Cadmium in vivo exposure alters stress response and endocrine-related genes in the freshwater snail Physa acuta. New biomarker genes in a new model organism

Establishment of a cell culture from Daphnia magna as an in vitro model for (eco)toxicology assays: Case study using Bisphenol A as a representative cytotoxic and endocrine disrupting chemical

Bisphenol A (BPA) is a widely used industrial compound found in polycarbonate plastics, epoxy resin, and various polymer materials, leading to its ubiquitous presence in the environment. The toxicity of BPA to aquatic organisms has been well documented following in vivo exposure scenarios, with known cytotoxic and endocrine-disrupting effects. As such, BPA was used in this study as a well-characterized chemical to implement more ethical and resource-efficient scientific practices in toxicity testing through new approach methods (NAMs). Due to the frequent use of Daphnia spp. as a model organism in toxicology, we developed an in vitro cell culture system from Daphnia magna embryos, with optimized medium to support cell longevity. The cultures were maintained for up to two months, demonstrating their stability and suitability for cytotoxicity studies. Using this novel system, lethal concentration 50 (LC50) values were determined at the 24 and 48 h time points following BPA exposure. Subsequently, oxidative stress, endocrine disruption, and DNA damage were assessed through gene expression, activity assays, and a comet assay in BPA-exposed cells. LC50 values of 52 µM and 20 µM BPA were calculated after 24 and 48 h exposures, respectively. BPA cells exposed to 20 and 52 µM had significantly increased GSH, GPx, and GST activity levels. mRNA expression analysis revealed significant upregulations in the expression of hsp70, hsp90, gst, gpx, vtg1, and cyp4, with downregulations of sod, cat, and ecr following BPA exposure. Furthermore, comet assays showed a significantly higher level of DNA damage induced by BPA compared to controls, with greater comet and tail lengths. This study established a novel in vitro Daphnia model, using BPA as a case study for determining toxic effects, further highlighting the importance and applicability of utilizing alternative methods in ecotoxicological research through reducing animal use.

Metals and metallothionein evolution in snails: a contribution to the concept of metal-specific functionality from an animal model group

This is a critical review of what we know so far about the evolution of metallothioneins (MTs) in Gastropoda (snails, whelks, limpets and slugs), an important class of molluscs with over 90,000 known species. Particular attention will be paid to the evolution of snail MTs in relation to the role of some metallic trace elements (cadmium, zinc and copper) and their interaction with MTs, also compared to MTs from other animal phyla. The article also highlights the important distinction, yet close relationship, between the structural and metal-selective binding properties of gastropod MTs and their physiological functionality in the living organism. It appears that in the course of the evolution of Gastropoda, the trace metal cadmium (Cd) must have played an essential role in the development of Cd-selective MT variants. It is shown how the structures and Cd-selective binding properties in the basal gastropod clades have evolved by testing and optimizing different combinations of ancestral and novel MT domains, and how some of these domains have become established in modern and recent gastropod clades. In this context, the question of how adaptation to new habitats and lifestyles has affected the original MT traits in different gastropod lineages will also be addressed. The 3D structures and their metal binding preferences will be highlighted exemplarily in MTs of modern littorinid and helicid snails. Finally, the importance of the different metal requirements and pathways in snail tissues and cells for the shaping and functionality of the respective MT isoforms will be shown.

Endosulfan exposure alters transcription of genes involved in the detoxification and stress responses in Physella acuta

Endosulfan is a persistent pesticide that has been in use for more than five decades. During this time, it has contaminated soil, air, and water reservoirs worldwide. It is extremely toxic and harmful to beneficial non-target invertebrates, aquatic life, and even humans upon consumption, which is one of the many dangers of this pesticide since it biomagnifies in the food chain. The effects of three endosulfan concentrations (1, 10, and 100 µg/L) on the freshwater snail Physella acuta, an invasive cosmopolitan species, were examined over a week-long exposure period. Alterations in the expression of ten genes related to stress and xenobiotic detoxification were measured against the endogenous controls rpL10 and GAPDH by Real-Time polymerase chain reaction. Four genes are described here for the first time in this species, namely Hsp60, Grp78, GSTk1, and GSTm1. The rest of genes were Hsp90, sHsp16.6, cyp2u1, cyp3a7, cyp4f22, and MRP1. cyp2u1, sHsp16.6, and Grp78 expression were all altered by endosulfan. These results suggest a low pesticide concentration activates the acute response in P. acuta by affecting detoxification and stress responses and alter endoplasmic reticulum function and lipid metabolism. Furthermore, the newly identified genes extend the number of processes and cellular locations that can be analyzed in this organism.

