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Rapid hair cell loss: a mouse model for cochlear lesions.

ABSTRACT: In comparison to other mammals, mice have proved extremely resistant to aminoglycoside-induced hair cell ablation in vivo. In this paper we examine the pattern and extent of cochlear lesions rapidly induced with a combination of a single dose of aminoglycoside (kanamycin) followed by a loop diuretic (bumetanide). With this protocol, the vestibular system was unaffected, but in the cochlea, there was extensive loss of outer hair cells (OHC) that commenced in the basal coil and progressed apically so that, by 48 h, OHC loss was almost complete. TUNEL-positive nuclei and activated caspase-3 labeling demonstrated that most OHC died via a classical apoptotic pathway. However, scattered debris within the OHC region suggested that many apoptotic cells ruptured prior to completion of apoptosis. Following lesion repair, supporting cells retained characteristics of differentiated cells but positional shift occurred. In comparison to OHC loss, inner hair cell (IHC) death was delayed and only observed in 50% of all cochleae examined even after extensive reorganization of the tissue. The coadmininstration of diuretic with FM1-43, used as a tracer for aminoglycoside uptake, indicated entry into IHC as readily as OHC, suggesting that the differential response to aminoglycoside was not due to differential uptake. Where IHC death was ongoing, there were indications of different modes of cell death: cells with morphological features of autophagy, necrosis, and apoptosis were apparent. In addition to damage to the organ of Corti, there was a significant and progressive decrease in strial thickness beginning as early as 7 days posttreatment. This was due predominantly to degeneration of marginal cells. The strial pathology resembled that reported after noise damage and with aging. This in vivo protocol provides a robust model in which to obtain extensive OHC loss in the mature cochleae of mice and is a means with which to examine different aspects of cochlear pathology in transgenic or mutant strains.

SUBMITTER: Taylor RR

PROVIDER: S-EPMC2536801 | biostudies-other | 2008 Mar

REPOSITORIES: biostudies-other

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Project description:Mutations in the CLRN1 gene cause Usher syndrome type 3 (USH3), a human disease characterized by progressive blindness and deafness. Clarin 1, the protein product of CLRN1, is a four-transmembrane protein predicted to be associated with ribbon synapses of photoreceptors and cochlear hair cells, and recently demonstrated to be associated with the cytoskeleton. To study Clrn1, we created a Clrn1 knockout (KO) mouse and characterized the histological and functional consequences of Clrn1 deletion in the retina and cochlea. Clrn1 KO mice do not develop a retinal degeneration phenotype, but exhibit progressive loss of sensory hair cells in the cochlea and deterioration of the organ of Corti by 4 months. Hair cell stereocilia in KO animals were longer and disorganized by 4 months, and some Clrn1 KO mice exhibited circling behavior by 5-6 months of age. Clrn1 mRNA expression was localized in the retina using in situ hybridization (ISH), laser capture microdissection (LCM), and RT-PCR. Retinal Clrn1 transcripts were found throughout development and adulthood by RT-PCR, although expression peaked at P7 and declined to undetectable levels in adult retina by ISH. LCM localized Clrn1 transcripts to the retinas inner nuclear layer, and WT levels of retinal Clrn1 expression were observed in photoreceptor-less retinas. Examination of Clrn1 KO mice suggests that CLRN1 is unnecessary in the murine retina but essential for normal cochlear development and function. This may reflect a redundancy in the mouse retina not present in human retina. In contrast to mouse KO models of USH1 and USH2, our data indicate that Clrn1 expression in the retina is restricted to the Müller glia. This is a novel finding, as most retinal degeneration associated proteins are expressed in photoreceptors, not in glia. If CLRN1 expression in humans is comparable to the expression pattern observed in mice, this is the first report of an inner retinal protein that, when mutated, causes retinal degeneration.

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Rapid hair cell loss: a mouse model for cochlear lesions.

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