Embryo exposure to elevated cortisol level leads to cardiac performance dysfunction in zebrafish

Emerging disinfection byproducts 3-bromine carbazole induces cardiac developmental toxicity via aryl hydrocarbon receptor activation in zebrafish larvae

3-bromine carbazole (3-BCZ) represents a group of emerging aromatic disinfection byproducts (DBP) detected in drinking water; however, limited information is available regarding its potential cardiotoxicity. To assess its impacts, zebrafish embryos were exposed to 0, 0.06, 0.14, 0.29, 0.58, 1.44 or 2.88 mg/L of 3-BCZ for 120 h post fertilization (hpf). Our results revealed that ≥1.44 mg/L 3-BCZ exposure induced a higher incidence of heart malformation and an elevated pericardial area in zebrafish larvae; it also decreased the number of cardiac muscle cells and thins the walls of the ventricle and atrium while increasing cardiac output and impeding cardiac looping. Furthermore, 3-BCZ exposure also exhibited significant effects on the transcriptional levels of genes related to both cardiac development (nkx2.5, vmhc, gata4, tbx5, tbx2b, bmp4, bmp10, and bmp2b) and cardiac function (cacna1ab, cacna1da, atp2a1l, atp1b2b, atp1a3b, and tnnc1a). Notably, N-acetyl-L-cysteine, a reactive oxygen species scavenger, may alleviate the failure of cardiac looping induced by 3-BCZ but not the associated cardiac dysfunction or malformation; conversely, the aryl hydrocarbon receptor agonist CH131229 can completely eliminate the cardiotoxicity caused by 3-BCZ. This study provides new evidence for potential risks associated with ingesting 3-BCZ as well as revealing underlying mechanisms responsible for its cardiotoxic effects on zebrafish embryos.

Gamma irradiation-induced offspring masculinization is associated with epigenetic changes in female zebrafish

Sex ratio variation is a key topic in ecology, because of its direct effects on population dynamics and thus, on animal conservation strategies. Among factors affecting sex ratio, types of sex determination systems have a central role, since some species could have a sex determined by genetic factors, environmental factors or a mix of those two. Yet, most studies on the factors affecting sex determination have focused on temperature or endocrine-disrupting chemicals (EDCs), and much less is known regarding other factors. Exposure to gamma irradiation was found to trigger offspring masculinization in zebrafish. Here we aimed at deciphering the potential mechanisms involved, by focusing on stress (i.e. cortisol) and epigenetic regulation of key genes involved in sex differentiation in fish. Cortisol levels in exposed and control (F0) zebrafish females' gonads were similar. However, irradiation increased the DNA methylation level of foxl2a and cyp19a1a in females of the F0 and F1 generation, respectively, while no effects were detected in testis. Overall, our results suggest that parental exposure could alter offspring sex ratio, at least in part by inducing methylation changes in ovaries.

Altered ovarian transcriptome is linked to early mortality and abnormalities in zebrafish embryos after maternal exposure to gamma irradiation

Recent laboratory studies focusing on multigenerational approach demonstrated drastic phenotypic effects after chronic fish irradiation exposure. No irradiation effect at phenotypic scale was observed for F0 (reproductive performances) while early mortality and malformations were observed in F1 offspring whether they were irradiated or not. The objective was to study molecular mechanisms likely to be involved in these phenotypic effects induced by parental irradiation. Thus, F0 adult zebrafish were irradiated for ten days until reproduction and maternal involvement in offspring development was assessed. Levels of maternal provided cortisol and vitellogenin, needed for embryo development, were not impacted by irradiation. However, maternal transcriptome highlighted irradiation effect on processes involved in oocyte development, as well as on essential maternal factors needed for offspring development. Therefore, this study highlighted the importance of parental exposure on offspring fate and of the importance of multigenerational exposure in risk assessment.

Reduced Transcriptome Analysis of Zebrafish Embryos Prioritizes Environmental Compounds with Adverse Cardiovascular Activities

Cardiovascular diseases are the leading cause of premature death in humans and remain a global public health challenge. While age, sex, family history, and false nutrition make a contribution, our understanding of compounds acting as cardiovascular disruptors is far from complete. Here, we aim to identify cardiovascular disruptors via a reduced transcriptome atlas (RTA) approach, which integrates large-scale transcriptome data sets of zebrafish and compiles a specific gene panel related to cardiovascular diseases. Among 767 gene expression profiles covering 81 environmental compounds, 11 priority compounds are identified with the greatest effects on the cardiovascular system at the transcriptional level. Among them, metals (AgNO₃, Ag nanoparticles, arsenic) and pesticides/biocides (linuron, methylparaben, triclosan, and trimethylchlorotin) are identified with the most significant effects. Distinct transcriptional signatures are further identified by the percentage values, indicating that different physiological endpoints exist among prioritized compounds. In addition, cardiovascular dysregulations are experimentally confirmed for the prioritized compounds via alterations of cardiovascular physiology and lipid profiles of zebrafish. The accuracy rate of experimental verification reaches up to 62.9%. The web-based RTA analysis tool, Cardionet, for rapid cardiovascular disruptor discovery was further provided at http://www.envh.sjtu.edu.cn/cardionet.jsp. Our integrative approach yields an efficient platform to discover novel cardiovascular-disrupting chemicals in the environment.

Cardiotoxicity of Zebrafish Induced by 6-Benzylaminopurine Exposure and Its Mechanism

6-BA is a common plant growth regulator, but its safety has not been conclusive. The heart is one of the most important organs of living organisms, and the cardiogenesis process of zebrafish is similar to that of humans. Therefore, based on wild-type and transgenic zebrafish, we explored the development of zebrafish heart under 6-BA exposure and its mechanism. We found that 6-BA affected larval cardiogenesis, inducing defective expression of key genes for cardiac development (myl7, vmhc, and myh6) and AVC differentiation (bmp4, tbx2b, and notch1b), ultimately leading to weakened cardiac function (heart rate, diastolic speed, systolic speed). Acridine orange staining showed that the degree of apoptosis in zebrafish hearts was significantly increased under 6-BA, and the expression of cell-cycle-related genes was also changed. In addition, HPA axis assays revealed abnormally expressed mRNA levels of genes and significantly increased cortisol contents, which was also consistent with the observed anxiety behavior in zebrafish at 3 dpf. Transcriptional abnormalities of pro- and anti-inflammatory factors in immune signaling pathways were also detected in qPCR experiments. Collectively, we found that 6-BA induced cardiotoxicity in zebrafish, which may be related to altered HPA axis activity and the onset of inflammatory responses under 6-BA treatment.

Are synthetic glucocorticoids in the aquatic environment a risk to fish?

The glucocorticosteroid, or glucocorticoid (GC), system is largely conserved across vertebrates and plays a central role in numerous vital physiological processes including bone development, immunomodulation, and modification of glucose metabolism and the induction of stress-related behaviours. As a result of their wide-ranging actions, synthetic GCs are widely prescribed for numerous human and veterinary therapeutic purposes and consequently have been detected extensively within the aquatic environment. Synthetic GCs designed for humans are pharmacologically active in non-mammalian vertebrates, including fish, however they are generally detected in surface waters at low (ng/L) concentrations. In this review, we assess the potential environmental risk of synthetic GCs to fish by comparing available experimental data and effect levels in fish with those in mammals. We found the majority of compounds were predicted to have insignificant risk to fish, however some compounds were predicted to be of moderate and high risk to fish, although the dataset of compounds used for this analysis was small. Given the common mode of action and high level of inter-species target conservation exhibited amongst the GCs, we also give due consideration to the potential for mixture effects, which may be particularly significant when considering the potential for environmental impact from this class of pharmaceuticals. Finally, we also provide recommendations for further research to more fully understand the potential environmental impact of this relatively understudied group of commonly prescribed human and veterinary drugs.

Triphenyl phosphate-induced pericardial edema is associated with elevated epidermal ionocytes within zebrafish embryos

Triphenyl phosphate (TPHP) is an organophosphate ester-based plasticizer and flame retardant. The objective of this study was to identify the potential role of epidermal ionocytes in mediating TPHP-induced pericardial edema within zebrafish embryos. Exposure to TPHP from 24 to 72 h post fertilization (hpf) resulted in a significant increase in pericardial edema and the number of ionocytes at 72 hpf relative to time-matched embryos treated with vehicle. In addition, co-exposure of embryos to mannitol (an osmotic diuretic) blocked TPHP-induced pericardial edema and effects on ionocyte abundance. However, knockdown of ATPase1a1.4 - an abundant Na⁺/K⁺-ATPase localized to epidermal ionocytes - mitigated TPHP-induced effects on ionocyte abundance but not pericardial edema, whereas co-exposure of embryos to ouabain - a Na⁺/K⁺-ATPase inhibitor - enhanced TPHP-induced pericardial edema but not ionocyte abundance. Overall, our findings suggest that TPHP may have multiple mechanisms of toxicity leading to an increase in ionocyte abundance and pericardial edema within developing zebrafish embryos.

