Apoptotic death of hair cells in mammalian vestibular sensory epithelia

Hair cell death was examined in cultured explants of vestibular organs from mature guinea pigs and gerbils. The effects of gentamicin were compared wi th those of staurosporine, a membrane-permeable kinase inhibitor that induc es programmed cell death in almost all cell types. Under the conditions use d staurosporine killed hair cells but supporting cells appeared unaffected, and a topographic pattern of differential sensitivity to staurosporine amo ngst hair cells, similar to that described for aminoglycoside antibiotics, was revealed. This suggests such differential sensitivity is an inherent pr operty of the hair cell population. Thin sectioning, and examination of who le mount preparations after application of the TUNEL procedure or after dou ble fluorescent labelling with phalloidin and with propidium iodide, which labels nuclei, revealed that hair cells after exposure to gentamicin show f eatures identical to those of apoptotic cells after exposure to staurospori ne. Furthermore, cells showing features of apoptosis constitute a major pro portion of the hair cells that are ultimately lost following exposure to ge ntamicin. Incubation of cultures with gentamicin in the presence of broad-s pectrum inhibitors of caspases, proteases involved specifically in the cell death pathway, prevented almost all of the hair cell deaths normally trigg ered by gentamicin. This confirms that apoptosis is the predominant mode of hair cell death after gentamicin exposure. Hair cells exposed to gentamici n in the presence of caspase inhibitors appeared to be preserved intact. Th is, and the thin section observations, suggests that apoptotic death is the fate of the majority of hair cells affected by that drug and that any sub- lethal damage to hair cells exposed to gentamicin does not result in signif icant morphological alterations. Hair cell death was also prevented by defe roxamine which has been shown to protect cochlear hair cells in vivo from t he effects of gentamicin. Explant cultures of mature vestibular organs may be, therefore, a useful model system for examining putative hair cell prote cting agents. (C) 2000 Elsevier Science B.V. All rights reserved.