The role of autophagy and ferroptosis in sensorineural hearing loss

Tranylcypromine upregulates Sestrin 2 expression to ameliorate NLRP3-related noise-induced hearing loss

JOURNAL/nrgr/04.03/01300535-202505000-00030/figure1/v/2024-07-28T173839Z/r/image-tiff Noise-induced hearing loss is the primary non-genetic factor contributing to auditory dysfunction. However, there are currently no effective pharmacological interventions for patients with noise-induced hearing loss. Here, we present evidence suggesting that the lysine-specific demethylase 1 inhibitor-tranylcypromine is an otoprotective agent that could be used to treat noise-induced hearing loss, and elucidate its underlying regulatory mechanisms. We established a mouse model of permanent threshold shift hearing loss by exposing the mice to white broadband noise at a sound pressure level of 120 dB for 4 hours. We found that tranylcypromine treatment led to the upregulation of Sestrin2 (SESN2) and activation of the autophagy markers light chain 3B and lysosome-associated membrane glycoprotein 1 in the cochleae of mice treated with tranylcypromine. The noise exposure group treated with tranylcypromine showed significantly lower average auditory brainstem response hearing thresholds at click, 4, 8, and 16 kHz frequencies compared with the noise exposure group treated with saline. These findings indicate that tranylcypromine treatment resulted in increased SESN2, light chain 3B, and lysosome-associated membrane glycoprotein 1 expression after noise exposure, leading to a reduction in levels of 4-hydroxynonenal and cleaved caspase-3, thereby reducing noise-induced hair cell loss. Additionally, immunoblot analysis demonstrated that treatment with tranylcypromine upregulated SESN2 expression via the autophagy pathway. Tranylcypromine treatment also reduced the production of NOD-like receptor family pyrin domain-containing 3 (NLRP3) production. In conclusion, our results showed that tranylcypromine treatment ameliorated cochlear inflammation by promoting the expression of SESN2, which induced autophagy, thereby restricting NLRP3-related inflammasome signaling, alleviating cochlear hair cell loss, and protecting hearing function. These findings suggest that inhibiting lysine-specific demethylase 1 is a potential therapeutic strategy for preventing hair cell loss and noise-induced hearing loss.

Regulation of the p53/SLC7A11/GPX4 Pathway by Gentamicin Induces Ferroptosis in HEI-OC1 Cells

BACKGROUND

Gentamicin is a commonly used aminoglycoside antibiotic, with ototoxicity as a significant side effect. Ferroptosis, an iron-dependent form of cell death, has been implicated in a variety of disorders. Whether ferroptosis impacts gentamicin ototoxicity is not yet known. The current work used an in-vitro model to examine the influence of gentamicin-induced ferroptosis on cochlear hair cell damage and probable molecular biological pathways.

METHODS

House Ear Institute-Organ of Corti 1 (HEI-OC1) cells were treated with different concentrations of gentamicin for 24 hours, with or without ferrostatin-1 pretreatment, to observe gentamicin-induced ferroptosis. The role of p53/solute carrier family 7 member 11 (SLC7A11)/glutathione peroxidase 4 (GPX4) signaling in gentamicin-induced ferroptosis was explored by pretreating cells with the p53 inhibitor pifithrin-α (PFT-α). We investigated the effect of gentamicin on cells by assessing cell viability. Cellular proteins were isolated and Western blots were performed to detect changes in the expression of p53, SLC7A11, and GPX4. Fluorescence staining was used to assess levels of reactive oxygen species. An enzymatic detection kit was used to detect glutathione, Fe, and malondialdehyde markers.

RESULTS

Gentamicin reduced cell viability, glutathione content, and SLC7A11 and GPX4 protein levels, and increased levels of p53 protein, reactive oxygen species, malondialdehyde, and Fe. These effects were largely blocked by pretreatment with ferrostatin-1. Pretreatment with the p53 inhibitor PFT-α prevented the gentamicin-induced reduction in SLC7A11 and GPX4, which alleviated several features of ferroptosis including glutathione depletion, iron overload, and lipid peroxidation build-up.

CONCLUSION

Gentamicin induces ferroptosis in the HEI-OC1 cell line, and the mechanism may be related to the p53/SLC7A11/GPX4 signaling pathway.

