A mutation in SLC22A4 encoding an organic cation transporter expressed in the cochlea strial endothelium causes human recessive non-syndromic hearing loss DFNB60

The Antioxidant Ergothioneine Alleviates Cisplatin-Induced Hearing Loss through the Nrf2 Pathway

Aims: Cisplatin (CDDP) is a commonly used chemotherapeutic agent for treating head and neck tumors. However, there is high incidence of ototoxicity in patients treated with CDDP, which may be caused by the excessive reactive oxygen species (ROS) generation in the inner ear. Many studies have demonstrated the strong antioxidant effects of ergothioneine (EGT). Therefore, we assumed that EGT could also attenuate cisplatin-induced hearing loss (CIHL) as well. However, the protective effect and mechanism of EGT on CIHL have not been elucidated as so far. In this study, we investigated whether EGT could treat CIHL and the mechanism. Results: In our study, we confirmed the protective effect of EGT on preventing CDDP-induced toxicity both in vitro and in vivo. The auditory brainstem response threshold shift in the EGT + CDDP treatment mice was 30 dB less than that in the CDDP treatment mice. EGT suppressed production of ROS and proapoptotic proteins both in tissue and cells. By silencing nuclear factor erythroid 2-related factor 2 (Nrf2), we confirmed that EGT protected against CIHL via the Nrf2 pathway. We also found that SLC22A4 (OCTN1), an important molecule involved in transporting EGT, was expressed in the cochlea. Innovation: Our results revealed the role of EGT in the prevention of CIHL by activating Nrf2/HO-1/NQO-1 pathway, and broadened a new perspective therapeutic target of EGT. Conclusion: EGT decreased ROS production and promoted the expression of antioxidative enzymes to maintain redox homeostasis in sensory hair cells. Overall, our results indicated that EGT may serve as a novel treatment drug to attenuate CIHL.

L-Ergothioneine slows the progression of age-related hearing loss in CBA/CaJ mice

The naturally occurring amino acid, l-ergothioneine (EGT), has immense potential as a therapeutic, having shown promise in the treatment of other disease models, including neurological disorders. EGT is naturally uptaken into cells via its specific receptor, OCTN1, to be utilized by cells as an antioxidant and anti-inflammatory. In our current study, EGT was administered over a period of 6 months to 25-26-month-old CBA/CaJ mice as a possible treatment for age-related hearing loss (ARHL), since presbycusis has been linked to higher levels of cochlear oxidative stress, apoptosis, and chronic inflammation. Results from the current study indicate that EGT can prevent aging declines of some key features of ARHL. However, we found a distinct sex difference for the response to the treatments, for hearing - Auditory Brainstem Responses (ABRs) and Distortion Product Otoacoustic Emissions (DPOAEs). Males exhibited lower threshold declines in both low dose (LD) and high dose (HD) test groups throughout the testing period and did not display some of the characteristic aging declines in hearing seen in Control animals. In contrast, female mice did not show any therapeutic effects with either treatment dose. Further confirming this sex difference, EGT levels in whole blood sampling throughout the testing period showed greater uptake of EGT in males compared to females. Additionally, RT-PCR results from three tissue types of the inner ear confirmed EGT activity in the cochlea in both males and females. Males and females exhibited significant differences in biomarkers related to apoptosis (Cas-3), inflammation (TNF-a), oxidative stress (SOD2), and mitochondrial health (PGC1a).These changes were more prominent in males as compared to females, especially in stria vascularis tissue. Taken together, these findings suggest that EGT has the potential to be a naturally derived therapeutic for slowing down the progression of ARHL, and possibly other neurodegenerative diseases. EGT, while effective in the treatment of some features of presbycusis in aging males, could also be modified into a general prophylaxis for other age-related disorders where treatment protocols would include eating a larger proportion of EGT-rich foods or supplements. Lastly, the sex difference discovered here, needs further investigation to see if therapeutic conditions can be developed where aging females show better responsiveness to EGT.

