Estrogen-dependent seasonal adaptations in the immune response of fish

Hepatic immune response of Coilia nasus infected with Anisakidae during ovarian development

Anisakidae parasitism is a prevalent disease in wild populations of Coilia nasus, and can result in a significant loss of germplasm resources. To elucidate the immune response mechanism of C. nasus livers to Anisakidae infection, we collected and analysed 18 parasitic and 18 non-parasitic livers at gonadal developmental stages II, III, and V using histopathology, molecular biology and transcriptome methods. The hepatic portal area of the parasitic group exhibited an increase in the fibrous stroma and thickened hepatic arteries with positive Ly-6G staining, indicating inflammation and immune responses in the liver. Hepatocyte cytokine levels and the expression of liver function-related genes indicated that fish livers responded similarly to Anisakidae parasitism across different gonadal developmental stages. Oxidative stress indices showed more intense changes in stage II samples, whereas gene expression levels of Nrf2 and C3 were significantly increased in parasitised livers during stage III and V. Liver transcriptome sequencing identified 2575 differentially expressed genes between the parasitic and non-parasitic groups at the three gonadal developmental stages. KEGG pathway analysis showed that natural killer cell-mediated cytotoxicity, the NOD-like receptor signaling pathway, neutrophil extracellular trap formation, and other immune pathways were significantly enriched. Expression patterns varied across developmental stages, suggesting that innate immunity was primarily responsible for the liver immune response to Anisakidae infection during C. nasus migration, possibly related to water temperature changes or shifts in the gonadal developmental stage. In summary, this study investigated the immune response of C. nasus to Anisakidae parasitism under natural conditions, focusing on reproductive aspects and environmental changes, thereby establishing a foundation for elucidating the molecular mechanisms underlying the immune response of Anisakidae in C. nasus.

Season affects the estrogen system and the immune response of common carp

The physiology of ectothermic animals, including fish, is strictly regulated by season-related external factors such as temperature or photoperiod. The immune response and the production of hormones, such as estrogens, are therefore also subject to seasonal changes. This study in common carp aimed to determine how the season affects the estrogen system and the immune response, including the antibacterial response during Aeromonas salmonicida infection. We compared the immune reaction in spring and autumn in the head kidney and liver and found that carp have higher levels of blood 17β-estradiol in autumn, while in the liver of these fish there is a higher constitutive expression of genes encoding vitellogenin, estrogen receptors and Cyp19 aromatase than in spring. Fish sampled in autumn also exhibited higher expression of immune-related genes in the liver. In contrast, in the head kidney from fish sampled in the autumn, the expression of genes encoding estrogen receptors and aromatase was lower than in spring, and a similar profile of expression was also measured in the head kidney for inos, arginases and il-10. In turn, during bacterial infection, we observed higher upregulation of the expression of inos, il-12p35, ifnγ-2, arginase 2 and il-10 in the liver of carp sampled in spring. In the liver of carp infected in spring a higher upregulation of the expression of the genes encoding CRPs was observed compared to fish infected during autumn. The opposite trend occurred in the head kidney, where the upregulation of the expression of the genes involved in the immune response was higher in fish infected in autumn than in those infected in spring. During the infection, also season-dependent changes occurred in the estrogen system. In conclusion, we demonstrated that season differentially affects the estrogenic and immune activity of the head kidney and liver. These results reinforce our previous findings that the endocrine and immune systems cooperate in maintaining homeostasis and fighting infection.

Links between reproduction and immunity in two sympatric wild marine fishes

According to life-history theory, limited resources can result in trade-offs between costly physiological functions. Particularly, it can be expected that individuals present lower immune function, or an alternative immunological strategy, during their reproductive compared to their non-reproductive season. Here we investigate the link between reproduction and immunity in two sympatric marine fish species, the rockfish Sebastes oculatus and the sandperch Pinguipes brasilianus. The results showed lower values of total white blood cells and spleen index, but higher levels of natural antibodies (only in females) in reproductive rockfish compared to non-reproductive ones. On the other hand, reproductively active sandperch showed lower levels of natural antibodies and a higher neutrophil to lymphocyte ratio and spleen index (only in males), compared to non-reproductive ones. Also, negative correlations between reproductive and immune parameters were observed in female rockfish at the individual level, but not in sandperch. Our results are consistent with the presence of different immunological strategies in reproductive and non-reproductive periods, with patterns that appear to be species-specific. This specificity suggests that various aspects of immunity might respond differentially to resource limitation, which could be associated with the disparate life-history strategies of the studied species. Alternatively, though not exclusively, the observed patterns could be driven by abiotic factors that characterize the reproductive season of each species (i.e., winter for rockfish, summer for sandperch). Our study contributes to ecoimmunological knowledge on free-living fish and highlights that detection of trade-offs can depend on the combination of study species, season, sex, and specific immune components measured.

Proteins journey-from marine to freshwater ecosystem: blood plasma proteomic profiles of pink salmon Oncorhynchus gorbuscha Walbaum, 1792 during spawning migration

The pink salmon (Oncorhynchus gorbuscha) is a commercial anadromous fish species of the family Salmonidae. This species has a 2-year life cycle that distinguishes it from other salmonids. It includes the spawning migration from marine to freshwater environments, accompanied by significant physiological and biochemical adaptive changes in the body. This study reveals and describes variability in the blood plasma proteomes of female and male pink salmon collected from three biotopes-marine, estuarine and riverine-that the fish pass through in spawning migration. Identification and comparative analysis of blood plasma protein profiles were performed using proteomics and bioinformatic approaches. The blood proteomes of female and male spawners collected from different biotopes were qualitatively and quantitatively distinguished. Females differed primarily in proteins associated with reproductive system development (certain vitellogenin and choriogenin), lipid transport (fatty acid binding protein) and energy production (fructose 1,6-bisphosphatase), and males in proteins involved in blood coagulation (fibrinogen), immune response (lectins) and reproductive processes (vitellogenin). Differentially expressed sex-specific proteins were implicated in proteolysis (aminopeptidases), platelet activation (β- and γ-chain fibrinogen), cell growth and differentiation (a protein containing the TGF_BETA_2 domain) and lipid transport processes (vitellogenin and apolipoprotein). The results are of both fundamental and practical importance, adding to existing knowledge of the biochemical adaptations to spawning of pink salmon, a representative of economically important migratory fish species.

