PPAR-γ ligands modulate effects of LPS in stimulated rat synovial fibroblasts

This work demonstrated the constitutive expression of peroxisome proliferator-activated receptor (PPAR)-gamma and PPAR-alpha in rat synovial fibroblasts at both mRNA and protein levels. A decrease in PPAR-gamma expression induced by 10 mug/ml lipopolysaccharide (LPS) was observed, whereas PPAR-alpha mRNA expression was not modified. 15-Deoxy-Delta (12,14)-prostaglandin J(2) (15d-PGJ(2)) dose-dependently decreased LPS-induced cyclooxygenase (COX)-2 (-80%) and inducible nitric oxide synthase (iNOS) mRNA expression (-80%), whereas troglitazone (10 muM) only inhibited iNOS mRNA expression (-50%). 15d-PGJ(2) decreased LPS-induced interleukin (IL)-1 beta (-25%) and tumor necrosis factor (TNF)-alpha (-40%) expression. Interestingly, troglitazone strongly decreased TNF-alpha expression (-50%) but had no significant effect on IL-1 beta expression. 15d-PGJ(2) was able to inhibit DNA-binding activity of both nuclear factor (NF)-kappaB and AP-1. Troglitazone had no effect on NF-kappaB activation and was shown to increase LPS-induced AP-1 activation. 15d-PGJ(2) and troglitazone modulated the expression of LPS-induced iNOS, COX-2, and proinflammatory cytokines differently. Indeed, troglitazone seems to specifically target TNF-alpha and iNOS pathways. These results offer new insights in regard to the anti-inflammatory potential of the PPAR-gamma ligands and underline different mechanisms of action of 15d-PGJ(2) and troglitazone in synovial fibroblasts.