Examination of VLC-PUFA-deficient photoreceptor terminals.
OBJECTIVE
Juvenile-onset autosomal dominant Stargardt-like macular dystrophy (STGD3) is caused by mutations in ELOVL4 (elongation of very long fatty acids-4), an elongase necessary for the biosynthesis of very long chain fatty acids (VLC-FAs ≥ C26). Photoreceptors are enriched with VLC polyunsaturated fatty acids (VLC-PUFAs), which are necessary for long-term survival of rod photoreceptors. The purpose of these studies was to determine the effect of deletion of VLC-PUFAs on rod synaptic function in retinas of mice conditionally depleted (KO) of Elovl4.


METHODS
Retina function was assessed in wild-type (WT) and KO by electroretinography. Outer plexiform structure was evaluated by immunofluorescence and transmission electron microscopy. Single-cell recordings measured rod ion channel operation and rod bipolar glutamate signaling. Sucrose gradient centrifugation was used to isolate synaptosomes from bovine retina. Proteins and lipids were analyzed by Western blotting and tandem mass spectroscopy, respectively.


RESULTS
Inner retinal responses (b-wave, oscillatory potentials, and scotopic threshold responses) of the ERG were decreased in the KO mice compared to controls. However the rod ion channel operation and bipolar glutamate responses were comparable between groups. Biochemical analysis revealed that conventional and ribbon synapses have VLC-PUFAs. Ultrastructural analysis showed that the outer plexiform layer was disorganized and the diameter of vesicles in rod terminals was smaller in the KO mice.


CONCLUSIONS
Very long chain PUFAs affect rod function by contributing to synaptic vesicle size, which may alter the dynamics of synaptic transmission, ultimately resulting in a loss of neuronal connectivity and death of rod photoreceptors.
Department of Cell Biology, University of Oklahoma Health Sciences Center, Oklahoma City, Oklahoma, United States Dean McGee Eye Institute, Oklahoma City, Oklahoma, United States.
Lea D
LD
Bennett
Dean McGee Eye Institute, Oklahoma City, Oklahoma, United States Oklahoma Center for Neuroscience, University of Oklahoma Health Sciences Center, Oklahoma City, Oklahoma, United States.
Blake R
BR
Hopiavuori
Dean McGee Eye Institute, Oklahoma City, Oklahoma, United States Department of Ophthalmology, University of Oklahoma Health Sciences Center, Oklahoma City, Oklahoma, United States.
Richard S
RS
Brush
Dean McGee Eye Institute, Oklahoma City, Oklahoma, United States Department of Ophthalmology, University of Oklahoma Health Sciences Center, Oklahoma City, Oklahoma, United States.
Michael
M
Chan
Department of Ophthalmology and Visual Sciences, University of Nebraska Medical Center, Omaha, Nebraska, United States.
Matthew J
MJ
Van Hook
Department of Ophthalmology and Visual Sciences, University of Nebraska Medical Center, Omaha, Nebraska, United States Department of Pharmacology and Experimental Neuroscience, University of Nebraska Medical Center, Omaha, Nebraska, United States.
Wallace B
WB
Thoreson
Department of Cell Biology, University of Oklahoma Health Sciences Center, Oklahoma City, Oklahoma, United States.
Robert E
RE
Anderson
D000818:Animals; D015153:Blotting, Western; D002417:Cattle; D004195:Disease Models, Animal; D004596:Electroretinography; D005136:Eye Proteins / Q000235:genetics* / Q000378:metabolism; D005231:Fatty Acids, Unsaturated / Q000172:deficiency*; D008055:Lipids / Q000032:analysis; D008268:Macular Degeneration / Q000151:congenital* / Q000235:genetics / Q000378:metabolism / Q000473:pathology; D008565:Membrane Proteins / Q000235:genetics* / Q000378:metabolism; D051379:Mice; D018345:Mice, Knockout; D046529:Microscopy, Electron, Transmission; D009154:Mutation; D020419:Photoreceptor Cells, Vertebrate / Q000378:metabolism* / Q000648:ultrastructure; D012160:Retina / Q000378:metabolism / Q000503:physiopathology / Q000648:ultrastructure; D009435:Synaptic Transmission; D013574:Synaptosomes / Q000378:metabolism / Q000648:ultrastructure*; D053719:Tandem Mass Spectrometry
C498834:Elovl4 protein, mouse; D005136:Eye Proteins; D005231:Fatty Acids, Unsaturated; D008055:Lipids; D008565:Membrane Proteins
ELOVL4; STDG3; VLC-PUFA