Assessment of glucocorticoids, sex steroids, and innate immunity in wild red-eared slider turtles (Trachemys scripta elegans)

When access to resources is limited, organisms must shift energy investment among physiological processes to survive, reproduce, and respond to unpredictable events. The shifting of these limited resources among processes may result in physiological tradeoffs, often mediated by glucocorticoids. We assessed relationships among the physiological processes of immunity, reproduction, and the stress response in wild adult red-eared slider turtles (Trachemys scripta elegans). Red-eared sliders exhibit a multi-clutching reproductive strategy that requires high energetic investment in reproduction at the beginning of the nesting season in females. Males mate in spring and undergo spermatogenesis and mating in late summer/early fall. We expected to observe tradeoffs when investment toward reproductive processes was particularly demanding. To test this, we subjected 123 individuals to a standardized acute stressor and collected blood to measure innate immunocompetence and circulating steroid hormone concentrations. Tradeoffs between female reproduction and immunocompetence occurred early in the nesting season. This high reproductive investment was evident by heightened circulating progesterone and reduced baseline innate immunity. Corticosterone (CORT) was also high during this period, indicating a role in facilitating allocation of energy. Tradeoffs were not as evident in males, though males upregulated innate immune function, baseline CORT, and testosterone prior to fall spermatogenesis and mating. Throughout the entire sampling period, both males and females increased CORT and immunocompetence following the acute standardized stressor. Taken together, we concluded that reproduction requires shifts in energy allocation in during the highest reproductive period for females but all individuals in this population remain able to respond to the standardized stressor even during increased reproductive investment. These findings reinforce the continuing evidence that physiological relationships are context-dependent and resource demands are dynamic across the reproductive season.

Sex and reproductive development impact skin mucosal epithelium immunity, antimicrobial capacity, and up-regulation of immune-related gene of goldfish (Carassius auratus)

This study evaluated the epidermis mucosal capacity of goldfish (Carassius auratus) during different stages of reproductive development in both females and males. In this regard, the activity of mucolytic immune enzymes, i.e., lysozyme, complement and peroxidase, as well as the activity of alkaline phosphatase (ALP) were evaluated. There were five stages for females i.e., immature (f1), cortical alveoli (f2), early and late-vitellogenesis (vtg) (f3 and f4) and ripe (f5); as well as two stages for males spermatogenesis (m1) and spermiation (m2). Some stages were also examined for the mucosal antimicrobial activity against specific pathogens. The results showed that the mucosal lysozyme activity increased significantly during vitellogenesis (P < 0.05), but no lysozyme activity was detected in plasma. On the contrary, the complement activity was only observed in female plasma, and it was significantly higher at f3 compared to the other developmental stages. Both the plasma and mucosal ALP and peroxidase activities showed a significant increase by female reproductive development with the highest amounts at f4. Contrary to the female, no significant changes were observed in plasma and mucosal immune agents and biochemistry of the male. The f5-staged goldfish showed the highest antimicrobial activities against Gram-positive bacteria, i.e., Streptococcus faecium, Staphylococcus aureus and Micrococcus luteus (P < 0.05). Our results also represented the up-regulation of lysozyme (c-lys) gene expression by effects of female maturational development in ovary, liver and skin, while male goldfish showed no significant changes in c-lys expression. Moreover, there were positive correlations between c-lys expression, mucosal lysozyme activity and calcium levels in females (P < 0.01). Overall, our findings revealed that vtg process improves mucosal innate immunity that leads to activate antimicrobial components at spawning season.

Immune function modulation during artificial ovarian maturation in Japanese eel (Anguilla japonica): A transcriptome profiling approach

The Japanese eel (Anguilla japonica) experiences dramatic internal and external environmental changes during its transoceanic reproductive migrations. Here, we assess immune function changes in the primary and secondary immune organs (head kidney and spleen) of A. japonica during artificial ovarian maturation at the previtellogenic (PV), midvitellogenic (MV), and ovulating (OV) stages by transcriptome analyses. Stress responses were also assessed by determining the serum concentrations of lysozyme, alkaline phosphatase, acid phosphatase, total antioxidant capacity, and superoxide dismutase. Our results showed that together with increased serum 17β-estrogen and testosterone, lysozyme activity and antioxidant capacity were suppressed during artificial ovarian maturation. Comparisons across these developmental stages identified 60 (head kidney) and 36 (spleen) differentially expressed genes associated with the immune system. Genes related to the key activation markers of innate immune function, such as CXCL10, CXCL11, CCL20, HSP90B, MMP9, and MMP13, were upregulated and significantly enriched in the interleukin-17 signaling pathway. Adaptive immune function-related genes (IGM and MHC1) were upregulated in the head kidney from PV to MV, and their levels increased thereafter in the spleen. Moreover, a correlation between Pax5 expression and IGM expression in the spleen of MV (IGM+/Pax5+) and OV (IGM++/Pax5-) stage suggests that adaptive immune function was enhanced during ovarian maturation. To our knowledge, the present study is the first to describe transcriptome profiling of immune organs during ovarian maturation in teleost. Our findings suggest that the interleukin-17 pathway and IgM may play important roles in spawning.

Integrated Omics Approaches Revealed the Osmotic Stress-Responsive Genes and Microbiota in Gill of Marine Medaka

This is the first study using the transcriptome and 16S rRNA gene sequencing to report the hypotonic responsive genes in gill cells and the compositions of gill microbiota in marine medaka. The overlapped glycosaminoglycan- and chitin-related pathways suggest host-bacterium interaction in fish gill during osmotic stress.

