Role of the Unfolded Protein Response in Photoreceptor Degeneration

项目摘要 分泌途径的客户蛋白在内质网（ER）中折叠成它们的天然形状， 分子伴侣和其他ER蛋白修饰酶催化的反应。在高分泌需求下， 这些活动被淹没，导致未折叠的蛋白质积累。如果不纠正，这种“ER应激” 增加了细胞退化和死亡的风险。光感受器，视网膜上的特殊神经元 负责光传导，具有任何人类细胞中最高的分泌负荷之一，使它们成为 特别容易受到内质网应激的影响。最近的证据表明致病性内质网应激是一种潜在的 色素性视网膜炎（RP）的原因，这是一种致盲性疾病，其特征是光感受器的逐渐丧失， 特别是在由于阻止其正确折叠的视紫红质突变的情况下。 未折叠蛋白在内质网中的积累触发了称为未折叠蛋白反应的信号通路 （普遍定期审议）。在可补救水平的ER应激下，适应性UPR（A-UPR）激活转录和表达。 翻译的变化来恢复体内平衡。然而，在不可补救的高ER应激下，这些适应性 措施失败，信号通路反而触发程序性细胞死亡-称为终端 普遍定期审议（T-UPR）。我们发现ER跨膜蛋白IRE 1 β，一个双功能的 激酶/核糖核酸内切酶（RNase）将A-UPR转化为T-UPR。在可矫正的ER应力期间，IRE 1 瞬时反式自磷酸化，导致其RNase通过A-UPR的移码剪接触发A-UPR。 编码转录因子XBP 1的mRNA。但在高/慢性ER应激下，IRE 1 β的激酶变得 过度磷酸化，导致RNA酶过度活化，导致ER定位的 mRNA和T-UPR事件包括：（1）分化细胞身份的丧失，（2）局部无菌炎症，和（3） 通过焦亡和凋亡的程序性细胞死亡。 我们假设IRE 1 β诱导的从A-UPR到T-UPR的转换有助于ER应激诱导的细胞凋亡。 光感受器丧失我们对R 01的总体目标是三个方面：（1）确定IRE 1 β信号转导在正常人中的作用。 光感受器健康;（2）阐明IRE 1通过其将A- 光感受器中的UPR转化为T-UPR;以及（3）使用我们最近开发的靶向光感受器中的IRE 1 β 激酶抑制剂，用于长期预防视网膜变性。我们的研究项目，将由三个 具有互补和协同技能的实验室以及经验丰富的合作者，承诺提供 对UPR在光感受器健康和退化中的作用的有力的机械见解， 确定UPR是否可以成功地被药物治疗以防止RP中的感光细胞损失。

PROJECT SUMMARY Client proteins of the secretory pathway fold to their native shapes in the endoplasmic reticulum (ER) through reactions catalyzed by chaperones and other ER protein-modifying enzymes. Under high secretory demand, these activities are overwhelmed, causing unfolded proteins to accumulate. If uncorrected, such “ER stress” increases the risk of cell degeneration and death. Photoreceptors, specialized neurons in the retina responsible for phototransduction, have one of the highest secretory burdens of any human cell, making them particularly susceptible to ER stress. Recent evidence has implicated pathogenic ER stress as a potential cause of retinitis pigmentosa (RP), a blinding disease marked by the progressive loss of photoreceptors, especially in cases due to mutations in rhodopsin that prevents its proper folding. Accumulation of unfolded proteins in the ER triggers signaling pathways called the unfolded protein response (UPR). Under remediable levels of ER stress, the adaptive UPR (A-UPR) activates transcriptional and translational changes that restore homeostasis. However, under irremediably high ER stress, these adaptive measures fail and the signaling pathways instead trigger programmed cell death—referred to as the terminal UPR (T-UPR). We discovered that the ER transmembrane protein IRE1, a bifunctional kinase/endoribonuclease (RNase), converts an A-UPR to a T-UPR. During rectifiable ER stress, IRE1 transiently trans-autophosphorylates, causing its RNase to trigger the A-UPR through frame-shift splicing of the mRNA encoding XBP1 transcription factor. But under high/chronic ER stress, IRE1's kinase becomes hyperphosphorylated, causing RNase hyperactivation that leads to massive degradation of ER-localized mRNA and T-UPR events including: (1) loss of differentiated cell identity, (2) local sterile inflammation, and (3) programmed cell death through pyroptosis and apoptosis. We hypothesize that an IRE1-induced switch from an A-UPR to a T-UPR contributes to ER stress-induced photoreceptor loss. Our overall goal for this R01 is threefold: (1) define the role of IRE1 signaling on normal photoreceptor health; (2) elucidate key underlying molecular mechanisms through which IRE1 converts an A- UPR to a T-UPR in photoreceptors; and (3) target IRE1 in photoreceptors using our recently developed kinase inhibitors for long-term prevention of retinal degeneration. Our research project, to be driven by three labs with complementary and synergistic skills as well as experienced collaborators, promises to provide powerful mechanistic insights into the role of the UPR in photoreceptor health and degeneration, and to establish whether the UPR can be successfully drugged to prevent photoreceptor loss in RP.