Pathobiology of pulmonary arterial hypertension and right ventricular failure

Determinants of an elevated pulmonary arterial pressure in patients with pulmonary arterial hypertension

Given the difficulty of diagnosing early-stage pulmonary arterial hypertension (PAH) due to the lack of signs and symptoms, and the risk of an open lung biopsy, the precise pathological features of presymptomatic stage lung tissue remain unknown. It has been suggested that the maximum elevation of the mean pulmonary arterial pressure (P_pa) is achieved during the early symptomatic stage, indicating that the elevation of the mean P_pa is primarily driven by the pulmonary vascular tone and/or some degree of pulmonary vascular remodeling completed during this stage. Recently, the examination of a rat model of severe PAH suggested that the severe PAH may be primarily determined by the presence of intimal lesions and/or the vascular tone in the early stage. Human data seem to indicate that intimal lesions are essential for the severely increased pulmonary arterial blood pressure in the late stage of the disease.

However, many questions remain. For instance, how does the pulmonary hemodynamics change during the course of the disease, and what drives the development of severe PAH? Although it is generally acknowledged that both pulmonary vascular remodeling and the vascular tone are important determinants of an elevated pulmonary arterial pressure, which is the root cause of the time-dependent progression of the disease? Here we review the recent histopathological concepts of PAH with respect to the progression of the lung vascular disease.

Mammalian target of rapamycin overexpression antagonizes chronic hypoxia-triggered pulmonary arterial hypertension via the autophagic pathway

Pulmonary arterial hypertension (PAH) is a progressive pulmonary vascular disorder with high morbidity and mortality, and is characterized by excessive growth of endothelial cells. Recently, the mammalian target of rapamycin (mTOR) has attracted increasing attention due to its potential as a therapeutic target against certain diseases associated with proliferative and metabolic abnormalities. However, the effect on mTOR on PAH has not yet been elucidated. In the present study, a marked downregulation of mTOR was observed in PAH patients. Following construction of a mouse model of PAH by chronic exposure to hypoxia, adenovirus-mediated upregulation of mTOR significantly attenuated right ventricular systolic pressure, right ventricular hypertrophy and wall thickness of pulmonary arterioles, indicating a protective effect of mTOR on PAH. Further analysis confirmed that mTOR overexpression inhibited autophagy triggered by hypoxia through blocking light chain 3 II expression and increasing p62 levels. In vitro, hypoxia enhanced the proliferation of human pulmonary artery endothelial cells (PAECs), which was markedly abrogated by mTOR overexpression. Of note, upregulation of mTOR inhibited the hypoxia-induced autophagy pathway, which contributed to cell proliferation, while silencing of autophagy by RNA interference with ATG5 significantly inhibited cell proliferation. In conclusion, the results of the present study suggested a potential protective effect of mTOR on the progression of PAH by suppressing PAEC proliferation through blocking the autophagic pathway. Therefore, the present study suggested that mTOR is a promising therapeutic agent against PAH.

Treatment for pulmonary arterial hypertension-associated right ventricular dysfunction

Pulmonary arterial hypertension (PAH) includes a heterogeneous group of diseases characterized by pulmonary vasoconstriction and remodeling of the lung circulation. Although PAH is a disease of the lungs, patients with PAH frequently die of right heart failure. Indeed, survival of patients with PAH depends on the adaptive response of the right ventricle (RV) to the changes in the lung circulation. PAH-specific drugs affect the function of the RV through afterload reduction and perhaps also through direct effects on the myocardium. Prostacyclins, type 5 phosphodiesterase inhibitors, and guanylyl cyclase stimulators may directly enhance myocardial contractility through increased cyclic adenosine and guanosine monophosphate availability. Although this may initially improve cardiac performance, the long-term effects on myocardial oxygen consumption and function are unclear. Cardiac effects of endothelin receptor antagonists may be opposite, as endothelin-1 is known to suppress cardiac contractility. Because PAH is increasingly considered as a disease with quasimalignant growth of cells in the pulmonary vascular wall, therapies are being developed that inhibit hypertrophy and angiogenesis, and promote apoptosis. The inherent danger of these therapies is a further compromise to the already ischemic, fibrotic, and dysfunctional RV. More recently, the right heart has been identified as a direct treatment target in PAH. The effects of well established therapies for left heart failure, such as β-adrenergic receptor blockers, inhibitors of the renin-angiotensin system, exercise training, and assist devices, are currently being investigated in PAH. Future treatment of patients with PAH will likely consist of a multifaceted approaches aiming to reduce the pressure in the lung circulation and improving right heart adaptation simultaneously.

Fatty acid metabolism in pulmonary arterial hypertension: role in right ventricular dysfunction and hypertrophy

Pulmonary arterial hypertension (PAH) is a complex, multifactorial disease in which an increase in pulmonary vascular resistance leads to increased afterload on the right ventricle (RV), causing right heart failure and death. Our understanding of the pathophysiology of RV dysfunction in PAH is limited but is constantly improving. Increasing evidence suggests that in PAH RV dysfunction is associated with various components of metabolic syndrome, such as insulin resistance, hyperglycemia, and dyslipidemia. The relationship between RV dysfunction and fatty acid/glucose metabolites is multifaceted, and in PAH it is characterized by a shift in utilization of energy sources toward increased glucose utilization and reduced fatty acid consumption. RV dysfunction may be caused by maladaptive fatty acid metabolism resulting from an increase in fatty acid uptake by fatty acid transporter molecule CD36 and an imbalance between glucose and fatty acid oxidation in mitochondria. This leads to lipid accumulation in the form of triglycerides, diacylglycerol, and ceramides in the cytoplasm, hallmarks of lipotoxicity. Current interventions in animal models focus on improving RV dysfunction through altering fatty acid oxidation rates and limiting lipid accumulation, but more specific and effective therapies may be available in the coming years based on current research. In conclusion, a deeper understanding of the complex mechanisms of the metabolic remodeling of the RV will aid in the development of targeted treatments for RV failure in PAH.

