Bogéa Tami H, Wen Runxia H, Moritz Orson L
Invest Ophthalmol Vis Sci. 2015 Dec;56(13):7947-55. doi: 10.1167/iovs.15-16799.
We previously reported a transgenic Xenopus laevis model of retinitis pigmentosa in which tadpoles express the bovine form of P23H rhodopsin (bP23H) in rod photoreceptors. In this model, retinal degeneration was dependent on light exposure. Here, we investigated ultrastructural changes that occurred in the rod photoreceptors of these retinas when exposed to light.
Tadpoles expressing bP23H in rods were transferred from constant darkness to a 12-hour light:12-hour dark (12L:12D) regimen. For comparison, transgenic tadpoles expressing an inducible form of caspase 9 (iCasp9) were reared in a 12L:12D regimen, and retinal degeneration was induced by administration of the drug AP20187. Tadpoles were euthanized at various time points, and eyes were processed for confocal light and transmission electron microscopy.
We observed defects in outer and inner segments of rods expressing bP23H that were aggravated by light exposure. Rod outer segments exhibited vesiculations throughout and were rapidly phagocytosed by the retinal pigment epithelium. In rod inner segments, we observed autophagic compartments adjacent to the endoplasmic reticulum and extensive vesiculation at later time points. These defects were not found in rods expressing iCasp9, which completely degenerated within 36 hours after drug administration.
Our results indicate that ultrastructural defects in outer and inner segment membranes of bP23H expressing rods differ from those observed in drug-induced apoptosis. We suggest that light-induced retinal degeneration caused by P23H rhodopsin occurs via cell death with autophagy, which may represent an attempt to eliminate the mutant rhodopsin and/or damaged cellular compartments from the secretory pathway.
我们之前报道了一种视网膜色素变性的转基因非洲爪蟾模型，其中蝌蚪在视杆光感受器中表达牛形式的P23H视紫红质（bP23H）。在该模型中，视网膜变性依赖于光照。在此，我们研究了这些视网膜的视杆光感受器在光照下发生的超微结构变化。
在视杆中表达bP23H的蝌蚪从持续黑暗转移到12小时光照：12小时黑暗（12L:12D）的光照方案。为作比较，将表达可诱导形式的半胱天冬酶9（iCasp9）的转基因蝌蚪饲养在12L:12D光照方案中，并通过给予药物AP20187诱导视网膜变性。在不同时间点对蝌蚪实施安乐死，并对眼睛进行共聚焦光镜和透射电子显微镜检查。
我们观察到表达bP23H的视杆的外段和内段存在缺陷，光照会加剧这些缺陷。视杆外段全程呈现出囊泡化，并迅速被视网膜色素上皮吞噬。在视杆内段，我们在后期观察到与内质网相邻的自噬区室和广泛的囊泡化。在表达iCasp9的视杆中未发现这些缺陷，其在给药后36小时内完全退化。
我们的结果表明，表达bP23H的视杆的外段和内段膜中的超微结构缺陷与药物诱导的细胞凋亡中观察到的不同。我们认为，由P23H视紫红质引起的光诱导视网膜变性是通过自噬性细胞死亡发生的，这可能代表了一种从分泌途径中清除突变视紫红质和/或受损细胞区室的尝试。
