The Sugen 5416/Hypoxia Mouse Model of Pulmonary Arterial Hypertension

MCJ: A mitochondrial target for cardiac intervention in pulmonary hypertension

Pulmonary hypertension (PH) can affect both pulmonary arterial tree and cardiac function, often leading to right heart failure and death. Despite the urgency, the lack of understanding has limited the development of effective cardiac therapeutic strategies. Our research reveals that MCJ modulates mitochondrial response to chronic hypoxia. MCJ levels elevate under hypoxic conditions, as in lungs of patients affected by COPD, mice exposed to hypoxia, and myocardium from pigs subjected to right ventricular (RV) overload. The absence of MCJ preserves RV function, safeguarding against both cardiac and lung remodeling induced by chronic hypoxia. Cardiac-specific silencing is enough to protect against cardiac dysfunction despite the adverse pulmonary remodeling. Mechanistically, the absence of MCJ triggers a protective preconditioning state mediated by the ROS/mTOR/HIF-1α axis. As a result, it preserves RV systolic function following hypoxia exposure. These discoveries provide a potential avenue to alleviate chronic hypoxia-induced PH, highlighting MCJ as a promising target against this condition.

Outcomes of pregnancy in mice with pulmonary hypertension induced by Hypoxia/SU5416

BACKGROUND

Pulmonary hypertension (PH) seriously affects the health of patients. We have found in clinical studies that PH has adverse effects on both maternal and offspring.

OBJECTIVE

To establish a animal model of PH induced by hypoxia/SU5416 and observe the effects of PH on pregnant mice and their fetuses.

METHODS

Twenty-four C57 mice aged 7-9 weeks were selected and divided into 4 groups with 6 mice in each group. ① Female mice with normal oxygen; ② Female mice with hypoxia/SU5416; ③ Pregnant mice with normal oxygen; ④ Pregnant mice with hypoxia/SU5416. After 19 days, weight, right ventricular systolic pressure (RVSP) and right ventricular hypertrophy index (RVHI) were compared in each group. Lung tissue and right ventricular blood were collected. The number and weight of fetal mice were also compared between the two pregnant groups.

RESULTS

There was no significant difference in RVSP and RVHI between female and pregnant mice under the same condition. Compared with normal oxygen condition, two groups of mice in hypoxia/SU5416 had poor development, RVSP and RVHI were significantly increased, the number of fetal mice was small, hypoplasia, degeneration and even abortion.

CONCLUSION

The model of mice PH was successfully established. PH affects the development and health of female and pregnant mice, and seriously affects the fetuses.

Polo-like kinase 1 promotes pulmonary hypertension

BACKGROUND

Pulmonary hypertension (PH) is a lethal vascular disease with limited therapeutic options. The mechanistic connections between alveolar hypoxia and PH are not well understood. The aim of this study was to investigate the role of mitotic regulator Polo-like kinase 1 (PLK1) in PH development.

METHODS

Mouse lungs along with human pulmonary arterial smooth muscle cells and endothelial cells were used to investigate the effects of hypoxia on PLK1. Hypoxia- or Sugen5416/hypoxia was applied to induce PH in mice. Plk1 heterozygous knockout mice and PLK1 inhibitors (BI 2536 and BI 6727)-treated mice were checked for the significance of PLK1 in the development of PH.

RESULTS

Hypoxia stimulated PLK1 expression through induction of HIF1α and RELA. Mice with heterozygous deletion of Plk1 were partially resistant to hypoxia-induced PH. PLK1 inhibitors ameliorated PH in mice.

CONCLUSIONS

Augmented PLK1 is essential for the development of PH and is a druggable target for PH.

Animal Disease Models and Patient-iPS-Cell-Derived In Vitro Disease Models for Cardiovascular Biology-How Close to Disease?

Currently, zebrafish, rodents, canines, and pigs are the primary disease models used in cardiovascular research. In general, larger animals have more physiological similarities to humans, making better disease models. However, they can have restricted or limited use because they are difficult to handle and maintain. Moreover, animal welfare laws regulate the use of experimental animals. Different species have different mechanisms of disease onset. Organs in each animal species have different characteristics depending on their evolutionary history and living environment. For example, mice have higher heart rates than humans. Nonetheless, preclinical studies have used animals to evaluate the safety and efficacy of human drugs because no other complementary method exists. Hence, we need to evaluate the similarities and differences in disease mechanisms between humans and experimental animals. The translation of animal data to humans contributes to eliminating the gap between these two. In vitro disease models have been used as another alternative for human disease models since the discovery of induced pluripotent stem cells (iPSCs). Human cardiomyocytes have been generated from patient-derived iPSCs, which are genetically identical to the derived patients. Researchers have attempted to develop in vivo mimicking 3D culture systems. In this review, we explore the possible uses of animal disease models, iPSC-derived in vitro disease models, humanized animals, and the recent challenges of machine learning. The combination of these methods will make disease models more similar to human disease.

