CNSC-55. UNCOVERING THE ROLE OF COLLAGEN EXTRACELLULAR MATRIX IN GLIOBLASTOMA BRAIN MICROENVIRONMENT TRANSFORMATION

Abstract Glioblastoma (GBM) is a highly malignant brain tumor characterized by diffuse infiltration and significant heterogeneity, without effective treatment. Mesenchymal-like (MES) glioma cells drive tumor aggression by promoting brain invasion and tumor microenvironment remodeling. Previous spatial transcriptomic analyses identified Collagen, particularly COL1A, as a key extracellular matrix (ECM) component, enriched in MES areas termed oncostreams. Depletion of COL1A1 disrupted oncostreams, influencing the tumor microenvironment to support cell survival, and migration. Reactive astrocytes and macrophages, essential components of the brain microenvironment, impact glioma progression. However, the interplay between glioma-secreted collagen and the brain microenvironment remains poorly understood. To elucidate this, we generated orthotopic mouse glioma models with high-collagen (NPD) and low-collagen (NPDshCol1A1). Our data revealed that downregulation of COL1A1 in glioma cells alters the abundance and spatial distribution of reactive astrocytes and macrophages/microglia. Immunofluorescence and flow cytometry analysis showed that tumors with low-collagen had decreased GFAP+ reactive astrocyte cells at the invasive edge and perivascular niche compared to high-collagen gliomas. Moreover, our results shows that high collagen levels may activate astrocytes through distant communication, as evidenced by the higher presence of reactive astrocytes in the contralateral cortex of NPD tumors. However, low-collagen tumors exhibited an increase in astrocytes (GFAP+) in the tumor core. Furthermore, high-collagen gliomas demonstrated increased macrophage infiltration, promoting an immunosuppressive environment. Using multiplex immunohistochemistry assays, we observed that reactive astrocytes along the invasive tumor edge were associated with glioma cells expressing elevated levels of COL1A1 and TGF-β ligand. In summary, our results show that glioma cell-expressed COL1A1 promotes the activation of peritumoral and perivascular brain-resident astrocytes and macrophages. The interactions of reactive astrocyte with glioma cells enriched in collagen form a feedback loop that enhances tumor invasion and vascular proliferation, suggesting that targeting the ECM-astrocyte interactions could disrupt these processes and offer a therapeutic avenue for GBM.