Abstract 175: The Role of ER-α, ER-ß, and AR in the FCG Model of Ischemic Brain Injury

Abstract

Background: Ischemic stroke is a sexually dimorphic disease. Females are protected from ischemic brain injury throughout most of the lifespan, but the contribution of hormones in this “ischemia resistant” phenotype remains unclear. The “four core genotype” (FCG) model is used to differentiate the effect of the chromosomal complement (XX vs. XY) from an animal’s gonadal (estrogen vs. testosterone producing) sex through examination of five genotypes XYMwt, XY-M, XXM, XXF, and XYF. XY-M FCG mice are made by the translocation of Sry from the Y chromosome to an autosome. Stroke sex differences have been largely attributed to the neuroprotective effects of estrogen. However, it remains unclear whether hormonal receptors can be influenced at the chromosomal level, which could further explain sexual dimorphism in stroke phenotypes. We hypothesize that the sex chromosome complement and transgene Sry (the testis determining gene found on the Y chromosome) contribute to the sexually dimorphic stroke phenotype. Methods: FCG animals were gonadectomized at 3 weeks of age. Animals were subjected to stroke at 8-12 weeks of age. Cytosolic samples were evaluated for androgen receptor (AR) and estrogen receptor (ER-α and ER-β) levels in sham and stroke samples. RT-PCR for Sry on the stroke hemisphere (delta-delta-CT) was performed on the FCG mice and wild type males. Results: Western blot analysis showed that XXM and XXF mice had significant stroke induced reduction in AR expression (p<0.01). No significant difference in the expression of ER-α was seen in sham and stroke mice among genotypes. ER-β expression increased significantly in XXM post stroke (p<0.05), but not in the other genotypes. RT-PCR analysis showed approximately 90-fold increase of mRNA expression of Sry in the phenotypes with the exogenous Sry (XYM and XXM) compared to WTM mice with endogenous Sry (p<0.05). Conclusion: XXM and XYM mice show an increase in Sry expression compared to WTM suggesting insertional and positional effects of Sry transgene. AR expression in XXM and XXF mice is influenced at the chromosomal level, suggesting effects of X chromosome dosage on AR expression. Stroke induced ER-β expression in XXM mice may be an effect of the interaction between transgene Sry and other hormonal axes.