Beneficial effect of annexin A1 in a model of experimental allergic conjunctivitis

Lack of Annexin A1 Exacerbates Inflammatory Response in Acute Endometritis Model

Annexin A1 (AnxA1) is a glucocorticoid-inducible protein and an important endogenous modulator of inflammation. However, its effect in the endometrial microenvironment is poorly explained. This study aimed to evaluate the role of endogenous AnxA1 in an endometritis mouse model induced by lipopolysaccharide (LPS). Female C57BL/6 wild-type (WT) and AnxA1-/- mice were divided into two groups: SHAM and LPS. To induce endometritis, mice received a vaginal infusion of 50 μL of LPS (1 mg/mL) dissolved in phosphate-buffered saline. After 24 h, the mice were euthanized, and blood and uteri samples were collected. The endometrium inflammatory scores were significantly increased in the LPS-treated group. AnxA1-/- mice from the LPS group demonstrated a significant increase in the number of degranulated mast cell levels compared to AnxA1-/- SHAM mice. The Western blotting analysis revealed that a lack of AnxA1 promoted the upregulation of NLRP3 and pro-IL-1β in the acute endometritis animal model compared to WT LPS animals. LPS-induced endometritis increased the number of blood peripheral leukocytes in both WT and AnxA1-/- mice compared with SHAM group mice (p < 0.001). AnxA1-/- mice also showed increased plasma levels of IL-1β (p < 0.01), IL-6, IL-10, IL-17, and TNF-α (p < 0.05) following LPS-induced endometritis. In conclusion, a lack of endogenous AnxA1 exacerbated the inflammatory response in an endometritis model via NLRP3 dysregulation, increased uterine mast cell activation, and plasma pro-inflammatory cytokine release.

Annexin A1 in the nervous and ocular systems

The therapeutic potential of Annexin A1, an important member of the Annexin superfamily, has become evident in results of experiments with multiple human systems and animal models. The anti-inflammatory and pro-resolving effects of Annexin A1 are characteristic of pathologies involving the nervous system. In this review, we initially describe the expression sites of Annexin A1, then outline the mechanisms by which Annexin A1 maintains the neurological homeostasis through either formyl peptide receptor 2 or other molecular approaches; and, finally, we discuss the neuroregenerative potential qualities of Annexin A1. The eye and the nervous system are anatomically and functionally connected, but the association between visual system pathogenesis, especially in the retina, and Annexin A1 alterations has not been well summarized. Therefore, we explain the beneficial effects of Annexin A1 for ocular diseases, especially for retinal diseases and glaucoma on the basis of published findings, and we explore present and future delivery strategies for Annexin A1 to the retina.

N-Formyl-Methionyl-Leucyl-Phenylalanine Plays a Neuroprotective and Anticonvulsant Role in Status Epilepticus Model

Status epilepticus (SE) is described as continuous and self-sustaining seizures, which triggers hippocampal neurodegeneration, inflammation, and gliosis. N-formyl peptide receptor (FPR) has been associated with inflammatory process. N-formyl-methionyl-leucyl-phenylalanine (fMLP) peptide plays an anti-inflammatory role, mediated by the activation of G-protein-coupled FPR. Here, we evaluated the influence of fMLP peptides on the behavior of limbic seizures, memory consolidation, and hippocampal neurodegeneration process. Male Wistar rats (Rattus norvegicus) received microinjections of pilocarpine in hippocampus (H-PILO, 1.2 mg/μL, 1 μL) followed by fMLP (1 mg/mL, 1 μL) or vehicle (VEH, saline 0.9%, 1 μL). During the 90 min of SE, epileptic seizures were analyzed according to the Racine's Scale. After 24 h of SE, memory impairment was assessed by the inhibitory avoidance test and the neurodegeneration process was evaluated in hippocampal areas. There was no change in latency and number of wet dog shake (WDS) after administration of fMLP. However, our results showed that the intrahippocampal infusion of fMLP reduced the severity of seizures, as well as the number of limbic seizures. In addition, fMLP infusion protected memory dysfunction followed by SE. Finally, the intrahippocampal administration of fMLP attenuated the process of neurodegeneration in both hippocampi. Taken together, our data suggest a new insight into the functional role of fMLP peptides, with important implications for their potential use as a therapeutic agent for the treatment of brain disorders, such as epilepsy. Schematic drawing on the neuroprotective and anticonvulsant role of fMLP during status epilepticus. Initially, a cannula was implanted in hippocampus and pilocarpine/saline was administered into the hippocampus followed by fMLP/saline (A-C). fMLP reduced seizure severity and neuronal death in the hippocampus, as well as protecting against memory deficit (D).

Annexin A1, A2, A5, and A6 involvement in human pathologies

The human genome codes for 12 annexins with highly homologous membrane-binding cores and unique amino termini, which endow each protein with its specific biological properties. Not unique to vertebrate biology, multiple annexin orthologs are present in almost all eukaryotes. Their ability to combine either dynamically or constitutively with membrane lipid bilayers is hypothetically the key property that has led to their retention and multiple adaptation in eukaryotic molecular cell biology. Annexin genes are differentially expressed in many cell types but their disparate functions are still being discovered after more than 40 years of international research. A picture is emerging from gene knock down and knock out studies of individual annexins that these are important supporters rather than critical players in organism development and normal cell and tissue function. However, they appear to be highly significant "early responders" toward challenges arising from cell and tissue abiotic or biotic stress. In humans, recent focus has been on involvement of the annexin family for its involvement in diverse pathologies, especially cancer. From what has become an exceedingly broad field of investigation, we have selected four annexins in particular: AnxA1, 2, 5, and 6. Present both within and external to cells, these annexins are currently under intensive investigation in translational research as biomarkers of cellular dysfunction and as potential therapeutic targets for inflammatory conditions, neoplasia, and tissue repair. Annexin expression and release in response to biotic stress appears to be a balancing act. Under- or over-expression in different circumstances appears to damage rather than restore a healthy homeostasis. This review reflects briefly on what is already known of the structures and molecular cell biology of these selected annexins and considers their actual and potential roles in human health and disease.

