Proliferative and migratory aptitude in pterygium

Pterygium is a chronic fibrovascular overgrowth on the corneal surface and is often associated with inflammation, astigmatism and obstructed vision. The common treatment is surgical removal but post-operative recurrences with more aggressive behavior are common. However, there is a controversy in the pathogenesis of primary pterygium between limbal stem cell failure versus proliferation. In this study, we explore the proliferative and migratory aptitude in pterygium by characterizing the growth and migration pattern of pterygial cells in the head (on the cornea), the neck (over the focal limbus), and the body (on the conjunctiva) epithelia of 12 full-length primary pterygia. Immunofluorescence and quantification analyses showed a spatial expression pattern of markers for stem cells, cell growth, and matrix metalloproteinases. Beside the basal epithelia in all three regions, p63α^strong cells were located in suprabasal layers in head, weak in the body and absent in neck. Pertinent cell proliferation in head than body epithelia was revealed by its higher colony-forming efficiency. ATP-binding cassette transporter glycoprotein family member-2 and cytokeratin-15 were found mainly in the body basal epithelia, similar to that in normal conjunctiva. Much fewer proliferating stem-like cells in the neck region supported the limbal failure as a cause of pterygium formation. Pax6, matrix metalloproteinase-2 and -9 were more expressed in the head than in the other two regions. Our results indicate the importance of pterygium head in tissue growth and invasion and its likely involvement in post-operation recurrence.