Modulating effect of serum on the stimulation of plasminogen activator inhibitor 2 production in human gingival fibroblasts by lipopolysaccharide and interleukin-1 beta

OBJECTIVE: Plasminogen activator inhibitor-2 (PAI-2) is an important counter proteolysis factor which helps protect tissues from inflammatory stress. The expression of PAI-2 can be modulated by various inflammatory stimulants and mediators. The aim of the present study was to investigate how serum factors, might modulate the effects of lipopolysaccharide (LPS) and interleukin-1beta on PAI-2 production by human gingival fibroblasts. METHODS: Human gingival fibroblasts were exposed to LPS derived from Actinobacillus actinomycetemcomitans or Escherichia coli and a commercial source of interleukin-1beta (IL-1beta). The expression of PAI-2 and its mRNA was monitored by Western blotting, RT-PCR, and Northern blotting. RESULTS: The results showed that the distribution of PAI-2 synthesised by human gingival fibroblasts (HGF) was mostly as an intracellular protein (47kDa). The presence of serum in the culture media was absolutely necessary for both the secretion of PAI-2 and for the effect of the inflammatory mediators (LPS and IL-1beta). A pattern of PAI-2 response in HGF after LPS stimulation was detected with a quick up-regulation of the PAI-2 mRNA, which was down regulated when extracellular PAI-2 (60kDa mass) levels reached plateau levels. The synthesis of PAI-2 by HGF, in terms of mRNA expression and protein synthesis, was more sensitive to stimulation with lower concentrations of LPS (10 ng/ml) than with higher LPS concentrations. CONCLUSIONS: PAI-2 is a serum dependent molecule with major cytosolic localisation in HGF. Its cellular accumulation and secretion can be modulated by bacterial LPS and IL-1beta through serum factors