Roles of metallothionein in copper homeostasis: responses to Cu-deficient diets in mice.

Metallothionein (MT) protects the body from both harmful non-essential and excessive essential metals. Copper (Cu) is an essential metal, and its concentration in the body is regulated at a constant level between excess and deficient ones. Cu accumulating in the livers of Wilson disease patients and its animal model, Long-Evans rats with a cinnamon-like coat color (LEC) rats, is in the form of Cu,Zn-MT, MT being an antioxidant. Contrary to the efficient production of MT in response to excessive accumulation of Cu in LEC rats, Cu-binding to MT only occurs marginally under normal conditions. However, the present study revealed that Cu binds to MT more with a severe Cu-deficiency. Namely, male C57BL/6J mice were fed a Cu-deficient diet (0.037 mg Cu/g) and deionized water containing trientine, and then the concentration and distribution of Cu were determined. It was suggested that the cessation of biliary excretion and limitation of the Cu supply to ceruloplasmin are the first responses on feeding of a Cu-deficient diet, followed by an increase in Cu-MT with maintenance of the Cu concentration in the liver. These results suggest that MT causes the recruitment of Cu in a Cu-deficient environment by sequestering Cu from degraded Cu-enzymes and delivering it to Cu chaperones.