Astrocytes promote pediatric glioma progression and enhance ex vivo tumor modeling

Abstract

Astrocytes constitute approximately 10-20% of all cells in the human brain and are generally tasked with maintaining tissue homeostasis. These cells support neuronal metabolism and ion transport, regulate the extracellular pH and neurotransmitter uptake, facilitate the flow of water and nutrients across the tissue, and are active peri-synaptic signaling participants. Astrocytes also play key roles in pathological processes including neuroinflammation, wound healing through glial scar formation, and neuronal degeneration. Previous studies have shown that untransformed astrocytes co-exist with cancerous cells in adult brain tumors, helping them grow, invade, and resist the effects of anti-tumor therapies. However, whether astrocytes also perform these functions in the setting of pediatric brain tumors is currently unknown. Efforts to study and model pediatric brain tumors in laboratories have mostly relied on simplified tumor cell monoculture models, with little consideration paid to the importance of normal cells to tumor physiology in vivo. I discovered that co-culturing patient-derived brain tumor cells in a brain-like synthetic extracellular matrix material with normal astrocytes promotes their proliferation and enables long-term maintenance and study of these cells ex vivo. This system particularly benefitted slower-growing tumor types, such as juvenile pilocytic astrocytomas, and enabled testing of investigational therapeutics. This new model system is a powerful tool that allows the study of primary pediatric brain tumors in a more authentic context and supports pre-clinical drug development efforts. In the specific context of a deadly form of pediatric brain tumor, diffuse midline glioma (DMG), I also identified novel roles for both normal astrocytes and astrocyte-like tumor cells in driving tumor growth, as well as invasiveness and therapeutic resistance. These effects are engendered by multiple modes of cell-cell signaling which enhance stem-like tumor cell proliferation and promote intracellular signaling pathways related to mesenchymal transformation, including activating STAT3. This work provides functional evidence for the importance of astrocytes in pediatric brain tumor pathophysiology and lays a foundation for further research into how they can be potentially exploited as a new therapeutic paradigm.