The antidepressant venlafaxine perturbs cardiac development and function in larval zebrafish

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

Glucocorticoid-Mediated Developmental Programming of Vertebrate Stress Responsivity

Glucocorticoids, vertebrate steroid hormones produced by cells of the adrenal cortex or interrenal tissue, function dynamically to maintain homeostasis under constantly changing and occasionally stressful environmental conditions. They do so by binding and thereby activating nuclear receptor transcription factors, the Glucocorticoid and Mineralocorticoid Receptors (MR and GR, respectively). The GR, by virtue of its lower affinity for endogenous glucocorticoids (cortisol or corticosterone), is primarily responsible for transducing the dynamic signals conveyed by circadian and ultradian glucocorticoid oscillations as well as transient pulses produced in response to acute stress. These dynamics are important determinants of stress responsivity, and at the systemic level are produced by feedforward and feedback signaling along the hypothalamus-pituitary-adrenal/interrenal axis. Within receiving cells, GR signaling dynamics are controlled by the GR target gene and negative feedback regulator fkpb5. Chronic stress can alter signaling dynamics via imperfect physiological adaptation that changes systemic and/or cellular set points, resulting in chronically elevated cortisol levels and increased allostatic load, which undermines health and promotes development of disease. When this occurs during early development it can "program" the responsivity of the stress system, with persistent effects on allostatic load and disease susceptibility. An important question concerns the glucocorticoid-responsive gene regulatory network that contributes to such programming. Recent studies show that klf9, a ubiquitously expressed GR target gene that encodes a Krüppel-like transcription factor important for metabolic plasticity and neuronal differentiation, is a feedforward regulator of GR signaling impacting cellular glucocorticoid responsivity, suggesting that it may be a critical node in that regulatory network.

Long-term exposure to cyprodinil causes abnormal zebrafish aggressive and antipredator behavior through the hypothalamic-pituitary-interrenal axis

Cyprodinil, one of the main pyrimidinamine fungicides, has been used to control fungal diseases in plants and vegetables worldwide. Previous studies have investigated the influences of cyprodinil on the developmental and reproductive toxicity of fish. However, it remains unknown whether it affects fish behaviors and the underlying mechanisms. In our current study, zebrafish, an ideal model animal for behavioral studies, were exposed to cyprodinil from fertilization to 240 days postfertilization at 0.1 μg/L (environmentally relevant concentration) and 1, 10 μg/L. Firstly, we observed that aggressive behavior of zebrafish was significantly enhanced after exposure to 0.1-10 μg/L cyprodinil and antipredator behavior was decreased after exposure. Cyprodinil exposure altered the adrenocorticotropic hormone and cortisol levels, which regulate cortisol homeostasis and were significantly reduced in all exposure groups (0.1-10 μg/L). In addition, most of the key genes in the hypothalamic-pituitary-interrenal gland axis, such as corticotropin-releasing hormone and melanocortin 2 receptor, were downregulated significantly in all exposure groups, which was consistent with the hormone levels. In addition, in the hypothalamus, the number of apoptotic cells increased in a dose-dependent manner in the cyprodinil exposure groups. Moreover, these changes were potentially responsible for the increased aggression of zebrafish during the mirror-like aggressive test and for the reduced antipredator behavior during the predator avoidance test. Overall, the data provided herein further our understanding of cyprodinil toxicity and can be used to assess the ecological effects of cyprodinil on the induction of abnormal behaviors at the environmental level.

Haemodynamic dependence of mechano-genetic evolution of the cardiovascular system in Japanese medaka

The progression of cardiac gene expression-wall shear stress (WSS) interplay is critical to identifying developmental defects during cardiovascular morphogenesis. However, mechano-genetics from the embryonic to larval stages are poorly understood in vertebrates. We quantified peak WSS in the heart and tail vessels of Japanese medaka from 3 days post fertilization (dpf) to 14 dpf using in vivo micro-particle image velocimetry flow measurements, and in parallel analysed the expression of five cardiac genes (fgf8, hoxb6b, bmp4, nkx2.5, smyd1). Here, we report that WSS in the atrioventricular canal (AVC), ventricular outflow tract (OFT), and the caudal vessels in medaka peak with inflection points at 6 dpf and 10-11 dpf instead of a monotonic trend. Retrograde flows are captured at the AVC and OFT of the medaka heart for the first time. In addition, all genes were upregulated at 3 dpf and 7 dpf, indicating a possible correlation between the two, with the cardiac gene upregulation preceding WSS increase in order to facilitate cardiac wall remodelling.

Sex steroid dynamics and mRNA transcript profiles of growth- and development-related genes during embryogenesis following induced follicular maturation in European eel

Hormones and mRNA transcripts of maternal origin deposited in the egg may affect early embryonic development in oviparous species. These hormones include steroids, such as estradiol-17β (E2), testosterone (T), 11-ketotestosterone (11-kt), 17α,20ß-dihydroxy-4-pregnen-3-one (DHP), and cortisol, which also play an important role in fish reproduction. In European eel, Anguilla anguilla, which does not reproduce naturally in captivity, vitellogenesis in female broodstock is commonly induced by administration of salmon or carp pituitary extract (PE) as an exogenous source of gonadotropins, while follicular maturation is stimulated by a priming dose of PE followed by provision of DHP as a maturation inducing hormone. In this regard, the main purpose of the present study was to evaluate effects of induced follicular maturation on reproductive success in European eel, focusing on maternal transfer and dynamics of steroids and mRNA transcripts of growth- and development-related genes throughout embryogenesis. The results showed that maternal blood plasma concentrations of E2, T and DHP were reflected in the unfertilized eggs. Moreover, a negative relationship between concentrations of E2 and DHP in eggs and embryos and quality parameters measured as fertilization success, cleavage abnormalities, embryonic survival, and hatch success was found. Concomitant mRNA transcript abundance analysis including genes involved in stress response (hsp70, hsp90), somatotropic axis (gh, igf1, igf2a, igf2b), lipid (cpt1a, cpt1b, pigf5) and thyroid metabolism (dio1, dio2, dio3, thrαb, thrβa, thrβb) varied among unfertilized egg batches. For the majority of genes, mRNA abundance increased during the maternal-to-zygotic transition in connection to activation of the transcription of the embryos own genome. mRNA abundance of dio1, cpt1a and cpt1b throughout embryogenesis was related to embryonic developmental competence. Notably, mRNA abundance of dio3 was positively associated with E2 concentrations, while the mRNA abundance of thrαb was negatively related to T concentrations in the unfertilized eggs, which may suggest an interaction between the thyroid and steroid hormone systems. Altogether, maternal plasma concentrations of E2 and DHP were reflected in the eggs, with high concentrations of these steroids in the eggs being negatively associated with embryonic developmental competence. Additionally, high transcript levels of two of the investigated genes (dio1, cpt1b) were positively associated with embryonic developmental competence. This study reveals maternal transfer of steroids and mRNA transcripts to the eggs, which may be significant contributors to the variability in embryonic survival observed in European eel captive reproduction.

Exposure to four chemical UV filters through contaminated sediment: impact on survival, hatching success, cardiac frequency, and aerobic metabolic scope in embryo-larval stage of zebrafish

UV filters are widely used in many pharmaceutical and personal care products such as sunscreen and cosmetics to protect from UV irradiation. Due to their hydrophobic properties and relative stability, they have a high capacity to accumulate in sediment. Little information is available on their ecotoxicity on fish. In aquatic ecosystems, fish eggs could be directly affected by UV filters through contact with contaminated sediment. The aim of this study was to investigate the individual toxicity of four UV filters: benzophenone-3 (BP3), butyl methoxydibenzoylmethane (BM), bis-ethylhexyloxyphenol methoxyphenyl triazine (BEMT), and methylene bis-benzotriazolyl tetramethylbutylphenol (MBBT), in embryo-larval stages of zebrafish Danio rerio. Fish eggs were exposed to single UV filters by contact with spiked sediment during 96 h at a concentration of 10 μg g^-1. Among the four UV filters tested, BP3 was the more toxic, reducing cardiac frequency and increasing standard metabolic rate of larvae.

