Screening on the differentially expressed miRNAs in zebrafish (Danio rerio) exposed to trace β-diketone antibiotics and their related functions

Analysis of key circRNA events in the AOP framework of TCS acting on zebrafish based on the data-driven

Triclosan (TCS) is a broad-spectrum antibiotic widely used in various personal care products. Research has found that exposure to TCS can cause toxic effects on organisms including neurotoxicity, cardiotoxicity, disorders of lipid metabolism, and abnormal vascular development, and the corresponding toxic mechanisms are gradually delving into the level of abnormal expression of miRNA regulating gene expression. Although the downstream mechanism of TCS targeting miRNA abnormal expression to induce toxicity is gradually improving, its upstream mechanism is still in a fog. Starting from the abnormal expression data of circRNA in zebrafish larvae induced by TCS, this study conducted a hierarchical analysis of the expression levels of all circRNAs, differential circRNAs, and trend circRNAs, and identified 29 key circRNA events regulating miRNA abnormal expression. In combination with GO and KEGG, the effects of TCS exposure were analyzed from the function and signaling pathway of the corresponding circRNA host gene. Furthermore, based on existing literature evidence about the biological toxicity induced by TCS targeting miRNA as data support, a competing endogenous RNAs (ceRNA) network characterizing the regulatory relationship between circRNA and miRNA was constructed and optimized. Finally, a comprehensive Adverse Outcome Pathway (AOP) framework of multiple levels of events including circRNA, miRNA, mRNA, pathway, and toxicity endpoints was established to systematically elucidate the toxic mechanism of TCS. Moreover, the rationality of the AOP framework was verified from the expression level of miRNA and adverse outcomes such as neurotoxicity, cardiotoxicity, oxidative stress, and inflammatory response by knockdown of circRNA48. This paper not only provides the key circRNA events for exploring the upstream mechanism of miRNA regulating gene expression but also provides an AOP framework for comprehensively demonstrating the toxicity mechanism of TCS on zebrafish, which is a theoretical basis for subsequent hazard assessment and prevention and control of TCS.

Silver nanoparticles induce liver inflammation through ferroptosis in zebrafish

As the most widely employed artificial nanomaterials, silver nanoparticles (AgNPs) have been implicated in oxidative stress-induced liver injury. Despite these observations, the precise mechanisms underpinning AgNPs-induced hepatotoxicity have yet to be fully elucidated. This study embarked on an intersectional analysis of the GEO dataset (GSE139560), which encompassed murine liver tissues subjected to AgNPs, alongside datasets related to ferroptosis. Through this approach, three pivotal ferroptosis-associated genes (Arrdc3, Txnip, and Egfr) were identified. Further integration with disease model analysis from GSE111407 and GSE183158 unveiled a significant association between AgNPs exposure and alterations in glucose metabolism and insulin signaling pathways, intricately linked with the identified key ferroptosis genes. This correlation fostered the hypothesis that ferroptosis significantly contributed to the hepatotoxicity triggered by AgNPs. Subsequent Gene Set Enrichment Analysis (GSEA) pointed to the activation of ferroptosis-associated pathways, specifically MAPK and PPAR, under AgNPs exposure. Examination of the miRNA-mRNA interaction network revealed co-regulated upstream miRNAs targeting these pivotal genes, establishing a nexus to ferroptosis and heightened liver susceptibility. Experimental validation employing an adult zebrafish model exposed to AgNPs from 90 to 120 dpf demonstrated elevated levels of Fe2+ and MDA in the zebrafish livers, along with conspicuous mitochondrial morphological alterations, thereby reinforcing the notion that AgNPs precipitate liver dysfunction predominantly through the induction of ferroptosis. These insights collectively underscore the role of ferroptosis in mediating the adverse effects of AgNPs on liver glucose metabolism and insulin sensitivity, culminating in liver dysfunction. Overall, these results enhance the understanding of nanomaterial-induced hepatotoxicity and inform strategies to mitigate such health risks.