Ranolazine reduces remodeling of the right ventricle and provoked arrhythmias in rats with pulmonary hypertension

Pulmonary arterial hypertension (PAH) is a progressive disease that often results in right ventricular (RV) failure and death. During disease progression, structural and electrical remodeling of the right ventricle impairs pump function, creates proarrhythmic substrates, and triggers for arrhythmias. Notably, RV failure and lethal arrhythmias are major contributors to cardiac death in patients with PAH that are not directly addressed by currently available therapies. Ranolazine (RAN) is an antianginal, anti-ischemic drug that has cardioprotective effects in experimental and clinical settings of left-sided heart dysfunction. RAN also has antiarrhythmic effects due to inhibition of the late sodium current in cardiomyocytes. We therefore hypothesized that RAN could reduce the maladaptive structural and electrical remodeling of the right ventricle and could prevent triggered ventricular arrhythmias in the monocrotaline rat model of PAH. Indeed, in both in vivo and ex vivo experimental settings, chronic RAN treatment reduced electrical heterogeneity (right ventricular-left ventricular action potential duration dispersion), shortened heart-rate corrected QT intervals in the right ventricle, and normalized RV dysfunction. Chronic RAN treatment also dose-dependently reduced ventricular hypertrophy, reduced circulating levels of B-type natriuretic peptide, and decreased the expression of fibrotic markers. In addition, the acute administration of RAN prevented isoproterenol-induced ventricular tachycardia/ventricular fibrillation and subsequent cardiovascular death in rats with established PAH. These results support the notion that RAN can improve the electrical and functional properties of the right ventricle, highlighting its potential benefits in the setting of RV impairment.

The need to recognize the pulmonary circulation and the right ventricle as an integrated functional unit: facts and hypotheses (2013 Grover Conference series)

For many patients with severe pulmonary arterial hypertension, heart failure-and, in particular, right heart failure-is the final chapter of their chronic illness. Targeted therapy for pulmonary hypertension is effective only if the right ventricular ejection fraction is maintained or improved. Because improvement of right heart function and reversal of right heart failure are treatment goals, it is important to investigate the cellular and molecular mechanisms that cause right heart failure. Here, we propose that right ventricular capillary rarefaction is an important hallmark of right heart failure and consider that the "sick lung circulation" and the pressure-overloaded right ventricle constitute a functional unit.

Emerging roles for histone deacetylases in pulmonary hypertension and right ventricular remodeling (2013 Grover Conference series)

Reversible lysine acetylation has emerged as a critical mechanism for controlling the function of nucleosomal histones as well as diverse nonhistone proteins. Acetyl groups are conjugated to lysine residues in proteins by histone acetyltransferases and removed by histone deacetylases (HDACs), which are also commonly referred to as lysine deacetylases. Over the past decade, many studies have shown that HDACs play crucial roles in the control of left ventricular (LV) cardiac remodeling in response to stress. Small molecule HDAC inhibitors block pathological hypertrophy and fibrosis and improve cardiac function in various preclinical models of LV failure. Only recently have HDACs been studied in the context of right ventricular (RV) failure, which commonly occurs in patients who experience pulmonary hypertension (PH). Here, we review recent findings with HDAC inhibitors in models of PH and RV remodeling, propose next steps for this newly uncovered area of research, and highlight potential for isoform-selective HDAC inhibitors for the treatment of PH and RV failure.

Vascular endothelial growth factor receptor 3 signaling contributes to angioobliterative pulmonary hypertension

The mechanisms involved in the development of severe angioobliterative pulmonary arterial hypertension (PAH) are multicellular and complex. Many of the features of human severe PAH, including angioobliteration, lung perivascular inflammation, and right heart failure, are reproduced in the Sugen 5416/chronic hypoxia (SuHx) rat model. Here we address, at first glance, the confusing and paradoxical aspect of the model, namely, that treatment of rats with the antiangiogenic vascular endothelial growth factor (VEGF) receptor 1 and 2 kinase inhibitor, Sugen 5416, when combined with chronic hypoxia, causes angioproliferative pulmonary vascular disease. We postulated that signaling through the unblocked VEGF receptor VEGFR3 (or flt4) could account for some of the pulmonary arteriolar lumen-occluding cell growth. We also considered that Sugen 5416-induced VEGFR1 and VEGFR2 blockade could alter the expression pattern of VEGF isoform proteins. Indeed, in the lungs of SuHx rats we found increased expression of the ligand proteins VEGF-C and VEGF-D as well as enhanced expression of the VEGFR3 protein. In contrast, in the failing right ventricle of SuHx rats there was a profound decrease in the expression of VEGF-B and VEGF-D in addition to the previously described reduction in VEGF-A expression. MAZ51, an inhibitor of VEGFR3 phosphorylation and VEGFR3 signaling, largely prevented the development of angioobliteration in the SuHx model; however, obliterated vessels did not reopen when animals with established PAH were treated with the VEGFR3 inhibitor. Part of the mechanism of vasoobliteration in the SuHx model occurs via VEGFR3. VEGFR1/VEGFR2 inhibition can be initially antiangiogenic by inducing lung vessel endothelial cell apoptosis; however, it can be subsequently angiogenic via VEGF-C and VEGF-D signaling through VEGFR3.