Site- and Individual-Level Contaminations Affect Infection Prevalence of an Emerging Infectious Disease of Amphibians

Emerging infectious disease outbreaks are one of multiple stressors responsible for amphibian declines globally. In the northeastern United States, ranaviral diseases are prevalent in amphibians and other ectothermic species, but there is still uncertainty as to whether their presence is leading to population-level effects. Further, there is also uncertainty surrounding the potential interactions among disease infection prevalence in free-ranging animals and habitat degradation (co-occurrence of chemical stressors). The present study was designed to provide field-based estimates of the relationship between amphibian disease and chemical stressors. We visited 40 wetlands across three protected areas, estimated the prevalence of ranavirus among populations of larval wood frogs and spotted salamanders, and assessed chemical and biological stressors in wetland habitats and larval amphibians using a suite of selected bioassays, screening tools, and chemical analyses. Ranavirus was detected on larval amphibians from each protected area with an estimated occupancy ranging from 0.27 to 0.55. Considerable variation in ranavirus occupancy was also observed within and among each protected area. Of the stressors evaluated, ranavirus prevalence was strongly and positively related to concentrations of metalloestrogens (metals with the potential to bind to estrogen receptors) and total metals in wetland sediments and weakly and negatively related to total pesticide concentrations in larval amphibians. These results can be used by land managers to refine habitat assessments to include such environmental factors with the potential to influence disease susceptibility. Environ Toxicol Chem 2022;41:781-791. © 2022 SETAC. This article has been contributed to by US Government employees and their work is in the public domain in the USA.

Proteomic changes in the extracellular environment of sea bass thymocytes exposed to 17α-ethinylestradiol in vitro

The thymus is an important immune organ providing the necessary microenvironment for the development of a diverse, self-tolerant T cell repertoire, which is selected to allow for the recognition of foreign antigens while avoiding self-reactivity. Thymus function and activity are known to be regulated by sex steroid hormones, such as oestrogen, leading to sexual dimorphisms in immunocompetence between males and females. The oestrogenic modulation of the thymic function provides a potential target for environmental oestrogens, such as 17α-ethynylestradiol (EE2), to interfere with the cross-talk between the endocrine and the immune system. Oestrogen receptors have been identified on thymocytes and the thymic microenvironment, but it is unclear how oestrogens regulate thymic epithelial and T cell communication including paracrine signalling. Much less is known regarding intrathymic signalling in fish. Secretomics allows for the analysis of complex mixtures of immunomodulatory signalling factors secreted by T cells. Thus, in the present study, isolated thymocytes of the European sea bass, Dicentrarchus labrax, were exposed in vitro to 30 nM EE2 for 4 h and the T cell-secretome (i.e., extracellular proteome) was analysed by quantitative label-free mass-spectrometry. Progenesis revealed a total of 111 proteins differentially displayed between EE2-treated and control thymocytes at an α-level of 5% and a 1.3-fold change cut off (n = 5-6). The EE2-treatment significantly decreased the level of 90 proteins. Gene ontology revealed the proteasome to be the most impacted pathway. In contrast, the abundance of 21 proteins was significantly increased, with cathepsins showing the highest level of induction. However, no particular molecular pathway was significantly altered for these upregulated proteins. To the best of our knowledge, this work represents the first study of the secretome of the fish thymus exposed to the environmental oestrogen EE2, highlighting the impact on putative signalling pathways linked to immune surveillance, which may be of crucial importance for fish health and defence against pathogens.

Impact of Estrogens Present in Environment on Health and Welfare of Animals

Simple Summary

Estrogens are a group of steroid hormones that recently have gained even more attention in the eyes of scientists. There is an ongoing discussion in the scientific community about their relevance as environmental contaminants and the danger they pose to animal health and welfare. In available literature we can find many examples of their negative effects and mechanisms that are involved with such phenomena.

Abstract

Nowadays, there is a growing interest in environmental pollution; however, knowledge about this aspect is growing at an insufficient pace. There are many potential sources of environmental contamination, including sex hormones—especially estrogens. The analyzed literature shows that estrone (E1), estradiol (E2), estriol (E3), and synthetic ethinyloestradiol (EE2) are the most significant in terms of environmental impact. Potential sources of contamination are, among others, livestock farms, slaughterhouses, and large urban agglomerations. Estrogens occurring in the environment can negatively affect the organisms, such as animals, through phenomena such as feminization, dysregulation of natural processes related to reproduction, lowering the physiological condition of the organisms, disturbances in the regulation of both proapoptotic and anti-apoptotic processes, and even the occurrence of neoplastic processes thus drastically decreasing animal welfare. Unfortunately, the amount of research conducted on the negative consequences of their impact on animal organisms is many times smaller than that of humans, despite the great richness and diversity of the fauna. Therefore, there is a need for further research to help fill the gaps in our knowledge.

17α-ethinylestradiol and 4-tert-octylphenol concurrently disrupt the immune response of common carp

The aquatic environment is massively polluted with endocrine-disrupting compounds (EDCs) including synthetic estrogens (e.g. 17α-ethinylestradiol, EE2) and alkylphenols (e.g. 4-tert-octylphenol, 4t-OP). A major mechanism of action for estrogenic EDCs is their interaction with estrogen receptors and consequently their modulation of the action of enzymes involved in steroid conversion e.g. aromatase CYP19. We now studied the effects of EE2 and 4t-OP on the anti-bacterial immune response of common carp. We investigated effects on the number/composition of inflammatory leukocytes and on the gene expression of mediators that regulate inflammation and EDC binding. In vitro we found that high concentrations of both EE2 and 4t-OP down-regulated IFN-γ2 and IFN-γ-dependent immune responses in LPS-stimulated monocytes/macrophages. Similarly, during bacterial infection in fish, in vivo treated with EE2 and 4t-OP, decreased gene expression of il-12p35 and of ifn-γ2 was found in the focus of inflammation. Moreover, during A. salmonicida-induced infection in EE2-treated carp, but not in fish fed with 4t-OP-treated food, we found an enhanced inflammatory reaction manifested by high number of inflammatory peritoneal leukocytes, including phagocytes and higher expression of pro-inflammatory mediators (inos, il-1β, cxcl8_l2). Furthermore, in the liver, EE2 down-regulated the expression of acute phase proteins: CRPs and C3. Importantly, both in vitro and in vivo, EDCs altered the expression of estrogen receptors: nuclear (erα and erβ) and membrane (gpr30). EDCs also induced up-regulation of the cyp19b gene. Our findings reveal that contamination of the aquatic milieu with estrogenic EDCs, may considerably violate the subtle and particular allostatic interactions between the immune response and endogenous estrogens and this may have negative consequences for fish health.

