Delayed activation of PPARγ by LPS and IFN-γ attenuates the oxidative burst in macrophages

Desensitization of macrophages is important during the development of sepsis. It was our intention to identify mechanisms that promote macrophage deactivation upon contact with endotoxin (LPS) and interferon-gamma (IFN-gamma) in vitro. Macrophage activation was achieved with 12-O-tetradecanoylphorbol 13-acetate (TPA), and the oxidative burst (i.e., oxygen radical formation) was followed by oxidation of the redox-sensitive dyes hydroethidine and dichlorodihy-drofluorescein diacetate, Prestimulation of macrophages for 15 h with a combination of LPS/IFN-gamma attenuated oxygen radical formation in response to TPA, Taking the anti-inflammatory properties of the peroxisome proliferator-activating receptory (PPAR gamma) into consideration, we established activation of PPAR gamma in response to LPS/IFN-gamma by an electrophoretic mobility shift, supershift, and a reporter gene assay. The reporter contains a triple PPAR-responsive element (PPRE) in front of a thymidine kinase minimal promoter driving the luciferase gene, We demonstrated that PPRE decoy oligonucleotides, supplied in front of LPS/IFN-gamma, allowed a full oxidative burst to recover upon TPA addition, Furthermore, we suppressed the oxidative burst by using the PPAR gamma agonists 15-deoxy-Delta (12,14)-prostaglandin J(2), BRL. 49653, or ciglitazone. No effect was observed with WY 14643, a PPAR alpha agonist, We conclude that activation of PPARs, most likely PPAR gamma, promotes macrophage desensitization, thus attenuating the oxidative burst, This process appears important during development of sepsis.