Pathobiology of pulmonary arterial hypertension and right ventricular failure

Animal models of pulmonary hypertension: Getting to the heart of the problem

Despite recent therapeutic advances, pulmonary hypertension (PH) remains a fatal disease due to the development of right ventricular (RV) failure. At present, no treatments targeted at the right ventricle are available, and RV function is not widely considered in the preclinical assessment of new therapeutics. Several small animal models are used in the study of PH, including the classic models of exposure to either hypoxia or monocrotaline, newer combinational and genetic models, and pulmonary artery banding, a surgical model of pure RV pressure overload. These models reproduce selected features of the structural remodelling and functional decline seen in patients and have provided valuable insight into the pathophysiology of RV failure. However, significant reversal of remodelling and improvement in RV function remains a therapeutic obstacle. Emerging animal models will provide a deeper understanding of the mechanisms governing the transition from adaptive remodelling to a failing right ventricle, aiding the hunt for druggable molecular targets.

Prognostic Significance of Systemic Arterial Stiffness Evaluated by Cardio-Ankle Vascular Index in Patients with Idiopathic Pulmonary Hypertension

BACKGROUND

In a previous study, the cardio-ankle vascular index (CAVI) was increased significantly in idiopathic pulmonary arterial hypertension (IPAH) patients compared to the healthy group and did not much differ from one in systemic hypertensives. In this study the relations between survival and CAVI was evaluated in patients with IPAH.

PATIENTS AND METHODS

We included 89 patients with new-diagnosed IPAH without concomitant diseases. Standard examinations, including right heart catheterization (RHC) and systemic arterial stiffness evaluation, were performed. All patients were divided according to CAVI value: the group with CAVI ≥ 8 (n = 18) and the group with CAVI < 8 (n = 71). The mean follow-up was 33.8 ± 23.7 months. Kaplan-Meier and Cox regression analysis were performed for the evaluation of our cohort survival and the predictors of death.

RESULTS

The group with CAVI≥8 was older and more severe compared to the group with CAVI< 8. Patients with CAVI≥8 had significantly reduced end-diastolic (73.79±18.94 vs 87.35±16.69 mL, P<0.009) and end-systolic (25.71±9.56 vs 33.55±10.33 mL, P<0.01) volumes of the left ventricle, the higher right ventricle thickness (0.77±0.12 vs 0.62±0.20 mm, P < 0.006), and the lower TAPSE (13.38±2.15 vs 15.98±4.4 mm, P<0.018). RHC data did not differ significantly between groups, except the higher level of the right atrial pressure in patients with CAVI≥ 8-11.38±7.1 vs 8.76±4.7 mmHg, P<0.08. The estimated overall survival rate was 61.2%. The CAVI≥8 increased the risk of mortality 2.34 times (CI 1.04-5.28, P = 0.041). The estimated Kaplan-Meier survival in the patients with CAVI ≥ 8 was only 46.7 ± 7.18% compared to patients with CAVI < 8 - 65.6 ± 4.2%, P = 0.035. At multifactorial regression analysis, the CAVI reduced but saved its relevance as death predictor - OR = 1.13, CI 1.001-1.871.

SUMMARY

We suggested the CAVI could be a new independent predictor of death in the IPAH population and could be used to better risk stratify this patient population if CAVI is validated as a marker in a larger multicenter trial.

Rhodiola crenulata extract decreases fatty acid oxidation and autophagy to ameliorate pulmonary arterial hypertension by targeting inhibiton of acylcarnitine in rats

Pulmonary arterial hypertension (PAH) is a devastating pulmonary circulation disease lacking high-efficiency therapeutics. The present study aims to decipher the therapeutic mechanism of Rhodiola crenulata, a well-known traditional chinese medicine with cardiopulmonary protection capacity, on PAH by exploiting functional lipidomics. The rat model with PAH was successfully established for first, following Rhodiola crenulata water extract (RCE) treatment, then analysis of chemical constituents of RCE was performed, additional morphologic, hemodynamic, echocardiographic measurements were examined, further targeted lipidomics assay was performed to identify differential lipidomes, at last accordingly mechanism assay was done by combining qRT-PCR, Western blot and ELISA. Differential lipidomes were identified and characterized to differentiate the rats with PAH from healthy controls, mostly assigned to acylcarnitines, phosphatidylcholines, sphingomyelin associated with the PAH development. Excitingly, RCE administration reversed high level of decadienyl-L-carnitine by the modulation of metabolic enzyme CPT1A in mRNA and protein level in serum and lung in the rats with PAH. Furthermore, RCE was observed to reduce autophagy, confirmed by significantly inhibited PPARγ, LC3B, ATG7 and upregulated p62, and inactivated LKB1-AMPK signal pathway. Notably, we accurately identified the constituents in RCE, and delineated the therapeutic mechansim that RCE ameliorated PAH through inhibition of fatty acid oxidation and autophagy. Altogether, RCE might be a potential therapeutic medicine with multi-targets characteristics to prevent the progression of PAH. This novel findings pave a critical foundation for the use of RCE in the treatment of PAH.

Pulmonary Hypertension in Obese Mice Is Accompanied by a Reduction in PPAR-γ Expression in Pulmonary Artery

Obesity and insulin resistance (IR) are well-studied risk factors for systemic cardiovascular disease, but their impact on pulmonary hypertension (PH) is not well clarified. This study aims to investigate if diet-induced obesity induces PH and if peroxisome-proliferator-activated receptor (PPAR-γ) and/or endoplasmic reticulum (ER) stress are involved in this process. Mice were maintained on a high-fat diet (HFD) for 4 months, and IR and PH were confirmed. In a separate group, after 4 months of HFD, mice were treated with pioglitazone (PIO) or 4-phenylbutyric acid for the last month. The results demonstrated that HFD for at least 4 months is able to increase pulmonary artery pressure, which is maintained, and this animal model can be used to investigate the link between IR and PH, without changes in ER stress in the pulmonary artery. There was also a reduction in circulating adiponectin and in perivascular adiponectin expression in the pulmonary artery, associated with a reduction in PPAR-γ expression. Treatment with PIO improved IR and PH and reversed the lower expression of adiponectin and PPAR-γ in the pulmonary artery, highlighting this drug as potential benefit for this poorly recognized complication of obesity.

DNA methyltransferase 3B deficiency unveils a new pathological mechanism of pulmonary hypertension

DNA methylation plays critical roles in vascular pathology of pulmonary hypertension (PH). The underlying mechanism, however, remains undetermined. Here, we demonstrate that global DNA methylation was elevated in the lungs of PH rat models after monocrotaline administration or hypobaric hypoxia exposure. We showed that DNA methyltransferase 3B (DNMT3B) was up-regulated in both PH patients and rodent models. Furthermore, Dnmt3b -/- rats exhibited more severe pulmonary vascular remodeling. Consistently, inhibition of DNMT3B promoted proliferation/migration of pulmonary artery smooth muscle cells (PASMCs) in response to platelet-derived growth factor-BB (PDGF-BB). In contrast, overexpressing DNMT3B in PASMCs attenuated PDGF-BB-induced proliferation/migration and ameliorated hypoxia-mediated PH and right ventricular hypertrophy in mice. We also showed that DNMT3B transcriptionally regulated inflammatory pathways. Our results reveal that DNMT3B is a previously undefined mediator in the pathogenesis of PH, which couples epigenetic regulations with vascular remodeling and represents a therapeutic target to tackle PH.

Pulmonary hypertensive crisis: A potential reason for right ventricle and pacemaker lead failure

Cardiac pacemakers have improved patient survival and quality of life, although malfunctions can be seen. We present the case of a girl with Seckel syndrome and congenital complete heart block. She had a single chamber permanent pacemaker in the right ventricle. When she referred us with a pulmonary hypertensive crisis (PHC), it was seen that the device was not pacing even in maximum threshold and pulse width values. After new epicardial lead implantation into the left ventricular apex, capture could be established again. For the cases presenting with capture failure, after eliminating lead-related problems and biochemical abnormalities, PHC should be kept in mind as a reason.

The selective PGI2 receptor agonist selexipag ameliorates Sugen 5416/hypoxia-induced pulmonary arterial hypertension in rats

Pulmonary arterial hypertension (PAH) is a lethal disease characterized by a progressive increase in pulmonary artery pressure due to an increase in vessel tone and occlusion of vessels. The endogenous vasodilator prostacyclin and its analogs are used as therapeutic agents for PAH. However, their pharmacological effects on occlusive vascular remodeling have not been elucidated yet. Selexipag is a recently approved, orally available and selective prostacyclin receptor agonist with a non-prostanoid structure. In this study, we investigated the pharmacological effects of selexipag on the pathology of chronic severe PAH in Sprague-Dawley and Fischer rat models in which PAH was induced by a combination of injection with the vascular endothelial growth factor receptor antagonist Sugen 5416 and exposure to hypoxia (SuHx). Oral administration of selexipag for three weeks significantly improved right ventricular systolic pressure and right ventricular (RV) hypertrophy in Sprague-Dawley SuHx rats. Selexipag attenuated the proportion of lung vessels with occlusive lesions and the medial wall thickness of lung arteries, corresponding to decreased numbers of Ki-67-positive cells and a reduced expression of collagen type 1 in remodeled vessels. Administration of selexipag to Fischer rats with SuHx-induced PAH reduced RV hypertrophy and mortality caused by RV failure. These effects were probably based on the potent prostacyclin receptor agonistic effect of selexipag on pulmonary vessels. Selexipag has been approved and is used in the clinical treatment of PAH worldwide. It is thought that these beneficial effects of prostacyclin receptor agonists on multiple aspects of PAH pathology contribute to the clinical outcomes in patients with PAH.

