Cytomegalovirus-induced sensorineural hearing loss with persistent cochlear inflammation in neonatal mice

Signaling pathways regulating the immune function of cochlear supporting cells and their involvement in cochlear pathophysiology

The inner ear, including the cochlea, used to be regarded as an immune-privileged site because of its immunologically isolated environment caused by the blood-labyrinthine barrier. Cochlear resident macrophages, which originate from the yolk sac or fetal liver during the embryonic stage and are maintained after birth, are distributed throughout various regions of the cochlear duct. Intriguingly, these cells are absent in the organ of Corti, where hair cells (HCs) and supporting cells (SCs) are located, except for a limited number of ionized calcium-binding adapter molecule 1 (Iba1)-positive cells. Instead, SCs exert glial functions varying from a quiescent to an emergency state. Notably, SCs acquire the nature of macrophages and begin to secrete inflammatory cytokines during viral infection in the organ of Corti, which is ostensibly unprotected owing to the lack of general resident macrophages. This review provides an overview of both positive and negative functions of SCs enabled to acquire macrophage phenotypes upon viral infection focusing on the signaling pathways that regulate these functions. The former function protects HCs from viral infection by inducting type I interferons, and the latter function induces HC death by necroptosis, leading to sensorineural hearing loss. Thus, SCs play contradictory roles as immune cells with acquired macrophage phenotypes; thereby, they are favorable and unfavorable to HCs, which play a pivotal role in hearing function.

Can Ganciclovir and Quercetin-P188 Ameliorate Cytomegalovirus Induced Hearing Loss?

OBJECTIVE

Determine whether combination therapy with ganciclovir (GCV) and a Quercetin-P188 solution improves hearing outcomes in a murine cytomegalovirus (CMV) model.

METHODS

BALB/c mice were infected with murine CMV on postnatal day 3 (p3). Quercetin was solubilized in saline using P188 (QP188). Treatment groups received either GCV, QP188, GCV and QP188, or P188 delivery vehicle BID at 12-hour intervals via intraperitoneal injection. All treatment groups were treated for 14 days starting at p3. Uninfected controls were treated with the combined regimen, saline or P188 delivery vehicle. Auditory thresholds were assessed using distortion product otoacoustic emission (DPOAE) and auditory brainstem response (ABR) testing at 4, 6, and 8 weeks of age. Temporal bones from separate CMV-infected groups were harvested at p10, and viral load was determined by quantitative polymerase chain reaction.

RESULTS

CMV-infected mice receiving combination therapy GCV+QP188 demonstrated statistically significant lower ABR (p < 0.001) and DPOAE thresholds (p < 0.001) compared with mice treated with GCV monotherapy, QP188 monotherapy, and P188 delivery vehicle at 4, 6, and 8 weeks of age. GCV+QP188 combination therapy, GCV monotherapy, and QP188 monotherapy resulted in a nonsignificant reduction in mean viral titers compared to P188 monotherapy (p = 0.08).

CONCLUSION

Combining GCV with the excipients quercetin and P188 effectively ameliorated CMV-induced sensorineural hearing loss in a murine model. This result may be partially explained by a reduction in viral titers in mouse temporal bones that correlate with in vitro studies demonstrating additive antiviral effect in cell culture.

LEVEL OF EVIDENCE

NA Laryngoscope, 134:1457-1463, 2024.

NADPH Oxidase 3: Beyond the Inner Ear

Reactive oxygen species (ROS) were formerly known as mere byproducts of metabolism with damaging effects on cellular structures. The discovery and description of NADPH oxidases (Nox) as a whole enzyme family that only produce this harmful group of molecules was surprising. After intensive research, seven Nox isoforms were discovered, described and extensively studied. Among them, the NADPH oxidase 3 is the perhaps most underrated Nox isoform, since it was firstly discovered in the inner ear. This stigma of Nox3 as "being only expressed in the inner ear" was also used by me several times. Therefore, the question arose whether this sentence is still valid or even usable. To this end, this review solely focuses on Nox3 and summarizes its discovery, the structural components, the activating and regulating factors, the expression in cells, tissues and organs, as well as the beneficial and detrimental effects of Nox3-mediated ROS production on body functions. Furthermore, the involvement of Nox3-derived ROS in diseases progression and, accordingly, as a potential target for disease treatment, will be discussed.

Hearing Following Prolonged and Delayed Ganciclovir Treatment in a Murine Cytomegalovirus Model

OBJECTIVE

Compare hearing outcomes utilizing standard, prolonged and delayed ganciclovir (GCV) therapy in a murine model of cytomegalovirus (CMV).

METHODS

BALB/c mice were inoculated with mouse cytomegalovirus (mCMV) or saline via intracerebral injection on postnatal day 3 (p3). Intraperitoneal GCV or saline was administered at 12 h intervals for the duration of the standard (p3-p17), delayed (p30-p44), or prolonged treatment windows (p3-p31). Auditory thresholds were assessed using distortion product otoacoustic emission (DPOAE) and auditory brainstem response (ABR) testing at 4, 6, and 8 weeks of age. Blood and tissue samples were harvested from mice on p17 and p37 one hour after GCV administration, and their concentrations were assessed via liquid chromatography-mass spectrometry.

RESULTS

A delayed course of GCV improved ABR but not DPOAE thresholds in mCMV-infected mice. A prolonged course of GCV did not provide better hearing thresholds than those administered standard treatment. The average GCV concentration in all 17-day-old mice tissue was significantly higher than those in older 37-day-old mice.

CONCLUSION

Delayed GCV treatment provided a hearing benefit on ABR over untreated mCMV infected mice. Prolonged CGV administration showed no benefit compared to a shorter duration GCV treatment. GCV drug concentrations both systemically and in the cochlea are much lower in older mice. These results have potential implications for the clinical management of cCMV infected children.

LEVEL OF EVIDENCE

NA Laryngoscope, 134:433-438, 2024.

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.

Brief summary

Macrophage ablation using PLX3397 was protective against cisplatin-induced ototoxicity and nephrotoxicity by limiting platinum accumulation in the inner ear and kidney.

CMV-induced Hearing Loss

Congenital cytomegalovirus (cCMV) infection is the most common fetal viral infection and contributes to about 25% of childhood hearing loss by the age of 4 years. It is the leading nongenetic cause of sensorineural hearing loss (SNHL). Infants born to seroimmune mothers are not completely protected from SNHL, although the severity of their hearing loss may be milder than that seen in those whose mothers had a primary infection. Both direct cytopathic effects and localized inflammatory responses contribute to the pathogenesis of cytomegalovirus (CMV)-induced hearing loss. Hearing loss may be delayed onset, progressive or fluctuating in nature, and therefore, a significant proportion will be missed by universal newborn hearing screening (NHS) and warrants close monitoring of hearing function at least until 5-6 years of age. A multidisciplinary approach is required for the management of hearing loss. These children may need assistive hearing devices or cochlear implantation depending on the severity of their hearing loss. In addition, early intervention services such as speech or occupational therapy could help better communication, language, and social skill outcomes. Preventive measures to decrease intrauterine CMV transmission that have been evaluated include personal protective measures, passive immunoprophylaxis and valacyclovir treatment during pregnancy in mothers with primary CMV infection. Several vaccine candidates are currently in testing and one candidate vaccine in phase 3 trials. Until a CMV vaccine becomes available, behavioral and educational interventions may be the most effective strategy to prevent maternal CMV infection.

