Zebrafish as a model to study cardiac development and human cardiac disease

Pentachloronitrobenzene Reduces the Proliferative Capacity of Zebrafish Embryonic Cardiomyocytes via Oxidative Stress

Pentachloronitrobenzene (PCNB) is an organochlorine protective fungicide mainly used as a soil and seed fungicide. Currently, there are few reports on the toxicity of PCNB to zebrafish embryo. Here, we evaluated the toxicity of PCNB in aquatic vertebrates using a zebrafish model. Exposure of zebrafish embryos to PCNB at concentrations of 0.25 mg/L, 0.5 mg/L, and 0.75 mg/L from 6 hpf to 72 hpf resulted in abnormal embryonic development, including cardiac malformation, pericardial edema, decreased heart rate, decreased blood flow velocity, deposition at yolk sac, shortened body length, and increased distance between venous sinus and arterial bulb (SV-BA). The expression of genes related to cardiac development was disordered. However, due to the unstable embryo status in the 0.75 mg/L exposure concentration group, the effect of PCNB on the expression levels of cardiac-related genes was not concentration-dependent. We found that PCNB increased reactive oxygen species stress levels in zebrafish, increased malondialdehyde (MDA) content and catalase (CAT) activity, and decreased superoxide dismutase (SOD) activity. The increased level of oxidative stress reduced the proliferation ability of zebrafish cardiomyocytes, and the expressions of zebrafish proliferation-related genes such as cdk-2, cdk-6, ccnd1, and ccne1 were significantly down-regulated. Astaxanthin (AST) attenuates PCNB-induced reduction in zebrafish cardiomyocyte proliferation by reducing oxidative stress levels. Our study shows that PCNB can cause severe oxidative stress in zebrafish, thereby reducing the proliferative capacity of cardiomyocytes, resulting in zebrafish cardiotoxicity.

Sbk2, a Newly Discovered Atrium-Enriched Regulator of Sarcomere Integrity

BACKGROUND

Heart development relies on tight spatiotemporal control of cardiac gene expression. Genes involved in this intricate process have been identified using animals and pluripotent stem cell-based models of cardio(myo)genesis. Recently, the repertoire of cardiomyocyte differentiation models has been expanded with iAM-1, a monoclonal line of conditionally immortalized neonatal rat atrial myocytes (NRAMs), which allows toggling between proliferative and differentiated (ie, excitable and contractile) phenotypes in a synchronized and homogenous manner.

METHODS

In this study, the unique properties of conditionally immortalized NRAMs (iAMs) were exploited to identify and characterize (lowly expressed) genes with an as-of-yet uncharacterized role in cardiomyocyte differentiation.

RESULTS

Transcriptome analysis of iAM-1 cells at different stages during one cycle of differentiation and subsequent dedifferentiation identified ≈13 000 transcripts, of which the dynamic changes in expression upon cardiomyogenic differentiation mostly opposed those during dedifferentiation. Among the genes whose expression increased during differentiation and decreased during dedifferentiation were many with known (lineage-specific) functions in cardiac muscle formation. Filtering for cardiac-enriched low-abundance transcripts, identified multiple genes with an uncharacterized role during cardio(myo)genesis including Sbk2 (SH3 domain binding kinase family member 2). Sbk2 encodes an evolutionarily conserved putative serine/threonine protein kinase, whose expression is strongly up- and downregulated during iAM-1 cell differentiation and dedifferentiation, respectively. In neonatal and adult rats, the protein is muscle-specific, highly atrium-enriched, and localized around the A-band of cardiac sarcomeres. Knockdown of Sbk2 expression caused loss of sarcomeric organization in NRAMs, iAMs and their human counterparts, consistent with a decrease in sarcomeric gene expression as evinced by transcriptome and proteome analyses. Interestingly, co-immunoprecipitation using Sbk2 as bait identified possible interaction partners with diverse cellular functions (translation, intracellular trafficking, cytoskeletal organization, chromatin modification, sarcomere formation).

CONCLUSIONS

iAM-1 cells are a relevant and suitable model to identify (lowly expressed) genes with a hitherto unidentified role in cardiomyocyte differentiation as exemplified by Sbk2: a regulator of atrial sarcomerogenesis.

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.

An EGFP Knock-in Zebrafish Experimental Model Used in Evaluation of the Amantadine Drug Safety During Early Cardiogenesis

Background

Drug exposure during gestation or in prematurely born children represents a significant risk to congenital heart disease (CHD). Amantadine is an antiviral agent also effective in the treatment of Parkinson’s disease. However, while its potential side effects associated with tetralogy of fallot (ToF) and birth defects were implicated, its underlying etiologic mechanisms of action remain unknown. Here, we report teratogenic effects of amantadine drug during early cardiogenesis through developing a novel zebrafish (Danio rerio) knock-in (KI) animal model and explore the underlying mechanisms.

Methods

Homologous recombination (HR) pathway triggered by CRISPR/Cas9 system was utilized to generate an enhanced green fluorescent protein (EGFP) KI zebrafish animal model. Dynamic fluorescence imaging coupled with a whole-mount in-situ hybridization (WISH) assay was employed to compare the spatial and temporal expression patterns of the EGFP reporter in the KI animal model with the KI-targeted endogenous gene. Heart morphology and EGFP expression dynamics in the KI animal models were monitored to assess cardiac side effects of different doses of amantadine hydrochloride. Expression of key genes required for myocardium differentiation and left–right (LR) asymmetry was analyzed using WISH and quantitative reverse transcription-PCR (RT-PCR).

Results

A novel EGFP KI line targeted at the ventricular myosin heavy chain (vmhc) gene locus was successfully generated, in which EGFP reporter could faithfully recapitulate the endogenous expression dynamics of the ventricle chamber-specific expression of the vmhc gene. Amantadine drug treatment-induced ectopic expression of vmhc gene in the atrium and caused cardiac-looping or LR asymmetry defects to dose-dependently during early cardiogenesis, concomitant with dramatically reduced expression levels of key genes required for myocardium differentiation and LR asymmetry.

Conclusion

We generated a novel zebrafish KI animal model in which EGFP reports the ventricle chamber-specific expression of vmhc gene dynamics that is useful to effectively assess drug safety on the cardiac morphology in vivo. Specifically, this study identified teratogenic effects of amantadine drug during early cardiogenesis dose dependent, which could be likely conveyed by inhibiting expression of key genes required for cardiac myocardium differentiation and LR asymmetry.

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.

Carboxin can induce cardiotoxicity in zebrafish embryos

Carboxin is a heterocyclic systemic fungicide, mainly used to prevent and control grain smut and wheat rust. Although its mammalian toxicity has been reported, its toxicity to acute exposure to aquatic animals is unknown. In our study, we used zebrafish as aquatic organisms to study Carboxin toxicity. Carboxin can cause developmental toxicity and cardiotoxicity in zebrafish embryos. Histopathological staining of cardiac sections reveals structural changes in zebrafish hearts, and fluorescence quantitative PCR results shows the heart developmental genes mRNA expression levels were disrupted significantly. Besides, carboxin can also cause oxidative stress and reactive oxygen species (ROS) accumulation in zebrafish embryos. The accumulation of ROS causes mitochondrial damage, which is where ATP energy is produced. So ATPase activities and gene expression level were measured and significantly decreased after exposure to carboxin. From the confocal images, the number of blood cells in the heart were decreased significantly after carboxin exposure. Besides, Carboxin exposure can inhibit myocardial cell proliferation. These are all causes to the heart failure, eventually leading to embryos death.

l-selenomethionine induces zebrafish embryo cardiovascular defects via down-regulating expression of lrp2b

Selenium plays crucial roles in maintaining the growth and development of vertebrates including humans. However, excessive selenium in cells will lead to developmental defects and disease. Selenium has been reported to cause severe malformation in zebrafish embryos, but there are few studies on the mechanism of selenium excess-induced cardiovascular defects. In this study, the fertilized zebrafish embryos were treated with selenium for 96 h post fertilization (hpf). Under selenium stress, wild-type embryos showed pericardial edema, heart rate decrease, ectopic accumulation of hemoglobin; fli1-eGFP transgenic zebrafish displayed intersegmental vessel injury; and myl7-eGFP transgenic zebrafish exhibited atrial area increase. RNA-seq data and qRT-PCR results indicated that the expressions of cardiovascular development genes were up-regulated in selenium-stressed embryos. The expressions of lipid metabolism-related and selenium metabolism-related genes were evaluated in embryos. Among the tested genes, the expression of lrp2b was down-regulated in both 24 hpf and 96 hpf embryos. Furthermore, lrp2b-knockdown embryos exhibited the cardiac defects similar to selenium-stress embryos, and the over-expression of lrp2b rescued the selenium-induced defects, indicating that lrp2b might play a key role in regulating selenium cardiotoxicity. In summary, our research evaluates the cardiotoxicity of excessive selenium, and reveals the molecular mechanism of cardiovascular defects in selenium-exposed zebrafish embryos.