Comparative impact of pristine and aged microplastics with triclosan on lipid metabolism in larval zebrafish: Unveiling the regulatory role of miR-217

The prevalence of microplastics (MPs), especially aged particles, interacting with contaminants like triclosan (TCS), raises concerns about their toxicological effects on aquatic life. This study focused on the impact of aged polyamide (APA) MPs and TCS on zebrafish lipid metabolism. APA MPs, with rougher surfaces and lower hydrophobicity, exhibited reduced TCS adsorption than unaged polyamide (PA) MPs. Co-exposure to PA/APA MPs and TCS resulted in higher TCS accumulation in zebrafish larvae, notably more with PA than APA. Larvae exposed to PA + TCS exhibited greater oxidative stress, disrupted lipid metabolism, and altered insulin pathway genes than those exposed to TCS. However, these negative effects were lessened in the APA + TCS group. Through miRNA-seq and miR-217 microinjection, it was revealed that PA + TCS co-exposure upregulated miR-217, linked to lipid metabolic disorders in zebrafish. Moreover, molecular docking showed stable interactions formed between PA, TCS, and the insulin signaling protein Pik3r2. This study demonstrated that PA and TCS co-exposure significantly inhibited the insulin signaling in zebrafish, triggering lipid metabolism dysregulation mediated by miR-217 upregulation, while APA and TCS co-exposure alleviated these disruptions. This research underscored the ecological and toxicological risks of aged MPs and pollutants in aquatic environments, providing crucial insights into the wider implications of MPs pollution.

Neurotoxic effects of 2-ethylhexyl diphenyl phosphate exposure on zebrafish larvae: Insight into inflammation-driven changes in early motor behavior

The extensive utilization and potential adverse impacts of the replacement flame-retardant 2-Ethylhexyl Diphenyl Phosphate (EHDPP) have raised concerns. Currently, there is limited knowledge regarding the developmental, neurological, and immunotoxic consequences of EHDPP exposure, as well as its potential behavioral outcomes. In this study, we undertook a comprehensive examination and characterization of the toxic effects over the EHDPP concentration range of 14-1400 nM. Our findings unveiled that EHDPP, even at an environmentally relevant concentration of 14 nM, exhibited excitatory neurotoxicity, eliciting a 13.5 % increase in the swimming speed of zebrafish larvae. This effect might be attributed to the potential influence of EHDPP on the release of neurotransmitters like serotonin and dopamine, which, in turn, mediated anxiety-like behavior in the zebrafish larvae. Conversely, sublethal dose EHDPP (1400 nM) exposure significantly suppressed the swimming vigor of zebrafish larvae, accompanied by morphological changes, abnormal behaviors, and alterations in intracerebral molecules. Transcriptomics revealed the underlying mechanism. The utilization of pathway inhibitors reshaped the inflammatory homeostasis and alleviated the toxicity induced by EHDPP exposure, anchoring the pivotal role played by the TLR4/NF-κB signaling pathway in EHDPP-induced adverse changes in zebrafish behavior and neurophysiology. This study observed the detrimental effects of EHDPP on fish sustainability at environmentally relevant concentrations, highlighting the practical significance for EHDPP risk management. Elucidating the toxic mechanisms of EHDPP will contribute to a deeper comprehension of how environmental pollutants can intricately influence human health.

Azithromycin induces neurotoxicity in zebrafish by interfering with the VEGF/Notch signaling pathway

Azithromycin (AZM) is a widely used antibiotic in both human and veterinary medicine, and its use has significantly increased during the COVID-19 pandemic. However, potential adverse effects of AZM on aquatic organisms have not been well studied. In this study, we explored the neurotoxicity of AZM in zebrafish and delved into its underlying mechanisms. Our results showed that AZM exposure resulted in a spectrum of detrimental effects in zebrafish, encompassing abnormal behaviors, damaged neuronal development, aberrant lateral line nervous system development, vascular malformations and perturbed expression of genes related to neural development. Moreover, we observed a concentration-dependent exacerbation of these neurotoxic manifestations with increasing AZM concentrations. Notably, AZM induced excessive cell apoptosis and oxidative stress damage. In addition, alterations in the expression levels of the genes involved in the VEGF/Notch signaling pathway were evident in AZM-exposed zebrafish. Consequently, we hypothesize that AZM may induce neurotoxicity by influencing the VEGF/Notch signaling pathway. To validate this hypothesis, we introduced a VEGF signaling inhibitor, axitinib, and a Notch signaling agonist, valproic acid, alongside AZM exposure. Remarkably, the administration of these rescue compounds significantly mitigated the neurotoxic effects induced by AZM. This dual verification provides compelling evidence that AZM indeed induces neurotoxicity during the early developmental stages of zebrafish, primarily through its interference with the VEGF/Notch pathway. Innovatively, our study reveals the molecular mechanism of AZM-induced neurotoxicity from the perspective of the close connection between blood vessels and nervous system. These findings provide new insights into the potential mechanisms underlying the neurotoxic effect of antibiotics and highlight the need for further investigation into the ecotoxicological effects of antibiotics on aquatic organisms and the potential risks to human health.

