lipiddroplets

Lipid droplets (LDs) are cytosolic organelles that store neutral lipids, principally triacylglycerols and cholesteryl esters, in a hydrophobic core insulated by a phospholipid monolayer. Their surface hosts proteins that regulate lipid storage and mobilization, including perilipin family members such as PLIN1, PLIN2, and PLIN3, plus lipases and trafficking factors.

They form in the endoplasmic reticulum as neutral lipids accumulate between its membrane leaflets and bud off into the cytosol, acquiring a phospholipid monolayer. Biogenesis involves proteins such as seipin and FIT proteins, and droplets can grow by lipid influx and fuse with other droplets, establishing contact with mitochondria and other organelles.

Core enzymes regulate mobilization of stored lipids. Adipose triglyceride lipase (ATGL) initiates lipolysis, with hormone-sensitive lipase (HSL) and monoglyceride lipase (MGL) completing breakdown. Perilipin proteins regulate lipase access and respond to hormonal signals, coordinating lipolysis with metabolic demand.

Functionally, lipid droplets act as energy reserves and sources of fatty acids for beta-oxidation, membrane synthesis, and signaling. Their size and number adapt to nutritional status, increasing with excess energy and decreasing during fasting or energy demand when lipolysis is stimulated.

Dysregulation of lipid droplets is linked to metabolic diseases such as obesity and non-alcoholic fatty liver disease, and droplets can be exploited by certain pathogens during infection. Research employs fluorescence and electron microscopy, lipidomics, and live-cell imaging to study their dynamics and interactions.