Sexual dimorphism of autism-like phenotypes in microglial eIF4E overexpression mice

Background: Autism spectrum disorder (ASD) is a group of neurodevelopmental disorders characterized by deficits in social communication and interaction, and restricted interests or repetitive behaviors. ASD is approximately four times more prevalent in males than in females. In this study, we investigated whether sex hormones or sex chromosomes underlie the male bias in ASD susceptibility. Methods: We used the MG4E mouse model, in which microglial eIF4E overexpression produces robust male-biased ASD-like phenotypes. To distinguish the contributions of sex hormones and sex chromosomes, MG4E mice were crossed with four-core-genotype (FCG) mice carrying Sry gene manipulations, generating eight genotypes of experimental mice. Social interaction and repetitive behaviors were assessed using standard behavioral assays. Dendritic spine density was quantified in Thy1-GFP mice. Expression of estrogen receptors (ERs) and androgen receptor (AR) was examined in microglia isolated from control and MG4E mice. Results: Sex hormones, rather than non-Sry genes on sex chromosomes, are responsible for the male-biased deficits in social interaction and the increase in dendritic spine density. At postnatal day 14, ERs were undetectable in microglia, whereas ER expression was readily detected in neurons. Conclusions: These findings demonstrate that sex hormones are a major determinant of the increased susceptibility of males to ASD-like phenotypes in MG4E mice. The absence of ER expression in microglia suggests that sex hormones may act indirectly through hormone-responsive neurons to regulate microglia-neuron interactions during neurodevelopment.