Soluble forms of the high-affinity fibroblast growth factor receptor in human vitreous fluid.

PURPOSE: Fibroblast growth factor-binding proteins (FGF-BPs) have been identified recently in blood and other biologic fluids and have been shown to be identical to a truncated form of the high-affinity cell surface FGF receptor. The authors examined the hypothesis that FGF-BPs also are present in human vitreous fluid.
METHODS: Vitreous fluid obtained from 12 patients was incubated overnight with heparin-Sepharose, FGF-2 heparin-Sepharose, and wheat germ agglutinin (WGA)-Sepharose, a lectin known to bind to high-affinity FGF receptors. The precipitated proteins were characterized by immunoblotting using two FGF receptor antibodies raised to either the extracellular domain of FGFR-1 or the intracellular domain of FGFR-1.
RESULTS: A 70- to 85-kd FGF-BP was detected in the vitreous in each of the 12 eyes examined. A 55-kd FGF-BP was detected in six of the samples. Both the 70-to 85-kDa and the 55-kDa proteins were precipitated by FGF-2 heparin-Sepharose but not by heparin-Sepharose alone, suggesting that the interaction was dependent on the presence of FGF-2. The proteins bound avidly to WGA-Sepharose. Western blot analysis revealed that the proteins were recognized by an antibody raised to the extracellular domain of the high-affinity FGF receptor but not by an antibody raised to the intracellular domain of the FGF receptor, indicating they are likely to be truncated portions of the extracellular domain of the high-affinity FGF receptor.
CONCLUSIONS: Vitreous fluid contains 70- to 85-kd and 55-kd FGF-BPs that have biochemical and immunologic characteristics similar to the extracellular domain of the high-affinity FGF receptor. These naturally occurring FGF-BPs may sequester free FGF in the vitreous cavity and may modulate the biologic activity of FGF in vitreoretinal diseases.