Cardiac function modulates endocardial cell dynamics to shape the cardiac outflow tract.
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ABSTRACT:
SUBMITTER: Sidhwani P
PROVIDER: S-EPMC7328156 | biostudies-literature |
REPOSITORIES: biostudies-literature
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Project description:We analyzed heart wall motion and blood flow dynamics in chicken embryos using in vivo optical coherence tomography (OCT) imaging and computational fluid dynamics (CFD) embryo-specific modeling. We focused on the heart outflow tract (OFT) region of day 3 embryos, and compared normal (control) conditions to conditions after performing an OFT banding intervention, which alters hemodynamics in the embryonic heart and vasculature. We found that hemodynamics and cardiac wall motion in the OFT are affected by banding in ways that might not be intuitive a priori. In addition to the expected increase in ventricular blood pressure, and increase blood flow velocity and, thus, wall shear stress (WSS) at the band site, the characteristic peristaltic-like motion of the OFT was altered, further affecting flow and WSS. Myocardial contractility, however, was affected only close to the band site due to the physical restriction on wall motion imposed by the band. WSS were heterogeneously distributed in both normal and banded OFTs. Our results show how banding affects cardiac mechanics and can lead, in the future, to a better understanding of mechanisms by which altered blood flow conditions affect cardiac development leading to congenital heart disease.
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Project description:Heart assembly requires input from two populations of progenitor cells, the first and second heart fields (FHF and SHF), that differentiate at distinct times and create different cardiac components. The cardiac outflow tract (OFT) is built through recruitment of late-differentiating, SHF-derived cardiomyocytes to the arterial pole of the heart. The mechanisms responsible for selection of an appropriate number of OFT cells from the SHF remain unclear. Here, we find that cell adhesion molecule 4 (cadm4) is essential for restricting the size of the zebrafish OFT. Knockdown of cadm4 causes dramatic OFT expansion, and overexpression of cadm4 results in a greatly diminished OFT. Moreover, cadm4 activity limits the production of OFT progenitor cells and the duration of their accumulation at the arterial pole. Together, our data suggest a role for cell adhesion in restraining SHF deployment to the OFT, perturbation of which could cause congenital OFT defects.
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Project description:Hemodynamic forces play an important role in sculpting the embryonic heart and its valves. Alteration of blood flow patterns through the hearts of embryonic animal models lead to malformations that resemble some clinical congenital heart defects, but the precise mechanisms are poorly understood. Quantitative understanding of the local fluid forces acting in the heart has been elusive because of the extremely small and rapidly changing anatomy. In this study, we combine multiple imaging modalities with computational simulation to rigorously quantify the hemodynamic environment within the developing outflow tract (OFT) and its eventual aortic and pulmonary valves. In vivo Doppler ultrasound generated velocity profiles were applied to Micro-Computed Tomography generated 3D OFT lumen geometries from Hamburger-Hamilton (HH) stage 16-30 chick embryos. Computational fluid dynamics simulation initial conditions were iterated until local flow profiles converged with in vivo Doppler flow measurements. Results suggested that flow in the early tubular OFT (HH16 and HH23) was best approximated by Poiseuille flow, while later embryonic OFT septation (HH27, HH30) was mimicked by plug flow conditions. Peak wall shear stress (WSS) values increased from 18.16 dynes/cm(2) at HH16 to 671.24 dynes/cm(2) at HH30. Spatiotemporally averaged WSS values also showed a monotonic increase from 3.03 dynes/cm(2) at HH16 to 136.50 dynes/cm(2) at HH30. Simulated velocity streamlines in the early heart suggest a lack of mixing, which differed from classical ink injections. Changes in local flow patterns preceded and correlated with key morphogenetic events such as OFT septation and valve formation. This novel method to quantify local dynamic hemodynamics parameters affords insight into sculpting role of blood flow in the embryonic heart and provides a quantitative baseline dataset for future research.
