Phenotypically Silent Bone Morphogenetic Protein Receptor 2 Mutations Predispose Rats to Inflammation-Induced Pulmonary Arterial Hypertension by Enhancing the Risk for Neointimal Transformation

MSC-derived exosomes attenuates pulmonary hypertension via inhibiting pulmonary vascular remodeling

BACKGROUND

Pulmonary hypertension (PH) is a serious cardiopulmonary disease with significant morbidity and mortality. Vascular obstruction leads to a continuous increase in pulmonary vascular resistance, vascular remodeling, and right ventricular hypertrophy and failure, which are the main pathological features of PH. Currently, the treatments for PH are very limited, so new methods are urgently needed. Msenchymal stem cells-derived exosomes have been shown to have significant therapeutic effects in PH, however, the mechanism still very blurry. Here, we investigated the possible mechanism by which umbilical cord mesenchymal stem cell-derived exosomes (hUC-MSC-EXO) inhibited monocrotaline (MCT)-induced pulmonary vascular remodeling in a rat model of PH by regulating the NF-κB/BMP signaling pathway. Our data revealed that hUC-MSC-EXO could significantly attenuate MCT-induced PH and right ventricular hypertrophy. Moreover, the protein expression level of BMPR2, BMP-4, BMP-9 and ID1 was significantly increased, but NF-κB p65, p-NF-κB-p65 and BMP antagonists Gremlin-1 was increased in vitro and vivo. Collectively, this study revealed that the mechanism of hUC-MSC-EXO attenuates pulmonary hypertension may be related to inhibition of NF-κB signaling to further activation of BMP signaling. The present study provided a promising therapeutic strategy for PH vascular remodeling.

STING Contributes to Pulmonary Hypertension by Targeting IFN and BMPR2 Signaling through Regulating of F2RL3

Pulmonary hypertension (PH) is an incurable disease characterized by pulmonary vascular remodeling. Endothelial injury and inflammation are the key triggers of disease initiation. Recent findings suggest that STING (stimulator of IFN genes) activation plays a critical role in endothelial dysfunction and IFN signaling. Here, we investigated the involvement of STING in the pathogenesis of PH. Patients with PH and rodent PH model samples, a Sugen 5416/hypoxia PH model, and pulmonary artery endothelial cells (PAECs) were used to evaluate the hypothesis. We found that the cyclic guanosine monophosphate-AMP synthase-STING signaling pathway was activated in lung tissues from rodent PH models and patients with PH and in TNF-α-induced PAECs in vitro. Specifically, STING expression was significantly elevated in the endothelial cells in PH disease settings. In the Sugen 5416/hypoxia mouse model, genetic knockout or pharmacological inhibition of STING prevented the progression of PH. Functionally, knockdown of STING reduced the proliferation and migration of PAECs. Mechanistically, STING transcriptionally regulates its binding partner F2RL3 (F2R-like thrombin or trypsin receptor 3) through the STING-NF-κB axis, which activated IFN signaling and repressed BMPR2 (bone morphogenetic protein receptor 2) signaling both in vitro and in vivo. Further analysis revealed that F2RL3 expression was increased in PH settings and identified negative feedback regulation of F2RL3/BMPR2 signaling. Accordingly, a positive correlation of expression amounts between STING and F2RL3/IFN-stimulated genes was observed in vivo. Our findings suggest that STING activation in PAECs plays a critical role in the pathobiology of PH. Targeting STING may be a promising therapeutic strategy for preventing the development of PH.

Emerging connectivity of programmed cell death pathways and pulmonary vascular remodelling during pulmonary hypertension

Pulmonary hypertension (PH) is a chronic progressive vascular disease characterized by abnormal pulmonary vascular resistance and pulmonary artery pressure. The major structural alteration during PH is pulmonary vascular remodelling, which is mainly caused by the imbalance between proliferation and apoptosis of pulmonary vascular cells. Previously, it was thought that apoptosis was the only type of programmed cell death (PCD). Soon afterward, other types of PCD have been identified, including autophagy, pyroptosis, ferroptosis and necroptosis. In this review, we summarize the role of the above five forms of PCD in mediating pulmonary vascular remodelling, and discuss their guiding significance for PH treatment. The current review could provide a better understanding of the correlation between PCD and pulmonary vascular remodelling, contributing to identify new PCD-associated drug targets for PH.

Pulmonary Hypertension Induced by Right Pulmonary Artery Occlusion: Hemodynamic Consequences of Bmpr2 Mutation

BACKGROUND

The primary genetic risk factor for heritable pulmonary arterial hypertension is the presence of monoallelic mutations in the BMPR2 gene. The incomplete penetrance of BMPR2 mutations implies that additional triggers are necessary for pulmonary arterial hypertension occurrence. Pulmonary artery stenosis directly raises pulmonary artery pressure, and the redirection of blood flow to unobstructed arteries leads to endothelial dysfunction and vascular remodeling. We hypothesized that right pulmonary artery occlusion (RPAO) triggers pulmonary hypertension (PH) in rats with Bmpr2 mutations.

METHODS AND RESULTS

Male and female rats with a 71 bp monoallelic deletion in exon 1 of Bmpr2 and their wild-type siblings underwent acute and chronic RPAO. They were subjected to full high-fidelity hemodynamic characterization. We also examined how chronic RPAO can mimic the pulmonary gene expression pattern associated with installed PH in unobstructed territories. RPAO induced precapillary PH in male and female rats, both acutely and chronically. Bmpr2 mutant and male rats manifested more severe PH compared with their counterparts. Although wild-type rats adapted to RPAO, Bmpr2 mutant rats experienced heightened mortality. RPAO induced a decline in cardiac contractility index, particularly pronounced in male Bmpr2 rats. Chronic RPAO resulted in elevated pulmonary IL-6 (interleukin-6) expression and decreased Gdf2 expression (corrected P value<0.05 and log2 fold change>1). In this context, male rats expressed higher pulmonary levels of endothelin-1 and IL-6 than females.

CONCLUSIONS

Our novel 2-hit rat model presents a promising avenue to explore the adaptation of the right ventricle and pulmonary vasculature to PH, shedding light on pertinent sex- and gene-related effects.

Reversal of pulmonary veno-occlusive disease phenotypes by inhibition of the integrated stress response

Pulmonary veno-occlusive disease (PVOD) is a rare form of pulmonary hypertension arising from EIF2AK4 gene mutations or mitomycin C (MMC) administration. The lack of effective PVOD therapies is compounded by a limited understanding of the mechanisms driving vascular remodeling in PVOD. Here we show that administration of MMC in rats mediates activation of protein kinase R (PKR) and the integrated stress response (ISR), which leads to the release of the endothelial adhesion molecule vascular endothelial (VE) cadherin (VE-Cad) in complex with RAD51 to the circulation, disruption of endothelial barrier and vascular remodeling. Pharmacological inhibition of PKR or ISR attenuates VE-Cad depletion, elevation of vascular permeability and vascular remodeling instigated by MMC, suggesting potential clinical intervention for PVOD. Finally, the severity of PVOD phenotypes was increased by a heterozygous BMPR2 mutation that truncates the carboxyl tail of the receptor BMPR2, underscoring the role of deregulated bone morphogenetic protein signaling in the development of PVOD.

