Pathology of Pulmonary Hypertension

Digital Spatial Profiling Identifies Distinct Molecular Signatures of Vascular Lesions in Pulmonary Arterial Hypertension

Rationale: Idiopathic pulmonary arterial hypertension (IPAH) is characterized by extensive pulmonary vascular remodeling caused by plexiform and obliterative lesions, media hypertrophy, inflammatory cell infiltration, and alterations of the adventitia. Objective: We sought to test the hypothesis that microscopic IPAH vascular lesions express unique molecular profiles, which collectively are different from control pulmonary arteries. Methods: We used digital spatial transcriptomics to profile the genomewide differential transcriptomic signature of key pathological lesions (plexiform, obliterative, intima+media hypertrophy, and adventitia) in IPAH lungs (n = 11) and compared these data with the intima+media hypertrophy and adventitia of control pulmonary artery (n = 5). Measurements and Main Results: We detected 8,273 transcripts in the IPAH lesions and control lung pulmonary arteries. Plexiform lesions and IPAH adventitia exhibited the greatest number of differentially expressed genes when compared with intima+media hypertrophy and obliterative lesions. Plexiform lesions in IPAH showed enrichment for 1) genes associated with transforming growth factor β signaling and 2) mutated genes affecting the extracellular matrix and endothelial-mesenchymal transformation. Plexiform lesions and IPAH adventitia showed upregulation of genes involved in immune and IFN signaling, coagulation, and complement pathways. Cellular deconvolution indicated variability in the number of vascular and inflammatory cells between IPAH lesions, which underlies the differential transcript profiling. Conclusions: IPAH lesions express unique molecular transcript profiles enriched for pathways involving pathogenetic pathways, including genetic disease drivers, innate and acquired immunity, hypoxia sensing, and angiogenesis signaling. These data provide a rich molecular-structural framework in IPAH vascular lesions that inform novel biomarkers and therapeutic targets in this highly morbid disease.

Prognostic value of pulmonary diffusing capacity for carbon monoxide and ventilation-perfusion SPECT findings in pulmonary arterial hypertension

Reduced pulmonary diffusing capacity for carbon monoxide (DLCO) can be observed in pulmonary arterial hypertension (PAH) and associates with increased mortality. However, the prognostic value of DLCO when corrected for haemoglobin (DLCOc), an independent modifier of DLCO, remains understudied. Additionally, the prognostic role of ventilation (V)-perfusion (Q) emission computed tomography (V/Q SPECT) findings in patients with PAH, which may concurrently be performed to rule out chronic thromboembolic pulmonary hypertension, is uncertain. A retrospective cohort study was conducted on 152 patients with PAH referred to a tertiary hospital for evaluation from January 2011 to January 2020. Lung function tests, clinical data and V/Q SPECT were ascertained. Cox regression analysis was performed to evaluate the association between DLCOc, DLCO and V/Q SPECT defects at referral with all-cause mortality. In equally adjusted Cox regression analysis, each percentage increase in DLCOc % predicted (%pred) (hazard ratio (HR) 0.97; 95% CI: 0.94-0.99) and DLCO%pred (HR 0.97; 95% CI: 0.94-0.99) was similarly associated with all-cause mortality. There was no detectable difference in area under the curve for prediction of all-cause mortality by DLCOc%pred and DLCO%pred (C-index 0.71 and 0.72, respectively, P = 0.85 for difference). None of the defects noted on V/Q SPECT were significantly associated with mortality, but mismatched defects were associated with lower values of DLCOc%pred and DLCO%pred. DLCOc%pred and DLCO%pred perform equally as prognostic markers in PAH, supporting the use of either metric when available for prognostic stratification.

The role of transcription factors in the pathogenesis and therapeutic targeting of vascular diseases

Transcription factors (TFs) constitute an essential component of epigenetic regulation. They contribute to the progression of vascular diseases by regulating epigenetic gene expression in several vascular diseases. Recently, numerous regulatory mechanisms related to vascular pathology, ranging from general TFs that are continuously activated to histiocyte-specific TFs that are activated under specific circumstances, have been studied. TFs participate in the progression of vascular-related diseases by epigenetically regulating vascular endothelial cells (VECs) and vascular smooth muscle cells (VSMCs). The Krüppel-like family (KLF) TF family is widely recognized as the foremost regulator of vascular diseases. KLF11 prevents aneurysm progression by inhibiting the apoptosis of VSMCs and enhancing their contractile function. The presence of KLF4, another crucial member, suppresses the progression of atherosclerosis (AS) and pulmonary hypertension by attenuating the formation of VSMCs-derived foam cells, ameliorating endothelial dysfunction, and inducing vasodilatory effects. However, the mechanism underlying the regulation of the progression of vascular-related diseases by TFs has remained elusive. The present study categorized the TFs involved in vascular diseases and their regulatory mechanisms to shed light on the potential pathogenesis of vascular diseases, and provide novel insights into their diagnosis and treatment.

Idiopathic and connective tissue disease-associated pulmonary arterial hypertension (PAH): Similarities, differences and the role of autoimmunity

Pre-capillary pulmonary arterial hypertension (PAH) is hemodynamically characterized by a mean pulmonary arterial pressure (mPAP) ≥ 20 mmHg, pulmonary capillary wedge pressure (PAWP) ≤15 mmHg and pulmonary vascular resistance (PVR) > 2. PAH is classified in six clinical subgroups, including idiopathic PAH (IPAH) and PAH associated to connective tissue diseases (CTD-PAH), that will be the main object of this review. The aim is to compare these two PAH subgroups in terms of epidemiology, histological and pathogenic findings in an attempt to define disease-specific features, including autoimmunity, that may explain the heterogeneity of response to therapy between IPAH and CTD-PAH.

Metabolomics in Pulmonary Hypertension-A Useful Tool to Provide Insights into the Dark Side of a Tricky Pathology

Pulmonary hypertension (PH) is a multifaceted illness causing clinical manifestations like dyspnea, fatigue, and cyanosis. If left untreated, it often evolves into irreversible pulmonary arterial hypertension (PAH), leading to death. Metabolomics is a laboratory technique capable of providing insights into the metabolic pathways that are responsible for a number of physiologic or pathologic events through the analysis of a biological fluid (such as blood, urine, and sputum) using proton nuclear magnetic resonance spectroscopy or mass spectrometry. A systematic review was finalized according to the PRISMA scheme, with the goal of providing an overview of the research papers released up to now on the application of metabolomics to PH/PAH. So, eighty-five papers were identified, of which twenty-four concerning PH, and sixty-one regarding PAH. We found that, from a metabolic standpoint, the hallmarks of the disease onset and progression are an increase in glycolysis and impaired mitochondrial respiration. Oxidation is exacerbated as well. Specific metabolic fingerprints allow the characterization of some of the specific PH and PAH subtypes. Overall, metabolomics provides insights into the biological processes happening in the body of a subject suffering from PH/PAH. The disarranged metabolic pathways underpinning the disease may be the target of new therapeutic agents. Metabolomics will allow investigators to make a step forward towards personalized medicine.

An emerging class of new therapeutics targeting TGF, Activin, and BMP ligands in pulmonary arterial hypertension

Pulmonary arterial hypertension (PAH) is an often fatal condition, the primary pathology of which involves loss of pulmonary vascular perfusion due to progressive aberrant vessel remodeling. The reduced capacity of the pulmonary circulation places increasing strain on the right ventricle of the heart, leading to death by heart failure. Currently, licensed therapies are primarily vasodilators, which have increased the median post-diagnosis life expectancy from 2.8 to 7 years. Although this represents a substantial improvement, the search continues for transformative therapeutics that reverse established disease. The genetics of human PAH heavily implicates reduced endothelial bone morphogenetic protein (BMP) signaling as a causal role for the disease pathobiology. Recent approaches have focused on directly enhancing BMP signaling or removing the inhibitory influence of pathways that repress BMP signaling. In this critical commentary, we review the evidence underpinning the development of two approaches: BMP-based agonists and inhibition of activin/GDF signaling. We also address the key considerations and questions that remain regarding these approaches.

