Gene mutations in primary ciliary dyskinesia related to otitis media

The interconnected relationships between middle ear bulla size, cavitation defects, and chronic otitis media revealed in a syndromic mouse model

High incidence of chronic otitis media is associated with human craniofacial syndromes, suggesting that defects in the formation of the middle ear and associated structures can have a knock-on effect on the susceptibility to middle ear inflammation. Patients with branchio-oto-renal (BOR) syndrome have several defects in the ear leading to both sensorineural and conductive hearing loss, including otitis media. 40% of BOR syndrome cases are due to Eya1 haploinsufficiency, with mouse models affecting Eya1, mimicking many of the defects found in patients. Here, we characterize the onset, consequences, and underlying causes of chronic otitis media in Eya1 heterozygous mice. Cavitation defects were evident in these mice from postnatal day (P)11 onwards, with mesenchyme around the promontory and attic regions of the middle ear space. This mesenchyme was still prominent in adult Eya1 heterozygous mice, while the wild-type littermates had fully aerated ears from P14 onwards. MicroCT analysis highlighted a significantly smaller bulla, confirming the link between bulla size defects and the ability of the mesenchyme to retract successfully. Otitis media was observed from P14, often presenting unilaterally, resulting in hyperplasia of the middle ear mucosa, expansion of secretory cells, defects in the motile cilia, and changes in basal epithelial cell markers. A high incidence of otitis media was identified in older mice but only associated with ears with retained mesenchyme. To understand the impact of the environment, the mouse line was rederived onto a super-clean environment. Cavitation defects were still evident at early stages, but these generally resolved over time, and importantly, no signs of otitis media were observed at 6 weeks. In conclusion, we show that a small bulla size is closely linked to defects in cavitation and the presence of retained mesenchyme. A delay in retraction of the mesenchyme predates the onset of otitis media, making the ears susceptible to its development. Early exposure to OM appears to exacerbate the cavitation defect, with mesenchyme evident in the middle ear throughout the animal’s life. This highlights that permanent damage to the middle ear can arise as a consequence of the early onset of OM.

The transcriptional landscape of the cultured murine middle ear epithelium in vitro

Otitis media (OM) is the most common paediatric disease and leads to significant morbidity. Although understanding of underlying disease mechanisms is hampered by complex pathophysiology, it is clear that epithelial abnormalities underpin the disease. The mechanisms underpinning epithelial remodelling in OM remain unclear. We recently described a novel in vitro model of mouse middle ear epithelial cells (mMEECs) that undergoes mucociliary differentiation into the varied epithelial cell populations seen in the middle ear cavity. We now describe genome wide gene expression profiles of mMEECs as they undergo differentiation. We compared the gene expression profiles of original (uncultured) middle ear cells, confluent cultures of undifferentiated cells and cells that had been differentiated for 7 days at an air liquid interface (ALI). >5000 genes were differentially expressed among the three groups of cells. Approximately 4000 genes were differentially expressed between the original cells and day 0 of ALI culture. The original cell population was shown to contain a mix of cell types, including contaminating inflammatory cells that were lost on culture. Approximately 500 genes were upregulated during ALI induced differentiation. These included some secretory genes and some enzymes but most were associated with the process of ciliogenesis. The data suggest that the in vitro model of differentiated murine middle ear epithelium exhibits a transcriptional profile consistent with the mucociliary epithelium seen within the middle ear. Knowledge of the transcriptional landscape of this epithelium will provide a basis for understanding the phenotypic changes seen in murine models of OM.

Summary: This paper presents a genome wide transcriptional analysis of murine middle ear epithelial cells as they undergo differentiation to a mucociliary phenotype representative of the native middle ear epithelium.

IFT46 Expression in the Nasal Mucosa of Primary Ciliary Dyskinesia Patients: Preliminary Study

Background

Primary ciliary dyskinesia (PCD) is characterised by an imbalance in mucociliary clearance leading to chronic respiratory infections. Cilia length is considered to be a contributing factor in cilia movement. Recently, IFT46 protein has been related to cilia length. Therefore, this work aims to study IFT46 expression in a PCD patients cohort and analyse its relationship with cilia length and function, as it was not previously described.

Materials and methods

The expression of one intraflagellar transport (IFT46) and two regulating ciliary architecture (FOXJ1 and DNAI2) genes, as well as cilia length of 27 PCD patients, were measured. PCD patients were diagnosed based on clinical data, and cilia function and ultrastructure. Gene expression was estimated by real-time RT-PCR and cilia length by electron microscopy in nasal epithelium biopsies.

