Metallothionein gene expression and secretion in white adipose tissue

White adipose tissue (WAT) has been examined to determine whether the gene encoding metallothionein (MT), a low-molecular-weight stress response prote in, is expressed in the tissue and whether MT may be a secretory product of adipocytes. The MT-1 gene was expressed in epididymal WAT, with MT-1 mRNA levels being similar in lean and obese (ob/ob) mice. MT-1 mRNA was found in each of the main adipose tissue sites (epididymal, perirenal, omental, sub cutaneous), and there was no major difference between depots. Separation of adipocytes from the stromal-vascular fraction of WAT indicated that the MT gene (MT-1 and MT-2) was expressed in adipocytes themselves. Treatment of mice with zinc had no effect on MT-1 mRNA levels in WAT, despite strong ind uction of MT-1 expression in the liver. MT-1 gene expression in WAT was als o unaltered by fasting or norepinephrine. However, administration of a beta (3)-adrenoceptor agonist, BRL-35153A, led to a significant increase in MT- 1 mRNA. On differentiation of fibroblastic preadipocytes to adipocytes in p rimary culture, MT was detected in the medium, suggesting that the protein may be secreted from WAT. It is concluded that WAT may be a significant sit e of MT production; within adipocytes, MT could play an antioxidant role in protecting fatty acids from damage.