Endothelin-1 decreases endothelial PPARγ signaling and impairs angiogenesis after chronic intrauterine pulmonary hypertension

Comparison of Different Treatments of Persistent Pulmonary Hypertension of the Newborn: A Systematic Review and Network Meta-Analysis

OBJECTIVES

Persistent pulmonary hypertension of the newborn (PPHN) is a life-threatening disease. Despite being considered the gold standard treatment scheme, inhaled nitric oxide (iNO) is not readily available in settings with limited resources. Therefore, in recent years, research on related drugs is being actively pursued. Herein, we aimed to use random-effects network meta-analysis to evaluate the efficacy and associated mortality of different PPHN therapies.

DATA SOURCES

We electronically searched the PubMed, Embase, and Cochrane Library for data up to January 27, 2023.

STUDY SELECTION

Randomized controlled trials involving neonates with PPHN assessing efficacy and mortality of various treatments.

DATA EXTRACTION

Details of study population, treatments, and outcomes were extracted.

DATA SYNTHESIS

Direct pairwise comparisons and a network meta-analysis was performed under random effects. The ranking probability was further assessed based on the surface under the cumulative ranking curve (SUCRA). We analyzed 23 randomized clinical trials involving 902 newborns with PPHN. Sixteen different treatment strategies were compared with each other and conventional therapy (CON). A median concentration of 10-20 parts per million (ppm) iNO (MNO) coupled with sildenafil orally administered at a dose of 1-3 mg/kg/dose every 6-8 hours (OSID) demonstrated the best efficacy (MNO + OSID vs. CON: odds ratio [OR] = 27.53, 95% CI, 2.36-321.75; SUCRA = 0.818, ranking first; moderate quality). OSID combined with milrinone administered IV also performed well in terms of efficacy (OSID + milrinone vs. CON: OR = 25.13, 95% CI = 1.67-377.78; SUCRA = 0.811, ranking second; low quality) and mortality reduction (CON vs. OSID + milrinone: OR = 25.13, 95% CI = 1.67-377.78; SUCRA = 0.786, ranking last; low quality).

CONCLUSIONS

MNO + OSID is the most effective PPHN treatment. If iNO is not available, OSID + milrinone is preferred.

Bosentan in the treatment of persistent pulmonary hypertension in newborns: a systematic review and meta-analysis

BACKGROUND

Persistent pulmonary hypertension of the newborn is a life-threatening condition that affects about 1-2 per 1,000 live births worldwide. Bosentan is an oral dual endothelin receptor antagonist that may have a beneficial effect on persistent pulmonary hypertension of the newborn by reducing pulmonary vascular resistance and improving oxygenation. However, its role in persistent pulmonary hypertension of the newborn remains unclear.

OBJECTIVES

To systematically evaluate the efficacy and safety of bosentan as an adjuvant therapy for persistent pulmonary hypertension of the newborn in newborns.

METHODS

We searched six English and two Chinese databases from their inception to 1 January 2023 following the Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines. We included randomised controlled trials and retrospective studies that compared bosentan with placebo or other drugs for persistent pulmonary hypertension of the newborn in newborns. We performed a meta-analysis using random-effects models and assessed the risk of bias and heterogeneity in the included studies.

RESULTS

We included 10 studies with a total of 550 participants. Bosentan significantly reduced the treatment failure rate (relative risk = 0.25, P < 0.001), pulmonary artery pressure (mean difference = -11.79, P < 0.001), and length of hospital stay (mean difference = -1.04, P = 0.003), and increased the partial pressure of oxygen (mean difference = 10.02, P < 0.001) and blood oxygen saturation (SpO2) (mean difference = 8.24, P < 0.001) compared with a placebo or other drugs. The occurrence of adverse reactions was not significantly different between bosentan and a placebo or other drugs.

CONCLUSIONS

Bosentan is effective in the treatment of persistent pulmonary hypertension of the newborn but adverse reactions such as abnormal liver function should be observed when using it.

Puerarin-V prevents the progression of hypoxia- and monocrotaline-induced pulmonary hypertension in rodent models

Pulmonary hypertension (PH) is a cardiopulmonary disease characterized by a progressive increase in pulmonary vascular resistance. One of the initial pathogenic factors of PH is pulmonary arterial remodeling under various stimuli. Current marketed drugs against PH mainly relieve symptoms without significant improvement in overall prognosis. Discovering and developing new therapeutic drugs that interfere with vascular remodeling is in urgent need. Puerarin is an isoflavone compound extracted from the root of Kudzu vine, which is widely used in the treatment of cardiovascular diseases. In the present study, we evaluated the efficacy of puerarin in the treatment of experimental PH. PH was induced in rats by a single injection of MCT (50 mg/kg, sc), and in mice by exposure to hypoxia (10% O2) for 14 days. After MCT injection the rats were administered puerarin (10, 30, 100 mg · kg-1 · d-1, i.g.) for 28 days, whereas hypoxia-treated mice were pre-administered puerarin (60 mg · kg-1 · d-1, i.g.) for 7 days. We showed that puerarin administration exerted significant protective effects in both experimental PH rodent models, evidenced by significantly reduced right ventricular systolic pressure (RVSP) and lung injury, improved pulmonary artery blood flow as well as pulmonary vasodilation and contraction function, inhibited inflammatory responses in lung tissues, improved resistance to apoptosis and abnormal proliferation in lung tissues, attenuated right ventricular injury and remodeling, and maintained normal function of the right ventricle. We revealed that MCT and hypoxia treatment significantly downregulated BMPR2/Smad signaling in the lung tissues and PPARγ/PI3K/Akt signaling in the lung tissues and right ventricles, which were restored by puerarin administration. In addition, we showed that a novel crystal type V (Puer-V) exerted better therapeutic effects than the crude form of puerarin (Puer). Furthermore, Puer-V was more efficient than bosentan (a positive control drug) in alleviating the abnormal structural changes and dysfunction of lung tissues and right ventricles. In conclusion, this study provides experimental evidence for developing Puer-V as a novel therapeutic drug to treat PH.

