Report of Workshop on Euthanasia for Zebrafish-A Matter of Welfare and Science

Gliovascular transcriptional perturbations in Alzheimer's disease reveal molecular mechanisms of blood brain barrier dysfunction

To uncover molecular changes underlying blood-brain-barrier dysfunction in Alzheimer's disease, we performed single nucleus RNA sequencing in 24 Alzheimer's disease and control brains and focused on vascular and astrocyte clusters as main cell types of blood-brain-barrier gliovascular-unit. The majority of the vascular transcriptional changes were in pericytes. Of the vascular molecular targets predicted to interact with astrocytic ligands, SMAD3, upregulated in Alzheimer's disease pericytes, has the highest number of ligands including VEGFA, downregulated in Alzheimer's disease astrocytes. We validated these findings with external datasets comprising 4,730 pericyte and 150,664 astrocyte nuclei. Blood SMAD3 levels are associated with Alzheimer's disease-related neuroimaging outcomes. We determined inverse relationships between pericytic SMAD3 and astrocytic VEGFA in human iPSC and zebrafish models. Here, we detect vast transcriptome changes in Alzheimer's disease at the gliovascular-unit, prioritize perturbed pericytic SMAD3-astrocytic VEGFA interactions, and validate these in cross-species models to provide a molecular mechanism of blood-brain-barrier disintegrity in Alzheimer's disease.

Rare genetic variation in fibronectin 1 (FN1) protects against APOEε4 in Alzheimer's disease

The risk of developing Alzheimer's disease (AD) significantly increases in individuals carrying the APOEε4 allele. Elderly cognitively healthy individuals with APOEε4 also exist, suggesting the presence of cellular mechanisms that counteract the pathological effects of APOEε4; however, these mechanisms are unknown. We hypothesized that APOEε4 carriers without dementia might carry genetic variations that could protect them from developing APOEε4-mediated AD pathology. To test this, we leveraged whole-genome sequencing (WGS) data in the National Institute on Aging Alzheimer's Disease Family Based Study (NIA-AD FBS), Washington Heights/Inwood Columbia Aging Project (WHICAP), and Estudio Familiar de Influencia Genetica en Alzheimer (EFIGA) cohorts and identified potentially protective variants segregating exclusively among unaffected APOEε4 carriers. In homozygous unaffected carriers above 70 years old, we identified 510 rare coding variants. Pathway analysis of the genes harboring these variants showed significant enrichment in extracellular matrix (ECM)-related processes, suggesting protective effects of functional modifications in ECM proteins. We prioritized two genes that were highly represented in the ECM-related gene ontology terms, (FN1) and collagen type VI alpha 2 chain (COL6A2) and are known to be expressed at the blood-brain barrier (BBB), for postmortem validation and in vivo functional studies. An independent analysis in a large cohort of 7185 APOEε4 homozygous carriers found that rs140926439 variant in FN1 was protective of AD (OR = 0.29; 95% CI [0.11, 0.78], P = 0.014) and delayed age at onset of disease by 3.37 years (95% CI [0.42, 6.32], P = 0.025). The FN1 and COL6A2 protein levels were increased at the BBB in APOEε4 carriers with AD. Brain expression of cognitively unaffected homozygous APOEε4 carriers had significantly lower FN1 deposition and less reactive gliosis compared to homozygous APOEε4 carriers with AD, suggesting that FN1 might be a downstream driver of APOEε4-mediated AD-related pathology and cognitive decline. To validate our findings, we used zebrafish models with loss-of-function (LOF) mutations in fn1b-the ortholog for human FN1. We found that fibronectin LOF reduced gliosis, enhanced gliovascular remodeling, and potentiated the microglial response, suggesting that pathological accumulation of FN1 could impair toxic protein clearance, which is ameliorated with FN1 LOF. Our study suggests that vascular deposition of FN1 is related to the pathogenicity of APOEε4, and LOF variants in FN1 may reduce APOEε4-related AD risk, providing novel clues to potential therapeutic interventions targeting the ECM to mitigate AD risk.

