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Abstract
S100A8, S100A9 and S100A12 are generally considered pro-inflammatory proteins because their expression is elevated in chronic inflammatory disorders. Hypohalous acids generated by activated phagocytes are scavenged by murine S100A8 and S100A9, suggesting a protective role in oxidative stress, but effects on human recombinant S100A8 and S100A9 are undefined. Hypohalous acids at low molar ratios (1:1) promoted structural changes in human S100A8 and S100A9 in vitro, generating two novel posttranslational modifications on Cys42 in S100A8, defined as oxathiazolidine-oxide and dioxide. Particular methionine residues in S100A9 were also modified.
S100A8 and S100A9 are increased in respiratory diseases in which reactive oxygen species are implicated and anti-oxidant mechanisms compromised. Oxidized S100A8 (oxS100A8) was prominent in asthmatic lung and significantly elevated in sputum, compared to controls, whereas S100A8 or S100A9 levels were not. Monomeric oxS100A8 was the major component in asthmatic sputum; modifications were similar to those generated by hypochlorous acid (HOCl) in vitro. Oxidized Met63/81/94 were variously present in S100A9 from asthmatic sputum, only oxidized Met63 was seen in control sputum. oxS100A8 and oxS100A9 did not form heterocomplexes and neutrophil adhesion to fibronectin, properties typical of the native complex, and antimicrobial activity was significantly compromised.
Inflammation is associated with increased risk of cardiovascular disease in chronic autoimmune diseases such as systemic lupus erythematosus (SLE) and with asthma. Serum levels of S100A8, S100A9 and S100A8/A9 were similar in patients with SLE and controls. Native and oxS100A8 were not apparent in Western blots of serum, and were located in HDL, possibly due to interaction with ApoAI. Carotid artery extracts indicated oxidant scavenging by S100A8 and S100A9. S100A8 protection of lipid-free ApoAI against oxidation by HOCl was Cys42-dependent. S100A8 and S100A9 reduced generation of hypochlorite-oxidized proteins in endothelial cells, suggesting a protective role for these proteins in the vasculature.
Results have broad implications in diseases where hypohalous acid oxidants are generated and support the notion that oxidant scavenging and subsequent post-translational modifications are functionally important, emphasizing a role for S100A8 and S100A9 in redox homeostasis in inflammation.