Perivascular-resident macrophage-like melanocytes in the inner ear are essential for the integrity of the intrastrial fluid-blood barrier. Proc Natl Acad Sci U S A. 2012;109:10388-10393. [PMID: 22689949 DOI: 10.1073/pnas.1205210109]

Low-intensity noise exposure takes an essential part in the mechanism of late-onset hereditary hearing loss caused by Abcc1 mutation

With the development of the social economy, we are exposed to increasing noise in our daily lives. Our previous work found an ABCC1(NM_004996.3:c.A1769G, NP_004987.2:p.N590S) variant which cosegregated with the patients in an autosomal dominant non-syndromic hearing loss family. At present, the specific mechanism of deafness caused by ABCC1 mutation is still not clear. Using the knock-in mouse model simulating human ABCC1 mutation, we found that the occurrence of family-related phenotypes was likely attributed to the combination of the mouse genotype and low-intensity noise. GSH and GSSG are important physiological substrates of ABCC1. The destruction of GSH-GSSG balance in the cochleae of both Abcc1N591S/+ mice and Abcc1N591S/N591S mice during low-intensity noise exposure may result in irreversible damage to the hair cells of the cochleae, consequently leading to hearing loss in mice. The findings offered a potential novel idea for the prevention and management of hereditary hearing loss within this family.

Increased Parenchymal Macrophages are associated with decreased Tyrosine Hydroxylase mRNA levels in the Substantia Nigra of people with Schizophrenia and Bipolar Disorder

Increased activation of inflammatory macrophages and altered expression of dopamine markers are found in the midbrains of people with schizophrenia (SZ). The relationship of midbrain macrophages to dopamine neurons has not been explored, nor is it known if changes in midbrain macrophages are also present in bipolar disorder (BD) or major depressive disorder (MDD). Herein, we determined whether there were differences in CD163+ cell density in the Substantia Nigra (SN), and cerebral peduncles (CP) of SZ, BD, and MDD compared to controls (CTRL). We also analyzed whether CD163 protein and dopamine-synthesizing enzyme tyrosine hydroxylase (TH) mRNA levels differed among diagnostic groups and if they correlated with the density of macrophages. Overall, perivascular CD163+ cell density was higher in the gray matter (SN) than in the white matter (CP). Compared to CTRL, we found increased density of parenchymal CD163+ cells in the SN of the three psychiatric groups and increased CD163 protein levels in SZ. CD163 protein was positively correlated with density of perivascular CD163+ cells. TH mRNA was reduced in SZ and BD and negatively correlated with parenchymal CD163+ cell density. We provide the first quantitative and molecular evidence of an increase in the density of parenchymal macrophages in the midbrain of major mental illnesses and show that the presence of these macrophages may negatively impact dopaminergic neurons.

Activated tissue-resident macrophages contribute to hair cell insults in noise-induced hearing loss in mice

Macrophages serve as the primary immune cell population and assume a pivotal role in the immune response within the damaged cochleae. Yet, the origin and role of macrophages in response to noise exposure remain controversial. Here, we take advantage of Ccr2RFP/+ Cx3cr1GFP/+ dual-reporter mice to identify the infiltrated and tissue-resident macrophages. After noise exposure, we reveal that activated resident macrophages change in morphology, increase in abundance, and migrate to the region of hair cells, leading to the loss of outer hair cells and the damage of ribbon synapses. Meanwhile, peripheral monocytes are not implicated in the noise-induced hair cell insults. These noise-induced activities of macrophages are abolished by inhibiting TLR4 signaling, resulting in alleviated insults of hair cells and partial recovery of hearing. Our findings indicate cochlear resident macrophages are pro-inflammatory and detrimental players in acoustic trauma and introduce a potential therapeutic target in noise-induced hearing loss.

ABCC1 deficiency potentiated noise-induced hearing loss in mice by impairing cochlear antioxidant capacity

The ABCC1 gene belongs to the ATP-binding cassette membrane transporter superfamily, which plays a crucial role in the efflux of various endogenous and exogenous substances. Mutations in ABCC1 can result in autosomal dominant hearing loss. However, the specific roles of ABCC1 in auditory function are not fully understood. Through immunofluorescence, we found that ABCC1 was expressed in microvascular endothelial cells (ECs) of the stria vascularis (StV) in the murine cochlea. Then, an Abcc1 knockout mouse model was established by using CRISPR/Cas9 technology to elucidate the role of ABCC1 in the inner ear. The ABR threshold did not significantly differ between WT and Abcc1-/- mice at any age studied. After noise exposure, the ABR thresholds of the WT and Abcc1-/- mice were significantly elevated. Interestingly, after 14 days of noise exposure, ABR thresholds largely returned to pre-exposure levels in WT mice but not in Abcc1-/- mice. Our subsequent experiments showed that microvascular integrity in the StV was compromised and that the number of outer hair cells and the number of ribbons were significantly decreased in the cochleae of Abcc1-/- mice post-exposure. Besides, the production of ROS and the accumulation of 4-HNE significantly increased. Furthermore, StV microvascular ECs were cultured to elucidate the role of ABCC1 in these cells under glucose oxidase challenge. Notably, 30 U/L glucose oxidase (GO) induced severe oxidative stress damage in Abcc1-/- cells. Compared with WT cells, the ROS and 4-HNE levels and the apoptotic rate were significantly elevated in Abcc1-/- cells. In addition, the reduced GSH/GSSG ratio was significantly decreased in Abcc1-/- cells after GO treatment. Taken together, Abcc1-/- mice are more susceptible to noise-induced hearing loss, possibly because ABCC1 knockdown compromises the GSH antioxidant system of StV ECs. The exogenous antioxidant N-acetylcysteine (NAC) may protect against oxidative damage in Abcc1-/- murine cochleae and ECs.

Macrophage depletion protects against cisplatin-induced ototoxicity and nephrotoxicity

Cisplatin is a widely used anticancer drug with notable side effects including ototoxicity and nephrotoxicity. Macrophages, the major resident immune cells in the cochlea and kidney, are important drivers of both inflammatory and tissue repair responses. To investigate the roles of macrophages in cisplatin-induced toxicities, we used PLX3397, a U.S. Food and Drug Administration-approved inhibitor of the colony-stimulating factor 1 receptor, to eliminate tissue-resident macrophages. Mice treated with cisplatin alone had considerable hearing loss (ototoxicity) and kidney injury (nephrotoxicity). Macrophage ablation resulted in significantly reduced hearing loss and had greater outer hair cell survival. Macrophage ablation also protected against cisplatin-induced nephrotoxicity, as evidenced by markedly reduced tubular injury and fibrosis. Mechanistically, our data suggest that the protective effect of macrophage ablation against cisplatin-induced ototoxicity and nephrotoxicity is mediated by reduced platinum accumulation in both the inner ear and the kidney. Together, our data indicate that ablation of tissue-resident macrophages represents an important strategy for mitigating cisplatin-induced ototoxicity and nephrotoxicity.

Relationship Between Cochlear Lateral Wall Changes and Endolymphatic Hydrops in Otitis Media

OBJECTIVES

Despite otitis media and various disease processes being associated with endolymphatic hydrops (EH), an exact explanation of the pathophysiology has yet to be reported. This study aimed to investigate the changes in the cochlear lateral wall structures and their potential correlation with the presence and severity of cochlear EH in acute and chronic otitis media cases. The investigations were conducted in both chinchilla animal model and human temporal bone specimens.

METHODS

We studied a total of 15 chinchilla and 25 human temporal bones from our collection, which were categorized into acute otitis media, chronic otitis media (COM), and control groups. Through quantitative analysis, we measured the area of cochlear lateral wall structures and observed the presence and the degree of EH using light microscopy.

RESULTS

No significant changes were determined in the area of the spiral ligament (p > 0.05) across the species. However, a significant (p < 0.05) decrease in the mean area of the stria vascularis in the basal turn was identified in COM groups compared to controls of both species. Chinchilla model additionally exhibited pathology extending to the lower mid turn. A negative correlation was found between the mean strial area and the severity of EH in both the animal model and human samples.

CONCLUSIONS

COM associated with significant changes in the stria vascularis that may lead to significant increase in the degree of EH. The presented animal model exhibited parallel findings with human samples, suggesting its viability as a valuable model for future studies.

