Molecular alterations caused by chronic cochlear depolarization in a mouse model of hearing loss

DIONISIO, L.; RIAS E.; CARIGNANO C; STUPNIKI S.; VERA M.; SPITZMAUL, G.

Buenos Aires

Congreso; REUNION DE SOCIEDADES DE BIOCIENCIAS 2021; 2021

SAIC SAI AAFE NANOMED-AR

The voltage-gated potassium (K+) channel KCNQ4 is the main responsible for the extrusion of the K+ that enters the cochlear sensory cells upon sound stimulation. Besides, outer hair cells (OHC) excitability is under control of the efferent neurons of the Medial Olivocochlear (MOC) system. In response to overstimulation, MOC cholinergic neurons activate the calcium-induced K+ channels BK and SK2, which extrude K+ out of the cell repolarizing the membrane. Intracellular accumulation of K+ leads to a chronic depolarization that may damage hair cells causing hearing loss (HL). KCNQ4 activity impairment is the main cause of DFNA2, a non-syndromic progressive HL. Using a mouse model lacking Kcnq4 (Kcnq4-/-), we reported that OHC death begins at the basal turn progressing to the apex in 3-6-week-old (W) animals. We hypothesized that the KCNQ4 absence causes MOC chronic overstimulation leading to activation of death pathways. Using immunofluorescence (IF), we evaluated the MOC terminals and observed a lower synaptic density and mislocalization of the efferent terminals contacting OHC in 4W Kcnq4-/- mice. In addition, we analyzed by qPCR the gene expression of the efferent components located in the MOC terminals. We detected a ~3.5-fold decrease in the mRNA expression of the nicotinic receptor α10 subunit with no changes in the α9 subunit, and a ~8-fold decrease in the mRNA expression of BK and SK2 in 4W Kcnq4-/- animals. Finally, we studied the possible pathways involved in OHC death. By IF, we found an increase of cleaved-caspase 3 expression in the OHC at the basal turn and gene expression analysis by qPCR revealed that the pro-apoptotic Bax transcript was upregulated while anti-apoptotic Bcl2 was downregulated in Kcnq4-/- mice. These results demonstrate an alteration of the efferent transmission in OHC that could contribute to the activation of the apoptotic pathway driving to OHC death.