Copper is an essential micronutrient in man and the reactions catalyzed by copper-containing enzymes play a key role in such vital processes as cellular respiration, antioxidant protection, connective tissue biosynthesis, amino acid metabolism, pigment formation and neurotransmitter and hormone biosynthesis. Deficiency states and inherited disorders of copper metabolism underscore this essential role for copper and hint at the complex biochemistry involved in determining copper transport and compartmentalization within the cell. Although the liver plays a central role in copper homeostasis regulating total body copper distribution and turnover little is known about the cellular or molecular mechanisms of hepatocyte copper metabolism due to the absence of sensitive methods to isolate or characterize the specific elements involved. In addition inherited defects in hepatic copper metabolism have been difficult to characterize because of the lack of accessible genetic models for study. The long term objective of these studies is to define the cellular and molecular determinants of human hepatocyte copper metabolism.
The specific aim of this proposal is to elucidate the mechanisms of copper incorporation into the blue copper oxidase ceruloplasmin. Ceruloplasmin is the principal copper protein synthesized and secreted by hepatocytes and the incorporation of copper into this protein is impaired in Wilson Disease. Recent work in our laboratory has resulted in both the development of methods to detect newly synthesized holoceruloplasmin following metabolic labeling of cells with 67 Cu and the identification of an inbred rat strain (LEC rat) with a hereditary hepatitis identical to Wilson disease. We now propose to extend these studies by directly examining the mechanisms for deficient holoceruloplasmin biosynthesis and excessive copper accumulation in the LEC rat hepatocyte. Through a combination of biochemical and molecular genetic approaches we will dissect the defect in cellular trafficking of copper within the LEC hepatocyte. These studies have direct relevance to the long-term objectives and should permit a broader understanding of the mechanisms of copper accumulation, apoceruloplasmin production and hepatocellular necrosis in Wilson Disease. Ultimately such a characterization of the mechanisms of hepatocyte copper metabolism will provide new insights into the biological roles of copper in human nutrition and disease.
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