The Anti-Tumorigenic Mushroom Agaricus blazei Murill Enhances IL-1β Production and Activates the NLRP3 Inflammasome in Human Macrophages

Tsung-Teng Huang,David M Ojcius,Cheng-Yeu Wu,Yi-Hui Wu,Chia-Chen Lu,Hsin-Chih Lai,Yun-Fei Ko,Tsui-Yin Wong,John D Young,Colin Combs

doi:10.1371/journal.pone.0041383

Abstract

Agaricus blazei Murill (AbM) has been reported to possess immune activity against tumors and infections through stimulation of mononuclear phagocytes. Recently, AbM extract was shown to induce the production of the pro-inflammatory cytokine, interleukin-1β (IL-1β), in human monocytes. IL-1β is a key pro-inflammatory cytokine produced by activated macrophages and monocytes and its secretion is strictly controlled by the inflammasome. The purpose of this study is to investigate the effect of AbM water extracts on the regulation of IL-1β production and activation of the NLRP3 inflammasome in human THP-1 macrophages. The NLRP3 inflammasome consists of an NLRP3 receptor, an adaptor protein called ASC, and the inflammatory protease, caspase-1. Typically, stimulation of immune cells with microbial products results in production of pro-IL-1β, but a second stress-related signal activates the inflammasome and caspase-1, leading to processing and secretion of IL-1β. Our results show that AbM enhances transcription of IL-1β and triggers NLRP3 inflammasome-mediated IL-1β secretion in human THP-1 macrophages. AbM-mediated IL-1β secretion was markedly reduced in macrophages deficient in NLRP3 and ASC, demonstrating that the NLRP3 inflammasome is essential for AbM-induced IL-1β secretion. In addition, caspase-1 was activated and involved in proteolytic cleavage and secretion of IL-1β in AbM-treated macrophages. AbM-mediated IL-1β secretion also decreased in cells treated with cathepsin B inhibitor, suggesting that AbM can induce the release of cathepsin B. Furthermore, our data show that AbM-induced inflammasome activation requires the release of ATP, binding of extracellular ATP to the purinergic receptor P2X7, the generation of reactive oxygen species, and efflux of potassium. Taken together, these findings reveal that AbM activates the NLRP3 inflammasome via multiple mechanisms, resulting in the secretion of IL-1β.

Highlights

The medicinal mushroom Agaricus blazei Murill (AbM), a member of the Basidiomycetes family, is an edible mushroom that grows wildly in the coastal Piedade area of Sao Paulo, Brazil
We demonstrate that incubation of THP-1 macrophages with AbM extracts results in NLRP3 inflammasome-dependent activation of caspase1 and secretion of mature IL-1b
THP-1 macrophages were treated with AbM extract at concentrations increasing from 0.1 to 5% for 24 h at 37uC

Summary

Introduction

The medicinal mushroom Agaricus blazei Murill (AbM), a member of the Basidiomycetes family, is an edible mushroom that grows wildly in the coastal Piedade area of Sao Paulo, Brazil. It has recently received great attention in folk medicine due to its use in the prevention of a variety of diseases, including cancer, chronic hepatitis, diabetes, arteriosclerosis and hyperlipidaemia [1]. Agaricus blazei Murill is rich in proteoglucans and different forms of b-glucans, such as b (1,3)-, b (1,4)- and b(1,6)-Dglucans [2,3]. An extensive study by Bernardshaw et al, (2005) showed that treatment with water-extracted AbM decreased bacteraemia and thereby increased the survival rate of mice when the mice were intraperitoneally infected with Streptococcus pneumonia serotype 6B [12]

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