Low doses of 15d-PGJ2 induce osteoblast activity in a PPAR-gamma independent manner.

Peroxisome proliferator-activated receptor-gamma (PPARγ) regulates both glucose metabolism and bone mass. Evidence suggests that the therapeutic modulation of PPARγ with synthetic agonists activity may elicit undesirable effects on bone. However, there is no information regarding its natural agonist 15d-PGJ2, besides its excellent anti-inflammatory action. In the present study the effects of 15d-PGJ2 on osteoblastic cells were determined. Osteoblastic cells (MC3T3) were cultured in an osteogenic medium in the presence of 1, 3 or 10 μM of 15d-PGJ2 during 21 days and alizarin and Von Kossa staining were employed. The protein expression (type-I collagen, osteonectin, osteopontin, RANKL, osteoprotegerin, HDAC-9c and PPAR-γ) was evaluated after 3 days in the presence of 15d-PGJ2 by western blotting and indirect immunofluorescence methods. The production of mineralized extracellular matrix was observed by transmission electron microscopy. After 72 h of culture, the mRNA was extracted for RT-qPCR analysis of RUNX expression. In the presence of all 3 tested 15d-PGJ2 doses, alizarin red and Von kossa staining were positive demonstrating the ability to the osteoblast differentiation. Type-I collagen and osteonectin proteins expression were up-regulated (p < 0.05) after 72 h in the presence of the smaller doses of 15d-PGJ2. In contrast, osteopontin, RANKL and OPG expression did not significantly alter. In the presence of 15d-PGJ2 it was possible to visualize mineralized nodules in the extracellular matrix confirmed with the increased RUNX mRNA expression. 15d-PGJ2 at small doses increased the osteoblast activity and the bone-related proteins expression.