Jacobson Samuel G, Aleman Tomas S, Cideciyan Artur V, Heon Elise, Golczak Marcin, Beltran William A, Sumaroka Alexander, Schwartz Sharon B, Roman Alejandro J, Windsor Elizabeth A M, Wilson James M, Aguirre Gustavo D, Stone Edwin M, Palczewski Krzysztof
Scheie Eye Institute, Department of Ophthalmology, School of Medicine, University of Pennsylvania, Philadelphia, PA 19104, USA.
Proc Natl Acad Sci U S A. 2007 Sep 18;104(38):15123-8. doi: 10.1073/pnas.0706367104. Epub 2007 Sep 11.
The visual (retinoid) cycle, the enzymatic pathway that regenerates chromophore after light absorption, is located primarily in the retinal pigment epithelium (RPE) and is essential for rod photoreceptor survival. Whether this pathway also is essential for cone photoreceptor survival is unknown, and there are no data from man or monkey to address this question. The visual cycle is naturally disrupted in humans with Leber congenital amaurosis (LCA), which is caused by mutations in RPE65, the gene that encodes the retinoid isomerase. We investigated such patients over a wide age range (3-52 years) for effects on the cone-rich human fovea. In vivo microscopy of the fovea showed that, even at the youngest ages, patients with RPE65-LCA exhibited cone photoreceptor loss. This loss was incomplete, however, and residual cone photoreceptor structure and function persisted for decades. Basic questions about localization of RPE65 and isomerase activity in the primate eye were addressed by examining normal macaque. RPE65 was definitively localized by immunocytochemistry to the central RPE and, by immunoblotting, appeared to concentrate in the central retina. The central retinal RPE layer also showed a 4-fold higher retinoid isomerase activity than more peripheral RPE. Early cone photoreceptor losses in RPE65-LCA suggest that robust RPE65-based visual chromophore production is important for cones; the residual retained cone structure and function support the speculation that alternative pathways are critical for cone photoreceptor survival.
视觉（视黄醛）循环是光吸收后使发色团再生的酶促途径，主要位于视网膜色素上皮（RPE）中，对视杆光感受器的存活至关重要。该途径对视锥光感受器的存活是否也至关重要尚不清楚，而且尚无来自人类或猴子的数据来回答这个问题。在患有莱伯先天性黑矇（LCA）的人类中，视觉循环会自然中断，LCA是由编码视黄醛异构酶的基因RPE65发生突变引起的。我们在较宽的年龄范围内（3至52岁）对这类患者进行了研究，以观察其对富含视锥细胞的人中央凹的影响。对中央凹的活体显微镜检查显示，即使在最年幼的患者中，RPE65-LCA患者也出现了视锥光感受器丧失。然而，这种丧失并不完全，残余的视锥光感受器结构和功能持续了数十年。通过检查正常猕猴，解决了关于RPE65和异构酶活性在灵长类动物眼中定位的基本问题。通过免疫细胞化学确定RPE65定位于中央RPE，通过免疫印迹法显示其似乎集中在中央视网膜。中央视网膜RPE层的视黄醛异构酶活性也比周边RPE高4倍。RPE65-LCA患者早期视锥光感受器丧失表明，基于RPE65的强大视觉发色团产生对视锥细胞很重要；残余保留的视锥细胞结构和功能支持了这样一种推测，即替代途径对视锥光感受器存活至关重要。
