Cochlear Transcriptome Following Acoustic Trauma and Dexamethasone Administration Identified by a Combination of RNA-seq and DNA Microarray

Ultrasound-Triggered NO Release to Promote Axonal Regeneration for Noise-Induced Hearing Loss Therapy

Intense noise poses a threat to spiral ganglion neurons (SGNs) in the inner ear, often resulting in limited axonal regeneration during noise injury and leading to noise-induced hearing loss (NIHL). Here, we propose an ultrasound-triggered nitric oxide (NO) release to enhance the sprouting and regeneration of injured axons in SGNs. We developed hollow silicon nanoparticles to load nitrosylated N-acetylcysteine, producing HMSN-SNO, which effectively protects NO from external interferences. Utilizing low-intensity ultrasound stimulation with bone penetration, we achieve the controlled release of NO from HMSN-SNO within the cochlea. In mice with NIHL, a rapid and extensive loss of synaptic connections between hair cells and SGNs is observed within 24 h after exposure to excessive noise. However, this loss could be reversed with the combined treatment, resulting in a hearing functional recovery from 83.57 to 65.00 dB SPL. This positive outcome is attributed to the multifunctional effects of HMSN-SNO, wherein they scavenge reactive oxygen species (ROS) to reverse the pathological microenvironment and simultaneously upregulate the CREB/BDNF/EGR1 signaling pathway, thereby enhancing neuroplasticity and promoting the regeneration of neuronal axons. These findings underscore the potential of nanomedicine for neuroplasticity modulation, which holds promise for advancing both basic research and the further treatment of neurological diseases.

Pharmacokinetics of monoclonal antibodies locally-applied into the middle ear of guinea pigs

Countless therapeutic antibodies are currently available for the treatment of a broad range of diseases. Some target molecules of therapeutic antibodies are involved in the pathogenesis of sensorineural hearing loss (SNHL), suggesting that SNHL may be a novel target for monoclonal antibody (mAb) therapy. When considering mAb therapy for SNHL, understanding of the pharmacokinetics of mAbs after local application into the middle ear is crucial. To reveal the fundamental characteristics of mAb pharmacokinetics following local application into the middle ear of guinea pigs, we performed pharmacokinetic analyses of mouse monoclonal antibodies to FLAG-tag (FLAG-mAbs), which have no specific binding sites in the middle and inner ear. FLAG-mAbs were rapidly transferred from the middle ear to the cochlear fluid, indicating high permeability of the round window membrane to mAbs. FLAG-mAbs were eliminated from the cochlear fluid 3 h after application, similar to small molecules. Whole-body autoradiography and quantitative assessments of cerebrospinal fluid and serum demonstrated that the biodistribution of FLAG-mAbs was limited to the middle and inner ear. Altogether, the pharmacokinetics of mAbs are similar to those of small molecules when locally applied into the middle ear, suggesting the necessity of drug delivery systems for appropriate mAb delivery to the cochlear fluid after local application into the middle ear.

Transcriptional response to mild therapeutic hypothermia in noise-induced cochlear injury

Introduction

Prevention or treatment for acoustic injury has been met with many translational challenges, resulting in the absence of FDA-approved interventions. Localized hypothermia following noise exposure mitigates acute cochlear injury and may serve as a potential avenue for therapeutic approaches. However, the mechanisms by which hypothermia results in therapeutic improvements are poorly understood.

Methods

This study performs the transcriptomic analysis of cochleae from juvenile rats that experienced noise-induced hearing loss (NIHL) followed by hypothermia or control normothermia treatment.

Results

Differential gene expression results from RNA sequencing at 24 h post-exposure to noise suggest that NIHL alone results in increased inflammatory and immune defense responses, involving complement activation and cytokine-mediated signaling. Hypothermia treatment post-noise, in turn, may mitigate the acute inflammatory response.

Discussion

This study provides a framework for future research to optimize hypothermic intervention for ameliorating hearing loss and suggests additional pathways that could be targeted for NIHL therapeutic intervention.

Integrative Functional Transcriptomic Analyses Implicate Shared Molecular Circuits in Sensorineural Hearing Loss

Sensorineural hearing loss (SNHL) is referred to as the most common type of hearing loss and typically occurs when the inner ear or the auditory nerve is damaged. Aging, noise exposure, and ototoxic drugs represent three main causes of SNHL, leading to substantial similarities in pathophysiological characteristics of cochlear degeneration. Although the common molecular mechanisms are widely assumed to underlie these similarities, its validity lacks systematic examination. To address this question, we generated three SNHL mouse models from aging, noise exposure, and cisplatin ototoxicity, respectively. Through constructing gene co-expression networks for the cochlear transcriptome data across different hearing-damaged stages, the three models are found to significantly correlate with each other in multiple gene co-expression modules that implicate distinct biological functions, including apoptosis, immune, inflammation, and ion transport. Bioinformatics analyses reveal several potential hub regulators, such as IL1B and CCL2, both of which are verified to contribute to apoptosis accompanied by the increase of (ROS) in in vitro model system. Our findings disentangle the shared molecular circuits across different types of SNHL, providing potential targets for the broad effective therapeutic agents in SNHL.

