Increased mitophagy protects cochlear hair cells from aminoglycoside-induced damage

Application of self-assembly palladium single-atom nanozyme over polyoxometalates in protection against neomycin-induced hearing loss by inhibiting ferroptosis

Deafness mainly results from irreversible impairment of hair cells (HCs), which may relate to oxidative stress, yet therapeutical solutions is lacked due to limited understanding on the exact molecular mechanism. Herein, mimicking the molecular structure of natural enzymes, a palladium (Pd) single-atom nanozyme (SAN) was fabricated, exhibiting superoxide dismutase and catalase activity, transforming reactive oxygen species (ROS) into O2 and H2O. We examined the involvement of Pd in neomycin-induced HCs loss in vitro and in vivo over zebrafish. Our results revealed that neomycin treatment induced apoptosis in HCs, resulting in substantial of ROS elevation in HEI-OC1 cells, decrease in mitochondrial membrane potential, and increase in lipid peroxidation and iron accumulation, ultimately leading to iron-mediated cell death. Noteworthy, Pd SAN treatment exhibited significant protective effects against HCs damage and impaired HCs function in zebrafish by inhibiting ferroptosis. Furthermore, the application of iron death inducer RSL3 resulted in notable exacerbation of neomycin-induced harm, which was mitigated by Pd administration. Our investigation demonstrates that antioxidants is promising for inhibiting ferroptosis and repairing of mitochondrial function in HCs and the enzyme-mimic SAN provides a good strategy for designing drugs alleviating neomycin-induced ototoxicity.

Hyperforin improves matrix stiffness induced nucleus pulposus inflammatory degeneration by activating mitochondrial fission

OBJECTIVE

The continuously increasing extracellular matrix stiffness during intervertebral disc degeneration promotes disease progression. In an attempt to obtain novel treatment methods, this study aims to investigate the changes in nucleus pulposus cells under the stimulation of a stiff microenvironment.

DESIGN

RNA sequencing and metabolomics experiments were combined to evaluate the primary nucleus pulposus and screen key targets under mechanical biological stimulation. Additionally, small molecules work in vitro were used to confirm the target regulatory effect and investigate the mechanism. In vivo, treatment effects were validated using a rat caudal vertebrae compression model.

RESULTS

Our research results revealed that by activating TRPC6, hyperforin, a herbaceous extract can rescue the inflammatory phenotype caused by the stiff microenvironment, hence reducing intervertebral disc degeneration (IDD). Mechanically, it activates mitochondrial fission to inhibit PFKFB3.

CONCLUSION

In summary, this study reveals the important bridging role of TRPC6 between mechanical stiffness, metabolism, and inflammation in the context of nucleus pulposus degeneration. TRPC6 activation with hyperforin may become a promising treatment for IDD.

Schisandrin B protect inner hair cells from cisplatin by inhibiting celluar oxidative stress and apoptosis

Cisplatin is an effective chemotherapeutic agent; however, ototoxicity is one of its negative effects that greatly limits the use of cisplatin in clinical settings. Previous research has shown that the most important process cisplatin damage to inner ear cells, such as hair cells (HCs), is the excessive production and accumulation of ROS. Schisandrin B (SchB), is a low-toxicity, inexpensive, naturally occurring antioxidant with a variety of pharmacological effects. Therefore, the potential antioxidant effects of SchB may be useful for cisplatin ototoxicity treatment. In this study, the effects of SchB on cochlear hair cell viability, ROS levels, and expression of apoptosis-related molecules were evaluated by CCK-8, immunofluorescence, flow cytometry, and qRT-PCR, as well as auditory brainstem response (ABR) and dysmorphic product otoacoustic emission (DPOAE) tests to assess the effects on inner ear function. The results showed that SchB treatment increased cell survival, prevented apoptosis, and reduced cisplatin-induced ROS formation. SchB treatment reduced the loss of cochlear HCs caused by cisplatin in exosome culture. In addition, SchB treatment attenuated cisplatin-induced hearing loss and HC loss in mice. This study demonstrates the ability of SchB to inhibit cochlear hair cell apoptosis and ROS generation and shows its potential therapeutic effect on cisplatin ototoxicity.

HMGA1 promotes the progression of esophageal squamous cell carcinoma by elevating TKT-mediated upregulation of pentose phosphate pathway

Esophageal squamous cell carcinoma (ESCC) possesses a poor prognosis and treatment outcome. Dysregulated metabolism contributes to unrestricted growth of multiple cancers. However, abnormal metabolism, such as highly activated pentose phosphate pathway (PPP) in the progression of ESCC remains largely unknown. Herein, we report that high-mobility group AT-hook 1 (HMGA1), a structural transcriptional factor involved in chromatin remodeling, promoted the development of ESCC by upregulating the PPP. We found that HMGA1 was highly expressed in ESCC. Elevated HMGA1 promoted the malignant phenotype of ESCC cells. Conditional knockout of HMGA1 markedly reduced 4-nitroquinoline-1-oxide (4NQO)-induced esophageal tumorigenesis in mice. Through the metabolomic analysis and the validation assay, we found that HMGA1 upregulated the non-oxidative PPP. With the transcriptome sequencing, we identified that HMGA1 upregulated the expression of transketolase (TKT), which catalyzes the reversible reaction in non-oxidative PPP to exchange metabolites with glycolytic pathway. HMGA1 knockdown suppressed the PPP by downregulating TKT, resulting in the reduction of nucleotides in ESCC cells. Overexpression of HMGA1 upregulated PPP and promoted the survival of ESCC cells by activating TKT. We further characterized that HMGA1 promoted the transcription of TKT by interacting with and enhancing the binding of transcription factor SP1 to the promoter of TKT. Therapeutics targeting TKT with an inhibitor, oxythiamine, reduced HMGA1-induced ESCC cell proliferation and tumor growth. Together, in this study, we identified a new role of HMGA1 in ESCCs by upregulating TKT-mediated activation of PPP. Our results provided a new insight into the role of HMGA1/TKT/PPP in ESCC tumorigenesis and targeted therapy.