Results and conclusions: While IFT46 expression was only diminished in patients with short cilia, FOXJ1, and DNAI2 expression were reduced in all PCD patient groups compared to controls levels. Among the PCD patients, cilia were short in 44% (5.9 ± 0.70 µm); nine of these (33% from the total) patients’ cilia also had an abnormal ultrastructure. Cilia length was normal in 33% of patients (6.4 ± 0.39 µm), and only three patients’ biopsies indicated decreased expression of dynein.

Primary Ciliary Dyskinesia Diagnostic Challenges: Understanding the Clinical Phenotype of the Puerto Rican RSPH4A Founder Mutation

Primary ciliary dyskinesia (PCD) is a rare, heterogeneous ciliopathy resulting in chronic oto-sino-pulmonary disease, bronchiectasis, newborn respiratory distress, and laterality defects. PCD diagnosis can be achieved by following diagnostic algorithms that include electron microscopy, genetics, and ancillary testing. Genetic mutations in more than 45 genes, including RSPH4A, can lead to PCD. RSPH4A mutations located on chromosome six, affect radial spokes and results in central complex apparatus abnormalities. The RSPH4A [c.921 + 3_6delAAGT] founder mutation was described as one cause of PCD without laterality defects in Puerto Rico. Additionally, there are further diagnostic challenges present in the Puerto Rican population to diagnose PCD. We describe the demographics, clinical features, and RSPH4A genetic variants in 13 patients with clinical PCD affecting 11 Puerto Ricans from unrelated families.

Rhinosinusitis in Pediatric Primary Ciliary Dyskinesia: Impact of Disease

Objectives

Primary ciliary dyskinesia (PCD) is a genetic disorder characterized by abnormal respiratory cilia ultrastructure and/or function causing defective mucociliary clearance. We investigated the extent and severity of rhinosinusitis in a large cohort of children with PCD and explored associations among risk factors, including genotype and sinus disease.

Study Design

Retrospective chart review.

Setting

Tertiary academic children’s hospital.

Subjects and Methods

A review was conducted with a patient registry at the PCD Foundation Center at our institution. Demographic, imaging, clinical, and operative data were reviewed through the institutional electronic health record system.

Results

Fifty-four subjects were identified with mean and median age at diagnosis of 5.2 and 4.0 years. The male:female ratio was 35%:65%. Sinus symptoms were present in 46 (85%) subjects, 22 of whom had chronic rhinosinusitis. Nineteen (35%) subjects underwent operative intervention, consisting of endoscopic sinus surgery (ESS; 16 patients) and maxillary lavage (3 patients). Nineteen subjects underwent adenoidectomy for PCD-related indications. Five sinus-related admissions in 3 subjects were noted during the study period, and no complication of rhinosinusitis occurred in the cohort. Genetic test results were available in 27 subjects, in whom 23 (85%) had biallelic mutations in a PCD gene. Demographic factors, Lund-Mackay score, and PCD genotype were not found to be predictors for ESS or hospitalization in our cohort.

Conclusion

While rhinosinusitis was common in our PCD cohort, most patients did not require ESS. Since complications of rhinosinusitis were uncommon, we recommend judicious surgical management tailored to the patient’s symptoms.

[Polypous pansinusitis with the deformation of the external nose in a 8 year-old child presenting with the primary ciliary dyskinesia syndrome]

This article reports a rare observation of the development of chronic polypous pansinusitis with deformation of the external nose in a 8 year-old child presenting with primary ciliary dyskinesia syndrome. The patient underwent multiple surgical interventions in the preceding period. The key argument in favour of the definitive diagnosis was the results of investigation of ciliated epithelium biopsy taken from the nasal cavity and bronchi in combination with the data obtained by diagnostic endoscopy of the nasal cavity and nasopharynx supplemented by computed tomography. The proposed treatment strategy including endoscopic endonasal pansinusotomy, antibacterial therapy taking into consideration the sensitivity of the seeded microorganism, and hormonal therapy proved optimal for the management of the given patient.

Cilia distribution and polarity in the epithelial lining of the mouse middle ear cavity

The middle ear conducts sound to the cochlea for hearing. Otitis media (OM) is the most common illness in childhood. Moreover, chronic OM with effusion (COME) is the leading cause of conductive hearing loss. Clinically, COME is highly associated with Primary Ciliary Dyskinesia, implicating significant contributions of cilia dysfunction to COME. The understanding of middle ear cilia properties that are critical to OM susceptibility, however, is limited. Here, we confirmed the presence of a ciliated region near the Eustachian tube orifice at the ventral region of the middle ear cavity, consisting mostly of a lumen layer of multi-ciliated and a layer of Keratin-5-positive basal cells. We also found that the motile cilia are polarized coordinately and display a planar cell polarity. Surprisingly, we also found a region of multi-ciliated cells that line the posterior dorsal pole of the middle ear cavity which was previously thought to contain only non-ciliated cells. Our study provided a more complete understanding of cilia distribution and revealed for the first time coordinated polarity of cilia in the epithelium of the mammalian middle ear, thus illustrating novel structural features that are likely critical for middle ear functions and related to OM susceptibility.

