Roles of Bak and Sirt3 in Paraquat-Induced Cochlear Hair Cell Damage

Antioxidative Stress-Induced Destruction to Cochlear Cells Caused by Blind Antioxidant Therapy

OBJECTIVE

Verification that blind and excessive use of antioxidants leads to antioxidant stress which exacerbates cochlear cell damage.

STUDY DESIGN

Basic research.

SETTING

The Third Affiliated Hospital of Sun Yat-Sen University.

METHODS

We compared and quantified hair cell-like house ear institute-organ of corti 1 (HEI-OC1) cell density, cell viability, and apoptosis caused by different concentrations of N-acetylcysteine (NAC) via Hoechst staining, Cell Counting Kit 8, Hoechst with propidium iodide staining, and Annexin V with propidium iodide (PI) staining. Apoptosis induced by high concentrations of M40403 and coenzyme Q10 in cochlear explants was analyzed and compared by cochlear dissection and activated caspase 3 labeling.

RESULTS

With the increase of NAC concentration (0-1000 μmol/L), cell density decreased consequently and reached the lowest at 1000 μmol/L (****P ≤ .0001). Cell viability is also declining (**P < .01). The number of Annexin V-fluorescein isothiocyanate-labeled cells and PI-labeled cells increased with increasing NAC concentration after treatment of HEI-OC1 cells for 48 hours. The proportion of apoptotic cells also rose (*P < .05, **P < .01). Cochlear hair cells (HCs) treated with low concentrations of M40403 and coenzyme Q10 for 48 hours showed no damage. When the concentrations of M40403 and coenzyme Q10 were increased (concentrations＞30 μmol/L), HC damage began, followed by a dose-dependent increase in HC loss (*P < .001, **P < .0001). Activated caspase-3 was clearly apparent in cochlear explants treated with 50 μmol/L M40403 and coenzyme Q10 compared with cochlear explants without added M40403 and coenzyme Q10.

CONCLUSION

These experimental results suggest that inappropriate application of antioxidants can cause severe damage to normal cochlear HCs.

Exogenous neuritin restores auditory following cochlear spiral ganglion neuron denervation of gerbils

Spiral ganglion neurons (SGNs) transmit sound signals received by hair cells to the auditory center to produce hearing. The quantity and function are important for maintaining normal hearing function. Limited by the regenerative capacity, SGNs are unable to regenerate spontaneously after injury. Various neurotrophic factors play an important role in the regeneration process. Neuritin is a neurite growth factor that plays an important role in neural plasticity and nerve injury repair. In this study, we used bioinformatics analysis to show that neuritin was negatively correlated with cochlear damage. Then, we aimed to establish a cochlear spiral ganglion-specific sensorineural deafness model in gerbils using ouabain and determine the effects of exogenous neuritin protein in protecting damaged cochlear SGNs and repairing damaged auditory nerve function. The provides a new research strategy and scientific basis for the prevention and treatment of sensorineural deafness caused by the loss of SGNs. We were discovered that neuritin is expressed throughout the development of the gerbil cochlea, primarily in the SGNs and Corti regions. The expression of neuritin was negatively correlated with the sensorineural deafness induced by ouabain. In vitro and in vivo revealed that neuritin significantly maintained the number and arrangement of SGNs and nerve fibers in the damaged cochlea and effectively protected the high-frequency listening function of gerbils.

Impacts of impaired mitochondrial dynamics in hearing loss: Potential therapeutic targets

Mitochondria are the powerhouse of the cells. Under physiological conditions, mitochondrial fission and fusion maintain a dynamic equilibrium in the cytoplasm, which is referred to as mitochondrial dynamics. As an important approach to regulating mitochondrial function and quantity, the role of mitochondrial dynamics has been demonstrated in the pathogenesis of various disease models, including brain damage, neurodegeneration, and stress. As the vital organ of the peripheral auditory system, the cochlea consumes a significant amount of energy, and the maintenance of mitochondrial homeostasis is essential for the cochlear auditory capacity. OPA1 functions as both a necessary gene regulating mitochondrial fusion and a pathogenic gene responsible for auditory neuropathy, suggesting that an imbalance in mitochondrial dynamics may play a critical role in hearing loss, but relevant studies are few. In this review, we summarize recent evidence regarding the role of mitochondrial dynamics in the pathogenesis of noise-induced hearing loss (NIHL), drug-induced hearing loss, hereditary hearing loss, and age-related hearing loss. The impacts of impaired mitochondrial dynamics on hearing loss are discussed, and the potential of mitochondrial dynamics for the prevention and treatment of hearing loss is considered.