Does Cell-Type-Specific Silencing of Monoamine Oxidase B Interfere with the Development of Right Ventricle (RV) Hypertrophy or Right Ventricle Failure in Pulmonary Hypertension?

Increased mitochondrial reactive oxygen species (ROS) formation is important for the development of right ventricular (RV) hypertrophy (RVH) and failure (RVF) during pulmonary hypertension (PH). ROS molecules are produced in different compartments within the cell, with mitochondria known to produce the strongest ROS signal. Among ROS-forming mitochondrial proteins, outer-mitochondrial-membrane-located monoamine oxidases (MAOs, type A or B) are capable of degrading neurotransmitters, thereby producing large amounts of ROS. In mice, MAO-B is the dominant isoform, which is present in almost all cell types within the heart. We analyzed the effect of an inducible cardiomyocyte-specific knockout of MAO-B (cmMAO-B KO) for the development of RVH and RVF in mice. Right ventricular hypertrophy was induced by pulmonary artery banding (PAB). RV dimensions and function were measured through echocardiography. ROS production (dihydroethidium staining), protein kinase activity (PamStation device), and systemic hemodynamics (in vivo catheterization) were assessed. A significant decrease in ROS formation was measured in cmMAO-B KO mice during PAB compared to Cre-negative littermates, which was associated with reduced activity of protein kinases involved in hypertrophic growth. In contrast to littermates in which the RV was dilated and hypertrophied following PAB, RV dimensions were unaffected in response to PAB in cmMAO-B KO mice, and no decline in RV systolic function otherwise seen in littermates during PAB was measured in cmMAO-B KO mice. In conclusion, cmMAO-B KO mice are protected against RV dilatation, hypertrophy, and dysfunction following RV pressure overload compared to littermates. These results support the hypothesis that cmMAO-B is a key player in causing RV hypertrophy and failure during PH.

A Novel Rat Model of Mild Pulmonary Hypertension Associated with Pulmonary Venous Congestion Induced by Left Pulmonary Vein Banding.

Pulmonary hypertension (PH) associated with left heart disease (PH-LHD) is the most common form of PH. In PH-LHD, changes in the pulmonary vasculature are assumed to be mainly caused by pulmonary venous congestion. However, the underlying mechanisms of this form of PH are poorly understood. We aimed to establish a model of PH associated with pulmonary venous congestion. Wistar-Kyoto rats underwent partial occlusion of the left pulmonary vein to induce pulmonary venous congestion or sham surgery and were assessed at various time points post-surgery (3, 6, 9, 12 weeks). In vivo cardiopulmonary phenotyping was performed by using echocardiography along with heart catheterization. Histomorphometry methods were used to assess pulmonary vascular remodeling (e.g., wall thickness, degree of muscularization). Left pulmonary vein banding (PVB) resulted in mildly elevated right ventricular systolic pressure and moderate right ventricular hypertrophy. In PVB rats, small- and medium-sized pulmonary vessels in the left lung were characterized by increased wall thickness and muscularization. Taken together, our data demonstrate that left PVB-induced pulmonary venous congestion is associated with pulmonary vascular remodeling and mild PH.

Disability from cardiovascular diseases at Osh city, Kyrgyz Republic.

Cardiovascular diseases (CVDs) are the leading global cause of death, contributing to health deterioration and increased healthcare expenses. Therefore, it is of interest to investigate the disability rates related to cardiovascular diseases at Osh city, Kyrgyz Republic. We report the prevalence of disability in both urban and rural areas, highlighting the impact of regional disparities in medical and social services. Data shows that adult cardiovascular disease impairment in Kyrgyzstan suggests challenges in accessing medical and social support, particularly in rural regions. Thus, the rural-urban divide in critical disability metrics impedes equitable research. Comprehensive assessments and interventions are imperative to mitigate cardiovascular diseases and associated disabilities in both rural and urban populations at Kyrgyz Republic.