MDM2-Mediated Ubiquitination of Angiotensin-Converting Enzyme 2 Contributes to the Development of Pulmonary Arterial Hypertension

BACKGROUND

Angiotensin-converting enzyme 2 (ACE2) converts angiotensin II, a potent vasoconstrictor, to angiotensin-(1-7) and is also a membrane protein that enables coronavirus disease 2019 (COVID-19) infectivity. AMP-activated protein kinase (AMPK) phosphorylation of ACE2 enhances ACE2 stability. This mode of posttranslational modification of ACE2 in vascular endothelial cells is causative of a pulmonary hypertension (PH)-protective phenotype. The oncoprotein MDM2 (murine double minute 2) is an E3 ligase that ubiquitinates its substrates to cause their degradation. In this study, we investigated whether MDM2 is involved in the posttranslational modification of ACE2 through its ubiquitination of ACE2, and whether an AMPK and MDM2 crosstalk regulates the pathogenesis of PH.

METHODS

Bioinformatic analyses were used to explore E3 ligase that ubiquitinates ACE2. Cultured endothelial cells, mouse models, and specimens from patients with idiopathic pulmonary arterial hypertension were used to investigate the crosstalk between AMPK and MDM2 in regulating ACE2 phosphorylation and ubiquitination in the context of PH.

RESULTS

Levels of MDM2 were increased and those of ACE2 decreased in lung tissues or pulmonary arterial endothelial cells from patients with idiopathic pulmonary arterial hypertension and rodent models of experimental PH. MDM2 inhibition by JNJ-165 reversed the SU5416/hypoxia-induced PH in C57BL/6 mice. ACE2-S680L mice (dephosphorylation at S680) showed PH susceptibility, and ectopic expression of ACE2-S680L/K788R (deubiquitination at K788) reduced experimental PH. Moreover, ACE2-K788R overexpression in mice with endothelial cell-specific AMPKα2 knockout mitigated PH.

CONCLUSIONS

Maladapted posttranslational modification (phosphorylation and ubiquitination) of ACE2 at Ser-680 and Lys-788 is involved in the pathogenesis of pulmonary arterial hypertension and experimental PH. Thus, a combined intervention of AMPK and MDM2 in the pulmonary endothelium might be therapeutically effective in PH treatment.

Interruption of vascular endothelial growth factor receptor 2 signaling induces a proliferative pulmonary vasculopathy and pulmonary hypertension

Pulmonary arterial hypertension is a severe and progressive disease characterized by a pulmonary vascular remodeling process with expansion of collateral endothelial cells and total vessel occlusion. Endothelial cells are believed to be at the forefront of the disease process. Vascular endothelial growth factor (VEGF) and its tyrosine kinase receptor, VEGF receptor-2 (VEGFR-2), play a central role in angiogenesis, endothelial cell protection, but also in the destabilization of endothelial barrier function. Therefore, we investigated the consequences of altered VEGF signaling in an experimental model, and looked for translational correlates of this observation in patients. We performed an endothelial cell-specific conditional deletion of the kinase insert domain protein receptor (kdr) gene, coding for VEGFR-2, in C57/BL6 mice (Kdr^∆end) and held them in an environmental chamber with 10% FiO₂ or under normoxia for 6 weeks. Kdr knockout led to a mild PH phenotype under normoxia that worsened under hypoxia. Kdr^∆end mice exhibited a significant increase in pulmonary arterial wall thickness, muscularization, and VEGFR-3⁺ endothelial cells obliterating the pulmonary artery vessel lumen. We observed the same proliferative vasculopathy in our rodent model as seen in patients receiving anti-angiogenic therapy. Serum VEGF-a levels were elevated both in the experimental model and in humans receiving bevacizumab. Interrupted VEGF signaling leads to a pulmonary proliferative arteriopathy in rodents after direct ablative gene manipulation of Kdr. Histologically, similar vascular lesions can be observed in patients receiving anti-VEGF treatment. Our findings illustrate the importance of VEGF signaling for maintenance of pulmonary vascular patency.

LincRNA-Cox2 promotes pulmonary arterial hypertension by regulating the let-7a-mediated STAT3 signaling pathway

It is well supported by the literature that the proliferation and migration of pulmonary arterial smooth muscle cells (PASMCs) are critical for the development of pulmonary arterial hypertension (PAH). Long intergenic noncoding RNA COX2 (lincRNA-COX2) is a regulator of inflammation and might be conducive to the progression of atherosclerosis, while its role in PAH is still unclear. This study was performed to explore the role and mechanism of lincRNA-COX2 in PASMCs proliferation and migration in an anaerobic environment. PASMCs were treated by hypoxia to construct PAH cell models. RT-PCR and western blot were recruited to evaluate the expression levels of lincRNA-COX2, miR-let-7a and STAT3. Their roles in proliferation and cell and migration of PASMCs were determined by the CCK-8 assay, wound-healing assay, and flow cytometry. In peripheral blood samples from PAH patients and hypoxic PASMCs, lincRNA-COX2 expression was enhanced. Silencing lincRNA-COX2 inhibited hypoxia-induced PASMCs proliferation by influencing the G2/M phase of the cell cycle. Meanwhile, lincRNA-COX2 regulated STAT3 through miR-let-7a and its effects on hypoxic PASMCs worked through miR-let-7a/STAT3 axis. To conclude, silencing lincRNA-COX2 attenuated the development of hypoxic PASMCs. LincRNA-COX2/miR-let-7a/STAT3 axis might be considered as a novel target to treat PAH.

Angiotensin converting enzyme 2 and angiotensin (1-7) axis in pulmonary arterial hypertension

BACKGROUND

In animal models of pulmonary arterial hypertension (PAH), angiotensin-converting enzyme (ACE)2 and angiotensin (Ang)-(1-7) have been shown to have vasodilatory, antiproliferative, antifibrotic and antihypertrophic properties. However, the status and role of the ACE2-Ang(1-7) axis in human PAH is incompletely understood.

METHODS

We studied 85 patients with a diagnosis of PAH of distinct aetiologies. 55 healthy blood donors paired for age and sex served as controls. Blood samples were obtained from the pulmonary artery in patients with PAH during right heart catheterisation. Peripheral blood was obtained for both groups. Ang(1-7) and -II were measured using zone capillary electrophoresis. Aldosterone, Ang(1-9), AngA and ACE2 were measured using ELISA, and ACE2 activity was determined enzymatically.

RESULTS

Of the 85 patients, 47 had idiopathic PAH, 25 had PAH associated with congenital heart disease and 13 had PAH associated with collagen vascular disease. Compared to controls, patients with PAH had a higher concentration of AngII (median 1.03, interquartile range 0.72-1.88 pmol·mL^-1 versus 0.19, 0.10-0.37 pmol·mL^-1; p<0.001) and of aldosterone (88.7, 58.7-132 ng·dL^-1 versus 12.9, 9.55-19.9 ng·dL^-1; p<0.001). Conversely, PAH patients had a lower concentration of Ang(1-7) than controls (0.69, 0.474-0.91 pmol·mL^-1 versus 4.07, 2.82-6.73 pmol·mL^-1; p<0.001), and a lower concentration of Ang(1-9) and AngA. Similarly, the ACE2 concentration was higher than in controls (8.7, 5.35-13.2 ng·mL^-1 versus 4.53, 1.47-14.3 ng·mL^-1; p=0.011), whereas the ACE2 activity was significantly reduced (1.88, 1.08-2.81 nmol·mL^-1 versus 5.97, 3.1-17.8 nmol·mL^-1; p<0.001). No significant differences were found among the three different aetiological forms of PAH.

CONCLUSIONS

The AngII-ACE2-Ang(1-7) axis appears to be altered in human PAH and we propose that this imbalance, in favour of AngII, plays a role in the pathogenesis of the severe PAH. Further mechanistic studies are warranted.

Changes in heart morphometric parameters over the course of a monocrotaline-induced pulmonary arterial hypertension rat model

Background

Aim of this study was to assess changes in cardiac morphometric parameters at different stages of pulmonary arterial hypertension (PAH) using a monocrotaline-induced rat model.

Methods

Four groups were distinguished: I–control, non-PAH (n = 18); II–early PAH (n = 12); III–end-stage PAH (n = 23); and IV–end-stage PAH with myocarditis (n = 7).

Results

Performed over the course of PAH in vivo echocardiography showed significant thickening of the right ventricle free wall (end-diastolic dimension), tricuspid annular plane systolic excursion reduction and decrease in pulmonary artery acceleration time normalized to cycle length. No differences in end-diastolic left ventricle free wall thickness measured in echocardiography was observed between groups. Significant increase of right ventricle and decrease of left ventricle systolic pressure was observed over the development of PAH. Thickening and weight increase (241.2% increase) of the right ventricle free wall and significant dilatation of the right ventricle was observed over the course of PAH (p < 0.001). Reduction in the left ventricle free wall thickness was also observed in end-stage PAH (p < 0.001). Significant trend in the left ventricle free wall weight decrease was observed over the course of PAH (p < 0.001, 24.3% reduction). Calculated right/left ventricle free wall weight ratio gradually increased over PAH stages (p < 0.001). The reduction of left ventricle diameter was observed in rats with end-stage PAH both with and without myocarditis (p < 0.001).

