Insulin-like growth factor signaling regulates the timing of sensory cell differentiation in the mouse cochlea

Otologic Symptoms Following Teprotumumab Administration in Patients with Thyroid Eye Disease

OBJECTIVE

Comprehensively characterize subjective otologic adverse events following teprotumumab administration with standardized patient reported outcome metrics. Understand the impact on patients' quality of life and perception of the medication.

STUDY DESIGN

Retrospective case series.

SETTING

Tertiary referral center.

PATIENTS

Thirty-two adults with thyroid eye disease treated with teprotumumab from 2020 to 2023.

MAIN OUTCOME MEASURES

Subjective hearing loss, tinnitus, dizziness (Dizziness Handicap Inventory), patulous eustachian tube (Eustachian Tube Dysfunction Questionnaire-7, Patulous Eustachian Tube Handicap Inventory-10), effect of hearing loss on quality of life, and decisional regret.

RESULTS

Half reported hearing loss (n = 16, 50%) while receiving teprotumumab. Onset was gradual in 75% of patients with onset at the sixth [IQR 5-7] infusion. It was nonfluctuating (93.8%), bilateral (100%), and did not return to baseline (93.8%). Of those reporting hearing loss, 37.5% reported dizziness and 87.5% reported tinnitus; 87.5% felt it affected quality of life, and 33.3% would opt to not receive the medication again. The median DHI score was 9 [0-35] in those with hearing loss compared to 0 [0-5] in those without hearing loss (p = 0.02, Wilcoxon rank sum). Based on the ETDQ-7, 37.5% of patients experienced eustachian tube dysfunction; 15.6% experienced symptoms of a patulous eustachian tube with a median PHI-10 score of 15 [3-24], indicating a mild handicap.

CONCLUSIONS

Many patients experience subjective hearing loss following teprotumumab administration, typically gradual in onset, nonfluctuating, bilateral, persistent, and significantly affecting quality of life. Patients may also experience comorbid vertigo and symptoms of eustachian tube dysfunction or patulous eustachian tube with variable severity.

Patterns of Teprotumumab-Induced Hearing Dysfunction: A Systematic Review

OBJECTIVE

Hearing loss has been reported after administration of the monoclonal antibody teprotumumab. The purpose of this study was to review available evidence regarding the patterns of teprotumumab-related ototoxicity.

DATA SOURCES

PubMed, EMBASE, and Cochrane Library.

REVIEW METHODS

A systematic review was performed using standardized methodology. Studies were included if they included subjects who were prescribed teprotumumab. Exclusion criteria included non-English articles, abstracts, letters/commentaries, case reports, and reviews. Subjects without both pre- and posttreatment audiometric data were also excluded. Bias was assessed using the Mixed Methods Appraisal Tool.

RESULTS

From an initial search of 76 articles, 7 studies reporting on 109 unique patients were included. Four studies were level 4 evidence, 1 study was level 3 evidence, and 2 studies were level 2 evidence. Mean age was 55 ± 14 years with a female predominance (64%). The most commonly reported symptoms were hearing loss (22%), followed by fullness (18%) and tinnitus (14%). In total, 41% of patients with available data met criteria for ototoxicity, all exhibiting shifts in the middle frequencies or higher. Fifteen (14%) patients underwent ultrahigh frequency audiometric testing and 8 (53%, 8/15) demonstrated shifts exclusively in this range.

CONCLUSION

Ototoxicity may occur in patients treated with teprotumumab. Hearing loss occurs primarily in higher frequencies, and routine hearing screening with ultrahigh frequency testing may be warranted. The true incidence of ototoxicity with teprotumumab remains unknown, and more data is needed to elucidate underlying mechanisms and develop strategies to minimize risks.

Tissue engineering strategies for spiral ganglion neuron protection and regeneration

Cochlear implants can directly activate the auditory system's primary sensory neurons, the spiral ganglion neurons (SGNs), via circumvention of defective cochlear hair cells. This bypass restores auditory input to the brainstem. SGN loss etiologies are complex, with limited mammalian regeneration. Protecting and revitalizing SGN is critical. Tissue engineering offers a novel therapeutic strategy, utilizing seed cells, biomolecules, and scaffold materials to create a cellular environment and regulate molecular cues. This review encapsulates the spectrum of both human and animal research, collating the factors contributing to SGN loss, the latest advancements in the utilization of exogenous stem cells for auditory nerve repair and preservation, the taxonomy and mechanism of action of standard biomolecules, and the architectural components of scaffold materials tailored for the inner ear. Furthermore, we delineate the potential and benefits of the biohybrid neural interface, an incipient technology in the realm of implantable devices. Nonetheless, tissue engineering requires refined cell selection and differentiation protocols for consistent SGN quality. In addition, strategies to improve stem cell survival, scaffold biocompatibility, and molecular cue timing are essential for biohybrid neural interface integration.

Stem Cell-Based Therapies for Auditory Hair Cell Regeneration in the Treatment of Hearing Loss

The incidence and prevalence of hearing loss is increasing globally at an accelerated pace. Hair cells represent the sensory receptors of auditory and vestibular systems. Hair cell absence, loss or degeneration due to congenital diseases, trauma, toxicity, infection or advancing age, results in disabling hearing loss. Regenerative medicine approaches consisting in stem cell-based hair cell rescue or regeneration, gene therapy, as well as cell and tissue engineering are expected to dramatically improve the therapeutic arsenal available for addressing hearing loss. Current strategies that are using different stem cell types to rescue or to induce hair cell proliferation and regeneration are presented. Gene and cell therapy methods that modulates transdifferentiation of surrounding cell types into hair cells are presented, together with their specific advantages and limitations. Several modalities for improving therapeutic targeting to the inner ear such as nanoparticle-mediated cell and gene delivery are introduced. Further steps in building more relevant high-throughput models for testing novel drugs and advanced therapies are proposed as a modality to accelerate translation to clinical settings.

Frequency and Patterns of Hearing Dysfunction in Patients Treated with Teprotumumab

PURPOSE

To better characterize the frequency and patterns of hearing dysfunction in patients who have received teprotumumab to treat thyroid eye disease.

DESIGN

Noncomparative case series.

PARTICIPANTS

Patients who underwent audiology testing before and after completion of teprotumumab infusions.

METHODS

A review of patients who underwent audiology testing before and after completion of teprotumumab infusions was carried out. Additional audiogram testing during treatment was included when available. Hearing function was analyzed using audiogram data measuring threshold hearing levels at specific frequencies. Basic demographic data as well as information regarding otologic symptoms also were obtained and analyzed.

MAIN OUTCOME MEASURES

Hearing loss demonstrated by a significant change in decibel hearing thresholds or that meets criteria for ototoxicity.

RESULTS

Twenty-two patients (44 ears) were included in the study, with baseline and most recent audiology testing after treatment ranging from 84 days before to 496 days after treatment. Fifteen patients (30 ears) also underwent testing during treatment starting after the second infusion up until the day of, but before, the eighth infusion. Hearing loss after treatment met criteria for ototoxicity in 17 of the 44 ears (38.6%), with 11 of the 22 patients (50.0%) meeting criteria in at least 1 ear. The pure-tone average decibel hearing levels (HLs) across all 44 ears demonstrated hearing loss after treatment (P = 0.0029), specifically at high (P = 0.0008) and middle frequencies (P = 0.0042), but not at low frequencies (P = 0.8344). Patients who were older also were more likely to experience hearing loss after treatment (P = 0.0048).

