TNFα Regulates SIRT1 Cleavage during Ocular Autoimmune Disease.

Elevated tumor necrosis factor (TNF) α levels are associated with chronic autoimmune diseases in which effects of TNFα on immune cells are multiple and complex. Analysis of uveitis in mice exhibiting severe autoimmune inflammation, resulting in a destructive subtotal loss of photoreceptors, revealed the presence of high plasma levels of TNFα and a significant population of CD4(+)TNFα(+) cells in the periphery and the eye at peak disease (TNFα(hi)). We have shown previously by pharmacological activation that the deacetylase Sirtuin 1 (SIRT1) has an anti-inflammatory role in a less severe, TNFα(lo) model of uveitis. We now show that SIRT1 activation fails to clinically suppress severe TNFα(hi) disease, whereas glucocorticoid treatment is successful. TNFα has been reported to mediate cleavage and inactivation of SIRT1 during inflammation, and at peak disease we observed both full-length and cleaved SIRT1 in draining lymph node cells. In vivo systemic TNFα blockade suppressed severe ocular disease and restricted SIRT1 cleavage in the periphery, maintaining full-length active SIRT1 protein. When combining a suboptimal TNFα blockade with SIRT1 activation, a synergistic suppression of severe disease compared with TNFα blockade alone occurred. Our data suggest a new role for TNFα in exacerbating the severity of autoimmune disease by regulating SIRT1 cleavage in draining lymph node effector cells. SIRT1 activation may be effective as an adjunctive treatment for inflammatory conditions not fully controlled by TNFα inhibitors.

Annexin-A1 restricts Th17 cells and attenuates the severity of autoimmune disease.

Annexin-A1 (Anx-A1) is an endogenous anti-inflammatory molecule and while described as a repressor of innate immune responses, the role of Anx-A1 in adaptive immunity, and in particular in T helper (Th) cell responses, remains controversial. We have used a T-cell mediated mouse model of retinal autoimmune disease to unravel the role of Anx-A1 in the development of autoreactive Th cell responses and pathology. RBP1-20-immunized C57BL/6 Anx-A1(-/-) mice exhibit significantly enhanced retinal inflammation and pathology as a result of an uncontrolled proliferation and activation of Th17 cells. This is associated with a limited capacity to induce SOCS3, resulting in un-restricted phosphorylation of STAT3. RBP1-20-specific CD4(+) cells from immunized Anx-A1(-/-) animals generated high levels of Th17 cells-associated cytokines. Following disease induction, daily systemic administration of human recombinant Anx-A1 (hrAnx-A1), during the afferent phase of disease, restrained autoreactive CD4(+) cell proliferation, reduced expression of pro-inflammatory cytokines IL-17, IFN-γ and IL-6 and attenuated autoimmune retinal inflammatory disease. Furthermore, in man, Anx-A1 serum levels when measured in active uveitis patient sera were low and associated with the detection of IgM and IgG anti-Anx-A1 antibodies when compared to healthy individuals. This data supports Anx-A1 as an early and critical regulator of Th17 cell driven autoimmune diseases such as uveitis.

Anti-inflammatory drugs, eicosanoids and the annexin A1/FPR2 anti-inflammatory system.

The action of anti-inflammatory and anti-allergic drugs on the eicosanoid system is briefly reviewed. In addition to the aspirin-like drugs, which directly inhibit the cyclo-oxygenase enzymes, other drugs such as the glucocorticoids and the cromones also inhibit the formation of eicosanoids. In the latter cases this is bought about through the release of a protein factor that acts through formyl peptide receptors on the target cell surface. Of growing interest, is the observation that this receptor is also a target for other eicosanoids, such as lipoxins and resolvins that modulate host defence systems.

Antiallergic cromones inhibit neutrophil recruitment onto vascular endothelium via annexin-A1 mobilization.

OBJECTIVE: To determine whether the inhibitory action of the antiallergic cromone "mast cell stabilizing" drugs on polymorphonuclear leukocyte (PMN) trafficking is mediated through an annexin-A1 (Anx-A1) dependent mechanism. METHODS AND RESULTS: Intravital microscopy was used to monitor the actions of cromones in the inflamed microcirculation. Reperfusion injury provoked a dramatic increase in adherent and emigrated leukocytes in the mesenteric vascular bed, associated with augmented tissue levels of myeloperoxidase. Nedocromil, 2 to 20 mg/kg, significantly (P<0.05) inhibited cell adhesion and emigration, as well as myeloperoxidase release, in wild-type but not Anx-A1(-/-) mice. Short pretreatment of human PMNs with nedocromil, 10 nmol/L, inhibited cell adhesion (P<0.05) in the flow chamber assay, and this effect was reversed by specific anti-AnxA1 or a combination of antiformyl peptide receptors 1 and 2, but not irrelevant control, antibodies. Western blotting experiments revealed that cromones stimulate protein kinase C-dependent phosphorylation and release Anx-A1 in human PMNs. CONCLUSIONS: We propose a novel mechanism to explain the antiinflammatory actions of cromones on PMN trafficking, an effect that has long puzzled investigators.

