Transgenic expression of human matrix metalloproteinase-9 augments monocrotaline-induced pulmonary arterial hypertension in mice

Text Mining-Based Drug Discovery for Connective Tissue Disease–Associated Pulmonary Arterial Hypertension

Background: The current medical treatments for connective tissue disease–associated pulmonary arterial hypertension (CTD-PAH) do not show favorable efficiency for all patients, and identification of novel drugs is desired.

Methods: Text mining was performed to obtain CTD- and PAH-related gene sets, and the intersection of the two gene sets was analyzed for functional enrichment through DAVID. The protein–protein interaction network of the overlapping genes and the significant gene modules were determined using STRING. The enriched candidate genes were further analyzed by Drug Gene Interaction database to identify drugs with potential therapeutic effects on CTD-PAH.

Results: Based on text mining analysis, 179 genes related to CTD and PAH were identified. Through enrichment analysis of the genes, 20 genes representing six pathways were obtained. To further narrow the scope of potential existing drugs, we selected targeted drugs with a Query Score ≥5 and Interaction Score ≥1. Finally, 13 drugs targeting the six genes were selected as candidate drugs, which were divided into four drug–gene interaction types, and 12 of them had initial drug indications approved by the FDA. The potential gene targets of the drugs on this list are IL-6 (one drug) and IL-1β (two drugs), MMP9 (one drug), VEGFA (three drugs), TGFB1 (one drug), and EGFR (five drugs). These drugs might be used to treat CTD-PAH.

Conclusion: We identified 13 drugs targeting six genes that may have potential therapeutic effects on CTD-PAH.

Novel Experimental Therapies for Treatment of Pulmonary Arterial Hypertension

Pulmonary arterial hypertension (PAH) is a progressive and devastating disease characterized by pulmonary artery vasoconstriction and vascular remodeling leading to vascular rarefaction with elevation of pulmonary arterial pressures and pulmonary vascular resistance. Often PAH will cause death from right heart failure. Current PAH-targeted therapies improve functional capacity, pulmonary hemodynamics and reduce hospitalization. Nevertheless, today PAH still remains incurable and is often refractory to medical therapy, underscoring the need for further research. Over the last three decades, PAH has evolved from a disease of unknown pathogenesis devoid of effective therapy to a condition whose cellular, genetic and molecular underpinnings are unfolding. This article provides an update on current knowledge and summarizes the progression in recent advances in pharmacological therapy in PAH.

Pediatric Pulmonary Hypertension: Definitions, Mechanisms, Diagnosis, and Treatment

Pediatric pulmonary hypertension (PPH) is a multifactorial disease with diverse etiologies and presenting features. Pulmonary hypertension (PH), defined as elevated pulmonary artery pressure, is the presenting feature for several pulmonary vascular diseases. It is often a hidden component of other lung diseases, such as cystic fibrosis and bronchopulmonary dysplasia. Alterations in lung development and genetic conditions are an important contributor to pediatric pulmonary hypertensive disease, which is a distinct entity from adult PH. Many of the causes of pediatric PH have prenatal onset with altered lung development due to maternal and fetal conditions. Since lung growth is altered in several conditions that lead to PPH, therapy for PPH includes both pulmonary vasodilators and strategies to restore lung growth. These strategies include optimal alveolar recruitment, maintaining physiologic blood gas tension, nutritional support, and addressing contributing factors, such as airway disease and gastroesophageal reflux. The outcome for infants and children with PH is highly variable and largely dependent on the underlying cause. The best outcomes are for neonates with persistent pulmonary hypertension (PPHN) and reversible lung diseases, while some genetic conditions such as alveolar capillary dysplasia are lethal. © 2021 American Physiological Society. Compr Physiol 11:2135-2190, 2021.

Redox and Inflammatory Signaling, the Unfolded Protein Response, and the Pathogenesis of Pulmonary Hypertension

Protein folding overload and oxidative stress disrupt endoplasmic reticulum (ER) homeostasis, generating reactive oxygen species (ROS) and activating the unfolded protein response (UPR). The altered ER redox state induces further ROS production through UPR signaling that balances the cell fates of survival and apoptosis, contributing to pulmonary microvascular inflammation and dysfunction and driving the development of pulmonary hypertension (PH). UPR-induced ROS production through ER calcium release along with NADPH oxidase activity results in endothelial injury and smooth muscle cell (SMC) proliferation. ROS and calcium signaling also promote endothelial nitric oxide (NO) synthase (eNOS) uncoupling, decreasing NO production and increasing vascular resistance through persistent vasoconstriction and SMC proliferation. C/EBP-homologous protein further inhibits eNOS, interfering with endothelial function. UPR-induced NF-κB activity regulates inflammatory processes in lung tissue and contributes to pulmonary vascular remodeling. Conversely, UPR-activated nuclear factor erythroid 2-related factor 2-mediated antioxidant signaling through heme oxygenase 1 attenuates inflammatory cytokine levels and protects against vascular SMC proliferation. A mutation in the bone morphogenic protein type 2 receptor (BMPR2) gene causes misfolded BMPR2 protein accumulation in the ER, implicating the UPR in familial pulmonary arterial hypertension pathogenesis. Altogether, there is substantial evidence that redox and inflammatory signaling associated with UPR activation is critical in PH pathogenesis.

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.

