Mouse model of enlarged vestibular aqueducts defines temporal requirement of Slc26a4 expression for hearing acquisition

Abstract

Mutations in human SLC26A4 are a common cause of hearing loss associated with enlarged vestibular aqueducts (EVA). SLC26A4 encodes pendrin, an anion-base exchanger expressed in inner ear epithelial cells that secretes HCO 3 -into endolymph. Studies of Slc26a4-null mice indicate that pendrin is essential for inner ear development, but have not revealed whether pendrin is specifically necessary for homeostasis. Slc26a4-null mice are profoundly deaf, with severe inner ear malformations and degenerative changes that do not model the less severe human phenotype. Here, we describe studies in which we generated a binary transgenic mouse line in which Slc26a4 expression could be induced with doxycycline. The transgenes were crossed onto the Slc26a4-null background so that all functional pendrin was derived from the transgenes. Varying the temporal expression of Slc26a4 revealed that E16.5 to P2 was the critical interval in which pendrin was required for acquisition of normal hearing. Lack of pendrin during this period led to endolymphatic acidification, loss of the endocochlear potential, and failure to acquire normal hearing. Doxycycline initiation at E18.5 or discontinuation at E17.5 resulted in partial hearing loss approximating the human EVA auditory phenotype. These data collectively provide mechanistic insight into hearing loss caused by SLC26A4 mutations and establish a model for further studies of EVA-associated hearing loss.

Pendrin Function and Regulation in <i>Xenopus</i> Oocytes

“…In the vestibular apparatus, pendrin is expressed in nonsensory epithelial cells surrounding sensory hair-cell patches in the saccule, utricle, and ampulla, and in a subset of cells of the endolymphatic sac terminating the vestibular aqueduct [5]. Lack of pendrinmediated Cl -/HCO 3 -exchange in the inner ear acidifies endolymph, thus promoting loss of the endocochlear potential and elevating endolymph [Ca 2+ ] [6,7], and likely contributes to enlargement of the cochlear lumen [8] and vestibular aqueduct through reduced volume absorption.…”

“…Lack of pendrinmediated Cl -/HCO 3 -exchange in the inner ear acidifies endolymph, thus promoting loss of the endocochlear potential and elevating endolymph [Ca 2+ ] [6,7], and likely contributes to enlargement of the cochlear lumen [8] and vestibular aqueduct through reduced volume absorption. Development of normal hearing in the mouse requires pendrin expression between e16.5 and p2 of embryonic and neonatal developent [5].…”

Transcriptional Regulation of the Pendrin Gene

“…Pendrin is expressed in several locations of the cochlea and the vestibule of the mouse inner ear [38,39]. This expression pattern involves regions important for endolymphatic fluid resorption, consistent with pendrin's essential role in the normal development and proper function of the inner ear [38].…”

Genetics of Nonsyndromic Recessively Inherited Moderate to Severe and Progressive Deafness in Humans

“…However, recently, transgenic mice with Slc26a4 expression inducible by doxycycline on a background of mice lacking endogenous pendrin expression were generated. It was demonstrated that expression of pendrin at early embryonic stages of E0-E17.5 was necessary and sufficient to restore normal hearing in Tg[E];Tg[R];Slc26a4 ∆ / ∆ mice (Choi et al, 2011). Ablating expression of Slc26A4 at this critical time results in complete or partial hearing loss in these mice, recapitatulating the phenotypes documented for many patients with mutations in SLC26A4 (Choi et al, 2011).…”