Conclusions

PAH leads to multidimensional changes in morphometric cardiac parameters. Right ventricle morphological and functional failure develop gradually from early stage of PAH, while left ventricle changes develop at the end stages of PAH.

A Novel Mechanism of Sildenafil Improving the Excessive Proliferation and H2S Production in Pulmonary Arterial Smooth Muscle Cells

The dysregulation of pulmonary arterial vasoactive mediators or excessive proliferation of pulmonary arterial smooth muscle cells (PASMCs) might result in contraction or remodeling of pulmonary blood vessels, leading to related lung diseases. Recent studies suggest that hydrogen sulfide (H2S), a gaseous vasodilator generated in the blood vessels by the enzymes cystathionine γ-lyase (CSE) and cystathionine-β-synthase (CBS), could induce the vasodilation, thus improving contraction or remodeling-induced lung diseases. In this study, we hypothesized that PASMCs could produce H2S and relax the pulmonary artery, and its mechanism is related to CSE, CBS, and TRPV4 channels by affecting both the excessive proliferation and pulmonary vasoconstriction in PASMCs. We found that the sildenafil treatment could remarkably promote H2S production and control the proliferation in PASMCs; meanwhile, the protein levels of CSE and CBS and the intracellular concentration of calcium could also be increased by sildenafil. Moreover, the effects of sildenafil could be reversed by a CBS inhibitor or a CSE inhibitor, indicating that sildenafil could affect CSE and CBS to modulate the production of H2S and the proliferation in rat PASMCs. Together, we demonstrated a new mechanism for sildenafil to modulate the synthesis of H2S and cell proliferation in PASMCs by affecting CSE and CBS. TRPV4-dependent Ca events and BMP4 may also be involved.

Effects of Different Types of Exercise Training on Pulmonary Arterial Hypertension: A Systematic Review

Pulmonary arterial hypertension (PAH) represents a chronic progressive disease characterized by high blood pressure in the pulmonary arteries leading to right heart failure. The disease has been a focus of medical research for many years due to its worse prognosis and limited treatment options. The aim of this study was to systematically assess the effects of different types of exercise interventions on PAH. Electronic databases were searched until July 2019. MEDLINE database was used as the predominant source for this paper. Studies with regards to chronic physical activity in adult PAH patients are compared on retrieving evidence on cellular, physiological, and psychological alterations in the PAH setting. Twenty human studies and 12 rat trials were identified. Amongst all studies, a total of 628 human subjects and 614 rats were examined. Regular physical activity affects the production of nitric oxygen and attenuates right ventricular hypertrophy. A combination of aerobic, anaerobic, and respiratory muscle training induces the strongest improvement in functional capacity indicated by an increase of 6 MWD and VO₂peak. In human studies, an increase of quality of life was found. Exercise training has an overall positive effect on the physiological and psychological components of PAH. Consequently, PAH patients should be encouraged to take part in regular exercise training programs.

The hallmarks of severe pulmonary arterial hypertension: the cancer hypothesis-ten years later

Severe forms of pulmonary arterial hypertension (PAH) are most frequently the consequence of a lumen-obliterating angiopathy. One pathobiological model is that the initial pulmonary vascular endothelial cell injury and apoptosis is followed by the evolution of phenotypically altered, apoptosis-resistant, proliferating cells and an inflammatory vascular immune response. Although there may be a vasoconstrictive disease component, the increased pulmonary vascular shear stress in established PAH is caused largely by the vascular wall pathology. In this review, we revisit the "quasi-malignancy concept" of severe PAH and examine to what extent the hallmarks of PAH can be compared with the hallmarks of cancer. The cancer model of severe PAH, based on the growth of abnormal vascular and bone marrow-derived cells, may enable the emergence of novel cell-based PAH treatment strategies.

Pathophysiology of Acute and Chronic Right Heart Failure

Right-sided heart failure (RHF) occurs from impaired contractility of the right ventricle caused by pressure, volume overload, or intrinsic myocardial contractile dysfunction. The development of subclinical right ventricle (RV) dysfunction or overt RHF is a negative prognostic indicator. Recent attention has focused on RV-specific inflammatory growth factors and mediators of myocardial fibrosis to elucidate the mechanisms leading to RHF and potentially guide the development of novel therapeutics. This article focuses on the distinct changes in RV structure, mechanics, and function, as well as molecular and inflammatory mediators involved in the pathophysiology of acute and chronic RHF.

Diagnostic and predictive values of plasma connective tissue growth factor in children with pulmonary hypertension associated with CHD

OBJECTIVE

To evaluate the diagnostic and predictive values of plasma connective tissue growth factor in children with pulmonary hypertension (PH)-related CHD.

PATIENTS AND METHODS

Forty patients with PH-related CHD were enrolled as group I, and 40 patients with CHD and no PH served as group II. Forty healthy children of matched age and sex served as a control group. Echocardiographic examinations and plasma connective tissue growth factor levels were performed for all included children. Cardiac catheterisation was performed for children with CHD only.

RESULTS

Plasma connective tissue growth factor levels were significantly higher in children with PH-related CHD compared to CHD-only patients and to control group and this elevation went with the severity of PH. There was a significant positive correlation between connective tissue growth factor levels and mean pulmonary pressure, pulmonary vascular resistance, and right ventricular diameter. A significant negative correlation was noticed between connective tissue growth factor levels, oxygen saturation, and right ventricular diastolic function. The sensitivity of plasma connective tissue growth factor as a diagnostic biomarker for PH was 95%, and the specificity was 90% at a cut-off value ≥650 pg/mL. The predictive value of plasma connective tissue growth factor for adverse outcome had a sensitivity of 88% and a specificity of 83% at a cut-off value ≥1900 pg/mL.

CONCLUSION

Connective tissue growth factor is a promising biomarker with good diagnostic and predictive values in children with PH-related CHD.

A20 attenuates hypoxia-induced pulmonary arterial hypertension by inhibiting NF-κB activation and pulmonary artery smooth muscle cell proliferation

PAH is a progressive disease characterized by uncontrolled proliferation of PASMCs. Zinc finger protein A20 is a negative feedback regulatory protein of NF-κB activity. The aim of this study was to evaluate zinc finger protein A20 can alleviate PAH in hypoxia exposed mice. C57BL/6 mice received a tail vein injection of adenovirus-mediated ad-A20 and ad-A20 shRNA were exposed to hypoxia. PASMCs isolated from rat pulmonary arteries were cultured in hypoxia, and were transfection of A20 adenovirus. Pulmonary hemodynamic parameters were measured by right heart catheterization. Pulmonary vascular morphological changes were analyzed by HE and α-SMA staining. The expression changes of A20, NF-κB and its downstream protein were detected. The expression of phospho-p65 was increased with the prolongation of hypoxia time. The expression of A20 in lung tissue of chronic hypoxia group decreased with the prolongation of hypoxia time. Adenovirus-mediated A20 (ad-A20) overexpression significantly attenuated the abnormally increased RVSP, RV/(LV + S) ratio, WT%, WA%, α-SMA and the pulmonary vessel muscularization. Ad-A20 treatment markedly attenuated the degradation of phospho-p65 and inhibited the induction of phospho-IκBα induced by hypoxia treatment. Furthermore, silencing A20 abolished the protection by anti-inflammatory activity and the inhibitory effect on cell proliferation. We showed that Zinc finger protein A20 can block NF-κB signaling pathway, alleviates the hypoxia-induced abnormal elevation of pulmonary arterial pressure, hyperproliferation of PASMCs and the pulmonary vascular remodeling.

Mesenchymal stromal cell-derived exosomes improve pulmonary hypertension through inhibition of pulmonary vascular remodeling

Background

Pulmonary hypertension (PH) is a life-threatening disease characterized by pulmonary vascular remodeling, right ventricular hypertrophy and failure. So far no effective treatment exists for this disease; hence, novel approaches are urgently needed. The aim of the present research was to observe the treatment effect of mesenchymal stromal cell derived exosomes and reveal the mechanism.

Methods

Monocrotaline (MCT)-induced PH in rats and hypoxia-induced cell damage model were established, respectively. Exosomes derived from the supernatant of human umbilical cord mesenchymal stem cells (MSC-exo) were injected into MCT-PH model rat or added into the cells cultured medium. Immunohistochemistry, quantitative real-time polymerase chain reaction (qRT-PCR) and western blot methods were used in vivo and vitro.

Results

The results showed that MSC-exo could significantly attenuate right ventricular (RV) hypertrophy and pulmonary vascular remodelling in MCT-PH rats. In the cell culture experiments, we found that MSC-exo could significantly inhibit hypoxia-induced pulmonary arterial endothelial cell (PAEC) apoptosis and pulmonary arterial smooth muscle cells (PASMC) proliferation. Furthermore, the pulmonary arterioles endothelial-to-mesenchymal transition (EndMT) was obviously suppressed. Moreover, the present study suggest that MSC-exo can significantly upregulate the expression of Wnt5a in MCT-PH rats and hypoxic pulmonary vascular cells. Furthermore, with Wnt5a gene silencing, the therapeutic effect of MSC-exo against hypoxia injury was restrained.

