Trisomy 16 mouse is an animal model suitable to study the pathogenic mechanisms of Down's syndrome (human trisomy 21). Since oxidative stress is strongly linked to the mental retardation in Down's syndrome, we focused our attention on the activation of stress response genes, using embryonic cortical cultures of trisomy 16 mouse and their euploid littermates. The objectives of this project are: 1. to determine metallothionein I/II level in trisomy 16 cells culture and in euploid cell cultures; 2. to determine the metallothionein I/II response to oxygen free radicals and metals in cortical tissue cultures of trisomy 16 mouse and euploid littermate. In the brain metallothionein I/II are expressed in astrocytes. Their physiological role expands from cellular defense in oxidative stress, cytokine responses during inflammation, to the upkeeping of cellular Zn and Cu homeostasis. Our data show that the density of metallothionein I/II immunoblots is higher in cortical cultures of trisomy 16 mouse when compared to that of euploid littermates. To verify whether the increase in metallothionein I/II in trisomy 16 cell culture was involved in increased oxidative stress, cells were cultured in presence of the antioxidant N-Acetyl-Cysteine (NAC). In the presence of NAC, the density of the protein bands of metallothionein I/II was normalized. Cells were also exposed to the ionotropic glutamate agonist, kainic acid (1-50 mM), the metabotropic glutamate agonist, (+/-) ACPD (1-50 mM), or H2O2 (1-10 mM). No further induction of metallothionein I/II was observed in trisomy 16 cell culture after any of these treatments. Instead, the density of metallothionein I/II immunoblots was increased after Pb exposure (25 mM) in both trisomy 16 and euploid cell cultures. The lack of metallothionein-response to H2O2 could be due to an altered H2O2 interaction on the level of the promoter of metallothionein I/II gene. In fact, two different elements in the promoter region, the metal response element and the anti-oxidant response element, may be good candidates to explore.
