Deafness due to degeneration of cochlear neurons in caspase-3-deficient mice

Mice that lack caspase-3, which functions in apoptosis, were generated by g ene targeting and shown to undergo hearing loss. The ABR threshold of the c aspase-3(-/-) mice was significantly elevated compared to that of caspase3( +/+) mice at 15 days of age and was progressively elevated further by 30 da ys. Distortion product otoacoustic emissions were not detectable in caspase -3(-/-) mice at 15 days of age. Caspase-3(-/-) mice exhibited marked degene ration of spiral ganglion neurons and a loss of inner and outer hair cells in the cochlea at 30 days of age, although no such changes were apparent at 15 days. The degenerating neurons manifested features, including cytoplasm ic vacuolization, distinct from those characteristic of apoptosis. Spiral g anglion neurons and cochlear hair cells thus appear to require caspase-3 fo r survival but not for initial development. The mapping of both the human c aspase-3 gene and the locus responsible for an autosomal dominant, nonsyndr omic form of hearing loss (DFNA24) to chromosome 4q35 suggests that the cas pase-3-/- mice may represent a model of this human condition. (C) 2001 Acad emic Press.