Interleukin-6 (IL-6) is a pleiotropic cytokine, whose plasma levels are elevated in inflammatory diseases such as atherosclerosis. We have previously reported that peroxisome proliferator-activated receptor ␣

Peroxisome proliferator-activated receptors (PPARs) are key players in lipid and glucose metabolism and are implicated in metabolic disorders predisposing to atherosclerosis, such as dyslipidaemia and diabetes. Whereas PPARgamma promotes lipid storage by regulating adipocyte differentiation, PPARalpha stimulates the beta-oxidative degradation of fatty acids. PPARalpha-deficient mice show a prolonged response to inflammatory stimuli, suggesting that PPARalpha is also a modulator of inflammation. Hypolipidaemic fibrate drugs are PPARalpha ligands that inhibit the progressive formation of atherosclerotic lesions, which involves chronic inflammatory processes, even in the absence of their atherogenic lipoprotein-lowering effect. Here we show that PPARalpha is expressed in human aortic smooth-muscle cells, which participate in plaque formation and post-angioplasty re-stenosis. In these smooth-muscle cells, we find that PPARalpha ligands, and not PPARgamma ligands, inhibit interleukin-1-induced production of interleukin-6 and prostaglandin and expression of cyclooxygenase-2. This inhibition of cyclooxygenase-2 induction occurs transcriptionally as a result of PPARalpha repression of NF-kappaB signalling. In hyperlipidaemic patients, fenofibrate treatment decreases the plasma concentrations of interleukin-6, fibrinogen and C-reactive protein. We conclude that activators of PPARalpha inhibit the inflammatory response of aortic smooth-muscle cells and decrease the concentration of plasma acute-phase proteins, indicating that PPARalpha in the vascular wall may influence the process of atherosclerosis and re-stenosis.

Peroxisome proliferator-activated receptors (PPARs) have been implicated in metabolic diseases, such as obesity, diabetes, and atherosclerosis, due to their activity in liver and adipose tissue on genes involved in lipid and glucose homeostasis. Here, we show that the PPAR␣ and PPAR␥ forms are expressed in differentiated human monocyte-derived macrophages, which participate in inflammation control and atherosclerotic plaque formation. Whereas PPAR␣ is already present in undifferentiated monocytes, PPAR␥ expression is induced upon differentiation into macrophages. Immunocytochemistry analysis demonstrates that PPAR␣ resides constitutively in the cytoplasm, whereas PPAR␥ is predominantly nuclear localized. Transient transfection experiments indicate that PPAR␣ and PPAR␥ are transcriptionally active after ligand stimulation. Ligand activation of PPAR␥, but not of PPAR␣, results in apoptosis induction of unactivated differentiated macrophages as measured by the TUNEL assay and the appearance of the active proteolytic subunits of the cell death protease caspase-3. However, both PPAR␣ and PPAR␥ ligands induce apoptosis of macrophages activated with tumor necrosis factor ␣/interferon ␥. Finally, PPAR␥ inhibits the transcriptional activity of the NFB p65/RelA subunit, suggesting that PPAR activators induce macrophage apoptosis by negatively interfering with the anti-apoptotic NFB signaling pathway. These data demonstrate a novel function of PPAR in human macrophages with likely consequences in inflammation and atherosclerosis.