© 2021 by the authors., 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., This research was funded by Spanish FEDER/CM, B2017/BMD-3688; FEDER/MICIN, PID2020-115274RB-I00-THEARPY and EU H2020-INTERREG, 0551_PSL_6_E grants to I.V.-N. and ACCI/ISCIII, ER19P5AC761 grant to L.R.-d.l.R. Á.G.-M. holds a FPU (FPU16/03308; MECD) contract. S.M.-C. and L.R.-d.l.R. hold CIBER ISCIII researcher contracts.

The current Research Topic tries to highlight some of the most relevant recent advances regarding sensorineural hearing loss (SNHL). The etiology of SNHL primarily involves hereditary factors, ototoxic drugs, noise, and aging, all of which trigger two main mechanisms: damage to the organ of Corti, namely mechanosensory hair cells (HCs) and non-sensory supporting cells (SCs), and/or loss of spiral ganglion neurons (SGNs) that subsequently form the auditory nerve and hence connect the inner ear to the brain., TJ was supported by the NIH/NIDCD (K08DC019683). IV-N was supported by PID2020-115274RB-I00 from the Spanish MCIN/AEI/10.13039/501100011033 and FEDER.

Cellular senescence is a stable anti-proliferative state, which has an essential role in cell balance control in diverse physiological and pathological settings (Chan and Narita, 2019; Gorgoulis et al., 2019). Senescence research is a highly dynamic field that has experienced a radical expansion over the last few years with the identification of the role of senescence in a growing list of diseases and physiological processes and the promise for therapeutic interventions based on senescence (Munoz-Espin and Serrano, 2014; Paez-Ribes et al., 2019). The current Research Topic aims to give an overview of the latest advances in this field highlighting the progress in understanding the mechanism of senescence and its link to disease in the nervous system and other organs. The issue includes a wide range of articles, including original research reports, mini-reviews, and reviews that explore diverse angles of this topic, showcasing the current trends in senescence research., Research in the authors’ laboratories was supported by the following grants: RTI2018-098520-B-I00 from the Spanish MCIN/AEI/10.13039/501100011033 and FEDER to IP. 2020ΣE01300001 from the Ministry of Development and Investment, 775 (Hippo) and 3782 (PACOREL) from the Hellenic Foundation for Research and Innovation, 70/3/8916 from NKUA-SARG, the Welfare Foundation for Social & Cultural Sciences (KIKPE), and H. Pappas donation to VG, PID2020-115274RB-I00 from the Spanish MCIN/AEI/10.13039/501100011033 and FEDER to IV-N. IP and IV-N were members of the Spanish Senescence Network, Senestherapy (RED2018-102698-T).

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., This research was funded by Spanish MCIN/AEI/10.13039/501100011033 THEARPYPID2020-115274RB-I00; 0551_PSL_6_E POCTEP FGCSIC/ PSL-INTERREG/FEDER NITROPROHEAR and CA20121 COST Action/EU—BenBedPhar grants to I.V.-N. Á.G.-M. holds an FPU (FPU16/03308; MECD) fellowship, and L.R.-d.l.R. holds a CIBER ISCIII researcher contract., Peer reviewed

[Background] The blood-labyrinth barrier (BLB) separates the inner ear from the circulation and is critical for maintaining ionic homeostasis and limiting the entry of deleterious agents. BLB integrity is disrupted by bacterial lipopolysaccharide (LPS), which elicits a strong inflammatory response in the inner ear leading to irreversible otic damage. Prolonged administration of systemic corticosteroids is the available treatment, but it shows both limited efficacy and major adverse effects. SPT-2101 is a novel in situ-forming gel formulation of dexamethasone allowing slow and sustained drug release after single intratympanic administration., [Methods] We used a rat model of LPS-induced injury to define the functional, cellular and molecular mechanisms associated to BLB dysfunction and the protection by SPT-2101. Hearing was assessed by auditory brainstem response (ABR) recording, BLB permeability by gadolinium dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI) and Evans blue extravasation. Gross cochlear histology and cellular alterations were studied by hematoxylin-eosin staining and immunofluorescence. RT-qPCR, PCR array and western blotting were used to assess transcriptional and protein changes., [Results] LPS-challenged rats showed BLB breakdown and altered permeability as shown by the progressive increase in cochlear gadolinium uptake and Evans blue incorporation. LPS administration increased the cochlear expression of the LPS toll-like receptors Tlr2 and co-receptor Cd14, pro-inflammatory cytokines and receptors such as Il1b and ll1r1, and also the oxidative stress and inflammasome mediators NRF2 and NLRP3. LPS also increased IBA1-positive macrophage infiltration in the lateral wall and spiral ganglion. A single intratympanic injection of SPT-2101 protected BLB integrity and prevented otic injury. Comparable effects were obtained by repeated administration of systemic dexamethasone, but not by a single dose. SPT-2101 administration normalized molecular inflammatory mediators and suppressed macrophage infiltration., [Conclusions] Our data indicate that single local administration of dexamethasone formulated as SPT-2101 protects BLB functional integrity during endotoxemia, providing a novel therapeutic opportunity to treat diseases related to BLB dysfunction., This work was funded by a CIBERER-ISCiii SPIRALTH-CIBERER ER17PE12 and MICINN/AEI PID2020-115274RB-I00 grants to IVN and SMC and with the support of Comunidad de Madrid MINA-CM P2022-BMD-7236 and COST Action CA20121 BedBenPhar. Open Access funding provided by Consejo Superior de Investigaciones Científicas. SMC, EL, JMB and LRR held CIBERER contracts.Open Access funding provided thanks to the CRUE-CSIC agreement with Springer Nature., Peer reviewed

