PS2APP Transgenic Mice, Coexpressing hPS2mut and hAPPswe, Show Age-Related Cognitive Deficits Associated with Discrete Brain Amyloid Deposition and Inflammation

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Abstract
Transgenic mice, expressing mutant β-amyloid precursor proteins (βAPPs), have lead to a better understanding of the pathophysiological processes in Alzheimer's disease (AD). In many of these models, however, the temporal development of cognitive decline and the relationship to Aβ deposition and inflammation are unclear. We now report a novel transgenic mouse line, PS2APP (PS2N141I× APPswe), which develops a severe cerebral amyloidosis in discrete brain regions, and present a cross-sectional analysis of these mice at 4, 8, 12, and 16 months of age. Each age cohort was investigated for changes in behavior, electrophysiology of synapse efficacy, ELISA-determined Aβ load, histopathology, and in immunoelectron microscopy. Cognitive deficits were first observed at 8 months when Aβ deposits and inflammation were restricted to discrete brain regions, namely the subiculum and frontolateral (motor and orbital) cortex. As early as 5 months, electron microscopy revealed the presence, in these regions, of pre-plaque, immunogold-labeled extracellular fibrillar Aβ. At the same age, increased levels of insoluble Aβ were detected by ELISA, with Aβ1-40levels exceeding those of Aβ1-42. Further cognitive decline occurred in an age-related manner, and this was accompanied by the spread of amyloidosis to ultimately affect not only neo- and limbic cortices, but also thalamic and pontine nuclei. Dentate gyrus post-tetanic potentiation was significantly attenuated at 17 months, and there were also significant differences in paired-pulse parameters. This systematic cross-sectional study of the behavioral and pathological changes in the PS2APP mouse indicates that it develops age-related cognitive decline associated with severe amyloidosis and inflammation in discrete brain regions and therefore is suitable for testing a range of potential symptomatic and disease-modifying therapies for AD.