Successful Treatment of Noise-Induced Hearing Loss by Mesenchymal Stromal Cells: An RNAseq Analysis of Protective/Repair Pathways

Mesenchymal stromal cells (MSCs) are an adult derived stem cell-like population that has been shown to mediate repair in a wide range of degenerative disorders. The protective effects of MSCs are mainly mediated by the release of growth factors and cytokines thereby modulating the diseased environment and the immune system. Within the inner ear, MSCs have been shown protective against tissue damage induced by sound and a variety of ototoxins. To better understand the mechanism of action of MSCs in the inner ear, mice were exposed to narrow band noise. After exposure, MSCs derived from human umbilical cord Wharton's jelly were injected into the perilymph. Controls consisted of mice exposed to sound trauma only. Forty-eight hours post-cell delivery, total RNA was extracted from the cochlea and RNAseq performed to evaluate the gene expression induced by the cell therapy. Changes in gene expression were grouped together based on gene ontology classification. A separate cohort of animals was treated in a similar fashion and allowed to survive for 2 weeks post-cell therapy and hearing outcomes determined. Treatment with MSCs after severe sound trauma induced a moderate hearing protective effect. MSC treatment resulted in an up-regulation of genes related to immune modulation, hypoxia response, mitochondrial function and regulation of apoptosis. There was a down-regulation of genes related to synaptic remodeling, calcium homeostasis and the extracellular matrix. Application of MSCs may provide a novel approach to treating sound trauma induced hearing loss and may aid in the identification of novel strategies to protect hearing.

Impact of Systemic versus Intratympanic Dexamethasone Administration on the Perilymph Proteome

Glucocorticoids are the first-line treatment for sensorineural hearing loss, but little is known about the mechanism of their protective effect or the impact of route of administration. The recent development of hollow microneedles enables safe and reliable sampling of perilymph for proteomic analysis. Using these microneedles, we investigate the effect of intratympanic (IT) versus intraperitoneal (IP) dexamethasone administration on guinea pig perilymph proteome. Guinea pigs were treated with IT dexamethasone (n = 6), IP dexamethasone (n = 8), or untreated for control (n = 8) 6 h prior to aspiration. The round window membrane (RWM) was accessed via a postauricular approach, and hollow microneedles were used to perforate the RWM and aspirate 1 μL of perilymph. Perilymph samples were analyzed by liquid chromatography-mass spectrometry-based label-free quantitative proteomics. Mass spectrometry raw data files have been deposited in an international public repository (MassIVE proteomics repository at https://massive.ucsd.edu/) under data set # MSV000086887. In the 22 samples of perilymph analyzed, 632 proteins were detected, including the inner ear protein cochlin, a perilymph marker. Of these, 14 proteins were modulated by IP, and three proteins were modulated by IT dexamethasone. In both IP and IT dexamethasone groups, VGF nerve growth factor inducible was significantly upregulated compared to control. The remaining adjusted proteins modulate neurons, inflammation, or protein synthesis. Proteome analysis facilitated by the use of hollow microneedles shows that route of dexamethasone administration impacts changes seen in perilymph proteome. Compared to IT administration, the IP route was associated with greater changes in protein expression, including proteins involved in neuroprotection, inflammatory pathway, and protein synthesis. Our findings show that microneedles can mediate safe and effective intracochlear sampling and hold promise for inner ear diagnostics.

The Immune System Can Hear Noise

As a stressor widely existing in daily life, noise can cause great alterations to the immune system and result in many physical and mental disorders, including noise-induced deafness, sleep disorders, cardiovascular diseases, endocrine diseases and other problems. The immune system plays a major role in maintaining homeostasis by recognizing and removing harmful substances in the body. Many studies have shown that noise may play vital roles in the occurrence and development of some immune diseases. In humans, both innate immunity and specific immunity can be influenced by noise, and different exposure durations and intensities of noise may exert various effects on the immune system. Short-term or low-intensity noise can enhance immune function, while long-term or high-intensity noise suppresses it. Noise can lead to the occurrence of noise-induced hearing loss (NIHL) through the production of autoantibodies such as anti-Hsp70 and anti-Hsp60 and exert adverse effects related to other immune-related diseases such as some autoimmune diseases and non-Hodgkin lymphoma. The neuroendocrine system, mainly including the hypothalamic-pituitary-adrenal (HPA) axis and the sympathetic-adrenal-medullary (SAM) system, is involved in the mechanisms of immune-related diseases induced by noise and gut microbiota dysfunction. In addition, noise exposure during pregnancy may be harmful to the immune system of the fetus. On the other hand, some studies have shown that music can improve immune function and alleviate the adverse effects caused by noise.

