Matrix metalloproteinase inhibitor attenuates cochlear lateral wall damage induced by intratympanic instillation of endotoxin

Mfsd2a regulates the blood-labyrinth-barrier formation and function through tight junctions and transcytosis

The Blood-Labyrinth Barrier (BLB) is pivotal for the maintenance of lymphatic homeostasis within the inner ear, yet the intricacies of its development and function are inadequately understood. The present investigation delves into the contribution of the Mfsd2a molecule, integral to the structural and functional integrity of the Blood-Brain Barrier (BBB), to the ontogeny and sustenance of the BLB. Our empirical findings delineate that the maturation of the BLB in murine models is not realized until approximately two weeks post-birth, with preceding stages characterized by notable permeability. Transcriptomic analysis elucidates a marked augmentation in Mfsd2a expression within the lateral wall of the cochlea in specimens exhibiting an intact BLB. Moreover, both in vitro and in vivo assays substantiate that a diminution in Mfsd2a expression detrimentally impacts BLB permeability and structural integrity, principally via the attenuation of tight junction protein expression and the enhancement of endothelial cell transcytosis. These insights underscore the indispensable role of Mfsd2a in ensuring BLB integrity and propose it as a viable target for therapeutic interventions aimed at the amelioration of hearing loss.

Extracellular ATP accelerates cell death and decreases tight junction protein ZO-1 in hypoxic cochlear strial marginal cells in neonatal rats

In the cochlear, extracellular ATP (eATP) plays an important role in both physiological and pathological processes, but its role in the hypoxic cochlear remains unclear. The present study aims to investigate the relationship between eATP and hypoxic marginal cells (MCs) in the stria vascularis in cochlear. Combining various methodologies, we found that eATP accelerates cell death and decreases tight junction protein zonula occludens-1 (ZO-1) in hypoxic MCs. Flow cytometry and western blot analyses revealed an increase in apoptosis levels and suppression of autophagy, indicating that eATP causes additional cell death by increasing the apoptosis of hypoxic MCs. Given that autophagy inhibits apoptosis to protect MCs under hypoxia, apoptosis is probably enchanced by suppressing autophagy. Interleukin-33(IL-33)/suppression of tumorigenicity-2(ST-2)/matrix metalloprotein 9(MMP9) pathway activation was also observed during the process. Further experiments involving the use of additional IL-33 protein and an MMP9 inhibitor indicated that this pathway is responsible for the damage to the ZO-1 protein in hypoxic MCs. Our study revealed the adverse effect of eATP on the survival and ZO-1 protein expression of hypoxic MCs, as well as the underlying mechanism.

A combined genome-wide association and molecular study of age-related hearing loss in H. sapiens

BACKGROUND

Sensorineural hearing loss is one of the most common sensory deficiencies. However, the molecular contribution to age-related hearing loss is not fully elucidated.

METHODS

We performed genome-wide association studies (GWAS) for hearing loss-related traits in the UK Biobank (N = 362,396) and selected a high confidence set of ten hearing-associated gene products for staining in human cochlear samples: EYA4, LMX1A, PTK2/FAK, UBE3B, MMP2, SYNJ2, GRM5, TRIOBP, LMO-7, and NOX4.

RESULTS

All proteins were found to be expressed in human cochlear structures. Our findings illustrate cochlear structures that mediate mechano-electric transduction of auditory stimuli, neuronal conductance, and neuronal plasticity to be involved in age-related hearing loss.

CONCLUSIONS

Our results suggest common genetic variation to influence structural resilience to damage as well as cochlear recovery after trauma, which protect against accumulated damage to cochlear structures and the development of hearing loss over time.

Intratympanic Lipopolysaccharide Elevates Systemic Fluorescent Gentamicin Uptake in the Cochlea

Objectives/Hypothesis

Lipopolysaccharide (LPS), a key component of bacterial endotoxins, activates macrophages and triggers the release of inflammatory cytokines in mammalian tissues. Recent studies have shown that intratympanic injection of LPS simulates acute otitis media (AOM) and results in morphological and functional changes in the inner ear. Here we established an AOM mouse model with LPS to investigate the uptake of ototoxic gentamicin in the inner ear, and elucidated the underlying mechanism by focusing on cochlear inflammation as a result of AOM.

