The first third-generation Alzheimer mouse, PLB1: Tissue analyses and histology

Recently, the usefulness of existing animal models for neurodegenerative diseases, including Alzheimer's disease, has been challenged regarding their face and predictive value. Therefore, we have developed a novel transgenic model of Alzheimer's disease using a targeted knock-in of human APP770swe/lon and tauP301L/R406W under the control of the forebrain specific CamKII promoter (PLB1double) and crossed these with PSEN expressing mice to generate a triple transgenic mouse PLB1triple (for background information, see accompanying abstracts). The tissue expression analyses were performed on transcriptional and translational level. Brain homogenates of 6-12 months old animals were analysed for transgenic mRNA expression via absolute quantitative real-time PCR (BioRad) normalised to mouse GAPDH housekeeping gene. Protein based expression and pathology was visualised by immuno-specific labelling and congophilic stains (tau: HT7; PS396 & AT8; APP: DE2B4, Congo Red, Thioflavin S). Transcriptional analyses yielded similar expression of transgenic mRNA in homo- and hemizygote PLB1triple mice where APP levels were approximately 3-fold higher than Tau. Heterozygote PLB1triple animals had about half transgenic mRNA expression of the corresponding genes (APP or Tau) than homo- or hemizygotes. These mRNA levels were stable over the analysed time points, and highly stable between animals of the same genotype. PLB1double mice had similar expression levels for both APP and Tau as the PLB1triple animals of the same age group. Human APP and tau protein expression were identified in hippocampal and cortical brain regions of 12 months old PLB1triple animals. Occasionally, congophilic plaques were present from 9 months of age onwards, indicating the mature nature of these aggregations. This novel 3rd generation knock-in mouse model for Alzheimer's disease presents itself with stable gene expression and disease-relevant hallmarks could be visualised immunocytochemically. Since gene expression was stable over time, and within a transgenic group, it offers a much more defined and reproducible model for the characterisation of this devastating neurodegenerative disease.