PPAR-γ agonist pioglitazone alleviates inflammatory response induced by lipopolysaccharides in osteoblast cells

Osteomyelitis is an acute or chronic inflammatory bone disease with a high disability rate. As an anti-inflammatory factor, peroxisome proliferator activated receptor-gamma (PPAR-gamma) is not only implicated in a variety of inflammatory responses but also regulates osteoblast differentiation and bone mass. However, the role of PPAR-gamma in osteomyelitis is not fully understood. In the present study, we demonstrated that PPAR-gamma showed a lower expression level in infected bone tissue of osteomyelitis patients as compared with uninfected bone tissue from nonosteomyelitis patients with fracture of the hip. We applied lipopolysaccharides (LPSs) in MC3T3-E1 osteoblast precursor cell line as an in vitro model for osteomyelitis. LPS treatment increased osteomyelitis-associated inflammatory cytokines such as interleukin-6 (IL-6) and tumor necrosis factor-alpha (TNF-alpha), whereas PPAR-gamma levels and cell viability in MC3T3-E1 cells were suppressed. PPAR-gamma antagonist GW9662 further enhanced IL-6 and TNF-alpha levels, and decreased cell viability in the presence of LPS treatment. In contrast, PPAR-gamma agonist pioglitazone antagonized the effect of LPS treatment in MC3T3-E1 cells. These findings suggest that PPAR-gamma downregulation is associated with the inflammation and progression of osteomyelitis, and PPAR-gamma agonist could serve as a therapeutic strategy to attenuate inflammatory responses. This study provides novel insights into the physiopathogenesis of osteomyelitis and future study is required to validate the findings in animal model and uncover the molecular mechanism of PPAR-gamma-dependent anti-inflammation in osteoblasts.