15-deoxy-Delta(12,14)-prostaglandin J(2) (15d-PGJ(2)) and an anti-diabetic thiazolidinedione, troglitazone (TRO) are peroxisome proliferator-activated receptor (PPAR)-gamma ligands, which regulate immuno-inflammatory reactions as well as adipocyte differentiation. We previously reported that 15d-PGJ(2) can suppress interleukin (IL)-1beta-induced prostaglandin E(2) (PGE(2)) synthesis in synoviocytes of rheumatoid arthritis (RA). IL-1 also stimulates PGE(2) synthesis in osteoblasts by regulation of cyclooxygenase (COX)-2 and regulates osteoclastic bone resorption in various diseases such as RA and osteoporosis. In this study, we investigated the feedback mechanism of the arachidonate cascade in mouse osteoblastic cells, MC3T3-E1 cells, which differentiate into mature osteoblasts. Treatment with 15d-PGJ(2) led to a significant increase in IL-1alpha-induced COX-2 expression and PGE(2) production in a dose dependent manner. The effect of 15d-PGJ(2) was stronger than that of TRO. However, it did not affect the expression of COX-1. In addition, cell viability of MC3T3-E1 cells was not changed in the condition we established. This means that 15d-PGJ(2) exerts a positive feedback regulation of the arachidonate cascade of PGE(2) in osteoblastic cells. These results may provide important information about the pathogenesis and treatment of bone resorption in a variety of diseases such as RA and osteoporosis.
Keywords: 15d-PGJ2; COX-2; PGE2; PPAR-γ; osteoblast.