Resolution Pharmacology: Focus on Pro-Resolving Annexin A1 and Lipid Mediators for Therapeutic Innovation in Inflammation

Chronic diseases that affect our society are made more complex by comorbidities and are poorly managed by the current pharmacology. While all present inflammatory etiopathogeneses, there is an unmet need for better clinical management of these diseases and their multiple symptoms. We discuss here an innovative approach based on the biology of the resolution of inflammation. Studying endogenous pro-resolving peptide and lipid mediators, how they are formed, and which target they interact with, can offer innovative options through augmenting the expression or function of pro-resolving pathways or mimicking their actions with novel targeted molecules. In all cases, resolution offers innovation for the treatment of the primary cause of a given disease and/or for the management of its comorbidities, ultimately improving patient quality of life. By implementing resolution pharmacology, we harness the whole physiology of inflammation, with the potential to bring a marked change in the management of inflammatory conditions.

Annexins as potential targets in ocular diseases

Annexins (AnxAs) are Ca2+/phospholipid-binding proteins extensively studied and generally involved in several diseases. Although evidence exists regarding the distribuition of AnxAs in the visual system, their exact roles and the exact cell types of the eye where these proteins are expressed are not well-understood. AnxAs have pro-resolving roles in infectious, autoimmune, degenerative, fibrotic and angiogenic conditions, making them an important target in ocular tissue homeostasis. This review summarizes the current knowledge on the distribution and function of AnxA1-8 isoforms under normal and pathological conditions in the visual system, as well as perspectives for ophthalmologic treatments, including the potential use of the AnxA1 recombinant and/or its mimetic peptide Ac2-26.

Effects of hyperosmolarity on annexin A1 on ocular surface epithelium in vitro

Osmotic stress is an important challenge to cell function. Dry eye pathology is characterized by elevated tear film osmolarity as consequence of decreased tear secretion and/or increased evaporation. Dry eye pathogenesis is not completely clarified. However, it is known that tear hyperosmolarity induces NLRP3 (nucleotide-binding oligomerization domain-like receptor family, pyrin domain-cointaining 3) inflammasome activation and inflammatory mediators release that leads to ocular surface damage. Annexin A1 is a protein involved in anti-inflammatory or pro-resolution actions in different tissues while its presence and biological role on ocular surface has been scarcely examined. In this study, potential changes in annexin A1 protein expression and secretion on the ocular surface after exposure to hyperosmolar conditions were evaluated. In addition, considering the significant role of inflammation in dry eye pathology, the potential anti-inflammatory activity of Ac2-26, an annexin A1 peptide mimicking its N-terminus, was assessed. Cytosolic and membrane staining was detected for annexin A1 in corneal and conjunctival epithelial cells. A native form of annexin A1 together with a truncated form were detected by western blot analysis. Under hyperosmotic conditions increased protein levels of intracellular and secreted annexin A1 as well as higher expression of its receptor Fpr2 (formyl peptide receptor type 2) were found. Treatment with mimetic peptide Ac2-26 ameliorated NLRP3 activation and interleukin 1β (IL-1β) release triggered by elevated osmolarity in corneal and conjunctival epithelial cells. These findings suggest a potential role of annexin A1 and its mimetic peptide modulating key inflammatory events associated to dry eye.

ANNEXIN A1: Roles in Placenta, Cell Survival, and Nucleus

The unbiased approaches of the last decade have enabled the collection of new data on the biology of annexin A1 (ANXA1) in a variety of scientific aspects, creating opportunities for new biomarkers and/or therapeutic purposes. ANXA1 is found in the plasma membrane, cytoplasm, and nucleus, being described at low levels in the nuclear and cytoplasmic compartments of placental cells related to gestational diabetic diseases, and its translocation from the cytoplasm to the nucleus has been associated with a response to DNA damage. The approaches presented here open pathways for reflection upon, and intrinsic clarification of, the modulating action of this protein in the response to genetic material damage, as well as its level of expression and cellular localization. The objective of this study is to arouse interest, with an emphasis on the mechanisms of nuclear translocation of ANXA1, which remain underexplored and may be beneficial in new inflammatory therapies.

Protective effects of annexin A1-derived peptide Ac2-26 on liver and kidney injuries induced by cisplatin in rats

AIMS

In this study we evaluated the effect of pharmacological treatment with annexin A1-derived peptide Ac_2-26 in an experimental model of toxicity induced by cisplatin.

MAIN METHODS

Male rats were divided into Sham (control), Cisplatin (received intraperitoneal injections of 10 mg/kg/day of cisplatin for 3 days) and Ac_2-26 (received intraperitoneal injections of 1 mg/kg/day of peptide, 15 min before cisplatin) groups.

KEY FINDINGS

After 6 h of the last dose of cisplatin, an acute inflammatory response was observed characterized by a marked increase in the number of neutrophils and GM-CSF, IL-1β, IL-6, IL-10 and TNF-α plasma levels. Treatment with Ac_2-26 produced higher levels of GM-CSF, corroborating the high numbers of neutrophils, and the anti-inflammatory cytokine IL-4. Ac_2-26 preserved the morphology of liver structures, preventing the damage caused by cisplatin, but did not reduce plasma levels of the hepatotoxicity biomarkers ARG1, GSTα and SDH. In the kidneys, the peptide maintained the markers of kidney damage CLU and KIM-1 at similar levels to the Sham group but did not avoid morphological changes caused by cisplatin. These effects of Ac_2-26 were associated with the reduction of Fpr1 and Fpr2 levels in the organs studied.