Study Design

Preclinical rodent animal model.

Methods

Fluorescently tagged gentamicin (GTTR) was systemically administered to mice with AOM. Iba1‐positive macrophage morphology and inner ear cytokine profile were evaluated by immunofluorescence technique and a mouse cytokine array kit, respectively.

Results

We observed characteristic symptoms of AOM in the LPS‐treated ears with elevated hearing thresholds indicating a conductive hearing loss. More importantly, the LPS‐induced AOM activated cochlear inflammatory responses, manifested by macrophage infiltration, particularly in the organ of Corti and the spiral ligament, in addition to the up‐regulation of proinflammatory cytokines. Meanwhile, GTTR uptake in the stria vascularis and sensory hair cells from all the LPS‐treated ears was significantly enhanced at 24, 48, and 72‐hour post‐treatment, as the most prominent enhancement was observed in the 48‐hour group.

Conclusion

In summary, this study suggests that the pathological cochlea is more susceptible to ototoxic drugs, including aminoglycosides, and justified the clinical concern of aminoglycoside ototoxicity in the AOM treatment. Laryngoscope, 131:E2573–E2582, 2021

Toll-like Receptor 4 Signaling and Downstream Neutrophilic Inflammation Mediate Endotoxemia-Enhanced Blood-Labyrinth Barrier Trafficking

HYPOTHESIS

Both toll-like receptor 4 (TLR4) and downstream neutrophil activity are required for endotoxemia-enhanced blood-labyrinth barrier (BLB) trafficking.

BACKGROUND

Aminoglycoside and cisplatin are valuable clinical therapies; however, these drugs often cause life-long hearing loss. Endotoxemia enhances the ototoxicity of aminoglycosides and cisplatin in a TLR4 dependent mechanism for which downstream proinflammatory signaling orchestrates effector immune cells including neutrophils. Neutrophil-mediated vascular injury (NMVI) can enhance molecular trafficking across endothelial barriers and may contribute to endotoxemia-enhanced drug-induced ototoxicity.

METHODS

Lipopolysaccharide (LPS) hypo-responsive TLR4-KO mice and congenitally neutropenic granulocyte colony-stimulating factor (GCSF) GCSF-KO mice were studied to investigate the relative contributions of TLR4 signaling and downstream neutrophil activity to endotoxemia-enhanced BLB trafficking. C57Bl/6 wild-type mice were used as a positive control. Mice were treated with LPS and 24 hours later cochleae were analyzed for gene transcription of innate inflammatory cytokine/chemokine signaling molecules, neutrophil recruitment, and vascular trafficking of the paracellular tracer biocytin-TMR.

RESULTS

Cochlear transcription of innate proinflammatory cytokines/chemokines was increased in endotoxemic C57Bl/6 and GCSF-KO, but not in TLR4-KO mice. More neutrophils were recruited to endotoxemic C57Bl/6 cochleae compared with both TLR4 and GCSF-KO cochleae. Endotoxemia enhanced BLB trafficking of biocytin-TMR in endotoxemic C57Bl/6 cochleae and this was attenuated in both TLR4 and GCSF-KO mice.

CONCLUSION

Together these results suggest that TLR4-mediated innate immunity cytokine/chemokine signaling alone is not sufficient for endotoxemia-enhanced trafficking of biocytin-TMR and that downstream neutrophil activity is required to enhance BLB trafficking. Clinically, targeting neutrophilic inflammation could protect hearing during aminoglycoside, cisplatin, or other ototoxic drug therapies.

Therapeutic hypothermia reduces cortical inflammation associated with utah array implants

OBJECTIVE

Neuroprosthetics hold tremendous promise to restore function through brain-computer interfaced devices. However, clinical applications of implantable microelectrodes remain limited given the challenges of maintaining neuronal signals for extended periods of time and with multiple biological mechanisms negatively affecting electrode performance. Acute and chronic inflammation, oxidative stress, and blood brain barrier disruption contribute to inconsistent electrode performance. We hypothesized that therapeutic hypothermia (TH) applied at the microelectrode insertion site will positively modulate both inflammatory and apoptotic pathways, promoting neuroprotection and improved performance in the long-term.

