Perchlorate Exposure Reduces Primordial Germ Cell Number in Female Threespine Stickleback

2,4-Dichlorophenol Increases Primordial Germ Cell Numbers via ESR2a-Dependent Pathway in Zebrafish Larvae

Previous studies have reported the feminizing effects of 2,4-dichlorophenol (2,4-DCP) on zebrafish (Danio rerio). However, the effect of 2,4-DCP on the number of primordial germ cells (PGCs), an indicator for early sex differentiation, remains elusive. In the present study, Tg (piwil1:egfp-UTR nanos3) zebrafish (GFP-labeled PGCs) were treated with 2,4-DCP (10, 20, and 40 μg/L) from 5 to 15 days postfertilization to explore the effect on PGC numbers and to elucidate associated molecular mechanisms. The results showed that 2,4-DCP exposure increased PGC numbers, as evidenced by larger GFP fluorescent areas, upregulated expressions of PGC marker genes (vasa and dnd), and raised the female ratio. Notably, the mRNA level of estrogen receptor 2a (esr2a) was also increased subsequently. Moreover, docking studies revealed stable 2,4-DCP interactions with ESR2a, speculating a role of ESR2a signaling pathway in 2,4-DCP toxicity. Furthermore, in esr2a knockout (esr2a^-/-) zebrafish, the effects of 2,4-DCP were considerably minimized, proving the involvement of the ESR2a signaling pathway in the 2,4-DCP-mediated increase in PGC numbers. Dual-luciferase reporter gene assay and point mutation studies demonstrated that 2,4-DCP-stimulated promoter activity was mediated by estrogen response element (ERE) located in -686/-674 of the vasa promoter and -731/-719 of the dnd promoter. Overall, 2,4-DCP can potentially enhance the expression of vasa and dnd by binding to zebrafish ESR2a, thus leading to increased PGC numbers and subsequent female-biased sex differentiation.

Potassium perchlorate effects on primordial germ cells of developing medaka larvae

Perchlorate is a chemical compound commonly used in military artillery and equipment. It has been detected in drinking water, air, soil, and breast milk. Exposure of humans to perchlorate can occur in the theater of war and areas adjacent to military training grounds. A high concentration of perchlorate has been found to affect reproduction in vertebrates, including fish. However, whether environmental concentrations of perchlorate can affect primordial germ cells (PGCs), the founders of sperm and eggs, is not clearly understood. In the present study, we examined the effects of 0, 10, 100, and 1000 μg/L potassium perchlorate exposure on the embryonic development of medaka and their PGCs. Perchlorate exposure delayed hatching time, reduced heartbeat, inhibited migration of PGCs, and increased developmental deformities in the larvae. The 10 and 20 mg/L concentrations of perchlorate were lethal to embryos, whereas vitamin C co-treatment (1 mg/L) completely blocked perchlorate-induced mortality. RNA-seq analysis of isolated PGCs showed a non-linear pattern in expression profiles of differentially altered genes. Significantly upregulated genes were found in PGCs from the 10 and 1000 μg/L groups, whereas the 100 μg/L groups showed the highest number of significantly downregulated genes. Gene ontology analysis predicted differentially expressed genes to be involved in proteolysis, metabolic processes, peptides activity, hydrolase activity, and hormone activity. Among the cellular components, extracellular, intracellular, sarcoplasmic, and 6-phosphofructokinase and membrane-bounded processes were affected. Ingenuity Pathway Analysis of PGC transcriptomes revealed thyroid hormone signaling to be affected by all concentrations of perchlorate. The present results suggested that perchlorate affected the development of medaka larvae and vitamin C was able to ameliorate perchlorate-induced embryo mortality. Additionally, perchlorate altered the global transcriptional network in PGCs in a non-linear fashion suggesting its potential effects on developing germ cells and fertility.

