Congenital hearing impairment associated with peripheral cochlear nerve dysmyelination in glycosylation-deficient muscular dystrophy

Abstract

Hearing loss (HL) is one of the most common sensory impairments and etiologically and genetically heterogeneous disorders in humans. Muscular dystrophies (MDs) are neuromuscular disorders characterized by progressive degeneration of skeletal muscle accompanied by non-muscular symptoms. Aberrant glycosylation of α-dystroglycan causes at least eighteen subtypes of MD, now categorized as MD-dystroglycanopathy (MD-DG), with a wide spectrum of non-muscular symptoms. Despite a growing number of MD-DG subtypes and increasing evidence regarding their molecular pathogeneses, no comprehensive study has investigated sensorineural HL (SNHL) in MD-DG. Here, we found that two mouse models of MD-DG, Large myd/myd and POMGnT1-KO mice, exhibited congenital, non-progressive, and mild-to-moderate SNHL in auditory brainstem response (ABR) accompanied by extended latency of wave I. Profoundly abnormal myelination was found at the peripheral segment of the cochlear nerve, which is rich in the glycosylated α-dystroglycan-laminin complex and demarcated by "the glial dome." In addition, patients with Fukuyama congenital MD, a type of MD-DG, also had latent SNHL with extended latency of wave I in ABR. Collectively, these findings indicate that hearing impairment associated with impaired Schwann cell-mediated myelination at the peripheral segment of the cochlear nerve is a notable symptom of MD-DG.

Mutations of MAP1B encoding a microtubule-associated phosphoprotein cause sensorineural hearing loss

“…These data suggest that Map1b deletion did not affect the function of hair cells but may alter the function of spiral ganglia neurons. These were further supported by the observations that MAP1B deficiency did not affect the morphologies in middle turns, apex, and basal turns of cochlea of mice, in contrast with those in mice bearing other deafness-causing gene mutations such as CDC14A (46)(47)(48). Strikingly, MAP1B deficiency in the mice cochlea altered the morphology and function of SGNs rather than inner hair cells or outer hair cells in other deafness genes such as LMO7 (48).…”

The integrity of cochlear hair cells is established and maintained through the localization of Dia1 at apical junctional complexes and stereocilia

“…Murine cochleae and modioli without cochlear nerves (hereafter SG) were dissected at P5 and lysed by sonication in homogenizing buffer containing Protease Inhibitor Cocktail (Nacalai Tesque, Kyoto, Japan), as described previously 53 , 54 . Total cell lysates were centrifuged at 12,000 × g for 5 min at 4 °C, and the supernatants were subjected to sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) followed by IB for 2 h at 23 °C using primary antibodies diluted in phosphate-buffered saline (PBS) and 0.03% TritonX-100 (TX) containing 0.5% bovine serum albumin (BSA).…”

“…Decalcified cochleae were embedded into paraffin blocks and cut into 12-μm slices on a Leica RM2125 RT (Leica Biosystems, Nussloch, Germany). Sections were immunostained after deparaffinization, as described previously 54 . To analyze cryostat sections of cochleae at P7-14, cochleae were fixed with 2% PFA in 0.1 M PB for 30 min, followed by decalcification in 0.12 M EDTA for 2 h at 23°C and dehydration in 30% sucrose at 4°C overnight.…”

“…Dried tissues, mounted on stages, were sputter-coated with gold in an Ion Sputter E-1010 (High-Technologies, Tokyo, Japan), and observed using a TM3030Plus SEM (Hitachi High-Technologies). For TEM analysis 54 , after block staining with 30% EM Stainer (Nisshin EM Co., Ltd., Japan) for 30 min at 23°C, tissues were dehydrated through a graded ethanol series, embedded in Spur Low-Viscosity Embedding Media (Polysciences Inc., Warrington, PA, USA) and polymerized at 70°C for 8 h. Ultrathin sections (thickness ∼100 nm) were cut on an ultramicrotome (EM-UC7; Leica Microsystems, Wetzlar, Germany), placed on copper grids, and stained with 30% EM Stainer for 20 min and lead citrate for 5 min at 23°C. The grids were examined on a Hitachi H-7100 (Hitachi High-Technologies) electron microscope at 75-110 kV.…”

Nox3-Derived Superoxide in Cochleae Induces Sensorineural Hearing Loss

“…Whole-mount inner ears or cochleae (with bone), surface preparations of cochleae (without bony structures), and 12 μm cryostat sections of dissected cochleae, all of which were first fixed with 4% PFA in 0.1 M phosphate buffer (PB; pH 7.4), were examined as previously described (Ueyama et al, 2014;Morioka et al, 2020). Samples for surface preparations and cryostat sections were decalcified in 0.12 M EDTA for 1 week at 4°C or for 2 days at 23°C.…”