From NSAIDs to Glucocorticoids and Beyond.

Our interest in inflammation and its treatment stems from ancient times. Hippocrates used willow bark to treat inflammation, and many centuries later, salicylic acid and its derivative aspirin's ability to inhibit cyclooxygenase enzymes was discovered. Glucocorticoids (GC) ushered in a new era of treatment for both chronic and acute inflammatory disease, but their potentially dangerous side effects led the pharmaceutical industry to seek other, safer, synthetic GC drugs. The discovery of the GC-inducible endogenous anti-inflammatory protein annexin A1 (AnxA1) and other endogenous proresolving mediators has opened a new era of anti-inflammatory therapy. This review aims to recapitulate the last four decades of research on NSAIDs, GCs, and AnxA1 and their anti-inflammatory effects.

Annexin A1 regulates hormone exocytosis through a mechanism involving actin reorganization.

The glucocorticoid-regulated protein annexin A1 is a potent inhibitor of hormone exocytosis in the neuroendocrine system, acting in a paracrine/juxtacrine manner. The signaling mechanism employed by annexin A1 in this process is uncertain, although we have recently presented evidence for a role of the formyl peptide receptor in vivo. We sought to characterize the mechanism of action of annexin A1 on exocytosis using the release of adrenocorticotrophin from the corticotroph-like cell line AtT20 as an in vitro model system. Through the comparison of adrenocorticotrophin release from cells expressing either wild-type annexin A1 or mutant forms, we show a critical involvement of phosphorylation on serine 27 and 45 in the translocation of the protein to the membrane and its inhibitory action on exocytosis. Moreover, we show, for the first time, that annexin A1-dependent inhibition of adrenocorticotrophin release involves the enhancement of actin polymerization to prevent exocytosis via formyl peptide receptor and Rho kinase signaling pathways. This finding has significant implications for the inhibitory actions of annexin A1 on exocytosis in other endocrine and immune contexts.

Endogenous Annexin-A1 Negatively Regulates Mast Cell-Mediated Allergic Reactions.

Mast cell stabilizers like cromoglycate and nedocromil are mainstream treatments for ocular allergy. Biochemical studies in vitro suggest that these drugs prevent mast cell degranulation through the release of Annexin-A1 (Anx-A1) protein. However, the direct effect of Anx-A1 gene deletion on mast cell function in vitro and in vivo is yet to be fully investigated. Hence, we aim to elucidate the role of Anx-A1 in mast cell function, both in vivo and in vitro, using a transgenic mouse model where the Anx-A1 gene has been deleted. Bone marrow-derived mast cells (BMDMCs) were cultured from wild-type animals and compared throughout their development to BMDMCs obtained from mice lacking the Anx-A1 gene. The mast cell differentiation, maturity, mediator, and cytokine release were explored using multiple biochemical techniques, such as Western blots, ELISA, and flow cytometry analysis. Electron microscopy was used to identify metachromatic granules content of cells. For in vivo studies, Balb/C wild-type and Anx-A1-deficient mice were divided into the following groups: group 1, a control receiving only saline, and group 2, which had been sensitized by prior exposure to short ragweed (SRW) pollen by topical contact with the conjunctival mucosae. Allergic conjunctivitis was evaluated blind after 24 h by trained observers scoring clinical signs. Electron micrographs of BMDMCs from Anx-A1-null mice revealed more vacuoles overall and more fused vacuoles than wild-type cells, suggesting enhanced secretory activity. Congruent with these observations, BMDMCs lacking the Anx-A1 gene released significantly increased amounts of histamine both spontaneously as well as in response to Ig-E-FcεRI cross-linking compared to those from wild-type mice. Interestingly, the spontaneous release of IL-5, IL-6, IL-9, and monocyte chemoattractant protein-1 (MCP-1) were also markedly increased with a greater production observed upon IgE cross-linking. This latter finding is congruent with augmented calcium mobilization in BMDMCs lacking the Anx-A1 gene. In vivo, when compared to wild-type animals, Anx-A1-deficient mice exposed to SRW pollen displayed exacerbated signs and symptoms of allergic conjunctivitis. Taken together, these results suggest Anx-A1 is an important non-redundant regulator of mast cell reactivity and particularly in allergen mediated allergic reactions.