A 28.6-kD small heat shock protein (MnHSP28.6) protects Macrobrachium nipponense against heavy metal toxicity and oxidative stress by virtue of its anti-aggregation activity

Small heat shock proteins (sHSPs) are ATP-independent chaperones and involved into various physiological and stress processes. In the present study, a 28.6-kD sHSP coding gene, MnHSP28.6, was cloned and characterized from the oriental river prawn Macrobrachium nipponense. Tissue distribution analysis via qPCR and western blot revealed that MnHSP28.6 predominantly expressed in muscle. The temporal transcription of MnHSP28.6 in muscle after bacterial challenge, heavy metal exposure and doxorubicin (DOX) injection was investigated by qPCR. The results showed that the expression of MnHSP28.6 were strongly enhanced by both Cd²⁺ and Cu²⁺ exposure, as well as DOX injection, but not by bacterial infection. Aggregation assays showed that recombinant MnHSP28.6 could effectively prevent temperature-induced aggregation of citrate synthase, and reduction-induced aggregation of insulin in vitro. MnHSP28.6 also could protect muscle extracts from heat-induced protein denaturation and superoxide dismutase (SOD) inactivation. Expressing MnHSP28.6 in E. coli conferred host cell impressive protection against H₂O₂ compared to control. These results suggest a protective role of MnHSP28.6 in maintaining protein homeostasis, preventing aggregation, promoting resistance to heavy metal and keeping redox balance.

Effects of cadmium on fecundity and defence ability of Drosophila melanogaster

Cadmium (chemical symbol, Cd) is an extremely common pollutant that poses a toxicity threat to organisms. Therefore, we tested Drosophila melanogaster fecundity, Cd accumulation, and activity of two enzymes following Cd stress and used quantitative real-time polymerase chain reaction (qPCR) to quantify the mRNA expression levels of several genes involved in fecundity and defence. D. melanogaster was placed in a medium containing different concentrations of Cd (13, 26, and 52 mg L^-1), following which, inductively coupled plasma atomic emission spectroscopy showed that Cd accumulation in Drosophila increased with the increase in its dietary intake. We also observed that Cd at these concentrations significantly prolonged the mating latency in females and reduced the number of eggs laid. However, the same Cd concentrations did not affect male fecundity. Acetylcholinesterase activity was only detected at 52 mg L^-1 Cd in both sexes, whereas glutathione S-transferase activity was inhibited at 26 and 52 mg L^-1 Cd in females. The results of qPCR indicated that exposure to 13-52 mg L^-1 Cd affected the expression of reproduction-related genes, including downregulation of enok and upregulation of dally and dpp. The same level of exposure also induced transcriptional responses from three defence-related genes (hsp70, gstd2, and gstd6). Taken together, the results revealed that Cd exposure might negatively affect the expression of genes associated with D. melanogaster reproduction and trigger the transcription of defence-related genes. We suggest that further analyses of fecundity and defence responses may help develop indicators of Cd toxicity and improve our understanding of antitoxin defences.