Bax deficiency extends the survival of Ku70 knockout mice that develop lung and heart diseases

Ku70 (Lupus Ku autoantigen p70) is essential in nonhomologous end joining DNA double-strand break repair, and ku70^−/− mice age prematurely because of increased genomic instability and DNA damage responses. Previously, we found that Ku70 also inhibits Bax, a key mediator of apoptosis. We hypothesized that Bax-mediated apoptosis would be enhanced in the absence of Ku70 and contribute to premature death observed in ku70^−/− mice. Here, we show that ku70^−/−bax^+/− and ku70^−/−bax^−/− mice have better survival, especially in females, than ku70^−/− mice, even though Bax deficiency did not decrease the incidence of lymphoma observed in a Ku70-null background. Moreover, we found that ku70^−/− mice develop lung diseases, like emphysema and pulmonary arterial (PA) occlusion, by 3 months of age. These lung abnormalities can trigger secondary health problems such as heart failure that may account for the poor survival of ku70^−/− mice. Importantly, Bax deficiency appeared to delay the development of emphysema. This study suggests that enhanced Bax activity exacerbates the negative impact of Ku70 deletion. Furthermore, the underlying mechanisms of emphysema and pulmonary hypertension due to PA occlusion are not well understood, and therefore ku70^−/− and Bax-deficient ku70^−/− mice may be useful models to study these diseases.

Increased eicosanoid levels in the Sugen/chronic hypoxia model of severe pulmonary hypertension

Inflammation and altered immunity are recognized components of severe pulmonary arterial hypertension in human patients and in animal models of PAH. While eicosanoid metabolites of cyclooxygenase and lipoxygenase pathways have been identified in the lungs from pulmonary hypertensive animals their role in the pathogenesis of severe angioobliterative PAH has not been examined. Here we investigated whether a cyclooxygenase-2 (COX-2) inhibitor or diethylcarbamazine (DEC), that is known for its 5-lipoxygenase inhibiting and antioxidant actions, modify the development of PAH in the Sugen 5416/hypoxia (SuHx) rat model. The COX-2 inhibitor SC-58125 had little effect on the right ventricular pressure and did not prevent the development of pulmonary angioobliteration. In contrast, DEC blunted the muscularization of pulmonary arterioles and reduced the number of fully obliterated lung vessels. DEC treatment of SuHx rats, after the lung vascular disease had been established, reduced the degree of PAH, the number of obliterated arterioles and the degree of perivascular inflammation. We conclude that the non-specific anti-inflammatory drug DEC affects developing PAH and is partially effective once angioobliterative PAH has been established.

O-linked β-N-acetylglucosamine transferase directs cell proliferation in idiopathic pulmonary arterial hypertension

BACKGROUND

Idiopathic pulmonary arterial hypertension (IPAH) is a cardiopulmonary disease characterized by cellular proliferation and vascular remodeling. A more recently recognized characteristic of the disease is the dysregulation of glucose metabolism. The primary link between altered glucose metabolism and cell proliferation in IPAH has not been elucidated. We aimed to determine the relationship between glucose metabolism and smooth muscle cell proliferation in IPAH.

METHODS AND RESULTS

Human IPAH and control patient lung tissues and pulmonary artery smooth muscle cells (PASMCs) were used to analyze a specific pathway of glucose metabolism, the hexosamine biosynthetic pathway. We measured the levels of O-linked β-N-acetylglucosamine modification, O-linked β-N-acetylglucosamine transferase (OGT), and O-linked β-N-acetylglucosamine hydrolase in control and IPAH cells and tissues. Our data suggest that the activation of the hexosamine biosynthetic pathway directly increased OGT levels and activity, triggering changes in glycosylation and PASMC proliferation. Partial knockdown of OGT in IPAH PASMCs resulted in reduced global O-linked β-N-acetylglucosamine modification levels and abrogated PASMC proliferation. The increased proliferation observed in IPAH PASMCs was directly impacted by proteolytic activation of the cell cycle regulator, host cell factor-1.

CONCLUSIONS

Our data demonstrate that hexosamine biosynthetic pathway flux is increased in IPAH and drives OGT-facilitated PASMC proliferation through specific proteolysis and direct activation of host cell factor-1. These findings establish a novel regulatory role for OGT in IPAH, shed a new light on our understanding of the disease pathobiology, and provide opportunities to design novel therapeutic strategies for IPAH.

The crossroads of iron with hypoxia and cellular metabolism. Implications in the pathobiology of pulmonary hypertension

The pathologic hallmark of pulmonary arterial hypertension (PAH) is pulmonary vascular remodeling, characterized by endothelial cell proliferation, smooth muscle hypertrophy, and perivascular inflammation, ultimately contributing to increased pulmonary arterial pressures. Several recent studies have observed that iron deficiency in patients with various forms of PAH is associated with worsened clinical outcome. Iron plays a key role in many cellular processes regulating the response to hypoxia, oxidative stress, cellular proliferation, and cell metabolism. Given the potential importance of iron supplementation in patients with the disease and the broad cellular functions of iron, we review its role in processes that pertain to PAH.