LEVEL OF EVIDENCE

N/A Laryngoscope, 2024.

The Stria Vascularis: Renewed Attention on a Key Player in Age-Related Hearing Loss

Age-related hearing loss (HL), or presbycusis, is a complex and heterogeneous condition, affecting a significant portion of older adults and involving various interacting mechanisms. Metabolic presbycusis, a type of age-related HL, is characterized by the dysfunction of the stria vascularis, which is crucial for maintaining the endocochlear potential necessary for hearing. Although attention on metabolic presbycusis has waned in recent years, research continues to identify strial pathology as a key factor in age-related HL. This narrative review integrates past and recent research, bridging findings from animal models and human studies, to examine the contributions of the stria vascularis to age-related HL. It provides a brief overview of the structure and function of the stria vascularis and then examines mechanisms contributing to age-related strial dysfunction, including altered ion transport, changes in pigmentation, inflammatory responses, and vascular atrophy. Importantly, this review outlines the contribution of metabolic mechanisms to age-related HL, highlighting areas for future research. It emphasizes the complex interdependence of metabolic and sensorineural mechanisms in the pathology of age-related HL and highlights the importance of animal models in understanding the underlying mechanisms. The comprehensive and mechanistic investigation of all factors contributing to age-related HL, including cochlear metabolic dysfunction, remains crucial to identifying the underlying mechanisms and developing personalized, protective, and restorative treatments.

CNS Resident Innate Immune Cells: Guardians of CNS Homeostasis

Although the CNS has been considered for a long time an immune-privileged organ, it is now well known that both the parenchyma and non-parenchymal tissue (meninges, perivascular space, and choroid plexus) are richly populated in resident immune cells. The advent of more powerful tools for multiplex immunophenotyping, such as single-cell RNA sequencing technique and upscale multiparametric flow and mass spectrometry, helped in discriminating between resident and infiltrating cells and, above all, the different spectrum of phenotypes distinguishing border-associated macrophages. Here, we focus our attention on resident innate immune players and their primary role in both CNS homeostasis and pathological neuroinflammation and neurodegeneration, two key interconnected aspects of the immunopathology of multiple sclerosis.

Molecular differences between neonatal and adult stria vascularis from organotypic explants and transcriptomics

Summary

The stria vascularis (SV), part of the blood-labyrinth barrier, is an essential component of the inner ear that regulates the ionic environment required for hearing. SV degeneration disrupts cochlear homeostasis, leading to irreversible hearing loss, yet a comprehensive understanding of the SV, and consequently therapeutic availability for SV degeneration, is lacking. We developed a whole-tissue explant model from neonatal and adult mice to create a robust platform for SV research. We validated our model by demonstrating that the proliferative behaviour of the SV in vitro mimics SV in vivo, providing a representative model and advancing high-throughput SV research. We also provided evidence for pharmacological intervention in our system by investigating the role of Wnt/β-catenin signaling in SV proliferation. Finally, we performed single-cell RNA sequencing from in vivo neonatal and adult mouse SV and revealed key genes and pathways that may play a role in SV proliferation and maintenance. Together, our results contribute new insights into investigating biological solutions for SV-associated hearing loss.

Significance

Hearing loss impairs our ability to communicate with people and interact with our environment. This can lead to social isolation, depression, cognitive deficits, and dementia. Inner ear degeneration is a primary cause of hearing loss, and our study provides an in depth look at one of the major sites of inner ear degeneration: the stria vascularis. The stria vascularis and associated blood-labyrinth barrier maintain the functional integrity of the auditory system, yet it is relatively understudied. By developing a new in vitro model for the young and adult stria vascularis and using single cell RNA sequencing, our study provides a novel approach to studying this tissue, contributing new insights and widespread implications for auditory neuroscience and regenerative medicine.

Highlights

- We established an organotypic explant system of the neonatal and adult stria vascularis with an intact blood-labyrinth barrier. - Proliferation of the stria vascularis decreases with age in vitro , modelling its proliferative behaviour in vivo . - Pharmacological studies using our in vitro SV model open possibilities for testing injury paradigms and therapeutic interventions. - Inhibition of Wnt signalling decreases proliferation in neonatal stria vascularis.- We identified key genes and transcription factors unique to developing and mature SV cell types using single cell RNA sequencing.

A novel model of sensorineural hearing loss induced by repeated exposure to moderate noise in mice: the preventive effect of resveratrol

Sensorineural hearing loss (SNHL) induced by noise has increased in recent years due to personal headphone use and noisy urban environments. The study shows a novel model of gradually progressive SNHL induced by repeated exposure to moderate noise (8-kHz octave band noise, 90-dB sound pressure level) for 1 hr exposure per day in BALB/cCr mice. The results showed that the repeated exposure led to gradually progressive SNHL, which was dependent on the number of exposures, and resulted in permanent hearing loss after 5 exposures. Repeated exposure to noise causes a loss of synapses between the inner hair cells and the peripheral terminals of the auditory nerve fibers. Additionally, there is a reduction in the expression levels of c-fos and Arc, both of which are indicators of cochlear nerve responses to noise exposure. Oral administration of resveratrol (RSV, 50 mg/kg/day) during the noise exposure period significantly prevented the noise exposure-induced synapse loss and SNHL. Furthermore, the study found that RSV treatment prevented the noise-induced increase in the gene expression levels of the proinflammatory cytokine interleukin-1β in the cochlea. These results demonstrated the potential usefulness of RSV in preventing noise-induced SNHL in the animal model established as gradually progressive SNHL.

Blood-Labyrinth Barrier in Health and Diseases: Effect of Hormetic Nutrients

Significance: The stria vascularis, located in the inner ear, consists of three layers, one of which is the blood-labyrinth barrier (BLB). It is formed by endothelial cells, sealed together to prevent the passage of toxic substances from the blood to the inner ear, by pericytes and perivascular-resident macrophage-like melanocyte. Recent Advances: There are various causes that lead to hearing loss, and among these are noise-induced and autoimmune hearing loss, ear disorders related to ototoxic medication, Ménière's disease, and age-related hearing loss. For all of these, major therapeutic interventions include drug-loaded nanoparticles, via intratympanic or intracochlear delivery. Critical Issues: Since many pathologies associated with hearing loss are characterized by a weakening of the BLB, in this review, the molecular mechanisms underlying the response to damage of BLB cellular components have been discussed. In addition, insight into the role of hormetic nutrients against hearing loss pathology is proposed. Future Directions: BLB cellular components of neurovascular cochlear unit play important physiological roles, owing to their impermeable function against all ototoxic substances that can induce damage. Studies are needed to investigate the cross talk occurring between these cellular components to exploit their possible role as novel targets for therapeutic interventions that may unravel future path based on the use of hormetic nutrients. Antioxid. Redox Signal. 40, 542-563.

Reactive Oxygen Species-Related Disruptions to Cochlear Hair Cell and Stria Vascularis Consequently Leading to Radiation-Induced Sensorineural Hearing Loss

Aims: Radiation-induced sensorineural hearing loss (RISNHL) is one of the major side effects of radiotherapy for head and neck cancers. At present, no effective clinical treatment or prevention is available for RISNHL. This study thus aimed to investigate the cochlear pathology so that the underlying mechanisms of RISNHL may be elucidated, consequently paving the way for potential protective strategies to be developed. Results: Functional and morphological impairment in the stria vascularis (SV) was observed after irradiation (IR), as indicated by endocochlear potential (EP) reduction, hyperpermeability, and SV atrophy. The expression of zonulae occludins-1 was found to have decreased after IR. The loss of outer hair cells (OHCs) occurred later than SV damage. The disruption to the SV and OHCs could be attributed to reactive oxygen species (ROS)-related damage. In addition, EP shifts and the loss of OHCs were reduced when ROS was reduced by N-acetylcysteine (NAC) in C57BL/6 mice, attenuating auditory threshold shifts. Innovation: The damage to the SV was found to occur before OHC loss. ROS-related damage accounted for SV damage and OHC loss. The incidences of SV damage and OHC loss were decreased through ROS modulation by NAC, subsequently preventing RISNHL, suggesting the possible role of NAC as a possible protective agent against RISNHL. Conclusion: The findings from this study suggest oxidative stress-induced early SV injury and late OHC loss to be the key factors leading to RISNHL. NAC prevents IR-induced OHC loss, and attenuates auditory brainstem response and EP shifts by regulating the level of oxidative stress. Antioxid. Redox Signal. 40, 470-491.

