Intraperitoneal injection into adult zebrafish

Daidzein ameliorates nonmotor symptoms of manganese-induced Parkinsonism in zebrafish model: Behavioural and biochemical approach

BACKGROUND AND PURPOSE

Parkinson's disease (PD) is a prevalent neurodegenerative movement disorder characterized by motor dysfunction. Environmental factors, especially manganese (Mn), contribute significantly to PD. Existing therapies are focused on motor coordination, whereas nonmotor features such as neuropsychiatric symptoms are often neglected. Daidzein (DZ), a phytoestrogen, has piqued interest due to its antioxidant, anti-inflammatory, and anxiolytic properties. Therefore, we anticipate that DZ might be an effective drug to alleviate the nonmotor symptoms of Mn-induced Parkinsonism.

EXPERIMENTAL APPROACH

Naïve zebrafish were exposed to 2 mM of Mn for 21 days and intervened with DZ. Nonmotor symptoms such as anxiety, social behaviour, and olfactory function were assessed. Acetylcholinesterase (AChE) activity and antioxidant enzyme status were measured from brain tissue through biochemical assays. Dopamine levels and histology were performed to elucidate neuroprotective mechanism of DZ.

KEY RESULTS

DZ exhibited anxiolytic effects in a novel environment and also improved intra and inter fish social behaviour. DZ improved the olfactory function and response to amino acid stimuli in Mn-induced Parkinsonism. DZ reduced brain oxidative stress and AChE activity and prevented neuronal damage. DZ increased DA level in the brain, collectively contributing to neuroprotection.

CONCLUSION AND IMPLICATIONS

DZ demonstrated a promising effect on alleviating nonmotor symptoms such as anxiety and olfactory dysfunction, through the mitigation of cellular damage. These findings underscore the therapeutic potential of DZ in addressing nonmotor neurotoxicity induced by heavy metals, particularly in the context of Mn-induced Parkinsonism.

Section Immunostaining for Protein Expression and Cell Proliferation Studies of Regenerating Fins

Adult zebrafish fins fully regenerate after resection, providing a highly accessible and remarkable vertebrate model of organ regeneration. Fin injury triggers wound epidermis formation and the dedifferentiation of injury-adjacent mature cells to establish an organized blastema of progenitor cells. Balanced cell proliferation and redifferentiation along with cell movements then progressively reestablish patterned tissues and restore the fin to its original size and shape. A mechanistic understanding of these coordinated cell behaviors and transitions requires direct knowledge of proteins in their physiological context, including expression, subcellular localization, and activity. Antibody-based staining of sectioned fins facilitates such high-resolution analyses of specific, native proteins. Therefore, such methods are mainstays of comprehensive, hypothesis-driven fin regeneration studies. However, section immunostaining requires labor-intensive, empirical optimization. Here, we present detailed, multistep procedures for antibody staining and co-detecting proliferating cells using paraffin and frozen fin sections. We include suggestions to avoid common pitfalls and to streamline the development of optimized, validated protocols for new and challenging antibodies.

Phospholipid isotope tracing reveals β-catenin-driven suppression of phosphatidylcholine metabolism in hepatocellular carcinoma

Background and Aims

Activating mutations in the CTNNB1 gene encoding β-catenin are among the most frequently observed oncogenic alterations in hepatocellular carcinoma (HCC). HCC with CTNNB1 mutations show profound alterations in lipid metabolism including increases in fatty acid oxidation and transformation of the phospholipidome, but it is unclear how these changes arise and whether they contribute to the oncogenic program in HCC.

Methods

We employed untargeted lipidomics and targeted isotope tracing to quantify phospholipid production fluxes in an inducible human liver cell line expressing mutant β-catenin, as well as in transgenic zebrafish with activated β-catenin-driven HCC.

Results

In both models, activated β-catenin expression was associated with large changes in the lipidome including conserved increases in acylcarnitines and ceramides and decreases in triglycerides. Lipid flux analysis in human cells revealed a large reduction in phosphatidylcholine (PC) production rates as assayed by choline tracer incorporation. We developed isotope tracing lipid flux analysis for zebrafish and observed similar reductions in phosphatidylcholine synthesis flux accomplished by sex-specific mechanisms.

Conclusions

The integration of isotope tracing with lipid abundances highlights specific lipid class transformations downstream of β-catenin signaling in HCC and suggests future HCC-specific lipid metabolic targets.

Parkinson's disease model in zebrafish using intraperitoneal MPTP injection

Introduction

Parkinson's disease (PD) is the second most common neurodegenerative disease that severely affects the quality of life of patients and their family members. Exposure to 1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) has been shown to reflect behavioral, molecular, and proteomic features of PD. This study aimed to assess the protocol for inducing PD following MPTP injection in adult zebrafish.

Methods

Fish were injected with 100 μg/g of MPTP intraperitoneally once or twice and then assessed on days 1 to 30 post-injection.

Results

Between one-time and two-time injections, there was no significant difference in most locomotor parameters, expressions of tyrosine hydroxylase-2 (th2) and dopamine transporter (dat) genes, and dopaminergic neurons (tyrosine hydroxylase positive, TH+ cells) counts. However, caspase-3 levels significantly differed between one- and two-time injections on the day 1 assessment.

Discussion

Over a 30-day period, the parameters showed significant differences in swimming speed, total distance traveled, tyrosine hydroxylase-1 (th1) and dat gene expressions, caspase-3 and glutathione protein levels, and TH+ cell counts. Days 3 and 5 showed the most changes compared to the control. In conclusion, a one-time injection of MPTP with delayed assessment on days 3 to 5 is a good PD model for animal studies.

A zebrafish model of combined saposin deficiency identifies acid sphingomyelinase as a potential therapeutic target

Sphingolipidoses are a subcategory of lysosomal storage diseases (LSDs) caused by mutations in enzymes of the sphingolipid catabolic pathway. Like many LSDs, neurological involvement in sphingolipidoses leads to early mortality with limited treatment options. Given the role of myelin loss as a major contributor toward LSD-associated neurodegeneration, we investigated the pathways contributing to demyelination in a CRISPR-Cas9-generated zebrafish model of combined saposin (psap) deficiency. psap knockout (KO) zebrafish recapitulated major LSD pathologies, including reduced lifespan, reduced lipid storage, impaired locomotion and severe myelin loss; loss of myelin basic protein a (mbpa) mRNA was progressive, with no changes in additional markers of oligodendrocyte differentiation. Brain transcriptomics revealed dysregulated mTORC1 signaling and elevated neuroinflammation, where increased proinflammatory cytokine expression preceded and mTORC1 signaling changes followed mbpa loss. We examined pharmacological and genetic rescue strategies via water tank administration of the multiple sclerosis drug monomethylfumarate (MMF), and crossing the psap KO line into an acid sphingomyelinase (smpd1) deficiency model. smpd1 mutagenesis, but not MMF treatment, prolonged lifespan in psap KO zebrafish, highlighting the modulation of acid sphingomyelinase activity as a potential path toward sphingolipidosis treatment.

Novel Insight into the Mechanisms of Neurotoxicity Induced by 6:6 PFPiA through Disturbing the Gut-Brain Axis

As alternatives to traditional per- and polyfluoroalkyl substances, perfluoroalkyl phosphonic acids (PFPiAs) are frequently detected in aquatic environments, but the neurotoxic effects and underlying mechanisms remain unclear. In this study, male zebrafish were exposed to 6:6 PFPiA (1 and 10 nM) for 28 days, which exhibited anxiety-like symptoms. Gut microbiome results indicated that 6:6 PFPiA significantly increased the abundance of Gram-negative bacteria, leading to enhanced levels of lipopolysaccharide (LPS) and inflammation in the gut. The LPS was delivered to the brain through the gut-brain axis (GBA), damaged the blood-brain barrier (BBB), stimulated neuroinflammation, and caused apoptosis as well as neural injury in the brain. This mechanism was verified by the fact that antibiotics reduced the LPS levels in the gut and brain, accompanied by reduced inflammatory responses and anxiety-like behavior. The BBB damage also resulted in the enhanced accumulation of 6:6 PFPiA in the brain, where it might bind strongly with and activate aryl hydrocarbon receptor (AhR) to induce brain inflammation directly. Additionally, as the fish received treatment with an inhibitor of AhR, the inflammation response and anxiety-like behavior decreased distinctly. This study sheds light on the new mechanisms of neurotoxicity-induced 6:6 PFPiA due to the interruption on GBA.