The Anti-allergic Cromones: Past, Present, and Future.

The anti-allergic cromones were originally synthesized in the 1960s by Fisons Plc, and the first drug to emerge from this program, disodium cromoglycate was subsequently marketed for the treatment of asthma and other allergic conditions. Whilst early studies demonstrated that the ability of the cromones to prevent allergic reactions was due to their 'mast cell stabilizing' properties, the exact pharmacological mechanism by which this occurred, remained a mystery. Here, we briefly review the history of these drugs, recount some aspects of their pharmacology, and discuss two new explanations for their unique actions. We further suggest how these findings could be used to predict further uses for the cromones.

Augmenting Endogenous Levels of Retinal Annexin A1 Suppresses Uveitis in Mice.

PURPOSE: The purpose of this study was to examine the expression of the anti-inflammatory protein Annexin A1 (AnxA1) in mice and human retinae during uveitis and to determine whether local administration of human recombinant AnxA1 (hrAnxA1) can suppress uveitis in mice. METHODS: Retinal sections from mice (healthy normal and uveitis) and postmortem human (no history of eye disease (n = 5) and uveitis (n = 7)) were stained for AnxA1 expression and imaged by immunofluorescence microscopy. AnxA1 cellular expression was determined by colabeling with CD45, glial fibrillary acidic protein (GFAP), and Iba-1 cells, with additional staining of AnxA1 receptors formyl peptide receptor 1 (FPR1) and FPRL1/FPR2. Mice with acute endotoxin-induced uveitis and chronic experimental autoimmune uveitis were treated locally by intravitreal injection with hrAnxA1, and disease was assessed by clinical scoring and quantification of leukocyte infiltrate via flow cytometry. RESULTS: Constitutive expression of AnxA1 was observed in both healthy mouse and human retinae, and its expression increased during uveitis compared to healthy controls. AnxA1 colocalizes predominantly with CD45+ cells, GFAP+ macroglia, and to a lesser extent, Iba-1+ myeloid cells. We also demonstrate that local treatment with hrAnxA1 attenuates the severity of uveitis in mice. CONCLUSIONS: These data indicate that locally expressed AnxA1 is elevated in the retina during intraocular inflammation. We demonstrate that local administration of hrAnxA1 to augment levels results in suppression of uveitis in mice. TRANSLATIONAL RELEVANCE: Our data suggest that elevated expression of retinal AnxA1 in human uveitis may be immunoregulatory and that local supplementation with hrAnxA1 may provide a potential novel treatment for inflammatory eye diseases such as noninfectious uveitis.

The role of the Annexin-A1/FPR2 system in the regulation of mast cell degranulation provoked by compound 48/80 and in the inhibitory action of nedocromil.

1.We investigated the role of Annexin (ANX)-A1 and its receptor, ALX/FPR2, in the regulation of mast cell degranulation produced by compound 48/80. 2.Both human cord-blood derived mast cells (CBDMCs) and murine bone marrow derived mast cells (BMDMCs) release phosphorylated ANX-A1 during treatment with glucocorticoids or the mast cell 'stabilising' drugs ketotifen and nedocromil. 3.Compound 48/80 also stimulated ANX-A1 phosphorylation and release and this was also potentiated by nedocromil. Anti-ANX-A1 neutralising monoclonal antibodies (Mabs) enhanced the release of pro-inflammatory mediators in response to compound 48/80. 4.Nedocromil and ketotifen potently inhibited the release of histamine, PGD2, tryptase and ß-hexosaminidase from mast cells challenged with compound 48/80. Anti-ANX-A1 neutralising Mabs prevented the inhibitory effect of these drugs. 5.BMDMCs derived from Anx-A1−/− mice were insensitive to the inhibitory effects of nedocromil or ketotifen but cells retained their sensitivity to the inhibitory action of hu-r-ANX-A1. 6.The fpr2/3 antagonist WRW4 blocked the action of nedocromil on PGD2, but not histamine, release. BMDMCs derived from fpr2/3−/− mice were insensitive to the inhibitory effects of nedocromil on PGD2, but not histamine release. 7.Compound 48/80 stimulated both p38 and JNK phosphorylation in CBDMCs and this was inhibited by nedocromil. Inhibition of p38 phosphorylation was ANX-A1 dependent. 8.We conclude that ANX-A1 is an important regulator of mast cell reactivity to compound 48/80 exerting a negative feedback effect through a mechanism that depends at least partly on the FPR receptor.

