Effects of sexual differentiation and APOE genotype on the development of Alzheimer-related pathology in female EFAD mice

Apolipoprotein E ε4 genotype ( APOE4 ), the most significant genetic risk factor for late-onset Alzheimer’s disease (AD), is associated with sexually dimorphic effects whereby higher risks are generally observed in women. Sex differences can arise in part from developmental processes of sexual differentiation, which yield permanent sex-specific phenotypes that can impact adult trajectories and vulnerabilities to various conditions. We investigated the potential contributions of sexual differentiation to the female bias of APOE4 in driving AD pathogenesis. Specifically, using the EFAD transgenic mouse model of AD that includes knock-in of human APOE3 or APOE4 , we examined the effects of experimental masculinization in perinatal female mice on adult patterns of AD-related pathology relative to control male and female mice. Both female sex and APOE4 genotype were associated with increased levels of β-amyloid pathologies. Masculinization resulted in expected systemic and neural phenotypes in adult animals. The effects of masculinization differed depending upon both outcome measure and APOE genotype. Intermediate phenotypes were the most common response to masculinization, though select aspects of AD-related endpoints, including the numbers of mature amyloid plaques, were reduced by masculinization of APOE4 female mice. These findings suggest that sexual differentiation in early life has modest effects on adult development of AD in females, a relationship that appeared stronger in the context of APOE4 . The results complement prior work establishing roles of sex chromosomes and age-related depletion of sex hormones in the sexual dimorphisms characteristic of AD and provide new insights into the organizational actions of sex hormones and how these interact with APOE genotype.