Efficacy and safety of bosentan in the treatment of persistent pulmonary hypertension of the newborn: a Metaanalysis

OBJECTIVES

To systematically evaluate the efficacy and safety of bosentan in the treatment of persistent pulmonary hypertension of the newborn (PPHN).

METHODS

Chinese Journal Full-text Database, Weipu Database, Wanfang Data, China Biology Medicine disc, PubMed, Web of Science, Embase, and Cochrane Library were searched for literature on bosentan in the treatment of PPHN published up to August 31, 2021.

RESULTS

A total of 8 randomized controlled trials were included for Meta analysis. The results of the Meta analysis showed that compared with the control group, the bosentan treatment group had a significantly lower treatment failure rate (RR=0.23, P<0.001), a significantly greater reduction in pulmonary artery pressure [mean difference (MD)=-11.79, P<0.001)], significantly greater increases in oxygen partial pressure (MD=10.21, P=0.006) and blood oxygen saturation (MD=8.30, P<0.001), and a significantly shorter length of hospital stay (MD=-1.35, P<0.001). The descriptive analysis showed that the bosentan treatment group had a lower degree of tricuspid regurgitation than the control group after treatment. The main adverse reactions of bosentan treatment included abnormal liver function, anemia and edema. The results of subgroup analysis based on treatment regimen, research area, and drug dose were consistent with those before stratification.

CONCLUSIONS

Bosentan is effective in the treatment of PPHN. However, when using bosentan, attention should be paid to adverse reactions such as abnormal liver function.

Common Variation in EDN1 Regulatory Regions Highlights the Role of PPARγ as a Key Regulator of Endothelin in vitro

Pulmonary Arterial Hypertension (PAH) is a rare disease caused by the obliteration of the pulmonary arterioles, increasing pulmonary vascular resistance and eventually causing right heart failure. Endothelin-1 (EDN1) is a vasoconstrictor peptide whose levels are indicators of disease progression and its pathway is one of the most common targeted by current treatments. We sequenced the EDN1 untranslated regions of a small subset of patients with PAH, predicted the effect in silico, and used a luciferase assay with the different genotypes to analyze its influence on gene expression. Finally, we used siRNAs against the major transcription factors (TFs) predicted for these regions [peroxisome proliferator-activated receptor γ (PPARγ), Krüppel-Like Factor 4 (KLF4), and vitamin D receptor (VDR)] to assess EDN1 expression in cell culture and validate the binding sites. First, we detected a single nucleotide polymorphism (SNP) in the 5' untranslated region (UTR; rs397751713) and another in the 3'regulatory region (rs2859338) that altered luciferase activity in vitro depending on their genotype. We determined in silico that KLF4/PPARγ could bind to the rs397751713 and VDR to rs2859338. By using siRNAs and luciferase assays, we determined that PPARγ binds differentially to rs397751713. PPARγ and VDR Knock-Down (KD) increased the EDN1 mRNA levels and EDN1 production in porcine aortic endothelial cells (PAECs), while PPARγ and KLF4 KD increased the EDN1 production in HeLa. In conclusion, common variants in EDN1 regulatory regions could alter EDN1 levels. We were able to validate that PPARγ binds in rs397751713 and is a key regulator of EDN1. In addition, KLF4 and VDR regulate EDN1 production in a cell-dependent manner, but VDR does not bind directly to the regions we studied.

Macitentan attenuates cardiovascular remodelling in infant rats with chronic lung disease

Background

Cardiovascular impairment contributes to increased mortality in preterm infants with chronic lung disease. Macitentan, an endothelin-1 receptor antagonist, has the potential to attenuate pulmonary and cardiovascular remodelling.

Methods

In a prospective randomized placebo-controlled intervention trial, Sprague–Dawley rats were exposed to 0.21 or 1.0 fraction of inspired oxygen (FiO2) for 19 postnatal days. Rats were treated via gavage with placebo or macitentan from days of life 5 to 19. Alveoli, pulmonary vessels, α-smooth muscle actin content in pulmonary arterioles, size of cardiomyocytes, right to left ventricular wall diameter ratio, and endothelin-1 plasma concentrations were assessed.

Results

FiO2 1.0 induced typical features of chronic lung disease with significant alveolar enlargement (p = 0.012), alveolar (p = 0.048) and pulmonary vessel rarefaction (p = 0.024), higher α-smooth muscle actin content in pulmonary arterioles (p = 0.009), higher right to left ventricular wall diameter ratio (p = 0.02), and larger cardiomyocyte cross-sectional area (p < 0.001). Macitentan treatment significantly increased pulmonary vessel count (p = 0.004) and decreased right to left ventricular wall diameter ratios (p = 0.002). Endothelin-1 plasma concentrations were higher compared to placebo (p = 0.015). Alveolar number and size, α-smooth muscle actin, and the cardiomyocyte cross-sectional area remained unchanged (all p > 0.05).

Conclusion

The endothelin-1 receptor antagonist macitentan attenuated cardiovascular remodelling in an infant rat model for preterm chronic lung disease. This study underscores the potential of macitentan to reduce cardiovascular morbidity in preterm infants with chronic lung disease.