Developmental senescence is a form of programmed senescence that contributes to morphogenesis during embryonic development. We showed recently that the SIX1 homeoprotein, an essential regulator of organogenesis, is also a repressor of adult cellular senescence. Alterations in the SIX/EYA pathway are linked to the human branchio-oto-renal (BOR) syndrome, a rare congenital disorder associated with defects in the ears, kidneys and branchial arches. Here, we have used Six1-deficient mice, an animal model of the BOR syndrome, to investigate whether dysfunction of senescence underpins the developmental defects associated with SIX1 deficiency. We have focused on the developing inner ear, an organ with physiological developmental senescence that is severely affected in Six1-deficient mice and BOR patients. We show aberrant levels and distribution of senescence markers in Six1-deficient inner ears concomitant with defective morphogenesis of senescent structures. Transcriptomic analysis and ex vivo assays support a link between aberrant senescence and altered morphogenesis in this model, associated with deregulation of the TGFβ/BMP pathway. Our results show that misregulation of embryo senescence may lead to genetic developmental disorders, significantly expanding the connection between senescence and disease., This work was supported by a grant from the Comunidad de Madrid (P2022/BMD-7393 to I.P.), and grants from Ministerio de Ciencia e Innovación/Agencia Estatal de Investigación and the European Regional Development Fund ‘A way of making Europe’ (RTI2018-098520-B-I00 and PID2021-122600OB-I00 to I.P.; PID2020-115274RB-I00 to I.V.-N.). Open Access funding provided by Consejo Superior de Investigaciones Científicas. Deposited in PMC for immediate release.

Inherited hearing impairment is a remarkably heterogeneous monogenic condition, involving hundreds of genes, most of them with very small (< 1%) epidemiological contributions. The exception is GJB2, the gene encoding connexin-26 and underlying DFNB1, which is the most frequent type of autosomal recessive non-syndromic hearing impairment (ARNSHI) in most populations (up to 40% of ARNSHI cases). DFNB1 is caused by different types of pathogenic variants in GJB2, but also by large deletions that keep the gene intact but remove an upstream regulatory element that is essential for its expression. Such large deletions, found in most populations, behave as complete loss-of-function variants, usually associated with a profound hearing impairment. By using CRISPR-Cas9 genetic edition, we have generated a murine model (Dfnb1em274) that reproduces the most frequent of those deletions, del(GJB6-D13S1830). Dfnb1em274 homozygous mice are viable, bypassing the embryonic lethality of the Gjb2 knockout, and present a phenotype of profound hearing loss (> 90 dB SPL) that correlates with specific structural abnormalities in the cochlea. We show that Gjb2 expression is nearly abolished and its protein product, Cx26, is nearly absent all throughout the cochlea, unlike previous conditional knockouts in which Gjb2 ablation was not obtained in all cell types. The Dfnb1em274 model recapitulates the clinical presentation of patients harbouring the del(GJB6-D13S1830) variant and thus it is a valuable tool to study the pathological mechanisms of DFNB1 and to assay therapies for this most frequent type of human ARNSHI., This work was supported by the Instituto de Salud Carlos III (ISCIII), Madrid, Spain, National Plan for Scientific and Technical Research and Innovation 2017–2020, with cofunding from the European Regional Development Fund, “A way to make Europe”, grant number PI20/00619 (to I. d. C.); by MINECO/FEDER THERAPY PID2020-115274RB-I00/AEI/10.13039/501100011033, CM IND2020/BMD-17454 and MINA-CM P2022/BMD7236 (to IVN); and by MINECO BIO2015-70978-R and intramural funds from Centro de Investigación Biomédica en Red de Enfermedades Raras (CIBERER) (to L.M.). SMC and BMB hold CIBERER-ISCIII contracts., Peer reviewed

