Cochlin-cleaved LCCL is a dual-armed regulator of the innate immune response in the cochlea during inflammation

A Novel COCH p.D544Vfs*3 Variant Associated with DFNA9 Sensorineural Hearing Loss Causes Pathological Multimeric Cochlin Formation

COCH (coagulation factor C homology) is one of the most frequently mutated genes of autosomal dominant non-syndromic hearing loss. Variants in COCH could cause DFNA9, which is characterized by late-onset hearing loss with variable degrees of vestibular dysfunction. In this study, we report a Chinese family with a novel COCH variant (c.1687delA) causing p.D544Vfs*3 in the cochlin. Comprehensive audiometric tests and vestibular function assessments were taken to acquire the phenotypic profile of the subjects. Next-generation sequencing was conducted and segregation analysis was carried out using Sanger sequencing. The proband presented mild vestibular symptoms and normal functional assessment results in almost every test, while the variant co-segregated with hearing impairment in the pedigree. The variant was located beyond the vWFA2 domain, which was predicted to affect the post-translational cleavage of the cochlin via molecular modeling analysis. Notably, in the overexpressing study, by transient transfecting the HEK 293T cells, we found that the p.D544Vfs*3 variant increased the formation of multimeric cochlin. Our result enriched the spectrum of DFNA9-linked pathological COCH variants and suggested that variants, causative of cochlin multimerization, could be related to DFNA9 with sensorineural hearing loss rather than serious vestibular symptoms.

Spatial architecture of the cochlear immune microenvironment in noise-induced and age-related sensorineural hearing loss

The cochlea encodes sound stimuli and transmits them to the central nervous system, and damage to sensory cells and synapses in the cochlea leads to hearing loss. The inner ear was previously considered to be an immune privileged organ to protect the auditory organ from reactions with the immune system. However, recent studies have revealed the presence of resident macrophages in the cochlea, especially in the spiral ligament, spiral ganglion, and stria vascularis. The tissue-resident macrophages are responsible for the detection, phagocytosis, and clearance of cellular debris and pathogens from the tissues, and they initiate inflammation and influence tissue repair by producing inflammatory cytokines and chemokines. Insult to the cochlea can activate the cochlear macrophages to initiate immune responses. In this review, we describe the distribution and functions of cochlear macrophages in noise-induced hearing impairment and age-related hearing disabilities. We also focus on potential therapeutic interventions concerning hearing loss by modulating local immune responses.

Advances in otolith-related protein research

Otoliths are biological crystals formed by a layer of calcium carbonate crystal that adhere to the ciliary surface of the utricular and saccular receptors in the vestibule of all vertebrates inner ear, enabling the utricle and saccule to better perceive the changes in linear and gravitational acceleration. However, the molecular etiology of otolith related diseases is still unclear. In this review, we have summarized the recent findings and provided an overview of the proteins that play important roles in otolith formation and maintenance (Otoconin-90, Otolin-1, Otolith Matrix Protein-1, Cochlin, Otogelin, α-Tectorin, β-Tectorin, Otopetrin-1, and Otopetrin-2, PMCA2, etc.), providing new insight for the prevention and management of benign paroxysmal positional vertigo (BPPV) with basis for otolith-related proteins as potential biomarkers of vestibular disease.

Genotype-Phenotype Correlations of Pathogenic COCH Variants in DFNA9: A HuGE Systematic Review and Audiometric Meta-Analysis

Pathogenic missense variants in COCH are associated with DFNA9, an autosomal dominantly inherited type of progressive sensorineural hearing loss with or without vestibular dysfunction. This study is a comprehensive overview of genotype-phenotype correlations using the PRISMA and HuGENet guidelines. Study characteristics, risk of bias, genotyping and data on the self-reported age of onset, symptoms of vestibular dysfunction, normative test results for vestibular function, and results of audiovestibular examinations were extracted for each underlying pathogenic COCH variant. The literature search yielded 48 studies describing the audiovestibular phenotypes of 27 DFNA9-associated variants in COCH. Subsequently, meta-analysis of audiometric data was performed by constructing age-related typical audiograms and by performing non-linear regression analyses on the age of onset and progression of hearing loss. Significant differences were found between the calculated ages of onset and progression of the audiovestibular phenotypes of subjects with pathogenic variants affecting either the LCCL domain of cochlin or the vWFA2 and Ivd1 domains. We conclude that the audiovestibular phenotypes associated with DFNA9 are highly variable. Variants affecting the LCCL domain of cochlin generally lead to more progression of hearing loss when compared to variants affecting the other domains. This review serves as a reference for prospective natural history studies in anticipation of mutation-specific therapeutic interventions.

