Zika virus infection causes widespread damage to the inner ear

Repeated low-intensity noise exposure exacerbates age-related hearing loss via RAGE signaling pathway

Repeated low-intensity noise exposure is prevalent in industrialized societies. It has long been considered risk-free until recent evidence suggests that the temporary threshold shift (TTS) induced by such exposure might be a high-risk factor for hearing loss. This study was conducted to further investigate the manner in which repeated low-intensity noise exposure contributed to hearing damage. Two-month-old C57BL/6 J mice were exposed to white noise at 96 dB SPL for 8 h per day over 7 days to induce TTS. Auditory brainstem response (ABR) was monitored to assess changes in hearing thresholds, tracking the effects of noise exposure until the mice reached 12 months of age. Our results indicated that noise-exposed mice exhibited accelerated age-related hearing loss spanning from high to low frequencies. Proteomics analysis revealed an upregulation in the receptor for the advanced glycation end-products (RAGE) signaling pathway, which was associated with an activated inflammatory response, vascular injury, and mitochondrial and synaptic dysfunction. Further analysis confirmed increased levels of inflammatory cytokines in the cochlear lymph fluid and significant macrophages infiltration in the cochlear lateral wall, accompanied by hyperpermeability of the blood-labyrinth barrier. Additionally, degenerated mitochondria in the outer hair cells and decreased synaptic ribbons in the inner hair cells were also observed. These pathological changes indicated that noise exposure damages the cochlear cellular components, increasing the cochlear susceptibility to age-related stress. Our findings suggest that TTS caused by repeated low-intensity noise exposure correlates with a severe sensorineural hearing loss during aging; targeting the RAGE signaling pathway may be a promising strategy to mitigate damage from low-intensity noise and slow down the progression of age-related hearing loss.

The Effects of Viral Infections on the Molecular and Signaling Pathways Involved in the Development of the PAOs

Cytomegalovirus infection contributes to 10-30% of congenital hearing loss in children. Vertebrate peripheral auditory organs include the outer, middle, and inner ear. Their development is regulated by multiple signaling pathways. However, most ear diseases due to viral infections are due to congenital infections and reactivation and affect healthy adults to a lesser extent. This may be due to the fact that viral infections affect signaling pathways that are important for the development of peripheral hearing organs. Therefore, an in-depth understanding of the relationship between viral infections and the signaling pathways involved in the development of peripheral hearing organs is important for the prevention and treatment of ear diseases. In this review, we summarize the effects of viruses on signaling pathways and signaling molecules in the development of peripheral auditory organs.

Human otic progenitor cell models of congenital hearing loss reveal potential pathophysiologic mechanisms of Zika virus and cytomegalovirus infections

Congenital hearing loss is a common chronic condition affecting children in both developed and developing nations. Viruses correlated with congenital hearing loss include human cytomegalovirus (HCMV) and Zika virus (ZIKV), which causes congenital Zika syndrome. The mechanisms by which HCMV and ZIKV infections cause hearing loss are poorly understood. It is challenging to study human inner ear cells because they are encased in bone and also scarce as autopsy samples. Recent advances in culturing human stem cell-derived otic progenitor cells (OPCs) have allowed us herein to describe successful in vitro infection of OPCs with HCMV and ZIKV, and also to propose potential mechanisms by which each viral infection could affect hearing. We find that ZIKV infection rapidly and significantly induces the expression of type I interferon and interferon-stimulated genes, while OPC viability declines, at least in part, from apoptosis. In contrast, HCMV infection did not appear to upregulate interferons or cause a reduction in cell viability, and instead disrupted expression of key genes and pathways associated with inner ear development and function, including Cochlin, nerve growth factor receptor, SRY-box transcription factor 11, and transforming growth factor-beta signaling. These findings suggest that ZIKV and HCMV infections cause congenital hearing loss through distinct pathways, that is, by inducing progenitor cell death in the case of ZIKV infection, and by disruption of critical developmental pathways in the case of HCMV infection.