Recent Progress in Generation of Inner Ear Organoid

Inner ear organoids play a crucial role in hearing research. In comparison to other animal models and 2D cell culture systems, inner ear organoids offer significant advantages for studying the mechanisms of inner ear development and exploring novel approaches to disease treatment. Inner ear organoids derived from human cells are more closely resemble normal human organs in development and function. The 3D culture system of the inner ear organoid enhances cell-cell interactions and mimics the internal environment. In this review, the progress and limitations of organoid culture methods derived from tissue-specific progenitors and pluripotent stem cells (PSCs) are summarized, which may offer new insights into generating organoids that closely resemble the inner ear in terms of morphology and function.

Multiple mechanisms of aminoglycoside ototoxicity are distinguished by subcellular localization of action

Mechanosensory hair cells of the inner ears and lateral line of vertebrates display heightened vulnerability to environmental insult, with damage resulting in hearing and balance disorders. An important example is hair cell loss due to exposure to toxic agents including therapeutic drugs such as the aminoglycoside antibiotics such as neomycin and gentamicin and antineoplastic agents. We describe two distinct cellular pathways for aminoglycoside-induced hair cell death in zebrafish lateral line hair cells. Neomycin exposure results in death from acute exposure with most cells dying within 1 hour of exposure. By contrast, exposure to gentamicin results primarily in delayed hair cell death, taking up to 24 hours for maximal effect. Washout experiments demonstrate that delayed death does not require continuous exposure, demonstrating two mechanisms where downstream responses differ in their timing. Acute damage is associated with mitochondrial calcium fluxes and can be alleviated by the mitochondrially-targeted antioxidant mitoTEMPO, while delayed death is independent of these factors. Conversely delayed death is associated with lysosomal accumulation and is reduced by altering endolysosomal function, while acute death is not sensitive to lysosomal manipulations. These experiments reveal the complexity of responses of hair cells to closely related compounds, suggesting that intervention focusing on early events rather than specific death pathways may be a successful therapeutic strategy.

Mitophagy-regulated Necroptosis plays a vital role in the nephrotoxicity of Fumonisin B1 in vivo and in vitro

Fumonisin B1 (FB1), one of the most widely distributed mycotoxins found in grains and feeds as contaminants, affects many organs including the kidney once ingested. However, the nephrotoxicity of FB1 remains to be further uncovered. The connection between necroptosis and nephrotoxicity of FB1 has been investigated in this study. The results showed that mice exposed to high doses of FB1 (2.25 mg/kg b.w.) developed kidney damage, with significant increases in proinflammatory cytokines (Il-6, Il-1β), kidney injury-related markers (Ngal, Ntn-1), and gene expressions linked to necroptosis (Ripk1, Ripk3, Mlkl). The concentration-dependent damage effects of FB1 on PK-15 cells contain cytotoxicity, cellular inflammatory response, and necroptosis. These FB1-induced effects can be neutralized by pretreatment with the necroptosis inhibitor Nec-1. Additionally, FB1 caused mitochondrial damage and mitophagy in vivo and in vitro, whereas Mdivi-1, a mitophagy inhibitor, prevented these effects on PK-15 cells as well as, more crucially, necroptosis. In conclusion, the RIPK1/RIPK3/MLKL signal route of necroptosis, which may be controlled by mitophagy, mediated nephrotoxicity of FB1. Our findings clarify the underlying molecular pathways of FB1-induced nephrotoxicity.

Potential role of modulating autophagy levels in sensorineural hearing loss

In recent years, extensive research has been conducted on the pathogenesis of sensorineural hearing loss (SNHL). Apoptosis and necrosis have been identified to play important roles in hearing loss, but they cannot account for all hearing loss. Autophagy, a cellular process responsible for cell self-degradation and reutilization, has emerged as a significant factor contributing to hearing loss, particularly in cases of autophagy deficiency. Autophagy plays a crucial role in maintaining cell health by exerting cytoprotective and metabolically homeostatic effects in organisms. Consequently, modulating autophagy levels can profoundly impact the survival, death, and regeneration of cells in the inner ear, including hair cells (HCs) and spiral ganglion neurons (SGNs). Abnormal mitochondrial autophagy has been demonstrated in animal models of SNHL. These findings indicate the profound significance of comprehending autophagy while suggesting that our perspective on this cellular process holds promise for advancing the treatment of SNHL. Thus, this review aims to clarify the pathogenic mechanisms of SNHL and the role of autophagy in the developmental processes of various cochlear structures, including the greater epithelial ridge (GER), SGNs, and the ribbon synapse. The pathogenic mechanisms of age-related hearing loss (ARHL), also known as presbycusis, and the latest research on autophagy are also discussed. Furthermore, we underscore recent findings on the modulation of autophagy in SNHL induced by ototoxic drugs. Additionally, we suggest further research that might illuminate the complete potential of autophagy in addressing SNHL, ultimately leading to the formulation of pioneering therapeutic strategies and approaches for the treatment of deafness.

