Heart function and hemodynamic analysis for zebrafish embryos

Hemodynamic and Structural Comparison of Human Fetal Heart Development Between Normally Growing and Hypoplastic Left Heart Syndrome-Diagnosed Hearts

Congenital heart defects (CHDs) affect a wide range of societies with an incidence rate of 1.0–1.2%. These defects initiate at the early developmental stage and result in critical health disorders. Although genetic factors play a role in the formation of CHDs, the occurrence of cases in families with no history of CHDs suggests that mechanobiological forces may also play a role in the initiation and progression of CHDs. Hypoplastic left heart syndrome (HLHS) is a critical CHD, which is responsible for 25–40% of all prenatal cardiac deaths. The comparison of healthy and HLHS hearts helps in understanding the main hemodynamic differences related to HLHS. Echocardiography is the most common imaging modality utilized for fetal cardiac assessment. In this study, we utilized echocardiographic images to compare healthy and HLHS human fetal hearts for determining the differences in terms of heart chamber dimensions, valvular flow rates, and hemodynamics. The cross-sectional areas of chamber dimensions are determined from 2D b-mode ultrasound images. Valvular flow rates are measured via Doppler echocardiography, and hemodynamic quantifications are performed with the use of computational fluid dynamics (CFD) simulations. The obtained results indicate that cross-sectional areas of the left and right sides of the heart are similar for healthy fetuses during gestational development. The left side of HLHS heart is underdeveloped, and as a result, the hemodynamic parameters such as flow velocity, pressure, and wall shear stress (WSS) are significantly altered compared to those of healthy hearts.

In vivo Evaluation of Non-viral NICD Plasmid-Loaded PLGA Nanoparticles in Developing Zebrafish to Improve Cardiac Functions

In the era of the advanced nanomaterials, use of nanoparticles has been highlighted in biomedical research. However, the demonstration of DNA plasmid delivery with nanoparticles for in vivo gene delivery experiments must be carefully tested due to many possible issues, including toxicity. The purpose of the current study was to deliver a Notch Intracellular Domain (NICD)-encoded plasmid via poly(lactic-co-glycolic acid) (PLGA) nanoparticles and to investigate the toxic environmental side effects for an in vivo experiment. In addition, we demonstrated the target delivery to the endothelium, including the endocardial layer, which is challenging to manipulate gene expression for cardiac functions due to the beating heart and rapid blood pumping. For this study, we used a zebrafish animal model and exposed it to nanoparticles at varying concentrations to observe for specific malformations over time for toxic effects of PLGA nanoparticles as a delivery vehicle. Our nanoparticles caused significantly less malformations than the positive control, ZnO nanoparticles. Additionally, the NICD plasmid was successfully delivered by PLGA nanoparticles and significantly increased Notch signaling related genes. Furthermore, our image based deep-learning analysis approach evaluated that the antibody conjugated nanoparticles were successfully bound to the endocardium to overexpress Notch related genes and improve cardiac function such as ejection fraction, fractional shortening, and cardiac output. This research demonstrates that PLGA nanoparticle-mediated target delivery to upregulate Notch related genes which can be a potential therapeutic approach with minimum toxic effects.

Wt1 transcription factor impairs cardiomyocyte specification and drives a phenotypic switch from myocardium to epicardium

During development, the heart grows by addition of progenitor cells to the poles of the primordial heart tube. In the zebrafish, Wilms tumor 1 transcription factor a (wt1a) and b (wt1b) genes are expressed in the pericardium, at the venous pole of the heart. From this pericardial layer, the proepicardium emerges. Proepicardial cells are subsequently transferred to the myocardial surface and form the epicardium, covering the myocardium. We found that while wt1a and wt1b expression is maintained in proepicardial cells, it is downregulated in pericardial cells that contribute cardiomyocytes to the developing heart. Sustained wt1b expression in cardiomyocytes reduced chromatin accessibility of specific genomic loci. Strikingly, a subset of wt1a- and wt1b-expressing cardiomyocytes changed their cell-adhesion properties, delaminated from the myocardium and upregulated epicardial gene expression. Thus, wt1a and wt1b act as a break for cardiomyocyte differentiation, and ectopic wt1a and wt1b expression in cardiomyocytes can lead to their transdifferentiation into epicardial-like cells.

Zebrafish as a Model to Study Vascular Elastic Fibers and Associated Pathologies

Many extensible tissues such as skin, lungs, and blood vessels require elasticity to function properly. The recoil of elastic energy stored during a stretching phase is provided by elastic fibers, which are mostly composed of elastin and fibrillin-rich microfibrils. In arteries, the lack of elastic fibers leads to a weakening of the vessel wall with an increased risk to develop cardiovascular defects such as stenosis, aneurysms, and dissections. The development of new therapeutic molecules involves preliminary tests in animal models that recapitulate the disease and whose response to drugs should be as close as possible to that of humans. Due to its superior in vivo imaging possibilities and the broad tool kit for forward and reverse genetics, the zebrafish has become an important model organism to study human pathologies. Moreover, it is particularly adapted to large scale studies, making it an attractive model in particular for the first steps of investigations. In this review, we discuss the relevance of the zebrafish model for the study of elastic fiber-related vascular pathologies. We evidence zebrafish as a compelling alternative to conventional mouse models.

Evaluation of Metal‐Organic Framework MIL-89 nanoparticles toxicity on embryonic zebrafish development

Metal-Organic Framework MIL-89 nanoparticles garnered remarkable attention for their widespread use in technological applications. However, the impact of these nanomaterials on human and environmental health is still limited, and concerns regarding the potential risk of exposure during manipulation is constantly rising. Therefore, the extensive use of nanomaterials in the medical field necessitates a comprehensive assessment of their safety and interaction with different tissues of the body system. In this study, we evaluated the systemic toxicity of nanoMIL-89 using Zebrafish embryos as a model system to determine the acute developmental effect. Zebrafish embryos were exposed to a range of nanoMIL-89 concentrations (1 – 300 µM) at 4 h post-fertilization (hpf) for up to 120 hpf. The viability and hatching rate were evaluated at 24–72 hpf, whereas the cardiac function was assessed at 72 and 96 hpf, and the neurodevelopment and hepatic steatosis at 120 hpf. Our study shows that nanoMIL-89 exerted no developmental toxicity on zebrafish embryos at low concentrations (1–10 µM). However, the hatching time and heart development were affected at high concentrations of nanoMIL-89 (> 30 µM). Our findings add novel information into the available data about the in vivo toxicity of nanoMIL-89 and demonstrate its innocuity and safe use in biological, environmental, and medical applications.

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NanoMIL-89 is not lethal for zebrafish embryos.

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High concentrations of nanoMIL-89 alter the heart development and delay the hatching time in zebrafish embryos.

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Low concentrations of nanoMIL-89 showed no significant organ specific toxicity effects on zebrafish embryos.

Microplastics induced developmental toxicity with microcirculation dysfunction in zebrafish embryos

Microplastics (MPs) and nanoplastics (NPs) have attracted worldwide attention as potential environmental pollutants. However, toxic effects of exposure to MPs and NPs on organisms at developmental stages have not been elucidated yet. In this study, zebrafish embryos at early stage were used to evaluate potential toxic effects of exposure to MPs with diameter of 1 μm and NPs with diameter of 0.4 μm. Solution containing NPs was optically more transparent than solution containing MPs at the same mass concentration. However, exposure to NPs induced significantly higher mortality rate of zebrafish embryos than exposure to MPs. Exposure to MPs or NPs caused pathological changes of caudal vein plexus. In addition, caudal tissues were impaired with inhibition of intact growth of zebrafish embryos. Peripheral microcirculation at caudal region was significantly deteriorated by exposure to MPs or NPs. However, systematic perfusion was still maintained with preservation of RBC velocity profiles regardless of exposure to MPs or NPs. This study provides a new insight to the use of plastics, demonstrating that exposure to MPs or NPs can lead to developmental disorder with significant impairment of growth and peripheral microcirculation dysfunction.

