Controlling the size of lipid droplets: lipid and protein factors

Recent advances have transformed our understanding of lipid droplets (LDs). Once regarded as inert lipid storage granules, LDs are now recognized as multi-functional organelles that affect many aspects of cell biology and metabolism. However, fundamental questions concerning the biogenesis and growth of LDs remain unanswered. Recent studies have uncovered novel modes of LD growth (including rapid/homotypic as well as slow/atypical LD fusion), and identified key proteins (e.g. Fsp27, seipin, FITM2 and perilipin 1) and lipids (e.g. phosphatidylcholine and phosphatidic acid) that regulate the size of LDs. Phospholipids appear to have an evolutionarily conserved role in LD growth. Protein factors may regulate LD expansion directly and/or indirectly through modulating the level and composition of phospholipids on LD surface.