Cisplatin drives mitochondrial dysregulation in sensory hair cells.

Cisplatin is a commonly used chemotherapy that causes permanent hearing loss by injuring cochlear hair cells. The underlying mechanisms that drive hair cell loss remain unknown, but mitochondria have emerged as potential mediators of cisplatin ototoxicity. Direct observation of changes in hair cell mitochondrial function are challenging because the mammalian inner ear is optically inaccessible. Here, we perform live in vivo imaging of hair cells within the zebrafish lateral-line organ to evaluate the role of mitochondria in cisplatin ototoxicity. Using a genetically encoded biosensor that measures cumulative mitochondrial activity in hair cells, we demonstrate that greater redox history increases susceptibility to cisplatin. Next, we conduct time-lapse imaging of individual hair cells to understand dynamic changes in mitochondrial homeostasis. We observe spikes in mitochondrial calcium and cytosolic calcium immediately prior to hair cell death. Furthermore, we use a mitochondrially-localized probe that fluoresces in the presence of cisplatin to show that cisplatin accumulates in hair cell mitochondria. Lastly, we demonstrate that this accumulation occurs before mitochondrial dysregulation, Caspase-3 activation, and ultimately, hair cell death. Our findings provide additional evidence that suggest mitochondria are integral to cisplatin ototoxicity and cisplatin directly targets hair cell mitochondria.