Rare genetic variation in Fibronectin 1 ( FN1 ) protects against APOEe4 in Alzheimer's disease

The risk of developing Alzheimer's disease (AD) significantly increases in individuals carrying the APOEε4 allele. Elderly cognitively healthy individuals with APOEε4 also exist, suggesting the presence of cellular mechanisms that counteract the pathological effects of APOEε4 ; however, these mechanisms are unknown. We hypothesized that APOEε4 carriers without dementia might carry genetic variations that could protect them from developing APOEε4- mediated AD pathology. To test this, we leveraged whole genome sequencing (WGS) data in National Institute on Aging Alzheimer's Disease Family Based Study (NIA-AD FBS), Washington Heights/Inwood Columbia Aging Project (WHICAP), and Estudio Familiar de Influencia Genetica en Alzheimer (EFIGA) cohorts and identified potentially protective variants segregating exclusively among unaffected APOEε4 carriers. In homozygous unaffected carriers above 70 years old, we identified 510 rare coding variants. Pathway analysis of the genes harboring these variants showed significant enrichment in extracellular matrix (ECM)-related processes, suggesting protective effects of functional modifications in ECM proteins. We prioritized two genes that were highly represented in the ECM-related gene ontology terms, (FN1) and collagen type VI alpha 2 chain ( COL6A2 ) and are known to be expressed at the blood-brain barrier (BBB), for postmortem validation and in vivo functional studies. The FN1 and COL6A2 protein levels were increased at the BBB in APOEε4 carriers with AD. Brain expression of cognitively unaffected homozygous APOEε4 carriers had significantly lower FN1 deposition and less reactive gliosis compared to homozygous APOEε4 carriers with AD, suggesting that FN1 might be a downstream driver of APOEε4 -mediated AD-related pathology and cognitive decline. To validate our findings, we used zebrafish models with loss-of-function (LOF) mutations in fn1b - the ortholog for human FN1 . We found that fibronectin LOF reduced gliosis, enhanced gliovascular remodeling and potentiated the microglial response, suggesting that pathological accumulation of FN1 could impair toxic protein clearance, which is ameliorated with FN1 LOF. Our study suggests vascular deposition of FN1 is related to the pathogenicity of APOEε4 , LOF variants in FN1 may reduce APOEε4 -related AD risk, providing novel clues to potential therapeutic interventions targeting the ECM to mitigate AD risk.

Metabolic exploration of the developmental abnormalities and neurotoxicity of Esculentoside B, the main toxic factor in Phytolaccae radix

P: radix is a perennial herb, and its extracts have various biological properties that make it a potential candidate for the treatment of tumors, edema, and lymphatic stasis. However, the main factor contributing to its toxicity are not clear. Here, we used a zebrafish toxicological model to study the main toxicity factor of P. radix and explore the potential mechanisms involved. The results revealed that Esculentoside B was the major toxic factor of P. radix. Exposure of zebrafish larvae to Esculentoside B caused developmental abnormalities, neurotoxicity and altered locomotor behavior. The combination of AChE activity and the expression levels of genes relevant to CNS development demonstrated that Esculentoside B is neurotoxic to zebrafish larvae, impairs their CNS development, and that AChE may be a toxic target of Esculentoside B. Metabolomic analysis has revealed that Esculentoside B exposure can disrupt D-Amino acid metabolism, protein export, autophagy, and mTOR signaling pathways in zebrafish larvae. These findings provide insights into the molecular mechanisms underlying EsB-induced neurotoxicity in zebrafish, which can facilitate further research and development of P. radix for safe consumption.

An RNA-seq time series of the medaka pituitary gland during sexual maturation

Directing both organismal homeostasis and physiological adaptation, the pituitary is a key endocrine gland in all vertebrates. One of its major tasks is to coordinate sexual maturation through the production and release of hormones stimulating gonad development. In order to study its developmental dynamics in the model fish medaka (Oryzias latipes), we sampled both the pituitary and the ovaries of 68 female fish. Of these, 55 spanned the entire course of sexual maturation from prepubertal juveniles to spawning adults. An additional 13 showed either considerably faster or slower growth and development than the majority of fish. We used histological examination of the ovaries to determine a histological maturation stage, and analyzed the pituitary glands using RNA-seq optimized for low input. Taken together, these data reveal the timing of hormone production priorities, and form a comprehensive resource for the study of their regulation.

