Targeted gene delivery of BMPR2 attenuates pulmonary hypertension

Fluorinated amphiphilic Poly(β-Amino ester) nanoparticle for highly efficient and specific delivery of nucleic acids to the Lung capillary endothelium

Endothelial cell dysfunction occurs in a variety of acute and chronic pulmonary diseases including pulmonary hypertension, viral and bacterial pneumonia, bronchopulmonary dysplasia, and congenital lung diseases such as alveolar capillary dysplasia with misalignment of pulmonary veins (ACDMPV). To correct endothelial dysfunction, there is a critical need for the development of nanoparticle systems that can deliver drugs and nucleic acids to endothelial cells with high efficiency and precision. While several nanoparticle delivery systems targeting endothelial cells have been recently developed, none of them are specific to lung endothelial cells without targeting other organs in the body. In the present study, we successfully solved this problem by developing non-toxic poly(β-amino) ester (PBAE) nanoparticles with specific structure design and fluorinated modification for high efficiency and specific delivery of nucleic acids to the pulmonary endothelial cells. After intravenous administration, the PBAE nanoparticles were capable of delivering non-integrating DNA plasmids to lung microvascular endothelial cells but not to other lung cell types. IVIS whole body imaging and flow cytometry demonstrated that DNA plasmid were functional in the lung endothelial cells but not in endothelial cells of other organs. Fluorination of PBAE was required for lung endothelial cell-specific targeting. Hematologic analysis and liver and kidney metabolic panels demonstrated the lack of toxicity in experimental mice. Thus, fluorinated PBAE nanoparticles can be an ideal vehicle for gene therapy targeting lung microvascular endothelium in pulmonary vascular disorders.

Defining the clinical validity of genes reported to cause pulmonary arterial hypertension

PURPOSE

Pulmonary arterial hypertension (PAH) is a rare, progressive vasculopathy with significant cardiopulmonary morbidity and mortality. Genetic testing is currently recommended for adults diagnosed with heritable, idiopathic, anorexigen-, hereditary hemorrhagic telangiectasia-, and congenital heart disease-associated PAH, PAH with overt features of venous/capillary involvement, and all children diagnosed with PAH. Variants in at least 27 genes have putative evidence for PAH causality. Rigorous assessment of the evidence is needed to inform genetic testing.

METHODS

An international panel of experts in PAH applied a semi-quantitative scoring system developed by the NIH Clinical Genome Resource to classify the relative strength of evidence supporting PAH gene-disease relationships based on genetic and experimental evidence.

RESULTS

Twelve genes (BMPR2, ACVRL1, ATP13A3, CAV1, EIF2AK4, ENG, GDF2, KCNK3, KDR, SMAD9, SOX17, and TBX4) were classified as having definitive evidence and 3 genes (ABCC8, GGCX, and TET2) with moderate evidence. Six genes (AQP1, BMP10, FBLN2, KLF2, KLK1, and PDGFD) were classified as having limited evidence for causal effects of variants. TOPBP1 was classified as having no known PAH relationship. Five genes (BMPR1A, BMPR1B, NOTCH3, SMAD1, and SMAD4) were disputed because of a paucity of genetic evidence over time.

CONCLUSION

We recommend that genetic testing includes all genes with definitive evidence and that caution be taken in the interpretation of variants identified in genes with moderate or limited evidence. Genes with no known evidence for PAH or disputed genes should not be included in genetic testing.

Pharmacotherapy of refractory pulmonary arterial hypertension

INTRODUCTION

Treatment of refractory pulmonary arterial hypertension (PAH) is challenging and rarely the focus of reviews. The purpose of this review is to discuss current treatment options of refractory PAH, along with the state of research of several new medications.

AREAS COVERED

We conducted a comprehensive PubMed search on the relevant literature on treating PAH, with a focus on approved and investigational interventions for high-risk patients. Our strategy used keywords 'Treatment' AND 'Pulmonary Hypertension,' without date restrictions, ensuring a thorough survey of available literature for our review.

EXPERT OPINION

By utilizing serial risk assessment to identify patients remaining intermediate or high-risk, more patients are likely to survive longer. This is done by earlier use of combination or triple therapy with prostacyclin drugs. Current medications for PAH are all essentially vasodilators that improve physiology, but do not truly modify the disease process. The potential application of new investigational medications is exciting as they work by novel pathways likely to change the landscape of refractory PAH treatment.

Ginsenoside Rg3 attenuates pulmonary fibrosis by inhibiting endothelial to mesenchymal transition

Pulmonary fibrosis (PF) is a progressive and chronic lung disease characterized by excessive extracellular matrix (ECM) deposition and fibroblast proliferation. Endothelial-to-mesenchymal transition (EndMT) serves as a source of fibroblasts and contributes to PF progression. Ginsenoside Rg3 (Rg3), a steroidal saponin extracted from ginseng, is known to have pharmacological effects on vascular diseases. We have previously demonstrated that Rg3 inhibits EndMT and prevents endothelial dysfunction. Thus, we hypothesized that Rg3 may be a potential therapeutic agent for PF-targeting EndMT. EndMT occurs in the lung tissue of a bleomycin-induced PF mouse model, which was confirmed by co-staining of endothelial and mesenchymal markers in the pulmonary vasculature and changes in the expression of these markers. Rg3 administration decreased EndMT and suppressed PF development. We also examined the effect of Rg3 in an in vitro EndMT model induced by co-treatment with TGF-β2 and IL-1β. Rg3 treatment alleviated the characteristics of EndMT such as spindle-shaped morphological changes, EndMT marker expression changes, Dil-Ac-LDL uptake and migratory properties. In addition, we demonstrated the mechanism by which Rg3 inhibits EndMT by regulating the Smad2/3 signaling pathway. Collectively, Rg3 can be a potential therapeutic agent for PF using the EndMT inhibition strategy, furthermore, it can be considered Rg3 as a therapeutic candidate for various EndMT-associated vascular diseases.

Metabolic reprogramming, oxidative stress, and pulmonary hypertension

Mitochondria are highly dynamic organelles essential for cell metabolism, growth, and function. It is becoming increasingly clear that endothelial cell dysfunction significantly contributes to the pathogenesis and vascular remodeling of various lung diseases, including pulmonary arterial hypertension (PAH), and that mitochondria are at the center of this dysfunction. The more we uncover the role mitochondria play in pulmonary vascular disease, the more apparent it becomes that multiple pathways are involved. To achieve effective treatments, we must understand how these pathways are dysregulated to be able to intervene therapeutically. We know that nitric oxide signaling, glucose metabolism, fatty acid oxidation, and the TCA cycle are abnormal in PAH, along with alterations in the mitochondrial membrane potential, proliferation, and apoptosis. However, these pathways are incompletely characterized in PAH, especially in endothelial cells, highlighting the urgent need for further research. This review summarizes what is currently known about how mitochondrial metabolism facilitates a metabolic shift in endothelial cells that induces vascular remodeling during PAH.

The endothelium in lung fibrosis: a core signaling hub in disease pathogenesis?

Pulmonary fibrosis (PF) is a progressive chronic lung disease characterized by excessive deposition of extracellular matrix (ECM) and structural destruction, associated with a severe 5-year mortality rate. The onset of the disease is thought to be triggered by chronic damage to the alveolar epithelium. Since the pulmonary endothelium is an important component of the alveolar-capillary niche, it is also affected by the initial injury. In addition to ensuring proper gas exchange, the endothelium has critical functional properties, including regulation of vascular tone, inflammatory responses, coagulation, and maintenance of vascular homeostasis and integrity. Recent single-cell analyses have shown that shifts in endothelial cell (EC) subtypes occur in PF. Furthermore, the increased vascular remodeling associated with PF leads to deteriorated outcomes for patients, underscoring the importance of the vascular bed in PF. To date, the causes and consequences of endothelial and vascular involvement in lung fibrosis are poorly understood. Therefore, it is of great importance to investigate the involvement of EC and the vascular system in the pathogenesis of the disease. In this review, we will outline the current knowledge on the role of the pulmonary vasculature in PF, in terms of abnormal cellular interactions, hyperinflammation, vascular barrier disorders, and an altered basement membrane composition. Finally, we will summarize recent advances in extensive therapeutic research and discuss the significant value of novel therapies targeting the endothelium.

