Key Signaling Pathways Regulate the Development and Survival of Auditory Hair Cells

Activation of Wnt/β-catenin signaling to increase B lymphoma Moloney murine leukemia virus insertion region 1 by lithium chloride attenuates the toxicity of cisplatin in the HEI-OC1 auditory cells

Cisplatin is widely used in anti-tumor therapy, but the ototoxicity caused by high-dose cisplatin often limits its efficacy, and the specific mechanism of cisplatin-induced cochlear damage is still not perfect. The Wnt/β-catenin signaling pathway is closely related to aging, embryonic development, and apoptosis. Meanwhile, B lymphoma Moloney murine leukemia virus insertion region 1 (BMI1) plays a certain role in the evolution and development of the inner ear and the occurrence and development of inner ear-related diseases. Our study intends to explore the role and specific mechanism of the Wnt/β-catenin signaling pathway and BMI1 in improving cisplatin ototoxicity. The appropriate experimental concentrations for each drug were selected by CCK-8 cell proliferation assay and Western Blot to detect apoptosis. The lentivirus transfection of HEI-OC1 cochlear hair cells was used to overexpress BMI1. Western Blot, qPCR, and immunofluorescence detected the activation of each component of BMI1 and Wnt/β-catenin signaling pathway in each experimental model. Wnt/β-catenin signaling pathway and BMI1 are jointly involved in cisplatin-induced cell injury. Low lithium chloride (LiCl) concentrations activated the Wnt/β-catenin pathway, increased BMI1 expression, and reduced cisplatin-induced hair cell injury. In contrast, overexpression of BMI1 inhibited the Wnt/β-catenin pathway and reduced hair cell injury. Meanwhile, the increased cisplatin-induced damage to hair cells by inhibiting BMI1 could not be rescued by LiCl. In conclusion, LiCl can ameliorate cisplatin ototoxicity by elevating BMI1 expression through activation of the Wnt/β-catenin pathway. Overexpression of BMI1 inhibits the Wnt/β-catenin pathway and reduces cisplatin-induced hair cell damage.

Silencing of TXNIP attenuates oxidative stress injury in HEI-OC1 by inhibiting the activation of NLRP3 and NF-κB

Sensorineural hearing loss (SNHL) is the most common type of hearing loss worldwide. The primary mechanism is oxidative injury to the cochlea as a result of oxidative stress. Therefore, exploring antioxidant strategies is particularly important in addressing SNHL.Thioredoxin-interacting protein (TXNIP) is an upstream target of oxidative stress-induced damage, and the NOD-like receptor protein 3 (NLRP3) and NF-κB pathways may be the main downstream molecular pathways, but this has not been reported in SNHL. Therefore, we investigated the molecular mechanism and role of TXNIP in oxidative stress injury induced by H2O2 in the HEI-OC1 auditory cells. To induce oxidative stress, HEI-OC1 cells were treated with H2O2. The TXNIP expression was measured by western blotting and Immunofluorescence. Intracellular TXNIP was knocked down using small interfering RNAs (siRNAs). Cell viability was measured by CCK8, total intracellular reactive oxygen species (ROS) by DCFH-DA, mitochondrial ROS by Mito-SOX, NLRP3, pro-caspase-1, total p65 NF-κB, and phospho-p65 NF-κB expression were measured by western blotting. Statistical analyses were performed using one-way analysis of variance, and p < 0.05 was considered statistically significant. We found that H2O2 treatment induced oxidative stress injury in HEI-OC1 cells, as evidenced by decreased cell viability and increased total intracellular and mitochondrial ROS levels (p < 0.05). TXNIP expression was elevated, and NLRP3 and NF-κB were activated (p < 0.05). Moreover, siRNA-TXINIP co-treatment reversed these changes and protected HEI-OC1 cells from oxidative stress (p < 0.05). We concluded that H2O2-induced oxidative stress in HEI-OC1 cells was alleviated by TXNIP inhibition. The finding may provide new insight into the prevention and treatment of SNHL.