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Project description:In response to cardiac damage, a mesothelial tissue layer enveloping the heart called the epicardium is activated to proliferate and accumulate at the injury site. Recent studies have implicated the epicardium in multiple aspects of cardiac repair: as a source of paracrine signals for cardiomyocyte survival or proliferation; a supply of perivascular cells and possibly other cell types such as cardiomyocytes; and as a mediator of inflammation. However, the biology and dynamism of the adult epicardium is poorly understood. To investigate this, we created a transgenic line to ablate the epicardial cell population in adult zebrafish. Here we find that genetic depletion of the epicardium after myocardial loss inhibits cardiomyocyte proliferation and delays muscle regeneration. The epicardium vigorously regenerates after its ablation, through proliferation and migration of spared epicardial cells as a sheet to cover the exposed ventricular surface in a wave from the chamber base towards its apex. By reconstituting epicardial regeneration ex vivo, we show that extirpation of the bulbous arteriosus-a distinct, smooth-muscle-rich tissue structure that distributes outflow from the ventricle-prevents epicardial regeneration. Conversely, experimental repositioning of the bulbous arteriosus by tissue recombination initiates epicardial regeneration and can govern its direction. Hedgehog (Hh) ligand is expressed in the bulbous arteriosus, and treatment with a Hh signalling antagonist arrests epicardial regeneration and blunts the epicardial response to muscle injury. Transplantation of Sonic hedgehog (Shh)-soaked beads at the ventricular base stimulates epicardial regeneration after bulbous arteriosus removal, indicating that Hh signalling can substitute for the influence of the outflow tract. Thus, the ventricular epicardium has pronounced regenerative capacity, regulated by the neighbouring cardiac outflow tract and Hh signalling. These findings extend our understanding of tissue interactions during regeneration and have implications for mobilizing epicardial cells for therapeutic heart repair.
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Project description:In vertebrate embryos, cardiac precursor cells of the primary heart field are specified in the lateral mesoderm. These cells converge at the ventral midline to form the linear heart tube, and give rise to the atria and the left ventricle. The right ventricle and the outflow tract are derived from an adjacent population of precursors known as the second heart field. In addition, the cardiac neural crest contributes cells to the septum of the outflow tract to separate the systemic and the pulmonary circulations. The amphibian heart has a single ventricle and an outflow tract with an incomplete spiral septum; however, it is unknown whether the cardiac neural crest is also involved in outflow tract septation, as in amniotes. Using a combination of tissue transplantations and molecular analyses in Xenopus we show that the amphibian outflow tract is derived from a second heart field equivalent to that described in birds and mammals. However, in contrast to what we see in amniotes, it is the second heart field and not the cardiac neural crest that forms the septum of the amphibian outflow tract. In Xenopus, cardiac neural crest cells remain confined to the aortic sac and arch arteries and never populate the outflow tract cushions. This significant difference suggests that cardiac neural crest cell migration into the cardiac cushions is an amniote-specific characteristic, presumably acquired to increase the mass of the outflow tract septum with the evolutionary need for a fully divided circulation.
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Project description:The human chromosome 22q11.2 region is susceptible to rearrangements during meiosis leading to velo-cardio-facial/DiGeorge/22q11.2 deletion syndrome (22q11DS) characterized by conotruncal heart defects (CTDs) and other congenital anomalies. The majority of individuals have a 3 Mb deletion whose proximal region contains the presumed disease-associated gene TBX1 (T-box 1). Although a small subset have proximal nested deletions including TBX1, individuals with distal deletions that exclude TBX1 have also been identified. The deletions are flanked by low-copy repeats (LCR22A, B, C, D). We describe cardiac phenotypes in 25 individuals with atypical distal nested deletions within the 3 Mb region that do not include TBX1 including 20 with LCR22B to LCR22D deletions and 5 with nested LCR22C to LCR22D deletions. Together with previous reports, 12 of 37 (32%) with LCR22B-D deletions and 5 of 34 (15%) individuals with LCR22C-D deletions had CTDs including tetralogy of Fallot. In the absence of TBX1, we hypothesized that CRKL (Crk-like), mapping to the LCR22C-D region, might contribute to the cardiac phenotype in these individuals. We created an allelic series in mice of Crkl, including a hypomorphic allele, to test for gene expression effects on phenotype. We found that the spectrum of heart defects depends on Crkl expression, occurring with analogous malformations to that in human individuals, suggesting that haploinsufficiency of CRKL could be responsible for the etiology of CTDs in individuals with nested distal deletions and might act as a genetic modifier of individuals with the typical 3 Mb deletion.
