Sex‐Dependent Differences in Amyloid‐β Deposition in a Mouse Model of Alzheimer's Disease

Abstract

Alzheimer's Disease (AD) is the leading cause of dementia and has a higher incidence in post-menopausal women than men by poorly understood mechanisms. AD is associated with amyloid-β (Aβ) plaques in the brain, in particular pyroglutamatylated Aβ (Aβ-pE3), which forms the core of the plaques, promoting further Aβ deposition. Accumulation of Aβ on the vasculature can lead to vascular rarefication, ultimately contributing to AD dementia. However, it is unknown if these parameters are altered in 5x-FAD females, a mouse model of AD, which can account for increased incidence of dementia. Thus, we hypothesized that female 5x-FAD mice would have a greater accumulation of Aβ and Aβ-pE3 plaques, as well as vascular rarefication, than males. Data are means ± SEM. Using histochemical methods, we labeled brain slices from 3-months-old male (n=8) and female (n=7) 5x-FAD mice with thioflavin-T, a fluorescent dye that binds to Aβ, and an antibody specific to Aβ-pE3. Plaque numbers were counted in the cortex and hippocampus. Thioflavin-T plaque density, expressed as plaques per mm², was higher in 5x-FAD females compared to males in the cortex (69.8 ± 21.8 vs 26.8 ± 4.8; p<0.05, one-tailed Mann-Whitney test), but not in the hippocampus (59.8 ± 22.0 vs 17.7 ± 2.1; p=0.095, one-tailed Mann-Whitney test). Aβ-pE3 plaque density was significantly higher in 5x-FAD females compared to males in both cortex (133.4 ± 31.2 vs 63.4 ± 7.9; p<0.05, one-tailed Mann-Whitney test) and hippocampus (89.9 ± 23.3 vs 35.6 ± 7.3; p<0.05, one-tailed Mann-Whitney test). To examine the vasculature, brain slices of 5x-FAD males (n=8) and females (n=7) and wild-type (WT) males (n=6) and females (n=4) were immunolabeled for collagen IV. Capillaries were then counted and expressed as capillary number per field of view. No significant differences in capillary numbers were observed between male 5x-FAD and WT mice (29.3 ± 1.3 vs 31.3 ± 0.9; p>0.05, one-tailed Student's t-test) or female 5x-FAD and WT mice (29.8 ± 2.6 vs 31.5 ± 1.3; p>0.05, one-tailed Student's t-test). Co-labeling these same sections with an Aβ-pE3 antibody showed little parenchymal microvascular Aβ in 5x-FAD males or females, expressed as percent of collagen IV volume covered by Aβ-pE3 (2.0 ± 0.3 vs 2.3 ± 0.7; p>0.05, one-tailed Student's t-test), and no sex differences. Aβ plaques were more prevalent in pial vessels of 5x-FAD males (n=4) and females (n=5) without sex differences, expressed as percent of pial vessels that are Aβ-positive (47.0 ± 10.7 vs 41.4 ± 8.2, one-tailed Student's t-test). These data suggest that Aβ and Aβ-pE3 accumulation is larger in females than males 5x-FAD, without differences in vascular Aβ. Contrary to our hypothesis, at 3-months of age, 5x-FAD females seem to be protected from parenchymal Aβ accumulation. Ongoing studies in the laboratory are investigating the cognitive status of these mice.