Survivin inhibition with YM155 ameliorates experimental pulmonary arterial hypertension

Background: Imbalance between cell proliferation and apoptosis underlies the development of pulmonary arterial hypertension (PAH). Current vasodilator treatment of PAH does not target the uncontrolled proliferative process in pulmonary arteries. Proteins involved in the apoptosis pathway may play a role in PAH and their inhibition might represent a potential therapeutic target. Survivin is a member of the apoptosis inhibitor protein family involved in cell proliferation. Objectives: This study aimed to explore the potential role of survivin in the pathogenesis of PAH and the effects of its inhibition. Methods: In SU5416/hypoxia-induced PAH mice we assessed the expression of survivin by immunohistochemistry, western-blot analysis, and RT-PCR; the expression of proliferation-related genes (Bcl2 and Mki67); and the effects of the survivin inhibitor YM155. In explanted lungs from patients with PAH we assessed the expression of survivin, BCL2 and MKI67. Results: SU5416/hypoxia mice showed increased expression of survivin in pulmonary arteries and lung tissue extract, and upregulation of survivin, Bcl2 and Mki67 genes. Treatment with YM155 reduced right ventricle (RV) systolic pressure, RV thickness, pulmonary vascular remodeling, and the expression of survivin, Bcl2, and Mki67 to values similar to those in control animals. Lungs of patients with PAH also showed increased expression of survivin in pulmonary arteries and lung extract, and also that of BCL2 and MKI67 genes, compared with control lungs. Conclusion: We conclude that survivin might be involved in the pathogenesis of PAH and that its inhibition with YM155 might represent a novel therapeutic approach that warrants further evaluation.

Regnase-1 Prevents Pulmonary Arterial Hypertension Through mRNA Degradation of Interleukin-6 and Platelet-Derived Growth Factor in Alveolar Macrophages

BACKGROUND

Pulmonary arterial hypertension (PAH) is a type of pulmonary hypertension (PH) characterized by obliterative pulmonary vascular remodeling, resulting in right-sided heart failure. Although the pathogenesis of PAH is not fully understood, inflammatory responses and cytokines have been shown to be associated with PAH, in particular, with connective tissue disease-PAH. In this sense, Regnase-1, an RNase that regulates mRNAs encoding genes related to immune reactions, was investigated in relation to the pathogenesis of PH.

METHODS

We first examined the expression levels of ZC3H12A (encoding Regnase-1) in peripheral blood mononuclear cells from patients with PH classified under various types of PH, searching for an association between the ZC3H12A expression and clinical features. We then generated mice lacking Regnase-1 in myeloid cells, including alveolar macrophages, and examined right ventricular systolic pressures and histological changes in the lung. We further performed a comprehensive analysis of the transcriptome of alveolar macrophages and pulmonary arteries to identify genes regulated by Regnase-1 in alveolar macrophages.

RESULTS

ZC3H12A expression in peripheral blood mononuclear cells was inversely correlated with the prognosis and severity of disease in patients with PH, in particular, in connective tissue disease-PAH. The critical role of Regnase-1 in controlling PAH was also reinforced by the analysis of mice lacking Regnase-1 in alveolar macrophages. These mice spontaneously developed severe PAH, characterized by the elevated right ventricular systolic pressures and irreversible pulmonary vascular remodeling, which recapitulated the pathology of patients with PAH. Transcriptomic analysis of alveolar macrophages and pulmonary arteries of these PAH mice revealed that Il6, Il1b, and Pdgfa/b are potential targets of Regnase-1 in alveolar macrophages in the regulation of PAH. The inhibition of IL-6 (interleukin-6) by an anti-IL-6 receptor antibody or platelet-derived growth factor by imatinib but not IL-1β (interleukin-1β) by anakinra, ameliorated the pathogenesis of PAH.

CONCLUSIONS

Regnase-1 maintains lung innate immune homeostasis through the control of IL-6 and platelet-derived growth factor in alveolar macrophages, thereby suppressing the development of PAH in mice. Furthermore, the decreased expression of Regnase-1 in various types of PH implies its involvement in PH pathogenesis and may serve as a disease biomarker, and a therapeutic target for PH as well.

