Tmic-30. hypoxia-induced complement component 3 promotes aggressive tumor growth in the glioblastoma microenvironment

Abstract Glioblastoma is the most aggressive primary adult brain tumor. Treatment includes surgery, irradiation and chemotherapy. Still, virtually all patients suffer a treatment resistant recurrent tumor. In previous studies from our lab, we have investigated the tumor microenvironment contribution to tumor progression, showing that stromal astrocytes become reactive upon irradiation and hypoxia and generate tumor-supportive conditions for glioblastoma cells. Common features of astrocyte reactivity in several neurological diseases, include upregulation of complement proteins including complement component 3 (C3). However, it remains unexplored if these complement proteins are expressed in stromal astrocytes in glioblastoma. In a genetically engineered glioma mouse model, C3 was expressed in the invasive front, hypoxic, and perivascular tumor areas. TCGA data analysis revealed an overall strong correlation between hypoxia and complement gene expression signatures in glioblastoma patients. Astrocytes and glioma cells cultured in hypoxic conditions upregulated C3, as well as other genes associated with an infiltrative phenotype of GBM. In hypoxia, glioma cell lines, but not astrocytes, upregulated the C3a Receptor. GBM tumor single-cell sequencing data confirmed a subpopulation of highly C3-expressing astrocytes, enriched for cellular pathways comprising epithelial mesenchymal transition (EMT), TNF-alpha, hypoxia, and IFN-signaling. In vitro, C3 enhanced proliferation of glioma cells specifically under hypoxic conditions. Blocking C3a-C3aR signaling in vivo prolonged survival of glioma-bearing mice both alone and in combination with radiotherapy. Overall, our data indicate a strong link between hypoxia and complement expression in the brain tumor microenvironment of glioblastoma, where local expression of complement proteins lead to tumor promoting signaling. Inhibition of C3a-C3aR enhanced survival of glioma-bearing mice and could represent a promising avenue for further investigations.