Mechanical stretching of pulmonary vein stimulates matrix metalloproteinase-9 and transforming growth factor-β1 through stretch-activated channel/MAPK pathways in pulmonary hypertension due to left heart disease model rats

Pulmonary hypertension due to left heart disease (PH-LHD) is a momentous pulmonary hypertension disease, and left heart disease is the most familiar cause. Mechanical stretching may be a crucial cause of vascular remodeling. While, the underlining mechanism of mechanical stretching-induced in remodeling of pulmonary vein in the early stage of PH-LHD has not been completely elucidated. In our study, the PH-LHD model rats were successfully constructed. After 25 days, doppler echocardiography and hemodynamic examination were performed. In addition, after treatment, the levels of matrix metalloproteinase-9 (MMP-9) and transforming growth factor-β1 (TGF-β1) were determined by ELISA, immunohistochemistry and western blot assays in the pulmonary veins. Moreover, the pathological change of pulmonary tissues was evaluated by H&E staining. Our results uncovered that left ventricular insufficiency and interventricular septal shift could be observed in PH-LHD model rats, and the right ventricular systolic pressure (RVSP) and mean left atrial pressure (mLAP) were also elevated in PH-LHD model rats. Meanwhile, we found that MMP-9 and TGF-β1 could be highly expressed in PH-LHD model rats. Besides, we revealed that stretch-activated channel (SAC)/mitogen-activated protein kinases (MAPKs) signaling pathway could be involved in the upregulations of MMP-9 and TGF-β1 mediated by mechanical stretching in pulmonary vein. Therefore, current research revealed that mechanical stretching induced the increasing expressions of MMP-9 and TGF-β1 in pulmonary vein, which could be mediated by activation of SAC/MAPKs signaling pathway in the early stage of PH-LHD.

Transcriptomic analysis identifies Toll-like and Nod-like pathways and necroptosis in pulmonary arterial hypertension

Inflammation and immunity play a causal role in the pathogenesis of pulmonary vascular remodelling and pulmonary arterial hypertension (PAH). However, the pathways and mechanisms by which inflammation and immunity contribute to pulmonary vascular remodelling remain unknown. RNA sequencing was used to analyse the transcriptome in control and rats injected with monocrotaline (MCT) for various weeks. Using the transcriptional profiling of MCT‐induced PAH coupled with bioinformatics analysis, we clustered the differentially expressed genes (DEGs) and chose the increased expression patterns associated with inflammatory and immune response. We found the enrichment of Toll‐like receptor (TLR) and Nod‐like receptor (NLR) pathways and identified NF‐κB‐mediated inflammatory and immune profiling in MCT‐induced PAH. Pathway‐based data integration and visualization showed the dysregulated TLR and NLR pathways, including increased expression of TLR2 and NLRP3, and their downstream molecules. Further analysis revealed that the activation of TLR and NLR pathways was associated with up‐regulation of damage‐associated molecular patterns (DAMPs) and RIPK3‐mediated necroptosis was involved in the generation of DAMPs in MCT‐induced PAH. Collectively, we identify RIPK3‐mediated necroptosis and its triggered TLR and NLR pathways in the progression of pulmonary vascular remodelling, thus providing novel insights into the mechanisms underlying inflammation and immunity in the pathogenesis of PAH.

Hypoxic mast cells accelerate the proliferation, collagen accumulation and phenotypic alteration of human lung fibroblasts

Pulmonary vascular remodeling and fibrosis are the critical pathological characteristics of hypoxic pulmonary hypertension. Our previous study demonstrated that hypoxia is involved in the functional alteration of lung fibroblasts, but the underlying mechanism has yet to be fully elucidated. The aim of the present study was to investigate the effect of mast cells on the proliferation, function and phenotype of fibroblasts under hypoxic conditions. Hypoxia facilitated proliferation and the secretion of proinflammatory cytokines, including tumor necrosis factor (TNF)‑α and interleukin (IL)‑6, in human mast cells (HMC‑1). RNA sequencing identified 2,077 upregulated and 2,418 downregulated mRNAs in human fetal lung fibroblasts (HFL‑1) cultured in hypoxic conditioned medium from HMC‑1 cells compared with normoxic controls, which are involved in various pathways, including extracellular matrix organization, cell proliferation and migration. Conditioned medium from hypoxic HMC‑1 cells increased the proliferation and migration capacity of HFL‑1 and triggered phenotypic transition from fibroblasts to myofibroblasts. A greater accumulation of collagen type I and III was also observed in an HFL‑1 cell culture in hypoxic conditioned medium from HMC‑1 cells, compared with HFL‑1 cells cultured in normoxic control medium. The expression of matrix metalloproteinase (MMP)‑9 and MMP‑13 was upregulated in HFL‑1 cells grown in hypoxic conditioned medium from HMC‑1 cells. Similar pathological phenomena, including accumulation of mast cells, activated collagen metabolism and vascular remodeling, were observed in a hypoxic rat model. The results of the present study provide direct evidence that the multiple effects of the hypoxic microenvironment and mast cells on fibroblasts contribute to pulmonary vascular remodeling, and this process appears to be among the most important mechanisms underlying hypoxic pulmonary hypertension.

Monocrotaline pyrrole induces pulmonary endothelial damage through binding to and release from erythrocytes in lung during venous blood reoxygenation

Monocrotaline has been widely used to establish an animal model of pulmonary hypertension, most frequently in rats. An important feature of this model resides in the selectivity of monocrotaline injury toward the pulmonary vascular endothelium versus the systemic vasculature when administrated at standard dosage. The toxic metabolite of monocrotaline, monocrotaline pyrrole, is transported by erythrocytes. This study aimed to reveal whether partial pressure of oxygen of blood determined the binding and release of monocrotaline pyrrole from erythrocytes in rats with one subcutaneous injection of monocrotatline at the standard dosage of 60 mg/kg. Our experiments demonstrated that monocrotaline pyrrole bound to and released from erythrocytes at the physiological levels of partial pressure of oxygen in venous and arterial blood, respectively, and then aggregated on pulmonary artery endothelial cells. Monocrotaline pyrrole-induced damage of endothelial cells was also dependent on partial pressure of oxygen. In conclusion, our results demonstrate the importance of oxygen partial pressure on monocrotaline pyrrole binding to erythrocytes and on aggregation and injury of pulmonary endothelial cells. We suggest that these mechanisms contribute to pulmonary selectivity of this toxic injury model of pulmonary hypertension.

