Stem cell-based approaches: Possible route to hearing restoration?

The potential of bone marrow derived mesenchymal stem cells in treating cisplatin induced sensorineural hearing loss in a guinea pig animal model

BACKGROUND

Sensorineural hearing loss (SNHL) is the most common sensory deficit worldwide. Current solutions for SNHL, including hearing aids, cochlear implants, and hearing assistive devices, do not provide consistent results and fail to address the underlying pathology of hair cell and ganglion cell damage. Stem cell therapy is a cornerstone in regenerative medicine. It provides new hope to treat SNHL by replacing/regenerating damaged hair cells and ganglion cells. Mesenchymal stem cells are an interesting choice in stem cell therapy.

AIM OF THE WORK

Evaluation of bone marrow derived mesenchymal stem cell (BM-MSC) transplantation to improve SNHL management.

METHODS

An experimental study was conducted using 40 recipient guinea pigs, randomly divided into four groups, along with 4 donor guinea pigs for bone marrow harvesting to isolate BM-MSC. Group I (12 animals) served as the control, receiving neither ototoxic drugs nor stem cell treatment. Group II (12 animals) received intraperitoneal cisplatin (1.5 mg/kg/day for 8 days) to induce sensorineural hearing loss, but no stem cell treatment. Group III (12 animals) received IP cisplatin to induce SNHL, followed by BM-MSC transplantation via round window injection one week later. Groups I, II, and III were euthanized 5 weeks after the last cisplatin injection, and their cochleae were examined using light microscopy, scanning electron microscopy, and fluorescent light microscopy to assess the effect of stem cell transplantation on the recovery of neurosensory tissue in the cochlea after cisplatin treatment. Group IV (4 animals) received IP cisplatin to induce SNHL, followed by transplantation of fluorescein-labeled BM-MSC (FLBM-MSC) via round window injection one week later and were euthanized after one week to study stem cell migration and homing.

RESULTS

Light Microscopy: Group I exhibited a normal structure in the organ of Corti, spiral ganglion, and stria vascularis. In contrast, Group II demonstrated degeneration in these areas. Group III showed a preserved structure in the organ of Corti, spiral ganglion, and stria vascularis, with statistically significant differences compared to Group II (p < .05). Scanning Electron Microscopy: Group I displayed normal ultrastructure of the organ of Corti, while Group II showed a loss of outer hair cells. Group III demonstrated preserved ultrastructure of the organ of Corti. Fluorescent Light Microscopy: In Group IV, transplanted cells were observed to home into the cochlear lateral wall, organ of Corti, and spiral ganglion.

CONCLUSION

The study showed that BM-MSCs, delivered via round window injection, can migrate to cochlear regions and protect key structures after cisplatin-induced SNHL in guinea pigs, suggesting their potential as a treatment for SNHL.

Exploring the Potential of Stem Cells: A Systematic Review on Cellular Therapy for Sensorineural Hearing Loss

Sensorineural hearing loss affects a significant portion of the global population, with its prevalence projected to rise sharply in the coming years. Most cases involve the degeneration of hair cells and spiral ganglion neurons within the inner ear, and current therapeutic options for hearing rehabilitation offer limited efficacy with variable outcomes among patients. This systematic review evaluates the existing evidence on stem cell therapy as an intervention for hearing loss, focusing on its impact on hearing restoration, quality of life, and safety. A thorough search of electronic databases and clinical trial registries identified randomized and quasi-randomized studies on this topic. Eight studies met the inclusion criteria, investigating various types of stem cells such as embryonic, umbilical cord, and inner ear cells administered intravenously or directly into the inner ear. Most studies used animal models to simulate hearing loss, while one was conducted in humans. Findings on hearing improvement were mixed, with some studies reporting significant improvements in hearing thresholds and others showing no effect. The safety of stem cell therapy was assessed in a single human study, which noted no significant adverse effects. While the results indicate potential therapeutic value, further human studies with standardized protocols and larger sample sizes are necessary to clarify the safety and effectiveness of stem cell therapy for sensorineural hearing loss.

A single-cell level comparison of human inner ear organoids with the human cochlea and vestibular organs

Inner ear disorders are among the most common congenital abnormalities; however, current tissue culture models lack the cell type diversity to study these disorders and normal otic development. Here, we demonstrate the robustness of human pluripotent stem cell-derived inner ear organoids (IEOs) and evaluate cell type heterogeneity by single-cell transcriptomics. To validate our findings, we construct a single-cell atlas of human fetal and adult inner ear tissue. Our study identifies various cell types in the IEOs including periotic mesenchyme, type I and type II vestibular hair cells, and developing vestibular and cochlear epithelium. Many genes linked to congenital inner ear dysfunction are confirmed to be expressed in these cell types. Additional cell-cell communication analysis within IEOs and fetal tissue highlights the role of endothelial cells on the developing sensory epithelium. These findings provide insights into this organoid model and its potential applications in studying inner ear development and disorders.

