |a The Author 2013. Published by ABBS Editorial Office in association with Oxford University Press on behalf of the Institute of Biochemistry and Cell Biology, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences. DOI: 10.1093/abbs/gmt090. Advance Access Publication 28 August 2013

Inhibition of the receptor of advanced glycation reverses pulmonary arterial hypertension

Pulmonary arterial (PA) hypertension (PAH) is a vasculopathy characterized by enhanced PA smooth muscle cells (PASMC) proliferation and suppressed apoptosis. A recent proteomic analysis of PAH lungs demonstrated that the receptor of advanced glycation endproducts (RAGE) is one of the most upregulated proteins in PAH patients. We hypothesized that RAGE could play a critical role in PAH etiology and progression. We demonstrated a specific RAGE overexpression in PAH lungs. In human PASMC, we showed that RAGE was implicated in the proliferative and apoptosis‐resistant phenotype. Recent studies demonstrated an altered BMPR2 (Bone Morphogenetic Protein Receptor 2)/PPARγ (Peroxisome Proliferator‐Activated Receptor gamma) axis in PAH. We showed that RAGE is accountable for BMPR2/PPARγ downregulation, thus regulating proliferation and apoptosis. In vivo, RAGE inhibition (siRNA nebulization) in rats with Sugen‐induced PAH showed decreased PA pressure and right ventricular hypertrophy, associated with a significant improvement in lung perfusion and decreased PA wall thickness. To conclude, we demonstrated the implication of RAGE in PAH etiology. Thus, RAGE inhibitors, which are in clinical phase II for Alzheimer's disease, represent potential therapeutic agents for PAH treatment.A Canadian Thoracic Society scholarship to JM and Canadian Institutes of Health Research grants to SB supported this work.

Circulating Angiogenic Modulatory Factors Predict Survival and Functional Class in Pulmonary Arterial Hypertension

The diagnosis of pulmonary arterial hypertension (PAH) is frequently delayed. We hypothesized that circulating angiogenic modulatory protein levels might correspond with vascular remodeling activity and serve as sensitive biomarkers of PAH. Levels of soluble endoglin (sEng), soluble vascular endothelial growth factor receptor-1 (sVEGFR1), N-terminal brain natriuretic peptide (NT-proBNP), C-reactive protein (CRP), and other biomarkers were measured in peripheral blood from 97 PAH patients, 16 first-degree relatives of idiopathic or heritable pulmonary arterial hypertension (HPAH) patients, and 56 controls, and correlated with disease, functional class, hemodynamic parameters, exercise capacity, and transplant-free survival. Endoglin expression was analyzed in lung tissues of six individuals with idiopathic or HPAH and four individuals without PAH. Levels of sEng, sVEGFR1, CRP, and NT-proBNP were elevated in Group I PAH of diverse etiologies, with sEng performing better than NT-proBNP in detecting PAH (receiver operator characteristic-area-under-the curve [ROC-AUC] of 0.82 ± 0.03 vs. 0.71 ± 0.05, P = 0.016). While sEng, sVEGFR1, and NT-proBNP correlated with New York Heart Association (NYHA) class, sEng levels were more sensitive than NT-proBNP in detecting NYHA Class I-II disease (ROC-AUC of 0.88 ± 0.05 vs. 0.67 ± 0.08, P = 0.028). sEng, sVEGFR1, CRP, and NT-proBNP predicted transplant-free survival by univariate Cox regression. After adjusting for NT-proBNP levels, each of the other three markers predicted transplant-free survival. In multivariate analysis, sEng and CRP were independent predictors of survival. Endoglin expression was markedly enhanced in the microvascular endothelium and endovascular lesions of PAH versus control lung tissues. Circulating angiogenic proteins sEng and sVEGFR1 are sensitive markers of prognosis and function in Group I PAH, including mildly symptomatic disease, and may provide unique noninvasive data reflecting underlying remodeling activity.

