Stroke in Estrogen Receptor-α–Deficient Mice

Abstract

Background and Purpose —Recent evidence suggests that endogenous estrogens or hormone replacement therapy can ameliorate brain damage from experimental stroke. Protective mechanisms involve enhanced cerebral vasodilation during ischemic stress as well as direct preservation of neuronal viability. We hypothesized that if the intracellular estrogen receptor subtype-α (ERα) is important to estrogen’s signaling in the ischemic brain, then ERα-deficient (knockout) (ERαKO) female mice would sustain exaggerated cerebral infarction damage after middle cerebral artery occlusion. Methods —The histopathology of cresyl violet–stained tissues was evaluated after reversible middle cerebral artery occlusion (2 hours, followed by 22 hours of reperfusion) in ERαKO transgenic and wild-type (WT) mice (C57BL/6J background strain). End-ischemic cerebral blood flow mapping was obtained from additional female murine cohorts by using [ ¹⁴ C]iodoantipyrine autoradiography. Results —Total hemispheric tissue damage was not altered by ERα deficiency in female mice: 51.9±10.6 mm ³ in ERαKO versus 60.5±5.0 mm ³ in WT. Striatal infarction was equivalent, 12.2±1.7 mm ³ in ERαKO and 13.4±1.0 mm ³ in WT mice, but cortical infarction was paradoxically smaller relative to that of the WT (20.7±4.5 mm ³ in ERαKO versus 30.6±4.1 mm ³ in WT). Intraocclusion blood flow to the parietal cortex was higher in ERαKO than in WT mice, likely accounting for the reduced infarction in this anatomic area. There were no differences in stroke outcomes by region or genotype in male animals. Conclusions —Loss of ERα does not enhance tissue damage in the female animal, suggesting that estrogen inhibits brain injury by mechanisms that do not depend on activation of this receptor subtype.