A critical evaluation of "leakage" at the cochlear blood-stria-barrier and its functional significance

The blood-labyrinth-barrier (BLB) is a semipermeable boundary between the vasculature and three separate fluid spaces of the inner ear, the perilymph, the endolymph and the intrastrial space. An important component of the BLB is the blood-stria-barrier, which shepherds the passage of ions and metabolites from strial capillaries into the intrastrial space. Some investigators have reported increased "leakage" from these capillaries following certain experimental interventions, or in the presence of inflammation or genetic variants. This leakage is generally thought to be harmful to cochlear function, principally by lowering the endocochlear potential (EP). Here, we examine evidence for this dogma. We find that strial capillaries are not exclusive, and that the asserted detrimental influence of strial capillary leakage is often confounded by hair cell damage or intrinsic dysfunction of the stria. The vast majority of previous reports speculate about the influence of strial vascular barrier function on the EP without directly measuring the EP. We argue that strial capillary leakage is common across conditions and species, and does not significantly impact the EP or hearing thresholds, either on evidentiary or theoretical grounds. Instead, strial capillary endothelial cells and pericytes are dynamic and allow permeability of varying degrees in response to specific conditions. We present observations from mice and demonstrate that the mechanisms of strial capillary transport are heterogeneous and inconsistent among inbred strains.

Complete Restoration of Hearing Loss and Cochlear Synaptopathy via Minimally Invasive, Single-Dose, and Controllable Middle Ear Delivery of Brain-Derived Neurotrophic Factor-Poly(dl-lactic acid-co-glycolic acid)-Loaded Hydrogel

Noise-induced hearing loss (NIHL) often accompanies cochlear synaptopathy, which can be potentially reversed to restore hearing. However, there has been little success in achieving complete recovery of sensorineural deafness using nearly noninvasive middle ear drug delivery before. Here, we present a study demonstrating the efficacy of a middle ear delivery system employing brain-derived neurotrophic factor (BDNF)-poly-(dl-lactic acid-co-glycolic acid) (PLGA)-loaded hydrogel in reversing synaptopathy and restoring hearing function in a mouse model with NIHL. The mouse model achieved using the single noise exposure (NE, 115 dBL, 4 h) exhibited an average 20 dBL elevation of hearing thresholds with intact cochlear hair cells but a loss of ribbon synapses as the primary cause of hearing impairment. We developed a BDNF-PLGA-loaded thermosensitive hydrogel, which was administered via a single controllable injection into the tympanic cavity of noise-exposed mice, allowing its presence in the middle ear for a duration of 2 weeks. This intervention resulted in complete restoration of NIHL at frequencies of click, 4, 8, 16, and 32 kHz. Moreover, the cochlear ribbon synapses exhibited significant recovery, whereas other cochlear components (hair cells and auditory nerves) remained unchanged. Additionally, the cochlea of NE treated mice revealed activation of tropomyosin receptor kinase B (TRKB) signaling upon exposure to BDNF. These findings demonstrate a controllable and minimally invasive therapeutic approach that utilizes a BDNF-PLGA-loaded hydrogel to restore NIHL by specifically repairing cochlear synaptopathy. This tailored middle ear delivery system holds great promise for achieving ideal clinical outcomes in the treatment of NIHL and cochlear synaptopathy.

Hyaluronic acid-ibuprofen conjugation: a novel ototherapeutic approach protecting inner ear cells from inflammation-mediated damage

There is a substantial need of effective drugs for the treatment of hearing loss, which affects nearly 500 million individuals globally. Hearing loss can be the result of intense or prolonged noise exposure, ototoxic drugs, infections, and trauma, which trigger inflammatory signaling cascades that lead to irreversible damage to cochlear structures. To address this, we developed and characterized a series of covalent conjugates of anti-inflammatory drugs to hyaluronic acid (HA), for potential use as topical ototherapeutics. These conjugates were tested in in vitro assays designed to mirror physiological processes typically observed with acoustic trauma. Intense noise exposure leads to macrophage recruitment to the cochlea and subsequent inflammatory damage to sensory cells. We therefore first tested our conjugates' ability to reduce the release of inflammatory cytokines in macrophages. This anti-inflammatory effect on macrophages also translated to increased cochlear cell viability. In our initial screening, one conjugate, ibuprofen-HA, demonstrated significantly higher anti-inflammatory potential than its counterparts. Subsequent cytokine release profiling of ibuprofen-HA further confirmed its ability to reduce a wider range of inflammatory markers, to a greater extent than its equivalent unconjugated drug. The conjugate's potential as a topical therapeutic was then assessed in previously developed tympanic and round window membrane tissue permeation models. As expected, our data indicate that the conjugate has limited tympanic membrane model permeability; however, it readily permeated the round window membrane model and to a greater extent than the unconjugated drug. Interestingly, our data also revealed that ibuprofen-HA was well tolerated in cellular and tissue cytocompatibility assays, whereas the unconjugated drug displayed significant cytotoxicity at equivalent concentrations. Moreover, our data highlighted the importance of chemical conjugation of ibuprofen to HA; the conjugate had improved anti-inflammatory effects, significantly reduced cytotoxicity, and is more suitable for therapeutic formulation. Overall, this work suggests that ibuprofen-HA could be a promising safe and effective topical ototherapeutic for inflammation-mediated cochlear damage.

CD163+ macrophages monitor enhanced permeability at the blood-dorsal root ganglion barrier

In dorsal root ganglia (DRG), macrophages reside close to sensory neurons and have largely been explored in the context of pain, nerve injury, and repair. However, we discovered that most DRG macrophages interact with and monitor the vasculature by sampling macromolecules from the blood. Characterization of the DRG vasculature revealed a specialized endothelial bed that transformed in molecular, structural, and permeability properties along the arteriovenous axis and was covered by macrophage-interacting pericytes and fibroblasts. Macrophage phagocytosis spatially aligned with peak endothelial permeability, a process regulated by enhanced caveolar transcytosis in endothelial cells. Profiling the DRG immune landscape revealed two subsets of perivascular macrophages with distinct transcriptome, turnover, and function. CD163+ macrophages self-maintained locally, specifically participated in vasculature monitoring, displayed distinct responses during peripheral inflammation, and were conserved in mouse and man. Our work provides a molecular explanation for the permeability of the blood-DRG barrier and identifies an unappreciated role of macrophages as integral components of the DRG-neurovascular unit.

Mitochondrial Regulation of Macrophages in Innate Immunity and Diverse Roles of Macrophages During Cochlear Inflammation

Macrophages are essential components of the innate immune system and constitute a non-specific first line of host defense against pathogens and inflammation. Mitochondria regulate macrophage activation and innate immune responses in various inflammatory diseases, including cochlear inflammation. The distribution, number, and morphological characteristics of cochlear macrophages change significantly across different inner ear regions under various pathological conditions, including noise exposure, ototoxicity, and age-related degeneration. However, the exact mechanism underlying the role of mitochondria in macrophages in auditory function remains unclear. Here, we summarize the major factors and mitochondrial signaling pathways (e.g., metabolism, mitochondrial reactive oxygen species, mitochondrial DNA, and the inflammasome) that influence macrophage activation in the innate immune response. In particular, we focus on the properties of cochlear macrophages, activated signaling pathways, and the secretion of inflammatory cytokines after acoustic injury. We hope this review will provide new perspectives and a basis for future research on cochlear inflammation.

Macrophage-related immune responses in inner ear: a potential therapeutic target for sensorineural hearing loss

Hearing loss is the most common sensory disorder in human beings. Cochlear sensory cells are the basis of hearing. Cochlear sensory cells suffer from various acute or chronic injuries, such as excessive sound stimulation, ototoxic drugs, and age-related degeneration. In response to these stresses, the cochlea develops an immune response. In recent years, studies have shown that the immune response of the inner ear has been regarded as one of the important pathological mechanisms of inner ear injury. Therapeutic interventions for inflammatory responses can effectively alleviate different types of inner ear injury. As the main immune cells in the inner ear, macrophages are involved in the process of inner ear injury caused by various exogenous factors. However, its specific role in the immune response of the inner ear is still unclear. This review focuses on discusses the dynamic changes of macrophages during different types of inner ear injury, and clarifies the potential role of macrophage-related immune response in inner ear injury.

