Bennett Lea D, Brush Richard S, Chan Michael, Lydic Todd A, Reese Kristen, Reid Gavin E, Busik Julia V, Elliott Michael H, Anderson Robert E
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 Chemistry, Michigan State University, East Lansing, Michigan, United States.
Invest Ophthalmol Vis Sci. 2014 Apr 10;55(5):3150-7. doi: 10.1167/iovs.14-13995.
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.
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.
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.
The VLC-PUFAs are important for rod, but not cone, function and for rod photoreceptor longevity.
常染色体显性遗传性斯塔加特样黄斑营养不良（STGD3）是一种青少年发病的疾病，由Elovl4（极长链脂肪酸延长酶4）基因突变引起。Elovl4催化C24及更长链脂肪酸（FAs）转化为极长链脂肪酸（VLC-FAs，≥C26）的第一步反应。光感受器中极长链多不饱和脂肪酸（VLC-PUFA）含量特别丰富。为了探究VLC-PUFA在光感受器中的作用，我们在小鼠视网膜中条件性敲除了Elovl4。
通过蛋白质免疫印迹法分析蛋白质，利用气相色谱（GC）-质谱联用、GC-火焰离子化检测和串联质谱法分析脂质。通过视网膜电图（ERG）评估视网膜功能，利用明场、免疫荧光和透射电子显微镜评估视网膜结构。
视网膜Elovl4的条件性敲除（KO）使RNA和蛋白质水平分别降低了91%和96%。与野生型（WT）水平相比，视网膜总VLC-PUFA降低了88%。与8周龄时相比，12个月大时掺入磷脂酰胆碱的视网膜VLC-PUFA含量减少。ERG a波振幅降低了22%，这与光感受器变性一致（光感受器损失11%）。对视杆细胞a波反应的分析未发现VLC-PUFA在视觉转导中起作用的证据。然而，视杆细胞b波振幅显著降低（>30%），这无法用光感受器的损失来解释。VLC-PUFA减少对视锥细胞ERG反应没有影响，12个月大时WT小鼠和KO小鼠之间的视锥细胞密度没有差异。
VLC-PUFA对视杆细胞功能及视杆细胞的存活时间很重要，但对视锥细胞功能不重要。