Genome-wide association analysis identifies a susceptibility locus for pulmonary arterial hypertension

Pulmonary arterial hypertension (PAH) is a rare, severe disease resulting from progressive obliteration of small-caliber pulmonary arteries by proliferating vascular cells. PAH can occur without recognized etiology (idiopathic PAH), be associated with a systemic disease or occur as a heritable form, with BMPR2 mutated in approximately 80% of familial and 15% of idiopathic PAH cases. We conducted a genome-wide association study (GWAS) based on 2 independent case-control studies for idiopathic and familial PAH (without BMPR2 mutations), including a total of 625 cases and 1,525 healthy individuals. We detected a significant association at the CBLN2 locus mapping to 18q22.3, with the risk allele conferring an odds ratio for PAH of 1.97 (1.59-2.45; P = 7.47 × 10(-10)). CBLN2 is expressed in the lung, and its expression is higher in explanted lungs from individuals with PAH and in endothelial cells cultured from explanted PAH lungs.

Immune and Inflammatory Cell Involvement in the Pathology of Idiopathic Pulmonary Arterial Hypertension

Pulmonary arterial hypertension (PAH) is characterized by vasoconstriction and vascular remodeling. Recent studies have revealed that immune and inflammatory responses play a crucial role in pathogenesis of idiopathic PAH. To systematically evaluate the number and cross-sectional distribution of inflammatory cells in different sizes of pulmonary arteries from explanted lungs of patients with idiopathic PAH versus healthy donor lungs and to demonstrate functional relevance by blocking stromal-derived factor-1 by the Spiegelmer NOX-A12 in monocrotaline-induced pulmonary hypertension in rats. Immunohistochemistry was performed on lung tissue sections from patients with idiopathic PAH and healthy donors. All positively stained cells in whole-lung tissue sections, surrounding the vessels, and in the different compartments of the vessels were counted. To study the effects of blocking SDF-1, rats with monocrotaline-induced pulmonary hypertension were treated with NOX-A12 from Day 21 to Day 35 after monocrotaline administration. We found a significant increase of the perivascular number of macrophages (CD68(+)), macrophages/monocytes (CD14(+)), mast cells (toluidine blue(+)), dendritic cells (CD209(+)), T cells (CD3(+)), cytotoxic T cells (CD8(+)), and helper T cells (CD4(+)) in vessels of idiopathic PAH lungs compared with control subjects. FoxP3(+) mononuclear cells were significantly decreased. In the monocrotaline model, the NOX-A12-induced reduction of mast cells, CD68(+) macrophages, and CD3(+) T cells was associated with improvement of hemodynamics and pulmonary vascular remodeling. Our findings reveal altered perivascular inflammatory cell infiltration in pulmonary vascular lesions of patients with idiopathic pulmonary arterial hypertension. Targeting attraction of inflammatory cells by blocking stromal-derived factor-1 may be a novel approach for treatment of PAH.

500 Translationally Controlled Tumor Protein (TCTP) Revealed by Proteomic Analysis of Patient-Specific Blood outgrowth Endothelial Cells in Heritable Pulmonary Arterial Hypertension