A gelatin-based feed for precise and non-invasive drug delivery to adult zebrafish

Although the use of adult zebrafish as a model organism has increased in recent years, there is room to refine methods, such as drug delivery, to make them less invasive and more precise. Here, we describe the development of a non-invasive gelatin-based feed method that is tailored to animals based on their body mass. The feed was readily eaten by zebrafish (<1 min) with minimal leaching of compound when placed in water (<5% in 5 min). As a proof of principle, we fed fish a NMDA receptor antagonist (MK-801, 4 mg kg-1) prior to the novel tank test. We found that MK-801 caused a general decrease in predator-avoidance/anxiety-like behavior (bottom dwelling) and an increase in locomotion in male fish, but not females. Our simple, easy to prepare and individually tailored gelatin-based feed enables precisely dosed, non-invasive drug delivery to adult-stage zebrafish for the first time.

Ghrelin regulates hyperactivity-like behaviors via growth hormone signaling pathway in zebrafish (Danio rerio)

INTRODUCTION

Ghrelin is originally identified as the endogenous ligand for the growth hormone secretagogue receptor (GHSR) and partially acts by stimulating growth hormone (GH) release. Our previous studies have identified GHRELIN as a novel susceptibility gene for human attention-deficit hyperactivity disorder (ADHD), and ghrelin-depleted zebrafish (Danio rerio) display ADHD-like behaviors. However, the underlying molecular mechanism how ghrelin regulates hyperactivity-like behaviors is not yet known.

RESULTS

Here, we performed RNA-sequencing analysis using adult ghrelin ^Δ/Δ zebrafish brains to investigate the underlying molecular mechanisms. We found that gh1 mRNA and genes related to the gh signaling pathway were significantly reduced at transcriptional expression levels. Quantitative polymerase chain reaction (qPCR) was performed and confirmed the downregulation of gh signaling pathway-related genes in ghrelin ^Δ/Δ zebrafish larvae and the brain of adult ghrelin ^Δ/Δ zebrafish. In addition, ghrelin ^Δ/Δ zebrafish displayed hyperactive and hyperreactive phenotypes, such as an increase in motor activity in swimming test and a hyperreactive phenotype under light/dark cycle stimulation, mimicking human ADHD symptoms. Intraperitoneal injection of recombinant human growth hormone (rhGH) partially rescued the hyperactivity and hyperreactive-like behaviors in ghrelin mutant zebrafish.

CONCLUSION

Our results indicated that ghrelin may regulate hyperactivity-like behaviors by mediating gh signaling pathway in zebrafish. And the protective effect of rhGH on ghrelin ^Δ/Δ zebrafish hyperactivity behavior provides new therapeutic clues for ADHD patients.

Zebrafish Models for Skeletal Muscle Senescence: Lessons from Cell Cultures and Rodent Models

Human life expectancy has markedly increased over the past hundred years. Consequently, the percentage of elderly people is increasing. Aging and sarcopenic changes in skeletal muscles not only reduce locomotor activities in elderly people but also increase the chance of trauma, such as bone fractures, and the incidence of other diseases, such as metabolic syndrome, due to reduced physical activity. Exercise therapy is currently the only treatment and prevention approach for skeletal muscle aging. In this review, we aimed to summarize the strategies for modeling skeletal muscle senescence in cell cultures and rodents and provide future perspectives based on zebrafish models. In cell cultures, in addition to myoblast proliferation and myotube differentiation, senescence induction into differentiated myotubes is also promising. In rodents, several models have been reported that reflect the skeletal muscle aging phenotype or parts of it, including the accelerated aging models. Although there are fewer models of skeletal muscle aging in zebrafish than in mice, various models have been reported in recent years with the development of CRISPR/Cas9 technology, and further advancements in the field using zebrafish models are expected in the future.

A protocol to characterize zebrafish LGP2 as a dual regulator of IFN response during viral infection

Here, we present a protocol to characterize zebrafish LGP2 as a dual regulator of interferon (IFN) response. We detail in vivo assays using time-lapse comparison of IFN response between wild-type and lgp2 knockout zebrafish following spring viraemia of carp virus (SVCV) infection. We also describe in vitro assays including titration of infection duration in SVCV-infected fish cells to determine changes in IFN response. This protocol is effective to illuminate a regulatory switch of LGP2 in fish cells toward virus infection. For complete details on the use and execution of this protocol, please refer to Gong et al. (2022).¹.

Characterization of neurobehavioral pattern in a zebrafish 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-induced model: A 96-hour behavioral study

Parkinson’s disease (PD) is the most common brain motor disorder, characterized by a substantial loss of dopaminergic neurons in the substantia nigra pars compacta (SNpc). Motor impairments, such as dyskinesia, bradykinesia, and resting tremors, are the hallmarks of PD. Despite ongoing research, the exact PD pathogenesis remains elusive due to the disease intricacy and difficulty in conducting human studies. Zebrafish (Danio rerio) has emerged as an ideal model for researching PD pathophysiology. Even though 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) has been used to induce PD in zebrafish, behavioural findings are frequently limited to a single time point (24 hours post-injection). In this sense, we aim to demonstrate the effects of MPTP on zebrafish swimming behaviour at multiple time points. We administered a single dosage of MPTP (200μg/g bw) via intraperitoneal injection (i/p) and assessed the locomotor activity and swimming pattern at 0h, 24h, and 96h post-injection through an open field test. Analysis of the behaviour revealed significant reductions in swimming velocity (cm/s) and distance travelled (cm), concurrent with an increase in freezing maintenance (duration and bouts) in zebrafish injected with MPTP. In addition, the MPTP-injected zebrafish exhibited complex swimming patterns, as measured by the turn angle, meander, and angular velocity, and showed abnormal swimming phenotypes, including freezing, looping, and erratic movement. To conclude, MPTP administration into adult zebrafish induced hypolocomotion and elicited motor incoordination. Plus, the effects of MPTP were observable 24 hours after the injection and still detectable 96 hours later. These findings contribute to the understanding of MPTP effects on adult zebrafish, particularly in terms of swimming behaviours, and may pave the way for a better understanding of the establishment of PD animal models in the future.

Bioreactor-grown exo- and endo-β-glucan from Malaysian Ganoderma lucidum: An in vitro and in vivo study for potential antidiabetic treatment

This study aims to identify the roles of exo-β-glucan (EPS-BG) and endo-β-glucan (ENS-BG) extracted from Ganoderma lucidum (GL) in inhibiting the alpha-glucosidase enzyme, a target mechanism for postprandial hyperglycaemia regulation. Upscale production of GL was carried out using a 10 L bioreactor. The zebrafish embryo toxicity test (ZFET) was carried out based on OECD guidelines. The hatching rate, survival rate, heart rate, morphological malformation, and teratogenic defects were observed and determined every 24 h from 0–120 h of post-exposure (hpe). For diabetes induction, adult zebrafish (3–4 months of age) were overfed and induced with three doses of 350 mg/kg streptozotocin (STZ) by intraperitoneal injection (IP) on three different days (days 1, 3, and 5). The oral sucrose tolerance test (OSTT) and anti-diabetic activity of EPS-BG and ENS-BG were evaluated (day 7) using the developed model (n = 15). This study showed that EPS is the most potent compound with the highest inhibitory effect toward the alpha-glucosidase enzyme with an IC₅₀ value of 0.1575 mg/ml compared to ENS extracts (IC₅₀ = 0.3479 mg/ml). Both EPS-BG and ENS-BG demonstrated a strong inhibition of alpha-glucosidase activity similar to the clinically approved alpha-glucosidase inhibitor, acarbose (IC₅₀ = 0.8107 mg/ml). ENS-BG is non-toxic toward zebrafish embryos with LC₅₀ of 0.92 mg/ml and showed no significant changes in ZE hatching and normal heart rate as compared to untreated embryos (161 beats/min). Teratogenic effects of ENS-BG (<1.0 mg/ml) on zebrafish embryonic development were not observed. The DM model of zebrafish was acquired after the third dose of STZ with a fasting BGL of 8.98 ± 0.28 mmol/L compared to the normal healthy group (4.23 ± 0.62 mmol/L). The BGL of DM zebrafish after 30 min treated with EPS-BG and ENS-BG showed a significant reduction (p < 0.0001). Both EPS-BG and ENS-BG significantly reduced DM zebrafish’s peak blood glucose and the area under the curve (AUC) in OSTT. Hence, EPS-BG and ENS-BG extracted from GL showed promising inhibition of the alpha-glucosidase enzyme and are considered non-toxic in ZE. Moreover, EPS-BG and ENS-BG reduced blood glucose levels and inhibited hyperglycemia in DM zebrafish.

