[Functional regulation of heparin-binding proteins and maintenance of vitreal transparency by intravitreal glucosaminoglycan].

Loss of vitreal transparency is common to many forms of visual impairment. Examples include bleeding from retinal neovascularization and presence of intraocular inflammation. To treat the vitreous opacity, it is essential to explore the pathology of each underlying disease. However, understanding the mechanisms of vitreous transparency is also important. This review shows that the vitreous contains a high concentration of soluble heparan sulfate, a glucosaminoglycan (sugar chain). This inhibits the aberrant growth of retinal vessels into the vitreous by inactivating the heparin-binding protein, the vascular endothelial growth factor (VEGF), that is secreted into the vitreous. In addition, the possibilities that intraocular soluble glucosaminoglycans can inhibit the function of another heparin-binding inflammatory cytokine, CCL2, and suppress the intraocular inflammation, are proposed. Thus, intravitreal glucosaminoglycan may serve as a common inhibitor of various heparin-binding proteins including VEGF and CCL2. The results suggest that sugar chains regulate the signaling of these proteins and suppress the intravitreal infiltration of vascular endothelial cells and inflammatory cells, contributing to the maintenance of vitreal transparency.