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O Nalovina, J Cai, P Hykin, M Boulton; The Role of the Angiopoietin/Tie-2 System in Retinal Neovascularisation . Invest. Ophthalmol. Vis. Sci. 2002;43(13):1317.
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Purpose: To investigate the interaction between the Tie-2 receptor and Angiopoietins -1 (Ang-1) and -2 (Ang-2) in bovine retinal microvascular endothelial cells (BRMEC) and microvascular pericytes. Methods: The expression of the Tie-2 receptor in cultured BRMEC and pericytes was analysed by immunoprecipitation with corresponding antibodies and Western blotting. Cultivated BRMEC were exposed to varying concentrations of Ang-1 and -2 (5 ng/ml - 400 ng/ml) for up to 48 h. The relative cell number was determined by monitoring the uptake of crystal violet by fixed cultures. Migration of BRMEC was measured using an in vitro wound healing model. Results: Western blotting analyses of whole cell lysates revealed that the Tie-2 receptor was expressed by both BRMEC and pericytes (a band at 140 kDa was detected). However, expression levels of Tie-2 were greatest for BRMEC. Ang-1 and Ang-2 exhibited no proliferative effect on endothelial cells. Ang-2 was only weakly mitogenic for pericytes (20% increase in cell number), meantime Ang-1 had no effect. Ang-1 led to a significant, dose-dependent increase in directed migration of BRMEC, up to 50% higher than unstimulated cells. Ang-2 over a wide dose range did not exert any chemotactic properties. Conclusion: The findings indicate that the Angiopoietin system may play a role in retinal neovascularisation via the Tie-2 receptor, which may be partially due to an increase in endothelial cells motility, a key step of angiogenesis. Furthermore, expression of the Tie-2 receptor on pericytes may allow their participation in the maintenance of capillary integrity, which is significantly disturbed, in diabetic retinopathy.
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