Direct cellular reprogramming and inner ear regeneration

Precise genetic control of ATOH1 enhances maturation of regenerated hair cells in the mature mouse utricle

Vestibular hair cells are mechanoreceptors critical for detecting head position and motion. In mammals, hair cell loss causes vestibular dysfunction as spontaneous regeneration is nearly absent. Constitutive expression of exogenous ATOH1, a hair cell transcription factor, increases hair cell regeneration, however, these cells fail to fully mature. Here, we profiled mouse utricles at 14 time points, and defined transcriptomes of developing and mature vestibular hair cells. To mimic native hair cells which downregulate endogenous ATOH1 as they mature, we engineered viral vectors carrying the supporting cell promoters GFAP and RLBP1. In utricles damaged ex vivo, both CMV-ATOH1 and GFAP-ATOH1 increased regeneration more effectively than RLBP1-ATOH1, while GFAP-ATOH1 and RLBP1-ATOH1 induced hair cells with more mature transcriptomes. In utricles damaged in vivo, GFAP-ATOH1 induced regeneration of hair cells expressing genes indicative of maturing type II hair cells, and more hair cells with bundles and synapses than untreated organs. Together our results demonstrate the efficacy of spatiotemporal control of ATOH1 overexpression in inner ear hair cell regeneration.

Roles of supporting cells in the maintenance and regeneration of the damaged inner ear: A literature review

The inner ear sensory epithelium consists of two major types of cells: hair cells (HCs) and supporting cells (SCs). Critical functions of HCs in the perception of mechanical stimulation and mechanosensory transduction have long been elucidated. SCs are indispensable components of the sensory epithelia, and they maintain the structural integrity and ionic environment of the inner ear. Once delicate inner ear epithelia sustain injuries (for example, due to ototoxic drugs or noise exposure), SCs respond immediately to serve as repairers of the epithelium and as adapters to become HC progenitors, aiming at morphological and functional recovery of the inner ear. This regenerative process is extensive in non-mammals, but is limited in the mammalian inner ear, especially in the mature cochlea. This review aimed to discuss the important roles of SCs in the repair of the mammalian inner ear.

Microbubble-assisted ultrasound for inner ear drug delivery

Treating pathologies of the inner ear is a major challenge. To date, a wide range of procedures exists for administering therapeutic agents to the inner ear, with varying degrees of success. The key is to deliver therapeutics in a way that is minimally invasive, effective, long-lasting, and without adverse effects on vestibular and cochlear function. Microbubble-assisted ultrasound ("sonoporation") is a promising new modality that can be adapted to the inner ear. Combining ultrasound technology with microbubbles in the middle ear can increase the permeability of the round window, enabling therapeutic agents to be delivered safely and effectively to the inner ear in a targeted manner. As such, sonoporation is a promising new approach to treat hearing loss and vertigo. This review summarizes all studies on the delivery of therapeutic molecules to the inner ear using sonoporation.

Adenovirus-mediated effects of Wnt and Notch signalling pathways on hair cell regeneration in mice

Some genes are delivered to cochleae by adenoviruses to restore partial hearing function. This provides promising prospects for gene therapies for hearing loss from hair cell damage. To study the adenovirus (AD)-mediated effect of the Wnt and Notch signalling pathways on hair cell regeneration in the mouse cochlea, we constructed a β-catenin-adenovirus (β-catenin-AD) to increase the activity of the Wnt signalling pathway and a NICD (intracellular domain of Notch1)-RNAi-adenovirus to decrease the activity of the Notch signalling pathway (NICD-RNAi-AD). Our study indicated that approximately 40% of supporting cells in the cochleae damaged by gentamicin were infected with the adenoviruses. Following the β-catenin-AD-mediated increase in Wnt signalling pathway activity, mitotic regeneration was increased, while direct transdifferentiation was increased after the NICD-RNAi-AD-mediated decrease in Notch signalling pathway activity. The expected synergistic interaction on hair cell regeneration was not obtained after coinfection of β-catenin-AD and NICD-RNAi-AD into the damaged cochleae, which might be due to the low cotransfection efficiency to supporting cells. Our study indicated that it may be possible to develop AD mediated gene therapies for hearing loss that act by regulating the Wnt and Notch signalling pathways.

Surgical Approach for Rapid and Minimally Traumatic Recovery of Human Inner Ear Tissues From Deceased Organ Donors

OBJECTIVE

To develop a surgical approach for rapid and minimally traumatic recovery of inner ear tissue from human organ and tissue donors to provide fresh tissue for use in inner ear research.

STUDY DESIGN

Exploration of novel surgical methodology and evaluation of the steps necessary for obtaining specimens from donors during the procurement of organs for transplantation.

