Ephrin A2 protein expression in the regeneration and plasticity of cochlear hair cells in chicken following kanamycin ototoxicity

The results from this study showed that the thresholds of brainstem auditory-evoked potentials peak following 10 successive days of intramuscular injection of Roman chickens with kanamycin, starting 3 days after birth. Fluorescence immunohistochemistry analysis revealed few ganglion cells positively labeled for Ephrin A2 in the cochlea of experimental chickens from 2 days before until 7 days after the last kanamycin injection. The number of Ephrin A2-positive ganglion cell bodies was increased at 15 days after the last injection and was similar to that in normal chickens at 30 days following the cessation of kanamycin treatment. These experimental findings indicate that Ephrin A2 protein expression in the acoustic ganglia is synchronized with the connection damage and regeneration of cochlear hair cells after kanamycin exposure. Ephrin A2 may play an important role in the regeneration and plasticity of cochlear hair cells in the chick cochlea following kanamycin ototoxicity.

Bhlhe40 protects cochlear hair cell-like HEI-OC1 cells against H_(2)O_(2) ‑triggered oxidative injury

Background:Cochlear hair cell injury is a common pathological feature of hearing loss.The basic helix-loop-helix family,member e40(Bhlhe40),a gene belonging to the basic helix-loop-helix(bHLH)family,exhibits strong transcriptional repression activity.Methods:Oxidative damage,in House Ear Institute-Organ of Corti 1(HEI-OC1)cells,was caused using hydrogen peroxide(H2O2).The Ad-Bhlhe40 particles were constructed to overexpress Bhlhe40 in HEI-OC1 cells.Various assays including cell counting kit-8(CCK-8),terminal deoxynucleotidyl transferase-mediated dUTP nick end-labeling assay(TUNEL),flow cytometry,immunofluorescence,and corresponding commercial kits were employed to investigate the impacts of Bhlhe40 on cell viability,apoptosis,oxidative stress levels,mitochondrial membrane potential and cellular senescence.Additionally,a dual-luciferase reporter assay was performed to confirm the targeting of the histone deacetylases 2(Hdac2)by Bhlhe40.Results:The results revealed that Bhlhe40 was downregulated in H_(2)O_(2)-treated HEI-OC1 cells,but its overexpression improved cell viability and mitigated H_(2)O_(2)-induced oxidative injury in HEI-OC1 cells with increase of superoxide dismutase(SOD),catalase(CAT)and glutathione peroxidase(GPx)activities and decrease of reactive oxygen species(ROS)levels.Besides,overexpression of Bhlhe40 suppressed H_(2)O_(2)-triggered cell senescence,as evidenced by the fact that the upregulation of P53,P21,and P16 in HEI-OC1 cells treated with H2O2 were all alleviated by Bhlhe40 overexpression.And we further verified that overexpression of Bhlhe40 could inhibit the expression of Hdac2,which may be related to the repression of Hdac2 transcription.Conclusion:This study suggests that Bhlhe40 plays a protective role against senescence and oxidative damage in cochlear hair cells exposed to H2O2.

Distribution and Functional Characteristics of Voltage-Gated Sodium Channels in Immature Cochlear Hair Cells

Voltage-gated sodium channels(VGSCs)are transiently expressed in cochlear hair cells before hearing onset and play an indispensable role in shaping spontaneous activity.In this study,we showed that Na^+currents shaped the spontaneous action potentials in developing mouse inner hair cells(IHCs)by decreasing the time required for the membrane potential to reach the action-potential threshold.In immature IHCs,we identified 9 known VGSC subtypes(Navl.la-l.9ot),among which Navl.7a was the most highly expressed subtype and the main contributor to Na+currents in developing hair cells.Electrophysiological recordings of two cochlea-specific Navi.7 variants(CbmNavl.7a and CbmNavl.7b)revealed a novel loss-of-function mutation(C934R)at the extracellular linker between segments 5 and 6 of domain II.In addition,post-transcriptional modification events,such as alternative splicing and RNA editing,amended the gating properties and kinetic features of CbmNavl.7a(C934).These results provide molecular and functional characteristics of VGSCs in mammalian IHCs and their contributions to spontaneous physiological activity during cochlear maturation.

