PR000868 (Project)

Description:Establishment and maintenance of pregnancy is dependent on progesterone synthesized by the corpus luteum (CL). The CL is known for the prominent presence of intracellular lipid droplets (LDs). However relatively little is known about the composition and function of these luteal LDs. Our objective was to identify the lipid composition of LDs from fully functional bovine CLs. Luteal LDs were isolated by flotation through a discontinuous sucrose gradient, lipids were then extracted using a standard Bligh and Dyer protocol, dried, and sent to Avanti Polar Lipids for lipidomics analysis. The samples were provided for lipidomic profiling of free sterols, cholesteryl esters, triglycerides, diacylglycerols, phospholipids, and sphingolipids. Molecular species were resolved by reversed-phase liquid chromatography in the presence of class and sub-class specific internal standard compounds added to each sample. The compounds were detected by tandem mass spectrometry (MS/MS) with scheduled multiple reaction monitoring (MRM) for mass-specific fragment ions according to the lipid class and molecular weight of the compound. Quantification of cholesterol, cholesteryl esters, triglycerides, and diglycerides were directly calculated with standards and internal standards from calibration response curves. The remaining lipid species were semi-quantization using the integrated area of each analyte’s MRM peak, divided by the appropriate internal standard peak area, and multiplied by the standard’s known concentration. Lipid concentrations were normalized to the corresponding protein concentration of each sample and as a mol % relative to total lipids or within each lipid class. Isolated luteal LDs were composed primarily of triglyceride (88%, mol% of lipid class to total lipids). Other neutral lipids included diacylglycerol, 2.9%; and cholesteryl esters, 1.5%. Polar lipids were primarily composed of phosphatidylcholine (3.1%), sphingomyelin (1.5%), phosphatidylinositol (0.9%), phosphatidylethanolamine (0.8%) and phosphatidylserine (0.4%). A number of other minor lipids representing less than 0.32% of the total lipid pool were also detected including phosphatidylglycerol, lysophospholipids, ceramides, and glycosylated ceramides. Lipid composition of bovine luteal LDs are distinct from LDs isolated from other tissues and in other species.