Mast Cells in Cardiac Remodeling: Focus on the Right Ventricle.

In response to various stressors, cardiac chambers undergo structural remodeling. Long-term exposure of the right ventricle (RV) to pressure or volume overload leads to its maladaptive remodeling, associated with RV failure and increased mortality. While left ventricular adverse remodeling is well understood and therapeutic options are available or emerging, RV remodeling remains underexplored, and no specific therapies are currently available. Accumulating evidence implicates the role of mast cells in RV remodeling. Mast cells produce and release numerous inflammatory mediators, growth factors and proteases that can adversely affect cardiac cells, thus contributing to cardiac remodeling. Recent experimental findings suggest that mast cells might represent a potential therapeutic target. This review examines the role of mast cells in cardiac remodeling, with a specific focus on RV remodeling, and explores the potential efficacy of therapeutic interventions targeting mast cells to mitigate adverse RV remodeling.

Surgical protocol for pulmonary artery banding in mice to generate a model of pressure-overload-induced right ventricular failure.

Right ventricular failure (RVF) is the leading cause of death in patients with pulmonary hypertension. Here, we present a protocol for pulmonary artery banding in mice to generate a model of pressure-overload-induced RVF. We describe steps for anesthesia of mice, endotracheal intubation, and pulmonary artery banding surgery. We then detail procedures for phenotyping and analysis. Our approach does not involve complete blockage of the pulmonary flow during clip placement and is, therefore, associated with low intraoperative mortality. For complete details on the use and execution of this protocol, please refer to Veith et al. (2020).1.

Osteopontin in Pulmonary Hypertension.

Pulmonary hypertension (PH) is a pathological condition with multifactorial etiology, which is characterized by elevated pulmonary arterial pressure and pulmonary vascular remodeling. The underlying pathogenetic mechanisms remain poorly understood. Accumulating clinical evidence suggests that circulating osteopontin may serve as a biomarker of PH progression, severity, and prognosis, as well as an indicator of maladaptive right ventricular remodeling and dysfunction. Moreover, preclinical studies in rodent models have implicated osteopontin in PH pathogenesis. Osteopontin modulates a plethora of cellular processes within the pulmonary vasculature, including cell proliferation, migration, apoptosis, extracellular matrix synthesis, and inflammation via binding to various receptors such as integrins and CD44. In this article, we provide a comprehensive overview of the current understanding of osteopontin regulation and its impact on pulmonary vascular remodeling, as well as consider research issues required for the development of therapeutics targeting osteopontin as a potential strategy for the management of PH.

Decreased plasma levels of the brain-derived neurotrophic factor correlate with right heart congestion in pulmonary arterial hypertension.

Background: The brain-derived neurotrophic factor (BDNF) may promote development of pulmonary hypertension and right ventricular (RV) failure. However, BDNF plasma levels were decreased in patients with left ventricular (LV) failure. Therefore, we investigated BDNF plasma levels in pulmonary hypertension patients and the role of BDNF in mouse models of pulmonary hypertension and isolated RV failure. Methods: BDNF plasma levels were correlated to pulmonary hypertension in two patient cohorts, including either post- and pre-capillary pulmonary hypertension patients (first cohort) or only pre-capillary pulmonary hypertension patients (second cohort). In the second cohort, RV dimensions and load-independent function were determined by imaging and pressure-volume catheter measurements, respectively. For induction of isolated RV pressure overload, heterozygous Bdnf knockout (Bdnf+/- ) mice were subjected to pulmonary arterial banding (PAB). For induction of pulmonary hypertension, mice with inducible knockout of BDNF in smooth muscle cells (Bdnf/Smmhc knockout) were exposed to chronic hypoxia. Results: Plasma BDNF levels were decreased in patients with pulmonary hypertension. Following adjustment for covariables, BDNF levels negatively correlated in both cohorts with central venous pressure. In the second cohort, BDNF levels additionally negatively correlated with RV dilatation. In animal models, BDNF downregulation attenuated RV dilatation in Bdnf+ /- mice after PAB or hypoxic Bdnf/Smmhc knockout mice, although they developed pulmonary hypertension to a similar extent. Conclusions: Similar to LV failure, circulating levels of BDNF were decreased in pulmonary hypertension patients, and low BDNF levels were associated with right heart congestion. Decreased BDNF levels did not worsen RV dilatation in animal models, and thus, may be the consequence, but not the cause of RV dilatation.