Hair cell-specific Myo15 promoter-mediated gene therapy rescues hearing in DFNB9 mouse model

Adeno-associated viral (AAV) vectors are increasingly used as vehicles for gene delivery to treat hearing loss. However, lack of specificity of the transgene expression may lead to overexpression of the transgene in nontarget tissues. In this study, we evaluated the expression efficiency and specificity of transgene delivered by AAV-PHP.eB under the inner ear sensory cell-specific Myo15 promoter. Compared with the ubiquitous CAG promoter, the Myo15 promoter initiates efficient expression of the GFP fluorescence reporter in hair cells, while minimizing non-specific expression in other cell types of the inner ear and CNS. Furthermore, using the Myo15 promoter, we constructed an AAV-mediated therapeutic system with the coding sequence of OTOF gene. After inner ear injection, we observed apparent hearing recovery in Otof-/- mice, highly efficient expression of exogenous otoferlin, and significant improvement in the exocytosis function of inner hair cells. Overall, our results indicate that gene therapy mediated by the hair cell-specific Myo15 promoter has potential clinical application for the treatment of autosomal recessive deafness and yet for other hereditary hearing loss related to dysfunction of hair cells.

Deferoxamine protects cochlear hair cells and hair cell-like HEI-OC1 cells against tert-butyl hydroperoxide-induced ototoxicity

Oxidative stress is the common mechanism of sensorineural hearing loss (SNHL) caused by many factors, such as noise, drugs and ageing. Here, we used tert-butyl hydroperoxide (t-BHP) to cause oxidative stress damage in HEI-OC1 cells and in an in vitro cochlear explant model. We observed lipid peroxidation, iron accumulation, mitochondrial shrinkage and vanishing of mitochondrial cristae, which caused hair cell ferroptosis, after t-BHP exposure. Moreover, the number of TUNEL-positive cells in cochlear explants and HEI-OC1 cells increased significantly, suggesting that t-BHP caused the apoptosis of hair cells. Administration of deferoxamine (DFOM) significantly attenuated t-BHP-induced hair cell loss and disordered hair cell arrangement in cochlear explants as well as HEI-OC1 cell death, including via apoptosis and ferroptosis. Mechanistically, we found that DFOM treatment reduced t-BHP-induced lipid peroxidation, iron accumulation and mitochondrial pathological changes in hair cells, consequently mitigating apoptosis and ferroptosis. Moreover, DFOM treatment alleviated GSH depletion caused by t-BHP and activated the Nrf2 signalling pathway to exert a protective effect. Furthermore, we confirmed that the protective effect of DFOM mainly depended on its ability to chelate iron by constructing Fth1 knockout (KO), TfR1 KO and Nrf2 KO HEI-OC1 cell lines using CRISPR/Cas9 technology and a Flag-Fth1 (overexpression) HEI-OC1 cell line using the FlpIn™ System. Our findings suggest that DFOM is a potential drug for SNHL treatment due to its ability to inhibit apoptosis and ferroptosis by chelating iron and scavenging reactive oxygen species (ROS).

Gene expression analysis of oxidative stress-related genes in the apical, middle, and basal turns of the cochlea

It can be observed from aminoglycoside-induced hair cell damage that the cochlea basal turn is more susceptible to trauma than the apex. Drug-induced hearing loss is closely related to oxidative damage. The basilar membrane directly exposed to these ototoxic drugs exhibits differences in damage, indicating that there is an inherent difference in the sensitivity to oxidative damage from the apex to the base of the cochlea. It has been reported that the morphology and characteristics of the cochlea vary from the apex to the base. Therefore, we investigated oxidative stress-related gene expression profiles in the apical, middle, and basal turns of the cochlea. The Oxidative Stress RT2 Profiler™ PCR Array revealed that three of the 84 genes (Mb, Mpo, and Ncf1) were upregulated in the middle turn compared to their level in the apical turn. Moreover, eight genes (Mb, Duox1, Ncf1, Ngb, Fmo2, Gpx3, Mpo, and Gstk1) were upregulated in the basal turn compared to their level in the apical turn. The qPCR verification data were similar to that of the PCR Array. We found that MPO was expressed in the rat cochlea and protected against gentamicin-induced hair cell death. This study summarized the data for the gradient of expression of oxidative stress-related genes in the cochlea and found potential candidate targets for prevention of ototoxic deafness, which may provide new insights for cochlear pathology.

Mitochondria in depression: The dysfunction of mitochondrial energy metabolism and quality control systems

BACKGROUND

Depression is the most disabling neuropsychiatric disorder, causing difficulties in daily life activities and social interactions. The exact mechanisms of depression remain largely unclear. However, some studies have shown that mitochondrial dysfunction would play a crucial role in the occurrence and development of depression.

