Glycosaminoglycan synthesis and composition in human fibroblasts during in vitro cellular aging (IMR-90)

The synthesis and turnover of sulfate-labeled glycosaminoglycans(35S-GAGs) has been investigated in diploid human embryo fibroblasts during in vitro cellular aging. With progressive subcultivation, there was a decreased incorporation of Na2(35)SO4 into 35S-GAGs released to the medium, but not into those accumulated at the cell surface. The composition of 35S-GAGs found in extracellular medium, cell surface (removable by gentle proteolysis), and intracellular compartments of the culture after 48-hr labeling did not change significantly with progressive subcultivation. Pulse-labeled 35S-GAGs moved from intracellular to surface and extracellular compartments more slowly in late-passage cultures. Addition of 1 mM beta-xyloside to both early- and late-passage cultures produced a ten-fold enhancement of extracellular 35S-GAG production without a concomitant increase in surface-associated 35S-GAG. We interpret the data of this study to mean that secreted and cell-surface glycosaminoglycans represent different pools and that cellular aging has its effect primarily upon the secreted pool of glycosaminoglycans. Late-passage fibroblasts demonstrate marked decreases in proliferation, culture density, fibronectin matrix, and gap-junction formation. Our results suggest that glycosaminoglycan synthesis and composition are not intimately related to these parameters.