BACKGROUND: Pulmonary arterial hypertension (PAH) is a lethal disease, characterized by excessive proliferation of pulmonary vascular cells. Hereditary PAH is mainly caused by “lossof-function” mutations in the bone morphogenetic protein type II receptor (Bmpr2). However, the mechanisms by which these mutations cause PAH remain unclear. AIM: To identify dysregulated proteins in blood-derived endothelial cells of PAH patients with Bmpr2 mutations compared with healthy controls that may contribute to the pathogenesis of this disease. METHODS: Blood-outgrowth endothelial cells (ECs) were expanded ex vivo from peripheral blood mononuclear cell samples of four patients with heritable PAH and four healthy subjects. Protein isolates were subjected to 2D gel electrophoresis and stained for total proteins with Sypro Ruby. Gels were scanned and subjected to quantitative computer-assisted analysis (PDQuest software) and differentially regulated proteins determined by statistical tests (p-value 0.05) were identified by mass spectrometry (LC-MS/MS). RESULTS: Of the 416 proteins detected, 11 were significantly downregulated in PAH cells, including proteins in pathways previously implicated in PAH (i.e. PKA and guanine nucleotide-binding protein). 11 proteins were significantly upregulated, including a number of cell growth regulatory proteins, notably translationally controlled tumor protein (TCTP). TCTP has previously been shown to be enriched in EC apoptotic nanovesicles and to mediate pro-survival signaling in adjacent cells. Increased expression of TCTP in PAH compared to healthy control cells was demonstrated in patient-derived blood outgrowth ECs in vitro. In addition, the potential role of TCTP in PAH was studied in vivo in the SU5416 (SU) rat model of severe, angioproliferative PAH. SU is a VEGFR2inhibitor which induces EC apoptosis followed by reactive pulmonary vascular cell proliferation causing obliterative pulmonary vascular lesions closely mimicking the human condition. Immunofluorescence staining revealed high expression of TCTP in arteriolar ECs of PAH lungs tightly localized to proliferating cells within occlusive intimal lesions; whereas, only minimal TCTP expression was seen in vascular ECs of normal lungs. CONCLUSIONS: Bmpr2 mutant ECs exhibited dysregulation of key proteins controlling vasodilation and EC growth. TCTP could play an important role in PAH, possibly mediating prosurvival signaling in smooth muscle cells in response to EC apoptosis and thereby contributing to the process of pulmonary vascular remodeling. CIHR, FRQS, Cambridge NIHR Biomedical Research Centre, UK

Modern Age Pathology of Pulmonary Arterial Hypertension

The impact of modern treatments of pulmonary arterial hypertension (PAH) on pulmonary vascular pathology remains unknown. To assess the spectrum of pulmonary vascular remodeling in the modern era of PAH medication. Assessment of pulmonary vascular remodeling and inflammation in 62 PAH and 28 control explanted lungs systematically sampled. Intima and intima plus media fractional thicknesses of pulmonary arteries were increased in the PAH group versus the control lungs and correlated with pulmonary hemodynamic measurements. Despite a high variability of morphological measurements within a given PAH lung and among all PAH lungs, distinct pathological subphenotypes were detected in cohorts of PAH lungs. These included a subset of lungs lacking intima or, most prominently, media remodeling, which had similar numbers of profiles of plexiform lesions as those in lungs with more pronounced remodeling. Marked perivascular inflammation was present in a high number of PAH lungs and correlated with intima plus media remodeling. The number of profiles of plexiform lesions was significantly lower in lungs of male patients and those never treated with prostacyclin or its analogs. Our results indicate that multiple features of pulmonary vascular remodeling are present in patients treated with modern PAH therapies. Perivascular inflammation may have an important role in the processes of vascular remodeling, all of which may ultimately lead to increased pulmonary artery pressure. Moreover, our study provides a framework to interpret and design translational studies in PAH.

Plexiform vasculopathy of severe pulmonary arterial hypertension and microRNA expression

Recent studies have revealed that microRNAs (miRNAs) play a key role in the control of angiogenesis and vascular remodeling. Specific miRNAs in plexiform vasculopathy of severe pulmonary arterial hypertension (PAH) in humans have not yet been investigated. We analyzed expression of miR-143/145 (vascular smooth muscle-specific), miR-126 (endothelial-specific) and related mRNAs in plexiform (PLs) and concentric lesions (CLs), which had been laser-microdissected from specimens of formalin-fixed, paraffin-embedded, explanted lungs of PAH patients (n = 12) and unaffected controls (n = 8). Samples were analyzed by real-time polymerase chain reaction, and protein expression was determined by immunohistochemistry. Expression levels of miR-143/145 and its target proteins (e.g., myocardin, smooth muscle myosin heavy chain) were found to be significantly higher in CLs than in PLs, whereas miR-126 and VEGF-A were significantly up-regulated in PLs when compared with CLs, indicating a more prominent angiogenic phenotype of PL. This correlates with a down-regulation of miR-204 as well as an up-regulation of miR-21 in PLs, which in turn corresponds to enhanced cell proliferation. Our findings show that morphologic changes of plexiform vasculopathy in the end-stage PAH lung are reflected by alterations at the miRNA level.

