Historical Aspects of Gene Therapy and Stem Cell Therapy in the Treatment of Hearing and Balance Disorder.

This review presents many but not all the major historical events that have led to our current understanding of gene and stem cell therapies for the treatment of hearing and balance disorders in animal models of these disorders. In order to better understand the application of these emerging therapies to the treatment of inner ear disorders in a clinical setting, it has been necessary to provide some genetic and pathobiology backgrounds from both animal models and clinical disorders. The current focus and goal of gene and stem cell therapies are directed toward understanding the effective treatment of animal models that mimic human disorders of hearing and balance.

Isolation and Characterization of Mammalian Otic Progenitor Cells that Can Differentiate into Both Sensory Epithelial and Neuronal Cell Lineages.

The mammalian inner ear mediates hearing and balance and during development generates both cochleo-vestibular ganglion neurons and sensory epithelial receptor cells, that is, hair cells and support cells. Cell marking experiments have shown that both hair cells and support cells can originate from a common progenitor. Here, we demonstrate the lineage potential of individual otic epithelial cell clones using three cell lines established by a combination of limiting dilution and gene-marking techniques from an embryonic day 12 (E12) rat otocyst.

A Regenerative Medicine Approach to the Treatment of Hearing, Balance, and Olfactory Disorders: What Is in the Future for Otolaryngology?

Regenerative medicine is being applied to many fields of medicine and is now starting to be considered and developed for application to treat hearing, balance, olfaction, and voice disorders. This special issue of the Anatomical Record with a series of over 20 papers covers many aspects of gene and stem cell therapies as they are developed for clinical applications in both in vitro and in vivo laboratory studies. These studies cover a wide range of approaches from gene editing in zebrafish with the latest technology (i.

Ultrastructural Characterization of Stem Cell-Derived Replacement Vestibular Hair Cells Within Ototoxin-Damaged Rat Utricle Explants.

The auditory apparatus of the inner ear does not show turnover of sensory hair cells (HCs) in adult mammals; in contrast, there are many observations supporting low-level turnover of vestibular HCs within the balance organs of mammalian inner ears. This low-level renewal of vestibular HCs exists during normal conditions and it is further enhanced after trauma-induced loss of these HCs. The main process for renewal of HCs within mammalian vestibular epithelia is a conversion/transdifferentiation of existing supporting cells (SCs) into replacement HCs.

Laminin-coated electrodes improve cochlear implant function and post-insertion neuronal survival.

The benefits of Cochlear implant (CI) technology depend among other factors on the proximity of the electrode array to the spiral ganglion neurons. Laminin, a component of the extracellular matrix, regulates Schwann cell proliferation and survival as well as reorganization of actin fibers within their cytoskeleton, which is necessary for myelination of peripheral axons. In this study we explore the effectiveness of laminin-coated electrodes in promoting neuritic outgrowth from auditory neurons towards the electrode array and the ability to reduce acoustic and electric auditory brainstem response (i.

TGF β-1 and WNT Signaling Pathways Collaboration Associated with Cochlear Implantation Trauma-Induced Fibrosis.

The crosstalk between TGF-β1 and WNT pathways has been proven to regulate aspects of the development and tissue homeostasis processes. Recently, it has been demonstrated this collaboration also takes place during fibrotic diseases, where TGF-β1 activates the WNT/β-catenin pathway that results in dedifferentiation of fibroblasts into myofibroblasts, increased production of extracellular matrix components and fibrosis. Independent studies show the functions of these molecules during the development of the inner ears in several different species.

l-N-acetylcysteine protects outer hair cells against TNFα initiated ototoxicity in vitro.

Objective: The present study is aimed at determining the efficacy and exploring the mechanisms by which l-N-acetylcysteine (l-NAC) provides protection against tumor necrosis factor-alpha (TNFα)-induced oxidative stress damage and hair cell loss in 3-day-old rat organ of Corti (OC) explants. Previous work has demonstrated a high level of oxidative stress in TNFα-challenged OC explants. TNFα can potentially play a significant role in hair cell loss following an insult to the inner ear.

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.

Comparison of packing material in an animal model of middle ear trauma.

Purpose: To compare the performance of absorbable gelatin sponge (AGS) with polyurethane foam (PUF) as middle ear packing material after mucosal trauma.

