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. 2010 May 26;30(21):7326-34.
doi: 10.1523/JNEUROSCI.1180-10.2010.

Genetic targeting aromatase in male amyloid precursor protein transgenic mice down-regulates beta-secretase (BACE1) and prevents Alzheimer-like pathology and cognitive impairment

Carrie McAllister  1 , Jiangang Long, Adrienne Bowers, Aaron Walker, Philip Cao, Shin-Ichiro Honda, Nobuhiro Harada, Matthias Staufenbiel, Yong Shen, Rena Li
Affiliations

Genetic targeting aromatase in male amyloid precursor protein transgenic mice down-regulates beta-secretase (BACE1) and prevents Alzheimer-like pathology and cognitive impairment

Carrie McAllister et al. J Neurosci. .

Abstract

As brain testosterone plays both androgenic and estrogenic actions due to its conversion into estrogen via aromatase naturally, it is unclear that the age-related reduction of testosterone increased risk of Alzheimer's disease (AD) in men is mediated through androgen alone or both androgen and estrogen mechanisms. Our previous studies using a gene-based approach in mouse model to block the conversion of testosterone into estrogen (aromatase gene knock-out, ArKO), found a depletion of estrogen and increase in testosterone endogenously in males. Here, we use crossing the ArKO mice with APP23 transgenic mice, a mouse model of AD, to produce APP23/Ar(+/-) mice to study the estrogen-independent effect of testosterone on AD. We found a significant reduction in brain plaque formation, improved cognitive function and increase NEP activity in male APP23/Ar(+/-) mice compared with age-matched male APP23 controls. In addition, we found, for the first time, a reduction of beta-secretase (BACE1) enzyme activity, mRNA level and protein expression in the male APP23/Ar(+/-) mice, suggesting that endogenous testosterone, independent from estrogen, may protect against AD in males via two major mechanisms, downregulation of BACE1 activities at transcriptional level to reduce beta amyloid production and upregulation of NEP activities to enhance bate amyloid degradation.