Preparatory immunity: Seasonality of mucosal skin defences and Batrachochytrium infections in Southern leopard frogs

Accurately predicting the impacts of climate change on wildlife health requires a deeper understanding of seasonal rhythms in host-pathogen interactions. The amphibian pathogen, Batrachochytrium dendrobatidis (Bd), exhibits seasonality in incidence; however, the role that biological rhythms in host defences play in defining this pattern remains largely unknown. The aim of this study was to examine whether host immune and microbiome defences against Bd correspond with infection risk and seasonal fluctuations in temperature and humidity. Over the course of a year, five populations of Southern leopard frogs (Rana [Lithobates] sphenocephala) in Tennessee, United States, were surveyed for host immunity, microbiome and pathogen dynamics. Frogs were swabbed for pathogen load and skin bacterial diversity and stimulated to release stored antimicrobial peptides (AMPs). Secretions were analysed to estimate total hydrophobic peptide concentrations, presence of known AMPs and effectiveness of Bd growth inhibition in vitro. The diversity and proportion of bacterial reads with a 99% match to sequences of isolates known to inhibit Bd growth in vitro were used as an estimate of predicted anti-Bd function of the skin microbiome. Batrachochytrium dendrobatidis dynamics followed the expected seasonal fluctuations-peaks in cooler months-which coincided with when host mucosal defences were most potent against Bd. Specifically, the concentration and expression of stored AMPs cycled synchronously with Bd dynamics. Although microbiome changes followed more linear trends over time, the proportion of bacteria that can function to inhibit Bd growth was greatest when risk of Bd infection was highest. We interpret the increase in peptide storage in the fall and the shift to a more anti-Bd microbiome over winter as a preparatory response for subsequent infection risk during the colder periods when AMP synthesis and bacterial growth is slow and pathogen pressure from this cool-adapted fungus is high. Given that a decrease in stored AMP concentrations as temperatures warm in spring likely means greater secretion rates, the subsequent decrease in prevalence suggests seasonality of Bd in this host may be in part regulated by annual immune rhythms, and dominated by the effects of temperature.

17β-Estradiol affects the innate immune response in common carp

Inflammation is the evolutionary conserved immune response to harmful stimuli such as pathogens or damaged cells. This multistep process acts by removing injurious stimuli and initiating the healing process. Therefore, it must be tightly regulated by cytokines, chemokines, and enzymes, as well as neuroendocrine mediators. In the present work, we studied the immunoregulatory properties of 17β-estradiol (E2) in common carp. We determined the in vitro effects of E2 on the activity/polarization of macrophages and the in vivo effects during Aeromonas salmonicida-induced inflammation. In vitro, E2 reduced the lipopolysaccharide (LPS)-stimulated expression of pro- and anti-inflammatory mediator genes but did not change the gene expression of the estrogen receptors and of aromatase CYP19. In contrast, in vivo in the head kidney of A. salmonicida-infected fish, E2-treated feeding induced an upregulation of gene expression of pro-inflammatory (il-12p35 and cxcb2) and anti-inflammatory (arginase 1, arginase 2, il-10, and mmp9) mediators. Moreover, in infected fish fed with E2-treated food, a higher gene expression of the estrogen receptors and of the aromatase CYP19 was found. Our results demonstrate that estrogens can modulate the carp innate immune response, though the in vitro and in vivo effects of this hormone are contrasting. This implies that estradiol not only induces a direct effect on macrophages but rather exerts immunomodulatory actions through indirect mechanisms involving other cellular targets.

Seasonal simulated photoperiods influence melatonin release and immune markers of pike perch Sander lucioperca

Melatonin is considered as the time-keeping hormone acting on important physiological functions of teleosts. While the influence of melatonin on reproduction and development is well described, its potential role on immune functions has little been considered. In order to better define an immune modulation by the melatonin hormone, we hypothesized that natural variations of photoperiod and subsequent changes in melatonin release profile may act on immune status of pikeperch. Therefore, we investigated during 70 days the effects of two photoperiod regimes simulating the fall and spring in western Europe, on pikeperch physiological and immune responses. Samples were collected at 04:00 and 15:00 at days 1, 37 and 70. Growth, plasma melatonin levels, innate immune markers and expression of immune-relevant genes in head kidney tissue were assessed. While growth and stress level were not affected by the seasonal simulated photoperiods, nocturnal levels of plasma melatonin were photoperiod-dependent. Innate immune markers, including lysozyme, complement, peroxidase and phagocytic activities, were stimulated by the fall-simulated photoperiod and a significant correlation was made with plasma melatonin. In addition to bring the first evidence of changes in fish immunocompetence related to photoperiod, our results provide an additional indication supporting the immunomodulatory action of melatonin in teleosts.

Immune response of teleost fish to helminth parasite infection

Abstract Fish immune systems have become the subject of several studies due to the growing development of aquaculture and fisheries, and the demand for healthy produce for human consumption. Among the parasites responsible for diseases in fish farming, helminths stand out because they cause infections in farmed fish and decrease food conversion, zootechnical performance and meat quality. In the present review, the components that participate in the innate and adaptive immune responses of teleost fish that have so far been described are presented in order to summarize the defenses that these hosts have recourse to, in combating different groups of helminth parasites.

