Expression of tissue factor pathway inhibitor in vascular smooth muscle cells and its regulation by growth factors

Tissue factor pathway inhibitor (TFPI) in vivo is thought to be synthesized mainly by endothelial cells. To date, no significant regulator of TFPI syn thesis has been described. Vascular smooth muscle cells (VSMC) express tiss ue factor in vitro and in vivo, which may contribute to Vascular thrombosis . We hypothesized that VSMC might also express TFPI. To determine this, we examined grouch-arrested coronary VSMC in culture and found that VSMC secre ted an amount of TFPI similar to that seen in endothelial cells. Immunohist ochemistry of normal human coronary arteries showed TFPI staining throughou t the media and intima of the vessel with localization to VSMC and endothel ial cells. To determine regulation of TFPI expression in VSMC, we examined the effects of serum stimulation on TFPI secretion and found that FBS induc ed a 5-fold increase in TFPI antigen and activity levels in conditioned med ium at 48 hours (P<0.001) when compared with serum-free conditions. A simil ar stimulatory effect was seen with 10% pooled human serum. Moreover, epide rmal growth factor and platelet-derived growth factor-B increased TFPI secr etion by 4- to 5-fold and 2- to 3-fold, respectively (P<0.05), and these gr owth factors accounted for approximate to 50% of the TFPI secretion effects of human serum. The serum effect was associated with a 3-fold increase in TFPI mRNA 24 hours after release from growth arrest and a 50% decrease in T FPI secretion after treatment with actinomycin D. Taken together, this stud y suggests that there is significant TFPI expression in VSMC in culture and in VSMC within the intima and media of the normal coronary artery wall. We present the first evidence for TFPI regulation by serum in VSMC and more s pecifically by its constituent growth factors, epidermal growth factor and platelet-derived growth factor-B.