4-octyl itaconate alleviates cisplatin-induced ferroptosis possibly via activating the NRF2/HO-1 signalling pathway

Ferroptosis, characterized by iron-dependent lipid reactive oxygen species (ROS) accumulation, plays a pivotal role in cisplatin-induced ototoxicity. Existing research has suggested that in cisplatin-mediated damage to auditory cells and hearing loss, ferroptosis is partially implicated. 4-Octyl itaconate (4-OI), derived from itaconic acid, effectively permeates cell membranes, showcasing potent anti-inflammatory as well as antioxidant effects in several disease models. Our study aimed to investigate the effect of 4-OI on cisplatin-induced ferroptosis and the underlying molecular mechanisms. The survival rates of HEI-OC1 cells and mice cochlea hair cells were measured by CCK8 and immunofluorescence, respectively. The auditory brainstem response (ABR) audiometry was used to detect changes in hearing thresholds in mice before and after treatment. Levels of ROS were evaluated by DCFH-DA. Real-time PCR quantified inflammatory cytokines TNF-α, IL-6 and IL-1β. Network Pharmacology and RNA sequencing (RNA-seq) analysis of the potential mechanism of 4-OI resistance to cisplatin-induced ferroptosis. The expressions of ferroptosis-related factors (GPX4, SLC7A11 and PTGS2) and important antioxidant factors (NRF2, HO-1, GCLC and NQO1) were tested by real-time PCR, Western blot and immunofluorescence. Results demonstrated cisplatin-induced significant ROS and inflammatory factor release, reduced NRF2 expression, hindered nuclear translocation and activated ferroptosis. Pretreatment with 4-OI exhibited anti-inflammatory and antioxidant effects, along with resistance to ferroptosis, ultimately mitigating cisplatin-induced cell loss. In the present study, we show that 4-OI inhibits cisplatin-induced ferroptosis possibly through activation of the NRF2/HO-1 signalling pathway, thereby exerting a protective effect against cisplatin-induced damage to auditory cells, and providing a new therapeutic strategy for cisplatin-induced hearing loss.

LINE-1 global DNA methylation, iron homeostasis genes, sex and age in sudden sensorineural hearing loss (SSNHL)

BACKGROUND

Sudden sensorineural hearing loss (SSNHL) is an abrupt loss of hearing, still idiopathic in most of cases. Several mechanisms have been proposed including genetic and epigenetic interrelationships also considering iron homeostasis genes, ferroptosis and cellular stressors such as iron excess and dysfunctional mitochondrial superoxide dismutase activity.

RESULTS

We investigated 206 SSNHL patients and 420 healthy controls for the following genetic variants in the iron pathway: SLC40A1 - 8CG (ferroportin; FPN1), HAMP - 582AG (hepcidin; HEPC), HFE C282Y and H63D (homeostatic iron regulator), TF P570S (transferrin) and SOD2 A16V in the mitochondrial superoxide dismutase-2 gene. Among patients, SLC40A1 - 8GG homozygotes were overrepresented (8.25% vs 2.62%; P = 0.0015) as well SOD2 16VV genotype (32.0% vs 24.3%; P = 0.037) accounting for increased SSNHL risk (OR = 3.34; 1.54-7.29 and OR = 1.47; 1.02-2.12, respectively). Moreover, LINE-1 methylation was inversely related (r2 = 0.042; P = 0.001) with hearing loss score assessed as pure tone average (PTA, dB HL), and the trend was maintained after SLC40A1 - 8CG and HAMP - 582AG genotype stratification (ΔSLC40A1 = + 8.99 dB HL and ΔHAMP = - 6.07 dB HL). In multivariate investigations, principal component analysis (PCA) yielded PC1 (PTA, age, LINE-1, HAMP, SLC40A1) and PC2 (sex, HFEC282Y, SOD2, HAMP) among the five generated PCs, and logistic regression analysis ascribed to PC1 an inverse association with moderate/severe/profound HL (OR = 0.60; 0.42-0.86; P = 0.0006) and with severe/profound HL (OR = 0.52; 0.35-0.76; P = 0.001).

CONCLUSION

Recognizing genetic and epigenetic biomarkers and their mutual interactions in SSNHL is of great value and can help pharmacy science to design by pharmacogenomic data classical or advanced molecules, such as epidrugs, to target new pathways for a better prognosis and treatment of SSNHL.

BDNF-enriched small extracellular vesicles protect against noise-induced hearing loss in mice

Noise-induced hearing loss (NIHL) is one of the most prevalent acquired sensorineural hearing loss etiologies and is characterized by the loss of cochlear hair cells, synapses, and nerve terminals. Currently, there are no agents available for the treatment of NIHL because drug delivery to the inner ear is greatly limited by the blood-labyrinth barrier. In this study, we used mesenchymal stem cell-derived small extracellular vesicles (MSC-sEVs) as nanoscale vehicles to deliver brain-derived neurotrophic factor (BDNF) and evaluated their protective effects in a mouse model of NIHL. Following intravenous administration, BDNF-loaded sEVs (BDNF-sEVs) efficiently increased the expression of BDNF protein in the cochlea. Systemic application of sEVs and BDNF-sEVs significantly attenuated noise-induced cochlear hair cell loss and NIHL in CBA/J mice. BDNF-sEVs also alleviated noise-induced loss of inner hair cell ribbon synapses and cochlear nerve terminals. In cochlear explants, sEVs and BDNF-sEVs effectively protected hair cells against H2O2-induced cell loss. Additionally, BDNF-sEVs remarkably ameliorated H2O2-induced oxidative stress, cell apoptosis, and cochlear nerve terminal degeneration. Transcriptomic analysis revealed that many mRNAs and miRNAs were involved in the protective actions of BDNF-sEVs against oxidative stress. Collectively, our findings reveal a novel therapeutic strategy of MSC-sEVs-mediated BDNF delivery for the treatment of NIHL.

