Ginsenoside Rg1 regulates innate immune responses in macrophages through differentially modulating the NF-κB and PI3K/Akt/mTOR pathways

Abstract

Ginsenoside Rg1 is one of the major active components of ginseng, which has been shown to regulate the immune response of hosts. However, the mechanism underlying the immunomodulatory effect of Rg1 is incompletely understood. In this study, we aimed to explore whether and how Rg1 regulates the innate immune response in macrophages. The results showed that Rg1 treatment significantly increased tumor necrosis factor (TNF)-α but decreased interleukin-6 (IL-6) protein expression in both lipopolysaccharide (LPS)-activated RAW 264.7 cells and mouse peritoneal macrophages. However, Rg1 reduced the mRNA levels of both cytokines in LPS-activated macrophages, which might be a consequence of decreased activation of IκB and nuclear factor-κB (NF-κB). Importantly, Rg1 treatment further promoted LPS-induced activation of the Akt/mechanistic target of rapamycin (mTOR) pathway, which is critical for controlling protein translation. The elevated Akt/mTOR signaling was likely responsible for increased production of TNF-α protein at the translational level, as suppression of this pathway by LY294002, an inhibitor of the upstream phosphatidylinositol 3-kinase (PI3K), abrogated such an enhancement of TNF-α protein expression even though its mRNA levels were conversely increased. These findings highlight a novel mechanism for Rg1 to regulate the innate immune response in macrophages through differentially modulating the NF-κB and PI3K/Akt/mTOR pathways.

Keywords: Ginsenoside Rg1; Interleukin-6; Lipopolysaccharide; Macrophages; Tumor necrosis factor-α; mTOR.