Role of cysteinyl leukotriene signaling in a mouse model of noise-induced cochlear injury

The role of cochlea extracellular matrix in age-related hearing loss

Age-related hearing loss (ARHL) is a common disease among the elderly. Although its pathogenesis remains unclear by now, it is widely accepted that ARHL is associated with the degenerative alterations within each component of the cochlea. Extracellular matrix (ECM) plays a crucial role in cochlear structure and function, providing not only structural support but also participating in vital physiological processes including the development, differentiation, survival of auditory sensory cells, and sound perception. ECM is implicated in the pathogenesis of various neurodegenerative diseases, with certain ECM proteins or associated molecules emerging as potential therapeutic targets. However, few research were carried out on ECM in the cochlea and ECM associated molecules in ARHL. This review aims to delineate the composition of ECM in the cochlea, the changes of the main ECM structure in the cochlea such as the tectorial membrane (TM), the basilar membrane (BM) and the spiral ligament (SL) during aging, as well as the role of ECM associated molecules in ARHL. We hope that this review will foster further research into ARHL.

The cochlear matrisome: Importance in hearing and deafness

The extracellular matrix (ECM) consists in a complex meshwork of collagens, glycoproteins, and proteoglycans, which serves a scaffolding function and provides viscoelastic properties to the tissues. ECM acts as a biomechanical support, and actively participates in cell signaling to induce tissular changes in response to environmental forces and soluble cues. Given the remarkable complexity of the inner ear architecture, its exquisite structure-function relationship, and the importance of vibration-induced stimulation of its sensory cells, ECM is instrumental to hearing. Many factors of the matrisome are involved in cochlea development, function and maintenance, as evidenced by the variety of ECM proteins associated with hereditary deafness. This review describes the structural and functional ECM components in the auditory organ and how they are modulated over time and following injury.

Study on Screening Core Biomarkers of Noise and Drug-Induced Hearing Loss Based on Transcriptomics

Background  Noise and drug-induced hearing loss (HL) is becoming more and more serious, but the integration and analysis based on transcriptomics and proteomics are lacking. On the one hand, this study aims to integrate existing public transcriptomic data on noise and gentamicin-induced HL. On the other hand, the study aims to establish the gentamicin and noise-induced HL model of guinea pigs, then to perform the transcriptomic and proteomic analyses. Through comprehensive analysis of the above data, we aim to screen, predict, and preliminarily verify biomarkers closely related to HL. Material and Methods  We screened the Gene Expression Omnibus database to obtain transcriptome data expression profiles of HL caused by noise and gentamicin, then constructed the guinea pig HL model and perform the transcriptomic and proteomic analyses. Differential expression and enrichment analysis were performed on public and self-sequenced data, and common differentially expressed genes (DEGs) and signaling pathways were obtained. Finally, we used proteomic data to screen for common differential proteins and validate common differential expression genes for HL. Results  By integrating the public data set with self-constructed model data set, we eventually obtained two core biomarkers of HL, which were RSAD2 and matrix metalloproteinase-3 (MMP3). Their main function is to regulate the development of sense organ in the inner ear and they are mainly involved in mitogen-activated protein kinase and phosphoinositol-3 kinase/protein kinase B signaling pathways. Finally, by integrating the proteomic data of the self-constructed model, we also found differential expression of MMP3 protein. This also preliminarily and partially verified the above-mentioned core biomarkers. Conclusion and Significance  In this study, public database and transcriptomic data of self-constructed model were integrated, and we screened out two core genes and various signal pathways of HL through differential analysis, enrichment analysis, and other analysis methods. Then, we preliminarily validated the MMP3 by proteomic analysis of self-constructed model. This study pointed out the direction for further laboratory verification of key biomarkers of HL, which is of great significance for revealing the core pathogenic mechanism of HL.

