Editorial: Sensory Hair Cell Death and Regeneration

Nanodelivery of antioxidant Agents: A promising strategy for preventing sensorineural hearing loss

Sensorineural hearing loss (SNHL), often stemming from reactive oxygen species (ROS) generation due to various factors such as ototoxic drugs, acoustic trauma, and aging, remains a significant health concern. Oxidative stress-induced damage to the sensory cells of the inner ear, particularly the non-regenerating hair cells, is a critical pathologic mechanism leading to SNHL. Despite the proven efficacy of antioxidants in mitigating oxidative stress, their clinical application for otoprotection is hindered by the limitations of conventional drug delivery methods. This review highlights the challenges associated with systemic and intratympanic administration of antioxidants, including the blood-labyrinthine barrier, restricted permeability of the round window membrane, and inadequate blood flow to the inner ear. To overcome these hurdles, the application of nanoparticles as a delivery platform for antioxidants emerges as a promising solution. Nanocarriers facilitate indirect drug delivery to the cochlea through the round and oval window membrane, optimising drug absorption while reducing dosage, Eustachian tube clearance, and associated side effects. Furthermore, the development of nanoparticles carrying antioxidants tailored to the intracochlear environment holds immense potential. This literature research aimed to critically examine the root causes of SNHL and ROS overproduction in the inner ear, offering insights into the application of nanoparticle-based drug delivery systems for safeguarding sensorineural hair cells. By focusing on the intricate interplay between oxidative stress and hearing loss, this research aims to contribute to the advancement of innovative therapeutic strategies for the prevention of SNHL.

OCT-based intra-cochlear imaging and 3D reconstruction: ex vivo validation of a robotic platform

PURPOSE

The small size of the cochlea, and its location deeply embedded in thick temporal bone, poses a challenge for intra-cochlear guidance and diagnostics. Current radiological imaging techniques are not able to visualize the cochlear microstructures in detail. Rotational optical coherence tomography (OCT) fibers show great potential for intra-cochlear guidance. The generated images could be used to map, and study, the tiny cochlear microstructures relevant for hearing.

METHODS

This work describes the design of a rotational OCT probe with an outer diameter of 0.9 mm. It further discusses a robotic system, which features a remote center of motion mechanism, dedicated to the probe's positioning, fine manipulation and stable insertion into the cochlear micro-spaces. Furthermore, the necessary calibration steps for 3D reconstruction are described, followed by a detailed quantitative analysis, comparing the 3D reconstructions using a synthetic, 2:1 scaled scala tympani model with a reconstruction from micro-CT, serving as the ground truth. Finally, the potential of the system is demonstrated by scanning a single ex vivo cadaveric human cochlea.

RESULTS

The study investigates five insertions in the same 2:1 scaled tympani model, along with their corresponding 3D reconstruction. The comparison with micro-CT results in an average root-mean-square error of 74.2 µm, a signed distance error of 38.1 µm and a standard deviation of 63.6 µm. The average F-score of the reconstructions, using a distance threshold of 100 and 74.2 µm, resulted in 83.0% and 71.8%, respectively. Insertion in the cadaveric human cochlea showed the challenges for straight insertion, i.e., navigating the hook region.

CONCLUSION

Overall, the system shows great potential for intra-cochlear guidance and diagnostics, due to the system's capability for precise and stable insertion into the basal turn in the scala tympani. The system, combined with the calibration procedure, results in detailed and precise 3D reconstructions.

Explore the effect of LLY-283 on the ototoxicity of auditory cells caused by cisplatin: A bioinformatic analysis based on RNA-seq

BACKGROUND

Cisplatin is a commonly used chemotherapeutic drug in clinics, and long-term application will lead to hearing impairment. LLY-283, an inhibitor of PRMT5, has not been reported in deafness. Our study aimed to explore the mechanism of LLY-283 in hearing impairment.

MATERIALS AND METHODS

First, we performed RNA-seq (cisplatin in the experimental group and DMSO in the control group) to obtain the biological processes mainly involved in differentially expressed genes (DEGs). CCK-8 and LDH experiments were used to observe the effect of LLY-283 on cisplatin-induced auditory cell injury. ROS experiment was used to monitor the impact of LLY-283 on oxidative damage of auditory cells. Effect of LLY-283 on apoptosis of auditory cells detected by TUNEL experiment. PCR and Western blotting were used to detect the expression of genes and proteins related to auditory cell apoptosis in LLY-283 cells. Meanwhile, we explored the effect of LLY-283 on the expression of PRMT5 in cisplatin-induced hearing impaired cells at RNA and protein levels.