Mice with humanized immune system as novel models to study HIV-associated pulmonary hypertension

People living with HIV and who receive antiretroviral therapy have a significantly improved lifespan, compared to the early days without therapy. Unfortunately, persisting viral replication in the lungs sustains chronic inflammation, which may cause pulmonary vascular dysfunction and ultimate life-threatening Pulmonary Hypertension (PH). The mechanisms involved in the progression of HIV and PH remain unclear. The study of HIV-PH is limited due to the lack of tractable animal models that recapitulate infection and pathobiological aspects of PH. On one hand, mice with humanized immune systems (hu-mice) are highly relevant to HIV research but their suitability for HIV-PH research deserves investigation. On another hand, the Hypoxia-Sugen is a well-established model for experimental PH that combines hypoxia with the VEGF antagonist SU5416. To test the suitability of hu-mice, we combined HIV with either SU5416 or hypoxia. Using right heart catheterization, we found that combining HIV+SU5416 exacerbated PH. HIV infection increases human pro-inflammatory cytokines in the lungs, compared to uninfected mice. Histopathological examinations showed pulmonary vascular inflammation with arterial muscularization in HIV-PH. We also found an increase in endothelial-monocyte activating polypeptide II (EMAP II) when combining HIV+SU5416. Therefore, combinations of HIV with SU5416 or hypoxia recapitulate PH in hu-mice, creating well-suited models for infectious mechanistic pulmonary vascular research in small animals.

Important Functions and Molecular Mechanisms of Mitochondrial Redox Signaling in Pulmonary Hypertension

Mitochondria are important organelles that act as a primary site to produce reactive oxygen species (ROS). Additionally, mitochondria play a pivotal role in the regulation of Ca²⁺ signaling, fatty acid oxidation, and ketone synthesis. Dysfunction of these signaling molecules leads to the development of pulmonary hypertension (PH), atherosclerosis, and other vascular diseases. Features of PH include vasoconstriction and pulmonary artery (PA) remodeling, which can result from abnormal proliferation, apoptosis, and migration of PA smooth muscle cells (PASMCs). These responses are mediated by increased Rieske iron–sulfur protein (RISP)-dependent mitochondrial ROS production and increased mitochondrial Ca²⁺ levels. Mitochondrial ROS and Ca²⁺ can both synergistically activate nuclear factor κB (NF-κB) to trigger inflammatory responses leading to PH, right ventricular failure, and death. Evidence suggests that increased mitochondrial ROS and Ca²⁺ signaling leads to abnormal synthesis of ketones, which play a critical role in the development of PH. In this review, we discuss some of the recent findings on the important interactive role and molecular mechanisms of mitochondrial ROS and Ca²⁺ in the development and progression of PH. We also address the contributions of NF-κB-dependent inflammatory responses and ketone-mediated oxidative stress due to abnormal regulation of mitochondrial ROS and Ca²⁺ signaling in PH.

Piperlongumine attenuates vascular remodeling in hypoxic pulmonary hypertension by regulating autophagy

OBJECTIVE

The aim of this study was to determine the therapeutic effect of piperlongumine on hypoxic pulmonary hypertension.

METHODS

A hypoxic pulmonary hypertension rat model was constructed, primary rat pulmonary artery smooth muscle cells (PASMCs) were isolated, and the proliferation of PASMCs was measured by Cell Counting Kit‑8 assay. The expression of autophagic proteins microtubule-associated protein 1 light chain 3B (LC3B) and P62 were examined by western blot. Autophagic flux in PASMCs was detected by tandem mRFP-GFP-LC3 fluorescence analysis.

RESULTS

Hypoxia-induced proliferation of PASMCs was significantly inhibited by piperlongumine exposure. Treatment with piperlongumine elevated LC3B II/LC3B I protein ratio and decreased the expression of P62 protein in both PASMCs and rat lung tissues. Tandem mRFP-GFP-LC3 fluorescence analysis showed that piperlongumine increased autophagic flux in PASMCs. Inhibition of autophagy using 3-methyladenine (3-MA) attenuated the inhibitory effect of piperlongumine on proliferation of PASMCs. Chronic hypoxia exposure led to a significant increase in rat right ventricle systolic pressure, right ventricular hypertrophy, wall thickness and area of pulmonary artery, and muscularization of pulmonary arterioles, which was obviously suppressed by administration of piperlongumine. 3-MA attenuated the alleviating effects of piperlongumine on pulmonary vascular remodeling.

CONCLUSIONS

Piperlongumine attenuates vascular remodeling in hypoxic pulmonary hypertension by regulating autophagy. Piperlongumine treatment may serve as a promising therapy for hypoxic pulmonary hypertension.