Mechanisms regarding cardiac toxicity triggered by up-regulation of miR-144 in larval zebrafish upon exposure to triclosan

Although triclosan (TCS) is ubiquitously detected in environmental media and organisms, little information is available on its cardiotoxicity and underlying mechanisms. Herein, acute TCS exposure (0.69-1.73 μM) to zebrafish from embryos (6 hpf) to larvae (72 hpf) resulted in cardiac development defects, including increased angle between atrium and ventricle, prolonged SV-BA distance, linearized heart and pericardial cyst in 72-hpf larvae. These malformations resulted from interfered oxidative-stress pathways, reflecting in accumulated ROS and MDA and inhibited SOD and CAT activities. By RT-qPCR, the transcription levels of four cardiac development-related marker genes were significantly up-regulated except for gata4. Besides, miR-144 was identified as a regulatory molecule of TCS-induced cardiac defects by integrating analyses of artificial intervene expression and RNA-Seq data. Interestingly, the target genes of miR-144 were found and interacted with the above marker genes through constructing protein-protein interaction networks. After intervening the expression of miR-144 by microinjecting and activating Wnt pathway by an agonist BML-284, we confirmed that up-regulated miR-144 suppressed the expression of angiogenesis-related genes and negatively regulated Wnt pathway, further triggering angiogenesis disorders and cardiac phenotypic malformation. These findings unravel the underlying molecular mechanisms regarding TCS-induced cardiac development toxicity, and contribute to early warning and risk management of TCS.

Understanding CNS Effects of Antimicrobial Drugs Using Zebrafish Models

Antimicrobial drugs represent a diverse group of widely utilized antibiotic, antifungal, antiparasitic and antiviral agents. Their growing use and clinical importance necessitate our improved understanding of physiological effects of antimicrobial drugs, including their potential effects on the central nervous system (CNS), at molecular, cellular, and behavioral levels. In addition, antimicrobial drugs can alter the composition of gut microbiota, and hence affect the gut-microbiota-brain axis, further modulating brain and behavioral processes. Complementing rodent studies, the zebrafish (Danio rerio) emerges as a powerful model system for screening various antimicrobial drugs, including probing their putative CNS effects. Here, we critically discuss recent evidence on the effects of antimicrobial drugs on brain and behavior in zebrafish, and outline future related lines of research using this aquatic model organism.

Toxicity mechanisms regulating bone differentiation and development defects following abnormal expressions of miR-30c targeted by triclosan in zebrafish

As a ubiquitous environmental estrogen-disrupting chemical, triclosan (TCS) can induce severe osteotoxicity; however, the underlying molecular mechanisms remain uncertain. Herein, we evaluated the toxic effects of TCS on the development of cartilage and osteogenesis in 5-dpf zebrafish. Under TCS exposure from 62.5 to 250 μg/L, several osteodevelopmental malformations were observed, such as defect of craniofacial cartilage, pharyngeal arch cartilage dysplasia, and impairments on skeletal mineralization. Further, the morphology of mature chondrocytes became swollen and deformed, their number decreased, nucleus displacement occurred, and most immature chondrocytes were crowded at both ends of ceratobranchial. SEM observation of larval caudal fin revealed that, the layer of collagen fibers and the mineralized calcium nodules were significantly decreased, with the collagen fibers becoming shorter upon TCS exposure. The activity of bone-derived alkaline phosphatase significantly reduced, and marker functional genes related to cartilage and osteoblast development were abnormally expressed. RNA-seq and bioinformatics analysis indicated, that changes in marker genes intimately related to the negative regulation of miR-30c-5p overexpression targeted by TCS, and the up-regulation of miR-30c induced bone developmental defects by inhibiting the bone morphogenetic protein (BMP) signaling pathway. These findings were confirmed by artificially intervening the expression of miR-30c and using BMP pathway agonists in vivo. In sum, TCS induced osteototoxicity by targeting miR-30c up-regulation and interfering in the BMP signaling pathway. These findings enhance mechanistic understanding of TCS-induced spontaneous bone disorders and bone metastatic diseases. Further research is necessary to monitor chronic TCS-exposure levels in surrounding environments and develop relevant safety precautions based on TCS environmental risk.