Systemic Sclerosis-Associated Pulmonary Arterial Hypertension: From Bedside to Bench and Back Again

Systemic sclerosis (SSc) is a heterogeneous disease characterized by autoimmunity, vasculopathy, and fibrosis which affects the skin and internal organs. One key aspect of SSc vasculopathy is pulmonary arterial hypertension (SSc-PAH) which represents a leading cause of morbidity and mortality in patients with SSc. The pathogenesis of pulmonary hypertension is complex, with multiple vascular cell types, inflammation, and intracellular signaling pathways contributing to vascular pathology and remodeling. In this review, we focus on shared molecular features of pulmonary hypertension and those which make SSc-PAH a unique entity. We highlight advances in the understanding of the clinical and translational science pertinent to this disease. We first review clinical presentations and phenotypes, pathology, and novel biomarkers, and then highlight relevant animal models, key cellular and molecular pathways in pathogenesis, and explore emerging treatment strategies in SSc-PAH.

Unlocking the Future: Pluripotent Stem Cell-Based Lung Repair

The human respiratory system is susceptible to a variety of diseases, ranging from chronic obstructive pulmonary disease (COPD) and pulmonary fibrosis to acute respiratory distress syndrome (ARDS). Today, lung diseases represent one of the major challenges to the health care sector and represent one of the leading causes of death worldwide. Current treatment options often focus on managing symptoms rather than addressing the underlying cause of the disease. The limitations of conventional therapies highlight the urgent clinical need for innovative solutions capable of repairing damaged lung tissue at a fundamental level. Pluripotent stem cell technologies have now reached clinical maturity and hold immense potential to revolutionize the landscape of lung repair and regenerative medicine. Meanwhile, human embryonic (HESCs) and human-induced pluripotent stem cells (hiPSCs) can be coaxed to differentiate into lung-specific cell types such as bronchial and alveolar epithelial cells, or pulmonary endothelial cells. This holds the promise of regenerating damaged lung tissue and restoring normal respiratory function. While methods for targeted genetic engineering of hPSCs and lung cell differentiation have substantially advanced, the required GMP-grade clinical-scale production technologies as well as the development of suitable preclinical animal models and cell application strategies are less advanced. This review provides an overview of current perspectives on PSC-based therapies for lung repair, explores key advances, and envisions future directions in this dynamic field.

Reversal of pulmonary veno-occlusive disease phenotypes by inhibition of the integrated stress response

Pulmonary veno-occlusive disease (PVOD) is a rare form of pulmonary hypertension arising from EIF2AK4 gene mutations or mitomycin C (MMC) administration. The lack of effective PVOD therapies is compounded by a limited understanding of the mechanisms driving the vascular remodeling in PVOD. We show that the administration of MMC in rats mediates the activation of protein kinase R (PKR) and the integrated stress response (ISR), which lead to the release of the endothelial adhesion molecule VE-Cadherin in the complex with Rad51 to the circulation, disruption of endothelial barrier, and vascular remodeling. Pharmacological inhibition of PKR or ISR attenuates the depletion of VE-Cadherin, elevation of vascular permeability, and vascular remodeling instigated by MMC, suggesting potential clinical intervention for PVOD. Finally, the severity of PVOD phenotypes was increased by a heterozygous BMPR2 mutation that truncates the carboxyl tail of BMPR2, underscoring the role of deregulated BMP signal in the development of PVOD.

Pursuing functional biomarkers in complex disease: Focus on pulmonary arterial hypertension

A major gap in diagnosis, classification, risk stratification, and prediction of therapeutic response exists in pulmonary arterial hypertension (PAH), driven in part by a lack of functional biomarkers that are also disease-specific. In this regard, leveraging big data-omics analyses using innovative approaches that integrate network medicine and machine learning correlated with clinically useful indices or risk stratification scores is an approach well-positioned to advance PAH precision medicine. For example, machine learning applied to a panel of 48 cytokines, chemokines, and growth factors could prognosticate PAH patients with immune-dominant subphenotypes at elevated or low-risk for mortality. Here, we discuss strengths and weaknesses of the most current studies evaluating omics-derived biomarkers in PAH. Progress in this field is offset by studies with small sample size, pervasive limitations in bioinformatics, and lack of standardized methods for data processing and interpretation. Future success in this field, in turn, is likely to hinge on mechanistic validation of data outputs in order to couple functional biomarker data with target-specific therapeutics in clinical practice.

Pathophysiological Involvement of Mast Cells and the Lipid Mediators in Pulmonary Vascular Remodeling

Mast cells are responsible for IgE-dependent allergic responses, but they also produce various bioactive mediators and contribute to the pathogenesis of various cardiovascular diseases, including pulmonary hypertension (PH). The importance of lipid mediators in the pathogenesis of PH has become evident in recent years, as exemplified by prostaglandin I2, the most central therapeutic target in pulmonary arterial hypertension. New bioactive lipids other than eicosanoids have also been identified that are associated with the pathogenesis of PH. However, it remains largely unknown how mast cell-derived lipid mediators are involved in pulmonary vascular remodeling. Recently, it has been demonstrated that mast cells produce epoxidized n-3 fatty acid (n-3 epoxides) in a degranulation-independent manner, and that n-3 epoxides produced by mast cells regulate the abnormal activation of pulmonary fibroblasts and suppress the progression of pulmonary vascular remodeling. This review summarizes the role of mast cells and bioactive lipids in the pathogenesis of PH. In addition, we introduce the pathophysiological role and therapeutic potential of n-3 epoxides, a mast cell-derived novel lipid mediator, in the pulmonary vascular remodeling in PH. Further knowledge of mast cells and lipid mediators is expected to lead to the development of innovative therapies targeting pulmonary vascular remodeling.

A p53-TLR3 axis ameliorates pulmonary hypertension by inducing BMPR2 via IRF3

Pulmonary arterial hypertension (PAH) features pathogenic and abnormal endothelial cells (ECs), and one potential origin is clonal selection. We studied the role of p53 and toll-like receptor 3 (TLR3) in clonal expansion and pulmonary hypertension (PH) via regulation of bone morphogenetic protein (BMPR2) signaling. ECs of PAH patients had reduced p53 expression. EC-specific p53 knockout exaggerated PH, and clonal expansion reduced p53 and TLR3 expression in rat lung CD117+ ECs. Reduced p53 degradation (Nutlin 3a) abolished clonal EC expansion, induced TLR3 and BMPR2, and ameliorated PH. Polyinosinic/polycytidylic acid [Poly(I:C)] increased BMPR2 signaling in ECs via enhanced binding of interferon regulatory factor-3 (IRF3) to the BMPR2 promoter and reduced PH in p53-/- mice but not in mice with impaired TLR3 downstream signaling. Our data show that a p53/TLR3/IRF3 axis regulates BMPR2 expression and signaling in ECs. This link can be exploited for therapy of PH.

Iron metabolism disorder regulated by BMP signaling in hypoxic pulmonary hypertension

BACKGROUNDS AND AIMS

Unexplained iron deficiency is associated with poorer survival in patients with pulmonary hypertension (PH). Bone morphogenetic protein (BMP) signaling and BMP protein type II receptor (BMPR2) expression are important in the pathogenesis of PH. BMP6 in hepatocytes is a central transcriptional regulator of the iron hormone hepcidin that controls systemic iron balance. This study aimed to investigate the effects of BMP signaling on iron metabolism and its implication in hypoxia-induced PH.

METHODS AND RESULTS

PH was induced in Sprague-Dawley Rats under hypoxia for 4 weeks. Compared with the control group, right ventricular systolic pressure and right ventricle hypertrophy index were both markedly increased, and serum iron level was significantly decreased with iron metabolic disorder in the hypoxia group. In cultured human pulmonary artery endothelial cells (HPAECs), hypoxia increased oxidative stress and apoptosis, which were reversed by supplementation with Fe agent. Meanwhile, iron chelator deferoxamine triggered oxidative stress and apoptosis in HPAECs, and treatment with antioxidant alleviated iron-deficiency-induced apoptosis by reducing reactive oxygen species production. Expression of hepcidin, BMP6 and hypoxia-inducible factor (HIF)-1α were significantly upregulated, while expression of BMPR2 was downregulated in hepatocytes in the hypoxia group, both in vivo and in vitro. Expression of hepcidin and HIF-1α were significantly increased by BMP6, while pretreatment with siRNA-BMPR2 augmented the enhanced expression of hepcidin and HIF-1α induced by BMP6.