[Morphological assessment of pulmonary vessels in pulmonary arterial hypertension associated with congenital heart disease]

Pulmonary vascular remodeling is the key structural alteration in pulmonary arterial hypertension associated with congenital heart disease (CHD). Changes in the pulmonary vessels in CHD generally occur in the inner and middle coats. This review considers the pathology of these changes and highlights some issues of a stereological approach to the morphometry of pulmonary vasculature. It also touches upon the issues of the morphology of pulmonary vessels in post-capillary and segmental pulmonary hypertension.

The roles of microRNAs played in lung diseases via regulating cell apoptosis

MicroRNAs (miRNAs) are a type of endogenous non-coding short-chain RNA, which plays a crucial role in the regulation of many essential cellular functions, including cellular migration, proliferation, invasion, autophagy, oxidative stress, apoptosis, and differentiation. The lung can be damaged by pathogenic microorganisms, as well as physical or chemical factors. Research has confirmed that miRNAs and lung cell apoptosis can affect the development and progression of several lung diseases. This article reviews the role of miRNAs in the development of lung disease through regulating host cell apoptosis.

The six-transmembrane protein Stamp2 ameliorates pulmonary vascular remodeling and pulmonary hypertension in mice

Six-transmembrane protein of prostate (Stamp2) protects from diabetes and atherosclerosis in mice via anti-inflammatory mechanisms. As chronic inflammation is a hallmark of pulmonary arterial hypertension (PAH), we investigated the role of Stamp2. Stamp2 expression was substantially reduced in the lung of humans with idiopathic PAH, as well as in experimental PAH. In Stamp2-deficient mice, hypoxia modestly aggravated pulmonary vascular remodeling and right ventricular pressure compared to WT. As endothelial cell (EC) and pulmonary arterial smooth muscle cell (PASMC) phenotypes drive remodeling in PAH, we explored the role of Stamp2. Knock-down of Stamp2 in human EC neither affected apoptosis, viability, nor release of IL-6. Moreover, Stamp2 deficiency in primary PASMC did not alter mitogenic or migratory properties. As Stamp2 deficiency augmented expression of inflammatory cytokines and numbers of CD68-positive cells in the lung, actions of Stamp2 in macrophages may drive vascular remodeling. Thus, PASMC responses were assessed following treatment with conditioned media of primary Stamp2^−/− or WT macrophages. Stamp2^−/− supernatants induced PASMC proliferation and migration stronger compared to WT. A cytokine array revealed CXCL12, MCP-1 and IL-6 as most relevant candidates. Experiments with neutralizing antibodies confirmed the role of these cytokines in driving Stamp2’s responses. In conclusion, Stamp2 deficiency aggravates pulmonary vascular remodeling via cross-talk between macrophages and PASMC. Despite a substantial pro-inflammatory response, the hemodynamic effect of Stamp2 deficiency is modest suggesting that additional mechanisms apart from inflammation are necessary to induce severe PAH.

A Notch3-Marked Subpopulation of Vascular Smooth Muscle Cells Is the Cell of Origin for Occlusive Pulmonary Vascular Lesions

BACKGROUND

Pulmonary arterial hypertension (PAH) is a fatal disease characterized by profound vascular remodeling in which pulmonary arteries narrow because of medial thickening and occlusion by neointimal lesions, resulting in elevated pulmonary vascular resistance and right heart failure. Therapies targeting the neointima would represent a significant advance in PAH treatment; however, our understanding of the cellular events driving neointima formation, and the molecular pathways that control them, remains limited.

METHODS

We comprehensively map the stepwise remodeling of pulmonary arteries in a robust, chronic inflammatory mouse model of pulmonary hypertension. This model demonstrates pathological features of the human disease, including increased right ventricular pressures, medial thickening, neointimal lesion formation, elastin breakdown, increased anastomosis within the bronchial circulation, and perivascular inflammation. Using genetic lineage tracing, clonal analysis, multiplexed in situ hybridization, immunostaining, deep confocal imaging, and staged pharmacological inhibition, we define the cell behaviors underlying each stage of vascular remodeling and identify a pathway required for neointima formation.

RESULTS

Neointima arises from smooth muscle cells (SMCs) and not endothelium. Medial SMCs proliferate broadly to thicken the media, after which a small number of SMCs are selected to establish the neointima. These neointimal founder cells subsequently undergoing massive clonal expansion to form occlusive neointimal lesions. The normal pulmonary artery SMC population is heterogeneous, and we identify a Notch3-marked minority subset of SMCs as the major neointimal cell of origin. Notch signaling is specifically required for the selection of neointimal founder cells, and Notch inhibition significantly improves pulmonary artery pressure in animals with pulmonary hypertension.