The intersection of stress, sex and immunity in fishes

While sexual dimorphism in immune responses has been documented in other vertebrates, evidence for a similar phenomenon in fish is lacking. Here, we review the relationship between immunity, stress, spawning, and sex hormones in fish to gain a better understanding of sex-based differences in fish immune responses and its consequences for aquaculture. It is well known that there is a strong link between the stress response and immune function in fish. In addition, research to date has demonstrated that sexual dimorphism in the stress response exists in many species; yet, the relationship between the sexual dimorphic stress responses and immune function has rarely been explored together. Aside from stress, spawning is also known to trigger changes in fish immune responses. Estrogens and androgens have been shown to modulate the immune system which could account for differences between the two sexes of fish when spawning; however, evidence regarding the sexual dimorphism of these changes varies between fishes and is likely related to the spawning strategy employed by a given species. Sex hormones are also used in aquaculture practices to produce monosex populations, and exposure to these hormones early in development has been shown to impact the development of immune organs in several fishes. While female fish are generally thought to be more robust than males, aquaculture practices should also consider the role that maternal stress has on the immune function of the offspring and what role this plays in compromising the immune response of farmed fish.

Selective serotonin reuptake inhibitor or serotonin-norepinephrine reuptake inhibitors and epidemiological characteristics associated with prenatal diagnosis of congenital heart disease

OBJECTIVE

Identify early pregnancy associations of congenital heart disease (CHD) in a multiethnic cohort.

METHODS

This retrospective observational cohort study compared the general obstetric population to women who gave birth at a referral centre in Australia between 2012 and 2017, after 20 weeks' of gestation, with a pregnancy affected by CHD. We defined mood disorder and anxiety as a history of self-reported or medically diagnosed anxiety, depression, postpartum depression or bipolar disorder.

RESULTS

We compared epidemiological factors between 30 842 general obstetric patients and 470 obstetric patients with a foetus affected by CHD. Multivariate analysis showed independent associations between CHD and use of selective serotonin reuptake inhibitors (SSRIs) or serotonin-norepinephrine reuptake inhibitors (SNRIs) in the first trimester (relative risk [RR] 4.14, 95% CI 2.58-6.65), history of anxiety or mood disorder with no SSRI/SNRI first trimester (RR 2.20, 95% CI 1.77-2.74), folate and/or pregnancy multivitamin use in the first trimester (RR 0.69, 95% CI 0.55-0.87) and increased risk with maternal age >40 years (RR 2.30, 95% CI 1.57-3.38).

CONCLUSIONS

Our data show maternal mood disorders with and without SSRI or SNRI use, maternal age >40 years and lack of multivitamin/folate use to be independently associated with CHD in pregnancy.

Suppression of Inflammation Delays Hair Cell Regeneration and Functional Recovery Following Lateral Line Damage in Zebrafish Larvae

Cochlear hair cells in human beings cannot regenerate after loss; however, those in fish and other lower species can. Recently, the role of inflammation in hair cell regeneration has been attracting the attention of scientists. In the present study, we investigated how suppression of inflammatory factors affects hair cell regeneration and the functional recovery of regenerated hair cells in zebrafish. We killed hair cells in the lateral line of zebrafish larvae with CuSO₄ to induce an inflammatory response and coapplied BRS-28, an anti-inflammatory agent to suppress the inflammation. The recovery of the hair cell number and rheotaxis was slower when CuSO₄ and BRS-28 were coapplied than when CuSO₄ was applied alone. The recovery of hair cell count lagged behind that of the calcium imaging signal during the regeneration. The calcium imaging signal in the neuromasts in the inflammation-inhibited group was weaker than that in the noninflammation-inhibited group at the early stage of regeneration, although it returned to normal at the late stage. Our study demonstrates that suppressing inflammation by BRS-28 delays hair cell regeneration and functional recovery when hair cells are damaged. We suspect that BRS-28 inhibits pro-inflammatory factors and thereby reduces the migration of macrophages to delay the regeneration of hair cells.

Hypoxia affects the ontogeny of the hypothalamus-pituitary-interrenal axis functioning in the lake whitefish (Coregonus clupeaformis)

Early life stages are sensitive to environmental insults and changes during critical developmental periods; this can often result in altered adult behaviour and physiology. Examining the development of the hypothalamus-pituitary-interrenal (HPI) axis and its responsiveness, or lack thereof, during development are important for understanding the short- and long-term impacts of stressors on embryonic and larval fish. We examined the ontogeny of the HPI axis in embryonic (21, 38, 63, 83 and 103 days post-fertilisation (dpf)) and larval (1, 2, 3 and 4 weeks post-hatch (wph)) lake whitefish (Coregonus clupeaformis) by quantifying changes in mRNA levels of several genes associated with HPI axis functioning and whole animal cortisol levels throughout development and in response to a severe or mild hypoxic stress. Cortisol, and crh, crhbp1, pomc and star transcripts were detected from the earliest embryonic age studied. Cortisol levels in control embryos decreased between 21 and 63 dpf, suggesting the utilisation of maternal cortisol deposits. However, by 83 dpf (70% developed) endogenous de novo synthesis had generated a 4.5-fold increase in whole embryo cortisol. Importantly, we provide novel data showing that the HPI axis can be activated even earlier. Whole body cortisol increased in eyed lake whitefish embryos (38 dpf; ~32% developed) in response to hypoxia stress. Coincident with this hypoxia-induced increase in cortisol in 38 dpf embryos were corresponding increases in crh, crhbp1, pomc and star transcript levels. Beyond 38 dpf, the HPI axis in lake whitefish embryos was hyporesponsive to hypoxia stress at all embryonic ages examined (63, 83 and 103 dpf; 54, 72 and 85% developed, respectively). Post-hatch, larvae responded to hypoxia with an increase in cortisol levels and HPI axis genes at 1 wph, but this response was lost and larvae appeared hyporesponsive at subsequent ages (2, 3 and 4 wph). Collectively our work demonstrates that during fish embryogenesis and the larval stage there are windows where the HPI axis is responsive and windows where it is truly hyporesponsive; both could be beneficial in ensuring undisrupted development particularly in the face of increasing environmental changes.

Effects of environmental steroid mixtures are regulated by individual steroid receptor signaling

Fish are exposed to steroids of different classes in contaminated waters, but their effects are not sufficiently understood. Here we employed an anti-sense technique using morpholino oligonucleotides to knockdown the glucocorticoid receptors (GRs, GRα and GRβ) and androgen receptor (AR) to investigate their role in physiological and transcriptional responses. To this end, zebrafish embryos were exposed to clobetasol propionate (CLO), androstenedione (A4) and mixtures containing different classes of steroids. CLO caused a decrease of spontaneous muscle contraction and increase of heart rate, as well as transcriptional induction of pepck1, fkbp5, sult2st3 and vitellogenin (vtg1) at 24 and/or 48 h post fertilization (hpf). Knockdown of GRs eliminated these effects, while knockdown of AR decreased the ar transcript but caused no expressional changes, except induction of sult2st3 after exposure to A4 at 24 hpf. Exposure to a mixture of 6 steroids comprising progesterone (P4) and three progestins, cyproterone acetate, dienogest, drospirenone, 17β-estradiol (E2) and CLO caused a significant induction of pepck1, sult2st3, vtg1 and per1a. Knockdown of GRs eliminated the physiological effects and the up-regulation of vtg1, sult2st3, pepck1, fkbp5 and per1a. Thus, as with CLO, responses in mixtures were regulated by GRs independently from the presence of other steroids. Exposure to a mixture comprising A4, CLO, E2 and P4 caused induction of vtg1, cyp19b, sult2st3 and fkbp5. Knockdown of AR had no effect, indicating that regulation of these genes occurred by the GRs and estrogen receptor (ER). Our findings show that in early embryos GRs cause vtg1 and sult2st3 induction in addition to known glucocorticoid target genes. Each steroid receptor regulated its own target genes in steroid mixtures independently from other steroids. However, enhanced expressional induction occurred for vtg1 and fkbp5 in steroid mixtures, indicating an interaction/cross-talk between GRs and ER. These findings have importance for the understanding of molecular effects of steroid mixtures.

Endogenous cortisol production and its relationship with feeding transitions in larval lake sturgeon (Acipenser fulvescens)

Our understanding of the importance of cortisol in the development of fishes largely stems from teleosts and in particular the zebrafish, Danio rerio. However, studies examining the ontogeny of the cortisol endocrine axis in acipenseriformes (sturgeon and paddlefish) have demonstrated similar general patterns during early development. Beginning with maternal deposition of cortisol in the egg, followed by development of de novo synthesis, a hypo-responsive period, and finally the ability of the fish to appropriately increase whole-body levels of cortisol in response to a stressor. In the present study, we demonstrate a similar pattern of ontogeny in the cortisol response in lake sturgeon over two-year classes. Whole-body levels of cortisol were examined over two cohorts and found to be different in both concentration and timing of endogenous production. The 2016 cohort were found to have relatively high levels of cortisol and developed to first feeding approximately six days faster than the 2017 cohort with lower levels of cortisol. In the 2017 cohort, mRNA expression of steroidogenic acute regulatory protein (StAR) and glucocorticoid receptor 1 (GR1) increased just prior to the increase in cortisol and associated onset of exogenous feeding. Treatment in metyrapone, an inhibitor of 11β-hydroxylase, significantly inhibited cortisol production and resulted in the inability of the fish to appropriately transition to exogenous feeding. Data suggest a potential key role for cortisol in lake sturgeon as they transition between diets during early life history.

