benzyloxycarbonylvalyl-alanyl-aspartyl-fluoromethyl-ketone and Hearing-Loss

DBA/2J mice are characterized by early onset hearing loss at about 3-4 weeks of age. Mutations in cadherin 23 (Cdh23) and fascin-2 (Fscn2) are responsible for the phenotypes, but the underlying mechanism is unknown. In the present study, DBA/2J mice displayed progressive hair cell loss and degeneration of spiral ganglion neurons (SGNs) after 2 weeks of age; however, the mRNA level of Caspase-3 in the inner ears was much higher at 2 weeks of age than that at 4 or 8 weeks of age. Moreover, transcriptional levels of Caspase-3 and Caspase-9 in the inner ears of DBA/2J mice were significantly higher than those of C57BL/6J mice at 2 or 8 weeks of age. Immunohistochemistry localized Caspase-3 and Caspase-9 mainly to the hair cells, SGNs and stria vascularis of the cochleae. To determine the significance of caspase-dependent apoptosis in the hearing loss, the pan-caspase inhibitor Z-VAD-FMK was given intraperitoneally to DBA/J2 mice over an 8-week period starting at one week of age. Blockage of caspases preserved hearing in the mice by more than 10 dB (dB) sound pressure level (SPL) of the ABR thresholds and significantly reduced outer hair cell loss at the basal turns of the cochleae. These results demonstrate that apoptosis in the cochleae of DBA/J2 mice contributes to the early onset of hearing loss, which can be attenuated by anti-apoptotic treatment.

Topics: Acoustic Stimulation; Amino Acid Chloromethyl Ketones; Animals; Apoptosis; Auditory Threshold; Caspase 3; Caspase 9; Caspase Inhibitors; Cochlea; Cytoprotection; Disease Models, Animal; Drug Administration Schedule; Evoked Potentials, Auditory, Brain Stem; Gene Expression Regulation; Genotype; Hearing Loss; Injections, Intraperitoneal; Mice, Inbred C57BL; Mice, Inbred DBA; Otoacoustic Emissions, Spontaneous; Phenotype; Time Factors

We report a novel mutation (erlong, erl) of the cadherin 23 (Cdh23) gene in a mouse model for DFNB12 characterized by progressive hearing loss beginning from postnatal day 27 (P27). Genetic and sequencing analysis revealed a 208 T >C transition causing an amino-acid substitution (70S-P). Caspase expression was upregulated in mutant inner ears. Hearing was preserved (up to 35-dB improvement) in pan-caspase inhibitor Z-VAD-FMK-treated mutants compared with untreated mutants (P<0.05). Outer hair cell (OHC) loss in the cochleae of Z-VAD-FMK-treated mutants was significantly reduced compared with those of untreated mice. Thus, the erl mutation can lead to hearing loss through apoptosis. This is the first genetic mouse model of hearing loss shown to respond to otoprotective drug therapy. The short interval from initial hearing loss to deafness (P27-P90) makes this model ideal for screening and validating otoprotective drugs.

Topics: Age Factors; Amino Acid Chloromethyl Ketones; Amino Acid Sequence; Animals; Cadherins; Disease Models, Animal; Drug Evaluation, Preclinical; Genetic Complementation Test; Hair Cells, Auditory, Outer; Hearing Loss; Mice; Mice, Inbred C3H; Mice, Inbred C57BL; Molecular Sequence Data; Neuroprotective Agents; Point Mutation