Transcriptome-Guided Identification of Drugs for Repurposing to Treat Age-Related Hearing Loss

Age-related hearing loss (ARHL) or presbycusis is a prevalent condition associated with social isolation, cognitive impairment, and dementia. Age-related changes in the cochlea, the auditory portion of the inner ear, are the primary cause of ARHL. Unfortunately, there are currently no pharmaceutical approaches to treat ARHL. To examine the biological processes underlying age-related changes in the cochlea and identify candidate drugs for rapid repurposing to treat ARHL, we utilized bulk RNA sequencing to obtain transcriptomes from the functional substructures of the cochlea—the sensorineural structures, including the organ of Corti and spiral ganglion neurons (OC/SGN) and the stria vascularis and spiral ligament (SV/SL)—in young (6-week-old) and old (2-year-old) C57BL/6 mice. Transcriptomic analyses revealed both overlapping and unique patterns of gene expression and gene enrichment between substructures and with ageing. Based on these age-related transcriptional changes, we queried the protein products of genes differentially expressed with ageing in DrugBank and identified 27 FDA/EMA-approved drugs that are suitable to be repurposed to treat ARHL. These drugs target the protein products of genes that are differentially expressed with ageing uniquely in either the OC/SGN or SV/SL and that interrelate diverse biological processes. Further transcriptomic analyses revealed that most genes differentially expressed with ageing in both substructures encode protein products that are promising drug target candidates but are, nevertheless, not yet linked to approved drugs. Thus, with this study, we apply a novel approach to characterize the druggable genetic landscape for ARHL and propose a list of drugs to test in pre-clinical studies as potential treatment options for ARHL.

Noise-Induced Hearing Loss: Updates on Molecular Targets and Potential Interventions

Noise overexposure leads to hair cell loss, synaptic ribbon reduction, and auditory nerve deterioration, resulting in transient or permanent hearing loss depending on the exposure severity. Oxidative stress, inflammation, calcium overload, glutamate excitotoxicity, and energy metabolism disturbance are the main contributors to noise-induced hearing loss (NIHL) up to now. Gene variations are also identified as NIHL related. Glucocorticoid is the only approved medication for NIHL treatment. New pharmaceuticals targeting oxidative stress, inflammation, or noise-induced neuropathy are emerging, highlighted by the nanoparticle-based drug delivery system. Given the complexity of the pathogenesis behind NIHL, deeper and more comprehensive studies still need to be fulfilled.

Effect of Specific Retinoic Acid Receptor Agonists on Noise-Induced Hearing Loss

Noise is one of the most common causes of hearing loss in industrial countries. There are many studies about chemical agents to prevent noise-induced hearing loss (NIHL). However, there is no commercially available drug yet. Retinoic acid is an active metabolite of Vitamin A; it has an anti-apoptic role in NIHL. This study aims to verify the differences among selective agonists of retinoic acid receptors (RARs) in NIHL. All-trans retinoic acid (ATRA), AM80 (selective retinoic acid receptor α agonist), AC261066 (Selective retinoic acid receptor β1 agonist), and CD1530 (Selective retinoic acid λ agonist) were injected to 6–7 weeks old CJ5BL/6 mice before noise (110 dB for 3 h) exposure. In the auditory brainstem response test pre-, post 1, 3, and 7 days after noise exposure, not only ATRA but all kinds of selective RAR agonists showed protective effects in hearing threshold and wave I amplitude. Though there was no significant difference in the level of protective effects between agonists, α agonist showed the most prominent effect in preserving hearing function as well as outer hair cells after noise exposure. In conclusion, selective agonists of RAR demonstrate comparable protective effects against NIHL to retinoic acid. Given that these selective RAR agonists have less side effects than retinoic acid, they may be promising potential drugs against NIHL.

Montelukast treatment protects nigral dopaminergic neurons against microglial activation in the 6-hydroxydopamine mouse model of Parkinson's disease

Although the main cause of degeneration of the nigrostriatal dopaminergic (DA) projection in Parkinson's disease (PD) is still controversial, many reports suggest that excessive inflammatory responses mediated by activated microglia can induce neurotoxicity in the nigrostriatal DA system in vivo. Montelukast, which plays an anti-inflammatory role, is used to treat patients with asthma. In addition, recent studies have reported that its administration could reduce neuroinflammatory activities, showing beneficial effects against various neuropathological conditions. These results suggest that montelukast may be a useful drug to alleviate inflammatory responses in PD, even though there are no reports showing its beneficial effects against neurotoxicity in the nigrostriatal DA system. In the present study, our results showed that treatment with montelukast could protect DA neurons against 6-hydroxydopamine (6-OHDA)-induced neurotoxicity and its administration significantly attenuated the production of neurotoxic cytokines such as tumor necrosis factor-α (TNFα) and interleukin-1β (IL-1β) from activated microglia in the substantia nigra (SN) and striatum following 6-OHDA treatment. Therefore, we suggest that montelukast can be used as a potential inhibitor of microglial activation to protect DA neurons in the adult brain against PD.

