Vestibular regeneration--experimental models and clinical implications

Bilateral Vestibular Weakness

Bilateral vestibular weakness (BVW) is a rare cause of imbalance. Patients with BVW complain of oscillopsia. In approximately half of the patients with BVW, the cause remains undetermined; in the remainder, the most common etiology by far is gentamicin ototoxicity, followed by much rarer entities such as autoimmune inner ear disease, meningitis, bilateral Ménière’s disease, bilateral vestibular neuritis, and bilateral vestibular schwannomas. While a number of bedside tests may raise the suspicion of BVW, the diagnosis should be confirmed by rotatory chair testing. Treatment of BVW is largely supportive. Medications with the unintended effect of vestibular suppression should be avoided.

Spatial and Age-Dependent Hair Cell Generation in the Postnatal Mammalian Utricle

Loss of vestibular hair cells is a common cause of balance disorders. Current treatment options for bilateral vestibular dysfunction are limited. During development, atonal homolog 1 (Atoh1) is sufficient and necessary for the formation of hair cells and provides a promising gene target to induce hair cell generation in the mammals. In this study, we used a transgenic mouse line to test the age and cell type specificity of hair cell induction in the postnatal utricle in mice. We found that forced Atoh1 expression in vivo can induce hair cell formation in the utricle from postnatal days 1 to 21, while the efficacy of hair cell induction is progressively reduced as the animals become older. In the utricle, the induction of hair cells occurs both within the sensory region and in cells in the transitional epithelium next to the sensory region. Within the sensory epithelium, the central region, known as the striola, is most subjective to the induction of hair cell formation. Furthermore, forced Atoh1 expression can promote proliferation in an age-dependent manner that mirrors the progressively reduced efficacy of hair cell induction in the postnatal utricle. These results suggest that targeting both cell proliferation and Atoh1 in the utricle striolar region may be explored to induce hair cell regeneration in mammals. The study also demonstrates the usefulness of the animal model that provides an in vivo Atoh1 induction model for vestibular regeneration studies.