Activation of Nrf2 inhibits ferroptosis and protects against oxaliplatin-induced ototoxicity

Oxaliplatin, as a third-generation platinum-based anticancer drug, is widely used in tumor therapy of many systems. Clinically, oxaliplatin has a number of serious side effects, most notably neuropathy and ototoxicity. The degeneration of cochlear hair cells is the main reason for the hearing loss caused by platinum-based drugs. However, the mechanism of oxaliplatin-induced cochlear hair cell death remains unclear. Ferroptosis is a novel cell injury pattern triggered by the accumulation of iron hydroperoxides in lipids and dependent on the participation of iron ions, which plays an important role in a variety of diseases. Whether ferroptosis is involved in oxaliplatin-induced ototoxicity has not been reported. In this study, we observed that oxaliplatin treatment resulted in lipid peroxidation and reactive oxygen species (ROS) accumulation in OC1 cells, which may be an early alteration in the occurrence of ferroptosis. Additional treatment with ferroptosis inducer or inhibitor significantly aggravated or ameliorated oxaliplatin-induced cytotoxicity. Similarly, inhibition of ferroptosis also protected cochlear hair cells against oxaliplatin-induced injury. In addition, the expression of nuclear factor erythroid 2-related factor2 (Nrf2) and heme oxygenase-1 (HO-1) was significantly increased after oxaliplatin treatment, and treatment with the Nrf2 agonist, resveratrol, dramatically attenuated cochlear hair cell damage induced by oxaliplatin. Activation of Nrf2 significantly decreased the expression of iron regulatory protein 2 (IRP-2) and reversed the expression of glutathione peroxidase 4 (GPX4). Collectively, our results demonstrated that activation of Nrf2 alleviates oxaliplatin-induced cochlear hair cell damage by inhibiting ferroptosis, which may be a new mechanism of oxaliplatin-induced ototoxicity.

Regulation of Hippo/YAP signaling pathway ameliorates cochlear hair cell injury by regulating ferroptosis

Cisplatin, which is effective for the treatment of solid tumors, also can induce cochlear hair cell damage. Therefore, this study was intended to explore how Hippo/YAP signaling pathway affects the cochlear hair cell injury by regulating ferroptosis. After cisplatin induction, or LAT1-IN-1 (YAP activator) and verteporfin (YAP inhibitor) treatment or transfection, the viability of HEI-OC1 cells was detected by cell counting kit-8 (CCK-8) assay. The iron level and the levels of oxidative stress markers (ROS, MDA and 4-HNE) were analyzed by iron assay kit, reactive oxygen species (ROS), malondialdehyde (MDA) and 4-hydroxynonenal (4-HNE) assay kits, respectively. The expression of ferritin light chain (FTL) in HEI-OC1 cells was detected by immunofluorescence and protein expressions of yes associated protein (YAP,) phosphorylated YAP (p-YAP), transferrin receptor (TFRC), glutathione peroxidase 4 (GPX4), acyl-CoA synthetase long-chain family member 4 (ACSL4) and solute carrier family 7 member 11 (SLC7A11) in HEI-OC1 cells were detected by western blot. The transcription of FTL and TFRC by YAP1 was verified by dual-luciferase reporter assay. The transfection efficiency of small interfering RNA (si-RNA) specific to FTL (siRNA-FTL) and TFRC (siRNA-TFRC) was confirmed by reverse transcription‑quantitative polymerase chain reaction (RT‑qPCR). As a result, cisplatin inhibited the viability of HEI-OC1 cells by increasing free Fe²⁺ level and decreasing FTL level. LAT1-IN-1 promoted the viability of cisplatin-induced HEI-OC1 cells by suppressing oxidative stress level, free Fe²⁺ level, ferroptosis and increasing FTL level, while the effect of verteporfin was the opposite. YAP1 transcriptionally regulated the expression of FTL and TFRC. Inhibition of FTL suppressed the viability of cisplatin-induced HEI-OC1 cells by increasing oxidative stress level, free Fe²⁺ level, ferroptosis and decreasing FTL level, while the effect of TFRC inhibition was the opposite. In conclusion, YAP1 ameliorated cochlear hair cell injury by upregulating FTL and TFRC to suppress ferroptosis.