AIMS

To summarize the known knowledge about the role of mitochondrial dysfunction in the pathogenesis of depression.

METHODS

We review the recent literature， including 105 articles, to summarize the mitochondrial energy metabolism and quality control systems in the occurrence and development of depression. Some antidepressants which may exert their effects by improving mitochondrial function are also discussed.

RESULTS

Impaired brain energy metabolism and (or) damaged mitochondrial quality control systems have been reported not only in depression patients but in animal models of depression. Although the classical antidepressants have not been specially designed to target mitochondria, the evidence suggests that many antidepressants may exert their effects by improving mitochondrial function.

CONCLUSIONS

This brief review focuses on the findings that implicate mitochondrial dysfunction and the quality control systems as important etiological factors in the context of depressive disorders. It will help us to understand the various concepts of mitochondrial dysfunction in the pathogenesis of depression, and to explore novel and more targeted therapeutic approaches for depression.

Mechanisms and otoprotective strategies of programmed cell death on aminoglycoside-induced ototoxicity

Aminoglycosides are commonly used for the treatment of life-threatening bacterial infections, however, aminoglycosides may cause irreversible hearing loss with a long-term clinical therapy. The mechanism and prevention of the ototoxicity of aminoglycosides are still limited although amounts of studies explored widely. Specifically, advancements in programmed cell death (PCD) provide more new perspectives. This review summarizes the general signal pathways in programmed cell death, including apoptosis, autophagy, and ferroptosis, as well as the mechanisms of aminoglycoside-induced ototoxicity. Additionally, novel interventions, especially gene therapy strategies, are also investigated for the prevention or treatment of aminoglycoside-induced hearing loss with prospective clinical applications.

Proteomic Analysis of the Mitochondrial Responses in P19 Embryonic Stem Cells Exposed to Florfenicol

Florfenicol (FLO) has been shown to elicit diverse toxic effects in plants, insects, and mammals. Previously, our investigations revealed that FLO induced abnormal cardiac development and early embryonic mortality in chicken embryos. However, the effect of FLO on mitochondrial responses in stem cells remains unclear. In this study, we show that FLO significantly diminishes proliferation viability and obstructs the directed differentiation of P19 stem cells (P19SCs) into cardiomyocytes. Proteomic analysis revealed 148 differentially expressed proteins in response to FLO. Functional analysis has pinpointed FLO interference with biological processes associated with oxidative phosphorylation within the mitochondria. In alignment with the results of proteomic analysis, we confirmed that FLO inhibits the expression of both nuclear DNA-encoded and mitochondrial DNA-encoded subunits of the electron transport chain. Subsequent experiments demonstrated that FLO disrupts mitochondrial dynamics and induces the mitochondrial unfolded protein response to maintain mitochondrial homeostasis. These findings collectively highlight the significance of mitochondrial dynamics and the mitochondrial unfolded protein response to mediate the decreased proliferation viability and directed differentiation potential in P19SCs treated with FLO. In conclusion, this study provides a comprehensive overview of mitochondrial responses to FLO-induced cytotoxicity and enhances our understandings of the molecular mechanisms underlying FLO-induced embryonic toxicity.

The Relevance of Autophagy within Inner Ear in Baseline Conditions and Tinnitus-Related Syndromes

Tinnitus is the perception of noise in the absence of acoustic stimulation (phantom noise). In most patients suffering from chronic peripheral tinnitus, an alteration of outer hair cells (OHC) starting from the stereocilia (SC) occurs. This is common following ototoxic drugs, sound-induced ototoxicity, and acoustic degeneration. In all these conditions, altered coupling between the tectorial membrane (TM) and OHC SC is described. The present review analyzes the complex interactions involving OHC and TM. These need to be clarified to understand which mechanisms may underlie the onset of tinnitus and why the neuropathology of chronic degenerative tinnitus is similar, independent of early triggers. In fact, the fine neuropathology of tinnitus features altered mechanisms of mechanic-electrical transduction (MET) at the level of OHC SC. The appropriate coupling between OHC SC and TM strongly depends on autophagy. The involvement of autophagy may encompass degenerative and genetic tinnitus, as well as ototoxic drugs and acoustic trauma. Defective autophagy explains mitochondrial alterations and altered protein handling within OHC and TM. This is relevant for developing novel treatments that stimulate autophagy without carrying the burden of severe side effects. Specific phytochemicals, such as curcumin and berberin, acting as autophagy activators, may mitigate the neuropathology of tinnitus.