CONCLUSIONS

Iron deficiency promoted oxidative stress and apoptosis in HPAECs in hypoxia-induced PH, and enhanced expression of hepcidin regulated by BMP6/BMPR2 signaling may contribute to iron metabolic disorder.

Transcription factors in the pathogenesis of pulmonary arterial hypertension-Current knowledge and therapeutic potential

Pulmonary arterial hypertension (PAH) is a disease characterized by elevated pulmonary vascular resistance and pulmonary artery pressure. Mortality remains high in severe cases despite significant advances in management and pharmacotherapy. Since currently approved PAH therapies are unable to significantly reverse pathological vessel remodeling, novel disease-modifying, targeted therapeutics are needed. Pathogenetically, PAH is characterized by vessel wall cell dysfunction with consecutive remodeling of the pulmonary vasculature and the right heart. Transcription factors (TFs) regulate the process of transcribing DNA into RNA and, in the pulmonary circulation, control the response of pulmonary vascular cells to macro- and microenvironmental stimuli. Often, TFs form complex protein interaction networks with other TFs or co-factors to allow for fine-tuning of gene expression. Therefore, identification of the underlying molecular mechanisms of TF (dys-)function is essential to develop tailored modulation strategies in PAH. This current review provides a compendium-style overview of TFs and TF complexes associated with PAH pathogenesis and highlights their potential as targets for vasculoregenerative or reverse remodeling therapies.

Sox17 Deficiency Promotes Pulmonary Arterial Hypertension via HGF/c-Met Signaling

BACKGROUND

In large-scale genomic studies, Sox17, an endothelial-specific transcription factor, has been suggested as a putative causal gene of pulmonary arterial hypertension (PAH); however, its role and molecular mechanisms remain to be elucidated. We investigated the functional impacts and acting mechanisms of impaired Sox17 (SRY-related HMG-box17) pathway in PAH and explored its potential as a therapeutic target.

METHODS

In adult mice, Sox17 deletion in pulmonary endothelial cells (ECs) induced PAH under hypoxia with high penetrance and severity, but not under normoxia.

RESULTS

Key features of PAH, such as hypermuscularization, EC hyperplasia, and inflammation in lung arterioles, right ventricular hypertrophy, and elevated pulmonary arterial pressure, persisted even after long rest in normoxia. Mechanistically, transcriptomic profiling predicted that the combination of Sox17 deficiency and hypoxia activated c-Met signaling in lung ECs. HGF (hepatocyte grow factor), a ligand of c-Met, was upregulated in Sox17-deficient lung ECs. Pharmacologic inhibition of HGF/c-Met signaling attenuated and reversed the features of PAH in both preventive and therapeutic settings. Similar to findings in animal models, Sox17 levels in lung ECs were repressed in 26.7% of PAH patients (4 of 15), while those were robust in all 14 non-PAH controls. HGF levels in pulmonary arterioles were increased in 86.7% of patients with PAH (13 of 15), but none of the controls showed that pattern.

CONCLUSIONS

The downregulation of Sox17 levels in pulmonary arterioles increases the susceptibility to PAH, particularly when exposed to hypoxia. Our findings suggest the reactive upregulation of HGF/c-Met signaling as a novel druggable target for PAH treatment.

New progress in diagnosis and treatment of pulmonary arterial hypertension

Pulmonary arterial hypertension (PAH) is a progressive disease. Although great progress has been made in its diagnosis and treatment in recent years, its mortality rate is still very significant. The pathophysiology and pathogenesis of PAH are complex and involve endothelial dysfunction, chronic inflammation, smooth muscle cell proliferation, pulmonary arteriole occlusion, antiapoptosis and pulmonary vascular remodeling. These factors will accelerate the progression of the disease, leading to poor prognosis. Therefore, accurate etiological diagnosis, treatment and prognosis judgment are particularly important. Here, we systematically review the pathophysiology, diagnosis, genetics, prognosis and treatment of PAH.

Evolving Concepts in Endothelial Pathobiology of Pulmonary Arterial Hypertension

Pulmonary arterial hypertension (PAH) is a deadly disease, characterized by increased vascular resistance, pulmonary arteriolar loss, and occlusive arterial remodeling, leading to eventual right heart failure. Evidence increasingly points to the pulmonary endothelium as a central actor in PAH. Endothelial cell apoptosis can result directly in distal lung arteriolar pruning and indirectly in the formation of complex and occlusive arterial lesions, reflecting an imbalance between endothelial injury and repair in the development and progression of PAH. Many of the mutations implicated in PAH are in genes, which are predominantly, or solely, expressed in endothelial cells, and the endothelium is a major target for therapeutic interventions to restore BMP signaling. We explore how arterial pruning can promote the emergence of occlusive arterial remodeling mediated by ongoing endothelial injury secondary to hemodynamic perturbation and pathological increases in luminal shear stress. The emerging role of endothelial cell senescence is discussed in the transition from reversible to irreversible arterial remodeling in advanced PAH, and we review the sometimes conflicting evidence that female sex hormones can both protect or promote vascular changes in disease. Finally, we explore the contribution of the endothelium to metabolic changes and the altered inflammatory and immune state in the PAH lung, focusing on the role of excessive TGFβ signaling. Given the complexity of the endothelial pathobiology of PAH, we anticipate that emerging technologies that allow the study of molecular events at a single cell level will provide answers to many of the questions raised in this review.

Sotatercept analog suppresses inflammation to reverse experimental pulmonary arterial hypertension

Sotatercept is an activin receptor type IIA-Fc (ActRIIA-Fc) fusion protein that improves cardiopulmonary function in patients with pulmonary arterial hypertension (PAH) by selectively trapping activins and growth differentiation factors. However, the cellular and molecular mechanisms of ActRIIA-Fc action are incompletely understood. Here, we determined through genome-wide expression profiling that inflammatory and immune responses are prominently upregulated in the lungs of a Sugen-hypoxia rat model of severe angio-obliterative PAH, concordant with profiles observed in PAH patients. Therapeutic treatment with ActRIIA-Fc-but not with a vasodilator-strikingly reversed proinflammatory and proliferative gene expression profiles and normalized macrophage infiltration in diseased rodent lungs. Furthermore, ActRIIA-Fc normalized pulmonary macrophage infiltration and corrected cardiopulmonary structure and function in Bmpr2 haploinsufficient mice subjected to hypoxia, a model of heritable PAH. Three high-affinity ligands of ActRIIA-Fc each induced macrophage activation in vitro, and their combined immunoneutralization in PAH rats produced cardiopulmonary benefits comparable to those elicited by ActRIIA-Fc. Our results in complementary experimental and genetic models of PAH reveal therapeutic anti-inflammatory activities of ActRIIA-Fc that, together with its known anti-proliferative effects on vascular cell types, could underlie clinical activity of sotatercept as either monotherapy or add-on to current PAH therapies.