Evolution and developmental expression of the sodium-iodide symporter (NIS, slc5a5) gene family: Implications for perchlorate toxicology

The vertebrate sodium-iodide symporter (NIS or SLC5A5) transports iodide into the thyroid follicular cells that synthesize thyroid hormone. The SLC5A protein family includes transporters of vitamins, minerals, and nutrients. Disruption of SLC5A5 function by perchlorate, a pervasive environmental contaminant, leads to human pathologies, especially hypothyroidism. Perchlorate also disrupts the sexual development of model animals, including threespine stickleback (Gasterosteus aculeatus) and zebrafish (Danio rerio), but the mechanism of action is unknown. To test the hypothesis that SLC5A5 paralogs are expressed in tissues necessary for the development of reproductive organs, and therefore are plausible candidates to mediate the effects of perchlorate on sexual development, we first investigated the evolutionary history of Slc5a paralogs to better understand potential functional trajectories of the gene family. We identified two clades of slc5a paralogs with respect to an outgroup of sodium/choline cotransporters (slc5a7); these clades are the NIS clade of sodium/iodide and lactate cotransporters (slc5a5, slc5a6, slc5a8, slc5a8, and slc5a12) and the SGLT clade of sodium/glucose cotransporters (slc5a1, slc5a2, slc5a3, slc5a4, slc5a10, and slc5a11). We also characterized expression patterns of slc5a genes during development. Stickleback embryos and early larvae expressed NIS clade genes in connective tissue, cartilage, teeth, and thyroid. Stickleback males and females expressed slc5a5 and its paralogs in gonads. Single-cell transcriptomics (scRNA-seq) on zebrafish sex-genotyped gonads revealed that NIS clade-expressing cells included germ cells (slc5a5, slc5a6a, and slc5a6b) and gonadal soma cells (slc5a8l). These results are consistent with the hypothesis that perchlorate exerts its effects on sexual development by interacting with slc5a5 or its paralogs in reproductive tissues. These findings show novel expression domains of slc5 genes in stickleback and zebrafish, which suggest similar functions across vertebrates including humans, and provide candidates to mediate the effects of perchlorate on sexual development.

Health Impacts of Perchlorate and Pesticide Exposure: Protocol for Community-Engaged Research to Evaluate Environmental Toxicants in a US Border Community

BACKGROUND

The Northern Arizona University (NAU) Center for Health Equity Research (CHER) is conducting community-engaged health research involving "environmental scans" in Yuma County in collaboration with community health stakeholders, including the Yuma Regional Medical Center (YRMC), Regional Center for Border Health, Inc. (RCBH), Campesinos Sin Fronteras (CSF), Yuma County Public Health District, and government agencies and nongovernmental organizations (NGOs) working on border health issues. The purpose of these efforts is to address community-generated environmental health hazards identified through ongoing coalitions among NAU, and local health care and research institutions.

OBJECTIVE

We are undertaking joint community/university efforts to examine human exposures to perchlorate and agricultural pesticides. This project also includes the parallel development of a new animal model for investigating the mechanisms of toxicity following a "one health" approach. The ultimate goal of this community-engaged effort is to develop interventions to reduce exposures and health impacts of contaminants in Yuma populations.

METHODS

All participants completed the informed consent process, which included information on the purpose of the study, a request for access to health histories and medical records, and interviews. The interview included questions related to (1) demographics, (2) social determinants of health, (3) health screening, (4) occupational and environmental exposures to perchlorate and pesticides, and (5) access to health services. Each participant provided a hair sample for quantifying the metals used in pesticides, urine sample for perchlorate quantification, and blood sample for endocrine assays. Modeling will examine the relationships between the concentrations of contaminants and hormones, demographics and social determinants of health, and health status of the study population, including health markers known to be impacted by perchlorate and pesticides.

RESULTS

We recruited 323 adults residing in Yuma County during a 1-year pilot/feasibility study. Among these, 147 residents were patients from either YRMC or RCBH with a primary diagnosis of thyroid disease, including hyperthyroidism, hypothyroidism, thyroid cancer, or goiter. The remaining 176 participants were from the general population but with no history of thyroid disorder. The pilot study confirmed the feasibility of using the identified community-engaged protocol to recruit, consent, and collect data from a difficult-to-access, vulnerable population. The demographics of the pilot study population and positive feedback on the success of the community-engaged approach indicate that the project can be scaled up to a broader study with replicable population health findings.