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

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

Complex roles of TGF-β signaling pathways in lung development and bronchopulmonary dysplasia

As survival of extremely preterm infants continues to improve, there is also an associated increase in bronchopulmonary dysplasia (BPD), one of the most significant complications of preterm birth. BPD development is multifactorial resulting from exposure to multiple antenatal and postnatal stressors. BPD has both short-term health implications and long-term sequelae including increased respiratory, cardiovascular, and neurological morbidity. Transforming growth factor β (TGF-β) is an important signaling pathway in lung development, organ injury, and fibrosis and is implicated in the development of BPD. This review provides a detailed account on the role of TGF-β in antenatal and postnatal lung development, the effect of known risk factors for BPD on the TGF-β signaling pathway, and how medications currently in use or under development, for the prevention or treatment of BPD, affect TGF-β signaling.

BMPR2 Mutation and Metabolic Reprogramming in Pulmonary Arterial Hypertension

Pulmonary arterial hypertension forms the first and most severe of the 5 categories of pulmonary hypertension. Disease pathogenesis is driven by progressive remodeling of peripheral pulmonary arteries, caused by the excessive proliferation of vascular wall cells, including endothelial cells, smooth muscle cells and fibroblasts, and perivascular inflammation. Compelling evidence from animal models suggests endothelial cell dysfunction is a key initial trigger of pulmonary vascular remodeling, which is characterised by hyperproliferation and early apoptosis followed by enrichment of apoptosis-resistant populations. Dysfunctional pulmonary arterial endothelial cells lose their ability to produce vasodilatory mediators, together leading to augmented pulmonary arterial smooth muscle cell responses, increased pulmonary vascular pressures and right ventricular afterload, and progressive right ventricular hypertrophy and heart failure. It is recognized that a range of abnormal cellular molecular signatures underpin the pathophysiology of pulmonary arterial hypertension and are enhanced by loss-of-function mutations in the BMPR2 gene, the most common genetic cause of pulmonary arterial hypertension and associated with worse disease prognosis. Widespread metabolic abnormalities are observed in the heart, pulmonary vasculature, and systemic tissues, and may underpin heterogeneity in responsivity to treatment. Metabolic abnormalities include hyperglycolytic reprogramming, mitochondrial dysfunction, aberrant polyamine and sphingosine metabolism, reduced insulin sensitivity, and defective iron handling. This review critically discusses published mechanisms linking metabolic abnormalities with dysfunctional BMPR2 (bone morphogenetic protein receptor 2) signaling; hypothesized mechanistic links requiring further validation; and their relevance to pulmonary arterial hypertension pathogenesis and the development of potential therapeutic strategies.

Pathophysiology and new advances in pulmonary hypertension

Pulmonary hypertension is a progressive and often fatal cardiopulmonary condition characterised by increased pulmonary arterial pressure, structural changes in the pulmonary circulation, and the formation of vaso-occlusive lesions. These changes lead to increased right ventricular afterload, which often progresses to maladaptive right ventricular remodelling and eventually death. Pulmonary arterial hypertension represents one of the most severe and best studied types of pulmonary hypertension and is consistently targeted by drug treatments. The underlying molecular pathogenesis of pulmonary hypertension is a complex and multifactorial process, but can be characterised by several hallmarks: inflammation, impaired angiogenesis, metabolic alterations, genetic or epigenetic abnormalities, influence of sex and sex hormones, and abnormalities in the right ventricle. Current treatments for pulmonary arterial hypertension and some other types of pulmonary hypertension target pathways involved in the control of pulmonary vascular tone and proliferation; however, these treatments have limited efficacy on patient outcomes. This review describes key features of pulmonary hypertension, discusses current and emerging therapeutic interventions, and points to future directions for research and patient care. Because most progress in the specialty has been made in pulmonary arterial hypertension, this review focuses on this type of pulmonary hypertension. The review highlights key pathophysiological concepts and emerging therapeutic directions, targeting inflammation, cellular metabolism, genetics and epigenetics, sex hormone signalling, bone morphogenetic protein signalling, and inhibition of tyrosine kinase receptors.

Lipid Nanoparticles for Nucleic Acid Delivery to Endothelial Cells

Endothelial cells play critical roles in circulatory homeostasis and are also the gateway to the major organs of the body. Dysfunction, injury, and gene expression profiles of these cells can cause, or are caused by, prevalent chronic diseases such as diabetes, cardiovascular disease, and cancer. Modulation of gene expression within endothelial cells could therefore be therapeutically strategic in treating longstanding disease challenges. Lipid nanoparticles (LNP) have emerged as potent, scalable, and tunable carrier systems for delivering nucleic acids, making them attractive vehicles for gene delivery to endothelial cells. Here, we discuss the functions of endothelial cells and highlight some receptors that are upregulated during health and disease. Examples and applications of DNA, mRNA, circRNA, saRNA, siRNA, shRNA, miRNA, and ASO delivery to endothelial cells and their targets are reviewed, as well as LNP composition and morphology, formulation strategies, target proteins, and biomechanical factors that modulate endothelial cell targeting. Finally, we discuss FDA-approved LNPs as well as LNPs that have been tested in clinical trials and their challenges, and provide some perspectives as to how to surmount those challenges.

The Role of Bone Morphogenetic Protein Receptor Type 2 (BMPR2) and the Prospects of Utilizing Induced Pluripotent Stem Cells (iPSCs) in Pulmonary Arterial Hypertension Disease Modeling

Pulmonary arterial hypertension (PAH) is a progressive disease characterized by increased pulmonary vascular resistance (PVR), causing right ventricular hypertrophy and ultimately death from right heart failure. Heterozygous mutations in the bone morphogenetic protein receptor type 2 (BMPR2) are linked to approximately 80% of hereditary, and 20% of idiopathic PAH cases, respectively. While patients carrying a BMPR2 gene mutation are more prone to develop PAH than non-carriers, only 20% will develop the disease, whereas the majority will remain asymptomatic. PAH is characterized by extreme vascular remodeling that causes pulmonary arterial endothelial cell (PAEC) dysfunction, impaired apoptosis, and uncontrolled proliferation of the pulmonary arterial smooth muscle cells (PASMCs). To date, progress in understanding the pathophysiology of PAH has been hampered by limited access to human tissue samples and inadequacy of animal models to accurately mimic the pathogenesis of human disease. Along with the advent of induced pluripotent stem cell (iPSC) technology, there has been an increasing interest in using this tool to develop patient-specific cellular models that precisely replicate the pathogenesis of PAH. In this review, we summarize the currently available approaches in iPSC-based PAH disease modeling and explore how this technology could be harnessed for drug discovery and to widen our understanding of the pathophysiology of PAH.