Materials And Methods: Using a randomized, controlled and blinded study design fifteen guinea pigs underwent middle ear surgery with mucosal trauma performed on both ears. One ear was packed with either PUF or AGS while the contralateral ear remained untreated and used as non-packed paired controls.

Electrode array-eluted dexamethasone protects against electrode insertion trauma induced hearing and hair cell losses, damage to neural elements, increases in impedance and fibrosis: A dose response study.

We evaluated the effects of dexamethasone base (DXMb) containing electrode arrays in a guinea pig model of cochlear implantation to determine if eluted DXMb could protect the cochlea against electrode insertion trauma (EIT)-induced: 1) loss of hair cells; 2) disruption of neural elements; 3) increases in hearing thresholds; 4) increased electrical impedance and 5) fibrosis. A guinea pig model of EIT-induced hearing and hair cell losses was used to test silicone electrode arrays that contained either 10%, 1%, 0.1%, or 0% levels of micronized DXMb.

Spiral ganglion cells and macrophages initiate neuro-inflammation and scarring following cochlear implantation.

Conservation of a patient's residual hearing and prevention of fibrous tissue/new bone formation around an electrode array are some of the major challenges in cochlear implant (CI) surgery. Although it is well-known that fibrotic tissue formation around the electrode array can interfere with hearing performance in implanted patients, and that associated intracochlear inflammation can initiate loss of residual hearing, little is known about the molecular and cellular mechanisms that promote this response in the cochlea. In vitro studies in neonatal rats and in vivo studies in adult mice were performed to gain insight into the pro-inflammatory, proliferative, and remodeling phases of pathological wound healing that occur in the cochlea following an electrode analog insertion.

Molecular regulation of auditory hair cell death and approaches to protect sensory receptor cells and/or stimulate repair following acoustic trauma.

Loss of auditory sensory hair cells (HCs) is the most common cause of hearing loss. This review addresses the signaling pathways that are involved in the programmed and necrotic cell death of auditory HCs that occur in response to ototoxic and traumatic stressor events. The roles of inflammatory processes, oxidative stress, mitochondrial damage, cell death receptors, members of the mitogen-activated protein kinase (MAPK) signal pathway and pro- and anti-cell death members of the Bcl-2 family are explored.

Mechanisms of programmed cell death signaling in hair cells and support cells post-electrode insertion trauma.

Conclusion: Programmed cell death (PCD) initially starts in the support cells (SCs) after electrode insertion trauma (EIT), followed by PCD in hair cells (HCs). Activation of caspase-3 was observed only in SCs. Protecting both SCs and HCs with selective otoprotective drugs at an early stage post implantation may help to preserve residual hearing.

Morphological and morphometric characterization of direct transdifferentiation of support cells into hair cells in ototoxin-exposed neonatal utricular explants.

We have studied aminoglycoside-induced vestibular hair-cell renewal using long-term culture of utricular macula explants from 4-day-old rats. Explanted utricles were exposed to 1 mM of gentamicin for 48 h, during 2nd and 3rd days in vitro (DIV), and then recovering in unsupplemented medium. Utricles were harvested at specified time points from the 2nd through the 28th DIV.

Otoprotective properties of mannitol against gentamicin induced hair cell loss.

Background: Gentamicin is a widely used antibiotic, which causes hearing loss because of destruction of auditory hair cells. Mannitol has been shown to have cytoprotective properties in the cochlea both in vitro and in vivo. Mannitol has been shown to be safe in concentrations up to 100 mM in organ of Corti explants.

Adult human nasal mesenchymal-like stem cells restore cochlear spiral ganglion neurons after experimental lesion.

A loss of sensory hair cells or spiral ganglion neurons from the inner ear causes deafness, affecting millions of people. Currently, there is no effective therapy to repair the inner ear sensory structures in humans. Cochlear implantation can restore input, but only if auditory neurons remain intact.

Short interfering RNA against Bax attenuates TNFα-induced ototoxicity in rat organ of Corti explants.

Objective: Evaluate the effectiveness of short interfering RNA against Bax (Bax siRNA) as a treatment for tumor necrosis factor α (TNFα)-induced auditory hair cell (HC) loss in rat organ of Corti (OC) explants.