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

Protein tyrosine phosphatase receptor-ζ1 (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 the regulation of heart-specific transcription factor genes. Echocardiography analysis in mice identified that both systolic and diastolic functions are affected in Ptprz1^−/− compared with Ptprz1^+/+ hearts, based on a dilated left ventricular (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 exhibited misregulated 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.

NEW & NOTEWORTHY Protein tyrosine phosphatase receptor ζ1 (PTPRZ1) is expressed in fetal but not adult heart and seems to affect heart development. In both mouse and zebrafish animal models, loss of PTPRZ1 results in dilated left ventricle cavity, decreased ejection fraction, and fraction shortening, with no signs of cardiac hypertrophy. PTPRZ1 also seems to be involved in atrioventricular canal specification, outflow tract morphogenesis, and heart angiogenesis. These results suggest that PTPRZ1 plays a role in heart development and support the hypothesis that it may be involved in 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.

Effect of Water-Pipe Smoking on the Normal Development of Zebrafish

Background: Among all types of tobacco consumption, Water-Pipe Smoking (WPS) is the most widely used in the Middle East and second-most in several other countries. The effect of WPS on normal development is not yet fully understood, thus the aim of this study is to explore the acute toxicity effects of WPS extract on zebrafish larvae. Methods: In this study, we compared the effects of WPS smoke condensates at concentrations varying from 50 to 200 µg/mL on developmental, cardiac, and behavioural (neurotoxicity) functions. Gene expression patterns of cardiac biomarkers were also evaluated by RT-qPCR. Results: Exposing zebrafish embryos to 50, 100, 150 and 200 µg/mL WPS for three days did not affect the normal morphology of Zebrafish embryos, as the tail flicking, behavioural and locomotion assays did not show any change. However, WPS deregulated cardiac markers including atrial natriuretic peptide (ANP/NPPA) and brain natriuretic peptide (BNP/NPPB). Furthermore, it induced apoptosis in a dose-dependent manner. Conclusion: Our data demonstrate that WPS can significantly affect specific cardiac parameters during the normal development of zebrafish. Further investigations are necessary to elucidate the pathogenic outcome of WPS on different aspects of human life, including pregnancy.

Dinitramine induces cardiotoxicity and morphological alterations on zebrafish embryo development

Dinitramine (DN), an herbicide in the dinitroaniline family, is used in agricultural areas to prevent unwanted plant growth. Dinitroaniline herbicides inhibit cell division by preventing microtubulin synthesis. They are strongly absorbed by the soil and can contaminate groundwater; however, the mode of action of these herbicides in non-target organisms remains unclear. In this study, we examined the developmental toxicity of DN in zebrafish embryos exposed to 1.6, 3.2, and 6.4 mg/L DN, compared to embryos exposed to DMSO (control) for 96 h. Visual assessments using transgenic zebrafish (fli1:eGFP) indicated abnormal cardiac development with enlarged ventricles and atria, decreased heartbeats, and impaired cardiac function. Along with cardiac development, vessel formation and angiogenesis were suppressed through activation of the inflammatory response. In addition, exposure to 6.4 mg/L DN for 96 h induced cell death, with upregulation of genes related to apoptosis. Our results showed that DN induced morphological changes and triggered an inflammatory response and apoptotic cell death that can impair embryonic growth and survival, providing an important mechanism of DN in aquatic organisms.

Discovery of Quinoline-Derived Trifluoromethyl Alcohols as Antiepileptic and Analgesic Agents That Block Sodium Channels

The discovery of novel analgesic agents with high potency, low toxicity and low addictive properties remain a priority. This study aims to identify the analgesic potential of quinoline derived α-trifluoromethylated alcohols (QTA) and their mechanism of action. We synthesized and characterized several compounds of QTAs and screened them for antiepileptic and analgesic activity using zebrafish larvae in high thorough-put behavior analyses system. Toxicity and behavioral screening of 9 compounds (C1-C9) identified four candidates (C2, C3, C7 and C9) with antiepileptic properties that induces specific and reversible reduction in photomotor activity. Importantly, compounds C2 and C3 relieved the thermal pain response in zebrafish larvae indicating analgesic property. Further, using novel in vivo CoroNa green assay, we show that compounds C2 and C3 block sodium channels and reduce inflammatory sodium signals released by peripheral nerve and tissue damage. Thus, we have identified novel QTA compounds with antiepileptic and analgesic properties which could alleviate neuropathic pain.

Developmental toxicity of procymidone to larval zebrafish based on physiological and transcriptomic analysis

As a broad-spectrum with low toxicity, procymidone (PCM), is widely used in agriculture and frequently observed in aquatic system, which may cause some impacts on aquatic organisms. Here, to determine the developmental toxicity of PCM, embryonic and larval zebrafish were exposed to PCM at 0, 1, 10, 100 μg/L in dehydrogenated natural water containing 0.01% acetone for 7 days. The results showed that high concentration of PCM could cause the pericardial edema and increase the heart rates in larval zebrafish, suggesting that PCM had developmental toxicity to zebrafish. We also observed that PCM exposure not only changed the physiological parameters including TBA, GLU and pyruvic acid, but also changed the transcriptional levels of glycolipid metabolism related genes. In addition, after transcriptomics analysis, a total of 1065 differentially expressed genes, including 456 up-regulated genes and 609 down-regulated genes, changed significantly in 100 μg/L PCM treated larval zebrafish. Interestingly, after GO (Gene Ontology) analysis, the different expression genes (DEGs) were mainly enriched to the three different biology processes including GABA-nervous, lipid Metabolism and response to drug. We also observed that the levels of GABA receptor related genes including gabrg2, gabbr1α, gabbr1 and gabra6α were inhibited by PCM exposure. Interestingly, the swimming distance of larval zebrafish had the tendency to decrease after PCM exposure, indicating that the nervous system was affected by PCM. Taken together, the results confirmed that the fungicide PCM could cause developmental toxicity by influencing the lipid metabolism and GABA mediated nervous system and behavior in larval zebrafish. We believed that the results could provide an important data for the influence of PCM on aquatic animals.

Haemodynamic dependence of mechano-genetic evolution of the cardiovascular system in Japanese medaka

The progression of cardiac gene expression-wall shear stress (WSS) interplay is critical to identifying developmental defects during cardiovascular morphogenesis. However, mechano-genetics from the embryonic to larval stages are poorly understood in vertebrates. We quantified peak WSS in the heart and tail vessels of Japanese medaka from 3 days post fertilization (dpf) to 14 dpf using in vivo micro-particle image velocimetry flow measurements, and in parallel analysed the expression of five cardiac genes (fgf8, hoxb6b, bmp4, nkx2.5, smyd1). Here, we report that WSS in the atrioventricular canal (AVC), ventricular outflow tract (OFT), and the caudal vessels in medaka peak with inflection points at 6 dpf and 10-11 dpf instead of a monotonic trend. Retrograde flows are captured at the AVC and OFT of the medaka heart for the first time. In addition, all genes were upregulated at 3 dpf and 7 dpf, indicating a possible correlation between the two, with the cardiac gene upregulation preceding WSS increase in order to facilitate cardiac wall remodelling.

