Department of Otolaryngology-Head and Neck Surgery, School of Medicine, Stanford University, Stanford, California 94305.
Department of Molecular and Cellular Physiology, School of Medicine, Stanford University, Stanford, California 94305.
J Neurosci. 2021 Apr 14;41(15):3331-3343. doi: 10.1523/JNEUROSCI.0975-20.2021. Epub 2021 Mar 11.
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 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 -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. 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.
声音检测在内耳通过耳蜗毛细胞的毛束的机械偏转而发生。毛束是一个顶端特化结构，由充满肌动蛋白的膜突起（称为静纤毛）组成，通过尖端连接（TLs）连接，将偏转力传递到机械转导通道。在这里，我们确定了听力损失相关基因对于机械转导过程是必需的。LOXHD1 由 15 个多蛋白脂氧合酶 α-毒素（PLAT）重复组成，在其他蛋白质中可以结合脂质和蛋白质。LOXHD1 沿静纤毛的长度分布。两种具有第 10 个 PLAT 重复突变的 LOXHD1 小鼠模型表现出机械转导缺陷（在两性中）。虽然突变的内毛细胞（IHC）中的机械转导电流在前一周与野生型水平相似，但在出生后第 11 天受到严重影响。机械转导表型的发作与出生后 LOXHD1 在毛束中的表达/定位的时间进展一致。在 -突变的 IHC 中观察到的机械转导缺陷不伴有毛束的形态缺陷或 TL 数量减少。使用免疫定位，我们发现上和下 TL 蛋白复合物的两种蛋白（Harmonin 和 LHFPL5）在突变体中得以维持，这表明机械转导机制存在但不可激活。这项工作确定了毛束发育中的一个新的 LOXHD1 依赖步骤，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引起的力，毛束由通过尖端连接连接的膜突起组成。机械转导机制在上和下 TL 蛋白复合物的末端形成蛋白复合物。本研究表明，LOXHD1 是一种多重复蛋白，当发生突变时会导致人类和小鼠听力损失，对于毛细胞的机械转导是必需的，但仅在后生后第一周后。通过免疫化学，我们证明该缺陷不是尖端连接复合物蛋白 Harmonin 或 LHFPL5 的定位错误引起的，这表明机械转导蛋白复合物得以维持。这项工作确定了毛束发育的一个新步骤，对于毛细胞的机械转导和听力都至关重要。
