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Bokkyoo Jun, Robert Follett Rosencrans, Hamilton E. Farris, Corinne Richards-Zawacki, William C Gordon, Nicolas G Bazan; Lipid profiling in a diurnal frog retina shows no VLC-PUFA. Invest. Ophthalmol. Vis. Sci. 2016;57(12):1735.
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© ARVO (1962-2015); The Authors (2016-present)
The goal of this project is to understand the fundamental roles of Docosahexaenoic acid (DHA) and Very-long-chain-poly-unsaturated-fatty-acids (VLC-PUFAs) in retinal function. DHA and VLC-PUFAs are relatively abundant in mouse, rat and human retina, but vary in other non-mammalian taxa with different visual ecologies. From a clinical point of view, VLC-PUFAs are important because they are synthesized by ELOVL4 enzyme, and mutated ELOVL4 results in photoreceptor degeneration. Evolutionarily, humans are diurnal primates. In order to understand the evolutionary conservation of this fundamental aspect of retinal biochemistry, we asked whether or not a diurnal frog exhibits similar DHA and VLC-PUFA enriched retinal cellular membranes.
Lipids were extracted from superior and inferior regions of diurnal frog retinas and loaded onto a liquid chromatography-mass spectrometer (LC-MS/MS) for analysis. We analyzed VLC-PUFA in phosphatidylcholine and phosphatidylethanolamine molecular species (with PC(28:0) as our internal standard) after naturally occurring isotopes were corrected using self-made programs. Triacylglycerols (TAG) are identified and analyzed as well.
PC spectra for both superior and inferior regions show no significant contribution from VLC-PUFAs. For both regions, DHA containing PCs are predominantly paired with fatty acids 16:0 and 18:0. Across the entire retina, a preponderance of PE species contain DHA, whereas relatively fewer PCs contain DHA. We also observe up to PE48:12 (22:6/26:6) species. With respect to regional differences, the superior has more DHA containing PCs than in the inferior. Additionally, greater diversity of TAG species is observed in the inferior retina as compared to the superior retina. Finally, higher concentrations of total esterified DHA are observed in the inferior retina, as compared to the superior retina.
Differing from human retina and murine retinas, VLC-PUFAs ranging from 32 carbons to 38 carbons are absent from the frog retina, especially in the PC species. Furthermore, diurnal amphibian retina appears to store DHA primarily in PEs, as opposed the typical mammalian DHA contained within PCs (including PC44:12). In conclusion, our results suggest the role of VLC-PUFAs differs across mammalia and amphibia.
This is an abstract that was submitted for the 2016 ARVO Annual Meeting, held in Seattle, Wash., May 1-5, 2016.
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