Early Life Glucocorticoid Exposure Modulates Immune Function in Zebrafish (Danio rerio) Larvae

In this study we have assessed the effects of increased cortisol levels during early embryonic development on immune function in zebrafish (Danio rerio) larvae. Fertilized eggs were exposed to either a cortisol-containing, a dexamethasone-containing (to stimulate the glucocorticoid receptor selectively) or a control medium for 6 h post-fertilization (0–6 hpf). First, we measured baseline expression of a number of immune-related genes (socs3a, mpeg1.1, mpeg1.2, and irg1l) 5 days post-fertilization (dpf) in larvae of the AB and TL strain to assess the effectiveness of our exposure procedure and potential strain differences. Cortisol and dexamethasone strongly up-regulated baseline expression of these genes independent of strain. The next series of experiments were therefore carried out in larvae of the AB strain only. We measured neutrophil/macrophage recruitment following tail fin amputation (performed at 3 dpf) and phenotypical changes as well as survival following LPS-induced sepsis (150 μg/ml; 4–5 dpf). Dexamethasone, but not cortisol, exposure at 0–6 hpf enhanced neutrophil recruitment 4 h post tail fin amputation. Cortisol and dexamethasone exposure at 0–6 hpf led to a milder phenotype (e.g., less tail fin damage) and enhanced survival following LPS challenge compared to control exposure. Gene-expression analysis showed accompanying differences in transcript abundance of tlr4bb, cxcr4a, myd88, il1β, and il10. These data show that early-life exposure to cortisol, which may be considered to be a model or proxy of maternal stress, induces an adaptive response to immune challenges, which seems mediated via the glucocorticoid receptor.

Long-term exposure of zebrafish to bisphenol S impairs stress function of hypothalamic-pituitary-interrenal axis and causes anxiety-like behavioral responses to novelty

Bisphenol S (BPS), a main substitute of bisphenol A, has been reported to induce multiple endocrine disrupting effects on animals, however, whether it can interfere with the corticosteroid-endocrine system still remains unknown. Furthermore, previous studies mainly investigated the influences of environmental pollutants on corticosteroid levels and gene expressions of hypothalamic-pituitary-interrenal/adrenal (HPI/A) axis, while the downstream toxic effects caused thereafter have not yet been fully elucidated. Considering the key role of cortisol, a primary corticosteroid hormone in teleost, in mediating stress adaptation and the highly positive correlation between cortisol level and anxious phenotype in the novel environment, we hypothesized that an imbalanced cortisol homeostasis due to environmental pollutant exposure may further affect the behavioral responses to novelty stress. In the present study, zebrafish, a valuable model in studying human stress physiology and anxiety behavior, were exposed to BPS from embryos to adults (120 days) at environmentally relevant concentrations (1 and 10 μg/L) and 100 μg/L. Results found that long-term exposure to BPS increased whole-body cortisol levels and caused abnormal expressions of HPI axis genes. Moreover, the excessive cortisol levels may be due to the inhibition of cortisol catabolism and excretion, as evidenced by the down-regulated expressions of hydroxysteroid 11-beta dehydrogenase 2 and hydroxysteroid 20-beta dehydrogenase 2 genes. More importantly, as we speculated, excessive cortisol levels may be responsible for the occurrence of anxiety-like behavioral responses indicated by longer latency, fewer time spent in the upper half, and more erratic movements in a 6-min novel tank test. Overall, our study provides basic data for the comprehensive understanding of BPS toxicity, and emphasizes environmental health risks of BPS in inducing anxiety syndrome at environmentally realistic concentrations.

Effects of new generation progestins, including as mixtures and in combination with other classes of steroid hormones, on zebrafish early life stages

Fish are exposed to progestins and steroid mixtures in contaminated waters but the ecotoxicological implications are not sufficiently known. Here we analyze effects of the new generation progestin dienogest (DNG) followed by investigating effects of mixtures of new generation progestins containing DNG, cyproterone acetate and drospirenone and the hormone progesterone. Furthermore, effects of this mixture were studied after adding 17β-estradiol (E2) and clobetasol propionate (CLO) in zebrafish embryos and larvae at concentrations between 0.01 and 10 μg/L. DNG showed only very minor transcriptional alterations among the 24 assessed genes with downregulation of the fshb transcript only. The progestin mixture caused weak induction of the lhb, cyp2k22 and sult2st3 transcripts. Addition of E2 to the mixture caused strong induction vtg1, cyp19b, esr1 and lhb, as well as downregulation of fshb from 0.01 μg/L onwards. Besides altering the same transcripts, addition of CLO altered glucocorticoid regulated genes mmp-9, mmp-13, g6pca, fkbp5 and irg1l. While each steroid class exhibited its specific activity independently in the mixture, sult2st3 and cyp2k22 were regulated by both E2 and CLO. Furthermore, CLO alone and in mixtures decreased spontaneous muscle contractions, increased heartrate and induced edema. Our study highlights the prominent effects of E2 and CLO in environmental steroid mixtures, while new generation progestins show relatively low activity.

The Genetics and Epigenetics of 22q11.2 Deletion Syndrome

Chromosome 22q11.2 deletion syndrome (22q11.2del) is a complex, multi-organ disorder noted for its varying severity and penetrance among those affected. The clinical problems comprise congenital malformations; cardiac problems including outflow tract defects, hypoplasia of the thymus, hypoparathyroidism, and/or dysmorphic facial features. Additional clinical issues that can appear over time are autoimmunity, renal insufficiency, developmental delay, malignancy and neurological manifestations such as schizophrenia. The majority of individuals with 22q11.2del have a 3 Mb deletion of DNA on chromosome 22, leading to a haploinsufficiency of ~106 genes, which comprise coding RNAs, noncoding RNAs, and pseudogenes. The consequent haploinsufficiency of many of the coding genes are well described, including the key roles of T-box Transcription Factor 1 (TBX1) and DiGeorge Critical Region 8 (DGCR8) in the clinical phenotypes. However, the haploinsufficiency of these genes alone cannot account for the tremendous variation in the severity and penetrance of the clinical complications among those affected. Recent RNA and DNA sequencing approaches are uncovering novel genetic and epigenetic differences among 22q11.2del patients that can influence disease severity. In this review, the role of coding and non-coding genes, including microRNAs (miRNA) and long noncoding RNAs (lncRNAs), will be discussed in relation to their bearing on 22q11.2del with an emphasis on TBX1.

Early life exposure to cortisol in zebrafish (Danio rerio): similarities and differences in behaviour and physiology between larvae of the AB and TL strains

Maternal stress and early life stress affect development. Zebrafish (Danio rerio) are ideally suited to study this, as embryos develop externally into free-feeding larvae. The objective of this study was therefore to assess the effects of increased levels of cortisol, mimicking thereby maternal stress, on larval physiology and behaviour. We studied the effects in two common zebrafish strains, that is, AB and Tupfel long-fin (TL), to assess strain dependency of effects. Fertilized eggs were exposed to a cortisol-containing medium (1.1 μmol/l) or control medium from 0 to 6 h following fertilization, after which at 5-day following fertilization, larval behaviour and baseline hypothalamus-pituitary-interrenal cells axis functioning were measured. The data confirmed earlier observed differences between AB larvae and TL larvae: a lower hypothalamus-pituitary-interrenal axis activity in TL larvae than AB larvae, and slower habituation to repeated acoustic/vibrational stimuli in TL larvae than AB larvae. Following cortisol treatment, increased baseline levels of cortisol were found in AB larvae but not TL larvae. At the behavioural level, increased thigmotaxis or 'wall hugging' was found in AB larvae, but decreased thigmotaxis in TL larvae; however, both AB larvae and TL larvae showed decreased habituation to repeated acoustic/vibrational stimuli. The data emphasize that strain is a critical factor in zebrafish research. The habituation data suggest a robust effect of cortisol exposure, which is likely an adaptive response to increase the likelihood of detecting or responding to potentially threatening stimuli. This may enhance early life survival. Along with other studies, our study underlines the notion that zebrafish may be a powerful model animal to study the effects of maternal and early life stress on life history.

