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M. Fannon, K. Forsten-Williams, C. L. Chu, A. Wildt, B. Zhao, M. A. Nugent; Sucrose Octasulfate Regulates VEGF165 Diffusion Through Descemet’s Membrane. Invest. Ophthalmol. Vis. Sci. 2010;51(13):5898.
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We have previously shown that sucrose octasulfate (SOS), a disaccharide heparin analog, exhibits heparin-like binding without significant anti-coagulative properties. Using bovine Descemet’s membrane, which is rich in heparan sulfate proteoglycan (HSPG), we showed that diffusion rates of fibroblast growth factor-2 (FGF-2) and heparin binding EGF-like growth factor (HB-EGF) were markedly accelerated by their association with SOS. The diffusion of epidermal growth factor (EGF), which does not bind heparin, was unchanged. However, when heparin was used rather than SOS, heparin-binding proteins did not diffuse through the membrane. We investigated whether a complex of SOS-VEGF would change the diffusion characteristics of VEGF.
Descemet’s membranes were isolated from adult bovine corneas, placed between two diffusion chambers, and transport was initiated with or without SOS (0.5 mg/ml). 1 mCi of 125I-VEGF was added to the source chamber. At various time points samples were removed from the receiver chamber, precipitated with trichloroacetic acid and quantitated in a gamma counter.
We observed that VEGF165, which binds heparin, demonstrated accelerated diffusion through Descemet’s membrane in the presence of SOS; whereas VEGF121, which does not bind heparin, showed no change with or without SOS.
The acceleration of VEGF165 diffusion through Descemet’s membrane suggests that VEGF165 binds to HSPG residing in the membrane, significantly retarding its diffusion by increasing its retention time. When in complex with SOS the heparin-binding sites are occupied and VEGF165 passes through the membrane with little retention, and its diffusion is accelerated. Presumably, the heparin-protein complex is too large to easily diffuse. This ability to alter membrane diffusion suggests a potential for SOS in depleting basement membrane stores of VEGF165.
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