Altered proteasome function in right ventricular hypertrophy

The unique hypertrophic and fibrotic features of neonatal right ventricle in response to pressure overload

Pediatric heart failure (HF) research remains in its infancy partly due to the lack of neonatal rat/mouse models of HF. The aim of the study is to introduce a neonatal rat/mouse model of right ventricular (RV) pressure overload (RVPO), a significant cause of pediatric HF, and to uncover the molecular features of RVPO-induced RV hypertrophy and fibrosis-the two most important transitional pathological states between normal and dysfunctional RV. Neonatal rat/mouse model of RVPO was established by pulmonary artery banding (PAB) surgery on postnatal day 1(P1) and confirmed by echocardiography and morphological examination on P7. Bulk RNA and single-cell RNA sequencing was performed on RV tissues, along with bulk RNA sequencing on RV cardiomyocytes, to screen a range of key genes and signaling pathways that are upregulated and that play critical roles in adult hypertrophy and fibrosis. The sequencing results were further verified by qRT-PCR and histological staining. Most of the pathways and associated genes, such as oxidative stress, inflammation, phosphodiesterase, proteasome, protein kinase, transforming growth factor, and angiotensin were not changed or downregulated in the neonatal RVPO model. This study reveals the unique features of hypertrophy and fibrosis in the neonatal RV in response to pressure overload, which partly explains why adult-effective anti-HF drugs fail to treat pediatric HF. More importantly, single-cell RNA sequencing data of the neonatal RV with pressure overload were documented, providing an important reference for future basic or clinical investigations on pediatric RV failure.

Identification of serum C4BPA as a potential diagnostic marker of right ventricular remodelling via proteomic analysis

AIMS

Right ventricular (RV) remodelling, a progressive condition characterized by maladaptive cardiac structural and functional changes, primarily results from prolonged pressure overload in patients with pulmonary hypertension (PH). Accurate, universal and easy-to-use biomarkers for assessing the severity of RV remodelling are lacking. This study aimed to identify serum proteins as potential biomarkers of RV remodelling using high-throughput proteomic analysis-based screening.

METHODS

Sprague-Dawley rats were subjected to sham surgery (control group) or pulmonary artery banding for 4 weeks with 2.3-mm diameter and 1.8-mm diameter rubber rings to induce mild and severe RV modelling, respectively. Serum proteomic profiling revealed 170 differentially expressed serum proteins (DEPs) among the three groups, and three DEPs gradually increased with worsening RV remodelling. Among the three DEPs, C4b-binding protein alpha chain (C4BPA) exhibited the highest upregulation in the severe group (6.93 vs. 16.5 ng/mL, P < 0.001), and linear regression analysis revealed a negative correlation between serum C4BPA levels and tricuspid annular plane systolic excursion (TAPSE) in rats [beta = -0.78, 95% confidence interval (CI) -14.5 to -7.11, P < 0.001]. The diagnostic power of C4BPA was further validated in 127 patients (34 with adaptive RV pressure overload, 36 with maladaptive RV pressure overload, 32 with left ventricular hypertrophy and 25 controls). Control and left ventricular hypertrophy patients exhibited lower serum C4BPA levels than the two RV groups, and serum C4BPA levels were higher in patients with maladaptive RV than in those with adaptive RV (754 vs. 524 pg/mL, P < 0.001). Linear regression analysis revealed a negative correlation between serum C4BPA levels and TAPSE in PH patients. The predictive power of C4BPA for maladaptive RV function in PH patients, indicated by receiver operating characteristic analysis (cut-off value 573 pg/mL, area under the curve 0.792), was as good as that of B-type natriuretic peptide (BNP). High serum C4BPA levels (≥573 pg/mL) were associated with lower TAPSE/pulmonary arterial systolic pressure ratios (P < 0.001) and higher BNP levels (P < 0.001).

CONCLUSIONS

Serum C4BPA may represent a novel diagnostic biomarker for RV pathological remodelling associated with RV maladaptation in PH patients.

ROR2 drives right ventricular heart failure via disruption of proteostasis

Background

No therapies exist to reverse right ventricular failure (RVF), and the molecular mechanisms that drive RVF remain poorly studied. We recently reported that the developmentally restricted noncanonical WNT receptor ROR2 is upregulated in human RVF in proportion to severity of disease. Here we test mechanistic role of ROR2 in RVF pathogenesis.