Triclosan targets miR-144 abnormal expression to induce neurodevelopmental toxicity mediated by activating PKC/MAPK signaling pathway

Although the previous research confirmed that triclosan (TCS) induced an estrogen effect by acting on a novel G-protein coupled estrogen-membrane receptor (GPER), the underlying mechanisms by which downstream pathways induce neurotoxicity remain unclear after TCS activation of GPER. By employing a series of techniques (Illumina miRNA-seq, RT-qPCR, and artificial intervention of miRNA expression), we screened out four important miRNAs, whose target genes were directly/indirectly involved in neurodevelopment and neurobehavior. Especially, the miR-144 up-regulation caused vascular malformation and severely affected hair-cell development and lateral-line-neuromast formation, thereby causing abnormal motor behavior. After microinjecting 1-2-cell embryos, the similar phenotypic malformations as those induced by TCS were observed, including aberrant neuromast, cuticular-plate development and motor behavior. By KEGG pathway enrichment analysis, these target genes were demonstrated to be mainly related to the PKC/MAPK signaling pathway. When a PKC inhibitor was used to suppress the PKC/MAPK pathway, a substantial alleviation of TCS-induced neurotoxicity was observed. Therefore, TCS acts on GPER to activate the downstream PKC/MAPK signaling pathway, further up-regulating miR-144 expression and causing abnormal modulation of these nerve-related genes to trigger neurodevelopmental toxicity. These findings unravel the molecular mechanisms of TCS-induced neurodegenerative diseases, and offer theoretical guidance for TCS-pollution early warning and management.

Triclosan induced zebrafish immunotoxicity by targeting miR-19a and its gene socs3b to activate IL-6/STAT3 signaling pathway

As a broad-spectrum antibacterial agent, triclosan (TCS) has been confirmed to possess potential immunotoxicity to organisms, but the underlying mechanisms remains unclear. Herein, with the aid of transgenic zebrafish strains Tg (coro1A: EGFP) and Tg (rag2: DsRed), we intuitively observed acute TCS exposure caused the drastic differentiation, abnormal development and distribution of innate immune cells, as well as barriers to formation of adaptive immune T cells. These abnormalities implied occurrence of the cytokine storm, which was further evidenced by expression changes of immune-related genes, and functional biomarkers. Based on transcriptome deep sequencing, target gene prediction and dual luciferase validation, the highly conservative and up-regulated miR-19a was chosen as the research target. Under TCS exposure, miR-19a up-regulation triggered down-regulation of its target gene socs3b, and simultaneously activated the downstream IL-6/STAT3 signaling pathway. Artificial over-expression and knock-down of miR-19a was realized by microinjecting agomir and antagomir, respectively, in 1-2-cell embryos. The miR-19a up-regulation inhibited socs3b expression to activate IL-6/STAT3 pathway, and yielded abnormal changes in the functional cytokine biomarkers, along with the sharp activation of immune responses. These findings disclose the molecular mechanisms regarding TCS-induced immunotoxicity, and offer important theoretical guidance for healthy safety evaluation and disease early warning from TCS pollution.

Integrated Analysis of mRNA- and miRNA-Seq in the Ovary of Rare Minnow Gobiocypris rarus in Response to 17α-Methyltestosterone