Effects of different pharmaceutical residues on embryos of fish species native to Central Europe

Environmental concentrations of pharmacologically active substances are increasing dramatically throughout the world, to the point where they are now considered a serious threat to the aquatic environment. This high occurrence of pharmaceutical residues in the aquatic environment is due to an increase in i) the prescription and consumption of drugs, and ii) their subsequent discharge into wastewater and its imperfect purification in wastewater treatment plants. Recent surveys have clearly shown that such substances can have serious negative effects on non-target organisms. In the present study, we tested the effects of several commonly used pharmaceuticals, such as antidepressants, analgesics and antibiotics, on the embryonic stages of different fishes. Specifically, we applied concentration ranges of tramadol, enrofloxacin and nortriptylined on a common toxicological model organism, the zebrafish (Danio rerio), and other species native to Central European freshwaters, i.e. common carp (Cyprinus carpio), catfish (Silurus glanis) and tench (Tinca tinca). Our results show that, though malformation and negative impacts on hatching and mortality were only observed at the highest test concentrations, gene expression indicated that even low environmentally relevant concentrations (0.1 μg/L) can cause significant changes in early development of embryo.

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.

Neuron navigator 3 (NAV3) is required for heart development in zebrafish

As a tightly controlled biological process, cardiogenesis requires the specification and migration of a suite of cell types to form a particular three-dimensional configuration of the heart. Many genetic factors are involved in the formation and maturation of the heart, and any genetic mutations may result in severe cardiac failures. The neuron navigator (NAV) family consists of three vertebrate homologs (NAV1, NAV2, and NAV3) of the neural guidance molecule uncoordinated-53 (UNC-53) in Caenorhabditis elegans. Although they are recognized as neural regulators, their expressions are also detected in many organs, including the heart, kidney, and liver. However, the functions of NAVs, regardless of neural guidance, remain largely unexplored. In our study, we found that nav3 gene was expressed in the cardiac region of zebrafish embryos from 24 to 48 h post-fertilization (hpf) by means of in situ hybridization (ISH) assay. A CRISPR/Cas9-based genome editing method was utilized to delete the nav3 gene in zebrafish and loss of function of Nav3 resulted in a severe deficiency in its cardiac morphology and structure. The similar phenotypic defects of the knockout mutants could recur by nav3 morpholino injection and be rescued by nav3 mRNA injection. Dual-color fluorescence imaging of ventricle and atrium markers further confirmed the disruption of the heart development in nav3-deleted mutants. Although the heart rate was not affected by the deletion of nav3, the heartbeat intensity was decreased in the mutants. All these findings indicate that Nav3 was required for cardiogenesis in developing zebrafish embryos.

Cardiotoxicity of sanguinarine via regulating apoptosis and MAPK pathways in zebrafish and HL1 cardiomyocytes

Sanguinarine, a plant phytoalexin, possesses extensive biological activities including antimicrobial, insecticidal, antitumor, anti-inflammatory and anti-angiogenesis effect. But its cardiotoxicity has rarely been studied. Here, we assess the cardiotoxicity of sanguinarine in vivo using larval zebrafish from 48 hpf to 96 hpf. The results show that sanguinarine caused severe malformation and the dysfunction of the heart including reductions of heart rate, red blood cell number, blood flow dynamics, stroke volume and increase of SV-BA distance, subintestinal venous congestion. Further studies showed that apoptosis in the zebrafish heart region was observed after sanguinarine exposure using TUNEL assay and AO staining method. In addition, the genes, such as sox9b, myl7, nkx2.5 and bmp10, which play crucial parts in the development and the function of the heart, were changed after sanguinarine treatment. caspase3, caspase9, bax and bcl2, apoptosis-related genes, were also altered by sanguinarine. Further studies were performed to study the cardiotoxicity in vitro using cardiomyocytes HL1 cell line. The results showed that remarkable increase of apoptosis and ROS level in HL1 cells were induced by sanguinarine. Moreover, the MAPK pathway (JNK and P38) were notably enhanced and involved in the cardiotoxicity induced by sanguinarine. Our findings will provide better understanding of sanguinarine in the toxic effect on heart.

Ticlopidine induces cardiotoxicity in zebrafish embryos through AHR-mediated oxidative stress signaling pathway

Ticlopidine has inhibitory effects on platelet aggregation via ADP (adenosine diphosphate), platelet release reaction and depolymerization. In clinical practice, it is commonly used to prevent heart, cerebrovascular and other thromboembolic diseases. However, ticlopidine has also been reported to have teratogenic effects on the heart, though its specific molecular mechanism remains unclear. In this study, zebrafish embryos were used as model organisms to examine the toxicity effect of ticlopidine. Zebrafish embryos exposed to 6, 7.5, and 9 mg/L ticlopidine solutions manifested several abnormalities, including body curvature, smaller eyes, slower absorption of the vitella sac, pericardial edema, slower heart rate, increased mortality, longer venous sinus - arterial ball (SV-BA) distance, and increased oxidative stress, which indicated developmental and cardiac toxicity. Abnormal expression of key genes related to heart development was observed, and the level of apoptotic gene expression was up-regulated. Further experiments revealed up-regulation of embryonic oxidative stress following ticlopidine exposure, leading to a decrease in cardiomyocyte proliferation. Conversely, the aromatic hydrocarbon receptor (AHR) inhibitor CH223191 protected embryos from the cardiotoxicity effect of ticlopidine, confirming further the role of up-regulated oxidative stress as the molecular mechanism of ticlopidine-induced cardiotoxicity in zebrafish. In conclusion, ticlopidine exposure leads to developmental and cardiotoxicity in zebrafish embryos. Therefore, further studies are warranted to ascertain such potential harms of ticlopidine in humans, which are vital in providing guidance in the safe use of drugs in clinical practice.

An integrative multiscale view of early cardiac looping

The heart is the first organ to form and function during the development of an embryo. Heart development consists of a series of events believed to be highly conserved in vertebrates. Development of heart begins with the formation of the cardiac fields followed by a linear heart tube formation. The straight heart tube then undergoes a ventral bending prior to further bending and helical torsion to form a looped heart. The looping phase is then followed by ballooning, septation, and valve formation giving rise to a four-chambered heart in avians and mammals. The looping phase plays a central role in heart development. Successful looping is essential for proper alignment of the future cardiac chambers and tracts. As aberrant looping results in various congenital heart diseases, the mechanisms of cardiac looping have been studied for several decades by various disciplines. Many groups have studied anatomy, biology, genetics, and mechanical processes during heart looping, and have proposed multiple mechanisms. Computational modeling approaches have been utilized to examine the proposed mechanisms of the looping process. Still, the exact underlying mechanism(s) controlling the looping phase remain poorly understood. Although further experimental measurements are obviously still required, the need for more integrative computational modeling approaches is also apparent in order to make sense of the vast amount of experimental data and the complexity of multiscale developmental systems. Indeed, there needs to be an iterative interaction between experimentation and modeling in order to properly find the gap in the existing data and to validate proposed hypotheses. This article is categorized under: Cardiovascular Diseases > Genetics/Genomics/Epigenetics Cardiovascular Diseases > Computational Models Cardiovascular Diseases > Molecular and Cellular Physiology.

Modeling Human Cardiac Arrhythmias: Insights from Zebrafish

Cardiac arrhythmia, or irregular heart rhythm, is associated with morbidity and mortality and is described as one of the most important future public health challenges. Therefore, developing new models of cardiac arrhythmia is critical for understanding disease mechanisms, determining genetic underpinnings, and developing new therapeutic strategies. In the last few decades, the zebrafish has emerged as an attractive model to reproduce in vivo human cardiac pathologies, including arrhythmias. Here, we highlight the contribution of zebrafish to the field and discuss the available cardiac arrhythmia models. Further, we outline techniques to assess potential heart rhythm defects in larval and adult zebrafish. As genetic tools in zebrafish continue to bloom, this model will be crucial for functional genomics studies and to develop personalized anti-arrhythmic therapies.