Inflammation and Organic Cation Transporters Novel (OCTNs)

Inflammation is a physiological condition characterized by a complex interplay between different cells handled by metabolites and specific inflammatory-related molecules. In some pathological situations, inflammation persists underlying and worsening the pathological state. Over the years, two membrane transporters namely OCTN1 (SLC22A4) and OCTN2 (SLC22A5) have been shown to play specific roles in inflammation. These transporters form the OCTN subfamily within the larger SLC22 family. The link between these proteins and inflammation has been proposed based on their link to some chronic inflammatory diseases such as asthma, Crohn's disease (CD), and rheumatoid arthritis (RA). Moreover, the two transporters show the ability to mediate the transport of several compounds including carnitine, carnitine derivatives, acetylcholine, ergothioneine, and gut microbiota by-products, which have been specifically associated with inflammation for their anti- or proinflammatory action. Therefore, the absorption and distribution of these molecules rely on the presence of OCTN1 and OCTN2, whose expression is modulated by inflammatory cytokines and transcription factors typically activated by inflammation. In the present review, we wish to provide a state of the art on OCTN1 and OCTN2 transport function and regulation in relationships with inflammation and inflammatory diseases focusing on the metabolic signature collected in different body districts and gene polymorphisms related to inflammatory diseases.

Investigating the ID3/SLC22A4 as immune-related signatures in ischemic stroke

BACKGROUND

Ischemic stroke (IS) is a fearful disease that can cause a variety of immune events. Nevertheless, precise immune-related mechanisms have yet to be systematically elucidated. This study aimed to identify immune-related signatures using machine learning and to validate them with animal experiments and single cell analysis.

METHODS

In this study, we screened 24 differentially expressed genes (DEGs) while identifying immune-related signatures that may play a key role in IS development through a comprehensive strategy between least absolute shrinkage and selection operation (LASSO) regression, support vector machine (SVM) and immune-related genes. In addition, we explored immune infiltration using the CIBERSORT algorithm. Finally, we performed validation in mouse brain tissue and single cell analysis.

RESULTS

We identified 24 DEGs for follow-up analysis. ID3 and SLC22A4 were finally identified as the better immune-related signatures through a comprehensive strategy among DEGs, LASSO, SVM and immune-related genes. RT-qPCR, western blot, and immunofluorescence revealed a significant decrease in ID3 and a significant increase in SLC22A4 in the middle cerebral artery occlusion group. Single cell analysis revealed that ID3 was mainly concentrated in endothelial_2 cells and SLC22A4 in astrocytes in the MCAO group. A CIBERSORT finds significantly altered levels of immune infiltration in IS patients.

CONCLUSIONS

This study focused on immune-related signatures after stroke and ID3 and SLC22A4 may be new therapeutic targets to promote functional recovery after stroke. Furthermore, the association of ID3 and SLC22A4 with immune cells may be a new direction for post-stroke immunotherapy.

In-depth genetic and molecular characterization of diaphanous related formin 2 (DIAPH2) and its role in the inner ear

Diaphanous related formins are regulatory cytoskeletal protein involved in actin elongation and microtubule stabilization. In humans, defects in two of the three diaphanous genes (DIAPH1 and DIAPH3) have been associated with different types of hearing loss. Here, we investigate the role of the third member of the family, DIAPH2, in nonsyndromic hearing loss, prompted by the identification, by exome sequencing, of a predicted pathogenic missense variant in DIAPH2. This variant occurs at a conserved site and segregated with nonsyndromic X-linked hearing loss in an Italian family. Our immunohistochemical studies indicated that the mouse ortholog protein Diaph2 is expressed during development in the cochlea, specifically in the actin-rich stereocilia of the sensory outer hair cells. In-vitro studies showed a functional impairment of the mutant DIAPH2 protein upon RhoA-dependent activation. Finally, Diaph2 knock-out and knock-in mice were generated by CRISPR/Cas9 technology and auditory brainstem response measurements performed at 4, 8 and 14 weeks. However, no hearing impairment was detected. Our findings indicate that DIAPH2 may play a role in the inner ear; further studies are however needed to clarify the contribution of DIAPH2 to deafness.

The Roles of Solute Carriers in Auditory Function

Solute carriers (SLCs) are important transmembrane transporters with members organized into 65 families. They play crucial roles in transporting many important molecules, such as ions and some metabolites, across the membrane, maintaining cellular homeostasis. SLCs also play important roles in hearing. It has been found that mutations in some SLC members are associated with hearing loss. In this review, we summarize SLC family genes related with hearing dysfunction to reveal the vital roles of these transporters in auditory function. This summary could help us understand the auditory physiology and the mechanisms of hearing loss and further guide future studies of deafness gene identification.