Screening of Mineralogenic and Osteogenic Compounds in Zebrafish—Tools to Improve Assay Throughput and Data Accuracy

Bone disorders affect millions of people worldwide and treatments currently available often produce undesirable secondary effects or have limited efficacy. It is therefore of the utmost interest for patients to develop more efficient drugs with reduced off-target activities. In the long process of drug development, screening and preclinical validation have recently gained momentum with the increased use of zebrafish as a model organism to study pathological processes related to human bone disorders, and the development of zebrafish high-throughput screening assays to identify bone anabolic compounds. In this review, we provided a comprehensive overview of the literature on zebrafish bone-related assays and evaluated their performance towards an integration into screening pipelines for the discovery of mineralogenic/osteogenic compounds. Tools available to standardize fish housing and feeding procedures, synchronize embryo production, and automatize specimen sorting and image acquisition/analysis toward faster and more accurate screening outputs were also presented.

A subset of gut leukocytes has telomerase-dependent "hyper-long" telomeres and require telomerase for function in zebrafish

BACKGROUND

Telomerase, the enzyme capable of elongating telomeres, is usually restricted in human somatic cells, which contributes to progressive telomere shortening with cell-division and ageing. T and B-cells cells are somatic cells that can break this rule and can modulate telomerase expression in a homeostatic manner. Whereas it seems intuitive that an immune cell type that depends on regular proliferation outbursts for function may have evolved to modulate telomerase expression it is less obvious why others may also do so, as has been suggested for macrophages and neutrophils in some chronic inflammation disease settings. The gut has been highlighted as a key modulator of systemic ageing and is a key tissue where inflammation must be carefully controlled to prevent dysfunction. How telomerase may play a role in innate immune subtypes in the context of natural ageing in the gut, however, remains to be determined.

RESULTS

Using the zebrafish model, we show that subsets of gut immune cells have telomerase-dependent"hyper-long" telomeres, which we identified as being predominantly macrophages and dendritics (mpeg1.1+ and cd45+mhcII+). Notably, mpeg1.1+ macrophages have much longer telomeres in the gut than in their haematopoietic tissue of origin, suggesting that there is modulation of telomerase in these cells, in the gut. Moreover, we show that a subset of gut mpeg1.1+ cells express telomerase (tert) in young WT zebrafish, but that the relative proportion of these cells decreases with ageing. Importantly, this is accompanied by telomere shortening and DNA damage responses with ageing and a telomerase-dependent decrease in expression of autophagy and immune activation markers. Finally, these telomerase-dependent molecular alterations are accompanied by impaired phagocytosis of E. coli and increased gut permeability in vivo.

CONCLUSIONS

Our data show that limiting levels of telomerase lead to alterations in gut immunity, impacting on the ability to clear pathogens in vivo. These are accompanied by increased gut permeability, which, together, are likely contributors to local and systemic tissue degeneration and increased susceptibility to infection with ageing.

Neurotoxicity of Chronic Co-Exposure of Lead and Ionic Liquid in Common Carp: Synergistic or Antagonistic?

Previous studies have indicated that the harmful heavy metal lead (Pb) contamination in aquatic systems has caused intelligence development disorders and nervous system function abnormalities in juveniles due to the increased permeability of the blood-brain barrier. Ionic liquids (ILs) are considered "green" organic solvents that can replace traditional organic solvents. Studies have found the presence of ILs in soil and water due to chemical applications or unintentional leakage. Therefore, what would happen if Pb interacted with ILs in a body of water? Could ILs enable Pb to more easily cross the blood-brain barrier? Therefore, we examined the combined exposure of Pb and ILs in common carp at low concentration (18.3 mg L^-1 of Pb(CH₃COO)₂•3 H₂O and 11 mg L^-1 of the IL 1-methyl-3-octylimidazolium chloride, 5% of their LC₅₀) for 28 days in the present study. The result of a neurobehavioral assay showed that chronic exposure of lead at lower concentrations significantly altered fish movement and neurobehaviors, indicating that lead exposure caused neurotoxicity in the carp. Increases in the neurotransmitter dopamine levels and injuries in the fish brain accounted for neurobehavioral abnormalities induced by lead exposure. Moreover, we also found that lead could easily cross the blood-brain barrier and caused significant bioaccumulation in the brain. Particularly, our study indicated that the ionic liquid could not synergistically promote blood-brain barrier permeability and hence failed to increase the absorption of lead in the fish brain, suggesting that the combined exposure of lead and ILs was not a synergistic effect but antagonism to the neurotoxicity. The results of this study suggested that ILs could recede the Pb induced neurotoxicity in fish.

Zebrafish: A New Promise to Study the Impact of Metabolic Disorders on the Brain

Zebrafish has become a popular model to study many physiological and pathophysiological processes in humans. In recent years, it has rapidly emerged in the study of metabolic disorders, namely, obesity and diabetes, as the regulatory mechanisms and metabolic pathways of glucose and lipid homeostasis are highly conserved between fish and mammals. Zebrafish is also widely used in the field of neurosciences to study brain plasticity and regenerative mechanisms due to the high maintenance and activity of neural stem cells during adulthood. Recently, a large body of evidence has established that metabolic disorders can alter brain homeostasis, leading to neuro-inflammation and oxidative stress and causing decreased neurogenesis. To date, these pathological metabolic conditions are also risk factors for the development of cognitive dysfunctions and neurodegenerative diseases. In this review, we first aim to describe the main metabolic models established in zebrafish to demonstrate their similarities with their respective mammalian/human counterparts. Then, in the second part, we report the impact of metabolic disorders (obesity and diabetes) on brain homeostasis with a particular focus on the blood-brain barrier, neuro-inflammation, oxidative stress, cognitive functions and brain plasticity. Finally, we propose interesting signaling pathways and regulatory mechanisms to be explored in order to better understand how metabolic disorders can negatively impact neural stem cell activity.

Long-term non-invasive drug treatments in adult zebrafish that lead to melanoma drug resistance

Zebrafish embryos are widely used for drug discovery, however, administering drugs to adult zebrafish is limited by current protocols that can cause stress. Here, we developed a drug formulation and administration method for adult zebrafish by producing food-based drug pellets that are consumed voluntarily. We applied this to zebrafish with BRAF-mutant melanoma, a model that has significantly advanced our understanding of melanoma progression, but not of drug resistance due to the limitations of current treatment methods. Zebrafish with melanomas responded to short-term, precise and daily dosing with drug pellets made with the BRAF^V600E inhibitor, vemurafenib. On-target drug efficacy was determined by phospho-Erk staining. Continued drug treatment led to the emergence, for the first time in zebrafish, of acquired drug resistance and melanoma relapse, modelling the responses seen in melanoma patients. This method presents a controlled, non-invasive approach that permits long-term drug studies and can be widely applied to adult zebrafish models.

Summary: We developed a precise drug-pellet dosing method for adult zebrafish melanoma models that can be widely applied to drug discovery in adult zebrafish.