Methods

ROR2 was overexpressed or knocked down in neonatal rat ventricular myocytes (NRVMs). ROR2-modified NRVMs were characterized using confocal microscopy, RNAseq, proteomics, proteostatic functional assays, and contractile properties with pacing. The impact of cardiac ROR2 expression was evaluated in mice by AAV9-mediated overexpression and by AAV9-mediated delivery of shRNA to knockdown ROR2 in a pulmonary artery banded pressure overload RVF model. ROR2-modified mice were evaluated by echocardiography, RV protein synthetic rates and proteasome activity.

Results

In NRVMs, we find that ROR2 profoundly dysregulates the coordination between protein translation and folding. This imbalance leads to excess protein clearance by the ubiquitin proteasome system (UPS) with dramatic impacts on sarcomere and cytoskeletal structure and function. In mice, forced cardiac ROR2 expression is sufficient to disrupt proteostasis and drive RVF, while conversely ROR2 knockdown partially rescues proteostasis and cardiac function in a pressure overload model of RVF.

Conclusions

In sum, ROR2 is a key driver of RVF pathogenesis through proteostatic disruption and, thus, provides a promising target to treat RVF.

Alterations of biaxial viscoelastic properties of the right ventricle in pulmonary hypertension development in rest and acute stress conditions

Introduction: The right ventricle (RV) mechanical property is an important determinant of its function. However, compared to its elasticity, RV viscoelasticity is much less studied, and it remains unclear how pulmonary hypertension (PH) alters RV viscoelasticity. Our goal was to characterize the changes in RV free wall (RVFW) anisotropic viscoelastic properties with PH development and at varied heart rates. Methods: PH was induced in rats by monocrotaline treatment, and the RV function was quantified by echocardiography. After euthanasia, equibiaxial stress relaxation tests were performed on RVFWs from healthy and PH rats at various strain-rates and strain levels, which recapitulate physiological deformations at varied heart rates (at rest and under acute stress) and diastole phases (at early and late filling), respectively. Results and Discussion: We observed that PH increased RVFW viscoelasticity in both longitudinal (outflow tract) and circumferential directions. The tissue anisotropy was pronounced for the diseased RVs, not healthy RVs. We also examined the relative change of viscosity to elasticity by the damping capacity (ratio of dissipated energy to total energy), and we found that PH decreased RVFW damping capacity in both directions. The RV viscoelasticity was also differently altered from resting to acute stress conditions between the groups-the damping capacity was decreased only in the circumferential direction for healthy RVs, but it was reduced in both directions for diseased RVs. Lastly, we found some correlations between the damping capacity and RV function indices and there was no correlation between elasticity or viscosity and RV function. Thus, the RV damping capacity may be a better indicator of RV function than elasticity or viscosity alone. These novel findings on RV dynamic mechanical properties offer deeper insights into the role of RV biomechanics in the adaptation of RV to chronic pressure overload and acute stress.

Target Fishing Reveals a Novel Mechanism of 1,2,4-Oxadiazole Derivatives Targeting Rpn6, a Subunit of 26S Proteasome

1,2,4-Oxadiazole derivatives, a class of Nrf2-ARE activators, exert an extensive therapeutic effect on inflammation, cancer, neurodegeneration, and microbial infection. Among these analogues, DDO-7263 is the most potent Nrf2 activator and used as the core structure for bioactive probes to explore the precise mechanism. In this work, we obtained compound 7, a mimic of DDO-7263, and biotin-labeled and fluorescein-based probes, which exhibited homologous biological activities to DDO-7263, including activating Nrf2 and its downstream target genes, anti-oxidative stress, and anti-inflammatory effects. Affinity chromatography and mass analysis techniques revealed Rpn6 as the potential target protein regulating the Nrf2 signaling pathway. In vitro affinity experiments further confirmed that DDO-7263 upregulated Nrf2 through binding to Rpn6 to block the assembly of 26S proteasome and the subsequent degradation of ubiquitinated Nrf2. These results indicated that Rpn6 is a promising candidate target to activate the Nrf2 pathway for protecting cells and tissues from oxidative, electrophilic, and exogenous microbial stimulation.