Plexiform Arteriopathy in Rodent Models of Pulmonary Arterial Hypertension

As time progresses, our understanding of disease pathology is propelled forward by technological advancements. Much of the advancements that aid in understanding disease mechanics are based on animal studies. Unfortunately, animal models often fail to recapitulate the entirety of the human disease. This is especially true with animal models used to study pulmonary arterial hypertension (PAH), a disease with two distinct phases. The first phase is defined by nonspecific medial and adventitial thickening of the pulmonary artery and is commonly reproduced in animal models, including the classic models (ie, hypoxia-induced pulmonary hypertension and monocrotaline lung injury model). However, many animal models, including the classic models, fail to capture the progressive, or second, phase of PAH. This is a stage defined by plexogenic arteriopathy, resulting in obliteration and occlusion of the small- to mid-sized pulmonary vessels. Each of these two phases results in severe pulmonary hypertension that directly leads to right ventricular hypertrophy, decompensated right-sided heart failure, and death. Fortunately, newly developed animal models have begun to address the second, more severe, side of PAH and aid in our ability to develop new therapeutics. Moreover, p38 mitogen-activated protein kinase activation emerges as a central molecular mediator of plexiform lesions in both experimental models and human disease. Therefore, this review will focus on plexiform arteriopathy in experimental animal models of PAH.

LncRNA H19 promotes the proliferation of pulmonary artery smooth muscle cells through AT1R via sponging let-7b in monocrotaline-induced pulmonary arterial hypertension

BACKGROUND

Pulmonary arterial hypertension (PAH) is related to inflammation, and the lncRNA H19 is associated with inflammation. However, whether PDGF-BB-H19-let-7b-AT1R axis contributes to the pathogenesis of PAH has not been thoroughly elucidated to date. This study investigated the role of H19 in PAH and its related mechanism.

METHODS

In the present study, SD rats, C57/BL6 mice and H19-/- mice were injected with monocrotaline (MCT) to establish a PAH model. H19 was detected in the cytokine-stimulated pulmonary arterial smooth muscle cells (PASMCs), serum and lungs of rats/mice. H19 overexpression and knockdown experiments were also conducted. A dual luciferase reporter assay was used to explore whether let-7b is a sponge miRNA of H19, and AT1R is a novel target of let-7b. A CCK-8 assay and flow cytometry were used to analyse cell proliferation.

RESULTS

The results showed that H19 was highly expressed in the serum and lungs of MCT-induced rats/mice, and H19 was upregulated by PDGF-BB in vitro. H19 upregulated AT1R expression via sponging miRNA let-7b following PDGF-BB stimulation. AT1R is a novel target of let-7b. Moreover, the overexpression of H19 and AT1R could facilitate PASMCs proliferation in vitro. H19 knockout protected mice from pulmonary artery remodeling and PAH following MCT treatment.

CONCLUSION

Our study showed that H19 is highly expressed in MCT-induced rodent lungs and upregulated by PDGF-BB. The H19-let-7b-AT1R axis contributed to the pathogenesis of PAH by stimulating PASMCs proliferation. The H19 knockout had a protective role in the development of PAH. H19 may be a potential tar-get for the treatment of PAH.

Role of extracellular matrix in the pathogenesis of pulmonary arterial hypertension

Pulmonary arterial hypertension (PAH) is characterized by remodeling of the extracellular matrix (ECM) of the pulmonary arteries with increased collagen deposition, cross-linkage of collagen, and breakdown of elastic laminae. Extracellular matrix remodeling occurs due to an imbalance in the proteolytic enzymes, such as matrix metalloproteinases, elastases, and lysyl oxidases, and tissue inhibitor of matrix metalloproteinases, which, in turn, results from endothelial cell dysfunction, endothelial-to-mesenchymal transition, and inflammation. ECM remodeling and pulmonary vascular stiffness occur early in the disease process, before the onset of the increase in the intimal and medial thickness and pulmonary artery pressure, suggesting that the ECM is a cause rather than a consequence of distal pulmonary vascular remodeling. ECM remodeling and increased pulmonary arterial stiffness promote proliferation of pulmonary vascular cells (endothelial cells, smooth muscle cells, and adventitial fibroblasts) through mechanoactivation of various signaling pathways, including transcriptional cofactors YAP/TAZ, transforming growth factor-β, transient receptor potential channels, Toll-like receptor, and NF-κB. Inhibition of ECM remodeling and mechanotransduction prevents and reverses experimental pulmonary hypertension. These data support a central role for ECM remodeling in the pathogenesis of the PAH, making it an attractive novel therapeutic target.

Pharmacokinetics and Bioavailability Study of Monocrotaline in Mouse Blood by Ultra-Performance Liquid Chromatography-Tandem Mass Spectrometry

BACKGROUND AND AIMS

The present study aimed to develop a simple and sensitive method for quantitative determination of monocrotaline (MCT) in mouse blood employing ultra-performance liquid chromatography-electrospray ionization tandem mass spectrometry (UPLC-ESI/MS/MS) using rhynchophylline as an internal standard.

METHODS

Proteins present in the blood samples were precipitated using acetonitrile. MCT was separated using a 1.7-μm ethylene bridged hybrid (BEH) C18 column (2.1 mm × 50 mm) with a gradient elution program and a constant flow rate of 0.4 mL/min. The LC mobile phase consisted of 10 mmol/L ammonium acetate (containing 0.1% formic acid) and acetonitrile. The total elution time was 4.0 min. The analytes were detected on a UPLC-ESI mass spectrometer in multiple reaction monitoring (MRM) mode and quantified.

RESULTS

The new method for the determination of MCT has a satisfactory linear detection range of 1-2000 ng/mL and excellent linearity (r = 0.9971). The lower limit of quantification (LLOQ) of MCT is 1.0 ng/mL. Intra- and interassay precisions of MCT were ≤13% with an accuracy from 96.2% to 106.6%. The average recovery of the new method was >75.0%, and matrix effects were between 89.0% and 94.3%. Based on the pharmacokinetics data, the bioavailability of MCT in mice was 88.3% after oral administration.

