TRIOBP promotes bidirectional radial stiffness gradients within the organ of Corti

Hearing depends on complex mechanical properties of the inner ear sensory epithelium. Yet, the individual contributions of different cell types to the stiffness spectrum of the sensory epithelium have not been thoroughly investigated. Using sub-100 nanometer spatial resolution PeakForce Tapping Atomic Force Microscopy (PFT-AFM), we mapped the Young’s modulus (stiffness) of the apical surface of different cells of freshly-dissected cochlear epithelium from wild-type mice and mice lacking the F-actin bundling protein TRIOBP-5 or TRIOBP-4 and TRIOBP-5. Variants of the genes encoding human and mouse TRIOBP are associated with deafness. We show that TRIOBP deficiency affects formation of supporting cell apical phalangeal microfilaments and bundled cortical F-actin of hair cell cuticular plates, softening the apical surface of the sensory epithelium. Unexpectedly, high-resolution PFT-AFM-mapping also revealed previously unrecognized reticular lamina radial stiffness gradients of opposite orientations in wild-type supporting and hair cells. Deafness-associated TRIOBP deficiencies significantly modified these bidirectional radial stiffness gradients. ### Competing Interest Statement The authors have declared no competing interest.