What have we learned from murine models of otitis media?

Otitis media: recent advances in otitis media vaccine development and model systems

Otitis media is an inflammatory disorder of the middle ear caused by airways-associated bacterial or viral infections. It is one of the most common childhood infections as globally more than 80% of children are diagnosed with acute otitis media by 3 years of age and it is a common reason for doctor's visits, antibiotics prescriptions, and surgery among children. Otitis media is a multifactorial disease with various genetic, immunologic, infectious, and environmental factors predisposing children to develop ear infections. Streptococcus pneumoniae, Haemophilus influenzae, and Moraxella catarrhalis are the most common culprits responsible for acute otitis media. Despite the massive global disease burden, the pathogenesis of otitis media is still unclear and requires extensive future research. Antibiotics are the preferred treatment to cure middle ear infections, however, the antimicrobial resistance rate of common middle ear pathogens has increased considerably over the years. At present, pneumococcal and influenza vaccines are administered as a preventive measure against otitis media, nevertheless, these vaccines are only beneficial in preventing carriage and/or disease caused by vaccine serotypes. Otitis media caused by non-vaccine serotype pneumococci, non-typeable H. influenza, and M. catarrhalis remain an important healthcare burden. The development of multi-species vaccines is an arduous process but is required to reduce the global burden of this disease. Many novel vaccines against S. pneumoniae, non-typeable H. influenza, and M. catarrhalis are in preclinical trials. It is anticipated that these vaccines will lower the disease burden and provide better protection against otitis media. To study disease pathology the rat, mouse, and chinchilla are commonly used to induce experimental acute otitis media to test new therapeutics, including antibiotics and vaccines. Each of these models has its advantages and disadvantages, yet there is still a need to develop an improved animal model providing a better correlated mechanistic understanding of human middle ear infections, thereby underpinning the development of more effective otitis media therapeutics. This review provides an updated summary of current vaccines against otitis media, various animal models of otitis media, their limitations, and some future insights in this field providing a springboard in the development of new animal models and novel vaccines for otitis media.

Resolution of otitis media in a humanized mouse model

Otitis media (OM) is one of the largest public health problems of children and has devastating impacts in developing countries. The substantial medical and human costs involved have led to research to understand the disease and improve treatment. Animal models of OM have yielded critical information about the immune, inflammatory and genetic mechanisms of OM. However, it is important to link animal studies to human immune and inflammatory responses. In recent years, "humanized" mice have become a valuable tool to study the human immune system in an animal model. Here we describe the first use of humanized mice to study OM. We demonstrate that humanized mice with a sufficient degree of engraftment recapitulate a normal middle ear (ME) inflammatory response to bacterial infection, including the recruitment of human immune cells, and exhibit normal recovery. Moreover, these animals exhibit regulated expression of human-specific immune and inflammatory genes in the ME. In contrast, mice with insufficient engraftment fail to resolve OM. This model has many potential uses in OM research, including using hematopoietic stem cells from patients with differing degrees of OM susceptibility, to understand the role of human immune responses in proneness to this common childhood disease.

