Effects of estrogen on temporal expressions of IL-1β and IL-1ra in rat organotypic hippocampal slices exposed to oxygen-glucose deprivation

Anti-inflammatory action of estrogen is involved in neuroprotection but the effects of estrogen on IL-1β and its endogenous antagonist (IL-1ra) have not been clearly defined in the ischemic brain. This study was performed to evaluate whether estrogen affects the expression of IL-1β or IL-1ra and the ratio of the two in the ischemic hippocampus. Rat organotypic hippocampal slices were treated with 17β estradiol (E2, 1 nM) for 7 days, exposed to oxygen-glucose deprivation (OGD) for 30 min, and then reperfused for 72 h. CA1 neuronal death quantified by propidium iodide (PI) staining and expressions of IL-1β and IL-1ra in slices measured by real-time PCR and Western blotting were examined. PI intensities in CA1 in slices treated with E2 were significantly reduced at 24 h and 72 h post-OGD, and IL-1β mRNA expressions were reduced at 6 h and 24 h post-OGD. In addition, IL-1ra mRNA was significantly overexpressed and the ratio of IL-1β to IL-1ra mRNA expression was reduced by E2 especially at 24 h. In terms of protein levels, E2 downregulated IL-1β but upregulated IL-1ra and thereby decreased the IL-1β/IL-1ra ratio at 24 h. These findings demonstrate that estrogen-induced protection is associated with a decrease in IL-1β and an increase in IL-1ra expression in the ischemic hippocampus during early reperfusion periods, which suggests that modulation of IL-1β/IL-1ra might be a part of anti-inflammatory effects of estrogen.