Single cell RNA sequencing provides novel cellular transcriptional profiles and underlying pathogenesis of presbycusis

Age-related hearing loss (ARHL) or presbycusis is associated with irreversible progressive damage in the inner ear, where the sound is transduced into electrical signal; but the detailed mechanism remains unclear. Here, we sought to determine the potential molecular mechanism involved in the pathogeneses of ARHL with bioinformatics methods. A single-cell transcriptome sequencing study was performed on the cochlear samples from young and aged mice. Detection of identified cell type marker allowed us to screen 18 transcriptional clusters, including myeloid cells, epithelial cells, B cells, endothelial cells, fibroblasts, T cells, inner pillar cells, neurons, inner phalangeal cells, and red blood cells. Cell-cell communications were analyzed between young and aged cochlear tissue samples by using the latest integration algorithms Cellchat. A total of 56 differentially expressed genes were screened between the two groups. Functional enrichment analysis showed these genes were mainly involved in immune, oxidative stress, apoptosis, and metabolic processes. The expression levels of crucial genes in cochlear tissues were further verified by immunohistochemistry. Overall, this study provides new theoretical support for the development of clinical therapeutic drugs.

FDA-Approved Tedizolid Phosphate Prevents Cisplatin-Induced Hearing Loss Without Decreasing Its Anti-tumor Effect

PURPOSE

Cisplatin is a low-cost clinical anti-tumor drug widely used to treat solid tumors. However, its use could damage cochlear hair cells, leading to irreversible hearing loss. Currently, there appears one drug approved in clinic only used for reducing ototoxicity associated with cisplatin in pediatric patients, which needs to further explore other candidate drugs.

METHODS

Here, by screening 1967 FDA-approved drugs to protect cochlear hair cell line (HEI-OC1) from cisplatin damage, we found that Tedizolid Phosphate (Ted), a drug indicated for the treatment of acute infections, had the best protective effect. Further, we evaluated the protective effect of Ted against ototoxicity in mouse cochlear explants, zebrafish, and adult mice. The mechanism of action of Ted was further explored using RNA sequencing analysis and verified. Meanwhile, we also observed the effect of Ted on the anti-tumor effect of cisplatin.

RESULTS

Ted had a strong protective effect on hair cell (HC) loss induced by cisplatin in zebrafish and mouse cochlear explants. In addition, when administered systemically, it protected mice from cisplatin-induced hearing loss. Moreover, antitumor studies showed that Ted had no effect on the antitumor activity of cisplatin both in vitro and in vivo. RNA sequencing analysis showed that the otoprotective effect of Ted was mainly achieved by inhibiting phosphorylation of ERK. Consistently, ERK activator aggravated the damage of cisplatin to HCs.

CONCLUSION

Collectively, these results showed that FDA-approved Ted protected HCs from cisplatin-induced HC loss by inhibiting ERK phosphorylation, indicating its potential as a candidate for preventing cisplatin ototoxicity in clinical settings.

The ndrg2 Gene Regulates Hair Cell Morphogenesis and Auditory Function during Zebrafish Development

Damages of sensory hair cells (HCs) are mainly responsible for sensorineural hearing loss, however, its pathological mechanism is not yet fully understood due to the fact that many potential deafness genes remain unidentified. N-myc downstream-regulated gene 2 (ndrg2) is commonly regarded as a tumor suppressor and a cell stress-responsive gene extensively involved in cell proliferation, differentiation, apoptosis and invasion, while its roles in zebrafish HC morphogenesis and hearing remains unclear. Results of this study suggested that ndrg2 was highly expressed in the HCs of the otic vesicle and neuromasts via in situ hybridization and single-cell RNA sequencing. Ndrg2 loss-of-function larvae showed decreased crista HCs, shortened cilia, and reduced neuromasts and functional HCs, which could be rescued by the microinjection of ndrg2 mRNA. Moreover, ndrg2 deficiency induced attenuated startle response behaviors to sound vibration stimuli. Mechanistically, there were no detectable HC apoptosis and supporting cell changes in the ndrg2 mutants, and HCs were capable of recovering by blocking the Notch signaling pathway, suggesting that ndrg2 was implicated in HC differentiation mediated by Notch. Overall, our study demonstrates that ndrg2 plays crucial roles in HC development and auditory sensory function utilizing the zebrafish model, which provides new insights into the identification of potential deafness genes and regulation mechanism of HC development.

