Identification and Localization of Type IV Collagen Chains in the Inner Ear Cochlea

Abstract

Mutations in the genes encoding the α3(IV), α4(IV) and α5(IV) chains of type IV collagen have been implicated in the pathogenesis of Alport's syndrome, a hereditary disorder characterized by progressive nephropathy and sensorineural deafness. The known expression of these chains in kidney basement membranes supports the contention that they play a crucial role in the ultrafiltration function. Whether they play a role in auditory signal transduction remains unknown as heretofore, they have not been identified in the inner ear. In the present study, the expression of type IV collagen in cochlea of the inner ear of guinea pigs was determined. All six α-chains of type IV collagen were identified by biochemical and immunological methods. By indirect immunofluorescence, α1(IV) and α2(IV) chains were localized to the spiral limbus, basilar membrane and tectorial membrane. The α3(IV), α4(IV), α5(IV) and α6(IV) chains localized exclusively to the tectorial membrane and basilar membrane. These results suggest a possible role of type IV collagen chains in the active tuning of the basilar and tectorial membrane, an essential step in frequency discrimination and amplification of auditory signals.