Binaprofen induces zebrafish liver injury via the mitochondrial pathway

Binaprofen (C18H23NO5) is a drug not commercially available that causes liver injury; however, the underlying mechanism is unknown. The aim of the present study was to determine the mechanism underlying binaprofen‑induced liver injury at the genetic level. Zebrafish were treated with binaprofen. Serum biomarkers [alanine transaminase (ALT), aspartate transaminase (AST) and lactate dehydrogenase (LDH)], malondialdehyde (MDA) and glutathione (GSH) content analysis, liver cell morphology examination, DAPI staining, electron microscopy, microarray analysis and reverse transcription‑quantitative (RT‑q)PCR were performed 12, 24 and 48 h post‑treatment to analyze the mechanism underlying binaprofen‑induced liver injury. Following exposure to binaprofen, zebrafish serum levels of ALT, AST and LDH increased; MDA content of liver tissue increased and GSH content decreased. Liver cells exhibited mild to moderate vacuolization and mitochondria exhibited vacuolization and disrupted cristae. Liver cell apoptosis rate increased. There were 190 common differentially expressed genes at 12, 24 and 48 h. Gene Ontology analysis showed that the function of downregulated genes was primarily associated with 'DNA replication', 'DNA metabolic process', 'cell cycle', 'cell redox homeostasis', 'mitochondrion' and 'lipid transport'. The function of upregulated genes was primarily associated with 'peroxisome proliferator', 'oxidation activity', 'peroxisome' and 'apoptosis'. Pathway analysis showed that downregulated genes were those pertaining to 'cell cycle', 'DNA replication', 'ribosome', 'spliceosome', 'pyrimidine metabolism', 'purine metabolism', upregulated genes were those pertaining to 'PPAR signaling pathway', 'p53 signaling pathway'; RT‑qPCR assay supported the microarray results. The mechanism underlying binaprofen‑induced liver injury was associated with lipid peroxidation and apoptosis. Binaprofen downregulated genes associated with lipid transport and anti‑apoptosis genes, upregulated pro‑apoptosis genes and induces liver cell injury via the mitochondrial signaling pathway.

FMNL2 regulates gliovascular interactions and is associated with vascular risk factors and cerebrovascular pathology in Alzheimer's disease

Alzheimer's disease (AD) has been associated with cardiovascular and cerebrovascular risk factors (CVRFs) during middle age and later and is frequently accompanied by cerebrovascular pathology at death. An interaction between CVRFs and genetic variants might explain the pathogenesis. Genome-wide, gene by CVRF interaction analyses for AD, in 6568 patients and 8101 controls identified FMNL2 (p = 6.6 × 10-7). A significant increase in FMNL2 expression was observed in the brains of patients with brain infarcts and AD pathology and was associated with amyloid and phosphorylated tau deposition. FMNL2 was also prominent in astroglia in AD among those with cerebrovascular pathology. Amyloid toxicity in zebrafish increased fmnl2a expression in astroglia with detachment of astroglial end feet from blood vessels. Knockdown of fmnl2a prevented gliovascular remodeling, reduced microglial activity and enhanced amyloidosis. APP/PS1dE9 AD mice also displayed increased Fmnl2 expression and reduced the gliovascular contacts independent of the gliotic response. Based on this work, we propose that FMNL2 regulates pathology-dependent plasticity of the blood-brain-barrier by controlling gliovascular interactions and stimulating the clearance of extracellular aggregates. Therefore, in AD cerebrovascular risk factors promote cerebrovascular pathology which in turn, interacts with FMNL2 altering the normal astroglial-vascular mechanisms underlying the clearance of amyloid and tau increasing their deposition in brain.

