Characterization of Neuronal Cell Death in the Spiral Ganglia of a Mouse Model of Endolymphatic Hydrops

Abstract

Hypothesis Spiral ganglion neurons (SGN) in the Phex Hyp-Duk male mouse, a murine model of postnatal endolymphatic hydrops (ELH) undergo progressive deterioration reminiscent of human and other animal models of ELH with features suggesting apoptosis as an important mechanism. Background Histological analysis of the mutant's cochlea demonstrates ELH by postnatal day (P) 21 and SGN loss by P90. The SGN loss appears to occur in a consistent topographic pattern beginning at the cochlear apex. Methods SGN were counted at P60, P90 and P120. Semi-quantitative reverse transcriptase-polymerase chain reaction (RT-PCR), quantitative PCR, and immunohistochemical analyses of activated caspases-3, -8 and -9 were performed on cochlear sections obtained from mutants and controls. Terminal deoxynucleotidyl transferase-mediated dUTP-biotin nick-end labeling assay (TUNEL) was carried out on two mutants and two controls. Results Corrected SGN counts in control mice were greater in the apical turn of the cochleae at P90 and P120, respectively (P<0.01). Increased expression of activated caspase-3,-8 and -9 was seen in the mutant. At later time-points, activated caspase expression gradually declined in the apical turns and increased in basal turns of the cochlea. Quantitative and semi-quantitative PCR analysis confirmed increased expression of caspase-3, -8 and -9 at P21 and P40. TUNEL staining demonstrated apoptosis at P90 in the apical and basal turns of the mutant cochleae. Conclusion SGN degeneration in the Phex Hyp-Duk/Y mouse appear to mimic patterns observed in other animals with ELH. Apoptosis plays an important role in the degeneration of the SGN in the Phex Hyp-Duk male mouse.

Otoprotective effects of mouse nerve growth factor in DBA/2J mice with early‐onset progressive hearing loss

“…Hair cells, spiral ganglion cells, and stria vascularis were observed under light microscopy (Leica DMI4000 B). SGN counts were carried out following the methods described previously (Semaan et al, ). The average value in four sections approaching the maximum area from a turn of each animal's cochlea was defined as the density for that turn.…”

Caspase-Mediated Apoptosis in the Cochleae Contributes to the Early Onset of Hearing Loss in A/J Mice

“…Hair cells, spiral ganglion cells, and stria vascularis were observed under light microscopy (Leica DMI4000 B, Leica Microsystems, Wetzlar, Germany). Spiral ganglion cell counts were carried out following the methods described previously ( Guillery, 2002 ; Semaan et al., 2013 ). The average value in four sections from a turn of each animal’s cochlea was defined as the density for that turn.…”

“…The reaction conditions were as follows: denature at 95℃ for 3 min, followed by 40 cycles of 94℃ for 15 s, 60℃ for 30 s, and 72℃ for 40 s, and a final extension at 72℃ for 10 min. The fold-change in genes relative to Gapdh was determined by the 2 (-ΔΔCt) method ( Semaan et al., 2013 ).…”

The use of animal models to study cell transplantation in neuropathic hearing loss

“…There is a wealth of literature and much debate in the field regarding the underlying pathology and this is largely beyond the scope of this review. However, the Phex mouse mutant may be a useful adjunct to the canon of MD research (Semaan et al, 2013). A mutation in the X-linked phosphate regulating gene (Phex) produces, amongst other bone-related abnormalities, endolymphatic hydrops.…”