Studies on visual cycles and their relevance to age-related macular degeneration

 描述（由申请人提供）： 视网膜相关性黄斑变性（AMD）是一种老年性致盲性疾病，在退伍军人群体中的患病率正在增加。目前还没有高度有效的治疗萎缩性（干性）AMD，这种疾病的最常见形式。现在认识到，维生素A代谢物全反式视黄醇可能在AMD的发病机制中起关键作用。全反式-视黄醛在光激活后从感光细胞中的视色素（视杆和视锥全息视蛋白）释放。为了维持视力，11-顺式-视黄醛必须连续地提供给感光细胞，以便维持足够水平的光敏全视蛋白。视杆和视锥光感受器从称为视觉循环的代谢途径接收11-顺式-视黄醇，其涉及位于视网膜色素上皮中的酶。有强有力的证据表明，视网膜中也存在另一种Müller细胞依赖性视觉周期，为视锥光感受器提供额外的视觉发色团，足以在白天照明条件下工作。通过靶向经典的视觉循环异构酶RPE 65来抑制11-顺式-视黄醛产生的药剂通过减少光暴露后释放的全反式-视黄醛的量来保护视网膜免受光诱导的损伤。这些药物已被提议作为AMD的潜在药物疗法。一种RPE依赖性视觉周期的抑制剂，称为emixustat，目前正在评估其在3期临床试验中减缓AMD进展的能力。RPE 65抑制剂作为治疗干性AMD的有效药剂具有很大的前景，但它们也对视锥光感受器和色觉具有不期望的副作用。这些麻烦的眼部副作用的起源仍有待阐明，但它们可能是由脱靶相互作用引起的 Müller细胞依赖性视觉周期的组成部分。或者，由于在发生AMD病理的人黄斑中视锥细胞多于视杆细胞，因此还可以想到，部分抑制Müller细胞依赖性视觉周期可能对AMD治疗有治疗益处。最近，在高通量表达筛选中鉴定了Müller细胞途径的候选类维生素A异构酶，称为鞘脂-Δ4-去饱和酶（DES 1）。这种Müller细胞定位酶最初被表征为二氢神经酰胺去饱和酶，在体外催化全反式视黄醇形成顺式视黄醇异构体，并在Rpe 65-/-小鼠中过表达时部分恢复视网膜功能。然而，这种酶对视锥细胞功能的生理贡献尚未研究。该提案旨在1）使用基因敲除小鼠模型评估DES 1对视锥细胞介导的视觉的生理贡献，以及2）利用最近获得的关于emixustat与RPE 65活性位点的结合模式的高分辨率结构信息来设计对RPE 65具有高选择性和改善的毒性特征的新型视觉周期抑制剂。将通过高分辨率成像和视网膜电描记术评估Des 1条件性敲除小鼠的视网膜结构和功能。结构指导的药物设计将用于产生高度选择性的RPE 65抑制剂，用于治疗干性AMD。

 DESCRIPTION (provided by applicant): Age-related macular degeneration (AMD) is a debilitating blinding disease of older age that is increasing in prevalence in the Veteran population. There are currently no highly effective therapies for atrophic (dry) AMD, the most common form of this disorder. It is now appreciated that the vitamin A metabolite, all-trans-retinal, likely plays a key role in the pathogenesis of AMD. All-trans-retinal is released from visual pigments (rod and cone holo-opsins) in photoreceptor cells following their activation by light. For sustained vision, 11-cis-retinal must e continuously provided to the photoreceptor cells so that sufficient levels of light-sensitive holo-opsins are maintained. Rod and cone photoreceptors receive 11-cis-retinal from a metabolic pathway known as the visual cycle, which involves enzymes located in the retinal pigment epithelium. There is strong evidence that an alternative, Müller cell-dependent visual cycle also exists in the retina to provide cone photoreceptors with an additional supply of visual chromophore adequate for operation under daytime lighting conditions. Agents that inhibit production of 11-cis-retinal by targeting the classical visual cycle isomerase, RPE65, protect against light-induced damage to the retina by reducing the amount of all-trans-retinal released after light exposure. These agents have been proposed as potential pharmacotherapies for AMD. One inhibitor of the RPE-dependent visual cycle, called emixustat, is currently being evaluated for its ability to slow AMD progression in a phase 3 clinical trial. RPE65 inhibitors hol great promise as effective agents for the treatment of dry AMD, but they also have undesirable side effects on cone photoreceptors and color vision. The origin of these troublesome ocular side effects remains to be elucidated, but they could potentially arise from off-target interaction with components of the Müller cell-dependent visual cycle. Alternatively, because of the abundance of cones over rods in the human macula where AMD pathology occurs it is also conceivable that partial inhibition of the Müller cell-dependent visual cycle could be therapeutically beneficial for AMD treatment. Recently, a candidate retinoid isomerase of the Müller cell-based pathway, called sphingolipid-Δ4-desaturase (DES1), was identified in a high-throughput expression screen. This Müller cell-localized enzyme, originally characterized as a dihydroceramide desaturase, was shown to catalyze formation of cis retinol isomers from all-trans-retinol in vitro and partially restore retinal function when overexpressed in Rpe65-/- mice. However, the physiological contribution of this enzyme to cone cell function has not yet been studied. This proposal aims to 1) evaluate the physiological contribution of DES1 to cone-mediated vision using knockout mouse models and 2) capitalize on recently acquired high-resolution structural information on the binding mode of emixustat to the RPE65 active site to design novel visual cycle inhibitors with high selectively towards RPE65 and improved toxicity profiles. Retinal structure and function in Des1 conditional knockout mice will be assessed by high resolution imaging and electroretinography. Structure-guided drug design will be used to generate highly selective RPE65 inhibitors for potential use in the treatment of dry AMD.