High-calorie diet results in reversible obesity-related glomerulopathy in adult zebrafish regardless of dietary fat

Obesity is a risk factor for the development of kidney disease. The role of diet in this association remains undetermined, in part due to practical limitations in studying nutrition in humans. In particular, the relative importance of calorie excess versus dietary macronutrient content is poorly understood. For example, it is unknown if calorie restriction modulates obesity-related kidney pathology. To study the effects of diet-induced obesity in a novel animal model, we treated zebrafish for 8 wk with diets varied in both calorie and fat content. Kidneys were evaluated by light and electron microscopy. We evaluated glomerular filtration barrier function using a dextran permeability assay. We assessed the effect of diet on podocyte sensitivity to injury using an inducible podocyte injury model. We then tested the effect of calorie restriction on the defects caused by diet-induced obesity. Fish fed a high-calorie diet developed glomerulomegaly (mean: 1,211 vs. 1,010 µm2 in controls, P = 0.007), lower podocyte density, foot process effacement, glomerular basement membrane thickening, tubular enlargement (mean: 1,038 vs. 717 µm2 in controls, P < 0.0001), and ectopic lipid deposition. Glomerular filtration barrier dysfunction and increased susceptibility to podocyte injury were observed with high-calorie feeding regardless of dietary fat content. These pathological changes resolved with 4 wk of calorie restriction. Our findings suggest that calorie excess rather than dietary fat drives obesity-related kidney dysfunction and that inadequate podocyte proliferation in response to glomerular enlargement may cause podocyte dysfunction. We also demonstrate the value of zebrafish as a novel model for studying diet in obesity-related kidney disease.NEW & NOTEWORTHY Obesity is a risk factor for kidney disease. The role of diet in this association is difficult to study in humans. In this study, zebrafish fed a high-calorie diet, regardless of fat macronutrient composition, developed glomerulomegaly, foot process effacement, and filtration barrier dysfunction, recapitulating the changes seen in humans with obesity. Calorie restriction reversed the changes. This work suggests that macronutrient composition may be less important than total calories in the development of obesity-related kidney disease.

Genotoxic and mutagenic effects of chlorothalonil on the estuarine fish Micropogonias furnieri (Desmarest, 1823)

Chlorothalonil is a fungicide widely used in agriculture as well as an active ingredient in antifouling paints. Although it causes toxic effects on non-target organisms and can accumulate in fish tissues, little is known about its sublethal effects. Thus, genotoxic and mutagenic effects of intraperitoneal injected chlorothalonil in Micropogonias furnieri, an estuarine fish of frequent human consumption and a promising test-organism for ecotoxicological assays, were assessed. Chlorothalonil showed to be genotoxic (DNA damage by comet assay) and mutagenic (micronuclei, nuclear buds, apoptotic fragments, and bilobed cells) even at the lowest dose tested (0.35 μg g^-1) and in a dose-dependent manner (0.35 and 3.5 μg g^-1) for micronuclei, apoptotic fragments, and bilobed cells. As genomic instability may lead to carcinogenesis, the present evidence can assist decision-makers in banning this compound since any benefit toward food production is outweighed by the hazard to aquatic ecosystems and human health.

Bacopa monnieri attenuates glutamate-induced nociception and brain mitochondrial toxicity in Zebrafish

Bacopa monnieri L. (BM; Family: Scrophulariaceae), commonly known as Brahmi, is traditionally used as a nootropic agent. BM also exhibits significant analgesic activity in experimental models of pain. However, the effect of Bacopa monnieri against glutamate-induced nociception in zebrafish is yet to be explored in experimental condition. Therefore, the present study was designed to evaluate the effect of BM against glutamate-induced nociception and brain mitochondrial toxicity in adult zebrafish (Danio rerio). BM at 0.625, 1.25 and 2.5 mg/ml was administered to adult zebrafish and after half an hour glutamate was injected through i.m. route of administration. Indomethacin was used as standard drug. After behavioral analysis, the fish were euthanized and the brain was isolated and stored for further biochemical analysis. BM (1.25 and 2.5 mg/ml) and indomethacin significantly attenuated the glutamate-induced increase in number of line crossing compared to control group animals. Additionally, BM (1.25 and 2.5 mg/ml) and indomethacin significantly reduced the glutamate induced increase in cytosolic calcium level. Further, there was a substantial improvement in mitochondrial function, integrity and bioenergetics in term of respiratory control rate and ADP/O in zebrafish brain. Moreover, BM (1.25 and 2.5 mg/ml) and indomethacin significantly reduced the glutamate-induced mitochondria-dependent apoptosis in zebrafish brain. Therefore, BM could be a potential alternative drug candidate in the management of pain.

Comparative Study in Zebrafish and Medaka Unravels the Mechanisms of Tissue Regeneration

Tissue regeneration has been in the spotlight of research for its fascinating nature and potential applications in human diseases. The trait of regenerative capacity occurs diversely across species and tissue contexts, while it seems to decline over evolution. Organisms with variable regenerative capacity are usually distinct in phylogeny, anatomy, and physiology. This phenomenon hinders the feasibility of studying tissue regeneration by directly comparing regenerative with non-regenerative animals, such as zebrafish (Danio rerio) and mice (Mus musculus). Medaka (Oryzias latipes) is a fish model with a complete reference genome and shares a common ancestor with zebrafish approximately 110–200 million years ago (compared to 650 million years with mice). Medaka shares similar features with zebrafish, including size, diet, organ system, gross anatomy, and living environment. However, while zebrafish regenerate almost every organ upon experimental injury, medaka shows uneven regenerative capacity. Their common and distinct biological features make them a unique platform for reciprocal analyses to understand the mechanisms of tissue regeneration. Here we summarize current knowledge about tissue regeneration in these fish models in terms of injured tissues, repairing mechanisms, available materials, and established technologies. We further highlight the concept of inter-species and inter-organ comparisons, which may reveal mechanistic insights and hint at therapeutic strategies for human diseases.

Taurine prevents MK-801-induced shoal dispersion and altered cortisol responses in zebrafish

Schizophrenia is a chronic neuropsychiatric disorder characterized by a shortened lifespan and significant impaired social and vocational functioning. Schizophrenic patients can present hypothalamic-pituitary-adrenal (HPA) axis dysfunctions and cortisol dysregulation, which play an important role on the etiology onset, exacerbation, and relapsing of symptoms. Based on its intrinsic neuroprotective properties, taurine is considered a promising substance with beneficial role on various brain disorders, including schizophrenia. Here, we evaluated the effects of taurine on shoaling behavior and whole-body cortisol levels in zebrafish treated with dizocilpine (MK-801), which elicits schizophrenia-like phenotypes in animal models. Briefly, zebrafish shoals (4 fish per shoal) were exposed to dechlorinated water or taurine (42, 150, or 400 mg/L) for 60 min. Then, saline (PBS, pH 7.4 or 2.0 mg/kg MK-801) were intraperitoneally injected and zebrafish behavior was recorded 15 min later. In general, MK-801 disrupted shoaling behavior and reduced whole-body cortisol levels in zebrafish. All taurine pretreatments prevented MK-801-induced increase in shoal area, while 400 mg/L taurine prevented the MK-801-induced alterations in neuroendocrine responses. Moreover, all taurine-pretreated groups showed increased geotaxis, supporting a modulatory role in the overall dispersion pattern of the shoal. Collectively, our novel findings show a potential protective effect of taurine on MK-801-induced shoal dispersion and altered neuroendocrine responses, fostering the use of zebrafish models to assess schizophrenia-like phenotypes.

Understanding sex differences in zebrafish pain- and fear-related behaviors

Sex is an important variable in translational biomedical research. While overt sex differences have been reported for pain and fear-like behaviors in humans and rodents, these differences in other popular model organisms, such as zebrafish, remain poorly understood. Here, we evaluate potential sex differences in zebrafish behavioral responses to pain (intraperitoneal administration of 5% acetic acid) and fear stimuli (exposure to alarm substance). Overall, both male and female zebrafish exposed to pain (intraperitoneal 5% acetic acid injection) show lesser distance traveled, fewer top entries and more writhing-like pain-related behavior vs. controls. However, female fish more robustly (than males) altered some other pain-like behaviors (e.g., increasing freezing episodes and time in top) in this model. In contrast, zebrafish of both sexes responded equally strongly to fear evoked by alarm substance exposure. Collectively, these findings emphasize the growing importance of studying sex differences in zebrafish, including pain models.