Cadmium significantly changes major morphometrical points and cardiovascular functional parameters during early development of zebrafish

Living organisms are commonly exposed to cadmium and other toxic metals. A vast body of research has shown the significant effects of these toxic metals on developmental processes. In order to study the role of toxic metals on early developmental stages of eukaryotes, we explored the effect of cadmium (Cd²⁺) contaminant on zebrafish. Thus, zebrafish embryos were exposed to 3 mg/L (16.7 μM) Cd²⁺ for 96 h and imaged every 24 h from the exposure onwards. Hatching rates of the eggs were determined at 72 h, followed by analyses at 96 h for: survival rate, morphometrical factors, and functional parameters of the cardiovascular system. Interestingly enough, significant hatching delays along with smaller cephalic region and some morphological abnormalities were observed in the treatment group. Moreover, substantial changes were noticed in the length of notochord and embryo, absorption of yolk sac with shorter extension, area of swimming bladder, as well as pericardium sac after Cd²⁺ treatment. Cadmium also caused significant abnormalities in heart physiology which could be the leading cause of mentioned morphological deformities. Herein, our results shine light on systematic acute embryological effects of cadmium in the early development of zebrafish for the first time.

Numerical Investigation of the Fetal Left Heart Hemodynamics During Gestational Stages

Flow-driven hemodynamic forces on the cardiac tissues have critical importance, and have a significant role in the proper development of the heart. These mechanobiological mechanisms govern the cellular responses for the growth and remodeling of the heart, where the altered hemodynamic environment is believed to be a major factor that is leading to congenital heart defects (CHDs). In order to investigate the mechanobiological development of the normal and diseased hearts, identification of the blood flow patterns and wall shear stresses (WSS) on these tissues are required for an accurate hemodynamic assessment. In this study, we focus on the left heart hemodynamics of the human fetuses throughout the gestational stages. Computational fetal left heart models are created for the healthy fetuses using the ultrasound images at various gestational weeks. Realistic inflow boundary conditions are implemented in the models using the Doppler ultrasound measurements for resolving the specific blood flow waveforms in the mitral valve. Obtained results indicate that WSS and vorticity levels in the fetal left heart decrease with the development of the fetus. The maximum WSS around the mitral valve is determined around 36 Pa at the gestational week of 16. This maximum WSS decreases to 11 Pa at the gestational week of 27, indicating nearly three-times reduction in the peak shear stress. These findings reveal the highly dynamic nature of the left heart hemodynamics throughout the development of the human fetus and shed light into the relevance of hemodynamic environment and development of CHDs.

Generation of a Triadin KnockOut Syndrome Zebrafish Model

Different forms of sudden cardiac death have been described, including a recently identified form of genetic arrhythmogenic disorder, named “Triadin KnockOut Syndrome” (TKOS). TKOS is associated with recessive mutations in the TRDN gene, encoding for TRIADIN, but the pathogenic mechanism underlying the malignant phenotype has yet to be completely defined. Moreover, patients with TKOS are often refractory to conventional treatment, substantiating the need to identify new therapeutic strategies in order to prevent or treat cardiac events. The zebrafish (Danio rerio) heart is highly comparable to the human heart in terms of functions, signal pathways and ion channels, representing a good model to study cardiac disorders. In this work, we generated the first zebrafish model for trdn loss-of-function, by means of trdn morpholino injections, and characterized its phenotype. Although we did not observe any gross cardiac morphological defect between trdn loss-of-function embryos and controls, we found altered cardiac rhythm that was recovered by the administration of arrhythmic drugs. Our model will provide a suitable platform to study the effect of TRDN mutations and to perform drug screening to identify new pharmacological strategies for patients carrying TRDN mutations.

A hybrid of light-field and light-sheet imaging to study myocardial function and intracardiac blood flow during zebrafish development

Biomechanical forces intimately contribute to cardiac morphogenesis. However, volumetric imaging to investigate the cardiac mechanics with high temporal and spatial resolution remains an imaging challenge. We hereby integrated light-field microscopy (LFM) with light-sheet fluorescence microscopy (LSFM), coupled with a retrospective gating method, to simultaneously access myocardial contraction and intracardiac blood flow at 200 volumes per second. While LSFM allows for the reconstruction of the myocardial function, LFM enables instantaneous acquisition of the intracardiac blood cells traversing across the valves. We further adopted deformable image registration to quantify the ventricular wall displacement and particle tracking velocimetry to monitor intracardiac blood flow. The integration of LFM and LSFM enabled the time-dependent tracking of the individual blood cells and the differential rates of segmental wall displacement during a cardiac cycle. Taken together, we demonstrated a hybrid system, coupled with our image analysis pipeline, to simultaneously capture the myocardial wall motion with intracardiac blood flow during cardiac development.

During the conception of the heart, cardiac muscular contraction and blood flow generate biomechanical forces to influence the functional and structural development. To elucidate the underlying biomechanical mechanisms, we have embraced the zebrafish system for the ease of genetic and pharmacological manipulations and its rapidity for organ development. However, acquiring the dynamic processes (space + time domain) in the small beating zebrafish heart remains a challenge. In the presence of a rapid heartbeat, microscopy is confined by temporal resolution to image the cardiac contraction and blood flow. In this context, we demonstrated an integrated light-sheet and light-field imaging system to visualize cardiac contraction along with the flowing blood cells inside the cardiac chambers. Assuming the periodicity of the cardiac cycle, we synchronized the image data in post-processing for 3-D reconstruction. We further quantified the velocity of the various regions of cardiac muscular contraction, and tracked the individual blood cells during the cardiac cycles. The time-dependent velocity maps allow for uncovering differential segments of cardiac contraction and relaxation, and for revealing the patterns of blood flow. Thus, our integrated light-sheet and light-field imaging system provides an experimental basis to further investigate cardiac function and development.

Knockdown of miR-26a in zebrafish leads to impairment of the anti-inflammatory function of TnP in the control of neutrophilia

Our recent data show the valuable potential of TnP for the development of a new and safe anti-inflammatory drug due to its ability to control the traffic and activation of leukocytes in response to inflammation. Although there is considerable knowledge surrounding the cellular mechanisms of TnP, less is known about the mechanistic molecular role of TnP underlying its immunomodulatory functions. Here, we conducted investigations to identify whether miRNAs could be one of the molecular bases of the therapeutic effect of TnP. Using a zebrafish model of neutrophilic inflammation with a combination of genetic gain- and loss-of-function approaches, we showed that TnP treatment was followed by up-regulation of only four known miRNAs, and mature dre-miR-26a-1, herein referred just as miR-26a was the first most highly expressed. The knockdown of miR-26a ubiquitously resulted in a significant reduction of miR-26a in embryos, accompanied by impaired TnP immunomodulatory function observed by the loss of the control of the removal of neutrophils in response to inflammation, while the overexpression increased the inhibition of neutrophilic inflammation promoted by TnP. The striking importance of miR-26a was confirmed when rescue strategies were used (morpholino and mimic combination). Our results identified miR-26a as an essential molecular regulator of the therapeutic action of TnP, and suggest that miR-26a or its targets could be used as promising therapeutic candidates for enhancing the resolution of inflammation.

Zebrafish as a Model for Anticancer Nanomedicine Studies

Nanomedicine is a new approach to fight against cancer by the development of anticancer nanoparticles (NPs) that are of high sensitivity, specificity, and targeting ability to detect cancer cells, such as the ability of Silica NPs in targeting epithelial cancer cells. However, these anticancer NPs require preclinical testing, and zebrafish is a useful animal model for preclinical studies of anticancer NPs. This model affords a large sample size, optical imaging, and easy genetic manipulation that aid in nanomedicine studies. This review summarizes the numerous advantages of the zebrafish animal model for such investigation, various techniques for inducing cancer in zebrafish, and discusses the methods to assess cancer development in the model and to test for the toxicity of the anticancer drugs and NPs. In addition, it summarizes the recent studies that used zebrafish as a model to test the efficacy of several different anticancer NPs in treating cancer.

