Abstract
Purpose::
Glycerophospholipids and sphingolipids function as important constituents of cell membranes and as precursors of second messengers in cellular signaling events. Perturbations in lipid metabolism may play a role in a wide array of degenerative conditions including diabetic retinopathy and macular degeneration. However, the precise lipid composition of retina has not been thoroughly investigated. Our goal was to identify and quantitate major and minor molecular species of membrane lipids and lipid second messengers in rat and human retina.
Methods::
Retinas were obtained from 12-14 week old Wistar rats and human donors 24-36 hours post-mortem. Shotgun lipidomic analysis of total retina lipids was conducted by nESI MS and MS/MS utilizing a triple quadrupole mass spectrometer. Specific lipid classes were analyzed by parent ion and neutral loss scans in both positive and negative ionization modes, while product ion scans were used to verify the identity of abundant ions and obtain structural information for unknown compounds. Lipid species were quantitated against internal lipid standards of known concentration.
Results::
Retina lipid analysis in a controlled population of rats revealed remarkable compositional homogeneity of lipid molecular species between animals. The most abundant species of retina phospholipids contained predominantly polyunsaturated fatty acids, and included (acyl chain total carbon:total double bonds) 40:6 Phosphatidyl Choline, 40:6 Phosphatidyl Ethanolamine, 40:6 Phosphatidyl Serine, and 38:4 Phosphatidyl Inositol. The most abundant sphingolipids included 18:0 Sphingomyelin and 18:0 Ceramide. Structural analysis was performed on a large number of unknown compounds. Intact lipid extracts were also obtained and analyzed from human retinas.
Conclusions::
The limited variability in lipid composition observed across multiple rat retinas will allow for controlled lipidomic studies utilizing rat as a model of retinal dysfunction. The ability to extend this analysis to human retinas has also been demonstrated.
Keywords: lipids • retina • cell membrane/membrane specializations