An antiproliferative heparan sulfate species produced by postconfluent smooth muscle cells

Heparan sulfate was isolated form the cell surface, cell pellet, and culture medium of exponentially growing as well as postconfluent bovine aortic smooth muscle cells (SMCs). After chromatography on DEAE- Sephadex and Sepharose 4B, the various mucopolysaccharides were examined for their ability to cause growth inhibition in a SMC bioassay. The heparan sulfate isolated from the surface of postconfluent SMCs possessed approximately eight times the antiproliferative potency per cell of the heparan sulfate obtained from the surface of exponentially growing SMCs. Heparan sulfate isolated from other fractions of exponentially growing or postconfluent SMCs possesses little growth inhibitory activity. The difference in the antiproliferative activities of heparan sulfate obtained from the surface of SMCs in the two growth states could not be attributed to the synthesis of a greater mass of mucopolysaccharide by postconfluent SMCs. Indeed, heparan sulfate isolated from the surface of the postconfluent SMCs exhibits a specific antiproliferative activity which is 13-fold greater than mucopolysaccharide obtained from the surface of exponentially growing SMCs and more than 40-fold greater than commercially available heparin. In addition, exponentially growing SMCs did not exhibit an enhanced ability to degrade the complex carbohydrate. Furthermore, other investigations indicate that the small amount of growth inhibitory activity intrinsic to heparan sulfate isolated from the surface of exponentially growing SMCs is due to residual, biologically active, mucopolysaccharide produced by the primary postconfluent SMCs from which the exponentially growing SMCs were derived. These studies suggest that bovine aortic SMCs are capable of controlling their own growth by the synthesis of a specific form of heparan sulfate with antiproliferative potency.