Deep learning-based framework for cardiac function assessment in embryonic zebrafish from heart beating videos

Zebrafish is a powerful and widely-used model system for a host of biological investigations, including cardiovascular studies and genetic screening. Zebrafish are readily assessable during developmental stages; however, the current methods for quantifying and monitoring cardiac functions mainly involve tedious manual work and inconsistent estimations. In this paper, we developed and validated a Zebrafish Automatic Cardiovascular Assessment Framework (ZACAF) based on a U-net deep learning model for automated assessment of cardiovascular indices, such as ejection fraction (EF) and fractional shortening (FS) from microscopic videos of wildtype and cardiomyopathy mutant zebrafish embryos. Our approach yielded favorable performance with accuracy above 90% compared with manual processing. We used only black and white regular microscopic recordings with frame rates of 5-20 frames per second (fps); thus, the framework could be widely applicable with any laboratory resources and infrastructure. Most importantly, the automatic feature holds promise to enable efficient, consistent, and reliable processing and analysis capacity for large amounts of videos, which can be generated by diverse collaborating teams.

Toxic effects and potential mechanisms of Fluxapyroxad to zebrafish (Danio rerio) embryos

Fluxapyroxad is a broad-spectrum and high-efficiency succinate dehydrogenase inhibitor fungicide that can control plant fungal pathogens on many crops. However, fluxapyroxad can enter the aquatic environment when applied in the field, which has an impact on the aquatic environment. The potential threat and toxicological mechanisms of fluxapyroxad in aquatic organisms remain poorly understood. In this study, zebrafish embryos were exposed to fluxapyroxad to investigate the toxic effects and potential mechanisms of fluxapyroxad. In the acute toxicity test, the lethal sensitivity rank of the zebrafish during the three stages was larvae (0.699 mg/L) > adult fish (0.913 mg/L) > embryo (1.388 mg/L). Fluxapyroxad induced abnormal spontaneous movement, malformations and decreased heartbeat, hatching percentage, and body length of the embryos. In the sublethal toxicity test, succinate dehydrogenase activity was significantly increased in all treatment groups, while the activities of the electron transport chain complex II and ATPase were markedly inhibited in 0.347 and 0.694 mg/L fluxapyroxad groups compared to that of the control group. Exposure to fluxapyroxad resulted in significant increases in MDA production, and GPx activity was significantly reduced at 0.694 mg/L. Moreover, caspase-3 activity was significantly increased in the 0.694 mg/L group, and the expression of the genes related to growth (bmp4 and lox) was inhibited after fluxapyroxad exposure. These results indicated that oxidative stress, cell apoptosis and mitochondrial damage might be the potential mechanism underlying the toxic effects of fluxapyroxad on zebrafish embryos.

Assessing Pressure-Volume Relationship in Developing Heart of Zebrafish In-Vivo

During embryogenesis, the developing heart transforms from a linear peristaltic tube into a multi-chambered pulsatile pump with blood flow-regulating valves. In this work, we report how hemodynamic parameters evolve during the heart's development, leading to its rhythmic pumping and blood flow regulation as a functioning organ. We measured the time course of intra-ventricular pressure from zebrafish embryos at 3, 4, and 5 days post fertilization (dpf) using the servo null method. We also measured the ventricular volume and monitored the opening/closing activity of the AV and VB valves using 4D selective plane illumination microscopy (SPIM). Our results revealed significant increases in peak systolic pressure, stroke volume and work, cardiac output, and power generation, and a total peripheral resistance decrease from zebrafish at 4, 5 dpf versus 3 dpf. These data illustrate that the early-stage zebrafish heart's increasing efficiency is synchronous with the expected changes in valve development, chamber morphology and increasing vascular network complexity. Such physiological measurements in tractable laboratory model organisms are critical for understanding how gene variants may affect phenotype. As the zebrafish emerges as a leading biomedical model organism, the ability to effectively measure its physiology is critical to its translational relevance.

Computational Modeling of Blood Flow Hemodynamics for Biomechanical Investigation of Cardiac Development and Disease

The heart is the first functional organ in a developing embryo. Cardiac development continues throughout developmental stages while the heart goes through a serious of drastic morphological changes. Previous animal experiments as well as clinical observations showed that disturbed hemodynamics interfere with the development of the heart and leads to the formation of a variety of defects in heart valves, heart chambers, and blood vessels, suggesting that hemodynamics is a governing factor for cardiogenesis, and disturbed hemodynamics is an important source of congenital heart defects. Therefore, there is an interest to image and quantify the flowing blood through a developing heart. Flow measurement in embryonic fetal heart can be performed using advanced techniques such as magnetic resonance imaging (MRI) or echocardiography. Computational fluid dynamics (CFD) modeling is another approach especially useful when the other imaging modalities are not available and in-depth flow assessment is needed. The approach is based on numerically solving relevant physical equations to approximate the flow hemodynamics and tissue behavior. This approach is becoming widely adapted to simulate cardiac flows during the embryonic development. While there are few studies for human fetal cardiac flows, many groups used zebrafish and chicken embryos as useful models for elucidating normal and diseased cardiogenesis. In this paper, we explain the major steps to generate CFD models for simulating cardiac hemodynamics in vivo and summarize the latest findings on chicken and zebrafish embryos as well as human fetal hearts.

Effect of left atrial ligation-driven altered inflow hemodynamics on embryonic heart development: clues for prenatal progression of hypoplastic left heart syndrome

Congenital heart defects (CHDs) are abnormalities in the heart structure present at birth. One important condition is hypoplastic left heart syndrome (HLHS) where severely underdeveloped left ventricle (LV) cannot support systemic circulation. HLHS usually initiates as localized tissue malformations with no underlying genetic cause, suggesting that disturbed hemodynamics contribute to the embryonic development of these defects. Left atrial ligation (LAL) is a surgical procedure on embryonic chick resulting in a phenotype resembling clinical HLHS. In this study, we investigated disturbed hemodynamics and deteriorated cardiac growth following LAL to investigate possible mechanobiological mechanisms for the embryonic development of HLHS. We integrated techniques such as echocardiography, micro-CT and computational fluid dynamics (CFD) for these analyses. Specifically, LAL procedure causes an immediate flow disturbance over atrioventricular (AV) cushions. At later stages after the heart septation, it causes hemodynamic disturbances in LV. As a consequence of the LAL procedure, the left-AV canal and LV volume decrease in size, and in the opposite way, the right-AV canal and right ventricle volume increase. According to our CFD analysis, LAL results in an immediate decrease in the left AV canal WSS levels for 3.5-day (HH21) pre-septated hearts. For 7-day post-septated hearts (HH30), LAL leads to further reduction in WSS levels in the left AV canal, and relatively increased WSS levels in the right AV canal. This study demonstrates the critical importance of the disturbed hemodynamics during the heart valve and ventricle development.

