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.

Estrogen treatment exerts a protective effect on experimental autoimmune encephalomyelitis (EAE) and is under clinical trial for multiple sclerosis therapy. Estrogens have been suspected to protect from CNS autoimmunity through their capacity to exert anti-inflammatory as well as neuroprotective effects. Despite the obvious impacts of estrogens on the pathophysiology of multiple sclerosis and EAE, the dominant cellular target that orchestrates the anti-inflammatory effect of 17β-estradiol (E2) in EAE is still ill defined. Using conditional estrogen receptor (ER) α-deficient mice and bone marrow chimera experiments, we show that expression of ERα is critical in hematopoietic cells but not in endothelial ones to mediate the E2 inhibitory effect on Th1 and Th17 cell priming, resulting in EAE protection. Furthermore, using newly created cell type-specific ERα-deficient mice, we demonstrate that ERα is required in T lymphocytes, but neither in macrophages nor dendritic cells, for E2-mediated inhibition of Th1/Th17 cell differentiation and protection from EAE. Lastly, in absence of ERα in host nonhematopoietic tissues, we further show that ERα signaling in T cells is necessary and sufficient to mediate the inhibitory effect of E2 on EAE development. These data uncover T lymphocytes as a major and nonredundant cellular target responsible for the anti-inflammatory effects of E2 in Th17 cell-driven CNS autoimmunity.