The BMP Receptor 2 in Pulmonary Arterial Hypertension: When and Where the Animal Model Matches the Patient

Effect of the TGF-β/BMP Signaling Pathway on the Proliferation of Yak Pulmonary Artery Smooth Muscle Cells under Hypoxic Conditions

To survive in low-oxygen environments, yaks effectively avoid hypoxia-induced pulmonary arterial hypertension through vascular remodeling. The TGF-β/BMP signaling pathway plays a key role in maintaining the homeostasis of pulmonary artery smooth muscle cells (PASMCs). However, little is known about the molecular regulatory mechanisms by which the TGF-β/BMP signaling pathway contributes to the proliferation of yak PASMCs. In this study, yak PASMCs were cultured in vitro, and a hypoxia model was constructed to investigate the effect of TGFβ/BMP signaling on yak PASMC proliferation. Hypoxia treatment increased the proliferation of yak PASMCs significantly. As the duration of hypoxia increased, the expression levels of TGF-β1 and the phosphorylation levels of Smad2/3 were upregulated significantly. The BMP signaling pathway was transiently activated by hypoxia, with increases in BMPR2 expression and Smad1/5 phosphorylation, and these changes were gradually reversed with prolonged hypoxia exposure. In addition, exogenous TGF-β1 activated the TGF-β signaling pathway, increased the phosphorylation levels of the downstream proteins Smad2 and Smad3, and increased the proliferation and migration rates of yak PASMCs significantly. Finally, treatment with noggin (an inhibitor of BMP signaling) significantly reduced BMPR2 protein expression levels and Smad1/5 phosphorylation levels and increased yak PASMC proliferation and migration rates. In summary, these results revealed that under hypoxic conditions, the dynamic regulation of the TGF-β/BMP signaling pathway promotes the proliferation of yak PASMCs.

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.

Endothelial Function in Pulmonary Arterial Hypertension: From Bench to Bedside

Pulmonary arterial hypertension is a complex pathology whose etiology is still not completely well clarified. The pathogenesis of pulmonary arterial hypertension involves different molecular mechanisms, with endothelial dysfunction playing a central role in disease progression. Both individual genetic predispositions and environmental factors seem to contribute to its onset. To further understand the complex relationship between endothelial and pulmonary hypertension and try to contribute to the development of future therapies, we report a comprehensive and updated review on endothelial function in pulmonary arterial hypertension.

The biased apelin receptor agonist, MM07, reverses Sugen/hypoxia-induced pulmonary arterial hypertension as effectively as the endothelin antagonist macitentan

Introduction: Pulmonary arterial hypertension (PAH) is characterised by endothelial dysfunction and pathological vascular remodelling, resulting in the occlusion of pulmonary arteries and arterioles, right ventricular hypertrophy, and eventually fatal heart failure. Targeting the apelin receptor with the novel, G protein-biased peptide agonist, MM07, is hypothesised to reverse the developed symptoms of elevated right ventricular systolic pressure and right ventricular hypertrophy. Here, the effects of MM07 were compared with the clinical standard-of-care endothelin receptor antagonist macitentan. Methods: Male Sprague-Dawley rats were randomised and treated with either normoxia/saline, or Sugen/hypoxia (SuHx) to induce an established model of PAH, before subsequent treatment with either saline, macitentan (30 mg/kg), or MM07 (10 mg/kg). Rats were then anaesthetised and catheterised for haemodynamic measurements, and tissues collected for histopathological assessment. Results: The SuHx/saline group presented with significant increases in right ventricular hypertrophy, right ventricular systolic pressure, and muscularization of pulmonary arteries compared to normoxic/saline controls. Critically, MM07 was as at least as effective as macitentan in significantly reversing detrimental structural and haemodynamic changes after 4 weeks of treatment. Discussion: These results support the development of G protein-biased apelin receptor agonists with improved pharmacokinetic profiles for use in human disease.

