Desensitization of Cone Visual Signaling Pathways

描述（由申请人提供）：脊椎动物视杆细胞和视锥细胞中的光转导由一系列精确定时的事件组成，这些事件是光感受器在宽范围的光强度下发挥功能所必需的。视杆细胞在昏暗的光线下工作，并且很容易对明亮的光线做出饱和反应，而视锥细胞恢复得更快，能够适应更强烈的光线。第二信使，如cGMP和Ca2+，已经众所周知，在杆和锥细胞的光转导级联和适应中发挥重要作用。另一种第二信使cAMP在光感受器中以光依赖性和昼夜节律依赖性的方式进行调节，这可能对适应也很重要。例如，cAMP合成的变化与杆和锥中的适应缺陷有关，这些缺陷改变了对内层视网膜的信号传导。有趣的是，PKA（cAMP的下游靶点）对感光细胞蛋白的磷酸化作用尚未得到充分研究。我们已经确定，视网膜特异性G蛋白偶联受体激酶，GRK1和GRK7，这在恢复和适应杆和锥中发挥关键作用，都是PKA在体外的底物。我们还表明，PKA的磷酸化降低了这些激酶磷酸化其底物的能力，视蛋白在体外。在这个建议中，我们提供了新的证据，这两种激酶在体内被PKA磷酸化，磷酸化受光的调节。我们建议使用小鼠作为模型来研究GRK1磷酸化PKA在恢复和适应中的作用的功能后果。我们的数据介绍了一种新的机制，调节感光细胞特异性GRKs，可能会影响多方面的光转导。 公共卫生相关性：视杆细胞和视锥细胞是脊椎动物视网膜中调节我们对光的视觉反应的细胞。视杆细胞负责昏暗的光线视觉，而视锥细胞在明亮的光线下起作用，并负责颜色视觉。已经观察到视杆细胞和视锥细胞在光反应的敏感性和动力学以及它们对遗传和环境诱导的疾病过程的易感性方面的显著差异。这项提议旨在分析GRK1的贡献，GRK1是一种在视杆细胞和视锥细胞中的视觉信号传导中非常重要的激酶，并且与静止性夜盲症等疾病有关。这些研究有望更好地理解视网膜用于适应不断变化的光线条件的机制。

DESCRIPTION (provided by applicant): Phototransduction in vertebrate rods and cones consists of a series of precisely timed events that are necessary for photoreceptors to function under a broad range of light intensities. While rods operate under dim light and are easily saturated in response to bright light, cones recover more rapidly and are able to adapt to much more intense light. Second messengers, such as cGMP and Ca2+, are already well-known to play important roles in the phototransduction cascade and adaptation in rods and cones. Another second messenger, cAMP, which is regulated both in a light- and a circadian-dependent manner in photoreceptors, may also be important for adaptation. For example, changes in cAMP synthesis are associated with defects in adaptation in rods and cones that alter signaling to the inner retina. Interestingly, phosphorylation of photoreceptor cell proteins by PKA, the downstream target of cAMP, has not been well-studied. We have determined that the retina-specific G protein-coupled receptor kinases, GRK1 and GRK7, which play critical roles in recovery and adaptation in rods and cones, are both substrates for PKA in vitro. We have also shown that phosphorylation by PKA reduces the ability of these kinases to phosphorylate their substrates, the opsins in vitro. In this proposal, we provide new evidence that both kinases are phosphorylated by PKA in vivo and that phosphorylation is regulated by light. We propose to use the mouse as a model to study the functional consequences of GRK1 phosphorylation by PKA on its role in recovery and adaptation. Our data introduce a novel mechanism for the regulation of photoreceptor cell- specific GRKs that may influence multiple facets of phototransduction. PUBLIC HEALTH RELEVANCE: Rods and cones are the cells in the vertebrate retina that mediate our visual response to light. Rods are responsible for dim light vision, whereas cones function in bright light and are responsible for color vision. Significant differences between rods and cones have been observed in the sensitivity and kinetics of the light responses as well as their susceptibility to genetically and environmentally induced disease processes. This proposal is designed to analyze the contributions of GRK1, a kinase that is important in visual signaling in both rods and cones and that has been implicated in disease such as stationary night blindness. These studies are expected to lead to a better understanding of the mechanisms in the retina used to adapt to changing light conditions.