SIGNIFICANCE

Pharmacological treatment with peptide Ac_2-26 partially protects the liver and kidneys against the deleterious effects caused by cisplatin in this experimental model.

Pharmacological treatment with annexin A1-derived peptide protects against cisplatin-induced hearing loss

Cisplatin is an antineoplastic agent widely used, and no effective treatments capable of preventing cisplatin-induced ototoxicity and neurotoxicity in humans have yet been identified. This study evaluated the effect of the anti-inflammatory annexin A1 (AnxA1)-derived peptide Ac_2-26 in a cisplatin-induced ototoxicity model. Wistar rats received intraperitoneal injections of cisplatin (10mg/kg/day) for 3 days to induce hearing loss, and Ac_2-26 (1mg/kg) was administered 15minutes before cisplatin administration. Control animals received an equal volume of saline. Hearing thresholds were measured by distortion product otoacoustic emissions (DPOAE) before and after treatments. Pharmacological treatment with Ac_2-26 protected against cisplatin-induced hearing loss, as evidenced by DPOAE results showing similar signal-noise ratios between the control and Ac_2-26-treated groups. These otoprotective effects of Ac_2-26 were associated with an increased number of ganglion neurons compared with the untreated cisplatin group. Additionally, Ac_2-26 treatment produced reduced immunoreactivity on cleaved caspase 3 and phosphorylated ERK levels in the ganglion neurons, compared to the untreated group, supporting the neuroprotective effects of the Ac_2-26. Our results suggest that Ac_2-26 has a substantial otoprotective effect in this cisplatin-induced ototoxicity model mediated by neuroprotection and the regulation of the ERK pathway.

Targeting the Annexin A1-FPR2/ALX pathway for host-directed therapy in dengue disease

Host immune responses contribute to dengue's pathogenesis and severity, yet the possibility that failure in endogenous inflammation resolution pathways could characterise the disease has not been contemplated. The pro-resolving protein Annexin A1 (AnxA1) is known to counterbalance overexuberant inflammation and mast cell (MC) activation. We hypothesised that inadequate AnxA1 engagement underlies the cytokine storm and vascular pathologies associated with dengue disease. Levels of AnxA1 were examined in the plasma of dengue patients and infected mice. Immunocompetent, interferon (alpha and beta) receptor one knockout (KO), AnxA1 KO, and formyl peptide receptor 2 (FPR2) KO mice were infected with dengue virus (DENV) and treated with the AnxA1 mimetic peptide Ac_2-26 for analysis. In addition, the effect of Ac_2-26 on DENV-induced MC degranulation was assessed in vitro and in vivo. We observed that circulating levels of AnxA1 were reduced in dengue patients and DENV-infected mice. Whilst the absence of AnxA1 or its receptor FPR2 aggravated illness in infected mice, treatment with AnxA1 agonistic peptide attenuated disease manifestationsatteanuated the symptoms of the disease. Both clinical outcomes were attributed to modulation of DENV-mediated viral load-independent MC degranulation. We have thereby identified that altered levels of the pro-resolving mediator AnxA1 are of pathological relevance in DENV infection, suggesting FPR2/ALX agonists as a therapeutic target for dengue disease.

Effects of Formyl Peptide Receptor Agonists Ac9-12 and WKYMV in In Vivo and In Vitro Acute Inflammatory Experimental Models

Formyl peptide receptors (Fprs) are a G-protein-coupled receptor family mainly expressed on leukocytes. The activation of Fpr1 and Fpr2 triggers a cascade of signaling events, leading to leukocyte migration, cytokine release, and increased phagocytosis. In this study, we evaluate the effects of the Fpr1 and Fpr2 agonists Ac_9-12 and WKYMV, respectively, in carrageenan-induced acute peritonitis and LPS-stimulated macrophages. Peritonitis was induced in male C57BL/6 mice through the intraperitoneal injection of 1 mL of 3% carrageenan solution or saline (control). Pre-treatments with Ac_9-12 and WKYMV reduced leukocyte influx to the peritoneal cavity, particularly neutrophils and monocytes, and the release of IL-1β. The addition of the Fpr2 antagonist WRW4 reversed only the anti-inflammatory actions of WKYMV. In vitro, the administration of Boc2 and WRW4 reversed the effects of Ac_9-12 and WKYMV, respectively, in the production of IL-6 by LPS-stimulated macrophages. These biological effects of peptides were differently regulated by ERK and p38 signaling pathways. Lipidomic analysis evidenced that Ac_9-12 and WKYMV altered the intracellular lipid profile of LPS-stimulated macrophages, revealing an increased concentration of several glycerophospholipids, suggesting regulation of inflammatory pathways triggered by LPS. Overall, our data indicate the therapeutic potential of Ac_9-12 and WKYMV via Fpr1 or Fpr2-activation in the inflammatory response and macrophage activation.