Sex-biased TGFβ signalling in pulmonary arterial hypertension

Pulmonary arterial hypertension (PAH) is a rare cardiovascular disorder leading to pulmonary hypertension and, often fatal, right heart failure. Sex differences in PAH are evident, which primarily presents with a female predominance and increased male severity. Disturbed signalling of the transforming growth factor-β (TGFβ) family and gene mutations in the bone morphogenetic protein receptor 2 (BMPR2) are risk factors for PAH development, but how sex-specific cues affect the TGFβ family signalling in PAH remains poorly understood. In this review, we aim to explore the sex bias in PAH by examining sex differences in the TGFβ signalling family through mechanistical and translational evidence. Sex hormones including oestrogens, progestogens, and androgens, can determine the expression of receptors (including BMPR2), ligands, and soluble antagonists within the TGFβ family in a tissue-specific manner. Furthermore, sex-related genetic processes, i.e. Y-chromosome expression and X-chromosome inactivation, can influence the TGFβ signalling family at multiple levels. Given the clinical and mechanistical similarities, we expect that the conclusions arising from this review may apply also to hereditary haemorrhagic telangiectasia (HHT), a rare vascular disorder affecting the TGFβ signalling family pathway. In summary, we anticipate that investigating the TGFβ signalling family in a sex-specific manner will contribute to further understand the underlying processes leading to PAH and likely HHT.

Human iPSCs as Model Systems for BMP-Related Rare Diseases

Disturbances in bone morphogenetic protein (BMP) signalling contribute to onset and development of a number of rare genetic diseases, including Fibrodysplasia ossificans progressiva (FOP), Pulmonary arterial hypertension (PAH), and Hereditary haemorrhagic telangiectasia (HHT). After decades of animal research to build a solid foundation in understanding the underlying molecular mechanisms, the progressive implementation of iPSC-based patient-derived models will improve drug development by addressing drug efficacy, specificity, and toxicity in a complex humanized environment. We will review the current state of literature on iPSC-derived model systems in this field, with special emphasis on the access to patient source material and the complications that may come with it. Given the essential role of BMPs during embryonic development and stem cell differentiation, gain- or loss-of-function mutations in the BMP signalling pathway may compromise iPSC generation, maintenance, and differentiation procedures. This review highlights the need for careful optimization of the protocols used. Finally, we will discuss recent developments towards complex in vitro culture models aiming to resemble specific tissue microenvironments with multi-faceted cellular inputs, such as cell mechanics and ECM together with organoids, organ-on-chip, and microfluidic technologies.

Human liver single nuclear RNA sequencing implicates BMPR2, GDF15, arginine, and estrogen in portopulmonary hypertension

Portopulmonary hypertension (PoPH) is a type of pulmonary vascular disease due to portal hypertension that exhibits high morbidity and mortality. The mechanisms driving disease are unknown, and transcriptional characteristics unique to the PoPH liver remain unexplored. Here, we apply single nuclear RNA sequencing to compare cirrhotic livers from patients with and without PoPH. We identify characteristics unique to PoPH in cells surrounding the central hepatic vein, including increased growth differentiation factor signaling, enrichment of the arginine biosynthesis pathway, and differential expression of the bone morphogenic protein type II receptor and estrogen receptor type I genes. These results provide insight into the transcriptomic characteristics of the PoPH liver and mechanisms by which PoPH cellular dysfunction might contribute to pulmonary vascular remodeling.

Differential expression spectrum and targeted gene prediction of tRNA-derived small RNAs in idiopathic pulmonary arterial hypertension

