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

Effectiveness of Dexmedetomidine as Myocardial Protector in Children With Classic Tetralogy of Fallot Having Corrective Surgery: A Randomized Controlled Trial

OBJECTIVES

Efficacy of dexmedetomidine (DEX) as a cardioprotective agent in Indonesian children undergoing classic tetralogy of Fallot (TOF) repair with cardiopulmonary bypass (CPB).

DESIGN

A prospective, parallel trial using block randomization along with double-blinded preparation of treatment agents by other parties.

SETTING

National Cardiovascular Center Harapan Kita, Indonesia.

PARTICIPANTS

Sixty-six children with classic TOF scheduled for corrective surgery. No children were excluded. All patients had fulfilled the criteria for analysis.

INTERVENTIONS

A total of 0.5 µg/kg bolus of DEX was added to the CPB priming solution, followed by 0.25 µg/kg/h maintenance during bypass. The placebo group used normal saline. Follow-ups were up to 30 days.

MEASUREMENTS AND MAIN RESULTS

Troponin I was lower in the DEX group at 6 hours (30.48 ± 19.33 v 42.73 ± 27.16, p = 0.039) and 24 hours after CPB (8.89 ± 5.42 v 14.04 ± 11.17, p = 0.02). Within a similar timeframe, DEX successfully lowered interleukin-6 (p = 0.03; p = 0.035, respectively). Lactate was lower in the Dex group at 1, 6, and 24 hours after CPB (p < 0.01; p = 0.048; p = 0.035; respectively). Dexmedetomidine increased cardiac output and index from 6 hours after bypass, but vice versa in systemic vascular resistance. Reduction of vasoactive inotropic score was seen during intensive care unit monitoring in the Dex group (p = 0.049). Nevertheless, DEX did not significantly affect the length of ventilation (p = 0.313), intensive care unit stay (p = 0.087), and mortality (p > 0.99).

CONCLUSIONS

Dexmedetomidine during CPB is an effective cardioprotective agent in TOF children having surgery. Postoperative mortality was comparable across groups.

The SGLT2i Dapagliflozin Reduces RV Mass Independent of Changes in RV Pressure Induced by Pulmonary Artery Banding

BACKGROUND

Sodium glucose linked transporter 2 (SGLT2) inhibition not only reduces morbidity and mortality in patients with diagnosed heart failure but also prevents the development of heart failure hospitalization in those at risk. While studies to date have focused on the role of SGLT2 inhibition in left ventricular failure, whether this drug class is efficacious in the treatment and prevention of right heart failure has not been explored.

HYPOTHESIS

We hypothesized that SGLT2 inhibition would reduce the structural, functional, and molecular responses to pressure overload of the right ventricle.

METHODS

Thirteen-week-old Fischer F344 rats underwent pulmonary artery banding (PAB) or sham surgery prior to being randomized to receive either the SGLT2 inhibitor: dapagliflozin (0.5 mg/kg/day) or vehicle by oral gavage. After 6 weeks of treatment, animals underwent transthoracic echocardiography and invasive hemodynamic studies. Animals were then terminated, and their hearts harvested for structural and molecular analyses.

RESULTS

PAB induced features consistent with a compensatory response to increased right ventricular (RV) afterload with elevated mass, end systolic pressure, collagen content, and alteration in calcium handling protein expression (all p < 0.05 when compared to sham + vehicle). Dapagliflozin reduced RV mass, including both wet and dry weight as well as normalizing the protein expression of SERCA 2A, phospho-AMPK and LC3I/II ratio expression (all p < 0.05).

SIGNIFICANCE

Dapagliflozin reduces the structural, functional, and molecular manifestations of right ventricular pressure overload. Whether amelioration of these early changes in the RV may ultimately lead to a reduction in RV failure remains to be determined.

Adverse remodelling in tetralogy of Fallot: From risk factors to imaging analysis and future perspectives

Although contemporary outcomes of initial surgical repair of tetralogy of Fallot (TOF) are excellent, the survival of adult patients remains significantly lower than that of the normal population due to the high incidence of heart failure, ventricular arrhythmias, and sudden cardiac death. The underlying mechanisms are only partially understood but involve an adverse biventricular response, so-called remodelling, to key stressors such as right ventricular (RV) pressure-and/or volume-overload, myocardial fibrosis, and electro-mechanical dyssynchrony. In this review, we explore risk factors and mechanisms of biventricular remodelling, from histological to electro-mechanical aspects, and the role of imaging in their assessment. We discuss unsolved challenges and future directions to better understand and treat the long-term sequelae of this complex congenital heart disease.