17α-Methyltestosterone (MT) is a synthetic androgen. The objective of this study was to explore the effects of exogenous MT on the growth and gonadal development of female rare minnow Gobiocypris rarus. Female G. rarus groups were exposed to 25–100 ng/L of MT for 7 days. After exposure for 7 days, the total weight and body length were significantly decreased in the 50-ng/L MT groups. The major oocytes in the ovaries of the control group were vitellogenic oocytes (Voc) and cortical alveolus stage oocytes (Coc). In the MT exposure groups, some fish had mature ovaries with a relatively lower proportion of mature oocytes, and the diameter of the perinucleolar oocytes (Poc) was decreased compared with those of the control group. Ovarian VTG, FSH, LH, 11-KT, E2, and T were significantly increased after exposure to 50 ng/L of MT for 7 days. Unigenes (73,449), 24 known mature microRNAs (miRNAs), and 897 novel miRNAs in the gonads of G. rarus were found using high-throughput sequencing. Six mature miRNAs (miR-19, miR-183, miR-203, miR-204, miR-205, and miR-96) as well as six differentially expressed genes (fabp3, mfap4, abca1, foxo3, tgfb1, and zfp36l1) that may be associated with ovarian development and innate immune response were assayed using qPCR. Furthermore, the miR-183 cluster and miR-203 were differentially expressed in MT-exposed ovaries of the different G. rarus groups. This study provides some information about the role of miRNA–mRNA pairs in the regulation of ovarian development and innate immune system, which will facilitate future studies of the miRNA–RNA-associated regulation of teleost reproduction.

Zebrafish as a Screening Model to Study the Single and Joint Effects of Antibiotics

The overuse of antibiotics combined with the limitation of wastewater facilities has resulted in drug residue accumulation in the natural environment. Thus, in recent years, the presence of antibiotic residues in the environment has raised concerns over the potential harmful effects on ecosystems and human health. The in vivo studies represent an essential step to study the potential impact induced by pharmaceutical exposure. Due to the limitations of traditional vertebrate model systems, zebrafish (Danio rerio) has recently emerged as a promising animal model to study the toxic effects of drugs and their therapeutic efficacy. The present review summarizes the recent advances made on the toxicity of seven representative classes of antibiotics, namely aminoglycosides, β-lactams, macrolides, quinolones, sulfonamides, tetracyclines and polyether antibiotics, in zebrafish, as well as the combined effects of antibiotic mixtures, to date. Despite a significant amount of the literature describing the impact of single antibiotic exposure, little information exists on the effects of antibiotic mixtures using zebrafish as an animal model. Most of the research papers on this topic have focused on antibiotic toxicity in zebrafish across different developmental stages rather than on their efficacy assessment.

Zebrafish (Danio rerio) as an excellent vertebrate model for the development, reproductive, cardiovascular, and neural and ocular development toxicity study of hazardous chemicals

In the past decades, the type of chemicals has gradually increased all over the world, and many of these chemicals may have a potentially toxic effect on human health. The zebrafish, as an excellent vertebrate model, is increasingly used for assessing chemical toxicity and safety. This review summarizes the efficacy of zebrafish as a model for the study of developmental toxicity, reproductive toxicity, cardiovascular toxicity, neurodevelopmental toxicity, and ocular developmental toxicity of hazardous chemicals, and the transgenic zebrafish as biosensors are used to detect the environmental pollutants.

Risk assessment of cardiotoxicity to zebrafish (Danio rerio) by environmental exposure to triclosan and its derivatives

Triclosan (TCS) and its two derivatives (2,4-dichlorophenol and 2,4,6-trichlorophenol) are priority pollutants that coexist in aquatic environments. Joint exposure of TCS, 2,4-dichlorophenol and 2,4,6-trichlorophenol, hereafter referred to as TCS-DT, contributes severe toxicity to aquatic organisms. There is currently a paucity of data regarding TCS-DT molecular toxicity, especially on cardiac diseases. We used zebrafish (Danio rerio) as a model organism, and evaluated the molecular-level cardiotoxicity induced by TCS-DT from embryonic to adult stages. TCS-DT exposure prominently led to phenotypic malformations, such as pericardial cysts, cardiac bleeding, increased SV-BA distance, decreased heart rate and reduced ejection fraction, as well as abnormal swimming behavior. Analyses of the GO and KEGG pathways revealed enrichment pathways related to cardiac development and screened for significantly down-regulated adrenaline signaling in cardiomyocytes. The cardiac marker genes (amhc, cmlc2, vmhc, and nkx2.5) were obtained through protein-protein interaction (PPI) networks, and expressed as down-regulation by WISH. After chronic exposure to TCS-DT from 30 to 90-dpf, both body mass and heart indexes prominently increased, showing myocardial hypertrophy, abnormal heart rate and histopathological injury. Heart tissue damage included disordered and ruptured myocardial fibers, broken and dissolved myofilaments, nuclear pyknosis, mitochondrial injury and inflammatory cell infiltration. Further, abnormal changes in a series of cardiac functions-related biomarkers, including superoxide dismutase, triglyceride, lactate dehydrogenase and creatinine kinase MB, provided evidence for cardiac pathological responses. These results highlight the molecular mechanisms involving TCS-DT induced cardiac toxicity, and provide theoretical data to guide prevention and treatment of pollutant-induced cardiac diseases.

