Pathophysiology of middle ear epithelium: a new role for prostaglandin E2

Mutation in Phex gene predisposes BALB/c-Phex(Hyp-Duk)/Y mice to otitis media

Genetic susceptibility underlying otitis media (OM) remains to be understood. We show in this study that mutation in Phex gene predisposes the BALB/c-Phex^Hyp-Duk/Y (abbreviated Hyp-Duk/Y) mice to OM, which occurs at post-natal day 21 (P21) with an average penetrance of 73%. The OM was identified by effusion in the middle ear cavity and/or thickening of middle ear mucosae, and was characterised by increase in goblet cells, deformity of epithelial cilia and higher expression of proliferating cell nuclear antigen (PCNA) in cells of the middle ear mucosae. Moreover, the transcription levels of Tlr2, Tlr4, Nfkb1, Ccl4, Il1b and Tnfα in the ears of the Hyp-Duk/Y mice at P35 were significantly upregulated, compared to those of the controls. Higher expression levels of TLR2, TLR4, NF-κB and TNF-α in the middle ears were demonstrated by immunohistochemistry (IHC). However, the OM in the mice was not prevented by azithromycin administration from gestational day 18 to P35. Further study showed that, in contrast to the low mRNA levels of Phex gene in the ears of the Hyp-Duk/Y mice, the mRNA level of Fgf23 was significantly elevated at P9, P14, P21 and P35. Meanwhile, mRNA levels of EP2 (PGE2 receptor), which expressed in the middle ear epithelia as demonstrated by IHC, were already increased at P14 even before the occurrence of OM, indicating that PGE2, an inflammatory mediator, is involved in the OM development in the mutants. Taking together, Phex mutation primarily up-regulates gene expression levels in FGF23 mediated pathways in the middle ears, resulting in cell proliferation and defence impairment at the mucosae and subsequently bacterial infection. The Hyp-Duk/Y mouse is a new genetic mouse model of OM.

Cyclooxygenase 2 expression in otitis media with effusion

OBJECTIVES

To study whether cyclooxygenase 2 (COX-2) plays a role in the development of otitis media with effusion (OME).

STUDY DESIGN/METHODS

An experimental model of endotoxin-induced OME was used in healthy BALB/c mice. Solutions of Salmonella typhimurium endotoxin were injected into the middle ears of the mice, and COX-2 expression in the middle ears was studied using reverse transcription-polymerase chain reaction (RT-PCR) and in situ hybridization (ISH).

RESULTS

Analysis by RT-PCR showed that COX-2 expression in the middle ear increased in a dose-dependent fashion after injection of endotoxin. ISH demonstrated that COX-2 had distinct expression patterns in the epithelium of middle ears with endotoxin-induced OME. COX-2 expression, however, was not detected in normal middle ears.

CONCLUSIONS

COX-2 expression may be one factor contributing to the development of OME.

Immortalization of rat eustachian tube epithelial cells by adenovirus 12-simian virus 40 hybrid virus

The eustachian tube epithelial cells play an important role in the initial pathogenesis of otitis media. In order to study the role of the eustachian tube epithelial cells in the pathogenesis of otitis media, we have established a rat eustachian tube epithelial cell line. The cell line was derived by infecting primary cultures of eustachian tube epithelial cells with the adenovirus 12-simian virus 40 (Adl2-SV40) hybrid virus. The immortalized cells have retained the morphological characteristics of the parental cells and show positive staining with anti-cytokeratin antibodies (a marker for epithelial cells), but not with anti-vimentin antibodies (a fibroblast marker). The cells have been in continuous culture for more than 10 months and have undergone 38 passages. Western blotting and cell staining have confirmed the expression of the SV40 T antigen and p53. Chromosomal analysis indicates that the cell line is aneuploid and derived from male rat epithelial cells. Together, our results suggest that the cell line originated from eustachian tube epithelial cells from a male rat and was successfully immortalized by the Ad12-SV40 virus.

Immortalization of chinchilla middle ear epithelial cells by adenovirus 12-simian virus 40 hybrid virus

In order to study the cellular and molecular mechanisms of the pathogenesis of otitis media, a chinchilla middle ear epithelial cell line (CMEE-1) with differentiated cell characteristics was established by infection of a primary culture with the adenovirus 12-simian virus 40 (Ad12-SV40) hybrid. This cell line has been in continuous culture for 42 passages, whereas the parent cells underwent senescence and died at the 8th passage. The cell line also retains epithelial morphology and expresses cytokeratin polypeptides 4, 7, and 18, characteristic markers for epithelia. In Western blots of cell proteins, bands at 94 and 53 kd were labeled after binding antibodies against SV40 large T antigen and p53, respectively. Karyotype analysis showed that the cell line is derived from chinchilla epithelial cells. These findings confirm that the cell line is a chinchilla epithelial cell immortalized by the hybrid virus.