Identification of 17 hearing impaired mouse strains in the TMGC ENU-mutagenesis screen.

The Tennessee Mouse Genome Consortium (TMGC) employed an N-ethyl-N-nitrosourea (ENU)-mutagenesis scheme to identify mouse recessive mutants with hearing phenotypes. We employed auditory brainstem responses (ABR) to click and 8, 16, and 32 kHz stimuli and screened 285 pedigrees (1819 mice of 8-11 weeks old in various mixed genetic backgrounds) each bred to carry a homozygous ENU-induced mutation. To define mutant pedigrees, we measured > or = 12 mice per pedigree in > or = 2 generations and used a criterion where the mean ABR threshold per pedigree was two standard deviations above the mean of all offspring from the same parental strain. We thus identified 17 mutant pedigrees (6%), all exhibiting hearing loss at high frequencies (> or = 16 kHz) with an average threshold elevation of 30-35 dB SPL. Interestingly, four mutants showed sex-biased hearing loss and six mutants displayed wide range frequency hearing loss. Temporal bone histology revealed that six of the first nine mutants displayed cochlear morphological defects: degeneration of spiral ganglia, spiral ligament fibrocytes or inner hair cells (but not outer hair cells) mostly in basal turns. In contrast to other ENU-mutagenesis auditory screens, our screen identified high-frequency, mild and sex-biased hearing defects. Further characterization of these 17 mouse models will advance our understanding of presbycusis and noise-induced hearing loss in humans.

[Orientation of three lysosomal enzymes in the mouse inner ear and hearing loss in enzyme gene deficiency].

OBJECTIVE: To determine the distribution and influence of lysosomal neuraminidase (Neul), protective protein/cathepsin A (PPCA) and beta-galactosidase (beta-gal) in the inner ear of the mouse, and to observe their auditory alterations in enzyme deficiency. METHODS: Six wild type (2 months postnatal) (Neu1+/+, PPCA+/+ and beta-gal+/+) mice were used, and Neu1, PPCA and beta-gal homozygous (Neu1-/-, PPCA-/- and beta-gal-/-) mice at the same age used as control in this experiment. The auditory thresholds were examined through the auditory brainstem responses (ABR) to click, which tone pips were 8, 16, and 32 kHz. The mice were intracardically perfused with 4% paraformaldehyde. The bulla were further fixed in 4% paraformaldehyde, processed and sectioned with paraffin embedded method. Immunohistochemistry was used to determine the cellular localizations of Neu1, PP-CA, and beta gal in the inner ear. RESULTS: There was a similar distributive pattern of Neu1, PPCA and betagal in the inner ear. Neu1 intense staining was observed in the cochlear spiral ganglion cells, spiral limbus, spiral ligament, vestibular ganglion cells, cristae, maculae hair cells, and weak staining in inner hair cells, outer hair cells, supplying cells of the organ of Corti and stria vascularis. The intense staining of PPCA and beta-gal were observed in the spiral ganglion and vestibular ganglion cells, and weak staining in the spiral limbus, spiral ligament, stria vascularis and organ of Corti. The inner ear exhibited no staining when Neul, PPCA and beta-gal were deficient, respectively. A positive staining of PPCA and beta-gal was presented in Neu1-/- mice, and as well as Neu1 and PPCA in beta-gal-/- mice. However, the staining of Neu1 was not presented, and only very weak staining of beta-gal in PPCA-/- mice. The auditory thresholds of Neul, PPCA, and beta-gal mice were elevated for 60-69 dB, 40-48 dB, and 7-10 dB above those of wildtype littermates, respectively. CONCLUSION: Neu1 PPCA and beta-gal are distributed in the inner ear of mouse, and the three enzymes also form a lysosomal multi-enzyme complex in the inner ear. The respective enzyme deficiencies can induce the hearing the loss of different levels.

[Clinical observation of sensorineural hearing loss in patients suffering from nasopharyngeal carcinoma after radiotherapy].