Role of the Purinergic P2Y2 Receptor in Pulmonary Hypertension

Pulmonary arterial hypertension (PAH), group 1 pulmonary hypertension (PH), is a fatal disease that is characterized by vasoconstriction, increased pressure in the pulmonary arteries, and right heart failure. PAH can be described by abnormal vascular remodeling, hyperproliferation in the vasculature, endothelial cell dysfunction, and vascular tone dysregulation. The disease pathomechanisms, however, are as yet not fully understood at the molecular level. Purinergic receptors P2Y within the G-protein-coupled receptor family play a major role in fluid shear stress transduction, proliferation, migration, and vascular tone regulation in systemic circulation, but less is known about their contribution in PAH. Hence, studies that focus on purinergic signaling are of great importance for the identification of new therapeutic targets in PAH. Interestingly, the role of P2Y2 receptors has not yet been sufficiently studied in PAH, whereas the relevance of other P2Ys as drug targets for PAH was shown using specific agonists or antagonists. In this review, we will shed light on P2Y receptors and focus more on the P2Y2 receptor as a potential novel player in PAH and as a new therapeutic target for disease management.

Hypertrophic signaling compensates for contractile and metabolic consequences of DNA methyltransferase 3A loss in human cardiomyocytes

The role of DNA methylation in cardiomyocyte physiology and cardiac disease remains a matter of controversy. We have recently provided evidence for an important role of DNMT3A in human cardiomyocyte cell homeostasis and metabolism, using engineered heart tissue (EHT) generated from human induced pluripotent stem cell (hiPSC)-derived cardiomyocytes carrying a knockout of the de novo DNA methyltransferase DNMT3A. Unlike isogenic control EHT, knockout EHT displayed morphological abnormalities such as lipid accumulations inside cardiomyocytes associated with impaired mitochondrial metabolism, as well as functional defects and impaired glucose metabolism. Here, we analyzed the role of DNMT3A in the setting of cardiac hypertrophy. We induced hypertrophic signaling by treatment with 50 nM endothelin-1 and 20 μM phenylephrine for one week and assessed EHT contractility, morphology, DNA methylation, and gene expression. While both knockout EHTs and isogenic controls showed the expected activation of the hypertrophic gene program, knockout EHTs were protected from hypertrophy-related functional impairment. Conversely, hypertrophic treatment prevented the metabolic consequences of a loss of DNMT3A, i.e. abolished lipid accumulation in cardiomyocytes likely by partial normalization of mitochondrial metabolism and restored glucose metabolism and metabolism-related gene expression of knockout EHT. Together, these data suggest an important role of DNA methylation not only for cardiomyocyte physiology, but also in the setting of cardiac disease.

Monitoring Endothelin-A Receptor Expression during the Progression of Atherosclerosis

Cardiovascular disease remains the most frequent cause of death worldwide. Atherosclerosis, an underlying cause of cardiovascular disease, is an inflammatory disorder associated with endothelial dysfunction. The endothelin system plays a crucial role in the pathogenesis of endothelial dysfunction and is involved in the development of atherosclerosis. We aimed to reveal the expression levels of the endothelin-A receptor (ET_AR) in the course of atherogenesis to reveal possible time frames for targeted imaging and interventions. We used the ApoE^−/− mice model and human specimens and evaluated ET_AR expression by quantitative rtPCR (qPCR), histology and fluorescence molecular imaging. We found a significant upregulation of ET_AR after 22 weeks of high-fat diet in the aortae of ApoE^−/− mice. With regard to translation to human disease, we applied the fluorescent probe to fresh explants of human carotid and femoral artery specimens. The findings were correlated with qPCR and histology. While ET_AR is upregulated during the progression of early atherosclerosis in the ApoE^−/− mouse model, we found that ET_AR expression is substantially reduced in advanced human atherosclerotic plaques. Moreover, those expression changes were clearly depicted by fluorescence imaging using our in-house designed ET_AR-Cy 5.5 probe confirming its specificity and potential use in future studies.

Extracellular Vesicles Attenuate Nitrofen-Mediated Human Pulmonary Artery Endothelial Dysfunction: Implications for Congenital Diaphragmatic Hernia

Congenital diaphragmatic hernia (CDH) leads to pathophysiologic pulmonary vasoreactivity. Previous studies show that mesenchymal stromal cell-derived extracellular vesicles (MSCEv) inhibit lung inflammation and vascular remodeling. We characterize MSCEv and human pulmonary artery endothelial cell (HPAEC) interaction, as well as the pulmonary artery (PA) response to MSCEv treatment. HPAECs were cultured with and without exposure to nitrofen (2,4-dichloro-phenyl-p-nitrophenylether) and treated with MSCEv. HPAEC viability, architecture, production of reactive oxygen species (ROS), endothelial dysfunction-associated protein levels (PPARγ, LOX-1, LOX-2, nuclear factor-κB [NF-κB], endothelial NO synthase [eNOS], ET-1 [endothelin 1]), and the nature of MSCEv-cellular interaction were assessed. Newborn rodents with and without CDH (nitrofen model and Sprague-Dawley) were treated with intravascular MSCEv or vehicle control, and their PAs were isolated. Contractility was assessed by wire myography. The contractile (KCL and ET-1) and relaxation (fasudil) responses were evaluated. HPAEC viability correlated inversely with nitrofen dose, while architectural compromise was directly proportional. There was a 2.1 × increase in ROS levels in nitrofen HPAECs (P < 0.001), and MSCEv treatment attenuated ROS levels by 1.5 × versus nitrofen HPAECs (P < 0.01). Nitrofen-induced alterations in endothelial dysfunction-associated proteins are shown, and exposure to MSCEv restored more physiologic expression. Nitrofen HPAEC displayed greater MSCEv uptake (80% increase, P < 0.05). Adenosine, a clathrin-mediated endocytosis inhibitor, decreased uptake by 46% (P < 0.05). CDH PA contraction was impaired with KCL (108.6% ± 1.4% vs. 112.0% ± 1.4%, P = 0.092) and ET-1 (121.7% ± 3.0% vs. 131.2% ± 1.8%, P < 0.01). CDH PA relaxation was impaired with fasudil (32.2% ± 1.9% vs. 42.1% ± 2.2%, P < 0.001). After MSCEv treatment, CDH PA contraction improved (125.9% ± 3.4% vs. 116.4 ± 3.5, P = 0.06), and relaxation was unchanged (32.5% ± 3.2% vs. 29.4% ± 3.1%, P = 0.496). HPAEC exposure to nitrofen led to changes consistent with vasculopathy in CDH, and MSCEv treatment led to a more physiologic cellular response. MSCEv were preferentially taken up by nitrofen-treated cells by clathrin-dependent endocytosis. In vivo, MSCEv exposure improved PA contractile response. These data reveal mechanisms of cellular and signaling alterations that characterize MSCEv-mediated attenuation of pulmonary vascular dysfunction in CDH-associated pulmonary hypertension.

