Induction of matrix metalloproteinases in keratinocytes by cholesteatoma debris and granulation tissue extracts

Although it is generally accepted that destruction and remodeling of tempor al bone associated with middle ear cholesteatoma is mainly caused by the ac tion of osteoclasts, it has been shown that neutral collagenases also play a role in predigesting the osteoid layer and exposing the mineralized bone to osteoclastic activity. Here we show that gelatinase B (matrix metallopro teinase-9) is over-expressed in cholesteatoma compared to external ear cana l skin (EACS). Expression of MMP-9 in cholesteatoma mainly occurs in suprab asal layers, and more rarely in basal layers of cholesteatoma epithelium, a s well as in inflammatory cells of the perimatrix. We further analyzed the influence of cholesteatoma debris, cholesteatoma granulation tissue, and ch olesteatoma components such as keratin, cholesterol and bacterial endotoxin on the expression of MMPs in EACS keratinocytes. We show that cholesteatom a debris and granulation tissue extract both induced the secretion of MMP-9 ) by EACS keratinocytes, while keratin, bacterial lipopolysaccharide (LPS) or cholesterol did not show any effect. We further performed co-incubation and immunoprecipitation experiments using neutralizing interleukin-1 alpha, EGF, TGF-beta, TGF-alpha, interleukin-6 and TNF-alpha antibodies. Inhibiti on of MMP-9 up-regulation by debris or granulation tissue extract could be revealed with diverse cytokine antibodies. The results are discussed with r egard to previously published studies.