Section on Sensory Cell Development and Function, National Institute on Deafness and Other Communication Disorders, National Institutes of Health, Bethesda, United States.
Department of Biology, Johns Hopkins University, Baltimore, United States.
Elife. 2022 Sep 1;11:e77775. doi: 10.7554/eLife.77775.
Sensory hair cells receive near constant stimulation by omnipresent auditory and vestibular stimuli. To detect and encode these stimuli, hair cells require steady ATP production, which can be accompanied by a buildup of mitochondrial byproducts called reactive oxygen species (ROS). ROS buildup is thought to sensitize hair cells to ototoxic insults, including the antibiotic neomycin. Work in neurons has shown that neurotransmission is a major driver of ATP production and ROS buildup. Therefore, we tested whether neurotransmission is a significant contributor to ROS buildup in hair cells. Using genetics and pharmacology, we disrupted two key aspects of neurotransmission in zebrafish hair cells: presynaptic calcium influx and the fusion of synaptic vesicles. We find that chronic block of neurotransmission enhances hair-cell survival when challenged with the ototoxin neomycin. This reduction in ototoxin susceptibility is accompanied by reduced mitochondrial activity, likely due to a reduced ATP demand. In addition, we show that mitochondrial oxidation and ROS buildup are reduced when neurotransmission is blocked. Mechanistically, we find that it is the synaptic vesicle cycle rather than presynaptic- or mitochondrial-calcium influx that contributes most significantly to this metabolic stress. Our results comprehensively indicate that, over time, neurotransmission causes ROS buildup that increases the susceptibility of hair cells to ototoxins.
感觉毛细胞受到无处不在的听觉和前庭刺激的持续刺激。为了检测和编码这些刺激，毛细胞需要稳定的 ATP 产生，这可能伴随着被称为活性氧 (ROS) 的线粒体副产物的积累。ROS 的积累被认为使毛细胞对耳毒性物质（包括抗生素新霉素）敏感。神经元的研究表明，神经递质传递是 ATP 产生和 ROS 积累的主要驱动因素。因此，我们测试了神经递质传递是否是毛细胞中 ROS 积累的重要因素。我们使用遗传学和药理学方法，破坏了斑马鱼毛细胞中神经递质传递的两个关键方面：突触前钙离子内流和突触小泡融合。我们发现，当受到耳毒性新霉素的挑战时，慢性阻断神经递质传递会增强毛细胞的存活。这种对耳毒性敏感性的降低伴随着线粒体活性的降低，这可能是由于 ATP 需求减少。此外，我们还表明，当阻断神经递质传递时，线粒体氧化和 ROS 积累会减少。从机制上讲，我们发现是突触小泡循环而不是突触前或线粒体钙离子内流对这种代谢应激贡献最大。我们的研究结果全面表明，随着时间的推移，神经递质传递会导致 ROS 积累，从而增加毛细胞对耳毒性物质的敏感性。