Adverse effects induced by chronic gamma irradiation in progeny of adult fish not affecting parental reproductive performance

Multigenerational studies have become of great interest in ecotoxicology since the consequence of parental exposure to contaminants on offspring generations was established in situ or in laboratory conditions. The present study mainly examined the chronic effects of external Cs-137 gamma irradiation exposure at 4 dose rates (control, 0.5, 5, and 50 mGy h^-1 ) on adult zebrafish (F0) exposed for 10 d and their progeny (F1) exposed or unexposed for 4 to 5 d. The main endpoints investigated included parental reproductive performance, embryo-larval survival, DNA alterations, and reactive oxygen species (ROS) production in F0 and F1. No effects on reproductive success, fecundity, or egg fertilization rate were observed. However, drastic effects were observed on F1 exposed to 50 mGy h^-1 , resulting in a mortality rate of 100%. The drastic effects were also observed when the progeny was not irradiated. It was demonstrated that the sensitivity of the embryos was mainly attributable to parental irradiation. Moreover, these drastic effects induced by adult irradiation disappeared over time when 10 d-irradiated adults were placed in a nonirradiated condition. Alterations in larval DNA were observed for the 3 dose rates, and an increase of ROS production was also shown for the 2 lowest dose rates. The present study improves our understanding of the consequences of parental exposure conditions to the progeny. Furthermore, it provides an incentive to take transmitted generational effects into account in ecological risk assessments. Environ Toxicol Chem 2019;38:2556-2567. © 2019 SETAC.

Environmental glucocorticoids corticosterone, betamethasone and flumethasone induce more potent physiological than transcriptional effects in zebrafish embryos

Many glucocorticoids occur in the aquatic environments but their adverse effects to fish are poorly known. Here we investigate effects of the natural glucocorticoid corticosterone and the synthetic glucocorticoids betamethasone and flumethasone in zebrafish embryos. Besides studying the effects of each steroid, we compared effects of natural with synthetic glucocorticoids, used as drugs. Exposure at concentrations of 1 μg/L and higher led to concentration-related decrease in spontaneous muscle contractions at 24 h post fertilization (hpf) and increase in heart rate at 48 hpf. Betamethasone showed a significant increase at 0.11 μg/L in heart rate. Corticosterone also accelerated hatching at 60 hpf at 0.085 μg/L. Transcription of up to 24 genes associated with different pathways showed alterations at 96 and 120 hpf for all glucocorticoids, although with low potency. Corticosterone caused transcriptional induction of interleukin-17, while betamethasone caused transcriptional down-regulation of the androgen receptor, aromatase and hsd11b2, indicating an effect on the sex hormone system. Furthermore, transcripts encoding proteins related to immune system regulation (irg1l, gilz) and fkbp5 were differentially expressed by corticosterone and betamethasone, while flumethasone caused only little effects, mainly alteration of the irg1l transcript. Our study shows that these glucocorticoids caused more potent physiological effects in early embryos than transcriptional alterations in hatched embryos, likely due to increased metabolism in later developmental stages. Thus, these glucocorticoids may be of concern for early stages of fish embryos in contaminated aquatic environments.

Early Developmental Stress Affects Subsequent Gene Expression Response to an Acute Stress in Atlantic Salmon: An Approach for Creating Robust Fish for Aquaculture?

Stress during early life has potential to program and alter the response to stressful events and metabolism in later life. Repeated short exposure of Atlantic salmon to cold water and air during embryonic (E), post-hatch (PH) or both phases of development (EPH) has been shown to alter the methylome and transcriptome and to affect growth performance during later life compared to untreated controls (CO). The aim of this study was to investigate how the transcriptome of these fish responds to subsequent acute stress at the start feeding stage, and to describe methylation differences that might steer these changes. EPH treated fish showed the strongest down-regulation of corticotropin releasing factor 1, up-regulation of glucocorticoid receptor and 3-oxo-5-alpha-steroid 4-dehydrogenase 2 gene expression and a suppressed cortisol response 3 hr after the acute stress, differences that could influence hormesis and be affecting how EPH fish cope and recover from the stress event. Growth hormone 2 and insulin-like growth factor 1 were more strongly down-regulated following acute stress in EPH treated fish relative to E, PH and CO fish. This indicates switching away from growth toward coping with stress following stressful events in EPH fish. Genes implicated in immune function such as major histocompatibility class 1A, T-cell receptor and toll-like receptor also responded to acute stress differently in EPH treated fish, indicating that repeated stresses during early life may affect robustness. Differential DNA methylation was detected in regions mapping <500 bases from genes differentially responding to acute stress suggesting the involvement of epigenetic mechanisms. Stress treatments applied during early development therefore have potential as a husbandry tool for boosting the productivity of aquaculture by affecting how fish respond to stresses at critical stages of production.

Microcystin-LR affects the hypothalamic-pituitary-inter-renal (HPI) axis in early life stages (embryos and larvae) of zebrafish

Frequencies and durations of blooms of cyanobacteria are increasing. Some cyanobacteria can produce cyanotoxins including microcystins (MCs). MCs are the most common toxic products of hazardous algal blooms (HABs), with the greatest potential for exposure and to cause toxicity. Recently, MCs have been shown to disrupt endocrine functions. In this study, for the first time, effects of MC-LR on the hypothalamic-pituitary-inter-renal (HPI) axis during early embryonic development (embryos/larvae) of zebrafish (Danio rerio), were investigated. Embryos/larvae of zebrafish were exposed to 1, 10, 100, or 300 μg MC-LR/L during the period of 4-168 h post-fertilization (hpf). Exposure to 300 μg MC-LR/L resulted in significantly greater concentrations of whole-body cortisol than those in controls. Expressions of genes along the HPI axis and mineralocorticoid receptor (MR-) and glucocorticoid receptor (GR-) centered gene networks were evaluated by use of quantitative real-time PCR. Expression of mRNA for crh was significantly down-regulated by exposure to 300 μg MC-LR/L, while expressions of crhbp, crhr1, and crhr2 were significantly up-regulated, relative to controls. MC-LR caused significantly lesser levels of mRNA for steroidogenic genes including hmgra, star, and cyp17, but expression of mRNA for hsd20b was significantly greater than that of controls. Treatment with MC-LR also altered profiles of transcription of MR- and GR-centered gene networks, which might result in multiple responses. Taken together, these results demonstrated that MC-LR affected the corticosteroid-endocrine system of larvae of zebrafish. This study provided valuable insights into molecular mechanisms behind potential toxicity and endocrine disruption of MCs.

Assessment of raw and ozonated oil sands process-affected water exposure in developing zebrafish: Associating morphological changes with gene expression

With the ever-increasing amounts of oil sands process-affected water (OSPW) accumulating from Canada's oil sands operations, its eventual release must be considered. As OSPW has been found to be both acutely and chronically toxic to aquatic organisms, remediation processes must be developed to lower its toxicity. Ozone treatment is currently being studied as a tool to facilitate the removal of organic constituents associated with toxicity. Biomarkers (e.g. gene expression) are commonly used when studying the effects of environmental contaminants, however, they are not always indicative of adverse effects at the whole organism level. In this study, we assessed the effects of OSPW exposure on developing zebrafish by linking gene expression to relevant cellular and whole organism level endpoints. We also investigated whether or not ozone treatment decreased biomarkers and any associated toxicity observed from OSPW exposure. The concentrations of classical naphthenic acids in the raw and ozonated OSPW used in this study were 16.9 mg/L and 0.6 mg/L, respectively. Ozone treatment reduced the total amount of naphthenic acids (NAs) in the OSPW sample by 92%. We found that exposure to both raw and ozonated OSPW had no effect on the survival of zebrafish embryos. The expression levels of biotransformation genes CYP1A and CYP1B were induced by raw OSPW exposure, with CYP1B being more highly expressed than CYP1A. In contrast, ozonated OSPW exposure did not increase the expression of CYP1A and only slightly induced CYP1B. A decrease in cardiac development and function genes (NKX2.5 and APT2a2a) was not associates with large changes in heart rate, arrhythmia or heart size. We did not find any indications of craniofacial abnormalities or of increased occurrence of apoptotic cells. Overall, our study found that OSPW was not overtly toxic to zebrafish embryos.