Environmental exposure to oestrogenic endocrine disruptors mixtures reflecting on gonadal sex steroids and gametogenesis of the neotropical fishAstyanax rivularis

Discharge of municipal wastewater promotes the entry of diverse oestrogenic compounds into the water bodies. This complex mixture of substances interferes in the steroidogenic pathway, being able to promote severe reproductive impairment in freshwater fish populations. The purpose of the present study was to evaluate the effects of oestrogenic endocrine disruptors (EDCs) mixture on gonadal sex steroids (testosterone, T; 11-ketotestosterone, 11-KT; 17β-oestradiol, E2; 17-hydroxyprogesterone, 17-OHP) in the peak of the reproductive season of Astyanax rivularis, correlating the results obtained with the proportion of germ cells and gonadal histopathology. Three sampling sites were chosen to conduct the study, one reference site (S1), without contamination by municipal wastewater and two sites (S2 and S3) receiving discharge of municipal wastewater. Males of A. rivularis presented higher concentrations of E2, lower androgens (T and 11-KT) in gonads when compared to males from site S1. Concentrations of 17-OHP did not present significant difference among sites. In sites S2 and S3, the proportion of early spermatocytes, spermatids and Leydig cells increased while spermatozoa decreased compared to fish from S1. The following gonadal histopathologies were detected in the male fishes: intersex gonads (28% in S3) and testicular degeneration with germinal epithelium exhibiting agglutinated germ cells masses and empty cysts (57% in S2 and 71% in S3). In females, concentrations of T, E2 and 17-OHP did not present significant difference among the sites, however higher 11-KT concentrations were detected in females from sites S2 and S3. A lower proportion of perinucleolar follicles and a higher incidence of vitellogenic follicles, besides, aged oocytes and the presence of eosinophilic proteinaceous fluid in the interstitial compartment were also found in females from impacted sites. These results indicate that the urbanization and consequent release of municipal wastewater containing oestrogenic compounds in the headwater creeks are altering the levels of sex hormones and gametogenesis of A. rivularis. Further studies should be performed to determine whether oestrogenic endocrine disrupters are disrupting the reproduction of A. rivularis.

Immune response of juvenile common carp (Cyprinus carpio L.) exposed to a mixture of sewage chemicals

Pharmaceuticals and household chemicals are important components of municipal sewage. Many of them are biologically active, disrupting not only hormonal regulation of aquatic animals but also, indirectly, disturbing their immunological protection. In the environment, chemicals rarely act as individual substances, but as elements of mixtures. Therefore, the aim of this study was to check whether the acute laboratory exposure of common carp juveniles to a mixture of ibuprofen, sodium dodecyl sulphate (SDS), dimethyl sulfoxide (DMSO) and 17 α-ethynylestradiol in increasing concentrations, modifies the levels of innate immunity (lysozyme, C-reactive protein) as well as general stress (metallothioneins, heat shock proteins HSP70) markers in brain, liver, gills, spleen and mucus. The levels of the markers were measured by an immunodetection technique. Not only do the pharmaceuticals and household chemicals impair immunological reactions of young carp in various tissues but also do that in a concentration-dependent manner in the liver, gills, spleen and mucus. This has a very important implication, since it may result in higher sensitivity of young fish to pathogens due to energy allocation to defence processes. The comparisons of the pattern of stress reactions in the studied organ samples indicated that mucus appeared to be a good, non-invasive material for monitoring of environmental state and fish conditions.

Immunotoxicity of estrogen and nonylphenol on apoptosis and expression of ERs in goldfish macrophage: Opening new avenue for discovering the role of experimental model systems and sexes

The expression of estrogen receptors (ERs) and their roles in important cell processes such as apoptosis in the macrophages exposed to estrogen/xenoestrogen have remained a complex secret. This study focused on the expression of estrogen receptors (ERs) and the stimulation of apoptosis in the macrophages from the two sexes of goldfish (Carassius auratus) exposed to 17-βestradiol (E2) and nonylphenol (NP) under in vivo and in vitro conditions. For the in vivo experiment, fish were exposed to NP (10^-6 M and 10^-7 M) and E2 (10^-6 M) for 24 days. Then, the head kidney macrophages from the male and the female goldfish were isolated and assayed. For the in vitro experiments, the macrophages derived from the two sexes were cultured in L-15 medium and exposed to E2 (150 nM) and NP (10 nM and 150 nM) for 3 days. The results showed that the three isoforms of ERs (ERα, ERβ₁, ERβ₂) were expressed in the goldfish macrophages. After the exposure of macrophages to NP and E2, sex-specific increase of ERs expression and apoptosis were observed (P < 0.05). The expression of ERα after NP treatment showed the highest alteration, with the response being concentration-dependent. The most alteration of ERs expression were observed in the in vivo experiment. This study provides insight to understand how exposure of the goldfish macrophages to E2 and NP can up-regulate the transcript levels of estrogen receptor subtypes and stimulate apoptosis.

Netting the Stress Responses in Fish

In the last decade, the concept of animal stress has been stressed thin to accommodate the effects of short-term changes in cell and tissue physiology, major behavioral syndromes in individuals and ecological disturbances in populations. Seyle's definition of stress as "the nonspecific (common) result of any demand upon the body" now encompasses homeostasis in a broader sense, including all the hierarchical levels in a networked biological system. The heterogeneity of stress responses thus varies within individuals, and stressors become multimodal in terms of typology, source and effects, as well as the responses that each individual elicits to cope with the disturbance. In fish, the time course of changes after stress strongly depends on several factors, including the stressful experiences in early life, the vertical transmission of stressful-prone phenotypes, the degree of individual phenotypic plasticity, the robustness and variety of the epigenetic network related to environmentally induced changes, and the intrinsic behavioral responses (individuality/personality) of each individual. The hierarchical heterogeneity of stress responses demands a code that may decrypt and simplify the analysis of both proximate and evolutionary causes of a particular stress phenotype. We propose an analytical framework, the stressotope, defined as an adaptive scenario dominated by common environmental selective pressures that elicit common multilevel acute stress-induced responses and produce a measurable allostatic load in the organism. The stressotope may constitute a blueprint of embedded interactions between stress-related variations in cell states, molecular mediators and systemic networks, a map of circuits that reflect the inherited and acquired stress responses in an ever-changing, microorganismal-loaded medium. Several features of the proposed model are discussed as a starting point to pin down the maximum common stress responses across immune-neuroendocrine relevant physiological levels and scenarios, including the characterization of behavioral responses, in fish.