Effects on tadpole snail gene expression after exposure to vinclozolin

The fungicide vinclozolin (Vz) is an endocrine disruptor with known anti-androgenic activity in vertebrates. However, there is a lack of information about the Vz mode of action in invertebrates, although some studies have shown that this compound can produce alterations in different species. Transcriptional activity was analyzed in the freshwater snail Physella acuta in order to elucidate putative cellular processes altered by this chemical during a response. In order to identify potential molecular biomarkers, a de novo transcriptome was generated for this species that constitutes a valuable source for future studies. This data, together with some already available data, permitted the identification of several genes related to detoxification mechanisms (Cyp2u1, Cyp3a7, Cyp4f22, GSTo1, GSTt2, and MRP1), stress response (Hsp20.4, Hsp17, Hsp16.6, and Cu,Zn-SOD), the hormonal system (Estrogen Receptor and Hsp90), apoptosis (Casp3), and copper homeostasis (ATOX1). Using quantitative Real-Time polymerase chain reaction, mRNA levels of these genes were examined in snails exposed to 20 or 200 µg/L Vz for 24 h. The results showed an overall weak response, with downregulation of Hsp20.4 and no statistically significant change for the other genes. These findings suggest that P. acuta can manage the concentrations of Vz found in the environment with no relevant activation of the pathways analyzed, although additional studies are needed for longer exposure times and including other metabolic pathways. The new genes described open the range of processes that can be studied at the molecular level in toxicity tests.

Combining the assessment of apical endpoints and gene expression in the freshwater snail Physa acuta after exposure to reclaimed water

Post-treatment wastewater reuses are diverse. Recreational and environmental restoration uses of reclaimed water (RW) can be potentially harmful to aquatic organisms. In this work the freshwater snail Physa acuta was exposed to RW (100%) and its dilution (RW 50%). A simple laboratory mixture of three emerging pollutants was used to address the complex problem of mixture toxicity of RW. Hence fortified reclaimed water (FRW), obtained by adding fluoxetine (400 μg FLX/L), perfluorooctane sulphonic acid (90 μg PFOS/L) and methylparaben (9 μg MP/L), was tested at two dilution percentages: 100% and 50%. The effects of the laboratory mixture of FLX, PFOS and MP on the test medium were also studied. Long-lasting effects, together with early molecular responses, were assessed. Fecundity (cumulative egg production) over 21 days and the hatching of produced eggs (F1) after another 21-day embryonic exposure were monitored. The gene expression of three genes was analysed after 24 h of exposure: two endocrine-related nuclear receptors (ERR and RXR) and one stress protein gene (Hsp70). This reproduction test, with additional assessments of the F1 recovered eggs' hatching success, showed that both RW and FRW significantly reduced fecundity. F1 hatching was affected only by FRW. The gene expression results showed that the RXR response was strikingly similar to the fecundity response, which suggests that this nuclear receptor is involved in the reproductive pathways of gastropods. ERR remained virtually unaltered. Hsp70 was overexpressed by the laboratory mixture in the test medium, but no effect was observed in the fortification of RW. This opposite effect and lack of response for F1 hatching produced by the laboratory mixture in the test medium highlighted the difficulty of predicting mixture effects. The experimental approach allowed us to test the effects caused by RW on P. acuta at different biological organisation levels. Thus, the combination of molecular biomarkers and ecological relevant endpoints is a good strategy to test complex mixtures like RW as it provides a framework to link mechanisms of action and whole organism effects when it is almost impossible to detect the pollutant(s) that cause toxic effects.

Effects of the synthetic estrogen 17-α-ethinylestradiol on Drosophila melanogaster: Dose and gender dependence

17-a-ethinylestradiol (EE2) belongs to the increasing list of Endocrine Disruptors Chemicals (EDCs), able to interfere with the endocrine system in both vertebrates and invertebrates. Regardless of its great dispersion in the environment, to date there is still little knowledge about its action mechanisms and harmful effects in invertebrates. To better evaluate its potential role in invertebrates, we used the model system Drosophila melanogaster, an insect in which the hormonal response has been widely described. The effects of EE2 in D.melanogaster adults have been evaluated by using life traits as well as molecular endpoints. It was found that EE2 significantly decreases survival and fertility in both sexes, with a higher effect in female flies, as well as affects the expression of the Ecdysone Receptor (EcR), Estrogen Related Receptor (ERR), Yolk protein2 (Yp2) and yolkless (yl) genes. In conclusion, our results suggest that EE2 treatment may have potential toxic and endocrine effects on Drosophila melanogaster adults of both sexes. In particular, our data provide an indication that, after EE2 treatment, two of the genes involved in the vitellogenesis process (yl and Yp2) are transcribed in adult males where are mostly silent, and suggest future studies forward their use as potential molecular markers to EDCs exposure in Drosophila male.