Circulating Microparticles Are Differentially Increased in Lowlanders and Highlanders with High Altitude Induced Pulmonary Hypertension during the Cold Season.

The role of microparticles (MPs) and cold in high altitude pulmonary hypertension (HAPH) remains unexplored. We investigated the impact of long-term cold exposure on the pulmonary circulation in lowlanders and high-altitude natives and the role of MPs. Pulmonary hemodynamics were evaluated using Doppler echocardiography at the end of the colder and warmer seasons. We further examined the miRNA content of MPs isolated from the study participants and studied their effects on human pulmonary artery smooth muscle (hPASMCs) and endothelial cells (hPAECs). Long-term exposure to cold environment was associated with an enhanced pulmonary artery pressure in highlanders. Plasma levels of CD62E-positive and CD68-positive MPs increased in response to cold in lowlanders and HAPH highlanders. The miRNA-210 expression contained in MPs differentially changed in response to cold in lowlanders and highlanders. MPs isolated from lowlanders and highlanders increased proliferation and reduced apoptosis of hPASMCs. Further, MPs isolated from warm-exposed HAPH highlanders and cold-exposed highlanders exerted the most pronounced effects on VEGF expression in hPAECs. We demonstrated that prolonged exposure to cold is associated with elevated pulmonary artery pressures, which are most pronounced in high-altitude residents. Further, the numbers of circulating MPs are differentially increased in lowlanders and HAPH highlanders during the colder season.

Right Heart Failure in Mice Upon Pressure Overload Is Promoted by Mitochondrial Oxidative Stress.

We sought to unravel pathomechanisms of the transition of maladaptive right ventricular (RV) remodeling to right heart failure (RHF) upon pressure overload. Exposure of C57BL/6J and C57BL/6N mice to pulmonary artery banding disclosed a tight relation of structural remodeling with afterload, but a dissociation from RV systolic function. Reduced release of mitochondrial reactive oxygen species in C57BL/6J mice prevented the development of RHF. In patients with left heart failure, increased oxidative damage in RV sections was associated with severely impaired RV function. In conclusion, reactive oxygen species are involved in the transition of maladaptive RV remodeling to RHF.

Clinical and Molecular Implications of Osteopontin in Heart Failure.

The matricellular protein osteopontin modulates cell-matrix interactions during tissue injury and healing. A complex multidomain structure of osteopontin enables it not only to bind diverse cell receptors but also to interact with various partners, including other extracellular matrix proteins, cytokines, and growth factors. Numerous studies have implicated osteopontin in the development and progression of myocardial remodeling in diverse cardiac diseases. Osteopontin influences myocardial remodeling by regulating extracellular matrix production, the activity of matrix metalloproteinases and various growth factors, inflammatory cell recruitment, myofibroblast differentiation, cardiomyocyte apoptosis, and myocardial vascularization. The exploitation of osteopontin loss- and gain-of-function approaches in rodent models provided an opportunity for assessment of the cell- and disease-specific contribution of osteopontin to myocardial remodeling. In this review, we summarize the recent knowledge on osteopontin regulation and its impact on various cardiac diseases, as well as delineate complex disease- and cell-specific roles of osteopontin in cardiac pathologies. We also discuss the current progress of therapeutics targeting osteopontin that may facilitate the development of a novel strategy for heart failure treatment.

SPARC, a Novel Regulator of Vascular Cell Function in Pulmonary Hypertension.

