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

 描述(由申请人提供)： 年龄相关性黄斑变性(AMD)是一种老年致弱致盲疾病，在退伍军人中的患病率正在上升。萎缩性(干性)AMD是这种疾病最常见的形式，目前还没有非常有效的治疗方法。现在人们认识到，维生素A的代谢物，全反式视网膜，可能在AMD的发病机制中起着关键作用。全反式视网膜是光感受器细胞受光激活后从视觉色素(视杆细胞和视锥细胞全视蛋白)中释放出来的。为了维持视力，11-顺式视网膜必须持续地提供给感光细胞，以维持足够水平的光敏全视蛋白。视杆和视锥感光器从被称为视觉周期的代谢途径中接收11顺式视网膜，该途径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依赖于Müler细胞的视觉周期，为视锥感光细胞提供额外的视觉色团供应，足以在白天的光照条件下工作。通过靶向经典的视觉周期异构酶RPE65来抑制11-顺式视网膜产生的药物，通过减少光暴露后释放的全反式视网膜的量来保护视网膜免受光诱导的损伤。这些药物已被认为是治疗AMD的潜在药物。一种RPE依赖的视觉周期抑制剂，名为ymxustat，目前正在进行3期临床试验，以评估其减缓AMD进展的能力。RPE65抑制剂有望成为治疗干性AMD的有效药物，但它们对视锥细胞光感受器和色觉也有不良的副作用。这些麻烦的眼部副作用的来源仍有待阐明，但它们可能是由靶外相互作用引起的。 与米勒细胞依赖的视觉周期的组成部分有关。或者，由于发生AMD病理的人类黄斑内视锥细胞上有丰富的视杆细胞，因此也可以想象部分抑制Müller细胞依赖的视觉周期对于AMD的治疗是有益的。最近，在高通量表达筛选中发现了Müler细胞途径的一个候选视黄酸异构酶，称为鞘磷脂-Δ4-去饱和酶。这种米勒细胞定位的酶，最初的特征是二氢神经酰胺去饱和酶，被证明在体外催化全反式视黄醇形成顺式视黄醇异构体，并在RPE65-/-小鼠中过表达时部分恢复视网膜功能。然而，该酶对锥体细胞功能的生理贡献尚未被研究。该建议旨在1)利用基因敲除小鼠模型评估DES1对视锥介导的视觉的生理贡献；2)利用最近获得的有关米昔司特与RPE65活性部位结合模式的高分辨率结构信息，设计出对RPE65具有高选择性和改善毒性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DES1条件性基因敲除小鼠的视网膜结构和功能。结构导向的药物设计将被用来产生高选择性的RPE65抑制剂，用于干性AMD的治疗。

 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.