Protein Binding to Lipid Droplets with Altered Ratios of Surface Phospholipids

Abstract

Alcoholic Fatty Liver Disease (AFLD) is characterized by an increase in lipid droplets in the liver after acute ingestion of alcohol. Previous experiments with a rat model of AFLD show hepatic lipid droplets contain altered levels of the predominant classes of phospholipids. Specifically, hepatic lipid droplets from AFLD rats were found with lower amounts of phosphatidylcholine (PC) relative to phosphatidylethanolamine (PE). Our experiments aim to determine if the altered phospholipid composition of AFLD lipid droplets causes differences in the numbers or types of lipid droplet‐associated proteins. We selected proteins based on their membrane binding motifs and roles in lipid droplet homeostasis. AML12 cells cultured in choline‐deficient media simulate the altered phospholipid composition of AFLD lipid droplets. We isolated lipid droplets from AML12 cells cultured with and without choline and examined proteins of interest by SDS‐PAGE and western blotting. We found equivalent levels of rab18 and lanosterol synthase in lipid droplet fractions from cells grown with and without choline. Alternatively, perilipin 1, perilipin 2, and CIDE‐C are predominantly found in lipid droplet fractions from cells grown without choline (with lower ratios of PC:PE). The proteins that are most influenced by lipid droplet surface composition are all predicted to associate with lipid droplets through amphipathic alpha helices. By evaluating how altered phospholipid monolayer composition affects the binding of lipid droplet proteins, we seek to further elucidate the biochemical pathways that contribute to AFLD.Support or Funding InformationThis research was supported by St. Olaf College and the TRIO McNair Scholars Program.