The antidepressant venlafaxine perturbs cardiac development and function in larval zebrafish

Venlafaxine, a selective serotonin and norepinephrine reuptake inhibitor, is a highly prescribed antidepressant and is detected at µg/L concentrations in waterways receiving municipal wastewater effluents. We previously showed that early-life venlafaxine exposure disrupted the normal development of the nervous system and reduces larval activity in zebrafish (Danio rerio). However, it is unclear whether the reduced swimming activity may be associated with impaired cardiac function. Here we tested the hypothesis that zygotic exposure to venlafaxine impacts the development and function of the larval zebrafish heart. Venlafaxine (0, 1 or 10 ng) was administered by microinjection into freshly fertilized zebrafish embryos (1-4 cell stage) to assess heart development and function during early-life stages. Venlafaxine deposition in the zygote led to precocious development of the embryo heart, including the timing of the first heartbeat, increased heart size, and a higher heart rate at 24- and 48-hours post-fertilization (hpf). Also, waterborne exposure to environmental levels of this antidepressant during early development increased the heart rate at 48 hpf of zebrafish larvae mimicking the zygotic deposition. The venlafaxine-induced higher heart rate in the embryos was abolished in the presence of NAN-190, an antagonist of the 5HT_1A receptor. Also, heart rate dropped below control levels in the 10 ng, but not 1 ng venlafaxine group at 72 and 96 hpf. An acute stressor reduced the venlafaxine-induced heart rate at 48 hpf but did not affect the already reduced heart rate at 72 and 96 hpf in the 10 ng venlafaxine group. Our results suggest that the higher heart rate in the venlafaxine group may be due to an enhanced serotonin stimulation of the 5HT_1A receptor. Taken together, early-life venlafaxine exposure disrupts cardiac development and has the potential to compromise the cardiovascular performance of larval zebrafish.

The effective use of blebbistatin to study the action potential of cardiac pacemaker cells of zebrafish (Danio rerio) during incremental warming

Blebbistatin potently inhibits actin-myosin interaction, preventing contractile activity of excitable cells including cardiac myocytes, despite electrical excitation of an action potential (AP). We collected intracellular microelectrode recordings of pacemaker cells located in the sinoatrial region (SAR) of the zebrafish heart at room temperature and during acute warming to investigate whether or not blebbistatin inhibition of contraction significantly alters pacemaker cell electrophysiology. Changes were evaluated based on 16 variables that characterized the AP waveform. None of these AP variables nor the spontaneous heart rate were significantly modified with the application of 10 μM blebbistatin when recordings were made at room temperature. Compared with the control group, the blebbistatin-treated group showed minor changes in the rate of spontaneous diastolic depolarization (P = 0.027) and the 50% and 80% repolarization (P = 0.008 and 0.010, respectively) in the 26°C–29°C temperature bin, but not at higher temperatures. These findings suggest that blebbistatin is an effective excitation-contraction uncoupler that does not appreciably affect APs generated in pacemaking cells of the SAR and can, therefore, be used in zebrafish cardiac studies.

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Blebbistatin uncouples excitation-contraction in zebrafish cardiomyocytes.

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Blebbistatin does not modify the pacemaker action potential variables.

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Temperature does not modify the effect of blebbistatin.

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First validation of the use of blebbistatin in adult fish.

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Methodology of intracellular microelectrode recording of zebrafish pacemaker cells.

Cyclosporine A Induces Cardiac Developmental Toxicity in Zebrafish by Up-Regulation of Wnt Signaling and Oxidative Stress

Due to the widely application of Cyclosporine A (CsA) as an immunosuppressant in clinic, it is necessary to study its potential toxicity. Therefore, we used zebrafish as a model animal to evaluate the toxicity of CsA on embryonic development. Exposure of zebrafish embryos to CsA at concentrations of 5 mg/L, 10 mg/L, and 15 mg/L from 12 hpf to 72 hpf resulted in abnormal embryonic development, including cardiac malformation, pericardial edema, decreased heart rate, decreased blood flow velocity, deposition at yolk sac, shortened body length, and increased distance between venous sinus and arterial bulb (SV-BA). The expression of genes related to cardiac development was disordered, and the apoptotic genes were up-regulated. Oxidative stress level was up-regulated and accumulated in pericardium in a dose-dependent manner. Astaxanthin (ATX) treatment could significantly alleviate zebrafish heart defects. CsA induced up-regulation of Wnt signaling in zebrafish, and IWR-1, an inhibitor of Wnt signaling pathway, could effectively rescue the heart defects induced by CsA. Together, our study indicated that CsA induced cardiac developmental toxicity in zebrafish larvae through up-regulating oxidative stress and Wnt signaling, contributing to a more comprehensive evaluation of the safety of the drug.

In vivo toxicity of bioreactor-grown biomass and exopolysaccharides from Malaysian tiger milk mushroom mycelium for potential future health applications

Natural mycelial biomass (MB) and exopolysaccharides (EPS) of Malaysian tiger milk mushroom Lignosus rhinocerus are considered high-end components due to their high commercial potential value in drug discovery. This study aims to evaluate the toxicity of the mushroom extracts' generated in a bioreactor using the zebrafish embryo toxicity (ZFET) model assay as a new therapy for treating asthma. Both MB and EPS extracts, at concentrations 0.16-10 mg/mL, were tested for ZFET and early development effects on Zebrafish Embryos (ZE) during 24-120 h post-fertilisation (HPF). Findings revealed that MB was deemed safe with an LC₅₀ of 0.77 mg/mL; the EPS were non-toxic (LC₅₀ of 0.41 mg/mL). Neither MB nor EPS delayed hatching nor teratogenic defects in the treated ZE at a 2.5 mg/mL dose. There were no significant changes in the ZE heart rate after treatments with MB (130 beats/min) and EPS (140 beats/min), compared to that of normal ZE (120-180 beats/min). Mixing both natural compounds MB and EPS did not affect toxicity using ZFET testing; thus, intimating their safe future use as therapeutic interventions. This represents the first study to have used the ZFET assay on MB and EPS extracts of L. rhinocerus for future health applications.

Ethoprophos induces cardiac toxicity in zebrafish embryos

Ethoprophos is an effective and widely pesticide that used in controlling nemathelminth and soil insect. However, ethoprophos has been frequently detected in environment and freshwater. The potential toxicity to aquatic organisms is still not be explored. In this study, zebrafish embryo model was used to evaluated the toxicity of ethoprophos during cardiovascular developmental process of zebrafish. Zebrafish embryos were separately exposed to 10 mg/L, 20 mg/L, 30 mg/L, 40 mg/L and 50 mg/L of ethoprophos exposure at 96 h post-fertilization (hpf), which induced cardiac defects, such as low heart rate, pericardium edema and long SV-BA distance, but had no influence to vascular development. Mechanistically, the expression of cardiac-related genes were abnormal. Moreover, ethoprophos exposure significantly increased oxidative stress in zebrafish embryos by inhibiting the production of antioxidant enzyme (SOD) and activating reactive oxygen species. Expectedly, some apoptosis genes were induced and the apoptotic cardiomyocytes were detected by acridine orange staining. In addition, ethoprophos exposure also inhibited the expression of genes in wnt signaling pathway, such as β-catenin, Axin2, GSK3β and Sox9b. BML284, an activator of wnt signaling pathway, can rescue the cardiotoxic effect of embryos. These results indicated that oxidative stress and blocking wnt signaling pathway were molecular basis of ethoprophos-induced injure in zebrafish. Generally, our study showed that ethoprophos exposure led to severe cardiotoxicity to zebrafish embryo.

Myocardial protective effect and transcriptome profiling of Naoxintong on cardiomyopathy in zebrafish

Background

Cardiomyopathy is a kind of cardiovascular diseases, which makes it more difficult for the heart to pump blood to other parts of the body, eventually leading to heart failure. Naoxintong (NXT), as a traditional Chinese Medicine (TCM) preparation, is widely used in the treatment of cardiovascular diseases, including cardiomyopathy, while its underlying mechanism has not been fully elucidated. The purpose of this study is to investigate the therapeutic effect of NXT on cardiomyopathy and its molecular mechanism in zebrafish model.

