Concentration dependent transcriptome responses of zebrafish embryos after exposure to cadmium, cobalt and copper

Cadmium impacts on calcium mineralization of zebrafish skeletal development and behavioral impairment

Cadmium (Cd) poses significant risks to aquatic organisms due to its toxicity and ability to disrupt the cellular processes. Given the similar atomic radius of Cd and calcium (Ca), Cd may potentially affect the Ca homeostasis, which can lead to impaired mineralization of skeletal structures and behavioral abnormalities. The formation of the spinal skeleton involves Ca transport and mineralization. In this study, we conducted an in-depth investigation on the effects of Cd at environmental concentrations on zebrafish (Danio rerio) skeletal development and the underlying molecular mechanisms. As the concentration of Cd increased, the accumulation of Cd in zebrafish larvae also rose, while the Ca content decreased significantly by 3.0 %-57.3 %, and vertebral deformities were observed. Transcriptomics analysis revealed that sixteen genes involved in metal absorption were affected. Exposure to 2 µg/L Cd significantly upregulated the expression of these genes, whereas exposure to 10 µg/L resulted in their downregulation. Consequently, exposure of zebrafish larvae to 10 µg/L of Cd inhibited the body segmentation growth and skeletal mineralization development by 29.1 %-56.7 %. This inhibition was evidenced by the downregulation of mineral absorption genes and decreased Ca accumulation. The findings of this study suggested that the inhibition of skeletal mineralization was likely attributed to the disruption of mineral absorption, thus providing novel insights into the mechanisms by which metal pollutants inhibit the skeletal development of fish.

Functionalized TiCu/TiCuN coating promotes osteoporotic fracture healing by upregulating the Wnt/β-catenin pathway

Osteoporosis results in decreased bone mass and insufficient osteogenic function. Existing titanium alloy implants have insufficient osteoinductivity and delayed/incomplete fracture union can occur when used to treat osteoporotic fractures. Copper ions have good osteogenic activity, but their dose-dependent cytotoxicity limits their clinical use for bone implants. In this study, titanium alloy implants functionalized with a TiCu/TiCuN coating by arc ion plating achieved a controlled release of copper ions in vitro for 28 days. The coated alloy was co-cultured with bone marrow mesenchymal stem cells and showed excellent biocompatibility and osteoinductivity in vitro. A further exploration of the underlying mechanism by quantitative real-time polymerase chain reaction and western blotting revealed that the enhancement effects are related to the upregulation of genes and proteins (such as axin2, β-catenin, GSK-3β, p-GSK-3β, LEF1 and TCF1/TCF7) involved in the Wnt/β-catenin pathway. In vivo experiments showed that the TiCu/TiCuN coating significantly promoted osteoporotic fracture healing in a rat femur fracture model, and has good in vivo biocompatibility based on various staining results. Our study confirmed that TiCu/TiCuN-coated Ti promotes osteoporotic fracture healing associated with the Wnt pathway. Because the coating effectively accelerates the healing of osteoporotic fractures and improves bone quality, it has significant clinical application prospects.

Zebrafish Heme Oxygenase 1a Is Necessary for Normal Development and Macrophage Migration

Heme oxygenase function is highly conserved between vertebrates where it plays important roles in normal embryonic development and controls oxidative stress. Expression of the zebrafish heme oxygenase 1 genes is known to be responsive to oxidative stress suggesting a conserved physiological function. In this study, we generate a knockout allele of zebrafish hmox1a and characterize the effects of hmox1a and hmox1b loss on embryonic development. We find that loss of hmox1a or hmox1b causes developmental defects in only a minority of embryos, in contrast to Hmox1 gene deletions in mice that cause loss of most embryos. Using a tail wound inflammation assay we find a conserved role for hmox1a, but not hmox1b, in normal macrophage migration to the wound site. Together our results indicate that zebrafish hmox1a has clearly a partitioned role from hmox1b that is more consistent with conserved functions of mammalian Heme oxygenase 1.

Advantages of omics technology for evaluating cadmium toxicity in zebrafish

In the last decade, several advancements have been made in omics technologies and they have been applied extensively in diverse research areas. Especially in toxicological research, omics technology can efficiently and accurately generate relevant data on the molecular dynamics associated with adverse outcomes. Toxicomics is defined as the combination of toxicology and omics technologies and encompasses toxicogenomics, toxicoproteomics, and toxicometabolomics. This paper reviews the trend of applying omics technologies to evaluate cadmium (Cd) toxicity in zebrafish (D. rerio). Cd is a toxic heavy metal posing several environmental concerns; however, it is being used widely in everyday life. Zebrafish embryos and larvae are employed as standard models for many toxicity tests because they share 71.4% genetic homology with humans. This study summarizes the toxicity of Cd on the nerves, liver, heart, skeleton, etc. of zebrafish and introduces detailed omics techniques to understand the results of the toxicomic studies. Finally, the trend of toxicity evaluation in the zebrafish model of Cd based on omics technology is presented.