Tensions in Taxonomies: Current Understanding and Future Directions in the Pathobiologic Basis and Treatment of Group 1 and Group 3 Pulmonary Hypertension

In the over 100 years since the recognition of pulmonary hypertension (PH), immense progress and significant achievements have been made with regard to understanding the pathophysiology of the disease and its treatment. These advances have been mostly in idiopathic pulmonary arterial hypertension (IPAH), which was classified as Group 1 Pulmonary Hypertension (PH) at the Second World Symposia on PH in 1998. However, the pathobiology of PH due to chronic lung disease, classified as Group 3 PH, remains poorly understood and its treatments thus remain limited. We review the history of the classification of the five groups of PH and aim to provide a state-of-the-art review of the understanding of the pathogenesis of Group 1 PH and Group 3 PH including insights gained from novel high-throughput omics technologies that have revealed heterogeneities within these categories as well as similarities between them. Leveraging the substantial gains made in understanding the genomics, epigenomics, proteomics, and metabolomics of PAH to understand the full spectrum of the complex, heterogeneous disease of PH is needed. Multimodal omics data as well as supervised and unbiased machine learning approaches after careful consideration of the powerful advantages as well as of the limitations and pitfalls of these technologies could lead to earlier diagnosis, more precise risk stratification, better predictions of disease response, new sub-phenotype groupings within types of PH, and identification of shared pathways between PAH and other types of PH that could lead to new treatment targets. © 2023 American Physiological Society. Compr Physiol 13:4295-4319, 2023.

Hypoxia-induced long non-coding RNA plasmacytoma variant translocation 1 upregulation aggravates pulmonary arterial smooth muscle cell proliferation by regulating autophagy via miR-186/Srf/Ctgf and miR-26b/Ctgf signaling pathways

BACKGROUND

The lncRNA PVT1 reportedly functions as a competing endogenous RNA (ceRNA) of miR-186 and miR-26b in different tissue types. In this study, we investigated the possible involvement of the miR-186/Srf/Ctgf and miR-26b/Ctgf signaling pathways in the pathogenesis of hypoxia-induced PAH.

METHODS

Expression of PVT1, miR-186, miR-26b, and Srf and Ctgf mRNAs were evaluated by real-time polymerase chain reaction. Protein expression of SRF, CTGF, LC3B-I, LC3B-II, and Beclin-I was evaluated using western blotting. The regulatory relationship between the lncRNA, miRNAs, and target mRNAs was explored using luciferase assays. Immunohistochemistry was used to evaluate the expression of SRF and CTGF in situ. MTT assay was performed to assess the proliferation of PASMCs.

RESULTS

Exposure to hypoxia markedly altered the expression of PVT1, Srf, Ctgf, miR-186, and miR-26b in a rat model. MiR-186 binding sites in the sequences of Srf mRNA and PVT1 were confirmed by luciferase assays, indicating that miR-186 may interact with both PVT1 and Srf mRNA. Additionally, miR-26b binding sites were identified in the sequences of Ctgf mRNA and PVT1, suggesting that miR-26b may interact with both PVT1 and Ctgf mRNA. In line with this, we found that overexpression of PVT1 reduced expression of miR-26b and miR-186 but activated expression of Srf, Ctgf, LC3B-II, and Beclin-I.

CONCLUSIONS

Upregulation of PVT1 by exposure to hypoxia promoted the expression of CTGF, leading to deregulation of autophagy and abnormal proliferation of PASMCs. Dysregulation of the miR-186/Srf/Ctgf and miR-26b/Ctgf signaling pathways may be involved in the pathogenesis of hypoxia-induced PASMCs.

Updated perspective of EPAS1 and the role in pulmonary hypertension

Pulmonary hypertension (PH) is a group of syndromes characterized by irreversible vascular remodeling and persistent elevation of pulmonary vascular resistance and pressure, leading to ultimately right heart failure and even death. Current therapeutic strategies mainly focus on symptoms alleviation by stimulating pulmonary vessel dilation. Unfortunately, the mechanism and interventional management of vascular remodeling are still yet unrevealed. Hypoxia plays a central role in the pathogenesis of PH and numerous studies have shown the relationship between PH and hypoxia-inducible factors family. EPAS1, known as hypoxia-inducible factor-2 alpha (HIF-2α), functions as a transcription factor participating in various cellular pathways. However, the detailed mechanism of EPAS1 has not been fully and systematically described. This article exhibited a comprehensive summary of EPAS1 including the molecular structure, biological function and regulatory network in PH and other relevant cardiovascular diseases, and furthermore, provided theoretical reference for the potential novel target for future PH intervention.

Nanoparticle endothelial delivery of PGC-1α attenuates hypoxia-induced pulmonary hypertension by attenuating EndoMT-caused vascular wall remodeling

Pulmonary hypertension (PH) induced by chronic hypoxia is characterized by thickening of pulmonary artery walls, elevated pulmonary vascular resistance, and right-heart failure. Dysfunction of endothelial cells is the hallmark event in the progression of PH. Among various mechanisms, endothelial to mesenchymal transition (EndoMT) has emerged as an important source of endothelial cell dysfunction in PH. However, the mechanisms underlying the EndoMT in PH remain largely unknown. Our results showed that peroxisome proliferator-activated receptor gamma coactivator 1-alpha (PGC-1α) expression was decreased in pulmonary arterial endothelial cells (PAECs) in PH patients and hypoxia-induced PH mouse model compared to the normal controls. Endothelial-specific overexpression of PGC-1α using nanoparticle delivery significantly attenuated the progression of PH, as shown by the significantly decreased right ventricular systolic pressure and diminished artery thickness as well as reduced vascular muscularization. Moreover, Endothelial-specific overexpression of PGC-1α blocked the EndoMT of PAECs during PH, indicating that loss of PGC-1α promotes PH development by mediating EndoMT, which damages the integrity of endothelium. Intriguingly, we found that PGC-1α overexpression rescued the expression of endothelial nitric oxide synthase in mouse lung tissues that was deceased by hypoxia treatment in vivo and in endothelial cells treated with TGF-β in vitro. Consistently, PAECs and vascular smooth muscle co-culture showed that overexpression of PGC-1α in PAECs increases nitric oxide release, which would likely diffuse to smooth muscle cells, where it activates specific protein kinases, and initiates SMC relaxation by diminishing the calcium flux. Endothelial-specific overexpression of PGC-1α also attenuated hypoxia-induced pulmonary artery stiffness which appeared to be caused by both the decreased endothelial nitric oxide production and increased vascular remodeling. Taken together, these results demonstrated that endothelial-specific delivery of PGC-1α prevents PH development by inhibiting EndoMT of PAECs and thus restoring endothelial function and reducing vascular remodeling.

Salt-inducible kinase 1 deficiency promotes vascular remodeling in pulmonary arterial hypertension via enhancement of yes-associated protein-mediated proliferation

Pulmonary arterial remodeling at an early stage, including excessive proliferation and migration of smooth muscle cells, is a hallmark of pulmonary arterial hypertension (PAH). Salt-inducible kinases (SIKs) have been increasingly reported to play a key role in smooth muscle cell proliferation and phenotype switching, which may be associated with arterial remodeling. However, the potential effects of SIK1 in PAH and the underlying mechanisms have not been explored. The aim of this study was to determine whether reduced expression or inactivation of SIK1 is associated with pulmonary arterial remodeling in PAH and to elucidate whether it is related to the Hippo/Yes-associated protein (YAP) pathway. Using mouse models of PAH and hypoxia-stimulated hPASMCs, we observed that SIK1 expression was robustly reduced in lung tissues of PAH mice and hPASMCs cultured under hypoxia. In hypoxia-induced PAH mice, pharmacological SIK inhibition or AAV9-mediated specific smooth muscle SIK1 knockdown strongly aggravated pathological changes caused by hypoxia, including right ventricular hypertrophy and small pulmonary arterial remodeling. Meanwhile, in hypoxia-stimulated hPASMCs, SIK1 knockdown or inhibition promoted proliferation and migration under hypoxia, accompanied by decreased phosphorylation and increased nuclear accumulation of YAP, while SIK1 overexpression inhibited hypoxia-induced proliferation, migration and nuclear translocation of YAP in hPASMCs. YAP knockdown attenuated the increase in cell proliferation induced by HG-9-91-01 treatment or SIK1 siRNA transfection under hypoxia in hPASMCs. Here, we identified SIK1 as an antiproliferative factor in hypoxia-induced pulmonary arterial remodeling via YAP-mediated mechanisms. These results show that targeting SIK1 may be a promising therapeutic strategy for the treatment of PAH.