CONCLUSIONS

Audiometric data demonstrate that teprotumumab influences hearing function, most significantly at higher frequencies and in older patients. Audiometric testing is critical for counseling patients regarding teprotumumab treatment. A protocol for monitoring hearing during treatment is needed to detect and manage hearing changes associated with teprotumumab use.

FINANCIAL DISCLOSURE(S)

Proprietary or commercial disclosure may be found in the Footnotes and Disclosures at the end of this article.

Insulin signaling in development

Nutrient intake is obligatory for animal growth and development, but nutrients alone are not sufficient. Indeed, insulin and homologous hormones are required for normal growth even in the presence of nutrients. These hormones communicate nutrient status between organs, allowing animals to coordinate growth and metabolism with nutrient supply. Insulin and related hormones, such as insulin-like growth factors and insulin-like peptides, play important roles in development and metabolism, with defects in insulin production and signaling leading to hyperglycemia and diabetes. Here, we describe the insulin hormone family and the signal transduction pathways activated by these hormones. We highlight the roles of insulin signaling in coordinating maternal and fetal metabolism and growth during pregnancy, and we describe how secretion of insulin is regulated at different life stages. Additionally, we discuss the roles of insulin signaling in cell growth, stem cell proliferation and cell differentiation. We provide examples of the role of insulin in development across multiple model organisms: Caenorhabditis elegans, Drosophila, zebrafish, mouse and human.

The neurobiology of insulin-like growth factor I: From neuroprotection to modulation of brain states

After decades of research in the neurobiology of IGF-I, its role as a prototypical neurotrophic factor is undisputed. However, many of its actions in the adult brain indicate that this growth factor is not only involved in brain development or in the response to injury. Following a three-layer assessment of its role in the central nervous system, we consider that at the cellular level, IGF-I is indeed a bona fide neurotrophic factor, modulating along ontogeny the generation and function of all the major types of brain cells, contributing to sculpt brain architecture and adaptive responses to damage. At the circuit level, IGF-I modulates neuronal excitability and synaptic plasticity at multiple sites, whereas at the system level, IGF-I intervenes in energy allocation, proteostasis, circadian cycles, mood, and cognition. Local and peripheral sources of brain IGF-I input contribute to a spatially restricted, compartmentalized, and timed modulation of brain activity. To better define these variety of actions, we consider IGF-I a modulator of brain states. This definition aims to reconcile all aspects of IGF-I neurobiology, and may provide a new conceptual framework in the design of future research on the actions of this multitasking neuromodulator in the brain.

Reduction of Teprotumumab-Induced Hearing Loss With Comparable Efficacy Using Half-Dose Therapy

Teprotumumab has been shown to be effective in the treatment of thyroid eye disease, a potentially vision-threatening condition. Adverse events, including sensorineural hearing loss, have been associated with teprotumumab. The authors present the case of a 64-year-old female who discontinued teprotumumab due to significant sensorineural hearing loss after 4 infusions, along with other adverse events. The patient was unresponsive to a subsequent course of intravenous methylprednisolone and orbital radiation, during which she experienced worsening thyroid eye disease symptoms. Teprotumumab was restarted 1 year later, at a half dose of 10 mg/kg for 8 infusions. Three months post-treatment, she retains resolution of double vision and orbital inflammatory signs, and significant improvement in proptosis. She tolerated all infusions with an overall reduction in the severity of her adverse events and without return of significant sensorineural hearing loss. The authors conclude that a lower dose of teprotumumab can be effective for patients with active moderate-severe thyroid eye disease who experience significant or intolerable adverse events.

Potential Ototoxicity of Insulin-like Growth Factor 1 Receptor Signaling Inhibitors: An In Silico Drug Repurposing Study of the Regenerating Cochlear Neuron Transcriptome

Spiral ganglion neurons (SGNs) connect cochlear hair cells with higher auditory pathways and their degeneration due to drug toxicity (ototoxicity) contributes to hearing loss. This study aimed to identify drug classes that are negatively correlated with the transcriptome of regenerating SGNs. Human orthologs of differentially expressed genes within the regenerating neonatal mouse SGN transcriptome were entered into CMap and the LINCS unified environment and perturbation-driven gene expression was analyzed. The CMap connectivity scores ranged from 100 (positive correlation) to -100 (negative correlation). Insulin-like growth factor 1/receptor (IGF-1/R) inhibitors were highly negatively correlated with the regenerating SGN transcriptome (connectivity score: -98.87). A systematic literature review of clinical trials and observational studies reporting otologic adverse events (AEs) with IGF-1/R inhibitors identified 108 reports (6141 treated patients). Overall, 16.9% of the treated patients experienced any otologic AE; the rate was highest for teprotumumab (42.9%). In a meta-analysis of two randomized placebo-controlled trials of teprotumumab, there was a significantly higher risk of hearing-related (pooled Peto OR [95% CI]: 7.95 [1.57, 40.17]) and of any otologic AEs (3.56 [1.35, 9.43]) with teprotumumab vs. a placebo, whether or not dizziness/vertigo AEs were included. These results call for close audiological monitoring during IGF-1-targeted treatment, with prompt referral to an otolaryngologist should otologic AEs develop.

Point Mutation in Prkra Alters miRNA Expression During Embryonic External Ear Development

Microtia is a congenital malformation of the external ear that can lead to conductive hearing impairment. In this study, we investigated the role of the Prkra gene in external ear development. We used advanced sequencing techniques to evaluate the differential expression of microRNAs (miRNAs) involved in external ear development in mouse embryos after point mutation in the Prkra gene. The Prkra Little ear mouse model was used to obtain mouse embryos at the E15.5 and E17.5 developmental stages, and changes in miRNA expression profiles were detected. Gene ontology and Kyoto Encyclopedia of Genes and Genomes functional annotations were performed on differentially expressed miRNAs, and existing and new miRNAs were studied. miRNAs were observed to be involved in multiple signaling pathways during the E15.5 and E17.5 developmental stages. The results show a correlation between miRNA regulation and external ear development in Prkra Little ear mice, and differences were detected in key regulatory miRNAs owing to point mutations in the Prkra gene. This study provides new insights into the biological mechanisms through which miRNAs regulate external ear development in mouse embryos. Changes in the mouse miRNA expression profiles can also provide insights into the pathogenesis of human congenital microtia at the level of miRNA regulation.