Inflammasome activation by viral infection: mechanisms of activation and regulation

Viral diseases are the most common problems threatening human health, livestock, and poultry industries worldwide. Viral infection is a complex and competitive dynamic biological process between a virus and a host/target cell. During viral infection, inflammasomes play important roles in the host and confer defense mechanisms against the virus. Inflammasomes are polymeric protein complexes and are considered important components of the innate immune system. These immune factors recognize the signals of cell damage or pathogenic microbial infection after activation by the canonical pathway or non-canonical pathway and transmit signals to the immune system to initiate the inflammatory responses. However, some viruses inhibit the activation of the inflammasomes in order to replicate and proliferate in the host. In recent years, the role of inflammasome activation and/or inhibition during viral infection has been increasingly recognized. Therefore, in this review, we describe the biological properties of the inflammasome associated with viral infection, discuss the potential mechanisms that activate and/or inhibit NLRP1, NLRP3, and AIM2 inflammasomes by different viruses, and summarize the reciprocal regulatory effects of viral infection on the NLRP3 inflammasome in order to explore the relationship between viral infection and inflammasomes. This review will pave the way for future studies on the activation mechanisms of inflammasomes and provide novel insights for the development of antiviral therapies.

The Pathogenesis of Cytomegalovirus and Other Viruses Associated with Hearing Loss: Recent Updates

Virus infection is one of the most common etiologies of hearing loss. Hearing loss associated with viral infection can be unilateral or bilateral, mild or severe, sudden or progressive, and permanent or recoverable. Many viruses cause hearing loss in adults and children; however, the pathogenesis of hearing loss caused by viral infection is not fully understood. This review describes cytomegalovirus, the most common virus causing hearing loss, and other reported hearing loss-related viruses. We hope to provide a detailed description of pathogenic characteristics and research progress on pathology, hearing phenotypes, possible associated mechanisms, treatment, and prevention measures. This review aims to provide diagnostic and treatment assistance to clinical workers.

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.

Hearing loss in outbred Hartley guinea pigs experimentally infected with Pichinde virus as a surrogate model of human mammarenaviral hemorrhagic fevers

Lassa fever (LF) is a neglected tropical disease that is caused by Lassa virus (LASV), a human hemorrhagic fever-causing mammarenavirus. A notable sequela of LF is sensorineural hearing loss (SNHL) that can develop in about 33% of the patients. Animal models of LF-associated SNHL have been limited in size and scope because LASV is a biosafety level 4 (BSL4) pathogen that requires its handling in a high biocontainment laboratory. In this report, we describe the development of an alternative arenavirus hearing loss model by infecting outbred Hartley guinea pigs with a virulent strain (rP18) of the Pichinde virus (PICV), which is a guinea pig-adapted mammarenavirus that has been used as a surrogate model of mammarenaviral hemorrhagic fevers in a conventional (BSL2) laboratory. By measuring auditory brainstem response (ABR) throughout the course of the virulent rP18 PICV infection, we noticed that some of the animals experienced an acute but transient level of hearing loss. Cochleae of hearing-impaired animals, but not of controls, had demonstrable viral RNA by quantitative RT-PCR, indicating the presence of virus in the affected inner ear with no overt histopathological changes. In contrast, neither the outbred Hartley guinea pigs infected with a known avirulent strain (rP2) of PICV nor those that were mock-infected showed any evidence of hearing loss or viral infection of the inner ear. This is the first report of an immunocompetent small animal model of mammarenavirus-induced hearing loss that can be used to evaluate potential therapeutics against virus-induced hearing impairment under a conventional laboratory setting.

Depletion of CD4 and CD8 T Cells Reduces Acute Disease and Is Not Associated with Hearing Loss in ML29-Infected STAT1-/- Mice

Lassa virus (LASV) is a zoonotic virus endemic to western Africa that can cause a potentially lethal and hemorrhagic disease, Lassa fever (LF). Survivors suffer a myriad of sequelae, most notably sudden onset sensorineural hearing loss (SNHL), the mechanism of which remains unclear. Unfortunately, studies aiming to identify the mechanism of these sequelae are limited due to the biosafety level 4 (BSL4) requirements of LASV itself. ML29, a reassortant virus proposed as an experimental vaccine candidate against LASV, is potentially an ideal surrogate model of LF in STAT1-/- mice due to similar phenotype in these animals. We intended to better characterize ML29 pathogenesis and potential sequelae in this animal model. Our results indicate that while both CD4 and CD8 T cells are responsible for acute disease in ML29 infection, ML29 induces significant hearing loss in a mechanism independent of either CD4 or CD8 T cells. We believe that this model could provide valuable information for viral-associated hearing loss in general.

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.

Selective Inner Hair Cell Loss in a Neonate Harbor Seal (Phoca vitulina)

Simple Summary

Congenital hearing loss (i.e., hearing impairment present at birth) is recognized in humans and other terrestrial species, but there is a lack of information on congenital malformations and associated hearing loss in pinnipeds (seals, sea lions, and walruses). Baseline knowledge on marine mammal inner ear malformations is essential to differentiate between congenital and acquired abnormalities, which may be caused by infectious agents, age, or anthropogenic interactions, such as noise exposure. Analysis of the cochlea of a neonate harbor seal (Phoca vitulina) revealed bilateral loss of inner hair cells (sensory cells responsible for transducing the auditory signal) while the outer hair cells (sensory cells responsible for sound amplification and frequency selectivity and sensitivity) were intact. The selective inner hair cell loss (up to 84.6% of loss) was more severe in the basal turn, where the high frequencies are encoded. Potential causes and consequences are discussed. This is the first report of a case of selective inner hair cell loss in a marine mammal neonate, likely congenital.

Abstract

Congenital hearing loss is recognized in humans and other terrestrial species. However, there is a lack of information on its prevalence or pathophysiology in pinnipeds. It is important to have baseline knowledge on marine mammal malformations in the inner ear, to differentiate between congenital and acquired abnormalities, which may be caused by infectious pathogens, age, or anthropogenic interactions, such as noise exposure. Ultrastructural evaluation of the cochlea of a neonate harbor seal (Phoca vitulina) by scanning electron microscopy revealed bilateral loss of inner hair cells with intact outer hair cells. The selective inner hair cell loss was more severe in the basal turn, where high-frequency sounds are encoded. The loss of inner hair cells started around 40% away from the apex or tip of the spiral, reaching a maximum loss of 84.6% of hair cells at 80–85% of the length from the apex. Potential etiologies and consequences are discussed. This is believed to be the first case report of selective inner hair cell loss in a marine mammal neonate, likely congenital.

Mechanism and Prevention of Spiral Ganglion Neuron Degeneration in the Cochlea

Sensorineural hearing loss (SNHL) is one of the most prevalent sensory deficits in humans, and approximately 360 million people worldwide are affected. The current treatment option for severe to profound hearing loss is cochlear implantation (CI), but its treatment efficacy is related to the survival of spiral ganglion neurons (SGNs). SGNs are the primary sensory neurons, transmitting complex acoustic information from hair cells to second-order sensory neurons in the cochlear nucleus. In mammals, SGNs have very limited regeneration ability, and SGN loss causes irreversible hearing loss. In most cases of SNHL, SGN damage is the dominant pathogenesis, and it could be caused by noise exposure, ototoxic drugs, hereditary defects, presbycusis, etc. Tremendous efforts have been made to identify novel treatments to prevent or reverse the damage to SGNs, including gene therapy and stem cell therapy. This review summarizes the major causes and the corresponding mechanisms of SGN loss and the current protection strategies, especially gene therapy and stem cell therapy, to promote the development of new therapeutic methods.