Brain perivascular macrophages: current understanding and future prospects

Brain perivascular macrophages are specialized populations of macrophages that reside in the space around cerebral vessels, such as penetrating arteries and venules. With the help of cutting-edge technologies, such as cell fate mapping and single-cell multi-omics, their multifaceted, pivotal roles in phagocytosis, antigen presentation, vascular integrity maintenance and metabolic regulation have more recently been further revealed under physiological conditions. Accumulating evidence also implies that perivascular macrophages are involved in the pathogenesis of neurodegenerative disease, cerebrovascular dysfunction, autoimmune disease, traumatic brain injury and epilepsy. They can act in either protective or detrimental ways depending on the disease course and stage. However, the underlying mechanisms of perivascular macrophages remain largely unknown. Therefore, we highlight potential future directions in research on perivascular macrophages, including the utilization of genetic mice and novel therapeutic strategies that target these unique immune cells for neuroprotective purposes. In conclusion, this review provides a comprehensive update on the current knowledge of brain perivascular macrophages, shedding light on their pivotal roles in central nervous system health and disease.

Contribution of circulating monocytes in maintaining homeostasis of resident macrophages in postnatal and young adult mouse cochlea

The percentage of macrophage subpopulations based on their origins in the adult cochlea remains unclear. This study aimed to elucidate the origins of cochlear macrophages during the onset phase and development of auditory function. We used three types of mice: wildtype ICR mice, colony-stimulating factor 1 receptor (Csf1r)-deficient mice, and Ms4a3Cre-Rosa tdTomato (Ms4a3tdT) transgenic mice. Macrophages were labeled with ionized calcium-binding adapter molecule 1 (Iba1), which is specific to more mature macrophages, and CD11b, which is specific to monocyte lineage. We investigated the spatial and temporal distribution patterns of resident macrophages in the cochlea during the postnatal and early adult stages. During the adult stages, the rate of monocytes recruited from the systemic circulation increased; moreover, Iba1+/CD11b- cochlear macrophages gradually decreased with age. Fate mapping of monocytes using Ms4a3tdT transgenic mice revealed an increased proportion of bone marrow-derived cochlear macrophages in the adult stage. Contrastingly, the proportion of yolk sac- and fetal liver-derived tissue-resident macrophages decreased steadily with age. This heterogeneity could be attributed to differences in environmental niches within the tissue or at the sub-tissue levels. Future studies should investigate the role of cochlear macrophages in homeostasis, inflammation, and other diseases, including infection, autoimmune, and metabolic diseases.

Sound conditioning strategy promoting paracellular permeability of the blood-labyrinth-barrier benefits inner ear drug delivery

The therapeutic effects of pharmaceuticals depend on their drug concentrations in the cochlea. Efficient drug delivery from the systemic circulation into the inner ear is limited by the blood-labyrinth-barrier (BLB). This study investigated a novel noninvasive sound conditioning (SC) strategy (90 dB SPL, 8-16 kHz, 2 h sound exposure) to temporally enhance BLB permeability in a controllable way, contributing to maximizing the penetration of pharmaceuticals from blood circulation into the cochlea. Trafficking of Fluorescein Isothiocyanate conjugated dextran and bovine serum albumin (FITC-dextran and FITC-BSA) demonstrated that paracellular leakage of BLB sustained for 6 h after SC, providing a controllable time window for systemic administration. Cochlear concentrations of dexamethasone (DEX) and dexamethasone phosphate (DEX-P), respectively transported by transcellular and paracellular pathways, showed a higher content of the latter one after SC, further confirming the key role of paracellular pathway in the SC-induced hyperpermeability. Results of high-throughput RNA-sequencing identified a series of tight junction (TJ)-associated genes after SC. The expressions of TJ (ZO-1) were reduced and irregular rearrangements of the junction were observed by transmission electron microscopy after SC. We further determined the inhibiting role of Rab13 in the recruitment of ZO-1 and later in the regulation of cellular permeability. Meanwhile, no significant change in the quantifications of endothelial caveolae vesicles after SC indicated that cellular transcytosis accounted little for the temporary hyperpermeability after SC. Based on these results, SC enhances the BLB permeability within 6 h and allows systemically applied drugs which tend to be transported by paracellular pathway to readily enter the inner ear, contributing to guiding the clinical medications on hearing loss.

Molecular Characteristics of Cisplatin-Induced Ototoxicity and Therapeutic Interventions

Cisplatin is a commonly used chemotherapeutic agent with proven efficacy in treating various malignancies, including testicular, ovarian, cervical, breast, bladder, head and neck, and lung cancer. Cisplatin is also used to treat tumors in children, such as neuroblastoma, osteosarcoma, and hepatoblastoma. However, its clinical use is limited by severe side effects, including ototoxicity, nephrotoxicity, neurotoxicity, hepatotoxicity, gastrointestinal toxicity, and retinal toxicity. Cisplatin-induced ototoxicity manifests as irreversible, bilateral, high-frequency sensorineural hearing loss in 40-60% of adults and in up to 60% of children. Hearing loss can lead to social isolation, depression, and cognitive decline in adults, and speech and language developmental delays in children. Cisplatin causes hair cell death by forming DNA adducts, mitochondrial dysfunction, oxidative stress, and inflammation, culminating in programmed cell death by apoptosis, necroptosis, pyroptosis, or ferroptosis. Contemporary medical interventions for cisplatin ototoxicity are limited to prosthetic devices, such as hearing aids, but these have significant limitations because the cochlea remains damaged. Recently, the U.S. Food and Drug Administration (FDA) approved the first therapy, sodium thiosulfate, to prevent cisplatin-induced hearing loss in pediatric patients with localized, non-metastatic solid tumors. Other pharmacological treatments for cisplatin ototoxicity are in various stages of preclinical and clinical development. This narrative review aims to highlight the molecular mechanisms involved in cisplatin-induced ototoxicity, focusing on cochlear inflammation, and shed light on potential antioxidant and anti-inflammatory therapeutic interventions to prevent or mitigate the ototoxic effects of cisplatin. We conducted a comprehensive literature search (Google Scholar, PubMed) focusing on publications in the last five years.

Macrophage Depletion Protects Against Cisplatin-Induced Ototoxicity and Nephrotoxicity

Cisplatin is a widely used and highly effective anti-cancer drug with significant side effects including ototoxicity and nephrotoxicity. Macrophages, the major resident immune cells in the cochlea and kidney, are important drivers of both inflammatory and tissue repair responses. To investigate the roles of macrophages in cisplatin-induced ototoxicity and nephrotoxicity, we used PLX3397, an FDA-approved inhibitor of the colony-stimulating factor 1 receptor (CSF1R), to eliminate tissue-resident macrophages during the course of cisplatin administration. Mice treated with cisplatin alone (cisplatin/vehicle) had significant hearing loss (ototoxicity) as well as kidney injury (nephrotoxicity). Macrophage ablation using PLX3397 resulted in significantly reduced hearing loss measured by auditory brainstem responses (ABR) and distortion-product otoacoustic emissions (DPOAE). Sensory hair cells in the cochlea were protected against cisplatin-induced death in mice treated with PLX3397. Macrophage ablation also protected against cisplatin-induced nephrotoxicity, as evidenced by markedly reduced tubular injury and fibrosis as well as reduced plasma blood urea nitrogen (BUN) and neutrophil gelatinase-associated lipocalin (NGAL) levels. Mechanistically, our data suggest that the protective effect of macrophage ablation against cisplatin-induced ototoxicity and nephrotoxicity is mediated by reduced platinum accumulation in both the inner ear and the kidney. Together our data indicate that ablation of tissue-resident macrophages represents a novel strategy for mitigating cisplatin-induced ototoxicity and nephrotoxicity.