Comparative immunological study of the snail Physella acuta (Hygrophila, Pulmonata) reveals shared and unique aspects of gastropod immunobiology

The freshwater snail Physella acuta was selected to expand the perspective of comparative snail immunology. Analysis of Physella acuta, belonging to the Physidae, taxonomic sister family to Planorbidae, affords family-level comparison of immune features characterized from Biomphalaria glabrata, the model snail often used to interpret general gastropod immunity. To capture constitutive and induced immune sequences, transcriptomes of an individual Physella acuta snail, 12 h post injection with bacteria (Gram -/+) and one sham-exposed snail were recorded with 454 pyrosequencing. Assembly yielded a combined reference transcriptome containing 24,288 transcripts. Additionally, genomic Illumina reads were obtained (∼15-fold coverage). Recovery of transcripts for two macin-like antimicrobial peptides (AMPs), 12 aplysianins, four LBP/BPIs and three physalysins indicated that Physella acuta shares a similar organization of antimicrobial defenses with Biomphalaria glabrata, contrasting a modest AMP arsenal with a diverse set of antimicrobial proteins. The lack of predicted transmembrane domains in all seven Physella acuta PGRP transcripts supports the notion that gastropods do not employ cell-bound PGRP receptors, different from ecdysozoan invertebrates yet similar to mammals (vertebrate deuterostomes). The well-documented sequence diversification by Biomphalaria glabrata FREPs (immune lectins comprising immunoglobulin superfamily domains and fibrinogen domains), resulting from somatic mutations of a large FREP gene family is hypothesized to be unique to Planorbidae; Physella acuta revealed just two bonafide FREP genes and these were not diversified. Furthermore, the flatworm parasite Echinostoma paraensei, confirmed here to infect both snail species, did not evoke from Physella acuta the abundant expression of FREP proteins at 2, 4 and 8 days post exposure that was previously observed from Biomphalaria glabrata. The Physella acuta reference transcriptome also revealed 24 unique transcripts encoding proteins consisting of a single fibrinogen-related domain (FReDs), with a short N-terminal sequence encoding either a signal peptide, transmembrane domain or no predicted features. The Physella acuta FReDs are candidate immune genes based on implication of similar sequences in immunity of bivalve molluscs. Overall, comparative analysis of snails of sister families elucidated the potential for taxon-specific immune features and investigation of strategically selected species will provide a more comprehensive view of gastropod immunity.

Bisphenol A (BPA) modulates the expression of endocrine and stress response genes in the freshwater snail Physa acuta

Bisphenol A (BPA), a known endocrine disrupting chemical (EDC) that can mimic the action of oestrogens by interacting with hormone receptors, is potentially able to influence reproductive functions in vertebrates and invertebrates. The freshwater pulmonate Physa acuta is a sensitive organism to xenobiotics appropriate for aquatic toxicity testing in environmental studies. This study was conducted to explore the effects of BPA on the Gastropoda endocrine system. The effects following a range of exposure times (5-96h) to BPA in P. acuta were evaluated at the molecular level by analysing changes in the transcriptional activity of the endocrine-related genes oestrogen receptor (ER), oestrogen-related receptor (ERR), and retinoid X receptor (RXR), as well as in genes involved in the stress response, such as hsp70 and hsp90. Real-time reverse transcriptase-polymerase chain reaction (qRT-PCR) analysis showed that BPA induced a significant increase in the mRNA levels of ER, ERR, and RXR, suggesting that these receptors could be involved in similar pathways or regulation events in the endocrine disruptor activity of this chemical at the molecular level in Gastropoda. Additionally, the hsp70 expression was upregulated after 5 and 72h of BPA exposures, but hsp90 was only upregulated after 5h of BPA exposure. Finally, we assessed the glutathione-S-transferase (GST) activity after BPA treatment and found that it was affected after 48h. In conclusion, these data provide, for the first time, evidences of molecular effects produced by BPA in the endocrine system of Gastropoda, supporting the potential of ER, ERR and RXR as biomarkers to analyse putative EDCs in ecotoxicological studies. Moreover, our results suggest that P. acuta is an appropriate sentinel organism to evaluate the effect of EDCs in the freshwater environment.

