CSIG-17. SCD5 PROTECTS GLIOBLASTOMA STEM CELLS FROM DEATH AND DIFFERENTIATION BY MODULATING INTRACELLULAR LIPID COMPOSITION

Abstract Glioblastoma (GBM) is the most common malignant brain cancer in adults, enriched in a small subpopulation of glioma stem cells (GSC), which can drive tumor recurrence and therapeutic resistance. Considerable evidence suggests that the endogenous levels of unsaturated fatty acids (FA) are crucial regulators of GSCs survival and self-renewal. Stearoyl-CoA desaturase-1 (SCD-1) is the most abundant desaturase in humans. We have previously shown that SCD1 activity is required for GSCs self-renewal and brain tumor initiation. However, SCD1 orthologous isoform, SCD5, has been poorly characterized and its potential role in GBM has not been previously reported. We have observed that SCD5 is highly enriched in GSC both at the mRNA and protein levels. Genetic downregulation of SCD5 in GSCs led to a remarkable decrease in stem cell markers, impaired cell viability and the ability to form neurospheres. Further, the downregulation of SCD5 in GSCs orthotopically implanted in mice resulted in delayed tumor growth and extended overall survival. Shotgun lipidomics in GSCs after either SCD1 or SCD5 knock-down revealed a largely distinctive lipidome profile, highlighting the divergent role of these two isoforms in GBM lipid metabolism. Surprisingly, lipidomics analysis showed that both SCD1 and SCD5 are required to synthesize a variety of lipid species involved in receptor tyrosine kinase (RTKs) and GPCRs signal transduction, directly linking FA synthesis with the oncogenic signaling. We confirmed these results by immunoblot analysis. Using specific tagging and immunofluorescence analysis, we observed that, despite a spatial overlap in SCD1 and SCD5 expression, SCD5 is uniquely present in some subcellular locations. This suggests that different functions of these isoforms could be related to different subcellular localization. Altogether, our results underscore a novel function of SCD isoforms in GSCs metabolism and highlight SCD5 as a potential therapeutic target for GBM.