The lipid droplet: a new organelle?

Lipid droplets (LD) are depots of neutral lipids that exist virtually in all cells. Until recently, they were considered to be in the same category as glycogen granules, simple inert storage sites for energy. There is now increasing evidence that LD interact dynamically with different organelles, probably as means of providing these organelles with lipids for their membrane expansion. However, most of the mechanisms driving LD biogenesis, growth and intracellular movement remain unknown. Recent data suggest that LD remain functionally connected to the endoplasmic reticulum (epsilon R) membrane and represent specialized epsilon R domains rather than independent organelles. Nevertheless, they represent important cellular structures for which dysfunctions may lead to human diseases such as lypodystrophies or neurodegenerative diseases.