Induction of metallothionein in astrocytes by cytokines and heavy metals

Immunohistochemical staining of human and rat brains for metallothionein (MT) using a monoclonal anti-MT antibody (MT45) revealed that protoplasmic astrocytes, which are densely localized in the gray matter, contain high levels of MT. Human U373MG astrocytoma cells were stimulated with interleukin (IL)-l or heavy metals to produce MT. When expression of MT in U373MG cells was analyzed by Northern blotting or indirect immunofluorescence using the MT45 antibody, it was found that IL-1 (≥ 10 U/ml), CdCl₂ (50 μM) and high concentrations of ZnCL (500 μM) induced marked biosynthesis of MT. IL-6 (up to 3, 000 U/ml) and lower concentrations of ZnCl₂ (10-50 μM), however, showed little inducing activity. Hippocampal astrocytes in primary culture produced a relatively high basal level of MT. The MT level increased in response to addition of IL-1 (≥ 10 U/ml), ZnCl₂ (50 μM) and CdCL (5 μM). However, the increase induced by IL-6 (1, 000 U/ml) was not very marked. The in vivo induction of MT in the brain by cytokines is not fully understood. How- ever, our data and other indirect evidence suggest that IL-1 may be a potent stimulator of MT induction in astrocytes. Furthermore, the astrocytoma cell line, U373MG, is a suitable in vitro system to analyze the expression of MT in astrocytes.