Contribution of fatty acid oxidation to the pathogenesis of pulmonary hypertension

Dysregulated metabolism characterizes both animal and human forms of pulmonary hypertension (PH). Enzymes involved in fatty acid metabolism have previously not been assessed in human pulmonary arteries affected by pulmonary arterial hypertension (PAH), and how inhibition of fatty acid oxidation (FAO) may attenuate PH remains unclear. Fatty acid metabolism gene transcription was quantified in laser-dissected pulmonary arteries from 10 explanted lungs with advanced PAH (5 idiopathic, 5 associated with systemic sclerosis), and 5 donors without lung diseases. Effects of oxfenicine, a FAO inhibitor, on female Sugen 5416-chronic hypoxia (SuHx) rats were studied in vivo using right heart catheterization, and ex vivo using perfused lungs and pulmonary artery ring segments. The impact of pharmacologic (oxfenicine) and genetic (carnitine palmitoyltransferase 1a heterozygosity) FAO suppression was additionally probed in mouse models of Schistosoma and hypoxia-induced PH. Potential mechanisms underlying FAO-induced PH pathogenesis were examined by quantifying ATP and mitochondrial mass in oxfenicine-treated SuHx pulmonary arterial cells, and by assessing pulmonary arterial macrophage infiltration with immunohistochemistry. We found upregulated pulmonary arterial transcription of 26 and 13 FAO genes in idiopathic and systemic sclerosis-associated PAH, respectively. In addition to promoting de-remodeling of pulmonary arteries in SuHx rats, oxfenicine attenuated endothelin-1-induced vasoconstriction. FAO inhibition also conferred modest benefit in the two mouse models of PH. Oxfenicine increased mitochondrial mass in cultured rat pulmonary arterial cells, and decreased the density of perivascular macrophage infiltration in pulmonary arteries of treated SuHx rats. In summary, FAO inhibition attenuated experimental PH, and may be beneficial in human PAH.

HIV and Schistosoma Co-Exposure Leads to Exacerbated Pulmonary Endothelial Remodeling and Dysfunction Associated with Altered Cytokine Landscape

HIV and Schistosoma infections have been individually associated with pulmonary vascular disease. Co-infection with these pathogens is very common in tropical areas, with an estimate of six million people co-infected worldwide. However, the effects of HIV and Schistosoma co-exposure on the pulmonary vasculature and its impact on the development of pulmonary vascular disease are largely unknown. Here, we have approached these questions by using a non-infectious animal model based on lung embolization of Schistosoma mansoni eggs in HIV-1 transgenic (HIV) mice. Schistosome-exposed HIV mice but not wild-type (Wt) counterparts showed augmented pulmonary arterial pressure associated with markedly suppressed endothelial-dependent vasodilation, increased endothelial remodeling and vessel obliterations, formation of plexiform-like lesions and a higher degree of perivascular fibrosis. In contrast, medial wall muscularization was similarly increased in both types of mice. Moreover, HIV mice displayed an impaired immune response to parasite eggs in the lung, as suggested by decreased pulmonary leukocyte infiltration, small-sized granulomas, and augmented residual egg burden. Notably, vascular changes in co-exposed mice were associated with increased expression of proinflammatory and profibrotic cytokines, including IFN-γ and IL-17A in CD4⁺ and γδ T cells and IL-13 in myeloid cells. Collectively, our study shows for the first time that combined pulmonary persistence of HIV proteins and Schistosoma eggs, as it may occur in co-infected people, alters the cytokine landscape and targets the vascular endothelium for aggravated pulmonary vascular pathology. Furthermore, it provides an experimental model for the understanding of pulmonary vascular disease associated with HIV and Schistosoma co-morbidity.

Benefits of Curcumin in the Vasculature: A Therapeutic Candidate for Vascular Remodeling in Arterial Hypertension and Pulmonary Arterial Hypertension?

Growing evidence suggests that hypertension is one of the leading causes of cardiovascular morbidity and mortality since uncontrolled high blood pressure increases the risk of myocardial infarction, aortic dissection, hemorrhagic stroke, and chronic kidney disease. Impaired vascular homeostasis plays a critical role in the development of hypertension-induced vascular remodeling. Abnormal behaviors of vascular cells are not only a pathological hallmark of hypertensive vascular remodeling, but also an important pathological basis for maintaining reduced vascular compliance in hypertension. Targeting vascular remodeling represents a novel therapeutic approach in hypertension and its cardiovascular complications. Phytochemicals are emerging as candidates with therapeutic effects on numerous pathologies, including hypertension. An increasing number of studies have found that curcumin, a polyphenolic compound derived from dietary spice turmeric, holds a broad spectrum of pharmacological actions, such as antiplatelet, anticancer, anti-inflammatory, antioxidant, and antiangiogenic effects. Curcumin has been shown to prevent or treat vascular remodeling in hypertensive rodents by modulating various signaling pathways. In the present review, we attempt to focus on the current findings and molecular mechanisms of curcumin in the treatment of hypertensive vascular remodeling. In particular, adverse and inconsistent effects of curcumin, as well as some favorable pharmacokinetics or pharmacodynamics profiles in arterial hypertension will be discussed. Moreover, the recent progress in the preparation of nano-curcumins and their therapeutic potential in hypertension will be briefly recapped. The future research directions and challenges of curcumin in hypertension-related vascular remodeling are also proposed. It is foreseeable that curcumin is likely to be a therapeutic agent for hypertension and vascular remodeling going forwards.

JAGGED-NOTCH3 signaling in vascular remodeling in pulmonary arterial hypertension

Within the pulmonary arterial tree, the NOTCH3 pathway is crucial in controlling vascular smooth muscle cell proliferation and maintaining smooth muscle cells in an undifferentiated state. Pulmonary arterial hypertension (PAH) is a fatal disease without cure, characterized by elevated pulmonary vascular resistance due to vascular smooth muscle cell proliferation in precapillary arteries, perivascular inflammation, and asymmetric neointimal hyperplasia. Here, we show that human PAH is characterized by overexpression of the NOTCH ligand JAGGED-1 (JAG-1) in small pulmonary artery smooth muscle cells and that JAG-1 selectively controls NOTCH3 signaling and cellular proliferation in an autocrine fashion. In contrast, the NOTCH ligand DELTA-LIKE 4 is minimally expressed in small pulmonary artery smooth muscle cells from individuals with PAH, inhibits NOTCH3 cleavage and signaling, and retards vascular smooth muscle cell proliferation. A new monoclonal antibody for the treatment of PAH, which blocks JAG-1 cis- and trans-induced cleavage of the NOTCH3 receptor in the pulmonary vasculature, was developed. Inhibition of JAG-1-induced NOTCH3 signaling in the lung reverses clinical and pathologic pulmonary hypertension in two rodent models of disease, without toxic side effects associated with nonspecific NOTCH inhibitors. Our data suggest opposing roles of NOTCH ligands in the pulmonary vasculature in pulmonary hypertension. We propose that selectively targeting JAG-1 activation of NOTCH3 may be an effective, safe strategy to treat PAH.

Perfusion imaging heterogeneity during NO inhalation distinguishes pulmonary arterial hypertension (PAH) from healthy subjects and has potential as an imaging biomarker

BACKGROUND

Without aggressive treatment, pulmonary arterial hypertension (PAH) has a 5-year mortality of approximately 40%. A patient's response to vasodilators at diagnosis impacts the therapeutic options and prognosis. We hypothesized that analyzing perfusion images acquired before and during vasodilation could identify characteristic differences between PAH and control subjects.

METHODS

We studied 5 controls and 4 subjects with PAH using HRCT and ¹³NN PET imaging of pulmonary perfusion and ventilation. The total spatial heterogeneity of perfusion (CV²_Qtotal) and its components in the vertical (CV²_Qvgrad) and cranio-caudal (CV²_Qzgrad) directions, and the residual heterogeneity (CV²_Qr), were assessed at baseline and while breathing oxygen and nitric oxide (O₂ + iNO). The length scale spectrum of CV²_Qr was determined from 10 to 110 mm, and the response of regional perfusion to O₂ + iNO was calculated as the mean of absolute differences. Vertical gradients in perfusion (Q_vgrad) were derived from perfusion images, and ventilation-perfusion distributions from images of ¹³NN washout kinetics.

RESULTS

O₂ + iNO significantly enhanced perfusion distribution differences between PAH and controls, allowing differentiation of PAH subjects from controls. During O₂ + iNO, CV²_Qvgrad was significantly higher in controls than in PAH (0.08 (0.055-0.10) vs. 6.7 × 10^-3 (2 × 10^-4-0.02), p < 0.001) with a considerable gap between groups. Q_vgrad and CV²_Qtotal showed smaller differences: - 7.3 vs. - 2.5, p = 0.002, and 0.12 vs. 0.06, p = 0.01. CV²_Qvgrad had the largest effect size among the primary parameters during O₂ + iNO. CV²_Qr, and its length scale spectrum were similar in PAH and controls. Ventilation-perfusion distributions showed a trend towards a difference between PAH and controls at baseline, but it was not statistically significant.

CONCLUSIONS

Perfusion imaging during O2 + iNO showed a significant difference in the heterogeneity associated with the vertical gradient in perfusion, distinguishing in this small cohort study PAH subjects from controls.

