Enhanced synthesis and accumulation of proteoglycans in cholesterol-enriched arterial smooth muscle cells.
To determine the effects of lipid accumulation on proteoglycan synthesis, we studied proteoglycan biosynthesis in rabbit aortic smooth muscle cells in culture. Cholesterol-enrichment was accomplished by incubating confluent smooth muscle cells with cationized low-density lipoprotein. Control and cholesterol-enriched cells were incubated with [35S]sulphate, [3H]glucosamine, or [3H]serine. Metabolically labelled proteoglycans in the cell layer and medium were quantified. During a 20 h incubation period, proteoglycan synthesis in cholesterol-enriched cells increased by 40-50% above that in control cells. A similar increase in precursor incorporation into proteoglycans was also noted following a short 15 min pulse. The cholesterol-enriched cells also showed a 45-50% increase over control rates in the intralysosomal accumulation of a large chondroitin sulphate proteoglycan and a small dermatan sulphate proteoglycan. The enhanced synthesis of proteoglycans in cholesterol-enriched cultures was inhibited by cycloheximide and actinomycin D, which are inhibitors of protein synthesis and transcription respectively. Proteoglycan turnover was investigated by pulse-chase analysis. Following a 2-h pulse, intracellular proteoglycans in cholesterol-enriched cells disappeared, having a half-life of 26.5 h compared with 2.8 h for those in the control cells. The amount of trypsin-releasable proteoglycan was significantly reduced in cholesterol-enriched cells. In addition, the degradation of proteoglycans was severely retarded in cholesterol-enriched cultures. The activities of three acid hydrolases, N-acetyl-beta-hexosaminidase, beta-glucuronidase and cathepsin C, were significantly reduced in cholesterol-enriched cells compared with activities in control cells. The results indicate that proteoglycan metabolism is altered in cholesterol-enriched smooth muscle cells.
Department of Medicine and Anatomy, Louisiana State University Medical Center, New Orleans.
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Vijayagopal
D000818:Animals; D001013:Aorta, Thoracic / Q000378:metabolism; D002412:Cations; D002455:Cell Division / Q000187:drug effects; D002458:Cell Fractionation; D002470:Cell Survival / Q000187:drug effects; D002478:Cells, Cultured; D002784:Cholesterol / Q000378:metabolism / Q000494:pharmacology*; D011508:Chondroitin Sulfate Proteoglycans / Q000302:isolation & purification / Q000378:metabolism; D002845:Chromatography; D003871:Dermatan Sulfate / Q000302:isolation & purification / Q000378:metabolism; D004705:Endocytosis; D005944:Glucosamine / Q000378:metabolism; D007700:Kinetics; D008077:Lipoproteins, LDL / Q000378:metabolism; D008247:Lysosomes / Q000201:enzymology; D009131:Muscle, Smooth, Vascular / Q000378:metabolism* / Q000648:ultrastructure; D011509:Proteoglycans / Q000096:biosynthesis*; D011817:Rabbits; D013431:Sulfates / Q000378:metabolism; D013462:Sulfur Radioisotopes; D014316:Tritium
D002412:Cations; D011508:Chondroitin Sulfate Proteoglycans; D008077:Lipoproteins, LDL; D011509:Proteoglycans; D013431:Sulfates; D013462:Sulfur Radioisotopes; C032649:dermatan sulfate proteoglycan; D014316:Tritium; D003871:Dermatan Sulfate; D002784:Cholesterol; D005944:Glucosamine