Loxhd1 Mutations Cause Mechanotransduction Defects in Cochlear Hair Cells.
Loxhd1 Mutations Cause Mechanotransduction Defects in Cochlear Hair Cells.
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DOI：
10.1523/jneurosci.0975-20.2021
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发表时间：
2021-04-14
期刊：
影响因子：
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通讯作者：
Grillet N
中科院分区：
文献类型：
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作者：
Trouillet A;Miller KK;George SS;Wang P;Ali NE;Ricci A;Grillet N
声音检测通过耳蜗毛细胞的毛束的机械偏转在内耳中发生。毛束是由肌动蛋白填充的膜突起（称为静纤毛）组成的顶端特化，所述膜突起通过尖端链接（TL）连接，所述尖端链接（TL）传递偏转力以门控机械转导通道。在这里，我们确定了听力损失相关的Loxhd 1/DFNB 77基因是机械转导过程所必需的。声音检测通过耳蜗毛细胞的毛束的机械偏转在内耳中发生。毛束是顶端特化结构，由充满肌动蛋白的膜突起（称为静纤毛）组成，这些突起通过尖端连接（TL）连接，尖端连接（TL）传递偏转力以门控机械传导通道。在这里，我们确定了听力损失相关的Loxhd 1/DFNB 77基因是机械转导过程所必需的。LOXHD 1由15个多囊蛋白脂氧合酶α毒素（PLAT）重复序列组成，在其他蛋白质中可以结合脂质和蛋白质。LOXHD 1在静纤毛上呈沿着分布。在第10个PLAT重复中具有突变的两个LOXHD 1小鼠模型表现出机械转导缺陷（在两种性别中）。虽然突变型内毛细胞（IHC）中的机械转导电流在出生后第一周与野生型水平相似，但它们在出生后第11天受到严重影响。机械转导表型的发病与出生后LOXHD 1在毛束中表达/定位的时间进展一致。在Loxhd 1突变型IHC中观察到的机械转导缺陷并不伴随着毛束的形态缺陷或TL数量的减少。使用免疫定位，我们发现，两个蛋白质的上，下TL蛋白复合物（协调蛋白和LHFPL 5）保持在突变体中，这表明机械转导机制存在，但不能激活。这项工作确定了毛束发育中的一个新的LOXHD 1依赖性步骤，该步骤对于成熟毛细胞中的机械转导以及小鼠和人类的正常听力功能至关重要。毛细胞通过毛束检测声音诱导的力，毛束由通过尖端链接连接的膜突起组成。机械转导机制在尖端-连接末端形成蛋白质复合物。目前的研究表明，LOXHD 1是一种多重复蛋白，在突变时导致人类和小鼠的听力损失，是毛细胞机械转导所必需的，但仅在出生后第一周后。使用免疫化学，我们证明了这种缺陷不是由尖端连接复合物蛋白Harmonin或LHFPL 5的错误定位引起的，这表明机械转导蛋白复合物被维持。这项工作确定了毛束发育的一个新步骤，这对毛细胞机械传导和听力都至关重要。
Sound detection happens in the inner ear via the mechanical deflection of the hair bundle of cochlear hair cells. The hair bundle is an apical specialization consisting of actin-filled membrane protrusions (called stereocilia) connected by tip links (TLs) that transfer the deflection force to gate the mechanotransduction channels. Here, we identified the hearing loss-associated Loxhd1/DFNB77 gene as being required for the mechanotransduction process. Sound detection happens in the inner ear via the mechanical deflection of the hair bundle of cochlear hair cells. The hair bundle is an apical specialization consisting of actin-filled membrane protrusions (called stereocilia) connected by tip links (TLs) that transfer the deflection force to gate the mechanotransduction channels. Here, we identified the hearing loss-associated Loxhd1/DFNB77 gene as being required for the mechanotransduction process. LOXHD1 consists of 15 polycystin lipoxygenase α-toxin (PLAT) repeats, which in other proteins can bind lipids and proteins. LOXHD1 was distributed along the length of the stereocilia. Two LOXHD1 mouse models with mutations in the 10th PLAT repeat exhibited mechanotransduction defects (in both sexes). While mechanotransduction currents in mutant inner hair cells (IHCs) were similar to wild-type levels in the first postnatal week, they were severely affected by postnatal day 11. The onset of the mechanotransduction phenotype was consistent with the temporal progression of postnatal LOXHD1 expression/localization in the hair bundle. The mechanotransduction defect observed in Loxhd1-mutant IHCs was not accompanied by a morphologic defect of the hair bundle or a reduction in TL number. Using immunolocalization, we found that two proteins of the upper and lower TL protein complexes (Harmonin and LHFPL5) were maintained in the mutants, suggesting that the mechanotransduction machinery was present but not activatable. This work identified a novel LOXHD1-dependent step in hair bundle development that is critical for mechanotransduction in mature hair cells as well as for normal hearing function in mice and humans. SIGNIFICANCE STATEMENT Hair cells detect sound-induced forces via the hair bundle, which consists of membrane protrusions connected by tip links. The mechanotransduction machinery forms protein complexes at the tip-link ends. The current study showed that LOXHD1, a multirepeat protein responsible for hearing loss in humans and mice when mutated, was required for hair-cell mechanotransduction, but only after the first postnatal week. Using immunochemistry, we demonstrated that this defect was not caused by the mislocalization of the tip-link complex proteins Harmonin or LHFPL5, suggesting that the mechanotransduction protein complexes were maintained. This work identified a new step in hair bundle development, which is critical for both hair-cell mechanotransduction and hearing.