The Ergothioneine Transporter (ETT): Substrates and Locations, an Inventory

In all vertebrates including mammals, the ergothioneine transporter ETT (obsolete name OCTN1; human gene symbol SLC22A4) is a powerful and highly specific transporter for the uptake of ergothioneine (ET). ETT is not expressed ubiquitously and only cells with high ETT cell-surface levels can accumulate ET to high concentration. Without ETT, there is no uptake because the plasma membrane is essentially impermeable to this hydrophilic zwitterion. Here, we review the substrate specificity and localization of ETT, which is prominently expressed in neutrophils, monocytes/macrophages, and developing erythrocytes. Most sites of strong expression are conserved across species, but there are also major differences. In particular, we critically analyze the evidence for the expression of ETT in the brain as well as recent data suggesting that the transporter SLC22A15 may transport also ET. We conclude that, to date, ETT remains the only well-defined biomarker for intracellular ET activity. In humans, the ability to take up, distribute, and retain ET depends principally on this transporter.

Targeting SOS1 overcomes imatinib resistance with BCR-ABL independence through uptake transporter SLC22A4 in CML

Resistance to the BCR-ABL inhibitor imatinib mesylate poses a major problem for the treatment of chronic myeloid leukemia. Imatinib resistance often results from a secondary mutation in BCR-ABL that interferes with drug binding. However, sometimes there is no mutation in BCR-ABL, and the basis of such BCR-ABL-independent imatinib mesylate resistance remains to be elucidated. SOS1, a guanine nucleotide exchange factor for Ras protein, affects drug sensitivity and resistance to imatinib. The depletion of SOS1 markedly inhibits cell growth either in vitro or in vivo and significantly increases the sensitivity of chronic myeloid leukemia cells to imatinib. Furthermore, LC-MS/MS and RNA-seq assays reveal that SOS1 negatively regulates the expression of SLC22A4, a member of the carnitine/organic cation transporter family, which mediates the active uptake of imatinib into chronic myeloid leukemia cells. HPLC assay confirms that intracellular accumulation of imatinib is accompanied by upregulation of SLC22A4 through SOS1 inhibition in both sensitive and resistant chronic myeloid leukemia cells. BAY-293, an inhibitor of SOS1/Ras, was found to depress proliferation and colony formation in chronic myeloid leukemia cells with resistance and BCR-ABL independence. Altogether these findings indicate that targeting SOS1 inhibition promotes imatinib sensitivity and overcomes resistance with BCR-ABL independence by SLC22A4-mediated uptake transport.

SLC22A4 Gene in Hereditary Non-syndromic Hearing Loss: Recurrence and Incomplete Penetrance of the p.C113Y Mutation in Northwest Africa

Inherited hearing loss is extremely heterogeneous both clinically and genetically. In addition, the spectrum of deafness-causing genetic variants differs greatly among geographical areas and ethnicities. The identification of the causal mutation in affected families allows early diagnosis, clinical follow-up, and genetic counseling. A large consanguineous family of Moroccan origin affected by autosomal recessive sensorineural hearing loss (ARSNHL) was subjected to genome-wide linkage analysis and exome sequencing. Exome-wide variant analysis and prioritization identified the SLC22A4 p.C113Y missense variant (rs768484124) as the most likely cause of ARSNHL in the family, falling within the unique significant (LOD score>3) linkage region on chromosome 5. Indeed, the same variant was previously reported in two Tunisian ARSNHL pedigrees. The variant is present in the homozygous state in all six affected individuals, but also in one normal-hearing sibling, suggesting incomplete penetrance. The mutation is absent in about 1,000 individuals from the Greater Middle East Variome study cohort, including individuals from the North African population, as well as in an additional seven deaf patients from the same geographical area, recruited and screened for mutations in the SLC22A4 gene. This study represents the first independent replication of the involvement of SLC22A4 in ARSNHL, highlighting the importance of the gene, and of the p.C113Y mutation, at least in the Northwest African population.