Hearing loss is a common side effect of many tumor treatments. However, hearing loss can also occur as a direct result of certain tumors of the nervous system, the most common of which are the vestibular schwannomas (VS). These tumors arise from Schwann cells of the vestibulocochlear nerve and their main cause is the loss of function of NF2, with 95 % of cases being sporadic and 5 % being part of the rare neurofibromatosis type 2 (NF2)-related Schwannomatosis. Genetic variations in NF2 do not fully explain the clinical heterogeneity of VS, and interactions between Schwann cells and their microenvironment appear to be critical for tumor development. Preclinical in vitro and in vivo models of VS are needed to develop prognostic biomarkers and targeted therapies. In addition to VS, other tumors can affect hearing. Meningiomas and other masses in the cerebellopontine angle can compress the vestibulocochlear nerve due to their anatomic proximity. Gliomas can disrupt several neurological functions, including hearing; in fact, glioblastoma multiforme, the most aggressive subtype, may exhibit early symptoms of auditory alterations. Besides, treatments for high-grade tumors, including chemotherapy or radiotherapy, as well as incomplete resections, can induce long-term auditory dysfunction. Because hearing loss can have an irreversible and dramatic impact on quality of life, it should be considered in the clinical management plan of patients with tumors, and monitored throughout the course of the disease., This work was funded by MICIN/FEDER THEARPY PID2020–115274RB-I00/AEI/10.13039/501100011033 (to IVN and SMC), CM IND2020/BMD-17454 (to IVN); and supported by MINA-CM P2022/BMD7236 and CONEXION NANOMEDICINA CSIC. SMC holds CIBERER-ISCIII contract., Peer reviewed

[Background] Familial Meniere’s disease (FMD) is a rare polygenic disorder of the inner ear. Mutations in the connexin gene family, which encodes gap junction proteins, can also cause hearing loss, but their role in FMD is largely unknown., [Methods] We retrieved exome sequencing data from 94 individuals in 70 Meniere's disease (MD) families. Through gene burden analysis, we calculated the enrichment of rare variants (allele frequency < 0.05) in connexins genes in FMD individuals compared with the reference population. The connexin monomer and the homomeric connexon structural models were predicted using AlphaFold2 and HDOCK. RT-qPCR and immunofluorescence were done in mice cochleae to identify expression of the mouse ortholog candidate gene Gjd3., [Results] We found an enrichment of rare missense variants in the GJD3 gene when comparing allelic frequencies in FMD (N = 94) with the Spanish reference population (OR = 3.9[1.92–7.91], FDR = 2.36E-03). In the GJD3 sequence, we identified a rare haplotype (TGAGT) composed of two missense, two synonymous, and one downstream variant. This haplotype was found in five individuals with FMD, segregating in three unrelated families with a total of ten individuals; and in another eight MD individuals. GJD3 encodes the gap junction protein delta 3, also known as human connexin 31.9 (Cx31.9). The protein model predicted that the NP_689343.3:p.(His175Tyr) missense variant could modify the interaction between connexins and the connexon assembly, affecting the homotypic GJD3 gap junction between cells. Our studies in mice revealed that Gjd3—encoding Gjd3 or mouse connexin 30.2 (Cx30.2)—was expressed in the organ of Corti and vestibular organs, particularly in the tectorial membrane, the base of inner and outer hair cells and the nerve fibers., [Conclusions] The present results describe a novel association between GJD3 and FMD, providing evidence that FMD is related to changes in the inner ear channels, and supporting a new role of tectorial membrane proteins in MD., JALE has received funds to support research on genetics in Meniere’s disease from The University of Sydney (K7013_B3413 Grant), Asociacion Sindrome de Meniere España (ASMES), and Meniere’s Society, UK. AGM has received funds from the Andalusian Health Department (Grant PI-0266–2021) and from CuresWithinReach and the Knight Family. JALE and AGM have received funds from the Andalusian Government (CECEU 2020, grant code: DOC_01677). IVN and SMC have received funds from PID2020-115274RB-I00 and PID2023-147347OB-I00 funded by MCIN/AEI/https://doi.org/10.13039/501100011033, MICIU/AEI/https://doi.org/10.13039/501100011033 and FEDER, UE; and COST Action CA20113 PROTEOCURE. AMPP was supported by a PhD scholarship from the Regional Ministry of Economic Transformation, Industry, Knowledge and Universities of Junta de Andalucía (Grant number PREDOC2021/00343)., Peer reviewed