IMPORTANCE

Congenital virus infections inflict substantial morbidity and devastating disease in neonates worldwide, and hearing loss is a common outcome. It has been difficult to study viral infections of the human hearing apparatus because it is embedded in the temporal bone of the skull. Recent technological advances permit the differentiation of otic progenitor cells (OPCs) from human-induced pluripotent stem cells. This paper is important for demonstrating that inner ear virus infections can be modeled in vitro using OPCs. We infected OPCs with two viruses associated with congenital hearing loss: human cytomegalovirus (HCMV), a DNA virus, or Zika virus (ZIKV), an RNA virus. An important result is that the gene expression and cytokine production profiles of HCMV/ZIKV-infected OPCs are markedly dissimilar, suggesting that mechanisms of hearing loss are also distinct. The specific molecular regulatory pathways identified in this work could suggest important targets for therapeutics.

Does a patient with acquired arbovirus infection have a hearing impairment? A scoping review of hearing changes in an adult with Dengue, Chikungunya, and Zika

OBJECTIVES

To identify and understand the evidence regarding hearing changes related to acquired Dengue, Chikungunya, and Zika virus infection in adult individuals.

METHODS

A scoping review was performed according to the recommendations of The Joanna Briggs Institute and guidelines of the Preferred Reporting Items for Systematic Reviews and Meta-Analyses extension for Scoping Reviews in the Embase, PubMed/Medline, ScienceDirect, Scopus, and Web of Science databases without restriction on language and year of publication. Case studies, observational studies, and clinical trials reporting hearing loss in adult subjects (>18-60 years of age) of both sexes with DENV, CHIKV, or ZIKV diagnosed by positive molecular/serological examination by RT-PCR or IgM/IgG by ELISA method were included.

RESULTS

Thirteen studies met the inclusion criteria and were selected for review. The occurrence of auditory symptoms caused by arboviroses and the presence of permanent or transient sensorineural hearing loss was variable in adults.

CONCLUSIONS

Dengue, Chikungunya, and Zika infections in adults are associated with a variety of auditory symptoms. The frequency of permanent or transient sensorineural hearing loss is low but not negligible.

Pathophysiology and mechanisms of hearing impairment related to neonatal infection diseases

The inner ear, the organ of equilibrium and hearing, has an extraordinarily complex and intricate arrangement. It contains highly specialized structures meticulously tailored to permit auditory processing. However, hearing also relies on both peripheral and central pathways responsible for the neuronal transmission of auditory information from the cochlea to the corresponding cortical regions. Understanding the anatomy and physiology of all components forming the auditory system is key to better comprehending the pathophysiology of each disease that causes hearing impairment. In this narrative review, the authors focus on the pathophysiology as well as on cellular and molecular mechanisms that lead to hearing loss in different neonatal infectious diseases. To accomplish this objective, the morphology and function of the main structures responsible for auditory processing and the immune response leading to hearing loss were explored. Altogether, this information permits the proper understanding of each infectious disease discussed.

Detection of West Nile Virus Envelope Protein in Brain Tissue with an Immunohistochemical Assay

Immunohistochemistry is a valuable tool for probing not only scientific questions but also clinical diagnoses. It provides power from localization of a protein within the milieu of a tissue section that may reflect positioning within or beyond the boundaries of a cell that is representative of the tissue at a discrete moment in time. The method can be applied broadly, including to tissues under normal, developmental, chemically, or genetically altered conditions and disease states.Disease manifesting from West Nile virus infection ranges from acute, systemic febrile symptoms to compromise of central nervous system function. Immunohistochemistry has been used to assess WNV infection in the nervous system in postmortem and experimental conditions, despite the lack of understanding of the precise route of viral entry. In addition to imprecise knowledge of initial viral entry into cells and whether entry is even the same between cell types, the fact that spontaneous viral mutations and environmental pressures from climate change may alter the prevalence of the disease state across geographical and climatological boundaries highlights the need for continued assessment of infection. Immunohistochemistry is a useful way to assess these aspects of WNV infection with the aim being to better understand the organs and cell types that are compromised by WNV infection. This chapter outlines how this can be carried out on brain tissue, but the procedures discussed can also be applied more broadly on tissue outside of the central nervous system.

