Suijun Chen

Activation of miR-34a/SIRT1/p53 signaling contributes to cochlear hair cell apoptosis: implications for age-related hearing loss

The molecular mechanisms underlying age-related hearing loss are not fully understood, and currently, there is no treatment for this disorder. MicroRNAs have recently been reported to be increasingly associated with age-related diseases and are emerging as promising therapeutic targets. In this study, miR-34a/Sirtuin 1 (SIRT1)/p53 signaling was examined in cochlear hair cells during aging. MiR-34a, p53 acetylation, and apoptosis increased in the cochlea of C57BL/6 mice with aging, whereas an age-related decrease in SIRT1 was observed. In the inner ear HEI-OC1 cell line, miR-34a overexpression inhibited SIRT1, leading to an increase in p53 acetylation and apoptosis. Moreover, miR-34a knockdown increased SIRT1 expression and diminished p53 acetylation, and apoptosis. Additionally, resveratrol, an activator of SIRT1, significantly rescued miR-34a overexpression-induced HEI-OC1 cell death and significantly reduced hearing threshold shifts and hair cell loss in C57BL/6 mice after a 2-month administration. Our results support a link between age-related cochlear hair cell apoptosis and miR-34a/SIRT1/p53 signaling, which may serve as a potential target for age-related hearing loss treatment.

SIRT1 expression in the cochlea and auditory cortex of a mouse model of age-related hearing loss.

SIRT1 is a highly conserved NAD(+)-dependent protein deacetylase known to have protective effects against a variety of age-related diseases. However, there is a lack of information concerning SIRT1 expression in the cochlea and auditory cortex of C57BL/6 mice, a mouse model of age-related hearing loss. Using RT-PCR and immunohistochemistry, we show that SIRT1 is abundantly expressed in the inner hair cells, strial marginal cells, strial intermediate cells, type I and type IV fibrocytes of the spiral ligament and spiral ganglion neurons. In addition, moderate SIRT1 is also detected in the outer hair cells and neurons of the auditory cortex. Associated with elevated hearing thresholds and hair cells loss during aging, there is also a significant reduction of SIRT1 expression in the cochlea and auditory cortex. The expression pattern of SIRT1 in the peripheral and central auditory system suggests that SIRT1 may play an important role in auditory function and therefore may serve as a protective molecule against age-related hearing loss.

Circulating miR-34a levels correlate with age-related hearing loss in mice and humans.

Age-related hearing loss (AHL) is a progressive neurodegenerative disease that is largely silent in its initial stages. There is no sensitive blood biomarker for diagnosis or early detection of AHL. MicroRNAs (miRNAs or miRs) are abundant and highly stable in blood, and have been recently described as powerful circulating biomarkers in a wide range of diseases. In the present study, we identified concordant increases in miR-34a levels in the cochlea, auditory cortex, and plasma of C57BL/6 mice during aging. These increases were accompanied by elevated hearing thresholds and greater loss of hair cells. Levels of miR-34a targets, silent information regulator 1 (SIRT1), B-cell lymphoma-2 (Bcl-2), and E2F transcription factor 3 (E2F3), in the cochlea, auditory cortex, and plasma decreased with aging inversely to miR-34a. Moreover, plasma miR-34a levels were significantly higher in patients with AHL compared with controls who had normal hearing and had a receiver-operating characteristic curve that distinguished AHL patients from controls. However, SIRT1, Bcl-2, and E2F3 showed no correlation with AHL in humans. In summary, circulating miR-34a level may potentially serve as a useful biomarker for early detection of AHL.

Evaluation of auditory cortical development in the early stages of post cochlear implantation using mismatch negativity measurement