Dydrogesterone affects the transcription of genes in GnRH and steroidogenesis pathways and increases the frequency of atretic follicles in zebrafish (Danio rerio)

Dydrogesterone (DDG) is a synthetic progestin broadly used in human and veterinary medicine and has been widely detected in aquatic environments. However, its potential effects on aquatic organisms are little documented. Here we investigate the short-term effects of DDG on the transcriptional and histological responses in adult zebrafish (Danio rerio). Adult zebrafish were exposed to 32.0, 305 and 2490 ng L^-1 of DDG for 14 days. Real time quantitative PCR analysis showed that DDG significantly increased transcripts of most genes involved in the gonadotropin-releasing hormone (GnRH) pathway in the brain of female. In contrast, apparent down-regulation of these gene transcriptions was observed in the brain of males. The transcription of cyp19a1a in the ovary had a 2.3 fold increase at 2490 ng L^-1 of DDG and the transcription of hsd17b2 at 305 and 2490 ng L^-1 in the testis was enhanced by approximately 2.0 fold and 2.4 fold, respectively. Histopathological analysis revealed exposure to 2490 ng L^-1 DDG significantly increased the percentage of atretic follicles in the ovary. The results of this study suggest that DDG has potential endocrine disrupting effects and affects the ovarian development in zebrafish.

Modelling the effect of season, sex, and body size on the three-spined stickleback, Gasterosteus aculeatus, cellular innate immunomarkers: A proposition of laboratory reference ranges

Innate immunomarkers reflect both environmental contamination and fish health status, providing useful information in environmental risk assessment studies. Nevertheless, the lack of knowledge about the effect of confounding factors can lead to data misinterpretation and false diagnoses. The aim of this study was to evaluate the impact of three confounding factors (season, sex and body size) on three-spined stickleback innate immunomarkers in laboratory conditions. Results shown strong seasonal variations in stickleback innate immunomarkers, with higher immune capacities in late winter-early spring and a disturbance during the spawning period in late spring-summer. Sex and body size had a season dependant effect on almost all tested immunomarkers. Reference ranges were established in laboratory-controlled conditions (i.e. laboratory reference ranges) and compared with data obtained from in vivo chemical expositions. The predictive power of the statistical model depended on the immunomarker, but the control data of the in vivo experiments, realized in same laboratory conditions, were globally well include in the laboratory reference ranges. Moreover, some statistical effects of the in vivo exposures were correlated with an augmentation of values outside the reference ranges, indicating a possible harmful effect for the organisms. As confounding factors influence is a major limit to integrate immunomarkers in biomonitoring programs, modelling their influence on studied parameter may help to better evaluated environmental contaminations.

Exposure to fluctuating temperatures leads to reduced immunity and to stress response in rattlesnakes

Ectothermic organisms often experience considerable variation in their body temperature throughout the circadian cycle. However, studies focusing on the measurement of physiological traits are usually performed under constant temperature regimes. This mismatch between thermal exposure in the field and experimental conditions could act as a stressor agent, since physiological functions are strongly influenced by temperature. Herein, we asked the question whether constant thermal regimes would cause a stress response and impact the immunity of the South American rattlesnake (Crotalus durissus) when compared to a fluctuating thermal regime. We addressed this question by determining heterophil:lymphocyte ratio (H:L), plasma bacteria killing ability (BKA) and corticosterone levels (CORT) in snakes kept under a constant temperature regime at 30°C, and under a fluctuating regime that oscillated between 25°C at nighttime to 35°C at daytime. The experiments had a mirrored design, in which half of the snakes were subjected to a fluctuating-to-constant treatment, while the other half was exposed to a constant-to-fluctuating treatment. The shift from constant to fluctuating thermal regime was accompanied by an increase in plasma CORT levels indicating the activation of a stress response. Exposure to a fluctuating thermal regime at the onset of the experiments induced a decrease in the BKA of rattlesnakes. H:L was not affected by treatments and, therefore, the shift between thermal regimes seems to have acted as a low intensity stressor. Our results suggest that the removal from temperatures close to the snakés preferred body temperature triggers a stress response in rattlesnakes.

Early-life exposure to the endocrine disruptor 17-α-ethinylestradiol induces delayed effects in adult brain, liver and ovotestis proteomes of a self-fertilizing fish

Early-life represents a critically sensitive window to endocrine disrupting chemicals, potentially leading to long-term repercussions on the phenotype later in life. The mechanisms underlying this phenomenon, referred to as the Developmental Origins of Health and Disease (DOHaD), are still poorly understood. To gain molecular understanding of these effects, we exposed mangrove rivulus (Kryptolebias marmoratus) for 28 days post hatching (dph) to 4 and 120 ng/L 17-α-ethinylestradiol, a model xenoestrogen. After 28 days, fish were raised for 140 days in clean water and we performed quantitative label-free proteomics on brain, liver and ovotestis of 168 dph adults. A total of 820, 888 and 420 proteins were robustly identified in the brain, liver and ovotestis, respectively. Effects of 17-α-ethinylestradiol were tissue and dose-dependent: a total of 31, 51 and 18 proteins were differentially abundant at 4 ng/L in the brain, liver and ovotestis, respectively, compared to 20, 25 and 39 proteins at 120 ng/L. Our results suggest that estrogen-responsive pathways, such as lipid metabolism, inflammation, and the innate immune system were affected months after the exposure. In addition, the potential perturbation of S-adenosylmethionine metabolism encourages future studies to investigate the role of DNA methylation in mediating the long-term effects of early-life exposures. SIGNIFICANCE: The Developmental Origins of Health and Disease (DOHaD) states that early life stages of humans and animals are sensitive to environmental stressors and can develop health issues later in life, even if the stress has ceased. Molecular mechanisms supporting DOHaD are still unclear. The mangrove rivulus is a new fish model species naturally reproducing by self-fertilization, making it possible to use isogenic lineages in which all individuals are highly homozygous. This species therefore permits to strongly reduce the confounding factor of genetic variability in order to investigate the effects of environmental stress on the phenotype. After characterizing the molecular phenotype of brain, liver and ovotestis, we obtained true proteomic reaction norms of these three organs in adults after early life stages have been exposed to the common endocrine disruptor 17-α-ethinylestradiol (EE2). Our study demonstrates long-term effects of early-life endocrine disruption at the proteomic level in diverse estrogen-responsive pathways 5 months after the exposure. The lowest tested and environmentally relevant concentration of 4 ng/L had the highest impact on the proteome in brain and liver, highlighting the potency of endocrine disruptors at low concentrations.