Early Life Inflammation and the Developing Hematopoietic and Immune Systems: The Cochlea as a Sensitive Indicator of Disruption

Emerging evidence indicates that perinatal infection and inflammation can influence the developing immune system and may ultimately affect long-term health and disease outcomes in offspring by perturbing tissue and immune homeostasis. We posit that perinatal inflammation influences immune outcomes in offspring by perturbing (1) the development and function of fetal-derived immune cells that regulate tissue development and homeostasis, and (2) the establishment and function of developing hematopoietic stem cells (HSCs) that continually generate immune cells across the lifespan. To disentangle the complexities of these interlinked systems, we propose the cochlea as an ideal model tissue to investigate how perinatal infection affects immune, tissue, and stem cell development. The cochlea contains complex tissue architecture and a rich immune milieu that is established during early life. A wide range of congenital infections cause cochlea dysfunction and sensorineural hearing loss (SNHL), likely attributable to early life inflammation. Furthermore, we show that both immune cells and bone marrow hematopoietic progenitors can be simultaneously analyzed within neonatal cochlear samples. Future work investigating the pathogenesis of SNHL in the context of congenital infection will therefore provide critical information on how perinatal inflammation drives disease susceptibility in offspring.

Murine Models of Central Nervous System Disease following Congenital Human Cytomegalovirus Infections

Human cytomegalovirus infection of the developing fetus is a leading cause of neurodevelopmental disorders in infants and children, leading to long-term neurological sequela in a significant number of infected children. Current understanding of the neuropathogenesis of this intrauterine infection is limited because of the complexity of this infection, which includes maternal immunological responses that are overlaid on virus replication in the CNS during neurodevelopment. Furthermore, available data from human cases are observational, and tissues from autopsy studies have been derived from only the most severe infections. Animal models of this human infection are also limited by the strict species specificity of cytomegaloviruses. However, informative models including non-human primates and small animal models have been developed. These include several different murine models of congenital HCMV infection for the study of CMV neuropathogenesis. Although individual murine models do not completely recapitulate all aspects of the human infection, each model has provided significant information that has extended current understanding of the neuropathogenesis of this human infection. This review will compare and contrast different murine models in the context of available information from human studies of CNS disease following congenital HCMV infections.

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.

Hearing Loss Caused by HCMV Infection through Regulating the Wnt and Notch Signaling Pathways

Hearing loss is one of the most prevalent sensory disabilities worldwide with huge social and economic burdens. The leading cause of sensorineural hearing loss (SNHL) in children is congenital cytomegalovirus (CMV) infection. Though the implementation of universal screening and early intervention such as antiviral or anti-inflammatory ameliorate the severity of CMV-associated diseases, direct and targeted therapeutics is still seriously lacking. The major hurdle for it is that the mechanism of CMV induced SNHL has not yet been well understood. In this review, we focus on the impact of CMV infection on the key players in inner ear development including the Wnt and Notch signaling pathways. Investigations on these interactions may gain new insights into viral pathogenesis and reveal novel targets for therapy.

Zika virus infection causes widespread damage to the inner ear

Zika virus (ZIKV) has been recently recognized as a causative agent of newborn microcephaly, as well as other neurological consequences. A less well recognized comorbidity of prenatal ZIKV infection is hearing loss, but cases of hearing impairment following adult ZIKV infection have also been recognized. Diminished hearing following prenatal ZIKV infection in a mouse model has been reported, but no cellular consequences were observed. We examined the effects of ZIKV infection on inner ear cellular integrity and expression levels of various proteins important for cochlear function in type I interferon receptor null (Ifnar1^-/-) mice following infection at 5-6 weeks of age. We show that ZIKV antigens are present in cells within the cochlear epithelium, lateral wall, spiral limbus and spiral ganglion. Here we show that ZIKV infection alters cochlear expression of genes that signal cell damage (S100B), transport fluids (AQP1), are gaseous transmitters (eNOs) and modulate immune response (F4/80). Morphological analyses shows that not only are cochlear structures compromised by ZIKV infection, but damage also occurs in vestibular end organs. ZIKV produces a graded distribution of cellular damage in the cochlea, with greatest damage in the apex similar to that reported for cytomegalovirus (CMV) infection. The graded distribution of damage may indicate a differential susceptibility to ZIKV along the cochlear tonotopic axis. Collectively, these data are the first to show the molecular and morphological damage to the inner ear induced by ZIKV infection in adults and suggests multiple mechanisms contributing to the hearing loss reported in the human population.

Role of Free Radical Formation in Murine Cytomegalovirus-Induced Hearing Loss

OBJECTIVES

The goal of the study was to determine whether reactive oxygen species (ROS) mediates cytomegalovirus (CMV)-induced labyrinthitis.

STUDY DESIGN

Murine model of CMV infection.

SETTING

University of Utah laboratory.

SUBJECTS AND METHODS

Nrf2 knockout mice were inoculated with murine CMV. Auditory brainstem response (ABR) and distortion product otoacoustic emissions (DPOAEs) were then performed on these and uninfected controls. BALB/c mice were inoculated with murine CMV to determine whether a marker for ROS production, dihydroethidium (DHE), is expressed 7 days after inoculation. Finally, 2 antioxidants-D-methionine and ACE-Mg (vitamins A, C, and E with magnesium)-were administered 1 hour before and after infection in inoculated mice for 14 days. Temporal bones were harvested at postnatal day 10 for DHE detection. ABR and DPOAE testing was done at postnatal day 30. Scanning electron microscopy was also performed at postnatal day 30 to evaluate outer hair cell integrity.

RESULTS

Nrf2-infected mice had worse hearing than uninfected mice (P < .001). A statistically significant increase in DHE fluorescence was detected in BALB/c-infected mice as compared with uninfected mice 7 days after inoculation. D-methionine- and ACE-Mg-treated mice demonstrated an attenuation of the DHE fluorescence and a significant improvement in ABR and DPOAE thresholds when compared with untreated infected controls (P < .0001). Scanning electron microscopy demonstrated less outer hair cell loss in the treated versus untreated infected controls.

CONCLUSION

These results demonstrate for the first time that excessive ROS mediates CMV-induced hearing loss in a mouse model.

