Vesicular glutamate transporter 3 is strongly upregulated in cochlear inner hair cells and spiral ganglion cells of developing circling mice

Vesicular glutamate transporter 3 (VGLUT3) plays a major role in hearing, and mice lacking the VGLUT3 are congenitally deaf due to absence of glutamate release at the inner hair cell afferent synapses. However, whether VGLUT3 is expressed normally in the cochleae of developing circling mice (homozygous (cir/cir) mice), the animal model for human deafness type DFNB6, has not been established. In this study, we investigated the developmental expression of VGLUT3 in cochlear inner hair cells (IHCs) and spiral ganglion cells (SGCs) of homozygous (cir/cir) mice from postnatal day (P)1 to P14 using immunofluorescence (IF) staining and Western blot. VGLUT3 immunoreactivity (IR) and protein expression increased progressively with age in homozygous (cir/cir) and control mice (heterozygous (+/cir) mice and ICR mice). The rank order of VGLUT3 IR in IHCs and SGCs in P14 mice was homozygous (cir/cir) mice = heterozygous (+/cir) mice > ICR mice. The rank order of total protein expression was homozygous (cir/cir) mice > heterozygous (+/cir) mice = ICR mice at P14. IF staining and Western blot analysis indicated that developmental VGLUT3 expression in cochleae was most prominent in homozygous (cir/cir) mice. The possible contribution of VGLUT3 upregulation in the cochlear degeneration is discussed.