Background: Idiopathic pulmonary arterial hypertension (PAH) is a potentially fatal pulmonary vascular disease with an extremely poor natural course. The limitations of current treatment and the unclear etiology and pathogenesis of idiopathic PAH require new targets and avenues of exploration involved in the pathogenesis of PAH. tRNA-derived small RNAs (tsRNAs), a new type of small non-coding RNAs, have a significant part in the progress of diverse diseases. However, the potential functions behind tsRNAs in idiopathic PAH remain unknown. Methods: Small RNA microarray was implemented on three pairs of plasma of idiopathic PAH patients and healthy controls to investigate and compare tsRNAs expression profiles. Validation samples were used for real-time polymerase chain reaction (Real-time PCR) to verify several dysregulated tsRNAs. Bioinformatic analysis was adopted to determine potential target genes and mechanisms of the validated tsRNAs in PAH. Results: Microarray detected 816 statistically significantly dysregulated tsRNAs, of which 243 tsRNAs were upregulated and 573 were downregulated in PAH. Eight validated tsRNAs in the results of Real-time PCR were concordant with the small RNA microarray: four upregulated (tRF3a-AspGTC-9, 5'tiRNA-31-GluCTC-16, i-tRF-31:54-Val-CAC-1 and tRF3b-TyrGTA-4) and four downregulated (5'tiRNA-33-LysTTT-4, i-tRF-8:32-Val-AAC-2, i-tRF-2:30-His-GTG-1, and i-tRF-15:31-Lys-CTT-1). The Gene Ontology analysis has shown that the verified tsRNAs are related to cellular macromolecule metabolic process, regulation of cellular process, and regulation of cellular metabolic process. It is disclosed that potential target genes of verified tsRNAs are widely involved in PAH pathways by Kyoto Encyclopedia of Genes and Genomes. Conclusion: This study investigated tsRNA profiles in idiopathic PAH and found that the dysregulated tsRNAs may become a novel type of biomarkers and possible targets for PAH.

Antiproliferative effect of selexipag active metabolite MRE-269 on pulmonary arterial smooth muscle cells from patients with chronic thromboembolic pulmonary hypertension

Chronic thromboembolic pulmonary hypertension (CTEPH) is a group 4 pulmonary hypertension (PH) characterized by nonresolving thromboembolism in the central pulmonary artery and vascular occlusion in the proximal and distal pulmonary artery. Medical therapy is chosen for patients who are ineligible for pulmonary endarterectomy or balloon pulmonary angioplasty or who have symptomatic residual PH after surgery or intervention. Selexipag, an oral prostacyclin receptor agonist and potent vasodilator, was approved for CTEPH in Japan in 2021. To evaluate the pharmacological effect of selexipag on vascular occlusion in CTEPH, we examined how its active metabolite MRE-269 affects platelet-derived growth factor-stimulated pulmonary arterial smooth muscle cells (PASMCs) from CTEPH patients. MRE-269 showed a more potent antiproliferative effect on PASMCs from CTEPH patients than on those from normal subjects. DNA-binding protein inhibitor (ID) genes ID1 and ID3 were found by RNA sequencing and real-time quantitative polymerase chain reaction to be expressed at lower levels in PASMCs from CTEPH patients than in those from normal subjects and were upregulated by MRE-269 treatment. ID1 and ID3 upregulation by MRE-269 was blocked by co-incubation with a prostacyclin receptor antagonist, and ID1 knockdown by small interfering RNA transfection attenuated the antiproliferative effect of MRE-269. ID signaling may be involved in the antiproliferative effect of MRE-269 on PASMCs. This is the first study to demonstrate the pharmacological effects on PASMCs from CTEPH patients of a drug approved for the treatment of CTEPH. Both the vasodilatory and the antiproliferative effect of MRE-269 may contribute to the efficacy of selexipag in CTEPH.

New Drugs and Therapies in Pulmonary Arterial Hypertension

Pulmonary arterial hypertension is a chronic, progressive disorder of the pulmonary vasculature with associated pulmonary and cardiac remodeling. PAH was a uniformly fatal disease until the late 1970s, but with the advent of targeted therapies, the life expectancy of patients with PAH has now considerably improved. Despite these advances, PAH inevitably remains a progressive disease with significant morbidity and mortality. Thus, there is still an unmet need for the development of new drugs and other interventional therapies for the treatment of PAH. One shortcoming of currently approved vasodilator therapies is that they do not target or reverse the underlying pathogenesis of the disease process itself. A large body of evidence has evolved in the past two decades clarifying the role of genetics, dysregulation of growth factors, inflammatory pathways, mitochondrial dysfunction, DNA damage, sex hormones, neurohormonal pathways, and iron deficiency in the pathogenesis of PAH. This review focuses on newer targets and drugs that modify these pathways as well as novel interventional therapies in PAH.

