Abstract 17177: Crosstalk and Synergism Between Local Brain-derived and Exogenous 17β-Estradiol in Regulating Rapid, Pro-survival Signaling in the Hippocampus Following Global Cerebral Ischemia

Abstract

Cardiac arrest-induced global cerebral ischemia (GCI) can lead to death of hippocampal CA1 neurons and cognitive impairment. Previous work has shown that the steroid hormone, 17β-estradiol (E2) is strongly neuroprotective against GCI, an effect that involves, in part, rapid signaling via the membrane estrogen receptor, GPR30. To gain greater insight into E2 actions, the current study examined: 1) whether GPR30 expression in the hippocampus changes after CGI, and 2) the role and potential crosstalk/synergism between local (brain-derived) and exogenous E2 in regulation of GPR30 and rapid prosurvival signaling after GCI. GCI was induced in adult ovariectomized female rats by a 4-vessel occlusion model (12-min occlusion). Vehicle or low diestrous levels of E2 were administered chronically by minipump beginning at the time of ovariectomy. The results showed that GPR30 expression in the hippocampal CA1 was unchanged at 3h, but significantly decreased at 1d and 3d after GCI. In contrast, aromatase expression showed an initial decrease at 3h, a rebound at 1day, and a robust elevation at 3 days after CGI. Administration of exogenous E2 increased both GPR30 and aromatase expression at 3h, 1d and 3d after GCI. Interestingly, central administration of the aromatase inhibitor, letrozole or aromatase antisense (AS) oligonucleotides abolished exogenous E2 enhancement of GPR30 and aromatase at 3d after GCI. Furthermore, letrozole and aromatase-AS treatment attenuated exogenous E2-induced phosphorylation/activation of prosurvival ERK1/2 and CREB following GCI, as well as exogenous E2-induced enhanced expression of BDNF, PSD95 and synaptophsin. As a whole, the results suggest that local-derived E2 may help mediate beneficial protective effects of exogenous E2 after GCI to enhance GPR30 expression, increase activation of ERK1/2-CREB-BDNF pro-survival signaling, and improve synaptic function.