Anesthesia Overdose Versus Rapid Cooling for Euthanasia of Adult Zebrafish

The rapid increase in zebrafish use needs to be accompanied by research into the refinement of procedures. The European (EU) Directive lists three possible euthanasia methods for fish: anesthetic overdose, electrical stunning, and concussion. However, for small fish such as zebrafish, concussion and electrical stunning are difficult to perform, leaving anesthetic overdose as the most used method. Our aim was to test the efficacy and side effects of anesthesia overdose using different anesthetics and the rapid cooling method to euthanize adult zebrafish. Adult mixed-sex AB zebrafish were randomly assigned to: 250 mg/L MS222; 20 mg/L propofol +100 mg/L lidocaine; 6 mg/L etomidate; 50 mg/L clove oil; and rapid cooling (water at 2°C-4°C). Two minutes after opercular movement ceased, animals were transferred into clean water for 20 min and recovery assessed, or decapitated and used for biochemical analysis of the gills, muscle, liver, and brain; for the histological analysis of the gills and muscle; or for the assessment of cortisol levels. No animal recovered; rapid cooling was the quickest and etomidate overdose was the slowest method to cease the opercular movements. There were no major differences between euthanasia methods regarding the biochemical or histological data. Cortisol levels were higher in the rapid cooling group, but only when compared with the propofol/lidocaine group. The use of a physical method of euthanasia, such as rapid cooling, is essential when chemicals, such as anesthetics, may interfere with postmortem analyses. Although anesthetic overdose can be used without major effects on the analyses conducted in this work, rapid cooling can be another option with the advantage of being simple to administer, easily available, affordable, and very quick; this decreases the potential duration of suffering, being more humane. Therefore, a change in EU legislation should be considered to include additional humane options for euthanasia, such as rapid cooling, for zebrafish and other small tropical fish.

Characterization of hormone-producing cell types in the teleost pituitary gland using single-cell RNA-seq

The pituitary is the vertebrate endocrine gland responsible for the production and secretion of several essential peptide hormones. These, in turn, control many aspects of an animal’s physiology and development, including growth, reproduction, homeostasis, metabolism, and stress responses. In teleost fish, each hormone is presumably produced by a specific cell type. However, key details on the regulation of, and communication between these cell types remain to be resolved. We have therefore used single-cell sequencing to generate gene expression profiles for 2592 and 3804 individual cells from the pituitaries of female and male adult medaka (Oryzias latipes), respectively. Based on expression profile clustering, we define 15 and 16 distinct cell types in the female and male pituitary, respectively, of which ten are involved in the production of a single peptide hormone. Collectively, our data provide a high-quality reference for studies on pituitary biology and the regulation of hormone production, both in fish and in vertebrates in general.

Measurement(s)	RNA-seq gene expression profiling assay
Technology Type(s)	tag based single cell RNA sequencing
Factor Type(s)	sex
Sample Characteristic - Organism	Oryzias latipes
Sample Characteristic - Environment	fresh water aquarium

Machine-accessible metadata file describing the reported data: 10.6084/m9.figshare.16592621

Histological Analysis of Gonads in Zebrafish

Zebrafish is an excellent system for the study of gonad development due to available genetic tools and its utilization as a human disease model. The zebrafish serves as an experimental system to model human disorders affecting the reproductive system, toxicological effects on fertility and sexual development, and hormonal regulation of fertility. Forward genetic screens have been used to uncover genetic causes of infertility and reverse genetic approaches have demonstrated that genes involved in germ cell development have similar functions in zebrafish and mammals. The most comprehensive picture of the gonad can be visualized by histology. There are a variety of methods that give excellent histology of zebrafish gonads. Below are methods for two staining approaches for the histology of paraffin-embedded zebrafish gonads.

MS-222 induces biochemical and transcriptional changes related to oxidative stress, cell proliferation and apoptosis in zebrafish embryos

MS-222, the most widely used anaesthetic in fish, has been shown to induce embryotoxic effects in zebrafish. However, the underlying molecular effects are still elusive. This study aimed to investigate the effects of MS-222 exposure during early developmental stages by evaluating biochemical and molecular changes. Embryos were exposed to 50, 100 or 150 mg L^-1 MS-222 for 20 min at one of three developmental stages (256-cell, 50% epiboly, or 1-4 somite stage) and oxidative-stress, cell proliferation and apoptosis-related parameters were determined at two time-points (8 and 26 hpf). Following exposure during the 256-cell stage, the biochemical redox balance was not affected. The genes associated with glutathione homeostasis (gstpi and gclc) were affected at 8 hpf, while genes associated with apoptosis (casp3a and casp6) and cellular proliferation (pcna) were found affected at 26 hpf. An inverted U-shaped response was observed at 8 hpf for catalase activity. After exposure at the 50% epiboly stage, the gclc gene associated with oxidative stress was found upregulated at 8 hpf, while gstpi was downregulated and casp6 was upregulated later on, coinciding with a decrease in glutathione peroxidase (GPx) activity and a non-monotonic elevation of protein carbonyls and casp3a. Additionally, MS-222 treated embryos showed a decrease in DCF-staining at 26 hpf. When exposure was performed at the 1-4 somite stage, a similar DCF-staining pattern was observed. The activity of GPx was also affected whereas RT-qPCR showed that caspase transcripts were dose-dependently increased (casp3a, casp6 and casp9). The pcna mRNA levels were also found to be upregulated while gclc was changed by MS-222. These results highlight the impact of MS-222 on zebrafish embryo development and its interference with the antioxidant, cell proliferation and cellular death systems by mechanisms still to be explained; however, the outcomes point to the Erk/Nrf2 signalling pathway as a target candidate.