Mechanism of autophagy mediated by IGF-1 signaling pathway in the neurotoxicity of lead in pubertal rats

Lead can damage neuron synapses in the hippocampus and cause synaptic plasticity losses, and learning, memory, and intelligence impairments. Previous studies have focused on the functional and structural plasticity of hippocampal synapses; however, the specific molecular mechanisms behind such impairments are not fully understood. This study aimed to elucidate the molecular mechanisms of cognitive impairment in rats following chronic lead exposure and mitigate or prevent lead toxicity in the central nervous system. We found that lead exposure caused significant damage to rat nervous systems, that is, compared with the control group, the lead treatment group had more autophagosomes in their hippocampal neurons; lower serum and hippocampal IGF-1 levels; lower hippocampal IGF-1, IGF-1R, PI3K, Akt, and mTOR gene expression; and upregulated hippocampal autophagy-associated proteins levels. Brain stereotactic technology was used to conduct autophagy inhibitor in vivo intervention experiments, and the results of these experiments suggest that the autophagy inhibitor DC661 inhibited lead-exposure-induced autophagy and autophagy-related gene expression in the rat hippocampus, possibly through activation of the IGF-1 pathway. Overall, our findings suggest that lead might activate hippocampal autophagy through the IGF-1/PI3K/Akt/mTOR signaling pathway. Therefore, this study provides a novel molecular mechanism underlying developmental toxicity in pubertal rats induced by lead exposure and provides a new target for anticipation and reversal of such neurotoxicity.

IGF-1 Controls Metabolic Homeostasis and Survival in HEI-OC1 Auditory Cells through AKT and mTOR Signaling

Insulin-like growth factor 1 (IGF-1) is a trophic factor for the nervous system where it exerts pleiotropic effects, including the regulation of metabolic homeostasis. IGF-1 deficiency induces morphological alterations in the cochlea, apoptosis and hearing loss. While multiple studies have addressed the role of IGF-1 in hearing protection, its potential function in the modulation of otic metabolism remains unclear. Here, we report that "House Ear Institute-organ of Corti 1" (HEI-OC1) auditory cells express IGF-system genes that are regulated during their differentiation. Upon binding to its high-affinity receptor IGF1R, IGF-1 activates AKT and mTOR signaling to stimulate anabolism and, concomitantly, to reduce autophagic catabolism in HEI-OC1 progenitor cells. Notably, IGF-1 stimulation during HEI-OC1 differentiation to mature otic cells sustained both constructive metabolism and autophagic flux, possibly to favor cell remodeling. IGF1R engagement and downstream AKT signaling promoted HEI-OC1 cell survival by maintaining redox balance, even when cells were challenged with the ototoxic agent cisplatin. Our findings establish that IGF-1 not only serves an important function in otic metabolic homeostasis but also activates antioxidant defense mechanisms to promote hair cell survival during the stress response to insults.

Neuroprotective role of insulin-like growth factor 1 in auditory and other nervous systems

Insulin-like growth factor 1 (IGF1) exerts an influence on almost every organ system in the body and plays an important role in growth, development, and metabolism. In the nervous system, IGF1 acts by promoting the development and growth of neurons and glial cells, differentiation of Schwann cells and their migration to axons, neurite outgrowth, and neuronal survival. The lack of IGF1 is associated with several pathological conditions, including severe prenatal growth retardation, postnatal growth failure, microcephaly, mental retardation, and bilateral sensorineural hearing loss. In addition to its physiological effects, based on the findings of in vivo and in vitro experiments and clinical trials, IGF1 is considered to play a potential role in the treatment of various types of neuronal damage. In this review, we discuss the potential use of IGF1 as a therapeutic molecule in the nervous system: (1) auditory system, including hair cells, cochlear ribbon synapses, auditory nerve, and central nervous systems, and (2) other peripheral nervous systems, especially the olfactory system and facial nerve. The role of IGF1 in the progression of age-related sensory deficits, especially hearing loss and olfactory dysfunction, is also discussed. Recent studies on IGF1 demonstrated that exogenous IGF1 can be applied in many fields, thus supporting the continued evaluation of IGF1 as a potential therapeutic molecule. Additional scientific investigations should be conducted to further supplement recent findings.

Cochlear Development; New Tools and Approaches

The sensory epithelium of the mammalian cochlea, the organ of Corti, is comprised of at least seven unique cell types including two functionally distinct types of mechanosensory hair cells. All of the cell types within the organ of Corti are believed to develop from a population of precursor cells referred to as prosensory cells. Results from previous studies have begun to identify the developmental processes, lineage restrictions and signaling networks that mediate the specification of many of these cell types, however, the small size of the organ and the limited number of each cell type has hampered progress. Recent technical advances, in particular relating to the ability to capture and characterize gene expression at the single cell level, have opened new avenues for understanding cellular specification in the organ of Corti. This review will cover our current understanding of cellular specification in the cochlea, discuss the most commonly used methods for single cell RNA sequencing and describe how results from a recent study using single cell sequencing provided new insights regarding cellular specification.

Hearing Dysfunction After Treatment With Teprotumumab for Thyroid Eye Disease

PURPOSE

To characterize the frequency, severity, and resolution of hearing dysfunction in patients treated with teprotumumab for thyroid eye disease (TED).

DESIGN

Prospective observational case series.

METHODS

Ophthalmic examination and adverse event assessment, including otologic symptoms, were performed at baseline, after infusions 2, 4, and 8, and at 6-month follow-up in consecutive patients who received at least 4 teprotumumab infusions. Laboratory test results were collected at baseline and during treatment. Audiometry, patulous eustachian tube (PET) testing, and otolaryngology evaluation were obtained for patients with new or worsening otologic symptoms, with a subset obtaining baseline and posttreatment testing.

RESULTS

Twenty-seven patients were analyzed (24 females, 3 males, average 56.3 years old). Twenty-two patients (81.5%) developed new subjective otologic symptoms, after a mean of 3.8 infusions (SD 1.8). At 39.2-week average follow-up after the last infusion, most patients with tinnitus (100%), ear plugging/fullness (90.9%), and autophony (83.3%) experienced symptom resolution, whereas only 45.5% (5 of 11) of patients with subjective hearing loss/decreased word comprehension experienced resolution. Six patients underwent baseline and posttreatment audiometry, 5 of whom developed teprotumumab-related sensorineural hearing loss (SNHL) and 1 patient also developed PET. Three of the 5 patients with teprotumumab-related SNHL had persistent subjective hearing loss at last follow-up. A prior history of hearing loss was discovered as a risk factor for teprotumumab-related SNHL (P = .008).

CONCLUSIONS

Hearing loss is a concerning adverse event of teprotumumab, and its mechanism and reversibility should be further studied. Until risk factors for hearing loss are better understood, we recommend baseline audiometry with PET testing and repeat testing if new otologic symptoms develop. Screening, monitoring, and prevention guidelines are needed.

Teprotumumab and Hearing Loss: Case Series and Proposal for Audiologic Monitoring

PURPOSE

To present a protocol for audiologic monitoring in the setting of teprotumumab treatment of thyroid eye disease, motivated by 4 cases of significant hearing loss, and review the relevant literature.

METHODS

Cases of hearing loss in the setting of teprotumumab were retrospectively elicited as part of a multi-institutional focus group, including oculoplastic surgeons, a neurotologist and an endocrinologist. A literature review was performed.

RESULTS

An aggregate of 4 cases of teprotumumab-associated hearing loss documented by formal audiologic testing were identified among 3 clinicians who had treated 28 patients.

CONCLUSIONS

Teprotumumab may cause a spectrum of potentially irreversible hearing loss ranging from mild to severe, likely resulting from the inhibition of the insulin-like growth factor-1 and the insulin-like growth factor-1 receptor pathway. Due to the novelty of teprotumumab and the lack of a comprehensive understanding of its effect on hearing, the authors endorse prospective investigations of hearing loss in the setting of teprotumumab treatment. Until the results of such studies are available, the authors think it prudent to adopt a surveillance protocol to include an audiogram and tympanometry before, during and after infusion, and when prompted by new symptoms of hearing dysfunction.