Pulmonary Vascular Remodeling in Pulmonary Hypertension

Pulmonary vascular remodeling is the critical structural alteration and pathological feature in pulmonary hypertension (PH) and involves changes in the intima, media and adventitia. Pulmonary vascular remodeling consists of the proliferation and phenotypic transformation of pulmonary artery endothelial cells (PAECs) and pulmonary artery smooth muscle cells (PASMCs) of the middle membranous pulmonary artery, as well as complex interactions involving external layer pulmonary artery fibroblasts (PAFs) and extracellular matrix (ECM). Inflammatory mechanisms, apoptosis and other factors in the vascular wall are influenced by different mechanisms that likely act in concert to drive disease progression. This article reviews these pathological changes and highlights some pathogenetic mechanisms involved in the remodeling process.

Insights into bone morphogenetic proteins in cardiovascular diseases

Bone morphogenetic proteins (BMPs) are secretory proteins belonging to the transforming growth factor-β (TGF-β) superfamily. These proteins play important roles in embryogenesis, bone morphogenesis, blood vessel remodeling and the development of various organs. In recent years, as research has progressed, BMPs have been found to be closely related to cardiovascular diseases, especially atherosclerosis, vascular calcification, cardiac remodeling, pulmonary arterial hypertension (PAH) and hereditary hemorrhagic telangiectasia (HHT). In this review, we summarized the potential roles and related mechanisms of the BMP family in the cardiovascular system and focused on atherosclerosis and PAH.

Cold exposure aggravates pulmonary arterial hypertension through increased miR-146a-5p, miR-155-5p and cytokines TNF-α, IL-1β, and IL-6

BACKGROUND

Cold temperatures can aggravate pulmonary diseases and promote pulmonary arterial hypertension (PAH); however, the underlying mechanism has not been fully explored.

AIM

To explore the effect of chronic cold exposure on the production of inflammatory cytokines and microRNAs (miRNAs) in a monocrotaline (MCT)-induced PAH model.

METHODS

Male Sprague Dawley rats were divided into a Control (23.5 ± 2 °C), Cold (5.0 ± 1 °C for ten days), MCT (60 mg/kg body weight i.p.), and MCT + Cold (ten days of cold exposure after 3 weeks of MCT injection). Hemodynamic parameters, right ventricle (RV) hypertrophy, and pulmonary arterial medial wall thickness were determined. IL-1β, IL-6, and TNF-α levels were determined using western blotting. miR-21-5p and -3p, miR-146a-5p and -3p, and miR-155-5p and -3p and plasma extracellular vesicles (EVs) and mRNA expression of Cd68, Cd163, Bmpr2, Smad5, Tgfbr2, and Smad3 were determined using RT-qPCR.

RESULTS

The MCT + Cold group had aggravated RV hypertrophy hemodynamic parameters, and pulmonary arterial medial wall thickness. In lungs of the MCT + Cold, group the protein levels of TNF-α, IL-1β, and IL-6 were higher than those in the MCT group. The mRNA expression of Cd68 and Cd163 were higher in the MCT + Cold group. miR-146a-5p and miR-155-5p levels were higher in the plasma EVs and lungs of the MCT + Cold group. Cold exposure promoted a greater decrease in miR-21-5p, Bmpr2, Smad5, Tgfbr2, and Smad3 mRNA expression in lungs of the MCT + Cold group.

CONCLUSION

Cold exposure aggravates MCT-induced PAH with an increase in inflammatory marker and miRNA levels in the plasma EVs and lungs.

