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

Abstract

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 (Enpp1asj/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 Enpp1asj/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 Enpp1asj 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.

STAT1 deficiency predisposes to spontaneous otitis media

“…incidence, while STAT1-KO mice of 9 and 18 weeks showed hearing impairment in 3 out of 8 and 7 out 13, respectively, suggesting a moderate incidence ranging from 37.5-54%. Similar high incidence of hearing loss of 90% has been also found in 12 weeks old Enpp1 asj/asj mice [3]. We might expect that the incidence of hearing impairment increases with age as previously shown [25].…”

“…We might expect that the incidence of hearing impairment increases with age as previously shown [25]. The ABR thresholds in C3H/HeJ and Enpp1 asj/asj mice also increased with age [3,9]. However, it was not always the case with the STAT1-KO mice.…”

“…Treatment outcomes vary across the patients with similar symptoms suggesting variation in the underlying pathophysiology probably due to genetic and environmental factors. An increasing number of candidate genes are associated to otitis media in humans and animals including Chd7, Eya4,Enpp1,Fbxo11,Lmna,Mcph1,Oxgr1,Slc25a21,Splunc1,Tgif1,Tlr4, TNFA among others [1][2][3][4][5][6][7][8][9]. While Tian et al found high incidence of hearing loss in Enpp1 asj/asj mice (90%), Tlr4-deficient mice presented around 50% cases of otitis media and Splunc1-deficient mice around 31% cases of otitis media [3,6,9].…”

Possible Effects of Proton Pump Inhibitors on Hearing Loss Development

“…There are several major studies revealing a significant positive correlation between otitis media in childhood and adult hearing loss, reporting reduced adult hearing thresholds in the entire frequency range if such infections occurred [26,27]. Tian et al designed a study to assess morphological and histological alterations in the middle ear during the course of otitis media with effusion [28]. In this study, researchers examined mice with a point mutation in the Enpp1 gene, which resulted in a high incidence of otitis media.…”

“…Evaluation at 12 weeks old showed hearing loss among 90% of the mutant mice, which was connected with otitis media with effusion. The morphological and histological alterations found in samples obtained from mice with hearing loss were: increased amount of inflammatory cells, thickened middle ear epithelium with fibrous polyps, increased amount of mucin-secreting goblet cells, 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 a tympanic membrane, some of which are typical symptoms of tympanosclerosis [28]. All of the abovementioned findings found a correlation between otitis media and hearing loss, and revealed a possible pathomechanism of that process.…”