SETTING

Donor procurement locations across multiple local hospitals and tissue processing at the microsurgical temporal bone laboratory.

PATIENTS TISSUE SOURCE

Human organ and tissue donors.

INTERVENTIONS

Dissection and procurement of the inner ear tissue.

MAIN OUTCOME MEASURES

Development of rapid and minimally traumatic inner ear tissue recovery. Primarily, establishing an efficient process which includes collaboration with transplant network, implementing a consent protocol, developing and training an on-call recovery team, and designing a portable surgical kit suitable for use in a variety of settings.

RESULTS

The extraction procedure is described in three consecutive steps: the trans-canal exposure, the approach to the vestibule with extraction of the vestibular organs; and the approach to extract inner ear tissues from the cochlear duct.

CONCLUSIONS

Organ and tissue donors are a promising and underutilized resource of inner ear organs for purposes of research and future translational studies. Using our modified technique through the trans-canal/trans-otic approach, we were able to extract tissues of the vestibular and auditory end organs in a timely manner.

Selection Criteria Optimal for Recovery of Inner Ear Tissues From Deceased Organ Donors

OBJECTIVE

To identify optimal conditions for recovering viable inner ear tissues from deceased organ donors.

SETTING

Tertiary recovery hospitals and Donor Network West Organ Recovery Center.

INTERVENTIONS

Recovering bilateral inner ear tissues and immunohistological analysis.

MAIN OUTCOME MEASURES

Immunohistochemical analysis of utricles from human organ donors after brain death (DBD) or donors after cardiac death (DCD).

RESULTS

Vestibular tissues from 21 organ donors (39 ears) were recovered. Of these, 18 donors (33 utricles) were examined by immunofluorescence. The sensory epithelium was present in seven utricles (two from DBD and five from DCD). Relative to DBD utricles, DCD organs more commonly displayed dense populations of hair cells and supporting cells. Relative to DBD, DCD had significantly shorter postmortem interval time to tissue recovery (<48 h). Compared to donors with no sensory epithelium, donors with intact and viable sensory epithelium (both DCD and DBD) had significantly shorter lag time to resuscitation prior to hospital admission (6.4 ± 9.2 vs 35.6 ± 23.7 min, respectively) as well as a shorter time between pronouncements of death to organ recovery (22.6 ± 30.4 vs 64.8 ± 22.8 h, respectively).

CONCLUSIONS

Organ donors are a novel resource for bilateral inner ear organs. Selecting tissue donors within defined parameters can optimize the quality of recovered inner ear tissues, thereby facilitating future research investigating sensory and nonsensory cells.

Age-Related Hearing Loss: Sensory and Neural Etiology and Their Interdependence

Age-related hearing loss (ARHL) is a common, increasing problem for older adults, affecting about 1 billion people by 2050. We aim to correlate the different reductions of hearing from cochlear hair cells (HCs), spiral ganglion neurons (SGNs), cochlear nuclei (CN), and superior olivary complex (SOC) with the analysis of various reasons for each one on the sensory deficit profiles. Outer HCs show a progressive loss in a basal-to-apical gradient, and inner HCs show a loss in a apex-to-base progression that results in ARHL at high frequencies after 70 years of age. In early neonates, SGNs innervation of cochlear HCs is maintained. Loss of SGNs results in a considerable decrease (~50% or more) of cochlear nuclei in neonates, though the loss is milder in older mice and humans. The dorsal cochlear nuclei (fusiform neurons) project directly to the inferior colliculi while most anterior cochlear nuclei reach the SOC. Reducing the number of neurons in the medial nucleus of the trapezoid body (MNTB) affects the interactions with the lateral superior olive to fine-tune ipsi- and contralateral projections that may remain normal in mice, possibly humans. The inferior colliculi receive direct cochlear fibers and second-order fibers from the superior olivary complex. Loss of the second-order fibers leads to hearing loss in mice and humans. Although ARHL may arise from many complex causes, HC degeneration remains the more significant problem of hearing restoration that would replace the cochlear implant. The review presents recent findings of older humans and mice with hearing loss.

The correlation between neonatal parameters and late-onset inner ear disorders in congenital cytomegalovirus infection: a 10-year population-based cohort study

OBJECTIVE

To evaluate the correlation of neonatal parameters with late-onset sensorineural hearing loss (SNHL) and vestibular dysfunction in individuals with congenital cytomegalovirus (cCMV) infection using the National Health Insurance Research Database (NHIRD) in Taiwan.

DESIGN

Retrospective cohort study.

SETTING

The whole Taiwanese population.

