Annexin A1 regulates neutrophil clearance by macrophages in the mouse bone marrow

Abstract

Under homeostatic conditions, a proportion of senescent CXCR4hi neutrophils home from the circulation back to the bone marrow, where they are phagocytosed by bone marrow macrophages. In this study, we have identified an unexpected role for the anti-inflammatory molecule annexin A1 (AnxA1) as a critical regulator of this process. We first observed that AnxA1−/− mice have significantly increased neutrophil numbers in their bone marrow while having normal levels of GM and G colony-forming units, monocytes, and macrophages. Although AnxA1−/− mice have more neutrophils in the bone marrow, a greater proportion of these cells are senescent, as determined by their higher levels of CXCR4 expression and annexin V binding. Consequently, bone marrow neutrophils from AnxA1−/− mice exhibit a reduced migratory capacity in vitro. Studies conducted in vitro also show that expression of AnxA1 is required for bone marrow macrophages, but not peritoneal macrophages, to phagocytose apoptotic neutrophils. Moreover, in vivo experiments indicate a defect in clearance of wild-type neutrophils in the bone marrow of AnxA1−/− mice. Thus, we conclude that expression of AnxA1 by resident macrophages is a critical determinant for neutrophil clearance in the bone marrow.— Dalli, J., Jones, C. P., Cavalcanti, D. M., Farsky, S. H., Perretti, M., Rankin, S. M. Annexin A1 regulates neutrophil clearance by macrophages in the mouse bone marrow.

The Role and Effects of Glucocorticoid-Induced Leucine Zipper in the Context of Inflammation Resolution

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“…Indeed, AnxA1 limits initial steps of inflammation, specifically the recruitment of leukocytes and generation of proinflammatory mediators. AnxA1 also acts on the resolution phase of inflammation by inducing apoptosis of neutrophils (14,15) and increasing efferocytosis by macrophages (16,17). Importantly, AnxA1 production and activities are involved in proresolution effects of GCs (18) and histone deacetylase inhibitors (19).…”

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