Multiple mutations in the Rhodopsin gene cause sector retinitis pigmentosa in humans and a corresponding light-exacerbated retinal degeneration (RD) in animal models. Previously we have shown that T4K rhodopsin requires photoactivation to exert its toxic effect. Here we further investigated the mechanisms involved in rod cell death caused by T4K rhodopsin in mixed male and female Xenopus laevis. In this model, RD was prevented by rearing animals in constant darkness but surprisingly also in constant light. RD was maximized by light cycles containing at least 1 h of darkness and 20 min of light exposure, light intensities >750 lux, and by a sudden light onset. Under conditions of frequent light cycling, RD occurred rapidly and synchronously, with massive shedding of ROS fragments into the RPE initiated within hours and subsequent death and phagocytosis of rod cell bodies. RD was minimized by reduced light levels, pretreatment with constant light, and gradual light onset. RD was prevented by genetic ablation of the retinal isomerohydrolase RPE65 and exacerbated by ablation of phototransduction components GNAT1, SAG, and GRK1. Our results indicate that photoactivated T4K rhodopsin is toxic, that cell death requires synchronized photoactivation of T4K rhodopsin, and that toxicity is mitigated by interaction with other rod outer segment proteins regardless of whether they participate in activation or shutoff of phototransduction. In contrast, RD caused by P23H rhodopsin does not require photoactivation of the mutant protein, as it was exacerbated by RPE65 ablation, suggesting that these phenotypically similar disorders may require different treatment strategies.

视紫红质基因的多重突变会导致人类出现扇区性色素性视网膜炎，并在动物模型中导致相应的光加剧性视网膜变性 (RD)。之前我们已经证明T4K视紫红质需要光活化才能发挥其毒性作用。在这里，我们进一步研究了 T4K 视紫红质引起雄性和雌性非洲爪蟾视杆细胞死亡的机制。在这个模型中，通过在持续黑暗中饲养动物来预防 RD，但令人惊讶的是，在持续光照下也能预防 RD。通过包含至少 1 小时黑暗和 20 分钟光照、光强度 >750 lux 的光周期以及突然光照，使 RD 最大化。在频繁的光循环条件下，RD 发生迅速且同步，数小时内开始大量 ROS 碎片脱落到 RPE 中，随后杆状细胞体死亡和吞噬。通过降低光照水平、用恒定光照进行预处理以及逐渐光照来最大程度地减少 RD。视网膜异构水解酶 RPE65 的基因消融可以预防 RD，而光转导成分 GNAT1、SAG 和 GRK1 的消融则加剧 RD。我们的结果表明，光激活的T4K视紫红质是有毒的，细胞死亡需要T4K视紫红质的同步光激活，并且通过与其他视杆外节蛋白的相互作用减轻毒性，无论它们是否参与光转导的激活或关闭。相比之下，由 P23H 视紫红质引起的 RD 不需要突变蛋白的光激活，因为 RPE65 消融会加剧 RD，这表明这些表型相似的疾病可能需要不同的治疗策略。