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Figures

Figure 1.
Figure 1.
Testosterone levels in male APP23, APP23/Ar+/− and WT mice. A, B, Total testosterone was detected by RIA in serum (A) and brain (B) extractions from male APP23/Ar+/− (n = 10), APP23 (n = 10), and WT (n = 10) mice at 6, 12, and 18 months of age. *p < 0.05 and **p < 0.001 compared with WT and APP23 control mice.
Figure 2.
Figure 2.
Analysis of amyloid levels, amyloid plaques and neuronal loss in the brains of 18-month-old APP23 and APP23/Ar+/− male mice. A, ELISA analysis of the reduced Aβ42/Aβ40 ratio in male APP23/Ar+/− mice compared with age-matched APP23. B, APP23 mice developed massive plaques in the cortex at the age of 18 months while small plaques were observed in the APP23/Ar+/− mice at the same age. C, The density of plaques from 19 mouse brain samples (APP23 n = 11 and APP23/Ar+/− n = 8) were analyzed. The density of plaques in APP23/Ar+/− mice were significantly less than in APP23 mice (**p < 0.001). D, Immunostaining of NeuN (1:1000) in the brain from an 18-month-old APP23 male mouse showed extensive neuronal loss in the CA3 region of the hippocampus (indicated in box) compared with the hippocampi from WT and APP23/Ar+/− male mice at the same age.
Figure 3.
Figure 3.
Testosterone downregulates BACE1 both in vivo and in vitro. At 18 months of age, the brains from male APP23 (n = 10) and APP23/Ar+/− (n = 8) mice were harvested and prepared for Western blot, immunostaining, enzyme activity analysis and mRNA measurement. A, The Western blot of APP, BACE1, c-terminal fragment, and C99 from 18-month-old mice is shown. B, The protein levels from the Western blot are presented as the ratio of the integrated optical density value (IDV) of the protein of interest to the IDV of β-actin. C, The levels of APP c-terminal fragment in the hippocampi of 18-month-old WT, APP23 and APP23/Ar+/− mice was detected by immunohistochemistry with anti-C-terminal antibody CT-20 (1:1000) and appears as intracellular dark brown staining as indicated by the arrows. D, BACE1 enzyme activity was measured from brain homogenize of 12- and 18-month-old APP23 and APP23/Ar+/− mice. E–H, The mRNA levels of BACE1 in 18-month old APP23 and APP23/Ar+/− male mice brains were detected by RT-PCR using 18S mRNA as a control (E), and the ratios of BACE1/18S mRNA were determined by densitometric analysis (F). The effect of testosterone (T) and actinomycin D (ActD) treatments on BACE1 and 18S mRNA levels in BACE transfected 293 cells was measured by real-time RT-PCR (G); the BACE1 mRNA levels were normalized to the 18S mRNA levels and were expressed relative to the vehicle-treated cells (H). *p < 0.05 compared with APP23 mice for B, D, and F; *p < 0.05 compared with vehicle-treated cells for H.
Figure 4.
Figure 4.
Protein expression and enzyme activity of IDE and NEP in APP23 and APP23/Ar+/− mice at various ages. A, Brain samples from APP23, APP23/Ar+/−, and WT mice at age of 18 months old were examined for IDE and NEP protein expression by Western blot. B, The relative amounts of IDE and NEP protein were determined by standard scanning densitometry. C, D, The enzyme activity levels of IDE (C) and NEP (D) in brains from APP23, APP23/Ar+/−, and WT mice at ages of 6, 12 and 18 months were detected. The brains were homogenized and incubated with fluorogenic substrate peptides. The increase in fluorescence occurred upon peptide bond cleavage and was detected during the first 20 min as fluorescence unit/min microgram protein. *p < 0.05 compared with APP23 mice; #p < 0.05 compared with WT mice.
Figure 5.
Figure 5.
Hole-board performance of APP23/Ar+/−, APP23, and WT male mice at various ages. Male APP23/Ar+/−, APP23, and WT mice were tested in the hole-board learning and memory paradigm (see Materials and Methods) at 6, 12, and 18 months of age. A, The scale value scores of male APP23/Ar+/− mice were higher at 12 and 18 months of age than at 6 months of age; and p < 0.05 compared with 6 months old. B–D, At the age of 18 months, APP23/Ar+/− mice (n = 6) demonstrated significantly better scale value scores (B), percentages of good trials (C), and target latencies (D) than did WT (n = 10) and APP23 (n = 7) mice. Data were expressed as mean of each score per trial (±SE) for the 10 trials of testing. The APP23/Ar+/− male mice not only found the target holes with fewer mistakes, but also found the target holes more quickly. *p < 0.05 compared with age-matched APP23 mice; #p < 0.05 compared with age-matched WT mice; &p < 0.05 compared to 6-month-old APP/Ar+/− mice.
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References

    1. Alexander GM, Packard MG, Hines M. Testosterone has rewarding affective properties in male rats: implications for the biological basis of sexual motivation. Behav Neurosci. 1994;108:424–428. - PubMed
    1. Azcoitia I, Sierra A, Veiga S, Honda S, Harada N, Garcia-Segura LM. Brain aromatase is neuroprotective. J Neurobiol. 2001;47:318–329. - PubMed
    1. Bertram L, Blacker D, Mullin K, Keeney D, Jones J, Basu S, Yhu S, McInnis MG, Go RC, Vekrellis K, Selkoe DJ, Saunders AJ, Tanzi RE. Evidence for genetic linkage of Alzheimer's disease to chromosome 10q. Science. 2000;290:2302–2303. - PubMed
    1. Brosnan-Watters G, Wozniak DF. A rotating holeboard procedure for testing drug effects on spatial learning and memory in mice. Brain Res Brain Res Protoc. 1997;1:331–338. - PubMed
    1. Cai H, Wang Y, McCarthy D, Wen H, Borchelt DR, Price DL, Wong PC. BACE1 is the major beta-secretase for generation of Abeta peptides by neurons. Nat Neurosci. 2001;4:233–234. - PubMed

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