Progranulin A Promotes Compensatory Hepatocyte Proliferation via HGF/c-Met Signaling after Partial Hepatectomy in Zebrafish

Compensatory hepatocyte proliferation and other liver regenerative processes are activated to sustain normal physiological function after liver injury. A major mitogen for liver regeneration is hepatocyte growth factor (HGF), and a previous study indicated that progranulin could modulate c-met, the receptor for HGF, to initiate hepatic outgrowth from hepatoblasts during embryonic development. However, a role for progranulin in compensatory hepatocyte proliferation has not been shown previously. Therefore, this study was undertaken to clarify whether progranulin plays a regulatory role during liver regeneration. To this end, we established a partial hepatectomy regeneration model in adult zebrafish that express a liver-specific fluorescent reporter. Using this model, we found that loss of progranulin A (GrnA) function by intraperitoneal-injection of a Vivo-Morpholino impaired and delayed liver regeneration after partial hepatectomy. Furthermore, transcriptome analysis and confirmatory quantitative real-time PCR suggested that cell cycle progression and cell proliferation was not as active in the morphants as controls, which may have been the result of comparative downregulation of the HGF/c-met axis by 36 h after partial hepatectomy. Finally, liver-specific overexpression of GrnA in transgenic zebrafish caused more abundant cell proliferation after partial hepatectomy compared to wild types. Thus, we conclude that GrnA positively regulates HGF/c-met signaling to promote hepatocyte proliferation during liver regeneration.

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

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

IMB-BZ as an Inhibitor Targeting ESX-1 Secretion System to Control Mycobacterial Infection

BACKGROUND

Resistance to anti-tuberculosis (TB) drug is a major issue in TB control, and demands the discovery of new drugs targeting virulence factor ESX-1.

METHODS

We first established a high-throughput screen (HTS) assay for the discovery of ESX-1 secretion inhibitors. The positive hits were then evaluated for the potency of diminishing the survival of virulent mycobacterium and reducing bacterial virulence. We further investigated the probability of inducing drug-resistance and the underlying mechanism using M-PFC.

RESULTS

A robust HTS assay was developed to identify small molecules that inhibit ESX-1 secretion without impairing bacterial growth in vitro. A hit named IMB-BZ specifically inhibits the secretion of CFP-10 and reduces virulence in an ESX-1-dependent manner, therefore resulting in significant reduction in intracellular and in vivo survival of mycobacteria. Blocking the CFP-10-EccCb1 interaction directly or indirectly underlies the inhibitory effect of IMB-BZ on the secretion of CFP-10. Importantly, our finding shows that the ESX-1 inhibitors pose low risk of drug resistance development by mycobacteria in vitro as compared with traditional anti-TB drug, and exhibit high potency against chronic mycobacterial infection.

CONCLUSION

Targeting ESX-1 may lead to the development of novel therapeutics for tuberculosis. IMB-BZ holds the potential for future development into a new anti-TB drug.

5-HT2C agonists and antagonists block different components of behavioral responses to potential, distal, and proximal threat in zebrafish

Serotonin (5-HT) receptors have been implicated in responses to aversive stimuli in mammals and fish, but its precise role is still unknown. Moreover, since at least seven families of 5-HT receptors exist in vertebrates, the role of specific receptors is still debated. Aversive stimuli can be classified as indicators of proximal, distal, or potential threat, initiating responses that are appropriate for each of these threat levels. Responses to potential threat usually involve cautious exploration and increased alertness, while responses to distal and proximal threat involve a fight-flight-freeze reaction. We exposed adult zebrafish to a conspecific alarm substance (CAS) and observed behavior during (distal threat) and after (potential threat) exposure, and treated with the 5-HT_2C receptor agonists MK-212 or WAY-161503 or with the antagonist RS-102221. The agonists blocked CAS-elicited defensive behavior (distal threat), but not post-exposure increases in defensive behavior (potential threat), suggesting inhibition of responses to distal threat. MK-212 blocked changes in freezing elicited by acute restraint stress, a model of proximal threat, while RS-102221 blocked changes in geotaxis elicited this stressor. We also found that RS-102221, a 5-HT_2C receptor antagonist, produced small effect on behavior during and after exposure to CAS. Preprint: https://www.biorxiv.org/content/10.1101/2020.10.04.324202; Data and scripts: https://github.com/lanec-unifesspa/5-HT-CAS/tree/master/data/5HT2C.

Decynium-22 affects behavior in the zebrafish light/dark test

Decynium-22 (D-22) is an inhibitor of the uptake2 system of monoamine clearance, resulting in increased levels of dopamine and norepinephrine (and in some cases serotonin) in the nervous system and elsewhere. Uptake2 is mediated by low-affinity, high-capacity transporters that are inhibited by glucocorticoids, suggesting a mechanism of fast glucocorticoid-monoamine interaction in the brain and a possible target for antidepressants. D-22 dose-dependently increased anxiety-like behavior in adult zebrafish exposed to the light/dark test, monotonically increasing scototaxis (dark preference), but affecting risk assessment with an inverted-U-shaped response. These results suggest that the uptake2 system has a role in defensive behavior in zebrafish, presenting a novel mechanism by which stress and glucocorticoids could produce fast neurobehavioral adjustments in vertebrates.

Clitorienolactones and Isoflavonoids of Clitorea ternatea Roots Alleviate Stress-Like Symptoms in a Reserpine-Induced Zebrafish Model

Clitorea ternatea has been used in Ayurvedic medicine as a brain stimulant to treat mental illnesses and mental functional disorders. In this study, the metabolite profiles of crude C. ternatea root extract (CTRE), ethyl acetate (EA), and 50% aqueous methanol (50% MeOH) fractions were investigated using ultrahigh-performance liquid chromatography–diode array detector–tandem mass spectrometry (UHPLC–DAD–MS/MS), while their effect on the stress-like behavior of zebrafish, pharmacologically induced with reserpine, was investigated. A total of 32 compounds were putatively identified, among which, a series of norneolignans, clitorienolactones, and various flavonoids (flavone, flavonol, isoflavone, and isoflavanone) was found to comprise the major constituents, particularly in the EA and 50% MeOH fractions. The clitorienolactones, presently unique to the species, were present in both the free and glycosylated forms in the roots. Both the EA and 50% MeOH fractions displayed moderate effects on the stress-induced zebrafish model, significantly decreasing freezing duration and elevating the total distance travelled and average velocity, 72 h post-treatment. The results of the present study provide further evidence that the basis for the use of C. ternatea roots in traditional medicine to alleviate brain-related conditions, such as stress and depression, is attributable to the presence of clitorienolactones and the isoflavonoidal constituents.

In vivo characterization of carbon dots-bone interactions: toward the development of bone-specific nanocarriers for drug delivery

Current treatments for osteoporosis and other bone degenerative diseases predominately rely on preventing further bone erosion rather than restoring bone mass, as the latter treatments can unintentionally trigger cancer development by undiscriminatingly promoting cell proliferation. One approach to circumvent this problem is through the development of novel chemical carriers to deliver drug agents specifically to bones. We have recently shown that carbon nanodots (C-dots) synthesized from carbon nanopowder can bind with high affinity and specificity to developing bones in the larval zebrafish. Larval bones, however, are physiologically different from adult bones in their growth, repair, and regeneration properties. Here we report that C-dots can bind to adult zebrafish bones and that this binding is highly specific to areas of appositional growth. C-dots deposition occurred within 30 minutes after delivery and was highly selective, with bones undergoing regeneration and repair showing higher levels of C-dots deposition than bones undergoing normal homeostatic turnover. Importantly, C-dots deposition did not interfere with bone regeneration or the animal’s health. Together, our results establish C-dots as a potential novel vehicle for the targeted delivery of drugs to treat adult bone disease.

Spatiotemporal imaging and pharmacokinetics of fluorescent compounds in zebrafish eleuthero-embryos after different routes of administration

Zebrafish (Danio rerio) is increasingly used to assess the pharmacological activity and toxicity of compounds. The spatiotemporal distribution of seven fluorescent alkyne compounds was examined during 48 h after immersion (10 µM) or microinjection (2 mg/kg) in the pericardial cavity (PC), intraperitoneally (IP) and yolk sac (IY) of 3 dpf zebrafish eleuthero-embryos. By modelling the fluorescence of whole-body contours present in fluorescence images, the main pharmacokinetic (PK) parameter values of the compounds were determined. It was demonstrated that especially in case of short incubations (1-3 h) immersion can result in limited intrabody exposure to compounds. In this case, PC and IP microinjections represent excellent alternatives. Significantly, IY microinjections did not result in a suitable intrabody distribution of the compounds. Performing a QSPkR (quantitative structure-pharmacokinetic relationship) analysis, LogD was identified as the only molecular descriptor that explains the final uptake of the selected compounds. It was also shown that combined administration of compounds (immersion and microinjection) provides a more stable intrabody exposure, at least in case of a prolonged immersion and compounds with LogD value > 1. These results will help reduce the risk of false negative results and can offer an invaluable input for future translational research and safety assessment applications.

