溶酶体神经氨酸酶基因缺乏小鼠听觉和耳形态学改变初步研究

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

目的研究溶酶体神经氨酸酶基因(Neu1)敲除小鼠听功能和耳形态学改变,探讨唾液酸沉积症听力损害的病理生理机制。方法应用听性脑干反应测试和常规颞骨连续切片观察3周、2个月和4个月龄的Neu1敲除纯合子(Neu1-/-)和野生型(Neu1+/+)小鼠听阈和光镜下外耳、中耳及内耳形态。结果3周龄的Neu1-/-小鼠,短声和短音8、16及32kHz听阈(声压级)较Neu1+/+提高50～55dB;2个月和4个月龄小鼠听阈提高60～68dB。Neu1-/-小鼠3周龄即有明显的中耳和内耳改变,特别是2个月和4个月龄有显著的外耳道堵塞和严重中耳炎,听小骨和耳蜗骨壁细胞、血管纹边缘层和中间层细胞、耳蜗螺旋神经节细胞、螺旋缘纤维细胞、前庭膜、基底膜及沿前庭阶外淋巴隙的间皮细胞明显囊泡化,但Corti器细胞正常。前庭神经节细胞、壶腹嵴及球囊毛细胞和支持细胞也呈现明显囊泡化。结论溶酶体神经氨酸酶的缺乏可导致较严重的听力损害和耳形态改变;外耳道阻塞或中耳炎和听骨改变可能引起传导性聋;耳蜗螺旋神经元、血管纹、螺旋缘、前庭膜和基底膜等细胞的溶酶体储积可能导致感音神经性聋。

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 （Neul ＋/＋ ） 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.