Temperature-sensitive SV40-immortalized rat middle ear epithelial cells

Isolation and Culture of Primary Mouse Middle Ear Epithelial Cells

Epithelial abnormalities underpin the development of the middle ear disease, otitis media (OM). Until now, a well-characterized in vitro model of the middle ear (ME) epithelium that replicates the complex cellular composition of the middle ear has not been available. This chapter describes the development of a novel in vitro model of mouse middle ear epithelial cells (mMECs), cultured at the air-liquid interface (ALI). This system enables recapitulation of the characteristics of the native murine ME epithelium. We demonstrate that mMECs undergo differentiation into the varied cell populations seen within the native middle ear. Overall, our mMEC culture system can help better understand the cell biology of the middle ear and improve our understanding of the pathophysiology of OM. The model also has the potential to serve as a platform for validation of treatments designed to reverse aspects of epithelial remodeling underpinning OM development.

An in vitro model of murine middle ear epithelium

Otitis media (OM), or middle ear inflammation, 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. There is currently a lack of a well-characterised in vitro model of the middle ear (ME) epithelium that replicates the complex cellular composition of the middle ear. Here, we report the development of a novel in vitro model of mouse middle ear epithelial cells (mMECs) at an air–liquid interface (ALI) that recapitulates the characteristics of the native murine ME epithelium. We demonstrate that mMECs undergo differentiation into the varied cell populations seen within the native middle ear. Proteomic analysis confirmed that the cultures secrete a multitude of innate defence proteins from their apical surface. We showed that the mMECs supported the growth of the otopathogen, nontypeable Haemophilus influenzae (NTHi), suggesting that the model can be successfully utilised to study host–pathogen interactions in the middle ear. Overall, our mMEC culture system can help to better understand the cell biology of the middle ear and improve our understanding of the pathophysiology of OM. The model also has the potential to serve as a platform for validation of treatments designed to reverse aspects of epithelial remodelling that underpin OM development.

Summary: Development and systematic characterisation of an in vitro otopathogenic infection model of the murine middle ear epithelium as a tool to better understand the complex pathophysiology of Otitis media.

Activation of the transforming growth factor beta pathway in bacterial otitis media

OBJECTIVES

Granulation tissue is common in otitis media (OM), yet little is known about the signaling pathways in the formation of granulation tissue in response to infections. In this study, we sought to investigate the activation of the transforming growth factor beta (TGF-beta) signaling pathway in the formation of granulation tissue in response to middle ear pathogens.

METHODS

Rat OM models were made by inoculating pneumococcus type 6A or nontypeable Haemophilus influenzae into the middle ear cavity or by obstructing the eustachian tube. Various pathway activities in the middle ear mucosa were analyzed with microarrays.

RESULTS

The TGF-beta signaling pathway was highly regulated in the middle ear cleft with bacterial OM, but not in the ears with eustachian tube obstruction. In ears with bacterial OM, the TGF-beta signaling pathway products were higher in Haemophilus-infected ears than in pneumococcus-infected ears.

CONCLUSIONS

Bacterial OM triggers granulation tissue to thrive in the middle ear cleft of rats. Nontypeable H influenzae is more potent than pneumococcus type 6A in the formation of granulation tissue. Eustachian tube obstruction alone did not contribute to granulation tissue formation in the middle ear.

The role of inhibitor of DNA-binding (Id1) in hyperproliferation of keratinocytes: the pathological basis for middle ear cholesteatoma from chronic otitis media

OBJECTIVES

A hallmark of cholesteatoma is hyperproliferation of keratinocytes with abundant production of keratins in the middle ear under chronic inflammatory conditions. However, little is known about the driving force of cellular proliferation and keratin production of cholesteatomal matrix. The purpose of this study was to investigate the cellular proliferation and keratin production of keratinocytes under the influence of Id1, a candidate transcription factor to cell proliferation.

MATERIALS AND METHODS

Keratinocytes were transfected with Id1 and the responses of keratinocytes to Id1 were studied by using cellular and molecular biologic methods.

RESULTS

Id1 positively contributed to the cell cycle progression and negatively to the p16(Ink4a) downregulation via the nuclear factor-kappa B (NF-κB)/cyclin D1 pathway. Id1 significantly increased the promoter activity of NF-κB which, in turn, up-regulated the expression of cyclin D1 and keratin 10 in keratinocytes. Specific NF-κB inhibitors (pyrrolidine dithiocarbamate, PDTC), or dominant-negative inhibitor (I kappa B alpha mutant, IκBαM) abrogated the Id1-induced cell proliferation and keratin 10 production whereas p65, a subunit of the NF-κB heterodimer and an enhancer of the NF-κB activity, strengthened the Id1-induced cell proliferation and keratin 10 production.

CONCLUSIONS

Id1 contributed to hyperproliferation of keratinocytes via enhancement of cell cycle progression, removal of cell cycle inhibition, and simultaneously increased keratin production.

Pneumococcal peptidoglycan-polysaccharides induce the expression of interleukin-8 in airway epithelial cells by way of nuclear factor-kappaB, nuclear factor interleukin-6, or activation protein-1 dependent mechanisms

Cell envelope compounds of bacteria trigger immune and inflammatory reactions by way of chemokines/cytokines. In this study, we demonstrated that pneumococcal peptidoglycan-polysaccharides (PGPS) induced the production of interleukin (IL)-8 by way of nuclear factor (NF)-kappaB, nuclear factor interleukin (NF-IL)6, and activation protein (AP)-1 dependent mechanisms in the human bronchial epithelial cells (NL-20) in a dose- and time-dependent manner in vitro, and the mutation of either the NF-kappaB, NF-IL6, or AP-1 binding sites in the promoter of IL-8 abrogated the IL-8 transcriptional activity. In a similar way, lipopolysaccharides induced the promoter activation of IL-8 in NL-20. However, the PGPS-induced IL-8 promoter activation in rodent middle ear epithelial cells required NF-kappaB and NF-IL6 but not AP-1.

Characterization of a temperature-sensitive mouse middle ear epithelial cell line

CONCLUSION

Temperature-sensitive mouse middle ear epithelial cells have been successfully established and characterized.

OBJECTIVE

Temperature-sensitive middle ear epithelial cell lines are essential for pathophysiologic studies of otitis media. They are useful for studying the pathogen-host interaction, receptor identification, signal transduction, cytokine/mucin production and cellular responses, especially for cell proliferation and differentiation. The purpose of this study was to establish a large T-antigen [simian virus 40 A-gene (SV40)] mutant-immortalized mouse middle ear epithelial cell line for otitis media studies.

MATERIAL AND METHODS

Primary culture of middle ear epithelial cells was established from the middle ear mucosa of an Immortomouse. The cells were transduced by a temperature-sensitive large T-antigen mutant and cultured for >50 passages. The expression of mRNA transcripts and proteins for epithelial cells was characterized by reverse transcriptase polymerase chain reaction (RT-PCR) and immunohistochemistry. The temperature-sensitive properties of cells cultured at 33 degree C and 39 degree C were evaluated using 3H-thymidine incorporation, Trypan blue exclusion and peroxisome proliferator-activated receptor-gamma activity.

RESULTS

Immortalized middle ear epithelial cells demonstrated a cobblestone-like monolayer culture. The cells expressed mucosal cell markers such as mucins, keratins and collagens. They proliferated at 33 degree C when the SV40 antigen was active and differentiated at 39 degree C when the SV40 antigen was inactive.