MicroRNA-190 regulates hypoxic pulmonary vasoconstriction by targeting a voltage-gated K⁺ channel in arterial smooth muscle cells

Pulmonary arterial hypertension (PAH) is associated with sustained vasoconstriction, profound structural remodeling of vasculatures and alterations in Ca(2+) homeostasis in arterial smooth muscle cells (SMCs), while the underlying mechanisms are still elusive. By regulating the expression of proteins, microRNAs (miRNAs) are known to play an important role in cell fates including differentiation, apoptosis and proliferation, and may be involved in the development of PAH. Based on our previous study, hypoxia produced a significant increase of the miR-190 level in the pulmonary artery (PA), here, we used synthetic miR-190 to mimic the increase in hypoxic conditions and showed evidence for the effects of miR-190 on pulmonary arterial vasoconstriction and Ca(2+) influx in arterial SMCs. Synthetic miR-190 remarkably enhanced the vasoconstriction responses to phenylephrine (PE) and KCl. The voltage-gated K(+) channel subfamily member, Kcnq5, mRNA was shown to be a target for miR-190. Meanwhile, miR-190 antisense oligos can partially reverse the effects of miR-190 on PASMCs and PAs. Therefore, these results suggest that miR-190 appears to be a positive regulator of Ca(2+) influx, and plays an important role in hypoxic pulmonary vascular constriction.

The right ventricle in pulmonary arterial hypertension

Pulmonary arterial hypertension (PAH) is a right heart failure syndrome. In early-stage PAH, the right ventricle tends to remain adapted to afterload with increased contractility and little or no increase in right heart chamber dimensions. However, less than optimal right ventricular (RV)-arterial coupling may already cause a decreased aerobic exercise capacity by limiting maximum cardiac output. In more advanced stages, RV systolic function cannot remain matched to afterload and dilatation of the right heart chamber progressively develops. In addition, diastolic dysfunction occurs due to myocardial fibrosis and sarcomeric stiffening. All these changes lead to limitation of RV flow output, increased right-sided filling pressures and under-filling of the left ventricle, with eventual decrease in systemic blood pressure and altered systolic ventricular interaction. These pathophysiological changes account for exertional dyspnoea and systemic venous congestion typical of PAH. Complete evaluation of RV failure requires echocardiographic or magnetic resonance imaging, and right heart catheterisation measurements. Treatment of RV failure in PAH relies on: decreasing afterload with drugs targeting pulmonary circulation; fluid management to optimise ventricular diastolic interactions; and inotropic interventions to reverse cardiogenic shock. To date, there has been no report of the efficacy of drug treatments that specifically target the right ventricle.

Effects of captopril on cardiovascular reflexes and respiratory mechanisms in rats submitted to monocrotaline-induced pulmonary arterial hypertension

BACKGROUND

Pulmonary Arterial Hypertension (PAH) is a disease associated with increased arteriolar resistance in the lungs. Due to hypoxemia, some physiological mechanisms can be posteriorly affected, including respiratory and cardiovascular reflexes, but this has not yet been fully investigated. This study aimed to evaluate how these mechanisms were affected by monocrotaline (MCT)-induced PAH and the possible therapeutic role of angiotensin converting enzyme inhibitor (ACEi), captopril, in reversing this remodeling process.

METHODS AND RESULTS

Groups of Wistar rats received MCT injections (60 mg kg(-1)). Three weeks later, they received captopril (CPT, 100 mg kg(-1)) in their drinking water (MCT + CPT) or water alone (MCT) for 2 weeks. As control, saline-treated animals received captopril in their drinking water (CPT) or water alone (CON), also for 2 weeks. Results showed that PAH was fully induced in the MCT group, evidenced by a high pulmonary index. Gasometrical and respiratory analyses showed hypoxemia and compensatory hyperventilation. CPT treatment brought these parameters to similar values to those observed in the CON group. We observed that autonomic dysfunction in the MCT group was suppressed by CPT. Finally, cardiovascular reflexes analysis showed increased chemoreflex responses in the MCT group, while baroreflex sensibility was decreased. Surprisingly, CPT normalized these reflex responses to values similar to the CON group.

CONCLUSIONS

The present study demonstrates that MCT-induced PAH induces compensatory respiratory responses, dysautonomia, and baroreflex dysfunction and increases chemoreflex responses. The data also indicate that CPT was effective in reversing these cardio-respiratory disorders, suggesting that ACEi could be a potential therapeutic target for PAH.

Endothelial nanomedicine for the treatment of pulmonary disease

INTRODUCTION

Even though pulmonary diseases are among the leading causes of morbidity and mortality in the world, exceedingly few life-prolonging therapies have been developed for these maladies. Relief may finally come from nanomedicine and targeted drug delivery.

AREAS COVERED

Here, we focus on four conditions for which the pulmonary endothelium plays a pivotal role: acute respiratory distress syndrome, primary graft dysfunction occurring immediately after lung transplantation, pulmonary arterial hypertension and pulmonary embolism. For each of these diseases, we first evaluate the targeted drug delivery approaches that have been tested in animals. Then we suggest a 'need specification' for each disease: a list of criteria (e.g., macroscale delivery method, stability, etc.) that nanomedicine agents must meet in order to warrant human clinical trials and investment from industry.