Metallothioneins of the urochordate Oikopleura dioica have Cys-rich tandem repeats, large size and cadmium-binding preference

Oikopleura dioica has the longest metallothionein described so far, made of repeats generated by a modular and step-wise evolution.

Challenging the Metallothionein (MT) Gene of Biomphalaria glabrata: Unexpected Response Patterns Due to Cadmium Exposure and Temperature Stress

Metallothioneins (MTs) are low-molecular-mass, cysteine-rich, metal binding proteins. In most animal species, they are involved in metal homeostasis and detoxification, and provide protection from oxidative stress. Gastropod MTs are highly diversified, exhibiting unique features and adaptations like metal specificity and multiplications of their metal binding domains. Here, we show that the MT gene of Biomphalaria glabrata, one of the largest MT genes identified so far, is composed in a unique way. The encoding for an MT protein has a three-domain structure and a C-terminal, Cys-rich extension. Using a bioinformatic approach involving structural and in silico analysis of putative transcription factor binding sites (TFBs), we found that this MT gene consists of five exons and four introns. It exhibits a regulatory promoter region containing three metal-responsive elements (MREs) and several TFBs with putative involvement in environmental stress response, and regulation of gene expression. Quantitative real-time polymerase chain reaction (qRT-PCR) data indicate that the MT gene is not inducible by cadmium (Cd) nor by temperature challenges (heat and cold), despite significant Cd uptake within the midgut gland and the high Cd tolerance of metal-exposed snails.

Biomphalaria glabrata Metallothionein: Lacking Metal Specificity of the Protein and Missing Gene Upregulation Suggest Metal Sequestration by Exchange Instead of through Selective Binding

The wild-type metallothionein (MT) of the freshwater snail Biomphalaria glabrata and a natural allelic mutant of it in which a lysine residue was replaced by an asparagine residue, were recombinantly expressed and analyzed for their metal-binding features with respect to Cd²⁺, Zn²⁺ and Cu⁺, applying spectroscopic and mass-spectrometric methods. In addition, the upregulation of the Biomphalaria glabrataMT gene was assessed by quantitative real-time detection PCR. The two recombinant proteins revealed to be very similar in most of their metal binding features. They lacked a clear metal-binding preference for any of the three metal ions assayed-which, to this degree, is clearly unprecedented in the world of Gastropoda MTs. There were, however, slight differences in copper-binding abilities between the two allelic variants. Overall, the missing metal specificity of the two recombinant MTs goes hand in hand with lacking upregulation of the respective MT gene. This suggests that in vivo, the Biomphalaria glabrata MT may be more important for metal replacement reactions through a constitutively abundant form, rather than for metal sequestration by high binding specificity. There are indications that the MT of Biomphalaria glabrata may share its unspecific features with MTs from other freshwater snails of the Hygrophila family.

HSP70 expression in Biomphalaria glabrata snails exposed to cadmium

In this study, the effects of the heavy metal cadmium on the stress protein HSP70 are investigated in freshwater mollusks Biomphalaria glabrata. Adult snails were exposed for 96h to CdCl₂ at concentrations ranging from 0.09 to 0.7mgL^-1 (LC_50/96h=0.34 (0.30-0.37). Time and concentration-dependent increases in the expression of HSP70 were observed at sub-lethal levels in the immunoblotting assay. Further, an increased survival to a lethal heat shock was observed in animals pre-exposed to a nonlethal concentration of cadmium, evidencing the induction of acquired tolerance. The present study demonstrated the inducibility of B. glabrata HSP70 by cadmium, a relevant environmental contaminant, at non-lethal levels, providing evidences that the assessment of HSP70 in B. glabrata can be regarded as a suitable biomarker for ecotoxicological studies.