Naoyasu Umeda

Colocalization of Tie2, Angiopoietin 2 and Vascular Endothelial Growth Factor in Fibrovascular Membrane from Patients with Retinopathy of Prematurity

Purpose: The tyrosine kinase receptor Tie2 and its ligands, the angiopoietins (Angs), play important roles in vascular integrity and neovascularization, modulating vascular endothelial growth factor (VEGF) activity. To elucidate the potential role of Angs and the Tie2 system in retinopathy of prematurity (ROP), we have investigated the expression of Angs, Tie2 and VEGF within fibroproliferative membranes in ROP. Methods: Fibroproliferative membranes were obtained from 38 cases with stage 5 ROP at the time of vitrectomy. Membranes were fixed in formalin and embedded in paraffin. Each specimen was serially sectioned for immunohistochemistry. Polyclonal antibodies specific for Ang1, Ang2, Tie2 and VEGF were used for immunostaining. Immunoreactivity for von Willebrand factor (factor VIII) was also assessed to confirm the identity of vascular endothelial cells. Results: Positive staining for Tie2 was observed in 23 of 38 specimens (60.5%). Tie2 was localized in vascularized regions of fibrovascular membranes and was co- expressed with VEGF and factor VIII. Ang2 stained positively in 18 of 38 (47.3%) serial sections where Tie2 was present, and was also co-expressed with VEGF and factor VIII. Ang1 was not generally observed in these specimens (3/38). Conclusions: VEGF and Ang2-Tie2 interactions may play an important role in the pathogenesis of ROP.

Non-Paralleled Increase of Hepatocyte Growth Factor and Vascular Endothelial Growth Factor in the Eyes with Angiogenic and Nonangiogenic Fibroproliferation

Vascular endothelial growth factor (VEGF) has been known as principal angiogenic factor in vasculogenesis, tumor angiogenesis and ocular angiogenesis. Currently, hepatocyte growth factor (HGF) has been reported to play a major role in ocular angiogenesis. We studied distribution of both growth factors in angiogenic and non-angiogenic fibroproliferation to determine the correlation of VEGF and HGF in retinal angiogenesis. Concentrations of VEGF and HGF molecules in vitreous samples from 27 eyes with angiogenic proliferative diabetic retinopathy (PDR) and 9 eyes with non-angiogenic proliferative vitreoretinopathy (PVR) were measured by enzyme-linked immunosorbent assay (ELISA). Vitreous samples with idiopathic macular role (IMH) served as a control. Concentrations of VEGF in the angiogenic PDR were 4.3 ± 5.8 ng/ml (mean ± SD), and were significantly higher than in non-angiogenic PVR (0.5 ± 0.1 ng/ml). No significant differences were observed on VEGF concentrations between PVR to control. On the contrary, HGF concentrations were significantly higher in PVR (22.5 ± 21.8 ng/ml) than in control (6.9 ± 5.2 ng/ml), those of PDR (24.0 ± 16.3 ng/ml) were also significantly higher than control. Among PDR samples, VEGF concentration was significantly higher than in the subgroup with higher angiogenic activity represented by iris neovascularization, although there were no significant differences on HGF concentration between the subgroups. Focal increases in HGF on fibroproliferation in the eye regardless of the involvement of angiogenesis were not in remarkable relation with angiogenic activity, unlike VEGF. These data suggested a more extensive role of HGF than VEGF strictly related to angiogenesis.