The role of TGF-β or BMPR2 signaling pathway-related miRNA in pulmonary arterial hypertension and systemic sclerosis

Pulmonary arterial hypertension (PAH) is a severe complication of connective tissue disease (CTD), causing death in systemic sclerosis (SSc). The past decade has yielded many scientific insights into microRNA (miRNAs) in PAH and SSc. This growth of knowledge has well-illustrated the complexity of microRNA (miRNA)-based regulation of gene expression in PAH. However, few miRNA-related SSc-PAH were elucidated. This review firstly discusses the role of transforming growth factor-beta (TGF-β) signaling and bone morphogenetic protein receptor type II (BMPR2) in PAH and SSc. Secondly, the miRNAs relating to TGF-β and BMPR2 signaling pathways in PAH and SSc or merely PAH were subsequently summarized. Finally, future studies might develop early diagnostic biomarkers and target-oriented therapeutic strategies for SSc-PAH and PAH treatment.

Overexpression of Msx1 in Mouse Lung Leads to Loss of Pulmonary Vessels Following Vascular Hypoxic Injury

Pulmonary arterial hypertension (PAH) is a progressive lung disease caused by thickening of the pulmonary arterial wall and luminal obliteration of the small peripheral arteries leading to increase in vascular resistance which elevates pulmonary artery pressure that eventually causes right heart failure and death. We have previously shown that transcription factor Msx1 (mainly expressed during embryogenesis) is strongly upregulated in transformed lymphocytes obtained from PAH patients, especially IPAH. Under pathological conditions, Msx1 overexpression can cause cell dedifferentiation or cell apoptosis. We hypothesized that Msx1 overexpression contributes to loss of small pulmonary vessels in PAH. In IPAH lung, MSX1 protein localization was strikingly increased in muscularized remodeled pulmonary vessels, whereas it was undetectable in control pulmonary arteries. We developed a transgenic mouse model overexpressing MSX1 (MSX1^OE) by about 4-fold and exposed these mice to normoxic, sugen hypoxic (3 weeks) or hyperoxic (100% 02 for 3 weeks) conditions. Under normoxic conditions, compared to controls, MSX1^OE mice demonstrated a 30-fold and 2-fold increase in lung Msx1 mRNA and protein expression, respectively. There was a significant retinal capillary dropout (p < 0.01) in MSX1^OE mice, which was increased further (p < 0.03) with sugen hypoxia. At baseline, the number of pulmonary vessels in MSX1^OE mice was similar to controls. In sugen-hypoxia-treated MSX1^OE mice, the number of small (0-25 uM) and medium (25-50 uM) size muscularized vessels increased approximately 2-fold (p < 0.01) compared to baseline controls; however, they were strikingly lower (p < 0.001) in number than in sugen-hypoxia-treated control mice. In MSX1^OE mouse lung, 104 genes were upregulated and 67 genes were downregulated compared to controls. Similarly, in PVECs, 156 genes were upregulated and 320 genes were downregulated from siRNA to MSX1^OE, and in PVSMCs, 65 genes were upregulated and 321 genes were downregulated from siRNA to MSX1^OE (with control in the middle). Many of the statistically significant GO groups associated with MSX1 expression in lung, PVECs, and PVSMCs were similar, and were involved in cell cycle, cytoskeletal and macromolecule organization, and programmed cell death. Overexpression of MSX1 suppresses many cell-cycle-related genes in PVSMCs but induces them in PVECs. In conclusion, overexpression of Msx1 leads to loss of pulmonary vessels, which is exacerbated by sugen hypoxia, and functional consequences of Msx1 overexpression are cell-dependent.

Fibroblast growth factors: the keepers of endothelial normalcy

Endothelial cells (ECs) under physiologic and pathologic conditions are capable of substantial plasticity that includes the endothelial-mesenchymal transition (EndMT). Notably, in the hypoxic pulmonary circulation EndMT likely drives increases in the pulmonary arterial blood pressure, leading to pulmonary arterial hypertension (PAH). However, it is unclear whether suppressing EndMT can prevent PAH development or mitigate established disease. In this issue of the JCI, Woo et al. generated mice with EC-specific deletion of FGFR1 and -2 and mice with EC-specific expression of a constitutively active FGFR1 to determine the role of FGF signaling in PAH. Mice with FGFR1/2 deletion in ECs that were exposed to hypoxic conditions developed extensive EndMT and more severe PAH than control mice. Animals with the constitutively active endothelial FGFR were protected from hypoxia-induced EndMT and PAH development. These findings suggest that FGF signaling may promote vascular resilience and prevent hypoxia-induced development of EndMT and PAH.

