Protein tyrosine phosphatase receptor zeta 1 deletion triggers defective heart morphogenesis in mice and zebrafish

Protein tyrosine phosphatase receptor zeta 1 (PTPRZ1) is a transmembrane tyrosine phosphatase receptor highly expressed in embryonic stem cells. In the present work, gene expression analyses of Ptprz1-/- and Ptprz1+/+ mice endothelial cells and hearts pointed to an unidentified role of PTPRZ1 in heart development through regulation of heart-specific transcription factor genes. Echocardiography analysis in mice identified that both systolic and diastolic functions are affected in Ptprz1-/- compared to Ptprz1+/+ hearts, based on a dilated LV cavity, decreased ejection fraction and fraction shortening, and increased angiogenesis in Ptprz1-/- hearts, with no signs of cardiac hypertrophy. A zebrafish ptprz1-/- knockout was also generated and exhibits mis-regulated expression of developmental cardiac markers, bradycardia and defective heart morphogenesis characterized by enlarged ventricles and defected contractility. A selective PTPRZ1 tyrosine phosphatase inhibitor affected zebrafish heart development and function in a way like what is observed in the ptprz1-/- zebrafish. The same inhibitor had no effect in the function of the adult zebrafish heart, suggesting that PTPRZ1 is not important for the adult heart function, in line with data from the human cell atlas showing very low to negligible PTPRZ1 expression in the adult human heart. However, in line with the animal models, Ptprz1 was expressed in many different cell types in the human fetal heart, such as valvar, fibroblast-like, cardiomyocytes and endothelial cells. Collectively, these data suggest that PTPRZ1 regulates cardiac morphogenesis in a way that subsequently affects heart function and warrant further studies for the involvement of PTPRZ1 in idiopathic congenital cardiac pathologies.

Cardioprotective responses to aerobic exercise-induced physiological hypertrophy in zebrafish heart

Herein, we aimed to establish an aerobic exercise-induced physiological myocardial hypertrophy zebrafish (Danio rerio) model and to explore the underlying molecular mechanism. After 4 weeks of aerobic exercise, the AMR and Ucrit of the zebrafish increased and the hearts were enlarged, with thickened myocardium, an increased number of myofilament attachment points in the Z-line, and increased compaction of mitochondrial cristae. We also found that the mTOR signaling pathway, angiogenesis, mitochondrial fusion, and fission event, and mitochondrial autophagy were associated with the adaptive changes in the heart during training. In addition, the increased mRNA expression of genes related to fatty acid oxidation and antioxidation suggested that the switch of energy metabolism and the maintenance of mitochondrial homeostasis induced cardiac physiological changes. Therefore, the zebrafish heart physiological hypertrophy model constructed in this study can be helpful in investigating the cardioprotective mechanisms in response to aerobic exercise.

The people behind the papers – Dennis de Bakker, Mara Bouwman and Jeroen Bakkers

ABSTRACT Unlike mammals, adult zebrafish are capable of regenerating their hearts without scarring after injury – a process that has great therapeutic potential. A new paper in Development investigates the role of Prxx1b, a transcription factor that is expressed in epicardial heart tissue after injury, to understand its role in the scar-free regeneration of the adult zebrafish heart. To hear more about the study, we caught up with joint first authors, Dennis De Bakker and Mara Bouwman, and the corresponding author, Jeroen Bakkers, the group leader at the Hubrecht Institute and professor of Molecular Cardiogenetics at the University Medical Center in Utrecht, The Netherlands.

Lamb1a regulates atrial growth by limiting second heart field addition during zebrafish heart development

During early vertebrate heart development the heart transitions from a linear tube to a complex asymmetric structure, a morphogenetic process which occurs simultaneously with growth of the heart. Cardiac growth during early heart morphogenesis is driven by deployment of cells from the Second Heart Field (SHF) into both poles of the heart. Laminin is a core component of the extracellular matrix (ECM), and although mutations in laminin subunits are linked with cardiac abnormalities, no role for laminin has been identified in early vertebrate heart morphogenesis. We identified tissue-specific expression of laminin genes in the developing zebrafish heart, supporting a role for laminins in heart morphogenesis. Analysis of heart development in lamb1a zebrafish mutant embryos reveals mild morphogenetic defects and progressive cardiomegaly, and that Lamb1a functions to limit heart size during cardiac development by restricting SHF addition. lamb1a mutants exhibit hallmarks of altered haemodynamics, and blocking cardiac contractility in lamb1a mutants rescues heart size and atrial SHF addition. Together this suggests that laminin mediates interactions between SHF deployment and cardiac biomechanics during heart development and growth in the developing embryo.