Increased diagnostic yield in a cohort of hearing loss families using a comprehensive stepwise strategy of molecular testing

Hearing loss is one of the most common sensory disorders in humans. This study proposes a stepwise strategy of deafness gene detection using multiplex PCR combined with high-throughput sequencing, Sanger sequencing, multiplex ligation-dependent probe amplification (MLPA), and whole-exome sequencing (WES) to explore its application in molecular diagnosis of hearing loss families. A total of 152 families with hearing loss were included in this study, the highest overall diagnosis rate was 73% (111/152). The diagnosis rate of multiplex PCR combined with high-throughput sequencing was 52.6% (80/152). One families was diagnosed by Sanger sequencing of GJB2 exon 1. Two families were diagnosed by MLPA analysis of the STRC gene. The diagnosis rate with additional contribution from WES was 18.4% (28/152). We identified 21 novel variants from 15 deafness genes by WES. Combining WES and deep clinical phenotyping, we diagnosed 11 patients with syndromic hearing loss (SHL). This study demonstrated improved diagnostic yield in a cohort of hearing loss families and confirmed the advantages of a stepwise strategy in the molecular diagnosis of hearing loss.

Exploring the effects and mechanisms of organophosphorus pesticide exposure and hearing loss

Many environmental factors, such as noise, chemicals, and heavy metals, are mostly produced by human activities and easily induce acquired hearing loss. Organophosphorus pesticides (OPs) constitute a large variety of chemicals and have high usage with potentiate damage to human health. Moreover, their metabolites also show a serious potential contamination of soil, water, and air, leading to a serious impact on people's health. Hearing loss affects 430 million people (5.5% of the global population), bringing a heavy burden to individual patients and their families and society. However, the potential risk of hearing damage by OPs has not been taken seriously. In this study, we summarized the effects of OPs on hearing loss from epidemiological population studies and animal experiments. Furthermore, the possible mechanisms of OP-induced hearing loss are elucidated from oxidative stress, DNA damage, and inflammatory response. Overall, this review provides an overview of OP exposure alone or with noise that leads to hearing loss in human and experimental animals.

Induced Pluripotent Stem Cells, a Stepping Stone to In Vitro Human Models of Hearing Loss

Hearing loss is the most prevalent sensorineural impairment in humans. Yet despite very active research, no effective therapy other than the cochlear implant has reached the clinic. Main reasons for this failure are the multifactorial nature of the disorder, its heterogeneity, and a late onset that hinders the identification of etiological factors. Another problem is the lack of human samples such that practically all the work has been conducted on animals. Although highly valuable data have been obtained from such models, there is the risk that inter-species differences exist that may compromise the relevance of the gathered data. Human-based models are therefore direly needed. The irruption of human induced pluripotent stem cell technologies in the field of hearing research offers the possibility to generate an array of otic cell models of human origin; these may enable the identification of guiding signalling cues during inner ear development and of the mechanisms that lead from genetic alterations to pathology. These models will also be extremely valuable when conducting ototoxicity analyses and when exploring new avenues towards regeneration in the inner ear. This review summarises some of the work that has already been conducted with these cells and contemplates future possibilities.

Achievements and Challenges in Transplantation of Mesenchymal Stem Cells in Otorhinolaryngology

Otorhinolaryngology enrolls head and neck surgery in various tissues such as ear, nose, and throat (ENT) that govern different activities such as hearing, breathing, smelling, production of vocal sounds, the balance, deglutition, facial animation, air filtration and humidification, and articulation during speech, while absence of these functions can lead to high morbidity and even mortality. Conventional therapies for head and neck damaged tissues include grafts, transplants, and artificial materials, but grafts have limited availability and cause morbidity in the donor site. To improve these limitations, regenerative medicine, as a novel and rapidly growing field, has opened a new therapeutic window in otorhinolaryngology by using cell transplantation to target the healing and replacement of injured tissues. There is a high risk of rejection and tumor formation for transplantation of embryonic stem cells (ESCs) and induced pluripotent stem cells (iPSCs); mesenchymal stem cells (MSCs) lack these drawbacks. They have easy expansion and antiapoptotic properties with a wide range of healing and aesthetic functions that make them a novel candidate in otorhinolaryngology for craniofacial defects and diseases and hold immense promise for bone tissue healing; even the tissue sources and types of MSCs, the method of cell introduction and their preparation quality can influence the final outcome in the injured tissue. In this review, we demonstrated the anti-inflammatory and immunomodulatory properties of MSCs, from different sources, to be safely used for cell-based therapies in otorhinolaryngology, while their achievements and challenges have been described too.

Building inner ears: recent advances and future challenges for in vitro organoid systems

While inner ear disorders are common, our ability to intervene and recover their sensory function is limited. In vitro models of the inner ear, like the organoid system, could aid in identifying new regenerative drugs and gene therapies. Here, we provide a perspective on the status of in vitro inner ear models and guidance on how to improve their applicability in translational research. We highlight the generation of inner ear cell types from pluripotent stem cells as a particularly promising focus of research. Several exciting recent studies have shown how the developmental signaling cues of embryonic and fetal development can be mimicked to differentiate stem cells into “inner ear organoids” containing otic progenitor cells, hair cells, and neurons. However, current differentiation protocols and our knowledge of embryonic and fetal inner ear development in general, have a bias toward the sensory epithelia of the inner ear. We propose that a more holistic view is needed to better model the inner ear in vitro. Moving forward, attention should be made to the broader diversity of neuroglial and mesenchymal cell types of the inner ear, and how they interact in space or time during development. With improved control of epithelial, neuroglial, and mesenchymal cell fate specification, inner ear organoids would have the ability to truly recapitulate neurosensory function and dysfunction. We conclude by discussing how single-cell atlases of the developing inner ear and technical innovations will be critical tools to advance inner ear organoid platforms for future pre-clinical applications.