Loss of lung microvascular endothelial Piezo2 expression impairs NO synthesis, induces EndMT, and is associated with pulmonary hypertension

Mechanical forces are translated into biochemical stimuli by mechanotransduction channels, such as the mechanically activated cation channel Piezo2. Lung Piezo2 expression has recently been shown to be restricted to endothelial cells. Hence, we aimed to investigate the role of Piezo2 in regulation of pulmonary vascular function and structure, as well as its contribution to development of pulmonary arterial hypertension (PAH). The expression of Piezo2 was significantly reduced in pulmonary microvascular endothelial cells (MVECs) from patients with PAH, in lung tissue from mice with a Bmpr2^+/R899X knock-in mutation commonly found in patients with pulmonary hypertension, and in lung tissue of monocrotaline (MCT) and sugen-hypoxia-induced PH (SuHx) PAH rat models, as well as from a swine model with pulmonary vein banding. In MVECs, Piezo2 expression was reduced in response to abnormal shear stress, hypoxia, and TGFβ stimulation. Functional studies in MVECs exposed to shear stress illustrated that siRNA-mediated Piezo2 knockdown impaired endothelial alignment, calcium influx, phosphorylation of AKT, and nitric oxide production. In addition, siPiezo2 reduced the expression of the endothelial marker PECAM-1 and increased the expression of vascular smooth muscle markers ACTA2, SM22a, and calponin. Thus, Piezo2 acts as a mechanotransduction channel in pulmonary MVECs, stimulating shear-induced production of nitric oxide and is essentially involved in preventing endothelial to mesenchymal transition. Its blunted expression in pulmonary hypertension could impair the vasodilator capacity and stimulate vascular remodeling, indicating that Piezo2 might be an interesting therapeutic target to attenuate progression of the disease.NEW & NOTEWORTHY The mechanosensory ion channel Piezo2 is exclusively expressed in lung microvascular endothelial cells (MVECs). Patient MVECs as well as animal models of pulmonary (arterial) hypertension showed lower expression of Piezo2 in the lung. Mechanistically, Piezo2 is required for calcium influx and NO production in response to shear stress, whereas stimuli known to induce endothelial to mesenchymal transition (EndMT) reduce Piezo2 expression in MVECs, and Piezo2 knockdown induces a gene and protein expression pattern consistent with EndMT.

MED1 Regulates BMP/TGF-β in Endothelium: Implication for Pulmonary Hypertension

BACKGROUND

Dysregulated BMP (bone morphogenetic protein) or TGF-β (transforming growth factor beta) signaling pathways are imperative in idiopathic and familial pulmonary arterial hypertension (PAH) as well as experimental pulmonary hypertension (PH) in rodent models. MED1 (mediator complex subunit 1) is a key transcriptional co-activator and KLF4 (Krüppel-like factor 4) is a master transcription factor in endothelium. However, MED1 and KLF4 epigenetic and transcriptional regulations of the BMP/TGF-β axes in pulmonary endothelium and their dysregulations leading to PAH remain elusive. We investigate the MED1/KLF4 co-regulation of the BMP/TGF-β axes in endothelium by studying the epigenetic regulation of BMPR2 (BMP receptor type II), ETS-related gene (ERG), and TGFBR2 (TGF-β receptor 2) and their involvement in the PH.

METHODS

High-throughput screening involving data from RNA-seq, MED1 ChIP-seq, H3K27ac ChIP-seq, ATAC-seq, and high-throughput chromosome conformation capture together with in silico computations were used to explore the epigenetic and transcriptional regulation of BMPR2, ERG, and TGFBR2 by MED1 and KLF4. In vitro experiments with cultured pulmonary arterial endothelial cells (ECs) and bulk assays were used to validate results from these in silico analyses. Lung tissue from patients with idiopathic PAH, animals with experimental PH, and mice with endothelial ablation of MED1 (EC-MED1^-/-) were used to study the PH-protective effect of MED1.

RESULTS

Levels of MED1 were decreased in lung tissue or pulmonary arterial endothelial cells from idiopathic PAH patients and rodent PH models. Mechanistically, MED1 acted synergistically with KLF4 to transactivate BMPR2, ERG, and TGFBR2 via chromatin remodeling and enhancer-promoter interactions. EC-MED1^-/- mice showed PH susceptibility. In contrast, MED1 overexpression mitigated the PH phenotype in rodents.

CONCLUSIONS

A homeostatic regulation of BMPR2, ERG, and TGFBR2 in ECs by MED1 synergistic with KLF4 is essential for the normal function of the pulmonary endothelium. Dysregulation of MED1 and the resulting impairment of the BMP/TGF-β signaling is implicated in the disease progression of PAH in humans and PH in rodent models.

Mechanistic and therapeutic perspectives of baicalin and baicalein on pulmonary hypertension: A comprehensive review

Pulmonary hypertension (PH) is a chronic and fatal disease, for which new therapeutic drugs and approaches are needed urgently. Baicalein and baicalin, the active compounds of the traditional Chinese medicine, Scutellaria baicalensis Georgi, exhibit a wide range of pharmacological activities. Numerous studies involving in vitro and in vivo models of PH have revealed that the treatment with baicalin and baicalein may be effective. This review summarizes the potential mechanisms driving the beneficial effects of baicalin and baicalein treatment on PH, including anti-inflammatory response, inhibition of pulmonary smooth muscle cell proliferation and endothelial-to-mesenchymal transformation, stabilization of the extracellular matrix, and mitigation of oxidative stress. The pharmacokinetics of these compounds have also been reviewed. The therapeutic potential of baicalin and baicalein warrants their continued study as natural treatments for PH.

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.

Overexpression of bone morphogenetic protein receptor type 2 suppresses transforming growth factor β-induced profibrotic responses in lung fibroblasts

MATERIALS AND METHODS

We investigated BMPR2 expression in pulmonary fibrosis and TGF-β/BMP signaling in lung fibroblasts. Then we evaluated the impact of BMPR2 upregulation using adenoviral transduction on TGF-β-induced Smad2/3 phosphorylation and fibronectin production in lung fibroblasts.

RESULTS

BMPR2 was distributed in airway epithelium and alveolar walls in rat lungs. BMPR2 expression was decreased in fibrotic lesions in the lungs of rats with bleomycin-induced pulmonary fibrosis and in human lung fibroblasts (HLFs) stimulated with TGF-β. Although Smad2/3 phosphorylation and fibronectin production were not suppressed solely by BMPs, phosphorylated Smad2/3 was decreased in BMPR2-transduced cells even without BMP stimulation. Fibronectin was decreased only when BMPR2-transduced HLFs were stimulated with BMP7 (but not BMP4). Similar results were also observed in IPF patient HLFs and rat lung fibroblasts.

CONCLUSIONS

BMPR2 expression was reduced in fibrotic lungs and lung fibroblasts stimulated with TGF-β. BMPR2 transduction to lung fibroblasts reduced Smad2/3 phosphorylation, and reduced fibronectin production when treated with BMP7. Upregulation of BMPR2 may be a possible strategy for treating pulmonary fibrosis.

Andrographolide Attenuates Established Pulmonary Hypertension via Rescue of Vascular Remodeling

Pulmonary hypertension (PH) is characterized by vascular remodeling caused by marked proliferation of pulmonary artery smooth muscle cells (PASMCs). Andrographolide (ANDRO) is a potent anti-inflammatory agent which possesses antioxidant, and has anticarcinogenic activity. The present study examined potential therapeutic effects of ANDRO on PH in both chronic hypoxia and Sugen5416/hypoxia mouse PH models. Effects of ANDRO were also studied in cultured human PASMCs isolated from either healthy donors or PH patients. In vivo, ANDRO decreased distal pulmonary arteries (PAs) remodeling, mean PA pressure and right ventricular hypertrophy in chronic hypoxia- and Sugen/hypoxia-induced PH in mice. ANDRO reduced cell viability, proliferation and migration, but increased cell apoptosis in the PASMCs isolated from PH patients. ANDRO also reversed the dysfunctional bone morphogenetic protein receptor type-2 (BMPR2) signaling, suppressed [Ca2⁺]_i elevation, reactive oxygen species (ROS) generation, and the upregulated expression of IL-6 and IL-8, ET-1 and VEGF in PASMCs from PH patients. Moreover, ANDRO significantly attenuated the activation of TLR4/NF-κB, ERK- and JNK-MAPK signaling pathways and reversed the inhibition of p38-MAPK in PASMCs of PH patients. Further, ANDRO blocked hypoxia-triggered ROS generation by suppressing NADPH oxidase (NOX) activation and augmenting nuclear factor erythroid 2-related factor 2 (Nrf2) expression both in vitro and in vivo. Conventional pulmonary vasodilators have limited efficacy for the treatment of severe PH. We demonstrated that ANDRO may reverse pulmonary vascular remodeling through modulation of NOX/Nrf2-mediated oxidative stress and NF-κB-mediated inflammation. Our findings suggest that ANDRO may have therapeutic value in the treatment of PH.