Deficiency of Axl aggravates pulmonary arterial hypertension via BMPR2

Pulmonary arterial hypertension (PAH), is a fatal disease characterized by a pseudo-malignant phenotype. We investigated the expression and the role of the receptor tyrosine kinase Axl in experimental (i.e., monocrotaline and Su5416/hypoxia treated rats) and clinical PAH. In vitro Axl inhibition by R428 and Axl knock-down inhibited growth factor-driven proliferation and migration of non-PAH and PAH PASMCs. Conversely, Axl overexpression conferred a growth advantage. Axl declined in PAECs of PAH patients. Axl blockage inhibited BMP9 signaling and increased PAEC apoptosis, while BMP9 induced Axl phosphorylation. Gas6 induced SMAD1/5/8 phosphorylation and ID1/ID2 increase were blunted by BMP signaling obstruction. Axl association with BMPR2 was facilitated by Gas6/BMP9 stimulation and diminished by R428. In vivo R428 aggravated right ventricular hypertrophy and dysfunction, abrogated BMPR2 signaling, elevated pulmonary endothelial cell apoptosis and loss. Together, Axl is a key regulator of endothelial BMPR2 signaling and potential determinant of PAH.

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.

Anti-Inflammatory Effect of Allicin Associated with Fibrosis in Pulmonary Arterial Hypertension

Pulmonary arterial hypertension (PAH) is characterized by pulmonary vascular remodeling. Recent evidence supports that inflammation plays a key role in triggering and maintaining pulmonary vascular remodeling. Recent studies have shown that garlic extract has protective effects in PAH, but the precise role of allicin, a compound derived from garlic, is unknown. Thus, we used allicin to evaluate its effects on inflammation and fibrosis in PAH. Male Wistar rats were divided into three groups: control (CON), monocrotaline (60 mg/kg) (MCT), and MCT plus allicin (16 mg/kg/oral gavage) (MCT + A). Right ventricle (RV) hypertrophy and pulmonary arterial medial wall thickness were determined. IL-1β, IL-6, TNF-α, NFκB p65, Iκβ, TGF-β, and α-SMA were determined by Western blot analysis. In addition, TNF-α and TGF-β were determined by immunohistochemistry, and miR-21-5p and mRNA expressions of Cd68, Bmpr2, and Smad5 were determined by RT-qPCR. Results: Allicin prevented increases in vessel wall thickness due to TNF-α, IL-6, IL-1β, and Cd68 in the lung. In addition, TGF-β, α-SMA, and fibrosis were lower in the MCT + A group compared with the MCT group. In the RV, allicin prevented increases in TNF-α, IL-6, and TGF-β. These observations suggest that, through the modulation of proinflammatory and profibrotic markers in the lung and heart, allicin delays the progression of PAH.

Single-Cell Study of Two Rat Models of Pulmonary Arterial Hypertension Reveals Connections to Human Pathobiology and Drug Repositioning

