Regulation of murine macrophage proinflammatory and anti-inflammatory cytokines by ligands for peroxisome proliferator-activated receptor-γ: counter-regulatory activity by IFN-γ

The prostaglandin, 15-deoxy Delta(12,14)-prostaglandin J2 (15d-PGJ2)(1), and thiazolidinediones are ligands for the nuclear receptor, peroxisome proliferator-activated receptor (PPAR)-gamma, which mediates anti-inflammatory activity by suppressing murine macrophage (Mphi) production of the inflammatory mediator, nitric oxide (NO). Here, we elucidated this anti-inflammatory activity further by investigating whether PPAR-gamma ligands regulated a panel of proinflammatory and anti-inflammatory cytokines produced by primary inflammatory murine Mphi (thioglycollate-elicited peritoneal exudate Mphi; PEM). Thiazolidinediones and 15d-PGJ2 suppressed lipopolysaccharide (LPS)-induced PEM production of NO and IL-12(p40) to a greater extent than IL-6 and TNF-alpha production. Whereas 15d-PGJ2 showed the greatest extent of suppression of proinflammatory mediator production, the thiazolidinedione, BRL49653, was the most potent compound studied. Surprisingly, treatment with the Mphi-activation cytokine, IFN-gamma, prevented PPAR-gamma ligands from suppressing the proinflammatory cytokines completely and reduced their suppression of NO production substantially, demonstrating that activation conditions affect PPAR-gamma-mediated, anti-inflammatory activity. Western analysis demonstrated that the antagonistic activity of IFN-gamma did not involve modulation of PPAR-gamma expression but showed that IFN-gamma interfered with PPAR-gamma ligand regulation of p42/p44 MAP kinase activation and the cytosolic disappearance of NF-kappaB upon LPS stimulation. Finally, we showed that PPAR-gamma ligands did not substantially modulate production of the anti-inflammatory cytokine, IL-10, and that antibody-mediated neutralization of IL-10 did not prevent the ligands from suppressing proinflammatory mediator production. In contrast to studies with noninflammatory human monocytes and Mphi, our results demonstrate that primary murine inflammatory Mphi are extremely sensitive to the anti-inflammatory activity of PPAR-gamma ligands. These results suggest that drugs such as thiazolidinediones may be most effective in suppressing Mphi activity early (i.e., in the absence of lymphocyte-derived IFN-gamma) in the inflammatory process.