Zebrafish as an integrative vertebrate model to identify miRNA mechanisms regulating toxicity

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Zebrafish are an established vertebrate model for toxicity studies.

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Zebrafish have a fully sequenced genome and the capability to create genetic models.

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Zebrafish have over 80 % homology for genes related to human disease.

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Functions of miRNAs in the zebrafish genome are being characterized.

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Zebrafish are ideal for mechanistic studies on how miRNAs regulate toxicity.

Zebrafish (Danio rerio) are an integrative vertebrate model ideal for toxicity studies. The zebrafish genome is sequenced with detailed characterization of all life stages. With their genetic similarity to humans, zebrafish models are established to study biological processes including development and disease mechanisms for translation to human health. The zebrafish genome, similar to other eukaryotic organisms, contains microRNAs (miRNAs) which function along with other epigenetic mechanisms to regulate gene expression. Studies have now established that exposure to toxins and xenobiotics can change miRNA expression profiles resulting in various physiological and behavioral alterations. In this review, we cover the intersection of miRNA alterations from toxin or xenobiotic exposure with a focus on studies using the zebrafish model system to identify miRNA mechanisms regulating toxicity. Studies to date have addressed exposures to toxins, particulate matter and nanoparticles, various environmental contaminants including pesticides, ethanol, and pharmaceuticals. Current limitations of the completed studies and future directions for this research area are discussed.

Effects of miR-181a-5p abnormal expression on zebrafish (Danio rerio) vascular development following triclosan exposure

Triclosan (TCS), one of the important bactericides, is widely used in personal care products, and its chronic exposure leads to severe toxic effects on the growth and development of blood vessels in zebrafish (Danio rerio). Herein, we screened out three differentially expressed miRNAs (miR-181a-5p, miR-132-3p and miR-128-3p) by sequencing and qRT-PCR analyses of 4-96-hpf TCS-exposed zebrafish, among which miR-181a-5p was found to regulate many signaling pathways involved in fatty acid biosynthesis and phosphatidylimositol signaling systems. By O-dianisidine staining, TCS-exposure resulted in decreased distribution of red blood cells and induced blood hypercoagulable state and thrombotic effects. Defective subintestinal veins (SIVs), and decreased branching and curvature of blood vessels were observed with increasing TCS-exposure concentrations. After microinjection of miR-181a-5p mimic and inhibitor, zebrafish malformation type and percentage were prominently increased such as distorted SIV vessels along with reduced venation and abnormal branches by ALP staining. Overexpressed miR-181a-5p had a greater effect on development and branching patterns of arteries and veins than its knockdown. By laser confocal microscopy observation, the 72-hpf Tg (flk1: mCherry) zebrafish obviously displayed vascular proliferation and ablation in the miR-181a-5p mimic group. Microinjection of miR-181a-5p mimics and inhibitors led to abnormal expressions (20-50%) of two key target genes (pax2a and vash2) by WISH, and increased malformation percentages (18-45%) by IOD analysis. Overexpression of vash2 led to the inhibitory or promoting effects on the expression of PI3K signaling pathway-related genes, proving that the effect of vash2 on development of blood vessels could be realized by inhibiting PI3K signaling pathway. These observations lay theoretical foundation for deep insight into the molecular mechanisms on TCS-induced cardiovascular diseases.