Stage-specific testicular protein levels of the oestrogen receptors (ERα and ERβ) and Cyp19 and association with oestrogenic contamination in the lambari Astyanax rivularis (Pisces: Characidae)

Oestrogens participate in various biological processes such as oogenesis, vitellogenesis and testicular development, but studies regarding the distribution and protein levels of oestrogen receptors (ERα and ERβ) and aromatase (Cyp19) in testis are rarely investigated in fish species. The aim of the present study was to analyse the expression pattern of ERα, ERβ and Cyp19 in testis of Astyanax rivularis and, in addition, to verify if oestrogenic contamination interferes in the expression levels of these proteins. Quarterly, field samplings were carried out during a reproductive cycle in a stream of the Upper Velhas River with a good conservation status (site S1). In the gonadal maturation peak (June), when ripe stage was most abundant, fish collection was made in three streams: S1, reference site, and S2 and S3, sites contaminated by untreated sewage. The results of immunohistochemistry demonstrated labelling of Cyp19 in Leydig cells and acidophilic granulocytes, but spermatogonia, Sertoli cells, spermatids and spermatozoa were also labelled. ERα was more widely distributed than ERβ being found in all developmental germ cell phases. On the other hand, ERβ was found only in spermatogonia and spermatocytes. During testicular maturation, ELISA levels for Cyp19, ERα and ERβ followed the gonadosomatic index (GSI) with significant higher values in the ripe stage. Regarding to endocrine disruption, the males exposed to domestic sewage presented significant higher expression of Cyp19 and ERα when compared to the non-exposed fish. Together, our results demonstrate expression patterns of Cyp19, ERα and ERβ in the testis of A. rivularis. In addition, we indicate ERα and Cyp19 as sensitive biomarkers for monitoring of oestrogenic contamination in freshwater environments.

Role of estrogens in fish immunity with special emphasis on GPER1

It is well accepted that estrogens, the primary female sex hormones, play a key role in modulating different aspects of the immune response. Moreover, estrogens have been linked with the sexual dimorphism observed in some immune disorders, such as chronic inflammatory and autoimmune diseases. Nevertheless, their effects are often controversial and depend on several factors, such as the pool of estrogen receptors (ERs) involved in the response. Their classical mode of action is through nuclear ERs, which act as transcription factors, promoting the regulation of target genes. However, it has long been noted that some of the estrogen-mediated effects cannot be explained by these classical receptors, since they are rapid and mediated by non-genomic signaling pathways. Hence, the interest in membrane ERs, especially in G protein-coupled estrogen receptor 1 (GPER1), has grown in recent years. Although the presence of nuclear ERs, and ER signaling, in immune cells in mammals and fish has been well documented, information on membrane ERs is much scarcer. In this context, the present manuscript aims to review our knowledge concerning the effect of estrogens on fish immunity, with special emphasis on GPER1. For example, the numerous tools developed over recent years allowed us to report for the first time that the regulation of fish granulocyte functions by estrogens through GPER1 predates the split of fish and tetrapods more than 450 million years ago, pointing to the relevance of estrogens as modulators of the immune responses, and the pivotal role of GPER1 in immunity.

Under control: The innate immunity of fish from the inhibitors' perspective

The innate immune response involves a concerted network of induced gene products, preformed immune effectors, biochemical signalling cascades and specialised cells. However, the multifaceted activation of these defensive measures can derail or overshoot and, if left unchecked, overwhelm the host. A plenty of regulatory devices therefore mediate the fragile equilibrium between pathogen defence and pathophysiological manifestations. Over the past decade in particular, an almost complete set of teleostean sequences orthologous to mammalian immunoregulatory factors has been identified in various fish species, which prove the remarkable conservation of innate immune-control concepts among vertebrates. This review will present the current knowledge on more than 50 teleostean regulatory factors (plus additional fish-specific paralogs) that are of paramount importance for controlling the clotting cascade, the complement system, pattern-recognition pathways and cytokine-signalling networks. A special focus lies on those immunoregulatory features that have emerged as potential biomarker genes in transcriptome-wide research studies. Moreover, we report on the latest progress in elucidating control elements that act directly with immune-gene-encoding nucleic acids, such as transcription factors, hormone receptors and micro- and long noncoding RNAs. Investigations into the function of teleostean inhibitory factors are still mainly based on gene-expression profiling or overexpression studies. However, in support of structural and in-vitro analyses, evidence from in-vivo trials is also available and revealed many biochemical details on piscine immune regulation. The presence of multiple gene copies in fish adds a degree of complexity, as it is so far hardly understood if they might play distinct roles during inflammation. The present review addresses this and other open questions that should be tackled by fish immunologists in future.

Duplicated membrane estrogen receptors in the European sea bass (Dicentrarchus labrax): Phylogeny, expression and regulation throughout the reproductive cycle

The numerous estrogen functions reported across vertebrates have been classically explained by their binding to specific transcription factors, the nuclear estrogen receptors (ERs). Rapid non-genomic estrogenic responses have also been recently identified in vertebrates including fish, which can be mediated by membrane receptors such as the G protein-coupled estrogen receptor (Gper). In this study, two genes for Gper, namely gpera and gperb, were identified in the genome of a teleost fish, the European sea bass. Phylogenetic analysis indicated they were most likely retained after the 3R teleost-specific whole genome duplication and raises questions about their function in male and female sea bass. Gpera expression was mainly restricted to brain and pituitary in both sexes while gperb had a widespread tissue distribution with higher expression levels in gill filaments, kidney and head kidney. Both receptors were detected in the hypothalamus and pituitary of both sexes and significant changes in gpers expression were observed throughout the annual reproductive season. In female pituitaries, gpera showed an overall increase in expression throughout the reproductive season while gperb levels remained constant. In the hypothalamus, gpera had a higher expression during vitellogenesis and decreased in fish entering the ovary maturation and ovulation stage, while gperb expression increased at the final atresia stage. In males, gpers expression was constant in the hypothalamus and pituitary throughout the reproductive cycle apart from the mid- to late testicular development stage transition when a significant up-regulation of gpera occurred in the pituitary. The differential sex, seasonal and subtype-specific expression patterns detected for the two novel gper genes in sea bass suggests they may have acquired different and/or complementary roles in mediating estrogens actions in fish, namely on the neuroendocrine control of reproduction.