Innate Immunity in the Middle Ear Mucosa

Otitis media (OM) encompasses a spectrum of clinical presentations ranging from the readily identifiable Acute OM (AOM), which is characterised by otalgia and fever, to chronic otitis media with effusion (COME) where impaired hearing due to middle ear effusion may be the only clinical symptom. Chronic suppurative OM (CSOM) presents as a more severe form of OM, involving perforation of the tympanic membrane. The pathogenesis of OM in these varied clinical presentations is unclear but activation of the innate inflammatory responses to viral and/or bacterial infection of the upper respiratory tract performs an integral role. This localised inflammatory response can persist even after pathogens are cleared from the middle ear, eustachian tubes and, in the case of respiratory viruses, even the nasal compartment. Children prone to OM may experience an over exuberant inflammatory response that underlies the development of chronic forms of OM and their sequelae, including hearing impairment. Treatments for chronic effusive forms of OM are limited, with current therapeutic guidelines recommending a "watch and wait" strategy rather than active treatment with antibiotics, corticosteroids or other anti-inflammatory drugs. Overall, there is a clear need for more targeted and effective treatments that either prevent or reduce the hyper-inflammatory response associated with chronic forms of OM. Improved treatment options rely upon an in-depth understanding of OM pathogenesis, particularly the role of the host innate immune response during acute OM. In this paper, we review the current literature regarding the innate immune response within the middle ear to bacterial and viral otopathogens alone, and as co-infections. This is an important consideration, as the role of respiratory viruses as primary pathogens in OM is not yet fully understood. Furthermore, increased reporting from PCR-based diagnostics, indicates that viral/bacterial co-infections in the middle ear are more common than bacterial infections alone. Increasingly, the mechanisms by which viral/bacterial co-infections may drive or maintain complex innate immune responses and inflammation during OM as a chronic response require investigation. Improved understanding of the pathogenesis of chronic OM, including host innate immune response within the middle ear is vital for development of improved diagnostic and treatment options for our children.

From Evidence to Clinical Guidelines in Antibiotic Treatment in Acute Otitis Media in Children

Acute otitis media (AOM) in children represents a public health concern, being one of the leading causes of health care visits and antibiotic prescriptions worldwide. The overall aim of this paper is to unravel the major current insights into the antibiotic treatment of AOM in children. Our approach is three-fold: 1. a preclinical evaluation of antibiotics in animal models of AOM stressing on the advantages of different species when testing for different schemes of antibiotics; 2. an overview on the new antimicrobial agents whose efficacy has been demonstrated in refractory cases of AOM in children; and 3. an analysis of the different guidelines stressing on the differences and similarities between the various schemes of antibiotic treatment. The preferred therapeutic agents remain amoxicillin and the amoxicillin-clavulanate combination for AOM caused by Streptococcus pneumoniae, whereas oral cephalosporin is preferred in AOM due to Moraxella catarrhalis and Haemophilus influenzae. As for the second and third line antimicrobial treatments, there is a wide variety of suggested antibiotic classes with variations in duration and posology. The decision to prescribe antimicrobial treatment as a first-line choice is based on the severity of the symptoms in 16 of the guidelines included in this review.

Transcript Analysis Reveals a Hypoxic Inflammatory Environment in Human Chronic Otitis Media With Effusion

Chronic otitis media with effusion (COME) is the most common cause of childhood hearing loss in the developed world. Underlying pathophysiology is not well understood, and in particular the factors that lead to the transition from acute to chronic inflammation. Here we present the first genome-wide transcript analysis of white blood cells in the effusion of children with COME. Analysis of microarray data for enriched pathways reveals upregulation of hypoxia pathways, which is confirmed using real-time PCR and determining VEGF protein titres. Other pathways upregulated in both mucoid and serous effusions include Toll-like receptor signaling, complement, and RANK-RANKL. Cytology reveals neutrophils and macrophages predominated in both serous and mucoid effusions, however, serous samples had higher lymphocyte and eosinophil differential counts, while mucoid samples had higher neutrophil differential counts. Transcript analysis indicates serous fluids have CD4+ and CD8+ T-lymphocyte, and NK cell signatures. Overall, our findings suggest that inflammation and hypoxia pathways are important in the pathology of COME, and targets for potential therapeutic intervention, and that mucoid and serous COME may represent different immunological responses.

