Redox Regulation of PPARg in Polarized Macrophages

The peroxisome proliferator-activated receptor (PPARg) is a central mediator of cellular lipid metabolism and immune cell responses during inflammation. This is facilitated by its role as a transcription factor as well as a DNA-independent protein interaction partner. We addressed how the cellular redox milieu in the cytosol and the nucleus of lipopolysaccharide (LPS)/interferon-g- (IFNg-) and interleukin-4- (IL4-) polarized macrophages (MF) initiates posttranslational modifications of PPARg, that in turn alter its protein function. Using the redox-sensitive GFP2 (roGFP2), we validated oxidizing and reducing conditions following classical and alternative activation of MF, while the redox status of PPARg was determined via mass spectrometry. Cysteine residues located in the zinc finger regions (amino acid fragments AA 90-115, AA 116-130, and AA 160-167) of PPARg were highly oxidized, accompanied by phosphorylation of serine 82 in response to LPS/IFNg, whereas IL4-stimulation provoked minor serine 82 phosphorylation and less cysteine oxidation, favoring a reductive milieu. Mutating these cysteines to alanine to mimic a redox modification decreased PPARg-dependent reporter gene transactivation supporting a functional shift of PPARg associated with the MF phenotype. These data suggest distinct mechanisms for regulating PPARg function based on the redox state of MF.