Ectopic Mineralization and Conductive Hearing Loss in Enpp1asj Mutant Mice, a New Model for Otitis Media and Tympanosclerosis

Otitis media (OM), inflammation of the middle ear, is a common cause of hearing loss in children and in patients with many different syndromic diseases. Studies of the human population and mouse models have revealed that OM is a multifactorial disease with many environmental and genetic contributing factors. Here, we report on otitis media-related hearing loss in asj (ages with stiffened joints) mutant mice, which bear a point mutation in the Enpp1 gene. Auditory-evoked brainstem response (ABR) measurements revealed that around 90% of the mutant mice (Enpp1^asj/asj) tested had moderate to severe hearing impairment in at least one ear. The ABR thresholds were variable and generally elevated with age. We found otitis media with effusion (OME) in all of the hearing-impaired Enpp1^asj/asj mice by anatomic and histological examinations. The volume and inflammatory cell content of the effusion varied among the asj mutant mice, but all mutants exhibited a thickened middle ear epithelium with fibrous polyps and more mucin-secreting goblet cells than controls. Other abnormalities observed in the Enpp1 mutant mice include over-ossification at the round window ridge, thickened and over-calcified stapedial artery, fusion of malleus and incus, and white patches on the inside of tympanic membrane, some of which are typical symptoms of tympanosclerosis. An excessive yellow discharge was detected in the outer ear canal of older asj mutant mice, with 100% penetrance by 5 months of age, and contributes to the progressive nature of the hearing loss. This is the first report of hearing loss and ear pathology associated with an Enpp1 mutation in mice. The Enpp1^asj mutant mouse provides a new animal model for studying tympanosclerotic otitis and otitis media with effusion, and also provides a specific model for the hearing loss recently reported to be associated with human ENPP1 mutations causing generalized arterial calcification of infancy and hypophosphatemic rickets.

Nasal Mucociliary Clearance in Adenoid Hypertrophy and Otitis Media with Effusion

Mucociliary clearance (MCC), which exists in many systems, is the first defensive mechanism of the human body. Nasal MCC has an important role in transporting the secretions of the nasal cavity and paranasal sinuses along with the trapped inhaled pathogens to the nasopharynx. Physiologic or pathologic situations that effect nasal MCC, such as temperature, humidity, nasal obstruction, allergic rhinitis, chronic infections, etc., lead to impaired MCC and related local or circumjacent system disorders. With this perspective, when a unified airway with a multiple disease principle is considered, investigating the relationship between adenoid hypertrophy (AH), otitis media with effusion (OME) and nasal MCC is logical. In this review, histological and physiologic properties of nasal MCC and its possible role involving pathologic situations such as AH and OME is discussed together with recent literature findings.

Otitis media in sperm-associated antigen 6 (Spag6)-deficient mice

Mammalian SPAG6 protein is localized to the axoneme central apparatus, and it is required for normal flagella and cilia motility. Recent studies demonstrated that the protein also regulates ciliogenesis and cilia polarity in the epithelial cells of brain ventricles and trachea. Motile cilia are also present in the epithelial cells of the middle ear and Eustachian tubes, where the ciliary system participates in the movement of serous fluid and mucus in the middle ear. Cilia defects are associated with otitis media (OM), presumably due to an inability to efficiently transport fluid, mucus and particles including microorganisms. We investigated the potential role of SPAG6 in the middle ear and Eustachian tubes by studying mice with a targeted mutation in the Spag6 gene. SPAG6 is expressed in the ciliated cells of middle ear epithelial cells. The orientation of the ciliary basal feet was random in the middle ear epithelial cells of Spag6-deficient mice, and there was an associated disrupted localization of the planar cell polarity (PCP) protein, FZD6. These features are associated with disordered cilia orientation, confirmed by scanning electron microscopy, which leads to uncoordinated cilia beating. The Spag6 mutant mice were also prone to develop OM. However, there were no significant differences in bacterial populations, epithelial goblet cell density, mucin expression and Eustachian tube angle between the mutant and wild-type mice, suggesting that OM was due to accumulation of fluid and mucus secondary to the ciliary dysfunction. Our studies demonstrate a role for Spag6 in the pathogenesis of OM in mice, possibly through its role in the regulation of cilia/basal body polarity through the PCP-dependent mechanisms in the middle ear and Eustachian tubes.