Study Design: Basic science.

Setting: Basic science laboratory, University of Miami Ear Institute.

Molecular mechanisms involved in cochlear implantation trauma and the protection of hearing and auditory sensory cells by inhibition of c-Jun-N-terminal kinase signaling.

Objectives/hypothesis: To investigate the molecular mechanisms involved in electrode insertion trauma (EIT) and to test the otoprotective effect of locally delivered AM-111.

Study Design: An animal model of cochlear implantation.

Methods: Guinea pigs' hearing thresholds were measured by auditory brainstem response (ABR) before and after cochlear implantation in four groups: EIT; pretreated with hyaluronate gel 30 minutes before EIT (EIT+Gel); pretreated with hyaluronate gel/AM-111 30 minutes before EIT (EIT+AM-111); and unoperated contralateral ears as controls.

Historical Aspects of Inner Ear Anatomy and Biology that Underlie the Design of Hearing and Balance Prosthetic Devices.

This review presents some of the major historical events that advanced the body of knowledge of the anatomy of the inner ear and its sensory receptors as well as the biology of these receptors that underlies the sensory functions of hearing and balance. This knowledge base of the inner ear's structure/function has been an essential factor for the design and construction of prosthetic devices to aid patients with deficits in their senses of hearing and balance. Prosthetic devices are now available for severely hearing impaired and deaf patients to restore hearing and are known as cochlear implants and auditory brain stem implants.

Conservation of hearing and protection of hair cells in cochlear implant patients' with residual hearing.

This review covers the molecular mechanisms involved in hair cell and hearing losses which can result from trauma generated during the process of cochlear implantation and the contributions of both the intrinsic and extrinsic cell death signaling pathways in producing these trauma/inflammation induced losses. Application of soft surgical techniques to conserve hearing and protect auditory sensory cells during the process of cochlear implantation surgery and insertion of the electrode array during the process of cochlear implantation are reviewed and discussed. The role of drug therapy and mode of drug delivery for the conservation of a cochlear implant patient's residual hearing is presented and discussed.

A novel organ of corti explant model for the study of cochlear implantation trauma.

This study presents a novel in vitro model of electrode insertion trauma-induced hair cell (HC) damage and loss and its application for testing the efficacy of otoprotective drugs. In the cochlear implant (CI) procedure as a treatment for profound deafness, an electrode array is surgically inserted to provide electrical stimulation to the auditory nerve. Mechanical trauma from insertion of a CI electrode into the scala tympani can lead to inflammation and a high level of oxidative stress, which can initiate the apoptosis of auditory HCs and intracochlear fibrosis.

Mannitol protects hair cells against tumor necrosis factor α-induced loss.

Hypothesis: Mannitol has otoprotective effects against tumor necrosis factor (TNF) α-induced auditory hair cell (HC) loss.

Background: Mannitol has been demonstrated to possess cytoprotective effects in several organ systems. Its protective effect on postischemic hearing loss has also been shown.

Morphological and morphometric characteristics of vestibular hair cells and support cells in long term cultures of rat utricle explants.

A method for long term culture of utricular macula explants is demonstrated to be stable and reproducible over a period of 28 days in vitro (DIV). This culture system for four-day-old rat utricular maculae is potentially suitable for studies of hair cell loss, repair and regeneration processes as they occur in post-natal mammalian inner ear sensory epithelia. The cellular events that occur within utricular macula hair cell epithelia during 28 days of culture are documented from serial sections.

Middle ear packing: comparison of materials in an animal model of mucosal trauma.

Objective: To compare absorbable gelatin sponge (AGS) with an injectable esterified hyaluronic acid (EHA) as middle ear packing material after mucosal trauma.

Study Design: Randomized, blinded, and controlled study.

Setting: Tertiary university-based hospital.

The injured cochlea as a target for inflammatory processes, initiation of cell death pathways and application of related otoprotectives strategies.

One of the causes of sensorineural hearing loss is the loss of auditory hair cells following exposure to environmental stresses. Auditory hair cell death in response to cochlear trauma occurs via both necrosis and apoptosis. Apoptosis of hair cells involves the caspase and MAPK/JNK pathways which are activated by oxidative stress and secretion of inflammatory cytokines in response to trauma.