Modulation of proteoglycan metabolism by aortic smooth muscle cells grown on collagen gels

The nature of the extracellular matrix may influence the types and amounts of proteoglycans synthesized by arterial smooth muscle cells. To determine if collagen modulates proteoglycan metabolism by these cells, arterial smooth muscle cells derived from aortic explants of the pigtail monkey (Macaca nemestrina) were cultured on both tissue culture plastic and hydrated type I collagen gels for 7 days. Cells were radiolabeled with Na2[35S]O4 during the final 48 hours of the growth period, and proteoglycans were extracted from the culture medium and cell layer by using 4 M guanidine hydrochloride in the presence of protease inhibitors. Cultures on collagen accumulated approximately 40% less [35S]O4 = -radiolabeled proteoglycan when compared to cultures on plastic. However, cells on collagen accumulated approximately 50% of their newly synthesized proteoglycan within the cell layer, while cells on plastic deposited less than 20% of their total radiolabeled proteoglycan in this culture compartment. Pulse-chase analysis indicated that the elevated accumulation of proteoglycan observed in the cell layer of collagen cultures was due, at least in part, to inhibition of turnover of these molecules. Cells on both collagen and plastic synthesized a large chondroitin sulfate proteoglycan which was secreted into the medium and deposited within the cell layer. On the other hand, cells on collagen synthesized a smaller iduronic acid-rich dermatan sulfate proteoglycan which was deposited only within the collagen gel and not secreted into the medium. By comparison, cells grown on plastic synthesized both a small glucuronic acid-rich dermatan sulfate proteoglycan which was secreted into the medium as well as an iduronic acid-rich dermatan sulfate which was present in the cell layer. Unlike the cell layer-derived dermatan sulfate proteoglycan isolated from the collagen gels, the majority of the cell layer-derived dermatan sulfate from cells on plastic was insensitive to papain treatment and thus identified as free glycosaminoglycan chains. Analysis of the total radiolabeled proteoglycans isolated under the two culture conditions indicated that cultures grown on collagen accumulate less chondroitin sulfate proteoglycan and heparan sulfate proteoglycan but over twice as much iduronic acid-rich dermatan sulfate proteoglycan. This culture system is offered as a model to determine the mechanisms by which collagen may in part regulate the metabolism of proteoglycans by arterial smooth muscle cells.