Effects of Essential Oil from Thymus vulgaris on Viability and Inflammation in Zebrafish Embryos

Innate immunity provides the initial response against pathogens and includes the inflammatory response. Regulation of the initiation and duration of neutrophil and mononuclear cell influx during inflammation determines both the successfulness of pathogen elimination and the level of resulting tissue damage. Zebrafish embryos provide excellent opportunities to visualize the inflammatory response. Neutrophil granules may be stained with Sudan black, and variation in neutrophil counts may be used to monitor the level of the response. Inflammation may be triggered by injuring the caudal fin, providing an opportunity for testing possible anti-inflammatory compounds in a whole-animal system. The use of homeopathic compounds as anti-inflammatory treatments is common in alternative medicine. Effects of unfractionated essential oil from Thymus vulgaris and its specific component, carvacrol, have been examined in cells in culture and in rodents. Our work extends this research to zebrafish, and includes toxicity and morphological studies as well as examination of anti-inflammatory effects following tail fin injury. Our results show that zebrafish are more sensitive to thyme oil compared to cells in culture, that cardiac defects arise due to thyme oil treatment, and that thyme oil reduces neutrophil infiltration during an inflammatory response.

The Primodos components Norethisterone acetate and Ethinyl estradiol induce developmental abnormalities in zebrafish embryos

Primodos was a hormone pregnancy test used between 1958-1978 that has been implicated with causing a range of birth defects ever since. Though Primodos is no longer used, it's components, Norethisterone acetate and Ethinyl estradiol, are used in other medications today including treatments for endometriosis and contraceptives. However, whether Primodos caused birth defects or not remains controversial, and has been little investigated. Here we used the developing zebrafish embryo, a human cell-line and mouse retinal explants to investigate the actions of the components of Primodos upon embryonic and tissue development. We show that Norethisterone acetate and Ethinyl estradiol cause embryonic damage in a dose and time responsive manner. The damage occurs rapidly after drug exposure, affecting multiple organ systems. Moreover, we found that the Norethisterone acetate and Ethinyl estradiol mixture can affect nerve outgrowth and blood vessel patterning directly and accumulates in the forming embryo for at least 24 hrs. These data demonstrate that Norethisterone acetate and Ethinyl estradiol are potentially teratogenic, depending on dose and embryonic stage of development in the zebrafish. Further work in mammalian model species are now required to build on these findings and determine if placental embryos also are affected by synthetic sex hormones and their mechanisms of action.

Cortisol elevation post-hatch affects behavioural performance in zebrafish larvae

Maternal cortisol is essential for cortisol stress axis development and de novo production of this steroid commences only after hatch in zebrafish (Danio rerio). However, very little is known about the effect of elevated cortisol levels, during the critical period of stress axis activation, on larval performance. We tested the hypothesis that elevated cortisol levels post-hatch affect behavioural performance and this is mediated by glucocorticoid receptor (GR) activation in zebrafish larvae. The behavioural response included measuring larval activity in response to alternating light and dark cycles, as well as thigmotaxis. Zebrafish larvae at 3days post-fertilization were exposed to waterborne cortisol for 24h to mimic a steroid response to an early-life stressor exposure. Also, larvae were exposed to waterborne RU-486 (a GR antagonist) either in the presence or absence of cortisol to confirm GR activation. Co-treatment with RU-486 completely abolished the upregulation of cortisol-induced 11β-hydroxysteroid dehydrogenase type 2 transcript abundance, confirming GR signalling. Cortisol-exposed larvae displayed increased locomotor activity irrespective of light condition, but showed no changes in thigmotaxis. This cortisol-mediated behavioural response was not affected by co-treatment with RU-486. Cortisol exposure also did not modify the transcript abundances of GR and mineralocorticoid receptor (MR) in zebrafish larvae. Altogether, cortisol stress axis activation post-hatch increases locomotor activity in zebrafish larvae. Our results suggest that GR signalling may not be involved in this behavioural response, leading to the proposal that cortisol action via MR signalling may influence locomotor activity in zebrafish larvae.

4-Phenoxyphenol-Functionalized Reduced Graphene Oxide Nanosheets: A Metal-Free Fenton-Like Catalyst for Pollutant Destruction

Metal-containing Fenton catalysts have been widely investigated. Here, we report for the first time a highly effective stable metal-free Fenton-like catalyst with dual reaction centers consisting of 4-phenoxyphenol-functionalized reduced graphene oxide nanosheets (POP-rGO NSs) prepared through surface complexation and copolymerization. Experimental and theoretical studies verified that dual reaction centers are formed on the C-O-C bridge of POP-rGO NSs. The electron-rich center around O is responsible for the efficient reduction of H₂O₂ to ^•OH, while the electron-poor center around C captures electrons from the adsorbed pollutants and diverts them to the electron-rich area via the C-O-C bridge. By these processes, pollutants are degraded and mineralized quickly in a wide pH range, and a higher H₂O₂ utilization efficiency is achieved. Our findings address the problems of the classical Fenton reaction and are useful for the development of efficient Fenton-like catalysts using organic polymers for different fields.

Active Glucocorticoids Have a Range of Important Adverse Developmental and Physiological Effects on Developing Zebrafish Embryos

Glucocorticoids in aquatic systems originating from natural excretion and medical use may pose a risk to fish. Here, we analyzed physiological and transcriptional effects of clobetasol propionate (CLO), cortisol and cortisone in zebrafish embryos as single compounds and binary mixtures. CLO and cortisol, but not cortisone showed a concentration-dependent decrease in muscle contraction, increase in heart rate, and accelerated hatching. CLO also induced immobilization and edema at high concentrations. Transcription analysis covering up to 26 genes showed that mostly genes related to glucose metabolism, immune system and development were differentially expressed at 91 ng/L and higher. CLO showed stronger effects on immune system genes than cortisol, which was characterized by upregulation of fkbp5, irg1l, gilz, and socs3, and development genes, matrix metalloproteinases mmp-9 and mmp-13, while cortisol led to stronger upregulation of the gluconeogenesis genes g6pca and pepck1. CLO also induced genes regulating the circadian rhythm, nr1d1 and per1a. In contrast, cortisone led to down-regulation of vitellogenin. Binary mixtures of cortisol and CLO mostly showed a similar activity as CLO alone on physiological and transcriptional end points but additive effects in heart rate and pepck1 upregulation, which indicates that mixtures of glucocorticoids may be of concern for developing fish.

Cardio-respirometry disruption in zebrafish (Danio rerio) embryos exposed to hydraulic fracturing flowback and produced water

Hydraulic fracturing to extract oil and natural gas reserves is an increasing practice in many international energy sectors. Hydraulic fracturing flowback and produced water (FPW) is a hyper saline wastewater returned to the surface from a fractured well containing chemical species present in the initial fracturing fluid, geogenic contaminants, and potentially newly synthesized chemicals formed in the fracturing well environment. However, information on FPW toxicological mechanisms of action remain largely unknown. Both cardiotoxic and respirometric responses were explored in zebrafish (Danio rerio) embryos after either an acute sediment-free (FPW-SF) or raw/sediment containing (FPW-S) fraction exposure of 24 and 48 h at 2.5% and 5% dilutions. A 48 h exposure to either FPW fraction in 24-72 h post fertilization zebrafish embryos significantly increased occurrences of pericardial edema, yolk-sac edema, and tail/spine curvature. In contrast, larval heart rates significantly decreased after FPW fraction exposures. FPW-S, but not FPW-SF, at 2.5% doses significantly reduced embryonic respiration/metabolic rates (MO₂), while for 5% FPW, both fractions reduced MO₂. Expression of select cardiac genes were also significantly altered in each FPW exposure group, implicating a cardiovascular system compromise as the potential cause for reduced embryonic MO₂. Collectively, these results support our hypothesis that organics are major contributors to cardiac and respiratory responses to FPW exposure in zebrafish embryos. Our study is the first to investigate cardiac and respiratory sub-lethal effects of FPW exposure, demonstrating that FPW effects extend beyond initial osmotic stressors and verifies the use of respirometry as a potential marker for FPW exposure.

Loss of αB-crystallin function in zebrafish reveals critical roles in the development of the lens and stress resistance of the heart

Genetic mutations in the human small heat shock protein αB-crystallin have been implicated in autosomal cataracts and skeletal myopathies, including heart muscle diseases (cardiomyopathy). Although these mutations lead to modulation of their chaperone activity in vitro, the in vivo functions of αB-crystallin in the maintenance of both lens transparency and muscle integrity remain unclear. This lack of information has hindered a mechanistic understanding of these diseases. To better define the functional roles of αB-crystallin, we generated loss-of-function zebrafish mutant lines by utilizing the CRISPR/Cas9 system to specifically disrupt the two αB-crystallin genes, αBa and αBb We observed lens abnormalities in the mutant lines of both genes, and the penetrance of the lens phenotype was higher in αBa than αBb mutants. This finding is in contrast with the lack of a phenotype previously reported in αB-crystallin knock-out mice and suggests that the elevated chaperone activity of the two zebrafish orthologs is critical for lens development. Besides its key role in the lens, we uncovered another critical role for αB-crystallin in providing stress tolerance to the heart. The αB-crystallin mutants exhibited hypersusceptibility to develop pericardial edema when challenged by crowding stress or exposed to elevated cortisol stress, both of which activate glucocorticoid receptor signaling. Our work illuminates the involvement of αB-crystallin in stress tolerance of the heart presumably through the proteostasis network and reinforces the critical role of the chaperone activity of αB-crystallin in the maintenance of lens transparency.