Insights on the Gut-Mesentery-Lung Axis in Pulmonary Arterial Hypertension: A Poorly Investigated Crossroad

Pulmonary arterial hypertension (PAH) is a life-threatening disease characterized by the hyperproliferation of vascular cells, including smooth muscle and endothelial cells. Hyperproliferative cells eventually obstruct the lung vasculature, leading to irreversible lesions that collectively drive pulmonary pressure to life-threatening levels. Although the primary cause of PAH is not fully understood, several studies have indicated it results from chronic pulmonary inflammation, such as observed in response to pathogens' infection. Curiously, infection by the intravascular parasite Schistosoma mansoni recapitulates several aspects of the widespread pulmonary inflammation that leads to development of chronic PAH. Globally, >200 million people are currently infected by Schistosoma spp., with about 5% developing PAH (Sch-PAH) in response to the parasite egg-induced obliteration and remodeling of the lung vasculature. Before their settling into the lungs, Schistosoma eggs are released inside the mesenteric veins, where they either cross the intestinal wall and disturb the gut microbiome or migrate to other organs, including the lungs and liver, increasing pressure. Spontaneous or surgical liver bypass via collateral circulation alleviates the pressure in the portal system; however, it also allows the translocation of pathogens, toxins, and antigens into the lungs, ultimately causing PAH. This brief review provides an overview of the gut-mesentery-lung axis during PAH, with a particular focus on Sch-PAH, and attempts to delineate the mechanism by which pathogen translocation might contribute to the onset of chronic pulmonary vascular diseases.

The Latest in Animal Models of Pulmonary Hypertension and Right Ventricular Failure

Pulmonary hypertension (PH) describes heterogeneous population of patients with a mean pulmonary arterial pressure >20 mm Hg. Rarely, PH presents as a primary disorder but is more commonly part of a complex phenotype associated with comorbidities. Regardless of the cause, PH reduces life expectancy and impacts quality of life. The current clinical classification divides PH into 1 of 5 diagnostic groups to assign treatment. There are currently no pharmacological cures for any form of PH. Animal models are essential to help decipher the molecular mechanisms underlying the disease, to assign genotype-phenotype relationships to help identify new therapeutic targets, and for clinical translation to assess the mechanism of action and putative efficacy of new therapies. However, limitations inherent of all animal models of disease limit the ability of any single model to fully recapitulate complex human disease. Within the PH community, we are often critical of animal models due to the perceived low success upon clinical translation of new drugs. In this review, we describe the characteristics, advantages, and disadvantages of existing animal models developed to gain insight into the molecular and pathological mechanisms and test new therapeutics, focusing on adult forms of PH from groups 1 to 3. We also discuss areas of improvement for animal models with approaches combining several hits to better reflect the clinical situation and elevate their translational value.

New Mutations and Pathogenesis of Pulmonary Hypertension: Progress and Puzzles in Disease Pathogenesis

Pulmonary arterial hypertension (PAH) is a complex multifactorial disease with poor prognosis characterized by functional and structural alterations of the pulmonary circulation causing marked increase in pulmonary vascular resistance, ultimately leading to right heart failure and death. Mutations in the gene encoding BMPRII-a receptor for the TGF-β (transforming growth factor-beta) superfamily-account for over 70% of families with PAH and ≈20% of sporadic cases. In recent years, however, less common or rare mutations in other genes have been identified. This review will consider how these newly discovered PAH genes could help to provide a better understanding of the molecular and cellular bases of the maintenance of the pulmonary vascular integrity, as well as their role in the PAH pathogenesis underlying occlusion of arterioles in the lung. We will also discuss how insights into the genetic contributions of these new PAH-related genes may open up new therapeutic targets for this, currently incurable, cardiopulmonary disorder.

CRISPR-mediated Bmpr2 point mutation exacerbates late pulmonary vasculopathy and reduces survival in rats with experimental pulmonary hypertension

Background

Patients with pulmonary arterial hypertension (PAH) carrying bone morphogenetic protein receptor type 2 (Bmpr2) mutations present earlier with severe hemodynamic compromise and have poorer survival outcomes than those without mutation. The mechanism underlying the worsening clinical phenotype of PAH with Bmpr2 mutations has been largely unaddressed in rat models of pulmonary hypertension (PH) because of the difficulty in reproducing progressive PH in mice and genetic modification in rats. We tested whether a clinically-relevant Bmpr2 mutation affects the progressive features of monocrotaline (MCT) induced-PH in rats.

Methods

A monoallelic single nucleotide insertion in exon 1 of Bmpr2 (+/44insG) was generated in rats using clustered regularly interspaced short palindromic repeats (CRISPR)/CRISPR-associated protein 9, then PH, pulmonary vascular disease (PVD) and survival after MCT injection with or without a phosphodiesterase type 5 inhibitor, tadalafil, administration were assessed.

Results

The +/44insG rats had reduced BMPR2 signalling in the lungs compared with wild-type. PH and PVD assessed at 3-weeks after MCT injection were similar in wild-type and +/44insG rats. However, survival at 4-weeks after MCT injection was significantly reduced in +/44insG rats. Among the rats surviving at 4-weeks after MCT administration, +/44insG rats had increased weight ratio of right ventricle to left ventricle plus septum (RV/[LV + S]) and % medial wall thickness (MWT) in pulmonary arteries (PAs). Immunohistochemical analysis showed increased vessels with Ki67-positive cells in the lungs, decreased mature and increased immature smooth muscle cell phenotype markers in the PAs in +/44insG rats compared with wild-type at 3-weeks after MCT injection. Contraction of PA in response to prostaglandin-F2α and endothelin-1 were significantly reduced in the +/44insG rats. The +/44insG rats that had received tadalafil had a worse survival with a significant increase in RV/(LV + S), %MWT in distal PAs and RV myocardial fibrosis compared with wild-type.

Conclusions

The present study demonstrates that the Bmpr2 mutation promotes dedifferentiation of PA smooth muscle cells, late PVD and RV myocardial fibrosis and adversely impacts both the natural and post-treatment courses of MCT-PH in rats with significant effects only in the late stages and warrants preclinical studies using this new genetic model to optimize treatment outcomes of heritable PAH.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12931-022-02005-w.

Mineralocorticoid receptor antagonist treatment of established pulmonary arterial hypertension improves interventricular dependence in the SU5416-hypoxia rat model

Treatment with mineralocorticoid receptor (MR) antagonists beginning at the outset of disease, or early thereafter, prevents pulmonary vascular remodeling in preclinical models of pulmonary arterial hypertension (PAH). However, the efficacy of MR blockade in established disease, a more clinically relevant condition, remains unknown. Therefore, we investigated the effectiveness of two MR antagonists, eplerenone (EPL) and spironolactone (SPL), after the development of severe right ventricular (RV) dysfunction in the rat SU5416-hypoxia (SuHx) PAH model. Cardiac magnetic resonance imaging (MRI) in SuHx rats at the end of week 5, before study treatment, confirmed features of established disease including reduced RV ejection fraction and RV hypertrophy, pronounced septal flattening with impaired left ventricular filling and reduced cardiac index. Five weeks of treatment with either EPL or SPL improved left ventricular filling and prevented the further decline in cardiac index compared with placebo. Interventricular septal displacement was reduced by EPL whereas SPL effects were similar, but not significant. Although MR antagonists did not significantly reduce pulmonary artery pressure or vessel remodeling in SuHx rats with established disease, animals with higher drug levels had lower pulmonary pressures. Consistent with effects on cardiac function, EPL treatment tended to suppress MR and proinflammatory gene induction in the RV. In conclusion, MR antagonist treatment led to modest, but consistent beneficial effects on interventricular dependence after the onset of significant RV dysfunction in the SuHx PAH model. These results suggest that measures of RV structure and/or function may be useful endpoints in clinical trials of MR antagonists in patients with PAH.