Abstract P303: Development Of Casper/myl7/annexin-5 Transparent Transgenic In-vivo Zebrafish Model To Study The Cardiomyocyte Function

The Zebrafish provided an excellent platform to study the genetic and molecular approach ofcardiac research. Zebrafish heart cells similar to human heart cells at the molecular level anddetermine gene functions that control cardiac function and dysfunction. In zebrafish heart, myl7is myosin 7 gene and identified as a regulatory gene orthologs to human MYL7. In the heart,Annexin5 activities contribute to cardiomyocyte dedifferentiation, proliferation and epicardial injuryresponses which leads to cardiac cell death by apoptosis and narcosis pathways. We aredeveloping annexin-5 activity in the cardiovascular function under normal and in metabolicaberration by generating homozygous Casper/ myl7:RFP; annexin-5:YFP transgenic zebrafish.By developing Casper/myl7/Annexin-5 transparent transgenic zebrafish model, we establish time-lapse in-vivo confocal microscopy to study of cellular phenotype/pathologies of thecardiomyocytes over time in newly developed strain to quantify changes in cardiomyocytemorphology and function overtime, comparing control and cardiac injury and cardio-oncologymodels. Transgenic zebrafish has normal type skin pigmentation background. In zebrafish,tracking of transgenic reporter activity in in-vivo is only possible in transparent stage. To maintaintransparency throughout the life, these strains crossbred with the skin transparent mutant Casper.Casper contributes to the study by integrating a transparent characteristic in adult zebrafish thatallows for simpler transparent visualization and observation. We develop casper transgenicprogenies through cross breeding with the transgenic strain of myl7:RFP;annexin-5:YFP .Confocal and fluorescent microscopy used to get accurate, precise imaging and to determinefluorescent protein being activated. 1.1: Generation of homozygous casper / myl7:RFP;annexin-5:YFP zebrafish (Generation F01-F05). 1.2: Screening and sorting the transgenic progeny andIn vivo imaging to validate cardiac morphology through in-vivo confocal imaging. Generation ofhomozygous casper / myl7:RFP;annexin-5:YFP zebrafish: Casper-Annexin5 homozygous stain:Cross breed casper and myl7/Annexin5 fish; F01: Generate the eggs from breeder and grow theembryo to attenuate larvae to screen for transgenic expression. F01 generation, larvae showtransgenic expression (47%). F02: transgenic expression larvae (39%). F02 heterozygous shownormal skin pattern; F03, larval show transgenic expression (43%). F04, transgenic larvae(90%).F04; 100% fishes are phenotypically casper; F05: heterozygous transgenic progeny togrow and continue to generate until achieve 100% homozygous casper-myl7-Annexin5 strain.These novel results provide in-vivo whole organism-based platform to design high throughputscreening and establish new horizon for drug discovery in the Cardiac Disease and Cardio-oncology.

Prrx1b restricts fibrosis and promotes Nrg1-dependent cardiomyocyte proliferation during zebrafish heart regeneration

Fibroblasts are activated to repair the heart following injury. Fibroblast activation in the mammalian heart leads to a permanent fibrotic scar that impairs cardiac function. In other organisms, like zebrafish, cardiac injury is followed by transient fibrosis and scar-free regeneration. The mechanisms that drive scarring versus scar-free regeneration are not well understood. Here we show that the homeo-box containing transcription factor Prrx1b is required for scar-free regeneration of the zebrafish heart as the loss of Prrx1b results in excessive fibrosis and impaired cardiomyocyte proliferation. Through lineage tracing and single-cell RNA-sequencing we find that Prrx1b is activated in epicardial-derived cells (EPDCs) where it restricts TGF-β ligand expression and collagen production. Furthermore, through combined in vitro experiments in human fetal EPDCs and in vivo rescue experiments in zebrafish, we conclude that Prrx1 stimulates Nrg1 expression and promotes cardiomyocyte proliferation. Collectively, these results indicate that Prrx1 is a key transcription factor that balances fibrosis and regeneration in the injured zebrafish heart.