Visual Abstract

Activation of the membrane estrogen receptor G-protein-coupled estrogen receptor (GPER) in ovariectomized mice via the GPER agonist G-1 mimics the beneficial effects of 17␤-estradiol (E 2 ) on hippocampal CA1 spine density and memory consolidation, yet the cellsignaling mechanisms mediating these effects remain unclear. The present study examined the role of actin polymerization and c-Jun N-terminal kinase (JNK) phosphorylation in mediating effects of dorsal hippocampally infused G-1 on CA1 dendritic spine density and consolidation of object recognition and spatial memories in ovariectomized mice. We first showed that object learning increased apical CA1 spine density in the dorsal hippocampus (DH) within 40 min. We then found that DH infusion of G-1 increased both CA1 spine density and phosphorylation of the actin polymerization regulator cofilin, suggesting that activation of GPER may increase spine morphogenesis through actin polymerization. As with memory consolidation in our previous work (Kim et al., 2016), effects of G-1 on CA1 spine density and cofilin phosphorylation depended on JNK phosphorylation in the DH. Also consistent with our previous findings, E 2 -induced cofilin phosphorylation was not dependent on GPER activation. Finally, we found that infusion of the actin polymerization inhibitor, latrunculin A, into the DH prevented G-1 from increasing apical CA1 spine density and enhancing both object recognition and spatial memory consolidation. Collectively, these data demonstrate that GPER-mediated hippocampal spinogenesis and memory consolidation depend on JNK and cofilin signaling, supporting a critical role for actin polymerization in the GPER-induced regulation of hippocampal function in female mice.

Development of estrogen therapies targeting the β (ERβ) but not α (ERα) estrogen receptor is critically needed for the treatment of negative menopausal symptoms, as ERα activation increases health risks like cancer. Here, we determined the effects of long-term oral treatment with EGX358, a novel highly selective ERβ agonist, on memory, vasodilation, and affect in young ovariectomized mice. Mice were orally gavaged daily for 9 weeks with vehicle, 17β-estradiol (E 2 ), the ERβ agonist diarylpropionitrile (DPN), or EGX358 at doses that enhance memory when delivered acutely. Tail skin temperature was recorded as a proxy for vasodilation following injection of vehicle or senktide, a tachykinin receptor 3 agonist used to model hot flashes. Anxiety-like behavior was assessed in the open field (OF) and elevated plus maze (EPM), and depression-like behavior was measured in the tail suspension (TST) and forced swim tests (FST). Finally, memory was assessed in object recognition (OR) and object placement (OP) tasks. E 2 , DPN, and EGX358 reduced senktide-mediated increases in tail skin temperature compared to vehicle. All three treatments also enhanced memory in the OR and OP tasks, whereas vehicle did not. Although E 2 increased time spent in the center of the OF, no other treatment effects were observed in the OF, EPM, TST, or FST. These data suggest that long-term ERβ activation can reduce hot flash-like symptoms and enhance spatial and object recognition memories in ovariectomized mice. Thus, the highly selective ERβ agonist EGX358 may be a promising avenue for reducing menopause-related hot flashes and memory dysfunction.

Background Women are at greater risk of Alzheimer’s Disease (AD) than men, and symptoms associated with the menopausal loss of circulating estrogens, including hot flashes, exacerbate cognitive decline and AD risk. Although estrogen‐based therapies reduce hot flashes and mitigate AD risk early in the menopausal transition, these treatments can increase risks of cancer, among other health issues. These adverse effects are mediated by the alpha (ERα), but not beta (ERβ), estrogen receptor isoform. Moreover, activation of ERβ facilitates memory formation and reduces hot flashes. Thus, ERβ‐selective therapies may promote memory function, reduce hot flashes, and diminish AD risk without complications associated with ERa. Our goal here was to determine whether chronic treatment with EGX358, a novel highly selective ERβ agonist developed by our group, could enhance memory and reduce hot flash‐like symptoms in a mouse model of menopause. Methods Eight‐week‐old ovariectomized C57BL/6 mice were orally gavaged each day for 10 weeks with vehicle, the highly potent estrogen 17β‐estradiol (E2; equal affinity for ERα and ERβ), the commercially available ERβ agonist diarylpropionitrile (DPN), or EGX358 (∼10x greater selectivity for ERβ than DPN). Compounds were administered at doses that enhance memory when delivered acutely. After two weeks of treatment, hot flash‐like symptoms were tested after subcutaneous injection of vehicle or senktide, a tachykinin receptor 3 agonist that induces hot flash‐like symptoms. Tail skin temperature was then recorded using a thermal camera for 30 minutes as a proxy for vasodilation. Six weeks later, mice were trained in object recognition (OR) and object placement (OP) tasks to test object and spatial memory, respectively. Memory in the OR and OP tasks was tested 48 and 24 hours later, respectively. Results E2, DPN, or EGX358 treatment reduced the senktide‐mediated increase in tail skin temperature. Furthermore, treatment with E2, DPN, or EGX358, but not vehicle, enhanced memory in the OR and OP tasks. Conclusions These data suggest that chronic EGX358 treatment can reduce hot flash‐like symptoms and improve spatial and object recognition memories. Therefore, ERβ activation may be a promising avenue for reducing menopause‐related hot flashes, memory dysfunction, and AD risk.