EXPERT OPINION

For the diseases profiled here, numerous nanomedicine agents have shown promise in animal models. However, to maximize the chances of creating products that reach patients, nanomedicine engineers and clinicians must work together and use each disease's need specification to guide the design of practical and effective nanomedicine agents.

Targeted delivery of genes to endothelial cells and cell- and gene-based therapy in pulmonary vascular diseases

Pulmonary arterial hypertension (PAH) is a devastating disease that, despite significant advances in medical therapies over the last several decades, continues to have an extremely poor prognosis. Gene therapy is a method to deliver therapeutic genes to replace defective or mutant genes or supplement existing cellular processes to modify disease. Over the last few decades, several viral and nonviral methods of gene therapy have been developed for preclinical PAH studies with varying degrees of efficacy. However, these gene delivery methods face challenges of immunogenicity, low transduction rates, and nonspecific targeting which have limited their translation to clinical studies. More recently, the emergence of regenerative approaches using stem and progenitor cells such as endothelial progenitor cells (EPCs) and mesenchymal stem cells (MSCs) have offered a new approach to gene therapy. Cell-based gene therapy is an approach that augments the therapeutic potential of EPCs and MSCs and may deliver on the promise of reversal of established PAH. These new regenerative approaches have shown tremendous potential in preclinical studies; however, large, rigorously designed clinical studies will be necessary to evaluate clinical efficacy and safety.

Molecular imaging of the pulmonary circulation in health and disease

The pulmonary circulation, at the unique crossroads between the left and the right heart, is submitted to large physiologic hemodynamic variations and possesses numerous important metabolic functions mediated through its vast endothelial surface. There are many pathologic conditions that can directly or indirectly affect the pulmonary vasculature and modify its physiology and functions. Pulmonary hypertension, the end result of many of these affections, is unfortunately diagnosed too late in the disease process, meaning that there is a crying need for earlier diagnosis and surrogate markers of disease progression and regression. By targeting endothelial, medial and adventitial targets of the pulmonary vasculature, novel molecular imaging agents could provide early detection of physiologic and biologic perturbation in the pulmonary circulation. This review provides the rationale for the development of molecular imaging agents for the diagnosis and follow-up of disorders of the pulmonary circulation and discusses promising targets for SPECT and positron emission tomographic imaging.

Iloprost reverses established fibrosis in experimental right ventricular failure

Prostacyclin and its analogues improve cardiac output and functional capacity in patients with pulmonary arterial hypertension (PAH); however, the underlying mechanism is not fully understood. We hypothesised that prostanoids have load-independent beneficial effects on the right ventricle (RV). Angio-obliterative PAH and RV failure were induced in rats with a single injection of SU5416 followed by 4 weeks of exposure to hypoxia. Upon confirmation of RV dysfunction and PAH, rats were randomised to 0.1 μg·kg(-1) nebulised iloprost or drug-free vehicle, three times daily for 2 weeks. RV function and treadmill running time were evaluated pre- and post-iloprost/vehicle treatment. Pulmonary artery banded rats were treated 8 weeks after surgery to allow for significant RV hypertrophy. Inhaled iloprost significantly improved tricuspid annulus plane systolic excursion and increased exercise capacity, while mean pulmonary artery pressure and the percentage of occluded pulmonary vessels remained unchanged. Rats treated with iloprost had a striking reduction in RV collagen deposition, procollagen mRNA levels and connective tissue growth factor expression in both SU5416/hypoxia and pulmonary artery banded rats. In vitro, cardiac fibroblasts treated with iloprost showed a reduction in transforming growth factor (TGF)-β1-induced connective tissue growth factor expression, in a protein kinase A-dependent manner. Iloprost decreased TGF-β1-induced procollagen mRNA expression as well as cardiac fibroblast activation and migration. Iloprost significantly induced metalloproteinase-9 gene expression and activity and increased the expression of autophagy genes associated with collagen degradation. Inhaled iloprost improves RV function and reverses established RV fibrosis partially by preventing collagen synthesis and by increasing collagen turnover.

Dissecting histone deacetylase role in pulmonary arterial smooth muscle cell proliferation and migration

Pulmonary Arterial Hypertension (PAH) is a rare and devasting condition characterized by elevated pulmonary vascular resistance and pulmonary artery pressure leading to right-heart failure and premature death. Pathologic alterations in proliferation, migration and survival of all cell types composing the vascular tissue play a key role in the occlusion of the vascular lumen. In the current study, we initially investigated the action of selective class I and class II HDAC inhibitors on the proliferation and migration of pulmonary artery smooth muscle cells (PASMCs) after exposure to Platelet Derived Growth Factor (PDGF). Class I HDAC inhibitors were able to counteract the hyperproliferative response to PDGF, reducing both proliferation and migration in PASMCs, while class II were ineffective. Selective silencing with siRNAs targeted against different HDACs revealed a major role of class I, and within this class, of HDAC1 in mediating PDGF-induced Akt Phosphorylation and Cyclin D1 (CycD1) expression. These results from these combinatorial approaches were further confirmed by the ability of a specific HDAC1 inhibitor to antagonize the PDGF action. The finding that HDAC1 is a major conductor of PDGF-induced patterning in PAH-PASMCs prompts the development of novel selective inhibitors of this member of class I HDACs as a potential tool to control lung vascular homeostasis in PAH.

