Abstract
Caveolins form plasmalemnal invaginated caveolae. They also locate around intracellular lipid droplets but their role in this location remains unclear. By studying primary adipocytes that highly express caveolin-1, we characterized the impact of caveolin-1 deficiency on lipid droplet proteome and lipidome. We identified several missing proteins on the lipid droplet surface of caveolin-deficient adipocytes and showed that the caveolin-1 lipid droplet pool is organized as multi-protein complexes containing cavin-1, with similar dynamics as those found in caveolae. On the lipid side, caveolin deficiency did not qualitatively alter neutral lipids in lipid droplet, but significantly reduced the relative abundance of surface phospholipid species: phosphatidylserine and lysophospholipids. Caveolin-deficient adipocytes can form only small lipid droplets, suggesting that the caveolin-lipid droplet pool might be involved in lipid droplet size regulation. Accordingly, we show that caveolin-1 concentration on adipocyte lipid droplets positively correlated with lipid droplet size in obese rodent models and human adipocytes. Moreover, rescue experiments by caveolin- green fluorescent protein in caveolin-deficient cells exposed to fatty acid overload demonstrated that caveolin-coated lipid droplets were able to grow larger than caveolin-devoid lipid droplets. Altogether, these data demonstrate that the lipid droplet-caveolin pool impacts on phospholipid and protein surface composition of lipid droplets and suggest a functional role on lipid droplet expandability.
Highlights
The most abundant lipid droplet surface proteins defined as the PAT family, consist of the adipocyte specific Perilipin, and the ubiquitous Adipocyte Differentiation-Related Protein (ADRP) and the Tail-Interacting Protein 47 (TIP47) [2], which actively participate in the control of lipid storage and mobilization
We ensured that this process was applicable to primary mouse adipocytes, in which lipid droplet size range exceeds by at least one order of magnitude that found in all other cell types
This study provides the first detailed characterization of the impact of caveolins on molecular composition of lipid droplets, and reveals several features of the adipocyte lipid droplet caveolin pool indicative of a role in facilitating size enlargement in response to lipid filling
Summary
They locate around intracellular lipid droplets but their role in this location remains unclear. Rescue experiments by caveolin- green fluorescent protein in caveolin-deficient cells exposed to fatty acid overload demonstrated that caveolin-coated lipid droplets were able to grow larger than caveolin-devoid lipid droplets. These data demonstrate that the lipid droplet-caveolin pool impacts on phospholipid and protein surface composition of lipid droplets and suggest a functional role on lipid droplet expandability.—Blouin, C. Lipid droplet analysis in caveolin-deficient adipocytes: alterations in surface phospholipid composition and maturation defects. Journal of Lipid Research Volume 51, 2010 945 presence of caveolins [primarily known as coating proteins of plasma membrane caveolae [9]] remains poorly understood
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