Whole transcriptome sequencing analysis of blood plasma-derived exosomes from immune-related hearing loss

BACKGROUND

Early diagnosis of immune-related hearing loss and timely treatment can prevent structural damage to the inner ear and contribute to hearing retention. Exosomal miRNAs, lncRNAs and proteins have great prospects as novel biomarkers for clinical diagnosis. Our study aimed to investigate the molecular mechanisms of exosomes or exosomal ceRNA regulatory networks in immune-related hearing loss.

METHODS

An immune-related hearing loss mice model was constructed by injection with inner ear antigen, and then the blood plasma samples of the mice were collected for exosomes isolation by ultra-centrifugation. Subsequently, the different exosomes were sent for whole transcriptome sequencing using Illumina platform. Finally, a ceRNA pair was chosen for validation by RT-qPCR and dual luciferase reporter gene assay.

RESULTS

The exosomes were successfully extracted from the blood samples of the control and the immune-related hearing loss mice. After sequencing, 94 differentially expressed (DE) lncRNAs, 612 DEmRNAs, and 100 DEmiRNAs were found in the immune-related hearing loss-associated exosomes. Afterwards, ceRNA regulatory networks consisting of 74 lncRNAs, 28 miRNAs and 256 mRNAs were proposed, and the genes in the ceRNA regulatory networks were significantly enriched in 34 GO terms of biological processes and 9 KEGG pathways. Finally, Gm9866 and Dusp7 were significantly up-regulated, while miR-185-5p level was declined in the exosomes from immune-related hearing loss, and Gm9866, miR-185-5p and Dusp7 interacted with each other.

CONCLUSIONS

Gm9866-miR-185-5p-Dusp7 was confirmed to be closely correlated with the occurrence and progression of immune-related hearing loss.

A systematic review of the monogenic causes of Non-Syndromic Hearing Loss (NSHL) and discussion of Current Diagnosis and Treatment options

Hearing impairment is one of the most widespread inheritable sensory disorder affecting at least 1 in every 1000 born. About two-third of hereditary hearing loss (HHL) disorders are non-syndromic. To provide comprehensive update of monogenic causes of non-syndromic hearing loss (NSHL), literature search has been carried out with appropriate keywords in the following databases-PubMed, Google Scholar, Cochrane library, and Science Direct. Out of 2214 papers, 271 papers were shortlisted after applying inclusion and exclusion criterion. Data extracted from selected papers include information about gene name, identified pathogenic variants, ethnicity of the patient, age of onset, gender, title, authors' name, and year of publication. Overall, pathogenic variants in 98 different genes have been associated with NSHL. These genes have important role to play during early embryonic development in ear structure formation and hearing development. Here, we also review briefly the recent information about diagnosis and treatment approaches. Understanding pathogenic genetic variants are helpful in the management of affected and may offer targeted therapies in future.

Untargeted metabolomics of the cochleae from two laryngeally echolocating bats

High-frequency hearing is regarded as one of the most functionally important traits in laryngeally echolocating bats. Abundant candidate hearing-related genes have been identified to be the important genetic bases underlying high-frequency hearing for laryngeally echolocating bats, however, extensive metabolites presented in the cochleae have not been studied. In this study, we identified 4,717 annotated metabolites in the cochleae of two typical laryngeally echolocating bats using the liquid chromatography-mass spectroscopy technology, metabolites classified as amino acids, peptides, and fatty acid esters were identified as the most abundant in the cochleae of these two echolocating bat species, Rhinolophus sinicus and Vespertilio sinensis. Furthermore, 357 metabolites were identified as significant differentially accumulated (adjusted p-value <0.05) in the cochleae of these two bat species with distinct echolocating dominant frequencies. Downstream KEGG enrichment analyses indicated that multiple biological processes, including signaling pathways, nervous system, and metabolic process, were putatively different in the cochleae of R. sinicus and V. sinensis. For the first time, this study investigated the extensive metabolites and associated biological pathways in the cochleae of two laryngeal echolocating bats and expanded our knowledge of the metabolic molecular bases underlying high-frequency hearing in the cochleae of echolocating bats.

