Extracellular matrix and inner ear development and function

The structures of the inner ear are replete with both structural ECM as well as intricate networks of basement membranes. Since the cochlea functions to translate physical sound waves into sensori-neural input, the structure of the ECM is centrally important to inner ear architecture. This matrix evolves as the cochlea matures with the appropriate physical characteristics to assist in the amplification of neural energy. Defects in this delicate structural balance are evident in mutant mice for tectorin α and β subunits in which structural changes in the tectorial membrane result in reduced efficiency or ablation of the cochlear amplifier function of the outer hair cells. The role of basement membranes in cochlear function is less clear. The dynamic transitions in basement membrane composition during development suggest cochlear basement membranes may function to direct differentiation and/or terminal cytodifferentiation of the complex cellular compartments of the cochlear epithelium. Direct evidence for such a functional role has not yet been provided. Thickening of the strial capillary basement membranes has been described in a number of pathologies that are accompanied by high-frequency sensori-neural hearing loss. Whether thickened strial capillary basement membranes result in loss of strial function awaits definitive proof.