Objective The aim of this study was to investigate auditory cortical development using mismatch negativity (MMN) in prelingual severe-to-profound hearing-impaired children from the stage of cochlear implant (CI) power-up to 6 months after power-up. Method Eighteen children were recruited and examined at the stage of CI initial power-up (M0), as well as several follow-up periods, that is, 1 month (M1), 3 months (M3), and 6 months (M6) after CI power-up. The MMN responses were measured using a 128-Channel Dense Array EEG System. The group average and individual MMN analysis were used to investigate the longitudinal changes of the MMN characteristics. The relationship between MMN characteristics and scores of categories of auditory performance (CAP) was also investigated. Results Although the MMN incidence was much lower at the periods of M0 and M1, significantly higher MMN incidence was found in M3 and M6. The MMN latencies decreased significantly from M3 to M6, but no significant difference in the amplitudes was found between these periods. There was a negative correlation between the increment of CAP scores and decrement of MMN latency from M3 to M6. Conclusion MMN incidence increment and latency decrement are likely to be the objective and noninvasive indicators for evaluating auditory central development at an early stage in children after cochlear implantation. Moreover, the latency decrement from M3 to M6 correlated significantly with the increment of the CAP scores, indicating a fast maturation period, which might be a key period for auditory rehabilitation.

Hypoxia-Inducible Factor and Vascular Endothelial Growth Factor Pathway for the Study of Hypoxia in a New Model of Otitis Media with Effusion

The hypoxia-inducible factor and vascular endothelial growth factor (HIF-VEGF) pathway in hypoxic conditions of the middle ear due to dysfunction of the eustachian tube is still unknown, but it is considered as one pathogenetic mechanism in otitis media. This study was designed to investigate the possible involvement of the HIF-VEFG pathway in otitis media with effusion induced by dysfunction of the eustachian tube. We adopted a soft palate approach to obstruct the orifice of the eustachian tube to establish otitis media in a rat model. Auditory evoked brainstem response and tympanometry were used as hearing function tests, hypoxia-related factors were examined by reverse transcriptase polymerase chain reaction (RT-PCR). The expression of hypoxia-related proteins was detected by Western blot and immunostaining. The model of otitis media with effusion was successfully induced by cauterizing the orifice of the eustachian tube. RT-PCR showed up-regulation of hypoxia-related factors in cauterized ears. Western blot and immunostaining showed that the expression of hypoxia-related proteins in cauterized ears was increased. Hypoxia-induced vascular proliferation and an increase in permeability may be one pathogenetic mechanism of otitis media due to dysfunction of the eustachian tube.

Effect of the combination of balloon Eustachian tuboplasty and tympanic paracentesis on intractable chronic otitis media with effusion

OBJECTIVE To evaluate the effect of the combination of balloon Eustachian tuboplasty (BET) and tympanic paracentesis (TP) on intractable chronic otitis media with effusion (COME). METHODS Ninety patients with intractable COME were included and randomly assigned to three groups: BET only (30 patients), BET+paracentesis (30 patients), and paracentesis only (30 patients). Otic endoscopic findings and tympanograms were recorded before the surgery and at the month 1, month 3, and month 6 follow-up evaluations. RESULTS Both the BET only and BET+paracentesis groups achieved better outcomes than the paracentesis group. The BET+paracentesis group exhibited better otic endoscopic scores than the BET only group (p<0.05) at 1month post-operation. However, no significant difference was found at month 3 or month 6 post-operation. No significant difference in the tympanograms was observed between these two groups at month 1, month 3, or month 6 post-operation. The otic endoscopic sign scores improved from month 1 to month 6 in the BET only group and from month 1 to month 3 in the BET+paracentesis group. The conversion of type B tympanograms improved from month 1 to month 6 in the BET and BET+paracentesis groups but not in the paracentesis only group. CONCLUSIONS Our results suggested that the combination of BET and TP was effective for intractable COME and can help shorten the recovery period for middle ear effusion.

Visual cortex activation decrement following cochlear implantation in prelingual deafened children

OBJECTIVE Visual take-over of the auditory cortex in prelingual deaf children has been widely reported. However, there have been few studies on visual cortex plasticity after cochlear implantation (CI). In this study, we investigated the hypothesis that extrinsic auditory stimulation following CI in prelingual deafened children can induce visual cortex plasticity. METHOD Visual evoked potentials (VEPs) were recorded in 37 CI children (4 groups with different use times) and 8 control subjects, in response to sound and nonsound stimuli. Latency and amplitude were analyzed for the P1, N1 and P2 components on the Oz electrode. Comparisons of VEP were conducted between the sound and nonsound stimuli and among different groups in order to view evidence of visual cortex reorganization. RESULTS The latency of the P2 component was significantly longer at the occipital site (Oz) in CI 0M than those in the other four groups. After the effect of age was excluded, a significant negative correlation was found between CI usage and P2 latency of nonsound stimuli. Occipital P1N1 latency and P1 amplitude were not affected by group or stimulus category. However, the N1 and P2 amplitudes were significantly larger in response to a sound stimulus than to a nonsound stimulus. CONCLUSION Our findings suggest that P2 latency develops with CI usage and may be a biomarker of visual cortex plasticity.

