Objective:
To determine the effects of peroxisome proliferator-activated receptor gamma (ppargamma) agonists on interleukin-1 (il-1) induction of nitric oxide (no) and matrix metalloproteinase 13 (mmp-13) in human chondrocytes.
Methods:
Ppargamma expression and synthesis in human chondrocytes were determined by reverse transcriptase-polymerase chain reaction (rt-pcr) and immunohistochemistry, respectively. chondrocytes were cultured with il-1beta, tumor necrosis factor alpha (tnfalpha), and il-17 in the presence or absence of ppargamma agonists, and no and mmp-13 synthesis and expression levels were measured. transient transfection experiments were performed with the 7-kb inducible no synthase (inos) and 1.6-kb mmp-13 human promoters, as well as with the ppargamma expression vector and the activator protein 1 (ap-1) and nuclear factor kappab (nf-kappab) reporter constructs.
Results:
Rt-pcr and immunohistochemical analysis revealed that human chondrocytes expressed and produced ppargamma. treatment of chondrocytes with ppargamma ligands brl 49653 and 15-deoxy-delta12,14-prostaglandin j2 (15d-pgj2), but not with pparalpha ligand wy 14643, decreased il-1beta-induced no and mmp-13 production in a dose-dependent manner. in addition, both inos and mmp-13 messenger rna were inhibited in the presence of 15d-pgj2. the inhibitory effect of ppargamma activation was not restricted to il-1beta, since tnfalpha- and il-17-induced no and mmp-13 production were also inhibited by 15d-pgj2. in transient transfection experiments, we showed that a constitutively active form of mitogen-activated protein kinase kinase kinase 1 (amekk-1) induced the mmp-13 and inos human promoter activity. this process was reduced by 15d-pgj2 and further inhibited by cotransfection with a ppargamma expression vector. similarly, in a ppargamma-dependent manner, 15d-pgj2 inhibited deltamekk-1-induced ap-1- and nf-kappab-luciferase reporter plasmid activation.
Conclusion:
The findings of this study demonstrate that ppargamma agonists inhibit il-1beta induction of both no and mmp-13 in human chondrocytes. the inhibition occurs at least at the transcriptional level through a ppargamma-dependent pathway, probably by interfering with the activation of ap-1 and nf-kappab.