[Background] Vestibular schwannomas (VS) are complex and heterogeneous human tumors arising from the Schwann cell compartment of the vestibulocochlear nerve. VS cause significant neurological deficit such as hearing loss and vestibular impairment, and in some cases death due to brainstem compression. There is an urgent need to find pharmacotherapies for VS since surgical removal and stereotactic radiosurgery are the only effective treatments. Cancer therapy based in the combination of drug-induced senescence and senolytics may provide an innovative pharmacological alternative for VS management., [Methods] Senescence-associated β-galactosidase (SA-β-GAL) activity detection assay, real-time polymerase chain reaction (RT-PCR), western blotting and immunofluorescence, together with viability assays were used to analyze the response to different chemotherapy drugs of the human VS HEI-193 cell line. Human VS tumor paraffin sections were also studied for SA-β-GAL-stained cells., [Results] We found that chemotherapy compounds induced genotoxic stress and cellular senescence in HEI-193 VS cells, as characterized by increased SA-β-GAL activity, growth arrest, increased levels of the cyclin-dependent kinase inhibitor p21 and the accumulation of DNA damage. These cellular senescence markers were also accompanied by an increase of senescence-associated secretory phenotype (SASP): IL6, IL8, IL1B and MMP1. Induction of senescence by chemotherapy rendered HEI-193 VS cells as druggable targets for senolytic compounds, as navitoclax. Thus, treatment with navitoclax selectively eliminated bleomycin-induced senescent HEI-193 VS cells by activating the extrinsic and intrinsic apoptosis pathways. Our data also show the presence of senescent cells, SA-β-GAL-positive stain, in human VS tumors, which are not present in healthy great auricular nerve sections., [Conclusions] These findings suggest that a one-two punch strategy of pro-senescence therapy induced by chemotherapy treatment followed by senolytic therapy represents a new paradigm for the pharmacological treatment of VS., This research was funded by Spanish MCIN/ AEI/ 10.13039/ 501100011033 THEARPY-PID2020-115274RB-I00, MINA-CM Madrid Innovative Neurotech Alliance P2022/BMD-7236, CA20113 COST Action EU- ProteoCure, CA23119 COST Action EU-SENESCENCE2030: Targeting Cell Senescence to Prevent Age-Related Diseases and the Spanish Senescence Network, Senestherapy (RED2018-102698-T) FEDER/ MICIN grants to I. V. -N., Peer reviewed

[Purpose] Vestibular schwannomas (VS) are benign tumors with variable clinical behavior. Recurrence after surgery is uncommon yet sometimes aggressive. Reliable molecular predictors of recurrence are lacking, and the correlation between genotype and phenotype is weak. This study aimed to identify molecular markers associated with recurrence in VS and explore their prognostic potential., [Methods] Retrospective case-control study of patients undergoing VS surgery between 2017 and 2024. RNA-Seq was conducted to identify molecular signatures associated with recurrence, and selected genes were validated using RT-qPCR. Recurrence-free and salvage surgery-free survival were analyzed by the extent of resection., [Results] 23 samples from 22 patients were analyzed, including 7 recurrent and 16 non-recurrent cases. 81 differentially expressed genes were identified in recurrent tumors, with enrichment of the MAPK (FDR = 7.9 × 10⁻⁴) and PI3K/AKT/mTOR (FDR = 0.038) pathways. Eight candidate genes were selected for validation: DCN (FC 4.34); DUSP5 (FC 4.20); CXCL8 (FC 3.25); JUND (FC 3.27); MYC (FC 2.45); MAFF (FC 3.79); SOD3 (FC 2.47) (all upregulated), and TNF (FC 0.16) (downregulated). RT-qPCR confirmed that CXCL8 and TNF were significantly elevated in tumors requiring early salvage surgery and in an NF2-associated Schwannomatosis case. No differences in recurrence-free or salvage surgery-free survival were observed between near-total and subtotal resections., [Conclusion] Recurrent VS exhibit a distinct molecular profile, highlighting IL-8 and TNFα as potential biomarkers and therapeutic targets. These findings support the development of a prognostic panel to guide personalized follow-up and treatment, particularly for high-risk patients. Further studies are needed before clinical implementation., This research was funded by Spanish Ministerio de Ciencia e Innovación/Agencia Estatal de Investigación MCIN/AEI/https://doi.org/10.13039/501100011033 THEARPY-PID2020-115274RB-I00 and Spanish Ministerio de Ciencia, Innovación y Universidades/Agencia Estatal de Investigación MICIU/AEI/https://doi.org/10.13039/501100011033 PROHEAR-PID2023-147347OB-I00 to Isabel Varela-Nieto. The authors thank the support from Madrid Innovative Neurotech Alliance MINA-CM P2022/BMD-7236 consortium and CSIC Rare Diseases Network (RER-Biomed)., Peer reviewed