The putative multidrug resistance protein MRP-7 inhibits methylmercury-associated animal toxicity and dopaminergic neurodegeneration in Caenorhabditis elegans

Exposome, Molecular Pathways and One Health: The Invertebrate Caenorhabditis elegans

Due to its preferred habitats in the environment, the free-living nematode Caenorhabditis elegans has become a realistic target organism for pollutants, including manufactured nanoparticles. In the laboratory, the invertebrate animal model represents a cost-effective tool to investigate the molecular mechanisms of the biological response to nanomaterials. With an estimated number of 22,000 coding genes and short life span of 2-3 weeks, the small worm is a giant when it comes to characterization of molecular pathways, long-term low dose pollutant effects and vulnerable age-groups. Here, we review (i) flows of manufactured nanomaterials and exposition of C. elegans in the environment, (ii) the track record of C. elegans in biomedical research, and (iii) its potential to contribute to the investigation of the exposome and bridge nanotoxicology between higher organisms, including humans. The role of C. elegans in the one health concept is taken one step further by proposing methods to sample wild nematodes and their molecular characterization by single worm proteomics.

ATP-binding cassette transporters and neurodegenerative diseases

ATP-binding cassette (ABC) transporters are one of the largest groups of transporter families in humans. ABC transporters mediate the translocation of a diverse range of substrates across cellular membranes, including amino acids, nucleosides, lipids, sugars and xenobiotics. Neurodegenerative diseases are a group of brain diseases that detrimentally affect neurons and other brain cells and are usually associated with deposits of pathogenic proteins in the brain. Major neurodegenerative diseases include Alzheimer's disease, Parkinson's disease and amyotrophic lateral sclerosis. ABC transporters are highly expressed in the brain and have been implicated in a number of pathological processes underlying neurodegenerative diseases. This review outlines the current understanding of the role of ABC transporters in neurodegenerative diseases, focusing on some of the most important pathways, and also suggests future directions for research in this field.

Ecotoxicity Risk of Low-Dose Methylmercury Exposure to Caenorhabditis elegans: Multigenerational Toxicity and Population Discrepancy

Methylmercury (MeHg) is a common organic form of mercury in water, which has been linked to several forms of biological toxicity. However, studies on the ecotoxicity risk of long-term exposure to low-dose MeHg are insufficient for the assessment of environmental safety. In the present study, the effects of MeHg on multiple generations (P0-F3) and population of Caenorhabditis elegans were investigated under long-term, low-dose exposure. We investigated the multigenerational toxicity of MeHg by analyzing reproductive and developmental indicators. According to our results, exposure to 100 nM MeHg had little effect on the parental generation (P0) but caused serious reproductive toxicity in the offspring (F1-F3), and the effect of MeHg was aggravated with each passing generation. The genes related to apoptosis and DNA damage were upregulated in the F3 generation. Pearson correlation analysis showed that the changes in these genes were closely related to the apoptosis of gonadal cells. Furthermore, chronic exposure to MeHg (from 100 to 1000 nM group) caused a sharp decline in population size and triggered the "bag of worms" phenotype. Genes related to vulvar development were downregulated in the F3 generation after treatment with 100 nM MeHg. These data suggest that long-term low-dose MeHg exposure adversely affected C. elegans and its offspring and triggered multigenerational toxicity and population discrepancy.

Genome-wide identification of ABC transporters in monogeneans

ATP-Binding Cassette (ABC) transporters are proteins that actively mediate the transport of a wide variety of molecules, including drugs. Thus, in parasitology, ABC transporters have gained attention as potential targets for therapeutic drugs. Among the parasitic Platyhelminthes, ABC transporters have been identified and classified in a few species of Trematoda and Cestoda but not in Monogenea. Monogeneans are mainly ectoparasites of marine and freshwater fish, although they can also be found on other aquatic organisms. Severe epizootics caused by monogeneans have been reported around the world, mainly in confined and/or overcrowded fish. The purpose of this study was to identify the ABC transporters in four species of monogeneans (Gyrodactylus salaris, Protopolystoma xenopodis, Eudiplozoon nipponicum and Neobenedenia melleni) for which genomic resources are publicly available. For comparative purposes, ABC transporters were also identified in endoparasitic (Schistosoma mansoni and Echinococcus granulosus) and free-living (Macrostomun lignano and Schmidtea mediterranea) platyhelminths. Thirty-two putative ABC transporters were identified in the genome of G. salaris, 40 in the genome of P. xenopodis, 46 in the transcriptome of E. nipponicum and 9 in a rather limited ESTs set available for N. melleni. Of the eight ABC subfamilies (A-H) known in metazoans, subfamily H was the only one not found in any monogenean species. In contrast, ABCC was the best represented subfamily. Phylogenetic analyses showed a few cases of one-to-one orthologous relationships, which agree with results from other metazoan species. We found some monogenean ABC members related to subfamilies B, C and G involved in drug resistance in humans. This information may be useful for future functional studies on ABC transporters in monogeneans.

(-)-Epigallocatechin-3-gallate attenuates the toxicity of methylmercury in Caenorhabditis elegans by activating SKN-1

(-)-Epigallocatechin-3-gallate (EGCG) found in tea is a natural activator of nuclear factor erythroid 2-related factor 2 (Nrf2), a primary regulator of the cellular defense system. The adverse health effects resulting from methylmercury (MeHg) exposure in humans are of worldwide concern. We hypothesized that EGCG could induce a Nrf2-mediated protective response to antagonize MeHg toxicity. Using the Caenorhabditis elegans (C. elegans) nematode model, we observed that EGCG activated SKN-1 (the functional ortholog of Nrf2 in C. elegans), as shown by the increased skn-1 mRNA level, induction of the gene gst-4, and enhanced SKN-1-mediated oxidative stress resistance that were indicated by elevation of total antioxidant ability and reductions in reactive oxygen species and malondialdehyde. Following exposure to MeHg, EGCG-treated C. elegans displayed increased survival rates, improved locomotion behaviors, decreased numbers of damaged neurons, and reduced oxidative damage compared to the controls. Moreover, the protective effects of EGCG against MeHg toxicity were counteracted by RNA-mediated interference of skn-1. These results demonstrated that EGCG could alleviate MeHg toxicity by upregulating the SKN-1-regulated protective response in C. elegans. Our study suggests a potentially beneficial effect of targeting Nrf2 by dietary EGCG in protecting humans against MeHg toxicity.

Human-induced pluripotent stems cells as a model to dissect the selective neurotoxicity of methylmercury

Methylmercury (MeHg) is a potent neurotoxicant affecting both the developing and mature central nervous system (CNS) with apparent indiscriminate disruption of multiple homeostatic pathways. However, genetic and environmental modifiers contribute significant variability to neurotoxicity associated with human exposures. MeHg displays developmental stage and neural lineage selective neurotoxicity. To identify mechanistic-based neuroprotective strategies to mitigate human MeHg exposure risk, it will be critical to improve our understanding of the basis of MeHg neurotoxicity and of this selective neurotoxicity. Here, we propose that human-based pluripotent stem cell cellular approaches may enable mechanistic insight into genetic pathways that modify sensitivity of specific neural lineages to MeHg-induced neurotoxicity. Such studies are crucial for the development of novel disease modifying strategies impinging on MeHg exposure vulnerability.