Annexin A1 Mimetic Peptide and Piperlongumine: Anti-Inflammatory Profiles in Endotoxin-Induced Uveitis

Uveitis is one of the main causes of blindness worldwide, and therapeutic alternatives are worthy of study. We investigated the effects of piperlongumine (PL) and/or annexin A1 (AnxA1) mimetic peptide Ac2-26 on endotoxin-induced uveitis (EIU). Rats were inoculated with lipopolysaccharide (LPS) and intraperitoneally treated with Ac2-26 (200 µg), PL (200 and 400 µg), or Ac2-26 + PL after 15 min. Then, 24 h after LPS inoculation, leukocytes in aqueous humor, mononuclear cells, AnxA1, formyl peptide receptor (fpr)1, fpr2, and cyclooxygenase (COX)-2 were evaluated in the ocular tissues, along with inflammatory mediators in the blood and macerated supernatant. Decreased leukocyte influx, levels of inflammatory mediators, and COX-2 expression confirmed the anti-inflammatory actions of the peptide and pointed to the protective effects of PL at higher dosage. However, when PL and Ac2-26 were administered in combination, the inflammatory potential was lost. AnxA1 expression was elevated among groups treated with PL or Ac2-26 + PL but reduced after treatment with Ac2-26. Fpr2 expression was increased only in untreated EIU and Ac2-26 groups. The interaction between Ac2-26 and PL negatively affected the anti-inflammatory action of Ac2-26 or PL. We emphasize that the anti-inflammatory effects of PL can be used as a therapeutic strategy to protect against uveitis.

Annexin A1 Mimetic Peptide Ac2-26 Modulates the Function of Murine Colonic and Human Mast Cells

Mast cells (MCs) are main effector cells in allergic inflammation and after activation, they release stored (histamine, heparin, proteases) and newly synthesized (lipid mediators and cytokines) substances. In the gastrointestinal tract the largest MC population is located in the lamina propria and submucosa whereas several signals such as the cytokine IL-4, seem to increase the granule content and to stimulate a remarkable expansion of intestinal MCs. The broad range of MC-derived bioactive molecules may explain their involvement in many different allergic disorders of the gastrointestinal tract. Annexin A1 (AnxA1) is a 37 KDa glucocorticoid induced monomeric protein selectively distributed in certain tissues. Its activity can be reproduced by mimetic peptides of the N-terminal portion, such as Ac2-26, that share the same receptor FPR-L1. Although previous reports demonstrated that AnxA1 inhibits MC degranulation in murine models, the effects of exogenous peptide Ac2-26 on intestinal MCs or the biological functions of the Ac2-26/FPR2 system in human MCs have been poorly studied. To determine the effects of Ac2-26 on the function of MCs toward the possibility of AnxA1-based therapeutics, we treated WT and IL-4 knockout mice with peptide Ac2-26, and we examined the spontaneous and compound 48/80 stimulated colonic MC degranulation and cytokine production. Moreover, in vitro, using human mast cell line HMC-1 we demonstrated that exogenous AnxA1 peptide is capable of interfering with the HMC-1 degranulation in a direct pathway through formyl peptide receptors (FPRs). We envisage that our results can provide therapeutic strategies to reduce the release of MC mediators in inflammatory allergic processes.

Protein and Antibody Engineering: Suppressing Degranulation of the Mast Cells and Type I Hypersensitivity Reaction

With an increase in atopic cases and owing to a significant role of mast cells in type I hypersensitivity, a therapeutic need to inhibit degranulation of mast cells has risen. Mast cells are notorious for IgE-mediated allergic response. Advancements have allowed researchers to improve clinical outcomes of already available therapies. Engineered peptides and antibodies can be easily manipulated to attain desired characteristics as per the biological environment. A number of these molecules are designed to target mast cells in order to regulate the release of histamine and other mediators, thereby controlling type I hypersensitivity response. The aim of this review paper is to highlight some of the significant molecules designed for the purpose.

Annexin Animal Models-From Fundamental Principles to Translational Research

Routine manipulation of the mouse genome has become a landmark in biomedical research. Traits that are only associated with advanced developmental stages can now be investigated within a living organism, and the in vivo analysis of corresponding phenotypes and functions advances the translation into the clinical setting. The annexins, a family of closely related calcium (Ca²⁺)- and lipid-binding proteins, are found at various intra- and extracellular locations, and interact with a broad range of membrane lipids and proteins. Their impacts on cellular functions has been extensively assessed in vitro, yet annexin-deficient mouse models generally develop normally and do not display obvious phenotypes. Only in recent years, studies examining genetically modified annexin mouse models which were exposed to stress conditions mimicking human disease often revealed striking phenotypes. This review is the first comprehensive overview of annexin-related research using animal models and their exciting future use for relevant issues in biology and experimental medicine.

Role of Annexin A1 in NLRP3 Inflammasome Activation in Murine Neutrophils

This study evaluated the role of endogenous and exogenous annexin A1 (AnxA1) in the activation of the NLRP3 inflammasome in isolated peritoneal neutrophils. C57BL/6 wild-type (WT) and AnxA1 knockout mice (AnxA1-/-) received 0.3% carrageenan intraperitoneally and, after 3 h, the peritoneal exudate was collected. WT and AnxA1-/- neutrophils were then stimulated with lipopolysaccharide, followed by the NLRP3 agonists nigericin or ATP. To determine the exogenous effect of AnxA1, the neutrophils were pretreated with the AnxA1-derived peptide Ac2-26 followed by the NLRP3 agonists. Ac2-26 administration reduced NLRP3-derived IL-1β production by WT neutrophils after nigericin and ATP stimulation. However, IL-1β release was impaired in AnxA1-/- neutrophils stimulated by both agonists, and there was no further impairment in IL-1β release with Ac2-26 treatment before stimulation. Despite this, ATP- and nigericin-stimulated AnxA1-/- neutrophils had increased levels of cleaved caspase-1. The lipidomics of supernatants from nigericin-stimulated WT and AnxA1-/- neutrophils showed potential lipid biomarkers of cell stress and activation, including specific sphingolipids and glycerophospholipids. AnxA1 peptidomimetic treatment also increased the concentration of phosphatidylserines and oxidized phosphocholines, which are lipid biomarkers related to the inflammatory resolution pathway. Together, our results indicate that exogenous AnxA1 negatively regulates NLRP3-derived IL-1β production by neutrophils, while endogenous AnxA1 is required for the activation of the NLRP3 machinery.