BACKGROUND: Pulmonary hypertension (PH) is a life-threatening disease, characterized by excessive pulmonary vascular remodeling, leading to elevated pulmonary arterial pressure and right heart hypertrophy. PH can be caused by chronic hypoxia, leading to hyper-proliferation of pulmonary arterial smooth muscle cells (PASMCs) and apoptosis-resistant pulmonary microvascular endothelial cells (PMVECs). On reexposure to normoxia, chronic hypoxia-induced PH in mice is reversible. In this study, the authors aim to identify novel candidate genes involved in pulmonary vascular remodeling specifically in the pulmonary vasculature. METHODS: After microarray analysis, the authors assessed the role of SPARC (secreted protein acidic and rich in cysteine) in PH using lung tissue from idiopathic pulmonary arterial hypertension (IPAH) patients, as well as from chronically hypoxic mice. In vitro studies were conducted in primary human PASMCs and PMVECs. In vivo function of SPARC was proven in chronic hypoxia-induced PH in mice by using an adeno-associated virus-mediated Sparc knockdown approach. RESULTS: C57BL/6J mice were exposed to normoxia, chronic hypoxia, or chronic hypoxia with subsequent reexposure to normoxia for different time points. Microarray analysis of the pulmonary vascular compartment after laser microdissection identified Sparc as one of the genes downregulated at all reoxygenation time points investigated. Intriguingly, SPARC was vice versa upregulated in lungs during development of hypoxia-induced PH in mice as well as in IPAH, although SPARC plasma levels were not elevated in PH. TGF-ß1 (transforming growth factor ß1) or HIF2A (hypoxia-inducible factor 2A) signaling pathways induced SPARC expression in human PASMCs. In loss of function studies, SPARC silencing enhanced apoptosis and reduced proliferation. In gain of function studies, elevated SPARC levels induced PASMCs, but not PMVECs, proliferation. Coculture and conditioned medium experiments revealed that PMVECs-secreted SPARC acts as a paracrine factor triggering PASMCs proliferation. Contrary to the authors' expectations, in vivo congenital Sparc knockout mice were not protected from hypoxia-induced PH, most probably because of counter-regulatory proproliferative signaling. However, adeno-associated virus-mediated Sparc knockdown in adult mice significantly improved hemodynamic and cardiac function in PH mice. CONCLUSIONS: This study provides evidence for the involvement of SPARC in the pathogenesis of human PH and chronic hypoxia-induced PH in mice, most likely by affecting vascular cell function.

Targeting peptidyl-prolyl isomerase 1 in experimental pulmonary arterial hypertension.

BACKGROUND: Pulmonary arterial hypertension (PAH) is a progressive disease characterised by pro-proliferative and anti-apoptotic phenotype in vascular cells, leading to pulmonary vascular remodelling and right heart failure. Peptidyl-prolyl cis/trans isomerase, NIMA interacting 1 (Pin1), a highly conserved enzyme, which binds to and catalyses the isomerisation of specific phosphorylated Ser/Thr-Pro motifs, acts as a molecular switch in multiple coordinated cellular processes. We hypothesised that Pin1 plays a substantial role in PAH, and its inhibition with a natural organic compound, Juglone, would reverse experimental pulmonary hypertension. RESULTS: We demonstrated that the expression of Pin1 was markedly elevated in experimental pulmonary hypertension (i.e. hypoxia-induced mouse and Sugen/hypoxia-induced rat models) and pulmonary arterial smooth muscle cells of patients with clinical PAH. In vitro Pin1 inhibition by either Juglone treatment or short interfering RNA knockdown resulted in an induction of apoptosis and decrease in proliferation of human pulmonary vascular cells. Stimulation with growth factors induced Pin1 expression, while its inhibition reduced the activity of numerous PAH-related transcription factors, such as hypoxia-inducible factor (HIF)-α and signal transducer and activator of transcription (STAT). Juglone administration lowered pulmonary vascular resistance, enhanced right ventribular function, improved pulmonary vascular and cardiac remodelling in the Sugen/hypoxia rat model of PAH and the chronic hypoxia-induced pulmonary hypertension model in mice. CONCLUSION: Our study demonstrates that targeting of Pin1 with small molecule inhibitor, Juglone, might be an attractive future therapeutic strategy for PAH and right heart disease secondary to PAH.