A second hit? Pulmonary arterial hypertension, BMPR2 mutation and exposure to prescription‐amphetamines

The second hit hypothesis in pulmonary hypertension refers to the development of pulmonary vascular disease in individuals at risk, after an additional exposure or “hit” to factors with potential injury to the pulmonary circulation, such as drugs or toxins. We here present a case of severe pulmonary hypertension diagnosed during the third trimester of pregnancy, in a patient with familial history of pulmonary hypertension, found to have a heterozygous mutation in the BMPR2 gene, who also had chronic exposure to prescription amphetamines. We hypothesize that exposure to prescription amphetamines could act as a second hit of pulmonary vascular injury in individuals at risk of pulmonary vascular disease.

Dysregulated Immunity in Pulmonary Hypertension: From Companion to Composer

Pulmonary hypertension (PH) represents a grave condition associated with high morbidity and mortality, emphasizing a desperate need for innovative and targeted therapeutic strategies. Cumulative evidence suggests that inflammation and dysregulated immunity interdependently affect maladaptive organ perfusion and congestion as hemodynamic hallmarks of the pathophysiology of PH. The role of altered cellular and humoral immunity in PH gains increasing attention, especially in pulmonary arterial hypertension (PAH), revealing novel mechanistic insights into the underlying immunopathology. Whether these immunophysiological aspects display a universal character and also hold true for other types of PH (e.g., PH associated with left heart disease, PH-LHD), or whether there are unique immunological signatures depending on the underlying cause of disease are points of consideration and discussion. Inflammatory mediators and cellular immune circuits connect the local inflammatory landscape in the lung and heart through inter-organ communication, involving, e.g., the complement system, sphingosine-1-phosphate (S1P), cytokines and subsets of, e.g., monocytes, macrophages, natural killer (NK) cells, dendritic cells (DCs), and T- and B-lymphocytes with distinct and organ-specific pro- and anti-inflammatory functions in homeostasis and disease. Perivascular macrophage expansion and monocyte recruitment have been proposed as key pathogenic drivers of vascular remodeling, the principal pathological mechanism in PAH, pinpointing toward future directions of anti-inflammatory therapeutic strategies. Moreover, different B- and T-effector cells as well as DCs may play an important role in the pathophysiology of PH as an imbalance of T-helper-17-cells (T_H17) activated by monocyte-derived DCs, a potentially protective role of regulatory T-cells (T_reg) and autoantibody-producing plasma cells occur in diverse PH animal models and human PH. This article highlights novel aspects of the innate and adaptive immunity and their interaction as disease mediators of PH and its specific subtypes, noticeable inflammatory mediators and summarizes therapeutic targets and strategies arising thereby.

Therapeutic Approaches for Treating Pulmonary Arterial Hypertension by Correcting Imbalanced TGF-β Superfamily Signaling

Pulmonary arterial hypertension (PAH) is a rare disease characterized by high blood pressure in the pulmonary circulation driven by pathological remodeling of distal pulmonary arteries, leading typically to death by right ventricular failure. Available treatments improve physical activity and slow disease progression, but they act primarily as vasodilators and have limited effects on the biological cause of the disease—the uncontrolled proliferation of vascular endothelial and smooth muscle cells. Imbalanced signaling by the transforming growth factor-β (TGF-β) superfamily contributes extensively to dysregulated vascular cell proliferation in PAH, with overactive pro-proliferative SMAD2/3 signaling occurring alongside deficient anti-proliferative SMAD1/5/8 signaling. We review the TGF-β superfamily mechanisms underlying PAH pathogenesis, superfamily interactions with inflammation and mechanobiological forces, and therapeutic strategies under development that aim to restore SMAD signaling balance in the diseased pulmonary arterial vessels. These strategies could potentially reverse pulmonary arterial remodeling in PAH by targeting causative mechanisms and therefore hold significant promise for the PAH patient population.

Pulmonary Arterial Hypertension: Emerging Principles of Precision Medicine across Basic Science to Clinical Practice

Pulmonary arterial hypertension (PAH) is an enigmatic and deadly vascular disease with no known cure. Recent years have seen rapid advances in our understanding of the molecular underpinnings of PAH, with an expanding knowledge of the molecular, cellular, and systems-level drivers of disease that are being translated into novel therapeutic modalities. Simultaneous advances in clinical technology have led to a growing list of tools with potential application to diagnosis and phenotyping. Guided by fundamental biology, these developments hold the potential to usher in a new era of personalized medicine in PAH with broad implications for patient management and great promise for improved outcomes.

Cell-to-Cell Crosstalk: A New Insight into Pulmonary Hypertension

Pulmonary hypertension (PH) is a disease with high pulmonary arterial pressure, pulmonary vasoconstriction, pulmonary vascular remodeling, and microthrombosis in complex plexiform lesions, but it has been unclear of the exact mechanism of PH. A new understanding of the pathogenesis of PH is occurred and focused on the role of crosstalk between the cells on pulmonary vessels and pulmonary alveoli. It was found that the crosstalks among the endothelial cells, smooth muscle cells, fibroblasts, pericytes, alveolar epithelial cells, and macrophages play important roles in cell proliferation, migration, inflammation, and so on. Therefore, the heterogeneity of multiple pulmonary blood vessels and alveolar cells and tracking the transmitters of cell communication could be conducive to the further insights into the pathogenesis of PH to discover the potential therapeutic targets for PH.

Smouldering fire or conflagration? An illustrated update on the concept of inflammation in pulmonary arterial hypertension

Pulmonary arterial hypertension (PAH) is a rare condition that is characterised by a progressive increase of pulmonary vascular resistances that leads to right ventricular failure and death, if untreated. The underlying narrowing of the pulmonary vasculature relies on several independent and interdependent biological pathways, such as genetic predisposition and epigenetic changes, imbalance of vasodilating and vasoconstrictive mediators, as well as dysimmunity and inflammation that will trigger endothelial dysfunction, smooth muscle cell proliferation, fibroblast activation and collagen deposition. Progressive constriction of the pulmonary vasculature, in turn, initiates and sustains hypertrophic and maladaptive myocardial remodelling of the right ventricle. In this review, we focus on the role of inflammation and dysimmunity in PAH which is generally accepted today, although existing PAH-specific medical therapies still lack targeted immune-modulating approaches.

Single-cell RNA sequencing reveals that BMPR2 mutation regulates right ventricular function via ID genes

Mutations in bone morphogenetic protein type II receptor (BMPR2) have been found in patients with congenital heart disease-associated pulmonary arterial hypertension (CHD-PAH). Our study aimed to clarify whether deficient BMPR2 signalling acts through downstream effectors, inhibitors of DNA-binding proteins (IDs), during heart development to contribute to the progress of PAH in CHD patients. To confirm that IDs are downstream effectors of BMPR2 signalling in cardiac mesoderm progenitors (CMPs) and contribute to PAH, we generated Cardiomyocytes (CMs)-specific Id 1/3 knockout mice (Ids cDKO), and 12/25 developed mild PAH with altered haemodynamic indices and pulmonary vascular remodelling. Moreover, we generated ID1 and ID3 double-knockout (IDs KO) human embryonic stem cells that recapitulated the BMPR2 signalling deficiency of CHD-PAH iPSCs. CMs differentiated from induced pluripotent stem cells (iPSCs) derived from CHD-PAH patients with BMPR mutations exhibited dysfunctional cardiac differentiation and reduced Ca²⁺ transients, as evidenced by confocal microscopy experiments. Smad1/5 phosphorylation and ID1 and ID3 expression were reduced in CHD-PAH iPSCs and in Bmpr2 ^+/- rat right ventricles. Moreover, Ultrasound revealed that 33% of Ids cDKO mice had detectable defects in their ventricular septum and pulmonary regurgitation. CMs isolated from the mouse right ventricles also showed reduced Ca²⁺ transients and shortened sarcomeres. Single-cell RNA(scRNA)-seq analysis revealed impaired differentiation of CMPs and downregulated USP9X expression in IDs KO cells compared with wild-type (WT) cells. We found that BMPR2 signals through IDs and USP9X to regulate cardiac differentiation, and the loss of ID1 and ID3 expression contributes to CM dysfunction in CHD-PAH patients with BMPR2 mutations.