Right ventricular failure in pulmonary hypertension: recent insights from experimental models

Right ventricular (RV) function is a critical determinant of the prognosis of patients with pulmonary hypertension (PH). Upon establishment of PH, RV dysfunction develops, leading to a gradual worsening of the condition over time, culminating in RV failure and premature mortality. Despite this understanding, the underlying mechanisms of RV failure remain obscure. As a result, there are currently no approved therapies specifically targeting the right ventricle. One contributing factor to the lack of RV-directed therapies is the complexity of the pathogenesis of RV failure as observed in animal models and clinical studies. In recent years, various research groups have begun utilizing multiple models, including both afterload-dependent and afterload-independent models, to investigate specific targets and pharmacological agents in RV failure. In this review, we examine various animal models of RV failure and the recent advancements made utilizing these models to study the mechanisms of RV failure and the potential efficacy of therapeutic interventions, with the ultimate goal of translating these findings into clinical practice to enhance the management of individuals with PH.

A review on experimental surgical models and anesthetic protocols of heart failure in rats

Heart failure (HF) is a serious health and economic burden worldwide, and its prevalence is continuously increasing. Current medications effectively moderate the progression of symptoms, and there is a need for novel preventative and reparative treatments. The development of novel HF treatments requires the testing of potential therapeutic procedures in appropriate animal models of HF. During the past decades, murine models have been extensively used in fundamental and translational research studies to better understand the pathophysiological mechanisms of HF and develop more effective methods to prevent and control congestive HF. Proper surgical approaches and anesthetic protocols are the first steps in creating these models, and each successful approach requires a proper anesthetic protocol that maintains good recovery and high survival rates after surgery. However, each protocol may have shortcomings that limit the study's outcomes. In addition, the ethical regulations of animal welfare in certain countries prohibit the use of specific anesthetic agents, which are widely used to establish animal models. This review summarizes the most common and recent surgical models of HF and the anesthetic protocols used in rat models. We will highlight the surgical approach of each model, the use of anesthesia, and the limitations of the model in the study of the pathophysiology and therapeutic basis of common cardiovascular diseases.

Molecular mechanisms and targets of right ventricular fibrosis in pulmonary hypertension

Right ventricular fibrosis is a stress response, predominantly mediated by cardiac fibroblasts. This cell population is sensitive to increased levels of pro-inflammatory cytokines, pro-fibrotic growth factors and mechanical stimulation. Activation of fibroblasts results in the induction of various molecular signaling pathways, most notably the mitogen-activated protein kinase cassettes, leading to increased synthesis and remodeling of the extracellular matrix. While fibrosis confers structural protection in response to damage induced by ischemia or (pressure and volume) overload, it simultaneously contributes to increased myocardial stiffness and right ventricular dysfunction. Here, we review state-of-the-art knowledge of the development of right ventricular fibrosis in response to pressure overload and provide an overview of all published preclinical and clinical studies in which right ventricular fibrosis was targeted to improve cardiac function.

Differential effect of basal vitamin D status in monocrotaline induced pulmonary arterial hypertension in normal and vitamin D deficient rats: Possible involvement of eNOS/TGF-β/α-SMA signaling pathways

Vitamin D deficiency is common and linked to poor prognosis in pulmonary arterial hypertension (PAH). We investigated the differential effect of basal vitamin D levels in monocrotaline (MCT) induced PAH in normal and vitamin D deficient (VDD) rats. Rats were fed a VDD diet and exposed to filtered fluorescent light to deplete vitamin D. Normal rats were pretreated with vitamin D 100 IU/d and treated with vitamin D 100 and 200 IU/d, while VDD rats received vitamin D 100 IU/d. Vitamin D receptor (VDR) silencing was done in human umbilical vein endothelial cells (HUVECs) using VDR siRNA. Calcitriol (50 nM/mL) was added to human pulmonary artery smooth muscle cells (HPASMCs) and HUVECs before and after the exposure to TGF-β (10 ng/mL). Vitamin D 100 IU/d pretreatment in normal rats up-regulated the expression of eNOS and inhibited endothelial to mesenchymal transition significantly and maximally. Vitamin D 100 IU/d treatment in VDD rats was comparable to vitamin D 200 IU/d treated normal rats. These effects were significantly attenuated by L-NAME (20 mg/kg), a potent eNOS inhibitor. Exposure to TGF- β significantly reduced the expression of eNOS and increased the mesenchymal marker expression in normal and VDR-silenced HUVECs and HPASMCs, which were averted by treatment and maximally inhibited by pretreatment with calcitriol (50 nM). To conclude, this study provided novel evidence suggesting the beneficial role of higher basal vitamin D levels, which are inversely linked with PAH severity.

