Department of Ophthalmology, University of Oklahoma Health Sciences Center, Oklahoma City, Oklahoma, United States Dean McGee Eye Institute, Oklahoma City, Oklahoma, United States.
Department of Ophthalmology and Vancouver Eye Care Center, University of British Columbia, Vancouver, Canada.
Invest Ophthalmol Vis Sci. 2014 May 15;55(6):3669-80. doi: 10.1167/iovs.13-13099.
Autosomal dominant Stargardt macular dystrophy caused by mutations in the Elongation of Very Long Chain fatty acids (ELOVL4) gene results in macular degeneration, leading to early childhood blindness. Transgenic mice and pigs expressing mutant ELOVL4 develop progressive photoreceptor degeneration. The mechanism by which these mutations cause macular degeneration remains unclear, but have been hypothesized to involve the loss of an ER-retention dilysine motif located in the extreme C-terminus. Dominant negative mechanisms and reduction in retinal polyunsaturated fatty acids also have been suggested. To understand the molecular mechanisms involved in disease progression in vivo, we addressed the hypothesis that the disease-linked C-terminal truncation mutant of ELOVL4 exerts a dominant negative effect on wild-type (WT) ELOVL4, altering its subcellular localization and function, which subsequently induces retinal degeneration and loss of vision.
We generated transgenic Xenopus laevis that overexpress HA-tagged murine ELOVL4 variants in rod photoreceptors.
Tagged or untagged WT ELOVL4 localized primarily to inner segments. However, the mutant protein lacking the dilysine motif was mislocalized to post-Golgi compartments and outer segment disks. Coexpression of mutant and WT ELOVL4 in rods did not result in mislocalization of the WT protein to outer segments or in the formation of aggregates. Full-length HA-tagged ELOVL4 lacking the dilysine motif (K308R/K310R) necessary for targeting the WT ELOVL4 protein to the endoplasmic reticulum was similarly mislocalized to outer segments.
We propose that expression and outer segment mislocalization of the disease-linked 5-base-pair deletion mutant ELOVL4 protein alters photoreceptor structure and function, which subsequently results in retinal degeneration, and suggest three possible mechanisms by which mutant ELOVL4 may induce retinal degeneration in STGD3.
常染色体显性遗传的 Stargardt 黄斑营养不良是由伸长酶超长链脂肪酸（ELOVL4）基因突变引起的，导致黄斑变性，从而导致儿童早期失明。表达突变 ELOVL4 的转基因小鼠和猪会发生进行性光感受器变性。这些突变导致黄斑变性的机制尚不清楚，但据推测涉及位于极端 C 末端的 ER 保留双赖氨酸基序的丢失。还提出了显性负机制和视网膜多不饱和脂肪酸减少。为了了解体内疾病进展的分子机制，我们提出了假设，即 ELOVL4 的疾病相关 C 末端截断突变体对野生型（WT）ELOVL4 产生显性负效应，改变其亚细胞定位和功能，随后诱导视网膜变性和视力丧失。
我们生成了过表达 HA 标记的鼠 ELOVL4 变体的转基因非洲爪蟾，该变体在杆状光感受器中表达。
标记或未标记的 WT ELOVL4 主要定位于内节。然而，缺乏双赖氨酸基序的突变蛋白被错误定位到高尔基体后区和外节盘。突变体和 WT ELOVL4 在杆状细胞中的共表达不会导致 WT 蛋白错误定位到外节或形成聚集体。缺乏内质网靶向 WT ELOVL4 所需的双赖氨酸基序（K308R/K310R）的全长 HA 标记的 ELOVL4 也被错误定位到外节。
我们提出，疾病相关的 5 个碱基对缺失突变 ELOVL4 蛋白的表达和外节定位错误改变了光感受器的结构和功能，随后导致视网膜变性，并提出了突变 ELOVL4 可能在 STGD3 中诱导视网膜变性的三种可能机制。