PARTICIPANTS

Patients with related diagnostic codes and examinations in their records were regarded as having cCMV infection. Each subject in that group was matched to 10 control individuals with noncongenital CMV infection on the basis of several neonatal parameters, including low gestational age, low birth weight, low Apgar score, maternal history of CMV infection and prolonged cCMV infection. A total of 5893 and 58 930 participants were enrolled in the study and control groups, respectively.

MAIN OUTCOME MEASURES

The main outcomes were the development of SNHL and the development of vestibular dysfunction within one year after birth as reflected by diagnostic codes and specific examinations. Cox proportional hazard regression was used to calculate the adjusted hazard ratio (HR) and 95% confidence interval (CI) of each primary outcome between the two groups.

RESULTS

Overall, 109 and 397 episodes of SNHL developed in the study group and the control group, respectively, and the study group demonstrated a significantly higher incidence of SNHL (adjusted HR: 2.56; 95% CI: 2.07-3.18). In addition, similar incidence rates of vestibular dysfunction were found in the study group and the control group, with 7 and 90 events, respectively (adjusted HR: 0.77; 95% CI: 0.36-1.67). In subgroup analyses, a higher incidence of SNHL was correlated with lower gestational age (GA) (adjusted HR: 2.09; 95% CI: 1.29-3.39), lower birth weight (BW) (adjusted HR: 2.05; 95% CI: 1.28-3.30) and prolonged cCMV infection (adjusted HR: 3.92; 95% CI: 1.95-7.88).

CONCLUSIONS

Low GA, low BW and a long disease course are significantly correlated with late-onset SNHL in cCMV infection.

Ultrasound Microbubbles Enhance the Efficacy of Insulin-Like Growth Factor-1 Therapy for the Treatment of Noise-Induced Hearing Loss

The application of insulin-like growth factor 1 (IGF-1) to the round window membrane (RWM) is an emerging treatment for inner ear diseases. RWM permeability is the key factor for efficient IGF-1 delivery. Ultrasound microbubbles (USMBs) can increase drug permeation through the RWM. In the present study, the enhancing effect of USMBs on the efficacy of IGF-1 application and the treatment effect of USMB-mediated IGF-1 delivery for noise-induced hearing loss (NIHL) were investigated. Forty-seven guinea pigs were assigned to three groups: the USM group, which received local application of recombinant human IGF-1 (rhIGF-1, 10 µg/µL) following application of USMBs to the RWM; the RWS group, which received IGF-1 application alone; and the saline-treated group. The perilymphatic concentration of rhIGF-1 in the USM group was 1.95- and 1.67- fold of that in the RWS group, 2 and 24 h after treatment, respectively. After 5 h of 118 dB SPL noise exposure, the USM group had the lowest threshold shift in auditory brainstem response, least loss of cochlear outer hair cells, and least reduction in the number of synaptic ribbons on postexposure day 28 among the three groups. The combination of USMB and IGF-1 led to a better therapeutic response to NIHL. Two hours after treatment, the USM group had significantly higher levels of Akt1 and Mapk3 gene expression than the other two groups. The most intense immunostaining for phosphor-AKT and phospho-ERK1/2 was detected in the cochlea in the USM group. These results suggested that USMB can be applied to enhance the efficacy of IGF-1 therapy in the treatment of inner ear diseases.

Cochlea cell-specific marker expression upon in vitro Hes1 knockdown

NOTCH pathway proteins, including the transcriptional factor HES1, play crucial roles in the development of the inner ear by means of the lateral inhibition mechanism, in which supporting cells have their phenotype preserved while they are prevented from becoming hair cells. Genetic manipulation of this pathway has been demonstrated to increase hair cell number. The present study aimed to investigate gene expression effects in hair cells and supporting cells after Hes1-shRNA lentivirus transduction in organotypic cultures of the organ of Corti from postnatal-day-3 mice. Forty-eight hours after in vitro knockdown, Hes1 gene expression was reduced at both mRNA and protein levels. Myo7a (hair cell marker) and Sox2 (progenitor cell marker) mRNA levels also significantly increased. The modulation of gene expression in the organ of Corti upon Hes1 knockdown is consistent with cell phenotypes related to lateral inhibition mechanism interference in the inner ear. The lentivirus-based expression of Hes1-shRNA is a valuable strategy for genetic interference in the organ of Corti and for future evaluation of its efficacy in protocols aiming at the regeneration of hair cells in vivo.