Loss of endothelin type B receptor function improves insulin sensitivity in rats

High salt intake (HS) is associated with obesity and insulin resistance. ET-1, a peptide released in response to HS, inhibits the actions of insulin on cultured adipocytes through ET-1 type B (ETB) receptors; however, the in vivo implications of ETB receptor activation on lipid metabolism and insulin resistance is unknown. We hypothesized that activation of ETB receptors in response to HS intake promotes dyslipidemia and insulin resistance. In normal salt (NS) fed rats, no significant difference in body mass or epididymal fat mass was observed between control and ETB deficient rats. After 2 weeks of HS, ETB-deficient rats had significantly lower body mass and epididymal fat mass compared to controls. Nonfasting plasma glucose was not different between genotypes; however, plasma insulin concentration was significantly lower in ETB-deficient rats compared to controls, suggesting improved insulin sensitivity. In addition, ETB-deficient rats had higher circulating free fatty acids in both NS and HS groups, with no difference in plasma triglycerides between genotypes. In a separate experiment, ETB-deficient rats had significantly lower fasting blood glucose and improved glucose and insulin tolerance compared to controls. These data suggest that ET-1 promotes adipose deposition and insulin resistance via the ETB receptor.

Persistent Pulmonary Hypertension of the Newborn: Pathophysiological Mechanisms and Novel Therapeutic Approaches

Persistent pulmonary hypertension of the newborn (PPHN) is one of the main causes of neonatal morbidity and mortality. It is characterized by sustained elevation of pulmonary vascular resistance (PVR), preventing an increase in pulmonary blood flow after birth. The affected neonates fail to establish blood oxygenation, precipitating severe respiratory distress, hypoxemia, and eventually death. Inhaled nitric oxide (iNO), the only approved pulmonary vasodilator for PPHN, constitutes, alongside supportive therapy, the basis of its treatment. However, nearly 40% of infants are iNO resistant. The cornerstones of increased PVR in PPHN are pulmonary vasoconstriction and vascular remodeling. A better understanding of PPHN pathophysiology may enlighten targeted and more effective therapies. Sildenafil, prostaglandins, milrinone, and bosentan, acting as vasodilators, besides glucocorticoids, playing a role on reducing inflammation, have all shown potential beneficial effects on newborns with PPHN. Furthermore, experimental evidence in PPHN animal models supports prospective use of emergent therapies, such as soluble guanylyl cyclase (sGC) activators/stimulators, l-citrulline, Rho-kinase inhibitors, peroxisome proliferator-activated receptor-γ (PPAR-γ) agonists, recombinant superoxide dismutase (rhSOD), tetrahydrobiopterin (BH4) analogs, ω-3 long-chain polyunsaturated fatty acids (LC-PUFAs), 5-HT2A receptor antagonists, and recombinant human vascular endothelial growth factor (rhVEGF). This review focuses on current knowledge on alternative and novel pathways involved in PPHN pathogenesis, as well as recent progress regarding experimental and clinical evidence on potential therapeutic approaches for PPHN.

Neutral endopeptidase inhibitors blunt kidney fibrosis by reducing myofibroblast formation

Kidney fibrosis is the common pathophysiological mechanism in end-stage renal disease characterized by excessive accumulation of myofibroblast-derived extracellular matrix. Natriuretic peptides have been demonstrated to have cyclic guanosine monophosphate (cGMP)-dependent anti-fibrotic properties likely due to interference with pro-fibrotic tissue growth factor β (TGF-β) signaling. However, in vivo, natriuretic peptides are rapidly degraded by neutral endopeptidases (NEP). In a unilateral ureteral obstruction (UUO) mouse model for kidney fibrosis we assessed the anti-fibrotic effects of SOL1, an orally active compound that inhibits NEP and endothelin-converting enzyme (ECE). Mice (n=10 per group) subjected to UUO were treated for 1 week with either solvent, NEP-/ECE-inhibitor SOL1 (two doses), reference NEP-inhibitor candoxatril or the angiotensin II receptor type 1 (AT₁₎-antagonist losartan. While NEP-inhibitors had no significant effect on blood pressure, they did increase urinary cGMP levels as well as endothelin-1 (ET-1) levels. Immunohistochemical staining revealed a marked decrease in renal collagen (∼55% reduction, P<0.05) and α-smooth muscle actin (α-SMA; ∼40% reduction, P<0.05). Moreover, the number of α-SMA positive cells in the kidneys of SOL1-treated groups inversely correlated with cGMP levels consistent with a NEP-dependent anti-fibrotic effect. To dissect the molecular mechanisms associated with the anti-fibrotic effects of NEP inhibition, we performed a 'deep serial analysis of gene expression (Deep SAGE)' transcriptome and targeted metabolomics analysis of total kidneys of all treatment groups. Pathway analyses linked increased cGMP and ET-1 levels with decreased nuclear receptor signaling (peroxisome proliferator-activated receptor [PPAR] and liver X receptor/retinoid X receptor [LXR/RXR] signaling) and actin cytoskeleton organization. Taken together, although our transcriptome and metabolome data indicate metabolic dysregulation, our data support the therapeutic potential of NEP inhibition in the treatment of kidney fibrosis via cGMP elevation and reduced myofibroblast formation.