CONCLUSIONS

The results suggest that the newly standardized method for quantitative determination of MCT in whole blood is fast, reliable, specific, sensitive, and suitable for pharmacokinetic studies of MCT after intravenous or intragastric administration.

The Role of Neutrophils and Neutrophil Elastase in Pulmonary Arterial Hypertension

Pulmonary arterial hypertension (PAH) is a severe vasculopathy characterized by the presence of fibrotic lesions in the arterial wall and the loss of small distal pulmonary arteries. The vasculopathy is accompanied by perivascular inflammation and increased protease levels, with neutrophil elastase notably implicated in aberrant vascular remodeling. However, the source of elevated elastase levels in PAH remains unclear. A major source of neutrophil elastase is the neutrophil, an understudied cell population in PAH. The principal function of neutrophils is to destroy invading pathogens by means of phagocytosis and NET formation, but proteases, chemokines, and cytokines implicated in PAH can be released by and/or prime and activate neutrophils. This review focuses on the contribution of inflammation to the development and progression of the disease, highlighting studies implicating neutrophils, neutrophil elastase, and other neutrophil proteases in PAH. The roles of cytokines, chemokines, and neutrophil elastase in the disease are discussed and we describe new insight into the role neutrophils potentially play in the pathogenesis of PAH.

Mechanobiological Feedback in Pulmonary Vascular Disease

Vascular stiffening in the pulmonary arterial bed is increasingly recognized as an early disease marker and contributor to right ventricular workload in pulmonary hypertension. Changes in pulmonary artery stiffness throughout the pulmonary vascular tree lead to physiologic alterations in pressure and flow characteristics that may contribute to disease progression. These findings have led to a greater focus on the potential contributions of extracellular matrix remodeling and mechanical signaling to pulmonary hypertension pathogenesis. Several recent studies have demonstrated that the cellular response to vascular stiffness includes upregulation of signaling pathways that precipitate further vascular remodeling, a process known as mechanobiological feedback. The extracellular matrix modifiers, mechanosensors, and mechanotransducers responsible for this process have become increasingly well-recognized. In this review, we discuss the impact of vascular stiffening on pulmonary hypertension morbidity and mortality, evidence in favor of mechanobiological feedback in pulmonary hypertension pathogenesis, and the major contributors to mechanical signaling in the pulmonary vasculature.

α-Solanine reverses pulmonary vascular remodeling and vascular angiogenesis in experimental pulmonary artery hypertension

OBJECTIVE

Similar to cancer, pulmonary arterial hypertension (PAH) is characterized by vascular remodeling, which leads to obliteration of the small pulmonary arteriole, with marked proliferation of pulmonary artery smooth muscle cells (PASMC) and/or endothelial cells dysfunction. Aberrant expression of tumor suppressor genes is closely associated with susceptibility to PAH. We hypothesized that α-solanine, a glycoalkaloid found in members of the nightshade family known to have antitumor activity in different cancers, reverses experimental PAH by activating the tumor suppressor-axis inhibition protein 2 (AXIN2).

METHODS AND RESULTS

We investigated the effects of α-solanine on PASMC proliferation and apoptosis by using 5-ethynyl-2'-deoxyuridine proliferation assay, proliferating cell nuclear antigen and Ki67 staining, TUNEL and Anexine V assays. Scratch wound healing and tube formation assays were also used to study migration of endothelial cells. In vitro, we demonstrated, using cultured human PASMC from PAH patients, that α-solanine reversed dysfunctional AXIN2, β-catenin and bone morphogenetic protein receptor type-2 signaling, whereas restored [Ca]i, IL-6 and IL-8, contributing to the decrease of PAH-PASMC proliferation and resistance to apoptosis. Meanwhile, α-solanine inhibits proliferation, migration and tube formation of PAH-pulmonary artery endothelial cells by inhibiting Akt/GSK-3α activation. In vivo, α-solanine administration decreases distal pulmonary arteries remodeling, mean pulmonary arteries pressure and right ventricular hypertrophy in both monocrotaline-induced and Sugen/hypoxia-induced PAH in mice.

CONCLUSION

This study demonstrates that AXIN2/β-catenin axis and Akt pathway can be therapeutically targeted by α-solanine in PAH. α-Solanine could be used as a new therapeutic strategy for the treatment of PAH.

Right ventricular fibrosis and dysfunction: Actual concepts and common misconceptions

Fibrosis and remodeling of the right ventricle (RV) are associated with RV dysfunction and mortality of patients with pulmonary hypertension (PH) but it is unknown how much RV fibrosis contributes to RV dysfunction and mortality. RV fibrosis manifests as fibroblast accumulation and collagen deposition which may be excessive. Although extracellular matrix deposition leads to elevated ventricular stiffness, it is not known to which extent it affects RV function. Various animal models of pulmonary hypertension have been established to investigate the role of fibrosis in RV dysfunction and failure. However, they do not perfectly resemble the human disease. In the current review we describe the major characteristics of RV fibrosis, molecular mechanisms regulating the fibrotic process, and discuss how therapeutic targeting of fibrosis might affect RV function.