Dynamin-related protein 1-mediated mitochondrial mitotic fission permits hyperproliferation of vascular smooth muscle cells and offers a novel therapeutic target in pulmonary hypertension.

Pulmonary arterial hypertension (PAH) is a lethal syndrome characterized by pulmonary vascular obstruction caused, in part, by pulmonary artery smooth muscle cell (PASMC) hyperproliferation. Mitochondrial fragmentation and normoxic activation of hypoxia-inducible factor-1α (HIF-1α) have been observed in PAH PASMCs; however, their relationship and relevance to the development of PAH are unknown. Dynamin-related protein-1 (DRP1) is a GTPase that, when activated by kinases that phosphorylate serine 616, causes mitochondrial fission. It is, however, unknown whether mitochondrial fission is a prerequisite for proliferation. We hypothesize that DRP1 activation is responsible for increased mitochondrial fission in PAH PASMCs and that DRP1 inhibition may slow proliferation and have therapeutic potential. Experiments were conducted using human control and PAH lungs (n=5) and PASMCs in culture. Parallel experiments were performed in rat lung sections and PASMCs and in rodent PAH models induced by the HIF-1α activator, cobalt, chronic hypoxia, and monocrotaline. HIF-1α activation in human PAH leads to mitochondrial fission by cyclin B1/CDK1-dependent phosphorylation of DRP1 at serine 616. In normal PASMCs, HIF-1α activation by CoCl(2) or desferrioxamine causes DRP1-mediated fission. HIF-1α inhibition reduces DRP1 activation, prevents fission, and reduces PASMC proliferation. Both the DRP1 inhibitor Mdivi-1 and siDRP1 prevent mitotic fission and arrest PAH PASMCs at the G2/M interphase. Mdivi-1 is antiproliferative in human PAH PASMCs and in rodent models. Mdivi-1 improves exercise capacity, right ventricular function, and hemodynamics in experimental PAH. DRP-1-mediated mitotic fission is a cell-cycle checkpoint that can be therapeutically targeted in hyperproliferative disorders such as PAH.

Serum Osteoprotegerin is Increased and Predicts Survival in Idiopathic Pulmonary Arterial Hypertension

We previously reported that osteoprotegerin (OPG) is regulated by pathways associated with pulmonary arterial hypertension (PAH), and is present at elevated levels within pulmonary vascular lesions and sera from patients with idiopathic PAH (IPAH). Since OPG is a naturally secreted protein, we investigated the relationship between serum OPG and disease severity and outcome in patients with IPAH and animal models. OPG mRNA expression was measured in pulmonary artery smooth muscle cells (PASMC) from pulmonary arteries of patients with and without IPAH. Serum concentrations of OPG were measured in a retrospective and prospective group of patients. OPG levels were compared with phenotypic data and other putative PAH biomarkers. Prognostic significance was assessed and levels compared with healthy controls. Correlation of OPG and pulmonary vascular remodeling was also performed in rodent models of PAH. OPG mRNA was significantly increased 2-fold in PASMC isolated from explanted PAH lungs compared with control. Serum OPG concentrations were markedly elevated in IPAH compared with controls. In Cohort 1 OPG levels significantly correlated with mean right atrial pressure and cardiac index, while in Cohort 2 significant correlations existed between age-adjusted OPG levels and gas transfer. In both cohorts an OPG concentration above a ROC-derived threshold of 4728 pg/ml predicted poorer survival. In two rodent models, OPG correlated with the degree of pulmonary vascular remodeling. OPG levels are significantly elevated in patients with idiopathic PAH and are of prognostic significance. The role of OPG as a potential biomarker and therapeutic target merits further investigation.