Efficient Reconstitution of Hepatic Microvasculature by Endothelin Receptor Antagonism in Liver Sinusoidal Endothelial Cells

Reconstitution of healthy endothelial cells in vascular beds offers opportunities for mechanisms in tissue homeostasis, organ regeneration, and correction of deficient functions. Liver sinusoidal endothelial cells express unique functions, and their transplantation is relevant for disease models and for cell therapy. As molecular targets for improving transplanted cell engraftment and proliferation will be highly significant, this study determined whether ET_A/B receptor antagonism by the drug bosentan could overcome cell losses due to cell transplantation-induced cytotoxicity. Cell engraftment and proliferation assays were performed with healthy wild-type liver sinusoidal endothelial cells transplanted into the liver of dipeptidylpeptidase IV knockout mice. Transplanted cells were identified in tissues by enzyme histochemistry. Cells with prospective ET_A/B antagonism engrafted significantly better in hepatic sinusoids. Moreover, these cells underwent multiple rounds of division under liver repopulation conditions. The gains of ET_A/B antagonism resulted from benefits in cell viability and membrane integrity. Also, in bosentan-treated cells, mitochondrial homeostasis was better maintained with less oxidative stress and DNA damage after injuries. Intracellular effects of ET_A/B antagonism were transduced by conservation of ataxia telangiectasia mutated protein, which directs DNA damage response. Therefore, ET_A/B antagonism in donor cells will advance vascular reconstitution. Extensive experience with ET_A/B antagonists will facilitate translation in people.

Current and Future Treatments for Persistent Pulmonary Hypertension in the Newborn

Persistent pulmonary hypertension in newborn (PPHN) is a serious and possibly fatal syndrome characterized by sustained foetal elevation of pulmonary vascular resistance at birth. PPHN may manifest secondary to other conditions as meconium aspiration syndrome, infection and congenital diaphragmatic hernia. This MiniReview provides the reader with an overview of current and future treatment options for patients with PPHN without congenital diaphragmatic hernia. The study is based on systematic searches in the databases PubMed and Cochrane Library and registered studies on Clinicaltrials.gov investigating PPHN. Inhaled nitric oxide (iNO) is well documented for treatment of PPHN, but 30% fail to respond to iNO. Other current treatment options could be sildenafil, milrinone, prostaglandin analogues and bosentan. There are several ongoing trials with sildenafil, but evidence is lacking for the other treatments and/or for the combination with iNO. Currently, there is no evidence for effect in PPHN of other treatments, for example tadalafil, macitentan, ambrisentan, riociguat and selexipag used for pulmonary arterial hypertension in adults. Experimental studies in animal models for PPHN suggest effect of a series of approaches including recombinant human superoxide dismutase, L-citrulline, Rho-kinase inhibitors and peroxisome proliferator-activated receptor-γ agonists. We conclude that iNO is the most investigated and the only approved pulmonary vasodilator for infants with PPHN. In the iNO non-responders, sildenafil currently seems to be the best alternative either alone or in combination with iNO. Systematic and larger clinical studies are required for testing the other potential treatments of PPHN.

Causative Effects of Genetically Determined High Maternal/Fetal Endothelin-1 on Preeclampsia-Like Conditions in Mice

Endothelin-1 (ET-1) is implicated in the pathophysiology of preeclampsia. An association between an EDN1 gene polymorphism with high ET-1 and preeclampsia was reported in humans, but their cause and effect relationships have not been defined. We examined the pregnancy effects in mice with a modified Edn1 allele that increases mRNA stability and thus ET-1 production. Heterozygous Edn1^H/+ females showed no obvious abnormalities before pregnancy, but when mated with wild-type (WT) males developed a full spectrum of preeclampsia-like phenotypes, including increased systolic blood pressure, proteinuria, glomerular endotheliosis, and intrauterine fetal growth restriction. At 7.5 days post-coitus, the embryos from Edn1^H/+ dams, regardless of their Edn1 genotype, lagged 12 hours in development compared with embryos from WT dams, had disoriented ectoplacental cones, and retained high E-cadherin expression. In contrast, WT females mated with Edn1^H/+ males, which also carried half of the fetuses with Edn1^H/+ genotype, showed a mild systolic blood pressure increase only. These WT dams had 2× higher plasma soluble fms-like tyrosine kinase-1 than WT dams mated with WT males. In human first trimester trophoblast cells, pharmacological doses of ET-1 increased the cellular sFlt1 transcripts and protein secretion via both type A and B ET-1 receptors. Our data demonstrate that high maternal ET-1 production causes preeclampsia-like phenotypes during pregnancy, affecting both initial stage of trophoblast differentiation/invasion and maternal peripheral vasculature during late gestation. High fetal ET-1 production, however, could cause increased soluble fms-like tyrosine kinase-1 in the maternal circulation and contribute to blood pressure elevation.