Gonadotropin Releasing Hormone (Gnrh) Triggers Neurogenesis in the Hypothalamus of Adult Zebrafish

Recently, it has been shown in adult mammals that the hypothalamus can generate new cells in response to metabolic changes, and tanycytes, putative descendants of radial glia, can give rise to neurons. Previously we have shown in vitro that neurospheres generated from the hypothalamus of adult zebrafish show increased neurogenesis in response to exogenously applied hormones. To determine whether adult zebrafish have a hormone-responsive tanycyte-like population in the hypothalamus, we characterized proliferative domains within this region. Here we show that the parvocellular nucleus of the preoptic region (POA) labels with neurogenic/tanycyte markers vimentin, GFAP/Zrf1, and Sox2, but these cells are generally non-proliferative. In contrast, Sox2+ proliferative cells in the ventral POA did not express vimentin and GFAP/Zrf1. A subset of the Sox2+ cells co-localized with Fezf2:GFP, a transcription factor important for neuroendocrine cell specification. Exogenous treatments of GnRH and testosterone were assayed in vivo. While the testosterone-treated animals showed no significant changes in proliferation, the GnRH-treated animals showed significant increases in the number of BrdU-labeled cells and Sox2+ cells. Thus, cells in the proliferative domains of the zebrafish POA do not express radial glia (tanycyte) markers vimentin and GFAP/Zrf1, and yet, are responsive to exogenously applied GnRH treatment.

Compressed Sensing-Based Super-Resolution Ultrasound Imaging for Faster Acquisition and High Quality Images

GOAL

Typical SRUS images are reconstructed by localizing ultrasound microbubbles (MBs) injected in a vessel using normalized 2-dimensional cross-correlation (2DCC) between MBs signals and the point spread function of the system. However, current techniques require isolated MBs in a confined area due to inaccurate localization of densely populated MBs. To overcome this limitation, we developed the ℓ1-homotopy based compressed sensing (L1H-CS) based SRUS imaging technique which localizes densely populated MBs to visualize microvasculature in vivo.

METHODS

To evaluate the performance of L1H-CS, we compared the performance of 2DCC, interior-point method based compressed sensing (CVX-CS), and L1H-CS algorithms. Localization efficiency was compared using axially and laterally aligned point targets (PTs) with known distances and randomly distributed PTs generated by simulation. We developed post-processing techniques including clutter reduction, noise equalization, motion compensation, and spatiotemporal noise filtering for in vivo imaging. We then validated the capabilities of L1H-CS based SRUS imaging technique with high-density MBs in a mouse tumor model, kidney, and zebrafish dorsal trunk, and brain.

RESULTS

Compared to 2DCC and CVX-CS algorithms, L1H-CS achieved faster data acquisition time and considerable improvement in SRUS image quality.

CONCLUSIONS AND SIGNIFICANCE

These results demonstrate that the L1H-CS based SRUS imaging technique has the potential to examine microvasculature with reduced acquisition and reconstruction time to acquire enhanced SRUS image quality, which may be necessary to translate it into clinics.

HDL biodistribution and brain receptors in zebrafish, using HDLs as vectors for targeting endothelial cells and neural progenitors

High density lipoproteins (HDLs) display pleiotropic functions such as anti-inflammatory, antioxidant, anti-protease, and anti-apoptotic properties. These effects are mediated by four main receptors: SCARB1 (SR-BI), ABCA1, ABCG1, and CD36. Recently, HDLs have emerged for their potential involvement in brain functions, considering their epidemiological links with cognition, depression, and brain plasticity. However, their role in the brain is not well understood. Given that the zebrafish is a well-recognized model for studying brain plasticity, metabolic disorders, and apolipoproteins, it could represent a good model for investigating the role of HDLs in brain homeostasis. By analyzing RNA sequencing data sets and performing in situ hybridization, we demonstrated the wide expression of scarb1, abca1a, abca1b, abcg1, and cd36 in the brain of adult zebrafish. Scarb1 gene expression was detected in neural stem cells (NSCs), suggesting a possible role of HDLs in NSC activity. Accordingly, intracerebroventricular injection of HDLs leads to their uptake by NSCs without modulating their proliferation. Next, we studied the biodistribution of HDLs in the zebrafish body. In homeostatic conditions, intraperitoneal injection of HDLs led to their accumulation in the liver, kidneys, and cerebral endothelial cells in zebrafish, similar to that observed in mice. After telencephalic injury, HDLs were diffused within the damaged parenchyma and were taken up by ventricular cells, including NSCs. However, they failed to modulate the recruitment of microglia cells at the injury site and the injury-induced proliferation of NSCs. In conclusion, our results clearly show a functional HDL uptake process involving several receptors that may impact brain homeostasis and suggest the use of HDLs as delivery vectors to target NSCs for drug delivery to boost their neurogenic activity.

Which Hyperglycemic Model of Zebrafish (Danio rerio) Suites My Type 2 Diabetes Mellitus Research? A Scoring System for Available Methods

Despite extensive studies on type 2 diabetes mellitus (T2DM), there is no definitive cure, drug, or prevention. Therefore, for developing new therapeutics, proper study models of T2DM is necessary to conduct further preclinical researches. Diabetes has been induced in animals using chemical, genetic, hormonal, antibody, viral, and surgical methods or a combination of them. Beside different approaches of diabetes induction, different animal species have been suggested. Although more than 85% of articles have proposed rat (genus Rattus) as the proper model for diabetes induction, zebrafish (Danio rerio) models of diabetes are being used more frequently in diabetes related studies. In this systematic review, we compare different aspects of available methods of inducing hyperglycemia referred as T2DM in zebrafish by utilizing a scoring system. Evaluating 26 approved models of T2DM in zebrafish, this scoring system may help researchers to compare different T2DM zebrafish models and select the best one regarding their own research theme. Eventually, glyoxalase1 (glo1-/-) knockout model of hyperglycemia achieved the highest score. In addition to assessment of hyperglycemic induction methods in zebrafish, eight most commonly proposed diabetic induction approval methods are suggested to help researchers confirm their subsequent proposed models.

Perillyl alcohol decreases the frequency and severity of convulsive-like behavior in the adult zebrafish model of acute seizures

This research aimed to assess the effect of perillyl alcohol (PA) on convulsive behavior in vivo using adult zebrafish (Danio rerio, both sexes). The seizures were induced with pentylenetetrazole (PTZ) intraperitoneally at 170 mg/kg, and diazepam (DZP) was used as the control anticonvulsant (2 mg/kg, oral); PA was tested at 10, 50, and 100 mg/kg orally. The groups had ten animals per group (total n = 60), observed for 10 minutes after seizure induction. We manually appraised typical seizure phenotypes for quantification and used an animal tracking software (Toxtrac) to assess the motor parameters. Next, we sought to find a mechanism of action for PA anticonvulsant activity in silico using a structure-based activity prediction server and molecular docking. The results show that PTZ induced seizure-like behavior in all untreated animals with hyperlocomotion episodes, seizure itself, posture loss, and immobility. DZP inhibited the seizures in all animals of the positive control group. PA, in turn, inhibited the occurrence of seizures in a dose-dependent manner, with frequencies of 90%, 70%, and 40% (for 10, 50, and 100 mg/kg, respectively). The PA treatments also decreased several seizure endpoints in a dose-dependent manner. Also, the difference of the group treated with highest dose of PA was statistically significant compared with the negative control group for all the endpoints assessed (p < 0.05, Kruskal-Wallis). The in silico analyses suggested that PA can affect the GABAergic system, which might be involved in its anticonvulsant activity, but other mechanisms cannot be ruled out. Overall, our results suggest an anticonvulsant potential in perillyl alcohol.

