Estrogen Mediates Neuroprotection and Anti-Inflammatory Effects during EAE through ER  Signaling on Astrocytes But Not through ER  Signaling on Astrocytes or Neurons

Abstract

Estrogens can signal through either estrogen receptor ␣ (ER␣) or ␤ (ER␤) to ameliorate experimental autoimmune encephalomyelitis (EAE), the most widely used mouse model of multiple sclerosis (MS). Cellular targets of estrogen-mediated neuroprotection are still being elucidated. Previously, we demonstrated that ER␣ on astrocytes, but not neurons, was critical for ER␣ ligand-mediated neuroprotection in EAE, including decreased T-cell and macrophage inflammation and decreased axonal loss. Here, we determined whether ER␤ on astrocytes or neurons could mediate neuroprotection in EAE, by selectively removing ER␤ from either of these cell types using Cre-loxP gene deletion. Our results demonstrated that, even though ER␤ ligand treatment was neuroprotective in EAE, this neuroprotection was not mediated through ER␤ on either astrocytes or neurons and did not involve a reduction in levels of CNS inflammation. Given the differential neuroprotective and anti-inflammatory effects mediated via ER␣ versus ER␤ on astrocytes, we looked for molecules within astrocytes that were affected by signaling through ER␣, but not ER␤. We found that ER␣ ligand treatment, but not ER␤ ligand treatment, decreased expression of the chemokines CCL2 and CCL7 by astrocytes in EAE. Together, our data show that neuroprotection in EAE mediated via ER␤ signaling does not require ER␤ on either astrocytes or neurons, whereas neuroprotection in EAE mediated via ER␣ signaling requires ER␣ on astrocytes and reduces astrocyte expression of proinflammatory chemokines. These findings reveal important cellular differences in the neuroprotective mechanisms of estrogen signaling through ER␣ and ER␤ in EAE.

Astrogliosis

“…For example, expression of structural filaments, such as GFAP or vimentin can be induced by signaling pathways associated with cAMP, STAT3, NF-kB, Rho-kinase, JNK, calci- (Brambilla et al 2005(Brambilla et al , 2009Okada et al 2006). Deletion of estrogen receptor-a, but not estrogen receptor-b, selectively from astrocytes diminishes the antiinflammatory and neuroprotective effects of estrogen on autoimmune inflammation (Spence et al 2011(Spence et al , 2013. In contrast, deletion of STAT3 or its associated membrane receptor GP130, markedly increases the spread of inflammation after traumatic injury, autoimmune disease, or infection (Okada et al 2006;Drogemuller et al 2008;Herrmann et al 2008;Haroon et al 2011;Wanner et al 2013).…”

Estrogen-mediated protection of experimental autoimmune encephalomyelitis: Lessons from the dissection of estrogen receptor-signaling in vivo

“…[29,73] Moreover, using conditional ERβ knock-out mouse models, it was reported that DPN-conferred neuroprotection was not dependent on ERβ-signaling in astrocytes nor in neurons, suggesting a role for oligodendrocytes as the primary targets of this ERβ ligand. [74] Indeed, DPN was shown to act through ERβ-signaling in oligodendrocytes not only to prevent demyelination, but also to promote remyelination. [75] Thus, it has been proposed that such ERβ-ligands could be used in combination with anti-inflammatory drugs in MS patients.…”

“…It has been shown that administration of E2 or ERα-specific agonists in mice during the chronic phase of active EAE was able to inhibit the expression of inflammatory chemokines CCL2 and CCL7 by astrocytes in vivo. [30,74] Using conditional knock-out mice, Spence et al showed that this neuroprotective action was mediated through ERα-signaling in astrocytes. [31,74] Altogether, these observations suggest that differences in ER-specific ligands are not only the result of distinct pharmacological effects, but that each ligand may have different cellular targets.…”

“…[30,74] Using conditional knock-out mice, Spence et al showed that this neuroprotective action was mediated through ERα-signaling in astrocytes. [31,74] Altogether, these observations suggest that differences in ER-specific ligands are not only the result of distinct pharmacological effects, but that each ligand may have different cellular targets. Interestingly, selective estrogen receptor modulators (SERMs) such as raloxifene and bazedoxifene have been recently shown to inhibit inflammatory mediator production by reactive astrocytes in vitro, which holds therapeutic promise against neuroinflammation in MS. [77,78] Taken together, these results indicate that beside the anti-inflammatory actions of E2/ERα in the periphery, estrogens or ER selective agonists may also mediate neuroprotective effects through classical ERα or ERβ expressed by distinct cellular targets in the CNS [ Figure 1].…”

“…Interestingly, selective estrogen receptor modulators (SERMs) such as raloxifene and bazedoxifene have been recently shown to inhibit inflammatory mediator production by reactive astrocytes in vitro, which holds therapeutic promise against neuroinflammation in MS. [77,78] Taken together, these results indicate that beside the anti-inflammatory actions of E2/ERα in the periphery, estrogens or ER selective agonists may also mediate neuroprotective effects through classical ERα or ERβ expressed by distinct cellular targets in the CNS [ Figure 1]. Although neuroprotective effects of E2 or ER-specific ligands have been shown in experimental models where mice were treated after chronic EAE onset [30] or using adoptive transfer of encephalitogenic CD4 T-cells, [74] it is still unclear whether the neuroprotective effects of ERα ligands, for instance, could still be observed in the complete absence of anti-inflammatory actions due to immune cell targeting in the periphery. …”