Hsp70/Bmi1-FoxO1-SOD Signaling Pathway Contributes to the Protective Effect of Sound Conditioning against Acute Acoustic Trauma in a Rat Model

Geniposide reduced oxidative stress-induced apoptosis in HK-2 cell through PI3K/AKT3/FOXO1 by m6A modification

Exogenous hydrogen peroxide (H2O2) may generate excessive oxidative stress, inducing renal cell apoptosis related with kidney dysfunction. Geniposide (GP) belongs to the iridoid compound with anti-inflammatory, antioxidant and anti-apoptotic effects. This study aimed to observe the intervention effect of GP on H2O2-induced apoptosis in human kidney-2 (HK-2) cells and to explore its potential mechanism in relation to N6-methyladenosine (m6A) RNA methylation. Cell viability, apotosis rate and cell cycle were tested separately after different treatments. The mRNA and protein levels of m6A related enzymes and phosphoinositide 3-kinase (PI3K)/a serine/threonine-specific protein kinase 3 (AKT3)/forkhead boxo 1 (FOXO1) and superoxide dismutase 2 (SOD2) were detected by reverse transcription-quantitative real-time PCR (RT-qPCR) and Western blot. The whole m6A methyltransferase activity and the m6A content were measured by ELISA-like colorimetric methods. The changes of m6A methylation levels of PI3K/AKT3/FOXO1 and SOD2 were determined by methylated RNA immunoprecipitation (MeRIP)-qPCR. Multiple comparisons were performed by ANOVA with Turkey's post hoc test. Exposed to 400 μmol/L H2O2, cells were arrested in G1 phase and the apoptosis rate increased, which were significantly alleviated by GP. Compared with the H2O2 apoptosis group, both the whole m6A RNA methyltransferase activity and the m6A contents were increased due to GP intervention. Besides, the SOD2 protein was increased, while PI3K and FOXO1 decreased. The m6A methylation level of AKT3 was negatively correlated with its protein level. Taken together, GP affects the global m6A methylation microenvironment and regulates the expression of PI3K/AKT3/FOXO1 signaling pathway via m6A modification, alleviating cell cycle arrest and apoptosis caused by oxidative stress in HK-2 cells with a good application prospect.

Polyphenols in Inner Ear Neurobiology, Health and Disease: From Bench to Clinics

There is substantial experimental and clinical interest in providing effective ways to both prevent and slow the onset of hearing loss. Auditory hair cells, which occur along the basilar membrane of the cochlea, often lose functionality due to age-related biological alterations, as well as from exposure to high decibel sounds affecting a diminished/damaged auditory sensitivity. Hearing loss is also seen to take place due to neuronal degeneration before or following hair cell destruction/loss. A strategy is necessary to protect hair cells and XIII cranial/auditory nerve cells prior to injury and throughout aging. Within this context, it was proposed that cochlea neural stem cells may be protected from such aging and environmental/noise insults via the ingestion of protective dietary supplements. Of particular importance is that these studies typically display a hormetic-like biphasic dose-response pattern that prevents the occurrence of auditory cell damage induced by various model chemical toxins, such as cisplatin. Likewise, the hormetic dose-response also enhances the occurrence of cochlear neural cell viability, proliferation, and differentiation. These findings are particularly important since they confirmed a strong dose dependency of the significant beneficial effects (which is biphasic), whilst having a low-dose beneficial response, whereas extensive exposures may become ineffective and/or potentially harmful. According to hormesis, phytochemicals including polyphenols exhibit biphasic dose-response effects activating low-dose antioxidant signaling pathways, resulting in the upregulation of vitagenes, a group of genes involved in preserving cellular homeostasis during stressful conditions. Modulation of the vitagene network through polyphenols increases cellular resilience mechanisms, thus impacting neurological disorder pathophysiology. Here, we aimed to explore polyphenols targeting the NF-E2-related factor 2 (Nrf2) pathway to neuroprotective and therapeutic strategies that can potentially reduce oxidative stress and inflammation, thus preventing auditory hair cell and XIII cranial/auditory nerve cell degeneration. Furthermore, we explored techniques to enhance their bioavailability and efficacy.

Apoptotic vesicles resist oxidative damage in noise-induced hearing loss through activation of FOXO3a-SOD2 pathway

BACKGROUND

Mesenchymal stem cell (MSC) transplantation is a promising therapeutic approach for noise-induced hearing loss (NIHL). As the indispensable role of apoptosis in MSC transplantation was raised, the benefits of MSC-derived apoptotic vesicles (apoVs) in several disease models have been proved. However, whether apoVs benefit in NIHL have not been studied yet.

METHODS

Female CBA/J mice and HEI-OC1 cells were used in this study. Flow cytometry, nanoparticle tracking analysis (NTA) and transmission electron microscopy (TEM) were used to characterize apoVs. Proteomic analysis was used to identify function proteins in apoVs. Immunofluorescence was used to reveal distribution pattern. Auditory brainstem response (ABR) test was used to measure the effect of apoVs treatment. DCFH-DA staining and MitoSOX staining were used to indicate oxidative damage. Western-blot and qRT-PCR were used to study the signaling pathways.