GDF-15 is abundantly expressed in plexiform lesions in patients with pulmonary arterial hypertension and affects proliferation and apoptosis of pulmonary endothelial cells

BackgroundGrowth-differentiation factor-15 (GDF-15) is a stress-responsive, transforming growth factor-β-related cytokine, which has recently been reported to be elevated in serum of patients with idiopathic pulmonary arterial hypertension (IPAH). The aim of the study was to examine the expression and biological roles of GDF-15 in the lung of patients with pulmonary arterial hypertension (PAH).MethodsGDF-15 expression in normal lungs and lung specimens of PAH patients were studied by real-time RT-PCR and immunohistochemistry. Using laser-assisted micro-dissection, GDF-15 expression was further analyzed within vascular compartments of PAH lungs. To elucidate the role of GDF-15 on endothelial cells, human pulmonary microvascular endothelial cells (HPMEC) were exposed to hypoxia and laminar shear stress. The effects of GDF-15 on the proliferation and cell death of HPMEC were studied using recombinant GDF-15 protein.ResultsGDF-15 expression was found to be increased in lung specimens from PAH patients, com-pared to normal lungs. GDF-15 was abundantly expressed in pulmonary vascular endothelial cells with a strong signal in the core of plexiform lesions. HPMEC responded with marked upregulation of GDF-15 to hypoxia and laminar shear stress. Apoptotic cell death of HPMEC was diminished, whereas HPMEC proliferation was either increased or decreased depending of the concentration of recombinant GDF-15 protein.ConclusionsGDF-15 expression is increased in PAH lungs and appears predominantly located in vascular endothelial cells. The expression pattern as well as the observed effects on proliferation and apoptosis of pulmonary endothelial cells suggest a role of GDF-15 in the homeostasis of endothelial cells in PAH patients.

Pulmonary Artery Endothelium Resident Endothelial Colony‐Forming Cells in Pulmonary Arterial Hypertension

Proliferative pulmonary vascular remodeling is the pathologic hallmark of pulmonary arterial hypertension (PAH) that ultimately leads to right heart failure and death. Highly proliferative endothelial cells known as endothelial colony-forming cells (ECFC) participate in vascular homeostasis in health as well as in pathological angiogenic remodeling in disease. ECFC are distinguished by the capacity to clonally proliferate from a single cell. The presence of ECFC in the human pulmonary arteries and their role in PAH pathogenesis is largely unknown. In this study, we established a simple technique for isolating and growing ECFC from cultured pulmonary artery endothelial cells (PAEC) to test the hypothesis that ECFC reside in human pulmonary arteries and that the proliferative vasculopathy of PAH is related to greater numbers and/or more proliferative ECFC in the pulmonary vascular wall. Flow cytometric forward and side scatter properties and aggregate correction were utilized to sort unmanipulated, single PAEC to enumerate ECFC in primary PAEC cultures derived from PAH and healthy lungs. After 2 weeks, wells were assessed for ECFC formation. ECFC derived from PAH PAEC were more proliferative than control. A greater proportion of PAH ECFC formed colonies following subculturing, demonstrating the presence of more ECFC with high proliferative potential among PAH PAEC. Human androgen receptor assay showed clonality of progeny, confirming that proliferative colonies were single cell-derived. ECFC expressed CD31, von Willebrand factor, endothelial nitric oxide synthase, caveolin-1 and CD34, consistent with an endothelial cell phenotype. We established a simple flow cytometry method that allows ECFC quantification using unmanipulated cells. We conclude that ECFC reside among PAEC and that PAH PAEC contain ECFC that are more proliferative than ECFC in control cultures, which likely contributes to the proliferative angiopathic process in PAH.

