Overexpression of Angiogenin in Pterygium Body Fibroblasts and Its Association With Proliferative Potency

Abstract

Angiogenin (ANG) originally was identified as an angiogenic tumor factor, and recently its biologic activity is extended to stimulating cell proliferation. With viewing pterygium as a tumorigenic mimicry, we investigated ANG profiles within pterygia. Expression levels of ANG were assessed using immunohistochemistry, RT-PCR, and Western blotting through examination of excised specimens and cultured fibroblasts from pterygium and conjunctiva tissues. The phenotypes of pterygia were classified by four grading indices, including recurrence, growth activity, pterygium body translucency (T), and vascularity (V). Then, ANG levels in pterygia were differentiated according to phenotypes of pterygia, and were compared to levels in normal conjunctiva. Furthermore, to investigate ANG-related acquisition of proliferative potency in fibroblasts, the correlation between ANG and α-smooth muscle actin (α-SMA) levels was evaluated. In immunohistochemistry, ANG was expressed strongly in pterygium stroma with all four severe phenotypes (with recurrence, active growth, thick body [T3], and marked vascularization [V3]), especially at the perivascular areas. There was a trend toward higher ANG expression in cultured fibroblasts of pterygia with severe phenotype, compared to those without and with normal conjunctiva. However, pterygium body V had a weak association with ANG expression. Additionally, Western blotting revealed a significant positive correlation between the expression levels of α-SMA and ANG. Overexpression of ANG in pterygium body fibroblasts might be involved in active pterygium growth with thick pterygium body formation and increased risk of recurrence. A possible mechanism for this finding includes ANG-related transition of pterygium fibroblasts to the proliferative state.