Vanillic Acid Alleviates Right Ventricular Function in Rats With MCT-Induced Pulmonary Arterial Hypertension

This study examined the molecular processes behind the effects of vanillic acid (VA) on right ventricular (RV) hypertrophy and function in rats with monocrotaline (MCT)-induced pulmonary arterial hypertension (PAH). There were 40 male Sprague‒Dawley (SD) rats that were separated into 4 groups: Control, PAH, MCT + VA (50 mg/kg/d), and MCT + VA (100 mg/kg/d). Male SD rats were injected with MCT once under the skin to create the PAH model (40 mg/kg). RV morphological properties were evaluated using Masson and hematoxylin and eosin (H&E) staining. Echocardiography was used to evaluate RV functioning and right ventricle–pulmonary artery (RV-PA) coupling. In addition, Rho-associated protein kinase (ROCK) pathway-related factors were evaluated using Western blotting. Enzyme-linked immunosorbent assay (ELISA) was used to detect inflammatory markers as well as atrial natriuretic peptide (ANP) and brain-type natriuretic peptide (BNP) in the blood of PAH rats. As a result, VA effectively reduced the development of RV cardiomyocyte hypertrophy and fibrosis in PAH rats; levels of ANP, BNP, and inflammatory markers in the blood of PAH rats were also significantly decreased by VA intervention. Additionally, VA enhanced RV functioning and RV-PA coupling in PAH rats. In response to VA, the expression of proteins related to the ROCK pathway (ROCK1, ROCK2, NFATc3, P-STAT3, and Bax) was downregulated, whereas Bcl-2 expression was elevated. This study found that VA could attenuate RV remodeling and improve RV-PA coupling in PAH rats. RV remodeling and dysfunction may be linked to the dysregulation of the ROCK pathway, and the protective action of VA on RV function may be due to a block in the ROCK signaling pathway or its downstream signaling molecules.

The thromboxane receptor antagonist NTP42 promotes beneficial adaptation and preserves cardiac function in experimental models of right heart overload

Background

Pulmonary arterial hypertension (PAH) is a progressive disease characterized by increased pulmonary artery pressure leading to right ventricular (RV) failure. While current PAH therapies improve patient outlook, they show limited benefit in attenuating RV dysfunction. Recent investigations demonstrated that the thromboxane (TX) A₂ receptor (TP) antagonist NTP42 attenuates experimental PAH across key hemodynamic parameters in the lungs and heart. This study aimed to validate the efficacy of NTP42:KVA4, a novel oral formulation of NTP42 in clinical development, in preclinical models of PAH while also, critically, investigating its direct effects on RV dysfunction.

Methods

The effects of NTP42:KVA4 were evaluated in the monocrotaline (MCT) and pulmonary artery banding (PAB) models of PAH and RV dysfunction, respectively, and when compared with leading standard-of-care (SOC) PAH drugs. In addition, the expression of the TP, the target for NTP42, was investigated in cardiac tissue from several other related disease models, and from subjects with PAH and dilated cardiomyopathy (DCM).

Results

In the MCT-PAH model, NTP42:KVA4 alleviated disease-induced changes in cardiopulmonary hemodynamics, pulmonary vascular remodeling, inflammation, and fibrosis, to a similar or greater extent than the PAH SOCs tested. In the PAB model, NTP42:KVA4 improved RV geometries and contractility, normalized RV stiffness, and significantly increased RV ejection fraction. In both models, NTP42:KVA4 promoted beneficial RV adaptation, decreasing cellular hypertrophy, and increasing vascularization. Notably, elevated expression of the TP target was observed both in RV tissue from these and related disease models, and in clinical RV specimens of PAH and DCM.

Conclusion

This study shows that, through antagonism of TP signaling, NTP42:KVA4 attenuates experimental PAH pathophysiology, not only alleviating pulmonary pathologies but also reducing RV remodeling, promoting beneficial hypertrophy, and improving cardiac function. The findings suggest a direct cardioprotective effect for NTP42:KVA4, and its potential to be a disease-modifying therapy in PAH and other cardiac conditions.

