Peroxisome proliferator-activated receptors in inflammation control

Peroxisome proliferator-activated receptors (PPARs) are ligand-activated transcription factors belonging to the nuclear receptor superfamily. PPAR alpha is highly expressed in liver, skeletal muscle, kidney, heart and the vascular wall. PPAR gamma is predominantly detected in adipose tissue, intestine and macrophages. PPARs are activated by fatty-acid derivatives and pharmacological agents such as fibrates and glitazones which are specific for PPAR alpha and PPAR gamma respectively. PPARs regulate lipid and lipoprotein metabolism, glucose homeostasis, cell proliferation and differentiation, and apoptosis. PPAR alpha controls intra- and extracellular lipid metabolisms whereas PPAR gamma triggers adipocyte differentiation and promotes lipid storage. In addition, PPARs also modulate the inflammatory response. PPAR activators have been shown to exert anti-inflammatory activities in various cell types by inhibiting the expression of proinflammatory genes such as cytokines, metalloproteases and acute-phase proteins. PPARs negatively regulate the transcription of inflammatory response genes by antagonizing the AP-1, nuclear factor-kappaB (NF-kappaB), signal transducer and activator of transcription and nuclear factor of activated T-cells signalling pathways and by stimulating the catabolism of proinflammatory eicosanoids. These recent findings indicate a modulatory role PPARs in inflammation with potential therapeutical applications in chronic inflammatory diseases.