Department of Ophthalmology, University of Massachusetts Medical School, Worcester, Massachusetts, USA.
Invest Ophthalmol Vis Sci. 2013 Jul 2;54(7):4503-11. doi: 10.1167/iovs.13-12140.
Mutations in the RP2 gene are associated with 10% to 15% of X-linked retinitis pigmentosa (XLRP), a debilitating disorder characterized by the degeneration of retinal rod and cone photoreceptors. The molecular mechanism of pathogenesis of photoreceptor degeneration in XLRP-RP2 has not been elucidated, and no treatment is currently available. This study was undertaken to investigate the pathogenesis of RP2-associated retinal degeneration.
We introduced loxP sites that flank exon 2, a mutational hotspot in XLRP-RP2, in the mouse Rp2 gene. We then produced Rp2-null allele using transgenic mice that expressed Cre-recombinase under control of the ubiquitous CAG promoter. Electroretinography (ERG), histology, light microscopy, transmission electron microscopy, and immunofluorescence microscopy were performed to ascertain the effect of ablation of Rp2 on photoreceptor development, function, and protein trafficking.
Although no gross abnormalities were detected in the Rp2(null) mice, photopic (cone) and scotopic (rod) function as measured by ERG showed a gradual decline starting as early as 1 month of age. We also detected slow progressive degeneration of the photoreceptor membrane discs in the mutant retina. These defects were associated with mislocalization of cone opsins to the nuclear and synaptic layers and reduced rhodopsin content in the outer segment of mutant retina prior to the onset of photoreceptor degeneration.
Our studies suggest that RP2 contributes to the maintenance of photoreceptor function and that cone opsin mislocalization represents an early step in XLRP caused by RP2 mutations. The Rp2(null) mice should serve as a useful preclinical model for testing gene- and cell-based therapies.
RP2 基因突变与 10%至 15%的 X 连锁视网膜色素变性（XLRP）有关，XLRP 是一种使人衰弱的疾病，其特征是视网膜杆状和锥状光感受器退化。XLRP-RP2 中光感受器退化的发病机制的分子机制尚未阐明，目前尚无治疗方法。本研究旨在探讨与 RP2 相关的视网膜变性的发病机制。
我们在小鼠 Rp2 基因中引入了侧翼为 XLRP-RP2 突变热点的外显子 2 的 loxP 位点。然后，我们使用在组成型 CAG 启动子控制下表达 Cre 重组酶的转基因小鼠产生 Rp2 缺失等位基因。通过视网膜电图（ERG）、组织学、光镜、透射电镜和免疫荧光显微镜检查，确定 Rp2 缺失对光感受器发育、功能和蛋白转运的影响。
尽管 Rp2(null) 小鼠未检测到明显的大体异常，但通过 ERG 测量的明适应（锥）和暗适应（杆）功能早在 1 月龄时就逐渐下降。我们还检测到突变体视网膜中光感受器膜盘的缓慢进行性退化。这些缺陷与视锥蛋白向核和突触层的定位错误以及突变体视网膜外节视黄醛含量减少有关，这些缺陷发生在光感受器退化之前。
我们的研究表明，RP2 有助于维持光感受器的功能，并且视锥蛋白的定位错误代表了由 RP2 突变引起的 XLRP 的早期步骤。Rp2(null) 小鼠应作为测试基因和细胞治疗的有用临床前模型。