Contrast-enhanced ultrasound imaging for assessing organ perfusion in rainbow trout (Oncorhynchus mykiss)

Contrast-enhanced ultrasound (CEUS) imaging has great potential as a non-lethal, inexpensive monitoring tool in aquatic toxicology. It is a well-established clinical imaging approach that combines real-time, quantitative assessment of organ blood flow, with morphological data. In humans, it has been extensively used to measure changes in blood flow that can be attributed to cancer, inflammation, and other biological abnormalities. However, it has yet to be explored as a tool for fish physiology or environmental toxicology. In this study, our goal was to determine if CEUS could be used to visualize and measure blood flow in the liver of a rainbow trout. All rainbow trout received two injections of an ultrasound contrast agent, microbubbles. A subset received a third injection after administration of propranolol, a non-specific beta1 & 2-blocker, to determine if changes in blood flow could be detected. Ultrasound contrast time-intensity curves (TIC) were obtained, fit to a lognormal model, and different perfusion parameters were calculated. Contrast enhancement was observed in all rainbow trout livers, with high percentage between repeated measurements, including blood flow (80.6 ± 27.3%), area under the curve (73.2 ± 14%), blood volume (84 ± 14.2%) and peak enhancement (86.7 ± 7.5%). After administration of propranolol, we detected a non-significant (p > 0.05) increase in area under the curve (102.6 ± 44.2%), peak enhancement (77.3 ± 106.4), blood volume (48.2 ± 74.5%), and decrease in hepatic blood flow (-17.3 ± 37.1%). These data suggest that CEUS imaging is suitable to measure organ blood flow in fish, and demonstrates tremendous potential for exploring different organs, fish species, and effects of chemical contaminants in future studies.

Early preclinical screening using zebrafish (Danio rerio) reveals the safety of the candidate anti-inflammatory therapeutic agent TnP

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TnP has been indicated for chronic inflammatory diseases, multiple sclerosis.

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Zebrafish is an alternative animal model for preclinical drug development.

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Preclinical toxicology studies have shown that TnP has a wide therapeutic index range from 1 nM to 10 μM.

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TnP did not induce cardiotoxic effect or cardiac dysfunction.

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TnP crossed the blood-brain barrier without causing neurotoxicity.

The patented anti-inflammatory peptide TnP had its effectiveness recently confirmed in vivo in a murine model of multiple sclerosis and asthma. In this work, the safety of the TnP was evaluated in investigative toxicology tests using zebrafish (Danio rerio) as a model. We conducted the OECD #236 test to investigate effects of the TnP on the survival, hatching performance, and morphological formation of zebrafish embryos. After determining these endpoints, morphometric analysis termination of locomotion eartbeat rate in zebrafish larvae were evaluated to identify adverse effects such as neurotoxicity and cardiotoxicity. The results highlight a wide therapeutic index for TnP with non-lethal and safe doses rom 1 nM to 10 μM, without causing neurotoxicity or cardiotoxic effect. The low frequencyf abnormalities by TnP was associated with high safety of the molecule and the developing embryo's ability to process and eliminate it. TnP crossed the blood-brain barrier without disturbing the normal architecture of forebrain, midbrain and hindbrain. Our data reinforce the importance of zebrafish as an accurate investigative toxicology model to assess acute toxicity as well as cardiotoxicity and neurotoxicity of molecules in the preclinical phase of development.

Early-Life Stress Regulates Cardiac Development through an IL-4-Glucocorticoid Signaling Balance

Stressful experiences early in life can increase the risk of cardiovascular diseases. However, it remains largely unknown how stress influences susceptibility to the disease onset. Here, we show that exposure to brain-processed stress disrupts myocardial growth by reducing cardiomyocyte mitotic activity. Activation of the glucocorticoid receptor (GR), the primary stress response pathway, reduces cardiomyocyte numbers, disrupts trabecular formation, and leads to contractile dysfunction of the developing myocardium. However, a physiological level of GR signaling is required to prevent cardiomyocyte hyperproliferation. Mechanistically, we identify an antagonistic interaction between the GR and the cytokine interleukin-4 (IL-4) as a key player in cardiac development. IL-4 signals transcription of key regulators of cell-cycle progression in cardiomyocytes via signal transducer and activator of transcription 3 (Stat3). GR, on the contrary, inhibits this signaling system. Thus, our findings uncover an interplay between stress and immune signaling pathways critical to orchestrating physiological growth of the heart.

Blood Vessel Imaging at Pre-Larval Stages of Zebrafish Embryonic Development

The zebrafish (Danio rerio) is an increasingly popular animal model biological system. In cardiovascular research, it has been used to model specific cardiac phenomena as well as to identify novel therapies for human cardiovascular disease. While the zebrafish cardiovascular system functioning is well examined at larval stages, the mechanisms by which vessel activity is initiated remain a subject of intense investigation. In this research, we report on an in vivo stain-free blood vessel imaging technique at pre-larval stages of zebrafish embryonic development. We have developed the algorithm for the enhancement, alignment and spatiotemporal analysis of bright-field microscopy images of zebrafish embryos. It enables the detection, mapping and quantitative characterization of cardiac activity across the whole specimen. To validate the proposed approach, we have analyzed multiple data cubes, calculated vessel images and evaluated blood flow velocity and heart rate dynamics in the absence of any anesthesia. This non-invasive technique may shed light on the mechanism of vessel activity initiation and stabilization as well as the cardiovascular system’s susceptibility to environmental stressors at early developmental stages.

Cardiac Morphogenesis: Specification of the Four-Chambered Heart

Early heart morphogenesis involves a process in which embryonic precursor cells are instructed to form a cyclic contracting muscle tube connected to blood vessels, pumping fluid. Subsequently, the heart becomes structurally complex and its size increases several orders of magnitude to functionally keep up with the demands of the growing organism. Programmed transcriptional regulatory networks control the early steps of cardiac development. However, already during the early stages of its assembly, the heart tube starts to produce electrochemical potentials, contractions, and flow, which are transduced into signals that feed back into the process of morphogenesis itself. Heart morphogenesis, thus, involves the interplay between progressively changing genetic networks, function, and shape. Morphogenesis is evolutionarily conserved, but species-specific differences occur and in mouse, for instance, distinct phases of development become overlapping and compounded in an extremely fast gestation. Here, we review the early morphogenesis of the chambered heart that maintains a circulation supporting development of an organism rapidly growing in size and requirements.

Particulate matter (PM10) induces cardiovascular developmental toxicity in zebrafish embryos and larvae via the ERS, Nrf2 and Wnt pathways

Particulate matter (PM10) is one of the most important indicators of the pollution that characterizes air quality. Epidemiological studies have shown that PM10 can cause cardiovascular-related diseases in the population. And, we studied the developmental toxicity of PM10 and the underlying mechanism of its effects on the cardiovascular system of zebrafish embryo/larva. Changes in cardiac morphology, sinus venosus and bulbus arteriosus (SV-BA) distance, heart rate, vascular subintestinalis, blood flow, returned blood volume, and reactive oxygen species (ROS) level were measured, and changes in the expression levels of certain genes were assessed via RT-PCR. The results showed that PM10 caused a significant increase in pericardial sac area and SV-BA distance, a decrease in heart rate, inhibition of vascular subintestinalis growth, blood flow obstruction, reduced venous return, and other cardiovascular toxicities. PM10 induced an increase in the ROS level and significant increases in the expression levels of ERS signalling pathway factors and Nrf2 signalling pathway factors. The expression levels of the Wnt pathway-related genes also showed significant changes. Furthermore, ROS inhibitor N-Acetyl-l-cysteine (NAC) could ameliorate the cardiovascular toxicity of PM10 in zebrafish larvae. It is speculated that PM10 may result in cardiovascular toxicity by inducing higher ROS levels in the body, which could then induce ERS and lead to defects in the expression of genes related to the Wnt signalling pathway. The Nrf2 signalling pathway was activated as a stress compensatory mechanism during the early stage of PM10-induced cardiovascular injury. However, it was insufficient to counteract the PM10-induced cardiovascular toxicity.

