INTERPLAY OF LIPID DROPLETS AND AUTOPHAGY REGULATES GLIOBLASTOMA SURVIVAL

Abstract

BACKGROUND: (blind field). METHODS: Live cell and time-lapse imaging, electronic and fluorescence microscopy, lipid analytic assay, nuclear magnetic resonance, western blotting, cell proliferation and cell death assay are performed to investigate lipid droplets (LDs) function in GBM. RESULTS: By analysis of brain tissues from GBM patients and xenografts via electronic microscopy and fluorescence imaging, our data firstly show that lipid droplets (LDs), special organelles to store excessive cholesteryl esters (CE) and triglycerides (TG), are largely enriched in tumor tissues but not detectable in normal brain tissues. Intriguingly, the role of LDs and how they are metabolized in cancer cells are completely unknown. We then show that GBM cells containing higher LD numbers are less sensitive to the treatments aiming to reduce cellular cholesterol levels. Furthermore, we find that removing cholesterol from cellular media, increasing cholesterol efflux by activation of liver X receptor (LXR), or depleting cholesterol from plasma membranes via β-methyl-cyclodextrin (β-MCD) treatment, strongly triggers autophagy to hydrolyze LDs and releases free cholesterol. This LD-derived cholesterol is shown to translocate to plasma membranes and maintain cellular cholesterol homeostasis. More interestingly, blocking autophagy leads to large amounts of LD accumulation and results in dramatic GBM cell death upon these treatments. CONCLUSIONS: Our data are the first to identify that LDs are the unique organelles enriched in GBM patient tumor tissues. Furthermore, we reveal a previously unrecognized pro-survival feedback and feed-forward metabolic reprogramming pathway through a LD-autophagy-cholesterol re-distribution process that maintains cholesterol homeostasis and GBM growth and survival. Our data suggest a novel therapeutic strategy to treat GBM by interrupting LD metabolism. SECONDARY CATEGORY: Neuropathology & Tumor Biomarkers.