Noise Exposures Causing Hearing Loss Generate Proteotoxic Stress and Activate the Proteostasis Network

Exposure to excessive sound causes noise-induced hearing loss through complex mechanisms and represents a common and unmet neurological condition. We investigate how noise insults affect the cochlea with proteomics and functional assays. Quantitative proteomics reveals that exposure to loud noise causes proteotoxicity. We identify and confirm hundreds of proteins that accumulate, including cytoskeletal proteins, and several nodes of the proteostasis network. Transcriptomic analysis reveals that a subset of the genes encoding these proteins also increases acutely after noise exposure, including numerous proteasome subunits. Global cochlear protein ubiquitylation levels build up after exposure to excess noise, and we map numerous posttranslationally modified lysines residues. Several collagen proteins decrease in abundance, and Col9a1 specifically localizes to pillar cell heads. After two weeks of recovery, the cochlea selectively elevates the abundance of the protein synthesis machinery. We report that overstimulation of the auditory system drives a robust cochlear proteotoxic stress response.

Drug development for noise-induced hearing loss

INTRODUCTION

Excessive exposure to noise is a common occurrence that contributes to approximately 50% of the non-genetic hearing loss cases. Researchers need to develop standardized preclinical models and identify molecular targets to effectively develop prevention and curative therapies.

AREAS COVERED

In this review, the authors discuss the many facets of human noise-induced pathology, and the primary experimental models for studying the basic mechanisms of noise-induced damage, making connections and inferences among basic science studies, preclinical proofs of concept and clinical trials.

EXPERT OPINION

Whilst experimental research in animal models has helped to unravel the mechanisms of noise-induced hearing loss, there are often methodological variations and conflicting results between animal and human studies which make it difficult to integrate data and translate basic outcomes to clinical practice. Standardization of exposure paradigms and application of -omic technologies will contribute to improving the effectiveness of transferring newly gained knowledge to clinical practice.

Immediate changes in transcription factors and synaptic transmission in the cochlea following acoustic trauma: A gene transcriptome study

Pathologic mechanisms in cochleae immediately following the onset of noise-induced hearing loss (NIHL) remain unclear. In this study, mice were exposed to 120 dB of octave band noise for 2 h to induce NIHL. Three hours after noise exposure, expression levels of the whole mouse genome in cochleae were analyzed by RNA-seq and DNA microarray. Differentially expressed genes (DEGs) exhibiting >2-fold upregulation or downregulation in noise-exposed cochleae compared to controls without noise exposure were identified. RNA-seq and microarray analyses identified 273 DEGs regulated at 3 h post-noise (51 upregulated and 222 downregulated). Bioinformatic analysis revealed that these DEGs were associated with the functional gene pathway "neuroactive ligand-receptor interaction" and included 28 genes encoding receptors for neurotransmitters such as gamma-aminobutyric acid and glutamate. Other DEGs included 25 genes encoding transcription factors. Downregulation of 4 neurotransmitter receptors (Gabra3, Gabra5, Gabrb1, Grm1) and upregulations of 5 transcription factors (Atf3, Dbp, Helt, Maff, Nr1d1) were validated by RT-PCR. The differentially regulated transcription factor Atf3 immunolocalized to supporting cells and hair cells in the organ of Corti at 12-h post-noise. The present data serve as a basis for further studies aimed at developing medical treatments for acute sensorineural hearing loss.

Intratympanically Delivered Steroids Impact Thousands More Inner Ear Genes Than Systemic Delivery

Objectives:

Glucocorticoids are given for sensorineural hearing loss, but little is known of their molecular impact on the inner ear. Furthermore, in spite of claims of improved hearing recovery with intratympanic delivery of steroids, no studies have actually documented the inner ear molecular functions that are enhanced with this delivery method.

Methods:

To assess steroid-driven processes in the inner ear, gene chip analyses were conducted on mice treated systemically with the glucocorticoids prednisolone or dexamethasone or the mineralocorticoid aldosterone. Other mice were given the same steroids intratympanically. Inner ears were harvested at 6 hours and processed on the Affymetrix 430 2.0 Gene Chip for expression of its 34 000 genes. Results were statistically analyzed for up or down expression of each gene against control (untreated) mice.

Results:

Analyses showed approximately 17 500 genes are normally expressed in the inner ear and steroids alter expression of 55% to 82% of these. Dexamethasone changed expression of 9424 (53.9%) inner ear genes following systemic injection but 14 899 ear genes (85%) if given intratympanically. A similar pattern was seen with prednisolone, as 7560 genes were impacted by oral delivery and 11 164 genes (63.8%) when given intratympanically. The mineralocorticoid aldosterone changed expression of only 268 inner ear genes if given orally, but this increased to 10 124 genes (57.9%) if injected intratympanically. Furthermore, the glucocorticoids given actually impacted more inner ear genes via the mineralocorticoid receptor than the glucocorticoid receptor.

Conclusions:

Thousands of inner ear genes were affected by steroids, and this number increased significantly if steroids were delivered intratympanically. Also, the impact of glucocorticoids on inner ear mineralocorticoid functions is more substantial than previously known. Thus, the application of therapeutic steroids for hearing loss needs to be reassessed in light of their more comprehensive impact on inner ear genes. Furthermore, simply ascribing the efficacy of steroids to immunosuppression no longer appears to be warranted.