The nematode Caenorhabditis elegans has emerged as an important animal model in various fields including neurobiology, developmental biology, and genetics. Characteristics of this animal model that have contributed to its success include its genetic manipulability, invariant and fully described developmental program, well-characterized genome, ease of maintenance, short and prolific life cycle, and small body size. These same features have led to an increasing use of C. elegans in toxicology, both for mechanistic studies and high-throughput screening approaches. We describe some of the research that has been carried out in the areas of neurotoxicology, genetic toxicology, and environmental toxicology, as well as high-throughput experiments with C. elegans including genome-wide screening for molecular targets of toxicity and rapid toxicity assessment for new chemicals. We argue for an increased role for C. elegans in complementing other model systems in toxicological research.

Polarized intracellular trafficking in epithelia is critical in development, immunity, and physiology to deliver morphogens, defensins, or ion pumps to the appropriate membrane domain. The mechanisms that control apical trafficking remain poorly defined. Using Caenorhabditis elegans, we characterize a novel apical secretion pathway involving multivesicularbodies and the release of exosomes at the apical plasma membrane. By means of two different genetic approaches, we show that the membrane-bound V0 sector of the vacuolar H+-ATPase (V-ATPase) acts in this pathway, independent of its contribution to the V-ATPase proton pump activity. Specifically, we identified mutations in the V0 “a” subunit VHA-5 that affect either the V0-specific function or the V0+V1 function of the V-ATPase. These mutations allowed us to establish that the V0 sector mediates secretion of Hedgehog-related proteins. Our data raise the possibility that the V0 sector mediates exosome and morphogen release in mammals.

Summary: In C. elegans, the skn‐1 gene encodes a transcription factor that resembles mammalian Nrf2 and activates a detoxification response. skn‐1 promotes resistance to oxidative stress (Oxr) and also increases lifespan, and it has been suggested that the former causes the latter, consistent with the theory that oxidative damage causes aging. Here, we report that effects of SKN‐1 on Oxr and longevity can be dissociated. We also establish that skn‐1 expression can be activated by the DAF‐16/FoxO transcription factor, another central regulator of growth, metabolism, and aging. Notably, skn‐1 is required for Oxr but not increased lifespan resulting from over‐expression of DAF‐16; concomitantly, DAF‐16 over‐expression rescues the short lifespan of skn‐1 mutants but not their hypersensitivity to oxidative stress. These results suggest that SKN‐1 promotes longevity by a mechanism other than protection against oxidative damage.

Aging (senescence) is characterized by the development of numerous pathologies, some of which limit lifespan. Key to understanding aging is discovery of the mechanisms (etiologies) that cause senescent pathology. In C. elegans, a major senescent pathology of unknown etiology is atrophy of its principal metabolic organ, the intestine. Here we identify a cause of not only this pathology but also of yolky lipid accumulation and redistribution (a form of senescent obesity): autophagy-mediated conversion of intestinal biomass into yolk. Inhibiting intestinal autophagy or vitellogenesis rescues both visceral pathologies and can also extend lifespan. This defines a disease syndrome leading to multimorbidity and contributing to late-life mortality. Activation of gut-to-yolk biomass conversion by insulin/IGF-1 signaling (IIS) promotes reproduction and senescence. This illustrates how major, IIS-promoted senescent pathologies in C. elegans can originate not from damage accumulation but from direct effects of futile, continued action of a wild-type biological program (vitellogenesis).

Parkinson's disease (PD)-mimicking drugs and pesticides, and more recently PD-associated gene mutations, have been studied in cell cultures and mammalian models to decipher the molecular basis of PD. Thus far, a dozen of genes have been identified that are responsible for inherited PD. However they only account for about 8% of PD cases, most of the cases likely involving environmental contributions. Environmental manganese (Mn) exposure represents an established risk factor for PD occurrence, and both PD and Mn-intoxicated patients display a characteristic extrapyramidal syndrome primarily involving dopaminergic (DAergic) neurodegeneration with shared common molecular mechanisms. To better understand the specificity of DAergic neurodegeneration, we studied Mn toxicity in vivo in Caenorhabditis elegans. Combining genetics and biochemical assays, we established that extracellular, and not intracellular, dopamine (DA) is responsible for Mn-induced DAergic neurodegeneration and that this process (1) requires functional DA-reuptake transporter (DAT-1) and (2) is associated with oxidative stress and lifespan reduction. Overexpression of the anti-oxidant transcription factor, SKN-1, affords protection against Mn toxicity, while the DA-dependency of Mn toxicity requires the NADPH dual-oxidase BLI-3. These results suggest that in vivo BLI-3 activity promotes the conversion of extracellular DA into toxic reactive species, which, in turn, can be taken up by DAT-1 in DAergic neurons, thus leading to oxidative stress and cell degeneration. In Parkinson's disease (PD), motor neurons that produce dopamine degenerate, leading to a characteristic syndrome including tremor, rigidity, and bradykinesia. The mechanisms leading to PD have been under intense investigation, identifying hereditary mutations responsible for about 8% of the cases. However, multiple environmental factors contribute to PD; and, amongst those, manganese (Mn) exposure from pesticides, industrial fumes, and gasoline additives has been robustly associated with PD. To gain insights into processes leading to the specific degeneration of dopaminergic neurons, we used a simple animal model, the nematode Caenorhabditis elegans, which, upon Mn exposure, recapitulates key molecular processes known to be involved in PD. Combining biochemistry and genetics, we demonstrate that dopamine secreted by the neurons and not intracellular dopamine is directly involved in the generation of toxic reactive oxygen species. We identify two essential mediators of this dopamine-dependent effect which are an extracellularly active enzyme called dual-oxidase and the dopamine re-uptake transporter. We also reveal that a transcription factor which is strongly expressed in two neurons involved in the regulation of aging is a powerful modulator of the dopamine-dependent toxicity. Our study establishes novel evidence of the link among PD, aging, and oxidative stress within the context of exposure to Mn.