Dihydromyricetin prevents monocrotaline-induced pulmonary arterial hypertension in rats

Pulmonary artery hypertension (PAH) is a chronic and deadly disease, for which effective medical treatments are lacking. Here, we investigated whether 2R,3R-dihydromyricetin (DHM) could prevent monocrotaline (MCT)-induced PAH in rats. The MCT-injected rats were treated with normal saline or DHM (100mg/kg body weight/d) for 4 weeks, followed by measurements of right ventricular systolic pressure (RVSP), right ventricular hypertrophy index (RVHI), pulmonary arterial remodeling (PAR), and expression levels of IL-6, TNF-α, and IL-10. In vitro, we assessed the role of DHM on IL-6-induced migration of primary human pulmonary arterial smooth muscle cells (HPASMCs). We found that DHM treatment attenuated changes in RVSP, RVHI, and PAR in MCT-injected PAH rats. The observed increase of IL-6 levels in PAH rats was inhibited by DHM treatment. In vitro, DHM pretreatment reduced IL-6-induced HPASMC migration. Furthermore, MCT- and IL-6-mediated increases in MMP9 and P-STAT3 (tyr705) PY-STAT3 levels were suppressed by DHM treatment in vivo and in vitro. These results suggest that DHM could prevent MCT-induced rat PAH and IL-6-induced HPASMC migration through a mechanism involving inhibiting of the STAT3/MMP9 axis.

Role of P2X7R in the development and progression of pulmonary hypertension

BACKGROUND

Pulmonary arterial hypertension (PAH) is a devastating disease that lacks sufficient treatment. Studies have shown that the Nod-like receptor family, pyrin domain containing 3 (NLRP3) inflammasome contributes to PAH pathogenesis, but the role of the upstream molecular P2X₇ receptor (P2X₇R) has remained unexplored. We investigated the role of P2X7R in the pathogenesis of PAH.

METHODS AND RESULTS

PH was induced by a single subcutaneous injection of monocrotaline (MCT) (60 mg/kg) on left pneumonectomised Sprague-Dawley rats, as validated by significant increases in pulmonary artery pressure and vessel wall thickness. Marked P2X₇R was detected by predominant PA immunostaining in lungs from PH rats. Western blot revealed a significant increase in the protein levels of P2X₇R as well as NLRP3 and caspase-1 in the diseased lung tissue compared with normal tissue. The rats received A-740003 (a selective P2X₇ receptor antagonist, 30 mg/kg) daily starting from 1 week before or 2 weeks after MCT injection. Consequently, A-740003 reversed the NLRP3 inflammasome upregulation, significantly decreased the mean right ventricular (RV) pressure and RV hypertrophy, and reversed pulmonary arterial remodelling 4 weeks after MCT injection, as both a pretreatment and rescue intervention. Notably, A-740003 significantly reduced macrophage and pro-inflammatory cytokine levels, as measured via bronchoalveolar lavage. The recruitment of macrophages as well as collagen fibre deposition in the perivascular areas were also reduced, as confirmed by histological staining.

CONCLUSIONS

P2X₇R contributes to the pathogenesis of PH, probably in association with activation of the NLRP3 inflammasome. Blockade of P2X7R might be applied as a novel therapeutic approach for the treatment of PAH.

Valsartan attenuates pulmonary hypertension via suppression of mitogen activated protein kinase signaling and matrix metalloproteinase expression in rodents

It has previously been demonstrated that the renin-angiotensin system is involved in the pathogenesis and development of pulmonary hypertension (PH). However, the efficacy of angiotensin II type I (AT1) receptor blockers in the treatment of PH is variable. The present study examined the effects of the AT1 receptor blocker valsartan on monocrotaline (MCT)‑induced PH in rats and chronic hypoxia‑induced PH in mice. The results demonstrated that valsartan markedly attenuated development of PH in rats and mice, as indicated by reduced right ventricular systolic pressure, diminished lung vascular remodeling and decreased right ventricular hypertrophy, compared with vehicle treated animals. Immunohistochemical analyses of proliferating cell nuclear antigen expression revealed that valsartan suppressed smooth muscle cell proliferation. Western blot analysis demonstrated that valsartan limited activation of p38, c‑Jun N‑terminal kinase 1/2 and extracellular signal‑regulated kinase 1/2 signaling pathways and significantly reduced MCT‑induced upregulation of pulmonary matrix metalloproteinases‑2 and ‑9, and transforming growth factor‑β1 expression. The results suggested that valsartan attenuates development of PH in rodents by reducing expression of extracellular matrix remodeling factors and limiting smooth muscle cell proliferation to decrease pathological vascular remodeling. Therefore, valsartan may be a valuable future therapeutic approach for the treatment of PH.

Monocrotaline Induces Endothelial Injury and Pulmonary Hypertension by Targeting the Extracellular Calcium-Sensing Receptor

BACKGROUND

Monocrotaline has been widely used to establish an animal model of pulmonary hypertension. The molecular target underlying monocrotaline-induced pulmonary artery endothelial injury and pulmonary hypertension remains unknown. The extracellular calcium-sensing receptor (CaSR) and particularly its extracellular domain hold the potential structural basis for monocrotaline to bind. This study aimed to reveal whether monocrotaline induces pulmonary hypertension by targeting the CaSR.

METHODS AND RESULTS

Nuclear magnetic resonance screening through WaterLOGSY (water ligand-observed gradient spectroscopy) and saturation transfer difference on protein preparation demonstrated the binding of monocrotaline to the CaSR. Immunocytochemical staining showed colocalization of monocrotaline with the CaSR in cultured pulmonary artery endothelial cells. Cellular thermal shift assay further verified the binding of monocrotaline to the CaSR in pulmonary arteries from monocrotaline-injected rats. Monocrotaline enhanced the assembly of CaSR, triggered the mobilization of calcium signaling, and damaged pulmonary artery endothelial cells in a CaSR-dependent manner. Finally, monocrotaline-induced pulmonary hypertension in rats was significantly attenuated or abolished by the inhibitor, the general or lung knockdown or knockout of CaSR.

CONCLUSIONS

Monocrotaline aggregates on and activates the CaSR of pulmonary artery endothelial cells to trigger endothelial damage and, ultimately, induces pulmonary hypertension.

