Temporal and brain region-specific elevations of soluble Amyloid-β 40-42 in the Ts65Dn mouse model of Down syndrome and Alzheimer's disease.

Down syndrome (DS) is a leading cause of intellectual disability that also results in hallmark Alzheimer's disease (AD) pathologies such as amyloid beta (Aβ) plaques and hyperphosphorylated tau. The Ts65Dn mouse model is commonly used to study DS, as trisomic Ts65Dn mice carry 2/3 of the triplicated gene homologues as occur in human DS. The Ts65Dn strain also allows investigation of mechanisms common to DS and AD pathology, with many of these triplicated genes implicated in AD; for example, trisomic Ts65Dn mice overproduce amyloid precursor protein (APP), which is then processed into soluble Aβ 40-42 fragments. Notably, Ts65Dn mice show alterations to the basal forebrain, which parallels the loss of function in this region observed in DS and AD patients early on in disease progression. However, a complete picture of soluble Aβ 40-42 accumulation in a region-, age-, and sex-specific manner has not yet been characterized in the Ts65Dn model. Here, we show that trisomic mice accumulate soluble Aβ 40-42 in the basal forebrain, frontal cortex, hippocampus, and cerebellum in an age-specific manner, with elevation in the frontal cortex and hippocampus as early as 4 months of age. Furthermore, we detected sex differences in accumulation of Aβ 40-42 within the basal forebrain, with females having significantly higher Aβ 40-42 at 7-8 months of age. Lastly, we show that APP expression in the basal forebrain and hippocampus inversely correlates with Aβ 40-42  levels. This spatial and temporal characterization of soluble Aβ 40-42 in the Ts65Dn model allows for further exploration of the role soluble Aβ plays in the progression of other AD-like pathologies in these key brain regions.