Role of the Unfolded Protein Response in Photoreceptor Degeneration

项目总结 分泌途径的客户蛋白在内质网(ER)中折叠成其自然形状 由伴侣和其他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。如果不加以纠正，这种“内质网压力” 增加细胞退化和死亡的风险。光感受器，视网膜中的特殊神经元 负责光传导，具有任何人类细胞中最高的分泌负担，使它们 特别容易受到内质网压力的影响。最近的证据表明，致病性内质网应激是一种潜在的 视网膜色素变性(RP)的原因，这是一种以光感受器进行性丧失为特征的致盲疾病， 特别是在由于视紫红质突变而阻止其正确折叠的情况下。 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)。在可补救的内质网应激水平下，适应性UPR(A-UPR)激活转录和 恢复动态平衡的翻译变化。然而，在不可挽回的高内质网压力下，这些适应性 措施失败，信号通路反而触发程序性细胞死亡--称为终末 UPR(T-UPR)。我们发现内质网跨膜蛋白IRE1，一个双功能的 激酶/核糖核酸内切酶(RNase)，将A-UPR转化为T-UPR。在可纠正的内质网应激期间，IRE1 瞬时反式自动磷酸化，导致其核糖核酸酶通过帧移位剪接触发A-UPR 编码XBP1转录因子的mRNA。但在高/慢性内质网应激下，IRE1的S激酶成为 过度磷酸化，导致核糖核酸酶过度激活，导致ER定位的大量降解 MRNA和T-UPR事件包括：(1)分化细胞特性的丧失，(2)局部不孕症炎症，和(3) 通过上睑下垂和细胞凋亡的程序性细胞死亡。 我们假设IRE1诱导的从A-UPR到T-UPR的转换参与了内质网应激诱导 光感受器丢失。我们对R01的总体目标有三个：(1)确定IRE1信号在正常情况下的作用 光感受器健康；(2)阐明IRE1转化A- 光感受器中的T-UPR；以及(3)利用我们最近开发的靶向光感受器中的IRE1 长期预防视网膜变性的激酶抑制剂。我们的研究项目，将由三个人推动 具有互补和协同能力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强大的机械论见解，以及 确定是否可以成功地给UPR下药以防止RP的光感受器丢失。

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.