在视网膜色素上皮(RPE)中高表达,RPE特异性65-kDa(RPE65)酶对于产生11-顺式视网膜(11cRAL)是必不可少的,视紫红质和视锥光色素的发色团。RPE65缺乏可导致Leber先天性黑蒙2型(LCA2),其中光漂白的全反式视网膜异构化为光敏11cRAL被阻断,最终导致严重的视网膜功能障碍和变性。相关的老鼠模型,它们是通过基因敲除或由自发突变引起的,形态学上存在早发性和快速视网膜视锥细胞变性,包括短波长敏感的视锥蛋白(S-视蛋白)的丢失和中波长敏感的视锥蛋白(M-视蛋白)的错位。研究表明,常规Rpe65基因替代疗法,由腺相关病毒(AAV)载体介导,可以恢复RPE65蛋白。然而,AAV转染和Rpe65转基因表达至少需要一到两周,并且该治疗不能完全阻断早发性视锥细胞变性。确定基因治疗前延迟视锥细胞变性的可行性,我们研究了11cRAL治疗对早期LCA2视网膜变性12(rd12)小鼠模型的影响.类似于人类患者,小鼠模型携带Rpe65基因的自发突变,导致内源性11cRAL再生中断。我们发现RPE65缺乏对啮齿动物视网膜血管没有明显影响。在红光照射下,从出生后(P)14天至P21天对rd12小鼠腹腔注射外源性11cRAL。最后一次注射三天后,使用暗视和明视视网膜电图观察到视网膜功能的显着恢复。使用光学相干断层扫描和对缺陷视网膜的组织学分析,我们发现了感光体外段(OS)厚度的变化;这种变化可以通过早期11cRAL治疗来挽救。此外,治疗特别保留了M-和S-视蛋白,两者都在视锥细胞内保持适当的定位,如野生型小鼠所示。相比之下,年龄匹配的未经治疗的rd12小鼠的特征是视网膜S-视蛋白丢失和M-视蛋白从感光细胞OS到内节的错误定位,外核层,或外丛状层。值得注意的是,11cRAL治疗不能长时间维持视网膜功能。最后一次注射后十天,视杆和M锥视网膜电图显著下降,S锥反应几乎熄灭。我们的研究结果表明,早期11cRAL治疗对于恢复rd12小鼠模型的视网膜功能和挽救形态学是有用的,早发性和快速的视锥变性可以在基因治疗之前延迟。
Highly expressed in the retinal pigment epithelium (RPE), the RPE-specific 65-kDa (RPE65) enzyme is indispensable to generate 11-cis-retinal (11cRAL), a
chromophore for rhodopsin and cone photopigments. RPE65 deficiency can lead to Leber congenital amaurosis type 2 (LCA2), in which the isomerization of photobleached all-trans-retinal into photosensitive 11cRAL is blocked, ultimately causing severe retinal dysfunction and degeneration. The related mouse models, which are constructed through gene knockout or caused by spontaneous mutations, morphologically present with early-onset and rapid retinal cone cells degeneration, including loss of short-wavelength-sensitive cone opsins (S-opsins) and mislocalization of medium-wavelength-sensitive cone opsins (M-opsins). Studies have shown that routine Rpe65 gene replacement therapy, mediated by an adeno-associated virus (AAV) vector, can restore RPE65 protein. However, AAV transfection and Rpe65 transgene expression require at least one to two weeks, and the treatment cannot fully block the early-onset cone degeneration. To determine the feasibility of delaying cone degeneration before gene therapy, we investigated the impact of 11cRAL treatment in an early-age LCA2 retinal degeneration 12 (rd12) mouse model. Similar to human patients, the mouse model carries a spontaneous mutation in the Rpe65 gene, which results in disrupted endogenous 11cRAL regeneration. We found that RPE65 deficiency did not notably affect rodent retinal vessels. Under red light illumination, the rd12 mice were intraperitoneally injected with exogenous 11cRAL from postnatal day (P) 14 to P21. Three days after the last injection, a notable recovery of retinal function was observed using scotopic and photopic electroretinograms. Using optical coherence tomography and histological analyses of the deficient retinas, we found changes in the thickness of the photoreceptor outer segment (OS); this change could be rescued by early 11cRAL treatment. In addition, the treatment notably preserved M- and S-opsins, both of which maintained appropriate localization inside cone cells, as shown by the wild-type mice. In contrast, the age-matched untreated rd12 mice were characterized by retinal S-opsin loss and M-opsin mislocalization from the photoreceptor OS to the inner segment, outer nuclear layer, or outer plexiform layer. Notably, 11cRAL treatment could not maintain retinal function for a long time. Ten days after the last injection, the rod and M-cone electroretinograms significantly decreased, and S-cone responses almost extinguished. Our findings suggest that early 11cRAL treatment is useful for restoring retinal function and rescuing morphology in the rd12 mouse model, and the early-onset and rapid cone degeneration can be delayed before gene therapy.