TMIC-35. MITOCHONDRIAL TRANSFER PROMOTES ASTROCYTE REACTIVITY IN GLIOBLASTOMA

Abstract Astrocytes are the most abundant glial cell in the brain and have been shown to adopt reactive phenotypes upon interaction with glioma cells. While tumor-associated astrocyte (TAA) reactivity is linked to increased inflammation, proliferation, invasion, and treatment resistance of glioblastoma (GBM), the mechanisms by which cancer cells reprogram TAA are poorly defined. We have previously shown that mitochondrial transfer from astrocytes to GBM cells via GAP43-dependent microtubes alters GBM cellular metabolism and increases tumorigenicity. However, the potential role of this communication mechanism in TAA function remains unknown. Patient-derived GBM cells (PDCs) were transduced with a mito-GFP lentiviral vector and were co-cultured with hTERT-immortalized, mito-mCherry human astrocytes. Using flow cytometry, we observed that the frequency of mitochondrial transfer to hTERT astrocytes was dependent on GBM cell type and noted transfer rates as high as ~40% in co-cultures with L1 PDCs. Utilizing high-resolution confocal microscopy, we subsequently confirmed co-localization of fluorescent protein signal with MitoTracker Deep Red and observed increases in mitochondrial biomass in transfer-positive astrocytes. To evaluate whether mitochondrial transfer occurs in the tumor microenvironment, we implanted immunocompromised mice with L1 mito-mCherry PDCs. Approximately 17.7% of mouse TAAs in the tumor core were positive for GBM mitochondria, whereas long-distance transfer was not observed in the contralateral hemisphere. Functionally, acquisition of tumor mitochondria promoted astrocyte proliferation as measured by cells in G2/M phase and significantly increased total cellular reactive oxygen species (ROS) levels. These findings highlight a process by which astrocytes may become reactive in response to increased ROS from GBM mitochondrial transfer. Future studies will investigate the cellular response to increased ROS in astrocytes and investigate potential links to inflammatory and immunosuppressive signaling. Elucidating how GBM-to-astrocyte mitochondrial transfer reprograms TAA would help identify therapeutic vulnerabilities that can be exploited by blocking mitochondrial transfer.