Selective estrogen-receptor modulators suppress microglial activation and neuronal cell death via an estrogen receptor-dependent pathway.

Growing evidence shows that steroid hormones, especially 17β-estradiol (E2), protect neuronal cells by attenuating excess activation of microglia. However, the use of E2 in the clinic is controversial because of its peripheral actions in reproductive organs and its potential to increase risk for endometrial cancer and breast cancer. Selective estrogen-receptor modulators (SERMs) bind to estrogen receptors (ERs), but their effects as ER agonists or antagonists are dependent on the target tissue. SERMs pose very little cancer risk as a result of their anti-estrogen action in reproductive organs, but their action in the brain is not well understood. In this study, we investigated the effects of SERMs tamoxifen (Tam) and raloxifene (Rlx) on microglial activation and subsequent neuronal injury. Tam and Rlx suppressed the increases in proinflammatory cytokines and chemokine expression that were induced by lipopolysaccharide (LPS) in rat primary microglia cultures. The microglial-conditioned media pretreated with Tam or Rlx significantly attenuated cellular injury in SH-SY5Y cells elicited by microglial-conditioned media treated with LPS alone. Rat primary microglia expressed ERα and ERβ primarily in the nucleus, and thus we examined the involvement of ERs in the suppressive action of Tam and Rlx on microglial activation using a pure ER antagonist, ICI182,780. Pretreatment with ICI182,780 abolished the suppressive effects of SERMs on microglial activation, as well as their protective action on SH-SY5Y cells. A luciferase assay using a vector with three estrogen response elements (EREs) revealed that Tam and Rlx activated ERE-mediated transcription in rat primary microglia. Taken together, these results suggest that Tam and Rlx suppress microglial activation and subsequent neuronal cell death via an ER-mediated transcription pathway. SERMs could represent a novel therapeutic strategy for disorders of the central nervous system based on their ability to suppress neuroinflammation.