Evaluation of the hair cell regeneration and claudin b and phoenix gene expression during exposure to low concentrations of cadmium and zinc in early developing zebrafish larvae

Zebrafish possess hair cells on the body surface similar to that of mammals inner hear, in particular in the neuromasts, and due to its ability in regenerating damaged hair cells, is regularly used as a powerful animal model to study in vivo cytotoxicity. Among the factors leading to hair cell disruption, metal ions are of particular concern since they are important environmental pollutants. To date, several studies on zebrafish hair cell regeneration after metal exposure exist, while no data on regeneration during continuous metal exposure are available. In the present study, neuromast hair cell disruption and regeneration were assessed in zebrafish larvae for the first time during zinc (Zn) and cadmium (Cd) continuous exposure and a visual and molecular approach was adopted. Fluorescent vital dye DASPEI was used to assess hair cell regeneration and the gene expression of claudin b (cldnb) and phoenix (pho), was analyzed. Metallotionein-2 (mt2) gene expression was used as standard molecular marker of metal toxicity and confirmed the higher toxicity of Cd compared to Zn. In addition, Cd caused a delay in hair cell regeneration compared to Zn. Molecular analysis showed cldnb gene expression increased in relation to the metal concentrations used, confirming the involvement of this gene in hair cell regeneration. On the contrary, a dramatic decrease of pho gene expression was observed in Cd exposed groups, suggesting a negative impact of Cd on pho expression, thus negatively interfering with hair cell regeneration in zebrafish larvae exposed to this metal.

Mathematical model of transmembrane potential dynamics of loach early embryogenesis

Heavy metals in the water environment are known to have a negative effect on the viability of fish in early development. We have discussed the influence of environmental factors on early embryo development from the viewpoint of the correlation adaptometry method. The analysis of time series with the subsequent construction of a mathematical model was used to determine the change in the greatest effect of certain types of ions on the values of the transmembrane potential for prognostic purposes. The membrane potential is accepted as an integral indicator of the state of the embryos. Structures of five elements of the same type were constructed for the time shifts from 0 to 180 minutes. Each element in the system characterizes the value of the transmembrane potential that was measured in a cell incubated in one of the five solutions during early embryo development. Mathematical models describing the cell membrane potential dynamics have been created and studied. It was noted that the transmembrane potential dynamics of embryo cells is dependent on a change in the value of the correlation coefficient between elements of the system. A decrease in the sum of the correlations between individual elements of the system with an increase in the magnitude of the time shift is established. The results of the numerical solutions of the system equations indicated the sequence of changes in the greatest effect of the incubation medium on the value of the membrane potential in cells. The study of the membrane potentials’ dynamics, using the total values of the strength of correlation, confirmed the influence of heavy metals in the incubation medium on the membrane potential of embryo cell in early development.

NOD-like receptor signaling pathway activation: A potential mechanism underlying negative effects of benzo(α)pyrene on zebrafish

Benzo(α)pyrene (BaP) is one of typical polycyclic aromatic hydrocarbons (PAHs) in aquatic environments and has been shown to cause toxic effects to aquatic animals. Although the negative effects of BaP have been investigated, the potential toxic mechanisms remain uncharacterized. To explore the potential mechanisms mediating the toxic effects of BaP, zebrafish (Danio rerio) were exposed to BaP for 15 days and the toxic effects of BaP in zebrafish liver were investigated using physiological and transcriptomic analyses. After 15-day BaP exposure, zebrafish liver exhibited abnormalities including increased cytoplasmic vacuolation, inflammatory cell infiltration, swelled nuclei and irregular pigmentation. BaP exposure also induced oxidative stress to the liver of zebrafish. Transcriptomic profiles revealed 5129 differentially expressed genes (DEGs) after 15-days of BaP exposure, and the vast majority of DEGs were up-regulated under BaP treatment. Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) analyses suggest that genes related to immune response were significantly dysregulated. Furthermore, the nucleotide-binding, oligomerization domain (NOD)-like receptor signaling pathway was significantly enriched and most of the genes in this pathway exhibited enhanced expression after BaP exposure. These results partially explained the mechanisms underlying the toxic effects of BaP on zebrafish liver. In conclusion, BaP has the potential to induce physiological responses in zebrafish liver through altering associated genes.