The role of immune cells in pulmonary hypertension: Focusing on macrophages

Pulmonary hypertension (PH) is a life-threatening pathological state with elevated pulmonary arterial pressure, resulting in right ventricular failure and heart functional failure. Analyses of human samples and rodent models of pH support the infiltration of various immune cells, including neutrophils, mast cells, dendritic cells, B-cells, T-cells, and natural killer cells, to the lungs and pulmonary perivascular regions and their involvement in the PH development. There is evidence that macrophages are presented in the pulmonary lesions of pH patients as first-line myeloid leucocytes. Macrophage accumulation and presence, both M1 and M2 phenotypes, is a distinctive hallmark of pH which plays a pivotal role in pulmonary artery remodeling through various cellular and molecular interactions and mechanisms, including CCL2 and CX3CL1 chemokines, adventitial fibroblasts, glucocorticoid-regulated kinase 1 (SGK1), crosstalk with other immune cells, leukotriene B4 (LTB4), bone morphogenetic protein receptor 2 (BMPR2), macrophage migration inhibitory factor (MIF), and thrombospondin-1 (TSP-1). In this paper, we reviewed the molecular mechanisms and the role of immune cells and responses are involved in PH development. We also summarized the polarization of macrophages in response to different stimuli and their pathological role and their infiltration in the lung of pH patients and animal models.

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.

Vascular Endothelial Cells: Heterogeneity and Targeting Approaches

Forming the inner layer of the vascular system, endothelial cells (ECs) facilitate a multitude of crucial physiological processes throughout the body. Vascular ECs enable the vessel wall passage of nutrients and diffusion of oxygen from the blood into adjacent cellular structures. ECs regulate vascular tone and blood coagulation as well as adhesion and transmigration of circulating cells. The multitude of EC functions is reflected by tremendous cellular diversity. Vascular ECs can form extremely tight barriers, thereby restricting the passage of xenobiotics or immune cell invasion, whereas, in other organ systems, the endothelial layer is fenestrated (e.g., glomeruli in the kidney), or discontinuous (e.g., liver sinusoids) and less dense to allow for rapid molecular exchange. ECs not only differ between organs or vascular systems, they also change along the vascular tree and specialized subpopulations of ECs can be found within the capillaries of a single organ. Molecular tools that enable selective vascular targeting are helpful to experimentally dissect the role of distinct EC populations, to improve molecular imaging and pave the way for novel treatment options for vascular diseases. This review provides an overview of endothelial diversity and highlights the most successful methods for selective targeting of distinct EC subpopulations.

Beyond TGFβ1 - novel treatment strategies targeting lung fibrosis

Fibrosis is a key feature of chronic lung diseases and occurs as a consequence of aberrant wound healing. TGFβ1 plays a major role in promoting fibrosis and is the primary target of current treatments that slow, but do not halt or reverse the progression of disease. Accumulating evidence suggests that additional mechanisms, including excessive airway contraction, inflammation and infections including COVID-19, can contribute to fibrosis. This review summarises experimental and clinical studies assessing the potential beneficial effects of novel drugs that possess a unique suite of complementary actions to oppose contraction, inflammation and remodelling, along with evidence that they also limit fibrosis. Translation of these promising findings is critical for the repurposing and development of improved therapeutics for fibrotic lung diseases.

Combination Therapy with STAT3 Inhibitor Enhances SERCA2a-Induced BMPR2 Expression and Inhibits Pulmonary Arterial Hypertension

Pulmonary arterial hypertension (PAH) is a devastating lung disease characterized by the progressive obstruction of the distal pulmonary arteries (PA). Structural and functional alteration of pulmonary artery smooth muscle cells (PASMC) and endothelial cells (PAEC) contributes to PA wall remodeling and vascular resistance, which may lead to maladaptive right ventricular (RV) failure and, ultimately, death. Here, we found that decreased expression of sarcoplasmic/endoplasmic reticulum Ca²⁺ ATPase 2a (SERCA2a) in the lung samples of PAH patients was associated with the down-regulation of bone morphogenetic protein receptor type 2 (BMPR2) and the activation of signal transducer and activator of transcription 3 (STAT3). Our results showed that the antiproliferative properties of SERCA2a are mediated through the STAT3/BMPR2 pathway. At the molecular level, transcriptome analysis of PASMCs co-overexpressing SERCA2a and BMPR2 identified STAT3 amongst the most highly regulated transcription factors. Using a specific siRNA and a potent pharmacological STAT3 inhibitor (STAT3i, HJC0152), we found that SERCA2a potentiated BMPR2 expression by repressing STAT3 activity in PASMCs and PAECs. In vivo, we used a validated and efficient model of severe PAH induced by unilateral left pneumonectomy combined with monocrotaline (PNT/MCT) to further evaluate the therapeutic potential of single and combination therapies using adeno-associated virus (AAV) technology and a STAT3i. We found that intratracheal delivery of AAV1 encoding SERCA2 or BMPR2 alone or STAT3i was sufficient to reduce the mean PA pressure and vascular remodeling while improving RV systolic pressures, RV ejection fraction, and cardiac remodeling. Interestingly, we found that combined therapy of AAV1.hSERCA2a with AAV1.hBMPR2 or STAT3i enhanced the beneficial effects of SERCA2a. Finally, we used cardiac magnetic resonance imaging to measure RV function and found that therapies using AAV1.hSERCA2a alone or combined with STAT3i significantly inhibited RV structural and functional changes in PNT/MCT-induced PAH. In conclusion, our study demonstrated that combination therapies using SERCA2a gene transfer with a STAT3 inhibitor could represent a new promising therapeutic alternative to inhibit PAH and to restore BMPR2 expression by limiting STAT3 activity.

Promising therapeutic approaches in pulmonary arterial hypertension

Pulmonary arterial hypertension (PAH) is a debilitating multifactorial disease characterized by progressive pulmonary vascular remodeling, elevated pulmonary arterial pressure, and pulmonary vascular resistance, resulting in right ventricular failure and subsequent death. Current available therapies do not reverse the disease, resulting in a persistent high morbidity and mortality. Thus, there is an urgent unmet medical need for novel effective therapies to better treat patients with PAH. Over the past few years, enthusiastic attempts have been made to identify novel effective therapies that address the essential roots of PAH with targeting key signaling pathways in both preclinical models and patients with PAH. This review aims to discuss the most emerging and promising therapeutic interventions in PAH pathogenesis.