Multi-organ toxicity induced by fine particulate matter PM2.5 in zebrafish (Danio rerio) model

The fine particulate matter (PM_2.5) in air pollution is a major public health concern and now known to contribute to severe diseases, therefore, a comprehensive understanding of PM_2.5-induced adverse effects in living organisms is needed urgently. This study was aimed to evaluate the toxicity of PM_2.5 on multi-organ systems in a zebrafish (Danio rerio) model. The embryonic toxicity induced by PM_2.5 was demonstrated by an increase in mortality and inhibition of hatching rate, in a dose- and time-dependent manner. PM_2.5 caused the pericardial edema, as well as reducing heart rate and cardiac output. The area of sub-intestinal vessels (SIVs) was significant reduced in Tg(fli-1:EGFP) transgenic zebrafish lines. Morphological defects and yolk sac retention were associated with hepatocyte injury. In addition, PM_2.5 disrupted the axonal integrity, altering of axon length and pattern in Tg(NBT:EGFP) transgenic lines. Genes involved in cardiac function (spaw, supt6h, cmlc1), angiogenesis (vegfr2a, vegfr2b), and neural function (gabrd, chrna3, npy8br) were markedly down-regulated; while genes linked to hepatic metabolism (cyp1a, cyp1b1, cyp1c1) were significantly up-regulated by PM_2.5. In summary, our data showed that PM_2.5 induced the cardiovascular toxicity, hepatotoxicity and neurotoxicity in zebrafish, suggested that PM_2.5 could cause multi-organ toxicity in aquatic organism.

Bigger is not better: cortisol-induced cardiac growth and dysfunction in salmonids

Stress and elevated cortisol levels are associated with pathological heart growth and cardiovascular disease in humans and other mammals. We recently established a link between heritable variation in post-stress cortisol production and cardiac growth in salmonid fish too. A conserved stimulatory effect of the otherwise catabolic steroid hormone cortisol is probably implied, but has to date not been established experimentally. Furthermore, whereas cardiac growth is associated with failure of the mammalian heart, pathological cardiac hypertrophy has not previously been described in fish. Here, we show that rainbow trout (Oncorhynchus mykiss) treated with cortisol in the diet for 45 days have enlarged hearts with lower maximum stroke volume and cardiac output. In accordance with impaired cardiac performance, overall circulatory oxygen-transporting capacity was diminished as indicated by reduced aerobic swimming performance. In contrast to the well-known adaptive/physiological heart growth observed in fish, cortisol-induced growth is maladaptive. Furthermore, the observed heart growth was associated with up-regulated signature genes of mammalian cardiac pathology, suggesting that signalling pathways mediating cortisol-induced cardiac remodelling in fish are conserved from fish to mammals. Altogether, we show that excessive cortisol can induce pathological cardiac remodelling. This is the first study to report and integrate the etiology, physiology and molecular biology of cortisol-induced pathological remodelling in fish.

Maternal cortisol stimulates neurogenesis and affects larval behaviour in zebrafish

Excess glucocorticoid transferred from stressed mother to the embryo affects developing vertebrate offspring, but the underlying programming events are unclear. In this study, we tested the hypothesis that increased zygotic glucocorticoid deposition, mimicking a maternal stress scenario, modifies early brain development and larval behaviour in zebrafish (Danio rerio). Cortisol was microinjected into the yolk at one cell-stage, to mimic maternal transfer, and the larvae [96 hours post-fertilization (hpf)] displayed increased activity in light and a reduction in thigmotaxis, a behavioural model for anxiety, suggesting an increased propensity for boldness. This cortisol-mediated behavioural phenotype corresponded with an increase in primary neurogenesis, as measured by incorporation of EdU at 24 hpf, in a region-specific manner in the preoptic region and the pallium, the teleostean homolog of the hippocampus. Also, cortisol increased the expression of the proneural gene neurod4, a marker of neurogenesis, in a region- and development-specific manner in the embryos. Altogether, excess zygotic cortisol, mimicking maternal stress, affects early brain development and behavioural phenotype in larval zebrafish. We propose a key role for cortisol in altering brain development leading to enhanced boldness, which may be beneficial in preparing the offspring to a stressful environment and enhancing fitness.

Stickleback embryos use ATP-binding cassette transporters as a buffer against exposure to maternally derived cortisol

Offspring from females that experience stressful conditions during reproduction often exhibit altered phenotypes and many of these effects are thought to arise owing to increased exposure to maternal glucocorticoids. While embryos of placental vertebrates are known to regulate exposure to maternal glucocorticoids via placental steroid metabolism, much less is known about how and whether egg-laying vertebrates can control their steroid environment during embryonic development. We tested the hypothesis that threespine stickleback (Gasterosteus aculeatus) embryos can regulate exposure to maternal steroids via active efflux of maternal steroids from the egg. Embryos rapidly (within 72 h) cleared intact steroids, but blocking ATP-binding cassette (ABC) transporters inhibited cortisol clearance. Remarkably, this efflux of cortisol was sufficient to prevent a transcriptional response of embryos to exogenous cortisol. Taken together, these findings suggest that, much like their placental counterparts, developing fish embryos can actively regulate their exposure to maternal cortisol. These findings highlight the fact that even in egg-laying vertebrates, the realized exposure to maternal steroids is mediated by both maternal and embryonic processes and this has important implications for understanding how maternal stress influences offspring development.

Glucocorticoids in Fish Eggs: Variation, Interactions with the Environment, and the Potential to Shape Offspring Fitness

Wild and captive vertebrates face multiple stressors that all have the potential to induce chronic maternal stress (i.e., sustained, elevated plasma glucocorticoids), resulting in embryo exposure to elevated maternally derived glucocorticoids. In oviparous taxa such as fish, maternally derived glucocorticoids in eggs are known for their capacity to shape offspring phenotype. Using a variety of methodologies, scientists have quantified maternally derived levels of egg cortisol, the primary glucocorticoid in fishes, and examined the cascading effects of egg cortisol on progeny phenotype. Here we summarize and interpret the current state of knowledge on egg cortisol in fishes and the relationships linking maternal stress/state to egg cortisol and offspring phenotype/fitness. Considerable variation in levels of egg cortisol exists across species and among females within a species; this variation is hypothesized to be due to interspecific differences in reproductive life history and intraspecific differences in female condition. Outcomes of experimental studies manipulating egg cortisol vary both inter- and intraspecifically. Moreover, while exogenous elevation of egg cortisol (as a proxy for maternal stress) induces phenotypic changes commonly considered to be maladaptive (e.g., smaller offspring size), emerging work in other taxa suggests that there can be positive effects on fitness when the offspring's environment is taken into account. Investigations into (i) mechanisms by which egg cortisol elicits phenotypic change in offspring (e.g., epigenetics), (ii) maternal and offspring buffering capacity of cortisol, and (iii) factors driving natural variation in egg cortisol and how this variation affects offspring phenotype and fitness are all germane to discussions on egg glucocorticoids as signals of maternal stress.

Corticosteroid Fludrocortisone Acetate Targets Multiple End Points in Zebrafish (Danio rerio) at Low Concentrations

Synthetic corticosteroids may pose an environmental risk to fish. Here, we describe multiend point responses of adult zebrafish (8 months old) upon 21-day exposure to a commonly prescribed corticosteroid, fludrocortisone acetate (FLU), at concentrations between 0.006 and 42 μg/L. No remarkable reproductive impacts were observed, while physiological effects, including plasma glucose level and blood leukocyte numbers were significant altered even at 42 ng/L. Ovary parameters and transcriptional analysis of hypothalamic-pituitary-gonadal-liver axis revealed negligible effects. Significant alterations of the circadian rhythm network were observed in the zebrafish brain. Transcripts of several biomarker genes, including per1a and nr1d1, displayed strong transcriptional changes, which occurred at environmental relevant concentrations of 6 and 42 ng/L FLU. Importantly, the development and behavior of F1 embryos were significant changed. Heartbeat, hatching success and swimming behavior of F1 embryos were all increased even at 6 and 42 ng/L. All effects were further confirmed by exposure of eleuthero-embryos. Significant transcriptional changes of biomarker genes involved in gluconeogenesis, immune response and circadian rhythm in eleuthero-embryos confirmed the observations in adult fish. Hatching success, heartbeat, and swimming activity were increased at 81 ng/L and higher, as with F1 embryos. These results provide novel insights into the understanding of potential environmental risks of corticosteroids.

