Predictors of estrogen's neuroprotective efficacy




Brock, Courtney
Toofan, Jessica
Rybalchenko, Nataliya
Sumien, Nathalie
Singh, Meharvan


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Purpose: The precipitous decline in ovarian hormones after the menopause may put women at greater risk for age-associated cognitive decline and serves as the basis for considering hormone therapy to support brain health, despite equivocal results in clinical trials studies to-date. Data from our lab show that estrogen replacement (after ovariectomy) in young animals increases brain-derived neurotrophic factor (BDNF) mRNA expression in the hippocampus. However, in middle-aged animals, the effect of 17b-estradiol (E2) is diminished, supporting the existence of a window of opportunity for these hormones, and thus, reason to explore the underlying molecular mechanisms. In this study, we evaluated the expression of BDNF, estrogen receptors (ERs), and other relevant molecules of cognition (TrkB, p75, and RbAp48) in young and middle-aged animals to determine if changes in their expression was correlated with the effect of estrogen. To better establish any causal relationship to our findings, we also conducted studies in vitro to determine which ERs are critical to mediating the effects of E2 on BDNF. Methods: In-Vivo: Real time rtPCR was used to evaluate the expression of BDNF, TrkB, p75, RbAp48, and ERa mRNA in the hippocampus of female ovariectomized (OVX) Sprague Dawley rats that were 4 months (young) and 10 months (middle-aged) of age. In-Vitro: The effect of E2 (10nM, 24 hours) on BDNF mRNA expression was evaluated in ERa transfected, differentiated SH-SY5Y cells (as a model of ER negative neurons). In parallel, we also evaluated the effect of E2 on cell viability (using the MTT assay). Results: Our in vivo data show that ERa, BDNF, TrkB, RbAp48 in hippocampal mRNA are significantly decreased in middle-aged OVX rats as compared to young OVX. There was also a significant increase in the pro-cell death p75 receptor in middle-aged rats. In vitro data revealed a significant increase in ERa mRNA expression post-transfection, with an approximate 30% transfection efficiency. Treatment of ERa-transfected SH-SY5Y cells with E2 did not induce a significant increase in BDNF, nor did it protect the cells from amyloid-beta-induced cytotoxicity. Conclusion: The hippocampal mRNA expression analyses we performed in vivo suggest that indeed, there are changes in relevant molecules of cognitive function with age, that in turn, could diminish the protective effects of E2. Further, ERa expression was not sufficient to mediate the effect of E2 on BDNF expression or cell viability.