Desensitization of Cone Visual Signaling Pathways

描述(申请人提供)：脊椎动物视杆和视锥中的光传导由一系列精确计时的事件组成，这些事件是光感受器在广泛的光强度范围内发挥作用所必需的。虽然圆锥体在暗光下工作，在强光下很容易饱和，但圆锥体恢复得更快，能够适应更强的光。第二信使，如cGMP和Ca~(2+)，已被认为在杆状和锥体的光转导级联和适应中发挥重要作用。另一种信使，cAMP，在光感受器中以依赖于光和昼夜节律的方式进行调节，可能对适应也很重要。例如，cAMP合成的变化与视杆细胞和视锥细胞的适应缺陷有关，这些缺陷改变了视网膜内部的信号。有趣的是，cAMP的下游靶标PKA对感光细胞蛋白的磷酸化还没有得到很好的研究。我们已经确定，视网膜特异的G蛋白偶联受体激酶GRK1和GRK7在视杆细胞和视锥细胞的恢复和适应中发挥关键作用，它们都是体外PKA的底物。我们还表明，在体外，PKA的磷酸化降低了这些激酶对其底物Opsins的磷酸化能力。在这个提议中，我们提供了新的证据，证明这两个激酶在体内都被PKA磷酸化，并且磷酸化受到光的调节。我们建议以小鼠为模型，研究PKA磷酸化GRK1对其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调节光感受器细胞特异性GRK的新机制，该机制可能影响光转导的多个方面。 与公共健康相关：视杆细胞和视锥细胞是脊椎动物视网膜中的细胞，负责调节我们对光的视觉反应。视杆细胞负责弱光视觉，而视锥细胞在强光下起作用，并负责颜色视觉。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敏感性方面，视杆细胞和视锥细胞之间存在着显著的差异。这项提议旨在分析GRK1的作用，GRK1是一种在视杆细胞和视锥细胞的视觉信号中都很重要的激酶，它与静止性夜盲等疾病有关。这些研究有望更好地理解视网膜中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.