Differential effects of cadmium on proteoglycan synthesis of arterial smooth muscle cells: increase in small dermatan sulfate proteoglycans, biglycan and decorin, in the extracellular matrix at low cell density

Abstract

Proteoglycans (PGs), especially chondroitin/dermatan sulfate proteoglycans (CS/DSPGs), accumulate and their composition variously changes in atherosclerotic vascular walls. Since cadmium causes atherosclerosis in experimental animals, PGs synthesized by cultured vascular smooth muscle cells after exposure to cadmium were characterized in the present study. Sparse and dense cultures of the cells were metabolically labeled with [ 35S]sulfate for 24 h in the presence of cadmium chloride at noncytotoxic levels (0.2 μM or less). The incorporation of [ 35S]sulfate into glycosaminoglycans was determined by the cetylpyridinium chloride precipitation method. The labeled PGs were characterized by DEAE-Sephacel ion exchange chromatography and Sepharose CL-4B molecular sieve chromatography. The M r and the glycosaminoglycan composition of small CS/DSPGs were analyzed by SDS-polyacrylamide gel electrophoresis and Sepharose CL-6B chromatography, respectively, before and after digestion with chondroitin ABC lyase or papain. The core proteins were identified by Western blot analysis. These experiments indicate that cadmium differentially acts on the PG synthesis when vascular smooth muscle cell density is low. Specifically, cadmium increased the accumulation of small CS/DSPGs identified as biglycan and decorin in the cell layer of sparse cells. However, the hydrodynamic size and the length of chondroitin/dermatan sulfate chains in the PGs were unaffected by cadmium. On the other hand, cadmium decreased other cell layer-associated PGs that were separated from biglycan and decorin by DEAE-Sephacel chromatography in the sparse cells; as the result, whole glycosaminoglycans were decreased in both the cell layer and the conditioned medium. It is therefore concluded that cadmium may change the composition of PGs in atherosclerotic plaques through induction of biglycan and decorin synthesis and inhibition of other PG synthesis in vascular smooth muscle cells.