Department of Ophthalmology, Medical University of South Carolina, Charleston, South Carolina, United States.
Department of Ophthalmology, University of Michigan School of Medicine, Ann Arbor, Michigan, United States.
Invest Ophthalmol Vis Sci. 2021 Feb 1;62(2):1. doi: 10.1167/iovs.62.2.1.
Bis-retinoids are a major component of lipofuscin that accumulates in the retinal pigment epithelium (RPE) in aging and age-related macular degeneration (AMD). Although bis-retinoids are known to originate from retinaldehydes required for the light response of photoreceptor cells, the relative contributions of the chromophore, 11-cis retinal, and photoisomerization product, all-trans retinal, are unknown. In photoreceptor outer segments, all-trans retinal, but not 11-cis retinal, is reduced by retinol dehydrogenase 8 (RDH8). Using Rdh8-/- mice, we evaluated the contribution of increased all-trans retinal to the formation and stability of RPE lipofuscin.
Rdh8-/- mice were reared in cyclic-light or darkness for up to 6 months, with selected light-reared cohorts switched to dark-rearing for the final 1 to 8 weeks. The bis-retinoid A2E was measured from chloroform-methanol extracts of RPE-choroid using HPLC-UV/VIS spectroscopy. Lipofuscin fluorescence was measured from whole flattened eyecups (excitation, 488 nm; emission, 565-725 nm).
Cyclic-light-reared Rdh8-/- mice accumulated A2E and RPE lipofuscin approximately 1.5 times and approximately 2 times faster, respectively, than dark-reared mice. Moving Rdh8-/- mice from cyclic-light to darkness resulted in A2E levels less than expected to have accumulated before the move.
Our findings establish that elevated levels of all-trans retinal present in cyclic-light-reared Rdh8-/- mice, which remain low in wild-type mice, contribute only modestly to RPE lipofuscin formation and accumulation. Furthermore, decreases in A2E levels occurring after moving cyclic-light-reared Rdh8-/- mice to darkness are consistent with processing of A2E within the RPE and the existence of a mechanism that could be a therapeutic target for controlling A2E cytotoxicity.
双视黄醛是脂褐素的主要成分之一，脂褐素在视网膜色素上皮 (RPE) 中积累，与衰老和年龄相关性黄斑变性 (AMD) 有关。虽然已知双视黄醛来源于光感受器细胞光反应所需的视黄醛，但发色团 11-顺式视黄醛和光异构产物全反式视黄醛的相对贡献尚不清楚。在光感受器外段，全反式视黄醛而非 11-顺式视黄醛被视黄醇脱氢酶 8 (RDH8) 还原。使用 Rdh8-/- 小鼠，我们评估了全反式视黄醛增加对视黄质形成和 RPE 脂褐素稳定性的贡献。
将 Rdh8-/- 小鼠饲养在循环光照或黑暗中长达 6 个月，选择光照饲养的实验组在最后 1 至 8 周转换为黑暗饲养。使用 HPLC-UV/VIS 光谱法从 RPE-脉络膜的氯仿-甲醇提取物中测量双视黄醛 A2E。使用全平面眼杯从荧光测量脂褐素荧光（激发，488nm；发射，565-725nm）。
与黑暗饲养的小鼠相比，循环光照饲养的 Rdh8-/- 小鼠分别以约 1.5 倍和 2 倍的速度更快地积累 A2E 和 RPE 脂褐素。将 Rdh8-/- 小鼠从循环光照转移到黑暗中会导致 A2E 水平低于预期在移动前积累的水平。
我们的研究结果表明，在循环光照饲养的 Rdh8-/- 小鼠中，高水平的全反式视黄醛（在野生型小鼠中仍保持低水平）仅对 RPE 脂褐素的形成和积累有适度贡献。此外，将循环光照饲养的 Rdh8-/- 小鼠转移到黑暗中后 A2E 水平的降低与 RPE 中 A2E 的处理一致，并且存在一种机制可能成为控制 A2E 细胞毒性的治疗靶点。