Methods

The zebrafish cardiomyopathy model was established using terfenadine (TFD) and treated with NXT. The therapeutic effect of NXT on cardiomyopathy was evaluated by measuring the heart rate, the distance between the sinus venosus and bulbus arteriosus (SV-BA), the pericardial area, and the blood flow velocity of zebrafish. Then, the zebrafish hearts were isolated and collected; transcriptome analysis of NXT on cardiomyopathy was investigated. Moreover, the heg1 mutant of zebrafish congenital cardiomyopathy model was used to further validate the therapeutic effect of NXT on cardiomyopathy. Additionally, UPLC analysis combined with the zebrafish model investigation was performed to identify the bioactive components of NXT.

Results

In the TFD-induced zebrafish cardiomyopathy model, NXT treatment could significantly restore the cardiovascular malformations caused by cardiac dysfunction. Transcriptome and bioinformatics analyses of the TFD and TFD  +  NXT treated zebrafish developing hearts revealed that the differentially expressed genes were highly enriched in biological processes such as cardiac muscle contraction and heart development. As a cardiac development protein associated with cardiomyopathy, HEG1 had been identified as one of the important targets of NXT in the treatment of cardiomyopathy. The cardiovascular abnormalities of zebrafish heg1 mutant could be recovered significantly from NXT treatment, including the expanded atrial cavity and blood stagnation. qRT-PCR analysis further showed that NXT could restore cardiomyopathy phenotype in zebrafish through HEG1-CCM signaling. Among the seven components identified in NXT, paeoniflorin (PF) and salvianolic acid B (Sal B) were considered to be the main bioactive ones with myocardial protection.

Conclusion

NXT presented myocardial protective effect and could restore myocardial injury and cardiac dysfunction in zebrafish; the action mechanism was involved in HEG1-CCM signaling.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13020-021-00532-0.

Highly Efficient Synthetic CRISPR RNA/Cas9-Based Mutagenesis for Rapid Cardiovascular Phenotypic Screening in F0 Zebrafish

The zebrafish is a valuable vertebrate model to study cardiovascular formation and function due to the facile visualization and rapid development of the circulatory system in its externally growing embryos. Despite having distinct advantages, zebrafish have paralogs of many important genes, making reverse genetics approaches inefficient since generating animals bearing multiple gene mutations requires substantial efforts. Here, we present a simple and robust synthetic CRISPR RNA/Cas9-based mutagenesis approach for generating biallelic F0 zebrafish knockouts. Using a dual-guide synthetic CRISPR RNA/Cas9 ribonucleoprotein (dgRNP) system, we compared the efficiency of biallelic gene disruptions following the injections of one, two, and three dgRNPs per gene into the cytoplasm or yolk. We show that simultaneous cytoplasmic injections of three distinct dgRNPs per gene into one-cell stage embryos resulted in the most efficient and consistent biallelic gene disruptions. Importantly, this triple dgRNP approach enables efficient inactivation of cell autonomous and cell non-autonomous gene function, likely due to the low mosaicism of biallelic disruptions. In support of this finding, we provide evidence that the F0 animals generated by this method fully phenocopied the endothelial and peri-vascular defects observed in corresponding stable mutant homozygotes. Moreover, this approach faithfully recapitulated the trunk vessel phenotypes resulting from the genetic interaction between two vegfr2 zebrafish paralogs. Mechanistically, investigation of genome editing and mRNA decay indicates that the combined mutagenic actions of three dgRNPs per gene lead to an increased probability of frameshift mutations, enabling efficient biallelic gene disruptions. Therefore, our approach offers a highly robust genetic platform to quickly assess novel and redundant gene function in F0 zebrafish.

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.

Left-handed cardiac looping by cell chirality is mediated by position-specific convergent extensions

In the embryonic heart development of mammals and birds, a straight initial heart tube undergoes left-handed helical looping, which is a remarkable and puzzling event. We are interested in the mechanism of this chiral helical looping. Recently, observations were reported that myocardial cells in the embryonic chick heart show intrinsic chirality of rotation. The chirality of myocardial cells, via anisotropic polarization of Golgi inside the cells, leads to a left-right (LR) asymmetry of cell shape. On cell boundaries of LR asymmetric cells, phosphorylated myosin and N-cadherin are enriched. Such LR asymmetric cellular circumstances lead to a large-scale three-dimensional chiral structure, the left-handed helical loop. However, the physical mechanism of this looping is unclear. Computer simulations were performed using a cell-based three-dimensional mathematical model assuming an anterior-rightward-biased contractile force of the cell boundaries on the ventral surface of the heart (orientation of a clock hand pointing to 10 to 11 o'clock). An initially straight heart tube was successfully remodeled to the left-handed helical tube via frequent convergent extension (CE) of collective cells, which corresponds to the previously reported observations of chick heart development. Although we assumed that the biased boundary contractile force was uniform all over the ventral side, orientations of the CEs became position specific on the anterior, posterior, right, and left regions on the ventral tube. Such position-specific CEs produced the left-handed helical loop. In addition, our results suggest the loop formation process consists of two distinct phases of preparation and explicit looping. Intrinsic cell properties of chirality in this investigation were discussed relating to extrinsic factors investigated by other researches. Finally, because CE is generally exerted in the axial developmental process across different animal species, we discussed the contribution of CE to the chiral heart structure across species of chick, mouse, Xenopus, and zebrafish.

PRC1 Stabilizes Cardiac Contraction by Regulating Cardiac Sarcomere Assembly and Cardiac Conduction System Construction

Cardiac development is a complex process that is strictly controlled by various factors, including PcG protein complexes. Several studies have reported the critical role of PRC2 in cardiogenesis. However, little is known about the regulation mechanism of PRC1 in embryonic heart development. To gain more insight into the mechanistic role of PRC1 in cardiogenesis, we generated a PRC1 loss-of-function zebrafish line by using the CRISPR/Cas9 system targeting rnf2, a gene encoding the core subunit shared by all PRC1 subfamilies. Our results revealed that Rnf2 is not involved in cardiomyocyte differentiation and heart tube formation, but that it is crucial to maintaining regular cardiac contraction. Further analysis suggested that Rnf2 loss-of-function disrupted cardiac sarcomere assembly through the ectopic activation of non-cardiac sarcomere genes in the developing heart. Meanwhile, Rnf2 deficiency disrupts the construction of the atrioventricular canal and the sinoatrial node by modulating the expression of bmp4 and other atrioventricular canal marker genes, leading to an impaired cardiac conduction system. The disorganized cardiac sarcomere and defective cardiac conduction system together contribute to defective cardiac contraction. Our results emphasize the critical role of PRC1 in the cardiac development.

Patterning of vertebrate cardiac progenitor fields by retinoic acid signaling

The influence of retinoic acid (RA) signaling on vertebrate development has a well-studied history. Cumulatively, we now understand that RA signaling has a conserved requirement early in development restricting cardiac progenitors within the anterior lateral plate mesoderm of vertebrate embryos. Moreover, genetic and pharmacological manipulations of RA signaling in vertebrate models have shown that proper heart development is achieved through the deployment of positive and negative feedback mechanisms, which maintain appropriate RA levels. In this brief review, we present a chronological overview of key work that has led to a current model of the critical role for early RA signaling in limiting the generation of cardiac progenitors within vertebrate embryos. Furthermore, we integrate the previous work in mice and our recent findings using zebrafish, which together show that RA signaling has remarkably conserved influences on the later-differentiating progenitor populations at the arterial and venous poles. We discuss how recognizing the significant conservation of RA signaling on the differentiation of these progenitor populations offers new perspectives and may impact future work dedicated to examining vertebrate heart development.

Melatonin mitigated circadian disruption and cardiovascular toxicity caused by 6-benzylaminopurine exposure in zebrafish

As a highly effective plant hormone, the overuse of 6-benzylaminopurine (6-BA) may pose potential threats to organisms and the environment. Melatonin is widely known for its regulation of sleep rhythm, and it also shows a beneficial effect in a variety of adverse situations. In order to investigate the harm of 6-BA to vertebrates and whether melatonin can reverse the toxicity induced by 6-BA, we analyzed the circadian rhythm and cardiovascular system of zebrafish, and further clarified the role of the thyroid endocrine system. The exposure of well-developed embryos started at 2 hpf, then 6-BA and/or melatonin were carried out. The results indicated that 6-BA disturbed the rhythmic activities of the larvae, increased wakefulness, correspondingly reduced their rest, and induced disrupted clock gene expression. Video analysis and qRT-PCR data found that zebrafish under 6-BA exposure showed obvious cardiovascular morphological abnormalities and dysfunction, and the mRNA levels of cardiovascular-related genes (nkx2.5, gata4, myl7, vegfaa and vegfab) were significantly down-regulated. In addition, altered thyroid hormone content and hypothalamus-pituitary-thyroid (HPT) axis-related gene expression were also clearly observed. 1umol/L of melatonin had little effect on zebrafish, but its addition could significantly alleviate the circadian disturbance and cardiovascular toxicity caused by 6-BA, and simultaneously played a regulatory role in thyroid system. Our research revealed the adverse effects of 6-BA on zebrafish larvae and the protective role of melatonin in circadian rhythm, cardiovascular and thyroid systems.

