Downregulated developmental processes in the postnatal right ventricle under the influence of a volume overload

Right ventricular volume overload reboots cardiomyocyte proliferation via immune responses

BACKGROUND

Right ventricular volume overload (RVVO) is one of the most important hemodynamic characteristics in children with congenital heart disease (CHD) and heart failure, and cardiomyocyte (CM) proliferation is one of the most vital factors for improving cardiac performance. However, whether and how RVVO reboots CM proliferation remains elusive.

METHODS AND RESULTS

We first created a neonatal RVVO mouse model via abdominal aorta and inferior vena cava-fistula microsurgery at postnatal day 7 (P7), the edge of CM proliferation window. We subsequently performed bulk RNA-seq, single cell RNA-seq/flow cytometry, and immunofluorescence staining on the right ventricles (RV) of RVVO mice at P14/P21, defined as prepubertal stage, revealing that RVVO temporarily reboots prepubertal CM proliferation via immune responses.

CONCLUSIONS

In considering the importance of RVVO and CM proliferation, this study may bring an opportunity to create a novel paradigm to treat pediatric CHDs or heart failure.

Hemodynamic Melody of Postnatal Cardiac and Pulmonary Development in Children with Congenital Heart Diseases

Hemodynamics is the eternal theme of the circulatory system. Abnormal hemodynamics and cardiac and pulmonary development intertwine to form the most important features of children with congenital heart diseases (CHDs), thus determining these children's long-term quality of life. Here, we review the varieties of hemodynamic abnormalities that exist in children with CHDs, the recently developed neonatal rodent models of CHDs, and the inspirations these models have brought us in the areas of cardiomyocyte proliferation and maturation, as well as in alveolar development. Furthermore, current limitations, future directions, and clinical decision making based on these inspirations are highlighted. Understanding how CHD-associated hemodynamic scenarios shape postnatal heart and lung development may provide a novel path to improving the long-term quality of life of children with CHDs, transplantation of stem cell-derived cardiomyocytes, and cardiac regeneration.

Volume overload impedes the maturation of sarcomeres and T-tubules in the right atria: a potential cause of atrial arrhythmia following delayed atrial septal defect closure

Introduction: Adult patients with atrial septal defects (ASD), the most common form of adult congenital heart disease, often die of arrhythmias, and the immaturity of cardiomyocytes contributes significantly to arrhythmias. ASD typically induces a left-to-right shunt, which then leads to the right atrium (RA) volume overload (VO). Whether or not VO contributes to RA cardiomyocyte immaturity and thereby causes arrhythmias in adult patients with ASD remains unclear. Methods: Here, we developed the first neonatal RA VO mouse model by creating a fistula between the inferior vena cava and abdominal aorta on postnatal day 7. RA VO was confirmed by increases in the mean flow velocity, mean pressure gradient, and velocity time integral across the tricuspid valve, and an increase in the RA diameter and RA area middle section. Results: We found that VO decreased the regularity and length of sarcomeres, and decreased the T-element density, regularity, and index of integrity of T-tubules in RA cardiomyocytes, suggesting that the two most important maturation hallmarks (sarcomere and T-tubules) of RA cardiomyocytes were impaired by VO. Accordingly, the calcium handling capacity of cardiomyocytes from postnatal day 21 (P21) RA was decreased by VO. VO caused a significant elongation of the PR interval. The expression of connexin 43 (Cx43) was decreased in RA VO. Moreover, gene ontology (GO) analysis of the downregulated genes in RA demonstrated that there was an abundance of enriched terms associated with sarcomeres and T-tubules exposed to VO. The results were further verified by qRT-PCR. Conclusions: In conclusion, the first neonatal RA VO mouse model was developed; furthermore, using this neonatal RA VO mouse model, we revealed that VO impeded RA sarcomere and T-tubule maturation, which may be the underlying causes of atrial arrhythmias in adult patients with ASD.

Ability of the Right Ventricle to Serve as a Systemic Ventricle in Response to the Volume Overload at the Neonatal Stage

BACKGROUND

In children with hypoplastic left heart syndrome (HLHS), volume overload (VO) is inevitable, and the right ventricle (RV) pumps blood into the systemic circulation. Understanding the molecular differences and their different responses to VO between the RV and left ventricle (LV) at the neonatal and highly plastic stages may improve the long-term management of children with HLHS.

