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

Cytomegalovirus host receptor expression in the human fetal inner ear

Fetal infection with human cytomegalovirus (hCMV) can cause sensorineural hearing loss and vestibular impairment, yet its pathogenesis remains unclear. This study aims to identify potential target cell types of hCMV in the human fetal inner ear. Viral particles use several envelope glycoproteins to enter target cells, including the pentameric complex, the trimeric complex and glycoprotein B. Platelet-derived growth factor receptor alpha (PDGFRA) serves as the receptor in fibroblasts, neuropilin-2 (NRP2) in epithelial, endothelial and dendritic cells as well as in leukocytes. Upon binding of these glycoproteins, glycoprotein B initiates membrane fusion which is proposed to be mediated by EGFR. When and where these proteins are expressed in the fetal inner ear during development is unknown. To address this, expression patterns of PDGFRA, NRP2 and EGFR were investigated in human fetal inner ear tissue using single-nucleus RNA sequencing data (first trimester: N = 2) and immunohistochemistry (first trimester: N = 6, second trimester: N = 5). PDGFRA gene and protein expression was detected in mesenchymal cells, NRP2 protein expression in epithelial cells and endothelial cells, and EGFR gene and protein expression in both epithelial cells and mesenchymal cells. Notably, all three receptors were present in tissue from the first and second trimesters. In conclusion, hCMV host receptors PDGFRA, NRP2 and EGFR are expressed in mesenchymal, epithelial and endothelial cells within the cochlea and vestibular organs during the first and second trimesters. These cell types may serve as targets for hCMV infection of the fetal inner ear.

Gram-negative Bacteria are Associated With Sensorineural Hearing Loss in Chronic Otitis Media

OBJECT

Chronic otitis media (COM) is an inflammatory disease that commonly presents with otorrhea and hearing loss. Bacteria-induced inflammation can cause inner ear damage, leading to sensorineural hearing loss (SNHL). This study aimed to compare the prevalence and severity of SNHL in patients with gram-negative versus gram-positive cultures and examine associations between the concentrations of circulating monocytes and neutrophils with bacteria species and SNHL.

METHODS

This was a retrospective study. Cholesteatoma or chronic suppurative otitis media patients with otorrhea were enrolled. Middle ear secretions were collected using sterile swabs under an otoscope, and sent for bacterial detection within 30 min. Pure tone audiometry and circulating leukocyte counts were recorded and analyzed in patients infected with different pathogens. Logistic regression analysis was used to identify the risk factors associated with SNHL.

RESULTS

A total of 137 patients were enrolled, including 45 patients infected with gram-negative bacteria, 41 with gram-positive bacteria, 20 with polymicrobial infection, and 31 with no bacterial growth. Logistic regression analysis showed that bacterial culture positive infections (OR = 7.265, 95% CI 2.219-23.786, p = 0.001) were an independent risk factor for SNHL. Patients with gram-negative bacteria had higher risks of SNHL (p < 0.0001) and more severe hearing loss (p = 0.005) than those with gram-positive bacteria. COM patients infected with gram-negative bacteria showed an increase in circulating monocytes, which correlated with the occurrence of SNHL (p = 0.0343).

CONCLUSION

Gram-negative bacteria are associated with elevated circulating monocyte counts and have a higher risk of severe SNHL.

LEVEL OF EVIDENCE

4 Laryngoscope, 134:3335-3341, 2024.

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.

Effects of Therapeutic Hypothermia on Macrophages in Mouse Cochlea Explants

Globally, over the next few decades, more than 2.5 billion people will suffer from hearing impairment, including profound hearing loss, and millions could potentially benefit from a cochlea implant. To date, several studies have focused on tissue trauma caused by cochlea implantation. The direct immune reaction in the inner ear after an implantation has not been well studied. Recently, therapeutic hypothermia has been found to positively influence the inflammatory reaction caused by electrode insertion trauma. The present study aimed to evaluate the hypothermic effect on the structure, numbers, function and reactivity of macrophages and microglial cells. Therefore, the distribution and activated forms of macrophages in the cochlea were evaluated in an electrode insertion trauma cochlea culture model in normothermic and mild hypothermic conditions. In 10-day-old mouse cochleae, artificial electrode insertion trauma was inflicted, and then they were cultured for 24 h at 37 °C and 32 °C. The influence of mild hypothermia on macrophages was evaluated using immunostaining of cryosections using antibodies against IBA1, F4/80, CD45 and CD163. A clear influence of mild hypothermia on the distribution of activated and non-activated forms of macrophages and monocytes in the inner ear was observed. Furthermore, these cells were located in the mesenchymal tissue in and around the cochlea, and the activated forms were found in and around the spiral ganglion tissue at 37 °C. Our findings suggest that mild hypothermic treatment has a beneficial effect on immune system activation after electrode insertion trauma.