Myeloperoxidase-dependent Lipid Peroxidation Promotes the Oxidative Modification of Cytosolic Proteins in Phagocytic Neutrophils

Abstract

Background: Neutrophils generate oxidants to kill microbes ingested into phagosomes, but extraphagosomal protein oxidation may also occur. Results: Specific neutrophil cytosolic proteins were carbonylated following phagocytosis; carbonylation was impaired by myeloperoxidase inhibitors or radical scavengers that inhibit lipid peroxidation. Conclusion: Lipid peroxidation in the phagosomal membrane leads to oxidation of cytosolic proteins. Significance: Protein oxidation may influence the function and fate of post-phagocytic neutrophils. Phagocytic neutrophils generate reactive oxygen species to kill microbes. Oxidant generation occurs within an intracellular phagosome, but diffusible species can react with the neutrophil and surrounding tissue. To investigate the extent of oxidative modification, we assessed the carbonylation of cytosolic proteins in phagocytic neutrophils. A 4-fold increase in protein carbonylation was measured within 15 min of initiating phagocytosis. Carbonylation was dependent on NADPH oxidase and myeloperoxidase activity and was inhibited by butylated hydroxytoluene and Trolox, indicating a role for myeloperoxidase-dependent lipid peroxidation. Proteomic analysis of target proteins revealed significant carbonylation of the S100A9 subunit of calprotectin, a truncated form of Hsp70, actin, and hemoglobin from contaminating erythrocytes. The addition of the reactive aldehyde 4-hydroxynonenal (HNE) caused carbonylation, and HNE-glutathione adducts were detected in the cytosol of phagocytic neutrophils. The post-translational modification of neutrophil proteins will influence the functioning and fate of these immune cells in the period following phagocytic activation, and provides a marker of neutrophil activation during infection and inflammation.