MECHANISMS OF ADAPTATION IN MAMMALIAN CONES

描述(申请人提供)：视锥细胞只占人类光感受器的5%，但对我们的白天视力至关重要。AMD是最突出的视锥视力障碍，对老年人有重大影响，视锥丢失会导致法律上的失明。这对美国的 哺乳动物视锥细胞作为白天光感受器的功能，即它们在被光破坏后迅速再生其视觉色素。这是通过两条途径实现的。典型的视网膜色素上皮(RPE)视觉周期为视杆细胞和视锥细胞提供11顺式视网膜生色团。相比之下，新的视网膜视觉周期依赖于Muller细胞提供11顺式视黄醇，只有视锥细胞通过一种未知的脱氢酶将其氧化为11顺式视网膜后才能利用这种视黄醇。正如我们在过去五年中证明的那样，视网膜视觉周期通过将视锥细胞的功能范围扩大到明亮的光线并通过驱动其快速的暗适应在白天视觉中发挥关键作用。哺乳动物视网膜中视锥细胞的稀少使得分子和生化视锥特异性研究极具挑战性。因此，使视锥细胞而不是视杆细胞能够使用视网膜视觉周期的分子机制尚不清楚。突变的RD7小鼠缺乏视杆转录因子Nr2e3，其视杆除了表达视锥基因外，还表达视锥基因的一个子集，这为我们提供了一个独特的机会来确定控制视网膜视觉周期的分子机制。这一提议的中心假设是，光感受器的分子特性控制着它们使用视网膜视觉周期的能力。具体地说，我们将证明在RD7视杆中视锥基因的子集的表达足以使它们能够使用11-顺式视黄醇进行色素再生和进入视网膜视觉周期。RD7视黄醇脱氢酶10(RDH10)的表达分析使我们能够确定视黄醇脱氢酶10(RDH10)是视锥细胞特异的基因，可能是视网膜视觉周期中氧化11顺式视黄醇的关键酶。我们将使用功能突变小鼠的丧失和获得来证明RDH10在视网膜视觉周期中的作用。总而言之，这里概述的实验将确定使视锥细胞进入视网膜视觉周期并快速再生其视觉色素的分子机制，这一特性对于白天视锥细胞在明亮和快速变化的光线条件下调节的视觉至关重要。 它们还将为治疗由RPE视觉周期错误引起的视力障碍提供新的治疗工具。

DESCRIPTION (provided by applicant): Cones represent only 5% of photoreceptors in humans, but are critical for our daytime vision. AMD, the most prominent cone vision disorder, has a major impact on the elderly, and cone loss results in legal blindness. It is critical for the function of mammalian cones as daytime photoreceptors that they regenerate their visual pigment rapidly following its destruction by light. This is made possible by two pathways. The canonical retinal pigment epithelium (RPE) visual cycle provides 11-cis retinal chromophore to both rods and cones. In contrast, the novel retina visual cycle relies on Muller cells to provide 11- cis retinol, which can be utilized only by cones after they oxidize it to 11-cis retinal by an unknown dehydrogenase. As we demonstrated over the past five years, the retina visual cycle plays a crucial role in daytime vision by extending the functional range of cones to bright light and by driving their rapid dark adaptation. The scarcity of cones in the mammalian retina makes molecular and biochemical cone-specific studies extremely challenging. As a result, the molecular mechanism that enables cones, but not rods, to use the retina visual cycle is not understood. The mutant rd7 mouse, which lacks the rod transcription factor Nr2e3 and has rods that in addition to its rod genes express a subset of cone genes, provides us with a unique opportunity to identify the molecular mechanism controlling access to the retina visual cycle. The central hypothesis of this proposal is that the molecular properties of photoreceptors control their ability to use the retina visual cycle. Specifically, we will demonstrate that the expressionof a subset of cone genes in the rd7 rods is sufficient to enable them to use 11-cis retinol for pigment regeneration and to access the retina visual cycle. Expression analysis of rd7 rods has allowed us to identify retinol dehydrogenase 10 (RDH10) as a cone-specific gene and the likely key enzyme that oxidizes 11-cis retinol as part of the retina visual cycle. We will use loss and gain of function mutant mice to demonstrate the role of RDH10 in the retina visual cycle. Collectively, the experiments outlined here will identify the molecular mechanism that enables cones to access the retina visual cycle and regenerate rapidly their visual pigment, a property that is critical for daytime, cone-mediated vision in bright and rapidly changing light conditions. They will also provide new therapeutic tools for the treatment of visual disorders caused by faulty RPE visual cycle.