Gene Therapy for Cardiovascular Disease: Basic Research and Clinical Prospects

In recent years, the vital role of genetic factors in human diseases have been widely recognized by scholars with the deepening of life science research, accompanied by the rapid development of gene-editing technology. In early years, scientists used homologous recombination technology to establish gene knock-out and gene knock-in animal models, and then appeared the second-generation gene-editing technology zinc-finger nucleases (ZFNs) and transcription activator-like effector nucleases (TALENs) that relied on nucleic acid binding proteins and endonucleases and the third-generation gene-editing technology that functioned through protein-nucleic acids complexes-CRISPR/Cas9 system. This holds another promise for refractory diseases and genetic diseases. Cardiovascular disease (CVD) has always been the focus of clinical and basic research because of its high incidence and high disability rate, which seriously affects the long-term survival and quality of life of patients. Because some inherited cardiovascular diseases do not respond well to drug and surgical treatment, researchers are trying to use rapidly developing genetic techniques to develop initial attempts. However, significant obstacles to clinical application of gene therapy still exists, such as insufficient understanding of the nature of cardiovascular disease, limitations of genetic technology, or ethical concerns. This review mainly introduces the types and mechanisms of gene-editing techniques, ethical concerns of gene therapy, the application of gene therapy in atherosclerosis and inheritable cardiovascular diseases, in-stent restenosis, and delivering systems.

BMPR2 promoter methylation and its expression in valvular heart disease complicated with pulmonary artery hypertension

Valvular heart disease (VHD) is a common heart disease that affects blood flow. It usually requires heart surgery. Valvular heart disease complicated with pulmonary artery hypertension (VHD-PAH) may be lethal due to heart failure that results from increased heart burden. It is important for these patients to seek early treatment in order to minimize the heart damage. However, there is no reliable diagnosis method in VHD. In this study, we found DNA methylation was increased at the promoter of BMPR2 gene in the VHD patients compared with the healthy controls. This finding was confirmed by an independent cohort study of VHD patients and healthy controls. In addition, BMPR2 mRNA levels were reduced in the plasma of the VHD patients. There is strong correlation between BMPR2 promoter DNA methylation and the severity of VHD. Indeed, we found that both BMPR2 promoter DNA methylation and BMPR2 mRNA levels in the plasma are good biomarkers of VHD by themselves, with the respective AUC value of 0.879 and 0.725, respectively. When they were used in combination, the diagnostic value was even better, with the AUC value of 0.93. Consistent with the results in the VHD patients, we observed decreased BMPR2 and increased fibrosis in the lung of a PAH model mouse. BMPR2 was also decreased in the hearts of the PAH mice, whereas BMP4 was increased. Furthermore, BMPR2 was reduced in the heart valve tissue samples of human VHD patients after valve replacement with moderate/severe PAH compared with those with mild PAH. There was also increased apoptosis in the hearts of the PAH mice. BMPR2 promoter DNA methylation and its expression appear to be good biomarkers for VHD. Our results also suggest that DNA methylation may cause PAH through deregulation of BMP signaling and increased apoptosis.

The roles of immune system and autoimmunity in pulmonary arterial hypertension: A Review

Pulmonary arterial hypertension (PAH) is a chronic disease characterized by increased pulmonary artery pressure which if left untreated, can lead to poor quality of life and ultimately death. It is a group of conditions and includes idiopathic PAH, familial/hereditary PAH and associated PAH. The condition has been studied for many years and its association with the immune system and in particular autoimmunity has been investigated. The mechanisms for the pathobiology of PAH are unclear although research has highlighted the role of adaptive and innate immune systems in its development. Diagnostics and therapeutic approaches range from cytokine treatments to the use of immunomodulating drugs, although there is still scope for improvements in the field. This article discusses the mechanisms linked to PAH, its association with other conditions and recent therapeutic interventions.

Clinical application of pulmonary vascular resistance in patients with pulmonary arterial hypertension

Pulmonary arterial hypertension is a type of malignant pulmonary vascular disease, which is mainly caused by the increase of pulmonary vascular resistance due to the pathological changes of the pulmonary arteriole itself, which eventually leads to right heart failure and death. As one of the diagnostic indicators of hemodynamics, pulmonary vascular resistance plays an irreplaceable role in the pathophysiology, diagnosis and treatment of pulmonary arterial hypertension. It provides more references for the evaluation of pulmonary arterial hypertension patients. This article summarizes the clinical application of pulmonary vascular resistance in patients with pulmonary arterial hypertension.

Sevoflurane prevents pulmonary vascular remodeling and right ventricular dysfunction in pulmonary arterial hypertension in rats

BACKGROUND

The cardioprotective properties of sevoflurane have been reported in studies of the left ventricle. However, whether this volatile anesthetic would also be beneficial for pulmonary vascular remodeling and associated right ventricular hypertrophy (RVH) remained to be explored. Here, we investigated the potential benefit of sevoflurane to right heart function in experimental pulmonary arterial hypertension (PAH).

METHODS

Adult Wistar rats received one dose peritoneal injection of monocrotaline (MCT, 60 mg/kg) or the equal volume of normal saline. Two weeks later, rats were treated with sevoflurane or sham exposure. PAH status and cardiac function were assessed by echocardiography weekly, and the body weight (BW) was monitored every week. After 6 weeks of exercise, Fulton's index calculation, histological observation, IL-6 and TNF-α immunohistochemical analyses, evaluation of MDA, SOD and GSH-Px levels and NF-κB and MAPK active determination were performed in lung and RV tissue samples.

RESULTS

MCT induced pulmonary vascular remodeling, RVH, increased Fulton's index (P<0.01), and right ventricular failure (RVF) in rats. Animals inhaled sevoflurane had an increased cardiac output (P<0.05) and lower incidence of RVF (P<0.05). Also, these animals had a reduced RVEDD, RVWTd and PAID (P<0.05), increased PV (P<0.05), reduced wall thickness and vascular wall area of pulmonary small vascular (vascular external diameter 50-150 um) (P<0.01), reduced RV fibrosis, and increased RV cardiomyocyte area (P<0.01). Furthermore, sevoflurane reduced IL-6 and TNF-α expression in lungs and heart (P<0.01), decreased level of MDA (P<0.01) and increased activity of SOD and GSH-Px (P<0.01). In addition, it decreased the activities of NF-κB and MAPK pathways (P<0.01).

CONCLUSION

Sevoflurane reduces pulmonary vascular remodeling and RVH in PAH induced by MCT in rats. This effect is likely due to down-regulation of inflammatory factors IL-6 and TNF-α, reduced level of oxidative stress and the inhibition of NF-κB and MAPK pathways.

Role of the Immune System Elements in Pulmonary Arterial Hypertension

Pulmonary arterial hypertension (PAH) is a relatively rare disease, but, today, its incidence tends to increase. The severe course of the disease and poor patient survival rate make PAH a major diagnostic and therapeutic challenge. For this reason, a thorough understanding of the pathogenesis of the disease is essential to facilitate the development of more effective therapeutic targets. Research shows that the development of PAH is characterized by a number of abnormalities within the immune system that greatly affect the progression of the disease. In this review, we present key data on the regulated function of immune cells, released cytokines and immunoregulatory molecules in the development of PAH, to help improve diagnosis and targeted immunotherapy.