Conclusions

Synthetically, our data provide a strong evidence for the therapeutic of MSC-exo on PH, more importantly, we confirmed that the mechanism was associated with up-regulation of the expression of Wnt5a. These results offer a theoretical basis for clinical prevention and treatment of PH.

Nonclassical Monocytes Sense Hypoxia, Regulate Pulmonary Vascular Remodeling, and Promote Pulmonary Hypertension

An increasing body of evidence suggests that bone marrow-derived myeloid cells play a critical role in the pathophysiology of pulmonary hypertension (PH). However, the true requirement for myeloid cells in PH development has not been demonstrated, and a specific disease-promoting myeloid cell population has not been identified. Using bone marrow chimeras, lineage labeling, and proliferation studies, we determined that, in murine hypoxia-induced PH, Ly6Clo nonclassical monocytes are recruited to small pulmonary arteries and differentiate into pulmonary interstitial macrophages. Accumulation of these nonclassical monocyte-derived pulmonary interstitial macrophages around pulmonary vasculature is associated with increased muscularization of small pulmonary arteries and disease severity. To determine if the sensing of hypoxia by nonclassical monocytes contributes to the development of PH, mice lacking expression of hypoxia-inducible factor-1α in the Ly6Clo monocyte lineage were exposed to hypoxia. In these mice, vascular remodeling and PH severity were significantly reduced. Transcriptome analyses suggest that the Ly6Clo monocyte lineage regulates PH through complement, phagocytosis, Ag presentation, and chemokine/cytokine pathways. Consistent with these murine findings, relative to controls, lungs from pulmonary arterial hypertension patients displayed a significant increase in the frequency of nonclassical monocytes. Taken together, these findings show that, in response to hypoxia, nonclassical monocytes in the lung sense hypoxia, infiltrate small pulmonary arteries, and promote vascular remodeling and development of PH. Our results demonstrate that myeloid cells, specifically cells of the nonclassical monocyte lineage, play a direct role in the pathogenesis of PH.

Medicinal Plants and Phytochemicals for the Treatment of Pulmonary Hypertension

Background

Pulmonary hypertension (PH) is a progressive disease that is associated with pulmonary arteries remodeling, right ventricle hypertrophy, right ventricular failure and finally death. The present study aims to review the medicinal plants and phytochemicals used for PH treatment in the period of 1994 – 2019.

Methods

PubMed, Cochrane and Scopus were searched based on pulmonary hypertension, plant and phytochemical keywords from August 23, 2019. All articles that matched the study based on title and abstract were collected, non-English, repetitive and review studies were excluded.

Results

Finally 41 studies remained from a total of 1290. The results show that many chemical treatments considered to this disease are ineffective in the long period because they have a controlling role, not a therapeutic one. On the other hand, plants and phytochemicals could be more effective due to their action on many mechanisms that cause the progression of PH.

Conclusion

Studies have shown that herbs and phytochemicals used to treat PH do their effects from six mechanisms. These mechanisms include antiproliferative, antioxidant, antivascular remodeling, anti-inflammatory, vasodilatory and apoptosis inducing actions. According to the present study, many of these medicinal plants and phytochemicals can have effects that are more therapeutic than chemical drugs if used appropriately.

Nintedanib improves cardiac fibrosis but leaves pulmonary vascular remodelling unaltered in experimental pulmonary hypertension

Aims

Pulmonary arterial hypertension (PAH) is associated with increased levels of circulating growth factors and corresponding receptors such as platelet derived growth factor, fibroblast growth factor and vascular endothelial growth factor. Nintedanib, a tyrosine kinase inhibitor targeting primarily these receptors, is approved for the treatment of patients with idiopathic pulmonary fibrosis. Our objective was to examine the effect of nintedanib on proliferation of human pulmonary microvascular endothelial cells (MVEC) and assess its effects in rats with advanced experimental pulmonary hypertension (PH).

Methods and results

Proliferation was assessed in control and PAH MVEC exposed to nintedanib. PH was induced in rats by subcutaneous injection of Sugen (SU5416) and subsequent exposure to 10% hypoxia for 4 weeks (SuHx model). Four weeks after re-exposure to normoxia, nintedanib was administered once daily for 3 weeks. Effects of the treatment were assessed with echocardiography, right heart catheterization, and histological analysis of the heart and lungs. Changes in extracellular matrix production was assessed in human cardiac fibroblasts stimulated with nintedanib. Decreased proliferation with nintedanib was observed in control MVEC, but not in PAH patient derived MVEC. Nintedanib treatment did not affect right ventricular (RV) systolic pressure or total pulmonary resistance index in SuHx rats and had no effects on pulmonary vascular remodelling. However, despite unaltered pressure overload, the right ventricle showed less dilatation and decreased fibrosis, hypertrophy, and collagen type III with nintedanib treatment. This could be explained by less fibronectin production by cardiac fibroblasts exposed to nintedanib.

Conclusion

Nintedanib inhibits proliferation of pulmonary MVECs from controls, but not from PAH patients. While in rats with experimental PH nintedanib has no effects on the pulmonary vascular pathology, it has favourable effects on RV remodelling.

Schistosomiasis-associated pulmonary arterial hypertension: a systematic review

Schistosomiasis-associated pulmonary arterial hypertension (Sch-PAH) is a life-threatening complication of chronic hepatosplenic schistosomiasis. It is suggested to be the leading cause of pulmonary arterial hypertension (PAH) worldwide. However, pathophysiological data on Sch-PAH are scarce. We examined the hypothesis that there are pronounced similarities in pathophysiology, haemodynamics, and survival of Sch-PAH and idiopathic PAH (iPAH).

This systematic review and meta-analysis was registered in the PROSPERO database (identifier CRD42018104066). A systematic search and review of the literature was performed according to PRISMA guidelines for studies published between 01 January 1990 and 29 June 2018.

For Sch-PAH, 18 studies evaluating pathophysiological mechanisms, eight studies on haemodynamics (n=277), and three studies on survival (n=191) were identified. 16 clinical registries reporting data on haemodynamics and survival including a total of 5792 patients with iPAH were included for comparison. Proinflammatory molecular pathways are involved in both Sch-PAH and iPAH. The transforming growth factor (TGF)-β signalling pathway is upregulated in Sch-PAH and iPAH. While there was no difference in mean pulmonary artery pressure (54±17 mmHg versus 55±15 mmHg, p=0.29), cardiac output (4.4±1.3 L·min−1versus 4.1±1.4 L·min−1, p=0.046), and cardiac index (2.6±0.7 L·min−1·m−2versus 2.3±0.8 L·min−1·m−2, p<0.001) were significantly higher in Sch-PAH compared to iPAH, resulting in a lower pulmonary vascular resistance in Sch-PAH (10±6 Woods units versus 13±7 Woods units, p<0.001). 1- and 3-year survival were significantly better in the Sch-PAH group (p<0.001).

Sch-PAH and iPAH share common pathophysiological mechanisms related to inflammation and the TGF-β signalling pathway. Patients with Sch-PAH show a significantly better haemodynamic profile and survival than patients with iPAH.

Systemic Arterial Stiffness in New Diagnosed Idiopathic Pulmonary Arterial Hypertension Patients

OBJECTIVE

We suggested: 1) patients with idiopathic pulmonary hypertension (IPAH) have active factors which could damage not only the pulmonary but systemic arteries too as in arterial hypertensive patients; 2) if these changes were present, they might correlate with other parameters influencing on the prognosis. This study is the first attempt to use cardio-ankle vascular index (CAVI) for the evaluation of systemic arterial stiffness in patients with IPAH.

METHODS

A total of 112 patients were included in the study: group 1 consisted of 45 patients with new diagnosed IPAH, group 2 included 32 patients with arterial hypertension, and in the control group were 35 healthy persons adjusted by age. Right heart catheterization, ECG, a 6-minute walk test (6MWT), echocardiography, blood pressure (BP) measurement and ambulatory BP monitoring, pulse wave elastic artery stiffness (PWVe; segment carotid-femoral arteries) and muscular artery stiffness (PWVm; segment carotid-radial arteries), CAVI, and N-terminal pro-B-type natriuretic peptide (NT-proBNP) level were provided. The Spearman correlation, a linear regression and multivariable binary logistic analysis were performed to indicate the predictors associated with PWV and CAVI.