Novel pathogenic mutations and further evidence for clinical relevance of genes and variants causing hearing impairment in Tunisian population

Introduction

Hearing impairment (HI) is characterized by complex genetic heterogeneity. The evolution of next generation sequencing, including targeted enrichment panels, has revolutionized HI diagnosis.

Objectives

In this study, we investigated genetic causes in 22 individuals with non-GJB2 HI.

Methods

We customized a Haloplex^HS kit to include 30 genes known to be associated with autosomal recessive nonsyndromic HI (ARNSHI) and Usher syndrome in North Africa.

Results

In accordance with the ACMG/AMP guidelines, we report 11 pathogenic variants; as follows; five novel variants including three missense (ESRRB-Tyr295Cys, MYO15A-Phe2089Leu and MYO7A-Tyr560Cys) and two nonsense (USH1C-Gln122Ter and CIB2-Arg104Ter) mutations; two previously reported mutations (OTOF-Glu57Ter and PNPT1-Glu475Gly), but first time identified among Tunisian families; and four other identified mutations namely WHRN-Gly808AspfsX11, SLC22A4-Cys113Tyr and two MYO7A compound heterozygous splice site variants that were previously described in Tunisia. Pathogenic variants in WHRN and CIB2 genes, in patients with convincing phenotype ruling out retinitis pigmentosa, provide strong evidence supporting their association with ARNSHI. Moreover, we shed lights on the pathogenic implication of mutations in PNPT1 gene in auditory function providing new evidence for its association with ARNSHI. Lack of segregation of a previously identified causal mutation OTOA-Val603Phe further supports its classification as variant of unknown significance. Our study reports absence of otoacoustic emission in subjects using bilateral hearing aids for several years indicating the importance of screening genetic alteration in OTOF gene for proper management of those patients.

Conclusion

In conclusion, our findings do not only expand the spectrum of HI mutations in Tunisian patients, but also improve our knowledge about clinical relevance of HI causing genes and variants.

The biology of ergothioneine, an antioxidant nutraceutical

Ergothioneine (ERG) is an unusual thio-histidine betaine amino acid that has potent antioxidant activities. It is synthesised by a variety of microbes, especially fungi (including in mushroom fruiting bodies) and actinobacteria, but is not synthesised by plants and animals who acquire it via the soil and their diet, respectively. Animals have evolved a highly selective transporter for it, known as solute carrier family 22, member 4 (SLC22A4) in humans, signifying its importance, and ERG may even have the status of a vitamin. ERG accumulates differentially in various tissues, according to their expression of SLC22A4, favouring those such as erythrocytes that may be subject to oxidative stress. Mushroom or ERG consumption seems to provide significant prevention against oxidative stress in a large variety of systems. ERG seems to have strong cytoprotective status, and its concentration is lowered in a number of chronic inflammatory diseases. It has been passed as safe by regulatory agencies, and may have value as a nutraceutical and antioxidant more generally.

Small fish, big prospects: using zebrafish to unravel the mechanisms of hereditary hearing loss

Over the past decade, advancements in high-throughput sequencing have greatly enhanced our knowledge of the mutational signatures responsible for hereditary hearing loss. In its present state, the field has a largely uncensored view of protein coding changes in a growing number of genes that have been associated with hereditary hearing loss, and many more that have been proposed as candidate genes. Sequencing data can now be generated using methods that have become widespread and affordable. The greatest hurdles facing the field concern functional validation of uncharacterized genes and rapid application to human diseases, including hearing and balance disorders. To date, over 30 hearing-related disease models exist in zebrafish. New genome editing technologies, including CRISPR/Cas9 will accelerate the functional validation of hearing loss genes and variants in zebrafish. Here, we discuss current progress in the field and recent advances in genome editing approaches.

