Introduction: Glioblastoma stem cells (GSCs) dominate the cellular hierarchy in GBM. They are able to self-renew and differentiate into tumor lineages, and are resistant to current therapies. It is unclear whether the GSC population in any given tumor is heterogeneous.
Methods: Using human GBM biospecimens engineered to express GFP upon activation of Notch signaling, we observed partial overlap between cells expressing cell surface CD133 and cells with activated Notch signaling, contrary to expectations based on prior literature. To further investigate heterogeneity within the GSC population, we isolated distinct GSC populations and characterized them.
Results: We found that CD133+(CD133+/Notch-) and Notch+(CD133-/Notch+) GSCs differ substantially in their transcriptome, metabolism and differentiation capacity, thus giving rise to histologically different tumors. CD133+ GSCs have increased expression of hypoxia-regulated genes, and are able to expand under hypoxic conditions by activating anaerobic glycolysis. In contrast, Notch+ GSCs are unable to activate glycolysis under hypoxic conditions, leading to decreased tumorsphere formation ability. Furthermore, CD133+ GSCs give rise to histologically homogeneous tumors devoid of large tumor vessels. Tumors initiated by Notch+ GSCs are marked by large perfusing vessels enveloped by pericytes. Using a lineage tracing system, which allows tracking of the progeny of Notch+ GSCs, we showed that pericytes are derived from Notch+ GSCs. In addition, Notch+ cells are able to give rise to all tumor lineages, as opposed to Notch- populations in vitro and in vivo, which have restricted differentiation capacity and do not generate Notch+ lineages. These findings suggest that Notch+ GSCs lie at the apex of GBM’s cellular hierarchy and are more multipotent than CD133+ GSCs.
Conclusions: GBM’s stem cell population is marked by cellular and metabolic heterogeneity. Discreet GSC subtypes are able to support tumor growth either by surviving in hypoxic conditions or supporting tumor angiogenesis by differentiating into pericytes.
Patient Care: The therapeutic implication of this research is that multiple cell types will have to be targeted for effective treatment of these tumors.
Learning Objectives: By the conclusion of this session, participants should be able to:
1) Describe the biological significance of stem cells in GBM;
2) Understand the concept of cellular and metabolic heterogeneity within the GSC population in any given GBM tumor.