Insulin-like Growth Factor 1 Signaling in Mammalian Hearing

Insulin-like growth factor 1 (IGF-1) is a peptide hormone belonging to the insulin family of proteins. Almost all of the biological effects of IGF-1 are mediated through binding to its high-affinity tyrosine kinase receptor (IGF1R), a transmembrane receptor belonging to the insulin receptor family. Factors, receptors and IGF-binding proteins form the IGF system, which has multiple roles in mammalian development, adult tissue homeostasis, and aging. Consequently, mutations in genes of the IGF system, including downstream intracellular targets, underlie multiple common pathologies and are associated with multiple rare human diseases. Here we review the contribution of the IGF system to our understanding of the molecular and genetic basis of human hearing loss by describing, (i) the expression patterns of the IGF system in the mammalian inner ear; (ii) downstream signaling of IGF-1 in the hearing organ; (iii) mouse mutations in the IGF system, including upstream regulators and downstream targets of IGF-1 that inform cochlear pathophysiology; and (iv) human mutations in these genes causing hearing loss.

Axon-glia interactions in the ascending auditory system

The auditory system detects and encodes sound information with high precision to provide a high-fidelity representation of the environment and communication. In mammals, detection occurs in the peripheral sensory organ (the cochlea) containing specialized mechanosensory cells (hair cells) that initiate the conversion of sound-generated vibrations into action potentials in the auditory nerve. Neural activity in the auditory nerve encodes information regarding the intensity and frequency of sound stimuli, which is transmitted to the auditory cortex through the ascending neural pathways. Glial cells are critical for precise control of neural conduction and synaptic transmission throughout the pathway, allowing for the precise detection of the timing, frequency, and intensity of sound signals, including the sub-millisecond temporal fidelity is necessary for tasks such as sound localization, and in humans, for processing complex sounds including speech and music. In this review, we focus on glia and glia-like cells that interact with hair cells and neurons in the ascending auditory pathway and contribute to the development, maintenance, and modulation of neural circuits and transmission in the auditory system. We also discuss the molecular mechanisms of these interactions, their impact on hearing and on auditory dysfunction associated with pathologies of each cell type.

Ceramide Kinase Inhibition Blocks IGF-1-Mediated Survival of Otic Neurosensory Progenitors by Impairing AKT Phosphorylation

Sphingolipids are bioactive lipid components of cell membranes with important signal transduction functions in health and disease. Ceramide is the central building block for sphingolipid biosynthesis and is processed to form structurally and functionally distinct sphingolipids. Ceramide can be phosphorylated by ceramide kinase (CERK) to generate ceramide-1-phosphate, a cytoprotective signaling molecule that has been widely studied in multiple tissues and organs, including the developing otocyst. However, little is known about ceramide kinase regulation during inner ear development. Using chicken otocysts, we show that genes for CERK and other enzymes of ceramide metabolism are expressed during the early stages of inner ear development and that CERK is developmentally regulated at the otic vesicle stage. To explore its role in inner ear morphogenesis, we blocked CERK activity in organotypic cultures of otic vesicles with a specific inhibitor. Inhibition of CERK activity impaired proliferation and promoted apoptosis of epithelial otic progenitors. CERK inhibition also compromised neurogenesis of the acoustic-vestibular ganglion. Insulin-like growth factor-1 (IGF-1) is a key factor for proliferation, survival and differentiation in the chicken otocyst. CERK inhibition decreased IGF-1-induced AKT phosphorylation and blocked IGF-1-induced cell survival. Overall, our data suggest that CERK is activated as a central element in the network of anti-apoptotic pro-survival pathways elicited by IGF-1 during early inner ear development.

Thyroid Eye Disease, Teprotumumab, and Hearing Loss: An Evolving Role for Otolaryngologists

Teprotumumab is a human monoclonal antibody and IGF-1R (insulin-like growth factor 1 receptor) inhibitor approved for treatment of thyroid eye disease in adults. Recent clinical trials have demonstrated side effects, notably hearing loss, in the treatment cohort as compared with the placebo cohort. These unexpected otologic side effects may be understood through a mechanistic understanding of IGF-1 (insulin-like growth factor 1). As otolaryngologists who historically play a significant role in the multidisciplinary treatment of thyroid disease and its associated complications, we should be aware of and monitor the otologic side effects of teprotumumab. Clinicians who prescribe teprotumumab should strongly consider monitoring patients' hearing with an audiologist and otolaryngologist.

Wnts regulate planar cell polarity via heterotrimeric G protein and PI3K signaling

In the mammalian cochlea, the planar cell polarity (PCP) pathway aligns hair cell orientation along the plane of the sensory epithelium. Concurrently, multiple cell intrinsic planar polarity (referred to as iPCP) modules mediate planar polarization of the hair cell apical cytoskeleton, including the kinocilium and the V-shaped hair bundle essential for mechanotransduction. How PCP and iPCP are coordinated during development and the roles of Wnt ligands in this process remain unresolved. Here we show that genetic blockade of Wnt secretion in the cochlear epithelium resulted in a shortened cochlear duct and misoriented and misshapen hair bundles. Mechanistically, Wnts stimulate Gi activity by regulating the localization of Daple, a guanine nucleotide exchange factor (GEF) for Gαi. In turn, the Gβγ complex signals through phosphoinositide 3-kinase (PI3K) to regulate kinocilium positioning and asymmetric localizations of a subset of core PCP proteins, thereby coordinating PCP and iPCP. Thus, our results identify a putative Wnt/heterotrimeric G protein/PI3K pathway for PCP regulation.

FGF20-FGFR1 signaling through MAPK and PI3K controls sensory progenitor differentiation in the organ of Corti

BACKGROUND

Fibroblast Growth Factor 20 (FGF20)-FGF receptor 1 (FGFR1) signaling is essential for cochlear hair cell (HC) and supporting cell (SC) differentiation. In other organ systems, FGFR1 signals through several intracellular pathways including MAPK (ERK), PI3K, phospholipase C ɣ (PLCɣ), and p38. Previous studies implicated MAPK and PI3K pathways in HC and SC development. We hypothesized that one or both would be important downstream mediators of FGF20-FGFR1 signaling for HC differentiation.

RESULTS

By inhibiting pathways downstream of FGFR1 in cochlea explant cultures, we established that both MAPK and PI3K pathways are required for HC differentiation while PLCɣ and p38 pathways are not. Examining the canonical PI3K pathway, we found that while AKT is necessary for HC differentiation, it is not sufficient to rescue the Fgf20-/- phenotype. To determine whether PI3K functions downstream of FGF20, we inhibited Phosphatase and Tensin Homolog (PTEN) in Fgf20-/- explants. Overactivation of PI3K resulted in a partial rescue of the Fgf20-/- phenotype, demonstrating a requirement for PI3K downstream of FGF20. Consistent with a requirement for the MAPK pathway for FGF20-regulated HC differentiation, we show that treating Fgf20-/- explants with FGF9 increased levels of dpERK.

