Stem Cell-Based Hair Cell Regeneration and Therapy in the Inner Ear

Conditional Overexpression of Serpine2 Promotes Hair Cell Regeneration from Lgr5+ Progenitors in the Neonatal Mouse Cochlea

Neonatal cochlear Lgr5+ progenitors retain limited hair cells (HCs) regenerative capacity, but the regulatory network remains incompletely defined. Serpin family E member 2 (Serpine2) is shown to participate in regulating proliferation and differentiation of cochlear Lgr5+ progenitors in the previous in vitro study. Here, the expression pattern and in vivo roles of Serpine2 in HC regeneration are explored by transgenic mice. It is found that Serpine2 is expressed in the mouse cochlea after birth with a downward trend as the mice age. In addition, Serpine2 conditional overexpression in vivo in Lgr5+ progenitors of neonatal mice cochlea results in an increased number of ectopic HCs in a dose-dependent manner. Serpine2 knockdown ex vivo and in vivo can inhibit HC regeneration. EdU assay and lineage tracing assay demonstrate these ectopic HCs likely originate from Lgr5+ progenitors through direct transdifferentiation rather than through mitotic regeneration. Moreover, single-nucleus RNA sequencing analysis and mRNA level validation reveal that conditionally overexpressed Serpine2 likely induces HC regeneration via inhibiting sonic hedgehog (SHH) signal pathway and inducing Atoh1 and Pou4f3 transcription factor. In brief, these data indicate that Serpine2 plays a pivotal role in HC regeneration from Lgr5+ progenitors in the neonatal mouse cochlea, and this suggests a new avenue for future research into HC regeneration.

Echoes in the night: How sleep quality influences auditory health

The intricate relationship between sleep disorders and hearing loss emerges as a burgeoning field of scholarly inquiry. Numerous studies have illuminated a potential correlation between the two, affecting the quality of life and overall health of individuals. Hearing loss, or auditory impairment, serves as a critical indicator of physiological dysfunction, casting a pall over the daily existence and professional endeavors of those affected, potentially leading to irreversible deafness if left untreated. Sleep disorders may cause physical and psychological changes that further affect hearing, while auditory dysfunction may detrimentally impact sleep experienced by individuals. Although certain studies have failed to find a direct link between sleep duration and hearing loss, it is evident that sleep-related issues do increase the risk of hearing loss. Thus, understanding the relationship between sleep disorders and hearing loss, alongside the underlying mechanisms, will help establish interventions aimed at enhancing sleep quality and safeguarding auditory health. This systematic review endeavors to elucidate the correlation between sleep disorders and hearing loss, offering valuable insights and guidance for future basic research and clinical applications.

CSF1R inhibition agents protect against cisplatin ototoxicity and synergize with immunotherapy for Head and Neck Squamous Cell Carcinoma

Immunotherapy has emerged as a promising therapeutic approach. However, limited research exists on combining cisplatin with CSF1/CSF1R immunotherapy in Head and Neck Squamous Cell Carcinoma. Furthermore, few studies have investigated concurrent immunotherapeutic strategies to mitigate cisplatin-induced ototoxicity.Developing otoprotective agents that simultaneously reduce cisplatin resistance and enhance therapeutic efficacy holds significant implications for future treatment modalities. In this investigation, we evaluated the safety and efficacy profile of CSF1R inhibitor (PLX3397). Our findings demonstrate that PLX3397 confers otoprotection in cisplatin-induced ototoxicity through cochlear macrophage depletion, synergizes with cisplatin inhibited tumor cell survival, migration, and invasion in vitro. Additionally, it significantly suppressed xenograft tumor lesion growth and angiogenesis in zebrafish models while modulating the polarization state of tumor-associated macrophages in vitro and inducing tumor immune activation. Our findings suggest that PLX3397 represents a promising immunotherapeutic agent, and its combination with cisplatin may constitute a novel therapeutic strategy for attenuating cisplatin-induced ototoxicity while synergistically enhancing immunotherapy for Head and Neck Squamous Cell Carcinoma.