Human blood-labyrinth barrier model to study the effects of cytokines and inflammation

Hearing loss is one of the 10 leading causes of disability worldwide. No drug therapies are currently available to protect or restore hearing. Inner ear auditory hair cells and the blood-labyrinth barrier (BLB) are critical for normal hearing, and the BLB between the systemic circulation and stria vascularis is crucial for maintaining cochlear and vestibular homeostasis. BLB defects are associated with inner ear diseases that lead to hearing loss, including vascular malformations, inflammation, and Meniere's disease (MD). Antibodies against proteins in the inner ear and cytokines in the cochlea, including IL-1α, TNF-α, and NF-kβ, are detected in the blood of more than half of MD patients. There is also emerging evidence of inner ear inflammation in some diseases, including MD, progressive sensorineural hearing loss, otosclerosis, and sudden deafness. Here, we examined the effects of TNF-α, IL6, and LPS on human stria vascularis-derived primary endothelial cells cultured together with pericytes in a Transwell system. By measuring trans-endothelial electrical resistance, we found that TNF-α causes the most significant disruption of the endothelial barrier. IL6 had a moderate influence on the barrier, whereas LPS had a minimal impact on barrier integrity. The prominent effect of TNF-α on the barrier was confirmed in the expression of the major junctional genes responsible for forming the tight endothelial monolayer, the decreased expression of ZO1 and OCL. We further tested permeability using 2 μg of daptomycin (1,619 Da), which does not pass the BLB under normal conditions, by measuring its passage through the barrier by HPLC. Treatment with TNF-α resulted in higher permeability in treated samples compared to controls. LPS-treated cells behaved similarly to the untreated cells and did not show differences in permeability compared to control. The endothelial damage caused by TNF-α was confirmed by decreased expression of an essential endothelial proteoglycan, syndecan1. These results allowed us to create an inflammatory environment model that increased BLB permeability in culture and mimicked an inflammatory state within the stria vascularis.

Distribution of macrophages in the developing cochlea of the common marmoset, a primate model animal

Introduction

Macrophages are essential immune cells in the cochlea that contribute to inflammation, tissue repair, and homeostasis. They also play an important role in local cochlear immunity. The developmental immigration and maturation of macrophages in the cochlea have been investigated and are considered essential for normal hearing acquisition. Most of our current knowledge regarding cochlear development is based on rodent models because of the ethical challenges of using human fetal samples for research. However, inter-species differences between rodents and humans have been reported. In this study, we used a primate animal model to investigate the distributions of macrophages in the developing cochlea. The common marmoset (Callithrix jacchus), a small monkey species that inhabits the New World, was used as the model.

Methods

We investigated the distribution of macrophages in the developing cochlea of the common marmoset by performing immunohistochemical analyses of cochlear tissue from common marmoset embryos at different development stages.

Results

We revealed detailed distribution changes in the macrophages of a primate animal model cochlea. This observation indicates that most of the changes in the general distribution of macrophages were well preserved between rodents and this primate. The distribution changes observed in the common marmoset were also compatible with observations in the human fetus; although, observations in the human fetus are limited. Our observations in this study also revealed several differences between common marmosets and rodents.

Conclusion

The time course of immunological development and maturations established in this study will aid in the study of the primate-specific developmental biology of the inner ear. These observations may eventually lead to new therapeutic strategies for hearing loss in humans. In addition, understanding the immunological steady-state of the cochlea may help in the study of age- and genetic-induced hearing loss and in the design of regenerative therapies.

Towards an Understanding of Microglia and Border-Associated Macrophages

The central nervous system (CNS) plays a crucial role in regulating bodily functions by sensing and integrating environmental cues and maintaining proper physiological conditions. Recent research has revealed that CNS functions are closely coordinated with the immune system. As even minor disturbances of the immune system in the CNS can lead to various dysfunctions, diseases, or even death, it is highly specialized and segregated from that in peripheral regions. Microglia in the parenchyma and macrophages at the interface between the CNS and peripheral regions are essential immune cells in the CNS that monitor environmental changes. Recent omics analyses have revealed that these cells exhibit highly heterogeneous populations. In this review, we summarize the functions and diversity of microglia in the brain parenchyma and those of macrophages in the border regions, such as the meninges, perivascular spaces, and choroid plexus.

Cochlear implant surgery facilitates intracochlear distribution of perioperative systemic steroids

BACKGROUND

Systemically administered steroids are widely utilised for hearing preservation therapies. More recently, steroids have been administered to achieve hearing protection after cochlear implant surgery. Currently there is a lack of understanding as to which administration route offers most therapeutic efficacy, local or systemic administration. Paramount to this are observations in animal studies that systemic administration following implantation offers hearing protection and reduced cochlear fibrosis, despite observations that perilymphatic levels are up to 10-fold higher after local administration in non-implanted cochleae.

AIMS/OBJECTIVES

This paper explores the impact that cochlear implantation and associated acute inflammation has on steroid distribution and uptake following systemic administration of dexamethasone.

MATERIAL AND METHODS

Eight guinea pigs received systemic dexamethasone 60 min prior to cochlear implantation. Implanted and contralateral non-implanted cochlea were harvested for tissue immunohistochemistry and detection of dexamethasone.

RESULTS

Cochleostomy with scala tympani implantation resulted in a significant increase in cochlear dexamethasone signal. This was most notable at the organ of Corti, stria vascularis, and blood product in the scala tympani.

CONCLUSIONS AND SIGNIFICANCE

This study demonstrates that the inner ear distribution of systemically administered steroids is enhanced following surgery for cochlear implantation and provides rationale for systemic perioperative steroids in hearing preservation surgery.

Complement factor B is essential for the proper function of the peripheral auditory system

Sensorineural hearing loss is associated with dysfunction of cochlear cells. Although immune cells play a critical role in maintaining the inner ear microenvironment, the precise immune-related molecular mechanisms underlying the pathophysiology of hearing loss remain unclear. The complement cascade contributes to the regulation of immune cell activity. Additionally, activation of the complement cascade can lead to the cellular opsonization of cells and pathogens, resulting in their engulfment and elimination by phagocytes. Complement factor B (fB) is an essential activator protein in the alternative complement pathway, and variations in the fB gene are associated with age-related macular degeneration. Here we show that mice of both sexes deficient in fB functional alleles (fB-/-) demonstrate progressive hearing impairment. Transcriptomic analysis of auditory nerves from adult mice detected 706 genes that were significantly differentially expressed between fB-/- and wild-type control animals, including genes related to the extracellular matrix and neural development processes. Additionally, a subset of differentially expressed genes was related to myelin function and neural crest development. Histological and immunohistochemical investigations revealed pathological alterations in auditory nerve myelin sheathes of fB-/- mice. Pathological alterations were also seen in the stria vascularis of the cochlear lateral wall in these mice. Our results implicate fB as an integral regulator of myelin maintenance and stria vascularis integrity, underscoring the importance of understanding the involvement of immune signaling pathways in sensorineural hearing loss.

Intrinsic mechanism and pharmacologic treatments of noise-induced hearing loss

Noise accounts for one-third of hearing loss worldwide. Regretfully, noise-induced hearing loss (NIHL) is deemed to be irreversible due to the elusive pathogenic mechanisms that have not been fully elucidated. The complex interaction between genetic and environmental factors, which influences numerous downstream molecular and cellular events, contributes to the NIHL. In clinical settings, there are no effective therapeutic drugs other than steroids, which are the only treatment option for patients with NIHL. Therefore, the need for treatment of NIHL that is currently unmet, along with recent progress in our understanding of the underlying regulatory mechanisms, has led to a lot of new literatures focusing on this therapeutic field. The emergence of novel technologies that modify local drug delivery to the inner ear has led to the development of promising therapeutic approaches, which are currently under clinical investigation. In this comprehensive review, we focus on outlining and analyzing the basics and potential therapeutics of NIHL, as well as the application of biomaterials and nanomedicines in inner ear drug delivery. The objective of this review is to provide an incentive for NIHL's fundamental research and future clinical translation.