Pulmonary hypertension in Kawasaki disease

This report describes the case of two pediatric patients who demonstrated echocardiographic evidence of pulmonary hypertension (PH) during the acute phase of Kawasaki disease. The etiology of PH development in this setting is currently unknown, but the authors hypothesize that pulmonary vasculitis may play a significant role. Fortunately, the PH appeared to be self-limited and resolved in both cases with routine treatment of Kawasaki disease.

State of the art: advanced imaging of the right ventricle and pulmonary circulation in humans (2013 Grover Conference series)

Pulmonary arterial hypertension (PAH) is a progressive disease characterized by remodeling and vasoconstriction of the pulmonary vasculature, ultimately leading to right ventricular (RV) failure and death. Recent developments in echocardiography, cardiovascular magnetic resonance imaging, computed tomography, and positron emission tomography allow advanced, noninvasive, in vivo assessment of the RV and have contributed to the identification of risk factors, prognostic factors, and monitoring of therapeutic responses in patients with PAH. Although far from reaching its future potential, these techniques have not only provided global RV assessment but also allowed evaluation of changes in cellular and molecular tissue processes, such as metabolism, oxygen balance and ischemia, angiogenesis, and apoptosis. Integrated application of these techniques could provide full insights into the different pathophysiological aspects of a failing RV in the setting of PAH. Recent advances in hybrid imaging have implemented simultaneous measurements of myocardial and vascular interactions and will be one of the most important potential future developments.

Pentraxin-3 and the right ventricle: the Multi-Ethnic Study of Atherosclerosis-Right Ventricle Study

Pentraxin-3 (PTX3) is a protein mediator of innate immunity that is elevated in the setting of left heart disease and pulmonary arterial hypertension. The relationship between PTX3 and right ventricular (RV) structure and function is not known. We included men and women with magnetic resonance imaging assessment of RV structure and function and measurement of PTX3 from the Multi-Ethnic Study of Atherosclerosis, a study of individuals free of clinical cardiovascular disease. Multivariable linear regression estimated associations between PTX3 protein levels and RV measures after adjusting for demographic characteristics, anthropometrics, smoking status, diabetes mellitus, hypertension, and corresponding left ventricular (LV) parameters. Instrumental variable analysis exploiting Mendelian randomization was attempted using two-stage least squares regression. The study sample included 1,779 participants with available PTX3 levels, RV measures, and all covariables. Mean PTX3 level was 2.1 ng/mL. Higher PTX3 was independently associated with greater RV mass and larger RV end-diastolic volume with and without adjustment for the corresponding LV parameters or C-reactive protein (all P < .05). There was no association between PTX3 and RV ejection fraction or stroke volume. Single-nucleotide polymorphisms were not associated with PTX3 protein levels or RV measures after accounting for race. Instrumental variable analysis could not be reliably performed. Higher PTX3 protein levels were associated with greater RV mass and larger RV end-diastolic volume. These associations were independent of common cardiovascular risk factors and LV morphologic changes. Inflammation is associated with differences in the pulmonary circulation-RV axis in adults without clinical cardiovascular disease.

Pulmonary arterial hypertension: challenges in translational research and a vision for change

Pulmonary arterial hypertension (PAH) is a vascular remodeling disease with a relentless course toward heart failure and early death. Existing PAH therapies, all of which were developed originally to treat systemic vascular diseases, cannot reverse the disease or markedly improve survival and are expensive. Although there has been a recent increase in the number of potential new therapies emerging from animal studies, less than 3% of the active PAH clinical trials are examining such therapies. There are many potential explanations for the translational gap in this complex multifactorial disease. We discuss these challenges and propose solutions that range from including clinical endpoints in animal studies and improving the rigor of human trials to conducting mechanistic early-phase trials and randomized trials with innovative designs based on personalized medicine principles. Global, independent patient and tissue registries and enhanced communication among academics, industry, and regulatory authorities are needed. The diversity of the mechanisms and pathology of PAH calls for broad comprehensive theories that encompass emerging evidence for contributions of metabolism and inflammation to PAH to support more effective therapeutic target identification.

N-acetylcysteine improves established monocrotaline-induced pulmonary hypertension in rats

Background

The outcome of patients suffering from pulmonary arterial hypertension (PAH) are predominantly determined by the response of the right ventricle to the increase afterload secondary to high vascular pulmonary resistance. However, little is known about the effects of the current available or experimental PAH treatments on the heart. Recently, inflammation has been implicated in the pathophysiology of PAH. N-acetylcysteine (NAC), a well-known safe anti-oxidant drug, has immuno-modulatory and cardioprotective properties. We therefore hypothesized that NAC could reduce the severity of pulmonary hypertension (PH) in rats exposed to monocrotaline (MCT), lowering inflammation and preserving pulmonary vascular system and right heart function.

Methods

Saline-treated control, MCT-exposed, MCT-exposed and NAC treated rats (day 14–28) were evaluated at day 28 following MCT for hemodynamic parameters (right ventricular systolic pressure, mean pulmonary arterial pressure and cardiac output), right ventricular hypertrophy, pulmonary vascular morphometry, lung inflammatory cells immunohistochemistry (monocyte/macrophages and dendritic cells), IL-6 expression, cardiomyocyte hypertrophy and cardiac fibrosis.