RESULTS

The groups were adjusted for principal characteristics influenced on arterial stiffness. IPAH patients had significantly (P<0.001 for all) shorter 6MWT distance and higher Borg dyspnea score than the patients with arterial hypertension (systolic/diastolic BP = 146.1±10.7/94.2±9.8 mmHg) and the control group = 330.2±14.6 vs 523.8±35.3 and 560.9±30.2 m respectively and 6.2±1.8 vs 1.2±2.1 and 0.9±2.8 points. The PWVm and PWVe were the highest in hypertensive patients (10.3±1.5 and 11.42±1.70 m/s). The control group and IPAH did not have significant differences in aorta BP, but PWVm/PWVe values were significantly (P<0.003/0.008) higher in IPAH patients than in the control group (8.1±1.9/8.49±1.92 vs 6.63±1.34/7.29±0.87 m/s). The CAVIs on both sides were significantly lower in the healthy subjects (5.91±0.99/5.98±0.87 right/left side). Patients with IPAH did not differ from the arterial hypertension patients by CAVIs in comparison with the control group (7.40±1.32/7.22±1.32 vs 7.19±0.78/7.2±1.1 PWVe) did not correlate with any parameters except uric acid. PWVm correlated with uric acid (r=0.58, P<0.001), NT-proBNP (r=0.33, P=0.03) and male gender (r=0.37, P=0.013) at Spearman analysis, but not at multifactorial linear regression analysis. The CAVI correlated with age and parameters characterized functional capacity (6MWT distance) and right ventricle function (NT-proBNP, TAPSE) at Spearman analysis and with age and TAPSE at multifactorial linear regression analysis. At binary logistic regression analysis CAVI > 8.0 at right and/or left side had a correlation with age, 6MWT distance, TAPSE, but an independent correlation was only with age (β=1.104, P=0.008, CI 1.026-1.189) and TAPSE (β=0.66, P=0.016, CI 0.474-0.925).

CONCLUSION

In spite of equal and at normal range BP level, the age-adjusted patients with IPAH had significantly stiffer arteries than the healthy persons and they were comparable with the arterial hypertensive patients. Arterial stiffness evaluated by CAVI correlated with age and TAPSE in IPAH patients. Based on our results it is impossible to conclude the pathogenesis of arterial stiffening in IPAH patients, but the discovered changes and correlations suggest new directions for further studies, including pathogenesis and prognosis researches.

Multiple roles of macrophage migration inhibitory factor in pulmonary hypertension

Pulmonary hypertension (PH) is a life-threatening condition arising from the loss and obstructive remodeling of the pulmonary arteries, leading to the sustained elevation of pulmonary arterial pressure (PAP) and pulmonary vascular resistance (PVR) and subsequently right ventricular (RV) failure and death. PH encompasses a group of multifactorial diseases, such as pulmonary arterial hypertension (PAH) and chronic thromboembolic PH, for which there is no treatment that can stop or reverse the progression of remodeling of the pulmonary vasculature. The identification of new molecular targets for the development of more effective drugs is thus urgently needed. In this context, macrophage migration inhibitory factor (MIF), a pleiotropic upstream proinflammatory mediator, is emerging as a promising molecular target, as it contributes to perivascular inflammation and pulmonary arterial remodeling, two key hallmarks of PAH that are not specifically targeted by currently approved therapies. The objective of this review is to summarize the scientific evidence on the pathogenic roles of MIF and its potential as a biomarker and therapeutic target in PH/PAH.

A new treatment for severe pulmonary arterial hypertension based on an old idea: inhibition of 5-lipoxygenase

It has been generally accepted that severe forms of pulmonary arterial hypertension are associated with inflammation. Plasma levels in patients with severe pulmonary arterial hypertension show elevated levels of interleukins and mediators of inflammation and histologically the diseased small pulmonary arterioles show infiltrates of inflammatory and immune cells. Here, we review the literature that connects pulmonary hypertension with the arachidonic acid/5-lipoxygenase-derived leukotriens. This mostly preclinical background data together with the availability of 5-lipoxygenase inhibitors and leukotriene receptor blockers provide the rationale for testing the hypothesis that 5-lipoxygenase products contribute to the pathobiology of severe pulmonary arterial hypertension in a subgroup of patients.

O-GlcNAc Transferase Regulates Angiogenesis in Idiopathic Pulmonary Arterial Hypertension

Idiopathic pulmonary arterial hypertension (IPAH) is considered a vasculopathy characterized by elevated pulmonary vascular resistance due to vasoconstriction and/or lung remodeling such as plexiform lesions, the hallmark of the PAH, as well as cell proliferation and vascular and angiogenic dysfunction. The serine/threonine hydroxyl-linked N-Acetylglucosamine (O-GlcNAc) transferase (OGT) has been shown to drive pulmonary arterial smooth muscle cell (PASMC) proliferation in IPAH. OGT is a cellular nutrient sensor that is essential in maintaining proper cell function through the regulation of cell signaling, proliferation, and metabolism. The aim of this study was to determine the role of OGT and O-GlcNAc in vascular and angiogenic dysfunction in IPAH. Primary isolated human control and IPAH patient PASMCs and pulmonary arterial endothelial cells (PAECs) were grown in the presence or absence of OGT inhibitors and subjected to biochemical assessments in monolayer cultures and tube formation assays, in vitro vascular sprouting 3D spheroid co-culture models, and de novo vascularization models in NODSCID mice. We showed that knockdown of OGT resulted in reduced vascular endothelial growth factor (VEGF) expression in IPAH primary isolated vascular cells. In addition, specificity protein 1 (SP1), a known stimulator of VEGF expression, was shown to have higher O-GlcNAc levels in IPAH compared to control at physiological (5 mM) and high (25 mM) glucose concentrations, and knockdown resulted in decreased VEGF protein levels. Furthermore, human IPAH PAECs demonstrated a significantly higher degree of capillary tube-like structures and increased length compared to control PAECs. Addition of an OGT inhibitor, OSMI-1, significantly reduced the number of tube-like structures and tube length similar to control levels. Assessment of vascular sprouting from an in vitro 3D spheroid co-culture model using IPAH and control PAEC/PASMCs and an in vivo vascularization model using control and PAEC-embedded collagen implants demonstrated higher vascularization in IPAH compared to control. Blocking OGT activity in these experiments, however, altered the vascular sprouting and de novo vascularization in IPAH similar to control levels when compared to controls. Our findings in this report are the first to describe a role for the OGT/O-GlcNAc axis in modulating VEGF expression and vascularization in IPAH. These findings provide greater insight into the potential role that altered glucose uptake and metabolism may have on the angiogenic process and the development of plexiform lesions. Therefore, we believe that the OGT/O-GlcNAc axis may be a potential therapeutic target for treating the angiogenic dysregulation that is present in IPAH.

Long non‐coding RNA expression profiling in the lungs of pulmonary arterial hypertension rats with acute inflammation

Background

We performed RNA-sequencing to investigate the changes and expression profiles in long non-coding RNAs (lncRNAs) and their potential functional roles in the lungs of pulmonary arterial hypertension rats responding to acute inflammation.

Methods

To establish a pulmonary arterial hypertension rat model, monocrotaline was injected intraperitoneally and lipopolysaccharide was given to induce acute inflammation. Selected lncRNAs were validated by quantitative real-time polymerase chain reaction (qRT-PCR). Bioinformatics analyses were carried out to predict the potential biological roles of key lncRNAs.

Results

Twenty-eight lncRNAs and seven mRNAs with elevated expression and 202 lncRNAs and 36 mRNAs with decreased expression were found in the lung tissues of lipopolysaccharide-treated pulmonary arterial hypertension rats compared with control group. The qRT-PCR validation results were consistent with the bioinformatics analysis. Gene ontology analyses showed that the mRNAs and lncRNAs were differentially expressed in different pathways regarding biological process, cellular components, and molecular function. The functions of differentially expressed messenger RNAs (DEmRNAs) and DElncRNAs were indicated by Kyoto Encyclopedia of Genes and Genomes enrichment.

Conclusion

The DEmRNAs co-expressed with DElncRNAs were obviously enriched in inflammation. DElncRNAs and DEmRNAs in the lungs of pulmonary arterial hypertension rats changed with acute inflammation may provide new insights into the pathogenesis of pulmonary arterial hypertension.

Hot topics in the mechanisms of pulmonary arterial hypertension disease: cancer-like pathobiology, the role of the adventitia, systemic involvement, and right ventricular failure

In order to intervene appropriately and develop disease-modifying therapeutics for pulmonary arterial hypertension, it is crucial to understand the mechanisms of disease pathogenesis and progression. We herein discuss four topics of disease mechanisms that are currently highly debated, yet still unsolved, in the field of pulmonary arterial hypertension. Is pulmonary arterial hypertension a cancer-like disease? Does the adventitia play an important role in the initiation of pulmonary vascular remodeling? Is pulmonary arterial hypertension a systemic disease? Does capillary loss drive right ventricular failure? While pulmonary arterial hypertension does not replicate all features of cancer, anti-proliferative cancer therapeutics might still be beneficial in pulmonary arterial hypertension if monitored for safety and tolerability. It was recognized that the adventitia as a cell-rich compartment is important in the disease pathogenesis of pulmonary arterial hypertension and should be a therapeutic target, albeit the data are inconclusive as to whether the adventitia is involved in the initiation of neointima formation. There was agreement that systemic diseases can lead to pulmonary arterial hypertension and that pulmonary arterial hypertension can have systemic effects related to the advanced lung pathology, yet there was less agreement on whether idiopathic pulmonary arterial hypertension is a systemic disease per se. Despite acknowledging the limitations of exactly assessing vascular density in the right ventricle, it was recognized that the failing right ventricle may show inadequate vascular adaptation resulting in inadequate delivery of oxygen and other metabolites. Although the debate was not meant to result in a definite resolution of the specific arguments, it sparked ideas about how we might resolve the discrepancies by improving our disease modeling (rodent models, large-animal studies, studies of human cells, tissues, and organs) as well as standardization of the models. Novel experimental approaches, such as lineage tracing and better three-dimensional imaging of experimental as well as human lung and heart tissues, might unravel how different cells contribute to the disease pathology.