Animal models of acute otitis media - A review with practical implications for laboratory research

Considerable animal research has focused on developing new strategies for the prevention and treatment of acute otitis media (AOM). Several experimental models of AOM have thus been developed. A PubMed search of the English literature was conducted from 1975 to July 2016 using the search terms "animal model" and "otitis media" from which 91 published studies were included for analysis, yielding 123 animal models. The rat, mouse and chinchilla are the preferred animals for experimental AOM models with their individual advantages and disadvantages. The most common pathogens used to create AOM are Streptococcus pneumoniae, Haemophilus influenzae and Moraxella catarrhalis. Streptococcus pneumoniae (types 3, 23 and 6A) and non-typeable Haemophilus influenzae (NTHi) are best options for inoculation into rat and mouse models. Adding viral pathogens such as RSV and Influenza A virus, along with creating ET dysfunction, are useful adjuncts in animal models of AOM. Antibiotic prophylaxis may interfere with the inflammatory response without a significant reduction in animal mortality.

A mouse-to-man candidate gene study identifies association of chronic otitis media with the loci TGIF1 and FBXO11

Chronic otitis media with effusion (COME) is the most common cause of hearing loss in children, and known to have high heritability. Mutant mouse models have identified Fbxo11, Evi1, Tgif1, and Nisch as potential risk loci. We recruited children aged 10 and under undergoing surgical treatment for COME from 35 hospitals in the UK, and their nuclear family. We performed association testing with the loci FBXO11, EVI1, TGIF1 and NISCH and sought to replicate significant results in a case-control cohort from Finland. We tested 1296 families (3828 individuals), and found strength of association with the T allele at rs881835 (p = 0.006, OR 1.39) and the G allele at rs1962914 (p = 0.007, OR 1.58) at TGIF1, and the A allele at rs10490302 (p = 0.016, OR 1.17) and the G allele at rs2537742 (p = 0.038, OR 1.16) at FBXO11. Results were not replicated. This study supports smaller studies that have also suggested association of otitis media with polymorphism at FBX011, but this is the first study to report association with the locus TGIF1. Both FBX011 and TGIF1 are involved in TGF-β signalling, suggesting this pathway may be important in the transition from acute to chronic middle ear inflammation, and a potential molecular target.

A mutation in Nischarin causes otitis media via LIMK1 and NF-κB pathways

Otitis media (OM), inflammation of the middle ear (ME), is a common cause of conductive hearing impairment. Despite the importance of the disease, the aetiology of chronic and recurrent forms of middle ear inflammatory disease remains poorly understood. Studies of the human population suggest that there is a significant genetic component predisposing to the development of chronic OM, although the underlying genes are largely unknown. Using N-ethyl-N-nitrosourea mutagenesis we identified a recessive mouse mutant, edison, that spontaneously develops a conductive hearing loss due to chronic OM. The causal mutation was identified as a missense change, L972P, in the Nischarin (NISCH) gene. edison mice develop a serous or granulocytic effusion, increasingly macrophage and neutrophil rich with age, along with a thickened, inflamed mucoperiosteum. We also identified a second hypomorphic allele, V33A, with only modest increases in auditory thresholds and reduced incidence of OM. NISCH interacts with several proteins, including ITGA5 that is thought to have a role in modulating VEGF-induced angiogenesis and vascularization. We identified a significant genetic interaction between Nisch and Itga5; mice heterozygous for Itga5-null and homozygous for edison mutations display a significantly increased penetrance and severity of chronic OM. In order to understand the pathological mechanisms underlying the OM phenotype, we studied interacting partners to NISCH along with downstream signalling molecules in the middle ear epithelia of edison mouse. Our analysis implicates PAK1 and RAC1, and downstream signalling in LIMK1 and NF-κB pathways in the development of chronic OM.

Otitis media (OM) is the most common cause of deafness in children and is primarily characterised by inflammation of the middle ear. It is the most common cause of surgery in children in the developed world, with many children developing recurrent and chronic forms of OM undergoing tympanostomy tube insertion. There is evidence that a significant genetic component contributes towards the development of recurrent and chronic forms of OM. The mouse has been a powerful tool for identifying the genes involved in chronic OM. In this study we identified and characterised edison, a novel mouse model of chronic OM that shares important features with the chronic disease in humans. A mutation in the Nisch gene causes edison mice to spontaneously develop OM following birth and subsequently develop chronic OM, with an associated hearing loss. Our molecular analysis of the mutation reveals the underlying pathological mechanisms and pathways involved in OM in the edison mouse, involving PAK1, RAC1 and downstream signalling in LIMK1 and NF-κB pathways. Identification of the edison mutant provides an important genetic disease model of chronic OM and implicates a new gene and genetic pathways involved in predisposition to OM.