Exploring Functional Differences between the Right and Left Ventricles to Better Understand Right Ventricular Dysfunction

The right and left ventricles have traditionally been studied as individual entities. Furthermore, modifications found in diseased left ventricles are assumed to influence on right ventricle alterations, but the connection is poorly understood. In this review, we describe the differences between ventricles under physiological and pathological conditions. Understanding the mechanisms that differentiate both ventricles would facilitate a more effective use of therapeutics and broaden our knowledge of right ventricle (RV) dysfunction. RV failure is the strongest predictor of mortality in pulmonary arterial hypertension, but at present, there are no definitive therapies directly targeting RV failure. We further explore the current state of drugs and molecules that improve RV failure in experimental therapeutics and clinical trials to treat pulmonary arterial hypertension and provide evidence of their potential benefits in heart failure.

The Role of HECT-Type E3 Ligase in the Development of Cardiac Disease

Despite advances in medicine, cardiac disease remains an increasing health problem associated with a high mortality rate. Maladaptive cardiac remodeling, such as cardiac hypertrophy and fibrosis, is a risk factor for heart failure; therefore, it is critical to identify new therapeutic targets. Failing heart is reported to be associated with hyper-ubiquitylation and impairment of the ubiquitin–proteasome system, indicating an importance of ubiquitylation in the development of cardiac disease. Ubiquitylation is a post-translational modification that plays a pivotal role in protein function and degradation. In 1995, homologous to E6AP C-terminus (HECT) type E3 ligases were discovered. E3 ligases are key enzymes in ubiquitylation and are classified into three families: really interesting new genes (RING), HECT, and RING-between-RINGs (RBRs). Moreover, 28 HECT-type E3 ligases have been identified in human beings. It is well conserved in evolution and is characterized by the direct attachment of ubiquitin to substrates. HECT-type E3 ligase is reported to be involved in a wide range of human diseases and health. The role of HECT-type E3 ligases in the development of cardiac diseases has been uncovered in the last decade. There are only a few review articles summarizing recent advancements regarding HECT-type E3 ligase in the field of cardiac disease. This study focused on cardiac remodeling and described the role of HECT-type E3 ligases in the development of cardiac disease. Moreover, this study revealed that the current knowledge could be exploited for the development of new clinical therapies.

Treatment Targets for Right Ventricular Dysfunction in Pulmonary Arterial Hypertension

Right ventricle (RV) dysfunction is the strongest predictor of mortality in pulmonary arterial hypertension (PAH), but, at present, there are no therapies directly targeting the failing RV. Although there are shared molecular mechanisms in both RV and left ventricle (LV) dysfunction, there are important differences between the 2 ventricles that may allow for the development of RV-enhancing or RV-directed therapies. In this review, we discuss the current understandings of the dysregulated pathways that promote RV dysfunction, highlight RV-enriched or RV-specific pathways that may be of particular therapeutic value, and summarize recent and ongoing clinical trials that are investigating RV function in PAH. It is hoped that development of RV-targeted therapies will improve quality of life and enhance survival for this deadly disease.

Establishment of adult right ventricle failure in ovine using a graded, animal-specific pulmonary artery constriction model

BACKGROUND

Right ventricle failure (RVF) is associated with serious cardiac and pulmonary diseases that contribute significantly to the morbidity and mortality of patients. Currently, the mechanisms of RVF are not fully understood and it is partly due to the lack of large animal models in adult RVF. In this study, we aim to establish a model of RVF in adult ovine and examine the structure and function relations in the RV.

METHODS

RV pressure overload was induced in adult male sheep by revised pulmonary artery constriction (PAC). Briefly, an adjustable hydraulic occluder was placed around the main pulmonary artery trunk. Then, repeated saline injection was performed at weeks 0, 1, and 4, where the amount of saline was determined in an animal-specific manner. Healthy, age-matched male sheep were used as additional controls. Echocardiography was performed bi-weekly and on week 11 post-PAC, hemodynamic and biological measurements were obtained.

RESULTS

This PAC methodology resulted in a marked increase in RV systolic pressure and decreases in stroke volume and tricuspid annular plane systolic excursion, indicating signs of RVF. Significant increases in RV chamber size, wall thickness, and Fulton's index were observed. Cardiomyocyte hypertrophy and collagen accumulation (particularly type III collagen) were evident, and these structural changes were correlated with RV dysfunction.

CONCLUSION

In summary, the animal-specific, repeated PAC provided a robust approach to induce adult RVF, and this ovine model will offer a useful tool to study the progression and treatment of adult RVF that is translatable to human diseases.