Abstract
BackgroundAlzheimer’s disease (AD), the most common cause of dementia, is characterized by the progressive deposition of amyloid-β (Aβ) peptides and neurofibrillary tangles. Mouse models of Aβ amyloidosis generated by knock-in (KI) of a humanized Aβ 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 Aβ pathology observed in AD: the Swedish (NL) mutation, which elevates total Aβ production; the Beyreuther/Iberian (F) mutation, which increases the Aβ42/Aβ40 ratio; and the Arctic (G) mutation, which promotes Aβ aggregation. AppNL-G-F mice harbor all three mutations and develop progressive Aβ 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 Aβ 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.ResultsAssessments 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.ConclusionAppNL/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.
Highlights
Alzheimer’s disease (AD), the most common cause of dementia, is characterized by the progressive deposition of amyloid-β (Aβ) peptides and neurofibrillary tangles
In AppNL-G-F/NL-G-F mice, age-dependent cortical Aβ amyloidosis began by 2 months and saturated around 7 months of age (Additional file 1: Fig. S1) [12]
As with the case of the first trial, AppNL-G-F/NL-G-F mice exhibited slight increases in the average total number of arm entries (Fig. 1g; F[2, 21] = 1.53, p = 0.240) and the distance travelled during the 10-min test (Additional file 2: Fig. S2c and d; F[2, 21] = 1.22, p = 0.316), these differences were not statistically significant with our sample size. These results suggest that 6–9-monthold AppNL-G-F/NL-G-F mice exhibit robust anxiolyticlike behavior, even after they have habituated to a test environment
Summary
Alzheimer’s disease (AD), the most common cause of dementia, is characterized by the progressive deposition of amyloid-β (Aβ) peptides and neurofibrillary tangles. The neuropathology of AD begins before overt cognitive symptoms, including the accumulation of amyloid-β peptide (Aβ) as extracellular plaques, aggregation of hyperphosphorylated tau as intracellular neurofibrillary tangles (NFTs), and activation of multiple neuroinflammatory pathways [3,4,5]. These brain pathologies are thought to induce neuronal cell loss in the hippocampus and cerebral cortex [3,4,5]. Overexpression of APP causes memory impairment without Aβ deposition in some App transgenic mice [8, 11], suggesting that the brains of these transgenic mouse models may have pathophysiological properties that are not relevant to AD pathogenesis
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