Imaging lipid droplet fusion and growth.

Lipid droplets (LDs) are highly dynamic cellular organelles found in most eukaryotic cell types. In white adipocytes, LDs grow into a characteristic unilocular morphology that is well suited for its specialized role as an efficient energy storage organelle. Overexpansion of LDs in white adipocytes results in the development of obesity and insulin resistance. Besides its central role in lipid storage and mobilization, LDs play crucial roles in various cellular processes including virus packaging, host defense, protein storage, and degradation. CIDE proteins, in particular Fsp27, initiates a unique LD fusion process in adipocytes by clustering and enriching at LD contact site and promoting neutral lipid exchange and transfer between contacted LDs. Here, we summarize our approaches to quantitatively measure intracellular LD size and neutral lipid exchange between LDs. Utilization of these methods has greatly facilitated our understanding of molecular pathways governing LD growth in adipocytes.