Vascular endothelial growth factor is required for regeneration of auditory hair cells in the avian inner ear

Hair cells in the auditory organ of the vertebrate inner ear are the sensory receptors that convert acoustic stimuli into electrical signals that are conveyed along the auditory nerve to the brainstem. Hair cells are highly susceptible to ototoxic drugs, infection, and acoustic trauma, which can cause cellular degeneration. In mammals, hair cells that are lost after damage are not replaced, leading to permanent hearing impairments. By contrast, supporting cells in birds and other non-mammalian vertebrates regenerate hair cells after damage, which restores hearing function. The cellular mechanisms that regulate hair cell regeneration are not well understood. We investigated the role of vascular endothelial growth factor (VEGF) during regeneration of auditory hair cells in chickens after ototoxic injury. Using RNA-Seq, immunolabeling, and in situ hybridization, we found that VEGFA, VEGFC, VEGFR1, VEGFR2, and VEGFR3 were expressed in the auditory epithelium, with VEGFA expressed in hair cells and VEGFR1 and VEGFR2 expressed in supporting cells. Using organotypic cultures of the chicken cochlear duct, we found that blocking VEGF receptor activity during hair cell injury reduced supporting cell proliferation as well as the numbers of regenerated hair cells. By contrast, addition of recombinant human VEGFA to organ cultures caused an increase in both supporting cell division and hair cell regeneration. VEGF's effects on supporting cells were preserved in isolated supporting cell cultures, indicating that VEGF can act directly upon supporting cells. These observations demonstrate a heretofore uncharacterized function for VEGF signaling as a critical positive regulator of hair cell regeneration in the avian inner ear.

Cytomegalovirus-induced pathology in human temporal bones with congenital and acquired infection

OBJECTIVE

Publications on histopathology of human temporal bones with cytomegalovirus (CMV) infection are limited. We aim to determine histopathology of the inner ears and the middle ears in human temporal bones with congenital and acquired CMV infections.

METHODS

Temporal bones from 2 infants with congenital and 2 adults with acquired CMV infection were evaluated by light microscopy.

RESULTS

Two infants with congenital CMV infection showed striking pathological changes in the inner ear. There was a hypervascularization of the stria vascularis in the cochlea of the first infant, but no obvious loss of outer and inner hair cells was seen in the organ of Corti. However, cytomegalic cells and a loss of outer hair cells were found in the cochlea of the second infant. The vestibular organs of both infants showed cytomegalic cells, mostly located on dark cells. There was a loss of type I and type II hair cells in the macula of the saccule and utricle. Loss of hair cells and degeneration of nerve fibers was also seen in the semicircular canals. Both infants with congenital infection showed abundant inflammatory cells and fibrous structures in the middle ear cavity. No evidence of cytomegalic cells and hair cell loss was found in the cochlea or vestibular labyrinth in acquired CMV infection.

CONCLUSIONS

In two infants with congenital CMV infection, the cochlea, vestibule, and middle ear were highly affected. Temporal bones of adult donors with acquired viral infection showed histological findings similar to donors of the same age without ear disease.

Virus-induced cochlear inflammation in newborn mice alters auditory function

Although human cytomegalovirus (HCMV) is a known cause of sensorineural hearing loss in infants with congenital HCMV (cCMV) infections, mechanisms that contribute to sensorineural hearing loss (SNHL) in infants with cCMV infection are not well defined. Using a murine model of CMV infection during auditory development, we have shown that peripheral infection of newborn mice with murine CMV (MCMV) results in focal infection of the cochlea and virus-induced cochlear inflammation. Approximately 50%-60% of infected mice exhibited increased auditory brainstem response (ABR) thresholds across a range of sound frequencies. Histological analyses of the cochlea in MCMV-infected mice with elevated ABR thresholds revealed preservation of hair cell (HC) number and morphology in the organ of Corti. In contrast, the number of spiral ganglion neurons (SGN), synapses, and neurites connecting the cochlear HC and SGN nerve terminals were decreased. Decreasing cochlear inflammation by corticosteroid treatment of MCMV-infected mice resulted in preservation of SGN and improved auditory function. These findings show that virus-induced cochlear inflammation during early auditory development, rather than direct virus-mediated damage, could contribute to histopathology in the cochlea and altered auditory function without significant loss of HCs in the sensory epithelium.

Sensorineural Hearing Loss After Adoptive Cell Immunotherapy for Melanoma Using MART-1 Specific T Cells: A Case Report and Its Pathophysiology

OBJECTIVE

To illustrate a case of sensorineural hearing loss (SNHL) after immunotherapy based on T cell receptor (TCR) gene therapy using modified T cells recognizing melanoma antigen recognized by T cells 1 for disseminated melanoma.

PATIENT

We present a 59-year-old woman with profound subacute bilateral SNHL including unilateral deafness after immunotherapy based on TCR gene therapy using modified T cells recognizing melanoma antigen recognized by T cells 1 for disseminated melanoma. Ten days after treatment, the patient developed hearing loss of 57 dB hearing loss air conduction at pure-tone average 0.5-1-2-4 kHz in the right ear, and >100 dB hearing loss air conduction at pure-tone average 0.5-1-2-4 in the left ear. The right ear recovered partially, while the left ear remained deaf, despite oral prednisolone (1.0 mg/kg) and salvage treatment with three transtympanic injections of 0.5 ml dexamethasone (4.0 mg/ml).

CONCLUSION

Based on our presented case and a vast amount of literature there is circumstantial evidence that TCR gene therapy for melanoma targets the perivascular macrophage-like melanocytes in the stria vascularis, resulting in SNHL. We suggest that SNHL after TCR gene therapy may be caused by a disruption of the blood-labyrinth-barrier and the endolymphatic potential and/or a sterile inflammation of the stria vascularis. In severe cases like our subject, we posit that endolymphatic hydrops or hair cell loss may cause irreversible and asymmetrical deafness. Steroid prophylaxis via transtympanic application is debatable.

Role of viral infection in sudden hearing loss

According to a recent epidemiological survey, the incidence of sudden sensorineural hearing loss (SSNHL) is increasing yearly. The cause of SSNHL is of great interest in research. To date, viral infection, vascular occlusion, abnormal cellular stress responses within the cochlea, and immune-mediated mechanisms are considered the most likely etiologies of this disease. Among these etiologies, the relationship between viral infection and sudden deafness has been unclear. In this review, we mainly discuss the viral hypothesis of SSNHL. There is little research proving or clearly indicating the pathogenesis of this disease. Further research is needed to elucidate the precise etiopathogenesis to better understand SSNHL and establish more suitable treatment to help restore hearing in affected patients.

Cytokine-Mediated Induction and Regulation of Tissue Damage During Cytomegalovirus Infection

Human cytomegalovirus (HCMV) is a β-herpesvirus with high sero-prevalence within the human population. Primary HCMV infection and life-long carriage are typically asymptomatic. However, HCMV is implicated in exacerbation of chronic conditions and associated damage in individuals with intact immune systems. Furthermore, HCMV is a significant cause of morbidity and mortality in the immunologically immature and immune-compromised where disease is associated with tissue damage. Infection-induced inflammation, including robust cytokine responses, is a key component of pathologies associated with many viruses. Despite encoding a large number of immune-evasion genes, HCMV also triggers the induction of inflammatory cytokine responses during infection. Thus, understanding how cytokines contribute to CMV-induced pathologies and the mechanisms through which they are regulated may inform clinical management of disease. Herein, we discuss our current understanding based on clinical observation and in vivo modeling of disease of the role that cytokines play in CMV pathogenesis. Specifically, in the context of the different tissues and organs in which CMV replicates, we give a broad overview of the beneficial and adverse effects that cytokines have during infection and describe how cytokine-mediated tissue damage is regulated. We discuss the implications of findings derived from mice and humans for therapeutic intervention strategies and our understanding of how host genetics may influence the outcome of CMV infections.

