Ventricular function and biomarkers in relation to repair and pulmonary valve replacement for tetralogy of Fallot

Objective Cardiac surgery may cause temporarily impaired ventricular performance and myocardial injury. We aim to characterise the response to perioperative injury for patients undergoing repair or pulmonary valve replacement (PVR) for tetralogy of Fallot (ToF). Methods We enrolled children undergoing ToF repair or PVR from four tertiary centres in a prospective observational study. Assessment - including blood sampling and speckle tracking echocardiography - occurred before surgery (T1), at the first follow-up (T2) and 1 year after the procedures (T3). Ninety-two serum biomarkers were expressed as principal components to reduce multiple statistical testing. RNA Sequencing was performed on right ventricular (RV) outflow tract samples. Results We included 45 patients with ToF repair aged 4.3 (3.4 - 6.5) months and 16 patients with PVR aged 10.4 (7.8 - 12.7) years. Ventricular function following ToF repair showed a fall-and-rise pattern for left ventricular global longitudinal strain (GLS) (-18±4 to -13±4 to -20±2, p &lt; 0.001 for each comparison) and RV GLS (-19±5 to -14±4 to 20±4, p &lt; 0.002 for each comparison). This pattern was not seen for patients undergoing PVR. Serum biomarkers were expressed as three principal components. These phenotypes are related to: (1) surgery type, (2) uncorrected ToF and (3) early postoperative status. Principal component 3 scores were increased at T2. This increase was higher for ToF repair than PVR. The transcriptomes of RV outflow tract tissue are related to patients' sex, rather than ToF-related phenotypes in a subset of the study population. Conclusions The response to perioperative injury following ToF repair and PVR is characterised by specific functional and immunological responses. However, we did not identify factors relating to (dis)advantageous recovery from perioperative injury. Trial registration number Netherlands Trial Register: NL5129.</p

Development, Proliferation, and Growth of the Mammalian Heart

During development, the embryonic heart grows by addition of cells from a highly proliferative progenitor pool and by subsequent precisely controlled waves of cardiomyocyte proliferation. In this period, the heart can compensate for cardiomyocyte loss by an increased proliferation rate of the remaining cardiomyocytes. This proliferative capacity is lost soon after birth, with heart growth continuing by an increase in cardiomyocyte volume. The failure of the injured adult heart to regenerate often leads to the development of heart failure, a major cause of death. With the recent observation of a small fraction of cardiomyocytes that appear to have retained the proliferative capacity within the adult heart, as well as the identification of developmental pathways such as the Hippo-signaling pathway that can invoke mature cardiomyocyte proliferation, more studies are taking a knowledge-based mechanistic approach to heart regeneration. A key question being asked is if this knowledge can be used therapeutically to reinitiate cardiomyocyte proliferation after injury such as myocardial infarction. In this respect, uncovering and understanding the mechanisms and conditions that give rise to a fully functional and adaptive heart in the developing embryo could provide us with the answers to many of the questions that are now being asked

Early Postnatal Cardiac Stress Does Not Influence Ventricular Cardiomyocyte Cell-Cycle Withdrawal

Congenital heart disease (CHD) is the most common birth defect. After birth, patients with CHD may suffer from cardiac stress resulting from abnormal loading conditions. However, it is not known how this cardiac burden influences postnatal development and adaptation of the ventricles. To study the transcriptional and cell-cycle response of neonatal cardiomyocytes to cardiac stress, we used a genetic mouse model that develops left ventricular volume overload within 2 weeks after birth. The increased volume load caused upregulation of the cardiac stress marker Nppa in the left ventricle and interventricular septum as early as 12 days after birth. Transcriptome analysis revealed that cardiac stress induced the expression of cell-cycle genes. This did not influence postnatal cell-cycle withdrawal of cardiomyocytes and other cell types in the ventricles as measured by Ki-67 immunostaining

Neuregulin-1 enhances cell-cycle activity, delays cardiac fibrosis, and improves cardiac performance in rat pups with right ventricular pressure load