CONCLUSIONS

Together, these data provide evidence that both MAPK and PI3K are important downstream mediators of FGF20-FGFR1 signaling during HC and SC differentiation.

Insulin-Like Growth Factor 1 on the Maintenance of Ribbon Synapses in Mouse Cochlear Explant Cultures

Hearing loss has become one of the most common disabilities worldwide. The synaptic connections between inner hair cells (IHCs) and spiral ganglion neurons have specialized synaptic constructions, termed ribbon synapses, which are important for auditory function. The ribbon synapses in the cochlea are quite vulnerable to various insults. As such, the maintenance of ribbon synapses is important for ensuring hearing function. Insulin-like growth factor 1 (IGF1) plays a critical role in the development and maintenance of the cochlea and has the potential to protect cochlear hair cells from various insults. In this study, we examined the role of IGF1 in the maintenance of ribbon synapses in cochlear explants of postnatal day four mice. We cultured cochlear explants with an IGF1 receptor antagonist, JB1, which is an IGF1 peptide analog. Results showed that exposure to JB1 for 24 h resulted in the loss of ribbon synapses. After an additional 24-h culture without JB1, the number of ribbon synapses spontaneously recovered. The application of exogenous IGF1 showed two different aspects of ribbon synapses. Low doses of exogenous IGF1 promoted the recovery of ribbon synapses, while it compromised the spontaneous recovery of ribbon synapses at high doses. Altogether, these results indicate that the paracrine or autocrine release of IGF1 in the cochlea plays a crucial role in the maintenance of cochlear ribbon synapses.

Characterization of the development of the mouse cochlear epithelium at the single cell level

Mammalian hearing requires the development of the organ of Corti, a sensory epithelium comprising unique cell types. The limited number of each of these cell types, combined with their close proximity, has prevented characterization of individual cell types and/or their developmental progression. To examine cochlear development more closely, we transcriptionally profile approximately 30,000 isolated mouse cochlear cells collected at four developmental time points. Here we report on the analysis of those cells including the identification of both known and unknown cell types. Trajectory analysis for OHCs indicates four phases of gene expression while fate mapping of progenitor cells suggests that OHCs and their surrounding supporting cells arise from a distinct (lateral) progenitor pool. Tgfβr1 is identified as being expressed in lateral progenitor cells and a Tgfβr1 antagonist inhibits OHC development. These results provide insights regarding cochlear development and demonstrate the potential value and application of this data set.

How the development of the cochlear epithelium is regulated is unclear. Here, the authors use single cell RNAseq analysis to provide insight into the transcriptional changes arising during development of the murine cochlear inner and outer hair cells.

Untargeted metabolomics reveals alterations in metabolites of lipid metabolism and immune pathways in the serum of rats after long-term oral administration of Amalaki rasayana

Amalaki rasayana, a traditional preparation, is widely used by Ayurvedic physicians for the treatment of inflammatory conditions, cardiovascular diseases, and cancer. Metabolic alterations induced by Amalaki rasayana intervention are unknown. We investigated the modulations in serum metabolomic profiles in Wistar rats following long-term oral administration of Amalaki rasayana. Global metabolic profiling was performed of the serum of rats administered with either Amalaki rasayana (AR) or ghee + honey (GH) for 18 months and control animals which were left untreated. Amalaki rasayana components were confirmed from AR extract using HR-LCMS analysis. Significant reductions in prostaglandin J2, 11-dehydrothromboxane B2, and higher levels of reduced glutathione and glycitein metabolites were observed in the serum of AR administered rats compared to the control groups. Eleven different metabolites classified as phospholipids, glycerophospholipids, glucoside derivatives, organic acids, and glycosphingolipid were exclusively observed in the AR administered rats. Pathway analysis suggests that altered metabolites in AR administered rats are those associated with different biochemical pathways of arachidonic acid metabolism, fatty acid metabolism, leukotriene metabolism, G-protein mediated events, phospholipid metabolism, and the immune system. Targeted metabolomics confirmed the presence of gallic acid, ellagic acid, and arachidonic acid components in the AR extract. The known activities of these components can be correlated with the altered metabolic profile following long-term AR administration. AR also activates IGF1R-Akt-Foxo3 signaling axis in heart tissues of rats administered with AR. Our study identifies AR components that induce alterations in lipid metabolism and immune pathways in animals which consume AR for an extended period.

Approaches for the study of epigenetic modifications in the inner ear and related tissues

DNA methylation and histone modifications such as methylation, acetylation, and phosphorylation, are two types of epigenetic modifications that alter gene expression. These additions to DNA regulatory elements or to the tails of histones can be inherited or can also occur de novo. Since epigenetic modifications can have significant effects on various processes at both the cellular and organismal level, there has been a rapid increase in research on this topic throughout all fields of biology in recent years. However, epigenetic research is relativity new for the inner ear field, likely due to the limited number of cells present and their quiescent nature. Here, we provide an overview of methods used to detect DNA methylation and histone modifications with a focus on those that have been validated for use with limited cell numbers and a discussion of the strengths and limitations for each. We also provide examples for how these methods have been used to investigate the epigenetic landscape in the inner ear and related tissues.

TGFβ2-induced senescence during early inner ear development

Embryonic development requires the coordinated regulation of apoptosis, survival, autophagy, proliferation and differentiation programs. Senescence has recently joined the cellular processes required to master development, in addition to its well-described roles in cancer and ageing. Here, we show that senescent cells are present in a highly regulated temporal pattern in the developing vertebrate inner ear, first, surrounding the otic pore and, later, in the otocyst at the endolymphatic duct. Cellular senescence is associated with areas of increased apoptosis and reduced proliferation consistent with the induction of the process when the endolymphatic duct is being formed. Modulation of senescence disrupts otic vesicle morphology. Transforming growth factor beta (TGFβ) signaling interacts with signaling pathways elicited by insulin-like growth factor type 1 (IGF-1) to jointly coordinate cellular dynamics required for morphogenesis and differentiation. Taken together, these results show that senescence is a natural occurring process essential for early inner ear development.

Expression of lipid-protein gene PLP2 in Liaoning cashmere goat

The relationship between PLP2 gene and cashmere fiber quality of Liaoning cashmere goat was investigated. The sheep fibroblast cells were treated with exogenous cytokines and melatonin, independently, and RNA interference, RT-PCR and in situ hybridization were utilized for investigating the PLP2 gene regulation mechanism underlying the Liaoning cashmere growth. The results showed that the expression of PLP2 gene in the prosperous and degenerative stage is higher than that of the primary follicle, indicating that the PLP2 gene promotes the secondary follicle, wherein the gene is expressed only in the inner root sheath, suggesting its correlation to hair loss. The results of RT-PCR showed that the trend of FGF5 expression in PLP2 gene was positively regulated. The influence of MT on the expression of PLP2 gene was negatively regulated, and the inhibition was gradually enhanced with the passage of time. Studies have confirmed that the Noggin gene is an inhibitor of the BMP signaling pathway. After the noggin gene interferes with the lentivirus infection, the expression of the PLP2 gene is downregulated. Therefore, the PLP2 gene, along with the other suppressor genes including the noggin gene, might affect the development of hair follicles by inhibiting the BMP（Bone morphogenetic proteins）pathway.

