APP and Alzheimer disease: Although younger transgenic AD mouse models widely used in the study are able to simulate the pathological and phenotypic defects of AD in many aspects, including Aβ protein deposition, and learning and memory deficits, they do not exhibit neuronal loss or brain atrophy like AD patients17; however, older transgenic AD models, such as the APP/PS1 model over 17–22 months of age and the APP/PS1/tau model over 12 months of age, do show signs of neurodegeneration17.