CONCLUSIONS

This work describes the first nongenetically driven murine model of pulmonary hypertension (PH) that generates robust and diffuse occlusive neointimal lesions across the pulmonary vascular bed and does so in a stereotyped timeframe. We uncover distinct cellular and molecular mechanisms underlying medial thickening and neointima formation and highlight novel transcriptional, behavioral, and pathogenic heterogeneity within pulmonary artery SMCs. In this model, inflammation is sufficient to generate characteristic vascular pathologies and physiological measures of human PAH. We hope that identifying the molecular cues regulating each stage of vascular remodeling will open new avenues for therapeutic advancements in the treatment of PAH.

Pulmonary artery banding is a relevant model to study the right ventricular remodeling and dysfunction that occurs in pulmonary arterial hypertension

Right ventricular (RV) dysfunction determines mortality in patients with pulmonary arterial hypertension (PAH) and RV pressure loading. Experimental models commonly use Sugen hypoxia (SuHx)-induced PAH, monocrotaline (MCT)-induced PAH, or pulmonary artery banding (PAB). Because PAH models cannot interrogate RV effects or therapies independent of pulmonary vascular effects, we aimed to compare RV function and fibrosis in experimental PAB vs. PAH. Thirty rats were randomized to either sham controls, PAB, SuHx-, or MCT-induced PAH. RV pressures and function were assessed by high-fidelity pressure-tipped catheters and by echocardiography. RV myocyte hypertrophy, fibrosis, and capillary density were quantified from hematoxylin-eosin, picrosirius red-stained, and CD31-immunostained RV sections, respectively. RV pressures and the RV-to-left ventricular pressure ratio were significantly increased in all three groups to a similar degree (PAB 65 ± 17 mmHg, SuHx 72 ± 16 mmHg, and MCT 70 ± 12 mmHg) vs. controls (23 ± 2 mmHg, all P < 0.01). RV dilatation, hypertrophy, and fibrosis were similarly increased, and capillary density decreased, in the three models (RV fibrosis; PAB 13.3 ± 3.6%, SuHx 9.8 ± 3.0% and MCT 10.9 ± 2.4% vs control 5.5 ± 1.1%, all P < 0.05). RV function was similarly decreased in all models vs. controls. We observed comparable RV dilatation, hypertrophy, systolic and diastolic dysfunction, fibrosis, and capillary rarefaction in rat models of PAB, SuHx-, and MCT-induced PAH. These results suggest that PAB, when sufficiently severe, induces features of maladaptive RV remodeling and can be used to investigate RV pathophysiology and therapy effects independent of pulmonary vascular resistance.NEW & NOTEWORTHY Although animal models of pulmonary arterial hypertension and pressure loading are important to study right ventricular (RV) pathophysiology, pulmonary arterial hypertension models cannot interrogate RV responses independent of pulmonary vascular effects. Comparing three commonly used rat models under similar elevated RV pressure, we found that all models resulted in comparable maladaptive RV remodeling and dysfunction. Thus, these findings suggest that the pulmonary artery banding model can be used to investigate mechanisms of RV dysfunction in RV pressure overload and the effect of potential therapies.

Metabolic Reprogramming in the Heart and Lung in a Murine Model of Pulmonary Arterial Hypertension

A significant glycolytic shift in the cells of the pulmonary vasculature and right ventricle during pulmonary arterial hypertension (PAH) has been recently described. Due to the late complications and devastating course of any variant of this disease, there is a great need for animal models that reproduce potential metabolic reprograming of PAH. Our objective is to study, in situ, the metabolic reprogramming in the lung and the right ventricle of a mouse model of PAH by metabolomic profiling and molecular imaging. PAH was induced by chronic hypoxia exposure plus treatment with SU5416, a vascular endothelial growth factor receptor inhibitor. Lung and right ventricle samples were analyzed by magnetic resonance spectroscopy. In vivo energy metabolism was studied by positron emission tomography. Our results show that metabolomic profiling of lung samples clearly identifies significant alterations in glycolytic pathways. We also confirmed an upregulation of glutamine metabolism and alterations in lipid metabolism. Furthermore, we identified alterations in glycine and choline metabolism in lung tissues. Metabolic reprograming was also confirmed in right ventricle samples. Lactate and alanine, endpoints of glycolytic oxidation, were found to have increased concentrations in mice with PAH. Glutamine and taurine concentrations were correlated to specific ventricle hypertrophy features. We demonstrated that most of the metabolic features that characterize human PAH were detected in a hypoxia plus SU5416 mouse model and it may become a valuable tool to test new targeting treatments of this severe disease.