Basic Fibroblast Growth Factor Controls the Expression and Molecular Structure of Heparan Sulfate in Corneal Endothelial Cells

Cultured bovine corneal endothelial cells express 5–8 ng basic fibroblast growth factor (bFGF)/mg cell protein and distribute it between the intracellular and pericellular compartment. Confluent cultures retain approximately 80% of the total bFGF intracellularly, whereas 20% is present in the pericellular (trypsin‐releasable) compartment. No bFGF can be detected in the culture medium. The presence of 1–2 ng/ml medium of endogenous or exogenous (human recombinant) bFGF is sufficient to support cell growth. Simultaneously, cells incorporate [ 35 S]sulfate and [ 3 H]glucosamine into the sulfated proteoglycans associated with the cell layer at a rate that is three times higher than in the absence of bFGF. The enhanced proteoglycan synthesis is accompanied by a shift in proteoglycan distribution. In control cells, cell‐associated heparan sulfate accounts for about 30% of the total glycosaminoglycans, whereas under the influence of bFGF the amount of heparan sulfate increases to approximately 60%. At the same time, the molecular structure of the heparan sulfate molecule undergoes bFGF‐specific changes as indicated by the [ 35 S]oligosaccharide pattern generated by heparitinase I degradation. The proportion of [ 35 S]oligosaccharides with greater than six monosaccharides decreases on account of disaccharides and tetrasaccharides under the influence of bFGF. Pretreatment of bFGF with neutralizing antibodies against bFGF abolishes its biological activity. The results suggest a bFGF‐dependent change in the rate of synthesis and structural features of the membrane‐associated heparan sulfate in corneal endothelial cells. The modification of the heparan sulfate structure could influence its bFGF‐binding and antiproliferative activity.