Immune responses in the mammalian inner ear and their implications for AAV-mediated inner ear gene therapy

Adeno-associated virus (AAV)-mediated inner ear gene therapy is a promising treatment option for hearing loss and dizziness. Several studies have shown that AAV-mediated inner ear gene therapy can be applied to various mouse models of hereditary hearing loss to improve their auditory function. Despite the increase in AAV-based animal and clinical studies aiming to rescue auditory and vestibular functions, little is currently known about the host immune responses to AAV in the mammalian inner ear. It has been reported that the host immune response plays an important role in the safety and efficacy of viral-mediated gene therapy. Therefore, in order for AAV-mediated gene therapy to be successfully and safely translated into patients with hearing loss and dizziness, a better understanding of the host immune responses to AAV in the inner ear is critical. In this review, we summarize the current knowledge on host immune responses to AAV-mediated gene therapy in the mammalian inner ear and other organ systems. We also outline the areas of research that are critical for ensuring the safety and efficacy of AAV-mediated inner ear gene therapy in future clinical and translational studies.

Chemiexcitation: Mammalian Photochemistry in the Dark†

Light is one way to excite an electron in biology. Another is chemiexcitation, birthing a reaction product in an electronically excited state rather than exciting from the ground state. Chemiexcited molecules, as in bioluminescence, can release more energy than ATP. Excited states also allow bond rearrangements forbidden in ground states. Molecules with low-lying unoccupied orbitals, abundant in biology, are particularly susceptible. In mammals, chemiexcitation was discovered to transfer energy from excited melanin, neurotransmitters, or hormones to DNA, creating the lethal and carcinogenic cyclobutane pyrimidine dimer. That process was initiated by nitric oxide and superoxide, radicals triggered by ultraviolet light or inflammation. Several poorly understood chronic diseases share two properties: inflammation generates those radicals across the tissue, and cells that die are those containing melanin or neuromelanin. Chemiexcitation may therefore be a pathogenic event in noise- and drug-induced deafness, Parkinson's disease, and Alzheimer's; it may prevent macular degeneration early in life but turn pathogenic later. Beneficial evolutionary selection for excitable biomolecules may thus have conferred an Achilles heel. This review of recent findings on chemiexcitation in mammalian cells also describes the underlying physics, biochemistry, and potential pathogenesis, with the goal of making this interdisciplinary phenomenon accessible to researchers within each field.

Three-dimensional mouse cochlea imaging based on the modified Sca/eS using confocal microscopy

The three-dimensional stria vascularis (SV) and cochlear blood vessel structure is essential for inner ear function. Here, modified Sca/eS, a sorbitol-based optical-clearing method, was reported to visualize SV and vascular structure in the intact mouse cochlea. Cochlear macrophages as well as perivascular-resident macrophage-like melanocytes were detected as GFP-positive cells of the CX3CR1^+/GFP mice. This study's method was effective in elucidating inner ear function under both physiological and pathological conditions.

Angiotropic melanocytes: Possibly a distinctive finding in extra-facial acquired dermal melanocytosis

BACKGROUND

Acquired dermal melanocytosis is a heterogenous group of hyperpigmented lesioins which predominantly involve the face.

AIM

The aim of this study was to study the clinical presentation and histopathology of cases with extra-facial acquired dermal melanocytosis.

METHODS

Retrospective record analysis was performed between May 2016 to August 2019 to retrieve cases of extra-facial acquired dermal melanocytosis seen at the out-patient department of dermatology at the All India Institute of Medical Sciences, Jodhpur. Consecutive cases with histopathologically proven diagnosis of acquired dermal melanocytosis were included. Documentation of variation in clinical presentation and histopathologic findings was done in light of the existing literature.

RESULTS

Overall, four cases of extra-facial acquired dermal melanocyosis (female:male = 1:3) were seen during the study period. The lone case on head and neck involved the ear lobule and peri-auricular area. The other three cases had involvement of the hand. The histopathology confirmed the diagnosis of dermal melanocytosis but revealed peculiar findings of angiotropic melanocytes and dilated capillaries.

LIMITATIONS

Small sample size and lack of comparison with perilesional normal skin were the limitations of this study.

CONCLUSION

The findings of angiotropic melanocytes may be unique to extra-facial acquired dermal melanocytosis. This might indicate interaction between dermal melanocytes and capillary endothelial cells. This finding along with dermal capillary ectasia may indicate a possible role for vascular lasers in the management of these disorders.

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.

Protective effect of anakinra on audiovestibular function in a murine model of endolymphatic hydrops

Introduction

Ménière's disease (MD), a common disease in the inner ear, is characterized by an increase in endolymph in the cochlear duct and vestibular labyrinth. The pathophysiology of the condition appears to be the immune response. Studies have shown that basal levels of the IL-1β increased in some MD patients.

Methods

Here, we used a murine model of endolymphatic hydrops (EH) to study the effect of anakinra on auditory and vestibular function. Mice were intraperitoneal injected with anakinra or saline before LPS by postauricular injection. Weight and disease severity were measured, histologic changes in auditory were assessed, and inflammation state was evaluated.

Results

We found that anakinra therapy reduced LPS-induced EH, alleviated LPS-induced hearing loss and vestibular dysfunction, and inhibited the expression of the inflammatory cytokines and macrophage infiltration in the cochlea of mice. We further demonstrated that anakinra ameliorated the disorganization and degeneration of myelin sheath, and reduced the neuron damage in cochlea of EH mice.

Discussion

Consequently, anakinra contributes to a promising therapeutic approach to MD, by restricting EH, alleviating auditory and vestibular function, inhibiting inflammation of the inner ear and protecting the cochlear nerve. Further investigations are needed to assess the potential therapeutic benefits of anakinra in patients with MD.

Macrophages in health and disease

The heterogeneity of tissue macrophages, in health and in disease, has become increasingly transparent over the last decade. But with the plethora of data comes a natural need for organization and the design of a conceptual framework for how we can better understand the origins and functions of different macrophages. We propose that the ontogeny of a macrophage-beyond its fundamental derivation as either embryonically or bone marrow-derived, but rather inclusive of the course of its differentiation, amidst steady-state cues, disease-associated signals, and time-constitutes a critical piece of information about its contribution to homeostasis or the progression of disease.

Update on Findings about Sudden Sensorineural Hearing Loss and Insight into Its Pathogenesis

Sudden sensorineural hearing loss (SSNHL) is routinely encountered and is one of the most common emergent diseases in otolaryngology clinics. However, the etiology of SSNHL remains unclear. Due to the inaccessibility of the living human inner ear for biopsy, studies investigating the etiology of SSNHL have been performed by analyzing data obtained from examinations using peripheral blood or imaging. We updated the findings obtained from serological, magnetic resonance imaging, genetic, and viral examinations to reveal the etiology of SSNHL. Regarding viral examination, we focused on sensorineural hearing loss associated with coronavirus disease (COVID-19) because the number of correlated reports has been increasing after the outbreak. The updated findings revealed the following three possible mechanisms underlying the development of SSNHL: thrombosis and resulting vascular obstruction in the cochlea, asymptomatic viral infection and resulting damage to the cochlea, and cochlear inflammation and resulting damage to the cochlea. Thrombosis and viral infection are predominant, and cochlear inflammation can be secondarily induced through viral infection or even thrombosis. The findings about sensorineural hearing loss associated with COVID-19 supported the possibility that asymptomatic viral infection is one of the etiologies of SSNHL, and the virus can infect inner ear tissues and directly damage them.

