Annexin-1 regulates macrophage IL-6 and TNF via glucocorticoid-induced leucine zipper.

Annexin-1 (ANXA1) is a mediator of the anti-inflammatory actions of endogenous and exogenous glucocorticoids (GC). The mechanism of ANXA1 effects on cytokine production in macrophages is unknown and is here investigated in vivo and in vitro. In response to LPS administration, ANXA1(-/-) mice exhibited significantly increased serum IL-6 and TNF compared with wild-type (WT) controls. Similarly, LPS-induced IL-6 and TNF were significantly greater in ANXA1(-/-) than in WT peritoneal macrophages in vitro. In addition, deficiency of ANXA1 was associated with impairment of the inhibitory effects of dexamethasone (DEX) on LPS-induced IL-6 and TNF in macrophages. Increased LPS-induced cytokine expression in the absence of ANXA1 was accompanied by significantly increased LPS-induced activation of ERK and JNK MAPK and was abrogated by inhibition of either of these pathways. No differences in GC effects on MAPK or MAPK phosphatase 1 were observed in ANXA1(-/-) cells. In contrast, GC-induced expression of the regulatory protein GILZ was significantly reduced in ANXA1(-/-) cells by silencing of ANXA1 in WT cells and in macrophages of ANXA1(-/-) mice in vivo. GC-induced GILZ expression and GC inhibition of NF-kappaB activation were restored by expression of ANXA1 in ANXA1(-/-) cells, and GILZ overexpression in ANXA1(-/-) macrophages reduced ERK MAPK phosphorylation and restored sensitivity of cytokine expression and NF-kappaB activation to GC. These data confirm ANXA1 as a key inhibitor of macrophage cytokine expression and identify GILZ as a previously unrecognized mechanism of the anti-inflammatory effects of ANXA1.

Annexin 1 negatively regulates IL-6 expression via effects on p38 MAPK and MAPK phosphatase-1.

Annexin 1 (Anx-1) is a mediator of the anti-inflammatory actions of glucocorticoids, but the mechanism of its anti-inflammatory effects is not known. We investigated the role of Anx-1 in the regulation of the proinflammatory cytokine, IL-6. Lung fibroblast cell lines derived from Anx-1(-/-) and wild-type (WT) mice were treated with dexamethasone and/or IL-1. IL-6 mRNA and protein were measured using real-time PCR and ELISA, and MAPK pathway activation was studied. Compared with WT cells, unstimulated Anx-1(-/-) cells exhibited dramatically increased basal IL-6 mRNA and protein expression. In concert with this result, Anx-1 deficiency was associated with increased basal phosphorylated p38, JNK, and ERK1/2 MAPKs. IL-1-inducible phosphorylated p38 was also increased in Anx-1(-/-) cells. The increase in IL-6 release in Anx-1(-/-) cells was inhibited by inhibition of p38 MAPK. Anx-1(-/-) cells were less sensitive to dexamethasone inhibition of IL-6 mRNA expression than WT cells, although inhibition by dexamethasone of IL-6 protein was similar. MAPK phosphatase-1 (MKP-1), a glucocorticoid-induced negative regulator of MAPK activation, was up-regulated by dexamethasone in WT cells, but this effect of dexamethasone was significantly impaired in Anx-1(-/-) cells. Treatment of Anx-1(-/-) cells with Anx-1 N-terminal peptide restored MKP-1 expression and inhibited p38 MAPK activity. These data demonstrate that Anx-1 is an endogenous inhibitory regulator of MAPK activation and IL-6 expression, and that Anx-1 is required for glucocorticoid up-regulation of MKP-1. Therapeutic manipulation of Anx-1 could provide glucocorticoid-mimicking effects in inflammatory disease.

Reduced leukocyte-endothelial cell interactions in the inflamed microcirculation of macrophage migration inhibitory factor-deficient mice.

OBJECTIVE: Macrophage migration inhibitory factor (MIF) is a proinflammatory cytokine with established roles in a range of inflammatory conditions. However, it is not known whether MIF influences inflammation via the direct promotion of leukocyte-endothelial cell interactions. Therefore, the aim of these experiments was to investigate the ability of MIF to regulate leukocyte-endothelial cell interactions in the inflamed microvasculature. METHODS: Intravital microscopy was used to examine postcapillary venules in the cremaster muscle and synovium of wild-type and MIF(-/-) mice. Leukocyte-endothelial cell interactions (rolling, adhesion, emigration) were compared under a range of inflammatory conditions. RESULTS: In cremasteric postcapillary venules of MIF(-/-) mice, lipopolysaccharide (LPS)-induced leukocyte rolling, adhesion, and emigration were significantly reduced relative to that in wild-type mice. Similar responses were observed in response to tumor necrosis factor alpha and histamine. Examination of the synovial microvasculature following exposure to carrageenan revealed that leukocyte rolling and adhesion in synovial postcapillary venules and leukocyte entry into the joint space were also reduced significantly in MIF(-/-) mice. In each of these models, the level of P-selectin-dependent rolling was reduced in MIF(-/-) mice. Despite this, no difference in P-selectin expression was observed following LPS treatment. However, microvascular shear forces were elevated in MIF(-/-) mice, raising a possible mechanism to explain the reduced interactions in these animals. CONCLUSION: MIF(-/-) mice consistently displayed a reduction in P-selectin-dependent rolling, suggesting that MIF exerts proinflammatory effects, in part, via the promotion of P-selectin-mediated rolling. Together, these data indicate that MIF promotes interactions between leukocytes and endothelial cells, thereby enhancing the entry of leukocytes into sites of inflammation.