Cytoplasmic lipid droplets (CLD) are organelle-like structures that function in neutral
lipid storage, transport and metabolism through the actions of specific surface-associated
proteins. Although diet and metabolism influence hepatic CLD levels, how they affect CLD
protein composition is largely unknown. We used non-biased, shotgun, proteomics in combination with metabolic analysis, quantitative immunoblotting, electron microscopy and confocal imaging to define the effects of low- and high-fat diets on CLD properties in fasted-refed mice. We found that the hepatic CLD
proteome is distinct from that of CLD from other mammalian tissues, containing
enzymes from multiple metabolic pathways. The hepatic CLD
proteome is also differentially affected by
dietary fat content and hepatic metabolic status. High fat feeding markedly increased the CLD surface density of
perilipin-2, a critical regulator of hepatic neutral
lipid storage, whereas it reduced CLD levels of
betaine-homocysteine S-methyltransferase, an
enzyme regulator of
homocysteine levels linked to
fatty liver disease and
hepatocellular carcinoma. Collectively our data demonstrate that the hepatic CLD
proteome is enriched in metabolic
enzymes, and that it is qualitatively and quantitatively regulated by diet and metabolism. These findings implicate CLD in the regulation of hepatic metabolic processes, and suggest that their properties undergo reorganization in response to hepatic metabolic demands.