MECHANISMS OF ADAPTATION IN MAMMALIAN CONES

描述（申请人提供）：视锥细胞光感受器在明亮的光线条件下发挥作用，对色彩感知和高时空分辨率的视觉至关重要。值得注意的是，与杆状细胞不同，锥状细胞即使在稳定的明亮光线下也能保持功能，并且适应黑暗的速度很快。这两种特性都需要发色团的快速循环来再生视锥色素。生化研究和典型色素上皮发色团循环途径的不足表明，可能存在位于视网膜中独立于色素上皮的第二种，锥体特异性发色团途径。该通路在生理条件下的功能、在光感受器生理中的作用及其调控尚未被研究。我们建议使用小鼠光感受器的单细胞和全视网膜记录来表征这种新视觉周期的生理功能。具体来说，我们将确定哺乳动物视网膜独立于色素上皮促进视锥细胞色素再生和暗适应的能力。我们将建立哺乳动物视网膜视觉周期在背景适应过程中扩大视锥细胞动态范围和在黑暗适应过程中加速视锥细胞敏感性恢复中的作用。我们将确定哺乳动物视网膜视觉周期的特异性是否基于视锥细胞而非视杆细胞氧化11-顺式视黄醇的能力，11-顺式视黄醇在视网膜内循环，并将其用于色素再生。我们将使用现有的转基因小鼠和药理学工具来表征该途径的关键步骤以及视网膜中表达的发色团结合蛋白对其的调节。总的来说，本提案中概述的实验试图建立使哺乳动物视锥细胞在快速变化的光线条件下发挥作用的机制，这是调节白天视觉的光感受器的基本属性。除了促进对视锥细胞生物学的理解外，我们对哺乳动物视网膜视觉周期的研究具有潜在的临床意义。本研究中研究的发色团结合蛋白突变与多种视觉障碍有关，包括Stargardt病、锥杆营养不良和黄斑变性。目前还没有针对这些疾病的治疗方法。我们的实验将为理解视网膜视觉周期中的特定缺陷如何产生锥体相关的视网膜疾病，以及开发针对锥体功能的新疗法奠定基础。公共卫生相关性：本提案中概述的实验旨在建立使哺乳动物视锥细胞在明亮光线下起作用的机制，这是调节白天视觉的光感受器的基本特性。这些研究将有助于我们了解正常和病理条件下调节哺乳动物视锥细胞功能的机制。

DESCRIPTION (provided by applicant): Cone photoreceptors function under bright light conditions and are essential for color perception and vision with high temporal and spatial resolution. Remarkably, unlike rods, cones remain functional even in steady bright light and dark adapt rapidly. Both of these properties require rapid recycling of chromophore for regeneration of cone visual pigment. Biochemical studies and shortcomings of the canonical pigment epithelium pathway for chromophore recycling indicate the possible existence of a second, cone- specific chromophore pathway located in the retina and independent of the pigment epithelium. The function of such a pathway under physiological conditions, its role in photoreceptor physiology, and its regulation have not been investigated. We propose to use single-cell and whole retina recordings from mouse photoreceptors to characterize the physiological function of this novel visual cycle. Specifically, we will determine the ability of mammalian retina to promote pigment regeneration and dark adaptation in cones independently of the pigment epithelium. We will establish the role of the mammalian retina visual cycle in extending the dynamic range of cones during background adaptation and in accelerating the recovery of cone sensitivity during dark adaptation. We will determine whether the specificity of the mammalian retina visual cycle is based on the ability of cones, and not rods, to oxidize 11-cis retinol, recycled within the retina, into 11-cis retinal and use it for pigment regeneration. We will use available genetically modified mice and pharmacological tools to characterize key steps in the pathway and their modulation by chromophore-binding proteins expressed in the retina. Collectively, the experiments outlined in this proposal seek to establish the mechanisms that enable mammalian cones to function in rapidly varying light conditions, an essential property for the photoreceptors that mediate daytime vision. In addition to advancing the understanding of cone cell biology, our studies of the mammalian retina visual cycle have potential clinical implications. Mutations in the chromophore-binding proteins investigated in this study have been associated with multiple visual disorders including Stargardt disease, cone-rod dystrophy, and macular degeneration. No treatments currently exist for these disorders. Our experiments will lay the foundation for understanding how specific defects in the retina visual cycle produce cone-related retinal disorders, as well as for the development of new treatments targeting specifically the function of cones. PUBLIC HEALTH RELEVANCE: The experiments outlined in this proposal seek to establish the mechanisms that enable mammalian cones to function in bright light, an essential property for the photoreceptors that mediate daytime vision. These studies will help us understand the mechanisms that regulate mammalian cone function under normal and pathological conditions.