AAV-mediated rescue of Eps8 expression in vivo restores hair-cell function in a mouse model of recessive deafness

The transduction of acoustic information by hair cells depends upon mechanosensitive stereociliary bundles that project from their apical surface. Mutations or absence of the stereociliary protein EPS8 cause deafness in humans and mice, respectively. knockout mice ( ) have hair cells with immature stereocilia and fail to become sensory receptors. Here, we show that exogenous delivery of using Anc80L65 in P1-P2 mice rescued the hair bundle structure of apical-coil hair cells. Rescued hair bundles correctly localize EPS8, WHIRLIN, MYO15, and BAIAP2L2, and generate normal mechanoelectrical transducer currents. Inner hair cells with normal-looking stereocilia re-expressed adult-like basolateral ion channels (BK and KCNQ4) and have normal exocytosis. The number of hair cells undergoing full recovery was not sufficient to rescue hearing in mice. Adeno-associated virus (AAV)-transduction of P3 apical-coil and P1-P2 basal-coil hair cells does not rescue hair cells, nor does Anc80L65-Eps8 delivery in adult mice. We propose that AAV-induced gene-base therapy is an efficient strategy to recover the complex hair-cell defects in mice. However, this therapeutic approach may need to be performed since, at postnatal ages, hair cells appear to have matured or accumulated damage beyond the point of repair.