3-hydroxy-3-methylglutaryl-coenzyme A (HMG-CoA) reductase (HMGCR) protects hair cells from cisplatin-induced ototoxicity in vitro: possible relation to the activities of p38 MAPK signaling pathway

The 3-hydroxy-3-methylglutaryl-coenzyme A (HMG-CoA) reductase (HMGCR) gene encodes rate-limiting enzyme in cholesterol biosynthesis, which is related to cell proliferation and mitochondrial function. The present study was designed to explore the expression of HMGCR in murine cochlear hair cells and HEI-OC1 cells and the possible mechanisms underpinning the actions of HMGCR in cisplatin-induced ototoxicity, with special attention given to p38 mitogen-activated protein kinase (MAPK) activities in vitro. The expressions of HMGCR, p-p38, cleaved caspase-3 and LC3B was measured by immunofluorescence and western blot. JC-1 staining and MitoSOX Red were used to detect mitochondria membrane potential (MMP) and reactive oxygen species (ROS) levels respectively. The apoptosis of auditory cells was assessed by TUNEL staining and flow cytometry. Protein levels of bcl2/bax and beclin1 were examined by western blot. We found that HMGCR was widely expressed in the auditory cells, of both neonatal mice and 2-month-old mice, in cytoplasm, nucleus and stereocilia. Moreover, 30 μM cisplatin elicited the formation of ROS, which, in turn, led to HMGCR reduction, activating p38 kinase-related apoptosis and autophagy in auditory cells. Meanwhile, co-treatment with ROS scavenger at a concentration of 2 mM, N-acetyl-L-cysteine (NAC), could alleviate the aforementioned changes. In addition, HMGCR silencing resulted in higher p38 MAPK-mediated apoptosis and autophagy under cisplatin injury. Taken together, we demonstrate that, for the first time, that HMGCR is expressed in the cochlear. Furthermore, HMGCR exerts protective benefit on auditory cells against cisplatin-mediated injury stimulated by ROS, culminating in regulation of p38 MAPK-dependent apoptosis and autophagy.

UBQLN2 and HSP70 participate in Parkin-mediated mitophagy by facilitating outer mitochondrial membrane rupture

Amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD) are two aging-related neurodegenerative diseases that share common key features, including aggregation of pathogenic proteins, dysfunction of mitochondria, and impairment of autophagy. Mutations in ubiquilin 2 (UBQLN2), a shuttle protein in the ubiquitin-proteasome system (UPS), can cause ALS/FTD, but the mechanism underlying UBQLN2-mediated pathogenesis is still uncertain. Recent studies indicate that mitophagy, a selective form of autophagy which is crucial for mitochondrial quality control, is tightly associated with neurodegenerative diseases including Alzheimer's disease, Parkinson's disease, and ALS. In this study, we show that after Parkin-dependent ubiquitination of damaged mitochondria, UBQLN2 is recruited to poly-ubiquitinated mitochondria through the UBA domain. UBQLN2 cooperates with the chaperone HSP70 to promote UPS-driven degradation of outer mitochondrial membrane (OMM) proteins. The resulting rupture of the OMM triggers the autophagosomal recognition of the inner mitochondrial membrane receptor PHB2. UBQLN2 is required for Parkin-mediated mitophagy and neuronal survival upon mitochondrial damage, and the ALS/FTD pathogenic mutations in UBQLN2 impair mitophagy in primary cultured neurons. Taken together, our findings link dysfunctional mitophagy to UBQLN2-mediated neurodegeneration.

The mitophagy pathway and its implications in human diseases

Mitochondria are dynamic organelles with multiple functions. They participate in necrotic cell death and programmed apoptotic, and are crucial for cell metabolism and survival. Mitophagy serves as a cytoprotective mechanism to remove superfluous or dysfunctional mitochondria and maintain mitochondrial fine-tuning numbers to balance intracellular homeostasis. Growing evidences show that mitophagy, as an acute tissue stress response, plays an important role in maintaining the health of the mitochondrial network. Since the timely removal of abnormal mitochondria is essential for cell survival, cells have evolved a variety of mitophagy pathways to ensure that mitophagy can be activated in time under various environments. A better understanding of the mechanism of mitophagy in various diseases is crucial for the treatment of diseases and therapeutic target design. In this review, we summarize the molecular mechanisms of mitophagy-mediated mitochondrial elimination, how mitophagy maintains mitochondrial homeostasis at the system levels and organ, and what alterations in mitophagy are related to the development of diseases, including neurological, cardiovascular, pulmonary, hepatic, renal disease, etc., in recent advances. Finally, we summarize the potential clinical applications and outline the conditions for mitophagy regulators to enter clinical trials. Research advances in signaling transduction of mitophagy will have an important role in developing new therapeutic strategies for precision medicine.

cdh23 affects congenital hearing loss through regulating purine metabolism

Introduction

The pathogenic gene CDH23 plays a pivotal role in tip links, which is indispensable for mechanoelectrical transduction in the hair cells. However, the underlying molecular mechanism and signal regulatory networks that influence deafness is still largely unknown.

Methods

In this study, a congenital deafness family, whole exome sequencing revealed a new mutation in the pathogenic gene CDH23, subsequently; the mutation has been validated using Sanger sequencing method. Then CRISPR/Cas9 technology was employed to knockout zebrafish cdh23 gene. Startle response experiment was used to compare with wide-type, the response to sound stimulation between wide-type and cdh23-/-. To further illustrate the molecular mechanisms underlying congenital deafness, comparative transcriptomic profiling and multiple bioinformatics analyses were performed.