Peripheral Auditory Nerve Impairment in a Mouse Model of Syndromic Autism

Dysfunction of the peripheral auditory nerve (AN) contributes to dynamic changes throughout the central auditory system, resulting in abnormal auditory processing, including hypersensitivity. Altered sound sensitivity is frequently observed in autism spectrum disorder (ASD), suggesting that AN deficits and changes in auditory information processing may contribute to ASD-associated symptoms, including social communication deficits and hyperacusis. The MEF2C transcription factor is associated with risk for several neurodevelopmental disorders, and mutations or deletions of MEF2C produce a haploinsufficiency syndrome characterized by ASD, language, and cognitive deficits. A mouse model of this syndromic ASD (Mef2c-Het) recapitulates many of the MEF2C haploinsufficiency syndrome-linked behaviors, including communication deficits. We show here that Mef2c-Het mice of both sexes exhibit functional impairment of the peripheral AN and a modest reduction in hearing sensitivity. We find that MEF2C is expressed during development in multiple AN and cochlear cell types; and in Mef2c-Het mice, we observe multiple cellular and molecular alterations associated with the AN, including abnormal myelination, neuronal degeneration, neuronal mitochondria dysfunction, and increased macrophage activation and cochlear inflammation. These results reveal the importance of MEF2C function in inner ear development and function and the engagement of immune cells and other non-neuronal cells, which suggests that microglia/macrophages and other non-neuronal cells might contribute, directly or indirectly, to AN dysfunction and ASD-related phenotypes. Finally, our study establishes a comprehensive approach for characterizing AN function at the physiological, cellular, and molecular levels in mice, which can be applied to animal models with a wide range of human auditory processing impairments.SIGNIFICANCE STATEMENT This is the first report of peripheral auditory nerve (AN) impairment in a mouse model of human MEF2C haploinsufficiency syndrome that has well-characterized ASD-related behaviors, including communication deficits, hyperactivity, repetitive behavior, and social deficits. We identify multiple underlying cellular, subcellular, and molecular abnormalities that may contribute to peripheral AN impairment. Our findings also highlight the important roles of immune cells (e.g., cochlear macrophages) and other non-neuronal elements (e.g., glial cells and cells in the stria vascularis) in auditory impairment in ASD. The methodological significance of the study is the establishment of a comprehensive approach for evaluating peripheral AN function and impact of peripheral AN deficits with minimal hearing loss.

Chronic suppurative otitis media causes macrophage-associated sensorineural hearing loss

Background

Chronic suppurative otitis media (CSOM) is the most common cause of permanent hearing loss in children in the developing world. A large component of the permanent hearing loss is sensory in nature and our understanding of the mechanism of this has so far been limited to post-mortem human specimens or acute infection models that are not representative of human CSOM. In this report, we assess cochlear injury in a validated Pseudomonas aeruginosa (PA) CSOM mouse model.

Methods

We generated persisters (PCs) and inoculated them into the mouse middle ear cavity. We tracked infection with IVIS and detected PA using RT-PCR. We assessed cochlear damage and innate immunity by Immunohistochemistry. Finally, we evaluated cytokines with multiplex assay and quantitative real-time PCR.

Results

We observed outer hair cell (OHC) loss predominantly in the basal turn of the cochlear at 14 days after bacterial inoculation. Macrophages, not neutrophils are the major immune cells in the cochlea in CSOM displaying increased numbers and a distribution correlated with the observed cochlear injury. The progression of the morphological changes suggests a transition from monocytes into tissue macrophages following infection. We also show that PA do not enter the cochlea and live bacteria are required for cochlear injury. We characterized cytokine activity in the CSOM cochlea.

Conclusions

Taken together, this data shows a critical role for macrophages in CSOM-mediated sensorineural hearing loss (SNHL).

Supplementary Information

The online version contains supplementary material available at 10.1186/s12974-022-02585-w.

Visualization of macrophage subsets in the development of the fetal human inner ear

Background

Human inner ear contains macrophages whose functional role in early development is yet unclear. Recent studies describe inner ear macrophages act as effector cells of the innate immune system and are often activated following acoustic trauma or exposure to ototoxic drugs. Few or limited literature describing the role of macrophages during inner ear development and organogenesis.

Material and Methods

We performed a study combining immunohistochemistry and immunofluorescence using antibodies against IBA1, CX3CL1, CD168, CD68, CD45 and CollagenIV. Immune staining and quantification was performed on human embryonic inner ear sections from gestational week 09 to 17.

Results

The study showed IBA1 and CD45 positive cells in the mesenchymal tissue at GW 09 to GW17. No IBA1 positive macrophages were detected in the sensory epithelium of the cochlea and vestibulum. Fractalkine (CX3CL1) signalling was initiated GW10 and parallel chemotactic attraction and migration of macrophages into the inner ear. Macrophages also migrated into the spiral ganglion, cochlear nerve, and peripheral nerve fibers and tissue-expressing CX3CL1. The mesenchymal tissue at all gestational weeks expressed CD163 and CD68.

Conclusion

Expressions of markers for resident and non-resident macrophages (IBA1, CD45, CD68, and CD163) were identified in the human fetal inner ear. We speculate that these cells play a role for the development of human inner ear tissue including shaping of the gracile structures.

Tumor necrosis factor-α mediated inflammation versus apoptosis in age-related hearing loss

An almost universal phenomenon occurring during aging is a state of chronic, low-grade, sterile inflammation. Inflammation is a crucial contributor to various age-related pathologies and natural processes in aging tissues. Tumor necrosis factor-α (TNF-α), a master regulator of the immune system, plays an important role in the propagation of inflammation. Recent research has found correlations between hearing loss and markers such as TNF-α. However, the intrinsic molecular mechanism by which TNF-α influences aging individuals’ increased risk of hearing loss remains unclear. In this study, we found that TNF-α expression gradually increased with age in DBA/2J mice. We then used recombinant TNF-α to upregulate TNF-α levels in House Ear Institute-Organ of Corti 1 (HEI-OC1) cells and found that low concentrations of TNF-α could activate the nuclear factor kappa B (NF-κB) transcriptional response to mediate hair cell survival, while high concentrations of TNF-α could activate the Caspase-3 cascade to mediate hair cell apoptosis, which preliminarily confirmed that a TNF-α mediated signaling pathway plays an important role in the pathogenesis of age-related hearing loss.

Otologic Manifestations of Psoriasis: A Systematic Review and Meta-Analysis

INTRODUCTION

Psoriatic skin lesions are often seen in the auricle and external auditory canal, but middle ear and inner ear manifestations are not easily identified. Several studies have indicated hearing loss and vestibular dysfunction with psoriasis, but the extent of association has not been well defined.

METHODS

A systematic search of PubMed, CINAHL, Scopus, and Cochrane Library was conducted following Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines. Included studies described audiometric or vestibular assessment of psoriasis patients. Meta-analysis was represented with odds ratios (ORs) or mean difference (MD) with 95% confidence intervals.

RESULTS

A total of 13 studies with 589 psoriasis patients and 617 healthy controls were included. Age did not significantly differ between psoriasis patients (47.1 [12.4] yr) and healthy controls (45.4 [11.2] yr). Psoriasis area and severity index score was 9.9 (8.4), and body surface area scores was 7.9 (14.7). Pure-tone audiometry analysis showed higher mean hearing thresholds in psoriasis patients compared with healthy controls across all frequencies, with the greatest difference at 4000 Hz (MD, 7.70 [4.46-10.94]; p < 0.00001). Speech reception thresholds were worse with psoriasis (MD, 3.53 [1.56-5.49]; p < 0.0001). Abnormal stapedial reflex was more common in psoriasis (OR, 5.19 [1.68-15.99]; p = 0.004). Abnormal vestibular testing was more common in psoriasis for caloric testing (OR, 13.12 [2.88-59.84]; p < 0.0001). Two additional studies of 41,681 psoriasis patients and 80,273 healthy controls found that psoriasis patients were at higher risk for sudden sensorineural hearing loss (OR, 1.50 [1.25-1.80]; p < 0.0001).

CONCLUSION

Our study shows that psoriasis is associated with hearing loss and vestibular dysfunction, but clinical significance remains undefined. The trends noted in our study require more investigation, and the pathophysiologic mechanisms need to be defined.

Recognition of Melanocytes in Immuno-Neuroendocrinology and Circadian Rhythms: Beyond the Conventional Melanin Synthesis

Melanocytes produce melanin to protect the skin from UV-B radiation. Notwithstanding, the spectrum of their functions extends far beyond their well-known role as melanin production factories. Melanocytes have been considered as sensory and computational cells. The neurotransmitters, neuropeptides, and other hormones produced by melanocytes make them part of the skin’s well-orchestrated and complex neuroendocrine network, counteracting environmental stressors. Melanocytes can also actively mediate the epidermal immune response. Melanocytes are equipped with ectopic sensory systems similar to the eye and nose and can sense light and odor. The ubiquitous inner circadian rhythm controls the body’s basic physiological processes. Light not only affects skin photoaging, but also regulates inner circadian rhythms and communicates with the local neuroendocrine system. Do melanocytes “see” light and play a unique role in photoentrainment of the local circadian clock system? Why, then, are melanocytes responsible for so many mysterious functions? Do these complex functional devices work to maintain homeostasis locally and throughout the body? In addition, melanocytes have also been shown to be localized in internal sites such as the inner ear, brain, and heart, locations not stimulated by sunlight. Thus, what can the observation of extracutaneous melanocytes tell us about the “secret identity” of melanocytes? While the answers to some of these intriguing questions remain to be discovered, here we summarize and weave a thread around available data to explore the established and potential roles of melanocytes in the biological communication of skin and systemic homeostasis, and elaborate on important open issues and propose ways forward.

