Molecular Probes for Tracking Lipid Droplet Membrane Dynamics

Abstract

Lipid droplets (LDs) and their membrane proteins play crucial roles in lipid metabolism, signaling, and information transport within cells. LDs feature a unique monolayer lipid membrane that has not been extensively studied due to the lack of suitable molecular probes that are able to distinguish this membrane from the LD lipid core. In this work, we present a three-pronged molecular probe design strategy that combines lipophilicity-based organelle targeting with microenvironment-dependent activation. As a proof-of-concept, we designed an LD membrane labeling pro-probe called LDM, which selectively localizes around LD membranes. Upon activation by the HClO/ClO− microenvironment that surrounds LDs, LDM pro-probe undergoes a color change and releases LDM-OH probe that binds to LD membrane proteins. This localizes the probe to the LD-associated protein space which is restricted to the membrane thus enabling visualization of the ring-like LD membrane. By utilizing LDM, we identified the dynamic mechanism of LD membrane contacts and their protein accumulation parameters. Furthermore, using LDM in liver cancer cells allowed us to examine the changes in LD/mitochondrial protein accumulation caused by the state of starvation these cells encounter. This led to the discovery that liver cancer cells respond to energy stress during hunger by enhancing LD-mitochondria interactions. Taken together, LDM represents the first molecular probe for imaging LD membranes in live cells, and represents an attractive tool for further investigations into the specific regulatory mechanisms and drug discovery associated with LD related metabolism diseases.

Keywords: Molecular Imaging, Cancer, Lipid droplets, Super-resolution Imaging