Murtha Kaitlin E, Sese Weintari D, Sleiman Kiah, Halpage Janith, Padyala Pravallika, Yang Yang, Hornak Aubrey J, Simmons Dwayne D
Department of Biology, Baylor University, Waco, TX, United States.
Front Neurol. 2024 Oct 23;15:1435749. doi: 10.3389/fneur.2024.1435749. eCollection 2024.
Cochlear outer hair cells (OHCs) play a fundamental role in the hearing sensitivity and frequency selectivity of mammalian hearing and are especially vulnerable to noise-induced damage. The OHCs depend on Ca homeostasis, which is a balance between Ca influx and extrusion, as well as Ca buffering by proteins and organelles. Alterations in OHC Ca homeostasis is not only an immediate response to noise, but also associated with impaired auditory function. However, there is little known about the contribution of Ca buffering proteins and organelles to the vulnerability of OHCs to noise. In this study, we used a knockout (KO) mouse model where oncomodulin (), the major Ca binding protein preferentially expressed in OHCs, is deleted. We show that KO mice were more susceptible to noise induced hearing loss compared to wildtype (WT) mice. Following noise exposure (106 dB SPL, 2 h), KO mice had higher threshold shifts and increased OHC loss and TUNEL staining, compared to age-matched WT mice. Mitochondrial morphology was significantly altered in KO OHCs compared to WT OHCs. Before noise exposure, KO OHCs showed decreased mitochondrial abundance, volume, and branching compared to WT OHCs, as measured by immunocytochemical staining of outer mitochondrial membrane protein, TOM20. Following noise exposure, mitochondrial proteins were barely visible in KO OHCs. Using a mammalian cell culture model of prolonged cytosolic Ca overload, we show that OCM has protective effects against changes in mitochondrial morphology and apoptosis. These experiments suggest that disruption of Ca buffering leads to an increase in noise vulnerability and mitochondrial-associated changes in OHCs.
耳蜗外毛细胞（OHCs）在哺乳动物听力的灵敏度和频率选择性方面发挥着重要作用，并且特别容易受到噪声诱导的损伤。OHCs依赖于钙稳态，即钙流入与排出之间的平衡，以及蛋白质和细胞器对钙的缓冲作用。OHCs钙稳态的改变不仅是对噪声的即时反应，还与听觉功能受损有关。然而，关于钙缓冲蛋白和细胞器对OHCs噪声易损性的作用，我们所知甚少。在本研究中，我们使用了一种基因敲除（KO）小鼠模型，其中在OHCs中优先表达的主要钙结合蛋白癌调蛋白（OCM）被敲除。我们发现，与野生型（WT）小鼠相比，OCM基因敲除小鼠更容易受到噪声诱导的听力损失。在噪声暴露（106 dB SPL，2小时）后，与年龄匹配的WT小鼠相比，OCM基因敲除小鼠的阈值变化更大，OHCs损失增加，TUNEL染色增强。与WT OHCs相比，OCM基因敲除的OHCs中线粒体形态发生了显著改变。在噪声暴露前，通过线粒体外膜蛋白TOM20的免疫细胞化学染色测量，与WT OHCs相比，OCM基因敲除的OHCs显示出线粒体丰度、体积和分支减少。噪声暴露后，OCM基因敲除的OHCs中线粒体蛋白几乎不可见。使用延长细胞质钙超载的哺乳动物细胞培养模型，我们发现OCM对线粒体形态变化和细胞凋亡具有保护作用。这些实验表明，钙缓冲的破坏导致OHCs对噪声的易损性增加以及与线粒体相关的变化。
