Cadmium chloride (CdCl₂)-induced metallothionein (MT) expression in neonatal rat primary astrocyte cultures

Metallothionein (MT) protein and mRNA levels were studied following exposure of rat neonatal primary astrocyte cultures to cadmium chloride (CdCl₂). MT mRNA was probed on Northern blots with a³²P labeled synthetic cDNA probe specific for rat MT mRNA. The probe hybridizes to a single mRNA with a size appropriate for MT, approximately 550 bases. Expression of MT-I mRNA in astrocyte monolayers exposed to 2 × 10^-6 M CdCl₂ for 6 h was increased approximately 5-fold (9.7 fg/μg total RNA) over MT-I mRNA levels in controls (2 fg/μg total RNA). MT-I mRNA could also be detected in untreated cells, suggesting constitutive MT expression in these cells. Western-blot analysis revealed a marked increase in MT protein levels upon exposure to CdCl₂ (1 × 10^-6 M; 96 h). Consistent with the constitutive expression of MTs both at the mRNA level and protein level, we have also demonstrated a time-dependent increase in MT-immunoreactivity in astrocytes exposed to CdCl₂. The present study suggests that astrocytes constitutively express MTs, and that MT-induction by CdCl₂ may be an example of a generalized increase in MTs in response to heavy metal exposure, thus protecting astrocytes, and perhaps also indirectly, juxtaposed neurons from the neurotoxic effects of heavy metals.