Effect of epithelial debridement on human cornea proteoglycans

Corneal transparency is attributed to the regular spacing and diameter of c ollagen fibrils, and proteoglycans may play a role in fibrillogenesis and m atrix assembly. Corneal scar tissue is opaque and this opacity is explained by decreased ultrastructural order that may be related to proteoglycan com position. Thus, the objectives of the present study were to characterize th e proteoglycans synthesized by human corneal explants and to investigate th e effect of mechanical epithelial debridement. Human corneas unsuitable for transplants were immersed in F-12 culture medium and maintained under tiss ue culture conditions. The proteoglycans synthesized in 24 h were labeled m etabolically by the addition of S-35-sulfate to the medium. These compounds were extracted by 4 M GuHCl and identified by a combination of agarose gel electrophoresis, enzymatic degradation with protease and muco-polysacchari dases, and immunoblotting. Decorin was identified as the main dermatan sulf ate proteoglycan and keratan sulfate proteoglycans were also prominent comp onents. When the glycosaminoglycan side chains were analyzed, only keratan sulfate and dermatan sulfate were detected (similar to 50% each). Neverthel ess, when these compounds were S-35-labeled metabolically, the label in der matan sulfate was,greater than in keratan sulfate, suggesting a lower synth esis rate for keratan sulfate. S-35-Heparan sulfate also appeared. The remo val of the epithelial layer caused a decrease in heparan sulfate labeling a nd induced the synthesis of dermatan sulfate by the stroma. The increased d eposit of dermatan sulfate proteoglycans in the stroma suggests a functiona l relationship between epithelium and stroma that could be related to the c orneal opacity that may appear after epithelial cell debridement.