Zebrafish as an Animal Model for Ocular Toxicity Testing: A Review of Ocular Anatomy and Functional Assays

Xenobiotics make their way into organisms from diverse sources including diet, medication, and pollution. Our understanding of ocular toxicities from xenobiotics in humans, livestock, and wildlife is growing thanks to laboratory animal models. Anatomy and physiology are conserved among vertebrate eyes, and studies with common mammalian preclinical species (rodent, dog) can predict human ocular toxicity. However, since the eye is susceptible to toxicities that may not involve a histological correlate, and these species rely heavily on smell and hearing to navigate their world, discovering visual deficits can be challenging with traditional animal models. Alternative models capable of identifying functional impacts on vision and requiring minimal amounts of chemical are valuable assets to toxicology. Human and zebrafish eyes are anatomically and functionally similar, and it has been reported that several common human ocular toxicants cause comparable toxicity in zebrafish. Vision develops rapidly in zebrafish; the tiny larvae rely on visual cues as early as 4 days, and behavioral responses to those cues can be monitored in high-throughput fashion. This article describes the comparative anatomy of the zebrafish eye, the notable differences from the mammalian eye, and presents practical applications of this underutilized model for assessment of ocular toxicity.

The effects of aliphatic alcohols and related acid metabolites in zebrafish embryos - correlations with rat developmental toxicity and with effects in advanced life stages in fish

The zebrafish embryo toxicity test (ZFET) is a simple medium-throughput test to inform about (sub)acute lethal effects in embryos. Enhanced analysis through morphological and teratological scoring, and through gene expression analysis, detects developmental effects and the underlying toxicological pathways. Altogether, the ZFET may inform about hazard of chemical exposure for embryonal development in humans, as well as for lethal effects in juvenile and adult fish. In this study, we compared the effects within a series of 12 aliphatic alcohols and related carboxylic acid derivatives (ethanol, acetic acid, 2-methoxyethanol, 2-methoxyacetic acid, 2-butoxyethanol, 2-butoxyacetic acid, 2-hydroxyacetic acid, 2-ethylhexan-1-ol, 2-ethylhexanoic acid, valproic acid, 2-aminoethanol, 2-(2-hydroxyethylamino)ethanol) in ZFET and early life stage (ELS, 28d) exposures, and compared ZFET results with existing results of rat developmental studies and LC50s in adult fish. High correlation scores were observed between compound potencies in ZFET with either ELS, LC50 in fish and developmental toxicity in rats, indicating similar potency ranking among the models. Compounds could be mapped to specific pathways in an adverse outcome pathway (AOP) network through morphological scoring and gene expression analysis in ZFET. Similarity of morphological effects and gene expression profiles in pairs of alcohols with their acid metabolites suggested metabolic activation of the parent alcohols, although with additional, metabolite-independent activity independent for ethanol and 2-ethylhexanol. Overall, phenotypical and gene expression analysis with these compounds indicates that the ZFET can potentially contribute to the AOP for developmental effects in rodents, and to predict toxicity of acute and chronic exposure in advanced life stages in fish.