Dataset of Swimming behavioral alterations in Danio rerio by Nemopilema nomurai jellyfish venom

This article reports data associated with Prakash et al. [1]. Nemopilema nomurai jellyfish venom (NnV) can lead to neurotoxicity in zebrafish (Danio rerio) model. In the present study, zebrafish were treated with NnV by intraperitoneal injection and the swimming behavior of each fish was evaluated using a score scale. The dose of NnV in each treatment group was based on the protein concentration of NnV. Swimming is the main locomotory movements in the fishes. NnV modulated the swimming behavior of Danio rerio in a dose-dependent manner. In this article provided data are directly related to the previously published research article – “Danio rerio as an alternative vertebrate model for jellyfish venom study: the toxinological aspects of Nemopilema nomurai venom” [1] where the downregulation of acetylcholinesterase activity as well as histopathological alterations were observed from the brain of Danio rerio treated with NnV. Here we provide datasets, including mortality rate table, swimming behavior graph, and videos of zebrafish after NnV envenomation.

Inhibition of GABAA-ρ receptors induces retina regeneration in zebrafish

A potential treatment for retinal diseases is to induce an endogenous Müller glia (MG)-derived regenerative response to replace damaged neurons. In contrast to mammalian MG, zebrafish MG are capable of mediating spontaneous regeneration. We seek to define the mechanisms that enable retina regeneration in zebrafish in order to identify therapeutic targets to induce mammalian retina regeneration. We previously used pharmacological and genetic methods to inhibit gamma aminobutyric acid A (GABA_A) receptors in undamaged zebrafish retinas and showed that such inhibition could induce initiation of retina regeneration, as measured by the dedifferentiation of MG and the appearance of MG-derived proliferating progenitor cells. Here, we show that inhibition of a pharmacologically distinct subset of GABA_A receptors (GABA_A-ρ) can also induce retina regeneration. Dual inhibition of both GABA receptor subtypes led to enhanced retina regeneration. Gene expression analyses indicate that inhibition of GABA_A-ρ receptors induces a canonical retinal regenerative response. Our results support a model in which decreased levels of GABA, such as would occur after retinal cell death or damage, induce dedifferentiation of MG and the generation of proliferating progenitor cells during zebrafish retina regeneration. Animal experiments were approved by the Vanderbilt's Institutional Animal Care and Use Committee (Protocol M1800200) on January 29, 2019.

β-lactamase inhibitory potential of kalafungin from marine Streptomyces in Staphylococcus aureus infected zebrafish

β-lactamase inhibitors are potent synergistic drugs to deteriorate the multidrug-resistant bacteria. Here, we report the β-lactamase inhibitory ability of kalafungin isolated from a marine sponge derived Streptomyces sp. SBRK1. The IC₅₀ value of the kalafungin was calculated as 225.37 ± 1.95 μM against β-lactamase. The enzyme kinetic analysis showed the Km value of 3.448 ± 0.7 μM and V_max value of 215.356 ± 8 μM/min and the inhibition mechanism was identified as uncompetitive type. Along with the antibacterial activity, the cell surface analysis of kalafungin treated Staphylococcus aureus cells revealed destruction of cell membrane in response to β-lactamase inhibition. Molecular docking studies have confirmed the binding property of kalafungin against β-lactamase with two hydrogen bonds. In vivo efficacy studies in the zebrafish model by green fluorescent protein expressing S. aureus infection, survival, safety and behavioral profile were reported. The toxicity and anti-infection revealed that the compound was evidently active and safe to all organs. In conclusion, this is the first report on kalafungin with β- lactamase inhibition and suggests that kalafungin may useful for synergic antibacterial therapy with β-lactam drugs to overcome β-lactamase-based resistance of any bacterial pathogens.

Stimulation of glycolysis promotes cardiomyocyte proliferation after injury in adult zebrafish

Cardiac metabolism plays a crucial role in producing sufficient energy to sustain cardiac function. However, the role of metabolism in different aspects of cardiomyocyte regeneration remains unclear. Working with the adult zebrafish heart regeneration model, we first find an increase in the levels of mRNAs encoding enzymes regulating glucose and pyruvate metabolism, including pyruvate kinase M1/2 (Pkm) and pyruvate dehydrogenase kinases (Pdks), especially in tissues bordering the damaged area. We further find that impaired glycolysis decreases the number of proliferating cardiomyocytes following injury. These observations are supported by analyses using loss-of-function models for the metabolic regulators Pkma2 and peroxisome proliferator-activated receptor gamma coactivator 1 alpha. Cardiomyocyte-specific loss- and gain-of-function manipulations of pyruvate metabolism using Pdk3 as well as a catalytic subunit of the pyruvate dehydrogenase complex (PDC) reveal its importance in cardiomyocyte dedifferentiation and proliferation after injury. Furthermore, we find that PDK activity can modulate cell cycle progression and protrusive activity in mammalian cardiomyocytes in culture. Our findings reveal new roles for cardiac metabolism and the PDK-PDC axis in cardiomyocyte behavior following cardiac injury.

Application of zebrafish to safety evaluation in drug discovery

Traditionally, safety evaluation at the early stage of drug discovery research has been done using in silico, in vitro, and in vivo systems in this order because of limitations on the amount of compounds available and the throughput ability of the assay systems. While these in vitro assays are very effective tools for detecting particular tissue-specific toxicity phenotypes, it is difficult to detect toxicity based on complex mechanisms involving multiple organs and tissues. Therefore, the development of novel high throughput in vivo evaluation systems has been expected for a long time. The zebrafish (Danio rerio) is a vertebrate with many attractive characteristics for use in drug discovery, such as a small size, transparency, gene and protein similarity with mammals (80% or more), and ease of genetic modification to establish human disease models. Actually, in recent years, the zebrafish has attracted interest as a novel experimental animal. In this article, the author summarized the features of zebrafish that make it a suitable laboratory animal, and introduced and discussed the applications of zebrafish to preclinical toxicity testing, including evaluations of teratogenicity, hepatotoxicity, and nephrotoxicity based on morphological findings, evaluation of cardiotoxicity using functional endpoints, and assessment of seizure and drug abuse liability.

Toxicity Analysis of Recombinant L-asparaginase I and II in Zebrafish

L-asparaginases are extensively applied in the treatment of Acute Lymphoblastic Leukemia (ALL). The treatment regime of ALL consists of asparaginase from E. coli or Erwinia. The survival rate post-chemotherapy has increased to < 90% in recent years. Asparaginase therapy has also resulted in numerous toxicities to patients receiving therapy. This study demonstrates the reaction of normal cells of Danio rerio to asparaginase therapy. L-asparaginase I and II used in the present study are from two probiotic Lactobacillus species in comparison with a commercial L-asparaginase of E. coli origin. Zebrafish adults were injected with 2500 U/kg body weight of L-asparaginase treatments. The expression of SOD 2, CAT, GST, GTP BP3, FADS2 were analyzed with EF1α as house-keeping gene. The p value obtained proves that the data are significant. The histology of the L-asparaginase I treated fishes showed dilated sinusoids in the liver and pseudocyst in the pancreas. The L-asparaginase II and commercial asparaginase showed no pathology.

Autophagy Activation in Zebrafish Heart Regeneration

Autophagy is an evolutionarily conserved process that plays a key role in the maintenance of overall cellular health. While it has been suggested that autophagy may elicit cardioprotective and pro-survival modulating functions, excessive activation of autophagy can also be detrimental. In this regard, the zebrafish is considered a hallmark model for vertebrate regeneration, since contrary to adult mammals, it is able to faithfully regenerate cardiac tissue. Interestingly, the role that autophagy may play in zebrafish heart regeneration has not been studied yet. In the present work, we hypothesize that, in the context of a well-established injury model of ventricular apex resection, autophagy plays a critical role during cardiac regeneration and its regulation can directly affect the zebrafish regenerative potential. We studied the autophagy events occurring upon injury using electron microscopy, in vivo tracking of autophagy markers, and protein analysis. Additionally, using pharmacological tools, we investigated how rapamycin, an inducer of autophagy, affects regeneration relevant processes. Our results show that a tightly regulated autophagic response is triggered upon injury and during the early stages of the regeneration process. Furthermore, treatment with rapamycin caused an impairment in the cardiac regeneration outcome. These findings are reminiscent of the pathophysiological description of an injured human heart and hence put forward the zebrafish as a model to study the poorly understood double-sword effect that autophagy has in cardiac homeostasis.

