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Lipid Droplet Proteins Involved in Lipolysis Target to Highly Organized, Rigid Membrane Structures

The significance of lipid droplets (LD) in lipid metabolism, cell signaling, and membrane trafficking is increasingly recognized, yet the influence of the LD phospholipid membrane structure on LD protein targeting and function remains unknown. To address this issue, the protein composition, lipid content, and membrane fluidity was determined in mouse adipocyte LD resolved by affinity chromatography to yield Perilipin or ADRP (adipose differentiation related protein) enriched LD. When compared to the ADRP‐enriched pool, Perilipin LD exhibited (i) Higher cholesterol/phospholipid and saturated/unsaturated fatty acid molar ratios giving rise to more rigid and ordered phospholipid membrane structures; (ii) Increased fluorescence polarizations in the presence of DPH‐TMA and NBD‐labeled cholesterol and sphingomyelin, also indicating increased membrane rigidity; and (iii) Elevated lipolytic activity, in keeping with the enriched presence of HSL, ATGL and CGI‐58 in the Perilipin‐enriched pool. Other LD proteins selectively partitioned between the two populations. Collectively, these results indicate that Perilipin and lipolytic LD proteins target to highly organized, rigid membranes, similar in structure to localized areas of the plasma membrane wherein cholesterol and fatty acid uptake/efflux occurs. This work was supported by USPHS, NIH DK 70965 (BPA)