Anti-allergic cromones inhibit histamine and eicosanoid release from activated human and murine mast cells by releasing Annexin A1.

BACKGROUND AND PURPOSE: Although the 'cromones' (di-sodium cromoglycate and sodium nedocromil) are used to treat allergy and asthma, their 'mast cell stabilising' mechanism of pharmacological action has never been convincingly explained. Here, we investigate the hypothesis that these drugs act by stimulating the release of the anti-inflammatory protein Annexin-A1 (Anx-A1) from mast cells. EXPERIMENTAL APPROACH: We used biochemical and immuno-neutralisation techniques to investigate the mechanism by which cromones suppress histamine and eicosanoid release from cord-derived human mast cells (CDMCs) or murine bone marrow-derived mast cells (BMDMCs) from wild type and Anx-A1 null mice. KEY RESULTS: CDMCs activated by IgE-FcRε1 crosslinking, released histamine and prostaglandin (PG) D2, which were inhibited (30-65%) by 5 min pre-treatment with cromoglycate (10 nM) or nedocromil (10 nM), as well as dexamethasone (2 nM) and human recombinant Anx-A1 (1-10 nM). In CDMCs cromones potentiated (2-5 fold) protein kinase C (PKC) phosphorylation and Anx-A1 phosphorylation and secretion (3-5 fold). Incubation of CDMCs with a neutralising anti-Anx-A1 monoclonal antibody reversed the cromone inhibitory effect. Nedocromil (10 nM) also inhibited (40-60%) the release of mediators from murine bone marrow derived-mast cells from wild type mice activated by compound 48/80 and IgE-FcRε1 cross-linking, but were inactive in such cells when these were prepared from Anx-A1 null mice or when the neutralising anti-Anx-A1 antibody was present. CONCLUSIONS AND IMPLICATIONS: We conclude that stimulation of phosphorylation and secretion of Anx-A1 is an important component of inhibitory cromone actions on mast cells, which could explain their acute pharmacological actions in allergy. These findings also highlight a new pathway for reducing mediator release from these cells.

Anti-allergic drugs and the Annexin-A1 system.

This paper, which was presented at the 17th JMRC 'John Robert Vane Memorial' Symposium, describes some recent work from the authors' laboratory that provides a tentative explanation for the anti-inflammatory effects produced by the cromoglycate-like anti-allergic drugs. Some of the implications of this finding are discussed.

Cromoglycate drugs suppress eicosanoid generation in U937 cells by promoting the release of Anx-A1.

Using biochemical, epifluorescence and electron microscopic techniques in a U937 model system, we investigated the effect of anti-allergic drugs di-sodium cromoglycate and sodium nedocromil on the trafficking and release of the anti-inflammatory protein Annexin-A1 (Anx-A1) when this was triggered by glucocorticoid (GC) treatment. GCs alone produced a rapid (within 5min) concentration-dependent activation of PKCalpha/beta (Protein Kinase C; EC 2.7.11.13) and phosphorylation of Anx-A1 on Ser(27). Both phosphoproteins accumulated at the plasma membrane and Anx-A1 was subsequently externalised thereby inhibiting thromboxane (Tx) B(2) generation. When administered alone, cromoglycate or nedocromil had little effect on this pathway however, in the presence of a fixed sub-maximal concentration of GCs, increasing amounts of the cromoglycate-like drugs caused a striking concentration-dependent enhancement of Anx-A1 and PKCalpha/beta phosphorylation, membrane recruitment and Anx-A1 release from cells resulting in greatly enhanced inhibition of TxB(2) generation. GCs also stimulated phosphatase accumulation at the plasma membrane of U937 cells. Both cromoglycate and nedocromil inhibited this enzymatic activity as well as that of a highly purified PP2A phosphatase preparation. We conclude that stimulation by the cromoglycate-like drugs of intracellular Anx-A1 trafficking and release (hence inhibition of eicosanoid release) is secondary to inhibition of a phosphatase PP2A (phosphoprotein phosphatase; EC 3.1.3.16), which probably forms part of a control loop to limit Anx-A1 release. These experiments provide a basis for a novel mechanism of action for the cromolyns, a group of drugs that have long puzzled investigators.