Cadmium (Cd) is a toxic heavy metal found in the environment as a product of industrial contamination, and is classified as a human carcinogen. Cd is a significant contributor to the cancer risk associated with cigarette smoke, and has been linked to lung, renal, prostate and testicular cancer. Within cells, Cd toxicity results in DNA damage, and oxidative stress, including the production of reactive oxygen species (ROS);however, cadmium is not redox active under biological conditions and cannot directly catalyze ROS production. Data recently obtained using Saccharomyces cerevisiae indicates that a significant contributor to Cd toxicity is the disruption of copper (Cu) metabolism within the cell. Cu is an essential transition metal that serves as a catalytic cofactor in numerous enzymes, but is tightly regulated within cells and is toxic at high concentrations. Both Cu and Cd have also been linked to aging in mammals. Changes in Cu metabolism accompany the aging process, and increased Cd resistance correlates with increased species lifespan. One possible explanation for this correlation is that long-lived species have developed more efficient cellular metabolism for responding to increases in Cu and other transition metals associated with Cd toxicity. This hypothesis would be consistent with the results from S. cerevisiae. However, differences in the Cd response mechanisms preclude direct extrapolation of results obtained in yeast to more complex, mammalian systems. We therefore propose a directed series of experiments to test the potential for a mechanistic linkage between Cu metabolism in mammalian cells and Cd toxicity. Specifically, we aim to: (1) Examine the impact of Cd on transition metal homeostasis in mammalian fibroblast cells, by assaying changes in total metal content and by mapping the subcellular distributions of Cu and other transition metals in normal and Cd-exposed cells using synchrotron X-ray fluorescence microprobe imaging;(2) Analyze the involvement of specific transition metal transporters and chaperones in the origins of Cd toxicity using RNAi gene silencing and metal depletion experiments;and (3) Compare the metal content and distributions in untreated and Cd-treated fibroblasts derived from the skin of short-lived, Cd-sensitive and long-lived, Cd-tolerant rodents. Together, these experiments will establish if large-scale disruption of transition metal homeostasis contributes to the molecular origins of Cd toxicity in mammals, as it does in yeast, and shed light on differences in metal homeostasis associated with increased lifespan.
Cadmium (Cd) is a toxic metal ion, a human carcinogen and a major contributor to the cancer risk associated with cigarette smoke. In yeast, Cd toxicity is linked to disruption of copper (Cu) metabolism;however, it is unknown if the same is true in mammals. The experiments proposed here will establish whether disrupting the homeostasis of Cu or other transition metals contributes to Cd toxicity in mammals, and examine the possibility that differences in metal metabolism contribute to the Cd tolerance of long-lived species.
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