RESULTS

Biological process analysis showed that DEGs were mainly enriched in the apoptotic process involved in morphogenesis (-Log10 P = 3.71). CCK-8 and LDH experiments confirmed that LLY-283 could save cisplatin-induced auditory cell injury. ROS experiments confirmed that LLY-283 could rescue cisplatin-induced oxidative damage to auditory cells. TUNEL experiments confirmed that LLY-283 could protect cisplatin-induced apoptosis of auditory cells. Meanwhile, LLY-283 could inhibit the expression of PRMT5 in auditory cells induced by cisplatin.

CONCLUSION

LLY-283 can rescue cisplatin-induced auditory cell apoptosis injury. LLY-283 can inhibit the increase in PRMT5 expression induced by cisplatin.

Stepwise Induction of Inner Ear Hair Cells From Mouse Embryonic Fibroblasts via Mesenchymal- to-Epithelial Transition and Formation of Otic Epithelial Cells

Although embryonic stem cells or induced pluripotent stem cells are able to differentiate into inner ear hair cells (HCs), they have drawbacks limiting their clinical application, including a potential risk of tumourigenicity. Direct reprogramming of fibroblasts to inner ear HCs could offer an alternative solution to this problem. Here, we present a stepwise guidance protocol to induce mouse embryonic fibroblasts to differentiate into inner ear HC-like cells (HCLs) via mesenchymal-to-epithelial transition and then acquisition of otic sensory epithelial cell traits by overexpression of three key transcription factors. These induced HCLs express multiple HC-specific proteins, display protrusions reminiscent of ciliary bundle structures, respond to voltage stimulation, form functional mechanotransduction channels, and exhibit a transcriptional profile of HC signature. Together, our work provides a new method to produce functional HCLs in vitro, which may have important implications for studies of HC development, drug discovery, and cell replacement therapy for hearing loss.

Phenotype of the Aging-Dependent Spontaneous Onset of Hearing Loss in DBA/2 Mice

Simple Summary

In this study, we confirmed the changes in hearing function and inner ear structure over a long period of time in DBA/2 mice, a laboratory animal model suitable for studying hearing loss. We believe that our study is the first to report findings regarding hearing function and structural changes in DBA/2 mice aged ≥34 weeks. These results are of significance for researchers and the scientific community using laboratory animal models.

Abstract

DBA/2 mice are a well-known animal model for hearing loss developed due to intrinsic properties of these animals. However, results on the phenotype of hearing loss in DBA/2 mice have been mainly reported at an early stage in mice aged ≤7 weeks. Instead, the present study evaluated the hearing ability at 5, 13, and 34 weeks of age using DBA/2korl mice. Auditory brainstem response test was performed at 8–32 KHz at 5, 13, and 34 weeks of age, and hearing loss was confirmed to be induced in a time-dependent manner. In addition, histopathological evaluation at the same age confirmed the morphological damage of the cochlea. The findings presented herein are the results of the long-term observation of the phenotype of hearing loss in DBA/2 mice and can be useful in studies related to aging-dependent hearing loss.

A subset of SMN complex members have a specific role in tissue regeneration via ERBB pathway-mediated proliferation

Spinal muscular atrophy (SMA) is the most common genetic disease in children. SMA is generally caused by mutations in the gene SMN1. The survival of motor neurons (SMN) complex consists of SMN1, Gemins (2-8), and Strap/Unrip. We previously demonstrated smn1 and gemin5 inhibited tissue regeneration in zebrafish. Here we investigated each individual SMN complex member and identified gemin3 as another regeneration-essential gene. These three genes are likely pan-regenerative, since they affect the regeneration of hair cells, liver, and caudal fin. RNA-Seq analysis reveals that smn1, gemin3, and gemin5 are linked to a common set of genetic pathways, including the tp53 and ErbB pathways. Additional studies indicated all three genes facilitate regeneration by inhibiting the ErbB pathway, thereby allowing cell proliferation in the injured neuromasts. This study provides a new understanding of the SMN complex and a potential etiology for SMA and potentially other rare unidentified genetic diseases with similar symptoms.

