Hear the sounds: the role of G protein-coupled receptors in the cochlea.

Sound is converted by hair cells in the cochlea into electrical signals, which are transmitted by spiral ganglion neurons (SGNs) and heard by the auditory cortex. G protein-coupled receptors (GPCRs) are crucial receptors that regulate a wide range of physiological functions in different organ and tissues. The research of GPCRs in the cochlea is essential for the understanding of the cochlea development, hearing disorders, and the treatment for hearing loss. Recently, several GPCRs have been found to play important roles in the cochlea. Frizzleds and Lgrs are dominant GPCRs that regulate stem cell self-renew abilities. Moreover, Frizzleds and Celsrs have been demonstrated to play core roles in the modulation of cochlear planar cell polarity (PCP). In addition, hearing loss can be caused by mutations of certain GPCRs, such as Vlgr1, Gpr156, S1P2, and Gpr126. And A1, A2A, and CB2 activation by agonists has protective functions on noise- or drug-induced hearing loss. Here, we review the key findings of GPCR in the cochlea and discuss the role of GPCR in the cochlea, such as stem cell fate, PCP, hearing loss, and hearing protection.