CNSC-90. REACTIVE ASTROCYTES AS DRIVERS OF GLIOBLASTOMA PROGRESSION: THE MODULATORY ROLE OF GLIOMA-DERIVED EXTRACELLULAR MATRIX

Abstract Glioblastoma (GBM) is the most aggressive primary brain tumor with limited treatment options and a dismal prognosis. Increasing evidence highlights reactive astrocytes (RAs) as active participants in the tumor microenvironment, where they acquire pro-tumorigenic transcriptional states that support glioma growth. However, the specific upstream mechanisms driving RA activation and their contribution to GBM malignancy remain unclear. In this study, we identify glioma-derived extracellular matrix (ECM), particularly collagen-I (COL I), as a key regulator of astrocyte reactivity. Using syngeneic mouse glioma models, we performed RNA-Scope and immunofluorescence analyses for GFAP and CHI3L1 to assess RA expression and spatial distribution. We observed that COL I-high tumors exhibited robust RA enrichment at the tumor border and contralateral cortex, whereas COL I-low tumors showed RA localization primarily within the tumor core. Bulk RNA sequencing of 95 (84 IDH-WT and 14 IDH1-Mut) clinical glioma samples, stratified by IDH-1 and COL I expression, revealed significant upregulation of RA-associated genes linked to the pro-tumorigenic Ast3 transcriptional state, including CHI3L1, CCL2, CHI3L2, C1R, IL1R1, ADAM12, SPOCD1, S100A11, SERPING1, and S100A10. Spatial transcriptomics (10X Visium HD) on a subset of the same glioma specimens further confirmed enrichment of RA-Ast3 signatures in COL I-high tumors, with co-localized RA clusters both within and surrounding COL I-rich regions. These findings support a model of transcriptional reprogramming of astrocytes in response to tumor-derived ECM. To explore potential paracrine mechanisms, we employed a non-contact Transwell co-culture system using glioma cells and normal mouse brain slices. Slices exposed to COL I-high glioma cells exhibited significantly increased GFAP expression compared to those exposed to COL I-low cells, indicating indirect activation of astrocytes via secreted factors. Collectively, our findings position reactive astrocytes as key mediators of GBM progression and identify collagen-I as a potent upstream modulator. These results suggest promising therapeutic targets aimed at disrupting glioma–astrocyte communication to inhibit tumor growth.