Insulin-like growth factor 1 promotes cochlear synapse regeneration after excitotoxic trauma in vitro

In the context of acquired sensorineural hearing loss (SNHL), cochlear hair cells have long been thought to be among the most vulnerable elements in mammalian cochleae. However, recent studies have indicated that the synaptic connection between inner hair cells (IHC) and spiral ganglion neurons (SGN) can be an important target for the treatment of SNHL. Our previous studies in patients with sudden SNHL demonstrated delayed and gradual hearing recovery following topical application of insulin-like growth factor 1 (IGF-1), suggesting that not only protective but also regenerative mechanisms may account for hearing recovery after treatment with IGF-1. We then hypothesized that IGF-1 has the potential to drive the regeneration of IHC-SGN synapses. To test this hypothesis, we investigated the effects of IGF-1 on IHC-SGN synapses using cochlear explant cultures from postnatal day 2 mice that had been damaged by exposure to the excitatory amino acids N-methyl-d-aspartate and kainate. Cochlear explants that lost IHC-SGN synapses upon exposure to excitatory amino acids were cultured with exogenous IGF-1 for an additional 48 h. We observed increased numbers of IHC-SGN synapses after exogenous IGF-1 application. Pharmacological inhibition of the IGF-1 receptor attenuated the restoration of IHC-SGN synapses by exogenous IGF-1. These findings indicated that IGF-1 induces regeneration of IHC-SGN synapses in cochlear explant cultures from postnatal day 2 mice. Therefore, in a future study we will perform in vivo experiments using adult mice to ascertain the effects of IGF-1 on the regeneration of IHC-SGN synapses.

The Role of Insulin-Like Growth Factor 1 in the Progression of Age-Related Hearing Loss

Aging is associated with impairment of sensorial functions and with the onset of neurodegenerative diseases. As pari passu circulating insulin-like growth factor 1 (IGF-1) bioavailability progressively decreases, we see a direct correlation with sensory impairment and cognitive performance in older humans. Age-related sensory loss is typically caused by the irreversible death of highly differentiated neurons and sensory receptor cells. Among sensory deficits, age-related hearing loss (ARHL), also named presbycusis, affects one third of the population over 65 years of age and is a major factor in the progression of cognitive problems in the elderly. The genetic and molecular bases of ARHL are largely unknown and only a few genes related to susceptibility to oxidative stress, excitotoxicity, and cell death have been identified. IGF-1 is known to be a neuroprotective agent that maintains cellular metabolism, activates growth, proliferation and differentiation, and limits cell death. Inborn IGF-1 deficiency leads to profound sensorineural hearing loss both in humans and mice. IGF-1 haploinsufficiency has also been shown to correlate with ARHL. There is not much information available on the effect of IGF-1 deficiency on other human sensory systems, but experimental models show a long-term impact on the retina. A secondary action of IGF-1 is the control of oxidative stress and inflammation, thus helping to resolve damage situations, acute or made chronic by aging. Here we will review the primary actions of IGF-1 in the auditory system and the underlying molecular mechanisms.

ESRP1 Mutations Cause Hearing Loss due to Defects in Alternative Splicing that Disrupt Cochlear Development

Alternative splicing contributes to gene expression dynamics in many tissues, yet its role in auditory development remains unclear. We performed whole-exome sequencing in individuals with sensorineural hearing loss (SNHL) and identified pathogenic mutations in Epithelial Splicing-Regulatory Protein 1 (ESRP1). Patient-derived induced pluripotent stem cells showed alternative splicing defects that were restored upon repair of an ESRP1 mutant allele. To determine how ESRP1 mutations cause hearing loss, we evaluated Esrp1-/- mouse embryos and uncovered alterations in cochlear morphogenesis, auditory hair cell differentiation, and cell fate specification. Transcriptome analysis revealed impaired expression and splicing of genes with essential roles in cochlea development and auditory function. Aberrant splicing of Fgfr2 blocked stria vascularis formation due to erroneous ligand usage, which was corrected by reducing Fgf9 gene dosage. These findings implicate mutations in ESRP1 as a cause of SNHL and demonstrate the complex interplay between alternative splicing, inner ear development, and auditory function.

Netrin 1 mediates protective effects exerted by insulin-like growth factor 1 on cochlear hair cells

Sensorineural hearing loss (SNHL) is mainly caused by the damage of cochlear hair cells (HCs). As HCs and supporting cells (SCs) do not proliferate in postnatal mammals, the loss of HCs and SCs is irreversible, emphasizing the importance of preserving their numbers to prevent SNHL. It is known that insulin-like growth factor 1 (IGF1) is instrumental in the treatment of SNHL. Our previous study indicates that IGF1 protects HCs against aminoglycoside by activating IGF1 receptor and its two major downstream pathways, PI3K/AKT and MEK/ERK, in SCs, which results in the upregulation of the expression of the Netrin1-encoding gene (Ntn1). However, the mechanisms underlying IGF1-induced protection of HCs via SC activation as well as the role of NTN1 in this process have not been elucidated. Here, we demonstrated that NTN1, similar to IGF1, promoted HC survival. NTN1 blocking antibody attenuated IGF1-induced HC protection from aminoglycoside, indicating that NTN1 is the effector molecule of IGF1 signaling during HC protection. In situ hybridization demonstrated that IGF1 potently induced Ntn1 expression in SCs. NTN1 receptors were abundantly expressed in the cochlea; among them, UNC5B mediated IGF1 protective effects on HCs, as NTN1 binding to UNC5B inhibited HC apoptosis. These results provide new insights into the mechanisms underlying IGF1 protection of cochlear HCs, suggesting a possibility of using NTN1 as a new treatment for SNHL.

Nonlinear Network Reconstruction from Gene Expression Data Using Marginal Dependencies Measured by DCOL

Reconstruction of networks from high-throughput expression data is an important tool to identify new regulatory relations. Given that nonlinear and complex relations exist between biological units, methods that can utilize nonlinear dependencies may yield insights that are not provided by methods using linear associations alone. We have previously developed a distance to measure predictive nonlinear relations, the Distance based on Conditional Ordered List (DCOL), which is sensitive and computationally efficient on large matrices. In this study, we explore the utility of DCOL in the reconstruction of networks, by combining it with local false discovery rate (lfdr)–based inference. We demonstrate in simulations that the new method named nlnet is effective in recovering hidden nonlinear modules. We also demonstrate its utility using a single cell RNA seq dataset. The method is available as an R package at https://cran.r-project.org/web/packages/nlnet.

Activation of PI3K signaling prevents aminoglycoside-induced hair cell death in the murine cochlea

Loss of sensory hair cells of the inner ear due to aminoglycoside exposure is a major cause of hearing loss. Using an immortalized multipotent otic progenitor (iMOP) cell line, specific signaling pathways that promote otic cell survival were identified. Of the signaling pathways identified, the PI3K pathway emerged as a strong candidate for promoting hair cell survival. In aging animals, components for active PI3K signaling are present but decrease in hair cells. In this study, we determined whether activated PI3K signaling in hair cells promotes survival. To activate PI3K signaling in hair cells, we used a small molecule inhibitor of PTEN or genetically ablated PTEN using a conditional knockout animal. Hair cell survival was challenged by addition of gentamicin to cochlear cultures. Hair cells with activated PI3K signaling were more resistant to aminoglycoside-induced hair cell death. These results indicate that increased PI3K signaling in hair cells promote survival and the PI3K signaling pathway is a target for preventing aminoglycoside-induced hearing loss.

