Cognitive and emotional alterations in App knock-in mouse models of Aß amyloidosis.

ABSTRACT

BACKGROUND: Alzheimer's disease (AD), the most common cause of dementia, is characterized by the progressive deposition of amyloid-ß (Aß) peptides and neurofibrillary tangles. Mouse models of Aß amyloidosis generated by knock-in (KI) of a humanized Aß sequence provide distinct advantages over traditional transgenic models that rely on overexpression of amyloid precursor protein (APP). In App-KI mice, three familial AD-associated mutations were introduced into the endogenous mouse App locus to recapitulate Aß pathology observed in AD the Swedish (NL) mutation, which elevates total Aß production; the Beyreuther/Iberian (F) mutation, which increases the Aß42/Aß40 ratio; and the Arctic (G) mutation, which promotes Aß aggregation. AppNL-G-F mice harbor all three mutations and develop progressive Aß amyloidosis and neuroinflammatory response in broader brain areas, whereas AppNL mice carrying only the Swedish mutation exhibit no overt AD-related pathological changes. To identify behavioral alterations associated with Aß pathology, we assessed emotional and cognitive domains of AppNL-G-F and AppNL mice at different time points, using the elevated plus maze, contextual fear conditioning, and Barnes maze tasks. RESULTS: Assessments of emotional domains revealed that, in comparison with wild-type (WT) C57BL/6J mice, AppNL-G-F/NL-G-F mice exhibited anxiolytic-like behavior that was detectable from 6 months of age. By contrast, AppNL/NL mice exhibited anxiogenic-like behavior from 15 months of age. In the contextual fear conditioning task, both AppNL/NL and AppNL-G-F/NL-G-F mice exhibited intact learning and memory up to 15-18 months of age, whereas AppNL-G-F/NL-G-F mice exhibited hyper-reactivity to painful stimuli. In the Barnes maze task, AppNL-G-F/NL-G-F mice exhibited a subtle decline in spatial learning ability at 8 months of age, but retained normal memory functions. CONCLUSION: AppNL/NL and AppNL-G-F/NL-G-F mice exhibit behavioral changes associated with non-cognitive, emotional domains before the onset of definitive cognitive deficits. Our observations consistently indicate that AppNL-G-F/NL-G-F mice represent a model for preclinical AD. These mice are useful for the study of AD prevention rather than treatment after neurodegeneration.