Estrogen-Induced Nongenomic Calcium Signaling Inhibits Lipopolysaccharide-Stimulated Tumor Necrosis Factor Alpha Production In Macrophages

Estrogen is traditionally thought to exert genomic actions through members of the nuclear receptor family. Here, we investigated the rapid nongenomic effects of 17 beta-estradiol (E-2) on tumor necrosis factor alpha (TNF-alpha) production following lipopolysaccharide (LPS) stimulation in mouse bone marrow-derived macrophages (BMMs). We found that LPS induced TNF-alpha production in BMMs via phosphorylation of p38 mitogen-activated protein kinase (MAPK). E-2 itself did not affect the MAPK pathway, although it attenuated LPS-induced TNF-alpha production through suppression of p38 MAPK activation. Recently, G protein-coupled receptor 30 (GPR30) was suggested to be a membrane estrogen receptor (mER) that can mediate nongenomic estradiol signaling. We found that BMMs expressed both intracellular estrogen receptors (iER) and mER GPR30. The specific GPR30 antagonist G-15 significantly blocked effects of estradiol on LPS-induced TNF-alpha production, whereas an iER antagonist did not. Moreover, E-2 induced a rapid rise in intracellular free Ca2+ that was due to the influx of extracellular Ca2+ and was not inhibited by an iER antagonist or silencing of iER. Ca2+ influx was also induced by an impermeable E-2 conjugated to BSA (E-2-BSA), which has been used to investigate the nongenomic effects of estrogen. Consequently, Ca2+, a pivotal factor in E-2-stimulated nongenomic action, was identified as the key mediator. The inhibitory effects of E-2 on LPS-induced TNF-alpha production and p38 MAPK phosphorylation were dependent on E-2-triggered Ca2+ influx because BAPTA, an intracellular Ca2+ chelator, prevented these effects. Taken together, these data indicate that E-2 can down-regulate LPS-induced TNF-alpha production via blockade of p38 MAPK phosphorylation through the mER-mediated nongenomic Ca2+ signaling pathway in BMMs.