Congenital Cytomegalovirus Infection Alters Olfaction Before Hearing Deterioration In Mice

In developed countries, cytomegalovirus (CMV)-infected newborns are at high risk of developing sensorineural handicaps such as hearing loss, requiring extensive follow-up. However, early prognostic tools for auditory damage in children are not yet available. In the fetus, CMV infection leads to early olfactory bulb (OB) damage, suggesting that olfaction might represent a valuable prognosis for neurological outcome of this viral infection. Here, we demonstrate that in utero CMV inoculation causes fetal infection and growth retardation in mice of both sexes. It disrupts OB normal development, leading to disproportionate OB cell layers and rapid major olfactory deficits. Olfaction is impaired as early as day 6 after birth in both sexes, long before the emergence of auditory deficits. Olfactometry in males reveals a long-lasting alteration in olfactory perception and discrimination, particularly in binary mixtures of monomolecular odorants. Although sensory inputs to the OB remain unchanged, hallmarks of autophagy are increased in the OB of 3-postnatal week-old mice, leading to local neuroinflammation and loss of neurons expressing tyrosine hydroxylase and calbindin. At the cellular level, we found CMV-infected cells and an increased number of apoptotic cells scattered throughout the OB layers, whereas cell proliferation in the neurogenic subventricular zone was decreased. These cellular observations were long-lasting, persisting up to 16 weeks after birth in both males and females and thus providing a mechanism supporting olfactory loss. Despite obvious differences in neurogenesis between human and mouse, these findings offer new strategies aimed at early detection of neurological dysfunctions caused by congenital infections.SIGNIFICANCE STATEMENT In developed countries, congenital cytomegalovirus (CMV)-infected newborns are at high risk of developing sensory handicaps such as hearing loss, thus requiring prolonged follow-up. In this study, we describe for the first time the functional impact of congenital CMV infection on the olfactory system and its associated sense of smell. We demonstrate that a mouse model of congenital CMV infection shows defects in olfactory bulb (OB) normal development and pronounced olfactory deficits affecting acuity and discrimination of odorants. These major olfactory deficits occur long before the emergence of auditory deficits through the upregulation of OB autophagy inducing local neuroinflammation and altered neuron content. Our findings provide new opportunities for designing olfactory means to monitor the possible neurological outcome during congenital CMV infection.

Berberine exerts antioxidant effects via protection of spiral ganglion cells against cytomegalovirus-induced apoptosis

Cytomegalovirus (CMV) is the leading cause of sensorineural hearing loss (SNHL) in children because of its damage to the cochlea and spiral ganglion cells. Therefore, it has become a top priority to devise new methods to effectively protect spiral ganglion cells from damage. Berberine (BBR) has gained attention for its vast beneficial biological effects through immunomodulation, and its anti-inflammatory and anti-apoptosis properties. However, the effect of BBR on spiral ganglion cells and molecular mechanisms are still unclear. This study aims to investigate whether BBR has an anti-apoptosis effect in CMV-induced apoptosis in cultured spiral ganglion cells and explore the possible mechanism. In this study, TUNEL and MTT assays significantly demonstrated that low doses of BBR did not promote cell apoptosis and they also inhibited the CMV-induced cultured spiral ganglion cell apoptosis. Immunofluorescence and Western blot assays indicated that the anti-apoptosis effect of BBR was related to Nox3. Mitochondrial calcium and Western blot assays revealed that NMDAR1 mediated this anti-apoptosis effect. Our results demonstrated that BBR exerted an anti-apoptosis effect against CMV in cultured spiral ganglion cells, and the mechanism is related to NMDAR1/Nox3-mediated mitochondrial reactive oxygen species (ROS) generation.

MicroRNA-182 inhibits HCMV replication through activation of type I IFN response by targeting FOXO3 in neural cells

Human cytomegalovirus (HCMV) has led to kinds of clinical disorders and great morbidity worldwide, such as sensorineural hearing loss (SNHL), mental retardation, and developmental delays in immunocompromised individuals. Congenital HCMV infection is a leading cause of birth defects, primarily manifesting as neurological disorders. Previous studies reported that HCMV has evolved a variety of mechanisms to evade the immune system, such as dysregulation of miRNAs. However, reports concerning the role of miRNA in HCMV infection in neural cells are limited. Here, we reported that a host microRNA, miR-182, was significantly up-regulated by HCMV infection in U-251MG and NPCs cells. Subsequently, our results of in vitro and in vivo experiments demonstrated that miR-182 was a positive regulator of interferon regulatory factor 7 (IRF7) by directly targeting FOXO3, resulting in the induction of IFN-I response and suppression of HCMV replication in neural cells. Taken together, our findings provide detailed molecular mechanisms of the antiviral function of miR-182 against HCMV infection in neural cells, and suggest an intrinsic anti-HCMV therapeutic target.

MCMV triggers ROS/NLRP3-associated inflammasome activation in the inner ear of mice and cultured spiral ganglion neurons, contributing to sensorineural hearing loss

Congenital cytomegalovirus (CMV) infection is the most common infectious cause of sensorineural hearing loss in children. While the importance of CMV-induced SNHL has been described, the mechanisms underlying its pathogenesis and the role of inflammatory responses remain elusive. The present study established an experimental model of hearing loss after systemic infection with murine CMV (MCMV) in newborn mice. Auditory brainstem responses were tested to evaluate hearing at 3 weeks, expression of inflammasome-associated factors was assessed by immunofluorescence, western blot analysis, reverse transcription-quantitative polymerase chain reaction and ELISA. MCMV sequentially induced inflammasome-associated factors. Furthermore, the inflammasome-associated factors were also increased in cultured spiral ganglion neurons infected with MCMV for 24 h. In addition, MCMV increased the content of reactive oxygen species (ROS). These results suggest that hearing loss caused by MCMV infection may be associated with ROS-induced inflammation.

Lassa fever-induced sensorineural hearing loss: A neglected public health and social burden

Although an association between Lassa fever (LF) and sudden-onset sensorineural hearing loss (SNHL) was confirmed clinically in 1990, the prevalence of LF-induced SNHL in endemic countries is still underestimated. LF, a viral hemorrhagic fever disease caused by Lassa virus (LASV), is endemic in West Africa, causing an estimated 500,000 cases and 5,000 deaths per year. Sudden-onset SNHL, one complication of LF, occurs in approximately one-third of survivors and constitutes a neglected public health and social burden. In the endemic countries, where access to hearing aids is limited, SNHL results in a decline of the quality of life for those affected. In addition, hearing loss costs Nigeria approximately 43 million dollars per year. The epidemiology of LF-induced SNHL has not been characterized well. The complication of LF induced by SNHL is also an important consideration for vaccine development and treatments. However, research into the mechanism has been hindered by the lack of autopsy samples and relevant small animal models. Recently, the first animal model that mimics the symptoms of SNHL associated with LF was developed. Preliminary data from the new animal model as well as the clinical case studies support the mechanism of immune-mediated injury that causes SNHL in LF patients. This article summarizes clinical findings of hearing loss in LF patients highlighting the association between LASV infection and SNHL as well as the potential mechanism(s) for LF-induced SNHL. Further research is necessary to identify the mechanism and the epidemiology of LF-induced SNHL.