Identification of induced and naturally occurring conductive hearing loss in mice using bone conduction

While many mouse models of hearing loss have been described, a significant fraction of the genetic defects in these models affect both the inner ear and middle ears. A common method used to separate inner-ear (sensory-neural) from middle-ear (conductive) pathologies in the hearing clinic is the combination of air-conduction and bone-conduction audiometry. In this report, we investigate the use of air- and bone-conducted evoked auditory brainstem responses to perform a similar separation in mice. We describe a technique by which we stimulate the mouse ear both acoustically and via whole-head vibration. We investigate the sensitivity of this technique to conductive hearing loss by introducing middle-ear lesions in normal hearing mice. We also use the technique to investigate the presence of an age-related conductive hearing loss in a common mouse model of presbycusis, the BALB/c mouse.

Innate Immunity: Orchestrating Inflammation and Resolution of Otitis Media

Otitis media (OM) is a common disease in young children, accounting for more office visits and surgeries than any other pediatric condition. It is associated with an estimated cost of five billion dollars annually in the USA. Moreover, chronic and recurrent middle ear (ME) disease leads to hearing loss during critical periods of language acquisition and learning leading to delays in reaching developmental milestones and risking permanent damage to the ME and inner ear in severe cases. Therefore, research to understand the disease pathogenesis and identify new therapeutics is important. Although OM is a multifactorial disease, targeting the molecular mechanisms that drive inflammation and OM resolution is critical. In this review, we discuss the current evidence suggesting that innate immune receptors and effectors play key roles in OM by mediating both the ME inflammatory responses and recovery.

Biofilm models of polymicrobial infection

Interactions between microbes are complex and play an important role in the pathogenesis of infections. These interactions can range from fierce competition for nutrients and niches to highly evolved cooperative mechanisms between different species that support their mutual growth. An increasing appreciation for these interactions, and desire to uncover the mechanisms that govern them, has resulted in a shift from monomicrobial to polymicrobial biofilm studies in different disease models. Here we provide an overview of biofilm models used to study select polymicrobial infections and highlight the impact that the interactions between microbes within these biofilms have on disease progression. Notable recent advances in the development of polymicrobial biofilm-associated infection models and challenges facing the study of polymicrobial biofilms are addressed.

The transcriptome of a complete episode of acute otitis media

BACKGROUND

Otitis media is the most common disease of childhood, and represents an important health challenge to the 10-15% of children who experience chronic/recurrent middle ear infections. The middle ear undergoes extensive modifications during otitis media, potentially involving changes in the expression of many genes. Expression profiling offers an opportunity to discover novel genes and pathways involved in this common childhood disease. The middle ears of 320 WBxB6 F1 hybrid mice were inoculated with non-typeable Haemophilus influenzae (NTHi) or PBS (sham control). Two independent samples were generated for each time point and condition, from initiation of infection to resolution. RNA was profiled on Affymetrix mouse 430 2.0 whole-genome microarrays.

RESULTS

Approximately 8% of the sampled transcripts defined the signature of acute NTHi-induced otitis media across time. Hierarchical clustering of signal intensities revealed several temporal gene clusters. Network and pathway enrichment analysis of these clusters identified sets of genes involved in activation of the innate immune response, negative regulation of immune response, changes in epithelial and stromal cell markers, and the recruitment/function of neutrophils and macrophages. We also identified key transcriptional regulators related to events in otitis media, which likely determine the expression of these gene clusters. A list of otitis media susceptibility genes, derived from genome-wide association and candidate gene studies, was significantly enriched during the early induction phase and the middle re-modeling phase of otitis but not in the resolution phase. Our results further indicate that positive versus negative regulation of inflammatory processes occur with highly similar kinetics during otitis media, underscoring the importance of anti-inflammatory responses in controlling pathogenesis.

