Background: The balance between matrix metalloproteinases (MMPs) and the tissue inhibitors of metalloproteinases (TIMPs) determines the extent of connective tissue degradation and remodeling.
Objective: To determine whether pterygium, characterized by fibrovascular invasion into the cornea, may in part be mediated by an increased activity of MMPs.
Materials and methods: Expression of transcripts and proteins of MMPs, TIMPs, and urokinase plasminogen activator (uPA) by cultured human pterygium head, body, and subconjunctival fibroblasts, and normal corneal and conjunctival fibroblasts were determined by Northern hybridization, enzyme-linked immunosorbent assay, Western blotting, zymography, and quantitative collagenase assay, respectively.
Results: Compared with normal conjunctival fibroblasts from 6 subjects, the expression of MMP-1 and MMP-3 transcripts was dramatically increased in pterygium head fibroblasts of 8 patients, but not in pterygium body fibroblasts of 6 patients. The protein levels and collagenolytic and caseinolytic activities of MMP-1 and/or MMP-3 were also markedly increased in pterygium head fibroblasts. The MMP-1 and MMP-3 proteins and activity decreased in order from pterygium head to body to subconjunctival fibroblasts. There was no difference in the transcript and protein expression of MMP-2, TIMP-1, TIMP-2, and uPA among these groups.
Conclusion: Pterygium head fibroblasts express increased mRNA, protein, and activities of MMP-1 and MMP-3.
Clinical relevance: Overexpression of MMP-1 and MMP-3, a phenotype previously linked with UV exposure in dermal fibroblasts to explain the pathologic finding of elastotic degeneration, suggests that pterygium head fibroblasts might be intrinsically altered by UV, which might be responsible for corneal invasion.