Annexin A1 released from apoptotic cells acts through formyl peptide receptors to dampen inflammatory monocyte activation via JAK/STAT/SOCS signalling.
Bottom Line: Supernatants from apoptotic neutrophils or the annexin A1 peptidomimetic Ac2-26 significantly reduced IL-6 signalling and the release of TNF-α from endotoxin-challenged monocytes.Ac2-26 activated STAT3 in a JAK-dependent manner, resulting in upregulated SOCS3 levels, and depletion of SOCS3 reversed the Ac2-26-mediated inhibition of IL-6 signalling.This identifies annexin A1 as part of the anti-inflammatory pattern of apoptotic cells and links the activation of FPRs to established signalling pathways triggering anti-inflammatory responses.
Affiliation: Centre for Molecular Biology of Inflammation, and Interdisciplinary Clinical Research Centre, Institute of Medical Biochemistry, University of Muenster, Muenster, Germany.Show MeSH
Mentions: To investigate whether Ac2-26-induced SOCS3 expression negatively regulates gp130 cytokines signalling, we first analysed the effect of Ac2-26 on IL-6 induced STAT3-activation. It is well known that IL-6 together with the signal transducer gp130 activates STAT3. As expected, IL-6 stimulation rapidly and robustly increased pY-STAT3 levels, reaching a maximum already 15 min after stimulation. This is in clear contrast to Ac2-26-elicited STAT3 phosphorylation, which occurred much later (Fig 7A, lanes 2 and 3). To test whether Ac2-26 elicited STAT3 activation is perturbed by pre-treatment with IL-6, monocytes were first stimulated with IL-6. After 90 min, when IL-6 induced STAT3 phosphorylation was already back to basal levels (not shown), Ac2-26 was given as a second stimulus and Ac2-26-elicited STAT3 phosphorylation was analysed. As presented in Fig 7A (lane 4), the STAT3 phosphorylation signal obtained in these cells was almost equivalent to the signal seen in cells stimulated with Ac2-26 only. This shows that STAT3 activation in response to Ac2-26 is not inhibited by pre-treatment with IL-6. Next, we tested for cross-inhibition of IL-6 signalling by Ac2-26 pre-treatment. Monocytes were pre-cultivated for 90 min in the presence of Ac2-26. At this time point, annexin-mediated STAT3 activation was back to basal levels (see Fig 4A). As shown in Fig 7A (lane 5), a subsequent 15 min stimulation with IL-6 resulted in decreased STAT3 phosphorylation as compared to treatment with IL-6 alone (Fig 7A, lane 2). Ac2-26 inhibited the IL-6-mediated STAT3 phosphorylation for up to 30 min of IL-6 application (not shown). To test whether the Ac2-26-induced upregulation of SOCS3 expression documented above (Fig 6) is the cause of impaired IL-6 signalling in the Ac2-26-treated monocytes, we performed stimulation experiments in monocytes, which had been treated with antisense phosphorothioate oligodeoxynucleotides (ODN; Sigma-Genosys) complementary to SOCS3 mRNA. A sense phosphorothioate ODN served as control. As expected, the response pattern of sense ODN treated monocytes was identical to that of control cells. In marked contrast, Ac2-26 was not able to interfere with IL-6-induced STAT3 activation in antisense ODN-treated monocytes (Fig 7B). These findings demonstrate that Ac2-26 negatively regulates IL-6 signalling via upregulation of SOCS3.
Affiliation: Centre for Molecular Biology of Inflammation, and Interdisciplinary Clinical Research Centre, Institute of Medical Biochemistry, University of Muenster, Muenster, Germany.