Dual ETA/ETB blockade with macitentan improves both vascular remodeling and angiogenesis in pulmonary arterial hypertension

Dysregulated metabolism and rarefaction of the capillary network play a critical role in pulmonary arterial hypertension (PAH) etiology. They are associated with a decrease in perfusion of the lungs, skeletal muscles, and right ventricle (RV). Previous studies suggested that endothelin-1 (ET-1) modulates both metabolism and angiogenesis. We hypothesized that dual ET_A/ET_B receptors blockade improves PAH by improving cell metabolism and promoting angiogenesis. Five weeks after disease induction, Sugen/hypoxic rats presented severe PAH with pulmonary artery (PA) remodeling, RV hypertrophy and capillary rarefaction in the lungs, RV, and skeletal muscles (microCT angiogram, lectin perfusion, CD31 staining). Two-week treatment with dual ET_A/ET_B receptors antagonist macitentan (30 mg/kg/d) significantly improved pulmonary hemodynamics, PA vascular remodeling, and RV function and hypertrophy compared to vehicle-treated animals (all P = 0.05). Moreover, macitentan markedly increased lung, RV and quadriceps perfusion, and microvascular density (all P = 0.05). In vitro, these effects were associated with increases in oxidative phosphorylation (oxPhox) and markedly reduced cell proliferation of PAH-PA smooth muscle cells (PASMCs) treated with macitentan without affecting apoptosis. While macitentan did not affect oxPhox, proliferation, and apoptosis of PAH-PA endothelial cells (PAECs), it significantly improved their angiogenic capacity (tube formation assay). Exposure of control PASMC and PAEC to ET-1 fully mimicked the PAH cells phenotype, thus confirming that ET-1 is implicated in both metabolism and angiogenesis abnormalities in PAH. Dual ET_A/ET_B receptor blockade improved the metabolic changes involved in PAH-PASMCs' proliferation and the angiogenic capacity of PAH-PAEC leading to an increased capillary density in lungs, RV, and skeletal muscles.

MicroRNA-27a/b mediates endothelin-1-induced PPARγ reduction and proliferation of pulmonary artery smooth muscle cells

The down-regulation of peroxisome proliferator-activated receptor γ (PPARγ) expression has been found to correlate with the proliferation of pulmonary artery smooth muscle cells (PASMC), pulmonary vascular remodeling and pulmonary hypertension, while the molecular mechanisms underlying PPARγ reduction in PASMC remain largely unclear. The aim of the current study is to address this issue. Endothelin-1 (ET-1) dose- and time-dependently resulted in PPARγ reduction and proliferation of primary cultured rat PASMC, which was accompanied by the activation of nuclear factor-kappaB (NF-κB) and subsequent induction of microRNA-27a/b (miR-27a/b) expression. Chromatin immunoprecipitation assay revealed that NF-κB directly bound to the promoter regions of miR-27a/b. Luciferase reporter assay identified that miR-27a/b directly regulates the expression of PPARγ in PASMC. Further study indicated that the presence of either NF-κB inhibitor pyrrolidinedithiocarbamate or prior silencing miR-27a/b with anti-miRNA oligonucleotides suppressed ET-1-induced PPARγ reduction and proliferation of PASMC, while overexpression of miR-27a/b reduced PPARγ expression and enhanced PASMC proliferation. Taken together, our study demonstrates that ET-1 stimulates miR-27a/b expression by activation of the NF-κB pathway, which in turn results in PPARγ reduction and contributes to ET-1-induced PASMC proliferation.

Endothelin-1-Rho kinase interactions impair lung structure and cause pulmonary hypertension after bleomycin exposure in neonatal rat pups

Bronchopulmonary dysplasia (BPD) is the chronic lung disease associated with premature birth, characterized by impaired vascular and alveolar growth. In neonatal rats bleomycin decreases lung growth and causes pulmonary hypertension (PH), which is poorly responsive to nitric oxide. In the developing lung, through Rho kinase (ROCK) activation, ET-1 impairs endothelial cell function; however, whether ET-1-ROCK interactions contribute to impaired vascular and alveolar growth in experimental BPD is unknown. Neonatal rats were treated daily with intraperitoneal bleomycin with and without selective ETA (BQ123/BQ610) and ETB (BQ788) receptor blockers, nonselective ET receptor blocker (ETRB) (bosentan), or fasudil (ROCK inhibitor). At day 14, lungs were harvested for morphometrics, and measurements of Fulton's index (RV/LV+S), medial wall thickness (MWT), and vessel density. Lung ET-1 protein and ROCK activity (phospho-MYPT-1:total MYPT-1 ratio) were also measured by Western blot analysis. Bleomycin increased lung ET-1 protein expression by 65%, RV/LV+S by 60%, mean linear intercept (MLI) by 212%, and MWT by 140% and decreased radial alveolar count (RAC) and vessel density by 40 and 44%, respectively (P < 0.01 for each comparison). After bleomycin treatment, fasudil and bosentan partially restored RAC and vessel density and decreased MLI, RV/LV+S, and MWT to normal values. Bleomycin increased ROCK activity by 120%, which was restored to normal values by bosentan but not selective ETRB. We conclude that ET-1-ROCK interactions contribute to decreased alveolar and vascular growth and PH in experimental BPD. We speculate that nonselective ETRB and ROCK inhibitors may be effective in the treatment of infants with BPD and PH.