Anti-inflammatory nutrition with high protein attenuates cardiac and skeletal muscle alterations in a pulmonary arterial hypertension model

Pulmonary arterial hypertension (PAH) is characterized by remodelling of the pulmonary arteries and right ventricle (RV), which leads to functional decline of cardiac and skeletal muscle. This study investigated the effects of a multi-targeted nutritional intervention with extra protein, leucine, fish oil and oligosaccharides on cardiac and skeletal muscle in PAH. PAH was induced in female C57BL/6 mice by weekly injections of monocrotaline (MCT) for 8 weeks. Control diet (sham and MCT group) and isocaloric nutritional intervention (MCT + NI) were administered. Compared to sham, MCT mice increased heart weight by 7%, RV thickness by 13% and fibrosis by 60% (all p < 0.05) and these were attenuated in MCT + NI mice. Microarray and qRT-PCR analysis of RV confirmed effects on fibrotic pathways. Skeletal muscle fiber atrophy was induced (P < 0.05) by 22% in MCT compared to sham mice, but prevented in MCT + NI group. Our findings show that a multi-targeted nutritional intervention attenuated detrimental alterations to both cardiac and skeletal muscle in a mouse model of PAH, which provides directions for future therapeutic strategies targeting functional decline of both tissues.

Prevention of progression of pulmonary hypertension by the Nur77 agonist 6-mercaptopurine: role of BMP signalling

Pulmonary arterial hypertension (PAH) is a progressive fatal disease characterised by abnormal remodelling of pulmonary vessels, leading to increased vascular resistance and right ventricle failure. This abnormal vascular remodelling is associated with endothelial cell dysfunction, increased proliferation of smooth muscle cells, inflammation and impaired bone morphogenetic protein (BMP) signalling. Orphan nuclear receptor Nur77 is a key regulator of proliferation and inflammation in vascular cells, but its role in impaired BMP signalling and vascular remodelling in PAH is unknown.

We hypothesised that activation of Nur77 by 6-mercaptopurine (6-MP) would improve PAH by inhibiting endothelial cell dysfunction and vascular remodelling.

Nur77 expression is decreased in cultured pulmonary microvascular endothelial cells (MVECs) and lungs of PAH patients. Nur77 significantly increased BMP signalling and strongly decreased proliferation and inflammation in MVECs. In addition, conditioned medium from PAH MVECs overexpressing Nur77 inhibited the growth of healthy smooth muscle cells. Pharmacological activation of Nur77 by 6-MP markedly restored MVEC function by normalising proliferation, inflammation and BMP signalling. Finally, 6-MP prevented and reversed abnormal vascular remodelling and right ventricle hypertrophy in the Sugen/hypoxia rat model of severe angioproliferative PAH.

Our data demonstrate that Nur77 is a critical modulator in PAH by inhibiting vascular remodelling and increasing BMP signalling, and activation of Nur77 could be a promising option for the treatment of PAH.

EXPRESS: Left ventricular early diastolic strain rate detected by two-dimensional speckle tracking echocardiography and disease severity in pre-capillary pulmonary hypertension

We investigated and compared the correlations between two-dimensional speckle tracking echocardiography detected left ventricular peak early diastolic strain rates (global: left ventricular global peak early diastolic strain rate; septum: left ventricular peak early diastolic strain rate of septum; free wall: left ventricular peak early diastolic strain rate of free wall) and disease severity in pre-capillary pulmonary hypertension. Seventy-four pre-capillary pulmonary hypertension patients (23 males and 51 females, 35 ± 13 years) and thirty healthy controls were consecutively recruited for two-dimensional speckle tracking echocardiography analyses in our study. Medical records of pre-capillary pulmonary hypertension patients were reviewed to capture clinical data; risk assessments were performed based on the 2015 ESC Guidelines. Compared with healthy controls, left ventricular global peak early diastolic strain rate was lower in pre-capillary pulmonary hypertension patients (1.11 ± 0.60 s−1 versus 1.47 ± 0.45 s−1, P = 0.001), especially that of the septum (1.13 ± 0.58 s−1 versus 1.68 ± 0.46 s−1, P<0.001). Linear correlation analyses showed significant but weak correlations between left ventricle diastolic parameters and peak oxygen consumption, N-terminal pro-brain natriuretic peptide, and conventional echocardiographic right ventricle parameters: E/E′, tricuspid annular plane systolic excursion, S′, and fractional area change. No or weak correlations were observed between left ventricle diastolic parameters and hemodynamics. Multivariate logistic regression analyses showed left ventricular global peak early diastolic strain rate (OR: 0.304; 95%CI: 0.101–0.911) and left ventricular peak early diastolic strain rate of septum (OR: 0.252; 95%CI: 0.075–0.848) independently predict intermediate–high risk of pulmonary hypertension patients, even adjusted by age, gender, and body mass index. Receive operating characteristic curves showed that all the three models had the capacity to predict intermediate–high risk of pulmonary hypertension patients, and the model including left ventricular peak early diastolic strain rate of septum showed the strongest predictive capacity (area under the curve = 0.76, 95%CI: 0.59–0.93). Two-dimensional speckle tracking echocardiography detected left ventricle diastolic function parameters are significantly correlated with clinical data and can independently predict intermediate–high risk in pre-capillary pulmonary hypertension patients; the dysfunction of interventricular septum may make major contribution.

Role of the Aryl Hydrocarbon Receptor/ARNT/Cytochrome P450 System in Pulmonary Vascular Diseases

RATIONALE

CYPs (cytochrome p450) are critically involved in the metabolism of xenobiotics and toxins. Given that pulmonary hypertension is strongly associated with environmental exposure, we hypothesize that CYPs play a role in the development and maintenance of pathological vascular remodeling.

OBJECTIVE

We sought to identify key CYPs that could link drug or hormone metabolism to the development of pulmonary hypertension.

METHODS AND RESULTS

We searched in Medline (PubMed) database, as well as http://www.clinicaltrials.gov, for CYPs associated with many key aspects of pulmonary arterial hypertension including, but not limited to, severe pulmonary hypertension, estrogen metabolism, inflammation mechanisms, quasi-malignant cell growth, drug susceptibility, and metabolism of the pulmonary arterial hypertension-specific drugs.

CONCLUSIONS

We postulate a hypothesis where the AhR (aryl hydrocarbon receptor) mediates aberrant cell growth via expression of different CYPs associated with estrogen metabolism and inflammation.

Long non‑coding RNA MALAT1 sponges miR‑124‑3p.1/KLF5 to promote pulmonary vascular remodeling and cell cycle progression of pulmonary artery hypertension

Previous studies have demonstrated that long non-coding RNA (lncRNA) is involved in vascular remodeling. The metastasis-associated lung adenocarcinoma transcript 1 (MALAT1) lncRNA is associated with the proliferation and migration of vascular smooth muscle and endothelial cells; however, its biological role in pulmonary artery hypertension (PAH) is currently unclear. The aim of the present study was to investigate the post-transcriptional regulation of MALAT1 in human pulmonary artery smooth muscle cells (HPASMCs). The results revealed that MALAT1 expression levels were significantly upregulated in the pulmonary arteries (PAs) and HPASMCs obtained from patients with PAH compared with adjacent normal PA tissues and HPASMCs. Knockdown of MALAT1 suppressed the viability and proliferation of HPASMCs and prevented cells entering the G₀/G₁ cell cycle phase. MALAT1 overexpression exerted the opposite effects. Bioinformatics analysis predicted complementary binding of hsa-microRNA (miR)-124-3p.1 with the 3′-untranslated region of MALAT1. Luciferase reporter assays and RNA immunoprecipitation experiments demonstrated molecular binding between MALAT1 and hsa-miR-124-3p.1. This resulted in the formation of an RNA-induced silencing complex. In addition, Kruppel-like factor 5 (KLF5) was confirmed to be a target gene of MALAT1/hsa-miR-124-3p.1. MALAT1 silencing did not inhibit the proliferation and migration of HPASMCs following knockdown of hsa-miR-124-3p.1. In addition, MALAT1 knockdown was demonstrated to attenuate the expression of KLF5. Following MALAT1 knockdown, the expression level of KLF5 was rescued by inhibition of hsa-miR-124-3p.1 expression. The results of the current study indicate that the MALAT1/hsa-miR-124-3p.1/KLF5 axis may serve a key role in HPASMCs. In addition, the results contribute to what is known regarding the role of MALAT1 in PAH development and provide a novel theoretical basis for the development of new therapeutic interventions for patients with PAH.