Immune responses to congenital cytomegalovirus infection

Human cytomegalovirus (HCMV) is the most common cause of viral infection acquired in utero. Even though the infection has been studied for several decades, immune determinants important for virus control and mechanisms of long-term sequelae caused by infection are still insufficiently characterized. Animal models of congenital HCMV infection provide unique opportunity to study various aspects of human disease. In this review, we summarize current knowledge on the role of immune system in congenital CMV infection, with emphasis on lessons learned from mouse model of congenital CMV infection.

Natural killer cells attenuate cytomegalovirus-induced hearing loss in mice

Congenital cytomegalovirus (CMV) infection is the most common non-hereditary cause of sensorineural hearing loss (SNHL) yet the mechanisms of hearing loss remain obscure. Natural Killer (NK) cells play a critical role in regulating murine CMV infection via NK cell recognition of the Ly49H cell surface receptor of the viral-encoded m157 ligand expressed at the infected cell surface. This Ly49H NK receptor/m157 ligand interaction has been found to mediate host resistance to CMV in the spleen, and lung, but is much less effective in the liver, so it is not known if this interaction is important in the context of SNHL. Using a murine model for CMV-induced labyrinthitis, we have demonstrated that the Ly49H/m157 interaction mediates host resistance in the temporal bone. BALB/c mice, which lack functional Ly49H, inoculated with mCMV at post-natal day 3 developed profound hearing loss and significant outer hair cell loss by 28 days of life. In contrast, C57BL/6 mice, competent for the Ly49H/m157 interaction, had minimal hearing loss and attenuated outer hair cell loss with the same mCMV dose. Administration of Ly49H blocking antibody or inoculation with a mCMV viral strain deleted for the m157 gene rendered the previously resistant C57BL/6 mouse strain susceptible to hearing loss to a similar extent as the BALB/c mouse strain indicating a direct role of the Ly49H/m157 interaction in mCMV-dependent hearing loss. Additionally, NK cell recruitment to sites of infection was evident in the temporal bone of inoculated susceptible mouse strains. These results demonstrate participation of NK cells in protection from CMV-induced labyrinthitis and SNHL in mice.

Cytomegalovirus (CMV) transmission from an infected mother to her fetus is a leading cause of permanent hearing loss in children, but the contributing processes are not clear. In this report, we utilized a mouse model, which recapitulates many features of congenital CMV mediated childhood hearing loss, to demonstrate that natural killer cells (NK), a component of early host immune response to infection, play a critical protective role in CMV-induced hearing loss. Specifically, we determined that NK cells interact with CMV infected cells through binding of the NK cell receptor, Ly49H, with a virally-encoded protein, m157, expressed on the cell surface of CMV infected inner ear cells, to mediate the protective effect. Findings from this study provide insight into the host immune response during CMV-induced hearing loss in mice.

Herpes simplex virus-1 and cytomegalovirus DNAs detection in the inner ear of implanted patients with non-congenital infection

CONCLUSIONS

The detection of cytomegalovirus (CMV) and herpes simplex virus-1 (HSV-1) genome in perilymph of patients with negative serology or clinical history for congenital infections supports the hypothesis that Herpesviridae, even after acquired postnatal infections, could remain in latent phase in the spiral ganglion and damage the cochlea by a possible subsequent reactivation. Further studies are needed to identify the markers of such reactivation.

OBJECTIVE

To identify the presence of certain viral species in the endolabyrinthic fluid of deaf patients with non-congenital infection. The research of viral DNA within the inner ear is the only direct way to increase our knowledge about the viral role in postnatal damage to the cochlea.

METHODS

Thirty-six patients (1-69 years) suffering from bilateral sensorineural hearing loss (SNHL) were subjected, during cochlear implant (CI) surgery, to a sample taking of inner ear fluid. Several types of viral genome (HSV, VZV, CMV, EBV and Enterovirus) were investigated in each sample through multiplex polymerase chain reaction (PCR) and reverse transcriptase-polymerase chain reaction (RT-PCR). Radiological exams, serology (specific IgG and IgM) and PCR of peripheral blood were also performed.

RESULTS

While the research of the viral genome in peripheral blood was negative in all patients, multiplex PCR on endolabyrinthic fluid samples was positive in three patients (two cases of CMV-DNA and one case of HSV-1 DNA).

Modulation of Microglial Cell Fcγ Receptor Expression Following Viral Brain Infection

Fcγ receptors (FcγRs) for IgG couple innate and adaptive immunity through activation of effector cells by antigen-antibody complexes. We investigated relative levels of activating and inhibitory FcγRs on brain-resident microglia following murine cytomegalovirus (MCMV) infection. Flow cytometric analysis of microglial cells obtained from infected brain tissue demonstrated that activating FcγRs were expressed maximally at 5 d post-infection (dpi), while the inhibitory receptor (FcγRIIB) remained highly elevated during both acute and chronic phases of infection. The highly induced expression of activating FcγRIV during the acute phase of infection was also noteworthy. Furthermore, in vitro analysis using cultured primary microglia demonstrated the role of interferon (IFN)γ and interleukin (IL)-4 in polarizing these cells towards a M1 or M2 phenotype, respectively. Microglial cell-polarization correlated with maximal expression of either FcγRIV or FcγRIIB following stimulation with IFNγ or IL-4, respectively. Finally, we observed a significant delay in polarization of microglia towards an M2 phenotype in the absence of FcγRs in MCMV-infected Fcer1g and FcgR2b knockout mice. These studies demonstrate that neuro-inflammation following viral infection increases expression of activating FcγRs on M1-polarized microglia. In contrast, expression of the inhibitory FcγRIIB receptor promotes M2-polarization in order to shut-down deleterious immune responses and limit bystander brain damage.

Congenital hearing loss

Congenital hearing loss (hearing loss that is present at birth) is one of the most prevalent chronic conditions in children. In the majority of developed countries, neonatal hearing screening programmes enable early detection; early intervention will prevent delays in speech and language development and has long-lasting beneficial effects on social and emotional development and quality of life. A diagnosis of hearing loss is usually followed by a search for an underlying aetiology. Congenital hearing loss might be attributed to environmental and prenatal factors, which prevail in low-income settings; congenital infections, particularly cytomegalovirus infection, are also a common risk factor for hearing loss. Genetic causes probably account for the majority of cases in developed countries; mutations can affect any component of the hearing pathway, in particular, inner ear homeostasis (endolymph production and maintenance) and mechano-electrical transduction (the conversion of a mechanical stimulus into electrochemical activity). Once the underlying cause of hearing loss is established, it might direct therapeutic decision making and guide prevention and (genetic) counselling. Management options include specific antimicrobial therapies, surgical treatment of craniofacial abnormalities and implantable or non-implantable hearing devices. An improved understanding of the pathophysiology and molecular mechanisms that underlie hearing loss and increased awareness of recent advances in genetic testing will promote the development of new treatment and screening strategies.

