Retinal sphingolipids and their very-long-chain fatty acid-containing species.
OBJECTIVE
Recent evidence suggests that ceramide metabolism plays an important role in retinal photoreceptor cell survival and apoptosis. The purpose of this study was to characterize sphingolipids in the retina with special emphasis on the very-long-chain-containing saturated (VLC-FA) and polyunsaturated (VLC-PUFA) fatty acid-containing species. The VLC-FAs and VLC-PUFAs are synthesized by the ELOVL4 protein, which is involved in human Stargardt's macular dystrophy type 3 (STGD3).


METHODS
Total lipids were extracted from retina and other tissues, and different sphingolipid classes were isolated and purified using various combinations of liquid- and solid-phase separation. Purified sphingolipids were analyzed by high-performance thin layer chromatography (HPTLC), gas chromatography (GC), and GC-MS (GC-mass spectrometry).


RESULTS
Nonsialylated sphingolipids (NSLs) comprised approximately 3.5% of total retinal lipids of which 70% was sphingomyelin. Ceramide and glycosylceramides (GCs) constituted<or=1% of total retinal lipids. Gangliosides (GGs), on the other hand, comprised approximately 3.0% of total retinal lipids. Fatty acid analysis of retinal NSLs indicated an abundance of saturated fatty acids, with the presence of VLC-FAs but not of VLC-PUFAs beyond 24 carbons. However, GG had significant levels of unsaturated, polyunsaturated, and VLC-PUFAs. Retinal rod outer segments (ROS) contained approximately 1% each of NSL and GG, and their fatty acid profile was not very different from whole retinal NSL and GG, respectively.


CONCLUSIONS
Retina has a total of 6% to 7% fatty acids that are N-linked to a sphingosine, which would be 11 to 13 mole % in comparison to phospholipids. The presence of VLC-FAs and VLC-PUFAs in retinal sphingolipids indicates that they may play role in ELOVL4-mediated Stargardt 3.
Brush
Richard S
RS
Department of Ophthalmology, Dean A. McGee Eye Institute, University of Oklahoma Health Sciences Center, Oklahoma City, Oklahoma 73104, USA.
Tran
Julie-Thu A
JT
Henry
Kimberly R
KR
McClellan
Mark E
ME
Elliott
Michael H
MH
Mandal
Md Nawajes A
MN
D000818:Animals; D001921:Brain / Q000378:metabolism; D002417:Cattle; D002462:Cell Membrane / Q000378:metabolism; D002849:Chromatography, Gas; D002855:Chromatography, Thin Layer; D005227:Fatty Acids / Q000302:isolation & purification / Q000378:metabolism*; D005231:Fatty Acids, Unsaturated / Q000302:isolation & purification / Q000378:metabolism*; D008401:Gas Chromatography-Mass Spectrometry; D008099:Liver / Q000378:metabolism; D008297:Male; D009928:Organ Specificity; D051381:Rats; D017382:Reactive Oxygen Species / Q000378:metabolism; D012160:Retina / Q000378:metabolism*; D012867:Skin / Q000378:metabolism; D013107:Sphingolipids / Q000302:isolation & purification / Q000378:metabolism*; D013737:Testis / Q000378:metabolism
D005227:Fatty Acids; D005231:Fatty Acids, Unsaturated; D017382:Reactive Oxygen Species; D013107:Sphingolipids
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