RESULTS

We found that apoVs can be endocytosed by hair cells through systemic administration. Importantly, apoVs administration effectively attenuated NIHL and reduced hair cell loss by resisting oxidative damage in vivo. Further, apoVs application activated forkhead box o3 (FOXO3a)-mitochondrial superoxide dismutase 2(SOD2) pathway, which may relate to signal transduction and activators of transcription 3 (STAT3) in apoVs.

CONCLUSIONS

These findings uncovered the role of apoVs in preventing NIHL and resisting oxidative damage, indicating that apoVs is a promising way for inner ear delivery and a prospective cell-free therapy for NIHL.

Cochlear Preconditioning as a Modulator of Susceptibility to Hearing Loss

Significance: Acquired sensorineural hearing loss is a major public health problem worldwide. The leading causes of sensorineural hearing loss are noise, aging, and ototoxic medications, with the key underlying pathology being damage to the cochlea. The review focuses on the phenomenon of preconditioning, in which the susceptibility to cochlear injury is reduced by exposing the ear to a stressful stimulus. Recent Advances: Cochlear conditioning has focused on the use of mono-modal conditioning, specifically conditioning the cochlea with moderate noise exposures before a traumatic exposure that causes permanent hearing loss. Recently, cross-modal conditioning has been explored more thoroughly, to prevent not only noise-induced hearing loss, but also age-related and drug-induced hearing losses. Critical Issues: Noise exposures that cause only temporary threshold shifts (TTSs) can cause long-term synaptopathy, injury to the synapses between the inner hair cells and spiral ganglion cells. This discovery has the potential to significantly alter the field of cochlear preconditioning with noise. Further, cochlear preconditioning can be the gateway to the development of clinically deployable therapeutics. Therefore, understanding the underlying mechanisms of conditioning is crucial for optimizing clinical protection against sensorineural hearing loss. Future Directions: Before the discovery of synaptopathy, noise exposures that caused only TTSs were believed to be either harmless or potentially beneficial. Any considerations of preconditioning with noise must consider the potential for injury to the synapses. Further, the discovery of different methods to precondition the cochlea against injury will yield new avenues for protection against hearing loss in the vulnerable populations. Antioxid. Redox Signal. 36, 1215-1228.

Metabolomics Analysis Reveals Alterations in Cochlear Metabolic Profiling in Mice with Noise-Induced Hearing Loss

Noise-induced hearing loss (NIHL) has always been an important occupational hazard, but the exact etiopathogenesis underlying NIHL remains unclear. Herein, we aimed to find metabolic biomarkers involved in the development of NIHL based on a mouse model using a gas chromatography coupled with mass spectrometry (GC-MS) metabolomics technique. We showed that the auditory brainstem response (ABR) thresholds at the frequencies of 4, 8, 12, 16, 24, and 32 kHz were all significantly elevated in the noise-exposed mice. Noise could cause outer hair cell (OHC) loss in the base of the cochlea. A total of 17 differential metabolites and 9 metabolic pathways were significantly affected following noise exposure. Spermidine acting as an autophagy modulator was found to be 2.85-fold higher in the noise-exposed group than in the control group and involved in β-alanine metabolism and arginine and proline metabolism pathways. Additionally, we demonstrated that LC3B and Beclin1 were expressed in the spiral ganglion neurons (SGNs), and their mRNA levels were increased after noise. We showed that SOD activity was significantly decreased in the cochlea of noise-exposed mice. Further experiments suggested that SOD1 and SOD2 proteins in the SGNs were all decreased following noise exposure. The upregulation of spermidine may induce LC3B- and Beclin1-mediated autophagy in the cochlear hair cells (HCs) through β-alanine metabolism and arginine and proline metabolism and be involved in the NIHL. ROS-mediated oxidative damage may be a pivotal molecular mechanism of NIHL. Taken together, spermidine can be regarded as an important metabolic marker for the diagnosis of NIHL.

Sirtuin-3 Protects Cochlear Hair Cells Against Noise-Induced Damage via the Superoxide Dismutase 2/Reactive Oxygen Species Signaling Pathway

Mitochondrial oxidative stress is involved in hair cell damage caused by noise-induced hearing loss (NIHL). Sirtuin-3 (SIRT3) plays an important role in hair cell survival by regulating mitochondrial function; however, the role of SIRT3 in NIHL is unknown. In this study, we used 3-TYP to inhibit SIRT3 and found that this inhibition aggravated oxidative damage in the hair cells of mice with NIHL. Moreover, 3-TYP reduced the enzymatic activity and deacetylation levels of superoxide dismutase 2 (SOD2). Subsequently, we administered adeno-associated virus-SIRT3 to the posterior semicircular canals and found that SIRT3 overexpression significantly attenuated hair cell injury and that this protective effect of SIRT3 could be blocked by 2-methoxyestradiol, a SOD2 inhibitor. These findings suggest that insufficient SIRT3/SOD2 signaling leads to mitochondrial oxidative damage resulting in hair cell injury in NIHL. Thus, ameliorating noise-induced mitochondrial redox imbalance by intervening in the SIRT3/SOD2 signaling pathway may be a new therapeutic target for hair cell injury.