Inhibition of the prolyl isomerase Pin1 improves endothelial function and attenuates vascular remodelling in pulmonary hypertension by inhibiting TGF-β signalling

Pulmonary arterial hypertension (PAH) is a devastating disease, characterized by obstructive pulmonary vascular remodelling ultimately leading to right ventricular (RV) failure and death. Disturbed transforming growth factor-β (TGF-β)/bone morphogenetic protein (BMP) signalling, endothelial cell dysfunction, increased proliferation of smooth muscle cells and fibroblasts, and inflammation contribute to this abnormal remodelling. Peptidyl-prolyl isomerase Pin1 has been identified as a critical driver of proliferation and inflammation in vascular cells, but its role in the disturbed TGF-β/BMP signalling, endothelial cell dysfunction, and vascular remodelling in PAH is unknown. Here, we report that Pin1 expression is increased in cultured pulmonary microvascular endothelial cells (MVECs) and lung tissue of PAH patients. Pin1 inhibitor, juglone significantly decreased TGF-β signalling, increased BMP signalling, normalized their hyper-proliferative, and inflammatory phenotype. Juglone treatment reversed vascular remodelling through reducing TGF-β signalling in monocrotaline + shunt-PAH rat model. Juglone treatment decreased Fulton index, but did not affect or harm cardiac function and remodelling in rats with RV pressure load induced by pulmonary artery banding. Our study demonstrates that inhibition of Pin1 reversed the PAH phenotype in PAH MVECs in vitro and in PAH rats in vivo, potentially through modulation of TGF-β/BMP signalling pathways. Selective inhibition of Pin1 could be a novel therapeutic option for the treatment of PAH.

Monocyte-released HERV-K dUTPase engages TLR4 and MCAM causing endothelial mesenchymal transition

We previously reported heightened expression of the human endogenous retroviral protein HERV-K deoxyuridine triphosphate nucleotidohydrolase (dUTPase) in circulating monocytes and pulmonary arterial (PA) adventitial macrophages of patients with PA hypertension (PAH). Furthermore, recombinant HERV-K dUTPase increased IL-6 in PA endothelial cells (PAECs) and caused pulmonary hypertension in rats. Here we show that monocytes overexpressing HERV-K dUTPase, as opposed to GFP, can release HERV-K dUTPase in extracellular vesicles (EVs) that cause pulmonary hypertension in mice in association with endothelial mesenchymal transition (EndMT) related to induction of SNAIL/SLUG and proinflammatory molecules IL-6 as well as VCAM1. In PAECs, HERV-K dUTPase requires TLR4-myeloid differentiation primary response-88 to increase IL-6 and SNAIL/SLUG, and HERV-K dUTPase interaction with melanoma cell adhesion molecule (MCAM) is necessary to upregulate VCAM1. TLR4 engagement induces p-p38 activation of NF-κB in addition to p-pSMAD3 required for SNAIL and pSTAT1 for IL-6. HERV-K dUTPase interaction with MCAM also induces p-p38 activation of NF-κB in addition to pERK1/2-activating transcription factor-2 (ATF2) to increase VCAM1. Thus in PAH, monocytes or macrophages can release HERV-K dUTPase in EVs, and HERV-K dUTPase can engage dual receptors and signaling pathways to subvert PAEC transcriptional machinery to induce EndMT and associated proinflammatory molecules.

Pulmonary Arterial Hypertension: Diagnosis, Treatment, and Novel Advances

The diagnosis and management of pulmonary arterial hypertension (PAH) includes several advances, such as a broader recognition of extrapulmonary vascular organ system involvement, validated point-of-care clinical assessment tools, and focus on the early initiation of multiple pharmacotherapeutics in appropriate patients. Indeed, a principal goal in PAH today is an early diagnosis for prompt initiation of treatment to achieve a minimal symptom burden; optimize the patient's biochemical, hemodynamic, and functional profile; and limit adverse events. To accomplish this end, clinicians must be familiar with novel risk factors and the revised hemodynamic definition for PAH. Fresh insights into the role of developmental biology (i.e., perinatal health) may also be useful for predicting incident PAH in early adulthood. Emergent or underused approaches to PAH management include a novel TGF-β ligand trap pharmacotherapy, remote pulmonary arterial pressure monitoring, next-generation imaging using inert gas-based magnetic resonance and other technologies, right atrial pacing, and pulmonary arterial denervation. These and other PAH state of the art advances are summarized here for the wider pulmonary medicine community.

Significance of BMPR2 mutations in pulmonary arterial hypertension

Pulmonary arterial hypertension (PAH) is a debilitating disease that results from progressive remodeling and inflammation of pulmonary arteries. PAH develops gradually, is difficult to diagnose, and has a high mortality rate. Although mutation in the bone morphogenetic protein receptor 2 (BMPR2) gene has been identified as the main genetic cause of PAH, the underlying pathways involving the pathophysiology of PAH are complex and still not fully understood. Endothelial dysfunction has been observed in PAH development that results in a multitude of disturbances in the cellular processes in pulmonary vessels. Changes in the pulmonary vasculature caused by the disruption of BMPR2 signaling are observed in three main vascular components; endothelial cells, smooth muscle cells, and fibroblasts. BMPR2 also has a prominent role in maintenance of the immune system. The disruption of BMPR2 signaling pathway causes an increased degree of inflammation and decreases the ability of the immune system to resolve it. Inflammatory processes and changes in pulmonary vasculature interact with one another, resulting in the progression of chronic PAH. In this review, we highlight the various components of vascular remodeling and immune response that are caused by disruption of BMPR2 signaling, including the clinical evidence and the prospects of these components as a potential target for PAH therapy. Indeed, development of drugs to target the pathogenic pathways involved in PAH may complement existing treatment regimens and improve patient prognosis.

ALDH1A3 Coordinates Metabolism With Gene Regulation in Pulmonary Arterial Hypertension

BACKGROUND

Metabolic alterations provide substrates that influence chromatin structure to regulate gene expression that determines cell function in health and disease. Heightened proliferation of smooth muscle cells (SMC) leading to the formation of a neointima is a feature of pulmonary arterial hypertension (PAH) and systemic vascular disease. Increased glycolysis is linked to the proliferative phenotype of these SMC.

METHODS

RNA sequencing was applied to pulmonary arterial SMC (PASMC) from PAH patients with and without a BMPR2 (bone morphogenetic receptor 2) mutation versus control PASMC to uncover genes required for their heightened proliferation and glycolytic metabolism. Assessment of differentially expressed genes established metabolism as a major pathway, and the most highly upregulated metabolic gene in PAH PASMC was aldehyde dehydrogenase family 1 member 3 (ALDH1A3), an enzyme previously linked to glycolysis and proliferation in cancer cells and systemic vascular SMC. We determined if these functions are ALDH1A3-dependent in PAH PASMC, and if ALDH1A3 is required for the development of pulmonary hypertension in a transgenic mouse. Nuclear localization of ALDH1A3 in PAH PASMC led us to determine whether and how this enzyme coordinately regulates gene expression and metabolism in PAH PASMC.

