Hypoxic Secretome and Exosomes Derived From Human Glioblastoma Cells (U87MG) Promote Protumorigenic Phenotype of Microglia in Vitro

Glioblastoma multiforme (GBM), a highly heterogeneous CNS tumor known for its highest incidence rates and poor prognosis has shown limited success in the therapies due to hypoxia-driving immune-suppression in the tumor microenvironment (TME). Emerging evidence highlights the involvement of tumor cell-derived exosomes in tumor-associated microglia polarization via transfer of exosomal onco-proteins and miRNAs. Although the regulatory role of long noncoding RNAs (lncRNAs) in immune signaling are known, its mechanism in microglial polarization via exosomes in GBM still remains poorly understood. In our study, we found that in comparison to the normoxic GBM-derived exosomes lncRNA H19 was significantly upregulated in hypoxic GBM-derived exosomes. Hypoxic GBM-derived exosomes and secretome (conditioned media) caused the reduction in the % phagocytosis of microglia as compared with the control group. Moreover, GBM secretome caused increase in the M2-specific genes (IL10, STAT-3, CD163, CD206) in microglia indicating its polarization to the protumorigenic (M2) phenotype. LncRNA H19 knocked down GBM-secretome treatment in microglia further reduced the STAT-3 expression indicating H19 mediated signaling. Overall, our results suggest the involvement of hypoxic exosomes and lncRNA H19 in microglial polarization and H19 as a potential target.