Results

The YO-PRO-1 assay result showed that in cdh23 deficient embryos, the YO-PRO-1 signal in inner ear and lateral line neuromast hair cells were completely lost. Startle response experiment showed that compared with wide-type, the response to sound stimulation decreased significantly in cdh23 mutant larvae. Comparative transcriptomic showed that the candidate genes such as atp1b2b and myof could affect hearing by regulating ATP production and purine metabolism in a synergetic way with cdh23. RT-qPCR results further confirmed the transcriptomics results. Further compensatory experiment showed that ATP treated cdh23-/- embryos can partially recover the mutant phenotype.

Conclusion

In conclusion, our study may shed light on deciphering the principal mechanism and provide a potential therapeutic method for congenital hearing loss under the condition of CDH23 mutation.

Crosstalk between autophagy and CSCs: molecular mechanisms and translational implications

Cancer stem cells(CSCs) play a key role in regulating tumorigenesis, progression, as well as recurrence, and possess typical metabolic characteristics. Autophagy is a catabolic process that can aid cells to survive under stressful conditions such as nutrient deficiency and hypoxia. Although the role of autophagy in cancer cells has been extensively studied, CSCs possess unique stemness, and their potential relationship with autophagy has not been fully analyzed. This study summarizes the possible role of autophagy in the renewal, proliferation, differentiation, survival, metastasis, invasion, and treatment resistance of CSCs. It has been found that autophagy can contribute to the maintenance of CSC stemness, facilitate the tumor cells adapt to changes in the microenvironment, and promote tumor survival, whereas in some other cases autophagy acts as an important process involved in the deprivation of CSC stemness thus leading to tumor death. Mitophagy, which has emerged as another popular research area in recent years, has a great scope when explored together with stem cells. In this study, we have aimed to elaborate on the mechanism of action of autophagy in regulating the functions of CSCs to provide deeper insights for future cancer treatment.

Research progress in delineating the pathological mechanisms of GJB2-related hearing loss

Hearing loss is the most common congenital sensory impairment. Mutations or deficiencies of the GJB2 gene are the most common genetic cause of congenital non-syndromic deafness. Pathological changes such as decreased potential in the cochlea, active cochlear amplification disorders, cochlear developmental disorders and macrophage activation have been observed in various GJB2 transgenic mouse models. In the past, researchers generally believed that the pathological mechanisms underlying GJB2-related hearing loss comprised a K⁺ circulation defect and abnormal ATP-Ca²⁺ signals. However, recent studies have shown that K⁺ circulation is rarely associated with the pathological process of GJB2-related hearing loss, while cochlear developmental disorders and oxidative stress play an important, even critical, role in the occurrence of GJB2-related hearing loss. Nevertheless, these research has not been systematically summarized. In this review, we summarize the pathological mechanisms of GJB2-related hearing loss, including aspects of K⁺ circulation, developmental disorders of the organ of Corti, nutrition delivery, oxidative stress and ATP-Ca²⁺ signals. Clarifying the pathological mechanism of GJB2-related hearing loss can help develop new prevention and treatment strategies.

Peroxisome Deficiency in Cochlear Hair Cells Causes Hearing Loss by Deregulating BK Channels

The peroxisome is a ubiquitous organelle in rodent cells and plays important roles in a variety of cell types and tissues. It is previously indicated that peroxisomes are associated with auditory function, and patients with peroxisome biogenesis disorders (PBDs) are found to have hearing dysfunction, but the specific role of peroxisomes in hearing remains unclear. In this study, two peroxisome-deficient mouse models (Atoh1-Pex5^-/- and Pax2-Pex5^-/- ) are established and it is found that peroxisomes mainly function in the hair cells of cochleae. Furthermore, peroxisome deficiency-mediated negative effects on hearing do not involve mitochondrial dysfunction and oxidative damage. Although the mammalian target of rapamycin complex 1 (mTORC1) signaling is shown to function through peroxisomes, no changes are observed in the mTORC1 signaling in Atoh1-Pex5^-/- mice when compared to wild-type (WT) mice. However, the expression of large-conductance, voltage-, and Ca2⁺ -activated K⁺ (BK) channels is less in Atoh1-Pex5^-/- mice as compared to the WT mice, and the administration of activators of BK channels (NS-1619 and NS-11021) restores the auditory function in knockout mice. These results suggest that peroxisomes play an essential role in cochlear hair cells by regulating BK channels. Hence, BK channels appear as the probable target for treating peroxisome-related hearing diseases such as PBDs.

SIRT3/GLUT4 signaling activation by metformin protect against cisplatin-induced ototoxicity in vitro

Cisplatin is highly effective for killing tumor cells. However, as one of its side effects, ototoxicity limits the clinical application of cisplatin. The mechanisms of cisplatin-induced ototoxicity have not been fully clarified yet. SIRT3 is a deacetylated protein mainly located in mitochondria, which regulates a variety of physiological processes in cells. The role of SIRT3 in cisplatin-induced hair cell injury has not been founded. In this study, primary cultured cochlear explants exposed to 5 μM cisplatin, as well as OC-1 cells exposed to 10 μM cisplatin, were used to establish models of cisplatin-induced ototoxicity in vitro. We found that when combined with cisplatin, metformin (75 μM) significantly up-regulated the expression of SIRT3 and alleviated cisplatin-induced apoptosis of hair cells. We regulated the expression of SIRT3 to explore the role of SIRT3 in cisplatin-induced auditory hair cell injury. Overexpression of SIRT3 promoted the survival of auditory hair cells and alleviated the apoptosis of auditory hair cells. In contrast, knockdown of SIRT3 impaired the protective effect of metformin and exacerbated cisplatin injury. In addition, we found that the protective effect of SIRT3 may be achieved by regulating GLUT4 translocation and rescuing impaired glucose uptake caused by cisplatin. Our study confirmed that upregulation of SIRT3 may antagonize cisplatin-induced ototoxicity, and provided a new perspective for the study of cisplatin-induced ototoxicity.

