In cortical cultures of trisomy 16 mouse brain the upregulated metallothionein-I/II fails to respond to H₂O₂ exposure or glutamate receptor stimulation

To assess whether a defective oxidative defense may contribute to Down's syndrome, we studied the regulation of the metallothionein(MT)-I/II isoforms in primary cultures of cerebral cortex from fetal trisomy 16 mice and their euploid littermates. Western blot analysis showed that MT-I/II was upregulated and the protein carbonyl content was higher in trisomy 16 compared with euploid cultures. Addition of N-acetyl-L-cysteine to the culture medium reduced the increment of MT-I/II in trisomy 16 cortical cells. In euploid, but not trisomic cortical cultures, kainic acid, trans-(+)-ACPD, or H₂O₂ exposure elicited a dose-dependent increase of the MT-I/II immunoblots. In trisomic cells, the MT-I/II immunoblot densities were not increased beyond their elevated basal levels. In contrast, 25 μM Pb induced MT-I/II, to a similar extent, in cortical cultures from euploid and trisomy 16 mice. This suggests that the antioxidant - but not the metal - response element of the MT-I/II promoter was altered by increased oxidative stress. Our data suggest that, in the trisomy 16 mouse, the effects of increased production of reactive oxygen species, due to the increased SOD-1, GluR5, or amyloid precursor protein gene dosage, is exacerbated by an insufficient or missing antioxidant response.