Imaging photoplethysmography and videocapillaroscopy enable noninvasive study of zebrafish cardiovascular system functioning

We report on the noninvasive method for in vivo study of fish's cardiovascular system, that is, the heart and the structure of vessels that carry blood throughout the body. The proposed approach is based on combined photoplethysmographic and videocapillaroscopic microscopic imaging and enables noncontact two-dimensional mapping of blood volume changes. We demonstrate that the obtained data allows precise measurements of heartbeat, blood flow velocity and other important parameters (see Videos S1 and S2). To validate the developed image processing technique, we have carried out multiple experiments on zebrafish-a well-proven informative model organism widely used to understand cardiac development. The proposed approach may be effective for the study of cardiovascular system formation and functioning as well as the impact of various influencing factors on them.

Validating the Paradigm That Biomechanical Forces Regulate Embryonic Cardiovascular Morphogenesis and Are Fundamental in the Etiology of Congenital Heart Disease

The goal of this review is to provide a broad overview of the biomechanical maturation and regulation of vertebrate cardiovascular (CV) morphogenesis and the evidence for mechanistic relationships between function and form relevant to the origins of congenital heart disease (CHD). The embryonic heart has been investigated for over a century, initially focusing on the chick embryo due to the opportunity to isolate and investigate myocardial electromechanical maturation, the ability to directly instrument and measure normal cardiac function, intervene to alter ventricular loading conditions, and then investigate changes in functional and structural maturation to deduce mechanism. The paradigm of "Develop and validate quantitative techniques, describe normal, perturb the system, describe abnormal, then deduce mechanisms" was taught to many young investigators by Dr. Edward B. Clark and then validated by a rapidly expanding number of teams dedicated to investigate CV morphogenesis, structure-function relationships, and pathogenic mechanisms of CHD. Pioneering studies using the chick embryo model rapidly expanded into a broad range of model systems, particularly the mouse and zebrafish, to investigate the interdependent genetic and biomechanical regulation of CV morphogenesis. Several central morphogenic themes have emerged. First, CV morphogenesis is inherently dependent upon the biomechanical forces that influence cell and tissue growth and remodeling. Second, embryonic CV systems dynamically adapt to changes in biomechanical loading conditions similar to mature systems. Third, biomechanical loading conditions dynamically impact and are regulated by genetic morphogenic systems. Fourth, advanced imaging techniques coupled with computational modeling provide novel insights to validate regulatory mechanisms. Finally, insights regarding the genetic and biomechanical regulation of CV morphogenesis and adaptation are relevant to current regenerative strategies for patients with CHD.

Cardiac function and blood flow hemodynamics assessment of zebrafish (Danio rerio) using high-speed video microscopy

BACKGROUND

In the last few decades, zebrafish (Danio rerio) were introduced as a model organism to investigate human diseases including cardiovascular and neuronal disorders. In most zebrafish investigations, cardiac function and blood flow hemodynamics need to be assessed to study the effects of the interference on the cardiovascular system. For heart function assessment, most important parameters include heart rate, cardiac output, ejection fraction, fractional area change, and fractional shortening.

METHODS

A 10 s high-speed video of beating heart and flowing blood within major vessels of zebrafish that are less than 5 days post fertilization (dpf) were recorded via a stereo microscope equipped with a high speed camera. The videos were analyzed using MicroZebraLab and image J software for the assessment of cardiac function.

RESULTS

Using the technique described here, we were able to simply yet effectively assess cardiac function and blood flow dynamics of normal zebrafish embryos. We believe that the practical method presented here will help cardiac researchers using the zebrafish as a model to examine cardiac function by using tools that could be available in their laboratory.

Deletion of c16orf45 in zebrafish results in a low fertilization rate and increased thigmotaxis

c16orf45 is located at 16p13.11, an important locus related to neurodevelopmental diseases. Clinical studies have demonstrated that c16orf45 is associated with various neurodevelopmental diseases. To further elucidate the effect of c16orf45 on neural development, we constructed a zebrafish model with a stably inherited c16orf45 deletion via CRISPR/Cas9 technology. We found that deletion of c16orf45 significantly reduced the zebrafish fertilization rate, and both females and males showed reduced fertility. Meanwhile, the homozygous c16orf45 knockout zebrafish showed a developmental delay at 24 hr postfertilization (hpf). However, morphological changes were not apparent after 2 days postfertilization (dpf). Notably, the results of behavioral experiments revealed increased thigmotaxis in c16orf45^{- / -} zebrafish at 2 months. In conclusion, these findings demonstrate that c16orf45 plays an important role in nervous system and reproductive system.

Discovery and identification of antithrombotic chemical markers in Gardenia Fructus by herbal metabolomics and zebrafish model

ETHNOPHARMACOLOGICAL RELEVANCE

Gardenia Fructus (GF), a traditional Chinese medicine for clearing heat and purging fire, has been reported to use to treat thrombotic related diseases, but the antithrombotic components are not clear.

AIM OF THE STUDY

To develop efficient research methods for discovering some representative antithrombotic compounds of GF.

MATERIALS AND METHODS

AB line zebrafish induced by arachidonic acid (AA) was used as a fast and trace-sample-required valuation model for antithrombptic effect of GF samples. Among nine samples of GF from different production areas, two samples with the largest difference in bioactivity were selected for downstream analysis. High-performance liquid chromatography coupled with quadrupole time-of-flight mass spectrometry (HPLC-Q-TOF/MS) was applied to detect compounds in the GF samples. And herbal metabolomics and grey correlation analysis (GCA) were used to identify crucial compounds with potential antithrombotic activity. Then the bioactivity of those important compounds was verified on the zebrafish model. Network pharmacology was used to explore the protein targets and signaling pathways of these compounds.

RESULTS

Among the GF samples, S1 (Huoshan City, Anhui Province), and S6 (Jichun City, Hubei Province), significantly differed in thrombus inhibiting bioactivity. HPLC-Q-TOF/MS identified a total of 614 compounds in each GF sample. 19 compounds were selected as important potential variables from metabolomics data by orthogonal partial least squares discriminant analysis (OPLS-DA). And 10 compounds among them were further found to be positively correlated with the antithrombotic bioactivity of GF by GCA. Finally, 3 compounds in them, geniposide, citric acid, and quinic acid, were confirmed as representative antithrombotic chemical markers of GF. Using network pharmacology analysis, some key protein targets, such as proto-oncogene tyrosine-protein kinase Src (SRC) and cyclin-dependent kinase 2 (CDK2), and some signaling pathways were found to supply powerful evidence about antithrombotic mechanisms of three compounds and GF.

CONCLUSIONS

This research have succeeded to discover and identify three representative antithrombotic compounds of GF using an efficient integrated research strategy we established, an Omics Discriminant-Grey Correlation-Biological Activity strategy. The antithrombotic chemical makers we found could also contribute to provided more accurate index components for comprehensive quality control of GF.

