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Deafness in occludin-deficient mice with dislocation of tricellulin and progressive apoptosis of the hair cells.

ABSTRACT: Occludin is the first identified protein in the tight junction (TJ), but its function has remained for the most part obscure. TJs have been demonstrated to play important roles in the inner ear function, and occludin is expressed in all the epithelial TJs in the inner ear. Thus, we examined the inner ears of occludin-deficient (Occ(-/-)) mice. Although inner ears initially developed normally in Occ(-/-) mice, apoptosis occurs in hair cells in the organ of Corti around day 12 after birth, and deafness develops. Since hair cell degeneration was not observed in cochlear explant cultures of Occ(-/-) mice, environmental changes were considered to be the trigger of cell death. As for the vestibular system, both the morphologies and functions are normal in Occ(-/-) mice. These phenotypes of Occ(-/-) mice are very similar with those of claudin-14 or claudin-9 deficient mice, leading us to speculate on the existence of imbalance induced by TJ abnormalities, such as localized ionic components. Moreover, the occludin deficiency led to dislocalization of tricellulin, a gene responsible for human deafness DFNB49. The deafness in Occ(-/-) mice may be due to this dislocalization of tricellulin.

SUBMITTER: Kitajiri S

PROVIDER: S-EPMC4133728 | biostudies-literature | 2014 Jul

REPOSITORIES: biostudies-literature

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Deafness in occludin-deficient mice with dislocation of tricellulin and progressive apoptosis of the hair cells.

Kitajiri Shin-Ichiro S Katsuno Tatsuya T Sasaki Hiroyuki H Ito Juichi J Furuse Mikio M Tsukita Shoichiro S

Biology open 20140725 8

Occludin is the first identified protein in the tight junction (TJ), but its function has remained for the most part obscure. TJs have been demonstrated to play important roles in the inner ear function, and occludin is expressed in all the epithelial TJs in the inner ear. Thus, we examined the inner ears of occludin-deficient (Occ(-/-)) mice. Although inner ears initially developed normally in Occ(-/-) mice, apoptosis occurs in hair cells in the organ of Corti around day 12 after birth, and dea ...[more]

PMID: 25063198

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Project description:Transmembrane channel-like protein isoform 1 (TMC1) is a major component of the mechano-electrical transducer (MET) channel in cochlear hair cells and is subject to numerous mutations causing deafness. We report a new dominant human deafness mutation, TMC1 p.T422K, and have characterized the homologous mouse mutant, Tmc1 p.T416K, which caused deafness and outer hair cell (OHC) loss by the fourth postnatal week. MET channels showed decreased Ca2+ permeability and resting open probability, but no change in single-channel conductance or expression. Three adjacent deafness mutations are TMC1 p.L416R, p.G417R, and p.M418K, the last homologous to the mouse Beethoven that exhibits similar channel effects. All substitute a positive for a neutral residue, which could produce charge screening in the channel pore or influence binding of an accessory subunit. Channel properties were compared in mice of both sexes between dominant (Tmc1 p.T416K, Tmc1 p.D569N) and recessive (Tmc1 p.W554L, Tmc1 p.D528N) mutations of residues near the putative pore of the channel. Tmc1 p.W554L and p.D569N exhibit reduced maximum current with no effect on single-channel conductance, implying a smaller number of channels transported to the stereociliary tips; this may stem from impaired TMC1 binding to LHFPL5. Tmc1 p.D528N, located in the pore's narrowest region, uniquely caused large reductions in MET channel conductance and block by dihydrostreptomycin (DHS). For Tmc1 p.T416K and Tmc1 p.D528N, transduction loss occurred between P15 and P20. We propose two mechanisms linking channel mutations and deafness: decreased Ca2+ permeability, common to all mutants, and decreased resting open probability in low Ca2+, confined to dominant mutations.SIGNIFICANCE STATEMENT Transmembrane channel-like protein isoform 1 (TMC1) is thought to be a major component of the mechanotransducer channel in auditory hair cells, but the protein organization and channel structure are still uncertain. We made four mouse lines harboring Tmc1 point mutations that alter channel properties, causing hair cell degeneration and deafness. These include a mouse homolog of a new human deafness mutation pT416K that decreased channel Ca2+ permeability by introducing a positively-charged amino acid in the putative pore. All mutations are consistent with the channel structure predicted from modeling, but only one, p.D528N near the external face of the pore, substantially reduced channel conductance and Ca2+ permeability and virtually abolished block by dihydrostreptomycin (DHS), strongly endorsing its siting within the pore.

Dataset Information

Deafness in occludin-deficient mice with dislocation of tricellulin and progressive apoptosis of the hair cells.

Publications

Deafness in occludin-deficient mice with dislocation of tricellulin and progressive apoptosis of the hair cells.

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