Autophagy regulates accumulation and functional activity of granulocytic myeloid-derived suppressor cells via STAT3 signaling in endotoxin shock.

Autophagy extensively participates in immune responses and inflammatory diseases. Myeloid-derived suppressor cells (MDSCs) are derived from CD11b+Gr1+ cells under pathological conditions and play an immunosuppressive role in the pathogenesis of cancer and inflammatory diseases. However, the role of autophagy in regulating the accumulation and activity of MDSCs remains unknown. In the present study, we evaluated the effects and mechanisms of autophagy on regulating accumulation and activity of MDSCs. We first found that granulocytic MDSCs (G-MDSCs), but not monocytic MDSCs (M-MDSCs), were accumulated in mice challenged by lipopolysaccharide (LPS) and showed an elevated autophagy activity. Pharmacological inhibition of autophagy significantly enhanced accumulation of G-MDSCs in vivo and in vitro. Notably, inhibition of autophagy enhanced the immunosuppressive activity of G-MDSCs on M1 macrophage polarization by promoting reactive oxygen species (ROS) production. Inhibition of autophagy promotes the phosphorylation of signal transducer and activator of transcription 3 (STAT3) in G-MDSCs, which is required for the accumulation and activity of MDSCs. In addition, in vivo pharmacological inhibition of autophagy significantly attenuated the condition of mice challenged by LPS. Thus, we conclude that inhibition of autophagy contributes to accumulation and immunosuppressive function of G-MDSCs by promoting the activation of STAT3 signaling, suggesting that autophagy may play a critical role in regulating accumulation and activity of MDSCs. Our study provides new insights into understanding the mechanisms of autophagy in regulating immune responses and pathogenesis of inflammatory diseases.