TMIC-14. CLEC5A REGULATES TAM POLARIZATION, TME IMMUNOSUPPRESSION AND DISEASE PROGRESSION IN GLIOBLASTOMA

Abstract

Abstract Glioblastoma, IDH-wildtype (WHO grade 4) is the most common primary malignant brain tumor of adults and is characterized by an immunosuppressive tumor microenvironment (TME) and poor clinical outcomes. CLEC5A is a gene whose expression enhances immune response in inflammatory and infectious diseases, yet its role in GBM immune regulation is unclear. Seurat analysis of scRNA-seq data and CIBERSORTx analysis of GBM RNA-seq data showed that tumor-associated macrophages (TAMs) account for the large majority of immune cells in the GBM, and that CLEC5A expression in this population (CD163+) is highest in hypoxic, peri-necrotic zones. Notably, among all immunosuppressive TAM related genes, CLEC5A expression shows the strongest association with poor clinical outcomes. Monocytes (THP-1 cells) exposed to GBM conditioned media exhibit enhanced CLEC5A and CD163 expression. Moreover, overexpression of CLEC5A by THP-1 cells enhances TAM polarization, migration toward glioma cells, and increased secretion of cytokines that mediate immunosuppression, including IL-1β, IL-4, IL-6, IL-8, IL-10 and IL-13. CLEC5A triggers the activation and phosphorylation of the Syk-Jak2-STAT3 signaling through its interaction with Syk, offering a potential therapeutic intervention. In addition, CLEC5A acts as a receptor, binding to Podoplanin (PDPN) expressed on GBM cells in the peri-necrotic TME, triggering CLEC5A-Syk-JAK-STAT3 signaling and highlighting their role in TAM polarization and the immunosuppressive TME. In vivo, silencing CLEC5A delayed glioma growth, prolonged survival and was associated with reduced CD163 and neoplastic Ki-67 expression. Collectively, we found that CLEC5A expression by TAMs is regulated by PDPN-CLEC5A-Syk-JAK-STAT3 signaling and enhances TAM polarization, TME immunosuppression and GBM growth.