Echoes of Renewal: Rebuilding the Mammalian Inner Ear

Hearing loss and dizziness are the most common sensory disorders worldwide. About 5% of the world's population is affected by disabling hearing loss, and the prevalence is projected to increase over the next several decades. Cochlear hair cells are essential in converting sound vibrations into electrical signals, which are then relayed centrally via the spiral ganglion neurons and lead to sound perception. The irreversible loss of cochlear hair cells is the most common pathology underlying sensorineural hearing loss in humans. In stark contrast, nonmammalian species such as chicken and zebrafish spontaneously regenerate hair cells from endogenous supporting cells after hair cell damage, and the mechanisms of this process are starting to be revealed. Advances in the understanding of inner ear hair cell development have led to novel protocols to efficiently generate mouse and human inner ear organoids. Several new and promising reprogramming approaches have recently been established to induce hair cell regeneration in the mature mouse cochlear and vestibular organs. In this review, we will discuss these recent advances, the implications for treatments for human hearing loss and balance dysfunction, and future directions of the field.