Auditory Phenotype and Histopathologic Findings of a Mutant Nlrp3 Expression Mouse Model

Objective

The pathogenesis of hearing loss in autoinflammatory disorders due to activation of the inflammasome remains incompletely understood. Previously no animals expressing mutant Nlrp3 (NOD-, LRR- and pyrin domain-containing protein 3) survived to an age when hearing evaluation was possible due to embryonic lethality. We aimed to establish a novel mouse model that manifests quantifiable hearing loss with other syndromic features due to alteration of Nlrp3 and investigate the audiologic and histopathologic phenotype in the cochlea to clarify how the genetic alterations of NLRP3 could induce autoinflammatory hearing loss.

Methods

To induce inner ear expression of the mutant Nlrp3, Nlrp3^D301NneoR mice were bred with Gfi1^Cre knock-in mice for conditional mutant Nlrp3 activation in the cochlea and hematopoietic cells. Hearing thresholds were measured. Hematoxylin-eosin sections of the cochlea, brain, kidney, and liver were examined under light microscopy. Immunohistochemical analyses using polyclonal anti-NLRP3 antibodies on cochlear whole-mount preparations and frozen sections were performed.

Results

We, for the first time in the literature, established a mouse model that manifests quantifiable hearing loss due to Nlrp3 alteration. ABR recordings of Nlrp3^D301NneoR/+; Gfi1^Cre/+ mice, albeit with limited life expectancy, exhibited severe to profound hearing loss at postnatal day 20 (P20). There was overall overexpression of mutant Nlrp3, and mutant Nlrp3 expression was noted in the spiral prominence, the outer sulcus region (Claudius cells and outer sulcus cells), the organ of Corti, the inner sulcus, and the spiral ganglion neurons in the cochlea. The hematoxylin-eosin sections of Nlrp3^D301NneoR/+; Gfi1^Cre/+ mice cochleae at P12 exhibited a disorganized organ of Corti between the outer hair cells/supporting Deiters' cells and basilar membrane compared with the normal phenotype mice, leading to a collapsed Nuel's space. This morphologic feature gradually returned to normal by P15. Varying degrees of inflammation with lymphocytic infiltrations were observed in the brain, kidney, and liver.

Conclusion

We report the first mutant Nlrp3 overexpression mouse model (Nlrp3^D301NneoR/+; Gfi1^Cre/+) that shows obvious overexpression of Nlrp3 in the cochlea, a transient developmental lag of the cochlea, and severe to profound hearing loss. We expect that this mouse line, which models human autoinflammatory hearing loss, could provide a valuable tool to elucidate the underlying pathogenic mechanism of inflammasome activation-mediated hearing loss.

Adenosine improves LPS-induced ROS expression and increasing in monolayer permeability of endothelial cell via acting on A2AR

Blood-labyrinth barrier (BLB) disruption plays a crucial role in the development of otitis media. The aims of our study was to explore the role and action mechanism of adenosine in LPS-induced endothelial cells (ECs) damage, which are one of the major principal cell type for blood-labyrinth barrier (BLB), and so as to assess the potential of adenosine to be used in the treatment of BLB disruption in animal experiment. In our study, ECs were treated with LPS to mimic BLB damage in vitro. Our data showed that adenosine at dosage of 1, 10, and 20 μM had no influence on the cell viability of ECs. LPS treatment obviously suppressed the expression of Occludin and Zonula occludens-1 (ZO-1) in ECs, which was partly recused by adenosine treatment. Meantime, LPS-induced increasing in reactive oxygen species (ROS) production and ECs permeability also was rescued by adenosine treatment. However, inhibition the A2A receptor (A2AR) could attenuate the influence of adenosine on LPS-treated ECs, indicating that adenosine alleviated LPS-induced BLB damage by activating A2AR. Moreover, the inhibition of adenosine to LPS-induced inactivation of AMPK/AKT signaling pathway was partly recused by A2AR suppression. In addition, Compound C (an AMPK inhibitor) decreased the expression of Occludin and ZO-1 in ECs following LPS combined with adenosine treatment. In conclusion, adenosine alleviates LPS-induced BLB damage via AMPK/AKT pathway through activation of A2AR. This work suggests that adenosine may be a candidate drug for the treatment of BLB dysfunction-related diseases.

LDL receptor-related protein 1 (LRP1), a novel target for opening the blood-labyrinth barrier (BLB)

Inner ear disorders are a cluster of diseases that cause hearing loss in more than 1.5 billion people worldwide. However, the presence of the blood-labyrinth barrier (BLB) on the surface of the inner ear capillaries greatly hinders the effectiveness of systemic drugs for prevention and intervention due to the low permeability, which restricts the entry of most drug compounds from the bloodstream into the inner ear tissue. Here, we report the finding of a novel receptor, low-density lipoprotein receptor-related protein 1 (LRP1), that is expressed on the BLB, as a potential target for shuttling therapeutics across this barrier. As a proof-of-concept, we developed an LRP1-binding peptide, IETP2, and covalently conjugated a series of model small-molecule compounds to it, including potential drugs and imaging agents. All compounds were successfully delivered into the inner ear and inner ear lymph, indicating that targeting the receptor LRP1 is a promising strategy to enhance the permeability of the BLB. The discovery of the receptor LRP1 will illuminate developing strategies for crossing the BLB and for improving systemic drug delivery for inner ear disorders.

Perivascular macrophages in high-fat diet-induced hypothalamic inflammation

Brain macrophages and microglia are centrally involved in immune surveillance of the central nervous system. Upon inflammatory stimuli, they become reactive and release key molecules to prevent further damage to the neuronal network. In the hypothalamic area, perivascular macrophages (PVMs) are the first line of host defence against pathogenic organisms, particles and/or substances from the blood. They are distributed throughout the circumventricular organ median eminence, wrapping endothelial cells from fenestrated portal capillaries and in the hypothalamic vascular network, where they are localised in the perivascular space of the blood-brain barrier (BBB). Some studies have indicated that PVMs from the hypothalamus increase the expression of inducible nitric oxide synthase and vascular endothelial growth factor upon feeding for a long time on a high-fat diet. This adaptive response contributes to the impairment of glucose uptake, facilitates BBB leakage and leads to increased lipid and inflammatory cell influx towards the hypothalamic parenchyma. Despite these early findings, there is still a lack of studies exploring the mechanisms by which PVMs contribute to the development of obesity-related hypothalamic dysfunction, particularly at the early stages when there is chemotaxis of peripheral myeloid cells into the mediobasal hypothalamus. Here, we reviewed the studies involving the ontogeny, hallmarks and main features of brain PVMs in vascular homeostasis, inflammation and neuroendocrine control. This review provides a framework for understanding the potential involvement of PVMs in diet-induced hypothalamic inflammation.

Role of Inner Ear Macrophages and Autoimmune/Autoinflammatory Mechanisms in the Pathophysiology of Inner Ear Disease

Macrophages play important roles in tissue homeostasis and inflammation. Recent studies have revealed that macrophages are dispersed in the inner ear and may play essential roles in eliciting an immune response. Autoinflammatory diseases comprise a family of immune-mediated diseases, some of which involve sensorineural hearing loss, indicating that similar mechanisms may underlie the pathogenesis of immune-mediated hearing loss. Autoimmune inner ear disease (AIED) is an idiopathic disorder characterized by unexpected hearing loss. Tissue macrophages in the inner ear represent a potential target for modulation of the local immune response in patients with AIED/autoinflammatory diseases. In this review, we describe the relationship between cochlear macrophages and the pathophysiology of AIED/autoinflammatory disease.