Section on Mechanobiology, National Institute of Biomedical Imaging and Bioengineering, National Institutes of Health, Bethesda, MD 20892.
Laboratory of Molecular Genetics, National Institute on Deafness and Other Communication Disorders, National Institutes of Health, Bethesda, MD 20892.
Proc Natl Acad Sci U S A. 2022 Jun 28;119(26):e2115190119. doi: 10.1073/pnas.2115190119. Epub 2022 Jun 23.
Hearing depends on intricate morphologies and mechanical properties of diverse inner ear cell types. The individual contributions of various inner ear cell types into mechanical properties of the organ of Corti and the mechanisms of their integration are yet largely unknown. Using sub-100-nm spatial resolution atomic force microscopy (AFM), we mapped the Young's modulus (stiffness) of the apical surface of the different cells of the freshly dissected P5-P6 cochlear epithelium from wild-type and mice lacking either Trio and F-actin binding protein (TRIOBP) isoforms 4 and 5 or isoform 5 only. Variants of are associated with deafness in human and in mutant mouse models. Remarkably, nanoscale AFM mapping revealed unrecognized bidirectional radial stiffness gradients of different magnitudes and opposite orientations between rows of wild-type supporting cells and sensory hair cells. Moreover, the observed bidirectional radial stiffness gradients are unbalanced, with sensory cells being stiffer overall compared to neighboring supporting cells. Deafness-associated TRIOBP deficiencies significantly disrupted the magnitude and orientation of these bidirectional radial stiffness gradients. In addition, serial sectioning with focused ion beam and backscatter scanning electron microscopy shows that a TRIOBP deficiency results in ultrastructural changes of supporting cell apical phalangeal microfilaments and bundled cortical F-actin of hair cell cuticular plates, correlating with messenger RNA and protein expression levels and AFM stiffness measurements that exposed a softening of the apical surface of the sensory epithelium in mutant mice. Altogether, this additional complexity in the mechanical properties of the sensory epithelium is hypothesized to be an essential contributor to frequency selectivity and sensitivity of mammalian hearing.
听力依赖于内耳细胞类型的复杂形态和机械特性。各种内耳细胞类型对 Corti 器官机械特性的个体贡献及其整合机制在很大程度上尚不清楚。使用亚 100nm 空间分辨率原子力显微镜（AFM），我们绘制了来自野生型和缺乏 Trio 和肌动蛋白结合蛋白（TRIOBP）异构体 4 和 5 或仅缺乏异构体 5 的 P5-P6 耳蜗上皮细胞的不同细胞的顶端表面的杨氏模量（硬度）。在人类和突变小鼠模型中， 的变体与耳聋有关。值得注意的是，纳米级 AFM 映射揭示了不同大小和相反方向的未被识别的双向径向刚度梯度，在野生型支持细胞和感觉毛细胞的行之间。此外，观察到的双向径向刚度梯度不平衡，感觉细胞总体上比相邻的支持细胞更硬。与耳聋相关的 TRIOBP 缺乏显著破坏了这些双向径向刚度梯度的幅度和方向。此外，使用聚焦离子束和背散射扫描电子显微镜进行的连续切片显示，TRIOBP 缺乏导致支持细胞顶端指状微丝和毛细胞表皮板皮质 F-肌动蛋白束的超微结构变化，与信使 RNA 和蛋白质表达水平以及 AFM 硬度测量相关，这些测量显示突变小鼠感觉上皮的顶端表面软化。总的来说，这种感觉上皮机械特性的额外复杂性被假设为哺乳动物听力的频率选择性和敏感性的重要贡献者。