Update on novel targets and potential treatment avenues in pulmonary hypertension

Pulmonary hypertension (PH) is a condition marked by a combination of constriction and remodeling within the pulmonary vasculature. It remains a disease without a cure, as current treatments were developed with a focus on vasodilatory properties but do not reverse the remodeling component. Numerous recent advances have been made in the understanding of cellular processes that drive pathologic remodeling in each layer of the vessel wall as well as the accompanying maladaptive changes in the right ventricle. In particular, the past few years have yielded much improved insight into the pathways that contribute to altered metabolism, mitochondrial function, and reactive oxygen species signaling and how these pathways promote the proproliferative, promigratory, and antiapoptotic phenotype of the vasculature during PH. Additionally, there have been significant advances in numerous other pathways linked to PH pathogenesis, such as sex hormones and perivascular inflammation. Novel insights into cellular pathology have suggested new avenues for the development of both biomarkers and therapies that will hopefully bring us closer to the elusive goal: a therapy leading to reversal of disease.

Emerging concepts in smooth muscle contributions to airway structure and function: implications for health and disease

Airway structure and function are key aspects of normal lung development, growth, and aging, as well as of lung responses to the environment and the pathophysiology of important diseases such as asthma, chronic obstructive pulmonary disease, and fibrosis. In this regard, the contributions of airway smooth muscle (ASM) are both functional, in the context of airway contractility and relaxation, as well as synthetic, involving production and modulation of extracellular components, modulation of the local immune environment, cellular contribution to airway structure, and, finally, interactions with other airway cell types such as epithelium, fibroblasts, and nerves. These ASM contributions are now found to be critical in airway hyperresponsiveness and remodeling that occur in lung diseases. This review emphasizes established and recent discoveries that underline the central role of ASM and sets the stage for future research toward understanding how ASM plays a central role by being both upstream and downstream in the many interactive processes that determine airway structure and function in health and disease.

Identification of HIF-2α-regulated genes that play a role in human microvascular endothelial sprouting during prolonged hypoxia in vitro

During prolonged hypoxic conditions, endothelial cells change their gene expression to adjust to the low oxygen environment. This process is mainly regulated by the hypoxia-inducible factors, HIF-1α and HIF-2α. Although endothelial cells do not form sprouts during prolonged hypoxic culturing, silencing of HIF-2α partially restores sprout formation. The present study identifies novel HIF-2α-target genes that may regulate endothelial sprouting during prolonged hypoxia. The gene expression profile of primary human microvascular endothelial cells (hMVECs) that were cultured at 20 % oxygen was compared to hMVECs that were cultured at 1 % oxygen for 14 days by using genome-wide RNA-sequencing. The differentially regulated genes in hypoxia were compared to the genes that were differentially regulated upon silencing of HIF-2α in hypoxia. Surprisingly, KEGG pathway analysis showed that metabolic pathways were enriched within genes upregulated in response to hypoxia and enriched within genes downregulated upon HIF-2α silencing. Moreover, 51 HIF-2α-regulated genes were screened for their role in endothelial sprouting in hypoxia, of which four genes ARRDC3, MME, PPARG and RALGPS2 directly influenced endothelial sprouting during prolonged hypoxic culturing. The manipulation of specific downstream targets of HIF-2α provides a new, but to be further evaluated, perspective for restoring reduced neovascularization in several pathological conditions, such as diabetic ulcers or other chronic wounds, for improvement of vascularization of implanted tissue-engineered scaffolds.

Pharmacologic strategies in neonatal pulmonary hypertension other than nitric oxide

Inhaled nitric oxide (iNO) is approved for use in persistent pulmonary hypertension of the newborn (PPHN) but does not lead to sustained improvement in oxygenation in one-third of patients with PPHN. Inhaled NO is less effective in the management of PPHN secondary to congenital diaphragmatic hernia (CDH), extreme prematurity, and bronchopulmonary dysplasia (BPD). Intravenous pulmonary vasodilators such as prostacyclin, alprostadil, sildenafil, and milrinone have been successfully used in PPHN resistant to iNO. Oral pulmonary vasodilators such as endothelin receptor antagonist bosentan and phosphodiesterase-5 inhibitors such as sildenafil and tadalafil are used both during acute and chronic phases of PPHN. In the absence of infection, glucocorticoids may also be effective in PPHN. Many of these pharmacologic agents are not approved for use in PPHN and our knowledge is based on case reports and small trials. Large multicenter randomized controlled trials with long-term follow-up are required to evaluate alternate pharmacologic strategies in PPHN.

Loss of PPARγ in endothelial cells leads to impaired angiogenesis

Tie2-promoter-mediated loss of peroxisome proliferator-activated receptor gamma (PPARγ, also known as PPARG) in mice leads to osteopetrosis and pulmonary arterial hypertension. Vascular disease is associated with loss of PPARγ in pulmonary microvascular endothelial cells (PMVEC); we evaluated the role of PPARγ in PMVEC functions, such as angiogenesis and migration. The role of PPARγ in angiogenesis was evaluated in Tie2CrePPARγ(flox/flox) and wild-type mice, and in mouse and human PMVECs. RNA sequencing and bioinformatic approaches were utilized to reveal angiogenesis-associated targets for PPARγ. Tie2CrePPARγ(flox/flox) mice showed an impaired angiogenic capacity. Analysis of endothelial progenitor-like cells using bone marrow transplantation combined with evaluation of isolated PMVECs revealed that loss of PPARγ attenuates the migration and angiogenic capacity of mature PMVECs. PPARγ-deficient human PMVECs showed a similar migration defect in culture. Bioinformatic and experimental analyses newly revealed E2F1 as a target of PPARγ in the regulation of PMVEC migration. Disruption of the PPARγ-E2F1 axis was associated with a dysregulated Wnt pathway related to the GSK3B interacting protein (GSKIP). In conclusion, PPARγ plays an important role in sustaining angiogenic potential in mature PMVECs through E2F1-mediated gene regulation.

