A, B, Histograms showing the total number of hilar GABAergic interneurons immunopositive for parvalbumin (PV) in female (A) or male (B) apoE-KI mice at the identified ages. Female apoE-KI mice show apoE genotype-independent and age-dependent effects, but no interaction between the two variables by 2-way ANOVA. Male apoE-KI mice show an age-dependent effect but no apoE genotype-dependent effect. There was no interaction between the two variables by 2-way ANOVA. C, D, Quantification of parvalbumin-positive hilar interneurons in female and male apoE3-KI (C) and apoE4-KI (D) mice at 1, 3, 6, 12, and 16 months of age (n = 6−12 mice per group). Both apoE3-KI and apoE4-KI mice show an effect of sex on parvalbumin interneuron numbers. An interaction between age and sex was present for both apoE genotypes (2-way ANOVA). *p<0.05; **p<0.01; ***p<0.001 in male apoE-KI mice compared to female apoE-KI mice at the same age (post-hoc Bonferroni test). E–H, Representative images (200x) of hilar sections stained with anti-parvalbumin antibodies. Shown are female apoE3-KI (E), female apoE4-KI (F), male apoE3-KI (G), and male apoE4-KI (H) mice at 16 months of age.