Increasing angiotensin-converting enzyme (ACE) 2/ACE axes ratio alleviates early pulmonary vascular remodeling in a porcine model of acute pulmonary embolism with cardiac arrest

BACKGROUND

Acute pulmonary embolism (APE) with cardiac arrest (CA) is characterized by high mortality in emergency due to pulmonary arterial hypertension (PAH). This study aims to determine whether early pulmonary artery remodeling occurs in PAH caused by massive APE with CA and the protective effects of increasing angiotensin-converting enzyme (ACE) 2-angiotensin (Ang) (1-7)-Mas receptor axis and ACE-Ang II-Ang II type 1 receptor (AT1) axis (ACE2/ACE axes) ratio on pulmonary artery lesion after return of spontaneous circulation (ROSC).

METHODS

To establish a porcine massive APE with CA model, autologous thrombus was injected into the external jugular vein until mean arterial pressure dropped below 30 mmHg (1 mmHg=0.133 kPa). Cardiopulmonary resuscitation and thrombolysis were delivered to regain spontaneous circulation. Pigs were divided into four groups of five pigs each: control group, APE-CA group, ROSC-saline group, and ROSC-captopril group, to examine the endothelial pathological changes and expression of ACE2/ACE axes in pulmonary artery with or without captopril.

RESULTS

Histological analysis of samples from the APE-CA and ROSC-saline groups showed that pulmonary arterioles were almost completely occluded by accumulated endothelial cells. Western blotting analysis revealed a decrease in the pulmonary arterial ACE2/ACE axes ratio and increases in angiopoietin-2/angiopoietin-1 ratio and expression of vascular endothelial growth factor (VEGF) in the APE-CA group compared with the control group. Captopril significantly suppressed the activation of angiopoietin-2/angiopoietin-1 and VEGF in plexiform lesions formed by proliferative endothelial cells after ROSC. Captopril also alleviated endothelial cell apoptosis by increasing the B-cell lymphoma-2 (Bcl-2)/Bcl-2-associated X (Bax) ratio and decreasing cleaved caspase-3 expression.

CONCLUSION

Increasing the ACE2/ACE axes ratio may ameliorate pulmonary arterial remodeling by inhibiting the apoptosis and proliferation of endothelial cells after ROSC induced by APE.

Murine models of sickle cell disease and beta-thalassemia demonstrate pulmonary hypertension with distinctive features

Sickle cell anemia and β-thalassemia intermedia are very different genetically determined hemoglobinopathies predisposing to pulmonary hypertension. The etiologies responsible for the associated development of pulmonary hypertension in both diseases are multi-factorial with extensive mechanistic contributors described. Both sickle cell anemia and β-thalassemia intermedia present with intra and extravascular hemolysis. And because sickle cell anemia and β-thalassemia intermedia share features of extravascular hemolysis, macrophage iron excess and anemia we sought to characterize the common features of the pulmonary hypertension phenotype, cardiac mechanics, and function as well as lung and right ventricular metabolism. Within the concept of iron, we have defined a unique pulmonary vascular iron accumulation in lungs of sickle cell anemia pulmonary hypertension patients at autopsy. This observation is unlike findings in idiopathic or other forms of pulmonary arterial hypertension. In this study, we hypothesized that a common pathophysiology would characterize the pulmonary hypertension phenotype in sickle cell anemia and β-thalassemia intermedia murine models. However, unlike sickle cell anemia, β-thalassemia is also a disease of dyserythropoiesis, with increased iron absorption and cellular iron extrusion. This process is mediated by high erythroferrone and low hepcidin levels as well as dysregulated iron transport due transferrin saturation, so there may be differences as well. Herein we describe common and divergent features of pulmonary hypertension in aged Berk-ss (sickle cell anemia) and Hbb^th/3+ (intermediate β-thalassemia) mice and suggest translational utility as proof-of-concept models to study pulmonary hypertension therapeutics specific to genetic anemias.

Hemopexin dosing improves cardiopulmonary dysfunction in murine sickle cell disease

Hemopexin (Hpx) is a crucial defense protein against heme liberated from degraded hemoglobin during hemolysis. High heme stress creates an imbalance in Hpx bioavailability, favoring heme accumulation and downstream pathophysiological responses leading to cardiopulmonary disease progression in sickle cell disease (SCD) patients. Here, we evaluated a model of murine SCD, which was designed to accelerate red blood cell sickling, pulmonary hypertension, right ventricular dysfunction, and exercise intolerance by exposure of the mice to moderate hypobaric hypoxia. The sequence of pathophysiology in this model tracks with circulatory heme accumulation, lipid oxidation, extensive remodeling of the pulmonary vasculature, and fibrosis. We hypothesized that Hpx replacement for an extended period would improve exercise tolerance measured by critical speed as a clinically meaningful therapeutic endpoint. Further, we sought to define the effects of Hpx on upstream cardiopulmonary function, histopathology, and tissue oxidation. Our data shows that tri-weekly administrations of Hpx for three months dose-dependently reduced heme exposure and pulmonary hypertension while improving cardiac pressure-volume relationships and exercise tolerance. Furthermore, Hpx administration dose-dependently attenuated pulmonary fibrosis and oxidative modifications in the lung and myocardium of the right ventricle. Observations in our SCD murine model are consistent with pulmonary vascular and right ventricular pathology at autopsy in SCD patients having suffered from severe pulmonary hypertension, right ventricular dysfunction, and sudden cardiac death. This study provides a translational evaluation supported by a rigorous outcome analysis demonstrating therapeutic proof-of-concept for Hpx replacement in SCD.

[Morphological assessment of pulmonary vessels in pulmonary arterial hypertension associated with congenital heart disease]

Pulmonary vascular remodeling is the key structural alteration in pulmonary arterial hypertension associated with congenital heart disease (CHD). Changes in the pulmonary vessels in CHD generally occur in the inner and middle coats. This review considers the pathology of these changes and highlights some issues of a stereological approach to the morphometry of pulmonary vasculature. It also touches upon the issues of the morphology of pulmonary vessels in post-capillary and segmental pulmonary hypertension.

Evidence supporting a role for circulating macrophages in the regression of vascular remodeling following sub-chronic exposure to hemoglobin plus hypoxia

Macrophages are a heterogeneous population with both pro- and anti-inflammatory functions play an essential role in maintaining tissue homeostasis, promoting inflammation under pathological conditions, and tissue repair after injury. In pulmonary hypertension, the M1 phenotype is more pro-inflammatory compared to the M2 phenotype, which is involved in tissue repair. The role of macrophages in the initiation and progression of pulmonary hypertension is well studied. However, their role in the regression of established pulmonary hypertension is not well known. Rats chronically exposed to hemoglobin (Hb) plus hypoxia (HX) share similarities to humans with pulmonary hypertension associated with hemolytic disease, including the presence of a unique macrophage phenotype surrounding distal vessels that are associated with vascular remodeling. These lung macrophages are characterized by high iron content, HO-1, ET-1, and IL-6, and are recruited from the circulation. Depletion of macrophages in this model prevents the development of pulmonary hypertension and vascular remodeling. In this study, we specifically investigate the regression of pulmonary hypertension over a four-week duration after rats were removed from Hb + HX exposure with and without gadolinium chloride administration. Withdrawal of Hb + HX reversed systolic pressures and right ventricular function after Hb + Hx exposure in four weeks. Our data show that depleting circulating monocytes/macrophages during reversal prevents complete recovery of right ventricular systolic pressure and vascular remodeling in this rat model of pulmonary hypertension at four weeks post exposure. The data presented offer a novel insight into the role of macrophages in the processes of pulmonary hypertension regression in a rodent model of Hb + Hx-driven disease.

A 1H NMR spectroscopic metabolomic study of the protective effects of irbesartan in a rat model of chronic mountain sickness

Chronic mountain sickness (CMS) is a significant pathology in most high-altitude regions globally, affecting the cardiopulmonary system and its mechanism is largely unknown. A metabonomic approach using ¹H nuclear magnetic resonance spectroscopy allows for detecting differential metabolites, which provides a global view and mechanisms during CMS development. In this study, we simulated a high-altitude environment to establish a rat model of CMS. Irbesartan was administered to CMS rats at three doses (6.75, 13.5, and 27 mg/kg) once a day for 15 days. HE staining and transmission electron microscopy were used to evaluate the effect of changes on the lung. Based on ¹H NMR spectra obtained from serum samples, partial least squares-discriminant analysis (PLS-DA) and its variant orthogonal PLS-DA (OPLS-DA) models were applied to distinguish the different groups. Histopathological sections showed that the alveolar structure was abnormal, inflammatory infiltration occurred in CMS rats, and CMS induced notable metabolic disorder according to the ¹H NMR result. However, irbesartan reversed the imbalanced metabolites via energy metabolism, amino acid metabolism, and taurine metabolism pathways, and its effect was also confirmed by the general signs and morphology of the lung. The results revealed that irbesartan as an effective therapeutic agent to improve CMS is warranted.