Characterization of decellularized left and right ventricular myocardial matrix hydrogels and their effects on cardiac progenitor cells

Congenital heart defects are the leading cause of right heart failure in pediatric patients. Implantation of c-kit+ cardiac-derived progenitor cells (CPCs) is being clinically evaluated to treat the failing right ventricle (RV), but faces limitations due to reduced transplant cell survival, low engraftment rates, and low retention. These limitations have been exacerbated due to the nature of cell delivery (narrow needles) and the non-optimal recipient microenvironment (reactive oxygen species (ROS)). Extracellular matrix (ECM) hydrogels derived from porcine left ventricular (LV) myocardium have emerged as a potential therapy to treat the ischemic LV and have shown promise as a vehicle to deliver cells to injured myocardium. However, no studies have evaluated the combination of an injectable biomaterial, such as an ECM hydrogel, in combination with cell therapy for treating RV failure. In this study we characterized LV and RV myocardial matrix (MM) hydrogels and performed in vitro evaluations of their potential to enhance CPC delivery, including resistance to forces experienced during injection and exposure to ROS, as well as their potential to enhance angiogenic paracrine signaling. While physical properties of the two hydrogels are similar, the decellularized LV and RV have distinct protein signatures. Both materials were equally effective in protecting CPCs against needle forces and ROS. CPCs encapsulated in either the LV MM or RV MM exhibited similar enhanced potential for angiogenic paracrine signaling when compared to CPCs in collagen. The RV MM without cells, however, likewise improved tube formation, suggesting it should also be evaluated as a potential standalone treatment.

Evidence of Failed Resolution Mechanisms in Arrhythmogenic Inflammation, Fibrosis and Right Heart Disease

Inflammation is a complex program of active processes characterized by the well-orchestrated succession of an initiation and a resolution phase aiming to promote homeostasis. When the resolution of inflammation fails, the tissue undergoes an unresolved inflammatory status which, if it remains uncontrolled, can lead to chronic inflammatory disorders due to aggravation of structural damages, development of a fibrous area, and loss of function. Various human conditions show a typical unresolved inflammatory profile. Inflammatory diseases include cancer, neurodegenerative disease, asthma, right heart disease, atherosclerosis, myocardial infarction, or atrial fibrillation. New evidence has started to emerge on the role, including pro-resolution involvement of chemical mediators in the acute phase of inflammation. Although flourishing knowledge is available about the role of specialized pro-resolving mediators in neurodegenerative diseases, atherosclerosis, obesity, or hepatic fibrosis, little is known about their efficacy to combat inflammation-associated arrhythmogenic cardiac disorders. It has been shown that resolvins, including RvD1, RvE1, or Mar1, are bioactive mediators of resolution. Resolvins can stop neutrophil activation and infiltration, stimulate monocytes polarization into anti-inflammatory-M2-macrophages, and activate macrophage phagocytosis of inflammation-debris and neutrophils to promote efferocytosis and clearance. This review aims to discuss the paradigm of failed-resolution mechanisms (FRM) potentially promoting arrhythmogenicity in right heart disease-induced inflammatory status.

Calpains as Potential Therapeutic Targets for Myocardial Hypertrophy

Despite advances in its treatment, heart failure remains a major cause of morbidity and mortality, evidencing an urgent need for novel mechanism-based targets and strategies. Myocardial hypertrophy, caused by a wide variety of chronic stress stimuli, represents an independent risk factor for the development of heart failure, and its prevention constitutes a clinical objective. Recent studies performed in preclinical animal models support the contribution of the Ca²⁺-dependent cysteine proteases calpains in regulating the hypertrophic process and highlight the feasibility of their long-term inhibition as a pharmacological strategy. In this review, we discuss the existing evidence implicating calpains in the development of cardiac hypertrophy, as well as the latest advances in unraveling the underlying mechanisms. Finally, we provide an updated overview of calpain inhibitors that have been explored in preclinical models of cardiac hypertrophy and the progress made in developing new compounds that may serve for testing the efficacy of calpain inhibition in the treatment of pathological cardiac hypertrophy.

