A unique hybrid characteristic having both pro- and anti-inflammatory phenotype transformed by repetitive low-dose lipopolysaccharide in C8-B4 microglia

Haruka Mizobuchi,Yoko Nakata,Shoko Tsutsui,Kazushi Yamamoto,Hiroyuki Inagawa,Gen-Ichiro Soma,Chie Kohchi,Masafumi Yamashita

doi:10.1038/s41598-020-65998-8

Abstract

Although lipopolysaccharide (LPS) is regarded as an inducer of inflammation, previous studies have suggested that repetitive low-dose LPS has neuroprotective effects via immunomodulation of microglia, resident macrophages of brain. However, microglia transformed by the stimulus of repetitive low-dose LPS (REPELL-microglia) are not well characterized, whereas microglia transformed by repetitive high-dose LPS are well studied as an endotoxin tolerance model in which the induction of pro-inflammatory molecules is suppressed. In this study, to characterize REPELL-microglia, the gene expression and phagocytic activity of REPELL-microglia were analyzed with the murine C8-B4 microglia cell line. The REPELL-microglia were characterized by a high expression of pro-inflammatory molecules (Nos2, Ccl1, IL-12B, and CD86), anti-inflammatory molecules (IL-10, Arg1, Il13ra2, and Mrc1), and neuroprotective molecules (Ntf5, Ccl7, and Gipr). In addition, the phagocytic activity of REPELL-microglia was promoted as high as that of microglia transformed by single low-dose LPS. These results suggest the potential of REPELL-microglia for inflammatory regulation, neuroprotection, and phagocytic clearance. Moreover, this study revealed that gene expression of REPELL-microglia was distinct from that of microglia transformed by repetitive high-dose LPS treatment, suggesting the diversity of microglia transformation by different doses of LPS.

Highlights

Lipopolysaccharide (LPS) is regarded as an inducer of inflammation, previous studies have suggested that repetitive low-dose LPS has neuroprotective effects via immunomodulation of microglia, resident macrophages of brain
It has been reported that pro-inflammatory molecules such as IL-1β, IL-6, and TNF-α are suppressed in microglia by repetitive high-dose LPS treatment[17,18,19,20,21,22]
IL-1β, IL-6, and TNF-α were suppressed in REPELL-microglia to data of past reports with a high-dose LPS model, REPELL-microglia did not exhibit global downregulation of pro-inflammatory molecules, but instead showed high expression of Nos[2], Ccl[1], IL-12B, and CD86 (Fig. 1)

Summary

Introduction

Lipopolysaccharide (LPS) is regarded as an inducer of inflammation, previous studies have suggested that repetitive low-dose LPS has neuroprotective effects via immunomodulation of microglia, resident macrophages of brain. Previous reports have shown that microglia, the resident macrophages (MΦ) of brain, contribute to amyloid β clearance by promoting phagocytosis[5,6] These results suggest that microglia are transformed by oral LPS treatment and gain the neuroprotective characteristics of high phagocytic activity and inflammatory regulation. Contrary to the detrimental effect of intraperitoneal administration of a single, high-dose of LPS to exacerbate Aβ accumulation, neuronal damage, and cognitive impairment[7,11,12], they showed that the opposing effects on the neuropathy by LPS (that is, worsening effect by single LPS treatment and healing effect by repetitive LPS treatment) were associated with different microglial characteristics Considering these results, it is reasonable to suppose that one of the requirements to induce a neuroprotective effect by LPS is repetitive and low-dose administration, and that the microglia transformed under this LPS condition play a critical role in the maintenance of brain homeostasis. Results demonstrated that REPELL-microglia are characterized by high phagocytic activity and high expression of pro-inflammatory, anti-inflammatory, and neuroprotective molecules, which are unique to low-dose LPS treatment

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