[The genetic aspects of occupational hearing impairment]

This article was designed to be the overview of the current literature publications concerning the identification of the genetic markers of susceptibility to the noise-induced loss of hearing. The analysis of these data has demonstrated that the major gene polymorphisms associated with the development of this pathological condition are localized in the genes encoding for the antioxidant systems, potassium homeostasis, and adhesion molecules as well as in the genes involved in intercellular coupling, the mechanisms underlying the cellular response to stress, activation and regulation of heat shock proteins, and signaling function of the immune system. It is concluded that the further investigations into the genetic aspects of the full-genome sequencing techniques and the search for genomic associations could greatly contribute to the development of personalized medicine and the reduction of risks of occupational noise-induced sensorineural impairment of hearing.

The Genomic Basis of Noise-induced Hearing Loss: A Literature Review Organized by Cellular Pathways

OBJECTIVE

Using Reactome, a curated Internet database, noise-induced hearing loss studies were aggregated into cellular pathways for organization of the emerging genomic and epigenetic data in the literature.

DATA SOURCES

PubMed and Reactome.org, a relational data base program systematizing biological processes into interactive pathways and subpathways based on ontology, cellular constituents, gene expression, and molecular components.

STUDY SELECTION

Peer-reviewed population and laboratory studies for the previous 15 years relating genomics and noise and hearing loss were identified in PubMed. Criteria included p values <0.05 with correction for multiple genes, a fold change of >1.5, or duplicated studies.

DATA EXTRACTION AND SYNTHESIS

One-hundred fifty-eight unique HGNC identifiers from 77 articles met the selection criteria, and were uploaded into the analysis program at http://reactome.org. These genes participated in a total of 621 cellular interactions in 21 of 23 pathways. Cellular response to stress with its attenuation phase, particularly in response to heat stress, detoxification of ROS, and specific areas of the immune system are predominant pathways identified as significantly 'overrepresented' (p values <0.1e-5 and false discovery rates <0.01).

CONCLUSION

Twenty-one of 23 of the designated pathways in Reactome have significant influence on noise-induced hearing loss, signifying a confluence of molecular pathways in reaction to acoustic trauma; however, cellular response to stress, including heat shock response, and other small areas of immune response were highly overrepresented. Yet-to-be-explored genomics areas include miRNA, lncRNA, copy number variations, RNA sequencing, and human genome-wide association study.

Preventive effect of genetic knockdown and pharmacological blockade of CysLT1R on lipopolysaccharide (LPS)-induced memory deficit and neurotoxicity in vivo

Previously we reported that cysteinyl leukotrienes (Cys-LTs) and the type 1 receptor for Cys-LTs (CysLT₁R) are related to amyloid β (Aβ)-induced neurotoxicity. The aim of the current study was to find out the role of CysLT₁R on lipopolysaccharide (LPS)-induced cognitive deficit and neurotoxicity. shRNA-mediated knockdown or pharmacological blockade (by pranlukast) of CysLT₁R were performed in ICR mice for 21days prior to systemic infusion of LPS. From day 22, LPS was administered for 7days and then a set of behavioral, histopathological and biochemical tests were employed to test memory, neuroinflammation and apoptotic responses in the mouse hippocampus. LPS (only)-treated mice showed poor performance in both Morris water maze (MWM) and Y-maze tests. However, shRNA-mediated knockdown or pranlukast-treated blockade of CysLT₁R improved performance of the mice in these tests. To find out the possible underlying mechanisms, we assessed several parameters such as microglial activation (by immunohistochemistry), level of CysLT₁R (by WB and qRT-PCR) and the inflammatory/apoptotic pathways (by ELISA or TUNEL or WB) in the mouse hippocampus. LPS-induced memory impairment was accompanied by activation of microglia, higher level of CysLT₁R, IL-1β, TNF-α and nuclear NF-κB p65. LPS also caused apoptosis in the hippocampus as detected by TUNEL staining, further supplemented by detection of increased Caspase-3 and a reduced Bcl-2/Bax ratio. All of these adverse changes in the mouse hippocampus were inhibited by pretreatment with CysLT₁R-shRNA and pranlukast. Through this study we suggest that CysLT₁R shares a strong correlation with LPS-associated memory deficit, neuroinflammation and apoptosis and CysLT₁R could be a novel target for preventive measures to intervene the progression of Alzheimer's disease (AD)-like phenotypes.

