Zhang Houbin, Fan Jie, Li Sha, Karan Sukanya, Rohrer Baerbel, Palczewski Krzysztof, Frederick Jeanne M, Crouch Rosalie K, Baehr Wolfgang
Department of Ophthalmology, University of Utah Health Science Center, Salt Lake City, Utah 84132, USA.
J Neurosci. 2008 Apr 9;28(15):4008-14. doi: 10.1523/JNEUROSCI.0317-08.2008.
Lecithin retinol acyl transferase (LRAT) and retinal pigment epithelium protein 65 (RPE65) are key enzymes of the retinoid cycle. In Lrat(-/-) and Rpe65(-/-) mice, models of human Leber congenital amaurosis, the retinoid cycle is disrupted and 11-cis-retinal, the chromophore of visual pigments, is not produced. The Lrat(-/-) and Rpe65(-/-) retina phenotype presents with rapid sectorial cone degeneration, and the visual pigments, S-opsin and M/L-opsin, fail to traffic to cone outer segments appropriately. In contrast, rod opsin traffics normally in mutant rods. Concomitantly, guanylate cyclase 1, cone T alpha-subunit, cone phosphodiesterase 6alpha' (PDE6alpha'), and GRK1 (G-protein-coupled receptor kinase 1; opsin kinase) are not transported to Lrat(-/-) and Rpe65(-/-) cone outer segments. Aberrant localization of these membrane-associated proteins was evident at postnatal day 15, before the onset of ventral and central cone degeneration. Protein levels of cone T alpha and cone PDE6alpha' were reduced, whereas their transcript levels were unchanged, suggesting posttranslational degradation. In an Rpe65(-/-)Rho(-/-) double knock-out model, trafficking of cone pigments and membrane-associated cone phototransduction polypeptides to the outer segments proceeded normally after 11-cis-retinal administration. These results suggest that ventral and central cone opsins must be regenerated with 11-cis-retinal to permit transport to the outer segments. Furthermore, the presence of 11-cis-retinal is essential for proper transport of several membrane-associated cone phototransduction polypeptides in these cones.
卵磷脂视黄醇酰基转移酶(LRAT)和视网膜色素上皮蛋白65(RPE65)是视黄醛循环的关键酶。在人类莱伯先天性黑蒙症模型Lrat(-/-)和Rpe65(-/-)小鼠中,视黄醛循环被破坏,视觉色素的发色团11-顺式视黄醛无法产生。Lrat(-/-)和Rpe65(-/-)视网膜表型表现为快速的扇形视锥细胞变性,视觉色素S-视蛋白和M/L-视蛋白无法正常转运到视锥细胞外段。相比之下,视杆视蛋白在突变视杆细胞中正常转运。同时,鸟苷酸环化酶1、视锥细胞Tα亚基、视锥细胞磷酸二酯酶6α'(PDE6α')和GRK1(G蛋白偶联受体激酶1;视蛋白激酶)无法转运到Lrat(-/-)和Rpe65(-/-)视锥细胞外段。这些膜相关蛋白的异常定位在出生后第15天就很明显,此时腹侧和中央视锥细胞变性尚未开始。视锥细胞Tα和视锥细胞PDE6α'的蛋白水平降低,而它们的转录水平未变,提示存在翻译后降解。在Rpe65(-/-)Rho(-/-)双敲除模型中,给予11-顺式视黄醛后,视锥色素和膜相关视锥细胞光转导多肽向视锥细胞外段的转运正常进行。这些结果表明,腹侧和中央视锥视蛋白必须用11-顺式视黄醛再生,才能转运到视锥细胞外段。此外,11-顺式视黄醛的存在对于这些视锥细胞中几种膜相关视锥细胞光转导多肽的正确转运至关重要。