LCCL peptide cleavage after noise exposure exacerbates hearing loss and is associated with the monocyte infiltration in the cochlea

Acoustic trauma induces an inflammatory response in the cochlea, resulting in debilitating hearing function. Clinically, amelioration of inflammation substantially prevents noise-induced hearing loss. The Limulus factor C, Cochlin, and Lgl1 (LCCL) peptide plays an important role in innate immunity during bacteria-induced inflammation in the cochlea. We aimed to investigate the LCCL-induced innate immune response to noise exposure and its impact on hearing function.

METHODS

We used Coch (encodes cochlin harboring LCCL peptide) knock-out and p.G88E knock-in mice to compare the immune responses before and after noise exposure. We explored their hearing function and hair cell degeneration. Moreover, we investigated distinct characteristics of immune responses upon noise exposure using flow cytometry and RNA sequencing.

RESULTS

One day after noise exposure, the LCCL peptide cleaved from cochlin increased over time in the perilymph space. Both Coch^-/- and Coch^G88E/G88E mutant mice revealed more preserved hearing following acoustic trauma compared to wild-type mice. The outer hair cells were more preserved in Coch^-/- than in wild-type mice upon noise exposure. The RNA sequencing data demonstrated significantly upregulated cell migration gene ontology in wild-type mice than in Coch^-/- mice following noise exposure, indicating that the infiltration of immune cells was dependent on cochlin. Notably, infiltrated monocytes from blood (C11b⁺/Ly6G^-/Ly6C⁺) were remarkably higher in wild-type mice than in Coch^-/- mice at 1 day after noise exposure.

CONCLUSIONS

Noise-induced hearing loss was attributed to over-stimulated cochlin, and led to the cleavage and secretion of LCCL peptide in the cochlea. The LCCL peptide recruited more monocytes from the blood vessels upon noise stimulation, thus highlighting a novel therapeutic target for noise-induced hearing loss.

Immunological mechanisms underlying progression of chronic wounds in recessive dystrophic epidermolysis bullosa

Hereditary epidermolysis bullosa (EB) is a mechanobullous skin fragility disorder characterized by defective epithelial adhesion, leading to mechanical stress‐induced skin blistering. Based on the level of tissue separation within the dermal‐epidermal junction, EB is categorized into simplex (EBS), junctional (JEB), dystrophic (DEB) and Kindler syndrome. There is no cure for EB, and painful chronic cutaneous wounds are one of the major complications in recessive (RDEB) patients. Although RDEB is considered a cutaneous disease, recent data support the underlying systemic immunological defects. Furthermore, chronic wounds are often colonized with pathogenic microbiota, leading to excessive inflammation and altered wound healing. Consequently, patients with RDEB suffer from a painful sensation of chronic, cutaneous itching/burning and an endless battle with bacterial infections. To improve their quality of life and life expectancy, it is important to prevent cutaneous infections, dampen chronic inflammation and stimulate wound healing. A clear scientific understanding of the immunological events underlying the maintenance of chronic poorly healing wounds in RDEB patients is necessary to improve disease management and better understand other wound healing disorders. In this review, we summarize current knowledge of the role of professional phagocytes, such as neutrophils, macrophages and dendritic cells, the role of T‐cell‐mediated immunity in lymphoid organs, and the association of microbiota with poor wound healing in RDEB. We conclude that RDEB patients have an underlying immunity defect that seems to affect antibacterial immunity.

Cochlin Deficiency Protects Against Noise-Induced Hearing Loss

Cochlin is the most abundant protein in the inner ear. To study its function in response to noise trauma, we exposed adolescent wild-type (Coch +/+ ) and cochlin knock-out (Coch -/-) mice to noise (8-16 kHz, 103 dB SPL, 2 h) that causes a permanent threshold shift and hair cell loss. Two weeks after noise exposure, Coch-/- mice had substantially less elevation in noise-induced auditory thresholds and hair cell loss than Coch + / + mice, consistent with cochlin deficiency providing protection from noise trauma. Comparison of pre-noise exposure thresholds of auditory brain stem responses (ABRs) and distortion product otoacoustic emissions (DPOAEs) in Coch-/- mice and Coch + / + littermates revealed a small and significant elevation in thresholds of Coch-/- mice, overall consistent with a small conductive hearing loss in Coch-/- mice. We show quantitatively that the pro-inflammatory component of cochlin, LCCL, is upregulated after noise exposure in perilymph of wild-type mice compared to unexposed mice, as is the enzyme catalyzing LCCL release, aggrecanase1, encoded by Adamts4. We further show that upregulation of pro-inflammatory cytokines in perilymph and cochlear soft-tissue after noise exposure is lower in cochlin knock-out than wild-type mice. Taken together, our data demonstrate for the first time that cochlin deficiency results in conductive hearing loss that protects against physiologic and molecular effects of noise trauma.