Peroxisome proliferator-activated receptor gamma activators inhibit interleukin-1 beta-induced nitric oxide and matrix metalloproteinase 13 production in human chondrocytes

Objective. To determine the effects of peroxisome proliferator-activated re ceptor gamma (PPAR gamma) agonists on interleukin-1 (IL-1) induction of nit ric oxide (NO) and matrix metalloproteinase 13 (MMP-13) in human chondrocyt es. Methods. PPAR gamma expression and synthesis in human chondrocytes were det ermined by reverse transcriptase-polymerase chain reaction (RT-PCR) and imm unohistochemistry, respectively. Chondrocytes were cultured with IL-1 beta, tumor necrosis factor alpha (TNF alpha), and IL-17 in the presence or abse nce of PPAR gamma agonists, and NO and MMP-13 synthesis and expression leve ls were measured. Transient transfection experiments were performed with th e 7-kb inducible NO synthase (iNOS) and 1.6-kb MMP-13 human promoters, as w ell as with the PPAR gamma expression vector and the activator protein 1 (A P-1) and nuclear factor kappaB (NF-kappaB) reporter constructs. Results. RT-PCR and immunohistochemical analysis revealed that human chondr ocytes expressed and produced PPAR gamma. Treatment of chondrocytes with PP AR gamma ligands BRL 49653 and 15-deoxy-Delta (12,14)- prostaglandin J(2) ( 15d-PGJ(2)), but not with PPAR alpha ligand Wy 14643, decreased IL-1 beta - induced NO and MMP-13 production in a dose-dependent manner. In addition, b oth iNOS and MMP-13 messenger RNA were inhibited in the presence of 15d-PGJ (2). The inhibitory effect of PPAR gamma activation was not restricted to I L-1 beta, since TNF alpha- and IL-17-induced NO and MMP-13 production were also inhibited by 15d-PGJ(2). In transient transfection experiments, we sho wed that a constitutively active form of mitogen-activated protein kinase k inase kinase 1 (Delta MEKK-1) induced the MMP-13 and MOS human promoter act ivity. This process was reduced by 15d-PGJ(2) and further inhibited by cotr ansfection with a PPAR gamma expression vector. Similarly, in a PPAR gamma -dependent manner, 15d-PGJ(2) inhibited Delta MEKK-1-induced AP-1- and NF-k appaB-luciferase reporter plasmid activation. Conclusion. The findings of this study demonstrate that PPAR gamma agonists inhibit IL-1 beta induction of both NO and MMP-13 in human chondrocytes. T he inhibition occurs at least at the transcriptional level through a PPAR g amma -dependent pathway, probably by interfering with the activation of AP- 1 and NF-kappaB.