Zinc is an essential nutrient that profoundly affects human health, as zinc deficiency and zinc excess both result in a broad spectrum of pathologies. Zinc plays many roles in biological systems, since zinc is essential for the function of many proteins and zinc modulates signal transduction pathways. A detailed understanding of zinc metabolism and homeostasis is critical for the development of new approaches for manipulating zinc to promote human health. There are major gaps in the current understanding of zinc metabolism in animals, since fundamental mechanisms used to take up, distribute, sense and excrete zinc are not well understood. Our long-term goal is to understand how a network of zinc transporters and binding proteins act in a coordinated fashion to regulate zinc metabolism in animals. This goal will be addressed by analyzing zinc importers, zinc exporters and new genes involved in zinc metabolism using mammalian cells and the genetically tractable model organism C. elegans. Understanding how a network of proteins controls zinc metabolism in an animal is an important objective of medical research, since the information may lead to new therapeutic approaches for diseases caused by abnormal zinc metabolism. Our preliminary results have established the powerful C. elegans model system for studies of zinc metabolism by the development of culture conditions that permit manipulation of dietary zinc, the creation of assays that measure zinc metabolism, and the identification of mutations in new genes that affect zinc metabolism. These results support three innovative hypotheses. (1) CDF-2 plays a critical role in zinc storage and detoxification by transporting zinc into the lumen of lysosome-related organelles. (2) Lysosome-related organelles adopt a bilobed morphology in response to high zinc conditions and provide a source of zinc that is mobilized during deficiency. (3) Histidine ammonia lyase plays an important role in zinc metabolism, and high levels of histidine promote zinc detoxification. To test these hypotheses, we propose two specific aims.
Aim 1 : Define the role of CDF-2 and lysosome-related organelles in zinc storage. Elucidate how a network proteins including CDF, ZIP and ferroportin function in a coordinated manner to regulate zinc storage and mobilization.
Aim 2 : Determine the function of histidine ammonia lyase and histidine in zinc metabolism in mammalian cells. Identify and characterize new genes that mediate zinc metabolism in C. elegans and mammals. These experiments build on our accomplishments in the previous grant period that established the C. elegans model system for studies of zinc metabolism. This proposal will extend these discoveries to vertebrate systems and exploit the powerful experimental advantages of C. elegans to elucidate how a network of genes regulates zinc storage and mobilization in a multicellular animal. Several prevalent human diseases such as Alzheimer's disease, stroke and cancer have been associated with abnormalities of zinc metabolism, and the results of these studies may suggest new therapeutic strategies for addressing disorders of zinc toxicity.
Zinc is an essential nutrient that is critical for human health, since zinc deficiency and excess both cause a wide range of health problems. This research will determine how animals protect themselves against excess zinc, and how zinc that is stored in times of excess can be used later in times of deficiency. These studies will suggest new strategies for treating diseases caused by zinc excess or deficiency.
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