Myosin VI Haploinsufficiency Reduced Hearing Ability in Mice

•Myosin VI haploinsufficiency leads to mild hearing loss in mice.•Heterozygous myosin VI knockout mice developed age-related stereocilia fusion.•The outer hair cells of aged mice decreased due to myosin VI haploinsufficiency.•The ribbon synapses of aged mice were decreased due to myosin VI haploinsufficiency. In human, myosin VI (MYO6) haploinsufficiency causes postlingual progressive hearing loss. Because the usefulness of mouse models remains unclear, we produced novel Myo6 null (−/−) mutant mice and analyzed the hearing phenotypes of Myo6+/− (+/−) heterozygous mutants. We first recorded and compared the auditory brainstem responses and distortion product otoacoustic emissions in control Myo6+/+ (+/+) wild-type and +/− mice. These hearing phenotypes of +/− mice were mild; however, we confirmed that +/− mice developed progressive hearing loss. In particular, the hearing loss of female +/− mice progressed faster than that of male +/− mice. The stereocilia bundles of +/− mice exhibited progressive taper loss in cochlear inner hair cells (IHCs) and outer hair cells (OHCs). The loss of OHCs in +/− heterozygotes occurred at an earlier age than in +/+ mice. In particular, the OHCs at the basal area of the cochlea were decreased in +/− mice. IHC ribbon synapses from the area at the base of the cochlea were significantly reduced in +/− mice. Thus, our study indicated that MYO6 haploinsufficiency affected the detection of sounds in mice, and we suggest that +/− mice with Myo6 null alleles are useful animal models for gene therapy and drug treatment in patients with progressive hearing loss due to MYO6 haploinsufficiency.