Cytomegalovirus (CMV) Infection Causes Degeneration of Cochlear Vasculature and Hearing Loss in a Mouse Model

Cytomegalovirus (CMV) infection is one of the most common causes of congenital hearing loss in children. We have used a murine model of CMV infection to reveal functional and structural cochlear pathogenesis. The cerebral cortex of Balb/c mice (Mus musculus) was inoculated with 2000 pfu (plaque forming units) of murine CMV on postnatal day 3. At 6 weeks of age, cochlear function was monitored using auditory brainstem response (ABR) and distortion product otoacoustic emission (DPOAE) measures. Histological assessment of cochlear vasculature using a corrosion cast technique was made at 8 weeks. Vascular casts of mCMV-damaged cochleas, and those of untreated control animals, were examined using scanning electron microscopy. We find very large variations in the degree of vascular damage in animals given identical viral injections (2000 pfu). The primary lesion caused by CMV infection is to the stria vascularis and to the adjacent spiral limbus capillary network. Capillary beds of the spiral ligament are generally less affected. The initial vascular damage is found in the mid-apical turn and appears to progress to more basal cochlear regions. After viral migration to the inner ear, the stria vascularis is the primary affected structure. We suggest that initial auditory threshold losses may relate to the poor development or maintenance of the endocochlear potential caused by strial dysfunction. Our increased understanding of the pathogenesis of CMV-related hearing loss is important for defining methods for early detection and treatment.

Pharmacokinetics and tissue diffusion of ganciclovir in mice and rats

BACKGROUND

Congenital cytomegalovirus (CMV) infection is the leading infectious cause of birth defects, mental retardation and non-genetic sensorineural hearing loss. Murine models have been developed in order to understand the pathophysiological mechanisms underlying these lesions. These models are being proposed for the validation of therapeutic protocols for clinical use. The aim of this preclinical study was to assess the pharmacokinetics of the reference antiviral molecule, ganciclovir, in order to optimize these protocols and confirm the diffusion of the molecule to the appropriate target zones.

METHODS

Transplacental and intracochlear diffusion of ganciclovir was evaluated in mice and rats. Pharmacokinetics was assessed in adult mice and pups after 5 consecutive days of intraperitoneal injection of ganciclovir. The occurrence of hematological side effects of ganciclovir was evaluated in the different blood cell lineages.

RESULTS

In adult rats, the intracochlear diffusion of ganciclovir was shown to achieve the same concentration as in blood. In gestating mice, transplacental diffusion was observed, with a fetal-to-maternal blood ratio of 0.5. In newborn mice, the plasma concentration profile of ganciclovir showed a peak at 2 h followed by a gradual decrease. In adult mice, the concentration peaked at 1 h, but became undetectable by 2 h after injection. Counts of white blood cells, red blood cells and platelets decreased significantly in ganciclovir-treated newborn mice.

CONCLUSION

Our data provide evidence for the intracochlear diffusion of the molecule, which may be relevant for the treatment of sensorineural hearing loss in congenitally-infected children.

Inflammasome activation in mouse inner ear in response to MCMV induced hearing loss

Objective

To identify presence of inflammasome activated in mouse cochlea with sensorineural hearing loss (SNHL) caused by cytomegalovirus (CMV) infection.

Method

MCMV was injected into the right cerebral hemisphere in neonatal BALB/c mice at 2000 pfu virus titers. Auditory brainstem responses (ABRs) were tested to evaluate hearing at 21 days. Histopathological studies were conducted to confirm localizations of MCMV infected cells in the inner ear. Expression of inflammasome related factors was assessed by immunofluorescence, Quantitative real-time PCR and Western blotting.

Results

In the mouse model of CMV induced SNHL, inflammasome related kinase Caspase-1 and downstream inflammatory factor IL-1β and IL-18 were found increased and activated after CMV infection in the cochlea. These factors could further up-regulate expression of IL-6 and TNF-α. These inflammatory factors are neurotoxicity and may contribute to hearing impairment. Furthermore, we also detected significantly increased AIM2 protein that accumulated in the SGN of cochleae with CMV infection.

Significance

We have shown that inflammasome as a novel inherent immunity mechanism may contribute to hearing impairment.

Conclusion

Our data indicate that imflammasome assemble in mouse inner ear in response to CMV infection. We have revealed a novel pathology event in CMV induced SNHL involving activation of inflammasome in mouse cochlea. Additionally, we have shown that inflammasome may be a novel target for prevention and treatment of CMV related SNHL.

Restricted infection of murine cytomegalovirus (MCMV) in neonatal mice with MCMV-induced sensorineural hearing loss

BACKGROUND

Congenital infection with human Cytomegalovirus (HCMV) is known to be a causative agent of sensorineural hearing loss (SNHL).

OBJECTIVES

To clarify the nongenetic etiology of SNHL by identifying the Cytomegalovirus (CMV)-infected region in the cochleae.

STUDY DESIGN

We established an animal model of SNHL by injecting neonatal Balb/c mice with intracerebral murine Cytomegalovirus (MCMV) within 24h after delivery.

RESULTS

At 3 weeks of age, unilateral and bilateral SNHL were observed in 24% (5/21) and 29% (6/21) of the mice, respectively. SNHL thereafter progressed, with 79% of mice developing bilateral SNHL by 6 weeks of age. MCMV antigens and DNA were detected in the spiral ganglion, and cells surrounding the meninges and scala tympani at 1 week of age. However, both MCMV antigens and DNA had completely disappeared by 2 weeks of age. It is possible that the MCMV reached the spiral ganglion via cerebrospinal fluid as the result of meningitis, as the stria vascularis was found to be MCMV antigen negative. Myosin VI expression in the outer hair cells was lost at 3 weeks of age. MCMV and myosin VI expression disappeared before and during SNHL progression, respectively.

CONCLUSIONS

There was a definite lag time between the period in which MCMV antigens/DNA-positive cells were observed and that in which SNHL developed and myosin VI-negative hair cells were observed. Further study is needed to explore the role of MCMV in the loss of myosin VI expression in the outer hair cells.

Pathological changes of the inner ear cochlea in different time windows of murine cytomegalovirus-induced hearing loss in a mouse model

CONCLUSIONS

Murine congenital cytomegalovirus (CMV) (MCMV) infection of the inner ear cochlea, which caused continuous pathological change, occurred on the third day after intracerebral injection and persisted for a very long time.

OBJECTIVE

Our study used the MCMV-induced hearing loss neonatal mouse model to investigate the pathological changes of the cochlea in different time windows.

METHODS

Sixty newborn BALB/c mice were randomly and equally divided into the experimental group (MCMV intracerebral injection) and control group (normal saline intracerebral injection). At 1, 3, 5, 7, and 21 days after intracerebral injection, cochleas were extracted and evaluated by MCMV-DNA PCR analysis and histopathological examination.

RESULTS

Two mice died before the end of the experiment in the experimental group, while there were no deaths in the control group. In the experimental group, the MCMV-DNA PCR samples did not show positive results in the gel electrophoresis until the 3-21 days after intracerebral injection, while no positive result was found in the control group. Pathological changes including hemorrhage and inflammatory cell infiltration of the scala vestibule and scala tympani began on the third day, spiral ganglion cell gap widening and cell thinning began on the seventh day, and scala tympani fibrosis began on the 14th day.

