[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.


CONCLUSIONS
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.
Department of Otolaryngology-Head and Neck Surgery, Second Xiangya Hospital, Central South University, Changsha 410011, China. yunkaiguo@yahoo.com
Yun-kai
YK
Guo
Ding-hua
DH
Xie
Xin-ming
XM
Yang
D000818:Animals; D001309:Auditory Threshold; D043402:Cathepsin A / Q000235:genetics* / Q000378:metabolism; D007758:Ear, Inner / Q000201:enzymology*; D016057:Evoked Potentials, Auditory, Brain Stem / Q000502:physiology; D006319:Hearing Loss, Sensorineural / Q000201:enzymology* / Q000235:genetics; D008247:Lysosomes / Q000201:enzymology; D051379:Mice; D018345:Mice, Knockout; D009439:Neuraminidase / Q000235:genetics* / Q000378:metabolism; D001616:beta-Galactosidase / Q000235:genetics* / Q000378:metabolism
D009439:Neuraminidase; D001616:beta-Galactosidase; D043402:Cathepsin A