Lipid Droplet Proteome Dynamics and Lipotoxicity

Abstract

Lipid droplets are ER‐derived neutral lipid storage organelles that function as cellular hubs of lipid metabolism, providing an “on demand” source of fatty acids for energy and sequestering fatty acids to protect cells from lipotoxic damage. Lipid droplet functions are controlled by associated integral and peripheral proteins. To understand the composition of lipid droplet proteomes, we recently developed a proximity labeling strategy to define high confidence lipid droplet proteomes. This approach uses lipid droplet‐targeted ascorbate peroxidase (APEX2), which enables the biotinylation of neighboring proteins in a spatially and temporally defined manner. Employing this method, we defined high confidence lipid droplet proteomes in multiple cell lines and identified pathways that impact lipid droplet proteome composition, uncovering a role for a ubiquitin‐dependent ER‐associated degradation (ERAD) pathway in the clearance of select lipid droplet proteins. A key function of lipid droplets is to sequester fatty acids to prevent lipotoxicity. To further understand how the cell responds to lipotoxic insults, we leveraged whole‐genome CRISPR‐Cas9 screens to dissect pathways that regulate lipid damage. For example, exploiting a synthetic lethal screening strategy, we discovered a new pathway that promotes cancer cell resistance to a regulated form of cell death known as ferroptosis, which involves the iron‐dependent accumulation of oxidatively damaged lipids. This study uncovered an unexpected role for non‐mitochondrial CoQ as a lipophilic antioxidant that prevents membrane damage. Together, our findings highlight the integration of systems level discovery approaches and cell biology methods as a powerful strategy to understand the mechanisms that regulate lipid droplets and lipotoxicity.Support or Funding InformationThis research was supported by grants from the National Institutes of Health (R00DK095921and R01GM112948) and from the American Heart Association (16GRNT30870005).