Activation of yes-associated protein mediates sphingosine-1-phosphate-induced proliferation and migration of pulmonary artery smooth muscle cells and its potential mechanisms

The aims of the present study were to examine the molecular mechanisms underlying sphingosine-1-phosphate (S1P)-induced rat pulmonary artery smooth muscle cells (PASMCs) proliferation/migration and to determine the effect of yes-associated protein (YAP) activation on S1P-induced PASMCs proliferation/migration and its potential mechanisms. S1P induced YAP dephosphorylation and nuclear translocation, upregulated microRNA-130a/b (miR-130a/b) expression, reduced bone morphogenetic protein receptor 2 (BMPR2), and inhibitor of DNA binding 1(Id1) expression, and promoted PASMCs proliferation and migration. Pretreatment of cells with Rho-associated protein kinase (ROCK) inhibitor Y27632 suppressed S1P-induced YAP activation, miR-130a/b upregulation, BMPR2/Id1 downregulation, and PASMCs proliferation/migration. Knockdown of YAP using small interfering RNA also suppressed S1P-induced alterations of miR-130a/b, BMPR2, Id1, and PASMCs behavior. In addition, luciferase reporter assay indicated that miR-130a/b directly regulated BMPR2 expression in PASMCs. Inhibition of miR-130a/b functions by anti-miRNA oligonucleotides attenuated S1P-induced BMPR2/Id1 downregulation and the proliferation and migration of PASMCs. Taken together, our study indicates that S1P induces activation of YAP through ROCK signaling and subsequently increases miR-130a/b expression, which, in turn, downregulates BMPR2 and Id1 leading to PASMCs proliferation and migration.

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.

Targeting the TGF-β signaling pathway for resolution of pulmonary arterial hypertension

Aberrant transforming growth factor-β (TGF-β) signaling activation is linked to pulmonary arterial hypertension (PAH). BMPR2 mutations perturb the balance between bone morphogenetic protein (BMP) and TGF-β pathways, leading to vascular remodeling, narrowing of the lumen of pulmonary vasculature, and clinical symptoms. This forum highlights the association of the TGF-β pathway with pathogenesis and therapeutic approaches.

Endothelial-to-Mesenchymal Transition in Pulmonary Arterial Hypertension

Endothelial-to-mesenchymal transition (EndMT) is a process that encompasses extensive transcriptional reprogramming of activated endothelial cells leading to a shift toward mesenchymal cellular phenotypes and functional responses. Initially observed in the context of embryonic development, in the last few decades EndMT is increasingly recognized as a process that contributes to a variety of pathologies in the adult organism. Within the settings of cardiovascular biology, EndMT plays a role in various diseases, including atherosclerosis, heart valvular disease, cardiac fibrosis, and myocardial infarction. EndMT is also being progressively implicated in development and progression of pulmonary hypertension (PH) and pulmonary arterial hypertension (PAH). This review covers the current knowledge about EndMT in PH and PAH, and provides comprehensive overview of seminal discoveries. Topics covered include evidence linking EndMT to factors associated with PAH development, including hypoxia responses, inflammation, dysregulation of bone-morphogenetic protein receptor 2 (BMPR2), and redox signaling. This review amalgamates these discoveries into potential insights for the identification of underlying mechanisms driving EndMT in PH and PAH, and discusses future directions for EndMT-based therapeutic strategies in disease management.

Molecular and Genetic Profiling for Precision Medicines in Pulmonary Arterial Hypertension

Pulmonary arterial hypertension (PAH) is a rare and chronic lung disease characterized by progressive occlusion of the small pulmonary arteries, which is associated with structural and functional alteration of the smooth muscle cells and endothelial cells within the pulmonary vasculature. Excessive vascular remodeling is, in part, responsible for high pulmonary vascular resistance and the mean pulmonary arterial pressure, increasing the transpulmonary gradient and the right ventricular “pressure overload”, which may result in right ventricular (RV) dysfunction and failure. Current technological advances in multi-omics approaches, high-throughput sequencing, and computational methods have provided valuable tools in molecular profiling and led to the identification of numerous genetic variants in PAH patients. In this review, we summarized the pathogenesis, classification, and current treatments of the PAH disease. Additionally, we outlined the latest next-generation sequencing technologies and the consequences of common genetic variants underlying PAH susceptibility and disease progression. Finally, we discuss the importance of molecular genetic testing for precision medicine in PAH and the future of genomic medicines, including gene-editing technologies and gene therapies, as emerging alternative approaches to overcome genetic disorders in PAH.

Endothelial to Mesenchymal Transition in the Cardiogenesis and Cardiovascular Diseases

Today, cardiovascular diseases remain a leading cause of morbidity and mortality worldwide. Endothelial to mesenchymal transition (EndMT) does not only play a major role in the course of development but also contributes to several cardiovascular diseases in adulthood. EndMT is characterized by down-regulation of the endothelial proteins and highly up-regulated fibrotic specific genes and extracellular matrix-forming proteins. EndMT is also a transforming growth factor-β-driven (TGF-β) process in which endothelial cells lose their endothelial characteristics and acquire a mesenchymal phenotype with expression of α-smooth muscle actin (α-SMA), fibroblast-specific protein 1, etc. EndMT is a vital process during cardiac development, thus disrupted EndMT gives rise to the congenital heart diseases, namely septal defects and valve abnormalities. In this review, we have discussed the main signaling pathways and mechanisms participating in the process of EndMT such as TGF-β and Bone morphogenetic protein (BMP), Wnt^#, and Notch signaling pathway and also studied the role of EndMT in physiological cardiovascular development and pathological conditions including myocardial infarction, pulmonary arterial hypertension, congenital heart defects, cardiac fibrosis, and atherosclerosis. As a perspective view, having a clear understanding of involving cellular and molecular mechanisms in EndMT and conducting Randomized controlled trials (RCTs) with a large number of samples for involving pharmacological agents may guide us into novel therapeutic approaches of congenital disorders and heart diseases.

Pulmonary Hypertension in Acute and Chronic High Altitude Maladaptation Disorders

Alveolar hypoxia is the most prominent feature of high altitude environment with well-known consequences for the cardio-pulmonary system, including development of pulmonary hypertension. Pulmonary hypertension due to an exaggerated hypoxic pulmonary vasoconstriction contributes to high altitude pulmonary edema (HAPE), a life-threatening disorder, occurring at high altitudes in non-acclimatized healthy individuals. Despite a strong physiologic rationale for using vasodilators for prevention and treatment of HAPE, no systematic studies of their efficacy have been conducted to date. Calcium-channel blockers are currently recommended for drug prophylaxis in high-risk individuals with a clear history of recurrent HAPE based on the extensive clinical experience with nifedipine in HAPE prevention in susceptible individuals. Chronic exposure to hypoxia induces pulmonary vascular remodeling and development of pulmonary hypertension, which places an increased pressure load on the right ventricle leading to right heart failure. Further, pulmonary hypertension along with excessive erythrocytosis may complicate chronic mountain sickness, another high altitude maladaptation disorder. Importantly, other causes than hypoxia may potentially underlie and/or contribute to pulmonary hypertension at high altitude, such as chronic heart and lung diseases, thrombotic or embolic diseases. Extensive clinical experience with drugs in patients with pulmonary arterial hypertension suggests their potential for treatment of high altitude pulmonary hypertension. Small studies have demonstrated their efficacy in reducing pulmonary artery pressure in high altitude residents. However, no drugs have been approved to date for the therapy of chronic high altitude pulmonary hypertension. This work provides a literature review on the role of pulmonary hypertension in the pathogenesis of acute and chronic high altitude maladaptation disorders and summarizes current knowledge regarding potential treatment options.

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.

Genetic Delivery and Gene Therapy in Pulmonary Hypertension

Pulmonary hypertension (PH) is a progressive complex fatal disease of multiple etiologies. Hyperproliferation and resistance to apoptosis of vascular cells of intimal, medial, and adventitial layers of pulmonary vessels trigger excessive pulmonary vascular remodeling and vasoconstriction in the course of pulmonary arterial hypertension (PAH), a subgroup of PH. Multiple gene mutation/s or dysregulated gene expression contribute to the pathogenesis of PAH by endorsing the proliferation and promoting the resistance to apoptosis of pulmonary vascular cells. Given the vital role of these cells in PAH progression, the development of safe and efficient-gene therapeutic approaches that lead to restoration or down-regulation of gene expression, generally involved in the etiology of the disease is the need of the hour. Currently, none of the FDA-approved drugs provides a cure against PH, hence innovative tools may offer a novel treatment paradigm for this progressive and lethal disorder by silencing pathological genes, expressing therapeutic proteins, or through gene-editing applications. Here, we review the effectiveness and limitations of the presently available gene therapy approaches for PH. We provide a brief survey of commonly existing and currently applicable gene transfer methods for pulmonary vascular cells in vitro and describe some more recent developments for gene delivery existing in the field of PH in vivo.