In vivo evaluation of bioprinted cardiac patches composed of cardiac-specific extracellular matrix and progenitor cells in a model of pediatric heart failure

Pediatric patients with congenital heart defects (CHD) often present with heart failure from increased load on the right ventricle (RV) due to both surgical methods to treat CHD and the disease itself. Patients with RV failure often require transplantation, which is limited due to lack of donor availability and rejection. Previous studies investigating the development and in vitro assessment of a bioprinted cardiac patch composed of cardiac extracellular matrix (cECM) and human c-kit + progenitor cells (hCPCs) showed that the construct has promise in treating cardiac dysfunction. The current study investigates in vivo cardiac outcomes of patch implantation in a rat model of RV failure. Patch parameters including cECM-inclusion and hCPC-inclusion are investigated. Assessments include hCPC retention, RV function, and tissue remodeling (vascularization, hypertrophy, and fibrosis). Animal model evaluation shows that both cell-free and neonatal hCPC-laden cECM-gelatin methacrylate (GelMA) patches improve RV function and tissue remodeling compared to other patch groups and controls. Inclusion of cECM is the most influential parameter driving therapeutic improvements, with or without cell inclusion. This study paves the way for clinical translation in treating pediatric heart failure using bioprinted GelMA-cECM and hCPC-GelMA-cECM patches.

The Effects of Healthy Aging on Right Ventricular Structure and Biomechanical Properties: A Pilot Study

Healthy aging has been associated with alterations in pulmonary vascular and right ventricular (RV) hemodynamics, potentially leading to RV remodeling. Despite the current evidence suggesting an association between aging and alterations in RV function and higher prevalence of pulmonary hypertension in the elderly, limited data exist on age-related differences in RV structure and biomechanics. In this work, we report our preliminary findings on the effects of healthy aging on RV structure, function, and biomechanical properties. Hemodynamic measurements, biaxial mechanical testing, constitutive modeling, and quantitative transmural histological analysis were employed to study two groups of male Sprague-Dawley rats: control (11 weeks) and aging (80 weeks). Aging was associated with increases in RV peak pressures (+17%, p = 0.017), RV contractility (+52%, p = 0.004), and RV wall thickness (+38%, p = 0.001). Longitudinal realignment of RV collagen (16.4°, p = 0.013) and myofibers (14.6°, p = 0.017) were observed with aging, accompanied by transmural cardiomyocyte loss and fibrosis. Aging led to increased RV myofiber stiffness (+141%, p = 0.003), in addition to a bimodal alteration in the biaxial biomechanical properties of the RV free wall, resulting in increased tissue-level stiffness in the low-strain region, while progressing into decreased stiffness at higher strains. Our results demonstrate that healthy aging may modulate RV remodeling via increased peak pressures, cardiomyocyte loss, fibrosis, fiber reorientation, and altered mechanical properties in male Sprague-Dawley rats. Similarities were observed between aging-induced remodeling patterns and those of RV remodeling in pressure overload. These findings may help our understanding of age-related changes in the cardiovascular fitness and response to disease.

Novel Therapeutic Targets for the Treatment of Right Ventricular Remodeling: Insights from the Pulmonary Artery Banding Model

Right ventricular (RV) function is the main determinant of the outcome of patients with pulmonary hypertension (PH). RV dysfunction develops gradually and worsens progressively over the course of PH, resulting in RV failure and premature death. Currently, approved therapies for the treatment of left ventricular failure are not established for the RV. Furthermore, the direct effects of specific vasoactive drugs for treatment of pulmonary arterial hypertension (PAH, Group 1 of PH) on RV are not fully investigated. Pulmonary artery banding (PAB) allows to study the pathogenesis of RV failure solely, thereby testing potential therapies independently of pulmonary vascular changes. This review aims to discuss recent studies of the mechanisms of RV remodeling and RV-directed therapies based on the PAB model.

Current Understanding of the Right Ventricle Structure and Function in Pulmonary Arterial Hypertension

Pulmonary arterial hypertension (PAH) is a disease resulting in increased right ventricular (RV) afterload and RV remodeling. PAH results in altered RV structure and function at different scales from organ-level hemodynamics to tissue-level biomechanical properties, fiber-level architecture, and cardiomyocyte-level contractility. Biomechanical analysis of RV pathophysiology has drawn significant attention over the past years and recent work has found a close link between RV biomechanics and physiological function. Building upon previously developed techniques, biomechanical studies have employed multi-scale analysis frameworks to investigate the underlying mechanisms of RV remodeling in PAH and effects of potential therapeutic interventions on these mechanisms. In this review, we discuss the current understanding of RV structure and function in PAH, highlighting the findings from recent studies on the biomechanics of RV remodeling at organ, tissue, fiber, and cellular levels. Recent progress in understanding the underlying mechanisms of RV remodeling in PAH, and effects of potential therapeutics, will be highlighted from a biomechanical perspective. The clinical relevance of RV biomechanics in PAH will be discussed, followed by addressing the current knowledge gaps and providing suggested directions for future research.

