Abnormal Tectorial Membranes in Sensorineural Hearing Loss: A Human Temporal Bone Study

Microvilli regulate the release modes of alpha-tectorin to organize the domain-specific matrix architecture of the tectorial membrane

The tectorial membrane (TM) is an apical extracellular matrix (ECM) in the cochlea essential for auditory transduction. The TM exhibits highly ordered domain-specific architecture. Alpha-tectorin/TECTA is a glycosylphosphatidylinositol (GPI)-anchored ECM protein essential for TM organization. Here, we identified that TECTA is released by distinct modes: proteolytic shedding by TMPRSS2 and GPI-anchor-dependent release from the microvillus tip. In the medial/limbal domain, proteolytically shed TECTA forms dense fibers. In the lateral/body domain produced by the supporting cells displaying dense microvilli, the proteolytic shedding restricts TECTA to the microvillus tip and compartmentalizes the collagen-binding site. The tip-localized TECTA, in turn, is released in a GPI-anchor-dependent manner to form collagen-crosslinking fibers, required for maintaining the spacing and parallel organization of collagen fibrils. Overall, we showed that distinct release modes of TECTA determine the domain-specific organization pattern, and the microvillus coordinates the release modes along its membrane to organize the higher-order ECM architecture.

Advanced Magnetic Resonance Imaging Sheds Light on the Distinct Pathophysiology of Various Types of Acute Sensorineural Hearing Loss

OBJECTIVE

To compare the findings of magnetic resonance imaging (MRI) with advanced protocols in patients with various types of acute sensorineural hearing loss (ASNHL).

STUDY DESIGN

Retrospective case review.

SETTING

Tertiary referral center.

PATIENTS

Two hundred eighty-seven patients with ASNHL.

INTERVENTIONS

All patients underwent MRI scanning, including heavily T2-weighted three-dimensional fluid-attenuated inversion recovery before and 4 hours after the intravenous administration of gadolinium contrast medium (delayed 3D-FLAIR). A hybrid of the reversed image of the positive endolymph signal and the native image of the perilymph signal image was constructed to visualize the endolymphatic space.

RESULTS

The detection rates of abnormal MRI findings vary significantly among different types of ASNHL. A hyperintense signal on delayed 3D-FLAIR was observed in all patients with intralabyrinthine schwannoma or vestibular schwannoma and 20.5% of patients with idiopathic sudden sensorineural hearing loss (ISSNHL) but was rarely observed in definite Ménière's disease (MD, 2.6%). In contrast, endolymphatic hydrops (EH) was frequently observed in patients with definite MD (79.5%) but was observed much less frequently in patients with ISSNHL (11.0%). In patients with cochlear MD and ALHL, detection rates of cochlear EH were similar to those with definite MD, whereas detection rates of vestibular EH were significantly lower than in patients with definite MD.

CONCLUSIONS

The significantly different detection rates of abnormal MRI findings among various types of ASNHL shed light on the distinct pathophysiology of each disorder. A diagnosis based on MRI findings with advanced protocols may help select treatment strategies and provide prognostic information for patients.

Assessment of prestin level changes as an inner-ear biomarker in patients with idiopathic sudden sensorineural hearing loss

Objective

To assess the correlation of serum prestin level and audiological findings in adults with idiopathic sudden sensorineural hearing loss.

Methods

Audiometry and serum prestin measurements were performed at study entry (T0), at day 14 (end of treatment, T1) and at day 30 (T2).

Results

A total of 25 idiopathic sudden sensorineural hearing loss patients and 25 healthy adults were included. The geometric mean prestin level in the case and control groups at T0 was 227.7 pg/ml and 130.5 pg/ml, respectively. The geometric mean prestin level in the case group demonstrated a downward trend at T1 and T2 (214.0 pg/ml and 180.1 pg/ml, respectively; p < 0.001). Of 17 patients with high baseline prestin levels (over 150 pg/ml), prestin levels tended to decrease in 11 patients, and 5 of them (45.5 per cent) showed good recovery.

Conclusion

The prestin concentrations increased in two-thirds of patients with idiopathic sudden sensorineural hearing loss. Future work is recommended to determine the location of injury.

The release of surface-anchored α-tectorin, an apical extracellular matrix protein, mediates tectorial membrane organization

The tectorial membrane (TM) is an apical extracellular matrix (ECM) that hovers over the cochlear sensory epithelium and plays an essential role in auditory transduction. The TM forms facing the luminal endolymph-filled space and exhibits complex ultrastructure. Contrary to the current extracellular assembly model, which posits that secreted collagen fibrils and ECM components self-arrange in the extracellular space, we show that surface tethering of α-tectorin (TECTA) via a glycosylphosphatidylinositol anchor is essential to prevent diffusion of secreted TM components. In the absence of surface-tethered TECTA, collagen fibrils aggregate randomly and fail to recruit TM glycoproteins. Conversely, conversion of TECTA into a transmembrane form results in a layer of collagens on the epithelial surface that fails to form a multilayered structure. We propose a three-dimensional printing model for TM morphogenesis: A new layer of ECM is printed on the cell surface concomitant with the release of a preestablished layer to generate the multilayered TM.