miR-34a/Bcl-2 signaling pathway contributes to age-related hearing loss by modulating hair cell apoptosis

MicroRNAs, such as miR-34, have been reported to influence age-related diseases. In this study, we explored the role of the miR-34a/Bcl-2 signaling pathway in age-related hearing loss (AHL). Using an AHL mouse model (C57BL/6), we found that the expression of miR-34a in the cochlea increased with age, whereas expression of Bcl-2 decreased. Increasing the amount of a miR-34a mimetic in a mouse auditory cell line (HEI-OC1) inhibited Bcl-2, leading to enhanced apoptosis; in contrast, miR-34a inhibition produced the opposite effect. Our results support a link between age-related cochlear hair cell apoptosis and miR-34a/Bcl-2 signaling. The latter may thus serve as a potential target for AHL therapy.

Activation of miR-34a impairs autophagic flux and promotes cochlear cell death via repressing ATG9A: implications for age-related hearing loss

Age-related hearing loss is a major unresolved public health problem. We have previously elucidated that the activation of cochlear miR-34a is correlated with age-related hearing loss in C57BL/6 mice. A growing body of evidence points that aberrant autophagy promotes cell death during the development of multiple age-related diseases. The aim of this study was to investigate the role of miR-34a-involved disorder of autophagy in the pathogenesis of age-related hearing loss. Our results showed that miR-34a expression was markedly upregulated in the aging cochlea accompanied with impairment of autophagic flux. In the inner ear HEI-OC1 cell line, miR-34a overexpression resulted in an accumulation of phagophores and impaired autophagosome–lysosome fusion, and led to cell death subsequently. Notably, autophagy-related protein 9A (ATG9A), an autophagy protein, was significantly decreased after miR-34a overexpression. Knockdown of ATG9A inhibited autophagy flux, which is similar to the effects of miR-34a overexpression. Moreover, ursodeoxycholic acid significantly rescued miR-34a-induced HEI-OC1 cell death by restoring autophagy activity. Collectively, these findings increase our understanding of the biological effects of miR-34a in the development of age-related hearing loss and highlight miR-34a as a promising therapeutic target for its treatment.

TREM-2 promotes acquired cholesteatoma-induced bone destruction by modulating TLR4 signaling pathway and osteoclasts activation

Triggering receptor expressed on myeloid cells (TREM) has been broadly studied in inflammatory disease. However, the expression and function of TREM-2 remain undiscovered in acquired cholesteatoma. The expression of TREM-2 was significantly higher in human acquired cholesteatoma than in normal skin from the external auditory canal, and its expression level was positively correlated with the severity of bone destruction. Furthermore, TREM-2 was mainly expressed on dendritic cells (DCs). In human acquired cholesteatoma, the expression of proinflammatory cytokines (IL-1β, TNF-α and IL-6) and matrix metalloproteinases (MMP-2, MMP-8 and MMP-9) were up-regulated, and their expression levels were positively correlated with TREM-2 expression. Osteoclasts were activated in human acquired cholesteatoma. In an animal model, TREM-2 was up-regulated in mice with experimentally acquired cholesteatoma. TREM-2 deficiency impaired the maturation of experimentally acquired cholesteatoma and protected against bone destruction induced by experimentally acquired cholesteatoma. Additional data showed that TREM-2 up-regulated IL-1β and IL-6 expression via TLR4 instead of the TLR2 signaling pathway and promoted MMP-2 and MMP-8 secretion and osteoclast activation in experimentally acquired cholesteatoma. Therefore, TREM-2 might enhance acquired cholesteatoma-induced bone destruction by amplifying the inflammatory response via TLR4 signaling pathways and promoting MMP secretion and osteoclast activation.