OBJECTIVE: To study the extent and incidence of sensorineural hearing loss (SNHL) after radiotherapy (RT). METHODS: Twenty-eight patients with diagnosed nasopharyngeal carcinoma (NPC) were selected. The pure-tone audiography, auditory brain stem evoked response (ABR), impedance audiometry and evoked otoacoustic emissions (EOAE) recordings were performed before RT, 1 month, 1, 2 and 5 years after RT. RESULTS: At 1 month after RT, there were 7.1 and 25.7 dB increased mean bone conduction (BC) thresholds at speech (0.5 - 4.0 kHz) and at high frequency (8.0 kHz), and their BC thresholds were statistically significant increase than those before RT, respectively (P < 0.001). At 1 year after RT, there were 17.6 and 28.1 dB increased respectively, and their thresholds were statistically significant increase than those at pre-irradiation (P < 0.001). There were also significant increases in thresholds than those at 1 month of post-irradiation (P <0.001 or P < 0.05). At 2 years after RT, 21 and 27.4 dB were increased at respective those two frequencies, and there was a statistically difference only at speech frequencies when compared with those at 1 year after RT (P < 0.05). At 5 years after RT, 26.7 and 35.8 dB were increased at these two frequencies, and there were significant increases in threshold than those before, 1 month, 1 and 2 years after RT, respectively (P < 0.001). From 1 month to 5 years after RT, 37. 5% to 94. 7% of ears had a BC hearing threshold of at least 15 dB losses at speech frequency, whereas the percentage at high frequency was 85.4 to 97.4%. Up to 63.2% and 73.7% of ears had 30 dB SNHL at least at speech and high frequency, respectively. Furthermore, the degree of mean threshold loss was greater at high frequency than at speech frequency. The mean value of wave I, III and V latency, and I -V interpeak latency intervals of ABR had no significant difference between at 1 month after RT and before RT (P > 0.05). The wave I , III and V latency, and I - V interpeak latency intervals at 1 year and 2 years were significantly prolonged when compared with those before and 1 month after RT (P < 0.05), but there were no significant difference between 1 year and 2 years after RT (P > 0.05). The wave I, III and V latency, and I -V interpeak latency intervals at 5 years after RT were also significantly longer than those before RT (P < 0.001). There were significant difference in wave I , III and V latency (P < 0.05), and no significant difference in wave I - V interpeak latency intervals (P > 0. 05) between 5 years after RT and 1 year or 2 years after RT. Seven of 10 ears at 1 year after RT and 4 of 7 ears at 5 years after RT had normal EOAE, but they all had abnormal ABR response. CONCLUSIONS: SNHL in NPC patients start soon after completion of RT, especially more commonly in high frequency. The incidence and the extent of hearing loss are increased with time of follow-up. The hearing impairment could occur in the cochlea and/or the retrocochlear auditory pathway, which show that the sensitivity of radiation damage may be different in different patient and anatomic site of auditory system.

[Morphological and functional alterations of ear in lysosomal neuraminidase gene deficient mouse].

OBJECTIVE: To observe the alterations of the auditory function and morphology of the ear in the mouse sialidosis models which has been generated by targeted deletion of lysosomal neuraminidase gene (Neul) and closely resembled the phenotypes in corresponding human conditions, and to explore pathophysiological mechanisms of hearing impairment. METHODS: Neul homozygous (Neul -/-) mice at 3 weeks, 2 and 4 months of age, and their wildtype littermates (Neu1 +/+) were examined for auditory thresholds through auditory brainstem responses (ABR) to click, 8, 16, and 32 kHz stimuli. Morphological analyses in ears were performed by series temporal bone section and light microscopy. RESULTS: Neul -/- mice at 3 weeks of age showed an elevated ABR threshold, 50-55 dB above those of Neul +/+ mice. Up to 2 and 4 months of age, their thresholds were further elevated for 60-68 dB. There were distinct pathological changes of middle and inner ear of 3 weeks of age in Neul -/- mice, especially at 2-4 months of age there were significant cerumen occlusion in the external auditory canal and severe otitis media. Vacuolation associated with lysosomal storage was observed within ossicles and cochlear bone cells, stria vascularis cells, spiral ganglion neurons and macrophages, spiral limbus, spiral prominence, Reissner's membrane cells, and the mesothelial cells of the perilymphatic scala and basilar membrane, but not within the organ of Corti. Vestibular ganglion neurons, hair cells and supporting cells in cristae and maculae also showed vacuolation. CONCLUSIONS: The deficiency of lysosomal neuraminidase may result in a serious hearing loss and morphological alterations of ear. The external auditory canal obstruction, otitis media and ossicle changes may cause conductive hearing loss, and the defects in lysosomal storage of neurons, stria vascularis, spiral limbus, Reissner's membrane and basilar membrane cells may contribute to sensorineural deafness.