Isoliquiritigenin triggers developmental toxicity and oxidative stress-mediated apoptosis in zebrafish embryos/larvae via Nrf2-HO1/JNK-ERK/mitochondrion pathway

Isoliquiritigenin (ISL) is an emerging natural flavonoid found in the roots of licorice, exhibits antioxidant, anti-cancer, anti-inflammatory, anti-allergic, cardioprotective, hepatoprotective and neuroprotective properties. However, the effect of ISL in embryonic development is yet to be elucidated, and the mechanisms underlying its target-organ toxicity and harmful side effects are still unclear. In the present study, we employed zebrafish embryos to study the developmental toxicity effect of ISL and its underlying mechanisms. Zebrafish embryos upon treatment with either vehicle control (0.1% DMSO) or ISL solutions for 4-96 h post fertilization (hpf) showed that ISL exposure instigated severe developmental toxicity in heart, liver, and nervous system. Mortality and morphological abnormalities were also observed. High concentrations of ISL exposure resulted in abnormal phenotypes and embryonic malformations including pericardial edema, swim bladder defects, yolk retention, curved body shape and shortening of body length. Moreover, ISL exposure led to significant loss of dopaminergic neurons accompanied by reduced locomotor behaviour. Apoptotic cells were predominantly located in the heart area of 96 hpf embryo. Additionally, ISL significantly increased the levels of reactive oxygen species, lipid peroxidation content and decreased antioxidant enzyme activities. The expressions pattern of apoptosis-related genes Bad, Cyto c, Caspase-9, Caspase-3 and Bax/Bcl-2 indicated that the oxidative stress-induced apoptosis triggered by ISL suggest involvement of Nrf2-HO1/JNK-ERK/mitochondrion pathways. In conclusion, here we provide first evidence that demonstrate ISL-induced dose-dependent developmental toxicity in zebrafish embryos. Furthermore, gene expression patterns in the embryos correlate the above and reveal potential genetic mechanisms of developmental toxicity.

Functional characterization of human myosin-binding protein C3 variants associated with hypertrophic cardiomyopathy reveals exon-specific cardiac phenotypes in zebrafish model

Myosin-binding protein C 3 (MYBPC3) variants are the most common cause of hypertrophic cardiomyopathy (HCM). HCM is a complex cardiac disorder due to its significant genetic and clinical heterogeneity. MYBPC3 variants genotype-phenotype associations remain poorly understood. We investigated the impact of two novel human MYBPC3 splice-site variants: V1: c.654+2_654+4dupTGG targeting exon 5 using morpholino MOe5i5; and V2: c.772+1G>A targeting exon 6 using MOe6i6; located within C1 domain of cMyBP-C protein, known to be critical in regulating sarcomere structure and contractility. Zebrafish MOe5i5 and MOe6i6 morphants recapitulated typical characteristics of human HCM with cardiac phenotypes of varying severity, including reduced cardiomyocyte count, thickened ventricular myocardial wall, a drastic reduction in heart rate, stroke volume, and cardiac output. Analysis of all cardiac morphological and functional parameters demonstrated that V2 cardiac phenotype was more severe than V1. Coinjection with synthetic human MYBPC3 messenger RNA (mRNA) partially rescued disparate cardiac phenotypes in each zebrafish morphant. While human MYBPC3 mRNA partially restored the decreased heart rate in V1 morphants and displayed increased percentages of ejection fraction, fractional shortening, and area change, it failed to revert the V1 ventricular myocardial thickness. These results suggest a possible V1 impact on cardiac contractility. In contrast, attempts to rescue V2 morphants only restored the ventricular myocardial wall hypertrophy phenotype but had no significant effect on impaired heart rate, suggesting a potential V2 impact on the cardiac structure. Our study provides evidence of an association between MYBPC3 exon-specific cardiac phenotypes in the zebrafish model providing important insights into how these genetic variants contribute to HCM disease.

Short-term developmental toxicity and potential mechanisms of the herbicide metamifop to zebrafish (Danio rerio) embryos

Metamifop is a novel aryloxyphenoxy propionate (AOPP) herbicide that is widely applied in paddy fields, which will inevitably enter aquatic environments and pose a risk to aquatic organisms. However, the potential threat and toxicological mechanisms of metamifop in aquatic organisms are poorly understood. In this study, zebrafish embryos were used to investigate the potential developmental toxicity and mechanisms of metamifop. The results showed that metamifop exhibited high acute toxicity to zebrafish, with 96 h-LC₅₀ values of 0.648 and 0.216 mg/L to embryos and larvae of 72 h post-hatching (hph), respectively. Decreased body lengths, heartbeat number, and hatching rates, and increased malformation rates of embryos were observed after 96 h of exposure to 0.38 mg/L or higher concentration of metamifop. Furthermore, oxidative stress was caused in embryos, with increased contents of reactive oxygen species (ROS) and malondialdehyde (MDA), and altered activities of superoxide dismutase (SOD), catalase (CAT), and glutathione peroxidase (GPx). Metamifop exposure clearly triggered cell apoptosis in embryos, result in the increase of Caspase-3 and Caspase-9 activities and up-regulation of apoptosis-related genes (bax, p53, apaf1, caspase-3, and caspase-9). Additionally, the transcriptions of innate immune-related genes (il-8, il-1b, and ifn) were increased in the groups treated with 0.25 and 0.5 mg/L of metamifop. These results indicate that metamifop induced developmental toxicity in zebrafish, and the potential toxicological mechanisms were related to oxidative stress, cell apoptosis, and the innate immune responses in embryos.

Deep learning enables automated volumetric assessments of cardiac function in zebrafish

Although the zebrafish embryo is a powerful animal model of human heart failure, the methods routinely employed to monitor cardiac function produce rough approximations that are susceptible to bias and inaccuracies. We developed and validated a deep learning-based image-analysis platform for automated extraction of volumetric parameters of cardiac function from dynamic light-sheet fluorescence microscopy (LSFM) images of embryonic zebrafish hearts. This platform, the Cardiac Functional Imaging Network (CFIN), automatically delivers rapid and accurate assessments of cardiac performance with greater sensitivity than current approaches.

This article has an associated First Person interview with the first author of the paper.

Summary: The authors present CFIN, a deep learning-based image-analysis platform to automatically analyze dynamic light-sheet fluorescence microscopy images and determine volumetric indices of cardiac function in embryonic zebrafish.

The First International Zebrafish Conference/Workshop in Qatar

A zebrafish conference/workshop was held in Qatar between April 13 and 17, 2019. The aim of the event was to promote zebrafish research in Qatar and in Middle East/Asia by bringing together local zebrafish researchers with international colleagues. Another aim was to give basic zebrafish training to interested researchers enabling them to initiate relevant zebrafish research. A total of 25 speakers and >150 attendees participated in the event from distinguished international and local institutions demonstrating the success of the event.

Adaptation of a Mice Doppler Echocardiography Platform to Measure Cardiac Flow Velocities for Embryonic Chicken and Adult Zebrafish

Ultrasonography is the most widely used imaging technique in cardiovascular medicine. In this technique, a piezoelectric crystal produces, sends, and receives high frequency ultrasound waves to the body to create an image of internal organs. It enables practical real time visualization in a non-invasive manner, making the modality especially useful to image dynamic cardiac structures. In the last few decades, echocardiography has been applied to in vivo cardiac disease models, mainly to rodents. While clinical echocardiography platforms can be used for relatively large animals such as pigs and rats, specialized systems are needed for smaller species. Theoretically, as the size of the imaged sample decreases, the frequency of the ultrasound transducer needed to image the sample increases. There are multiple modes of echocardiography imaging. In Doppler mode, erythrocytes blood flow velocities are measured from the frequency shift of the sent ultrasound waves compared to received echoes. Recorded data are then used to calculate cardiac function parameters such as cardiac output, as well as the hemodynamic shear stress levels in the heart and blood vessels. The multi-mode (i.e., b-mode, m-mode, Pulsed Doppler, Tissue Doppler, etc.) small animal ultrasound systems in the market can be used for most in vivo cardiac disease models including mice, embryonic chick and zebrafish. These systems are also associated with significant costs. Alternatively, there are more economical single-mode echocardiography platforms. However, these are originally built for mice studies and they need to be tested and evaluated for smaller experimental models. We recently adapted a mice Doppler echocardiography system to measure cardiac flow velocities for adult zebrafish and embryonic chicken. We successfully assessed cardiac function and hemodynamic shear stress for normal as well as for diseased embryonic chicken and zebrafish. In this paper, we will present our detailed protocols for Doppler flow measurements and further cardiac function analysis on these models using the setup. The protocols will involve detailed steps for animal stabilization, probe orientation for specific measurements, data acquisition, and data analysis. We believe this information will help cardiac researchers to establish similar echocardiography platforms in their labs in a practical and economical manner.

