P17.25 * GLIOMA-INITIATING CELL INDUCED INTERLEUKIN-6 PRODUCTION IS MEDIATED BY TOLL-LIKE RECEPTOR 4 IN MICROGLIA

Abstract

OBJECTIVE: Malignant gliomas are the most frequent primary tumours of the brain with poor clinical prognosis. Infiltrating peripheral macrophages and resident microglia that constitute the dominant tumour-[[Unsupported Character - Codename ­]]-infiltrating cells in glioblastoma are induced by the glioma cells to become immunosuppressive and tumour supportive. Glioma-[[Unsupported Character - Codename ­]]-initiating cells (GIC) could potentially promote this pro-[[Unsupported Character - Codename ­]]-tumorigenic phenotype. Exploring the interaction between GIC and glioma associated microglia/macrophages (GAM) may offer us an opportunity to further understand the cellular and molecular features of the GIC niche. We here investigate the potential of GIC versus bulk cells to induce a pro-[[Unsupported Character - Codename ­]]- tumorigenic microglial cytokine profile. METHODS: In the present study we stimulated primary cultured microglia with glioma conditioned medium (GCM) from GICs enriched or depleted GL261 cells and cytokine levels were determined by FlowCytomix. RESULTS: An almost 4-[[Unsupported Character - Codename ­]]-fold upregulation in microglial IL-[[Unsupported Character - Codename ­]]-6 secretion was observed using GCM from GICs while the secretion was unchanged with GCM from GICs depleted GL261 cells. Since Toll-[[Unsupported Character - Codename ­]]-like receptors are pattern recognition receptors that are responsible for pro-[[Unsupported Character - Codename ­]]-inflammatory cytokines release, we screened through all the TLRs and identified TLR4 as the main TLR controlling microglial IL-[[Unsupported Character - Codename ­]]-6 secretion. IL-[[Unsupported Character - Codename ­]]-6R and gp130 are highly expressed in GICs but not in microglial cells. The implantation of GL261-[[Unsupported Character - Codename ­]]-EGFP cells into IL-[[Unsupported Character - Codename ­]]-6 -[[Unsupported Character - Codename ­]]-/-[[Unsupported Character - Codename ­]]- mice resulted in significantly smaller tumours as compared to wild-[[Unsupported Character - Codename ­]]- type control mice. IL-[[Unsupported Character - Codename ­]]-6 and IL-[[Unsupported Character - Codename ­]]-6R are also expressed in human gliomas (which contain up to 30% microglia/macrophages) and inversely correlates with patient survival. CONCLUSIONS: Our results show that GICs, but not the bulk glioma cells initiate microglial IL-[[Unsupported Character - Codename ­]]-6 secretion. IL-[[Unsupported Character - Codename ­]]-6 in turn promotes glioma cell growth and invasion.