Mechanisms of Sensory Hair Cell Death and Survival

描述(申请人提供)：人类的听力和平衡障碍通常是由于感觉毛细胞的死亡造成的。这些细胞对噪声暴露、衰老和一些治疗药物(包括氨基糖苷类抗生素和抗肿瘤药物顺铂)引起的死亡很敏感。这个研究项目的目标是了解毛细胞死亡和存活的分子机制。详细了解这些细胞机制对于设计旨在预防听力损失的治疗方法至关重要。诱导热休克蛋白(HSPs)响应细胞应激是一种普遍存在的高度保守的反应，在许多系统中都能显著抑制细胞凋亡。我们的数据表明，Hsp70的诱导是内耳的一种关键的应激反应，可以促进暴露在主要应激源下的毛细胞的存活。热休克蛋白70保护毛细胞死亡的机制(S)尚不清楚。我们的数据表明，Hsp70的诱导主要发生在支持细胞，毛细胞中的诱导很少，提示支持细胞介导了Hsp70对毛细胞死亡的保护作用。我们假设Hsp70由支持细胞分泌，并被毛细胞内化，在毛细胞中，它既是分子伴侣，又是凋亡信号的抑制因子。提出了四组实验来验证这一假设：目标1是确定支持细胞Hsp70是否对于Hsp70保护毛细胞死亡的作用是必要的和充分的。目的2确定Hsp70的抗凋亡和伴侣活性在介导其抗毛细胞死亡保护作用中的作用。目的3确定支持细胞热休克蛋白70的保护作用是否由支持细胞分泌热休克蛋白70和毛细胞内化热休克蛋白70介导。目标4是确定在应激反应中介导毛细胞支持细胞通讯的细胞间信号。从临床的角度来看，清楚地了解耳毒性药物引起毛细胞死亡和存活的机制，对于合理设计旨在预防听力损失和由它们引起的平衡障碍的联合治疗至关重要。我们的数据表明，HSP70对氨基糖苷类和顺铂引起的毛细胞死亡具有保护作用，因此它是这两类耳毒性药物的潜在治疗靶点。从基础科学的角度，这个项目解决了压力下毛细胞中支持生存和支持死亡信号之间相互作用的细胞生物学。此外，这项研究项目还考察了毛细胞和支持细胞之间相互作用的基本性质。 公共卫生相关性：这个项目的重点是暴露在治疗药物中导致的听力损失，这种药物每年至少损害50万美国人的内耳。该项目旨在研究暴露于这些药物的内耳感觉细胞死亡和存活的潜在机制。了解这些机制将指导旨在预防耳毒性药物引起的听力损失的治疗方法的开发。

DESCRIPTION (provided by applicant): Human hearing and balance impairments are often due to death of sensory hair cells. These cells are sensitive to death induced by noise exposure, aging, and some therapeutic drugs, including the aminoglycoside antibiotics and the antineoplastic agent cisplatin. The goal of this research program is to understand the molecular mechanisms underlying hair cell death and survival. Understanding these cellular mechanisms in detail will be critical for the design of therapies aimed at preventing hearing loss. Induction of heat shock proteins (Hsps) in response to cellular stress is a ubiquitous and highly-conserved response that can significantly inhibit apoptosis in many systems. Our data indicate that Hsp70 induction is a critical stress response in the inner ear that can promote survival of hair cells exposed to major stressors. The mechanism(s) underlying the protective effect of Hsp70 against hair cell death are not known. Our data indicate that Hsp70 induction occurs primarily in supporting cells with little induction in hair cells, suggesting that supporting cells mediate the protective effect of Hsp70 against hair cell death. We hypothesize that Hsp70 is secreted by supporting cells and internalized by hair cells, where it acts as both a molecular chaperone and an inhibitor of apoptotic signaling. Four groups of experiments are proposed to test this hypothesis: Aim 1 is to determine if supporting cell Hsp70 is necessary and sufficient for the protective effect of Hsp70 against hair cell death. Aim 2 is to determine the roles of the anti-apoptotic and chaperone activities of Hsp70 in mediating its protective effect against hair cell death. Aim 3 is to determine if the protective effect of supporting cell Hsp70 is mediated by secretion of Hsp70 by supporting cells and internalization by hair cells. Aim 4 is to determine the intercellular signals that mediate hair cell-supporting cell communication in response to stress. From a clinical perspective, a clear understanding of the mechanisms underlying hair cell death and survival in response to ototoxic drugs will be critical to the rational design of co-therapies aimed at preventing hearing loss and balance disturbances caused by them. Our data indicate that Hsp70 is protective against hair cell death caused by both aminoglycosides and cisplatin, and thus it represents a potential therapeutic target for both classes of ototoxic drugs. From a basic science perspective, this project addresses the cellular biology of interactions between pro-survival and pro-death signaling in hair cells under stress. In addition, this research program examines the fundamental nature of the interactions between hair cells and supporting cells. PUBLIC HEALTH RELEVANCE: This project is focused on hearing loss caused by exposure to therapeutic drugs that damage the inner ears of at least half a million Americans every year. This project is designed to examine the mechanisms underlying the death and survival of sensory cells in the inner ear exposed to these drugs. Understanding these mechanisms will guide the development of therapies aimed at preventing hearing loss caused by ototoxic drugs.