APPROACH

A custom device and thermoelectric system were designed to deliver controlled TH locally to the cortical implant site at the time of microelectrode array insertion and immediately following surgery. The TH paradigm was derived from in vivo cortical temperature measurements and finite element modeling of temperature distribution profiles in the cortex. Male Sprague-Dawley rats were implanted with non-functional Utah microelectrodes arrays (UMEA) consisting of 4 × 4 grid of 1.5 mm long parylene-coated silicon shanks. In one group, TH was applied to the implant site for two hours following the UMEA implantation, while the other group was implanted under normothermic conditions without treatment. At 48 h, 72 h, 7 d and 14 d post-implantation, mRNA expression levels for genes associated with inflammation and apoptosis were compared between normothermic and hypothermia-treated groups.

MAIN RESULTS

The custom system delivered controlled TH to the cortical implant site and the numerical models confirmed that the temperature decrease was confined locally. Furthermore, a one-time application of TH post UMEA insertion significantly reduced the acute inflammatory response with a reduction in the expression of inflammatory regulating cytokines and chemokines.

SIGNIFICANCE

This work provides evidence that acutely applied hypothermia is effective in significantly reducing acute inflammation post intracortical electrode implantation.

Expression of macrophage migration inhibitory factor and CD74 in the inner ear and middle ear in lipopolysaccharide-induced otitis media

CONCLUSION

Significant expression of macrophage migration inhibitory factor and its receptor (CD74) was observed in both the middle ear and inner ear in experimental otitis media in mice. Modulation of macrophage migration inhibitory factor and its signaling pathway might be useful in the management of inner ear inflammation due to otitis media.

OBJECTIVES

Inner ear dysfunction secondary to otitis media has been reported. However, the specific mechanisms involved are not clearly understood. The aim of this study is to investigate the expression of macrophage migration inhibitory factor and CD74 in the middle ear and inner ear in lipopolysaccharide-induced otitis media.

METHOD

BALB/c mice received a transtympanic injection of either lipopolysaccharide or phosphate-buffered saline (PBS). The mice were sacrificed 24 h after injection, and temporal bones were processed for polymerase chain reaction (PCR) analysis, histologic examination, and immunohistochemistry.

RESULTS

PCR examination revealed that the lipopolysaccharide-injected mice showed a significant up-regulation of macrophage migration inhibitory factor in both the middle ear and inner ear as compared with the PBS-injected control mice. The immunohistochemical study showed positive reactions for macrophage migration inhibitory factor and CD74 in infiltrating inflammatory cells, middle ear mucosa, and inner ear in the lipopolysaccharide-injected mice.

Hyperhomocysteinemia, MMPs and Cochlear Function: A Short Review

Hyperhomocysteinemia (HHCY) has been demonstrated to affect cochlear microvasculature as well as cochlear epithelial cells directly, with a resultant alteration of the expression of matrix metalloproteinases (MMPs) and their inhibitors, tissue inhibitors of metalloproteinases (TIMPs). Hence, ascertaining the optimum concentration of MMPs and TIMPs in the cochlea could help to inhibit hearing loss due to HHCY by the administration of appropriate MMP inhibitors, Since infections/inflammations as well as ototoxic antibiotics have a similar mechanism of otic pathology, the cochlear damage they cause could also be similarly prevented.

Lipopolysaccharide-induced middle ear inflammation disrupts the cochlear intra-strial fluid-blood barrier through down-regulation of tight junction proteins