Contractile and hemodynamic forces coordinate Notch1b-mediated outflow tract valve formation

Biomechanical forces and endothelial-to-mesenchymal transition (EndoMT) are known to mediate valvulogenesis. However, the relative contributions of myocardial contractile and hemodynamic shear forces remain poorly understood. We integrated 4-D light-sheet imaging of transgenic zebrafish models with moving-domain computational fluid dynamics to determine effects of changes in contractile forces and fluid wall shear stress (WSS) on ventriculobulbar (VB) valve development. Augmentation of myocardial contractility with isoproterenol increased both WSS and Notch1b activity in the developing outflow tract (OFT) and resulted in VB valve hyperplasia. Increasing WSS in the OFT, achieved by increasing blood viscosity through EPO mRNA injection, also resulted in VB valve hyperplasia. Conversely, decreasing myocardial contractility by Tnnt2a morpholino oligonucleotide (MO) administration, 2,3-butanedione monoxime treatment, or Plcγ1 inhibition completely blocked VB valve formation, which could not be rescued by increasing WSS or activating Notch. Decreasing WSS in the OFT, achieved by slowing heart rate with metoprolol or reducing viscosity with Gata1a MO, did not affect VB valve formation. Immunofluorescent staining with the mesenchymal marker, DM-GRASP, revealed that biomechanical force-mediated Notch1b activity is implicated in EndoMT to modulate valve morphology. Altogether, increases in WSS result in Notch1b- EndoMT-mediated VB valve hyperplasia, whereas decreases in contractility result in reduced Notch1b activity, absence of EndoMT, and VB valve underdevelopment. Thus, we provide developmental mechanotransduction mechanisms underlying Notch1b-mediated EndoMT in the OFT.

Fluid forces shape the embryonic heart: Insights from zebrafish

Heart formation involves a complex series of tissue rearrangements, during which regions of the developing organ expand, bend, converge, and protrude in order to create the specific shapes of important cardiac components. Much of this morphogenesis takes place while cardiac function is underway, with blood flowing through the rapidly contracting chambers. Fluid forces are therefore likely to influence the regulation of cardiac morphogenesis, but it is not yet clear how these biomechanical cues direct specific cellular behaviors. In recent years, the optical accessibility and genetic amenability of zebrafish embryos have facilitated unique opportunities to integrate the analysis of flow parameters with the molecular and cellular dynamics underlying cardiogenesis. Consequently, we are making progress toward a comprehensive view of the biomechanical regulation of cardiac chamber emergence, atrioventricular canal differentiation, and ventricular trabeculation. In this review, we highlight a series of studies in zebrafish that have provided new insight into how cardiac function can shape cardiac morphology, with a particular focus on how hemodynamics can impact cardiac cell behavior. Over the long-term, this knowledge will undoubtedly guide our consideration of the potential causes of congenital heart disease.

Characterization of Endothelial Cilia Distribution During Cerebral-Vascular Development in Zebrafish ( Danio rerio)

Objective- Endothelial cells (ECs) sense and respond to flow-induced mechanical stress, in part, via microtubule-based projections called primary cilia. However, many critical steps during vascular morphogenesis occur independent of flow. The involvement of cilia in regulating these stages of cranial vascular morphogenesis is poorly understood because cilia have not been visualized in primary head vessels. The objective of this study was to investigate involvement of cilia in regulating the early stages of cranial vascular morphogenesis. Approach and Results- Using high-resolution imaging of the Tg(kdrl:mCherry-CAAX) y171 ;(bactin::Arl13b:GFP) zebrafish line, we showed that cilia are enriched in the earliest formed cranial vessels that assemble via vasculogenesis and in angiogenic hindbrain capillaries. Cilia were more prevalent around the boundaries of putative intravascular spaces in primary and angiogenic vessels. Loss of cardiac contractility and blood flow, because of knockdown of cardiac troponin T type 2a ( tnnt2a) expression, did not affect the distribution of cilia in primary head vasculature. In later stages of development, cilia were detected in retinal vasculature, areas of high curvature, vessel bifurcation points, and during vessel anastomosis. Loss of genes crucial for cilia biogenesis ( ift172 and ift81) induced intracerebral hemorrhages in an EC-autonomous manner. Exposure to high shear stress induced premature cilia disassembly in brain ECs and was associated with intracerebral hemorrhages. Conclusions- Our study suggests a functional role for cilia in brain ECs, which is associated with the emergence and remodeling of the primary cranial vasculature. This cilia function is flow-independent, and cilia in ECs are required for cerebral-vascular stability.

Using Zebrafish for Investigating the Molecular Mechanisms of Drug-Induced Cardiotoxicity

Over the last decade, the zebrafish (Danio rerio) has emerged as a model organism for cardiovascular research. Zebrafish have several advantages over mammalian models. For instance, the experimental cost of using zebrafish is comparatively low; the embryos are transparent, develop externally, and have high fecundity making them suitable for large-scale genetic screening. More recently, zebrafish embryos have been used for the screening of a variety of toxic agents, particularly for cardiotoxicity testing. Zebrafish has been shown to exhibit physiological responses that are similar to mammals after exposure to medicinal drugs including xenobiotics, hormones, cancer drugs, and also environmental pollutants, including pesticides and heavy metals. In this review, we provided a summary for recent studies that have used zebrafish to investigate the molecular mechanisms of drug-induced cardiotoxicity. More specifically, we focused on the techniques that were exploited by us and others for cardiovascular toxicity assessment and described several microscopic imaging and analysis protocols that are being used for the estimation of a variety of cardiac hemodynamic parameters.

Hemodynamic Studies for Analyzing the Teratogenic Effects of Drugs in the Zebrafish Embryo

Investigations of teratogenic effects of drugs generally involve testing the drug on animals and zebrafish embryo is a commonly used animal model for that purpose. In these studies, cardiovascular function of the animals needs to be evaluated to reveal the influence of exposure on the development of the cardiovascular system as well as on the growth of the whole animal. Here, relevant microscopy imaging and analysis protocols are described to calculate a variety of hemodynamic parameters for zebrafish embryos exposed to clinical drugs.

Biomechanics of the Circulating Tumor Cell Microenvironment

Circulating tumor cells (CTCs) exist in a microenvironment quite different from the solid tumor tissue microenvironment. They are detached from matrix and exposed to the immune system and hemodynamic forces leading to the conclusion that life as a CTC is "nasty, brutish, and short." While there is much evidence to support this assertion, the mechanisms underlying this are much less clear. In this chapter we will specifically focus on biomechanical influences on CTCs in the circulation and examine in detail the question of whether CTCs are mechanically fragile, a commonly held idea that is lacking in direct evidence. We will review multiple lines of evidence indicating, perhaps counterintuitively, that viable cancer cells are mechanically robust in the face of exposures to physiologic shear stresses that would be encountered by CTCs during their passage through the circulation. Finally, we present emerging evidence that malignant epithelial cells, as opposed to their benign counterparts, possess specific mechanisms that enable them to endure these mechanical stresses.