OBJECTIVES: Right ventricular (RV) failure is a leading cause of death in patients with congenital heart disease. RV failure is kept at bay during childhood. Limited proliferation of cardiomyocytes is present in the postnatal heart. We propose that cardiomyocyte proliferation improves RV adaptation to pressure load (PL). We studied adaptation in response to increased RV PL and the role of increased cardiomyocyte cell cycle activity (CCA) in rat pups growing into adulthood. METHODS: We induced RV PL at day of weaning in rats (3 weeks; 30-40 g) by pulmonary artery banding and followed rats into adulthood (300 g). We performed histological analyses and RNA sequencing analysis. To study the effects of increased cardiomyocyte cell cycle activity, we administered neuregulin-1 (NRG1), a growth factor involved in cardiac development. RESULTS: PL induced an increase in CCA, with subsequent decline of CCA (sham/PL at 4 weeks: 0.14%/0.83%; P = .04 and 8 weeks: 0.00%/0.00%; P = .484) and cardiac function (cardiac index: control/PL 4 weeks: 4.41/3.29; P = .468 and 8 weeks: 3.57/1.44; P = .024). RNA sequencing analysis revealed delayed maturation and increased CCA pathways. NRG1 stimulated CCA (PL vehicle/NRG1 at 2 weeks: 0.62%/2.28%; P = .003), improved cardiac function (cardiac index control vs vehicle/NRG1 at 2 weeks: 4.21 vs 3.07/4.17; P = .009/.705) and postponed fibrosis (control vs vehicle/NRG1 at 4 weeks: 1.66 vs 4.82%/2.97%; P = .009/.078) in RV PL rats during childhood. CONCLUSIONS: RV PL during growth induces a transient CCA increase. Further CCA stimulation improves cardiac function and delays fibrosis. This proof-of-concept study shows that stimulation of CCA can improve RV adaptation to PL in the postnatal developing heart and might provide a new approach to preserve RV function in patients with congenital heart disease

Conserved NPPB+ Border Zone Switches From MEF2- to AP-1-Driven Gene Program

BACKGROUND: Surviving cells in the postinfarction border zone are subjected to intense fluctuations of their microenvironment. Recently, border zone cardiomyocytes have been specifically implicated in cardiac regeneration. Here, we defined their unique transcriptional and regulatory properties, and comprehensively validated new molecular markers, including Nppb, encoding B-type natriuretic peptide, after infarction. METHODS: Transgenic reporter mice were used to identify the Nppb-positive border zone after myocardial infarction. Transcriptome analysis of remote, border, and infarct zones and of purified cardiomyocyte nuclei was performed using RNA-sequencing. Top candidate genes displaying border zone spatial specificity were histologically validated in ischemic human hearts. Mice in which Nppb was deleted by genome editing were subjected to myocardial infarction. Chromatin accessibility landscapes of border zone and control cardiomyocyte nuclei were assessed by using assay for transposase-accessible chromatin using sequencing. RESULTS: We identified the border zone as a spatially confined region transcriptionally distinct from the remote myocardium. The transcriptional response of the border zone was much stronger than that of the remote ventricular wall, involving acute downregulation of mitochondrial oxidative phosphorylation, fatty acid metabolism, calcium handling, and sarcomere function, and the activation of a stress-response program. Analysis of infarcted human hearts revealed that the transcriptionally discrete border zone is conserved in humans, and led to the identification of novel conserved border zone markers including NPPB, ANKRD1, DES, UCHL1, JUN, and FOXP1. Homozygous Nppb mutant mice developed acute and lethal heart failure after myocardial infarction, indicating that B-type natriuretic peptide is required to preserve postinfarct heart function. Assay for transposase-accessible chromatin using sequencing revealed thousands of cardiomyocyte lineage-specific MEF2-occupied regulatory elements that lost accessibility in the border zone. Putative injury-responsive enhancers that gained accessibility were highly associated with AP-1 (activator protein 1) binding sites. Nuclear c-Jun, a component of AP-1, was observed specifically in border zone cardiomyocytes. CONCLUSIONS: Cardiomyocytes in a discrete zone bordering the infarct switch from a MEF2-driven homeostatic lineage-specific to an AP-1-driven injury-induced gene expression program. This program is conserved between mouse and human, and includes Nppb expression, which is required to prevent acute heart failure after infarction