METHODS AND RESULTS

A neonatal rat ventricular VO model was established by the creation of a fistula between the inferior vena cava and the abdominal aorta on postnatal day 1 (P1) and confirmed by echocardiographic and histopathological analyses. Transcriptomic analysis demonstrated that some of the major differences between a normal neonatal RV and LV were associated with the thyroid hormone and insulin signaling pathways. Under the influence of VO, the levels of insulin receptors and thyroid hormone receptors were significantly increased in the LV but decreased in the RV. The transcriptomic analysis also demonstrated that under the influence of VO, the top two common enriched pathways between the RV and LV were the insulin and thyroid hormone signaling pathways, whereas the RV-specific enriched pathways were primarily associated with lipid metabolism and arrhythmogenic right ventricular cardiomyopathy (ARVC); further, the LV-specific enriched pathways were primarily associated with nucleic acid metabolism and microRNAs in cancer.

CONCLUSIONS

Insulin and thyroid hormones may play critical roles in the differences between a neonatal RV and LV as well as their common responses to VO. Regarding the isolated responses to VO, the RV favors an ARVC change and the LV favors a reduction in microRNAs in cancer. The current study suggests that insulin, thyroid hormone, and cancer-associated microRNAs are potential therapeutic targets that should be explored by basic science studies to improve the function of the RV to match that of the LV.

Molecular Changes in Prepubertal Left Ventricular Development Under Experimental Volume Overload

Background

Left ventricular (LV) volume overload (VO), commonly found in patients with chronic aortic regurgitation (AR), leads to a series of left ventricular (LV) pathological responses and eventually irreversible LV dysfunction. Recently, questions about the applicability of the guideline for the optimal timing of valvular surgery to correct chronic AR have been raised in regard to both adult and pediatric patients. Understanding how VO regulates postnatal LV development may shed light on the best timing of surgical or drug intervention.

Methods and Results

Prepubertal LV VO was induced by aortocaval fistula (ACF) on postnatal day 7 (P7) in mice. LV free walls were analyzed on P14 and P21. RNA-sequencing analysis demonstrated that normal (P21_Sham vs.P14_Sham) and VO-influenced (P21_VO vs. P14_VO) LV development shared common terms of Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) in the downregulation of cell cycle activities and the upregulation of metabolic and sarcomere maturation. The enriched GO terms associated with cardiac condition were only observed in normal LV development, while the enriched GO terms associated with immune responses were only observed in VO-influenced LV development. These results were further validated by the examination of the markers of cell cycle, maturation, and immune responses. When normal and VO-influenced LVs of P21 were compared, they were different in terms of immune responses, angiogenesis, percentage of Ki67-positive cardiomyocytes, mitochondria number, T-tubule regularity, and sarcomere regularity and length.

Conclusions

A prepubertal LV VO mouse model was first established. VO has an important influence on LV maturation and development, especially in cardiac conduction, suggesting the requirement of an early correction of AR in pediatric patients. The underlying mechanism may be associated with the activation of immune responses.

Volume Overload Initiates an Immune Response in the Right Ventricle at the Neonatal Stage

Background: Pulmonary regurgitation caused by the correction or palliation of pediatric tetralogy of Fallot (TOF) leads to chronic right ventricular (RV) volume overload (VO), which induces adolescent RV dysfunction. A better understanding of the molecular mechanism by which VO initiates neonatal RV remodeling may bring new insights into the post-surgical management of pediatric TOF. Methods and Results: We created a fistula between the abdominal aorta and inferior vena cava on postnatal day 1 (P1) using a rat model to induce neonatal VO. Echocardiography revealed that the velocity and velocity- time-integral of the pulmonary artery (PA) were significantly elevated, and hematoxylin and eosin (H&E) staining showed that the diameter of the RV significantly increased. RNA-seq analysis of the RV on P7 indicated that the top 10 enriched Gene Ontology (GO) terms and the top 20 enriched terms in the Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis were associated with immune responses. Flow-cytometric analysis demonstrated that the number of CD4+and CD8+ immune cells were significantly augmented in the VO group compared with the sham group. Conclusions: A neonatal cardiac VO rat model on P1 was successfully created, providing a platform for studying the molecular biology of neonatal RV under the influence of VO. VO - induces an immune response at the neonatal stage (from P1 to P7), suggesting that immune responses may be an initiating factor for neonatal RV remodeling under the influence of VO and that immunosuppressants may be used to prevent pediatric RV remodeling caused by VO.