CONCLUSIONS

Using a community-engaged approach, the research protocol provided substantial evidence regarding the effectiveness of designing and implementing culturally relevant recruitment and dissemination processes that combine laboratory findings and public health information. Future findings will elucidate the mechanisms of toxicity and the population health effects of the contaminants of concern, as well as provide a new animal model to develop precision medicine capabilities for the population.

INTERNATIONAL REGISTERED REPORT IDENTIFIER (IRRID)

DERR1-10.2196/15864.

Perchlorate exposure does not induce obesity or non-alcoholic fatty liver disease in zebrafish

Perchlorate is a water-soluble contaminant found throughout the United States and many other countries. Perchlorate competitively inhibits iodide uptake at the sodium/iodide symporter, reducing thyroid hormone synthesis, which can lead to hypothyroidism and metabolic syndromes. Chronic perchlorate exposure induces hepatic steatosis and non-alcoholic fatty liver disease (NAFLD) in developing threespine stickleback (Gasterosteus aculeatus). We hypothesized that perchlorate would also induce zebrafish (Danio rerio) to develop phenotypes consistent with NAFLD and to accumulate lipids throughout the body. We exposed zebrafish embryos to four concentrations of perchlorate treated water (10μg/L, 10mg/L, 30mg/L, and 100mg/L) and a control (0mg/L) over the course of 133 days. Adult zebrafish were euthanized, sectioned, H&E and Oil Red-O stained, and analyzed for liver morphology and whole body lipid accumulation. In a representative section of the liver, we counted the number of lipid droplets and measured the area of each droplet and the total lipid area. For whole body analysis, we calculated the ratio of lipid area to body area within a section. We found that zebrafish exposed to perchlorate did not differ in any measured liver variables or whole body lipid area when compared to controls. In comparison to stickleback, we see a trend that control stickleback accumulate more lipids in their liver than do control zebrafish. Differences between the species indicate that obesogenic effects due to perchlorate exposure are not uniform across fish species, and likely are mediated by evolutionary differences related to geographic location. For example, high latitude fishes such as stickleback evolved to deposit lipid stores for over-winter survival, which may lead to more pronounced obesogenic effects than seen in tropical fish such as zebrafish.

Combined effects of perchlorate and hexavalent chromium on the survival, growth and reproduction of Daphnia carinata

Perchlorate and hexavalent chromium (Cr(VI)) are common cocontaminants in aquatic environments due to their high water solubility, stability, mobility, and some coapplications. However, few studies have investigated their combined toxicity to organisms. In this work, we studied the acute and chronic toxicities of perchlorate and Cr(VI), alone and in combination, with survival, growth, and reproduction as endpoints using Daphnia carinata as a model organism. For a single contaminant, Cr(VI) was found to be more toxic than perchlorate to D. carinata not only in terms of survival but also in terms of growth and reproduction. In regard to the combined pattern, the interactive effects on survival, growth, and reproduction were mainly additivity, antagonism, and synergism, respectively, suggesting that the interactive response of perchlorate and Cr(VI) is endpoint-specific. Due to significant synergism, over 21 days of observation, the inhibition of 0.1 mg/L perchlorate and 0.2 mg/L Cr(VI) on cumulative offspring per female in the first seven broods reached 63.9 ± 3.6%, suggesting that long-term exposure to perchlorate and Cr(VI) at environmentally relevant concentrations may affect D. carinata reproduction in the natural environment. Our results will be significant for understanding the complicated combined toxicity of perchlorate and Cr to aquatic organisms.

Sodium perchlorate induces non-alcoholic fatty liver disease in developing stickleback

Perchlorate is a pervasive, water-soluble contaminant that competitively inhibits the sodium/iodide symporter, reducing the available iodide for thyroid hormone synthesis. Insufficient iodide uptake can lead to hypothyroidism and metabolic syndromes. Because metabolism, obesity and non-alcoholic fatty liver disease (NAFLD) are tightly linked, we hypothesized that perchlorate would act as an obesogen and cause NAFLD via accumulation of lipids in liver of developing threespine stickleback (Gasterosteus aculeatus). We performed an upshift/downshift exposure regime (clean water to perchlorate treated water or perchlorate treated water to clean water) on stickleback embryos at two concentrations (30 mg/L and 100 mg/L) plus the control (0 mg/L) over the course of 305 days. Adult stickleback were euthanized, H&E stained and analyzed for liver morphology. Specifically, we counted the number of lipid droplets, and measured the area of each droplet and the total lipid area of a representative section of liver. We found that perchlorate treated fish had more and larger lipid droplets, and a larger percentage of lipid in their liver than control fish. These data indicate that perchlorate causes NAFLD and hepatic steatosis in stickleback at concentrations commonly found at contaminated sites. These data also indicate the potential of perchlorate to act as an obesogen. Future studies should investigate the obesogenic capacity of perchlorate by examining organ specific lipid accumulation and whether perchlorate induces these effects at concentrations commonly found in drinking water. Work is also needed to determine the mechanisms by which perchlorate induces lipid accumulation.

