Metabolism of Cell Surface-Associated Sulfated Glycosaminoglycans in Cultured Human Smooth Muscle Cells

Abstract

Smooth muscle cells grown from human aorta synthesize chondroitin sulfate, dermatan sulfate, and heparan sulfate as sulfated glycosaminoglycans. These polymers are found mainly extracellularly and in association with the cell membrane. Each compartment is characterized by a distinct distribution pattern of sulfated glycosaminoglycans, though considerable variability was noted between different cell lines. On incubation of the cells in the presence of [35S]sulfate for up to 72 h, no significant change in the distribution pattern of newly synthesized extracellular and membrane-associated glycosaminoglycans was found. Prelabeling experiments revealed that pericellular glycosaminoglycans are metabolically heterogenous. They leave their compartment with half-lives of less than 10 h and 1-3 days, respectively. During the initial period of the chase experiment (up to 12 h), about equal proportions of the material disappeared either by shedding into the culture medium or by endocytosis. Thereafter, release of macromolecules into the medium exceeded endocytotic uptake. None of the individual glycosaminoglycans on the cell surface showed a clear preference for its removal either by shedding or by endocytosis. Cell surface-associated glycosaminoglycans are neither direct precursors of the extracellular glycosaminoglycans, nor do they represent mainly extracellular glycosaminoglycans which are in the process of endocytosis.