The role of annexin A1 in Candida albicans and Candida auris infections in murine neutrophils

Annexin A1 (AnxA1) is an anti-inflammatory protein expressed in various cell types, especially macrophages and neutrophils. Because neutrophils play important roles in infections and inflammatory processes and the relationship between AnxA1 and Candida spp. infections is not well-understood, our study examined whether AnxA1 can serve as a target protein for the regulation of the immune response during fungal infections. C57BL/6 wild-type (WT) and AnxA1 knockout (AnxA1^-/-) peritoneal neutrophils were coinfected with Candida albicans or Candida auris for 4 h. AnxA1^-/- neutrophils exhibited a marked increase in cyclooxygenase 2 (COX-2), phosphorylated extracellular signal-related kinase (ERK), p-38, and c-Jun N-terminal kinase (JNK) levels after coinfection with both Candida spp. A lipidomics approach showed that AnxA1 deficiency produced marked differences in the supernatant lipid profiles of both control neutrophils and neutrophils coinfected with Candida spp. compared with WT cells, especially the levels of glycerophospholipids and glycerolipids. Our results showed that endogenous AnxA1 regulates the neutrophil response under fungal infection conditions, altering lipid membrane organization and metabolism.

Ac2-26 mimetic peptide of annexin A1 to treat severe COVID-19: A hypothesis

The Coronavirus Diseases-2019 (COVID-19) pandemic leads many researchers around the world to study the SARS-CoV-s2 infection and pathology to find a treatment for it. This generates a massive production of papers including pre-clinical, clinical and revisions but till now no specific treatment were identified. Meanwhile, like other coronavirus infections, COVID-19 leads to the cytokine storm syndrome resulting in hyperinflammation, exacerbated immune response and multiple organ dysfunctions indicating that drugs that modulate this response, as glucocorticoids could be a treatment option. However glucocorticoids have several side effects or usage limitations. In this sense a drug with anti-inflammatory effects and capable to reduce inflammation but with less after-effects could be a powerful tool to combat COVID-19. Thus the Ac2-26 Mimetic Peptide of Annexin A1 emerges as a possible therapy. The peptide has many anti-inflammatory effects described including the reduction of interleukin (IL)-6, one of the main mediators of cytokine storm syndrome. Therefore the hypothesis to use the Ac2-26 peptide to treat severe COVID-19 will be highlighted in this paper.

Annexin A1 Regulates NLRP3 Inflammasome Activation and Modifies Lipid Release Profile in Isolated Peritoneal Macrophages

Annexin A1 (AnxA1) is a potent anti-inflammatory protein that downregulates proinflammatory cytokine release. This study evaluated the role of AnxA1 in the regulation of NLRP3 inflammasome activation and lipid release by starch-elicited murine peritoneal macrophages. C57bl/6 wild-type (WT) and AnxA1-null (AnxA1^-/-) mice received an intraperitoneal injection of 1.5% starch solution for macrophage recruitment. NLRP3 was activated by priming cells with lipopolysaccharide for 3 h, followed by nigericin (1 h) or ATP (30 min) incubation. As expected, nigericin and ATP administration decreased elicited peritoneal macrophage viability and induced IL-1β release, more pronounced in the AnxA1^-/- cells than in the control peritoneal macrophages. In addition, nigericin-activated AnxA1^-/- macrophages showed increased levels of NLRP3, while points of co-localization of the AnxA1 protein and NLRP3 inflammasome were detected in WT cells, as demonstrated by ultrastructural analysis. The lipidomic analysis showed a pronounced release of prostaglandins in nigericin-stimulated WT peritoneal macrophages, while ceramides were detected in AnxA1^-/- cell supernatants. Different eicosanoid profiles were detected for both genotypes, and our results suggest that endogenous AnxA1 regulates the NLRP3-derived IL-1β and lipid mediator release in macrophages.

Heparin Attenuates Visceral Apoptosis in a Swine Model of Hemorrhagic Shock and Reperfusion Injury

BACKGROUND

The use of unfractionated heparin in hypovolemic shock, aortic clamping, and visceral reperfusion is still not established, despite evidence of inhibition of early cell damage. This study investigated the potential protective effect of unfractionated heparin on hepatic and renal apoptosis in a porcine ischemia and reperfusion model.

METHODS

Twenty-one male swine (Sus scrofa) were divided into 3 groups: sham (n = 5), heparin (n = 8), and nonheparin (n = 8). The heparin and nonheparin groups underwent hypovolemic shock for 30 min, supraceliac aortic clamping for 1 h and reperfusion for 3 h. Unfractionated heparin 200 mg/kg was administered to the heparin group during aortic clamping. Hemodynamic and laboratory parameters were monitored, including aminotransferase and serum urea. Histological lesion scores were applied to hematoxylin and eosin-stained liver and kidney sections. Apoptosis quantification was performed by caspase-3 immunohistochemistry.

RESULTS

The proposed model caused a severe cardiocirculatory disturbance in the heparin and nonheparin groups, observed by the carotid-femoral pressure gradient and lactic acidosis. There was no significant difference in hemodynamic and laboratory parameters between these two groups. The mean values of liver and renal histological lesion scores did not present any significant differences. Caspase-3 immunoexpression was lower in the heparin than the nonheparin group for both liver and kidney.

CONCLUSIONS

Attenuation of liver and kidney cell apoptosis in pigs undergoing systemic heparinization suggests a potential use for heparin in modulating cell death under critical hemodynamic conditions.

