Summary

Chi3l1 (Chitinase 3-like 1) is a secreted protein highly expressed in glioblastoma. Here, we show that exposure of glioma stem cells (GSCs) to Chi3l1 reduces the CD133 + /SOX2 + cells and increases the CD44 + /Chi3l1 + cells. Chi3l1 binds to CD44 and induces phosphorylation and nuclear translocation of beta-catenin, Akt and STAT3. Single cell RNA-seq and RNA velocity following incubation of GSCs with Chi3l1 show significant changes in GSC state dynamics driving GSCs towards a mesenchymal expression profile and reducing transition probabilities towards terminal cellular states. ATAC-seq reveals that Chi3l1 increases accessibility of promoters containing MAZ transcription factor footprint. Inhibition of MAZ directly regulates genes with highest expression in cellular clusters exhibiting significant cell state transitions. Finally, targeting Chi3l1 in vivo with a blocking antibody, resets the transcriptomic profile of glioblastoma and inhibits tumor growth. Our work implicates Chi3l1 as modulator of GSC cellular states and demonstrates pre-clinical efficacy of anti-Chi3l1 antibody treatment.