Exosomes Secreted by Inflammatory Cytokine Stimulated Glioma Cells Carry a Repertoire of Proteins Which Influence Progression of Glioblastoma Multiforme

Astrocytes constitutively secrete exosomes, a set of distinct nanovesicles (30–100 nm) of endosomal origin. In glioblastoma multiforme (GBM), exosomes are involved in mediating intercellular communication by their ability to deliver potentially oncogenic cargo leading to modulation of tissue microenvironment and progression of GBM. Inflammation and oxidative stress have been demonstrated to be connected in the development of GBM. Additionally, pro‐inflammatory cytokines like interleukin‐1 beta (IL‐1β) and tumor necrosis factor‐alpha (TNF‐α) are upregulated in the brain and elevated in serum following radiation therapy in patients with primary GBM tumors. Among others, these cytokines play an important role in progression of neuroinflammation and inflammation driven tumor re‐growth after treatment. Methods Media from cultured glial cell lines was subjected to sequential centrifugation to isolate exosomes. Exosomes were characterized by presence of exosomal markers and electron microscopy (EM). Exosomal proteins were analyzed by mass spectrometry (MS). Cell based assays were used to investigate the effect of exosomes secreted by cytokine stimulated cells. Results Here we present evidence showing that exosomes (~70–80nm in size) secreted by cytokine‐stimulated glioma cells rescue both glial and neuronal cells from oxidative stress induced cell death. Our MS analysis demonstrates profound changes in exosomal proteome following IL‐1β and TNF‐α stimulation of glioma cells which may explain how GBM tumors manipulate their microenvironment to grow and respond to treatment. Many of the proteins identified are involved in pathways promoting remodeling of extracellular matrix (ECM), biological adhesion, developmental processes and progression of inflammation leading to cancer growth and development. Conclusions Increases in cytokine levels in GBM patient brains, either due to disease or radiation, lead to qualitative and quantitative changes in the exosomal proteome. The role and function of proteins present in exosomes secreted by cytokine stimulated cells, in part, explains aggressiveness, resistance to anti‐cancer therapies and high incidence of recurrence of GBM. Our study demonstrates the role of the tissue microenvironment in dictating exosomal content secreted by glioma cells, in the aggressive progression of GBM and their ability to determine the fate of target or recipient cells. Support or Funding Information NIH/NEI EY011352‐14