FosL1 Is a Novel Target of Levetiracetam for Suppressing the Microglial Inflammatory Reaction

Kouji Niidome,Ruri Taniguchi,Mayumi Tsuji,Takeshi Yamazaki,Yasuhiro Ishihara,Kouichi Itoh

doi:10.3390/ijms222010962

Abstract

We previously showed that the antiepileptic drug levetiracetam (LEV) inhibits microglial activation, but the mechanism remains unclear. The purpose of this study was to identify the target of LEV in microglial activity suppression. The mouse microglial BV-2 cell line, cultured in a ramified form, was pretreated with LEV and then treated with lipopolysaccharide (LPS). A comprehensive analysis of LEV targets was performed by cap analysis gene expression sequencing using BV-2 cells, indicating the transcription factors BATF, Nrf-2, FosL1 (Fra1), MAFF, and Spic as candidates. LPS increased AP-1 and Spic transcriptional activity, and LEV only suppressed AP-1 activity. FosL1, MAFF, and Spic mRNA levels were increased by LPS, and LEV only attenuated FosL1 mRNA expression, suggesting FosL1 as an LEV target. FosL1 protein levels were increased by LPS treatment and decreased by LEV pretreatment, similar to FosL1 mRNA levels. The FosL1 siRNA clearly suppressed the expression of TNFα and IL-1β. Pilocarpine-induced status epilepticus increased hippocampus FosL1 expression, along with inflammation. LEV treatment significantly suppressed FosL1 expression. Together, LEV reduces FosL1 expression and AP-1 activity in activated microglia, thereby suppressing neuroinflammation. LEV might be a candidate for the treatment of several neurological diseases involving microglial activation.

Highlights

Microglia function in immune surveillance in the brain and are activated by inflammatory stimulation, which causes their morphology to change from ramified to amoeboid
LEV largely suppressed the expression of TNFα and IL-1β in the mouse microglial cell line BV-2 activated by LPS (Figure 1A)
LEV suppressed the increases in TNFα and IL-1β expression observed in standard error (SE)-induced epileptogenesis elicited by PILO (Figure 1B)

Summary

Introduction

Microglia function in immune surveillance in the brain and are activated by inflammatory stimulation, which causes their morphology to change from ramified to amoeboid. Activated microglia produce humoral factors such as inflammatory cytokines and remove foreign substances in the brain to protect neurons. Excessive microglial activation causes neuroinflammation, which can injure the normal brain. Neuroinflammation is considered a pathological mechanism of several neurological diseases, such as Alzheimer s disease, cerebral stroke, and epilepsy [1,2,3]. It is important to suppress abnormal microglial activation for the treatment or prevention of a number of neurological diseases. Microglial activation and neuroinflammation, which are observed during epileptogenesis after brain injury, can play an important role in the onset of seizures [6,7]. Neuroinflammation has the possibility of decreasing the seizure threshold, which shifts the neural excitation/inhibition balance toward excitation by modulating neural channel activity and/or neurotransmitter uptake or release [8,9]. Targeting inflammation mediated by microglia during epileptogenesis could be a strategy for preventing post-braininsult epilepsy

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