Gene expression vs. sequence divergence: comparative transcriptome sequencing among natural Rhinolophus ferrumequinum populations with different acoustic phenotypes

BACKGROUND

Although the sensory drive hypothesis can explain the geographic variation in echolocation frequencies of some bat species, the molecular mechanisms underlying this phenomenon are still unclear. The three lineages of greater horseshoe bat (Rhinolophus ferrumequinum) in China (northeast, central-east, and southwest) have significant geographic variation in resting frequencies (RF) of echolocation calls. Because their cochleae have an acoustic fovea that is highly sensitive to a narrow range of frequencies, we reported the transcriptomes of cochleae collected from three genetic lineages of R. ferrumequinum, which is an ideal organism for studying geographic variation in echolocation signals, and tried to understand the mechanisms behind this bat phenomenon by analyzing gene expression and sequence variation.

RESULTS

A total of 8190 differentially expressed genes (DEGs) were identified. We identified five modules from all DEGs that were significantly related to RF or forearm length (FL). DEGs in the RF-related modules were significantly enriched in the gene categories involved in neural activity, learning, and response to sound. DEGs in the FL-related modules were significantly enriched in the pathways related to muscle and actin functions. Using 21,945 single nucleotide polymorphisms, we identified 18 candidate unigenes associated with hearing, five of which were differentially expressed among the three populations. Additionally, the gene ERBB4, which regulates diverse cellular processes in the inner ear such as cell proliferation and differentiation, was in the largest module. We also found 49 unigenes that were under positive selection from 4105 one-to-one orthologous gene pairs between the three R. ferrumequinum lineages and three other Chiroptera species.

CONCLUSIONS

The variability of gene expression and sequence divergence at the molecular level might provide evidence that can help elucidate the genetic basis of geographic variation in echolocation signals of greater horseshoe bats.

Baicalin attenuates gentamicin-induced cochlear hair cell ototoxicity

Gentamicin can lead to cochlear hair cells associated ototoxicity by inducing apoptosis and oxidative stress, which can be alleviated by baicalin, one flavonoid extracted from the root of Scutellaria baicalensis. The role of baicalin in protecting gentamicin-induced hearing loss is unclear. Interference with oxidative stress was investigated in this study using House Ear Institute-Organ of Corti1 (HEI-OC1) cells, which were simultaneously treated with baicalin (0-400 μm) and gentamicin (0.2 or 1 mm). MTT was used to assay cell viability and apoptosis was detected with Annexin V-fluorescein isothiocyanate staining. The production of reactive oxygen species was indicated by 2,7-dichlorofluorescein diacetate fluorescence intensity and mitochondrial depolarization was assayed by JC1-mitochondrial membrane potential assay. Poly(ADP-ribose) polymerase (PARP), cleaved-caspase 3 and cleaved-PARP expression were analyzed with western blot. Baicalin improved the viability of HEI-OC1 cells and significantly reduced the oxidative stress and mitochondrial depolarization compared with the gentamicin treatment group. Gentamicin treatment increased the activation of PARP and caspase-3, while such an increase could be downregulated by baicalin. Baicalin attenuates gentamicin-induced cochlear hair cells ototoxicity, and such inhibition may be mediated by the regulation of reactive oxygen species production, mitochondrial depolarization, and caspase-3 and PARP activation.

In vitro culture of mammalian inner ear hair cells

Auditory function in vertebrates depends on the transduction of sound vibrations into electrical signals by inner ear hair cells. In general, hearing loss resulting from hair cell damage is irreversible because the human ear has been considered to be incapable of regenerating or repairing these sensory elements following severe injury. Therefore, regeneration and protection of inner ear hair cells have become an exciting, rapidly evolving field of research during the last decade. However, mammalian auditory hair cells are few in number, experimentally inaccessible, and barely proliferate postnatally in vitro. Various in vitro primary culture systems of inner ear hair cells have been established by different groups, although many challenges remain unresolved. Here, we briefly explain the structure of the inner ear, summarize the published methods of in vitro hair cell cultures, and propose a feasible protocol for culturing these cells, which gave satisfactory results in our study. A better understanding of in vitro hair cell cultures will substantially facilitate research involving auditory functions, drug development, and the isolation of critical molecules involved in hair cell biology.