Melatonin Alleviates the Oxygen-Glucose Deprivation/Reperfusion-Induced Pyroptosis of HEI-OC1 Cells and Cochlear Hair Cells via MT-1,2/Nrf2 (NFE2L2)/ROS/NLRP3 Pathway

Substantial evidence suggests that pyroptosis is involved in renal, cerebral, and myocardial ischemia-reperfusion injury. However, whether pyroptosis is involved in ischemia-reperfusion injury of cochlear hair cells has not been explored. In this study, we examined the effects of melatonin on the oxygen-glucose deprivation/reperfusion (OGD/R) of hair cell-like House Ear Institute-Organ of Corti 1 (HEI-OC1) cells and cochlear hair cells in vitro to mimic cochlear ischemia-reperfusion injury in vivo. We found that melatonin treatment protected the HEI-OC1 and cochlear hair cells against OGD/R-induced cell pyroptosis and reduced the expression level of ROS in these cells. However, these effects were completely abolished by the application of luzindole (a non-selective melatonin receptor blocker) and largely offset by the use of ML385 (an nuclear factor erythroid 2-related factor 2 (Nrf2) inhibitor). These findings suggest that melatonin alleviates OGD/R-induced pyroptosis of the hair cell-like HEI-OC1 cells and cochlear hair cells via the melatonin receptor 1A (MT-1) and melatonin receptor 1B (MT-2)/Nrf2 (NFE2L2)/ROS/NLRP3 pathway, which may provide credible evidence for melatonin being used as a potential drug for the treatment of idiopathic sudden sensorineural hearing loss in the future.

Adenovirus-mediated SIRT1 protects cochlear strial marginal cells in a D-gal-induced senescent model in vitro

BACKGROUND

A primary obstacle in age-related hearing loss (ARHL) study is the lack of accelerated senescent models in vitro that explore the precise underlying mechanism in different types of ARHL. The damage to strial marginal cells (SMCs) is a subset of strial presbycusis-associated pathological changes. We aimed to establish a D-galactose (D-gal)-induced SMCs senescent model and study the effect of deacetylase sirtuin 1 (SIRT1) on presbycusis in vitro.

METHODS

SMCs from C57BL/6J neonatal mice were cultured and treated with D-gal to establish accelerated senescent models. And then D-gal-induced SMCs were transfected with adenovirus (Ad)-SIRT1-GFP or Ad-GFP. Oxidative stress and mitochondrial DNA (mtDNA) damage were determined by histological analysis or RT-PCR. Western blotting (WB) and RT-PCR were used to evaluate protein and mRNA levels of superoxide dismutase 2 (SOD2) and SIRT1, respectively. Additionally, apoptosis was investigated by WB and TUNEL staining.

RESULTS

D-gal-induced SMCs exhibited several characteristics of senescence, including increased the level of 8-hydroxy-2'-deoxyguanosine, which is a marker of DNA oxidative damage, and elevated the amount of mtDNA 3860-bp deletion, which is a common type of mtDNA damage in the auditory system of mice. SIRT1 overexpression effectively inhibited these changes by upregulating the level of SOD2, thereby inhibiting cytochrome c translocation from mitochondria to cytoplasm, inhibiting cell apoptosis, and ultimately delaying aging in the D-gal-induced senescent SMCs.

CONCLUSIONS

Altogether, the evidence suggests that the D-gal-induced SMCs accelerated aging model is successfully established, and SIRT1 overexpression protects SMCs against oxidative stress by enhancing SOD2 expression in ARHL.

Mitophagy in ototoxicity

Mitochondrial dysfunction is associated with ototoxicity, which is caused by external factors. Mitophagy plays a key role in maintaining mitochondrial homeostasis and function and is regulated by a series of key mitophagy regulatory proteins and signaling pathways. The results of ototoxicity models indicate the importance of this process in the etiology of ototoxicity. A number of recent investigations of the control of cell fate by mitophagy have enhanced our understanding of the mechanisms by which mitophagy regulates ototoxicity and other hearing-related diseases, providing opportunities for targeting mitochondria to treat ototoxicity.

Mitochondrial dysfunction in hearing loss: Oxidative stress, autophagy and NLRP3 inflammasome

Sensorineural deafness becomes an inevitable worldwide healthy problem, yet the current curative therapy is limited. Emerging evidences demonstrate mitochondrial dysfunction plays a vital role of in the pathogenesis of deafness. Reactive oxygen species (ROS)-induced mitochondrial dysfunction combined with NLRP3 inflammasome activation is involved in cochlear damage. Autophagy not only clears up undesired proteins and damaged mitochondria (mitophagy), but also eliminate excessive ROS. Appropriate enhancement of autophagy can reduce oxidative stress, inhibit cell apoptosis, and protect auditory cells. In addition, we further discuss the interplays linking ROS generation, NLRP3 inflammasome activation, and autophagy underlying the pathogenesis of deafness, including ototoxic drugs-, noise- and aging-related hearing loss.

