Testosterone regulation of Alzheimer-like neuropathology in male 3xTg-AD mice involves both estrogen and androgen pathways

Abstract

Normal, age-related depletion of the androgen testosterone is a risk factor for Alzheimer's disease (AD) in men. Previously, we reported that experimental androgen depletion significantly accelerates development of AD-like neuropathology in the 3xTg-AD triple-transgenic mouse model of AD, an effect prevented by androgen treatment. Because testosterone is metabolized in brain into both the androgen dihydrotestosterone (DHT) and the estrogen 17β-estradiol (E2), testosterone can mediate its effects through androgen and or estrogen pathways. To define the role of androgen and estrogen pathways in regulation of AD-like neuropathology, we compared the effects of testosterone (T) and its metabolites DHT and E2 in male 3xTg-AD mice depleted of endogenous sex steroid hormones by gonadectomy (GDX). Male 3xTg-AD mice were sham GDX or GDX, immediately treated with vehicle, T, DHT, or E2, and 4 months later evaluated for two indices of AD-like neuropathology, β-amyloid (Aβ) accumulation and tau hyperphosphorylation. In comparison to sham GDX mice, we observed a significant increase in Aβ accumulation in GDX mice in subiculum, hippocampus, and amygdala. Treatment of GDX mice with T prevented the increased Aβ accumulation in all three brain regions. DHT treatment yielded similar results, significantly reducing Aβ accumulation across brain regions. Interestingly, E2 prevented Aβ accumulation in hippocampus but exerted only partial effects in subiculum and amygdala. Levels of tau hyperphosphorylation in sham GDX male 3xTg-AD mice were modest and only slightly increased by GDX. Treatment of GDX mice with T or E2 but not DHT reduced tau hyperphosphorylation to levels lower than observed in sham animals. These data suggest that testosterone regulates Aβ pathology through androgen and estrogen pathways and reduces tau pathology largely through estrogen pathways. These findings further define hormone pathways involved in regulation of AD-related pathology, information that is important for understanding disease etiology and developing pathway-specific hormone interventions.

Fig. 1

Hormone regulation of Aβ in subiculum of male 3xTg-AD mice. Representative high magnification photomicrographs show Aβ immunoreactivity in male 3xTg-AD mice in the following treatment groups: Sham GDX (A), GDX+PL (B), GDX+DHT (C), GDX+T (D), and GDX +E2 (E). Scale bar = 100μm. (F) Levels of Aβ immunoreactive load in subiculum were quantified across groups. Data show mean Aβ load values (± SEM). * Denotes p < 0.05 in comparison to Sham GDX (Sham) group, # denotes p < 0.05 versus GDX+PL group.

Fig. 2

Hormone regulation of Aβ in hippocampus CA1 of male 3xTg-AD mice. Representative high magnification photomicrographs show Aβ immunoreactivity in male 3xTg-AD mice in the following treatment groups: Sham GDX (A), GDX+PL (B), GDX+DHT (C), GDX+T (D), and GDX +E2 (E). Scale bar = 100μm. (F) Levels of Aβ immunoreactive load in CA1 of hippocampus were quantified across groups. Data show mean Aβ load values (± SEM). * Denotes p < 0.05 in comparison to Sham GDX (Sham) group, # denotes p < 0.05 versus GDX+PL group.

Fig. 3

Hormone regulation of Aβ in amygdala of male 3xTg-AD mice. Representative high magnification photomicrographs show Aβ immunoreactivity in male 3xTg-AD mice in the following treatment groups: Sham GDX (A), GDX+PL (B), GDX+DHT (C), GDX+T (D), and GDX +E2 (E). Scale bar = 100μm. (F) Levels of Aβ immunoreactive load in amygdala were quantified across groups. Data show mean Aβ load values (± SEM). * Denotes p < 0.05 in comparison to Sham GDX (Sham) group, # denotes p < 0.05 versus GDX+PL group.

Fig. 4

Age and regulation of tau hyperphosphorylation in male 3xTg-AD mice. (A–C) Representative photomicrographs show tau immunoreactivity with the phospho-specific antibody AT8 in hippocampus CA1 of Sham GDX male 3xTg-AD mice at (A) age 3 mo, (B) age 7 mo, and (C) age 13 mo old. Scale bar = 100 μm. (D) High magnification photomicrograph of a cell strongly immunoreactive for AT8 antibody. Scale bar = 25μm. (E) Levels of tau hyperphosphorylation were quantified by counts of cells strongly immunoreactive for AT8. Data show mean numbers (± SEM) of AT8-immunoreactive cells in Sham GDX males at ages 3 mo, 7 mo, and 13 mo. * Denotes p < 0.05 in comparison to 3 mo group. (F) Data show mean numbers (± SEM) of AT8-immunoreactive cells in Sham GDX (Sham), GDX+PL, GDX+DHT, GDX+T, and GDX+E2 mice at age 7 mo. * Denotes p < 0.05 in comparison to Sham group, and # denotes p < 0.05 in comparison to GDX+PL group.