Comparative gene expression study of the vestibular organ of the Igf1 deficient mouse using whole-transcript arrays

The auditory and vestibular organs form the inner ear and have a common developmental origin. Insulin like growth factor 1 (IGF-1) has a central role in the development of the cochlea and maintenance of hearing. Its deficiency causes sensorineural hearing loss in man and mice. During chicken early development, IGF-1 modulates neurogenesis of the cochleovestibular ganglion but no further studies have been conducted to explore the potential role of IGF-1 in the vestibular system. In this study we have compared the whole transcriptome of the vestibular organ from wild type and Igf1(-/-) mice at different developmental and postnatal times. RNA was prepared from E18.5, P15 and P90 vestibular organs of Igf1(-/-) and Igf1(+/+) mice and the transcriptome analysed in triplicates using Affymetrix(®) Mouse Gene 1.1 ST Array Plates. These plates are whole-transcript arrays that include probes to measure both messenger (mRNA) and long intergenic non-coding RNA transcripts (lincRNA), with a coverage of over 28 thousand coding transcripts and over 7 thousands non-coding transcripts. Given the complexity of the data we used two different methods VSN-RMA and mmBGX to analyse and compare the data. This is to better evaluate the number of false positives and to quantify uncertainty of low signals. We identified a number of differentially expressed genes that we described using functional analysis and validated using RT-qPCR. The morphology of the vestibular organ did not show differences between genotypes and no evident alterations were observed in the vestibular sensory areas of the null mice. However, well-defined cellular alterations were found in the vestibular neurons with respect their number and size. Although these mice did not show a dramatic vestibular phenotype, we conducted a functional analysis on differentially expressed genes between genotypes and across time. This was with the aim to identify new pathways that are involved in the development of the vestibular organ as well as pathways that maybe affected by the lack of IGF-1 and be associated to the morphological changes of the vestibular neurons that we observed in the Igf1(-/-) mice.

Protein-engineered hydrogel encapsulation for 3-D culture of murine cochlea

HYPOTHESIS

Elastin-like protein (ELP) hydrogel helps maintain the three-dimensional (3-D) cochlear structure in culture.

BACKGROUND

Whole-organ culture of the cochlea is a useful model system facilitating manipulation and analysis of live sensory cells and surrounding nonsensory cells. The precisely organized 3-D cochlear structure demands a culture method that preserves this delicate architecture; however, current methods have not been optimized to serve such a purpose.

METHODS

A protein-engineered ELP hydrogel was used to encapsulate organ of Corti isolated from neonatal mice. Cultured cochleae were immunostained for markers of hair cells and supporting cells. Organ of Corti hair cell and supporting cell density and organ dimensions were compared between the ELP and nonencapsulated systems. These culture systems were then compared with noncultured cochlea.

RESULTS

After 3 days in vitro, vital dye uptake and immunostaining for sensory and nonsensory cells show that encapsulated cochlea contain viable cells with an organized architecture. In comparison with nonencapsulated cultured cochlea, ELP-encapsulated cochleae exhibit higher densities of hair cells and supporting cells and taller and narrower organ of Corti dimensions that more closely resemble those of noncultured cochleae. However, we found compromised cell viability when the culture period extended beyond 3 days.

CONCLUSION

We conclude that the ELP hydrogel can help preserve the 3-D architecture of neonatal cochlea in short-term culture, which may be applicable to in vitro study of the physiology and pathophysiology of the inner ear.

The RNA-binding protein LIN28B regulates developmental timing in the mammalian cochlea

Proper tissue development requires strict coordination of proliferation, growth, and differentiation. Strict coordination is particularly important for the auditory sensory epithelium, where deviations from the normal spatial and temporal pattern of auditory progenitor cell (prosensory cell) proliferation and differentiation result in abnormal cellular organization and, thus, auditory dysfunction. The molecular mechanisms involved in the timing and coordination of auditory prosensory proliferation and differentiation are poorly understood. Here we identify the RNA-binding protein LIN28B as a critical regulator of developmental timing in the murine cochlea. We show that Lin28b and its opposing let-7 miRNAs are differentially expressed in the auditory sensory lineage, with Lin28b being highly expressed in undifferentiated prosensory cells and let-7 miRNAs being highly expressed in their progeny-hair cells (HCs) and supporting cells (SCs). Using recently developed transgenic mouse models for LIN28B and let-7g, we demonstrate that prolonged LIN28B expression delays prosensory cell cycle withdrawal and differentiation, resulting in HC and SC patterning and maturation defects. Surprisingly, let-7g overexpression, although capable of inducing premature prosensory cell cycle exit, failed to induce premature HC differentiation, suggesting that LIN28B's functional role in the timing of differentiation uses let-7 independent mechanisms. Finally, we demonstrate that overexpression of LIN28B or let-7g can significantly alter the postnatal production of HCs in response to Notch inhibition; LIN28B has a positive effect on HC production, whereas let-7 antagonizes this process. Together, these results implicate a key role for the LIN28B/let-7 axis in regulating postnatal SC plasticity.

C-Raf deficiency leads to hearing loss and increased noise susceptibility

The family of RAF kinases transduces extracellular information to the nucleus, and their activation is crucial for cellular regulation on many levels, ranging from embryonic development to carcinogenesis. B-RAF and C-RAF modulate neurogenesis and neuritogenesis during chicken inner ear development. C-RAF deficiency in humans is associated with deafness in the rare genetic insulin-like growth factor 1 (IGF-1), Noonan and Leopard syndromes. In this study, we show that RAF kinases are expressed in the developing inner ear and in adult mouse cochlea. A homozygous C-Raf deletion in mice caused profound deafness with no evident cellular aberrations except for a remarkable reduction of the K⁺ channel Kir4.1 expression, a trait that suffices as a cause of deafness. To explore the role of C-Raf in cellular protection and repair, heterozygous C-Raf^+/− mice were exposed to noise. A reduced C-RAF level negatively affected hearing preservation in response to noise through mechanisms involving the activation of JNK and an exacerbated apoptotic response. Taken together, these results strongly support a role for C-RAF in hearing protection.

IGF-1 deficiency causes atrophic changes associated with upregulation of VGluT1 and downregulation of MEF2 transcription factors in the mouse cochlear nuclei

Insulin-like growth factor 1 (IGF-1) is a neurotrophic protein that plays a crucial role in modulating neuronal function and synaptic plasticity in the adult brain. Mice lacking the Igf1 gene exhibit profound deafness and multiple anomalies in the inner ear and spiral ganglion. An issue that remains unknown is whether, in addition to these peripheral abnormalities, IGF-1 deficiency also results in structural changes along the central auditory pathway that may contribute to an imbalance between excitation and inhibition, which might be reflected in abnormal auditory brainstem responses (ABR). To assess such a possibility, we evaluated the morphological and physiological alterations in the cochlear nucleus complex of the adult mouse. The expression and distribution of the vesicular glutamate transporter 1 (VGluT1) and the vesicular inhibitory transporter (VGAT), which were used as specific markers for labeling excitatory and inhibitory terminals, and the involvement of the activity-dependent myocyte enhancer factor 2 (MEF2) transcription factors in regulating excitatory synapses were assessed in a 4-month-old mouse model of IGF-1 deficiency and neurosensorial deafness (Igf1 (-/-) homozygous null mice). The results demonstrate decreases in the cochlear nucleus area and cell size along with cell loss in the cochlear nuclei of the deficient mouse. Additionally, our results demonstrate that there is upregulation of VGluT1, but not VGAT, immunostaining and downregulation of MEF2 transcription factors together with increased wave II amplitude in the ABR recording. Our observations provide evidence of an abnormal neuronal cytoarchitecture in the cochlear nuclei of Igf1 (-/-) null mice and suggest that the increased efficacy of glutamatergic synapses might be mediated by MEF2 transcription factors.