Injury-Induced Shedding of Extracellular Vesicles Depletes Endothelial Cells of Cav-1 (Caveolin-1) and Enables TGF-β (Transforming Growth Factor-β)-Dependent Pulmonary Arterial Hypertension

Objective- To determine whether pulmonary arterial hypertension is associated with endothelial cell (EC)-Cav-1 (caveolin-1) depletion, EC-derived extracellular vesicle cross talk with macrophages, and proliferation of Cav-1 depleted ECs via TGF-β (transforming growth factor-β) signaling. Approach and Results- Pulmonary vascular disease was induced in Sprague-Dawley rats by exposure to a single injection of VEGFRII (vascular endothelial growth factor receptor II) antagonist SU5416 (Su) followed by hypoxia (Hx) plus normoxia (4 weeks each-HxSu model) and in WT (wild type; Tie2.Cre-; Cav1 lox/lox) and EC- Cav1-/- (Tie2.Cre+; Cav1 fl/fl) mice (Hx: 4 weeks). We observed reduced lung Cav-1 expression in the HxSu rat model in association with increased Cav-1+ extracellular vesicle shedding into the circulation. Whereas WT mice exposed to hypoxia exhibited increased right ventricular systolic pressure and pulmonary microvascular thickening compared with the group maintained in normoxia, the remodeling was further increased in EC- Cav1-/- mice indicating EC Cav-1 expression protects against hypoxia-induced pulmonary hypertension. Depletion of EC Cav-1 was associated with reduced BMPRII (bone morphogenetic protein receptor II) expression, increased macrophage-dependent TGF-β production, and activation of pSMAD2/3 signaling in the lung. In vitro, in the absence of Cav-1, eNOS (endothelial NO synthase) dysfunction was implicated in the mechanism of EC phenotype switching. Finally, reduced expression of EC Cav-1 in lung histological sections from human pulmonary arterial hypertension donors was associated with increased plasma concentration of Cav-1, extracellular vesicles, and TGF-β, indicating Cav-1 may be a plasma biomarker of vascular injury and key determinant of TGF-β-induced pulmonary vascular remodeling. Conclusions- EC Cav-1 depletion occurs, in part, via Cav-1+ extracellular vesicle shedding into the circulation, which contributes to increased TGF-β signaling, EC proliferation, vascular remodeling, and pulmonary arterial hypertension.

Beneficial effects of mesenchymal stem cell delivery via a novel cardiac bioscaffold on right ventricles of pulmonary arterial hypertensive rats

Right ventricular failure (RVF) is a common cause of death in patients suffering from pulmonary arterial hypertension (PAH). The current treatment for PAH only moderately improves symptoms, and RVF ultimately occurs. Therefore, it is necessary to develop new treatment strategies to protect against right ventricle (RV) maladaptation despite PAH progression. In this study, we hypothesize that local mesenchymal stem cell (MSC) delivery via a novel bioscaffold can improve RV function despite persistent PAH. To test our hypothesis, we induced PAH in adult rats with SU5416 and chronic hypoxia exposure; treated with rat MSCs delivered by intravenous injection, intramyocardial injection, or epicardial placement of a bioscaffold; and then examined treatment effectiveness by in vivo pressure-volume measurement, echocardiography, histology, and immunohistochemistry. Our results showed that compared with other treatment groups, only the MSC-seeded bioscaffold group resulted in RV functional improvement, including restored stroke volume, cardiac output, and improved stroke work. Diastolic function indicated by end-diastolic pressure-volume relationship was improved by the local MSC treatments or bioscaffold alone. Cardiomyocyte hypertrophy and RV fibrosis were both reduced, and von Willebrand factor expression was restored by the MSC-seeded bioscaffold treatment. Overall, our study suggests a potential new regenerative therapy to rescue the pressure-overload failing RV with persistent pulmonary vascular disease, which may improve quality of life and/or survival of PAH patients. NEW & NOTEWORTHY We explored the effects of mesenchymal stem cell-seeded bioscaffold on right ventricles (RVs) of rats with established pulmonary arterial hypertension (PAH). Some beneficial effects were observed despite persistent PAH, suggesting that this may be a new therapy for RV to improve quality of life and/or survival of PAH patients.

Blood Outgrowth and Proliferation of Endothelial Colony Forming Cells are Related to Markers of Disease Severity in Patients with Pulmonary Arterial Hypertension

In pulmonary arterial hypertension (PAH), lung-angioproliferation leads to increased pulmonary vascular resistance, while simultaneous myocardial microvessel loss contributes to right ventricular (RV) failure. Endothelial colony forming cells (ECFC) are highly proliferative, angiogenic cells that may contribute to either pulmonary vascular obstruction or to RV microvascular adaptation. We hypothesize ECFC phenotypes (outgrowth, proliferation, tube formation) are related to markers of disease severity in a prospective cohort-study of 33 PAH and 30 healthy subjects. ECFC were transplanted in pulmonary trunk banded rats with RV failure. The presence of ECFC outgrowth in PAH patients was associated with low RV ejection fraction, low central venous saturation and a shorter time to clinical worsening (5.4 months (0.6–29.2) vs. 36.5 months (7.4–63.4), p = 0.032). Functionally, PAH ECFC had higher proliferative rates compared to control in vitro, although inter-patient variability was high. ECFC proliferation was inversely related to RV end diastolic volume (R² = 0.39, p = 0.018), but not pulmonary vascular resistance. Tube formation-ability was similar among donors. Normal and highly proliferative PAH ECFC were transplanted in pulmonary trunk banded rats. While no effect on hemodynamic measurements was observed, RV vascular density was restored. In conclusion, we found that ECFC outgrowth associates with high clinical severity in PAH, suggesting recruitment. Transplantation of highly proliferative ECFC restored myocardial vascular density in pulmonary trunk banded rats, while RV functional improvements were not observed.

Divergent changes of p53 in pulmonary arterial endothelial and smooth muscle cells involved in the development of pulmonary hypertension

The tumor-suppressive role of p53, a transcription factor that regulates the expression of many genes, has been linked to cell cycle arrest, apoptosis, and senescence. The noncanonical function or the pathogenic role of p53 has more recently been implicated in pulmonary vascular disease. We previously reported that rapid nuclear accumulation of hypoxia-inducible factor (HIF)-1α in pulmonary arterial smooth muscle cells (PASMCs) upregulates transient receptor potential channels and enhances Ca²⁺ entry to increase cytosolic Ca²⁺ concentration ([Ca²⁺]_cyt). Also, we observed differences in HIF-1α/2α expression in PASMCs and pulmonary arterial endothelial cells (PAECs). Here we report that p53 is increased in PAECs, but decreased in PASMCs, isolated from mice with hypoxia-induced pulmonary hypertension (PH) and rats with monocrotaline (MCT)-induced PH (MCT-PH). The increased p53 in PAECs from rats with MCT-PH is associated with an increased ratio of Bax/Bcl-2, while the decreased p53 in PASMCs is associated with an increased HIF-1α. Furthermore, p53 is downregulated in PASMCs isolated from patients with idiopathic pulmonary arterial hypertension compared with PASMCs from normal subjects. Overexpression of p53 in normal PASMCs inhibits store-operated Ca²⁺ entry (SOCE) induced by passive depletion of intracellularly stored Ca²⁺ in the sarcoplasmic reticulum, while downregulation of p53 enhances SOCE. These data indicate that differentially regulated expression of p53 and HIF-1α/2α in PASMCs and PAECs and the cross talk between p53 and HIF-1α/2α in PASMCs and PAECs may play an important role in the development of PH via, at least in part, induction of PAEC apoptosis and PASMC proliferation.

Early versus late cardiac remodeling during right ventricular pressure load and impact of preventive versus rescue therapy with endothelin-1 receptor blockers

Pulmonary artery banding (PAB) causes right ventricular (RV) dysfunction, biventricular fibrosis, and apoptosis, which are attenuated by endothelin-1 receptor blockade (ERB). Little is known about the time course of remodeling and whether early versus late ERB confers improved outcome. PAB was performed in five groups of rabbits: Shams, 3-wk PAB (3W), 6-wk PAB (6W), 6-wk PAB + ERB administered from day 1 (6WERB1), and 6-wk PAB + ERB administered from day 21 (6WERB21). Biventricular development of profibrotic molecular signaling, fibrosis, apoptosis, and conductance catheter and echocardiography function were studied. Thirty-three rabbits [ n = 6–7 per group; 3.00 (0.23) kg, mean (SD)] developed half to full systemic RV pressures. Biventricular profibrotic signaling and collagen deposition [RV collagen: Shams 3.8 (0.58) vs. 3W 8.69 (2.52) vs. 6W 8.83 (4.02)%, P < 0.005] and apoptosis [RV: Shams 8.32 (3.2) vs. 3W 55.95 (47.55) vs. 6W 38.85 (17.26) apoptotic cells per microfield, P < 0.0005] increased with PAB. Early and late ERB attenuated fibrosis [RV: 6WERB1 5.55 (1.18), 6WERB21 5.63 (0.72)%] and apoptosis [RV: 6WERB1 11.1 (5.25), 6WERB21 20.24 (7.16) apoptotic cells per microfield, P < 0.0001 vs. 6W]. RV dimensions progressively increased at 3W and 6W and decreased with early ERB [end-diastolic dimensions: Shams 0.4 (0.13) vs. 3W 0.55 (0.78) vs. 6W 0.78 (0.25) vs. 6WERB1 0.71 (0.26) vs. 6WERB21 0.49 (0.23) cm, P < 0.05]. Despite increased RV contractility with PAB [RV end-systolic pressure-volume relationship: Shams 3.76 (1.76) vs. 3W 12.21 (3.44) vs. 6W 19.4 (6.88) mmHg/ml], biventricular function and cardiac output [Shams 196.1 (39.73) vs. 3W 149.9 (34.82) vs. 6W 151 (31.69) ml/min] worsened in PAB groups and improved with early and late ERB [6WERB1 202.8 (26.8), 6WERB21 194.8 (36.93) ml/min, P < 0.05 vs. PAB]. In conclusion, RV pressure overload induces early biventricular fibrosis, apoptosis, remodeling, and dysfunction that worsens with persistent RV hypertension. This remodeling is attenuated by early and late ERB.