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.

Glucocorticoid receptor modulators CpdX and CpdX-D3 exhibit the same in vivo antiinflammatory activities as synthetic glucocorticoids

We previously reported that the nonsteroidal compound CpdX, which was initially characterized 20 y ago as a possible gestagen and, shortly afterward, as a possible drug for treatments of inflammatory diseases, selectively triggers the NFκB/AP1-mediated tethered indirect transrepression function of the glucocorticoid receptor (GR), and could therefore be a selective glucocorticoid receptor agonistic modulator (SEGRAM). We now demonstrate that, upon administration to the mouse, CpdX and one of its deuterated derivatives, CpdX-D3, repress as efficiently as a synthetic glucocorticoid (e.g., Dexamethasone) an induced skin atopic dermatitis, an induced psoriasis-like inflammation, a house dust mite (HDM)-induced asthma-like allergic lung inflammation, a collagen-induced arthritis, an induced ulcerative colitis, and an ovalbumin-induced allergic conjunctivitis. Interestingly, in the cases of an HDM-induced asthma-like allergic lung inflammation and of a collagen-induced arthritis, the CpdX antiinflammatory activity was selectively exerted by one of the two CpdX enantiomers, namely, CpdX(eA) or CpdX-D3(eA).

Annexin A1 peptide and endothelial cell-conditioned medium modulate cervical tumorigenesis

Cervical cancer is one of the leading causes of cancer death in women worldwide, and its tumorigenesis can be influenced by the microenvironment. The anti-inflammatory protein annexin A1 (ANXA1) has been reported to be associated with cancer progression and metastasis, suggesting that it plays a role in regulating tumour cell proliferation. Here, we examined the effect of the N-terminal peptide Ac2-26 of ANXA1 on the HaCaT cell line (normal) and HeLa cell line (cervical cancer) co-cultured with endothelium cell-conditioned medium (HMC). Treatment with Ac2-26 decreased proliferation and increased motility of cervical cancer cells, but did not affect cellular morphology or viability. Combined HMC stimulus and Ac2-26 treatment resulted in an increase in apoptotic HeLa cells, upregulated expression of MMP2, and downregulated expression of COX2,EP3 and EP4. In conclusion, Ac2-26 treatment may modulate cellular and molecular mechanisms underlying cervical carcinogenesis.

Annexin A1-derived peptide Ac2-26 in a pilocarpine-induced status epilepticus model: anti-inflammatory and neuroprotective effects

Background

The inflammatory process has been described as a crucial mechanism in the pathophysiology of temporal lobe epilepsy. The anti-inflammatory protein annexin A1 (ANXA1) represents an interesting target in the regulation of neuroinflammation through the inhibition of leukocyte transmigration and the release of proinflammatory mediators. In this study, the role of the ANXA1-derived peptide Ac_2-26 in an experimental model of status epilepticus (SE) was evaluated.

Methods

Male Wistar rats were divided into Naive, Sham, SE and SE+Ac_2-26 groups, and SE was induced by intrahippocampal injection of pilocarpine. In Sham animals, saline was applied into the hippocampus, and Naive rats were only handled. Three doses of Ac_2-26 (1 mg/kg) were administered intraperitoneally (i.p.) after 2, 8 and 14 h of SE induction. Finally, 24 h after the experiment-onset, rats were euthanized for analyses of neuronal lesion and inflammation.

Results

Pilocarpine induced generalised SE in all animals, causing neuronal damage, and systemic treatment with Ac_2-26 decreased neuronal degeneration and albumin levels in the hippocampus. Also, both SE groups showed an intense influx of microglia, which was corroborated by high levels of ionised calcium binding adaptor molecule 1(Iba-1) and monocyte chemoattractant protein-1 (MCP-1) in the hippocampus. Ac_2-26 reduced the astrocyte marker (glial fibrillary acidic protein; GFAP) levels, as well as interleukin-1β (IL-1β), interleukin-6 (IL-6) and growth-regulated alpha protein (GRO/KC). These effects of the peptide were associated with the modulation of the levels of formyl peptide receptor 2, a G-protein-coupled receptor that binds to Ac_2-26, and the phosphorylated extracellular signal-regulated kinase (ERK) in the hippocampal neurons.

Conclusions

The data suggest a neuroprotective effect of Ac_2-26 in the epileptogenic processes through downregulation of inflammatory mediators and neuronal loss.

Lack of Endogenous Annexin A1 Increases Mast Cell Activation and Exacerbates Experimental Atopic Dermatitis

Annexin A1 (AnxA1) is a protein with potent anti-inflammatory actions and an interesting target that has been poorly explored in skin inflammation. This work evaluated the lack of endogenous AnxA1 in the progression of ovalbumin (OVA)-induced atopic dermatitis (AD)-like skin lesions. OVA/Alum-immunized C57BL/6 male wild-type (WT) and AnxA1 null (AnxA1^-/-) mice were challenged with drops containing OVA on days 11, 14–18 and 21–24. The AnxA1^-/- AD group exhibited skin with intense erythema, erosion and dryness associated with increased skin thickness compared to the AD WT group. The lack of endogenous AnxA1 also increased IgE relative to WT animals, demonstrating exacerbation of the allergic response. Histological analysis revealed intense eosinophilia and mast-cell activation in AD animals, especially in AnxA1^-/-. Both AD groups increased skin interleukin (IL)-13 levels, while IL-17A was upregulated in AnxA1^-/- lymph nodes and mast cells. High levels of phosphorylated ERK were detected in keratinocytes from AD groups. However, phospho-ERK levels were higher in the AnxA1^-/- when compared to the respective control groups. Our results suggest AnxA1 as an important therapeutic target for inflammatory skin diseases.