Organic Cation Transporters in Human Physiology, Pharmacology, and Toxicology

Individual cells and epithelia control the chemical exchange with the surrounding environment by the fine-tuned expression, localization, and function of an array of transmembrane proteins that dictate the selective permeability of the lipid bilayer to small molecules, as actual gatekeepers to the interface with the extracellular space. Among the variety of channels, transporters, and pumps that localize to cell membrane, organic cation transporters (OCTs) are considered to be extremely relevant in the transport across the plasma membrane of the majority of the endogenous substances and drugs that are positively charged near or at physiological pH. In humans, the following six organic cation transporters have been characterized in regards to their respective substrates, all belonging to the solute carrier 22 (SLC22) family: the organic cation transporters 1, 2, and 3 (OCT1–3); the organic cation/carnitine transporter novel 1 and 2 (OCTN1 and N2); and the organic cation transporter 6 (OCT6). OCTs are highly expressed on the plasma membrane of polarized epithelia, thus, playing a key role in intestinal absorption and renal reabsorption of nutrients (e.g., choline and carnitine), in the elimination of waste products (e.g., trimethylamine and trimethylamine N-oxide), and in the kinetic profile and therapeutic index of several drugs (e.g., metformin and platinum derivatives). As part of the Special Issue Physiology, Biochemistry, and Pharmacology of Transporters for Organic Cations, this article critically presents the physio-pathological, pharmacological, and toxicological roles of OCTs in the tissues in which they are primarily expressed.

Practical aspects of inner ear gene delivery for research and clinical applications

The application of gene therapy is widely expanding in research and continuously improving in preparation for clinical applications. The inner ear is an attractive target for gene therapy for treating environmental and genetic diseases in both the auditory and vestibular systems. With the lack of spontaneous cochlear hair cell replacement, hair cell regeneration in adult mammals is among the most important goals of gene therapy. In addition, correcting gene defects can open up a new era for treating inner ear diseases. The relative isolation and small size of the inner ear dictate local administration routes and carefully calculated small volumes of reagents. In the current review, we will cover effective timing, injection routes and types of vectors for successful gene delivery to specific target cells within the inner ear. Differences between research purposes and clinical applications are also discussed.

Transcriptomic Analyses of Inner Ear Sensory Epithelia in Zebrafish

Analysis of gene expression has the potential to assist in the understanding of multiple cellular processes including proliferation, cell-fate specification, senesence, and activity in both healthy and disease states. Zebrafish model has been increasingly used to understand the process of hearing and the development of the vertebrate auditory system. Within the zebrafish inner ear, there are three otolith organs, each containing a sensory macula of hair cells. The saccular macula is primarily involved in hearing, the utricular macula is primarily involved in balance and the function of the lagenar macula is not completely understood. The goal of this study is to understand the transcriptional differences in the sensory macula associated with different otolith organs with the intention of understanding the genetic mechanisms responsible for the distinct role each organ plays in sensory perception. The sensory maculae of the saccule, utricle, and lagena were dissected out of adult Et(krt4:GFP)^sqet4 zebrafish expressing green fluorescent protein in hair cells for transcriptional analysis. The total RNAs of the maculae were isolated and analyzed by RNA GeneChip microarray. Several of the differentially expressed genes are known to be involved in deafness, otolith development and balance. Gene expression among these otolith organs was very well conserved with less than 10% of genes showing differential expression. Data from this study will help to elucidate which genes are involved in hearing and balance. Furthermore, the findings of this study will assist in the development of the zebrafish model for human hearing and balance disorders. Anat Rec, 303:527-543, 2020. © 2019 American Association for Anatomy.

Genetic Hearing Loss and Gene Therapy

Genetic hearing loss crosses almost all the categories of hearing loss which includes the following: conductive, sensory, and neural; syndromic and nonsyndromic; congenital, progressive, and adult onset; high-frequency, low-frequency, or mixed frequency; mild or profound; and recessive, dominant, or sex-linked. Genes play a role in almost half of all cases of hearing loss but effective treatment options are very limited. Genetic hearing loss is considered to be extremely genetically heterogeneous. The advancements in genomics have been instrumental to the identification of more than 6,000 causative variants in more than 150 genes causing hearing loss. Identification of genes for hearing impairment provides an increased insight into the normal development and function of cells in the auditory system. These defective genes will ultimately be important therapeutic targets. However, the auditory system is extremely complex which requires tremendous advances in gene therapy including gene vectors, routes of administration, and therapeutic approaches. This review summarizes and discusses recent advances in elucidating the genomics of genetic hearing loss and technologies aimed at developing a gene therapy that may become a treatment option for in the near future.