Human γ-Herpesviruses Epstein-Barr Virus and Human Herpesvirus-8 Are Not Detected in the Lungs of Patients With Severe Pulmonary Arterial Hypertension

In susceptible individuals, multiple events may trigger pulmonary vascular remodeling and pulmonary arterial hypertension (PAH). Human herpesvirus-8 (HHV-8), a γ-herpesvirus homologous with Epstein-Barr virus (EBV), was suggested to act as a "second hit" in the development of PAH in susceptible patients. Although there is indirect evidence from in vitro and animal studies in favor of a link between γ-herpesviruses and the pathophysiology of PAH, results remain controversial. Therefore, we investigated the presence of EBV and HHV-8 in the lungs of patients with PAH. Thirty-four lungs explanted from French patients with end-stage PAH (mean age, 38 ± 14 years; 19 women) were studied. Tissue samples were incorporated into tissue microarrays. Normal lung tissues served as negative controls. Kaposi sarcoma tissue served as a positive control for HHV-8, and EBV-associated lymphoma served as a positive control for EBV. The presence of HHV-8 was investigated with immunohistochemistry and polymerase chain reaction. The presence of EBV was investigated with immunohistochemistry and in situ hybridization. For HHV-8, none of PAH lung samples showed a "stippling" nuclear pattern classically observed in HHV-8-positive Kaposi sarcoma lesions. When studied by polymerase chain reaction, all cases remained negative. For EBV, none of the PAH lung samples showed positive staining, whatever the technique applied. HHV-8 and EBV cannot be detected in the lungs of patients with end-stage PAH. The role of these γ-herpesviruses in the pathophysiology of PAH is, therefore, unlikely.

Peptide-Directed Highly Selective Targeting of Pulmonary Arterial Hypertension

Pulmonary arterial hypertension (PAH) is a disorder of the pulmonary vasculature associated with elevated pulmonary vascular resistance. Despite recent advances in the treatment of PAH, with eight approved clinical therapies and additional therapies undergoing clinical trials, PAH remains a serious life-threatening condition. The lack of pulmonary vascular selectivity and associated systemic adverse effects of these therapies remain the main obstacles to successful treatment. Peptide-mediated drug delivery that specifically targets the vasculature of PAH lungs may offer a solution to the lack of drug selectivity. Herein, we show highly selective targeting of rat PAH lesions by a novel cyclic peptide, CARSKNKDC (CAR). Intravenous administration of CAR peptide resulted in intense accumulation of the peptide in monocrotaline-induced and SU5416/hypoxia-induced hypertensive lungs but not in healthy lungs or other organs of PAH rats. CAR homed to all layers of remodeled pulmonary arteries, ie, endothelium, neointima, medial smooth muscle, and adventitia, in the hypertensive lungs. CAR also homed to capillary vessels and accumulated in the interstitial space of the PAH lungs, manifesting its extravasation activity. These results demonstrated the remarkable ability of CAR to selectively target PAH lung vasculature and effectively penetrate and spread throughout the diseased lung tissue. These results suggest the clinical utility of CAR in the targeted delivery of therapeutic compounds and imaging probes to PAH lungs.

Proteomic Analysis of Lung Tissues From Patients With Pulmonary Arterial Hypertension

Pulmonary arterial hypertension is a disorder of vascular remodeling causing increased resistance to pulmonary blood flow. The expression of proteins in lungs from pulmonary arterial hypertension patients was investigated in an unbiased approach to further understand the pathobiology of this disease. Label-free liquid chromatography tandem mass spectrometry was used to compare protein profiles in surgical samples of lungs from 8 patients with pulmonary arterial hypertension and 8 control subjects. More than 300 proteins were detected. On the basis of robust criteria, the levels of 25 proteins varied between the 2 groups. The majority of upregulated proteins were associated with cell growth, proliferation, and cell metabolism. Novel findings included an increased expression of chloride intracellular channel 4, receptor for advanced glycation end products, and periostin. Increased expression of chloride intracellular channel 4, a multifunctional protein involved in angiogenesis, and several signaling pathways implicated in pulmonary arterial hypertension--transforming growth factor-β, vascular endothelial growth factor, and bone morphogenetic protein--was confirmed by Western blotting and localized predominantly to endothelial cells in occlusive and plexiform vascular lesions. Label-free proteomics identified differences in the expression of several proteins in the pulmonary arterial hypertension lung, many of which are relevant to the disease process. Increased expression of chloride intracellular channel 4 may be pertinent to the disorganized angiogenesis of plexiform lesions.