Toll-like receptor 4-mediated ROS signaling pathway involved in Ganoderma atrum polysaccharide-induced tumor necrosis factor-α secretion during macrophage activation

Abstract

Ganoderma atrum has been used as Chinese traditional medicine and healthful mushroom for thousands of years. The polysaccharide is regarded as the major bioactive substances in G. atrum. To delineate the underlying mechanism and signaling cascade involved in the immunomodulatory property of G. atrum polysaccharide (PSG-1). Specifically, this study is designed to examine the possibility of TLR4 as a candidate receptor interacted with G. atrum polysaccharide (PSG-1) and elucidate the role of reactive oxygen species (ROS) in PSG-1-induced tumor necrosis factor-α (TNF-α) production during macrophage activation. Flow cytometric and confocal laser-scanning microscopy analysis showed that fluorescence-labeled PSG-1 bind specifically to the macrophages. Moreover, PSG-1 stimulated TNF-α secretion of peritoneal macrophages from C3H/HeN mice, but not from C3H/HeJ mice. PSG-1-indcued TNF-α production was suppressed by anti-TLR4 mAb. Furthermore, ROS production was mediated by TLR4, and NADPH oxidase-derived ROS act as upstream of phosphoinositide 3-kinase(PI3K)/Akt/mitogen-activated protein kinases(MAPKs)/nuclear factor(NF)-κB signaling pathway in the regulation of PSG-1 stimulated TNF-α production. Taken together, we conclude that PSG-1 induces TNF-α secretion through TLR4/ROS/PI3K/Akt/MAPKs/NF-κB pathways during macrophage activation. Our findings provide a molecular basis for the potential of PSG-1 as a novel immunomodulatory agent.