Endothelial cells inhibit smooth muscle cell secretion of hyaluronanic acid

Objective: Hyaluronanic acid is a glycosaminoglycan that is present soon after arterial injury and that may augment the smooth muscle cell (SMC) response to injury. The effect of bovine endothelial cells (ECs) on bovine SMC hyaluronanic-acid synthesis was assessed with a bilayer coculture model. Methods: Hyaluronanic acid was measured in conditioned media by means of radioimmunoassay and in the cell matrix by histochemistry and point hit quantitation. The receptor for hyaluronic acid-mediated motility (RHAMM) expression, which is increased by hyaluronanic acid, was measured by means of immunoblot. Results: Hyaluronanic acid levels in the conditioned media of SMCs cultured alone (425 +/- 30 mu g/ml/10(6) cells) were greater at 48 hours when compared with SMCs cocultured with ECs (212 +/- 30 mu g/ml/10(6) cells; p < 0.01). Histochemical stain for hyaluronanic acid showed increased hyaluronanic acid in SMCs cultured alone at all time points studied. This finding was confirmed by point hit quantitation at all time points (p < 0.05). Cocultured SMCs had a 50% +/- 17% reduction in RHAMM as compared with SMCs cultured alone (p = 0.08). Conclusions: ECs inhibit SMC hyaluronanic acid synthesis and RHAMM expression. This inhibition may be an important mechanism by which ECs modify the SMC response to injury.