The independence of signaling pathways mediating increased expression of plasminogen activator inhibitor type 1 in HepG2 cells exposed to free fatty acids or triglycerides.

We have shown that both free fatty acids (FFA) and triglycerides (TG) increase expression of plasminogen activator inhibitor type 1 (PAI-1) in vivo and in vitro. To determine signaling mechanisms responsible, HepG2 cells were exposed to FFA, emulsified TG, or the combination. The combination of FFA and TG increased PAI-1 to a greater extent than either agent alone (fold induction: 0.45mM FFA 1.7 +/- 0.2, 1,000 mg/dl TG 1.9 +/- 0.1, both 2.3 +/- 0.2, n=10, p<0.05 for comparison of combination with either alone). Cells transfected with PAI-1 5' flanking region containing the 4G or 5G polymorphism displayed similar activity in response to FFA, but modestly greater activity with the 4G polymorphism in response to TG (fold induction: 5G-1.28 +/- 0.14 and 4G-1.46 +/- 0.13, n=6, p < 0.05 for comparison). Deletion analyses demonstrated that FFA and TG induce PAI-1 expression through distinct regions of the promoter. Inhibition of protein kinase C inhibited the response to FFA but not TG. Accordingly, increased FFA and TG contribute to increased PAI-1 through independent mechanisms.