Modulation of copper transporters in protection against cisplatin-induced cochlear hair cell damage

Cisplatin belongs to platinum-based drugs and is widely used in cancer chemotherapy.Ototoxicity is one of the major dose limiting side-effects of cisplatin.For toxicity to occur cisplatin must first be transported from the bloodstream into cochlear cells.Three copper transporters are considered pathways for regulating the uptake and translocation of cisplatin into cells:Ctr1,ATP7A and ATP7B.Our recent study with cochlear organotypic cultures shows that cochlear hair cells can be destroyed by cisplatin at low concentrations from 10μm to 100μn.However,high doses of cisplatin cannot damage hair cells,maybe due to intrinsic feedback reactions that increase export of platinum by ATP7B when the platinum concentration is high in extracellular space.Cimitidine is a specific copper transporter inhibitor that can block the entrance of copper and platinum,and may prevent cisplatin-induced cochlear hair cell injury.To evaluate this hypothesis,we treated cochlear organotypic cultures with cisplatin (10 μm or 50 μm) alone,or cisplatin combined with cimitidine at concentrations ranging from 10-2000 μm for 48 hours.cisplatin at 10 μm damaged about 20% hair cells.In contrast,when cimitidine (10 μm,100 μm and 2000 μm) was added to the culture,near 100% cochlear hair cell survived.At higher concentration (50 μm),cisplatin destroyed about 80% of cochlear hair cells.However,100 μmcimitidine rescued about 50% hair cells from cisplatin damage,and 2000μm cimitidine protected about 80% hair cells.The data of western blot showed that CTR1 and ATP7B expressions were increased in cisplatin treated cochlear tissue,but cimitidine significantly reduced CTR1 and ATP7B.In addition,ATP7A expression was depressed a little after cisplatin treatment.Considering that Ctr1 is involved in copper and platinum influx,but the ATP7A and ATP7B are copper export transporters,the results suggest that cimitidine can effectively block the entrance by copper transporters and stop the influx of cisplatin.

EFFECTS OF DIABETES ON HEARING AND COCHLEAR STRUCTURES

Diabetes mellitus (DM) is a chronic systemic disease characterized by hyperglycemia, with various patho-genic mechanisms. From absolute or relative insulin deficiency, patients with DM often demonstrate vari-ous levels of metabolic disorders. Major clinical manifestations of DM include metabolic disorders, vascu-lar lesions, circulatory disturbances and neurologic complications. Along with advances in DM research, re-ports of DM related tinnitus and hearing impairment have increased continuously. Research on DM related auditory system dysfunction has focused on cochlear microcirculation, cellular homeostasis, genetics and ag-ing. Cochlear microcirculation plays an important role in cochlear physiology and its disorders are associat-ed with many inner ear diseases. Ischemia and subsequent reperfusion seen in cochlear microcirculation dis-orders are important factors in hearing damage. Understanding cochlear microcirculation and structural as well as functional changes in DM patients with hearing loss and their causal factors will help reveal patho-genic mechanisms in diabetic hearing loss and provide new ideas in developing interventions and preventing damages caused by diabetes.

Protective effects of the cochlear efferent system on the outer hair cells against intense sound:evidences from DPOAEs

It has been revealed in recent years that contralateral acoustic stimulation can affect cochlear active mechanisms through activating medial olivocochlear system (MOC) of the cochlear efferent nerve fibers. The MOC is therefore postulated to exert protective effects on outer hair cells (OHCs) under intense sound condition. In this study the effects of 4 kHz intense tone exposure on distortion product otoacoustic emissions (DPOAEs) in guinea pigs with and without contralateral white noise stimulation were observed so that to investigate the protective effects of MOC on OHCs. The results showed that DPOAEs obviously deceased after the intense tone exposure in all animals, while both the amplitude reduction and the affected frequency range of DPOAEs were smaller in animals with simultaneously delivered contralateral white noise during the tone exposure than that in animals without colltralateral acoustic stimulation. The above results may suggest some protective nature of the contralateral sound stimulating effects which might be mediated through the activity of MOC. These perhaps can serve as the evidence that the protective mechanism against intense sound operates in the outer hair cells which are strongly innervated by MOC

PTEN inhibitor bisperoxovanadium protects against noise-induced hearing loss

Studies have shown that phosphatase and tensin homolog deleted on chromosome ten(PTEN)participates in the regulation of cochlear hair cell survival.Bisperoxovanadium protects against neurodegeneration by inhibiting PTEN expression.However,whether bisperoxovanadium can protect against noise-induced hearing loss and the underlying mechanism remains unclear.In this study,we established a mouse model of noise-induced hearing loss by exposure to 105 dB sound for 2 hours.We found that PTEN expression was increased in the organ of Corti,including outer hair cells,inner hair cells,and lateral wall tissues.Intraperitoneal administration of bisperoxovanadium decreased the auditory threshold and the loss of cochlear hair cells and inner hair cell ribbons.In addition,noise exposure decreased p-PI3K and p-Akt levels.Bisperoxovanadium preconditioning or PTEN knockdown upregulated the activity of PI3K-Akt.Bisperoxovanadium also prevented H_(2)O_(2)-induced hair cell death by reducing mitochondrial reactive oxygen species generation in cochlear explants.These findings suggest that bisperoxovanadium reduces noise-induced hearing injury and reduces cochlear hair cell loss.

