Zinc is an essential trace metal that has integral roles in numerous biological processes, including enzymatic function, protein structure, and cell signaling pathways. Both excess and deficiency of zinc can lead to detrimental effects on development and metabolism, resulting in abnormalities and disease. We altered the zinc balance within Caenorhabditis elegans to examine how changes in zinc burden affect longevity and healthspan in an invertebrate animal model. We found that increasing zinc levels in vivo with excess dietary zinc supplementation decreased the mean and maximum lifespan, whereas reducing zinc levels in vivo with a zinc-selective chelator increased the mean and maximum lifespan in C. elegans. We determined that the lifespan shortening effects of excess zinc required expression of DAF-16, HSF-1 and SKN-1 proteins, whereas the lifespan lengthening effects of the reduced zinc may be partially dependent upon this set of proteins. Furthermore, reducing zinc levels led to greater nuclear localization of DAF-16 and enhanced dauer formation compared to controls, suggesting that the lifespan effects of zinc are mediated in part by the insulin/IGF-1 pathway. Additionally, zinc status correlated with several markers of healthspan in worms, including proteostasis, locomotion and thermotolerance, with reduced zinc levels always associated with improvements in function. Taken together, these data support a role for zinc in regulating both development and lifespan in C. elegans, and that suggest that regulation of zinc homeostasis in the worm may be an example of antagonistic pleiotropy.

Parkinson's disease (PD) is a debilitating motor and cognitive neurodegenerative disorder for which there is no cure. While aging is the major risk factor for developing PD, clear environmental risks have also been identified. Environmental exposure to the metal manganese (Mn) is a prominent risk factor for developing PD and occupational exposure to high levels of Mn can cause a syndrome known as manganism, which has symptoms that closely resemble PD. In this study, we developed a model of manganism in the environmentally tractable nematode, Caenorhabditis elegans. We find that, in addition to previously described modes of Mn toxicity, which primarily include mitochondrial dysfunction and oxidative stress, Mn exposure also significantly antagonizes protein homeostasis, another key pathological feature associated with PD and many age-related neurodegenerative diseases. Mn treatment activates the ER unfolded protein response, severely exacerbates toxicity in a disease model of protein misfolding, and alters aggregate solubility. Further, aged animals, which have previously been shown to exhibit decreased protein homeostasis, are particularly susceptible to Mn toxicity when compared to young animals, indicating the aging process sensitizes animals to metal toxicity. Mn exposure also significantly alters iron (Fe) and calcium (Ca) homeostasis, which are important for mitochondrial and ER health and which may further compound toxicity. These finding indicate that modeling manganism in C. elegans can provide a useful platform for identifying therapeutic interventions for ER stress, proteotoxicity, and age-dependent susceptibilities, key pathological features of PD and other related neurodegenerative diseases.

Parkinson's disease (PD) is largely an idiopathic disease that includes contributions from both genetic and environmental factors, with aging itself being the largest risk factor. These combined susceptibility factors are believed to accumulatively contribute to initiation and progression of Parkinson's disease. Although most cases of PD are idiopathic, rare genetic forms of the disease do exist. In these cases, an important unanswered question is why mutations that cause the disease have come to be maintained within the human population? One possibility is based on what is known as the Antagonist Pleiotropic Theory (APT) of Aging, a theory that states that genes that confer reproductive benefit early in life may result in detrimental effects with post-reproductive aging. Mutations in the PARKIN gene are associated with PD in humans. We have made a series of observations in the model organism Caenorhabditis elegans in which, the worms carrying a mutation of the homozygous gene, pdr-1, displayed increased reproductive fitness. This suggests that familial parkin mutation may have a beneficial effect in terms of natural selection even though its known clinical effect in PD patients bearing this mutation is detrimental. This data provides the first clues as to why this particular PD-related mutation may be maintained within the population. I have investigated the mechanism of this newly identified phenotype and if environmental factors alter this affect. Specifically, we have asked whether increased fitness may be due to enhanced mitochondrial function during reproduction. Additionally, we contemplate if the environmental factor manganese (Mn), which has been identified as a risk factor for the disease, alters reproductive fitness in relation to this gene mutation. Do changes in fecundity in the pdr-1 mutants correlate with effects on mitochondrial function? Does Mn metabolism effect reproductive fitness? Discussion pdr-1(lg103) confers increased reproductive fitness pdr-1 mutant worms median lifespan increased with Mn treatment pdr-1(lg103) acts differently than pdr-1(gk448) under heat stress pdr-1(lg103) may confer evolutionary fitness The mechanism(s) of increased reproductive fitness (Darwinian fitness) in a single allele Mitochondrial dysfunction in recruitment for mitophagy by PARKIN may play a role in the mechanism of Darwinian fitness Conclusion Acknowledgments References