Metallothionein is expressed in adipocytes of brown fat and is induced by catecholamines and zinc

Metallothionein (MT) is thought to have an antioxidant function and is stro ngly expressed during activation of thermogenesis and increased oxidative s tress in brown adipose tissue (BAT). Localization and regulation of MT expr ession in BAT was therefore investigated in rats and mice. Immunohistochemi cal analysis of BAT from rats exposed to 4 degrees C for 24 h showed that M T and uncoupling protein 1 (UCP1) were coexpressed in differentiated adipoc ytes, and both cytoplasmic and nuclear localization of MT was observed. Col d induction of MT-1 expression in BAT was also observed in mice. Administra tion of norepinephrine to rats and isoproterenol to mice stimulated MT and UCP1 expression in BAT, implying a sympathetically mediated pathway for MT induction. In mice, zinc, and particularly dexamethasone, induced MT-2 expr ession in BAT and liver. Surprisingly, zinc also induced UCP1 in BAT, sugge sting that elevated zinc may induce thermogenesis. We conclude that express ion of MT in mature brown adipocytes upon beta-adrenoceptor activation is c onsistent with a role in protecting against physiological oxidative stress or in facilitating the mobilization or utilization of energy reserves.