Effect of reduced retinal VLC-PUFA on rod and cone photoreceptors.
OBJECTIVE
Autosomal dominant Stargardt-like macular dystrophy (STGD3) is a juvenile-onset disease that is caused by mutations in Elovl4 (elongation of very long fatty acids-4). The Elovl4 catalyzes the first step in the conversion of C24 and longer fatty acids (FAs) to very long-chain FAs (VLC-FAs, ≥C26). Photoreceptors are particularly rich in VLC polyunsaturated FAs (VLC-PUFA). To explore the role of VLC-PUFAs in photoreceptors, we conditionally deleted Elovl4 in the mouse retina.


METHODS
Proteins were analyzed by Western blotting and lipids by gas chromatography (GC)-mass spectrometry, GC-flame ionization detection, and tandem mass spectrometry. Retina function was assessed by electroretinography (ERG), and structure was evaluated by bright field, immunofluorescence, and transmission electron microscopy.


RESULTS
Conditional deletion (KO) of retinal Elovl4 reduced RNA and protein levels by 91% and 96%, respectively. Total retina VLC-PUFAs were reduced by 88% compared to the wild type (WT) levels. Retinal VLC-PUFAs incorporated in phosphatidylcholine were less abundant at 12 months compared to 8-week-old levels. Amplitudes of the ERG a-wave were reduced by 22%, consistent with photoreceptor degeneration (11% loss of photoreceptors). Analysis of the rod a-wave responses gave no evidence of a role for VLC-PUFA in visual transduction. However, there were significant reductions in rod b-wave amplitudes (>30%) that could not be explained by loss of rod photoreceptors. There was no effect of VLC-PUFA reduction on cone ERG responses, and cone density was not different between the WT and KO mice at 12 months of age.


CONCLUSIONS
The VLC-PUFAs are important for rod, but not cone, function and for rod photoreceptor longevity.
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
Department of Cell Biology, University of Oklahoma Health Sciences Center, Oklahoma City, Oklahoma, United States Dean McGee Eye Institute, Oklahoma City, Oklahoma, United States.
Richard S
RS
Brush
Department of Cell Biology, University of Oklahoma Health Sciences Center, Oklahoma City, Oklahoma, United States Dean McGee Eye Institute, Oklahoma City, Oklahoma, United States.
Michael
M
Chan
Department of Chemistry, Michigan State University, East Lansing, Michigan, United States.
Todd A
TA
Lydic
Department of Chemistry, Michigan State University, East Lansing, Michigan, United States.
Kristen
K
Reese
Department of Chemistry, Michigan State University, East Lansing, Michigan, United States Department of Biochemistry and Molecular Biology, Michigan State University, East Lansing, Michigan, United States.
Gavin E
GE
Reid
Department of Physiology, Michigan State University, East Lansing, Michigan, United States.
Julia V
JV
Busik
Dean McGee Eye Institute, Oklahoma City, Oklahoma, United States Department of Ophthalmology, University of Oklahoma Health Sciences Center, Oklahoma City, Oklahoma, United States Oklahoma Center for Neuroscience, University of Oklahoma Health Sciences Center, Oklahoma City, Oklahoma, United States.
Michael H
MH
Elliott
Department of Cell Biology, University of Oklahoma Health Sciences Center, Oklahoma City, Oklahoma, United States Dean McGee Eye Institute, Oklahoma City, Oklahoma, United States Department of Ophthalmology, University of Oklahoma Health Sciences Center, Oklahoma City, Oklahoma, United States Oklahoma Center for Neuroscience, University of Oklahoma Health Sciences Center, Oklahoma City, Oklahoma, United States.
Robert E
RE
Anderson
D000818:Animals; D004195:Disease Models, Animal; D004596:Electroretinography; D005136:Eye Proteins / Q000235:genetics* / Q000378:metabolism; D005231:Fatty Acids, Unsaturated / Q000172:deficiency / Q000502:physiology*; D017353:Gene Deletion; D008268:Macular Degeneration / Q000151:congenital* / Q000378:metabolism / Q000503:physiopathology; D008565:Membrane Proteins / Q000235:genetics* / Q000378:metabolism; D051379:Mice; D046529:Microscopy, Electron, Transmission; D012160:Retina / Q000378:metabolism; D017949:Retinal Cone Photoreceptor Cells / Q000166:cytology / Q000502:physiology*; D017948:Retinal Rod Photoreceptor Cells / Q000166:cytology / Q000502:physiology*
C498834:Elovl4 protein, mouse; D005136:Eye Proteins; D005231:Fatty Acids, Unsaturated; D008565:Membrane Proteins
Elovl4; STDG3; VLC-PUFA