3D Bioprinting Inner Ear Organ of Corti Organoids Induce Hair Cell Regeneration

Hearing loss is often regarded as "invisible disability" which seriously affects the quality of life. The majority of hearing loss cases are caused by the damage to inner ear hair cells or connected spiral ganglion cells, and there is a lack of effective treatment measures. In recent years, significant progress has been made in the use of two-dimensional (2D) culture systems to induce the regeneration of auditory cells. However, the regenerated hair cells cannot form effective functional ciliary bundles under the 2D system, let alone establish synaptic contact with spiral ganglion cells, so they cannot truly achieve physiological repair of hearing. In this study, our aim is to construct a three-dimensional (3D) organ of Corti organoid through 3D bioprinting, which combines "3D culture scaffold + multiple induction signals + inner ear stem cells." Then we evaluate the effects of the organoids on the differentiation of inner ear stem cells into auditory cells. We found that the organoids promoted adhesion and growth of inner ear stem cells, as well as the production of hair cells and nerve cells. The research may develop a novel approach for studying auditory cell regeneration and hearing loss repair.

Implication of GPRASP2 in the Proliferation and Hair Cell-Forming of Cochlear Supporting Cells

G protein-coupled receptor-associated sorting protein 2 (GPRASP2) has been identified as the causative gene for X-linked recessive syndromic hearing loss (SHL) in our previous study. However, the role of GPRASP2 in auditory function remains unclear. The present study demonstrated that Gprasp2 overexpression in mouse organoids promoted the proliferation of supporting cells (SCs), which was mainly mediated by the Hedgehog signalling pathway. Meanwhile, GPRASP2 promoted hair cell (HC) formation from SCs via β-catenin signalling. In addition, GPRASP2 deficiency resulted in increased lysosomal degradation of SMO protein, leading to decreased expression of β-catenin and the Hedgehog pathway transcription factor GLI1. In neomycin-treated mouse cochlear explant, the smoothened agonist (SAG) recured the HC loss and further facilitated AAV-ie-Gprasp2 to promote the proliferation of SCs and formation of HCs. Our results suggested that GPRASP2 could be a potential candidate for gene therapy in the regeneration of HCs.

Hesperidin activates Nrf2 to protect cochlear hair cells from cisplatin-induced damage

Cisplatin is widely employed in clinical oncology as an anticancer chemotherapy drug in clinical practice and is known for its severe ototoxic side effects. Prior research indicates that the accumulation of reactive oxygen species (ROS) plays a pivotal role in cisplatin's inner ear toxicity. Hesperidin is a flavanone glycoside extracted from citrus fruits that has anti-inflammatory and antioxidant effects. Nonetheless, the specific pharmacological actions of hesperidin in alleviating cisplatin-induced ototoxicity remain elusive. The transcription factor nuclear factor erythroid 2-related factor 2 (Nrf2) is a critical mediator of the cellular oxidative stress response, is influenced by hesperidin. Activation of Nrf2 was shown to have a protective effect against cisplatin-induced ototoxicity. The potential of hesperidin to stimulate Nrf2 in attenuating cisplatin's adverse effects on the inner ear warrants further investigation. This study employs both in vivo and in vitro models of cisplatin ototoxicity to explore this possibility. Our results reveal that hesperidin mitigates cisplatin-induced ototoxicity by activating the Nrf2/NQO1 pathway in sensory hair cells, thereby reducing ROS accumulation, preventing hair cell apoptosis, and alleviating hearing loss.

Apigenin attenuates cisplatin-induced hair cell damage in the zebrafish lateral line

Cisplatin, a widely used chemotherapy drug, is notorious for causing ototoxicity, which leads to irreversible sensorineural hearing loss by damaging cochlear sensory hair cells (HCs), spiral ganglion neurons (SGNs), and the stria vascularis (SV). Mechanisms include DNA adduct formation, mitochondrial dysfunction, oxidative stress, and inflammation, ultimately triggering cell death pathways like apoptosis, necroptosis, pyroptosis, or ferroptosis. Apigenin, a natural flavonoid found in various foods and beverages, possesses antioxidant, anti-inflammatory, and anti-tumor properties. Despite these benefits, its potential to mitigate cisplatin-induced ototoxicity remains unexplored. To investigate, we administered varying concentrations of apigenin (1 μM, 20 μM, 100 μM, and 250 μM) alongside cisplatin (200 μM) to zebrafish larvae at 5 days post fertilization. Cisplatin significantly reduced lateral line HCs, impacting auditory function as shown in startle response tests. However, co-administration with apigenin preserved lateral line HCs and mitigated cisplatin-induced hearing loss. In larvae exposed to cisplatin, TUNEL assay confirmed significant HCs apoptosis, which apigenin effectively countered by suppressing reactive oxygen species accumulation in lateral line HCs. RNA-seq analysis highlighted apigenin's role in modulating apoptosis-related pathways, supporting its protective effects against cisplatin-induced ototoxicity. These findings underscore apigenin's potential as a crucial protective agent against cisplatin-induced ototoxicity, meriting further investigation for clinical applications.

