Fibrocytes in the cochlea of the mammalian inner ear: their molecular architecture, physiological properties, and pathological relevance

Abstract

Fibroblasts are a cell type that dominates connective tissues in a broad array of organs and plays key roles in formation of the extracellular matrix and wound healing. The cochlea of the mammalian inner ear harbors loose connective tissues such as the spiral ligament and spiral limbus, and their cellular components are called “fibrocytes.” The fibrocytes in the ligament are functionally differentiated and specialized for ion transport that is essential for proper actions of the cochlea. Molecular biological and histological assays have shown that these cells express specific types of ion channels and transporters. Results of in vivo electrophysiological experiments have integrated activities of individual channels and transporters into the ionic flow that circulates throughout the organ and maintains the electrochemical properties in various tissues and extracellular fluids. Moreover, analyses of deafness genes in humans as well as transgenic experiments on mice recently revealed the relevance of fibrocyte dysfunction to hearing disorders. In this review article, we not only describe molecular architecture and physiological and pathological significance of cochlear fibrocytes but also provide insights into next-generation therapies targeting these cells.