Purpose: Pterygia are a common, benign, fibrovascular, and infiltrative process of the corneal-conjunctival junction of unknown pathogenesis. Matrix metalloproteinases (MMPs) are a family of proteolytic enzymes active against all components of the extracellular matrix, whose activity is specifically neutralized by tissue inhibitors of MMPs (TIMPs). In the current study the hypothesis was that MMPs and TIMPs may actively participate in the formation and progression of pterygia.
Methods: In this study, 25 pterygium specimens and 15 normal conjunctival biopsies obtained from subjects undergoing surgery for glaucoma and cataract, were processed for immunohistochemistry or in situ hybridization. Pterygium epithelial cells (PECs) were cultured under serum-free conditions and exposed to proinflammatory cytokines to determine both the mRNA and protein expression profiles of MMPs and TIMPs.
Results: Collagenase-1 and gelatinase A were expressed in all pterygia examined, specifically localized to the epithelium (directly adjacent to collagen type III), with gelatinase B expression exclusively associated with neutrophils. No collagenase-1 or gelatinase A was detected in normal conjunctiva. TIMP-1 and -3 were localized to epithelial cells with additional TIMP-3 immunoreactivity detected in the extracellular matrix, endothelial cells and leukocytes of all diseased tissue. TIMP-3 protein was evident in 4 of 15 normal conjunctiva. Induction of collagenase-1, gelatinase A, and TIMP-1 mRNA and protein was demonstrated in epithelial cells treated with tumor necrosis factor-alpha and interleukin-1alpha, whereas TIMP-3 expression was unaltered.
Conclusions: This is the first study to document the cellular expression of MMPs and TIMPs in pterygia and cultured human PECs. MMPs and TIMPs may contribute to the inflammation, tissue remodeling, and angiogenesis that characterize pterygia. Understanding the role these proteins play may lead to novel therapies intended to reduce the progressive nature of pterygia.