Results

The treatment with NAC significantly decreased pulmonary vascular remodeling, lung inflammation, and improved total pulmonary resistance (from 0.71 ± 0.05 for MCT group to 0.50 ± 0.06 for MCT + NAC group, p < 0.05). Right ventricular function was also improved with NAC treatment associated with a significant decrease in cardiomyocyte hypertrophy (625 ± 69 vs. 439 ± 21 μm² for MCT and MCT + NAC group respectively, p < 0.001) and heart fibrosis (14.1 ± 0.8 vs. 8.8 ± 0.1% for MCT and MCT + NAC group respectively, p < 0.001).

Conclusions

Through its immuno-modulatory and cardioprotective properties, NAC has beneficial effect on pulmonary vascular and right heart function in experimental PH.

Targeted delivery of pulmonary arterial endothelial cells overexpressing interleukin-8 receptors attenuates monocrotaline-induced pulmonary vascular remodeling

OBJECTIVE

Interleukin-8 (IL-8) receptors IL8RA and IL8RB (IL8RA/B) on neutrophil membranes bind to IL-8 with high affinity and play a critical role in neutrophil recruitment to sites of injury and inflammation. This study tested the hypothesis that administration of rat pulmonary arterial endothelial cells (ECs) overexpressing IL8RA/B can accelerate the adhesion of ECs to the injured lung and inhibit monocrotaline-induced pulmonary inflammation, arterial thickening and hypertension, and right ventricular hypertrophy.

APPROACH AND RESULTS

The treatment groups included 10-week-old ovariectomized Sprague-Dawley rats that received subcutaneous injection of PBS (vehicle), a single injection of monocrotaline (monocrotaline alone, 60 mg/kg, SC), monocrotaline followed by intravenous transfusion of ECs transduced with the empty adenoviral vector (null-EC), and monocrotaline followed by intravenous transfusion of ECs overexpressing IL8RA/B (1.5 × 10(6) cells/rat). Two days or 4 weeks after monocrotaline treatment, endothelial nitric oxide synthase, inducible nitric oxide synthase, cytokine-induced neutrophil chemoattractant-2β (IL-8 equivalent in rat), and monocyte chemoattractant protein-1 expression, neutrophil and macrophage infiltration into pulmonary arterioles, and arteriolar and alveolar morphology were measured by histological and immunohistochemical techniques. Proinflammatory cytokine/chemokine protein levels were measured by Multiplex rat-specific magnetic bead-based sandwich immunoassay in total lung homogenates. Transfusion of ECs overexpressing IL8RA/B significantly reduced monocrotaline-induced neutrophil infiltration and proinflammatory mediator (IL-8, monocyte chemoattractant protein-1, inducible nitric oxide synthase, cytokine-induced neutrophil chemoattractant, and macrophage inflammatory protein-2) expression in lungs and pulmonary arterioles and alveoli, pulmonary arterial pressure, and pulmonary arterial and right ventricular hypertrophy and remodeling.

CONCLUSIONS

These provocative findings suggest that targeted delivery of ECs overexpressing IL8RA/B is effective in repairing the injured pulmonary vasculature.

Increased Pericyte Coverage Mediated by Endothelial-Derived Fibroblast Growth Factor-2 and Interleukin-6 Is a Source of Smooth Muscle–Like Cells in Pulmonary Hypertension

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.

Role of endothelial nitric oxide synthase and collagen metabolism in right ventricular remodeling due to pulmonary hypertension

BACKGROUND

Pulmonary hypertension (PH) causes elevated right ventricular (RV) systolic pressure, RV remodeling and finally RV failure to death. However, the mechanisms of RV remodeling in PH remain to be fully elucidated.

METHODS AND RESULTS

RV autopsy samples from 6 PH patients with RV failure against 3 age- and sex-matched controls were first examined. Next, RV remodeling in 2 mouse models of chronic hypoxia-induced PH with endothelial nitric oxide synthase-deficient (eNOS(-/-)) and collagenase-resistant knock-in (Col(R/R)) mice were examined. In humans, RV failure was associated with RV hypertrophy, interstitial and perivascular fibrosis, decreased RV capillary density and increased macrophage recruitment. Furthermore, immunostaining showed that perivascular matrix metalloproteinase-2 was increased in PH patients with RV failure. In animals, both hypoxic eNOS(-/-) and Col(R/R) mice developed a greater extent of RV hypertrophy, perivascular remodeling and macrophage infiltration compared with wild-type mice. Capillary rarefaction was developed in hypoxic eNOS(-/-) mice, while Col(R/R) mice were able to increase their capillary density in the RV in response to chronic hypoxia. Both mouse models showed increased autophagy even under normoxic condition.

CONCLUSIONS

These results indicate that RV remodeling occurs early during PH development through fibrosis, perivascular remodeling, capillary rarefaction and autophagy, in which the eNOS pathway and collagen metabolism might be involved.

Right heart adaptation to pulmonary arterial hypertension: physiology and pathobiology

Survival in patients with pulmonary arterial hypertension (PAH) is closely related to right ventricular (RV) function. Although pulmonary load is an important determinant of RV systolic function in PAH, there remains a significant variability in RV adaptation to pulmonary hypertension. In this report, the authors discuss the emerging concepts of right heart pathobiology in PAH. More specifically, the discussion focuses on the following questions. 1) How is right heart failure syndrome best defined? 2) What are the underlying molecular mechanisms of the failing right ventricle in PAH? 3) How are RV contractility and function and their prognostic implications best assessed? 4) What is the role of targeted RV therapy? Throughout the report, the authors highlight differences between right and left heart failure and outline key areas of future investigation.

