Light Activation of Retinal Insulin Receptor Signaling

描述(申请人提供)：我们实验室在过去十年的研究发现，在杆状感光细胞中存在一种新的光依赖型胰岛素受体(IR)信号通路。我们发现IR的激活对视杆细胞的存活具有重要的功能，因为它在视杆细胞中的缺失导致了神经保护性生存信号的丧失。这个新的途径使用生长因子受体结合蛋白(Grb14)，IR的上游调节因子，并且需要光漂白视紫红质来膜靶向。Grb14保护杆状感光器的光依赖IR激活，使其免受PTP1B去磷酸化的影响。光激活的IR随后与细胞生存因子磷脂酰肌醇3-激酶(PI3K)相关，从而调节下游的生存途径。这些研究表明，视紫红质光激发可能触发了经典转导蛋白激活以外的信号事件。最近，由于全身应用胰岛素延迟了视锥细胞光感受器的死亡，提示IR信号通路对于视锥细胞光感受器存活具有重要意义。我们发现，胰岛素样生长因子-1受体(IGF-1R)也激活了光应激下杆状体内的PI3K和Akt生存通路。我们的假设是IR/IGF-1R信号通路对视杆细胞和视锥细胞的存活和维持结构和功能具有重要作用。我们项目的长期目标是更好地了解为视杆细胞和视锥感光细胞提供神经保护的细胞内信号通路。本研究的具体目的是探讨IR和IGF-1R在光感受器结构和功能调节中的作用。为此，我们将确定Grb14激活IR的机制，并确定IR和IGF-1R在视杆细胞和视锥细胞中的功能作用。我们将利用遗传、分子和生化方法的组合来解决我们的特定目标。这些研究结果将有助于更好地理解IR和IGF-1R信号在光感受器结构、功能和存活中的作用。 与公共健康相关：胰岛素受体(IR)和胰岛素信号蛋白广泛分布于中枢神经系统(CNS)。中枢神经系统IR信号的失调与阿尔茨海默病和帕金森病等神经退行性疾病的发病机制有关。在视网膜视杆中，IR信号具有神经保护作用，最近有研究表明，胰岛素延缓了视网膜色素变性动物模型中视锥感光细胞的死亡。除IR外，胰岛素样生长因子-1受体(IGF-1R)也在视杆细胞和视锥细胞中表达，但其功能作用尚不清楚。我们的研究表明，蛋白酪氨酸磷酸酶1B(PTP1B)负向调节IR的神经保护性生存信号。我们的研究还表明，视紫红质光漂白缺陷和视紫红质基因突变增强了PTP1B的活性，这种激活的活性可能下调IR生存信号。控制PTP1B活性，激活IR信号，对视杆细胞和视锥细胞都有持续的神经保护作用。我们针对PTP1B的新的创新方法将促进我们工作的未来翻译应用，目标是将我们的发现应用于人类视网膜变性的临床护理。这项拨款申请中提出的研究将有助于了解IR和IGF-1R在光感受器结构、功能和生存中的功能作用。

DESCRIPTION (provided by applicant): Studies from our laboratory over the past decade have found the existence of a novel light-dependent insulin receptor (IR) signaling pathway in rod photoreceptors. We have discovered that IR activation is functionally important for rod survival, since its deletion in rods resulted in the loss of neuroprotective survival signaling. This novel pathway uses growth factor receptor bound protein (Grb14), an upstream regulator of IR, and requires photobleaching of rhodopsin for membrane targeting. Grb14 protects light-dependent IR activation in rod photoreceptors against dephosphorylation by PTP1B. Light-activated IR is subsequently associated with phosphoinositide 3-kinase (PI3K), a cell survival factor, and thus regulates the downstream survival pathway. These studies suggest that rhodopsin photoexcitation may trigger signaling events alternative to the classical transducin activation. Recently, it was suggested that the IR signaling pathway is important for cone photoreceptor survival in retinitis pigmentosa (RP) models since systemic administration of insulin delays the death of cone photoreceptors. We found that insulin-like growth factor-1 receptor (IGF-1R) also activates PI3K and Akt survival pathway in rods under light stress. It is our hypothesis that IR/IGF-1R signaling pathways are important for survival and maintenance of rod and cone photoreceptor structure and function. The long-term goal of our project is to gain a greater understanding of the intracellular signaling pathways that provide neuroprotection to both rod and cone photoreceptor cells. The specific objective is to investigate the role of IR and IGF-1R in the regulation of photoreceptor structure and function. To this end, we will determine the mechanism by which Grb14 activates the IR and determine the functional roles of IR and IGF-1R in both rod and cone photoreceptor cells. We will utilize a combination of genetic, molecular, and biochemical approaches to address our specific aims. Results from these studies will lead to a better understanding the roles of IR and IGF-1R signaling in photoreceptor structure, function and survival. PUBLIC HEALTH RELEVANCE: Insulin receptors (IR) and insulin signaling proteins are widely distributed throughout the central nervous system (CNS). Disregulation of IR signaling in the CNS has been linked to the pathogenesis of neurodegenerative disorders such as Alzheimer's and Parkinson's disease. In retinal rods, IR signaling is neuroprotective, and recently it was shown that insulin delays the death of cone photoreceptor in retinitis pigmentosa animal models. Besides IR, insulin-like growth factor-1 receptors (IGF-1R) are also expressed in both rods and cones; however, their functional role has not been elucidated. Our studies suggest that protein tyrosine phosphatase 1B (PTP1B) negatively regulated neuroprotective survival signaling of the IR. Our studies also suggest that a defect in the photobleaching of rhodopsin and mutations in rhodopsin gene enhances the activity of PTP1B and this activated activity could down regulate the IR survival signaling. Controlling the PTP1B activity and activating the IR signaling would provide sustained neuroprotection to both rods and cones. Our new and innovative approaches to target PTP1B will facilitate future translational application of our work, with the goal of applying our findings to the clinical care of human retinal degenerations. Studies proposed in this grant application would help to understand the functional roles of IR and IGF-1R in photoreceptor structure, function and survival.