遗传性耳聋致病机理和药物新靶点的研究

Age-related hearing loss (AHL) involves mutations of the cadherin 23 (Cdh23) gene in the cochlear hair cells of humans and mouse models. We have reported a novel recessive mutation erlong (erl is the symbol for the mutation; CDH23<erl> is the symbol for the mutated protein) that is characterized by progressive hearing loss beginning from postnatal day 27 (P27). The short interval from normal hearing to deafness (P27–P90) and quick onset of hearing loss at high frequencies make this model ideal for evaluating otoprotective drugs. It is reported that some early-onset hearing loss patients had Cdh23 mutations with similar phenotypes as the Cdh23<erl/erl> mutants. Hearing loss was associated with the induction of hair cell apoptosis, but what is unknown is why the Cdh23 mutations induced apoptosis. This project aims to test the hypothesis that the erl mutations induce CDH23erl protein accumulated in the endoplasmic reticulum (ER) area, which then causes Unfolded Protein Response (UPR) and apoptosis. We will investigate UPR signaling in the pathogenesis of hearing loss. Specifically, this project aims to: (1) Test the hypothesis that the CDH23<erl> protein is accumulated in the ER area. (2) Test the hypothesis that the ER accumulation of CDH23<erl> protein in the ER causes UPR and ER stress that leads to apoptosis through the eIF2α–CHOP pathway. This proposal shifts the paradigm of research on auditory hair cell degeneration and regeneration by showing that a mutant protein induces ER stress, thereby leading to hair cell loss. These studies will provide new targets to explore protective therapies for age-related hearing loss.

耳聋与耳蜗Cdh23基因突变有关。我们新发现的小鼠隐性突变，erlong（erl，突变基因；CDH23erl，突变蛋白），从正常听力到全聋间隔时间短，该模型适用于筛选和验证听力保护药物。据报道，一些耳聋患者具有的Cdh23突变与Cdh23erl/erl突变有类似的表型。听力损失与毛细胞的凋亡有关。但是Cdh23基因突变为何导致凋亡？本研究将测试这一假设：erl突变导致CDH23erl蛋白在内质网（ER）滞留，从而诱导未折叠蛋白反应（UPR），UPR信号可能诱导细胞凋亡。实验目的：测试假设（1）CDH23erl蛋白在ER内积累。（2）ER累积的CDH23erl蛋白引起UPR和内质网应激（ER stress），通过eIF2α-CHOP途径导致细胞凋亡。本项研究提供了一个新思路，将转变听觉毛细胞退化和再生的研究方向，表明突变蛋白诱发ER stress导致毛细胞丢失，并探索保护听力的治疗新靶点。

听力损失作为最常见的感觉障碍性疾病之一，影响着全球约 3.6 亿人的生活质量，其中75岁以上的老年人约有一半存在听力损失。造成听力损失的很大一部分原因是由于内耳毛细胞的损伤，而对于哺乳动物来说，内耳毛细胞的不可再生，使得该疾病无法达到良好的治愈效果。本课题组利用Cdh23 erl/erl （erl小鼠）和其他渐进性耳聋模型小鼠，完成了有关渐进性耳聋或年龄相关性耳聋的发病机制及多种听力保护药物筛选工作的研究。1）对erl小鼠听力损失发生机制进行研究，证明内质网应激（ER stress）细胞信号通路参与erl小鼠模型内耳毛细胞凋亡从而导致听力损失的假说，阐明ER stress细胞信号通路在毛细胞凋亡通路中的发生机制。2）利用erl小鼠模型和年龄相关性耳聋模型DBA/2J小鼠，评价了不同药物的听力保护作用效果，包括选择性eIF2去磷酸化抑制剂（Salubrinal）、四苯基丁酸（4-Phenylbutyric acid，4-PBA）和鼠神经生长因子（mNGF），阐明分子作用机制，为临床治疗渐进性耳聋提供了新的研究方向。3）利用年龄相关性耳聋模型C57BL/6J小鼠的耳蜗组织样本进行表达谱测序，发现参与老年性耳聋发生发展的非编码RNA及其发病机制。4）在BXD重组近交系（recombinant inbred，RI）小鼠中发现针对老年性耳聋的听力保护基因在发挥作用。本项目主要阐明了在erl小鼠模型中，ER stress细胞信号通路与年龄相关性听力损失的致病机制相关，并发现了几种有效保护听力损失的药物，对临床用药应用指导具有巨大的参考价值。已发表并标注该项目资助的SCI论文共有24篇，其中作为通讯作者共发表12篇，作为共同作者发表12篇，并申请专利1项。