Unveiling dynamic alterations of lipid droplet polarity during NAFLD-triggered lipophagy utilizing a far-red fluorescent probe with large stokes shift

Lipophagy as a form of autophagy, can degrade lipid droplets, thereby acting as a critical regulator of cellular lipid metabolism, helping maintain the intracellular lipid homeostasis. In this study, we developed LP-SCUN, a far-red fluorescent probe for pinpointing lipid droplets with high sensitivity to solvent polarity. This probe allows for in situ imaging of lipophagy, tracking how lipid droplets move from non-polar to polar environments within lysosomes, leading to noticeable changes in fluorescence signals. The triphenylamine and triethylene glycol monomethyl ether groups of LP-SCUN facilitated its selective binding toward lipid droplets. Significantly, lipophagy and subsequent formation of autolysosomes decreased the environmental polarity, leading to a significant decrease in red fluorescence intensity (λ_ex = 500 nm and λ_em = 643 nm). As such LP-SCUN was suitable for the in situ and real-time tracking of the cellular lipophagic processes. With this research we used LP-SCUN to elucidate the mechanism of lipid metabolism in liver cells of palmitate-induced hyperlipidemia cell models and high-fat diet-induced hyperlipidemia animal models. The results indicated that non-alcoholic fatty liver disease (NAFLD) can trigger an increase in cell lipophagy levels, while the inhibition of cell lipophagy can effectively alleviate the damage caused by NAFLD to cells and liver tissue in mice.