Regulatory mechanisms of miR-96 and miR-184 abnormal expressions on otic vesicle development of zebrafish following exposure to β-diketone antibiotics

Chronic ototoxicity of β-diketone antibiotics (DKAs) to zebrafish (Danio rerio) was explored in detail by following abnormal expressions of two hearing-related miRNAs. Dose-dependent down-regulation of miR-96 and miR-184 was observed in otoliths during embryonic-larval development. Continuous DKA exposure to 120-hpf larva decreased sensitivity to acoustic stimulation. Development of otolith was delayed in treatment groups, showing unclear boundaries and vacuolization at 72-hpf, and utricular enlargement as well as decreased saccular volume in 96-hpf or latter larval otoliths. If one miRNA was knocked-down and another over-expressed, only a slight influence on morphological development of the otic vesicle occurred, but knocked-down or over-expressed miRNA both significantly affected zebrafish normal development. Injection of miR-96, miR-184 or both micRNA mimics to yolk sac resulted in marked improvement of otic vesicle phenotype. However, hair cell staining showed that only the injected miR-96 mimic restored hair cell numbers after DKA exposure, demonstrating that miR-96 played an important role in otic vesicle development and formation of hearing, while miR-184 was only involved in otic vesicle construction during embryonic development. These observations advance our understanding of hearing loss owing to acute antibiotic exposure and provide theoretical guidance for early intervention and gene therapy for drug-induced diseases.

Dietary Lactobacillus plantarum ST-III alleviates the toxic effects of triclosan on zebrafish (Danio rerio) via gut microbiota modulation

The probiotics, Lactobacillus plantarum ST-III, plays an important role in modulating microbiota and alleviating intestinal metabolic disorders. Herein, we reported that Lactobacillus increases biodiversity of zebrafish gut flora, and attenuates toxic effects from chronic triclosan (TCS) exposure. Lactobacillus-feeding recovered the species and amount of microorganisms in the intestines of zebrafish, and inhibited toxin production by saprophytic bacterial growth. Abnormal physiological indexes and malonaldeyhde content resulting from TCS exposure were effectively alleviated. Additionally, lipid-metabolism disorders, such as increased triglyceride and total cholesterol levels, were attenuated by a probiotics diet. The number of CD4⁺ T cell lymphocytes in the lamina propria of the duodenal mucosa was decreased in zebrafish receiving a Lactobacillus diet compared to the TCS-exposed group, showing a consistent expression trend for six immune genes (NF-κB, IL-1β, TNF-α, lysozyme, TLR4α, IL-10) in the intestinal mucosa. Histopathological observations of intestines, spleen and kidney showed that TCS exposure produced severe damage to the morphology and structure of immune and metabolism-related organs. Lactobacillus was capable of mitigating this damage, but bile salt hydrolase, an active extract of Lactobacillus, was not an effective mitigation strategy. The Lactobacillus-induced decrease in the number of inflammatory cells confirmed its role in preventing inflammatory injury. Three behavioral tests (T-maze, bottom dwelling and social interaction) indicated that a probiotics diet improved zebrafish movement and learning/memory capacity, effectively alleviating anxiety behavior due to TCS exposure. These findings inform development of beneficial strategies to alleviate intestinal metabolic syndromes and neurodegenerative diseases resulting from exposure to environmental contaminants through modifying gut flora with a probiotics diet.

Lipid metabolism disorder induced by up-regulation of miR-125b and miR-144 following β-diketone antibiotic exposure to F0-zebrafish (Danio rerio)

β-Diketone antibiotics (DKAs) are widely used in human and veterinary medicine to prevent and treat a large variety of infectious diseases. Long-term DKA exposure to zebrafish can result in lipid metabolism disorders and liver function abnormalities. Based on our previous miRNA-seq analyses, miR-144 and miR-125b were identified as target genes regulating lipid metabolism. DKA-exposure at 12.5 and 25 mg/L significantly increased the expressions of miR-144 and miR-125b. The expression levels for the two miRNAs exhibited an inverse relationship with their lipid-metabolism-related target genes (ppardb, bcl2a, pparaa and pparda). Over-expression and inhibition of miR-144 and miR-125b were observed by micro-injection of agomir-144, agomir-125b, antagomir-144 and antagomir-125b. The over-expression of miR-144 and miR-125b enhanced lipid accumulation and further induced lipid-metabolism-disorder syndrome in F1-zebrafish. The expression of ppardb and bcl2a in whole-mount in situ hybridization was in general agreement with results from qRT-PCR and was concentration-dependent. Oil red O and H&E staining, as well as related physiological and biochemical indexes, showed that chronic DKA exposure resulted in lipid-metabolism-disorder in F0-adults, and in F1-larvae fat accumulation, increased lipid content, abnormal liver function and obesity. The abnormal levels of triglyceride (TG) and total cholesterol (TCH) in DKA-exposed zebrafish increased the risk of hyperlipidemia, atherosclerosis and coronary heart disease. These observations improve our understanding of mechanisms leading to liver disease from exposure to environmental pollution, thereby having relevant practical significance in health prevention, early intervention, and gene therapy for drug-induced diseases.