Murine CMV-induced hearing loss is associated with inner ear inflammation and loss of spiral ganglia neurons

Congenital human cytomegalovirus (HCMV) occurs in 0.5–1% of live births and approximately 10% of infected infants develop hearing loss. The mechanism(s) of hearing loss remain unknown. We developed a murine model of CMV induced hearing loss in which murine cytomegalovirus (MCMV) infection of newborn mice leads to hematogenous spread of virus to the inner ear, induction of inflammatory responses, and hearing loss. Characteristics of the hearing loss described in infants with congenital HCMV infection were observed including, delayed onset, progressive hearing loss, and unilateral hearing loss in this model and, these characteristics were viral inoculum dependent. Viral antigens were present in the inner ear as were CD3+ mononuclear cells in the spiral ganglion and stria vascularis. Spiral ganglion neuron density was decreased after infection, thus providing a mechanism for hearing loss. The lack of significant inner ear histopathology and persistence of inflammation in cochlea of mice with hearing loss raised the possibility that inflammation was a major component of the mechanism(s) of hearing loss in MCMV infected mice.

Congenital infection with human cytomegalovirus (HCMV) is the most common viral infection of the fetus and occurs in 0.5–2.0% of all live births in most regions in the world. Infection of the fetus can result in a spectrum of end-organ disease, including long term damage to the central nervous system (CNS). Although less than 10% of infected infants exhibit clinical evidence of end-organ disease, up to 10% of the total number of infected infants develop hearing loss. Mechanisms of disease leading to hearing loss are poorly understood because of the limited availability of pathological specimens and accessibility of the inner ear. Existing small animal models fail to recapitulate many features of this infection of the inner ear. In this report we describe a mouse model in which newborn animals infected peripherally with murine CMV develop hearing loss following hematogenous spread of virus to the inner ear. Hearing loss occurs in 30–50% of animals and characteristics of hearing loss in infants with congenital HCMV infection, including delayed onset of hearing loss, progressive hearing loss, and unilateral hearing loss were present in infected mice. Our findings suggest that host derived inflammatory responses and not direct virus-mediated cytopathology are responsible for hearing loss. Findings from this study provide insight into potential mechanisms of hearing loss in infants with congenital HCMV infection.

Animal models of human cytomegalovirus congenital infection

Human cytomegalovirus (HCMV) infection is highly species-specific, which means that it is unable to productively infect laboratory animals. Despite this caveat, studies of animal CMV counterparts in their natural hosts have revealed significant correlations with observed neuropathological effects of congenital HCMV infection and have improved our understanding of host responses to vaccination. The biological relatedness between human and animal CMVs has been confirmed by phylogenetic analyses; the conservation of ‘core' genes that are essential for virus replication as well as genes that contribute similar mechanisms for virus persistence in their respective host species. The common animal models of HCMV congenital infection include Rhesus CMV (RhCMV), guinea-pig CMV (GPCMV) and mouse CMV (MCMV). Whilst animal models of CMV do not fully recapitulate HCMV infection, they each offer specific advantages in understanding HCMV congenital/perinatal infection (summarised in Table 1).

MicroRNA miR-21 attenuates human cytomegalovirus replication in neural cells by targeting Cdc25a

Congenital human cytomegalovirus (HCMV) infection is a leading cause of birth defects, primarily manifesting as neurological disorders. HCMV infection alters expression of cellular microRNAs (miRs) and induces cell cycle arrest, which in turn modifies the cellular environment to favor virus replication. Previous observations found that HCMV infection reduces miR-21 expression in neural progenitor/stem cells (NPCs). Here, we show that infection of NPCs and U-251MG cells represses miR-21 while increasing the levels of Cdc25a, a cell cycle regulator and known target of miR-21. These opposing responses to infection prompted an investigation of the relationship between miR-21, Cdc25a, and viral replication. Overexpression of miR-21 in NPCs and U-251MG cells inhibited viral gene expression, genome replication, and production of infectious progeny, while shRNA-knockdown of miR-21 in U-251MG cells increased viral gene expression. In contrast, overexpression of Cdc25a in U-251MG cells increased viral gene expression and production of infectious progeny and overcame the inhibitory effects of miR-21 overexpression. Three viral gene products-IE1, pp71, and UL26-were shown to inhibit miR-21 expression at the transcriptional level. These results suggest that Cdc25a promotes HCMV replication and elevation of Cdc25a levels after HCMV infection are due in part to HCMV-mediated repression of miR-21. Thus, miR-21 is an intrinsic antiviral factor that is modulated by HCMV infection. This suggests a role for miR-21 downregulation in the neuropathogenesis of HCMV infection of the developing CNS.

IMPORTANCE

Human cytomegalovirus (HCMV) is a ubiquitous pathogen and has very high prevalence among population, especially in China, and congenital HCMV infection is a major cause for birth defects. Elucidating virus-host interactions that govern HCMV replication in neuronal cells is critical to understanding the neuropathogenesis of birth defects resulting from congenital infection. In this study, we confirm that HCMV infection downregulates miR-21 but upregulates Cdc25a. Further determined the negative effects of cellular miRNA miR-21 on HCMV replication in neural progenitor/stem cells and U-251MG glioblastoma/astrocytoma cells. More importantly, our results provide the first evidence that miR-21 negatively regulates HCMV replication by targeting Cdc25a, a vital cell cycle regulator. We further found that viral gene products of IE1, pp71, and UL26 play roles in inhibiting miR-21 expression, which in turn causes increases in Cdc25a and benefits HCMV replication. Thus, miR-21 appears to be an intrinsic antiviral factor that represents a potential target for therapeutic intervention.

Models of vertical cytomegalovirus (CMV) transmission and pathogenesis

Despite the considerable clinical impact of congenital human cytomegalovirus (HCMV) infection, the mechanisms of maternal-fetal transmission and the resultant placental and fetal damage are largely unknown. Here, we discuss animal models for the evaluation of CMV vaccines and virus-induced pathology and particularly explore surrogate human models for HCMV transmission and pathogenesis in the maternal-fetal interface. Studies in floating and anchoring placental villi and more recently, ex vivo modeling of HCMV infection in integral human decidual tissues, provide unique insights into patterns of viral tropism, spread, and injury, defining the outcome of congenital infection, and the effect of potential antiviral interventions.

Immunobiology of congenital cytomegalovirus infection of the central nervous system—the murine cytomegalovirus model

Congenital human cytomegalovirus infection is a leading infectious cause of long-term neurodevelopmental sequelae, including mental retardation and hearing defects. Strict species specificity of cytomegaloviruses has restricted the scope of studies of cytomegalovirus infection in animal models. To investigate the pathogenesis of congenital human cytomegalovirus infection, we developed a mouse cytomegalovirus model that recapitulates the major characteristics of central nervous system infection in human infants, including the route of neuroinvasion and neuropathological findings. Following intraperitoneal inoculation of newborn animals with mouse cytomegalovirus, the virus disseminates to the central nervous system during high-level viremia and replicates in the brain parenchyma, resulting in a focal but widespread, non-necrotizing encephalitis. Central nervous system infection is coupled with the recruitment of resident and peripheral immune cells as well as the expression of a large number of pro-inflammatory cytokines. Although infiltration of cellular constituents of the innate immune response characterizes the early immune response in the central nervous system, resolution of productive infection requires virus-specific CD8(+) T cells. Perinatal mouse cytomegalovirus infection results in profoundly altered postnatal development of the mouse central nervous system and long-term motor and sensory disabilities. Based on an enhanced understanding of the pathogenesis of this infection, prospects for novel intervention strategies aimed to improve the outcome of congenital human cytomegalovirus infection are proposed.