Difference between the glycosaminoglycans synthetized by corneal and cutaneous fibroblasts in culture

Although fibroblasts retain similar morphologic characteristics in various tissues, a body of evidence suggests that these cells possess disparate characteristics in different tissues. Keratan sulfate I, a specific product of the corneal fibroblast, is synthesized by the cornea in vivo and by organ cultures of the cornea in the absence of an associated corneal epithelium and endothelium. Confluent cultures of isolated corneal fibroblasts appear to lose this capacity, and the question of whether they produce any keratan sulfate in culture has remained uncertain, owing to the variable sensitivity and specificity of the different analytical methods employed. This study compares the 35S-sulfate- and 3H-glucosamine-labeled glycosaminoglycans produced by confluent cultures of human corneal and cutaneous fibroblasts with those synthesized by corneal organ cultures with different analytical techniques. Using the analytical method of sequential enzymatic degradation, confluent cultures of corneal fibroblasts, but not cutaneous fibroblasts, were found to synthesize and secrete into the nutrient medium a small quantity of sulfate glycosaminoglycans that was susceptible to keratan sulfate endo-beta-galactosidase (Pseudomonas)--an enzyme that degrades corneal keratan sulfate to oligosaccharides of variable size and sulfation. These difference between isolated corneal and cutaneous fibroblasts support the concept that fibroblasts, although ubiquitous, not only manifest metabolic differences but can retain some of these differences when isolated from other cells. Although cutaneous fibroblasts do not produce significant quantities of sulfated material with the attributes of keratan sulfate, they do incorporate 3H-glucosamine into macromolecules that are susceptible to keratan sulfate endo-beta-galactosidase. Most of the sulfated glycosaminoglycans produced by organ cultures of the cornea, which were susceptible to this enzyme, eluted from Dowex 1-X2(Cl-) with a salt concentration of less than 2 M. This observation, together with the findings of others, indicates that the traditional belief that corneal keratan sulfate elutes from Dowex 1-Cl predominantly in the 3 M NaCl fraction needs to be reevaluated.