Polysaccharide purified from Ganoderma lucidum inhibits spontaneous and Fas-mediated apoptosis in human neutrophils through activation of the phosphatidylinositol 3 kinase/Akt signaling pathway

Ganoderma lucidum has been widely used as a remedy to promote health and longevity in China. The polysaccharide component with a branched (1→3)-β-D-glucan moiety from G. lucidum (PS-G) has shown evidence of enhancement of immune responses and of eliciting anti-tumor effects. In this study, we investigated the effect of PS-G on neutrophil viability, which is manifested by spontaneous apoptosis. Annexin V staining and MTT assays reveal that PS-G is able to inhibit spontaneous and Fas-induced neutrophil apoptosis, and this effect of PS-G is enhanced by the presence of zVAD (a caspase inhibitor) and GM-CSF. The antiapoptotic effect of PS-G is diminished by the presence of wortmannin and LY294002 (two PI-3K inhibitors), but is not altered by PD98059 (a MEK inhibitor). Western blotting indicates the stimulating effect of PS-G on Akt phosphorylation and its inhibition of procaspase 3 degradation, which occurs in neutrophils undergoing spontaneous apoptosis or triggered death by Fas. Taken together, PS-G elicitation of antiapoptotic effects on neutrophils primarily relies on activation of Akt-regulated signaling pathways.