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

Disabling hearing loss is the most common sensorineural disability worldwide.It affects around 466 million people and its incidence is expected to rise to around 900 million people by 2050,according to World Health Organization estimates.Most cases of hearing impairment are due to the degeneration of hair cells(HCs)in the cochlea,mechano-receptors that transduce incoming sound information into electrical signals that are sent to the brain.Damage to these cells is mainly caused by exposure to aminoglycoside antibiotics and to some anti-cancer drugs such as cisplatin,loud sounds,age,infections and genetic mutations.Hearing deficits may also result from damage to the spiral ganglion neurons that innervate cochlear HCs.Differently from what is observed in avian and nonmammalian species,there is no regeneration of missing sensory cell types in the adult mammalian cochlea,what makes hearing loss an irreversible process.This review summarizes the research that has been conducted with the aim of developing cell-based strategies that lead to sensory cell replacement in the adult cochlea and,ultimately,to hearing restoration.Two main lines of research are discussed,one directed toward the transplantation of exogenous replacement cells into the damaged tissue,and another that aims at reactivating the regenerative potential of putative progenitor cells in the adult inner ear.Results from some of the studies that have been conducted are presented and the advantages and drawbacks of the various approaches discussed.

Distortion product otoacoustic emissions in newborn babies with and without late-term maternal iron deficiency anaemia

Background:Studies on animals have demonstrated that maternal iron deficiency anaemia(IDA)could result in decreased cochlear sensory hair cells and reduced amplitudes of distortion-product otoacoustic emissions(DPOAEs)of young guinea pigs.Thus,it is essential to study the functioning of cochlear hair cells using DPOAEs in human newborn babies with maternal IDA.The current study explores maternal IDA’s effect on DPOAEs in newborn babies.Method:A total of 110 newborn babies with gestational age≥34 weeks were considered and a‘betweensubjects’design was used.The participants were divided into 3 groups-“Normal”(61 babies without maternal IDA),“Mild”(28 babies with mild maternal IDA)and“Moderate”(21 babies with moderate maternal IDA).The cord blood was collected and the DPOAEs were recorded for each baby for a range of frequencies(1 k 8 kHz)and a range of intensities(7040 dB SPL in 10 dB steps).Results:The analysis of both DP-gram and DP input-output(I/O)function showed that there was no significant difference(p>0.05)across the normal,mild,and moderate groups in the overall presence of DPOAEs as well as the amplitude across frequencies or intensities(7040 dB SPL).Also,the overall correlation of RBC indices with DPOAE amplitude across frequencies as well as the slope of the I/O function showed no relationship.Conclusion:The current study concludes that there is no effect of late-term maternal IDA on the DPOAEs of newborn babies.

D-AP5 blocks the increase of intracellular free Ca^(2+) induced by glutamate in isolated cochlear IHCs

Objective To investigate the effect of D-AP5 (D-2-amino-5-phosphonopentanoate, a specific NMDA-antagonist) on the increase of intracellular free Ca 2+ concentration ([Ca 2+ ] i) induced by glutamate in isolated cochlear inner hair cells (IHCs), and to detect the autoreceptors of the IHC membrane. Methods When a laser scanning confocal microscope (LSCM) was used, the exogenous glutamate (Glu)-induced changes in [Ca 2+ ] i of isolated IHCs and OHCs of guinea pig cochlea were observed with fluo-3, a fluorescent probe for [Ca 2+ ] i. After D-AP5 or CNQX (6--cyano--7--nitroguinoxaline--2, 3--dione, a specific AMPA- antagonist) was administrated, the exogenous glutamate (Glu)-induced changes in [Ca 2+ ] i of isolated IHCs were recorded. Results In the presence of a low concentration Glu (3.85?μmol/L), there was an increase of [Ca 2+ ] i in IHCs, whereas there was no change in OHCs. When 50?μmol/L of D-AP5 was administrated in advance, Glu did not induce a corresponding increase in [Ca 2+ ] i in IHCs, and 50?μmol/L of CNQX did not completely block the increase of [Ca 2+ ] i in IHCs. Conclusions These results suggest that the autoreceptors existing in the IHC membrane are mainly of NMDA type, while there are relatively few AMPA receptors. Exogenous Glu is capable of increasing [Ca 2+ ] i in IHCs by acting on the NMDA autoreceptor of IHCs in a positive feedback manner.

Hidden hearing loss:current perspectives and potential therapies

Hidden hearing loss(HHL),an auditory dysfunction that has gained much recent attention,has the hallmarks of speech discrimination and intelligibility deficits with normal or near-normal hearing thresholds.The pathological mechanisms of HHL are complicated and are not yet fully understood.HHL can be resulted from disorders of the central nervous system such as auditory cortex,and/or pathological changes of inner ear.Thus far,2 pathological phenomena,synaptopathy and auditory nerve demyelination,have been reported as underlying causes of otogenic HHL.Here,we review the clinical and physiological characteristics of HHL as well as the molecular pathological mechanisms of otogenic HHL and aim to allude to potential therapy targets for clinical applications in the future.