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Annexin A1 Is a Physiological Modulator of Neutrophil Maturation and Recirculation Acting on the CXCR4/CXCL12 Pathway

Neutrophil production and traffic in the body compartments is finely controlled, and the strong evidences support the role of CXCL12/CXCR4 pathway on neutrophil trafficking to and from the bone marrow (BM). We recently showed that the glucocorticoid‐regulated protein, Annexin A1 (AnxA1) modulates neutrophil homeostasis and here we address the effects of AnxA1 on steady‐state neutrophil maturation and trafficking. For this purpose, AnxA1−/− and Balb/C wild‐type mice (WT) were donors of BM granulocytes and mesenchymal stem cells and blood neutrophils. In vivo treatments with the pharmacological AnxA1 mimetic peptide (Ac2‐26) or the formyl peptide receptor (FPR) antagonist (Boc‐2) were used to elucidate the pathway of AnxA1 action, and with the cytosolic glucocorticoid antagonist receptor RU 38486. Accelerated maturation of BM granulocytes was detected in AnxA1−/− and Boc2‐treated WT mice, and was reversed by treatment with Ac2‐26 in AnxA1−/− mice. AnxA1 and FPR2 were constitutively expressed in bone marrow granulocytes, and their expressions were reduced by treatment with RU38486. Higher numbers of CXCR4+ neutrophils were detected in the circulation of AnxA1−/− or Boc2‐treated WT mice, and values were rescued in Ac2‐26‐treated AnxA1−/− mice. Although circulating neutrophils of AnxA1−/− animals were CXCR4+, they presented reduced CXCL12‐induced chemotaxis. Moreover, levels of CXCL12 were reduced in the bone marrow perfusate and in the mesenchymal stem cell supernatant from AnxA1−/− mice, and in vivo and in vitro CXCL12 expression was re‐established after Ac2‐26 treatment. Collectively, these data highlight AnxA1 as a novel determinant of neutrophil maturation and the mechanisms behind blood neutrophil homing to BM via the CXCL12/CXCR4 pathway. J. Cell. Physiol. 231: 2418–2427, 2016. © 2016 Wiley Periodicals, Inc.