Stromal expression of matrix metalloprotease-9 in middle ear cholesteatomas.

Background: Matrix metalloprotease-9 (MMP-9) plays an important role in the degradation of extracellular matrix (ECM). In cholesteatoma there are significant changes in the composition of the ECM, supporting the view of a disturbed cell-ECM interaction. It has been reported that in cholesteatoma tissues, MMP-9 is expressed in epithelial cells but not in stromal cells. In this study, we report conflicting results regarding the identity of the cholesteatoma cells that express MMP-9.

Methods: An immunohistochemical assay was performed to examine the expression of MMP-9 in 25 cases (formalin-fixed paraffin-embedded sections) of cholesteatoma, using an MMP-9-specific monoclonal antibody.

Results: In all cholesteatomas examined, MMP-9 was expressed in the stromal cells but not in the epithelial cells. MMP-9 immunostaining was undetectable in external auditory meatal skin (n = 5) and tympanic membrane (n = 3).

Conclusions: These results suggest that the MMP-9 expressed in stromal cells may be involved in the disturbed cell-ECM interaction associated with the process of cholesteatoma formation.