Anti-angiogenic role of angiostatin during corneal wound healing

The purpose of this study is to determine whether angiostatin is involved in maintaining corneal avascularity after wounding. We generated polyclonal rabbit anti-mouse angiostatin antibodies directed against each of the five kringle domains, (K1-5) and anti-mouse plasmin B chain antibodies. Mouse corneas were immunostained with anti-K1 angiostatin antibody after excimer laser keratectomy. Corneal epithelial cell lysate was harvested and angiostatin was isolated using lysine sepharose. Purified plasminogen was incubated with lysate of mouse corneal epithelial cells from wild type mice in the presence or absence of MMP inhibitors. Angiostatin activity was determined using calf pulmonary artery endothelial (CPAE) cell proliferation assay with and without angiostatin immunoprecipitation; and corneal neovascularization was assayed by intrastromal injection of anti-plasminogen, anti-K1-3 or anti-B chain antibodies after corneal wounding. Using the anti-mouse angiostatin antibodies that we generated, we confirmed that angiostatin-like molecules were expressed in the corneal epithelium and in cultured corneal epithelial cells. Western blotting after incubation of scraped corneal epithelial cell lysate with purified plasminogen showed reduction of the plasminogen bands at 6, 12, and 24 hr, respectively. Complete cleavage of plasminogen occurred by 48 hr. Functional assays in which corneal epithelial cell extracts were incubated with CPAE cells resulted in inhibition of vascular endothelial cell proliferation. Depletion experiments using anti-angiostatin (K1) antibodies resulted in a 25 +/- 1.2% increase in vascular endothelial cell proliferation as compared to 12 +/- 1.8% using the protein A control (p < 0.05). Corneal neovascularization was observed after excimer laser keratectomy when anti-angiostatin antibodies were injected into the cornea (65 +/- 13%) which was significantly higher than when plasmin B chain antibodies were injected (10 +/- 2.6%; p < 0.05). Plasminogen and angiostatin are produced in the cornea. They may play a role in preventing vascularization and may contribute to the maintenance of corneal avascularity after excimer laser keratectomy.