Irbesartan ameliorates chronic mountain sickness in a rat model via the cholesterol metabolism: An iTRAQ -based proteomics analysis

OBJECTIVE

To study the effects of irbesartan on pulmonary artery lesions in a rat model with chronic mountain sickness (CMS) and identify the biomarkers involved.

METHODS

In this study, we used a rat model of CMS to evaluate the therapeutic effect of irbesartan by measuring pulmonary artery pressure and evaluating the histopathology of the pulmonary artery. We also used proteomics technology to identify differentially expressed proteins (DEPs) in the serum and performed bioinformatics analysis. Results were then verified by enzyme linked immunosorbent assay (ELISA) and immunohistochemistry (IHC).

RESULTS

Irbesartan treatment induced a significant decrease (P < 0.05) in the pulmonary artery pressure of CMS rats. Histopathological and electron microscope further confirmed that high altitude hypoxia induced changes in the structure of the pulmonary artery tissue and caused ultrastructural lesions. Proteomics analysis identified 40 DEPs; bioinformatics analysis further revealed that the cholesterol metabolism pathway plays a crucial role in the occurrence of CMS. ELISA and IHC verified that several DEPs (Apo-A1, Apo-C1, Apo-E, IGF-1, Profilin1, and Col1a1) represent critical biological markers in pulmonary artery disease caused by CMS.

CONCLUSIONS

Irbesartan significantly improved pulmonary artery damage in a rat model of CMS possibly by impacting on the cholesterol metabolism pathway and by reducing damage to vascular endothelial cells. Irbesartan also inhibited the expression levels of IGF-1, Profilin1 and Col1a1 to relieve pulmonary artery pressure and improve lung function by inhibiting vascular remodeling. Several proteins were identified as potential biomarkers of CMS, including Apo-A1, Apo-C1, Apo-E, IGF-1, Profilin1, and Col1a1.

Pulmonary vasculopathy in explanted lungs from patients with interstitial lung disease undergoing lung transplantation

BACKGROUND

Pulmonary hypertension (PH) causes increased morbidity and mortality in patients with interstitial lung diseases (ILD). Classification schemes, while well-characterised for the vasculopathy of idiopathic PH, have been applied, unchallenged, to ILD-related PH. We evaluated pulmonary arterial histopathology in explanted human lung tissue from patients who were transplanted for advanced fibrotic ILD.

METHODS

Lung explants from 38 adult patients who underwent lung transplantation were included. Patients were divided into three groups: none, mild/moderate and severe PH by mean pulmonary artery pressure (mPAP) measured at pre lung transplantation right heart catheterisation (RHC). Grading of pulmonary vasculopathy according to Heath and Edwards scheme, and prelung transplantation evaluation data were compared between the groups.

RESULTS

38 patients with fibrotic ILDs were included, the majority (21) with idiopathic pulmonary fibrosis. Of the 38 patients, 18 had severe PH, 13 had mild/moderate PH and 7 had no PH by RHC. 16 of 38 patients had severe pulmonary arterial vasculopathy including vascular occlusion with intimal fibrosis and/or plexiform lesions. There were no correlations between mPAP and lung diffusion with the severity of pulmonary arterial pathological grade (Spearman's rho=0.14, p=0.34, rho=0.11, p=0.49, respectively).

CONCLUSIONS

Patients with end stage ILD had severe pulmonary arterial vasculopathy in their explanted lungs irrespective of the presence and/or severity of PH as measured by RHC. These findings suggest that advanced pulmonary arterial vasculopathy is common in patients with advanced fibrotic ILD and may develop prior to the clinical detection of PH by RHC.

Ethyl Pyruvate Alleviates Pulmonary Hypertension through the Suppression of Pulmonary Artery Smooth Muscle Cell Proliferation via the High Mobility Group Protein B1/Receptor for Advanced Glycation End-Products Axis

Purpose: Pulmonary arterial hypertension (PAH) is a formidable disease with no effective treatment at present. With the goal of developing potential therapies, we attempted to determine whether ethyl pyruvate (EP) could alleviate PAH and its mechanism.

Methods: Pulmonary smooth muscle cells were cultured in conventional low-oxygen environments, and cellular proliferation was monitored after treatment with either EP or phosphate-balanced solution (PBS). Expression of high mobility group protein B1 (HMGB1) and receptor for advanced glycation end-products (RAGE) protein were detected by western blot. After hyperkinetic PAH rat models were treated with EP, hemodynamic data were collected. Right ventricular hypertrophy and pulmonary vascular remodeling were evaluated. Expression of HMGB1 and RAGE protein was also detected.

Results: In vitro, proliferative activity increased in low-oxygen environments, but was inhibited by EP treatment. Furthermore, Western blotting showed the decreased expression of HMGB1 and RAGE protein after EP treatment. In vivo, pulmonary artery pressures were attenuated with EP. Right ventricular hypertrophy and pulmonary vascular remodeling were also reversed. Additionally, the expression levels of HMGB1 and RAGE were reduced in lung tissues.

Conclusions: EP can alleviate PAH by suppressing the proliferation of pulmonary artery smooth muscle cells via inhibition of HMGB1/RAGE expression.

Roles of Genetic Predisposition in the Sex Bias of Pulmonary Pathophysiology, as a Function of Estrogens : Sex Matters in the Prevalence of Lung Diseases

In addition to studies focused on estrogen mediation of sex-different regulation of systemic circulations, there is now increasing clinical relevance and research interests in the pulmonary circulation, in terms of sex differences in the morbidity and mortality of lung diseases such as inherent-, allergic- and inflammatory-based events. Thus, female predisposition to pulmonary artery hypertension (PAH) is an inevitable topic. To better understand the nature of sexual differentiation in the pulmonary circulation, and how heritable factors, in vivo- and/or in vitro-altered estrogen circumstances and changes in the live environment work in concert to discern the sex bias, this chapter reviews pulmonary events characterized by sex-different features, concomitant with exploration of how alterations of genetic expression and estrogen metabolisms trigger the female-predominant pathological signaling. We address the following: PAH (Sect.7.2) is characterized as an estrogenic promotion of its incidence (Sect. 7.2.2), as a function of specific germline mutations, and as an estrogen-elicited protection of its prognosis (Sect.7.2.1). More detail is provided to introduce a less recognized gene of Ephx2 that encodes soluble epoxide hydrolase (sEH) to degrade epoxyeicosatrienic acids (EETs). As a susceptible target of estrogen, Ephx2/sEH expression is downregulated by an estrogen-dependent epigenetic mechanism. Increases in pulmonary EETs then evoke a potentiation of PAH generation, but mitigation of its progression, a phenomenon similar to the estrogen-paradox regulation of PAH. Additionally, the female susceptibility to chronic obstructive pulmonary diseases (Sect. 7.3) and asthma (Sect.7.4), but less preference to COVID-19 (Sect. 7.5), and roles of estrogen in their pathogeneses are briefly discussed.

COCO/DAND5 inhibits developmental and pathological ocular angiogenesis

Neovascularization contributes to multiple visual disorders including age-related macular degeneration (AMD) and retinopathy of prematurity. Current therapies for treating ocular angiogenesis are centered on the inhibition of vascular endothelial growth factor (VEGF). While clinically effective, some AMD patients are refractory or develop resistance to anti-VEGF therapies and concerns of increased risks of developing geographic atrophy following long-term treatment have been raised. Identification of alternative pathways to inhibit pathological angiogenesis is thus important. We have identified a novel inhibitor of angiogenesis, COCO, a member of the Cerberus-related DAN protein family. We demonstrate that COCO inhibits sprouting, migration and cellular proliferation of cultured endothelial cells. Intravitreal injections of COCO inhibited retinal vascularization during development and in models of retinopathy of prematurity. COCO equally abrogated angiogenesis in models of choroidal neovascularization. Mechanistically, COCO inhibited TGFβ and BMP pathways and altered energy metabolism and redox balance of endothelial cells. Together, these data show that COCO is an inhibitor of retinal and choroidal angiogenesis, possibly representing a therapeutic option for the treatment of neovascular ocular diseases.

Candidate Genes Identified in Systemic Sclerosis-Related Pulmonary Arterial Hypertension Were Associated with Immunity, Inflammation, and Cytokines

Background

Pulmonary complications of systemic sclerosis (SSc), including pulmonary arterial hypertension (PAH), are the leading causes of patient death. However, the precise molecular mechanisms of its etiology are unclear. This study's objective was to identify the candidate genes involved in the progression of SSc-PAH and investigate the genes' function.

