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Abstract

Objective

To study the potency of 2 peroxisome proliferator–activated receptor γ (PPARγ) agonists, 15-deoxy-Δ12,14-prostaglandin J2 (15-deoxy-PGJ2) and rosiglitazone, to modulate the expression of interleukin-1 receptor antagonist (IL-1Ra) in rat synovial fibroblasts.

Methods

Levels of messenger RNA for IL-1Ra and PPAR isotypes (α, β/δ, γ) were assessed by real-time polymerase chain reaction in rat synovial fibroblasts exposed to 10 ng/ml of IL-1β. PPAR levels were assessed by Western blotting and secreted IL-1Ra levels by immunoassay. The potency of PPARγ agonists and the PPARβ/δ agonist GW-501516 on IL-1Ra levels was tested in the range of 1–10 μM and at 100 pM, respectively. The contribution of PPARγ to the effects of rosiglitazone on IL-1Ra secretion was examined either by its overexpression or by inhibition using wild-type or dominant-negative constructs and the antagonist GW-9662 (10 μM), respectively. The dominant-negative strategy was also performed to investigate the possible contribution of PPARβ/δ and NF-κB activation.

Results

IL-1β–induced IL-1Ra production was increased by 10 μM rosiglitazone but was reduced dose-dependently by 15-deoxy-PGJ2. Both agonists lowered IL-1β secretion, but rosiglitazone alone reduced the imbalance of IL-1β/IL-1Ra toward basal levels. Enhancement of IL-1β–induced IL-1Ra production by rosiglitazone was not affected by PPARγ overexpression or by its inhibition with dominant-negative PPARγ or GW-9662. Inhibition of NF-κB was also ineffective against rosiglitazone but abolished the stimulating effect of IL-1β on IL-1Ra. All PPAR isotypes were expressed constitutively in rat synoviocytes, but PPARγ decreased dramatically upon IL-1β exposure, whereas PPARβ/δ remained stable. Dominant-negative PPARβ/δ abolished the enhancement of IL-1Ra by rosiglitazone, whereas GW-501516 reproduced the effect of rosiglitazone on IL-1Ra secretion.

Conclusion

Rosiglitazone stimulates IL-1Ra production by a PPARβ/δ mechanism in activated rat synovial fibroblasts, further contributing to its potential antiarthritic properties and opening new perspectives for the modulation of inflammatory genes by specific PPAR agonists in articular cells.