Abstract
IDH1-mutated gliomas are slow growing brain tumours, which progress into high-grade gliomas. They present intra-tumoural cell heterogeneity, but no good markers are available to distinguish the different cell subtypes. The molecular mechanisms underlying the formation of this cell diversity is also ill defined. Here we report that the SOX9 and OLIG1 transcription factors, which specifically label astrocytes and oligodendrocytes in the normal brain, reveal the presence of two largely non-overlapping tumoural populations in IDH1-mutated oligodendrogliomas and astrocytomas. Astro-like SOX9+ cells additionally stain for APOE, CRYAB, ID4, KCNN3, while oligo-like OLIG1+ cells stain for ASCL1, EGFR, IDH1, PDGFRA, PTPRZ1, SOX4, and SOX8. GPR17, an oligodendrocytic marker, was expressed by both cells. These two sub-populations appear to have distinct BMP, NOTCH1, and MAPK active pathways as stainings for BMP4, HEY1, HEY2, p-SMAD1/5 and p-ERK were higher in SOX9+ cells. We used primary cultures and a new cell line to explore the influence of NOTCH1 activation and BMP treatment on low-grade glioma cell phenotype. This revealed that NOTCH1 globally reduced oligodendrocytic markers and IDH1 expression while upregulating APOE, CRYAB, HEY1/2 and an electrophysiologically Ca2+-activated apamin-sensitive K+ channel (KCNN3/SK3). This was accompanied by reduction in proliferation. Similar effects of NOTCH1 activation were observed in non-tumoural human oligodendrocytic cells, which additionally induced strong SOX9 expression. BMP treatment reduced OLIG1/2 expression and strongly upregulated CRYAB and NOGGIN, a negative regulator of BMP. The presence of astro-like SOX9+ and oligo-like OLIG1+ cells in diffuse low-grade gliomas raise new questions about their role in the pathology.