Targeting cholinergic cells in a mouse model of Alzheimer's disease: Validating a quadruple transgenic model

Alzheimer's disease (AD) is an increasing health and social problem worldwide with prevalent cholinergic cell involvement. To reveal the details of the exact mechanisms, further preclinical studies in animals are needed. Our aim was to create a mouse model that represents the progression of AD with easy cholinergic manipulation. The 3xTg-AD and ChAT-Cre strains were crossbred. After serial genotyping, a colony, homozygote for all four genes (PSEN1, APPSwe, tauP301L and Cre; 3xAD-ChAT-Cre) was established. The presence of amyloid-β (Aβ) plaques and phosphor-Tau (pTau) aggregates was confirmed by immunohistochemistry. To test the functionality of the Cre enzyme, a stimulating DREADD virus (AAV8-hSyn-DIO-hM3Dq-mCherry) was injected unilaterally into the nucleus basalis magnocellularis, and clozapine-N-oxide-induced c-Fos activation was compared between the two hemispheres. Behavioral characterization was performed using the Y-maze, social discrimination (SDT), single pellet reaching (SPR), fox odor (FOT), and splash tests (ST). Food, water consumption and body weight change were investigated. Immunostaining and RNAscope confirmed the expression of Cre in ChAT-positive cells and the progressive appearance of pathological hallmarks (Aβ and pTau). The c-Fos activity was significantly increased in the virus-injected hemisphere. Compared with control mice, 3xAD-ChAT-Cre mice showed decreased locomotion (Y-maze, SDT, FOT), increased anxiety (FOT, ST) and weaker fine motor skills (SPR). In conclusion, newly created animals have a functional Cre recombinase enzyme in cholinergic cells. Additionally, the animals presented the pathophysiological hallmarks of AD in specific brain areas and maintained the typical behavioral alterations previously reported in 3xTg-AD mice. Thus, this strain seems to be appropriate for further studies.