Involvement of the annexin A1-Fpr anti-inflammatory system in the ocular allergy

Annexin A1 (ANXA1)-formyl peptide receptor (Fpr) system is potent effective mediators in the control of the inflammatory response. In this study, we evaluate the potential involvement of the Fpr family in the protective effect of the mimetic peptide of ANXA1 (ANXA1_2-26) using an experimental allergic conjunctivitis (AC) model in mice. Ovalbumin (OVA)/Alum-immunized wild-type (WT) and ANXA1-null (ANXA1^-/-) Balb/c mice (days 0 and 7) were challenged by eye drops containing OVA on days 14-16, and two groups received ANXA1_2-26 alone or with Fpr antagonist Boc2 intraperitoneally during challenged days. As expected, plasma IgE anti-OVA levels increased significantly in the OVA-immunized WT and ANXA1^-/- mice, supporting the efficacy of AC model. AC increased Fpr1 and Fpr2 levels in the conjunctiva and the lack of endogenous ANXA1 exacerbated Fpr2 expression only. In contrast, administering ANXA1_2-26 in the WT mice diminished Fpr2 levels in the conjunctiva, and the effect was reverted by Boc2. Ultrastructural analysis showed the co-localization of Fpr2 and ANXA1 in the plasma membrane of mast cells (MCs), eosinophils and neutrophils, supporting this system as being operative in the AC. Boc2 abrogated the ANXA1_2-26 effect by increasing the MC degranulation and the eosinophil influx in the conjunctiva, and these findings were supported by peroxidase eosinophil, eotaxin and MC protease levels. Additionally, the ANXA1_2-26-Fpr system in the AC was associated with the activation of ERK and JNK. Collectively, the data provided in vivo supports the anti-allergic effects of the ANXA1-Fpr system and may serve as a therapeutic target in this ocular disorder.

Specialized Pro-resolving Mediators Regulate Alveolar Fluid Clearance during Acute Respiratory Distress Syndrome

Objective

Acute respiratory distress syndrome (ARDS) is an acute and lethal clinical syndrome that is characterized by the injury of alveolar epithelium, which impairs active fluid transport in the lung, and impedes the reabsorption of edema fluid from the alveolar space. This review aimed to discuss the role of pro-resolving mediators on the regulation of alveolar fluid clearance (AFC) in ARDS.

Data Sources

Articles published up to September 2017 were selected from the PubMed, with the keywords of "alveolar fluid clearance" or "lung edema" or "acute lung injury" or "acute respiratory distress syndrome", and "specialized pro-resolving mediators" or "lipoxin" or "resolvin" or "protectin" or "maresin" or "alveolar epithelial cells" or "aspirin-triggered lipid mediators" or "carbon monoxide and heme oxygenase" or "annexin A1".

Study Selection

We included all relevant articles published up to September 2017, with no limitation of study design.

Results

Specialized pro-resolving mediators (SPMs), as the proinflammatory mediators, not only upregulated epithelial sodium channel, Na,K-ATPase, cystic fibrosis transmembrane conductance regulator (CFTR), and aquaporins levels, but also improved Na,K-ATPase activity to promote AFC in ARDS. In addition to the direct effects on ion channels and pumps of the alveolar epithelium, the SPMs also inhibited the inflammatory cytokine expression and improved the alveolar epithelial cell repair to enhance the AFC in ARDS.

Conclusions

The present review discusses a novel mechanism for pulmonary edema fluid reabsorption. SPMs might provide new opportunities to design "reabsorption-targeted" therapies with high degrees of precision in controlling ALI/ARDS.

Galectin-3: role in ocular allergy and potential as a predictive biomarker

Aims

To evaluate galectin-3 (Gal-3), a β-galactoside binding protein, as a possible biomarker in ocular allergy and further investigated the role of endogenous Gal-3 in a murine model of ovalbumin (OVA)-induced allergic conjunctivitis (AC).

Methods

Conjunctival impression cytology specimens from control and patients with severe vernal keratoconjunctivitis, treated or untreated, were used to evaluate Gal-3 expression by immunocytochemistry. To investigate the mechanism of action of Gal-3, OVA-immunised BALB/c male wild-type (WT) and Gal-3 null (Gal-3-/-) mice were challenged with eye drops containing OVA on days 14–16 with a subset of animals pretreated with 0.03% tacrolimus (TC) or dexamethasone (Dex).

Results

Patients with AC and OVA-sensitised WT mice exhibited increased levels of Gal-3 in the conjunctiva compared with control, an effect reverted by the action of Dex and TC therapy. Twenty-four hours after the final OVA challenge, total and anti-OVA IgE levels increased significantly in the blood of OVA-sensitised WT and Gal-3-/- mice compared with controls, supporting the efficacy of the AC model. The lack of endogenous Gal-3 exacerbated the local inflammatory response, increasing the influx of eosinophils and mast cell activation. Additionally, OVA-sensitised Gal-3-/- animals exhibited increased CD4+ expression in the eyes as well as eotaxin, IL-4, IL-13 and interferon-γ levels in the tear fluid compared with WT animals.

Conclusion

Gal-3 contributes to the pathogenesis of ocular allergy and represents a relevant therapeutic target.

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.