CONCLUSIONS

The results characterize the global gene response during otitis media and identify key signaling and transcription factor networks that control the defense of the middle ear against infection. These networks deserve further attention, as dysregulated immune defense and inflammatory responses may contribute to recurrent or chronic otitis in children.

Myringotomy in the Junbo mouse model of chronic otitis media alleviates inflammation and cellular hypoxia

OBJECTIVES/HYPOTHESIS

Ventilation of the chronically inflamed middle ear is a key outcome in functional middle ear surgery. Grommets eliminate middle ear effusion, but there is also evidence that they downregulate inflammation. The reason for this is not understood, but there is little to suggest alteration in eustachian tube ventilatory capacity. Previous work has shown that the Junbo mouse model of chronic otitis media has hypoxic middle ear mucosa and bulla fluid leucocytes. Here we explore whether surgical ventilation may alleviate chronic otitis media through downregulation of hypoxia.

STUDY DESIGN

Surgical intervention on a mouse model of disease.

METHODS

We established patency of myringotomy incision as 5 days in wild-type mice. We performed unilateral myringotomy on three cohorts of mice: 10 wild-type controls, 12 Junbo mice, and 15 Junbo mice with additional removal of middle ear effusion. A small cohort of these mice were labeled in vivo by intraperitoneal injection of pimonidazole to identify tissue hypoxia. Tissues were assessed for mucoperiosteal thickening and pimonidazole labeling, comparing operated to nonoperated ears.

RESULTS

Ventilation of the inflamed Junbo middle ear revealed significant reduction in inflammatory thickening associated with loss of pimonidazole labeling, suggesting resolution of cellular hypoxia.

CONCLUSIONS

Surgical ventilation may achieve therapeutic effect through alleviation of cellular hypoxia in the chronically inflamed middle ear. Targeted molecular therapy of hypoxia signaling may offer future alternative therapy for chronic otitis media.

Targeting of Slc25a21 is associated with orofacial defects and otitis media due to disrupted expression of a neighbouring gene

Homozygosity for Slc25a21^{tm1a(KOMP)Wtsi} results in mice exhibiting orofacial abnormalities, alterations in carpal and rugae structures, hearing impairment and inflammation in the middle ear. In humans it has been hypothesised that the 2-oxoadipate mitochondrial carrier coded by SLC25A21 may be involved in the disease 2-oxoadipate acidaemia. Unexpectedly, no 2-oxoadipate acidaemia-like symptoms were observed in animals homozygous for Slc25a21^{tm1a(KOMP)Wtsi} despite confirmation that this allele reduces Slc25a21 expression by 71.3%. To study the complete knockout, an allelic series was generated using the loxP and FRT sites typical of a Knockout Mouse Project allele. After removal of the critical exon and neomycin selection cassette, Slc25a21 knockout mice homozygous for the Slc25a21^{tm1b(KOMP)Wtsi} and Slc25a21^{tm1d(KOMP)Wtsi} alleles were phenotypically indistinguishable from wild-type. This led us to explore the genomic environment of Slc25a21 and to discover that expression of Pax9, located 3′ of the target gene, was reduced in homozygous Slc25a21^{tm1a(KOMP)Wtsi} mice. We hypothesize that the presence of the selection cassette is the cause of the down regulation of Pax9 observed. The phenotypes we observed in homozygous Slc25a21^{tm1a(KOMP)Wtsi} mice were broadly consistent with a hypomorphic Pax9 allele with the exception of otitis media and hearing impairment which may be a novel consequence of Pax9 down regulation. We explore the ramifications associated with this particular targeted mutation and emphasise the need to interpret phenotypes taking into consideration all potential underlying genetic mechanisms.