Approaches to treat pulmonary arterial hypertension by targeting bmpr2 - from cell membrane to nucleus

Pulmonary arterial hypertension (PAH) is estimated to affect between 10-50 people per million worldwide. The lack of cure and devastating nature of the disease means that treatment is crucial to arrest rapid clinical worsening. Current therapies are limited by their focus on inhibiting residual vasoconstriction rather than targeting key regulators of the cellular pathology. Potential disease-modifying therapies may come from research directed towards causal pathways involved in the cellular and molecular mechanisms of disease. It is widely acknowledged, that targeting reduced expression of the critical bone morphogenetic protein type-2 receptor (BMPR2) and its associated signalling pathways is a compelling therapeutic avenue to explore. In this review we highlight the advances that have been made in understanding this pathway and the therapeutics that are being tested in clinical trials and the clinic to treat PAH.

Endothelial to Mesenchymal Transition in Pulmonary Vascular Diseases

Lung diseases, such as pulmonary hypertension and pulmonary fibrosis, are life-threatening diseases and have common features of vascular remodeling. During progression, extracellular matrix protein deposition and dysregulation of proteolytic enzymes occurs, which results in vascular stiffness and dysfunction. Although vasodilators or anti-fibrotic therapy have been mainly used as therapy owing to these characteristics, their effectiveness does not meet expectations. Therefore, a better understanding of the etiology and new therapeutic approaches are needed. Endothelial cells (ECs) line the inner walls of blood vessels and maintain vascular homeostasis by protecting vascular cells from pathological stimuli. Chronic stimulation of ECs by various factors, including pro-inflammatory cytokines and hypoxia, leads to ECs undergoing an imbalance of endothelial homeostasis, which results in endothelial dysfunction and is closely associated with vascular diseases. Emerging studies suggest that endothelial to mesenchymal transition (EndMT) contributes to endothelial dysfunction and plays a key role in the pathogenesis of vascular diseases. EndMT is a process by which ECs lose their markers and show mesenchymal-like morphological changes, and gain mesenchymal cell markers. Despite the efforts to elucidate these molecular mechanisms, the role of EndMT in the pathogenesis of lung disease still requires further investigation. Here, we review the importance of EndMT in the pathogenesis of pulmonary vascular diseases and discuss various signaling pathways and mediators involved in the EndMT process. Furthermore, we will provide insight into the therapeutic potential of targeting EndMT.

TWIST1 Drives Smooth Muscle Cell Proliferation in Pulmonary Hypertension via Loss of GATA-6 and BMPR2

Rationale: The bHLH (basic helix-loop-helix) transcription factor TWIST1 (Twist-related protein 1) controls cell proliferation and differentiation in tissue development and disease processes. Recently, endothelial TWIST1 has been linked to pulmonary hypertension (PH) and endothelial-to-mesenchymal transition, yet the role of TWIST1 in smooth muscle cells (SMCs) remains so far unclear.Objectives: To define the role of TWIST1 in SMCs in the pathogenesis of PH.Methods: SMC-specific TWIST1-deficient mice, SMC-specific TWIST1 silencing in rats, mass spectrometry, immunoprecipitation, and chromatin immunoprecipitation were used to delineate the role of SMC TWIST1 in PH.Measurements and Main Results: In pulmonary vessels from patients with PH and rodent PH models, TWIST1 expression was markedly increased and predominantly localized to SMCs. SMC-specific TWIST1 deficiency or silencing attenuated the development of PH and distal vessel muscularization in chronically hypoxic mice and in monocrotaline-treated rats. In vitro, TWIST1 inhibition or silencing prevented pulmonary artery SMC proliferation and migration. Mechanistically, the observed effects were mediated, at least in part, by TWIST1-dependent degradation of GATA-6 (GATA-binding protein 6). BMPR2 (bone morphogenetic protein receptor-2) was identified as a novel downstream target of GATA-6, which directly binds to its promoter. Inhibition of TWIST1 promoted the recruitment of GATA-6 to the BMPR2 promoter and restored BMPR2 functional expression.Conclusions: Our findings identify a key role for SMC TWIST1 in the pathogenesis of lung vascular remodeling and in PH that is partially mediated via reduced GATA-6-dependent BMPR2 expression. Inhibition of SMC TWIST1 may constitute a new therapeutic strategy for the treatment of PH.

The protective effects of MSC-EXO against pulmonary hypertension through regulating Wnt5a/BMP signalling pathway

The aim of the study was to explore the mechanism of mesenchymal stem cell‐derived exosomes (MSC‐EXO) to protect against experimentally induced pulmonary hypertension (PH). Monocrotaline (MCT)‐induced rat model of PH was successfully established by a single intraperitoneal injection of 50 mg/kg MCT, 3 weeks later the animals were treated with MSC‐EXO via tail vein injection. Post‐operation, our results showed that MSC‐EXO could significantly reduce right ventricular systolic pressure (RVSP) and the right ventricular hypertrophy index, attenuate pulmonary vascular remodelling and lung fibrosis in vivo. In vitro experiment, the hypoxia models of pulmonary artery endothelial cell (PAEC) and pulmonary vascular smooth muscle cell (PASMC) were used. We found that the expression levels of Wnt5a, Wnt11, BMPR2, BMP4 and BMP9 were increased, but β‐catenin, cyclin D1 and TGF‐β1 were decreased in MSC‐EXO group as compared with MCT or hypoxia group in vivo or vitro. However, these increased could be blocked when cells were transfected with Wnt5a siRNA in vitro. Taken together, these results suggested that the mechanism of MSC‐EXO to prevent PH vascular remodelling may be via regulation of Wnt5a/BMP signalling pathway.

Periostin

Rationale:

POSTN (Periostin) is an ECM (extracellular matrix) protein involved in tissue remodeling in response to injury and a contributing factor in tumorigenesis, suggesting that POSTN plays a role in the pathogenesis of pulmonary hypertension (PH).

Objective:

We aimed to gain insight into the mechanistic contribution of POSTN in experimental mouse models of PH and correlate these findings with PH in humans.

Methods and Results:

We used genetic epistasis approaches in human pulmonary artery endothelial cells (hPAECs), human pulmonary artery smooth muscle cells, and experimental mouse models of PH (Sugen 5416/hypoxia or chronic hypoxia) to discern the role of POSTN and its relationship to HIF (hypoxia-inducible factor)-1α signaling. We found that POSTN expression was correlated with the extent of PH in mouse models and in humans. Decreasing POSTN improved hemodynamic and cardiac responses in PH mice, blunted the release of growth factors and HIF-1α, and reversed the downregulated BMPR (bone morphogenetic protein receptor)-2 expression in hPAECs from patients with PH, whereas increasing POSTIN had the opposite effects and induced a hyperproliferative and promigratory phenotype in both hPAECs and human pulmonary artery smooth muscle cells. Overexpression of POSTN-induced activation of HIFs and increased the production of ET (endothelin)-1 and VEGF (vascular endothelial growth factor) in hPAECs. SiRNA-mediated knockdown of HIF-1α abolished the proangiogenic effect of POSTN. Blockade of TrkB (tyrosine kinase receptor B) attenuated the effect of POSTN on HIF-1α expression, while inhibition of HIF-1α reduced the expression of POSTN and TrkB. These results suggest that hPAECs produce POSTN via a HIF-1α-dependent mechanism.

