Thyroid hormone-deficient period prior to the onset of hearing is associated with reduced levels of β-tectorin protein in the tectorial membrane: Implication for hearing loss

Abstract

The genes for α- and β-tectorin encode the major noncollagenous proteins of the tectorial membrane. Recently, a targeted deletion of the mouse α-tectorin gene was found to cause loss of cochlear sensitivity (1). Here we describe that mRNA levels for β-tectorin, but not α-tectorin, are significantly reduced in the cochlear epithelium under constant hypothyroid conditions and that levels of β-tectorin protein in the tectorial membrane are lower. A delay in the onset of thyroid hormone supply prior to onset of hearing, recently described to result in permanent hearing defects and loss of active cochlear mechanics (2), can also lead to permanently reduced β-tectorin protein levels in the tectorial membrane. β-Tectorin protein levels remain low in the tectorial membrane up to one year after the onset of thyroid hormone supply has been delayed until postnatal day 8 or later and are associated with an abnormally structured tectorial membrane and the loss of active cochlear function. These data indicate that a simple delay in thyroid hormone supply during a critical period of development can lead to low β-tectorin levels in the tectorial membrane and suggest for the first time that β-tectorin may be required for development of normal hearing.