Mechanism of Apoptotic Cell Death in Cholesteatoma Epithelium

Abstract

BACKGROUND AND OBJECTIVES: Accumulation of keratin debris in the middle ear is one of the characteristics of the cholesteatoma. It is related to increased rate of cell death and differentiation of keratinocytes compare to normal skin. This kind of cell death is known as apoptosis. In this study, we plan to investigate the apoptotic cell death and expression of Fas in both normal and cholesteatoma epithelia. MATERIALS AND METHODS: Seven cholesteatomas and retroauricular skins were obtained from patients undergoing middle ear operations. Detection of the fragmented DNA in apoptosis was done by in situ TUNEL methods and agarose gel electrophoresis. For the morphologic confirmation of apoptosis, transmission electron microscopy (TEM) was done. Immunohistochemistry was also performed for detection of Fas expression on the tissue. RESULTS: In TUNEL staining, many positive staining nuclei were observed in upper layers of cholesteatoma epithelium whereas a few positive cells were found on the granular layer of retroauricular skin. Typical "ladder pattern" was seen on the gel electrophoresis of the genomic DNA of cholesteatoma. On TEM study, we observed condensation of chromatin in the keratinocytes of the cholesteatoma epithelium. Immunohistochemical studies revealed that Fas protein was expressed in all layers of cholesteatoma epithelium, while retroauricular skin showed weak reactions only in the granular layer. CONCLUSION: We confirmed that increased apoptosis and up-regulated expression of Fas in cholesteatoma epithelium. Since Fas is known as apoptosis triggering protein, the authors suggest that accumulation of keratin debris is due to increased apoptotic cell death and further investigation should be needed about the mechanism of cell death in cholesteatoma.