Endothelial cell stimulation of smooth muscle glycosaminoglycan synthesis can be accounted for by transforming growth factor beta activity

Abstract

Endothelial cell conditioned medium (ECCM) contains a factor which markedly stimulates smooth muscle cell (SMC) glycosaminoglycan (GAG) synthesis. We report here that the factor responsible is transforming growth factor beta (TGF-β) as assessed by (1) protease and thiol sensitivity, (2) heat and acid enhancement of ECCM activity, and (3) neutralisation of ECCM activity by anti-TGF-β-immunoglobulin. Anti-TGF-β-neutralisation was effective against increases in both sulphated and non-sulphated GAG. Previous studies showed that ECCM from EC of varying densities stimulated individual GAG to varying degrees. ECCM from low density EC preferentially stimulated hyaluronic acid (HA) whereas ECCM from intermediate and high density cultures stimulated increasing amounts of sulphated GAG. Exposure of SMC to varying concentrations of TGF-β produced a similar pattern of response. Very low amounts of TGF-β (< 10–500 pg/10 cells) stimulated a marked and significant increase in HA synthesis. Increase in chondroitin sulphate 4 6 was most marked at TGF-β levels from 500–1000 pg/10 6 cells. At levels above 1000 pg/10 6 cells both HA and sulphated GAG synthesis decreased but still remained elevated above controls. These findings indicate that TGF-β alone can account for the changes in SMC GAG synthesis stimulated by ECCM. It was also found, however, that heat-treated SMC conditioned medium stimulated SMC GAG synthesis, thus SMC may contribute to the control of their own GAG synthesis through autocrine TGF-β activity.