The effect of an adaptation to hypoxia on cardiac tolerance to ischemia/reperfusion.

The acute myocardial infarction (AMI) and sudden cardiac death (SCD), both associated with acute cardiac ischemia, are one of the leading causes of adult death in economically developed countries. The development of new approaches for the treatment and prevention of AMI and SCD remains the highest priority for medicine. A study on the cardiovascular effects of chronic hypoxia (CH) may contribute to the development of these methods. Chronic hypoxia exerts both positive and adverse effects. The positive effects are the infarct-reducing, vasoprotective, and antiarrhythmic effects, which can lead to the improvement of cardiac contractility in reperfusion. The adverse effects are pulmonary hypertension and right ventricular hypertrophy. This review presents a comprehensive overview of how CH enhances cardiac tolerance to ischemia/reperfusion. It is an in-depth analysis of the published data on the underlying mechanisms, which can lead to future development of the cardioprotective effect of CH. A better understanding of the CH-activated protective signaling pathways may contribute to new therapeutic approaches in an increase of cardiac tolerance to ischemia/reperfusion.

Genetic deletion of p66shc and/or cyclophilin D results in decreased pulmonary vascular tone.

AIMS: The pulmonary vascular tone and hypoxia-induced alterations of the pulmonary vasculature may be regulated by the mitochondrial membrane permeability transition pore (mPTP) that controls mitochondrial calcium load and apoptosis. We thus investigated, if the mitochondrial proteins p66shc and cyclophilin D (CypD) that regulate mPTP opening affect the pulmonary vascular tone. METHODS AND RESULTS: Mice deficient for p66shc (p66shc-/-), CypD (CypD-/-), or both proteins (p66shc/CypD-/-) exhibited decreased pulmonary vascular resistance (PVR) compared to wild-type mice determined in isolated lungs and in vivo. In contrast, systemic arterial pressure was only lower in CypD-/- mice. As cardiac function and pulmonary vascular remodelling did not differ between genotypes, we determined alterations of vascular contractility in isolated lungs and calcium handling in pulmonary arterial smooth muscle cells (PASMC) as underlying reason for decreased PVR. Potassium chloride (KCl)-induced pulmonary vasoconstriction and KCl-induced cytosolic calcium increase determined by Fura-2 were attenuated in all gene-deficient mice. In contrast, KCl-induced mitochondrial calcium increase determined by the genetically encoded Mito-Car-GECO and calcium retention capacity were increased only in CypD-/- and p66shc/CypD-/- mitochondria indicating that decreased mPTP opening affected KCl-induced intracellular calcium peaks in these cells. All mouse strains showed a similar pulmonary vascular response to chronic hypoxia, while acute hypoxic pulmonary vasoconstriction was decreased in gene-deficient mice indicating that CypD and p66shc regulate vascular contractility but not remodelling. CONCLUSIONS: We conclude that p66shc specifically regulates the pulmonary vascular tone, while CypD also affects systemic pressure. However, only CypD acts via regulation of mPTP opening and mitochondrial calcium regulation.

Role of the Purinergic P2Y2 Receptor in Pulmonary Hypertension.