Evaluation of fentanyl toxicity and metabolism using a zebrafish model

The increased abuse of novel drugs has created a critical need for cheap and rapid in vivo models to understand whole organism drug-induced toxicity and metabolic impacts. One such model is zebrafish, which share many similarities to human. Assays have been developed for behavioral, toxicity, and metabolism elucidation following chemical exposure. The zebrafish model provides the advantage of assessing these parameters within a single study. Previous zebrafish studies have evaluated the behavioral effects of fentanyl, but not developmental toxicity and its relation to metabolism. In this study, we evaluate the effects of fentanyl on the development of wild-type (TL strain) zebrafish and its metabolism over 4 days. Fertilized eggs were exposed to six concentrations of fentanyl (0.01, 0.1, 1, 10, 50, and 100 μM) through embryo media incubated at 28-29°C. Observations included egg coagulation, somite formation, heartbeat, tail and yolk morphology, pericardial formation, and swim bladder inflation. The incubation media was analyzed for the presence of metabolites using a targeted metabolomics approach. Fentanyl concentration caused significant effects on survival and development, with notable defects to the tail, yolk, and pericardium at 50 and 100 μM. Despropionyl fentanyl (4-ANPP), β-hydroxy fentanyl, and norfentanyl were detected in zebrafish larvae. We present a single in vivo model to assess toxicity and metabolism of fentanyl exposure in a vertebrate model system. Our findings provide a foundation for further investigations into fentanyl's mechanism of action and translation to human drug exposure.

Integration of multiple imaging platforms to uncover cardiovascular defects in adult zebrafish

Aims

Mammalian models have been instrumental in investigating adult heart function and human disease. However, electrophysiological differences with human hearts and high costs motivate the need for non-mammalian models. The zebrafish is a well-established genetic model to study cardiovascular development and function; however, analysis of cardiovascular phenotypes in adult specimens is particularly challenging as they are opaque.

Methods and results

Here, we optimized and combined multiple imaging techniques including echocardiography, magnetic resonance imaging, and micro-computed tomography to identify and analyse cardiovascular phenotypes in adult zebrafish. Using alk5a/tgfbr1a mutants as a case study, we observed morphological and functional cardiovascular defects that were undetected with conventional approaches. Correlation analysis of multiple parameters revealed an association between haemodynamic defects and structural alterations of the heart, as observed clinically.

Conclusion

We report a new, comprehensive, and sensitive platform to identify otherwise indiscernible cardiovascular phenotypes in adult zebrafish.

Of form and function: Early cardiac morphogenesis across classical and emerging model systems

The heart is the earliest organ to develop during embryogenesis and is remarkable in its ability to function efficiently as it is being sculpted. Cardiac heart defects account for a high burden of childhood developmental disorders with many remaining poorly understood mechanistically. Decades of work across a multitude of model organisms has informed our understanding of early cardiac differentiation and morphogenesis and has simultaneously opened new and unanswered questions. Here we have synthesized current knowledge in the field and reviewed recent developments in the realm of imaging, bioengineering and genetic technology and ex vivo cardiac modeling that may be deployed to generate more holistic models of early cardiac morphogenesis, and by extension, new platforms to study congenital heart defects.

Cardiac toxicity assessment of pendimethalin in zebrafish embryos

Pendimethalin (PND) is one of the best sellers of selective herbicide in the world and has been frequently detected in the water. However, little is known about its effects on cardiac development. In this study, we used zebrafish to investigate the developmental and cardiac toxicity of PND. We exposed the zebrafish embryos with a serial of concentrations at 3, 4, and 5 mg/L at 5.5-72 h post-fertilization (hpf). We found that PND exposure can reduce the heart rate, survival rate, and body length of zebrafish embryos. Furthermore, we identified many malformations including pericardial and yolk sac edema, spinal deformity, and cardiac looping abnormality. In addition, PND increased the expression of reactive oxygen species and malondialdehyde and reduced the activity of superoxide dismutase (Antioxidant enzymes); We examined the expression of cardiac development-related genes and the apoptosis markers, and found changes of the following marker: vmhc, nppa, tbx5a, nkx2.5, gata4, tbx2b and FoxO1, bax, bcl-2, p53, casp-9, casp-3. Our data showed that activation of Wnt pathway can rescue the cardiac abnormalities caused by PND. Our results provided new evidence for the toxicity of PND and suggested that the PND residual should be treated as a hazard in the environment.

Developmental phenotypic and transcriptomic effects of exposure to nanomolar levels of metformin in zebrafish

Metformin is found in the majority of lakes and streams in the United States, leading to widespread environmental exposure. Results of the present study indicate that extended duration metformin exposure at critical developmental periods leads to decreased survival rates in zebrafish (danio rerio), an NIH approved human model. Significant abnormalities are seen with extended duration metformin exposure from 4 h post fertilization up to 5 days post fertilization, although short term metformin exposure for 24 h at 4-5 days post fertilization did not lead to any significant abnormalities. Both extended and short term duration did however have an impact on locomotor activity of zebrafish, and several genes involved in neurological and cardiovascular development were differentially expressed after exposure to metformin. The changes seen in behavior, gene expression and morphological abnormalities caused by metformin exposure should be examined further in future studies in order to assess their potential human health implications as metformin prescriptions continue to increase worldwide.

Toxic effects of broflanilide exposure on development of zebrafish (Danio rerio) embryos and its potential cardiotoxicity mechanism

Diamide insecticides are a threat to aquatic organisms but the toxicity of broflanilide remains largely undefined. In this study, to clarify the risk of broflanilide to aquatic organisms and explore its possible mechanism, lethal and sub-lethal exposure of zebrafish embryos were performed. The acute toxicity LC₅₀ (50% lethal concentration) (96 h) of broflanilide to zebrafish embryos and larvae were 3.72 mg/L and 1.28 mg/L, respectively. It also caused toxic symptoms including reduced heart rate, pericardial edema, yolk sac edema and shortened larval body length at ≥ 0.2 mg/L. Understanding the cellular and molecular changes underlying developmental toxicity in early stages of zebrafish may be very important to further improvement of this study. Here, we found cell apoptosis in embryonic heart, significant up-regulation in expression of genes associated with apoptosis and increased activity of caspase-9. In particular, we detected the levels of genes and TBX5 (T-box protein 5) related to cardiac development, which were significantly increased in this study and may be contribution to the cardiotoxicity of embryos. In general, our results identified the aquatic toxicity of broflanilide to the early stage of zebrafish and provide insights into the underlying mechanism in developmental toxicity especially cardiotoxicity of embryos.

Advances in Cardiac Development and Regeneration Using Zebrafish as a Model System for High-Throughput Research

Heart disease is the leading cause of death in the United States and worldwide. Understanding the molecular mechanisms of cardiac development and regeneration will improve diagnostic and therapeutic interventions against heart disease. In this direction, zebrafish is an excellent model because several processes of zebrafish heart development are largely conserved in humans, and zebrafish has several advantages as a model organism. Zebrafish transcriptomic profiles undergo alterations during different stages of cardiac development and regeneration which are revealed by RNA-sequencing. ChIP-sequencing has detected genome-wide occupancy of histone post-translational modifications that epigenetically regulate gene expression and identified a locus with enhancer-like characteristics. ATAC-sequencing has identified active enhancers in cardiac progenitor cells during early developmental stages which overlap with occupancy of histone modifications of active transcription as determined by ChIP-sequencing. CRISPR-mediated editing of the zebrafish genome shows how chromatin modifiers and DNA-binding proteins regulate heart development, in association with crucial signaling pathways. Hence, more studies in this direction are essential to improve human health because they answer fundamental questions on cardiac development and regeneration, their differences, and why zebrafish hearts regenerate upon injury, unlike humans. This review focuses on some of the latest studies using state-of-the-art technology enabled by the elegant yet simple zebrafish.