The role of autophagy and ferroptosis in sensorineural hearing loss

Hearing loss has become a common sensory defect in humans. Because of the limited regenerative ability of mammalian cochlear hair cells (HCs), HC damage (caused by ototoxic drugs, aging, and noise) is the main risk factor of hearing loss. However, how HCs can be protected from these risk factors remains to be investigated. Autophagy is a process by which damaged cytoplasmic components are sequestered into lysosomes for degradation. Ferroptosis is a novel form of non-apoptotic regulated cell death involving intracellular iron overloading and iron-dependent lipid peroxide accumulation. Recent studies have confirmed that autophagy is associated with ferroptosis, and their crosstalk may be the potential therapeutic target for hearing loss. In this review, we provide an overview of the mechanisms of ferroptosis and autophagy as well as their relationship with HC damage, which may provide insights for a new future in the protection of HCs.

Approaches to Mitigate Mitochondrial Dysfunction in Sensorineural Hearing Loss

Mitochondria are highly dynamic multifaceted organelles with various functions including cellular energy metabolism, reactive oxygen species (ROS) generation, calcium homeostasis, and apoptosis. Because of these diverse functions, mitochondria are key regulators of cell survival and death, and their dysfunction is implicated in numerous diseases, particularly neurodegenerative disorders such as Alzheimer's Disease, Parkinson's Disease, and Huntington's Disease. One of the most common neurodegenerative disorders is sensorineural hearing loss (SNHL). SNHL primarily originates from the degenerative changes in the cochlea, which is the auditory portion of the inner ear. Many cochlear cells contain an abundance of mitochondria and are metabolically highly active, rendering them susceptible to mitochondrial dysfunction. Indeed, the causal role of mitochondrial dysfunction in SNHL progression is well established, and therefore, targeted for treatment. In this review, we aim to compile the emerging findings in the literature indicating the role of mitochondrial dysfunction in the progression of sensorineural hearing loss and highlight potential therapeutics targeting mitochondrial dysfunction for hearing loss treatment.

Kölliker’s organ-supporting cells and cochlear auditory development

The Kölliker’s organ is a transient cellular cluster structure in the development of the mammalian cochlea. It gradually degenerates from embryonic columnar cells to cuboidal cells in the internal sulcus at postnatal day 12 (P12)–P14, with the cochlea maturing when the degeneration of supporting cells in the Kölliker’s organ is complete, which is distinct from humans because it disappears at birth already. The supporting cells in the Kölliker’s organ play a key role during this critical period of auditory development. Spontaneous release of ATP induces an increase in intracellular Ca²⁺ levels in inner hair cells in a paracrine form via intercellular gap junction protein hemichannels. The Ca²⁺ further induces the release of the neurotransmitter glutamate from the synaptic vesicles of the inner hair cells, which subsequently excite afferent nerve fibers. In this way, the supporting cells in the Kölliker’s organ transmit temporal and spatial information relevant to cochlear development to the hair cells, promoting fine-tuned connections at the synapses in the auditory pathway, thus facilitating cochlear maturation and auditory acquisition. The Kölliker’s organ plays a crucial role in such a scenario. In this article, we review the morphological changes, biological functions, degeneration, possible trans-differentiation of cochlear hair cells, and potential molecular mechanisms of supporting cells in the Kölliker’s organ during the auditory development in mammals, as well as future research perspectives.

Characteristics of sound localization in children with unilateral microtia and atresia and predictors of localization improvement when using a bone conduction device

This study aimed to determine the characteristics of sound localization in children with unilateral microtia and atresia (UMA) and the influence of a non-surgical bone conduction device (BCD). Hearing benefits were evaluated by the word recognition score (WRS), speech reception threshold, the international outcome inventory for hearing aids (IOI-HA), and the Speech, Spatial, and Qualities of Hearing Test for Parent (SSQ-P). Sound localization was measured using broadband noise stimuli randomly played from seven loudspeakers at different stimulus levels [65, 70, and 75 dB sound pressure levels (SPLs)]. The average unaided WRS and speech-to-noise ratio (SNR) for UMA patients was 18.27 ± 14.63 % and −5 ± 1.18 dB SPL, and the average aided WRS and SNR conspicuously changed to 85.45 ± 7.38 % and −7.73 ± 1.42 dB SPL, respectively. The mean IOI-HA score was 4.57 ± 0.73. Compared to the unaided condition, the mean SSQ-P score in each domain improved from 7.08 ± 2.5, 4.86 ± 2.27, and 6.59 ± 1.4 to 8.72 ± 0.95, 7.61 ± 1.52, and 8.55 ± 1.09, respectively. In the sound localization test, some children with UMA were able to detect sound sources quite well and the sound localization abilities did not deteriorate with the non-surgical BCD. Our study concludes that for children with UMA, the non-surgical BCD provided a definite benefit on speech recognition and high satisfaction without deteriorating their sound localization abilities. It is an efficient and safe solution for the early hearing intervention of these patients.