Differential composition of DHA and very-long-chain PUFAs in rod and cone photoreceptors

Martin-Paul Agbaga,Dana K Merriman,Richard S Brush,Todd A Lydic,Shannon M Conley,Muna I Naash,Shelley Jackson,Amina S Woods,Gavin E Reid,Julia V Busik,Robert E Anderson

doi:10.1194/jlr.m082495

Abstract

Long-chain PUFAs (LC-PUFAs; C20-C22; e.g., DHA and arachidonic acid) are highly enriched in vertebrate retina, where they are elongated to very-long-chain PUFAs (VLC-PUFAs; C 28) by the elongation of very-long-chain fatty acids-4 (ELOVL4) enzyme. These fatty acids play essential roles in modulating neuronal function and health. The relevance of different lipid requirements in rods and cones to disease processes, such as age-related macular degeneration, however, remains unclear. To better understand the role of LC-PUFAs and VLC-PUFAs in the retina, we investigated the lipid compositions of whole retinas or photoreceptor outer segment (OS) membranes in rodents with rod- or cone-dominant retinas. We analyzed fatty acid methyl esters and the molecular species of glycerophospholipids (phosphatidylcholine, phosphatidylethanolamine, and phosphatidylserine) by GC-MS/GC-flame ionization detection and ESI-MS/MS, respectively. We found that whole retinas and OS membranes in rod-dominant animals compared with cone-dominant animals had higher amounts of LC-PUFAs and VLC-PUFAs. Compared with those of rod-dominant animals, retinas and OS membranes from cone-dominant animals also had about 2-fold lower levels of di-DHA (22:6/22:6) molecular species of glycerophospholipids. Because PUFAs are necessary for optimal G protein-coupled receptor signaling in rods, these findings suggest that cones may not have the same lipid requirements as rods.

Highlights

Long-chain PUFAs (LC-PUFAs; C20–C22; e.g., DHA and arachidonic acid) are highly enriched in vertebrate retina, where they are elongated to very-long-chain PUFAs (VLC-PUFAs; C 28) by the elongation of very-long-chain fatty acids-4 (ELOVL4) enzyme
To determine the enrichment and purity of outer segment (OS) membrane preparations, equal amounts of protein of OS membranes from WT mouse (C57B6/J), neural leucine zipper transcription (Nrl)+/ mouse, Nrl / mouse, rat, and thirteen-lined ground squirrel (TLGS) retinas were resolved on SDS-PAGE, as described by Laemmli [44], and either stained with silver nitrate or immunoblotted with anti-opsin, anti-rod transducin, anti-M-opsin, or anti-actin antibodies (Fig. 1A, B)
Because 22:6n3 is necessary for optimal G protein-coupled receptor signaling in rods, these findings suggest that cones and cone signaling may not have the same lipid requirements as rods

Summary

Introduction

Long-chain PUFAs (LC-PUFAs; C20–C22; e.g., DHA and arachidonic acid) are highly enriched in vertebrate retina, where they are elongated to very-long-chain PUFAs (VLC-PUFAs; C 28) by the elongation of very-long-chain fatty acids-4 (ELOVL4) enzyme. These fatty acids play essential roles in modulating neuronal function and health. DHA is essential for normal development of rod function in the rat retina, first demonstrated by our laboratory in 1973 and 1975 [5, 6] In these studies, rats deficient in PUFAs had reduced electroretinographic responses [5].

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Discussion

Conclusion