Rationale: The role of macrophage iron in the physiopathology of atherosclerosis is an open question that needs to be clarified. In atherosclerotic lesions, recruited macrophages are submitted to cytokines and oxidized lipids which influence their phenotype. An important phenotypic population driven by oxidized phospholipids is the Mox macrophages which present unique biological properties but their iron phenotype is not well described.
Objective: To investigate the effect of Mox polarization by oxidized LDL (oxLDL) on macrophage iron metabolism in the absence or presence of proinflammatory stimuli.
Methods: Bone marrow-derived macrophages were treated with different sources of LDL and/or LPS/IFNγ (M1 activator). Expression of ferroportin (Slc40a1, alias Fpn), heme oxygenase-1 (Hmox1), H- and L-ferritin (Fth1 and Ftl1), hepcidin (Hamp), ceruloplasmin (Cp) and interleukine-6 (Il6) was followed by quantitative PCR. FPN and HMOX1 protein expression was analyzed by immunofluorescence and in-cell-Western blotting.
Results: Mox macrophages expressed increased Hmox1 and Fth1 levels with basal FPN protein levels despite the significant increase of Fpn mRNA. Upregulation of Hmox1 and Fpn mRNA was specific to LDL oxidative modification and mediated by NRF2. The downregulation of both Cp isoforms and the upregulation of Hamp expression observed in Mox macrophages suggest that FPN mediated iron export could be compromised. Simultaneous exposure to oxLDL and LPS/IFNγ leads to a mixed Mox/M1 phenotype that is closer to M1.
Conclusion: A microenvironment rich in oxLDL and proinflammatory cytokines could promote macrophage iron retention and lipid accumulation profiles, a specific cell phenotype that likely contributes to lesion development and plaque instability in atherosclerosis.
Keywords: Atherosclerosis; Iron metabolism; Macrophage; Mox; Oxidized LDL; Proinflammatory stimuli.
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