Background: The peroxisome proliferator-activated receptor g (PPAR g) is a nuclear hormone receptor that binds lipophilic ligands. The receptor acts as ligand-dependent transcription factor, which upon activation decreases the production of pro-inflammatory cytokines, and of reactive nitrogen species in monocytes/macrophages. Previous findings account for the activation of PPAR g by a nitroalkene derivative of linoleic acid (18:2), nitrolinoleic acid (LNO2). LNO2 is formed via nitric oxide (NO)–dependent oxidative reactions in inflammatory processes and can be decomposed, yielding NO and linoleic acid. As NO activates the p21Ras-MAP kinases signaling pathway, we are investigating the participation of the p21Ras-MAP kinases signaling pathway in the activation of PPAR g by LNO2.
Methods: LNO2 was synthesized from linoleic acid and NO2BF4. LNO2 was purified and characterized using HPLC and LC-ESI/MS/MS-based techniques. The eletrophoretic mobility shift assay was used to evaluate the LNO2-mediated activation of PPAR g in THP-1 cells, a human monocytic cell line. Western blot analysis was used to evaluate the participation of the MAP kinases ERK 1/2 and p38 in the PPAR g activation by LNO2.
Results: LNO2 at physiologically relevant concentrations (10 nM) activates PPARg. By contrast, linoleic acid a natural ligand for PPARg only activated the receptor at much higher concentrations (10 mM). LNO2 (10 nM) activated the ERK1/2 MAP kinases but had no effects on p38 MAP kinase. In addition, the MEK inhibitor PD98059 blocked PPAR g activation by LNO2, suggesting a connection between ERK1/2 MAP kinases and the activation of this transcription factor.
Concluding remarks: Our observations suggest a new mechanism involving the participation of the ERK1/2 MAP kinases in the activation of PPAR g by LNO2.
Financial Support: FAPESP/CNPQ - Instituto do Milênio Redoxoma.