Activation of EP₂ receptor suppresses poly(I: C) and LPS‐mediated inflammation in primary microglia and organotypic hippocampal slice cultures: Contributing role for MAPKs

Abstract

Brain inflammation is a critical factor involved in neurodegeneration. Recently, the prostaglandin E (PGE ) downstream members were suggested to modulate neuroinflammatory responses accompanying neurodegenerative diseases. In this study, we investigated the protective effects of prostaglandin E receptor 2 (EP ) during TLR3 and TLR4-driven inflammatory response using in vitro primary microglia and ex vivo organotypic hippocampal slice cultures (OHSCs). Depletion of microglia from OHSCs differentially affected TLR3 and TLR4 receptor expression. Poly(I:C) induced the production of prostaglandin E in OHSCs by increasing cyclooxygenase (COX-2) and microsomal prostaglandin E synthase (mPGES)-1. Besides, stimulation of OHSCs and microglia with Poly(I:C) upregulated EP receptor expression. Co-stimulation of OHSCs and microglia with the EP agonist butaprost reduced inflammatory mediators induced by LPS and Poly(I:C). In Poly(I:C) challenged OHSCs, butaprost almost restored microglia ramified morphology and reduced Iba1 immunoreactivity. Importantly, microglia depletion prevented the induction of inflammatory mediators following Poly(I:C) or LPS challenge in OHSCs. Activation of EP receptor reversed the Poly(I:C)/LPS-induced phosphorylation of the mitogen activated protein kinases (MAPKs) ERK, p38 MAPK and c-Jun N-terminal kinase (JNK) in microglia. Collectively, these data identify an anti-inflammatory function for EP signaling in diverse innate immune responses, through a mechanism that involves the mitogen-activated protein kinases pathway.

Histamine 2/3 receptor agonists alleviate perioperative neurocognitive disorders by inhibiting microglia activation through the PI3K/AKT/FoxO1 pathway in aged rats

“…It has been reported that primary microglia can be activated by 10 ng/ml LPS [ 46 , 47 ]. In our in vitro experiments, primary microglia were pretreated with 10 μM H2R/H3R agonists 30 min before exposure to 10 ng/ml LPS.…”

Role of Microglia TLRs in Neurodegeneration

“…Different stimuli may lead to increased expression of microglia TLRs, such as hypoxia (Smith et al, 2013 ; Yao et al, 2013 ), LPS (Kielian et al, 2005 ; Yousif et al, 2018 ), Poly(I:C; Yousif et al, 2018 ), kainic acid (Wang et al, 2015 ; Hu and Mao, 2016 ), α-synuclein (Béraud et al, 2011 ; Daniele et al, 2015 ) and amyloid beta (Aβ; Jana et al, 2008 ; Richard et al, 2008 ; Caldeira et al, 2017 ).…”

“…TLR3 is less studied in respect to neurodegenerative diseases, although it may be involved in neuroinflammation. For example, incubation of microglia with Poly(I:C), a TLR3 agonist, increases the synthesis of COX-2, mPGES-1 and prostaglandin E 2 release (de Oliveira et al, 2016 ), and increased the expression of TLR3 (Yousif et al, 2018 ). The production of these inflammatory mediators might contribute to neurodegenerative processes observed in some conditions.…”

Discovery of 2-Piperidinyl Phenyl Benzamides and Trisubstituted Pyrimidines as Positive Allosteric Modulators of the Prostaglandin Receptor EP2

“…Cyclooxygenase-2 (COX-2), the inducible form of COX, is dynamically regulated by synaptic activities, 1 and is rapidly upregulated in the brain after cerebral ischemia 2,3 and other neurological insults. 4–12 As a major enzymatic product of COX2 in the cerebral cortex, prostaglandin E2 (PGE 2 ) can activate four G protein-coupled receptors (GPCRs) named EP1 through EP4, that together regulate a myriad of physiological and pathological signaling events. For instance, the EP1 receptor is coupled to G α q that mediates the mobilization of cytosolic Ca 2+ , resulting in the activation of protein kinase C (PKC); EP2 and EP4 are associated with G α s that activates adenylyl cyclase, leading to cAMP-dependent signaling; EP3 is mainly coupled to G α i and its activation downregulates cytosolic cAMP.…”