Middle ear infection (or inflammation) is the most common pathological condition that causes fluid to accumulate in the middle ear, disrupting cochlear homeostasis. Lipopolysaccharide, a product of bacteriolysis, activates macrophages and causes release of inflammatory cytokines. Many studies have shown that lipopolysaccharides cause functional and structural changes in the inner ear similar to that of inflammation. However, it is specifically not known how lipopolysaccharides affect the blood-labyrinth barrier in the stria vascularis (intra-strial fluid–blood barrier), nor what the underlying mechanisms are. In this study, we used a cell culture-based in vitro model and animal-based in vivo model, combined with immunohistochemistry and a vascular leakage assay, to investigate lipopolysaccharide effects on the integrity of the mouse intra-strial fluid–blood barrier. Our results show lipopolysaccharide-induced local infection significantly affects intra-strial fluid–blood barrier component cells. Pericytes and perivascular-resident macrophage-like melanocytes are particularly affected, and the morphological and functional changes in these cells are accompanied by substantial changes in barrier integrity. Significant vascular leakage is found in the lipopolysaccharide treated-animals. Consistent with the findings from the in vivo animal model, the permeability of the endothelial cell monolayer to FITC-albumin was significantly higher in the lipopolysaccharide-treated monolayer than in an untreated endothelial cell monolayer. Further study has shown the lipopolysaccharide-induced inflammation to have a major effect on the expression of tight junctions in the blood barrier. Lipopolysaccharide was also shown to cause high frequency hearing loss, corroborated by previous reports from other laboratories. Our findings show lipopolysaccharide-evoked middle ear infection disrupts inner ear fluid balance, and its particular effects on the intra-strial fluid–blood barrier, essential for cochlear homeostasis. The barrier is degraded as the expression of tight junction-associated proteins such as zona occludens 1, occludin, and vascular endothelial cadherin are down-regulated.

Sudden sensorineural hearing loss and polymorphisms in iron homeostasis genes: new insights from a case-control study

Background. Even if various pathophysiological events have been proposed as explanations, the putative cause of sudden hearing loss remains unclear. Objectives. To investigate and to reveal associations (if any) between the main iron-related gene variants and idiopathic sudden sensorineural hearing loss. Study Design. Case-control study. Materials and Methods. A total of 200 sudden sensorineural hearing loss patients (median age 63.65 years; range 10-92) were compared with 400 healthy control subjects. The following genetic variants were investigated: the polymorphism c.-8CG in the promoter of the ferroportin gene (FPN1; SLC40A1), the two isoforms C1 and C2 (p.P570S) of the transferrin protein (TF), the amino acidic substitutions p.H63D and p.C282Y in the hereditary hemochromatosis protein (HFE), and the polymorphism c.-582AG in the promoter of the HEPC gene, which encodes the protein hepcidin (HAMP). Results. The homozygous genotype c.-8GG of the SLC40A1 gene revealed an OR for ISSNHL risk of 4.27 (CI 95%, 2.65-6.89; P = 0.001), being overrepresented among cases. Conclusions. Our study indicates that the homozygous genotype FPN1 -8GG was significantly associated with increased risk of developing sudden hearing loss. These findings suggest new research should be conducted in the field of iron homeostasis in the inner ear.

ALH-L1005 attenuates endotoxin induced inner ear damage

OBJECTIVE

To assess whether this compound (ALH-L1005) is conceivably an effective agent in protecting against cochlear damage induced by LPS.

MATERIALS AND METHODS

Tube formation using human umbilical vein endothelial cell (HUVEC) and matrix metalloproteinase (MMP)-9 inhibition assay was performed. 24 guinea pigs were randomly divided into three groups. Intratympanic instillation of LPS (n=8) as negative control, instillation of oxytetracycline 1h after LPS as positive control (n=8), and intratympanic instillation of ALH-L1005 (n=8) 1h after LPS were considered experimental group. Evaluation by auditory brainstem response (ABR) measurement, cochlear blood flow, and blood-labyrinth barrier (BLB) permeability were performed. Cochlear hair cells were observed by field emission-scanning electron microscopy (FE-SEM). MMP-9 activation was measured by gelatin zymography.

RESULTS

For HUVEC, the tube formation was suppressed in a dose dependant manner. ALH-L1005 inhibited the MMP-9 activity prominently. It also attenuated the elevation of LPS-induced hearing threshold shift and recovery of CBF. By FE-SEM, cochlear hair cells could be preserved in experimental group. ALH-L1005 significantly reduced the BLB opening compared to LPS group. Active MMP-9 expression could be detected in the LPS group. In contrast to ALH-L1005 group, active MMP-9 expression was not detected.

CONCLUSION

Our results conclude that ALH-L1005 showed a protective effect in the cochlear lateral wall damage induced by LPS.