Genetics and genomic medicine in Tunisia

Genetics and genomic medicine in Tunisia.

Inner Ear Hair Cell Protection in Mammals against the Noise-Induced Cochlear Damage

Inner ear hair cells are mechanosensory receptors that perceive mechanical sound and help to decode the sound in order to understand spoken language. Exposure to intense noise may result in the damage to the inner ear hair cells, causing noise-induced hearing loss (NIHL). Particularly, the outer hair cells are the first and the most affected cells in NIHL. After acoustic trauma, hair cells lose their structural integrity and initiate a self-deterioration process due to the oxidative stress. The activation of different cellular death pathways leads to complete hair cell death. This review specifically presents the current understanding of the mechanism exists behind the loss of inner ear hair cell in the auditory portion after noise-induced trauma. The article also explains the recent hair cell protection strategies to prevent the damage and restore hearing function in mammals.

Recent Advancements in the Regeneration of Auditory Hair Cells and Hearing Restoration

Neurosensory responses of hearing and balance are mediated by receptors in specialized neuroepithelial sensory cells. Any disruption of the biochemical and molecular pathways that facilitate these responses can result in severe deficits, including hearing loss and vestibular dysfunction. Hearing is affected by both environmental and genetic factors, with impairment of auditory function being the most common neurosensory disorder affecting 1 in 500 newborns, as well as having an impact on the majority of elderly population. Damage to auditory sensory cells is not reversible, and if sufficient damage and cell death have taken place, the resultant deficit may lead to permanent deafness. Cochlear implants are considered to be one of the most successful and consistent treatments for deaf patients, but only offer limited recovery at the expense of loss of residual hearing. Recently there has been an increased interest in the auditory research community to explore the regeneration of mammalian auditory hair cells and restoration of their function. In this review article, we examine a variety of recent therapies, including genetic, stem cell and molecular therapies as well as discussing progress being made in genome editing strategies as applied to the restoration of hearing function.

Navigating genetic diagnostics in patients with hearing loss

PURPOSE OF REVIEW

In the age of targeted genomic enrichment and massively parallel sequencing, there is no more efficient genetic testing method for the diagnosis of hereditary hearing loss. More clinical tests are on the market, which can make choosing good tests difficult.

RECENT FINDINGS

More and larger comprehensive genetic studies in patients with hearing loss have been published recently. They remind us of the importance of looking for both single nucleotide variation and copy number variation in all genes implicated in nonsyndromic hearing loss. They also inform us of how a patient's history and phenotype provide essential information in the interpretation of genetic data.

SUMMARY

Choosing the most comprehensive genetic test improves the chances of a genetic diagnosis and thereby impacts clinical care.

The unique electrical properties in an extracellular fluid of the mammalian cochlea; their functional roles, homeostatic processes, and pathological significance

The cochlea of the mammalian inner ear contains an endolymph that exhibits an endocochlear potential (EP) of +80 mV with a [K(+)] of 150 mM. This unusual extracellular solution is maintained by the cochlear lateral wall, a double-layered epithelial-like tissue. Acoustic stimuli allow endolymphatic K(+) to enter sensory hair cells and excite them. The positive EP accelerates this K(+) influx, thereby sensitizing hearing. K(+) exits from hair cells and circulates back to the lateral wall, which unidirectionally transports K(+) to the endolymph. In vivo electrophysiological assays demonstrated that the EP stems primarily from two K(+) diffusion potentials yielded by [K(+)] gradients between intracellular and extracellular compartments in the lateral wall. Such gradients seem to be controlled by ion channels and transporters expressed in particular membrane domains of the two layers. Analyses of human deafness genes and genetically modified mice suggested the contribution of these channels and transporters to EP and hearing. A computational model, which reconstitutes unidirectional K(+) transport by incorporating channels and transporters in the lateral wall and connects this transport to hair cell transcellular K(+) fluxes, simulates the circulation current flowing between the endolymph and the perilymph. In this model, modulation of the circulation current profile accounts for the processes leading to EP loss under pathological conditions. This article not only summarizes the unique physiological and molecular mechanisms underlying homeostasis of the EP and their pathological relevance but also describes the interplay between EP and circulation current.