Recent advances in the mechanisms of lung alveolarization and the pathogenesis of bronchopulmonary dysplasia

Alveolarization is the process by which the alveoli, the principal gas exchange units of the lung, are formed. Along with the maturation of the pulmonary vasculature, alveolarization is the objective of late lung development. The terminal airspaces that were formed during early lung development are divided by the process of secondary septation, progressively generating an increasing number of alveoli that are of smaller size, which substantially increases the surface area over which gas exchange can take place. Disturbances to alveolarization occur in bronchopulmonary dysplasia (BPD), which can be complicated by perturbations to the pulmonary vasculature that are associated with the development of pulmonary hypertension. Disturbances to lung development may also occur in persistent pulmonary hypertension of the newborn in term newborn infants, as well as in patients with congenital diaphragmatic hernia. These disturbances can lead to the formation of lungs with fewer and larger alveoli and a dysmorphic pulmonary vasculature. Consequently, affected lungs exhibit a reduced capacity for gas exchange, with important implications for morbidity and mortality in the immediate postnatal period and respiratory health consequences that may persist into adulthood. It is the objective of this Perspectives article to update the reader about recent developments in our understanding of the molecular mechanisms of alveolarization and the pathogenesis of BPD.

Impaired pulmonary vascular development in bronchopulmonary dysplasia

Bronchopulmonary dysplasia (BPD), the chronic lung disease associated with preterm birth, results from the disruption of normal pulmonary vascular and alveolar growth. Though BPD was once described as primarily due to postnatal injury from mechanical ventilation and oxygen therapy after preterm birth, it is increasingly appreciated that BPD results from antenatal and perinatal factors that interrupt lung development in infants born at the extremes of prematurity. The lung in BPD consists of a simplified parenchymal architecture that limits gas exchange and leads to increased cardiopulmonary morbidity and mortality. This review outlines recent advances in the understanding of pulmonary vascular development and describes how the disruption of these mechanisms results in BPD. We point to future therapies that may augment postnatal vascular growth to prevent and treat this severe chronic lung disease.

Altered pulmonary artery endothelial-smooth muscle cell interactions in experimental congenital diaphragmatic hernia

BACKGROUND

Pulmonary hypertension (PH) secondary to vascular remodeling contributes to poor outcomes in congenital diaphragmatic hernia (CDH), however mechanisms responsible are unknown. We hypothesized that pulmonary artery endothelial cell (PAEC) dysfunction contributes to smooth muscle cell (SMC) hyperplasia in experimental CDH.

METHODS

PAEC and SMC were isolated from fetal sheep with experimental CDH and controls. SMC growth was assessed alone and with SOD plus catalase and during coculture with control or CDH PAEC with and without ET-1 siRNA transfection. ET-1 protein was measured in PAEC and SMC lysates and supernatant. ROS production was measured in normal and CDH PAECs with and without ET-1 siRNA. PAEC growth and tube formation were measured with SOD plus catalase.

RESULTS

CDH SMC growth was decreased and increased with coculture with CDH PAEC more than control PAEC. Treatment of CDH PAEC with SOD plus catalase or ET-1 siRNA prevented the increase in SMC growth seen with coculture. ET-1 protein was increased in CDH PAEC and SMC. ROS production was increased in CDH PAEC and decreased with ET-1 SiRNA. SOD plus catalase restored CDH PAEC growth and tube formation.

CONCLUSION

PAEC dysfunction in experimental CDH increases SMC proliferation via ET-1 induced ROS production by PAEC.

NEMO modulates radiation-induced endothelial senescence of human umbilical veins through NF-κB signal pathway

Recently several laboratories have reported that radiation induces senescence in endothelial cells. Senescent cells can secrete multiple growth-regulatory proteins, some of which affect tumor growth, survival, invasion or angiogenesis. The purpose of this study was to explore the mechanisms of radiation-induced senescence and its effects on angiogenesis in human umbilical vein endothelial cells (HUVECs). HUVECs were either pretreated with or without PS1145 prior to irradiation with 0-8 Gy. PS1145 is a novel, highly specific small-molecule inhibitor of nuclear factor kappa B essential modulator (NEMO). MTT assays showed that in HUVECs untreated with PS1145, there was an increase in the number of radiation-induced senescence-like endothelial cells 5 days after 8 Gy irradiation, while pretreatment with PS1145 significantly ameliorated the induction in senescence of HUVECs compared to the control group. Electrophoretic mobility shift assay (EMSA) showed that pretreatment with PS1145 inhibited the radiation-induced NF-κB activation, which regulates cell fate in response to genotoxic stress. In addition, Western blotting demonstrated less translocation of p65 from cytoplasm to nucleus. Furthermore, real-time polymerase chain reaction (PCR) showed that pretreatment with PS1145 inhibited the increase of mRNA expressions of interleukin-6 (IL-6) and p53-induced death domain (PIDD) protein, which have been show to play crucial roles in both senescence and apoptosis (P < 0.05). TUNEL staining revealed an increase in apoptotic HUVECs in the group pretreated with PS1145 after irradiation. The series of functional assays further showed that radiation-induced senescence-like HUVECs had malfunctions in migration, invasion and formation of capillary-like structures, compared with the sham-irradiated and untreated, irradiated groups. Taken together, these findings indicate that the angiogenic capacity of radiation-induced senescence-like HUVECs decreased, and that irradiation caused vascular endothelial cells to gain a senescence-like phenotype through the DSB/NEMO/NF-κB signal pathway. The data suggests that NEMO may be a critical switch that regulates cellular senescence and apoptosis caused by exposure to radiation, and provides new clues for the clinical potential of the combination of radiotherapy and angiogenesis inhibitors.

Adaptation and remodelling of the pulmonary circulation in pulmonary hypertension

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