Germ cell depletion in zebrafish leads to incomplete masculinization of the brain

Zebrafish sex differentiation is under the control of multiple genes, but also relies on germ cell number for gonadal development. Morpholino and chemical mediated germ cell depletion leads to sterile male development in zebrafish. In this study we produced sterile males, using a dead end gene morpholino, to determine gonadal-brain interactions. Germ cell depletion following dnd inhibition downregulated the germ cell markers, vasa and ziwi, and later the larvae developed as sterile males. Despite lacking proper testis, the gonadal 11-ketotestosterone (11-KT) and estradiol (E2) levels of sterile males were similar to wild type males. Qualitative analysis of sexual behavior of sterile males demonstrated that they behaved like wild type males. Furthermore, we observed that brain 11-KT and E2 levels in sterile males remained the same as in the wild type males. In female brain, 11-KT was lower in comparison to wild type males and sterile males, while E2 was higher when compared to wild type males. qRT-PCR analysis revealed that the liver transcript profile of sterile adult males was similar to wild type males while the brain transcript profile was similar to wild type females. The results demonstrate that proper testis development may not be a prerequisite for male brain development in zebrafish but that it may be needed to fully masculinize the brain.

Spatio-temporal distribution of perchlorate and its toxicity in Hydrilla verticillata

The spatio-temporal distribution of perchlorate in water sources around an ammonium perchlorate production unit and its toxicity response on a dominant aquatic plant, Hydrilla verticillata are reported in this study. Samples (n=453) from ground water (open well) and surface water sources within 5km from the production unit over a period of 12 months (2014, June - 2015, May) were screened for ClO₄^-. During the period, ClO₄^-concentration in ground water samples close to the production unit increased to >40,000μg/L, and ClO₄^- was detected at 1740μg/L in well water 1.6km away from the production unit. A community pond in the area also showed an increase in ClO₄^- level up to 29,000μg/L. In all water sources, ClO₄^- level was maximum during the rainy season (July, monsoon). A natural degradation of ClO₄^- was not observed in the area as evident from its persistent level and spreading to more areas. H. verticillata, the dominant vegetation in the pond exhibited severe toxic response like massive decay and loss of photosynthetic pigments such as chlorophyll and carotene due to ClO₄^- exposure. The plant accumulated ClO₄^- up to 60^±0.8mg/kg wet weight with a Bio-Concentration Factor 2.06±0.005. This is the first report on spatio-temporal distribution of ClO₄^- at higher levels in a natural environment and its toxicity response to plants under natural condition.

Protective effects of melatonin and ghrelin on spermatogenesis: A narrative review of the literature

Spermatocytogenesis starts from lumens of seminiferous cords and after migration to the basal membrane ends to the lumens again. We attempt to review the protective effects of melatonin and ghrelin on Spermatocytogenesis and in particular on spermatogonial stem cells, as two rather newly-discovered hormones. Testicular freezing prior to chemotherapy and radiotherapy is one of the ways of preserving fertility in children with cancer. The freezing has two methods of slow-freezing (cryopreservation) and rapid-freezing (vitrification). Administration of melatonin can maintain the quality of the germ cells underwent such processes, as well as ghrelin, can protect germ cells from the toxicities secondary to ischemic injuries, and pathologic apoptosis. This review indicates that in vitro or in vivo administration of melatonin or ghrelin, could be effective to preserve fertilization and also they can be used in assisted reproductive technologies to improve the quality of sperms. Future original studies should be propelled toward human studies, of course with observing the ethics.