Pulmonary arterial hypertension (PAH), group 1 pulmonary hypertension (PH), is a fatal disease that is characterized by vasoconstriction, increased pressure in the pulmonary arteries, and right heart failure. PAH can be described by abnormal vascular remodeling, hyperproliferation in the vasculature, endothelial cell dysfunction, and vascular tone dysregulation. The disease pathomechanisms, however, are as yet not fully understood at the molecular level. Purinergic receptors P2Y within the G-protein-coupled receptor family play a major role in fluid shear stress transduction, proliferation, migration, and vascular tone regulation in systemic circulation, but less is known about their contribution in PAH. Hence, studies that focus on purinergic signaling are of great importance for the identification of new therapeutic targets in PAH. Interestingly, the role of P2Y2 receptors has not yet been sufficiently studied in PAH, whereas the relevance of other P2Ys as drug targets for PAH was shown using specific agonists or antagonists. In this review, we will shed light on P2Y receptors and focus more on the P2Y2 receptor as a potential novel player in PAH and as a new therapeutic target for disease management.

An Exaggerated Rise in Pulmonary Artery Pressure in a High-Altitude Dweller during the Cold Season.

Chronic hypoxia-induced sustained pulmonary vasoconstriction and vascular remodeling lead to mild-to-moderate elevation of pulmonary artery pressure in high-altitude residents. However, in some of them, severe pulmonary hypertension may develop. Besides hypoxia, high-altitude residents also face other environmental challenges such as low ambient temperatures. We describe a case of a 49-year-old woman of Kyrgyz ethnicity with abnormally increased pulmonary artery pressure, revealed by Doppler echocardiography. Significantly elevated pulmonary artery pressure was detected in late winter and this was not associated with right ventricular hypertrophy or right ventricular dysfunction. Repeat echocardiography performed in late summer disclosed a significant attenuation of pulmonary artery pressure elevation, with no changes in right ventricular performance parameters. This case illustrates that, in susceptible individuals, long-term cold exposure could induce an abnormal pulmonary artery pressure rise, which can be reversed during warm seasons as in our patient. In certain circumstances, however, additional factors could contribute to a sustained pulmonary artery pressure increase and the development of persistent pulmonary hypertension, which often leads to right heart failure and premature death.

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.

Cardiomyocytes-specific deletion of monoamine oxidase B reduces irreversible myocardial ischemia/reperfusion injury.

Monoamine oxidase B (MAO-B), a protein localized at the outer mitochondrial membrane, catalyzes the oxidative deamination of biogenic amines thereby producing reactive oxygen species (ROS). Increased ROS formation contributes to myocardial ischemia/reperfusion (I/R); however, the importance of different ROS producing enzymes for increased I/R-induced ROS formation and the subsequent I/R injury is still a matter of debate. Here we describe the first cardiomyocytes-specific MAO-B knockout mouse and test the hypothesis that lack of cardiomyocyte MAO-B protects the heart from I/R injury. A cardiac-specific and tamoxifen-inducible MAO-B knockout mouse (MAO-B KO) was generated using the Cre/lox system; Cre-negative MAO-Bfl/fl littermates served as controls (WT). Lack of MAO-B was verified by Western blot and immunohistochemistry. Cardiac function of MAO-B KO and WT was analyzed by echocardiography, quantification of mitochondrial ROS production, and measurement of myocardial infarct size (in % of ventricle) in hearts exposed to global I/R using the Langendorff technique. MAO-B protein expression was significantly down-regulated in MAO-B KO mice after two weeks of tamoxifen feeding followed by ten weeks of feeding with normal chow. ROS formation stimulated by the MAO-B-specific substrate ß-phenylethylamin (PEA; 250 µM) was significantly lower in mitochondria isolated from MAO-B KO compared to WT hearts (WT 4.5 ± 0.8 a. u.; MAO-B KO 1.2 ± 0.3 a. u.). Echocardiography revealed no significant differences in LV dimensions as well as ejection fraction (EF) between WT and MAO-B KO mice (EF: WT 67.3 ± 8.8%; MAO-B KO 67.7 ± 6.5%). After I/R, infarct size was significantly lower in MAO-B KO hearts (WT 69.3 ± 15.1%; MAO-B KO 46.8 ± 12.0%). CONCLUSION: Lack of cardiomyocytes-specific MAO-B reduces infarct size suggesting that MAO-B activity contributes to acute reperfusion injury.