Oleic acid-induced defective autolysosome shows impaired lipid degradation

Recent studies suggest an alternative pathway of lipid breakdown called lipophagy, which delivers lipid droplets (LDs) to lysosomes for degradation of LDs. However, molecular mechanisms regulating lipophagy are still largely unknown. In this study, we evaluated the effect of oleic acid (OA) on lipophagy in cells. We found that OA treatment results in accumulation of p62 and LC3-II proteins and reduces red fluorescence in cells stably expressing mCherry-GFP-LC3. In addition, OA inhibits the co-localization of LC3 with LAMP1 under serum-deprived condition, suggesting that OA blocks autophagosome-lysosome fusion. In the cells with ATG5 or ULK1 gene deletion, LDs did not increase upon OA treatment more than in wild type cells. However, cell starvation following OA removal resulted in reduced lipid accumulation by lipophagy and recovery of autophagy flux, suggesting that the specific condition of OA treatment and cell starvation are important for lipophagy flux activity. •Autolysosome is inhibited in oleic acid-treated cells under serum starvation.•ATG5 or ULK1 deficiency did not show further increase in the lipid accumulation than the wild types.•OA inhibits autophagy flux by blocking autophagosome-lysosome fusion.•Defective autolysosome by OA results in impaired lipid degradation.