SB2301-mediated perturbation of membrane composition in lipid droplets induces lipophagy and lipid droplets ubiquitination

The small molecule SB2301 activates lipophagy and alters lipid droplet membrane composition, with the ethanolamine-phosphate cytidylyltransferase 2 (PCYT2) being a potential target of the compound. Lipid droplets (LDs) are involved in various biological events in cells along with their primary role as a storage center for neutral lipids. Excessive accumulation of LDs is highly correlated with various diseases, including metabolic diseases. Therefore, a basic understanding of the molecular mechanism of LD degradation would be beneficial in both academic and industrial research. Lipophagy, a selective autophagy mechanism/LD degradation process, has gained increased attention in the research community. Herein, we sought to elucidate a novel lipophagy mechanism by utilizing the LD-degrading small molecule, SB2301, which activates ubiquitin-mediated lipophagy. Using a label-free target identification method, we revealed that ethanolamine-phosphate cytidylyltransferase 2 (PCYT2) is a potential target protein of SB2301. We also demonstrated that although SB2301 does not modulate PCYT2 function, it induces the cellular translocation of PCYT2 to the LD surface and spatially increases the phosphatidylethanolamine (PE)/phosphatidylcholine (PC) ratio of the LD membrane, causing LD coalescence, leading to the activation of lipophagy process to maintain energy homeostasis.

Automated summary

The small molecule SB2301 activates lipophagy and alters lipid droplet membrane composition, with the ethanolamine-phosphate cytidylyltransferase 2 (PCYT2) being a potential target of the compound. The excessive accumulation of lipid droplets is associated with various diseases, and understanding the molecular mechanism of LD degradation is important for academic and industrial research. Lipophagy, a selective autophagy process, has gained attention in the research community. This study reveals a novel lipophagy mechanism through the use of SB2301, which activates ubiquitin-mediated lipophagy. The potential target protein PCYT2 is identified, and SB2301 induces PCYT2 translocation to the LD surface and alters the LD membrane composition, leading to the activation of the lipophagy process.