Inhibition of MMP-9 by green tea catechins and prediction of their interaction by molecular docking analysis

Green tea polyphenolic catechins have been shown to prevent various types of diseases such as pulmonary hypertension (PAH), cancer and cardiac and neurological disorders. Matrix metalloproteinases (MMPs) play an important role in the development of PAH. The present study demonstrated that among the four green tea catechins (EGCG, ECG, EC and EGC), EGCG and ECG inhibit pro-/active MMP-9 activities in pulmonary artery smooth muscle cell culture supernatant. Based on the above, we investigated the interactions of pro-/active MMP-9 with the green tea catechins by computational methods. In silico molecular docking analysis revealed a strong interaction between pro-/active MMP-9 and EGCG/ECG, and galloyl group appears to be responsible for this enhanced interaction. The molecular docking studies corroborate our experimental observation that EGCG and ECG are mainly active in preventing both the proMMP-9 and MMP-9 activities.

Absence of the inflammasome adaptor ASC reduces hypoxia-induced pulmonary hypertension in mice

Pulmonary hypertension is a serious condition that can lead to premature death. The mechanisms involved are incompletely understood although a role for the immune system has been suggested. Inflammasomes are part of the innate immune system and consist of the effector caspase-1 and a receptor, where nucleotide-binding oligomerization domain-like receptor pyrin domain-containing 3 (NLRP3) is the best characterized and interacts with the adaptor protein apoptosis-associated speck-like protein containing a caspase-recruitment domain (ASC). To investigate whether ASC and NLRP3 inflammasome components are involved in hypoxia-induced pulmonary hypertension, we utilized mice deficient in ASC and NLRP3. Active caspase-1, IL-18, and IL-1β, which are regulated by inflammasomes, were measured in lung homogenates in wild-type (WT), ASC(-/-), and NLRP3(-/-) mice, and phenotypical changes related to pulmonary hypertension and right ventricular remodeling were characterized after hypoxic exposure. Right ventricular systolic pressure (RVSP) of ASC(-/-) mice was significantly lower than in WT exposed to hypoxia (40.8 ± 1.5 mmHg vs. 55.8 ± 2.4 mmHg, P < 0.001), indicating a substantially reduced pulmonary hypertension in mice lacking ASC. Magnetic resonance imaging further supported these findings by demonstrating reduced right ventricular remodeling. RVSP of NLRP3(-/-) mice exposed to hypoxia was not significantly altered compared with WT hypoxia. Whereas hypoxia increased protein levels of caspase-1, IL-18, and IL-1β in WT and NLRP3(-/-) mice, this response was absent in ASC(-/-) mice. Moreover, ASC(-/-) mice displayed reduced muscularization and collagen deposition around arteries. In conclusion, hypoxia-induced elevated right ventricular pressure and remodeling were attenuated in mice lacking the inflammasome adaptor protein ASC, suggesting that inflammasomes play an important role in the pathogenesis of pulmonary hypertension.

Eukaryotic elongation factor 2 kinase mediates monocrotaline-induced pulmonary arterial hypertension via reactive oxygen species-dependent vascular remodeling

Pulmonary arterial (PA) hypertension (PAH) is a progressive and lethal disease that is caused by increased vascular contractile reactivity and structural remodeling. These changes contribute to increasing pulmonary peripheral vascular resistance, finally leading to right heart failure and death. Eukaryotic elongation factor 2 kinase (eEF2K) is a Ca2+/calmodulin-dependent protein kinase. We previously revealed that eEF2K protein increases in the mesenteric artery from spontaneously hypertensive rats and partly mediates the development of hypertension via a promotion of ROS-dependent vascular inflammatory responses and proliferation and migration of vascular smooth muscle cells. However, a role of eEF2K in the pathogenesis of PAH is unknown. In the present study, we tested the hypothesis that eEF2K may be involved in the pathogenesis of PAH. PAH was induced by a single intraperitoneal injection of monocrotaline (MCT; 60 mg/kg) to rats. A specific eEF2K inhibitor, A-484954 (2.5 mg·kg−1·day−1), was intraperitoneally injected for 14 days. Long-term A-484954 treatment inhibited MCT-induced increased PA pressure. It was revealed that A-484954 inhibited MCT-induced PA hypertrophy and fibrosis but not impairment of endothelium-dependent and -independent relaxation. Furthermore, A-484954 inhibited MCT-induced NADPH oxidase-1 expression and ROS generation as well as matrix metalloproteinase-2 activation. In conclusion, the present results suggest that eEF2K at least partly mediates MCT-induced PAH via stimulation of vascular structural remodeling perhaps through NADPH oxidase-1/ROS/matrix metalloproteinase-2 pathway.

A novel p38 mitogen-activated protein kinase/Elk-1 transcription factor-dependent molecular mechanism underlying abnormal endothelial cell proliferation in plexogenic pulmonary arterial hypertension

Plexiform lesions (PLs), the hallmark of plexogenic pulmonary arterial hypertension (PAH), contain phenotypically altered, proliferative endothelial cells (ECs). The molecular mechanism that contributes to EC proliferation and formation of PLs is poorly understood. We now show that a decrease in intersectin-1s (ITSN-1s) expression due to granzyme B (GrB) cleavage during inflammation associated with PAH and the high p38/Erk1/2(MAPK) activity ratio caused by the GrB/ITSN cleavage products lead to EC proliferation and selection of a proliferative/plexiform EC phenotype. We used human pulmonary artery ECs of PAH subjects (EC(PAH)), paraffin-embedded and frozen human lung tissue, and animal models of PAH in conjunction with microscopy imaging, biochemical, and molecular biology approaches to demonstrate that GrB cleaves ITSN-1s, a prosurvival protein of lung ECs, and generates two biologically active fragments, an N-terminal fragment (GrB-EH(ITSN)) with EC proliferative potential and a C-terminal product with dominant negative effects on Ras/Erk1/2. The proliferative potential of GrB-EH(ITSN) is mediated via sustained phosphorylation of p38(MAPK) and Elk-1 transcription factor and abolished by chemical inhibition of p38(MAPK). Moreover, lung tissue of PAH animal models and human specimens and EC(PAH) express lower levels of ITSN-1s compared with controls and the GrB-EH(ITSN) cleavage product. Moreover, GrB immunoreactivity is associated with PLs in PAH lungs. The concurrent expression of the two cleavage products results in a high p38/Erk1/2(MAPK) activity ratio, which is critical for EC proliferation. Our findings identify a novel GrB-EH(ITSN)-dependent pathogenic p38(MAPK)/Elk-1 signaling pathway involved in the poorly understood process of PL formation in severe PAH.

