Changes of glycosaminoglycan synthesis during in vitro ageing of human fibroblasts (WI-38).
Synthesis rates of glycosaminoglycans by WI-38 cultures (diploid, human fibroblasts exhibiting a limited number of population doublings in vitro) were determined by incorporation of 35S-sulfate of 14C-glucosamine into cellular and extracellular glycosaminoglycans at different passage levels before phase out. A progressive decline in the synthesis of cellular and extracellular glycosaminoglycans occured during the last (about 4) population doublings. 35S-sulfate incorporation into extracellular glycosaminoglycans appeared to be somewhat more reduced than 14-C-glucosamine incorporation during the last passages. Analysis of the distribution pattern of incorporated label into various glycosaminoglycan types (hyaluronic acid, chondroitin sulfate, dermatan sulfate and possibly heparan sulfate) revealed an age-related relatively stonger decline of 14C-glucosamine incorporation into cellular and extracellular hyaluronic acid and of 35S-sulfate into extracellular chondroitin sulfate in comparison with the other glycosaminoglycan types. Addition of exogenous glycosaminoglycans (chondroitin-4-sulfate, chondroitin-6-sulfate, dermatan sulfate, hyaluronic acid, heparan sulfate, heparin) at 100 microgram/ml to the culture media during the last 7 to 10 population doublings before phase out did not increase the total number of population-doublings. Heparin exhibited a significant growth inhibitory effect at 100 or 500 microgram/ml. The changes in glycosaminoglycan metabolism are interpreted as an expression of cellular ageing, and such an in vitro system offers a model for analyzing the factors involved in or causing the induction respectively prevention of this functional change.
Changes of glycosaminoglycan synthesis during in vitro ageing of human fibroblasts (WI-38). Synthesis rates of glycosaminoglycans by WI-38 cultures (diploid, human fibroblasts exhibiting a limited number of population doublings in vitro) were determined by incorporation of 35S-sulfate of 14C-glucosamine into cellular and extracellular glycosaminoglycans at different passage levels before phase out. A progressive decline in the synthesis of cellular and extracellular glycosaminoglycans occured during the last (about 4) population doublings. 35S-sulfate incorporation into extracellular glycosaminoglycans appeared to be somewhat more reduced than 14-C-glucosamine incorporation during the last passages. Analysis of the distribution pattern of incorporated label into various glycosaminoglycan types (hyaluronic acid, chondroitin sulfate, dermatan sulfate and possibly heparan sulfate) revealed an age-related relatively stonger decline of 14C-glucosamine incorporation into cellular and extracellular hyaluronic acid and of 35S-sulfate into extracellular chondroitin sulfate in comparison with the other glycosaminoglycan types. Addition of exogenous glycosaminoglycans (chondroitin-4-sulfate, chondroitin-6-sulfate, dermatan sulfate, hyaluronic acid, heparan sulfate, heparin) at 100 microgram/ml to the culture media during the last 7 to 10 population doublings before phase out did not increase the total number of population-doublings. Heparin exhibited a significant growth inhibitory effect at 100 or 500 microgram/ml. The changes in glycosaminoglycan metabolism are interpreted as an expression of cellular ageing, and such an in vitro system offers a model for analyzing the factors involved in or causing the induction respectively prevention of this functional change.