Parental exposure to cadmium chloride causes developmental toxicity and thyroid endocrine disruption in zebrafish offspring

Cadmium is a common heavy metal pollutant. Previous studies have found that long-term cadmium exposure can cause damage to multiple organs/systems in humans and experimental animals; however, there are few studies that elucidate its effects on offspring development, discuss whether it can be transmitted to offspring from the parent, and debate whether it affects the functional development of the thyroid hormone system in offsprings. In this study, sexually mature zebrafish were exposed to different concentrations of cadmium chloride (0.01 μmol/L, 0.1 μmol/L, and 1 μmol/L) to study reproductive toxicity. It was found that parental zebrafish exposed to 1 μmol/L of cadmium chloride produced offsprings with different degrees of malformation. At 5 days post-fertilization (dpf), the levels of 3,5,3'-triiododenosine (T3) and thyroxine (T4) in the zebrafish were decreased. At 10 dpf, the T4 and T3 levels in the zebrafish of the offspring were significantly reduced. At the same time, the expression of thyroid receptor (trα and trβ) genes in five dpf larvae was significantly up-regulated in the 1 μmol/L treatment group relative to the control group. The mRNAs of thyroid hormone synthesis and metabolism-related genes (tshβ, dio1, dio2, ugt1ab, and ttr) were significantly up-regulated in the 0.1 μmol/L and 1 μmol/L treatment groups. This study demonstrates that parental cadmium chloride exposure produces reproductive toxicity in zebrafish and that the effects can be transferred from the parent to the offspring, resulting in developmental toxicity in the thyroid endocrine system.

Exposure to cadmium causes inhibition of otolith development and behavioral impairment in zebrafish larvae

Otolith consisting largely of calcium carbonate, fibrous and proteins, is vital for maintaining body balance and/or hearing of fish. The formation of otolith involves Ca²⁺ transport and deposition. In the present study, we investigated the effects of Cd²⁺ on otoliths development by using zebrafish embryos as model. The results showed that exposure to Cd²⁺ inhibited the utricular and saccular otoliths growth, indicated by reduced lateral areas. Swimming speeds were reduced and a losing balance control was observed in Cd²⁺ exposed larvae. The genes related to Ca²⁺ transport (e.g. plasma membrane Ca²⁺-ATPase isoform 2, pmca2; Ca²⁺-ATPase isoform 2, atp2b1a) and regulation (e.g. parathyroid hormone ligand type-1, pth1; stanniocalcin isoform 1, stc1) were significantly downregulated. However, the adverse effects of Cd²⁺ on otoliths growth and swimming activity can be protected by supplementation of Ca²⁺ in exposure medium. Body burden of Cd²⁺ in larvae was reduced upon the supplement with Ca²⁺. The overall results suggest that exposure to Cd²⁺ can inhibit influx of Ca²⁺, leading to less deposition of CaCO₃ for otolith growth, and finally result in impaired balance control and swimming activity in zebrafish larvae.

Map and model-moving from observation to prediction in toxicogenomics

BACKGROUND

Chemicals induce compound-specific changes in the transcriptome of an organism (toxicogenomic fingerprints). This provides potential insights about the cellular or physiological responses to chemical exposure and adverse effects, which is needed in assessment of chemical-related hazards or environmental health. In this regard, comparison or connection of different experiments becomes important when interpreting toxicogenomic experiments. Owing to lack of capturing response dynamics, comparability is often limited. In this study, we aim to overcome these constraints.

RESULTS

We developed an experimental design and bioinformatic analysis strategy to infer time- and concentration-resolved toxicogenomic fingerprints. We projected the fingerprints to a universal coordinate system (toxicogenomic universe) based on a self-organizing map of toxicogenomic data retrieved from public databases. Genes clustering together in regions of the map indicate functional relation due to co-expression under chemical exposure. To allow for quantitative description and extrapolation of the gene expression responses we developed a time- and concentration-dependent regression model. We applied the analysis strategy in a microarray case study exposing zebrafish embryos to 3 selected model compounds including 2 cyclooxygenase inhibitors. After identification of key responses in the transcriptome we could compare and characterize their association to developmental, toxicokinetic, and toxicodynamic processes using the parameter estimates for affected gene clusters. Furthermore, we discuss an association of toxicogenomic effects with measured internal concentrations.

CONCLUSIONS

The design and analysis pipeline described here could serve as a blueprint for creating comparable toxicogenomic fingerprints of chemicals. It integrates, aggregates, and models time- and concentration-resolved toxicogenomic data.