Reproductive toxicity of β-diketone antibiotic mixtures to zebrafish (Danio rerio)

So far, few data are available on the reproductive toxicological assessment of β-diketone antibiotics (DKAs), a class of ubiquitous pseudo-persistent pollutant, in zebrafish (Danio rerio). Herein, we reported the reproductive effects of DKAs by means of transcriptome analysis (F1-zebrafish), changes in a series of reproductive indices (F0-zebrafish) and histopathological observations. A total of 1170, 983 and 1399 genes were found to be differentially expressed when compared control vs. 6.25mg/L, control vs. 12.5mg/L and 6.25 vs. 12.5mg/L DKA-exposure treatments, respectively. Among three comparison groups, 670, 569 and 821 genes were respectively assigned for GO analyses based on matches with sequences of known functions. In 149 KEGG-noted metabolic pathways, the preferential one was the MAPK (mitogen-activated protein kinase) signaling pathway, followed by oxidative phosphorylation, neuroactive ligand-receptor interaction and so on. By qPCR verification, 6 genes (c6ast4, igfbp1b, mrpl42, tnnc2, emc4 and ddit4) showed consistent gene expression with those identified by transcriptome sequencing. Due to DKA-exposure, the concentrations of plasma estradiol and testosterone, and the gonado-somatic index were significantly dose-dependently declined. Also, DKA-exposure led to declining in zebrafish reproductive capacity, reflecting in fertilization, hatchability and egg production. Histopathological observations demonstrated that zebrafish ovary and testis suffered serious damage after DKA-exposure. The 4-oxo-TEMP signals increased obviously with increasing DKA-exposed concentrations, implying disruption of balance between generation and clearance of ¹O₂. In summary, DKAs not only produce reproductive toxicological effects on F0-zebrafish, but also result in adverse consequences for growth and development of F1-zebrafish.

Screening and functional identification of lncRNAs under β-diketone antibiotic exposure to zebrafish (Danio rerio) using high-throughput sequencing

Long non-coding RNAs (lncRNAs) have attracted considerable research interest, but so far no data are available on the roles of lncRNAs and their target genes under chronic β-diketone antibiotic (DKAs) exposure to zebrafish (Danio rerio). Herein, we identified 1.66, 3.07 and 3.36×10⁴ unique lncRNAs from the 0, 6.25 and 12.5mg/L DKA treatment groups, respectively. In comparison with the control group, the 6.25 and 12.5mg/L treatments led to up-regulation of 2064 and 2479 lncRNAs, and down-regulation of 778 and 954 lncRNAs, respectively. Of these, 44 and 39 lncRNAs in the respective 6.25 and 12.5mg/L treatments displayed significant differential expression. Volcano and Venn diagrams of the differentially expressed lncRNAs were constructed on the basis of the differentially expressed lncRNAs. After analyzing 10 lncRNAs and potential target genes, a complex interaction network was constructed between them. The consistency of 7 target genes (tenm3, smarcc1b, myo9ab, ubr4, hoxb3a, mycbp2 and CR388046.3), co-regulated by 3 lncRNAs (TCONS_00129029, TCONS_00027240 and TCONS_00017790), was observed between their qRT-PCR and transcriptomic sequencing. By in situ hybridization (ISH), abnormal expression of 3 lncRNAs was observed in hepatic and spleen tissues, suggesting that they might be target organs for DKAs. A similar abnormal expression of two immune-related target genes (plk3 and syt10), co-regulated by the 3 identified lncRNAs, was observed in liver and spleen by ISH. Histopathological observations demonstrated hepatic parenchyma vacuolar degeneration and clot formation in hepatic tissues, and uneven distribution of brown metachromatic granules and larger nucleus in spleen tissues resulting from DKA exposure. Overall, DKA exposure led to abnormal expression of some lncRNAs and their potential target genes, and these genes might play a role in immune functions of zebrafish.