Inhibition of STAT3- and MAPK-dependent PGE2 synthesis ameliorates phagocytosis of fibrillar β-amyloid peptide (1-42) via EP2 receptor in EMF-stimulated N9 microglial cells

Abstract

BackgroundProstaglandin E2 (PGE2)-involved neuroinflammatory processes are prevalent in several neurological conditions and diseases. Amyloid burden is correlated with the activation of E-prostanoid (EP) 2 receptors by PGE2 in Alzheimer’s disease. We previously demonstrated that electromagnetic field (EMF) exposure can induce pro-inflammatory responses and the depression of phagocytosis in microglial cells, but the signaling pathways involved in phagocytosis of fibrillar β-amyloid (fAβ) in microglial cells exposed to EMF are poorly understood. Given the important role of PGE2 in neural physiopathological processes, we investigated the PGE2-related signaling mechanism in the immunomodulatory phagocytosis of EMF-stimulated N9 microglial cells (N9 cells).MethodsN9 cells were exposed to EMF with or without pretreatment with the selective inhibitors of cyclooxygenase-2 (COX-2), Janus kinase 2 (JAK2), signal transducer and activator of transcription 3 (STAT3), and mitogen-activated protein kinases (MAPKs) and antagonists of PG receptors EP1-4. The production of endogenous PGE2 was quantified by enzyme immunoassays. The phagocytic ability of N9 cells was evaluated based on the fluorescence intensity of the engulfed fluorescent-labeled fibrillar β-amyloid peptide (1-42) (fAβ42) measured using a flow cytometer and a fluorescence microscope. The effects of pharmacological agents on EMF-activated microglia were investigated based on the expressions of JAK2, STAT3, p38/ERK/JNK MAPKs, COX-2, microsomal prostaglandin E synthase-1 (mPGES-1), and EP2 using real-time PCR and/or western blotting.ResultsEMF exposure significantly increased the production of PGE2 and decreased the phagocytosis of fluorescent-labeled fAβ42 by N9 cells. The selective inhibitors of COX-2, JAK2, STAT3, and MAPKs clearly depressed PGE2 release and ameliorated microglial phagocytosis after EMF exposure. Pharmacological agents suppressed the phosphorylation of JAK2-STAT3 and MAPKs, leading to the amelioration of the phagocytic ability of EMF-stimulated N9 cells. Antagonist studies of EP1-4 receptors showed that EMF depressed the phagocytosis of fAβ42 through the PGE2 system, which is linked to EP2 receptors.ConclusionsThis study indicates that EMF exposure could induce phagocytic depression via JAK2-STAT3- and MAPK-dependent PGE2-EP2 receptor signaling pathways in microglia. Therefore, pharmacological inhibition of PGE2 synthesis and EP2 receptors may be a potential therapeutic strategy to combat the neurobiological deterioration that follows EMF exposure.Electronic supplementary materialThe online version of this article (doi:10.1186/s12974-016-0762-9) contains supplementary material, which is available to authorized users.

PDE4 inhibitor rolipram inhibits the expression of microsomal prostaglandin E synthase‐1 by a mechanism dependent on MAP kinase phosphatase‐1

“…) and recently also in murine microglial cells (He et al. ), which findings support our current results.…”

“…Accordingly, JNK inhibitor was found to suppress the expression of mPGES-1 in J774 macrophages to an extent comparable with that of rolipram, whereas the specific inhibitor of p38 did not have any significant effect. Apart from our study, the dephosphorylation of JNK as a mechanism behind decreased expression of mPGES-1 has previously been presented in rat neonatal cardiomyocytes (Degousee et al 2006), mouse peritoneal macrophages (Cardeno et al 2014) and recently also in murine microglial cells (He et al 2016), which findings support our current results.…”

“…; He et al. ). On the other hand, anti‐inflammatory effects of the PDE4 inhibitor rolipram (Korhonen et al.…”

“…In addition, mPGES-1 expression has been reported to be upregulated by p38 and/or JNK MAP kinases. (Han et al 2002;Masuko-Hongo et al 2004;Degousee et al 2006;de Oliveira et al 2008;B age et al 2010;He et al 2016). On the other hand, anti-inflammatory effects of the PDE4 inhibitor rolipram (Korhonen et al 2013), like those of dexamethasone (Kassel et al 2001;Abraham et al 2006;Shipp et al 2010) and aurothiomalate (Nieminen et al 2010) have been shown to be mediated by enhanced expression of the anti-inflammatory phosphatase MKP-1 which leads to reduced activity of MAP kinases through dephosphorylation.…”

TREM2 Regulates Heat Acclimation-Induced Microglial M2 Polarization Involving the PI3K-Akt Pathway Following EMF Exposure

“…Consistent with previous studies of neuroprotective functions after HA (Shein et al, 2007a), we found that HA was shown to not alter cell state, and suppressed the production of pro-inflammatory cytokines and increased the production of anti-inflammatory cytokines in N9 cells 12 h after a 20-min EMF exposure (Figure 1). The 20-min EMF treatment was identified as a threshold condition representing the time of duration beyond which cytotoxicity significantly increases as explained in a previous study (He et al, 2016). In addition, based on the previous time effect experiments of EMF-induced pro-inflammatory responses (Yang et al, 2010;He et al, 2014), the threshold 12-h recovery time after EMF exposure with prominent pro-inflammatory activity was employed in the present study.…”