Investigating the Role of Estrogen Receptor Alpha in Alzheimer’s Disease Pathogenesis in Down Syndrome

Abstract

AbstractBackgroundPeople with Down syndrome (DS) have a higher risk of developing Alzheimer disease (AD), due to an extra copy of the amyloid precursor protein (APP) gene on chromosome 21. Overexpression of APP is associated with increased production of amyloid beta (Aβ) in DS, and contributes to early onset of AD. Some studies suggest women with DS are at a higher risk for AD, while others find the opposite. Sex differences may be mediated by estrogen, which is critically involved in neuronal survival and modulation. We hypothesized that lower levels of ERα protein would correlate with increasing AD pathology in DS.MethodWe examined 34 brains (frontal and occipital cortices) of people with DS and DS with AD. Serial sections were immunostained for phosphorylated tau (pTau ‐AT8) and Aβ (6E10) along with ERα and quantified using QuPath. Spearman rank correlations using log transformed % load data were calculated, Kruskal‐Wallis was used to compare men (n = 19) and women(n = 15).ResultNo significant differences in protein levels of ERα, Aβ, or tau were observed when comparing men and women with DS. However, we found higher levels of ERα protein were associated with higher levels of Aβ in the gray matter of the occipital cortex (r = 0.7078; p = 0.0005) in all cases. This positive correlation was driven primarily by women. Females with DS showed a significant positive association with Aβ and ERα (r = 0.93; p = 0.00012) whereas men showed a weaker trend (r = 0.62; p = 0.057). In contrast, no significant associations between ERα, Aβ or pTau were observed in the frontal cortex. PTau measures in the occipital cortex in women with DS were positively associated with ERα (r = 0.61; p = 0.055), whereas men with DS showed a slight negative, though not significant association (r = ‐0.29; p = 0.41). There was no such trend in the frontal cortex.ConclusionThese results suggest ERα, in contrast to our original hypothesis, may be increasing in response to AD pathology to preserve neuronal health in the occipital cortex. Lack of similar positive associations in the frontal cortex may be related to AD progression, with the occipital cortex being affected later in disease, giving us the opportunity to observe increased ERα.