Conclusions:

Our study reveals that POSTN expression is increased in human and animal models of PH and fosters PH development via a positive feedback loop between HIF-1α and POSTN during hypoxia. We propose that manipulating POSTIN expression may be an efficacious therapeutic target in the treatment of PH. Our results also suggest that POSTN may serve as a biomarker to estimate the severity of PH.

Endothelial BMPR2 Loss Drives a Proliferative Response to BMP (Bone Morphogenetic Protein) 9 via Prolonged Canonical Signaling

Supplemental Digital Content is available in the text.

Pulmonary arterial hypertension is a disease of proliferative vascular occlusion that is strongly linked to mutations in BMPR2—the gene encoding the BMPR-II (BMP [bone morphogenetic protein] type II receptor). The endothelial-selective BMPR-II ligand, BMP9, reverses disease in animal models of pulmonary arterial hypertension and suppresses the proliferation of healthy endothelial cells. However, the impact of BMPR2 loss on the antiproliferative actions of BMP9 has yet to be assessed.

Protein tyrosine phosphatase L1 represses endothelial-mesenchymal transition by inhibiting IL-1β/NF-κB/Snail signaling

Endothelial-mesenchymal transition (EnMT) plays a pivotal role in various diseases, including pulmonary hypertension (PH), and transcription factors like Snail are key regulators of EnMT. In this study we investigated how these factors were regulated by PH risk factors (e.g. inflammation and hypoxia) in human umbilical vein endothelial cells (HUVECs). We showed that treatment with interleukin 1β (IL-1β) induced EnMT of HUVECs via activation of NF-κB/Snail pathway, which was further exacerbated by knockdown of protein tyrosine phosphatase L1 (PTPL1). We demonstrated that PTPL1 inhibited NF-κB/Snail through dephosphorylating and stabilizing IκBα. IL-1β or hypoxia could downregulate PTPL1 expression in HUVECs. The deregulation of PTPL1/NF-κB signaling was validated in a monocrotaline-induced rat PH (MCT-PH) model and clinical PH specimens. Our findings provide novel insights into the regulatory mechanisms of EnMT, and have implications for identifying new therapeutic targets for clinical PH.

Endothelial to mesenchymal transition (EndMT) and vascular remodeling in pulmonary hypertension and idiopathic pulmonary fibrosis

INTRODUCTION

Idiopathic pulmonary fibrosis (IPF) is a chronic, progressive, and irreversible fibrotic disease associated with respiratory failure. The disease remains idiopathic, but repeated alveolar epithelium injury, disruption of alveolar-capillary integrity, abnormal vascular repair, and pulmonary vascular remodeling are considered possible pathogenic mechanisms. Also, the development of comorbidities such as pulmonary hypertension (PH) could further impact disease outcome, quality of life and survival rates in IPF.

AREAS COVERED

The current review provides a comprehensive literature survey of the mechanisms involved in the development and manifestations of IPF and their links to PH pathology. This review also provides the current understanding of molecular mechanisms that link the two pathologies and will specifically decipher the role of endothelial to mesenchymal transition (EndMT) along with the possible triggers of EndMT. The possibility of targeting EndMT as a therapeutic option in IPF is discussed.

EXPERT OPINION

With a steady increase in prevalence and mortality, IPF is no longer considered a rare disease. Thus, it is of utmost importance and urgency that the underlying profibrotic pathways and mechanisms are fully understood, to enable the development of novel therapeutic strategies.

Pharmacology of Pulmonary Arterial Hypertension: An Overview of Current and Emerging Therapies

Pulmonary arterial hypertension is a rare and devastating disease characterized by an abnormal chronic increase in pulmonary arterial pressure above 20 mmHg at rest, with a poor prognosis if not treated. Currently, there is not a single fully effective therapy, even though a dozen of drugs have been developed in the last decades. Pulmonary arterial hypertension is a multifactorial disease, meaning that several molecular mechanisms are implicated in its pathology. The main molecular pathways regulating the pulmonary vasomotor tone-endothelin, nitric oxide, and prostacyclin-are the most biologically and therapeutically explored to date. However, drugs targeting these pathways have already found their limitations. In the last years, translational research and clinical trials have made a strong effort in suggesting and testing novel therapeutic strategies for this disease. These approaches involve targeting the main molecular pathways with novel drugs, drug repurposing for novel targets, and also using combinatorial therapies. In this review, we summarize current strategies and drugs targeting the endothelin, nitric oxide, and prostacyclin pathways, as well as, the emerging new drugs proposed to cope with vascular remodelling, metabolic switch, perivascular inflammation, epigenetic modifications, estrogen deregulation, serotonin, and other neurohumoral mechanisms characteristic of this disease. Nowadays, pulmonary arterial hypertension remains an incurable disease; however, the incoming new knowledge makes us believe that new promising therapies are coming to the clinical arena soon.

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

Background: Mutations in bone morphogenetic protein receptor type II (BMPR2) are leading to the development of hereditary pulmonary arterial hypertension (PAH). In non-hereditary forms of PAH, perturbations in the transforming growth factor-β (TGF-β)/BMP-axis are believed to cause deficient BMPR2 signaling by changes in receptor expression, the activity of the receptor and/or downstream signaling. To date, BMPR2 expression and its activity in the lungs of patients with non-hereditary PAH is poorly characterized. In recent decades, different animal models have been used to understand the role of BMPR2 signaling in PAH pathophysiology. Specifically, the monocrotaline (MCT) and Sugen-Hypoxia (SuHx) models are extensively used in interventional studies to examine if restoring BMPR2 signaling results in PAH disease reversal. While PAH is assumed to develop in patients over months or years, pulmonary hypertension in experimental animal models develops in days or weeks. It is therefore likely that modifications in BMP and TGF-β signaling in these models do not fully recapitulate those in patients. In order to determine the translational potential of the MCT and SuHx models, we analyzed the BMPR2 expression and activity in the lungs of rats with experimentally induced PAH and compared this to the BMPR2 expression and activity in the lungs of PAH patients. Methods: the BMPR2 expression was analyzed by Western blot analysis and immunofluorescence (IF) microscopy to determine the quantity and localization of the receptor in the lung tissue from normal control subjects and patients with hereditary or idiopathic PAH, as well as in the lungs of control rats and rats with MCT or SuHx-induced PAH. The activation of the BMP pathway was analyzed by determining the level and localization of phosphorylated Smad1/5/8 (pSmad 1/5/8), a downstream mediator of canonical BMPR2 signaling. Results: While BMPR2 and pSmad 1/5/8 expression levels were unaltered in whole lung lysates/homogenates from patients with hereditary and idiopathic PAH, IF analysis showed that BMPR2 and pSmad 1/5/8 levels were markedly decreased in the pulmonary vessels of both PAH patient groups. Whole lung BMPR2 expression was variable in the two PAH rat models, while in both experimental models the expression of BMPR2 in the lung vasculature was increased. However, in the human PAH lungs, the expression of pSmad 1/5/8 was downregulated in the lung vasculature of both experimental models. Conclusion: BMPR2 receptor expression and downstream signaling is reduced in the lung vasculature of patients with idiopathic and hereditary PAH, which cannot be appreciated when using human whole lung lysates. Despite increased BMPR2 expression in the lung vasculature, the MCT and SuHx rat models did develop PAH and impaired downstream BMPR2-Smad signaling similar to our findings in the human lung.

