Glioblastoma stem cell (GSC)-derived PD-L1-containing exosomes activates AMPK/ULK1 pathway mediated autophagy to increase temozolomide-resistance in glioblastoma

Abstract Temozolomide (TMZ)-resistance hampers the therapeutic efficacy of this drug for glioblastoma (GBM) treatment in clinic, and emerging evidences suggested that exosomes from GBM-derived stem cells (GSCs) contributed to this process, but the detailed mechanisms are still largely unknown. In the present study, we reported that GSCs derived programmed death-ligand 1 (PD-L1) containing exosomes activated AMPK/ULK1 pathway mediated protective autophagy enhanced TMZ-resistance in GBM in vitro and in vivo. Specifically, we noticed that continuous low-dose TMZ stimulation promoted GSCs generation and PD-L1 containing exosomes (PD-L1-ex) secretion in GBM cells, and that PD-L1-ex inhibited cell apoptosis and promoted cell autophagy to increased TMZ-resistance in GBM cells, which were reversed by co-treating cells with the autophagy inhibitor 3-methyladenine (3-MA). Consistently, upregulation of PD-L1 also increased TMZ-resistance in TS-GBM cells, and silencing of PD-L1 sensitized TR-GBM cells to TMZ. In addition, PD-L1-ex activated AMPK/ULK1 pathway to induce autophagy in TMZ treated GBM cells, and the inhibitors for AMPK (compound C) and ULK1 (SBI-0206965) promoted cell apoptosis in GBM cells co-treated with PD-L1-ex and high-dose TMZ. Finally, we evidenced that PD-L1-ex promoted tumor growth and Ki67 protein expressions to increase TMZ-resistance in GBM in vivo. Collectively, we concluded that GSCs-derived PD-L1-ex activated AMPK1/ULK1 signaling cascade mediated autophagy to increase TMZ-resistance in GBM, and this study provided potential strategies to improve the therapeutic efficacy of TMZ in GBM.