Chronic effects of hydroxypropyl-β-cyclodextrin on reproduction in the American flagfish (Jordanella floridae) over one complete life cycle

Understanding the environmental risks of pharmaceuticals and personal care products (PPCPs) has become very important in the field of aquatic toxicology. Hydroxylpropyl-β-cyclodextrin (HPβCD) is an amphiphilic, toroidal shaped molecule with the ability to form noncovalent inclusion complexes with a variety of guest molecules. The molecule can reduce volatility as well as improve the aqueous solubility of apolar guest compounds and is an emerging PPCP. As such, HPβCD is the active ingredient in Febreze (Procter & Gamble) and is extensively used as an excipient in the pharmaceutical industry. With the potential for entering the environment through waste-water treatment plant (WWTP) effluent, HPβCD poses an unknown risk to nontarget aquatic biota. A 145-d chronic full life-cycle exposure using American flagfish (Jordanella floridae) was completed using flow-through nominal concentrations of 0 µg/L (control), 5 µg/L, 16 µg/L, 50 µg/L, 160 µg/L, 500 µg/L, and 1600 μg/L of HPβCD maintained via a peristaltic pump. Fecundity, growth, and liver somatic index were all monitored, and no significant difference was found between treatments and controls (p > 0.05). However, a significant increase in the gonadosomatic index was observed in females exposed to HPβCD (p ≤ 0.05). Reduced offspring growth was observed after exposure in the same manner as the parental generation (p ≤ 0.05). Furthermore, an acute copper toxicity challenge assay was conducted on second-generation flagfish larvae, and a decrease in copper tolerance was observed in larval progeny from parents exposed to HPβCD. Environ Toxicol Chem 2016;35:1358-1363. © 2015 SETAC.

Physiological and Behavioral Effects of Exposure to Environmentally Relevant Concentrations of Prednisolone During Zebrafish (Danio rerio) Embryogenesis

The presence of synthetic glucocorticoids within the aquatic environment has been highlighted as a potential environmental concern as they may mimic the role of endogenous glucocorticoids during vertebrate ontogeny. Prednisolone is a commonly prescribed synthetic glucocorticoid which has been repeatedly detected in the environment. This study investigated the impact of environmentally relevant concentrations of prednisolone (0.1, 1, and 10 μg/L) during zebrafish embryogenesis using physiological and behavioral end points which are known to be mediated by endogenous glucocorticoids. The frequency of spontaneous muscle contractions (24 hpf) was significantly reduced by prednisolone and 0.1 μg/L increased the distance embryos swam in response to a mechanosensory stimulus (48 hpf). The percentage of embryos hatched significantly increased following prednisolone treatment (1 and 10 μg/L), while growth and mortality were unaffected. The onset of heart contraction was differentially affected by prednisolone while heart rate and oxygen consumption both increased significantly throughout embryogenesis. No substantial effect on the axial musculature was observed. Morphological changes to the lower jaw were detected at 96 hpf in response to 1 μg/L of prednisolone. Several parameters of swim behavior were also significantly affected. Environmentally relevant concentrations of prednisolone therefore alter early zebrafish ontogeny and significantly affect embryo behavior.

Programming of the hypothalamic-pituitary-interrenal axis by maternal social status in zebrafish (Danio rerio)

The present study examined the effects of maternal social status, with subordinate status being a chronic stressor, on development and activity of the stress axis in zebrafish embryos and larvae. Female zebrafish were confined in pairs for 48 h to establish dominant/subordinate hierarchies; their offspring were reared to 144 h post-fertilization (hpf) and sampled at five time points over development. No differences were detected in maternal cortisol contribution, which is thought to be an important programmer of offspring phenotype. However, once zebrafish offspring began to synthesize cortisol de novo (48 hpf), larvae of dominant females exhibited significantly lower baseline cortisol levels than offspring of subordinate females. These lower cortisol levels may reflect reduced hypothalamic-pituitary-interrenal (HPI) axis activity, because corticotropin-releasing factor (crf) and cytochrome p450 side chain cleavage enzyme (p450scc) mRNA levels also were lower in larvae from dominant females. Moreover, baseline mRNA levels of HPI axis genes continued to be affected by maternal social status beyond 48 hpf. At 144 hpf, stress-induced cortisol levels were significantly lower in offspring of subordinate females. These results suggest programming of stress axis function in zebrafish offspring by maternal social status, emphasizing the importance of maternal environment and experience on offspring stress axis activity.

Triclosan is a mitochondrial uncoupler in live zebrafish

Triclosan (TCS) is a synthetic antimicrobial agent used in many consumer goods at millimolar concentrations. As a result of exposure, TCS has been detected widely in humans. We have recently discovered that TCS is a proton ionophore mitochondrial uncoupler in multiple types of living cells. Here, we present novel data indicating that TCS is also a mitochondrial uncoupler in a living organism: 24-hour post-fertilization (hpf) zebrafish embryos. These experiments were conducted using a Seahorse Bioscience XF^e 96 Extracellular Flux Analyzer modified for bidirectional temperature control, using the XF96 spheroid plate to position and measure one zebrafish embryo per well. Using this method, after acute exposure to TCS, the basal oxygen consumption rate (OCR) increases, without a decrease in survival or heartbeat rate. TCS also decreases ATP-linked respiration and spare respiratory capacity and increases proton leak: all indicators of mitochondrial uncoupling. Our data indicate, that TCS is a mitochondrial uncoupler in vivo, which should be taken into consideration when assessing the toxicity and/or pharmaceutical uses of TCS. This is the first example of usage of a Seahorse Extracellular Flux Analyzer to measure bioenergetic flux of a single zebrafish embryo per well in a 96-well assay format. The method developed in this study provides a high-throughput tool to identify previously unknown mitochondrial uncouplers in a living organism. Copyright © 2016 John Wiley & Sons, Ltd.

Maternal Cortisol Mediates Hypothalamus-Pituitary-Interrenal Axis Development in Zebrafish

In zebrafish (Danio rerio), de novo synthesis of cortisol in response to stressor exposure commences only after hatch. Maternally deposited cortisol is present during embryogenesis, but a role for this steroid in early development is unclear. We tested the hypothesis that maternal cortisol is essential for the proper development of hypothalamus-pituitary-interrenal (HPI) axis activity and the onset of the stressor-induced cortisol response in larval zebrafish. In this study, zygotic cortisol content was manipulated by microinjecting antibody to sequester this steroid, thereby making it unavailable during embryogenesis. This was compared with embryos containing excess cortisol by microinjection of exogenous steroid. The resulting larval phenotypes revealed distinct treatment effects, including deformed mesoderm structures when maternal cortisol was unavailable and cardiac edema after excess cortisol. Maternal cortisol unavailability heightened the cortisol stress response in post-hatch larvae, whereas excess cortisol abolished the stressor-mediated cortisol elevation. This contrasting hormonal response corresponded with altered expression of key HPI axis genes, including crf, 11B hydroxylase, pomca, and star, which were upregulated in response to reduced cortisol availability and downregulated when embryos had excess cortisol. These findings for the first time underscore a critical role for maternally deposited cortisol in programming HPI axis development and function in zebrafish.

Maternal stress-associated cortisol stimulation may protect embryos from cortisol excess in zebrafish

Abnormal embryo cortisol level causes developmental defects and poor survival in zebrafish (Danio rerio). However, no study has demonstrated that maternal stress leads to higher embryo cortisol content in zebrafish. We tested the hypothesis that maternal stress-associated elevation in cortisol levels increases embryo cortisol content in this asynchronous breeder. Zebrafish mothers were fed cortisol-spiked food for 5 days, to mimic maternal stress, followed by daily breeding for 10 days to monitor temporal embryo cortisol content. Cortisol treatment increased mean embryo yield, but the daily fecundity was variable among the groups. Embryo cortisol content was variable in both groups over a 10-day period. A transient elevation in cortisol levels was observed in the embryos from cortisol-fed mothers only on day 3, but not on subsequent days. We tested whether excess cortisol stimulates 11βHSD2 expression in ovarian follicles as a means to regulate embryo cortisol deposition. Cortisol treatment in vitro increased 11β HSD2 levels sevenfold, and this expression was regulated by actinomycin D and cycloheximide suggesting tight regulation of cortisol levels in the ovarian follicles. We hypothesize that cortisol-induced upregulation of 11βHSD2 activity in the ovarian follicles is a mechanism restricting excess cortisol incorporation into the eggs during maternal stress.