Modeling glioblastoma heterogeneity to decipher its biology

Abstract: Glioblastoma multiforme (GBM) is the most common and lethal form of primary brain tumor that mainly affects adults. GBM displays remarkable intra- and inter-tumoral heterogeneity and contains a subpopulation of cells named glioma stem cells that is believed to be responsible for tumor maintenance, progression and recurrence.We have established and characterized a biobank of 48 cell lines derived from GBM patients. The cells were explanted and maintained as adherent cultures in serum-free, defined neural stem cell medium. These GBM cells (GCs) displayed NSC marker expression in vitro, had orthotopic tumor initiating capability in vivo, harboured genomic alterations characteristic of GBM and represented all four TCGA molecular subtypes. Our newly established biobank is also connected with a database (www.hgcc.se) that provides all molecular and clinical data. This resource provides a valuable platform of valid in vitro and in vivo models for basic GBM research and drug discovery.By using RCAS/tv-a mouse models for glioma, we found that GBMs originating from a putative NSC origin caused more tumorigenic GCs that had higher self-renewal abilities than those originating from putative glial precursor cell origin. By transcriptome analysis a mouse cell origin (MCO) gene signature was generated to cluster human GCs and GBM tissue samples and a functional relationship between the differentiation state of the initially transformed cell and the phenotype of GCs was discovered, which provides the basis for a new predictive MCO-based patient classification.LGR5 was found to be highly expressed in the most malignant mouse GC lines of putative NSC origin and also enriched in proneural GBMs characterized by PDGFRA alterations and OLIG2 up-regulation. By overexpressing or depleting LGR5 we discovered that high LGR5 expression in proneural GC lines increased the tumorigenicity, self-renewal and invasive capacities of the cells and could potentiate WNT signalling through its ligand RSPO1. Through transcriptome analysis we identified the candidate genes CCND2, PDGFRA, OLIG2, DKK1 that were found to be regulated by LGR5.In the last study, we found that mouse OPCs could initiate both astrocytic and oligdendroglial gliomas, which indicated that oncogenic signalling is dominant to cell of origin in affecting the histology of gliomas.