KCNQ4 channel is required for outer hair cell survival, postnatal maturation and efferent innervation

Abstract

INTRODUÇÃO: KCNQ4 is a voltage-gated K+ channel essential for hearing. Impairment of its function produces a chronic depolarization of hair cells (HC) leading to cell death, and hearing loss (HL). The mechanism of cell death remains unknown. A protective pathway is carried out by the efferent system by the activation of its synapses, restoring membrane potential. However, its contribution to KCNQ4-related HL is unknown. OBJETIVOS: Our aim is to evaluate the molecular, tissue and functional alterations of HCs and their efferent connectivity in a mouse model of HL, which is a knock-out for the KCNQ4 channel (Kcnq4-/- ) (Nº083/2016). MÉTODOS: In the WT and Kcnq4-/- mice we performed immunofluorescence (IF) combined with superresolution-confocal microscopy, quantitative PCR (qPCR), Auditory brainstem response (ABR) and Distortion product of otoacoustic emissions (DPOAE) assays. RESULTADOS: In 4 postnatal-weeks-old (W) Kcnq4-/- animals, using IF, we found an increase of cleaved CASPASE-3 expression in outer hair cells (OHC) from the basal turn. Moreover, qPCR analysis revealed that the expression ratio between the pro- and anti-apoptotic factors Bax/Bcl2 was ~76-fold higher. We also found mislocalization of the membrane protein PRESTIN and of the efferent synapses (~30%) that contact OHC. Furthermore, we found no changes in terminals volume but a 40% decrease in the number of synapses/OHC in Kcnq4-/- mice. By contrast, both genotypes at 2W exhibited the same immature wiring pattern. To test the hearing function, we performed ABR showing a significant threshold shift of 20-48 dB SPL in the 5.6-45.25 kHz frequency range. Besides, DPOAE test revealed a threshold shift of ~12-20 dB SPL in the 8-45.25 kHz range. CONCLUSÕES: We found new insights into the mechanism of HL in the Kcnq4-/- mice. While the basal OHCs die by apoptosis, hearing function is impaired in all cochlear regions