Analysis of cochlear outer hair cell degeneration in a mouse model of DFNA2 deafness.

CARIGNANO, C.; BARILA, E.P.; RIAS, E.; SPITZMAUL, G.

Villa Carlos Paz

Workshop; Current Advances on Neurodegeneration: from Molecular Biology to Translational Medicine; 2017

Alexander von Humobldt Foundation

Hearing loss (HL) is the decrease in the acoustic sensitivity in both ears below 25 dB. It can be conductive (alterations in middle ear) or neurosensorial (alterations in the inner ear or auditory pathway). HL can be generated by environmental, genetic or both factors. More than 50% of HL cases have a genetic cause and can be nonsyndromic (70%) or in combination with other defects (syndromic). According to their inheritance, nonsyndromic deafness are classified in autosomic dominant (DFNA), recessive (DFNB) or X-linked (DFN). DFNA2 is a slowly progressing deafness characterized by neurosensorial loss starting early in adulthood at high frequencies and progressing to middle frequencies at the age of 50. Mutations in KCNQ4 channel, the voltage-activated K+ channel expressed in the basal membrane of outer hair cells (OHCs), are the main responsible of DFNA2 deafness. KCNQ4 participate in K+ recycling from OHC and an impairment in its functioning leads to a sustained depolarization of this cell, initiating cell degeneration by still unknown mechanisms. To analyze the role of KCNQ4 channel we use a mouse model that lacks its expression (Kcnq4-/- mouse), leading to cell death. Our aim is to determine the process of OHCs degeneration that progress over time analyzing cell death in different segments of the cochlea from Kcnq4-/- mouse. For this we dissected cochleas from wild type (WT) and Kcnq4-/- mice and analyzed by immunofluorescence the presence of OHCs in whole mount preparations. Our results indicate that at 4 weeks-old age, the number of OHCs decreases around 20% in Kcnq4-/- compared to WT mice (from 374±26 (n=9) to 294±76 (n=12) cells/mm, respectively). The degenerative process advances in the next 2 weeks increasing 10% the amount of cell death and extends further in the following weeks. OHCs loss is different depending on the cochlear turns: basal, middle and apical. We determine a much higher disappearance of OHCs in basal turn compared to the other two. In KO mice, at 6 weeks-old the number of OHCs in the basal fragment decreases 60% while it is around 25 % in the other two fragments. Additionally, our preliminary analysis suggest that OHC death is higher in the middle row than in the outer and inner rows. We concluded that cell degeneration progresses at a rate of ~5 % cell loss/week, starting at the basal turn, suggesting a higher expression or functionality of KNCQ4 channel in OHCs from the basal fragment.