Atoh1 overexpression promotes Guinea pig bone marrow mesenchymal stem cells to differentiate into neural stem cell

Sensorineural hearing loss (SNHL) is a prevalent condition in otolaryngology. A key obstacle is finding effective strategies for regenerating damaged cochlear hair cells in adult animals. A practical and reliable approach has been developed to create a superior cell source for stem cell transplantation in the inner ear to treat SNHL. Atoh1 is involved in the differentiation of neurons, intestinal secretory cells, and mechanoreceptors including auditory hair cells, and thus plays an important role in neurogenesis. Lentivirus-mediated transfection of bone marrow mesenchymal stem cells (BMSCs) was utilized to achieve stable expression of the essential transcription factor Atoh1, which is crucial for developing auditory hair cells without compromising cell survival. By manipulating the induction conditions through altering the cell growth environment using anti-adherent culture, the synergistic impact of basic fibroblast growth factor (bFGF) and epidermal growth factor (EGF) was effectively applied to significantly improve the differentiation efficiency of bone marrow-derived mesenchymal stem cells (BMSC) into neural stem cells (NSCs) following Atoh1 transfection, thereby reducing the induction time. The study indicated that the newly proposed transdifferentiation method effectively transformed BMSCs into NSCs in a controlled environment, presenting a potential approach for stem cell transplantation to promote hair cell regeneration.

The miR-182-5p/GPX4 Pathway Contributes to Sevoflurane-Induced Ototoxicity via Ferroptosis

Our study aimed to investigate the role of ferroptosis in sevoflurane-induced hearing impairment and explore the mechanism of the microRNA-182-5p (miR-182-5p)/Glutathione Peroxidase 4 (GPX4) pathway in sevoflurane-induced ototoxicity. Immunofluorescence staining was performed using myosin 7a and CtBP2. Cell viability was assessed using the CCK-8 kit. Fe2+ concentration was measured using FerroOrange and Mi-to-FerroGreen fluorescent probes. The lipid peroxide level was assessed using BODIPY 581/591 C11 and MitoSOX fluorescent probes. The auditory brainstem response (ABR) test was conducted to evaluate the hearing status. Bioinformatics tools and dual luciferase gene reporter analysis were used to confirm the direct targeting of miR-182-5p on GPX4 mRNA. GPX4 and miR-182-5p expression in cells was assessed by qRT-PCR and Western blot. Ferrostatin-1 (Fer-1) pretreatment significantly improved hearing impairment and damage to ribbon synapses in mice caused by sevoflurane exposure. Immunofluorescence staining revealed that Fer-1 pretreatment reduced intracellular and mitochondrial iron overload, as well as lipid peroxide accumulation. Our findings indicated that miR-182-5p was upregulated in sevoflurane-exposed HEI-OC1 cells, and miR-182-5p regulated GPX4 expression by binding to the 3'UTR of GPX4 mRNA. The inhibition of miR-182-5p attenuated sevoflurane-induced iron overload and lipid peroxide accumulation. Our study elucidated that the miR-182-5p/GPX4 pathway was implicated in sevoflurane-induced ototoxicity by promoting ferroptosis.

The Suppression of Ubiquitin C-Terminal Hydrolase L1 Promotes the Transdifferentiation of Auditory Supporting Cells into Hair Cells by Regulating the mTOR Pathway

In mammals, hearing loss is irreversible due to the lack of the regenerative capacity of the auditory epithelium. However, stem/progenitor cells in mammalian cochleae may be a therapeutic target for hearing regeneration. The ubiquitin proteasome system plays an important role in cochlear development and maintenance. In this study, we investigated the role of ubiquitin C-terminal hydrolase L1 (UCHL1) in the process of the transdifferentiation of auditory supporting cells (SCs) into hair cells (HCs). The expression of UCHL1 gradually decreased as HCs developed and was restricted to inner pillar cells and third-row Deiters' cells between P2 and P7, suggesting that UCHL1-expressing cells are similar to the cells with Lgr5-positive progenitors. UCHL1 expression was decreased even under conditions in which supernumerary HCs were generated with a γ-secretase inhibitor and Wnt agonist. Moreover, the inhibition of UCHL1 by LDN-57444 led to an increase in HC numbers. Mechanistically, LDN-57444 increased mTOR complex 1 activity and allowed SCs to transdifferentiate into HCs. The suppression of UCHL1 induces the transdifferentiation of auditory SCs and progenitors into HCs by regulating the mTOR pathway.