Comparison of pharmacological activity of macitentan and bosentan in preclinical models of systemic and pulmonary hypertension

AIMS

The endothelin (ET) system is a tissular system, as the production of ET isoforms is mostly autocrine or paracrine. Macitentan is a novel dual ETA/ETB receptor antagonist with enhanced tissue distribution and sustained receptor binding properties designed to achieve a more efficacious ET receptor blockade. To determine if these features translate into improved efficacy in vivo, a study was designed in which rats with either systemic or pulmonary hypertension and equipped with telemetry were given macitentan on top of maximally effective doses of another dual ETA/ETB receptor antagonist, bosentan, which does not display sustained receptor occupancy and shows less tissue distribution.

MAIN METHODS

After establishing dose-response curves of both compounds in conscious, hypertensive Dahl salt-sensitive and pulmonary hypertensive bleomycin-treated rats, macitentan was administered on top of the maximal effective dose of bosentan.

KEY FINDINGS

In hypertensive rats, macitentan 30 mg/kg further decreased mean arterial blood pressure (MAP) by 19 mm Hg when given on top of bosentan 100 mg/kg (n=9, p<0.01 vs. vehicle). Conversely, bosentan given on top of macitentan failed to induce an additional MAP decrease. In pulmonary hypertensive rats, macitentan 30 mg/kg further decreased mean pulmonary artery pressure (MPAP) by 4 mm Hg on top of bosentan (n=8, p<0.01 vs. vehicle), whereas a maximal effective dose of bosentan given on top of macitentan did not cause any additional MPAP decrease.

SIGNIFICANCE

The add-on effect of macitentan on top of bosentan in two pathological models confirms that this novel compound can achieve a superior blockade of ET receptors and provides evidence for greater maximal efficacy.

Changes in Right Ventricular Function Measured by Cardiac Magnetic Resonance Imaging in Patients Receiving Pulmonary Arterial Hypertension–Targeted Therapy

Background—

Most measures that predict survival in pulmonary hypertension (PH) relate directly to, or correlate with, right ventricular (RV) function. Direct assessment of RV function using noninvasive techniques such as cardiac MRI may therefore be an appropriate way of determining response to therapy and monitoring disease progression in PH.

Methods and Results—

In this pan-European study, 91 patients with PH (mean pulmonary arterial pressure 46±15 mm Hg) underwent clinical and cardiac MRI assessments at baseline and after 12 months of disease-targeted therapy (predominantly endothelin receptor antagonists [47.3%] or phosphodiesterase type-5 inhibitors [25.3%]). At month 12, functional class had improved in 21 patients, was unchanged in 63 patients, and had deteriorated in 7 patients. Significant improvements were achieved in RV and left ventricular ejection fraction ( P <0.001 and P =0.0007, respectively), RV stroke volume index ( P <0.0001), and left ventricular end-diastolic volume index ( P =0.0015). Increases in 6-minute walk distance were significant ( P <0.0001) and correlated with change in RV ejection fraction and left ventricular end-diastolic volume, although correlation coefficients were low (r=0.28, P =0.01 and r=0.26, P =0.02, respectively).

Conclusions—

On-treatment changes in cardiac MRI–derived variables from left and right sides of the heart reflected changes in functional class and survival in patients with PH. Direct measurement of RV function using cardiac MRI can fully assess potential benefits of treatment in PH.

Progressive right ventricular functional and structural changes in a mouse model of pulmonary arterial hypertension

Right ventricle (RV) dysfunction occurs with progression of pulmonary arterial hypertension (PAH) due to persistently elevated ventricular afterload. A critical knowledge gap is the molecular mechanisms that govern the transition from RV adaptation to RV maladaptation, which leads to failure. Here, we hypothesize that the recently established mouse model of PAH, via hypoxia and SU5416 treatment (HySu), captures that transition from adaptive to maladaptive RV remodeling including impairments in RV function and decreases in the efficiency of RV interactions with the pulmonary vasculature. To test this hypothesis, we exposed C57BL6 male mice to 0 (control), 14, 21, and 28 days of HySu and then obtained synchronized RV pressure and volume measurements in vivo. With increasing HySu exposure duration, arterial afterload increased monotonically, leading to a continuous increase in RV stroke work, RV fibrosis, and RV wall stiffening (P < 0.05). RV contractility increased at 14 days of HySu exposure and then plateaued (P < 0.05). As a result, ventricular–vascular coupling efficiency tended to increase at 14 days and then decrease. Our results suggest that RV remodeling may begin to shift from adaptive to maladaptive with increasing duration of HySu exposure, which would mimic changes in RV function with PAH progression found clinically. However, for the duration of HySu exposure used here, no drop in cardiac output was found. We conclude that the establishment of a mouse model for overt RV failure due to PAH remains an important task.

This article describes the progressive changes in mouse right ventricle (RV) structure and function during the pulmonary arterial hypertension development. The findings may shed light on the transition from adaptive to maladaptive RV remodeling, which eventually leads to failure.

Evidence for the involvement of type I interferon in pulmonary arterial hypertension

RATIONALE

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.

OBJECTIVE

To explore the role of type I IFN in PAH.

METHODS AND RESULTS

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.

CONCLUSIONS

These data indicate that type I IFN, via an action of IFNAR1, mediates PAH.