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

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Abstract
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 Na235SO4 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 β‐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.