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Project description:Coarctation of the aorta (CoA) and hypoplastic left heart syndrome (HLHS) have been reported in rare individuals with large terminal deletions of chromosome 15q26. However, no single gene important for left ventricular outflow tract (LVOT) development has been identified in this region. Using array-comparative genomic hybridization, we identified two half-siblings with CoA with a 2.2 Mb deletion on 15q26.2, inherited from their mother, who was mosaic for this deletion. This interval contains an evolutionary conserved, protein-coding gene, MCTP2 (multiple C2-domains with two transmembrane regions 2). Using gene-specific array screening in 146 individuals with non-syndromic LVOT obstructive defects, another individual with HLHS and CoA was found to have a de novo 41 kb intragenic duplication within MCTP2, predicted to result in premature truncation, p.F697X. Alteration of Mctp2 gene expression in Xenopus laevis embryos by morpholino knockdown and mRNA overexpression resulted in the failure of proper OT development, confirming the functional importance of this dosage-sensitive gene for cardiogenesis. Our results identify MCTP2 as a novel genetic cause of CoA and related cardiac malformations.
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Project description:In mammals, the outflow tract (OFT) of the developing heart septates into the base of the pulmonary artery and aorta to guide deoxygenated right ventricular blood into the lungs and oxygenated left ventricular blood into the systemic circulation. Accordingly, defective OFT septation is a life-threatening condition that can occur in both syndromic and nonsyndromic congenital heart disease. Even though studies of genetic mouse models have previously revealed a requirement for VEGF-A, the class 3 semaphorin SEMA3C, and their shared receptor neuropilin 1 (NRP1) in OFT development, the precise mechanism by which these proteins orchestrate OFT septation is not yet understood. Here, we have analyzed a complementary set of ligand-specific and tissue-specific mouse mutants to show that neural crest-derived SEMA3C activates NRP1 in the OFT endothelium. Explant assays combined with gene-expression studies and lineage tracing further demonstrated that this signaling pathway promotes an endothelial-to-mesenchymal transition that supplies cells to the endocardial cushions and repositions cardiac neural crest cells (NCCs) within the OFT, 2 processes that are essential for septal bridge formation. These findings elucidate a mechanism by which NCCs cooperate with endothelial cells in the developing OFT to enable the postnatal separation of the pulmonary and systemic circulation.
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Project description:AimsThe adapter protein p130Cas, encoded by the Bcar1 gene, is a key regulator of cell movement, adhesion, and cell cycle control in diverse cell types. Bcar1 constitutive knockout mice are embryonic lethal by embryonic days (E) 11.5-12.5, but the role of Bcar1 in embryonic development remains unclear. Here, we investigated the role of Bcar1 specifically in cardiovascular development and defined the cellular and molecular mechanisms disrupted following targeted Bcar1 deletions.Methods and resultsWe crossed Bcar1 floxed mice with Cre transgenic lines allowing for cell-specific knockout either in smooth muscle and early cardiac tissues (SM22-Cre), mature smooth muscle cells (smMHC-Cre), endothelial cells (Tie2-Cre), second heart field cells (Mef2c-Cre), or neural crest cells (NCC) (Pax3-Cre) and characterized these conditional knock outs using a combination of histological and molecular biology techniques. Conditional knockout of Bcar1 in SM22-expressing smooth muscle cells and cardiac tissues (Bcar1SM22KO) was embryonically lethal from E14.5-15.5 due to severe cardiovascular defects, including abnormal ventricular development and failure of outflow tract (OFT) septation leading to a single outflow vessel reminiscent of persistent truncus arteriosus. SM22-restricted loss of Bcar1 was associated with failure of OFT cushion cells to undergo differentiation to septal mesenchymal cells positive for SMC-specific α-actin, and disrupted expression of proteins and transcription factors involved in epithelial-to-mesenchymal transformation (EMT). Furthermore, knockout of Bcar1 specifically in NCC (Bcar1PAX3KO) recapitulated part of the OFT septation and aortic sac defects seen in the Bcar1SM22KO mutants, indicating a cell-specific requirement for Bcar1 in NCC essential for OFT septation. In contrast, conditional knockouts of Bcar1 in differentiated smooth muscle, endothelial cells, and second heart field cells survived to term and were phenotypically normal at birth and postnatally.ConclusionOur work reveals a cell-specific requirement for Bcar1 in NCC, early myogenic and cardiac cells, essential for OFT septation, myocardialization and EMT/cell cycle regulation and differentiation to myogenic lineages.
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