CD4 T-cell depletion prevents Lassa fever associated hearing loss in the mouse model

Lassa virus (LASV) is the causative agent of Lassa fever (LF), which presents as a lethal hemorrhagic disease in severe cases. LASV-induced hearing loss in survivors is a huge socioeconomic burden, however, the mechanism(s) leading to hearing loss is unknown. In this study, we evaluate in a mouse LF model the auditory function using auditory brainstem response (ABR) and distortion product otoacoustic emissions (DPOAE) to determine the mechanisms underlying LASV-induced hearing loss. In the process, we pioneered measures of ABR and DPOAE tests in rodents in biosafety level 4 (BSL-4) facilities. Our T cell depletion studies demonstrated that CD4 T-cells play an important role in LASV-induced hearing loss, while CD8 T-cells are critical for the pathogenicity in the acute phase of LASV infection. Results presented in this study may help to develop future countermeasures against acute disease and LASV-induced hearing loss.

Embryonic and Neonatal Mouse Cochleae Are Susceptible to Zika Virus Infection

Congenital Zika Syndrome (CZS) is caused by vertical transmission of Zika virus (ZIKV) to the gestating human fetus. A subset of CZS microcephalic infants present with reduced otoacoustic emissions; this test screens for hearing loss originating in the cochlea. This observation leads to the question of whether mammalian cochlear tissues are susceptible to infection by ZIKV during development. To address this question using a mouse model, the sensory cochlea was explanted at proliferative, newly post-mitotic or maturing stages. ZIKV was added for the first 24 h and organs cultured for up to 6 days to allow for cell differentiation. Results showed that ZIKV can robustly infect proliferating sensory progenitors, as well as post-mitotic hair cells and supporting cells. Virus neutralization using ZIKV-117 antibody blocked cochlear infection. AXL is a cell surface molecule known to enhance the attachment of flavivirus to host cells. While Axl mRNA is widely expressed in embryonic cochlear tissues susceptible to ZIKV infection, it is selectively downregulated in the post-mitotic sensory organ by E15.5, even though these cells remain infectible. These findings may offer insights into which target cells could potentially contribute to hearing loss resulting from fetal exposure to ZIKV in humans.

Congenital Deafness and Recent Advances Towards Restoring Hearing Loss

Congenital hearing loss is the most common birth defect, estimated to affect 2-3 in every 1000 births. Currently there is no cure for hearing loss. Treatment options are limited to hearing aids for mild and moderate cases, and cochlear implants for severe and profound hearing loss. Here we provide a literature overview of the environmental and genetic causes of congenital hearing loss, common animal models and methods used for hearing research, as well as recent advances towards developing therapies to treat congenital deafness. © 2021 The Authors.

Nanoparticles for the Treatment of Inner Ear Infections

The inner ear is sensitive to various infections of viral, bacterial, or fungal origin, which, if left untreated, may lead to hearing loss or progress through the temporal bone and cause intracranial infectious complications. Due to its isolated location, the inner ear is difficult to treat, imposing an acute need for improving current therapeutic approaches. A solution for enhancing antimicrobial treatment performance is the use of nanoparticles. Different inorganic, lipidic, and polymeric-based such particles have been designed, tested, and proven successful in the controlled delivery of medication, improving drug internalization by the targeted cells while reducing the systemic side effects. This paper makes a general presentation of common inner ear infections and therapeutics administration routes, further focusing on newly developed nanoparticle-mediated treatments.