RESULTS

ALDH1A3 mRNA and protein were increased in PAH versus control PASMC, and ALDH1A3 was required for their highly proliferative and glycolytic properties. Mice with Aldh1a3 deleted in SMC did not develop hypoxia-induced pulmonary arterial muscularization or pulmonary hypertension. Nuclear ALDH1A3 converted acetaldehyde to acetate to produce acetyl coenzyme A to acetylate H3K27, marking active enhancers. This allowed for chromatin modification at NFYA (nuclear transcription factor Y subunit α) binding sites via the acetyltransferase KAT2B (lysine acetyltransferase 2B) and permitted NFY-mediated transcription of cell cycle and metabolic genes that is required for ALDH1A3-dependent proliferation and glycolysis. Loss of BMPR2 in PAH SMC with or without a mutation upregulated ALDH1A3, and transcription of NFYA and ALDH1A3 in PAH PASMC was β-catenin dependent.

CONCLUSIONS

Our studies have uncovered a metabolic-transcriptional axis explaining how dividing cells use ALDH1A3 to coordinate their energy needs with the epigenetic and transcriptional regulation of genes required for SMC proliferation. They suggest that selectively disrupting the pivotal role of ALDH1A3 in PAH SMC, but not endothelial cells, is an important therapeutic consideration.

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.

PPARγ-p53-Mediated Vasculoregenerative Program to Reverse Pulmonary Hypertension

RATIONALE

In pulmonary arterial hypertension (PAH), endothelial dysfunction and obliterative vascular disease are associated with DNA damage and impaired signaling of BMPR2 (bone morphogenetic protein type 2 receptor) via two downstream transcription factors, PPARγ (peroxisome proliferator-activated receptor gamma), and p53.

OBJECTIVE

We investigated the vasculoprotective and regenerative potential of a newly identified PPARγ-p53 transcription factor complex in the pulmonary endothelium.

METHODS AND RESULTS

In this study, we identified a pharmacologically inducible vasculoprotective mechanism in pulmonary arterial and lung MV (microvascular) endothelial cells in response to DNA damage and oxidant stress regulated in part by a BMPR2 dependent transcription factor complex between PPARγ and p53. Chromatin immunoprecipitation sequencing and RNA-sequencing established an inducible PPARγ-p53 mediated regenerative program regulating 19 genes involved in lung endothelial cell survival, angiogenesis and DNA repair including, EPHA2 (ephrin type-A receptor 2), FHL2 (four and a half LIM domains protein 2), JAG1 (jagged 1), SULF2 (extracellular sulfatase Sulf-2), and TIGAR (TP53-inducible glycolysis and apoptosis regulator). Expression of these genes was partially impaired when the PPARγ-p53 complex was pharmacologically disrupted or when BMPR2 was reduced in pulmonary artery endothelial cells (PAECs) subjected to oxidative stress. In endothelial cell-specific Bmpr2-knockout mice unable to stabilize p53 in endothelial cells under oxidative stress, Nutlin-3 rescued endothelial p53 and PPARγ-p53 complex formation and induced target genes, such as APLN (apelin) and JAG1, to regenerate pulmonary microvessels and reverse pulmonary hypertension. In PAECs from BMPR2 mutant PAH patients, pharmacological induction of p53 and PPARγ-p53 genes repaired damaged DNA utilizing genes from the nucleotide excision repair pathway without provoking PAEC apoptosis.

CONCLUSIONS

We identified a novel therapeutic strategy that activates a vasculoprotective gene regulation program in PAECs downstream of dysfunctional BMPR2 to rehabilitate PAH PAECs, regenerate pulmonary microvessels, and reverse disease. Our studies pave the way for p53-based vasculoregenerative therapies for PAH by extending the therapeutic focus to PAEC dysfunction and to DNA damage associated with PAH progression.

Targeting transforming growth factor-β receptors in pulmonary hypertension

The transforming growth factor-β (TGF-β) superfamily includes several groups of multifunctional proteins that form two major branches, namely the TGF-β-activin-nodal branch and the bone morphogenetic protein (BMP)-growth differentiation factor (GDF) branch. The response to the activation of these two branches, acting through canonical (small mothers against decapentaplegic (Smad) 2/3 and Smad 1/5/8, respectively) and noncanonical signalling pathways, are diverse and vary for different environmental conditions and cell types. An extensive body of data gathered in recent years has demonstrated a central role for the cross-talk between these two branches in a number of cellular processes, which include the regulation of cell proliferation and differentiation, as well as the transduction of signalling cascades for the development and maintenance of different tissues and organs. Importantly, alterations in these pathways, which include heterozygous germline mutations and/or alterations in the expression of several constitutive members, have been identified in patients with familial/heritable pulmonary arterial hypertension (PAH) or idiopathic PAH (IPAH). Consequently, loss or dysfunction in the delicate, finely-tuned balance between the TGF-β-activin-nodal branch and the BMP-GDF branch are currently viewed as the major molecular defect playing a critical role in PAH predisposition and disease progression. Here we review the role of the TGF-β-activin-nodal branch in PAH and illustrate how this knowledge has not only provided insight into understanding its pathogenesis, but has also paved the way for possible novel therapeutic approaches.

Endothelial Dysfunction in Pulmonary Hypertension: Cause or Consequence?

Pulmonary arterial hypertension (PAH) is a rare, complex, and progressive disease that is characterized by the abnormal remodeling of the pulmonary arteries that leads to right ventricular failure and death. Although our understanding of the causes for abnormal vascular remodeling in PAH is limited, accumulating evidence indicates that endothelial cell (EC) dysfunction is one of the first triggers initiating this process. EC dysfunction leads to the activation of several cellular signalling pathways in the endothelium, resulting in the uncontrolled proliferation of ECs, pulmonary artery smooth muscle cells, and fibroblasts, and eventually leads to vascular remodelling and the occlusion of the pulmonary blood vessels. Other factors that are related to EC dysfunction in PAH are an increase in endothelial to mesenchymal transition, inflammation, apoptosis, and thrombus formation. In this review, we outline the latest advances on the role of EC dysfunction in PAH and other forms of pulmonary hypertension. We also elaborate on the molecular signals that orchestrate EC dysfunction in PAH. Understanding the role and mechanisms of EC dysfunction will unravel the therapeutic potential of targeting this process in PAH.

NDUFA4L2 in smooth muscle promotes vascular remodeling in hypoxic pulmonary arterial hypertension

Pulmonary arterial hypertension (PAH) is characterized by a progressive increase in pulmonary vascular resistance and obliterative pulmonary vascular remodelling (PVR). The imbalance between the proliferation and apoptosis of pulmonary artery smooth muscle cells (PASMCs) is an important cause of PVR leading to PAH. Mitochondria play a key role in the production of hypoxia-induced pulmonary hypertension (HPH). However, there are still many issues worth studying in depth. In this study, we demonstrated that NADH dehydrogenase (ubiquinone) 1 alpha subcomplex 4 like 2 (NDUFA4L2) was a proliferation factor and increased in vivo and in vitro through various molecular biology experiments. HIF-1α was an upstream target of NDUFA4L2. The plasma levels of 4-hydroxynonene (4-HNE) were increased both in PAH patients and hypoxic PAH model rats. Knockdown of NDUFA4L2 decreased the levels of malondialdehyde (MDA) and 4-HNE in human PASMCs in hypoxia. Elevated MDA and 4-HNE levels might be associated with excessive ROS generation and increased expression of 5-lipoxygenase (5-LO) in hypoxia, but this effect was blocked by siNDUFA4L2. Further research found that p38-5-LO was a downstream signalling pathway of PASMCs proliferation induced by NDUFA4L2. Up-regulated NDUFA4L2 plays a critical role in the development of HPH, which mediates ROS production and proliferation of PASMCs, suggesting NDUFA4L2 as a potential new therapeutic target for PAH.