Connexin 43 Acts as a Proapoptotic Modulator in Cisplatin-Induced Auditory Cell Death

AIMS

Gap junction coupling is known to play a role in intercellular communication by the Good Samaritan effect or bystander effect. Nonjunctional connexins (Cxs) may also play certain gap junction-independent roles in cell death or survival. The purpose of the present study was to investigate the role of junctional and nonjunctional Cxs in ototoxic drug-induced auditory cell death by focusing on Cx43 in the cochlea.

RESULTS

Nonjunctional Cx43 conditions were prepared by low confluence culture (5 × 10³/cm²) or a trafficking inhibitor, brefeldin A (BFA), in auditory cells, and short lengthened Cx43s with amino-terminal (NT; amino acids 1-256) or carboxy-terminal (CT; amino acids 257-382) were transfected into Cx-deficient HeLa cells to avoid gap junction formation. Knockdown of nonchannel Cx43 (small interfering RNA [siRNA]) inhibited Cis-diamminedichloroplatinum (cisplatin)-induced cell death regardless of gap junction formation; however, a gap junction blocker, 18 alpha-glycyrrhetinic acid (18α-GA), showed inhibitory effect only under the junctional condition. BFA did not show any additive influence on the inhibitory effect of siRNA Cx43. Shortened Cx43-transfected HeLa cells also resulted in a significant increase in cell death under cisplatin. In the animal studies with cisplatin-treated rats, hearing thresholds of auditory brainstem response were significantly preserved by a gap junction blocker, carbenoxolone, showing much more preserved stereocilia of hair cells in scanning electron microscopic findings. Innovation and Conclusion: Cx43 plays a proapoptotic role in cisplatin-induced auditory cell death in both junctional and nonjunctional conditions. Targeting the Cx-mediated signaling control may be helpful in designing new therapeutic strategies for drug-induced ototoxicity. Antioxid. Redox Signal. 25, 623-636.

Gene expression profiling of the inner ear

The identification of transcriptional differences has served as an important starting point in understanding the molecular mechanisms behind biological processes and systems. The developmental biology of the inner ear, the biology of hearing and of course the pathology of deafness are all processes that warrant a molecular description if we are to improve human health. To this end, technological innovation has meant that larger scale analysis of gene transcription has been possible for a number of years now, extending our molecular analysis of genes to beyond those that are currently in vogue for a given system. In this review, some of the contributions gene profiling has made to understanding developmental, pathological and physiological processes in the inner ear are highlighted.

Mechanisms of sensorineural cell damage, death and survival in the cochlea

The majority of acquired hearing loss, including presbycusis, is caused by irreversible damage to the sensorineural tissues of the cochlea. This article reviews the intracellular mechanisms that contribute to sensorineural damage in the cochlea, as well as the survival signaling pathways that can provide endogenous protection and tissue rescue. These data have primarily been generated in hearing loss not directly related to age. However, there is evidence that similar mechanisms operate in presbycusis. Moreover, accumulation of damage from other causes can contribute to age-related hearing loss (ARHL). Potential therapeutic interventions to balance opposing but interconnected cell damage and survival pathways, such as antioxidants, anti-apoptotics, and pro-inflammatory cytokine inhibitors, are also discussed.