Otitis media in a mouse model for Down syndrome

Abstract

The Ts65Dn mouse shares many phenotypic characteristics of human Down syndrome. Here, we report that otitis media, characterized by effusion in the middle ear and hearing loss, was prevalent in Ts65Dn mice. Of the 53 Ts65Dn mice tested, 81.1% had high auditory-evoked brainstem response (ABR) thresholds for at least one of the stimulus frequencies (click, 8 kHz, 16 kHz and 32 kHz), in at least one ear. The ABR thresholds were variable and showed no tendency toward increase with age, from 2 to 7 months of age. Observation of pathology in mice, aged 3-4 months, revealed middle ear effusion in 11 of 15 Ts65Dn mice examined, but only in two of 11 wild-type mice. The effusion in each mouse varied substantially in volume and inflammatory cell content. The middle ear mucosae were generally thickened and goblet cells were distributed with higher density in the epithelium of the middle ear cavity of Ts65Dn mice as compared with those of wild-type controls. Bacteria of pathogenic importance to humans also were identified in the Ts65Dn mice. This is the first report of otitis media in the Ts65Dn mouse as a model characteristic of human Down syndrome.

Figure 2

A time-course observation of the ABR thresholds in the right ears of Ts65Dn (Ts) mice and wild-type (euploid) mice. For Ts65Dn mice of ages from 2 to 7 months (n = 8, 8, 9, 15, 7 and 6, respectively, in each sub-group), the individual ABR thresholds at all stimulus frequencies of click (a), 8 kHz (b), 16 kHz (c) and 32 kHz (d) were variable, but the overall tendency was relatively stable at each of the stimulus frequencies, compared with the ABR thresholds of the wild-type mice (n = 5, 8, 7, 5, 6 and 5, respectively, in each sub-group). The mean ABR thresholds in the Ts65Dn mice were about 15 dB SPL higher than the mean thresholds of wild-type mice at all stimulus frequencies measured, with significance indicated by asterisks (*P< 0.05; **P< 0.01). Error bars indicate standard deviation from the mean at each time point, for each mouse group.

Figure 1

Comparison of the mean ABR thresholds of right ears from wild-type (euploid) mice and from Ts65Dn (Ts) mice, at ages ranging from 2 to 7 months. The results showed that the mean ABR thresholds to click stimuli and pure-tone stimulus (8 kHz, 16 kHz or 32 kHz) in the Ts65Dn mice (n = 53) were significantly higher than those of the wild-type control (n = 36). Error bars indicate standard deviation from the mean of each group. *P< 0.001.

Figure 4

Representative figures to visualize goblet cells in the middle ear mucosae of Ts65Dn (Ts) mice and wild-type controls (euploid). Few goblet cells could be found in the middle ear mucosa in the control mouse (a). By contrast, the goblet cells were present at high density among other cells in the epithelium of the middle ear cavity of Ts65Dn mouse [(b) typical goblet cells are indicated by arrows]. Goblet cells have a distinctly polarized morphology in which the nucleus stains black in colour at the cell bas, and the mucus stains a deep rose colour in the middle and apical portions of the cell. Scale bars = 20 μm.

Figure 3

Representative histological images of inflammation in the right middle and inner ears in three different Ts65Dn (Ts) mice. (a), (b) and (c) Middle ear (ME) inflammation with effusion in the middle ear space. The walls (W) of the middle ears became thickened, in sample (c) especially. (d–f) Enlarged images from comparable areas (indicated by squares in solid line) in (a), (b) and (c), respectively, to show the effusion content in the middle ears, with a few inflammatory cells (serous) in (d), modest inflammatory cells (mucoid) in (e) and a large amount of inflammatory cells (purulent) and fibrous proliferation (arrow F) in (f). Polymorphonuclear cells were indicated by arrows in (e) and (f). (g–i) Enlarged images of the cochleae (indicated by squares in broken line) from (a), (b) and (c) respectively. In the mice with middle ear effusion, the cochleae also were involved, especially in scala tympani (ST), revealing serous labyrinthitis as indicated by arrowheads. SV, scala vestibuli; SM, scala media; RM, Reissner’s membrane; StV, stria vascularis; SG, spiral ganglion; OHC, outer hair cell. Scale bars = 500 μm in panels a–c, 20 μm in d–f and 100 μm in panels g–i.