Abstract
Plasminogen activator inhibitor-1 (PAI-1) levels are regulated by inflammatory cytokines. In human umbilical vein endothelial cells (HUVECs), PAI-1 expression is regulated by interleukin-1β (IL1), transforming growth factor-β (TGF) and tumor necrosis factor-α (TNF), but not by interleukin-6 (IL6). TNF and epidermal growth factor (EGF) increase both PAI-1 as well as IL6 expression in human subcutaneous fat cell-derived human microvascular endothelial cells (SF-MECs). We investigated further the potential for differential response opf PAI-1 production by these diverse endothelial cells to IL6, ILl, and TNF. Treatment of SF-MECs with recombinant human IL6 and TNF (rhIL6 & rTNF) caused a maximum 3- to 3.4-fold increase in PAI-1 levels whereas rIL1 slightly decreased PAI-1 levels. In contrast, HUVECs showed increased production of PAL1 by rIL1 and rTNF but not by rhIL6. rhIL6-induced-PAI-1 production in SF-MECs was significant by 6 hr of treatment, and was specifically inhibited to basal levels by neutralizing antibodies to IL6. 3.2-fold increases in PAL1 mRNA steady-state levels assayed on quantitative slot blots were inhibited by either cycloheximide or α-amanitin, indicating that de novo protein and mRNA synthesis precede rhIL6 stimulation of PAI-1 mRNA levels. Nuclear run-on studies show that elevated PAI-1 levels are due to increased transcription of the PAI-1 gene. Lipopolysaccharide (LPS) treatment of SF-MECs and HUVECs stimulated PAI-1 and IL6 production within 24 hrs. At the same time, LPS induced IL6 to about 6 ng/ml in SF-MECs, similar to the 5 ng/ml of rhIL6 which maximally stimulated SF-MEC PAI-1 production. In contrast to HUVECs, LPS stimulation of PAI-1 levels in SF-MECs was specifically inhibited about 50% by anti-IL6. The observation that rILl decreases SF-MEC PAI-1 levels correlates with the the finding that LPS treatment in the presence of anti-IL1-β causes increased PAI-1 levels conJared with LPS alone. We suggest the existence of differential cytokine regulation of the PAI-1 gene among different human endothelial cell types, possibly involving IL6- and IL1-mediated autocrine mechanisms.