Combinatorial Atoh1 and Gfi1 induction enhances hair cell regeneration in the adult cochlea

Mature mammalian cochlear hair cells (HCs) do not spontaneously regenerate once lost, leading to life-long hearing deficits. Attempts to induce HC regeneration in adult mammals have used over-expression of the HC-specific transcription factor Atoh1, but to date this approach has yielded low and variable efficiency of HC production. Gfi1 is a transcription factor important for HC development and survival. We evaluated the combinatorial effects of Atoh1 and Gfi1 over-expression on HC regeneration using gene transfer methods in neonatal cochlear explants, and in vivo in adult mice. Adenoviral over-expression of Atoh1 and Gfi1 in cultured neonatal cochlear explants resulted in numerous ectopic HC-like cells (HCLCs), with significantly more cells in Atoh1 + Gfi1 cultures than Atoh1 alone. In vitro, ectopic HCLCs emerged in regions medial to inner HCs as well as in the stria vascularis. In vivo experiments were performed in mature Pou4f3DTR mice in which HCs were completely and specifically ablated by administration of diphtheria toxin. Adenoviral expression of Atoh1 or Atoh1 + Gfi1 in cochlear supporting cells induced appearance of HCLCs, with Atoh1 + Gfi1 expression leading to 6.2-fold increase of new HCLCs after 4 weeks compared to Atoh1 alone. New HCLCs were detected throughout the cochlea, exhibited immature stereocilia and survived for at least 8 weeks. Combinatorial Atoh1 and Gfi1 induction is thus a promising strategy to promote HC regeneration in the mature mammalian cochlea.

Knockdown of Foxg1 in Sox9+ supporting cells increases the trans-differentiation of supporting cells into hair cells in the neonatal mouse utricle

Foxg1 plays important roles in regeneration of hair cell (HC) in the cochlea of neonatal mouse. Here, we used Sox9-CreER to knock down Foxg1 in supporting cells (SCs) in the utricle in order to investigate the role of Foxg1 in HC regeneration in the utricle. We found Sox9 an ideal marker of utricle SCs and bred Sox9^CreER/+Foxg1^loxp/loxp mice to conditionally knock down Foxg1 in utricular SCs. Conditional knockdown (cKD) of Foxg1 in SCs at postnatal day one (P01) led to increased number of HCs at P08. These regenerated HCs had normal characteristics, and could survive to at least P30. Lineage tracing showed that a significant portion of newly regenerated HCs originated from SCs in Foxg1 cKD mice compared to the mice subjected to the same treatment, which suggested SCs trans-differentiate into HCs in the Foxg1 cKD mouse utricle. After neomycin treatment in vitro, more HCs were observed in Foxg1 cKD mice utricle compared to the control group. Together, these results suggest that Foxg1 cKD in utricular SCs may promote HC regeneration by inducing trans-differentiation of SCs. This research therefore provides theoretical basis for the effects of Foxg1 in trans-differentiation of SCs and regeneration of HCs in the mouse utricle.

Advances in Inner Ear Therapeutics for Hearing Loss in Children

Purpose of review

Hearing loss is a common congenital sensory disorder with various underlying causes. Here, we review and focus on genetic, infectious, and ototoxic causes and recent advances in inner ear therapeutics.

Recent findings

While hearing aids and cochlear implantation are the mainstay of treatment for pediatric hearing loss, novel biological therapeutics are being explored. Recent preclinical studies report positive results in viral-mediated gene transfer techniques and surgical approaches to the inner ear for genetic hearing loss. Novel pharmacologic agents, on the other hand, show promising results in reducing aminoglycoside and cisplatin ototoxicity. Clinical trials are underway to evaluate the efficacy of antivirals for cytomegalovirus-related hearing loss, and its pathogenesis and other potential therapeutics are currently under investigation.

Summary

Individualized therapies for genetic and infectious causes of sensorineural hearing loss in animal models as well as pediatric patients show promising results, with their potential efficacy being active areas of research.

Using Sox2 to alleviate the hallmarks of age-related hearing loss

Age-related hearing loss (ARHL) is the most prevalent sensory deficit. ARHL reduces the quality of life of the growing population, setting seniors up for the enhanced mental decline. The size of the needy population, the structural deficit, and a likely research strategy for effective treatment of chronic neurosensory hearing in the elderly are needed. Although there has been profound advancement in auditory regenerative research, there remain multiple challenges to restore hearing loss. Thus, additional investigations are required, using novel tools. We propose how the (1) flat epithelium, remaining after the organ of Corti has deteriorated, can be converted to the repaired-sensory epithelium, using Sox2. This will include (2) developing an artificial gene regulatory network transmitted by (3) large viral vectors to the flat epithelium to stimulate remnants of the organ of Corti to restore hair cells. We hope to unite with our proposal toward the common goal, eventually restoring a functional human hearing organ by transforming the flat epithelial cells left after the organ of Corti loss.