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.

Identification of Target Proteins Involved in Cochlear Hair Cell Progenitor Cytotoxicity following Gentamicin Exposure

Given the non-labile, terminal differentiation of inner-ear sensory cells, preserving their function is critical since sensory cell damage results in irreversible hearing loss. Gentamicin-induced cytotoxicity is one of the major causes of sensory cell damage and consequent sensorineural hearing loss. However, the precise molecular mechanisms and target proteins involved in ototoxicity are still unknown. The objective of the present study was to identify target proteins involved in gentamicin-induced cytotoxicity to better characterize the molecular pathways involved in sensory cell damage following ototoxic drug administration using House Ear Institute-Organ of Corti 1 (HEI-OC1) cells and high-performance liquid chromatography coupled with tandem mass spectrometry (HPLC-MS/MS). We identified several unique proteins involved in gentamicin-induced cytotoxicity, expression of which were further confirmed using confocal microscopy. Further investigation of these pathways can inform the design and discovery of novel treatment modalities to prevent sensory cell damage and preserve their function.

Triclosan targets miR-144 abnormal expression to induce neurodevelopmental toxicity mediated by activating PKC/MAPK signaling pathway

Although the previous research confirmed that triclosan (TCS) induced an estrogen effect by acting on a novel G-protein coupled estrogen-membrane receptor (GPER), the underlying mechanisms by which downstream pathways induce neurotoxicity remain unclear after TCS activation of GPER. By employing a series of techniques (Illumina miRNA-seq, RT-qPCR, and artificial intervention of miRNA expression), we screened out four important miRNAs, whose target genes were directly/indirectly involved in neurodevelopment and neurobehavior. Especially, the miR-144 up-regulation caused vascular malformation and severely affected hair-cell development and lateral-line-neuromast formation, thereby causing abnormal motor behavior. After microinjecting 1-2-cell embryos, the similar phenotypic malformations as those induced by TCS were observed, including aberrant neuromast, cuticular-plate development and motor behavior. By KEGG pathway enrichment analysis, these target genes were demonstrated to be mainly related to the PKC/MAPK signaling pathway. When a PKC inhibitor was used to suppress the PKC/MAPK pathway, a substantial alleviation of TCS-induced neurotoxicity was observed. Therefore, TCS acts on GPER to activate the downstream PKC/MAPK signaling pathway, further up-regulating miR-144 expression and causing abnormal modulation of these nerve-related genes to trigger neurodevelopmental toxicity. These findings unravel the molecular mechanisms of TCS-induced neurodegenerative diseases, and offer theoretical guidance for TCS-pollution early warning and management.

Agmatine Alleviates Cisplatin-Induced Ototoxicity by Activating PI3K/AKT Signaling Pathway

