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

Utilizing Single Cell RNA-Sequencing to Implicate Cell Types and Therapeutic Targets for SSNHL in the Adult Cochlea

OBJECTIVE

To identify genes implicated in sudden sensorineural hearing loss (SSNHL) and localize their expression in the cochlea to further explore potential pathogenic mechanisms and therapeutic targets.

STUDY DESIGN

Systematic literature review and bioinformatics analysis.

DATA SOURCES

The following sources were searched from inception through July 2, 2020: PubMed-NCBI, MEDLINE, Embase, CINAHL, Cochrane Library, ClinicalTrials.gov, OpenGrey, GreyNet, GreyLiterature Report, and European Union Clinical Trials Registry. PubMed-NCBI and MEDLINE were additionally searched for human temporal bone histopathologic studies related to SSNHL.

METHODS

Literature review of candidate SSNHL genes was conducted according to PRISMA guidelines. Existing temporal bone studies from SSNHL patients were analyzed to identify the most commonly affected inner ear structures. Previously published single-cell and single-nucleus RNA-Seq datasets of the adult mouse stria vascularis, as well as postnatal day 7 and 15 mouse cochlear hair cells and supporting cells, were utilized for localization of the SSNHL-related genes curated through literature review.

CONCLUSIONS

We report 92 unique single nucleotide polymorphisms (SNPs) in 76 different genes that have been investigated in relation to SSNHL in the literature. We demonstrate that a subset of these genes are expressed by cell types in the adult mouse stria vascularis and organ of Corti, consistent with findings from temporal bone studies in human subjects with SSNHL. We highlight several potential genetic targets relevant to current and possible future SSNHL treatments.

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

Lipopolysaccharide disrupts the cochlear blood-labyrinth barrier by activating perivascular resident macrophages and up-regulating MMP-9

OBJECTIVE

To determine the distribution of perivascularresident macrophages (PVMs) in BLB and their relationship with capillaries, and to explore the possible mechanisms responsible for lipopolysaccharide (LPS)-induced activation of PVMs and the breakdown of BLB.

METHODS

Adult Balb/c mice were either trans-tympanically injected with LPS, or mock-treated. Auditory brainstem response was tested before and 48 h after treatments. Distribution of pericytes, PVMs and capillaries was analyzed by immunohistochemical staining, and BLB permeability was estimated by FITC-dextran leakage assay. Ultrastructure of stria vascularis was examined by transmission electron microscope. Protein and mRNA level of matrix metallopeptidase 9 (MMP-9), zona occludens-1 (ZO-1), interleukin-33 (IL-33) and its receptor suppression of tumorigenicity 2 (ST2) was measured by IHC and qRT-PCR.

RESULTS

Unlike pericytes that surround one capillary, PVMs branched to connect with more than one capillary. LPS caused hearing loss in mice. Following LPS challenge, cochleae showed vascular leakage in stria vascularis, and PVMs presented morphological changes including reduced contact with capillaries. TEM revealed a reduced number of tight junction contact points between endothelial cells and a wider space between PVMs, pericytes and endothelial cells. The mRNA and protein levels of MMP-9 and ST2 in stria vascularis were up-regulated, while ZO-1 were down-regulated after exposure to LPS.

CONCLUSIONS

Our results suggest that PVMs may play a more significant role than pericytes in maintaining the integrity of BLB. Our findings also reveal a possible mechanism contributing to LPS-induced activation of PVMs, breakdown of BLB and hearing loss.

Cochlear Capillary Pericytes

Capillary pericytes in the cochlea of mammals are-compared to pericytes in other tissues, like the CNS-relatively poorly researched. To begin with, there is still a considerable debate as to whether the very last precapillary arterioles should-due to their contractile properties-may be considered to be pericytes.However, cochlear capillary pericytes have shifted into the center of attention in the past decade. Most mammals show a considerable number of pericytes in the stria vascularis of the cochlea-up to 1300 in a mouse alone. This high number may be explained by the observation that cochlear capillary pericytes may be differentiated into different subgroups, depending on the immune markers that are expressed by them. Corresponding with these subpopulations, cochlear pericytes fulfill three core functions in the physiology of the cochlea: Formation of the intrastrial blood-fluid barrier-Pericytes monitor the ion, fluid, and nutrient household and aid in the homeostasis thereof. Regulation of cochlear blood flow-By contraction on relaxation, pericytes contribute to the regulation of cochlear blood flow, a paramount function parameter of the cochlea. Immune response-Pericytes actually contribute to the immune response in inflammation of the cochlea. Due to these central roles in the physiology of the cochlea, pericytes actually play a major role in numerous cochlear pathologies, including, but not limited to, sudden sensorineural hearing loss, acoustic trauma, and inflammation of the cochlea.