Rationale: The cellular and molecular landscape and translational value of commonly used models of pulmonary arterial hypertension (PAH) are poorly understood. Single-cell transcriptomics can enhance molecular understanding of preclinical models and facilitate their rational use and interpretation.Objectives: To determine and prioritize dysregulated genes, pathways, and cell types in lungs of PAH rat models to assess relevance to human PAH and identify drug repositioning candidates.Methods: Single-cell RNA sequencing was performed on the lungs of monocrotaline (MCT), Sugen-hypoxia (SuHx), and control rats to identify altered genes and cell types, followed by validation using flow-sorted cells, RNA in situ hybridization, and immunofluorescence. Relevance to human PAH was assessed by histology of lungs from patients and via integration with human PAH genetic loci and known disease genes. Candidate drugs were predicted using Connectivity Map.Measurements and Main Results: Distinct changes in genes and pathways in numerous cell types were identified in SuHx and MCT lungs. Widespread upregulation of NF-κB signaling and downregulation of IFN signaling was observed across cell types. SuHx nonclassical monocytes and MCT conventional dendritic cells showed particularly strong NF-κB pathway activation. Genes altered in SuHx nonclassical monocytes were significantly enriched for PAH-associated genes and genetic variants, and candidate drugs predicted to reverse the changes were identified. An open-access online platform was developed to share single-cell data and drug candidates (http://mergeomics.research.idre.ucla.edu/PVDSingleCell/).Conclusions: Our study revealed the distinct and shared dysregulation of genes and pathways in two commonly used PAH models for the first time at single-cell resolution and demonstrated their relevance to human PAH and utility for drug repositioning.

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.

Altered TGFβ/SMAD Signaling in Human and Rat Models of Pulmonary Hypertension: An Old Target Needs Attention

Recent translational studies highlighted the inhibition of transforming growth factor (TGF)-β signaling as a promising target to treat pulmonary arterial hypertension (PAH). However, it remains unclear whether alterations in TGF-β signaling are consistent between PAH patients and animal models. Therefore, we compared TGF-β signaling in the lungs of PAH patients and rats with experimental PAH induced by monocrotaline (MCT) or SU5416+hypoxia (SuHx). In hereditary PAH (hPAH) patients, there was a moderate increase in both TGFβR2 and pSMAD2/3 protein levels, while these were unaltered in idiopathic PAH (iPAH) patients. Protein levels of TGFβR2 and pSMAD2/3 were locally increased in the pulmonary vasculature of PAH rats under both experimental conditions. Conversely, the protein levels of TGFβR2 and pSMAD2/3 were reduced in SuHx while slightly increased in MCT. mRNA levels of plasminogen activator inhibitor (PAI)-1 were increased only in MCT animals and such an increase was not observed in SuHx rats or in iPAH and hPAH patients. In conclusion, our data demonstrate considerable discrepancies in TGFβ-SMAD signaling between iPAH and hPAH patients, as well as between patients and rats with experimental PAH.

Regulation of circular RNAs act as ceRNA in a hypoxic pulmonary hypertension rat model

To explore potential critical genes and identify circular RNAs (circRNAs) that act as the competitive endogenous RNA (ceRNA) in a hypoxic pulmonary hypertension (HPH) rat model. Constructed rat model, and a bioinformatics method was used to analyse differentially expressed (DE) genes and construct a circRNA-miRNA-mRNA ceRNA regulatory network. Then, qRT-PCR was used to verify. The significant DEcircRNAs/DEmiRNAs/DEmRNAs was showed, and a ceRNA network with 8 DEcircRNAs, 9 DEmiRNAs and 46 DEmRNAs were constructed. The functional enrichment suggested the inflammatory response, NF-κB signalling, MAPK cascade and Toll-like receptor were associated with HPH. Further assessment confirmed that circ_002723, circ_008021, circ_016925 and circ_020581 could have a potential ceRNA mechanism by sponging miR-23a or miR-21 to control downstream target gene and be involved in the pathophysiology of HPH. The qRT-PCR validation results were consistent with the RNA-Seq results. This study revealed potentially important genes, pathways and ceRNA regulatory networks in HPH.

Editorial Special Issue TGF-beta/BMP Signaling Pathway

The transforming growth factor β (TGF-β) superfamily plays key roles in development and tissue homeostasis, controlling the maintenance and regeneration of mature tissues. Cytokines belonging to this family can be multifunctional (TGF-β and bone morphogenetic proteins, BMPs) or develop highly specialized functions (anti-Müllerian hormone, AMH, or growth differentiation factor 8, myostatin, GDF8) and they control a variety of cellular processes such as proliferation, differentiation, cell death, adhesion and movement, metabolism, pluripotency and stemness. (...).