Cisplatin-induced ototoxicity can be partially attributed to excessive reactive oxygen species (ROS) production, and agmatine is well-known for the activation of the phosphoinositide-3-kinase (PI3K)/protein kinase B (AKT) pathway to inhibit ROS production. Whether agmatine could be used to alleviate cisplatin-induced ototoxicity is investigated. Cisplatin-exposed House Ear Institute-Organ of Corti 1 (HEI-OC1) cells and cochlear explants showed increased ROS production detected by 2',7'-dichlorodihydrofluorescein diacetate (DCFH-DA) staining and decreased cell viability detected by Cell Counting Kit-8 (CCK-8) or Myosin 7a staining, which could be reversed by the agmatine pretreatment. Cisplatin intraperitoneally injected C57BL/6 mice demonstrated damaged auditory function as indicated by distortion products otoacoustic emissions (DPOAEs) and auditory brainstem response (ABR) assays, and trans-tympanically administrated agmatine in the left ears could partly prevent the auditory function loss. Mechanistically, downregulated B-cell lymphoma 2 (Bcl-2) expression, upregulated Bcl2-associated x (Bax) expression, and diminished p-PI3K and p-AKT expression were detected in cisplatin-exposed HEI-OC1 cells and cochlear explants, which could be prevented by the pretreatment with agmatine. Our investigation demonstrates that agmatine pretreatment could alleviate cisplatin-induced ototoxicity with the activation of PI3K/AKT signaling pathway.

c-Myb protects cochlear hair cells from cisplatin-induced damage via the PI3K/Akt signaling pathway

The transcription factor c-Myb is vital for cell survival, proliferation, differentiation, and apoptosis. We have previously reported that c-Myb knockdown exacerbates neomycin-induced damage to cochlea cells. However, the function and regulation of c-Myb in the mammalian inner ear remains unclear. Here, we first found that the expression of c-Myb in cochlear HCs was downregulated after cisplatin damage in vivo. Next, to investigate the role of c-Myb in HCs treated with cisplatin, the recombinant virus AAV-ie-CAG-Myb-HA (AAV-c-Myb) that overexpresses c-Myb was constructed and transfected into HCs. The protein expression of c-Myb was effectively up-regulated in cultured cochlear HCs after the virus transfection, which increased cochlear HC viability, decreased HC apoptosis and reduced intracellular reactive oxygen species (ROS) levels after cisplatin injury in vitro. The overexpression of c-Myb in HCs after AAV-c-Myb transfection in vivo also promoted HC survival, improved the hearing function of mice and reduced HC apoptosis after cisplatin injury. Furthermore, c-Myb-HC conditional knockout mice (Prestin; c-Myb-cKO) in which c-Myb expression is downregulated only in cochlear OHCs were generated and the cisplatin-induced HCs loss, apoptosis and hearing deficit were all exacerbated in Prestin; c-Myb-cKO mice treated with cisplatin in vivo. Finally, mechanistic studies showed that upregulation of the PI3K/Akt signaling pathway by c-Myb contributed to the increased HC survival after cisplatin exposure in vitro. The findings from this work suggest that c-Myb might serve as a new target for the prevention of cisplatin-induced HC damage and hearing loss.

MECOM promotes supporting cell proliferation and differentiation in cochlea

Permanent damage to hair cells (HCs) is the leading cause of sensory deafness. Supporting cells (SCs) are essential in the restoration of hearing in mammals because they can proliferate and differentiate to HCs. MDS1 and EVI1 complex locus (MECOM) is vital in early development and cell differentiation and regulates the TGF-β signaling pathway to adapt to pathophysiological events, such as hematopoietic proliferation, differentiation and cells death. In addition, MECOM plays an essential role in neurogenesis and craniofacial development. However, the role of MECOM in the development of cochlea and its way to regulate related signaling are not fully understood. To address this problem, this study examined the expression of MECOM during the development of cochlea and observed a significant increase of MECOM at the key point of auditory epithelial morphogenesis, indicating that MECOM may have a vital function in the formation of cochlea and regeneration of HCs. Meanwhile, we tried to explore the possible effect and potential mechanism of MECOM in SC proliferation and HC regeneration. Findings from this study indicate that overexpression of MECOM markedly increases the proliferation of SCs in the inner ear, and the expression of Smad3 and Cdkn2b related to TGF signaling is significantly down-regulated, corresponding to the overexpression of MECOM. Collectively, these data may provide an explanation of the vital function of MECOM in SC proliferation and trans-differentiation into HCs, as well as its regulation. The interaction between MECOM, Wnt, Notch and the TGF-β signaling may provide a feasible approach to induce the regeneration of HCs.