Animal models of pulmonary hypertension: Getting to the heart of the problem

Despite recent therapeutic advances, pulmonary hypertension (PH) remains a fatal disease due to the development of right ventricular (RV) failure. At present, no treatments targeted at the right ventricle are available, and RV function is not widely considered in the preclinical assessment of new therapeutics. Several small animal models are used in the study of PH, including the classic models of exposure to either hypoxia or monocrotaline, newer combinational and genetic models, and pulmonary artery banding, a surgical model of pure RV pressure overload. These models reproduce selected features of the structural remodelling and functional decline seen in patients and have provided valuable insight into the pathophysiology of RV failure. However, significant reversal of remodelling and improvement in RV function remains a therapeutic obstacle. Emerging animal models will provide a deeper understanding of the mechanisms governing the transition from adaptive remodelling to a failing right ventricle, aiding the hunt for druggable molecular targets.

Asymmetric Regional Work Contributes to Right Ventricular Fibrosis, Inefficiency, and Dysfunction in Pulmonary Hypertension versus Regurgitation

BACKGROUND

Right ventricular (RV) pressure loading from pulmonary hypertension (PH) and volume loading from pulmonary regurgitation (PR) lead to RV dysfunction, a critical determinant of clinical outcomes, but their impact on regional RV mechanics and fibrosis is poorly characterized. The aim of this study was to test the hypothesis that regional myocardial mechanics and efficiency in RV pressure and volume loading are associated with RV fibrosis and dysfunction.

METHODS

Eight PH, six PR, and five sham-control rats were studied. The PH rat model was induced using Sugen5416, a vascular endothelial growth factor receptor 2 inhibitor, combined with chronic hypoxia. PR rats were established by surgical laceration of the pulmonary valve leaflets. Six (n = 4) or 9 (n = 4) weeks after Sugen5416 and hypoxia and 12 weeks after PR surgery, myocardial strain and RV pressure were measured and RV pressure-strain loops generated. We further studied RV regional mechanics in 11 patients with PH. Regional myocardial work was calculated as the pressure-strain loop area (mm Hg ∙ %). Regional myocardial work efficiency was quantified through wasted work (ratio of systolic lengthening to shortening work). The relation of regional myocardial work to RV fibrosis and dysfunction was analyzed.

RESULTS

In rats, PH and PR induced similar RV dilatation, but fractional area change (%) was lower in PH than in PR. RV lateral wall work was asymmetrically higher in PH compared with sham, while septal work was similar to sham. In PR, lateral and septal work were symmetrically higher versus sham. Myocardial wasted work ratio was asymmetrically increased in the PH septum versus sham. Fibrosis in the RV lateral wall, but not septum, was higher in PH than PR. RV fibrosis burden was linearly related to regional work and to measures of RV systolic and diastolic function but not to wasted myocardial work ratio. Patients with PH demonstrated similar asymmetric and inefficient regional myocardial mechanics.

CONCLUSIONS

Asymmetric RV work and increased wasted septal work in experimental PH are associated with RV fibrosis and dysfunction. Future investigation should examine whether assessment of asymmetric regional RV work and efficiency can predict clinical RV failure and influence patient management.

'There and Back Again'-Forward Genetics and Reverse Phenotyping in Pulmonary Arterial Hypertension

Although the invention of right heart catheterisation in the 1950s enabled accurate clinical diagnosis of pulmonary arterial hypertension (PAH), it was not until 2000 when the landmark discovery of the causative role of bone morphogenetic protein receptor type II (BMPR2) mutations shed new light on the pathogenesis of PAH. Since then several genes have been discovered, which now account for around 25% of cases with the clinical diagnosis of idiopathic PAH. Despite the ongoing efforts, in the majority of patients the cause of the disease remains elusive, a phenomenon often referred to as "missing heritability". In this review, we discuss research approaches to uncover the genetic architecture of PAH starting with forward phenotyping, which in a research setting should focus on stable intermediate phenotypes, forward and reverse genetics, and finally reverse phenotyping. We then discuss potential sources of "missing heritability" and how functional genomics and multi-omics methods are employed to tackle this problem.