SMAD1 deficiency in either endothelial or smooth muscle cells can predispose mice to pulmonary hypertension

A deficiency in bone morphogenetic protein receptor type 2 (BMPR2) signaling is a central contributor in the pathogenesis of pulmonary arterial hypertension (PAH). We have recently shown that endothelial-specific Bmpr2 deletion by a novel L1Cre line resulted in pulmonary hypertension. SMAD1 is one of the canonical signal transducers of the BMPR2 pathway, and its reduced activity has been shown to be associated with PAH. To determine whether SMAD1 is an important downstream mediator of BMPR2 signaling in the pathogenesis of PAH, we analyzed pulmonary hypertension phenotypes in Smad1-conditional knockout mice by deleting the Smad1 gene either in endothelial cells or in smooth muscle cells using L1Cre or Tagln-Cre mouse lines, respectively. A significant number of the L1Cre(+);Smad1 (14/35) and Tagln-Cre(+);Smad1 (4/33) mutant mice showed elevated pulmonary pressure, right ventricular hypertrophy, and a thickening of pulmonary arterioles. A pulmonary endothelial cell line in which the Bmpr2 gene deletion can be induced by 4-hydroxy tamoxifen was established. SMAD1 phosphorylation in Bmpr2-deficient cells was markedly reduced by BMP4 but unaffected by BMP7. The sensitivity of SMAD2 phosphorylation by transforming growth factor-β1 was enhanced in the Bmpr2-deficient cells, and the inhibitory effect of transforming growth factor-β1-mediated SMAD2 phosphorylation by BMP4 was impaired in the Bmpr2-deficient cells. Furthermore, transcript levels of several known transforming growth factor-β downstream genes implicated in pulmonary hypertension were elevated in the Bmpr2-deficient cells. Taken together, these data suggest that SMAD1 is a critical mediator of BMPR2 signaling pertinent to PAH, and that an impaired balance between BMP4 and transforming growth factor-β1 may account for the pathogenesis of PAH.

Reactive oxygen species as therapeutic targets in pulmonary hypertension

Pulmonary hypertension (PH) is characterized by a progressive elevation of pulmonary arterial pressure due to alterations of both pulmonary vascular structure and function. This disease is rare but life-threatening, leading to the development of right heart failure. Current PH treatments, designed to target altered pulmonary vascular reactivity, include vasodilating prostanoids, phosphodiesterase-5 inhibitors and endothelin-1 receptor antagonists. Although managing to slow the progression of the disease, these molecules still do not cure PH. More effective treatments need to be developed, and novel therapeutic strategies, targeting in particular vascular remodelling, are currently under investigation. Reactive oxygen species (ROS) are important physiological messengers in vascular cells. In addition to atherosclerosis and other systemic vascular diseases, emerging evidence also support a role of ROS in PH pathogenesis. ROS production is increased in animal models of PH, associated with NADPH oxidases increased expression, in particular of several Nox enzymes thought to be the major source of ROS in the pulmonary vasculature. These increases have also been observed in vitro and in vivo in humans. Moreover, several studies have shown either the deleterious effect of agents promoting ROS generation on pulmonary vasculature or, conversely, the beneficial effect of antioxidant agents in animal models of PH. In these studies, ROS production has been directly linked to pulmonary vascular remodelling, endothelial dysfunction, altered vasoconstrictive responses, inflammation and modifications of the extracellular matrix, all important features of PH pathophysiology. Altogether, these findings indicate that ROS are interesting therapeutic targets in PH. Blockade of ROS-dependent signalling pathways, or disruption of sources of ROS in the pulmonary vasculature, targeting in particular Nox enzymes, represent promising new therapeutic strategies in this disease.

Etanercept attenuates short-term cigarette-smoke-exposure-induced pulmonary arterial remodelling in rats by suppressing the activation of TNF-a/NF-kB signal and the activities of MMP-2 and MMP-9

The pathogenesis of cigarette-smoke-exposure-induced pulmonary vasculature impairment is unclear. Cigarette-smoke-exposure-induced the accumulation of tumour necrosis factor-alpha (TNF-α) and upregulates the expression and activities of matrix metalloproteinases (MMPs) involved in smoke-induced vascular remodelling, which are important processes in the pathogenesis of vasculature impairment. The TNF-α antagonist Etanercept is an anti-inflammatory drug with a potential role in regulating MMP expression. To determine the effect of Etanercept on short-term smoke-induced pulmonary arteriole impairment and investigate its possible mechanism, male Sprague-Dawley rats were exposed to cigarette-smoke daily for two weeks in both the absence and presence of Etanercept. Cigarette-smoke-exposure-induced elevation of mean pulmonary artery pressures and medial hypertrophy of pulmonary arterioles were partially reduced by Etanercept. Up-regulation of the expression and activities of MMP-2 and MMP-9, induced by cigarette-smoke, were also suppressed significantly by Etanercept. Furthermore, Etanercept treatment significantly attenuated cigarette-smoke-induced TNFα accumulation and activation of nuclear factor NF-kB signal. These results suggest that Etanercept have the protective effects in cigarette-smoke-induced pulmonary vascular remodelling, with the attenuation of the up-regulated expression and activities of MMP-2 and MMP-9 and activation of TNF-α/NF-kB signal pathway probably being involved as part of its mechanism. Our study might provide insight into the development of new interventions for vasculature impairment.

