Lipidomic analysis of lipid droplets from murine hepatocytes reveals distinct signatures for nutritional stress

Liver steatosis can be induced by fasting or high fat diet. We investigated by lipidomic analysis whether such metabolic states are reflected in the lipidome of hepatocyte lipid droplets (LD) from mice fed normal chow diet (FED), fasted before sacrifice (FAS), or fed a high fat diet (HFD). LC-MS/MS at levels of lipid species profiles and of lipid molecular species uncovered first a FAS phenotype enriched in triacylglycerol (TG) molecular species having very long-chain polyunsaturated fatty acyl (VLC-PUFA) residues and an HFD phenotype with less unsaturated TG species in addition to characteristic marker species. Nutritional stress did not result in dramatic structural alterations in diacylglycerol (DG) and phospholipid (PL) classes. Moreover, molecular species of bulk TG and of DG indicated concomitant de novo TG synthesis and lipase-catalyzed degradation to be active in LD. DG species with VLC-PUFA residues would be preferred precursors for phosphatidylcholine (PC) species, the others for TG molecular species. In addition, molecular species of PL classes fitted the hepatocyte Kennedy and PEMT pathways. We demonstrate that lipidomic analysis of lipid droplets enables phenotyping nutritional stress. TG species are best suited for such phenotyping, whereas structural analysis of TG, DG and PL molecular species furnishes metabolic insights.