Immune-Specific Expression and Estrogenic Regulation of the Four Estrogen Receptor Isoforms in Female Rainbow Trout (Oncorhynchus mykiss)

Genomic actions of estrogens in vertebrates are exerted via two intracellular estrogen receptor (ER) subtypes, ERα and ERβ, which show cell- and tissue-specific expression profiles. Mammalian immune cells express ERs and are responsive to estrogens. More recently, evidence became available that ERs are also present in the immune organs and cells of teleost fish, suggesting that the immunomodulatory function of estrogens has been conserved throughout vertebrate evolution. For a better understanding of the sensitivity and the responsiveness of the fish immune system to estrogens, more insight is needed on the abundance of ERs in the fish immune system, the cellular ratios of the ER subtypes, and their autoregulation by estrogens. Consequently, the aims of the present study were (i) to determine the absolute mRNA copy numbers of the four ER isoforms in the immune organs and cells of rainbow trout, Oncorhynchus mykiss, and to compare them to the hepatic ER numbers; (ii) to analyse the ER mRNA isoform ratios in the immune system; and, (iii) finally, to examine the alterations of immune ER mRNA expression levels in sexually immature trout exposed to 17β-estradiol (E2), as well as the alterations of immune ER mRNA expression levels in sexually mature trout during the reproductive cycle. All four ER isoforms were present in immune organs—head kidney, spleen-and immune cells from head kidney and blood of rainbow trout, but their mRNA levels were substantially lower than in the liver. The ER isoform ratios were tissue- and cell-specific, both within the immune system, but also between the immune system and the liver. Short-term administration of E2 to juvenile female trout altered the ER mRNA levels in the liver, but the ERs of the immune organs and cells were not responsive. Changes of ER gene transcript numbers in immune organs and cells occurred during the reproductive cycle of mature female trout, but the changes in the immune ER profiles differed from those in the liver and gonads. The correlation between ER gene transcript numbers and serum E2 concentrations was only moderate to low. In conclusion, the low mRNA numbers of nuclear ER in the trout immune system, together with their limited estrogen-responsiveness, suggest that the known estrogen actions on trout immunity may be not primarily mediated through genomic actions, but may involve other mechanisms, such as non-genomic pathways or indirect effects.

Effects of Sex Steroids on Fish Leukocytes

In vertebrates, in addition to their classically reproductive functions, steroids regulate the immune system. This action is possible mainly due to the presence of steroid receptors in the different immune cell types. Much evidence suggests that the immune system of fish is vulnerable to xenosteroids, which are ubiquitous in the aquatic environment. In vivo and in vitro assays have amply demonstrated that oestrogens interfere with both the innate and the adaptive immune system of fish by regulating the main leukocyte activities and transcriptional genes. They activate nuclear oestrogen receptors and/or G-protein coupled oestrogen receptor. Less understood is the role of androgens in the immune system, mainly due to the complexity of the transcriptional regulation of androgen receptors in fish. The aim of this manuscript is to review our present knowledge concerning the effect of sex steroid hormones and the presence of their receptors on fish leukocytes, taking into consideration that the studies performed vary as regard the fish species, doses, exposure protocols and hormones used. Moreover, we also include evidence of the probable role of progestins in the regulation of the immune system of fish.

Oestrogen receptor distribution related to functional thymus anatomy of the European sea bass, Dicentrarchus labrax

In jawed vertebrates, the crosstalk between immune and endocrine system as well as many fundamental mechanisms of T cell development are evolutionary conserved. Oestrogens affect mammalian thymic function and plasticity, but the mechanisms of action and the oestrogen receptors involved remain unclear. To corroborate the oestrogenic regulation of thymic function in teleosts and to identify the implicated oestrogen receptor subtypes, we examined the distribution of nuclear and membrane oestrogen receptors within the thymus of the European Sea bass, Dicentrarchus labrax, in relation to its morpho-functional organisation. Immunohistological analysis specified thymus histology and organisation in teleosts and described, for the first time, Hassall's corpuscle like structures in the medulla of sea bass. All oestrogen receptors were expressed at the transcript and protein level, both in T cells and in stromal cells belonging to specific functional areas. These observations suggest complex regulatory actions of oestrogen on thymic function, notably through the stromal microenvironment, comprising both, genomic and non-genomic pathways that are likely to affect T cell maturation and trafficking processes. Comparison with birds, rodents and humans supports the thymic localization of oestrogen receptors and suggests that oestrogens modulate T cell maturation in all gnathostomes.

Stress differentially affects the systemic and leukocyte estrogen network in common carp

Both systemic and locally released steroid hormones, such as cortisol and estrogens, show immunomodulatory actions. This research gives evidence that circulating and leukocyte-derived estrogens can be involved in the regulation of the immune response in common carp, during homeostasis and upon restraining stress. It was found that stress reduced level of blood 17β-estradiol (E2) and down-regulated the gene expression of components of the "classical" estrogen system: the nuclear estrogen receptors and the aromatase CYP19, in the hypothalamus, the pituitary and in the ovaries. In contrast, higher gene expression of the nuclear estrogen receptors and cyp19a was found in the head kidney of stressed animals. Moreover, stress induced changes in the E2 level and in the estrogen sensitivity at local/leukocyte level. For the first time in fish, we showed the presence of physiologically relevant amounts of E2 and the substrates for its conversion (estrone - E1 and testosterone - T) in head kidney monocytes/macrophages and found that its production is modulated upon stress. Moreover, stress reduced the sensitivity of leukocytes towards estrogens, by down-regulation the expression of the erb and cyp19 genes in carp phagocytes. In contrast, era expression was up-regulated in the head kidney monocytes/macrophages and in PBLs derived from stressed animals. We hypothesize that, the increased expression of ERα, that was observed during stress, can be important for the regulation of leukocyte differentiation, maturation and migration. In conclusion, these results indicate that, in fish, the estrogen network can be actively involved in the regulation of the systemic and local stress response and the immune response.