A brief overview of mouse models of pulmonary arterial hypertension: problems and prospects

Many chronic pulmonary diseases are associated with pulmonary hypertension (PH) and pulmonary vascular remodeling, which is a term that continues to be used to describe a wide spectrum of vascular abnormalities. Pulmonary vascular structural changes frequently increase pulmonary vascular resistance, causing PH and right heart failure. Although rat models had been standard models of PH research, in more recent years the availability of genetically engineered mice has made this species attractive for many investigators. Here we review a large amount of data derived from experimental PH reports published since 1996. These studies using wild-type and genetically designed mice illustrate the challenges and opportunities provided by these models. Hemodynamic measurements are difficult to obtain in mice, and right heart failure has not been investigated in mice. Anatomical, cellular, and genetic differences distinguish mice and rats, and pharmacogenomics may explain the degree of PH and the particular mode of pulmonary vascular adaptation and also the response of the right ventricle.

Transgenic expression of human matrix metalloproteinase-1 attenuates pulmonary arterial hypertension in mice

PAH (pulmonary arterial hypertension) is a debilitating and life-threatening disease, often affecting young people. We specifically expressed human MMP-1 (matrix metalloproteinase-1) in mouse macrophages and examined its effects in attenuating the decompensating features of MCT (monocrotaline)-induced PAH. Measurement of RV (right ventricular) pressure revealed a 2.5-fold increase after treatment with MCT, which was reduced to 1.5-fold in MMP-1 transgenic mice. There was conspicuous pulmonary inflammation with chronic infiltration of mononuclear cells after the administration of MCT, which was significantly diminished in transgenic mice. Furthermore, transgenic mice showed decreased collagen deposition compared with WT (wild-type). Staining for Mac-3 (macrophage-3) and α-SMA (α-smooth muscle actin) revealed extensive infiltration of macrophages and medial hypertrophy of large pulmonary vessels with complete occlusion of small arteries respectively. These changes were markedly reduced in MMP-1 transgenic mice compared with WT. Western blotting for molecules involved in cell multiplication and proliferation depicted a significant decrease in the lung tissue of transgenic mice after the treatment with MCT. In conclusion, the present study demonstrated that transgenic expression of human MMP-1 decreased proliferation of smooth muscle cells and prevented excessive deposition of collagen in the pulmonary arterial tree. Our results indicate that up-regulation of MMP-1 could attenuate the debilitation of human PAH and provide an option for therapeutic intervention.

Pleiotropic effects of statins in distal human pulmonary artery smooth muscle cells

BACKGROUND

Recent clinical data suggest statins have transient but significant effects in patients with pulmonary arterial hypertension. In this study we explored the molecular effects of statins on distal human pulmonary artery smooth muscle cells (PASMCs) and their relevance to proliferation and apoptosis in pulmonary arterial hypertension.

METHODS

Primary distal human PASMCs from patients and controls were treated with lipophilic (simvastatin, atorvastatin, mevastatin and fluvastatin), lipophobic (pravastatin) and nitric-oxide releasing statins and studied in terms of their DNA synthesis, proliferation, apoptosis, matrix metalloproteinase-9 and endothelin-1 release.

RESULTS

Treatment of human PASMCs with selected statins inhibited DNA synthesis, proliferation and matrix metalloproteinase-9 production in a concentration-dependent manner. Statins differed in their effectiveness, the rank order of anti-mitogenic potency being simvastatin > atorvastatin > > pravastatin. Nevertheless, a novel nitric oxide-releasing derivative of pravastatin (NCX 6550) was effective. Lipophilic statins, such as simvastatin, also enhanced the anti-proliferative effects of iloprost and sildenafil, promoted apoptosis and inhibited the release of the mitogen and survival factor endothelin-1. These effects were reversed by mevalonate and the isoprenoid intermediate geranylgeranylpyrophosphate and were mimicked by inhibitors of the Rho and Rho-kinase.

CONCLUSIONS

Lipophilic statins exert direct effects on distal human PASMCs and are likely to involve inhibition of Rho GTPase signalling. These findings compliment some of the recently documented effects in patients with pulmonary arterial hypertension.

Pulmonary oxidative stress is increased in cyclooxygenase-2 knockdown mice with mild pulmonary hypertension induced by monocrotaline

The aim of this study was to examine the role of cyclooxygenase-2 (COX-2) and downstream signaling of prostanoids in the pathogenesis of pulmonary hypertension (PH) using mice with genetically manipulated COX-2 expression. COX-2 knockdown (KD) mice, characterized by 80–90% suppression of COX-2, and wild-type (WT) control mice were treated weekly with monocrotaline (MCT) over 10 weeks. Mice were examined for cardiac hypertrophy/function and right ventricular pressure. Lung histopathological analysis was performed and various assays were carried out to examine oxidative stress, as well as gene, protein, cytokine and prostanoid expression. We found that MCT increased right ventricular systolic and pulmonary arterial pressures in comparison to saline-treated mice, with no evidence of cardiac remodeling. Gene expression of endothelin receptor A and thromboxane synthesis, regulators of vasoconstriction, were increased in MCT-treated lungs. Bronchoalveolar lavage fluid and lung sections demonstrated mild inflammation and perivascular edema but activation of inflammatory cells was not predominant under the experimental conditions. Heme oxygenase-1 (HO-1) expression and indicators of oxidative stress in lungs were significantly increased, especially in COX-2 KD MCT-treated mice. Gene expression of NOX-4, but not NOX-2, two NADPH oxidase subunits crucial for superoxide generation, was induced by ∼4-fold in both groups of mice by MCT. Vasodilatory and anti-aggregatory prostacyclin was reduced by ∼85% only in MCT-treated COX-2 KD mice. This study suggests that increased oxidative stress-derived endothelial dysfunction, vasoconstriction and mild inflammation, exacerbated by the lack of COX-2, contribute to the pathogenesis of early stages of PH when mild hemodynamic changes are evident and not yet accompanied by vascular and cardiac remodeling.