Exosomes reflect the hypoxic status of glioma cells and mediate hypoxia-dependent activation of vascular cells during tumor development

TLDR

Hypoxia is a key driver of tumor aggressiveness, yet how glioma cells adapt and communicate with their microenvironment under low oxygen remains unclear. This study investigates whether exosomes released by glioblastoma multiforme (GBM) cells mediate hypoxia‑dependent intercellular signaling. The authors isolated exosome‑like vesicles from GBM cells cultured under hypoxic or normoxic conditions, characterized their mRNA and protein cargo, and tested their effects on endothelial cells, pericytes, and GBM cells in vitro and in a mouse xenograft model. Hypoxic exosomes were enriched in prognostic markers such as MMPs, IL‑8, PDGFs, caveolin‑1, and lysyl oxidase, promoted angiogenesis, activated endothelial and pericyte PI3K/AKT signaling, stimulated GBM autocrine migration, increased tumor vascularization and proliferation, and reduced tumor hypoxia in vivo, demonstrating that exosome cargo reflects donor oxygenation and drives hypoxia‑dependent tumor progression.

Abstract

Hypoxia, or low oxygen tension, is a major regulator of tumor development and aggressiveness. However, how cancer cells adapt to hypoxia and communicate with their surrounding microenvironment during tumor development remain important questions. Here, we show that secreted vesicles with exosome characteristics mediate hypoxia-dependent intercellular signaling of the highly malignant brain tumor glioblastoma multiforme (GBM). In vitro hypoxia experiments with glioma cells and studies with patient materials reveal the enrichment in exosomes of hypoxia-regulated mRNAs and proteins (e.g., matrix metalloproteinases, IL-8, PDGFs, caveolin 1, and lysyl oxidase), several of which were associated with poor glioma patient prognosis. We show that exosomes derived from GBM cells grown at hypoxic compared with normoxic conditions are potent inducers of angiogenesis ex vivo and in vitro through phenotypic modulation of endothelial cells. Interestingly, endothelial cells were programmed by GBM cell-derived hypoxic exosomes to secrete several potent growth factors and cytokines and to stimulate pericyte PI3K/AKT signaling activation and migration. Moreover, exosomes derived from hypoxic compared with normoxic conditions showed increased autocrine, promigratory activation of GBM cells. These findings were correlated with significantly enhanced induction by hypoxic compared with normoxic exosomes of tumor vascularization, pericyte vessel coverage, GBM cell proliferation, as well as decreased tumor hypoxia in a mouse xenograft model. We conclude that the proteome and mRNA profiles of exosome vesicles closely reflect the oxygenation status of donor glioma cells and patient tumors, and that the exosomal pathway constitutes a potentially targetable driver of hypoxia-dependent intercellular signaling during tumor development.