Methods

The gene expression profiles of GSE33463 were obtained from the Gene Expression Omnibus (GEO) database. A free-scale gene coexpression network was constructed using the weighted gene coexpression network analysis (WGCNA) to explore the association between gene sets and clinical features and identify candidate biomarkers. Then, gene ontology analysis was performed. A second dataset was used, GSE19617, to validate the hub genes. The verified hub genes' potential function was further explored using gene set enrichment analysis (GSEA).

Results

Through average link-level clustering, a total of seven modules were classified. A total of 938 hub genes were identified in the key module, and the key module's function mainly enriched was related to chemokine activities. Subsequently, four candidate genes, BTG3, CCR2, RAB10, and TMEM60, were filtered. The expression levels of these four hub genes were consistent in the GSE19617 and GSE33463 datasets. We plotted the ROC curve of the hub genes (all AUC > 0.70). Furthermore, the results of the GSEA for hub genes were correlated with complement and inflammatory responses.

Conclusions

The hub genes (BTG3, CCR2, RAB10, and TMEM60) performed well in distinguishing the SSc-PAH patients from controls, and some biological functions, related to immunity, inflammation, and cytokines, might pave the way for follow-up studies on the diagnosis and treatment of SSc-PAH.

Prevalence and outcomes of pulmonary hypertension after percutaneous closure of atrial septal defect: a systematic review and meta-analysis

BACKGROUND

Atrial septal defect (ASD) is a common form of congenital heart disease. Significant shunts may increase the risk of developing pulmonary hypertension (PH). We aimed to describe current PH definitions, evaluate PH prevalence and the effect of PH on outcomes in patients undergoing percutaneous ASD closure.

METHODS

EMBASE, MEDLINE and Cochrane databases were systematically searched. Studies reporting PH prevalence or mean systolic pulmonary arterial pressure (sPAP) before and after percutaneous ASD closure in adults were included. We conducted meta-analyses to obtain summary estimates for PH prevalence and mean sPAP.

RESULTS

15 articles with a total of 1073 patients met the eligibility criteria. Studies applied variable PH definitions. PH prevalence and mean sPAP levels decreased in all studies after closure. The pooled PH prevalence decreased from 44% (95% CI 29-60%) to 18% (95% CI 8-27%). The overall standardised mean difference in sPAP was 1.12 (95% CI 0.81-1.44) and 1.62 (95% CI 1.00-2.23) in cohort and case-series studies respectively indicating a large decrease. The pooled standard mean difference among the younger and older patients were different, 1.25 (95% CI 0.78-1.71) and 0.91 (95% CI 0.56-1.27), respectively. A high degree of between-study heterogeneity was noted.

CONCLUSIONS

Both PH prevalence and mean sPAP decrease after ASD closure. Larger, prospective studies with consistent PH definitions using the recommended measurement modality are warranted.

Nitric Oxide Stroke Volume Index as a New Hemodynamic Prognostic Parameter for Patients with Pulmonary Arterial Hypertension

The aim of the study was to determine the prognostic value of hemodynamic parameters measured during initial diagnostic right heart catheterization (RHC) in standard conditions and using a nitric oxide reversibility test. A retrospective observational study of 62 patients with pulmonary arterial hypertension (PAH) was performed. Clinical, biochemical, echocardiographic, and hemodynamic data obtained at the time of the PAH diagnosis were precisely analyzed. Patients were followed for five years. Death or lung transplantation was considered as a primary endpoint. The mean follow-up period was 1090 ± 703 days and the median age was 46.84 years. In the studied group, 25 patients survived, 36 patients died, and one underwent a lung transplantation. From all the examined parameters, only stroke volume index during reversibility test with iNO (SVI_{(NO test)}) (HR = 0.910; 95% confidence interval 0.878–0.944; p < 0.001) and initial arterial oxygen saturation (SaO₂) (HR = 0.910; 95% confidence interval 0.843–0.982; p = 0.015) have been established as independent predictors of death or lung transplantation in the five-year follow–up. An SVI_{(NO test)} value above 39.86 mL/m² was associated with 100% five-year survival rate (AUC = 0.956; 95% confidence interval 0.899–1.000; p < 0.001; specificity/sensitivity: 100/84%). The results of the analysis suggest that the SVI_{(NO test)} measured during the initial diagnostic RHC could be a very valuable prognostic factor in the PAH patients.

Effects of exercise rehabilitation training on patients with pulmonary hypertension

Pulmonary hypertension (PH) comprises a group of pathophysiological syndromes characterized by elevated pulmonary artery pressure and pulmonary vascular resistance, which lead to right ventricular overload, and even right heart failure. PH has a poor prognosis and severely leads to a decline in quality of life. Historically, patients with PH were advised to limit their physical activity. However, an increasing number of studies have reported the safety and efficacy of exercise rehabilitation training in PH. This review briefly examined and summarized the effects of exercise rehabilitation training on PH patients reported in the recent literature. The findings of the reviewed studies indicate that exercise rehabilitation training in PH patients has beneficial effects in terms of exercise capacity and quality of life, vascular and right ventricle remodelling, inflammatory response, muscular function and oxidative stress. However, the underlying mechanisms and appropriate exercise strategies (e.g. the duration and intensity of exercise) still need to be explored. In conclusion, exercise rehabilitation training of the appropriate intensity and frequency can improve the prognosis and quality of life of PH patients. The training should be monitored by professional staff and be provided as an adjunct to pharmacological treatment. Larger clinical trials are required to confirm the safety and efficacy of exercise rehabilitation training in PH.

Remodeling of the pulmonary artery in idiopathic pleuroparenchymal fibroelastosis

Idiopathic pleuroparenchymal fibroelastosis (IPPFE) is a rare subtype of idiopathic interstitial pneumonia that consists of alveolar septal elastosis and intra-alveolar collagenosis, which is predominantly located in the upper lobes. The aim of this study was to examine the remodeling of the pulmonary arteries in patients with IPPFE. This study included 18 patients with IPPFE, 24 patients with idiopathic pulmonary fibrosis (IPF), and 5 patients without pulmonary disease as controls. We selected muscular pulmonary arteries and calculated the percentage of the thickness of each layer of the wall (intima, media, and adventitia) in relation to the external diameter. We also quantified the percentage of areas of elastic fiber in the media divided by the whole area of the media (medial elastic fiber score). The percentage of adventitial thickness in IPPFE was significantly higher than that in IPF and in control lungs. The percentage of medial thickness did not differ statistically between IPPFE and IPF. However, the medial elastic fiber score in IPPFE was also significantly larger than that in IPF and control lungs. These results suggest that collagenous thickening of the adventitia and medial elastosis are distinct histological features in the muscular pulmonary arteries of patients with IPPFE.

Reciprocal actions of constrictor prostanoids and superoxide in chronic hypoxia-induced pulmonary hypertension: roles of EETs

Epoxyeicosatrienoic acids (EETs) are synthesized from arachidonic acid by CYP/epoxygenase and metabolized by soluble epoxide hydrolase (sEH). Roles of EETs in hypoxia-induced pulmonary hypertension (HPH) remain elusive. The present study aimed to investigate the underlying mechanisms, by which EETs potentiate HPH. Experiments were conducted on sEH knockout (sEH-KO) and wild type (WT) mice after exposure to hypoxia (10% oxygen) for three weeks. In normal/normoxic conditions, WT and sEH-KO mice exhibited comparable pulmonary artery acceleration time (PAAT), ejection time (ET), PAAT/ET ratio, and velocity time integral (VTI), along with similar right ventricular systolic pressure (RVSP). Chronic hypoxia significantly reduced PAAT, ET, and VTI, coincided with an increase in RVSP; these impairments were more severe in sEH-KO than WT mice. Hypoxia elicited downregulation of sEH and upregulation of CYP2C9 accompanied with elevation of CYP-sourced superoxide, leading to enhanced pulmonary EETs in hypoxic mice with significantly higher levels in sEH-KO mice. Isometric tension of isolated pulmonary arteries was recorded. In addition to downregulation of eNOS-induced impairment of vasorelaxation to ACh, HPH mice displayed upregulation of thromboxane A₂ (TXA₂) receptor, paralleled with enhanced pulmonary vasocontraction to a TXA₂ analog (U46619) in an sEH-KO predominant manner. Inhibition of COX-1 or COX-2 significantly prevented the enhancement by ∼50% in both groups of vessels, and the remaining incremental components were eliminated by scavenging of superoxide with Tiron. In conclusion, hypoxia-driven increases in EETs, intensified COXs/TXA₂ signaling, great superoxide sourced from activated CYP2C9, and impaired NO bioavailability work in concert, to potentiate HPH development.