Single-cell analysis uncovers that metabolic reprogramming by ErbB2 signaling is essential for cardiomyocyte proliferation in the regenerating heart

While the heart regenerates poorly in mammals, efficient heart regeneration occurs in zebrafish. Studies in zebrafish have resulted in a model in which preexisting cardiomyocytes dedifferentiate and reinitiate proliferation to replace the lost myocardium. To identify which processes occur in proliferating cardiomyocytes we have used a single-cell RNA-sequencing approach. We uncovered that proliferating border zone cardiomyocytes have very distinct transcriptomes compared to the nonproliferating remote cardiomyocytes and that they resemble embryonic cardiomyocytes. Moreover, these cells have reduced expression of mitochondrial genes and reduced mitochondrial activity, while glycolysis gene expression and glucose uptake are increased, indicative for metabolic reprogramming. Furthermore, we find that the metabolic reprogramming of border zone cardiomyocytes is induced by Nrg1/ErbB2 signaling and is important for their proliferation. This mechanism is conserved in murine hearts in which cardiomyocyte proliferation is induced by activating ErbB2 signaling. Together these results demonstrate that glycolysis regulates cardiomyocyte proliferation during heart regeneration.

Heart attacks are a common cause of death in the Western world. During a heart attack, oxygen levels in the affected part of the heart decrease, which causes heart muscle cells to die. In humans the dead cells are replaced by a permanent scar that stabilizes the injury but does not completely heal it. As a result, individuals have a lower quality of life after a heart attack and are more likely to die from a subsequent attack.

Unlike humans, zebrafish are able to regenerate their hearts after injury: heart muscle cells close to a wound divide to produce new cells that slowly replace the scar tissue and restore normal function to the area. It remains unclear, however, what stimulates the heart muscle cells of zebrafish to start dividing. To address this question, Honkoop, de Bakker et al. used a technique called single-cell sequencing to study heart muscle cells in wounded zebrafish hearts.

The experiments identified a group of heart muscle cells close to the site of the wound that multiplied to repair the damage. This group of cells had altered their metabolism compared to other heart muscle cells so that they relied on a pathway called glycolysis to produce the energy and building blocks they needed to proliferate. Blocking glycolysis impaired the ability of the heart muscle cells to divide, indicating that this switch is necessary for the heart to regenerate. Further experiments showed that a signaling cascade, which includes the molecules Nrg1 and ErbB2, induces heart muscle cells in both zebrafish and mouse hearts to switch to glycolysis and undergo division.

These findings indicate that activating glycolysis in heart muscle cells may help to stimulate the heart to regenerate after a heart attack or other injury. The next step following on from this work is to develop methods to activate glycolysis and promote cell division in injured hearts.

Zebrafish as a preclinical in vivo screening model for nanomedicines

The interactions of nanomedicines with biological environments is heavily influenced by their physicochemical properties. Formulation design and optimization are therefore key steps towards successful nanomedicine development. Unfortunately, detailed assessment of nanomedicine formulations, at a macromolecular level, in rodents is severely limited by the restricted imaging possibilities within these animals. Moreover, rodent in vivo studies are time consuming and expensive, limiting the number of formulations that can be practically assessed in any one study. Consequently, screening and optimisation of nanomedicine formulations is most commonly performed in surrogate biological model systems, such as human-derived cell cultures. However, despite the time and cost advantages of classical in vitro models, these artificial systems fail to reflect and mimic the complex biological situation a nanomedicine will encounter in vivo. This has acutely hampered the selection of potentially successful nanomedicines for subsequent rodent in vivo studies. Recently, zebrafish have emerged as a promising in vivo model, within nanomedicine development pipelines, by offering opportunities to quickly screen nanomedicines under in vivo conditions and in a cost-effective manner so as to bridge the current gap between in vitro and rodent studies. In this review, we outline several advantageous features of the zebrafish model, such as biological conservation, imaging modalities, availability of genetic tools and disease models, as well as their various applications in nanomedicine development. Critical experimental parameters are discussed and the most beneficial applications of the zebrafish model, in the context of nanomedicine development, are highlighted.

Sulphated polysaccharide from Sargassum myriocystum confers protection against gentamicin-induced nephrotoxicity in adult zebrafish

The beneficial effect of purified fraction of sulphated polysaccharide extracted from Sargassum myriocystum (SMP) was examined on the gentamicin-induced nephrotoxicity in adult zebrafish. The major purified fractions (SMP1, SMP2 and SMP3) were obtained by anion-exchange and size-exclusion chromatography and characterized by FTIR, GCMS and NMR. The in vitro antioxidant activities of all purified SMP fractions were analysed. The SMP2 showed maximum carbohydrate, sulphate and fucose content with strong antioxidant activity than other fractions. Further, we evaluated the efficacy of SMP2 against gentamicin-induced nephrotoxicity in zebrafish model. The SMP2 administered group showed a significant attenuation in oxidative stress and histopathological alterations observed in renal tissues of gentamicin treated group. Moreover, the SMP2 supressed renal mRNA expression levels of KIM-1, NF-κB, TNF-α and IL-6 in dose-dependent manner. Thus, the present study suggests that the SMP2 is a potent antioxidant with anti-inflammatory and renoprotective properties that ameliorated the GEN induced nephrotoxicity in adult zebrafish.

Insulin-like growth factor binding proteins inhibit oocyte maturation of zebrafish

The function of insulin-like growth factor (Igf) system in ovary has attracted much attention, but the role of Igf binding proteins (Igfbps) in ovary is still largely unknown. In this study, the role of Igfbps in oocyte maturation was investigated in zebrafish. The expression of all eight identified Igfbps except Igfbp6b could be detected in the adult ovary and exhibited differential expression profiles during folliculogenesis. The expression of several Igfbps is dynamically changed during oocyte maturation induced by human chorionic gonadotropin (hCG). By treatment of an Igfbps inhibitor NBI-31772 in vitro, the oocyte maturation could be stimulated in a clear dose-, time- and stage-dependent manner. Such effects were also observed by administration of NBI-31772 in vivo. Igfbps are differentially expressed in both follicular cells and oocytes, but the effect of NBI-31772 could only be found in intact follicles and not in the denuded oocytes. Previous studies have demonstrated that Igf3 is the major Igf member in regulating oocyte maturation of zebrafish. Interestingly, NBI-31772 could increase the effect of Igf3 on oocyte maturation. Furthermore, we found the effect of NBI-31772 on oocyte maturation could be blocked by an Igf type 1 receptor inhibitor BMS-536924 in vitro, suggesting the Igfbps can inhibit the oocyte maturation via Igf/Igf1r pathway. Together, we provided the first evidence in fish that Igfbps inhibit oocyte maturation of zebrafish.

Taurine prevents memory consolidation deficits in a novel alcohol-induced blackout model in zebrafish

Ethanol is one of the most consumed substance worldwide that impairs learning and memory processes, resulting in amnesia or blackout. Due to the genetic conservation, rich behavioral repertoire, and high pharmacological tractability, the zebrafish (Danio rerio) has emerged as a powerful model organism for assessing preventive strategies against the noxious effects of ethanol in vertebrates. Here, we used an inhibitory avoidance apparatus to investigate the potential preventive effects of taurine in a novel ethanol-induced amnesia model in zebrafish. The experimental tank consisted of two compartments of the same size, one dark and another white, which were separated by a guillotine-type door. Three parallel metal bars coupled to an electrical stimulator were connected on each lateral wall of the dark compartment as electrical stimulus source. Differences on the latency to enter the dark compartment were used as retention indexes. A mild electric shock (125 mA, 3 ± 0.2 V) at 10 and 1000 Hz did not promote significant learning, while 100 Hz facilitated memory retention. Posttraining administration of MK-801 blocked this response, reinforcing the predictive validity of the test. Treatments were performed immediately after the training session using the 100 Hz frequency. Animals were exposed to water (control), taurine (42, 150, 400 mg/L), ethanol (0.25%, 1.0% v/v) or taurine plus ethanol to assess the effects on memory consolidation. Test session was performed 24 h following training. Ethanol at 0.25% did not affect memory consolidation, but 1.0% impaired memory without changing locomotion. Although taurine alone did not modulate learning, all concentrations tested exerted prevented ethanol-induced memory impairment. Overall, we describe a novel ethanol-induced blackout model, where a high ethanol concentration acutely impairs memory consolidation in zebrafish. Moreover, since taurine showed a protective role, we reinforce the growing utility of zebrafish models for assessing the deleterious effects of ethanol and potential therapeutic strategies.