Application of insulin-like growth factor-1 in the treatment of inner ear disorders

Sensorineural hearing loss (SNHL) is considered an intractable disease, given that hair and supporting cells (HCs and SCs) of the postnatal mammalian cochlea are unable to regenerate. However, with progress in regenerative medicine in the 21st century, several innovative approaches for achieving regeneration of inner ear HCs and SCs have become available. These methods include stem cell transplantation, overexpression of specific genes, and treatment with growth factors. Insulin-like growth factor-1 (IGF-1) is one of the growth factors that are involved in the development of the inner ear. Treatment with IGF-1 maintains HC numbers in the postnatal mammalian cochlea after various types of HC injuries, with activation of two major pathways downstream of IGF-1 signaling. In the aminoglycoside-treated neonatal mouse cochlear explant culture, promotion of the cell-cycle in SCs as well as inhibition of HC apoptosis was observed in the IGF-1-treated group. Activation of downstream molecules was observed in SCs and, in turn, SCs contribute to the maintenance of HC numbers. Using comprehensive analysis of the gene expression, the candidate effector molecules of the IGF-1 signaling pathway in the protection of HCs were identified as Netrin1 and Gap43. Based on these studies, a clinical trial has sought to investigate the effects of IGF-1 on SNHL. Sudden SNHL (SSHL) that was refractory to systemic steroids was treated with IGF-1 in a gelatin hydrogel and the outcome was compared with a historical control of hyperbaric oxygen therapy. The proportion of patients showing hearing improvement was significantly higher in the IGF-1-treatment group at 24 weeks after treatment than in the control group. A randomized clinical trial is ongoing to compare the effect of IGF-1 treatment with that of intra-tympanic steroids for SSHL that is refractory to systemic steroids.

Treatment with N- and C-terminal peptides of parathyroid hormone-related protein partly compensate the skeletal abnormalities in IGF-I deficient mice

Insulin-like growth factor-I (IGF-I) deficiency causes growth delay, and IGF-I has been shown to partially mediate bone anabolism by parathyroid hormone (PTH). PTH-related protein (PTHrP) is abundant in bone, and has osteogenic features by poorly defined mechanisms. We here examined the capacity of PTHrP (1-36) and PTHrP (107-111) (osteostatin) to reverse the skeletal alterations associated with IGF-I deficiency. Igf1-null mice and their wild type littermates were treated with each PTHrP peptide (80 µg/Kg/every other day/2 weeks; 2 males and 4 females for each genotype) or saline vehicle (3 males and 3 females for each genotype). We found that treatment with either PTHrP peptide ameliorated trabecular structure in the femur in both genotypes. However, these peptides were ineffective in normalizing the altered cortical structure at this bone site in Igf1-null mice. An aberrant gene expression of factors associated with osteoblast differentiation and function, namely runx2, osteoprotegerin/receptor activator of NF-κB ligand ratio, Wnt3a , cyclin D1, connexin 43, catalase and Gadd45, as well as in osteocyte sclerostin, was found in the long bones of Igf1-null mice. These mice also displayed a lower amount of trabecular osteoblasts and osteoclasts in the tibial metaphysis than those in wild type mice. These alterations in Igf1-null mice were only partially corrected by each PTHrP peptide treatment. The skeletal expression of Igf2, Igf1 receptor and Irs2 was increased in Igf1-null mice, and this compensatory profile was further improved by treatment with each PTHrP peptide related to ERK1/2 and FoxM1 activation. In vitro, PTHrP (1-36) and osteostatin were effective in promoting bone marrow stromal cell mineralization in normal mice but not in IGF-I-deficient mice. Collectively, these findings indicate that PTHrP (1-36) and osteostatin can exert several osteogenic actions even in the absence of IGF-I in the mouse bone.

Expression of SOCSs in human prostate cancer and their association in prognosis

Suppressors of cytokine signaling (SOCS) proteins have been identified as negative feedback regulators of cytokine-mediated signaling in various tissues, and demonstrated to play critical roles in tumorigenesis and tumor development of different cancers. The involvement of SOCSs in human prostate cancer (PCa) has not been fully elucidated. Thus, the aim of this study is to investigate the expression patterns and the clinical significance of SOCSs in PCa. The expression changes of SOCSs at mRNA and protein levels in human PCa tissues compared with adjacent benign prostate tissues were, respectively, detected by using real-time quantitative reverse transcriptase-polymerase chain reaction (QRT-PCR) and immunohistochemistry analyses. The associations of SOCSs expression with clinicopathological features and clinical outcome of PCa patients were further statistically analyzed. Among SOCSs, both QRT-PCR and immunohistochemistry analyses found that SOCS2 expression was upregulated (at mRNA level: change ratio = 1.98, P = 0.031; at protein level: 5.12 ± 0.60 vs. 2.68 ± 0.37, P = 0.016) and SOCS6 expression was downregulated (at mRNA level: change ratio = -1.65, P = 0.008; at protein level: 3.03 ± 0.32 vs. 4.0.72 ± 0.39, P = 0.004) in PCa tissues compared with those in non-cancerous prostate tissues. In addition, the upregulation of SOCS2 in PCa tissues was correlated with the lower Gleason score (P < 0.001), the absence of metastasis (P < 0.001) and the negative PSA failure (P = 0.009); the downregulation of SOCS6 tended to be found in PCa tissues with the higher Gleason score (P = 0.016), the advanced pathological stage (P = 0.007), the positive metastasis (P = 0.020), and the positive PSA failure (P = 0.032). Furthermore, both univariate and multivariate analyses showed that the downregulation of SOCS2 was an independent predictor of shorter biochemical recurrence-free survival. Our data offer the convincing evidence for the first time that the dysregulation of SOCS2 and SOCS6 may be associated with the aggressive progression of PCa. SOCS2 may be potential markers for prognosis in PCa patients.

Coupling the cell cycle to development and regeneration of the inner ear

Cell cycle exit and acquirement of a postmitotic state is essential for the proper development of organs. In the present review, we examine the role of the cell cycle control in the sensory epithelia of the mammalian inner ear. We describe the roles of the core cell cycle regulators in the proliferation of prosensory cells and in the initiation and maintenance of terminal mitosis of the sensory epithelia. We also discuss how other intracellular signalling may influence the cell cycle. Finally, we address the question of whether manipulations of the cell cycle may have the potential to create replacement cells for the damaged inner sensory epithelia.