Sex, Gender, and Sex Hormones in Pulmonary Hypertension and Right Ventricular Failure

Pulmonary hypertension (PH) encompasses a syndrome of diseases that are characterized by elevated pulmonary artery pressure and pulmonary vascular remodeling and that frequently lead to right ventricular (RV) failure and death. Several types of PH exhibit sexually dimorphic features in disease penetrance, presentation, and progression. Most sexually dimorphic features in PH have been described in pulmonary arterial hypertension (PAH), a devastating and progressive pulmonary vasculopathy with a 3-year survival rate <60%. While patient registries show that women are more susceptible to development of PAH, female PAH patients display better RV function and increased survival compared to their male counterparts, a phenomenon referred to as the "estrogen paradox" or "estrogen puzzle" of PAH. Recent advances in the field have demonstrated that multiple sex hormones, receptors, and metabolites play a role in the estrogen puzzle and that the effects of hormone signaling may be time and compartment specific. While the underlying physiological mechanisms are complex, unraveling the estrogen puzzle may reveal novel therapeutic strategies to treat and reverse the effects of PAH/PH. In this article, we (i) review PH classification and pathophysiology; (ii) discuss sex/gender differences observed in patients and animal models; (iii) review sex hormone synthesis and metabolism; (iv) review in detail the scientific literature of sex hormone signaling in PAH/PH, particularly estrogen-, testosterone-, progesterone-, and dehydroepiandrosterone (DHEA)-mediated effects in the pulmonary vasculature and RV; (v) discuss hormone-independent variables contributing to sexually dimorphic disease presentation; and (vi) identify knowledge gaps and pathways forward. © 2020 American Physiological Society. Compr Physiol 10:125-170, 2020.

Therapeutic Challenges And Advances In The Management Of Systemic Sclerosis-Related Pulmonary Arterial Hypertension (SSc-PAH)

Systemic sclerosis (SSc) is a rare autoimmune disorder with multi-organ involvement. SSc-associated pulmonary arterial hypertension (SSc-PAH) is one of the leading causes of morbidity and mortality in the SSc population. With advances in our understanding of pulmonary arterial hypertension (PAH) diagnosis and treatment, outcomes for all PAH patients have significantly improved. While SSc-PAH patients have also benefited from these advances, significant challenges remain. Diagnosis of PAH is a challenging endeavor in SSc patients who often have many co-existing pulmonary and cardiac comorbidities. Given the significantly elevated prevalence and lifetime risk of PAH in the SSc population, screening for SSc-PAH is a critically useful strategy. Treatment with pulmonary arterial (PA) vasodilators has resulted in a dramatic improvement in the survival and quality of life of PAH patients. While therapy with PA vasodilators is beneficial in SSc-PAH patients, therapy effects appear to be attenuated when compared to responses in patients with idiopathic PAH (IPAH). This review attempts to chronicle and summarize the advances in our understanding of the optimal screening strategies to identify PAH in patients with SSc. The article also reviews the advances in the therapeutic and risk stratification strategies for SSc-PAH patients.

Clinical outcomes stratified by baseline functional class after initial combination therapy for pulmonary arterial hypertension

Background

Initial combination therapy with ambrisentan and tadalafil reduced the risk of clinical failure events for treatment-naïve participants with pulmonary arterial hypertension (PAH) as compared to monotherapy. Previous studies in PAH have demonstrated greater treatment benefits in more symptomatic participants.

Methods

AMBITION was an event-driven, double-blind study in which participants were randomized 2:1:1 to once-daily initial combination therapy with ambrisentan 10 mg plus tadalafil 40 mg, ambrisentan 10 mg plus placebo, or tadalafil 40 mg plus placebo. In this pre-specified subgroup analysis, we compared the efficacy data between those with functional class (FC) II vs. FC III symptoms at baseline.

Results

This analysis included 500 participants in the previously defined primary analysis set (n = 155 FC II, n = 345 FC III). Comparing combination therapy to pooled monotherapy, the risk of clinical failure events was reduced by 79% (hazard ratio, 0.21 [95% confidence interval: 0.071, 0.63]) for FC II patients and 42% (hazard ratio, 0.58 [95% confidence interval: 0.39, 0.86]) for FC III patients. In a post-hoc analysis, the risk of first hospitalization for worsening PAH was also reduced by combination therapy, particularly for FC II patients (0 combination vs. 11 [14%] pooled monotherapy). Adverse events were frequent but comparable between the subgroups.

Conclusions

Treatment benefit from initial combination therapy appeared at least as great for FC II as for FC III participants. Hospitalizations for worsening PAH were not observed in FC II participants assigned to combination. The present data support an initial combination strategy for newly diagnosed patients even when symptoms are less severe.

Funded by Gilead Sciences, Inc. and GlaxoSmithKline; AMBITION ClinicalTrials.gov number, NCT01178073.

Supplementary information

Supplementary information accompanies this paper at 10.1186/s12931-019-1180-1.

Endothelial and Smooth Muscle Cell Interaction via FoxM1 Signaling Mediates Vascular Remodeling and Pulmonary Hypertension

RATIONALE

Angioproliferative vasculopathy is a hallmark of pulmonary arterial hypertension (PAH). However, little is known about how endothelial cell (EC) and smooth muscle cell (SMC) crosstalk regulates the angioproliferative vascular remodeling.

OBJECTIVES

To investigate the role of EC and SMC interaction and underlying signaling pathways in pulmonary hypertension (PH) development.

METHODS

SMC-specific Foxm1 (forkhead box M1) or Cxcr4 knockout mice, EC-specific Foxm1 or Egln1 knockout mice, and EC-specific Egln1/Cxcl12 double knockout mice were used to assess the role of FoxM1 on SMC proliferation and PH. Lung tissues and cells from patients with PAH were used to validate clinical relevance. FoxM1 inhibitor thiostrepton was used in Sugen 5416/hypoxia- and monocrotaline-challenged rats.

MEASUREMENTS AND MAIN RESULTS

FoxM1 expression was markedly upregulated in lungs and pulmonary arterial SMCs of patients with idiopathic PAH and four discrete PH rodent models. Mice with SMC- (but not EC-) specific deletion of Foxm1 were protected from hypoxia- or Sugen 5416/hypoxia-induced PH. The upregulation of FoxM1 in SMCs induced by multiple EC-derived factors (PDGF-B, CXCL12, ET-1, and MIF) mediated SMC proliferation. Genetic deletion of endothelial Cxcl12 in Egln1^Tie2Cre mice or loss of its cognate receptor Cxcr4 in SMCs in hypoxia-treated mice inhibited FoxM1 expression, SMC proliferation, and PH. Accordingly, pharmacologic inhibition of FoxM1 inhibited severe PH in both Sugen 5416/hypoxia and monocrotaline-challenged rats.

CONCLUSIONS

Multiple factors derived from dysfunctional ECs induced FoxM1 expression in SMCs and activated FoxM1-dependent SMC proliferation, which contributes to pulmonary vascular remodeling and PH. Thus, targeting FoxM1 signaling represents a novel strategy for treatment of idiopathic PAH.

Blood outgrowth endothelial cells overexpressing eNOS mitigate pulmonary hypertension in rats: a unique carrier cell enabling autologous cell-based gene therapy

We have investigated a unique cell type, blood outgrowth endothelial cells (BOEC), as a cell-based gene therapy approach to pulmonary hypertension. BOEC are bona fide endothelial cells, obtained from peripheral blood, that can be expanded to vast numbers, and are amenable to both cryopreservation and genetic modification. We established primary cultures of rat BOEC and genetically altered them to over-express human eNOS plus green fluorescent protein (rBOEC/eNOS) or to express GFP only (rBOEC/GFP). We gave monocrotaline to rats on day 0, and they developed severe pulmonary hypertension. As a Prevention model, we infused saline or rBOEC/GFP or rBOEC/eNOS on day 3, and then examined endpoints on day 24. The rBOEC/eNOS recipients developed elevated NOx (serum and lung) and less severe: elevation of right ventricular systolic pressure (RVSP), right ventricular hypertrophy, and pulmonary arteriolar muscularization and loss of alveolar density. As an Intervention model, we waited until day 21 to give the test infusions, and we examined endpoints on day 35. The rBOEC/eNOS recipients again developed elevated NOx and manifested the same improvements. Indeed, rBOEC/eNOS infusion not only prevented worsening of RVSP but also partially reversed established arteriolar muscularization. These data suggest that BOEC may be useful as a carrier cell for genetic strategies targeting pulmonary hypertension. Their properties render BOEC amenable to preclinical and scale-up studies, available for autologous therapies, and tolerant of modification and storage for potential future use in patients at risk for PAH, eg, as defined by genetics or medical condition.

