OS05.4.A THE GLIOBLASTOMA HYPOXIC NICHE REWIRES LIPID-LADEN MACROPHAGE PHENOTYPES IN AN ONTOGENY DEPENDENT MANNER

Abstract BACKGROUND Tumor-associated macrophages (TAMs) play a central role in driving tumor growth in glioblastoma by shaping tumor immunity and modulating the tumor microenvironment, making them attractive therapeutic targets. Glioblastoma TAMs originate from two develeopmental lineages: brain-resident microglia and monocyte-derived macrophages (MDMs). These distinct origins influence their roles in cancer, complicating the design of targeted therapies to prevent functional redundancy. Here, we aimed to explore the ontogenetic diversity of TAMs and their pro-tumorigenic phenotypes in glioblastoma. MATERIAL AND METHODS We leveraged a multi-omic approach, namely scRNAseq, ATACseq, Visium spatial transcriptomics, lipidomics and immunofluoresence microscopy to characterize the TAM landscape within specific niches of murine glioblastoma tumors. RESULTS We identified a novel subpopulation of metabolically-rewired macrophages, which we coined lipid-laden macrophages (LLMs) due to their accumulation of lipid droplets as a result of myelin recycling. Interestingly, LLMs transfer myelin-derived lipids to fuel the high metabolic demand of cancer cells and boost their proliferation. The LLM pool is enriched in microglia and mainly localizes within hypoxic niches. Hypoxia plays a dual role in LLM formation based on macrophage ontogeny, enhancing myelin turnover in microglia while suppressing it in bone marrow-derived macrophages. Upon radiotherapy, microglia-LLMs transition towards a more inflammatory state through epigenetic rewiring, whereas MDM-LLMs become more immunosupressive. This suggests that LLMs have unique functions dependent on developmental origin and disease stage. To further investigate how LLMs evolve within hypoxic niches during disease progression, we are currently leveraging 10X Xenium spatial transcriptomics on murine glioblastoma at different timepoints during radiotherapy treatment CONCLUSION Taken together, our work reveals an ontogeny- and hypoxia-dependent metabolic interplay between TAMs and cancer cells, laying the foundation for the discovery of ontogeny-dependent metabolic targeting strategies in glioblastoma.