Degeneration rates of cochlear hair cells and neurons in a DFNA2 deafness model

DIONISIO, L.; CARIGNANO C; BARILA E; RIAS E; AZTIRIA E; SPITZMAUL, G.

Mar del Plata

Congreso; LXIII Reunión Anual de la Sociedad Argentina de Investigación Clínica (SAIC); 2018

SAIC SAI SAFIS 2018

DFNA2 deafness is an autosomal dominant disease with progressive hearing loss, caused by mutations in voltage-activated potassium channel KCNQ4. In DFNA2, Inner and Outer Hair Cells (IHC and OHC), remain chronically depolarized leading to cell death, tissue degeneration and hearing loss. Transgenic mice with a mutated allele in Kcnq4 gene (Kcnq4-/-) develop a hearing loss syndrome similar to DFNA2.Our aim is to characterize the degeneration rate of HC and spiral ganglion neurons (SGN) in the Kcnq4-/- mouse as a model of DFNA2 deafness. First, using qPCR and immunohistochemistry, we evaluated mRNA and protein expression, in different cochlear segments at several ages of wild-type mice (WT). We observed a decrease in KCNQ4 levels at apical turn compared to basal/middle ones (p=0.0035) at all ages. Next, we performed whole-mount cytocochleograms for evaluating HC density along the 5%-segments (S) of the entire cochlear length, in WT and Kcnq4-/- mice from 3 to 58 postnatal weeks (W). Thus, we determined the IHC and OHC death rate at each S and age. We observed that, for IHC and OHC, cell death starts at basal turn increasing towards the apex with age in Kcnq4-/- mice. Moreover, cell death rate is slower in basal than in distal segments, but starts earlier in OHC (8W) than IHC (40W). Furthermore, by scan electron microscopy, we observed that in Kcnq4-/- mice cell degeneration becomes apparent up to 4W at basal segments, showing impaired cell integrity and stereocilia disorganization. Finally, we analysed SGN survival in WT and Kcnq4-/- mice in each segment at different ages. Kcnq4-/- animals showed neuronal loss up to 40W for basal and apical segments (p