Dynamic and diverse changes in the functional properties of vascular smooth muscle cells in pulmonary hypertension

Pulmonary hypertension (PH) is the end result of interaction between pulmonary vascular tone and a complex series of cellular and molecular events termed 'vascular remodelling'. The remodelling process, which can involve the entirety of pulmonary arterial vasculature, almost universally involves medial thickening, driven by increased numbers and hypertrophy of its principal cellular constituent, smooth muscle cells (SMCs). It is noted, however that SMCs comprise heterogeneous populations of cells, which can exhibit markedly different proliferative, inflammatory, and extracellular matrix production changes during remodelling. We further consider that these functional changes in SMCs of different phenotype and their role in PH are dynamic and may undergo significant changes over time (which we will refer to as cellular plasticity); no single property can account for the complexity of the contribution of SMC to pulmonary vascular remodelling. Thus, the approaches used to pharmacologically manipulate PH by targeting the SMC phenotype(s) must take into account processes that underlie dominant phenotypes that drive the disease. We present evidence for time- and location-specific changes in SMC proliferation in various animal models of PH; we highlight the transient nature (rather than continuous) of SMC proliferation, emphasizing that the heterogenic SMC populations that reside in different locations along the pulmonary vascular tree exhibit distinct responses to the stresses associated with the development of PH. We also consider that cells that have often been termed 'SMCs' may arise from many origins, including endothelial cells, fibroblasts and resident or circulating progenitors, and thus may contribute via distinct signalling pathways to the remodelling process. Ultimately, PH is characterized by long-lived, apoptosis-resistant SMC. In line with this key pathogenic characteristic, we address the acquisition of a pro-inflammatory phenotype by SMC that is essential to the development of PH. We present evidence that metabolic alterations akin to those observed in cancer cells (cytoplasmic and mitochondrial) directly contribute to the phenotype of the SM and SM-like cells involved in PH. Finally, we raise the possibility that SMCs transition from a proliferative to a senescent, pro-inflammatory and metabolically active phenotype over time.

NADPH Oxidase 4 Regulates Inflammation in Ischemic Heart Failure: Role of Soluble Epoxide Hydrolase

Aims: Oxidative stress is implicated in cardiomyocyte cell death and cardiac remodeling in the failing heart. The role of NADPH oxidase 4 (NOX4) in cardiac adaptation to pressure overload is controversial, but its function in myocardial ischemic stress has not been thoroughly elucidated. This study examined the function of NOX4 in the pathogenesis of ischemic heart failure, utilizing mouse models, cell culture, and human heart samples. Results:Nox4^-/- mice showed a protective phenotype in response to permanent left anterior descending coronary artery ligation with smaller infarction area, lower cardiomyocyte cross-sectional area, higher capillary density, and less cell death versus wild-type (WT) mice. Nox4^-/- mice had lower activity of soluble epoxide hydrolase (sEH), a potent regulator of inflammation. Nox4^-/- mice also showed a 50% reduction in the number of infiltrating CD68⁺ macrophages in the peri-infarct zone versus WT mice. Adenoviral overexpression of NOX4 in cardiomyoblast cells increased sEH expression and activity and CCL4 and CCL5 levels; inhibition of sEH activity in NOX4 overexpressing cells attenuated the cytokine levels. Human hearts with ischemic cardiomyopathy showed adverse cardiac remodeling, increased NOX4 and sEH protein expression and CCL4 and CCL5 levels compared with control nonfailing hearts. Innovation and Conclusion: These data from the Nox4^-/- mouse model and human heart tissues show for the first time that oxidative stress from increased NOX4 expression has a functional role in ischemic heart failure. One mechanism by which NOX4 contributes to ischemic heart failure is by increasing inflammatory cytokine production via enhanced sEH activity.

Hypercoagulability in Pulmonary Hypertension

Pulmonary hypertension (PH) is divided into varied pathophysiological and etiologic groupings, as classified by the World Health Organization (WHO). Pulmonary arterial hypertension (PAH), which falls under WHO group 1 PH, is a progressive and potentially fatal disease characterized by a vasoconstrictive, proliferative, and thrombotic phenotype, which leads to increased pulmonary artery pressure, right heart failure, and death. Pathologically, in situ thromboses are found in the small distal pulmonary arteries. Dysregulation of coagulation, platelet function, and endothelial cells may contribute to a prothrombotic state. There is mixed evidence for the use of anticoagulation or antiplatelet therapy in PAH patients.

Hypoxia Upregulates Estrogen Receptor β in Pulmonary Artery Endothelial Cells in a HIF-1α-Dependent Manner

17β-Estradiol (E2) attenuates hypoxia-induced pulmonary hypertension (HPH) through estrogen receptor (ER)-dependent effects, including inhibition of hypoxia-induced endothelial cell proliferation; however, the mechanisms responsible for this remain unknown. We hypothesized that the protective effects of E2 in HPH are mediated through hypoxia-inducible factor 1α (HIF-1α)-dependent increases in ERβ expression. Sprague-Dawley rats and ERα or ERβ knockout mice were exposed to hypobaric hypoxia for 2-3 weeks. The effects of hypoxia were also studied in primary rat or human pulmonary artery endothelial cells (PAECs). Hypoxia increased expression of ERβ, but not ERα, in lungs from HPH rats as well as in rat and human PAECs. ERβ mRNA time dependently increased in PAECs exposed to hypoxia. Normoxic HIF-1α/HIF-2α stabilization increased PAEC ERβ, whereas HIF-1α knockdown decreased ERβ abundance in hypoxic PAECs. In turn, ERβ knockdown in hypoxic PAECs increased HIF-2α expression, suggesting a hypoxia-sensitive feedback mechanism. ERβ knockdown in hypoxic PAECs also decreased expression of the HIF inhibitor prolyl hydroxylase 2 (PHD2), whereas ERβ activation increased PHD2 and decreased both HIF-1α and HIF-2α, suggesting that ERβ regulates the PHD2/HIF-1α/HIF-2α axis during hypoxia. Whereas hypoxic wild-type or ERα knockout mice treated with E2 demonstrated less pulmonary vascular remodeling and decreased HIF-1α after hypoxia compared with untreated hypoxic mice, ERβ knockout mice exhibited increased HIF-2α and an attenuated response to E2 during hypoxia. Taken together, our results demonstrate a novel and potentially therapeutically targetable mechanism whereby hypoxia, via HIF-1α, increases ERβ expression and the E2-ERβ axis targets PHD2, HIF-1α, and HIF-2α to attenuate HPH development.

Therapeutic Targeting of Vascular Remodeling and Right Heart Failure in Pulmonary Arterial Hypertension with a HIF-2α Inhibitor

RATIONALE

Pulmonary arterial hypertension (PAH) is a devastating disease characterized by progressive vasoconstriction and obliterative vascular remodeling that leads to right heart failure (RHF) and death. Current therapies do not target vascular remodeling and RHF, and result in only modest improvement of morbidity and mortality.

OBJECTIVES

To determine whether targeting HIF-2α (hypoxia-inducible factor-2α) with a HIF-2α-selective inhibitor could reverse PAH and RHF in various rodent PAH models.

METHODS

HIF-2α and its downstream genes were evaluated in lung samples and pulmonary arterial endothelial cells and smooth muscle cells from patients with idiopathic PAH as well as various rodent PAH models. A HIF-2α-selective inhibitor was used in human lung microvascular endothelial cells and in Egln1Tie2Cre mice, and in Sugen 5416/hypoxia- or monocrotaline-exposed rats.

MEASUREMENTS AND MAIN RESULTS

Upregulation of HIF-2α and its target genes was observed in lung tissues and isolated pulmonary arterial endothelial cells from patients with idiopathic PAH and three distinct rodent PAH models. Pharmacological inhibition of HIF-2α by the HIF-2α translation inhibitor C76 (compound 76) reduced right ventricular systolic pressure and right ventricular hypertrophy and inhibited RHF and fibrosis as well as obliterative pulmonary vascular remodeling in Egln1Tie2Cre mice and Sugen 5416/hypoxia PAH rats. Treatment of monocrotaline-exposed PAH rats with C76 also reversed right ventricular systolic pressure, right ventricular hypertrophy, and pulmonary vascular remodeling; prevented RHF; and promoted survival.

CONCLUSIONS

These findings demonstrate that pharmacological inhibition of HIF-2α is a promising novel therapeutic strategy for the treatment of severe vascular remodeling and right heart failure in patients with PAH.