Apigetrin treatment attenuates LPS-induced acute otitis media though suppressing inflammation and oxidative stress

The natural course of otitis media in children is acute and self-limiting. Nevertheless, about 10-20% children could experience recurrent or persistent otitis media. Thus, finding effective candidate to prevent acute otitis media is urgently required. In our study, mouse acute otitis media model was constructed by lipopolysaccharide (LPS) injection into the middle ear of mice via the tympanic membrane. Apigetrin (APT) is a flavonoid isolated from various herbal medicines, possessing anti-inflammatory and anti-oxidative bioactivities. However, if APT could attenuate acute otitis media in LPS-induced animal models, little is to be known. Hematoxylin and eosin (H&E) staining suggested that APT treatment reduced LPS-induced higher mucosa thickness. LPS-triggered inflammatory response was also inhibited by APT, as evidenced by the down-regulated neutrophils and macrophages. Additionally, the reduced inflammatory factors, including interleukin-1β (IL-lβ), tumor necrosis factor α (TNF-α), IL-6 and vascular endothelial growth factor (VEGF) were observed in APT-treated mice with acute otitis media. The process was associated with the inhibition of toll-like receptor 4 (TLR4)/nuclear factor kappa B (NF-κB) pathway, which was proved by the blockage of TLR4, MyD88, p-IKKα, p-IκBα, and p-NF-κB using western blot analysis. Moreover, the production of reactive oxygen species (ROS) caused by LPS was also reduced by APT through promoting anti-oxidants, involving superoxide dismutase (SOD) activity, heme oxygenase-1 (HO-1), NADP(H) quinone oxidoreductase 1 (NQO-1) and nuclear factor erythroid 2-related factor 2 (Nrf2) expressions. In contrast, high levels of MDA and kelch-like ECH-associated protein 1 (Keap 1) in LPS-treated mice were down-regulated by APT, which might be associated with the inactivation of NF-κB. In vitro, APT exhibited anti-inflammatory and anti-oxidant effects with little cytotoxicity in LPS-stimulated cells. Together, the data above indicated that APT could ameliorate acute otitis media through inhibiting inflammation and oxidative stress.

MIF protects against oxygen-glucose deprivation-induced ototoxicity in HEI-OC1 cochlear cells by enhancement of Akt-Nrf2-HO-1 pathway

Ischemia and oxidative stress play crucial roles in the pathophysiology of sudden sensorineural hearing loss (SSNHL). Macrophage migration inhibitory factor (MIF) is a pro-inflammatory cytokine and serves an important role in hearing function. The present study was designed to evaluate the effect of MIF on oxygen-glucose deprivation (OGD)-induced ototoxicity and to elucidate its molecular mechanism. In HEI-OC1 auditory cells, OGD reduced cell viability and increased supernatant lactate dehydrogenase (LDH) and MIF in a time-dependent manner. However, the reduced cell viability exerted by OGD was attenuated by antioxidant and MIF. Luciferase reporter assay demonstrated that MIF could activate NF-E2-related factor 2 (Nrf2), and real-time PCR showed increased mRNA expressions of Nrf2 and two Nrf2-responsive genes, including heme oxygenase-1 (HO-1) and NAD(P)H:quinone oxidoreductase 1 (NQO1). MIF also suppressed oxidative stress induced by OGD, as demonstrated by decreased MDA and increased GSH in cellular supernatant. Inhibition of Nrf2 using siRNA suppressed HO-1 protein expression, the protective effect on OGD-induced injury and decrease in oxidative stress by MIF. Moreover, MIF prevented OGD-induced reduction of Akt1 phosphorylation at Ser473. LY294002, an inhibitor of PI3K/Akt signaling, attenuated the enhancement of Nrf2 protein and protective effect of MIF in OGD-treated cochlear cells. We demonstrate that MIF protects cochlear cells against OGD-induced injury through activation of Akt-Nrf2-HO-1 pathway.

Aminophylline restores glucocorticoid sensitivity in a guinea pig model of sudden sensorineural hearing loss induced by lipopolysaccharide

Glucocorticoids have been used to treat hearing loss and vestibular dysfunction for many years. However, some reports have indicated that a subset of patients with these disorders exhibit glucocorticoid insensitivity or resistance. A reduction in histone deacetylase 2 (HDAC2) activity and expression has been reported to play a critical role in glucocorticoid resistance. Here, we investigated the protective effects of aminophylline on HDAC2 expression and glucocorticoid sensitivity in lipopolysaccharide (LPS)-induced sudden sensorineural hearing loss in guinea pigs. We assessed hearing recovery in LPS-applied guinea pigs, which were either left untreated or were systemically treated with either dexamethasone, aminophylline, or a combination of the two. We utilized fluorescence microscopy and enzyme-linked immunosorbent assay to analyze the distribution patterns of HDAC2 and detect its levels in the cochlea. We used hematoxylin-eosin staining to examine cochlear histopathological changes. In the absence of treatment, significant hearing loss was detected in LPS-exposed animals. A synergistic effect was observed between aminophylline and dexamethasone in maintaining HDAC2 expression levels, preventing hearing loss in LPS-exposed animals and reducing cochlear damage. This study indicates that aminophylline can restore glucocorticoid sensitivity, which provides a new approach to treating patients with hearing disorders who are refractory to glucocorticoids.