Effects of a Novel GPR55 Antagonist on the Arachidonic Acid Cascade in LPS-Activated Primary Microglial Cells.

Soraya Wilke Saliba,Florian Ferver,Dominique Endres,Matthias Apweiler,Bernd L Fiebich,Franziska Gläser,Stefan Bräse,Albrecht Keil,Thomas Hurrle,Anke Deckers,Nicole Volz

doi:10.3390/ijms22052503

Abstract

Neuroinflammation is a crucial process to maintain homeostasis in the central nervous system (CNS). However, chronic neuroinflammation is detrimental, and it is described in the pathogenesis of CNS disorders, including Alzheimer’s disease (AD) and depression. This process is characterized by the activation of immune cells, mainly microglia. The role of the orphan G-protein-coupled receptor 55 (GPR55) in inflammation has been reported in different models. However, its role in neuroinflammation in respect to the arachidonic acid (AA) cascade in activated microglia is still lacking of comprehension. Therefore, we synthesized a novel GPR55 antagonist (KIT 10, 0.1–25 µM) and tested its effects on the AA cascade in lipopolysaccharide (LPS, 10 ng / mL)-treated primary rat microglia using Western blot and EIAs. We show here that KIT 10 potently prevented the release of prostaglandin E2 (PGE2), reduced microsomal PGE2 synthase (mPGES-1) and cyclooxygenase-2 (COX-2) synthesis, and inhibited the phosphorylation of Ikappa B-alpha (IκB-α), a crucial upstream step of the inflammation-related nuclear factor-kappaB (NF-κB) signaling pathway. However, no effects were observed on COX-1 and -2 activities and mitogen-activated kinases (MAPK). In summary, the novel GPR55 receptor antagonist KIT 10 reduces neuroinflammatory parameters in microglia by inhibiting the COX-2/PGE2 pathway. Further experiments are necessary to better elucidate its effects and mechanisms. Nevertheless, the modulation of inflammation by GPR55 might be a new therapeutic option to treat CNS disorders with a neuroinflammatory background such as AD or depression.

Highlights

MAPK signaling is involved in the regulation of inflammatory events [16] and we have demonstrated in activated microglia that the activation of JNK, extracellular signal-regulated kinase (ERK), and p38 MAPK are implicated in the regulation of COX-2/mPGES-1/prostaglandin E2 (PGE2) levels, important proteins involved in neuroinflammation mediating fever [17,18,19]
MAPK signaling is involved in the regulation of inflammatory events [30] and we have demonstrated that the activation of JNK, ERK, and p38 MAPK are implicated in the regulation of COX-2/PGE2 levels in activated microglia [17,18,19]
Microglial cells are the resident macrophages of the central nervous system (CNS), responsible for the initiation, amplification, and/or equalization of the inflammatory response by the synthesis of inflammatory mediators, like cytokines, prostaglandins (PGs), and free radicals [3,4,5]

Summary

Introduction

Neuroinflammation is well characterized by the activation of glial cells, mainly microglia, which leads to the release of inflammatory mediators [2]. Microglial cells are the first line of defense in the central nervous system (CNS) and exert an anti-inflammatory role being neuroprotective and implicated in the resolution of the inflammatory event by phagocytosis and tissue repair. For reasons that are still not clear, microglia have a detrimental role, where the deregulated microglia response by inducing a pro-inflammatory phenotype releasing pro-inflammatory mediators including cytokines such as tumor necrosis factor (TNF) α, interleukin-6 (IL-6), and IL-1β, prostaglandins (PGs), reactive oxygen species (ROS), and nitric oxide (NO) resulting in progressive neurotoxic consequences and neurodegeneration [3,4,5]

Methods

Results

Conclusion