Transgenic mice overexpressing human acetylcholinesterase and the Swedish amyloid precursor protein mutation: effect of nicotine treatment.

Acetylcholinesterase (AChE) is shown to promote deposition of beta-amyloid (Abeta) peptides and to enhance Abeta toxicity. Tg2576 (transgenic mice carrying the Swedish mutation of amyloid precursor protein, APPswe) mice and mice overexpressing human synaptic acetylcholinesterase (AChE-S) were crossed (hAChE-Tg//APPswe), to study the effects of brain Abeta, from 1 to 10 months of age, under the constant influence of AChE-S. The effect of nicotine treatment was also evaluated in these mice since we have previously shown that nicotine dramatically decreases Abeta levels in single transgenic APPswe mice. Already at 1 and 3 months, hAChE-Tg// APPswe mice showed increased levels of cortical insoluble Abeta1-40 and Abeta1-42 compared with APPswe mice, whereas APPswe mice displayed increased soluble Abeta1-40. Abeta plaques were detected at 7 months, thus before onset of plaque formation in APPswe mice. No differences were found in [125I]alpha-bungarotoxin binding sites or hippocampal glial fibrillary acidic protein (GFAP) immunoreactivity between hAChE-Tg//APPswe, and APPswe mice at either 1 or 10 months of age. L(-)-Nicotine (final dose 0.45 mg/kg) treatment twice daily for 10 days to 14-month-old hAChE-Tg// APPswe mice increased cortical insoluble Abeta1-40 levels, while both L(-)- and D(+)-nicotine (final dose 0.45 mg/kg) increased soluble Abeta1-42. L(-)-Nicotine reduced hippocampal GFAP immunoreactivity both in hAChE-Tg//APPswe mice and non-transgenic controls, while D(+)-nicotine caused a decrease only in hAChE-Tg//APPswe mice. Moreover, D(+)-nicotine increased the [125I]alpha-bungarotoxin binding sites in the hippocampus, and cortex of the hAChE-Tg//APPswe mice. In conclusion, already at a very young age, hAChE-Tg// APPswe mice exhibit increased levels of aggregated Abeta compared with APPswe mice, due to the possible interaction between Abeta and AChE-S, whereas APPswe mice exhibit increased soluble Abeta. The interaction between Abeta and AChE-S may also explain the different effect of nicotine on Abeta pathology in the hAChE-Tg//APPswe mice. The results in this study emphasize the importance of using different transgenic mouse models for evaluating the effect of new drug candidates for the treatment of Alzheimer's disease.