Differential expression of matrix metalloproteinases and their tissue inhibitors at the advancing pterygium head.

PURPOSE Pterygia are a proliferative and inflammatory growth of limbal epithelial stem cell origin, characterized by corneal tissue invasion and extensive matrix remodeling including the destruction of Bowman's layer (BL). The purpose of this study was to determine the expression of matrix metalloproteinases (MMPs) and tissue inhibitors of MMPs (TIMPs) at the advancing pterygium edge. METHODS Formalin-fixed, paraffin-embedded whole eyes (n = 11) with pterygia attached, were serially sectioned and analyzed immunohistochemically to determine the spatial distribution of four MMPs and three TIMPs. Tear samples were collected from other patients with pterygia (n = 11) and displayed by gelatin zymography. RESULTS Collagenase-1 was expressed by pterygium epithelial cells, corneal stromal fibroblasts and pterygium fibroblasts that had migrated between the epithelium and BL at the advancing pterygium edge. Collagenase-3 and gelatinases A and B were detected in all pterygia, intensely staining columnar epithelial cells directly adjacent to the denatured BL. In addition, gelatinase A immunoreactivity was observed on BL. Immunoreactivity for TIMP-1 and -3 paralleled that of the gelatinases, with more intense staining in epithelial cells and fibroblasts where BL was absent. TIMP-2 was faintly detected in pterygium epithelial cells but intensely stained pterygium fibroblasts. Gelatinase B was the most abundant gelatinolytic enzyme present in tears, elevated approximately twofold in eyes with pterygia versus the contralateral control eyes. CONCLUSIONS This investigation is the first to identify the expression pattern of MMPs and TIMPs at the advancing pterygium edge in specimens of human eyes and in tears derived from patients with pterygia. These enzymes may be responsible for the destruction of BL, and their pattern of differential expression suggests that each may play a selective role in the pathogenesis of pterygia.