Roles of myeloperoxidase and GAPDH in interferon-gamma production of GM-CSF-dependent macrophages

Interferon (IFN)-gamma is highly expressed in atherosclerotic lesions and may have an important role in atherogenesis. Myeloperoxidase (MPO), the most abundant protein in neutrophils, is a marker of plaque vulnerability and a possible bridge between inflammation and cardiovascular disease. Granulocyte-macrophage colony-stimulating factor (GM-CSF) has also been implicated in the pathogenesis of atherosclerosis. The present study investigated the role of neutrophil activation in atherosclerosis. Adherent macrophages were obtained from primary cultures of human mononuclear cells. Expression of IFN-gamma protein by GM-CSF-dependent-macrophages was investigated by enzyme-linked immunosorbent assay after stimulation with MPO. GM-CSF enhanced macrophage expression of the mannose receptor (CD206), which is involved in MPO uptake. MPO increased IFN-gamma production by GM-CSF-dependent macrophages in a concentration-dependent manner. Pretreatment of macrophages with small interfering RNA (siRNA) for CD206 or extracellular signal-regulated kinase (ERK)-2 attenuated IFN-gamma production, while siRNA for ERK-1 did not. GAPDH is known to bind to adenylate/uridylate (AU)-rich elements of RNA and may influence IFN-gamma protein expression by binding to the AU-rich element of IFN-gamma mRNA. Interestingly, pretreatment with siRNA for GAPDH significantly reduced IFN-gamma production by macrophages, while it did not affect TF protein expression. In conclusion, MPO upregulates IFN-gamma production by GM-CSF-dependent-macrophages via the CD206/ERK-2 signaling pathway, while silencing GAPDH reduces IFN-gamma production.