Nitazoxanide induced myocardial injury in zebrafish embryos by activating oxidative stress response

Nitazoxanide (NTZ) is a broad-spectrum antiparasitic and antiviral drug (thiazole). However, although NTZ has been extensively used, there are no reports concerning its toxicology in vertebrates. This study used the zebrafish as a vertebrate model to evaluate the safety of NTZ and to analyse the related molecular mechanisms. The experimental results showed that zebrafish embryos exposed to NTZ had cardiac malformation and dysfunction. NTZ also significantly inhibited proliferation and promoted apoptosis in cardiomyocytes. Transcriptomic analysis used compared gene expression levels between zebrafish embryos in the NTZ treatment and the control groups identified 200 upregulated genes and 232 downregulated genes. Analysis by Kyoto encyclopaedia of genes and genomes (KEGG) and gene ontology (GO) showed that signal pathways on cardiomyocyte development were inhibited while the oxidative stress pathways were activated. Further experiments showed that NTZ increased the content of reactive oxygen species (ROS) in the hearts of zebrafish. Antioxidant gadofullerene nanoparticles (GFNPs) significantly alleviated the developmental toxicity to the heart, indicating that NTZ activated the oxidative stress response to cause embryonic cardiomyocyte injury in zebrafish. This study provides evidence that NTZ causes developmental abnormalities in the cardiovascular system of zebrafish.

Effect of flupyradifurone on zebrafish embryonic development

Evaluation of the toxicity of pesticide residues on non-target organisms in the ecosystem is an important part of pesticide environmental risk assessment. Flupyradifurone is a new type of butenolide insecticide produced by Bayer, who claims it to be "low toxic" to non-target organisms in the environment. However, there is little evidence in the literature to show how flupyradifurone affects aquatic organism development. In the current study, zebrafish embryos were treated with 0.1, 0.15, and 0.2 mg/mL of flupyradifurone within 6.0-72 h past fertilization (hpf). We found that the half-lethal concentration (LC₅₀) of flupyradifurone for zebrafish embryos at 96 hpf was 0.21 mg/mL. Flupyradifurone decreases the heart rate, survival rate, and body length of zebrafish embryos. The flupyradifurone treatment also led to the failure of heart looping, and pericardial edema. Moreover, flupyradifurone increased the level of reactive oxygen species (ROS) and decreased the enzymatic catalysis of catalase (CAT) and superoxide dismutase (SOD). Alterations were induced in the transcription of apoptosis-related genes (bcl-2, bax, bax/bcl-2, p53 and caspase-9) and the heart development-related genes (gata4, myh6, nkx2.5, nppa, tbx2b, tbx5 and vmhc). In the current study, new evidences have been provided regarding the toxic effects of flupyradifurone and the risk of its residues in agricultural products and the environment.

Early-life exposure to tris (1,3-dichloro-2-propyl) phosphate caused multigenerational neurodevelopmental toxicity in zebrafish via altering maternal thyroid hormones transfer and epigenetic modifications

Tris (1,3-dichloro-2-propyl) phosphate (TDCIPP), an alternative to brominated flame retardants, might pose an exposure risk to humans and wild animals during fetal development. Our recent study suggested that short-term TDCIPP exposure during early development caused sex-dependent behavioral alteration in adults. In the present study, multigenerational neurodevelopmental toxicity upon early-life exposure of parental zebrafish was evaluated, and the possible underlying mechanisms were further explored. Specifically, after embryonic exposure (0-10 days post-fertilization, dpf) to TDCIPP (0, 0.01, 0.10, and 1.00 μM), zebrafish larvae were cultured in clean water until the sexually matured to produce progeny (F1). The results confirmed neurodevelopmental toxicity in F1 larvae characterized by changes of developmental endpoints, reduced thigmotaxis, as well as altered transcription of genes including myelin basic protein a (mbpa), growth associated protein (gap43) and synapsin IIa (syn2a). Sex-specific changes in thyroid hormones (THs) indicated the relationship of abnormal THs levels with previously reported neurotoxicity in adult females after early-life exposure to TDCIPP. Similar changing profiles of TH levels (increased T3 and decreased T4) in adult females and F1 eggs, but not in F1 larvae, suggested that the TH disruptions were primarily inherited from the maternal fish. Further results demonstrated hypermethylation of global DNA and key genes related to TH transport including transthyretin (ttr) and solute carrier family 16 member 2 (slc16a2), which might affect the transport of THs to target tissues, thus at least partially contributing to the neurodevelopmental toxicity in F1 larvae. Overall, our results confirmed that early-life TDCIPP exposure of parental fish could affect the early neurodevelopment of F1 offspring. The underlying mechanism could involve altered TH levels inherited from maternal zebrafish and epigenetic modifications in F1 larvae.

Characterization and preliminary safety evaluation of nano-SiO2 isolated from instant coffee

The physiological and toxicological evaluation of nano-silicon dioxide (nano-SiO2) particles in food is important for ensuring food safety. In this study, nano-SiO2 particles isolated from five brands of instant coffee, were structurally characterized using transmission electron microscopy, X-ray diffraction, Fourier-transform infrared spectroscopy, dynamic light scattering, and zeta potential analyses. Their toxicity was assessed by measuring cell viability, membrane integrity, and reactive oxygen species (ROS) levels in model gastrointestinal cells (GES-1 and Caco-2). Additionally, mortality, deformity rate, heart rate and death of whole zebra fish embryos were measured. The five types of nano-SiO2 samples comprised amorphous particles with a purity of approximately 99%, which met the food additive standard. Considering that the original particle size ranged from 10 to 50 nm, the samples were classified as nano-SiO2 food additives. Nano-SiO2 did not significantly impact the activity of GES-1 or Caco-2 cells, and no significant cell membrane damage was observed (Caco-2 cells exhibited mild micro damage); however, a slight increase in intracellular RPS levels was detected. Moreover, nano-SiO2 was found to cause head deformity, pericardial edema, yolk sac edema and tail bending. Collectively, the results show that nano-SiO2 time- and dose-dependently affects GES-1 and Caco-2 cell viability, as well as the mortality, heart rate, and abnormality rate of zebra fish embryos. Specifically, a high concentration (≥ 200 μg/mL) and long exposure time (≥ 48 h) of food additive nano-SiO2 affected GES-1, Caco-2 cells, and the gastrointestinal tract in zebra fish embryos.

ZFTool: A Software for Automatic Quantification of Cancer Cell Mass Evolution in Zebrafish

Background: Zebrafish (Danio rerio) is a model organism for the study of human cancer. Compared with the murine model, the zebrafish model has several properties ideal for personalized therapies. The transparency of the zebrafish embryos and the development of the pigment-deficient ”casper“ zebrafish line give the capacity to directly observe cancer formation and progression in the living animal. Automatic quantification of cellular proliferation in vivo is critical to the development of personalized medicine. Methods: A new methodology was defined to automatically quantify the cancer cellular evolution. ZFTool was developed to establish a base threshold that eliminates the embryo autofluorescence, automatically measures the area and intensity of GFP (green-fluorescent protein) marked cells, and defines a proliferation index. Results: The proliferation index automatically computed on different targets demonstrates the efficiency of ZFTool to provide a good automatic quantification of cancer cell evolution and dissemination. Conclusion: Our results demonstrate that ZFTool is a reliable tool for the automatic quantification of the proliferation index as a measure of cancer mass evolution in zebrafish, eliminating the influence of its autofluorescence.

Nuciferine Attenuates Doxorubicin-Induced Cardiotoxicity: An In Vitro and In Vivo Study

Chemotherapeutic drugs are a known factor that impairs the system of life due to their severe side effects. A more worrying fact is that the patients administered with doxorubicin fall under the risk of cardiotoxicity. The evolution of exploring plant-derived compounds is a possible way to combat health issues in therapeutic applications. Hence, this study focuses on the protective effect of plant-based compound nuciferine (NFN) against doxorubicin-induced cardiotoxicity in both in vitro and in vivo models. In this investigation, nuciferine significantly reduces DOX-mediated cardiotoxicity by mitigating reactive oxygen species, thereby preventing DNA fragmentation, regulating apoptosis genes and reducing the caspase 3/7 levels in vitro. Besides, nuciferine has shown significant protection against DOX-induced cardiac impairment and the upregulation of cardiogenic markers in vivo. The DOX-induced oxidative stress can be mitigated via enhancing the endogenous antioxidants, thereby controlling ROS-mediated apoptosis. In virtue of these potential features, nuciferine can be a budding candidate to address therapeutic needs.