Neuron-glia interaction through Serotonin-BDNF-NGFR axis enables regenerative neurogenesis in Alzheimer's model of adult zebrafish brain

It was recently suggested that supplying the brain with new neurons could counteract Alzheimer’s disease (AD). This provocative idea requires further testing in experimental models in which the molecular basis of disease-induced neuronal regeneration could be investigated. We previously found that zebrafish stimulates neural stem cell (NSC) plasticity and neurogenesis in AD and could help to understand the mechanisms to be harnessed for developing new neurons in diseased mammalian brains. Here, by performing single-cell transcriptomics, we found that amyloid toxicity-induced interleukin-4 (IL4) promotes NSC proliferation and neurogenesis by suppressing the tryptophan metabolism and reducing the production of serotonin. NSC proliferation was suppressed by serotonin via down-regulation of brain-derived neurotrophic factor (BDNF)-expression in serotonin-responsive periventricular neurons. BDNF enhances NSC plasticity and neurogenesis via nerve growth factor receptor A (NGFRA)/ nuclear factor 'kappa-light-chain-enhancer' of activated B-cells (NFkB) signaling in zebrafish but not in rodents. Collectively, our results suggest a complex neuron-glia interaction that regulates regenerative neurogenesis after AD conditions in zebrafish.

Can regeneration of lost neurons counteract neurodegenerative disease? This study shows that serotonergic neurons alter neural stem cell proliferation and neurogenesis via a complex neuron-glia interaction involving interleukin-4, BDNF and NGF receptor in a zebrafish model of Alzheimer's disease.

"But It's Just a Fish": Understanding the Challenges of Applying the 3Rs in Laboratory Aquariums in the UK

Adopting a social science perspective and qualitative methodology on the problem of laboratory fish welfare, this paper examines some underlying social factors and drivers that influence thinking, priorities and implementation of fish welfare initiatives and the 3Rs (Replacement, Reduction and Refinement) for fish. Drawing on original qualitative interviews with stakeholders, animal technologists and scientists who work with fish-especially zebrafish-to illustrate the case, this paper explores some key social factors influencing the take up of the 3Rs in this context. Our findings suggest the relevance of factors including ambient cultural perceptions of fish, disagreements about the evidence on fish pain and suffering, the discourse of regulators, and the experiences of scientists and animal technologists who develop and put the 3Rs into practice. The discussion is focused on the UK context, although the main themes will be pertinent around the world.

Zebrafish: Housing and husbandry recommendations

This article provides recommendations for the care of laboratory zebrafish (Danio rerio) as part of the further implementation of Annex A to the European Convention on the protection of vertebrate animals used for experimental and other scientific purposes, EU Commission Recommendation 2007/526/EC and the fulfilment of Article 33 of EU Directive 2010/63, both concerning the housing and care of experimental animals. The recommendations provide guidance on best practices and ranges of husbandry parameters within which zebrafish welfare, as well as reproducibility of experimental procedures, are assured.

Husbandry procedures found today in zebrafish facilities are numerous. While the vast majority of these practices are perfectly acceptable in terms of zebrafish physiology and welfare, the reproducibility of experimental results could be improved by further standardisation of husbandry procedures and exchange of husbandry information between laboratories. Standardisation protocols providing ranges of husbandry parameters are likely to be more successful and appropriate than the implementation of a set of fixed guidance values neglecting the empirically successful daily routines of many facilities and will better reflect the wide range of environmental parameters that characterise the natural habitats occupied by zebrafish.

A joint working group on zebrafish housing and husbandry recommendations, with members of the European Society for Fish Models in Biology and Medicine (EUFishBioMed) and of the Federation of European Laboratory Animal Science Associations (FELASA) has been given a mandate to provide guidelines based on a FELASA list of parameters, ‘Terms of Reference’.

10th European Zebrafish Meeting 2017, Budapest: Husbandry Workshop Summary

A husbandry workshop on July 3, 2017, at the 10th European Zebrafish Meeting in Budapest, Hungary (July 3-July 7, 2017), focused on the standardization, optimization, and streamlining of fish facility procedures. Standardization can be achieved for example by developing novel software and hardware tools, such as a fish facility database for husbandry and environmental facility management (Zebrabase, Oltova), or a hand-held, air-pressurized fish feeder for consistent food distribution (Blowfish, Argenton). Streamlining is achieved when work hours are reduced, as with the standardized fish feeder, or by limiting the number and types of fish diets and observing the effect on animal welfare and performance (Barton). Testing the characteristics of new fish diets and observing whether they produce better experimental outcomes (Certal) optimizes diets and improves fish productivity. Collectively, the workshop presentations emphasized how consistency and harmonization of husbandry procedures within and across aquatic facilities yield reproducible scientific outcomes.