Mechanisms of Sensory Hair Cell Death and Survival

描述（由申请人提供）：人类听力和平衡障碍通常是由于感觉毛细胞的死亡。这些细胞对噪音暴露、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。本研究计划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且高度保守的反应，在许多系统中可以显著抑制细胞凋亡。我们的数据表明，Hsp70诱导是内耳中一个关键的应激反应，可以促进暴露于主要应激源的毛细胞的存活。Hsp70对毛细胞死亡的保护作用的机制尚不清楚。我们的数据表明，Hsp70的诱导主要发生在支持细胞中，而对毛细胞的诱导很少，这表明支持细胞介导了Hsp70对毛细胞死亡的保护作用。我们假设Hsp70由支持细胞分泌，并由毛细胞内化，在毛细胞中，它既是分子伴侣，又是凋亡信号传导的抑制剂。我们提出了四组实验来验证这一假设：目的1是确定支持细胞Hsp70对于Hsp70对毛细胞死亡的保护作用是否必要和充分。目的2是确定Hsp70的抗凋亡和伴侣活性在介导其对毛细胞死亡的保护作用中的作用。目的3确定支持细胞Hsp70的保护作用是否通过支持细胞分泌Hsp70和毛细胞内化介导。目的4是确定细胞间信号，介导毛细胞支持细胞通讯，以应对压力。从临床角度来看，清楚地了解毛细胞对耳毒性药物的死亡和存活机制，对于合理设计旨在预防由耳毒性药物引起的听力损失和平衡障碍的联合疗法至关重要。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，因此它代表了这两类耳毒性药物的潜在治疗靶点。从基础科学的角度出发，本项目研究了毛细胞在应激条件下促生存和促死亡信号相互作用的细胞生物学。此外，本研究项目探讨毛细胞和支持细胞之间相互作用的基本性质。

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.