Impaired Cx43 gap junction endocytosis causes morphological and functional defects in zebrafish

Gap junctions mediate direct cell-to-cell communication by forming channels that physically couple cells, thereby linking their cytoplasm, permitting the exchange of molecules, ions, and electrical impulses. Gap junctions are assembled from connexin (Cx) proteins, with connexin 43 (Cx43) being the most ubiquitously expressed and best studied. While the molecular events that dictate the Cx43 life cycle have largely been characterized, the unusually short half-life of connexins of only 1-5 hours, resulting in constant endocytosis and biosynthetic replacement of gap junction channels has remained puzzling. The Cx43 C-terminal (CT) domain serves as the regulatory hub of the protein affecting all aspects of gap junction function. Here, deletion within the Cx43 CT (amino acids 256-289), a region known to encode key residues regulating gap junction turnover is employed to examine the effects of dysregulated Cx43 gap junction endocytosis using cultured cells (Cx43^∆256-289) and a zebrafish model (cx43^lh10). We report that this CT deletion causes defective gap junction endocytosis as well as increased gap junction intercellular communication (GJIC). Increased Cx43 protein content in cx43^lh10 zebrafish, specifically in the cardiac tissue, larger gap junction plaques and longer Cx43 protein half-lives coincide with severely impaired development. Our findings demonstrate for the first time that Cx43 gap junction endocytosis is an essential aspect of gap junction function and when impaired, gives rise to significant physiological problems as revealed here for cardiovascular development and function. [Media: see text] [Media: see text] [Media: see text] [Media: see text] [Media: see text].

Development of Tg(UAS:SEC-Hsa.ANXA5-YFP,myl7:RFP); Casper(roy-/-,nacre-/-) Transparent Transgenic In Vivo Zebrafish Model to Study the Cardiomyocyte Function

The zebrafish provided an excellent platform to study the genetic and molecular approach of cellular phenotype-based cardiac research. We designed a novel protocol to develop the transparent transgenic zebrafish model to study annexin-5 activity in the cardiovascular function by generating homozygous transparent skin Casper(roy^−/−,nacre^−/−); myl7:RFP; annexin-5:YFP transgenic zebrafish. The skin pigmentation background of any vertebrate model organism is a major obstruction for in vivo confocal imaging to study the transgenic cellular phenotype-based study. By developing Casper(roy^−/−,nacre^−/−); myl7; annexin-5 transparent transgenic zebrafish strain, we established time-lapse in vivo confocal microscopy to study cellular phenotype/pathologies of cardiomyocytes over time to quantify changes in cardiomyocyte morphology and function over time, comparing control and cardiac injury and cardio-oncology. Casper contributes to the study by integrating a transparent characteristic in adult zebrafish that allows for simpler transparent visualization and observation. The Casper(roy^−/−,nacre^−/−) transgenic progenies developed through cross-breeding with the transgenic strain of Tg(UAS:SEC-Hsa.ANXA5-YFP,myl7:RFP). Confocal and fluorescent microscopy were being used to obtain accurate, precise imaging and to determine fluorescent protein being activated. This study protocol was conducted under two sections; 1.1: Generation of homozygous Tg(UAS:SEC-Hsa.ANXA5-YFP,myl7:RFP); Casper(roy^−/−,nacre^−/−) zebrafish (generation F01-F06) and 1.2: Screening and sorting the transparent transgenic progeny and in vivo imaging to validate cardiac morphology through in vivo confocal imaging. We coined the newly developed strain as Tg(UAS:SEC-Hsa.ANXA5-YFP,myl7:RFP); Casper(roy^−/−,nacre^−/−)^gmc1. Thus, the newly developed strain maintains transparency of the skin throughout the entire life of zebrafish and is capable of application of a non-invasive in vivo imaging process. These novel results provide an in vivo whole organism-based platform to design high-throughput screening and establish a new horizon for drug discovery in cardiac cell death and cardio-oncology therapeutics and treatment.

Pyridaben induced cardiotoxicity during the looping stages of zebrafish (Danio rerio) embryos

Pyridaben is a widely used acaricide in agriculture and reaches a high concentration (97 μg/L) in paddy water for a short time when pyridaben was applied to rice. However, its toxicity to aquatic organisms is still poorly understood. Therefore, we assessed the pyridaben cardiotoxicity to aquatic organisms using the zebrafish (Danio rerio) model. We found that pyridaben is highly toxic to aquatic organisms, and LC₅₀ of pyridaben for zebrafish at 72 hpf was 100.6 μg/L. Pyridaben caused severe cardiac malformations and functional abnormalities. Morphologic abnormity included severe pericardial edema, cardiomegaly, decreased cardiomyocytes, thinning of the myocardial layer, linear heart, and increased the distance between sinus venous and bulbus arteriosus (SV-BA). Functional failure included arrhythmia, heart failure, and reduced pumping efficiency. The genes involved in heart development, WNT signaling, BMP signaling, ATPase, and cardiac troponin C were abnormally expressed in the pyridaben treatment group. Exposure to pyridaben increased oxidative stress and induced cell apoptosis. The above causes may lead to cardiac toxicity. The results suggest that pyridaben exposure induced elevated oxidative stress through the WNT signaling pathway, which in turn led to apoptosis in the heart and cardiotoxicity. Besides, pyridaben exposure at the critical stage of cardiac looping (24-36 hpf) resulted in the greatest cardiotoxicity. The chorion reduced the entry of pyridaben and protected zebrafish embryos, resulting in cardiotoxicity second only to the stage of cardiac looping. The study should provide valuable information that pyridaben exposure causes cardiotoxicity in zebrafish embryos and have potential health risks for other aquatic organisms and humans.

The effect of absent blood flow on the zebrafish cerebral and trunk vasculature

The role of blood flow in vascular development is complex and context-dependent. In this study, we quantify the effect of the lack of blood flow on embryonic vascular development on two vascular beds, namely the cerebral and trunk vasculature in zebrafish. We perform this by analysing vascular topology, endothelial cell (EC) number, EC distribution, apoptosis, and inflammatory response in animals with normal blood flow or absent blood flow. We find that absent blood flow reduced vascular area and EC number significantly in both examined vascular beds, but the effect is more severe in the cerebral vasculature, and severity increases over time. Absent blood flow leads to an increase in non-EC-specific apoptosis without increasing tissue inflammation, as quantified by cerebral immune cell numbers and nitric oxide. Similarly, while stereotypic vascular patterning in the trunk is maintained, intra-cerebral vessels show altered patterning, which is likely to be due to vessels failing to initiate effective fusion and anastomosis rather than sprouting or path-seeking. In conclusion, blood flow is essential for cellular survival in both the trunk and cerebral vasculature, but particularly intra-cerebral vessels are affected by the lack of blood flow, suggesting that responses to blood flow differ between these two vascular beds.

Developmental toxicity caused by sanguinarine in zebrafish embryos via regulating oxidative stress, apoptosis and wnt pathways

Sanguinarine, derived from the root of Sanguinaria canadensis, have multiple biological activities, such as antimicrobial, insecticidal, antitumor, anti-inflammatory and anti-angiogenesis effect, but little is known about its toxicity on normal embryonic development. Here, we study the developmental toxicity using zebrafish model. Notably, sanguinarine caused a significant increase of the malformation rate and decrease of hatching rates and body length of zebrafish embryos. Sanguinarine also impaired the normal development of heart, liver and nerve system of zebrafish embryos. Further, the ROS level and MDA concentrations were remarkably increased, while the activity of T-SOD was decreased. In addition, obvious increase of apoptosis were observed by AO staining or TUNEL assay. Further studies showed that the oxidative stress-, apoptosis-related genes were changed, while genes of nrf2 and wnt pathways were inhibited by sangunarine. To sum up, our study will be helpful to understand the adverse effect of sanguinarine on embryonic development and the underlying molecular mechanism.

Bixafen causes cardiac toxicity in zebrafish (Danio rerio) embryos

Bixafen (BIX) is a succinate dehydrogenase inhibitor (SDHI)-class fungicide that is used to control crop diseases. However, data on the toxicity of BIX to zebrafish are limited. Here, zebrafish embryos were exposed to 0.1, 0.3, and 0.9 μM BIX. After BIX exposure, zebrafish embryos exhibited cardiac dysplasia and dysfunction, including pericardial edema, reduced heart rate, and drastically decreased erythrocytes in the cardiac area; the severity of these negative effects increased with BIX concentration and the duration of BIX exposure. In addition, the transcription levels of erythropoiesis-related genes decreased significantly in BIX-treated embryos, as compared to untreated control embryos. Similarly, compared with the control, key genes responsible for cardiac development (myh6, nkx2.5, and myh7) also exhibited dysregulated expression patterns in response to BIX treatment, suggesting that BIX might specifically affect cardiac development. Finally, cell apoptosis was induced in embryos after BIX treatment. In combination, our results suggested that exposure to BIX induced cardiac toxicity in zebrafish. These data will be valuable for future evaluations of the environmental risks of BIX.

