Emerging PPARγ-Independent Role of PPARγLigands in Lung Diseases

Abstract

Peroxisome proliferator activated receptor (PPAR)-γis a nuclear hormone receptor that is activated by multiple agonists including thiazolidinediones, prostaglandins, and synthetic oleanolic acids. Many PPARγligands are under investigation as potential therapies for human diseases. These ligands modulate multiple cellular pathways via both PPARγ-dependent and PPARγ-independent mechanisms. Here, we review the role of PPARγand PPARγligands in lung disease, with emphasis on PPARγ-independent effects. PPARγligands show great promise in moderating lung inflammation, as antiproliferative agents in combination to enhance standard chemotherapy in lung cancer and as treatments for pulmonary fibrosis, a progressive fatal disease with no effective therapy. Some of these effects occur when PPARγis pharmaceutically antagonized or genetically PPARγand are thus independent of classical PPARγ-dependent transcriptional control. Many PPARγligands demonstrate direct binding to transcription factors and other proteins, altering their function and contributing to PPARγ-independent inhibition of disease phenotypes. These PPARγ-independent mechanisms are of significant interest because they suggest new therapeutic uses for currently approved drugs and because they can be used as probes to identify novel proteins and pathways involved in the pathogenesis or treatment of disease, which can then be targeted for further investigation and drug development.