17β-Estradiol Promotes TLR4-Triggered Proinflammatory Mediator Production through Direct Estrogen Receptor α Signaling in Macrophages In Vivo

Abstract

17β-estradiol (E2) has been shown to promote the expression of inflammatory mediators by LPS-activated tissue resident macrophages through estrogen receptor α (ERα) signaling. However, it remained to be determined whether E2 similarly influences macrophages effector functions under inflammatory conditions in vivo, and whether this action of E2 resulted from a direct effect on macrophages. We show in this study that chronic E2 administration to ovariectomized mice significantly increased both cytokine (IL-1β, IL-6, and TNF-α) and inducible NO synthase mRNA abundance in thioglycolate (TGC)-elicited macrophages. The proinflammatory action of E2 was also evidenced at the level of released IL-1β and IL-6 by ex vivo LPS-activated macrophages. E2 concomitantly inhibited PI3K activity as well as Akt phosphorylation in TGC-elicited macrophages, suggesting that E2 promoted TLR-dependent macrophage activation by alleviating this suppressive signaling pathway. Indeed, this effect was abolished in the presence of the inhibitor wortmannin, demonstrating a key functional link between inhibition of PI3K activity and the E2 action on macrophage functions. Endogenous estrogens levels circulating in ovary-intact mice were sufficient to promote the above described actions. Finally, thanks to a CreLox strategy, targeted disruption of ERα gene in macrophages totally abolished the effect of E2 on the expression of inflammatory mediators by both resident and TGC-elicited peritoneal macrophages. In conclusion, we demonstrate that estrogens, through the activation of ERα in macrophages in vivo, enhance their ability to produce inflammatory mediators and cytokines upon subsequent TLR activation.

Differences in Hematopoietic Stem Cells Contribute to Sexually Dimorphic Inflammatory Responses to High Fat Diet-induced Obesity

“…7, A and B). Whereas in male mice, TLR4 activation is linked to myelopoiesis, Calippe et al (40) identified that estrogen signaling itself may influence TLR presence and activation state, and further studies have shown an effect of LPS responsiveness being reduced in females (41,42). These studies demonstrated that ER␣ activation itself stimulates TLR production of cytokines, priming the system for future dietary challenge.…”

Estrogens and atherosclerosis: insights from animal models and cell systems

“…Moreover, E 2 treatment of animals resulted in the inhibition of phosphoinositide kinase-3 (PI3K) activity and AKT phosphorylation in LPS-activated macrophages, whereas NF-kB p65 transcriptional activity was concomitantly increased. Further studies showed that targeted disruption of ERa gene in macrophages totally abolished the effect of E 2 on the expression of inflammatory mediators by peritoneal macrophages, thus indicating that E 2 directly targeted these cells to exert pro-inflammatory effects (Calippe et al 2010). The same group noticed that ERa-mediated signaling is required for optimal dendritic cell function as assessed by MHC-II and CD86 expression and pro-inflammatory cytokine production (IL6 and IL12) and that estrogens enhance susceptibility to experimental myasthenia gravis by augmenting dendritic cell activation and proinflammatory Th1 response (Delpy et al 2005, Douin-Echinard et al 2008.…”

“…One of the bestdescribed endothelial actions of E 2 is stimulation of nitric oxide (NO) production, which depends on both genomic (expression of endothelial NO synthase (eNOS)) and nongenomic effects (activation of phosphatidylinositol 3-kinase and protein kinase AKT, phosphorylation of eNOS) (Arnal et al 2010, Chow et al 2010. Because the ability of E 2 to promote an increase in eNOS activity and NO-dependent vasorelaxation are abolished in ERa KO mice and are emulated by highly selective ERa agonists, modulation of NO production by E 2 is likely mediated by ERa (Arnal et al 2010, Bolego et al 2010. However, treatment of endothelial cells with E 2 also stimulates covalent adduction of a nitrosyl group to cysteins (S-nitrosylation), which represents a key route for NO to directly modulate protein functions and which depends on ERb (Zhang et al , 2012.…”

“…Studies on animal models of atherosclerosis provided compelling evidence that physiological estrogen levels potently attenuate both early and advanced stages of atherosclerosis lesion development in females and suggested similar protective effects in males. Using tissue-specific KO and/or highly selective ER agonists, these studies clearly defined endothelial cells as a primary target of the anti-atherogenic action of estrogens, demonstrated that non-nuclear ERa signaling plays a crucial role in this respect, and allowed dissecting the effects on cardiovascular endpoints from uterotrophic response (Arnal et al 2010, Bolego et al 2010. It could also be established that ERb signaling contributes to atheroprotective effects exerted by estrogens and this has been attributed primarily to the modulatory effects on smooth muscle and probably also on macrophage function.…”

Prenatal exposure to bisphenol-A is associated with Toll-like receptor–induced cytokine suppression in neonates

“…At present, we do not know whether the influence of BPA on TLR-triggered cytokine response is a result of direct effect of BPA on TLR expression or the result of an indirect effect of BPA that disrupted downstream signaling events. Nevertheless, several experimental studies have shown that BPA can alter cytokine production via the P13K/Akt, the MAPK/AP-1, or the NF-κB pathways, whereas no influence was observed on TLR4 surface expression (21,24,25). The observation from our study that IL-10 response to TLR ligands remained unperturbed by BPA concentration might also give indirect evidence that BPA had no direct effect on TLR expression, because theoretically, all cytokine production would have been altered if TLR expression, being the origin of the signaling pathway, was modified.…”