Towards spatio-temporally resolved developmental cardiac gene regulatory networks in zebrafish

Heart formation in the zebrafish involves a rapid, complex series of morphogenetic events in three-dimensional space that spans cardiac lineage specification through to chamber formation and maturation. This process is tightly orchestrated by a cardiac gene regulatory network (GRN), which ensures the precise spatio-temporal deployment of genes critical for heart formation. Alterations of the timing or spatial localisation of gene expression can have a significant impact in cardiac ontogeny and may lead to heart malformations. Hence, a better understanding of the cellular and molecular basis of congenital heart disease relies on understanding the behaviour of cardiac GRNs with precise spatiotemporal resolution. Here, we review the recent technical advances that have expanded our capacity to interrogate the cardiac GRN in zebrafish. In particular, we focus on studies utilising high-throughput technologies to systematically dissect gene expression patterns, both temporally and spatially during heart development.

Cytochrome P450-dependent biotransformation capacities in embryonic, juvenile and adult stages of zebrafish (Danio rerio)-a state-of-the-art review

Given the strong trend to implement zebrafish (Danio rerio) embryos as translational model not only in ecotoxicological, but also toxicological testing strategies, there is an increasing need for a better understanding of their capacity for xenobiotic biotransformation. With respect to the extrapolation of toxicological data from zebrafish embryos to other life stages or even other organisms, qualitative and quantitative differences in biotransformation pathways, above all in cytochrome P450-dependent (CYP) phase I biotransformation, may lead to over- or underestimation of the hazard and risk certain xenobiotic compounds may pose to later developmental stages or other species. This review provides a comprehensive state-of-the-art overview of the scientific knowledge on the development of the CYP1-4 families and corresponding phase I biotransformation and bioactivation capacities in zebrafish. A total of 68 publications dealing with spatiotemporal CYP mRNA expression patterns, activities towards mammalian CYP-probe substrates, bioactivation and detoxification activities, as well as metabolite profiling were analyzed and included in this review. The main results allow for the following conclusions: (1) Extensive work has been done to document mRNA expression of CYP isoforms from earliest embryonic stages of zebrafish, but juvenile and adult zebrafish have been largely neglected so far. (2) There is insufficient understanding of how sex- and developmental stage-related differences in expression levels of certain CYP isoforms may impact biotransformation and bioactivation capacities in the respective sexes and in different developmental stages of zebrafish. (3) Albeit qualitatively often identical, many studies revealed quantitative differences in metabolic activities of zebrafish embryos and later developmental stages. However, the actual relevance of age-related differences on the outcome of toxicological studies still needs to be clarified. (4) With respect to current remaining gaps, there is still an urgent need for further studies systematically assessing metabolic profiles and capacities of CYP isoforms in zebrafish. Given the increasing importance of Adverse Outcome Pathway (AOP) concepts, an improved understanding of CYP capacities appears essential for the interpretation and outcome of (eco)toxicological studies.

Automatic Segmentation and Cardiac Mechanics Analysis of Evolving Zebrafish Using Deep Learning

Background: In the study of early cardiac development, it is essential to acquire accurate volume changes of the heart chambers. Although advanced imaging techniques, such as light-sheet fluorescent microscopy (LSFM), provide an accurate procedure for analyzing the heart structure, rapid, and robust segmentation is required to reduce laborious time and accurately quantify developmental cardiac mechanics. Methods: The traditional biomedical analysis involving segmentation of the intracardiac volume occurs manually, presenting bottlenecks due to enormous data volume at high axial resolution. Our advanced deep-learning techniques provide a robust method to segment the volume within a few minutes. Our U-net-based segmentation adopted manually segmented intracardiac volume changes as training data and automatically produced the other LSFM zebrafish cardiac motion images. Results: Three cardiac cycles from 2 to 5 days postfertilization (dpf) were successfully segmented by our U-net-based network providing volume changes over time. In addition to understanding each of the two chambers' cardiac function, the ventricle and atrium were separated by 3D erode morphology methods. Therefore, cardiac mechanical properties were measured rapidly and demonstrated incremental volume changes of both chambers separately. Interestingly, stroke volume (SV) remains similar in the atrium while that of the ventricle increases SV gradually. Conclusion: Our U-net-based segmentation provides a delicate method to segment the intricate inner volume of the zebrafish heart during development, thus providing an accurate, robust, and efficient algorithm to accelerate cardiac research by bypassing the labor-intensive task as well as improving the consistency in the results.

Naoxintong restores ischemia injury and inhibits thrombosis via COX2-VEGF/ NFκB signaling

ETHNOPHARMACOLOGICAL RELEVANCE

Naoxintong (NXT) is a traditional Chinese medicine preparation that is often used in combination with aspirin in the treatment of cardiovascular diseases (CVD). One of the main symptoms of CVD is hypoxic-ischemia (HI). The purpose of this study is to find out the molecular nodes targeted by NXT and its related molecular pathways in vascular repair.

MATERIALS AND METHODS

First, human vein umbilical endothelial cells (EA.hy926) were utilized to set up the Oxygen-Glucose Deprivation-Reoxygenation (OGD/R) model and treated with NXT. Cell proliferation, damage and apoptosis were detected by MTT, LDH, and flow cytometry assays. Second, transcriptional responses of OGD/R cells to NXT treatment were investigated. qRT-PCR, western blotting and inhibitor assays were performed. Third, the anti-thrombotic effect of NXT was evaluated by the zebrafish thrombosis model. Morphological observation, histological staining and qRT-PCR assays were implemented on zebrafish model to further observe in vivo the therapeutic effects of NXT on ischemia and thrombosis.

RESULTS

In OGD/R EA.hy926 cells, NXT treatment could reduce ischemic vascular injury, increase cell viability and decrease the proportion of apoptosis. Through RNA-seq analysis, 183 differentially expressed genes (DEGs) were screened with 110 up-regulated genes and 73 down-regulated genes between OGD/R and OGD/R + NXT treated EA.hy926 cells. VEGF and NFκB pathways were enriched. Among these genes, COX2 was identified as one of important targets via which NXT could restore vascular injury. COX2 inhibitor (NS-398), and aspirin, a drug that prevents the development of CVD by targeting COX2, exhibited similar effects to NXT in the treatment of OGD/R EA.hy926 cells. In zebrafish thrombosis model, NXT could attenuate tail venous thrombus and recover the quantity of heart red blood cells. Furthermore, NXT could prevent the formulation of thrombosis and eliminate inflammation in zebrafish by COX2-VEGF/NFκB signaling.

CONCLUSION

Our studies implicated that NXT could restore HI injury and inhibit thrombosis through COX2-VEGF/NFκB signaling, which is consistent with the molecular target of aspirin. This finding might explain the principle of NXT combined with aspirin in the treatment of cardiovascular diseases.

A Heterozygous Mutation in Cardiac Troponin T Promotes Ca2+ Dysregulation and Adult Cardiomyopathy in Zebrafish

Cardiomyopathies are a group of heterogeneous diseases that affect the muscles of the heart, leading to early morbidity and mortality in young and adults. Genetic forms of cardiomyopathy are caused predominantly by mutations in structural components of the cardiomyocyte sarcomeres, the contractile units of the heart, which includes cardiac Troponin T (TnT). Here, we generated mutations with CRISPR/Cas9 technology in the zebrafish tnnt2a gene, encoding cardiac TnT, at a mutational “hotspot” site to establish a zebrafish model for genetic cardiomyopathies. We found that a heterozygous tnnt2a mutation deleting Arginine at position 94 and Lysine at position 95 of TnT causes progressive cardiac structural changes resulting in heart failure. The cardiac remodeling is presented by an enlarged atrium, decreased ventricle size, increased myocardial stress as well as increased fibrosis. As early as five days post fertilization, larvae carrying the TnT RK94del mutation display diastolic dysfunction and impaired calcium dynamics related to increased Ca²⁺ sensitivity. In conclusion, adult zebrafish with a heterozygous TnT-RK94del mutation develop cardiomyopathy as seen in patients with TnT mutations and therefore represent a promising model to study disease mechanisms and to screen for putative therapeutic compounds.