Pulmonary arterial hypertension specific therapy: The old and the new

Pulmonary arterial hypertension (PAH) is a vascular disorder associated with high morbidity and mortality rate and is characterized by pulmonary vascular remodeling and increased pulmonary vascular resistance, ultimately resulting in right ventricular failure and death. Over the past few decades, significant advances in the understanding of the epidemiology, pathogenesis, and pathophysiology of pulmonary arterial hypertension have occured. This has led to the development of disease specific treatment including prostanoids, endothelin receptor antagonists, phosphodiesterase inhibitors, and soluble guanylate cyclase stimulators. These therapies significantly improve exercise capacity, quality of life, pulmonary hemodynamics, but none of the current treatments are actually curative and long-term prognosis remains poor. Thus, there is a clear need to develop new therapies. Several potential pharmacologic agents for the treatment of pulmonary arterial hypertension are under clinical development and some promising results with these treatments have been reported. These agents include tyrosine protein kinase inhibitors, rho-kinase inhibitors, synthetically produced vasoactive intestinal peptide, antagonists of the 5-HT2 receptors, and others. This article will review several of these promising new therapies and will discuss the current evidence regarding their potential benefit in pulmonary arterial hypertension.

Reversal of Hypoxic Pulmonary Hypertension by Hypoxia-Inducible Overexpression of Angiotensin-(1-7) in Pulmonary Endothelial Cells

Hypoxia-induced pulmonary vascular constriction and structure remodeling are the main causes of hypoxic pulmonary hypertension. In the present study, an adeno-associated virus vector, containing Tie2 promoter and hypoxia response elements, was designed and named HTSFcAng(1-7). Its targeting, hypoxic inducibility, and vascular relaxation were examined in vitro, and its therapeutic effects on hypobaric hypoxia-induced pulmonary hypertension were examined in rats. Transfection of HTSFcAng(1-7) specifically increased the expression of angiotensin-(1-7) in endothelial cells in normoxia. Hypoxia increased the expression of angiotensin-(1-7) in HTSFcAng(1-7)-transfected endothelial cells. The condition medium from HTSFcAng(1-7)-transfected endothelial cells inhibited the hypoxia-induced proliferation of pulmonary artery smooth muscle cells, relaxed the pulmonary artery rings, totally inhibited hypoxia-induced early contraction, enhanced maximum relaxation, and reversed phase II constriction to sustained relaxation. In hypoxic pulmonary hypertension rats, treatment with HTSFcAng(1-7) by nasal drip adeno-associated virus significantly reversed hypoxia-induced hemodynamic changes and pulmonary artery-wall remodeling, accompanied by the concomitant overexpression of angiotensin-(1-7), mainly in the endothelial cells in the lung. Therefore, hypoxia-inducible overexpression of angiotensin-(1-7) in pulmonary endothelial cells may be a potential strategy for the gene therapy of hypoxic pulmonary hypertension.

Drug Treatment of Pulmonary Hypertension in Children

Pulmonary arterial hypertension (PAH) is a rare disease in infants and children that is associated with significant morbidity and mortality. The disease is characterized by progressive pulmonary vascular functional and structural changes resulting in increased pulmonary vascular resistance and eventual right heart failure and death. In many pediatric patients, PAH is idiopathic or associated with congenital heart disease and rarely is associated with other conditions such as connective tissue or thromboembolic disease. PAH associated with developmental lung diseases such as bronchopulmonary dysplasia or congenital diaphragmatic hernia is increasingly more recognized in infants and children. Although treatment of the underlying disease and reversal of advanced structural changes have not yet been achieved with current therapy, quality of life and survival have improved significantly. Targeted pulmonary vasodilator therapies, including endothelin receptor antagonists, prostacyclin analogs, and phosphodiesterase type 5 inhibitors have resulted in hemodynamic and functional improvement in children. The management of pediatric PAH remains challenging as treatment decisions depend largely on results from evidence-based adult studies and the clinical experience of pediatric experts. This article reviews the current drug therapies and their use in the management of PAH in children.

Paeoniflorin Ameliorates Chronic Hypoxia/SU5416-Induced Pulmonary Arterial Hypertension by Inhibiting Endothelial-to-Mesenchymal Transition

Background

Endothelial cells dysfunction is one of the hallmark pathogenic features of pulmonary arterial hypertension (PAH). Paeoniflorin (PF) is a monoterpene glycoside with endothelial protection, vasodilation, antifibrotic, anti–inflammatory and antioxidative properties. However, the effects of PF on PAH remain unknown.

Methods

Here, we investigated the efficacy of PF in the SU5416/hypoxia (SuHx) rat model of PAH. Human pulmonary arterial endothelial cells (HPAECs) were exposed to 1% O₂ with or without PF treatment.

Results

Hemodynamics analysis showed that prophylactic treatment with PF (300 mg/kg i.g. daily for 21 days) significantly inhibited chronic hypoxia/SU5416-induced elevations of right ventricular systolic pressure (RVSP) and right ventricular hypertrophy index in rats. Meanwhile, PF significantly reduced pulmonary vascular remodeling, as well as alleviated collagen deposition in lungs and right ventricles in SuHx rats. Additionally, PF inhibited SuHx–induced down-regulation of endothelial marker (vascular endothelial cadherin) and up-regulation of mesenchymal markers (fibronectin and vimentin) in lung, suggesting that PF could inhibit SuHx–induced endothelial-to-mesenchymal transition (EndMT) in lung. Further in vitro studies confirmed that PF treatment suppressed hypoxia-induced EndMT in HPAECs, which was abolished by the knockdown of bone morphogenetic protein receptor type 2 (BMPR2) in HPAECs.

Conclusion

Taken together, our findings suggest that PF ameliorates BMPR2 down-regulation-mediated EndMT and thereafter alleviates SuHx–induced PAH in rats.

Protective effect of hydrogen sulfide on monocrotaline‑induced pulmonary arterial hypertension via inhibition of the endothelial mesenchymal transition

Endothelial‑to‑mesenchymal transition (EndMT) serves an important role in the vascular remodeling of pulmonary arterial hypertension (PAH). However, little is known about the correlation between hydrogen sulfide (H2S), a protective gaseous mediator in PAH and the process of EndMT. Male Sprague‑Dawley rats (10 weeks old) received a single dose of monocrotaline (MCT; i.p., 60 mg/kg) and were randomly treated with NaHS [an H2S donor; intraperitoneal (i.p.) 1 mg/kg/day], DL‑propagylglycine (an inhibitor of H2S synthesis; PAG; i.p., 10 mg/kg/day) or saline, 7 days after MCT injection. Rats were sacrificed 21 days after MCT injection. A selection of human pulmonary artery endothelial cells (HPAECs) were pretreated with NaHS or saline and stimulated with transforming growth factor (TGF)‑β1 (10 ng/ml), and the other HPAECs were transfected with a cystathionine γ‑lyase (CSE, an H2S synthesizing enzyme) plasmid and subsequently stimulated with TGF‑β1. NaHS was indicated to inhibit EndMT and PAH progression by inhibiting the induction of the nuclear factor (NF)‑κB‑Snail pathway. In contrast, the depletion of H2S formation by PAG exacerbated EndMT and PAH by activating NF‑κB‑Snail molecules. In HPAECs, NaHS dose‑dependently inhibited TGF‑β1‑induced EndMT and the activation of the NF‑κB‑Snail pathway. Transfection with a CSE plasmid significantly repressed TGF‑β1‑induced expression of the mesenchymal marker and upregulated the expression of the endothelial marker, which was accompanied by the suppression of the NF‑κB‑Snail pathway. The inhibitory effect of CSE overexpression on TGF‑β1‑induced EndMT was significantly reversed by pretreatment with PAG. In conclusion, the current study provides novel information elucidating the beneficial effect of H2S on PAH through inhibiting the induction of the NF‑κB‑Snail pathway and the subsequent process of EndMT in pulmonary arteries.