NEW & NOTEWORTHY Our results in a rabbit model of progressive right ventricular (RV) pressure loading indicate that biventricular fibrosis, apoptosis, and dysfunction are already present when RV hypertension is reached at 3 wk of progressive pulmonary artery banding. These findings worsen with persistent RV hypertension to 6 wk and are attenuated with both early and late endothelin-1 receptor blockade, with some advantages to early therapy. These findings highlight the role of endothelin-1 in driving biventricular remodeling secondary to RV hypertension and suggest that early therapy with an endothelin-1 receptor blocker may be beneficial in attenuating biventricular remodeling but that late therapy is also effective.

Natural Antioxidants as Potential Therapy, and a Promising Role for Melatonin Against Pulmonary Hypertension

Plasma and serum samples, and lung/heart tissue of pulmonary hypertension (PH) patients and animal models of PH display elevated oxidative stress. Moreover, the severity of PH and levels of oxidative stress increase concurrently, which suggests that oxidative stress could be utilized as a biomarker for PH progression. Accumulating evidence has well established that oxidative stress is also key role player in the development of PH. Preclinical studies have demonstrated that natural antioxidants improved PH condition, and, therefore, antioxidant therapy has been proposed as a potential therapeutic strategy against PH. These natural antioxidants include medicinal plant extracts and compounds such as resveratrol and melatonin. Recent studies suggest that melatonin provides health benefit against PH, by enhancing antioxidant capacity, increasing vasodilation, counteracting lung and cardiac fibrosis, and stunting right ventricular (RV) hypertrophy/failure. This chapter comprehensively reviews and discusses a variety of natural antioxidants and their efficacy in modulating experimental PH. This chapter also demonstrates that antioxidant therapy remains a therapeutic strategy for PH, and particularly identifies melatonin as a safe, cost-effective, and promising antioxidant therapy.

Pentose Shunt, Glucose-6-Phosphate Dehydrogenase, NADPH Redox, and Stem Cells in Pulmonary Hypertension

Redox signaling plays a critical role in the pathophysiology of cardiovascular diseases. The pentose phosphate pathway is a major source of NADPH redox in the cell. The activities of glucose-6-phosphate dehydrogenase (the rate-limiting enzyme in the pentose shunt) and glucose flux through the shunt pathway is increased in various lung cells including, the stem cells, in pulmonary hypertension. This chapter discusses the importance of the shunt pathway and glucose-6-phosphate dehydrogenase in the pathogenesis of pulmonary artery remodeling and occlusive lesion formation within the hypertensive lungs.

BMPR2 mutations and endothelial dysfunction in pulmonary arterial hypertension (2017 Grover Conference Series)

Despite the discovery more than 15 years ago that patients with hereditary pulmonary arterial hypertension (HPAH) inherit BMP type 2 receptor ( BMPR2) mutations, it is still unclear how these mutations cause disease. In part, this is attributable to the rarity of HPAH and difficulty obtaining tissue samples from patients with early disease. However, in addition, limitations to the approaches used to study the effects of BMPR2 mutations on the pulmonary vasculature have restricted our ability to determine how individual mutations give rise to progressive pulmonary vascular pathology in HPAH. The importance of understanding the mechanisms by which BMPR2 mutations cause disease in patients with HPAH is underscored by evidence that there is reduced BMPR2 expression in patients with other, more common, non-hereditary form of PAH, and that restoration of BMPR2 expression reverses established disease in experimental models of pulmonary hypertension. In this paper, we focus on the effects on endothelial function. We discuss some of the controversies and challenges that have faced investigators exploring the role of BMPR2 mutations in HPAH, focusing specifically on the effects different BMPR2 mutation have on endothelial function, and whether there are qualitative differences between different BMPR2 mutations. We discuss evidence that BMPR2 signaling regulates a number of responses that may account for endothelial abnormalities in HPAH and summarize limitations of the models that are used to study these effects. Finally, we discuss evidence that BMPR2-dependent effects on endothelial metabolism provides a unifying explanation for the many of the BMPR2 mutation-dependent effects that have been described in patients with HPAH.

Dominant Role for Regulatory T Cells in Protecting Females Against Pulmonary Hypertension

RATIONALE

Pulmonary arterial hypertension (PH) is a life-threatening condition associated with immune dysregulation and abnormal regulatory T cell (Treg) activity, but it is currently unknown whether and how abnormal Treg function differentially affects males and females.

OBJECTIVE

To evaluate whether and how Treg deficiency differentially affects male and female rats in experimental PH.

METHODS AND RESULTS

Male and female athymic rnu/rnu rats, lacking Tregs, were treated with the VEGFR2 (vascular endothelial growth factor receptor 2) inhibitor SU5416 or chronic hypoxia and evaluated for PH; some animals underwent Treg immune reconstitution before SU5416 administration. Plasma PGI₂ (prostacyclin) levels were measured. Lung and right ventricles were assessed for the expression of the vasoprotective proteins COX-2 (cyclooxygenase 2), PTGIS (prostacyclin synthase), PDL-1 (programmed death ligand 1), and HO-1 (heme oxygenase 1). Inhibitors of these pathways were administered to athymic rats undergoing Treg immune reconstitution. Finally, human cardiac microvascular endothelial cells cocultured with Tregs were evaluated for COX-2, PDL-1, HO-1, and ER (estrogen receptor) expression, and culture supernatants were assayed for PGI₂ and IL (interleukin)-10. SU5416-treatment and chronic hypoxia produced more severe PH in female than male athymic rats. Females were distinguished by greater pulmonary inflammation, augmented right ventricular fibrosis, lower plasma PGI₂ levels, decreased lung COX-2, PTGIS, HO-1, and PDL-1 expression and reduced right ventricular PDL-1 levels. In both sexes, Treg immune reconstitution protected against PH development and raised levels of plasma PGI₂ and cardiopulmonary COX-2, PTGIS, PDL-1, and HO-1. Inhibiting COX-2, HO-1, and PD-1 (programmed death 1)/PDL-1 pathways abrogated Treg protection. In vitro, human Tregs directly upregulated endothelial COX-2, PDL-1, HO-1, ERs and increased supernatant levels of PGI₂ and IL-10.

CONCLUSIONS

In 2 animal models of PH based on Treg deficiency, females developed more severe PH than males. The data suggest that females are especially reliant on the normal Treg function to counteract the effects of pulmonary vascular injury leading to PH.

EP4 Agonist L-902,688 Suppresses EndMT and Attenuates Right Ventricular Cardiac Fibrosis in Experimental Pulmonary Arterial Hypertension

Right ventricular (RV) hypertrophy is characterized by cardiac fibrosis due to endothelial–mesenchymal transition (EndMT) and increased collagen production in pulmonary arterial hypertension (PAH) patients, but the mechanisms for restoring RV function are unclear. Prostanoid agonists are effective vasodilators for PAH treatment that bind selective prostanoid receptors to modulate vascular dilation. The importance of prostanoid signaling in the RV is not clear. We investigated the effects of the EP4-specific agonist L-902,688 on cardiac fibrosis and TGF-β-induced EndMT. EP4-specific agonist treatment reduced right ventricle fibrosis in the monocrotaline (MCT)-induced PAH rat model. L-902,688 (1 µM) attenuated TGF-β-induced Twist and α-smooth muscle actin (α-SMA) expression, but these effects were reversed by AH23848 (an EP4 antagonist), highlighting the crucial role of EP4 in suppressing TGF-β-induced EndMT. These data indicate that the selective EP4 agonist L-902,688 attenuates RV fibrosis and suggest a potential approach to reducing RV fibrosis in patients with PAH.

Twist1 in Hypoxia-induced Pulmonary Hypertension through Transforming Growth Factor-β-Smad Signaling

Pulmonary hypertension (PH) is a devastating pulmonary vascular disease characterized by aberrant muscularization of the normally nonmuscularized distal pulmonary arterioles. The expression of the transcription factor, Twist1, increases in the lungs of patients with pulmonary arterial hypertension. However, the mechanisms by which Twist1 controls the pathogenesis of PH remain unclear. It is becoming clear that endothelial-to-mesenchymal transition (EndMT) contributes to various vascular pathologies, including PH; Twist1 is known to mediate EndMT. In this report, we demonstrate that Twist1 overexpression increases transforming growth factor (TGF) β receptor2 (TGF-βR2) expression and Smad2 phosphorylation, and induces EndMT in cultured human pulmonary arterial endothelial (HPAE) cells, whereas a mutant construct of Twist1 at the serine 42 residue (Twist1S42A) fails to induce EndMT. We also implanted fibrin gel supplemented with HPAE cells on the mouse lung, and found that these HPAE cells form vascular structures and that Twist1-overexpressing HPAE cells undergo EndMT in the gel, whereas Twist1S42A-overexpressing cells do not. Furthermore, hypoxia-induced EndMT is inhibited in endothelial cells overexpressing Twist1S42A mutant construct in vitro. Hypoxia-induced accumulation of α-smooth muscle actin-positive cells in the pulmonary arterioles is attenuated in Tie2-specific Twist1 conditional knockout mice in vivo. These findings suggest that Twist1 serine 42 phosphorylation plays a key role in EndMT through TGF-β signaling and that modulation of Twist1 phosphorylation could be an effective strategy for managing PH.