Icaritin inhibits neuroinflammation by regulating microglial polarization through GPER-ERK-NF-κB signaling pathway in cerebral ischemic rat

Abstract

BackgroundActivated microglia play a key role in initiating the in ammatory cascade following ischemic stroke and exert proin ammatory or anti-in ammatory effects depending on whether they are polarized toward the M1 or M2 phenotype. The present study investigated the regulatory effect of Icaritin (ICT) on microglial polarization in rats after cerebral ischemia/reperfusion injury (CI/RI) and explored the possible antiin ammatory mechanisms of ICT. MethodsA rat model of transient middle cerebral artery occlusion (tMCAO) was established. Following treatment with ICT, a G protein coupled estrogen receptor (GPER) inhibitor or an extracellular signal regulated kinase (ERK) inhibitor, the Garcia scale and rotarod test were used to assess neurological and locomotor function. 2,3,5-Triphenyltetrazolium chloride (TTC) and Fluoro-Jade C (FJC) staining were used to evaluate the infarct volume and neuronal death. The levels of in ammatory factors in the ischemic penumbra were evaluated by enzyme-linked immunosorbent assay (ELISA). In addition, Western blotting, immuno uorescence and quantitative PCR (qPCR) were used to measure the expression levels of markers of different microglial phenotypes and proteins related to the GPER-ERK-NF-κB signaling pathway. ResultsWe found that ICT treatment signi cantly decreased the cerebral infarct volume, brain water content and uorescence intensity of FJC; improved the Garcia score; increased the latency to fall and rotation speed in the rotarod test; inhibited the expression of IL-1β, TNF-α, Iba1, CD40, CD68 and p-P65-NF-κB; and increased the levels of CD206 and p-ERK. U0126 (an inhibitor of ERK) and G15 (a selective antagonist of GPER) antagonized these effects. ConclusionsThese ndings indicate that ICT plays roles in inhibiting the in ammatory response and achieving neuroprotection by regulating GPER-ERK-NF-κB signaling and then inhibits microglial activation and M1 polarization while promoting M2 polarization, which provides new therapeutic strategy against cerebral ischemia stroke.