title: Overexpression of Bcl-2 prevents neomycin-induced hair cell death and caspase-9 activation in the adult mouse utricle in vitro.
abstract: Mechanosensory hair cells of the inner ear are especially sensitive to death induced by exposure to aminoglycoside antibiotics. This aminoglycoside-induced hair cell death involves activation of an intrinsic program of cellular suicide. Aminoglycoside-induced hair cell death can be prevented by broad-spectrum inhibition of caspases, a family of proteases that mediate apoptotic and programmed cell death in a wide variety of systems. More specifically, aminoglycoside-induced hair cell death requires activation of caspase-9. Caspase-9 activation requires release of mitochondrial cytochrome c into the cytoplasm, indicating that aminoglycoside-induced hair cell death is mediated by the mitochondrial (or "intrinsic") cell death pathway. The Bcl-2 family of pro-apoptotic and anti-apoptotic proteins are important upstream regulators of the mitochondrial apoptotic pathway. Bcl-2 is an anti-apoptotic protein that localizes to the mitochondria and promotes cell survival by preventing cytochrome c release. Here we have utilized transgenic mice that overexpress Bcl-2 to examine the role of Bcl-2 in neomycin-induced hair cell death. Overexpression of Bcl-2 significantly increased hair cell survival following neomycin exposure in organotypic cultures of the adult mouse utricle. Furthermore, Bcl-2 overexpression prevented neomycin-induced activation of caspase-9 in hair cells. These results suggest that the expression level of Bcl-2 has important effects on the pathway(s) important for the regulation of aminoglycoside-induced hair cell death.
authors.affiliation: Virginia Merrill Bloedel Hearing Research Center, University of Washington, Seattle, 98195-7293, USA.
authors.forename: Lisa L
authors.initials: LL
authors.lastname: Cunningham
authors.forename: Jonathan I
authors.initials: JI
authors.lastname: Matsui
authors.forename: Mark E
authors.initials: ME
authors.lastname: Warchol
authors.forename: Edwin W
authors.initials: EW
authors.lastname: Rubel
mesh_terms: D000818:Animals; D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D017209:Apoptosis / Q000187:drug effects; D053453:Caspase 9; D020169:Caspases / Q000378:metabolism*; D002470:Cell Survival / Q000187:drug effects; D004789:Enzyme Activation / Q000187:drug effects; D006199:Hair Cells, Auditory, Inner / Q000187:drug effects* / Q000473:pathology; D007150:Immunohistochemistry; D051379:Mice; D008822:Mice, Transgenic; D018613:Microscopy, Confocal; D009355:Neomycin / Q000494:pharmacology*; D009924:Organ Culture Techniques; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000096:biosynthesis*; D012444:Saccule and Utricle / Q000187:drug effects / Q000378:metabolism / Q000473:pathology
chemical_list: D000900:Anti-Bacterial Agents; D019253:Proto-Oncogene Proteins c-bcl-2; C506434:Casp9 protein, mouse; D053453:Caspase 9; D020169:Caspases; D009355:Neomycin