Annexins - insights from knockout mice

Annexins are a highly conserved protein family that bind to phospholipids in a calcium (Ca2+) - dependent manner. Studies with purified annexins, as well as overexpression and knockdown approaches identified multiple functions predominantly linked to their dynamic and reversible membrane binding behavior. However, most annexins are found at multiple locations and interact with numerous proteins. Furthermore, similar membrane binding characteristics, overlapping localizations and shared interaction partners have complicated identification of their precise functions. To gain insight into annexin function in vivo, mouse models deficient of annexin A1 (AnxA1), A2, A4, A5, A6 and A7 have been generated. Interestingly, with the exception of one study, all mice strains lacking one or even two annexins are viable and develop normally. This suggested redundancy within annexins, but examining these knockout (KO) strains under stress conditions revealed striking phenotypes, identifying underlying mechanisms specific for individual annexins, often supporting Ca2+ homeostasis and membrane transport as central for annexin biology. Conversely, mice lacking AnxA1 or A2 show extracellular functions relevant in health and disease that appear independent of membrane trafficking or Ca2+ signaling. This review will summarize the mechanistic insights gained from studies utilizing mouse models lacking members of the annexin family.

Role of the glucocorticoid-induced leucine zipper gene in dexamethasone-induced inhibition of mouse neutrophil migration via control of annexin A1 expression

The glucocorticoid-induced leucine zipper (GILZ) gene is a pivotal mediator of the anti-inflammatory effects of glucocorticoids (GCs) that are known to regulate the function of both adaptive and innate immunity cells. Our aim was to investigate the role of GILZ in GC-induced inhibition of neutrophil migration, as this role has not been investigated before. We found that GILZ expression was induced by dexamethasone (DEX), a synthetic GC, in neutrophils, and that it regulated migration of these cells into inflamed tissues under DEX treatment. Of note, inhibition of neutrophil migration was not observed in GILZ-knockout mice with peritonitis that were treated by DEX. This was because DEX was unable to up-regulate annexin A1 (Anxa1) expression in the absence of GILZ. Furthermore, we showed that GILZ mediates Anxa1 induction by GCs by transactivating Anxa1 expression at the promoter level via binding with the transcription factor, PU.1. The present findings shed light on the role of GILZ in the mechanism of induction of Anxa1 by GCs. As Anxa1 is an important protein for the resolution of inflammatory response, GILZ may represent a new pharmacologic target for treatment of inflammatory diseases.-Ricci, E., Ronchetti, S., Pericolini, E., Gabrielli, E., Cari, L., Gentili, M., Roselletti, E., Migliorati, G., Vecchiarelli, A., Riccardi, C. Role of the glucocorticoid-induced leucine zipper gene in dexamethasone-induced inhibition of mouse neutrophil migration via control of annexin A1 expression.

Annexin A1 Is Involved in the Resolution of Inflammatory Responses during Leishmania braziliensis Infection

Leishmaniases are diseases caused by several Leishmania species. Leishmania (Viannia) braziliensis can cause localized cutaneous leishmaniasis (LCL), which heals spontaneously, or mucosal leishmaniasis (ML), characterized by chronic and intense inflammation and scanty parasitism. Annexin A1 (AnxA1) is a protein involved in modulation and resolution of inflammation through multiple mechanisms. In the present study, the role of AnxA1 was investigated in L. braziliensis-infected BALB/c mice. AnxA1 levels increased at the peak of tissue lesion and parasitism in infected mice. AnxA1 increased also after L. braziliensis infection of BALB/c (wild-type [WT]) bone marrow derived macrophages. Despite a lower parasite intake, parasite burden in bone marrow-derived macrophages from AnxA1^-/- mice was similar to WT and associated with an early increase of TNF-α and, later, of IL-10. AnxA1^-/- mice controlled tissue parasitism similarly to WT animals, but they developed significantly larger lesions at later stages of infection, with a more pronounced inflammatory infiltrate and increased specific production of IFN-γ, IL-4, and IL-10. AnxA1^-/- mice also presented higher phosphorylation levels of ERK-1/2 and p65/RelA (NF-κB) and inducible NO synthase expression, suggesting that AnxA1 may be involved in modulation of inflammation in this model of experimental leishmaniasis. Finally, assessment of AnxA1 levels in sera from patients with LCL or ML revealed that ML patients had higher levels of serum AnxA1 than did LCL patients or control subjects. Collectively, these data indicate that AnxA1 is actively expressed during L. braziliensis infection. In the absence of AnxA1, mice are fully able to control parasite replication, but they present more intense inflammatory responses and delayed ability to resolve their lesion size.

An inhibitor peptide of toll-like receptor 2 shows therapeutic potential for allergic conjunctivitis

Allergic conjunctivitis (AC) is an inflammatory disease of the conjunctiva, which is characterized by antigen challenge and toll-like receptor 2 (TLR2) activation. Here, a designed small peptide ZY12 was found to contain therapeutic potential in staphylococcal enterotoxin B (SEB)-induced AC model. ZY12 treatment showed the remission of clinical signs, plasma total IgE levels, number of mast cells and the proportion of degranulated mast cell in AC mice. Levels of Th2 cytokines (IL-4, IL-5, IL-13) in the lymph nodes or spleen were significantly decreased while those of Th1 cytokine (IFN-γ) were increased in ZY12 treated group, suggesting a protective role of ZY12 in AC by mediating the balance of Th1/Th2 cytokines. Importantly, ZY12 significantly inhibited TLR2 expression in conjunctival tissue. Combined its therapeutic effects with TLR2 inhibitory function, ZY12 might be an ideal candidate for the development of new therapeutic agent for allergic disease.

Annexin A1 promotes timely resolution of inflammation in murine gout

Gout is a self-limited inflammatory disease caused by deposition of monosodium urate (MSU) crystals in the joints. Resolution of inflammation is an active process leading to restoration of tissue homeostasis. Here, we studied the role of Annexin A1 (AnxA1), a glucocorticoid-regulated protein that has anti-inflammatory and proresolving actions, in resolution of acute gouty inflammation. Injection of MSU crystals in the knee joint of mice induced inflammation that was associated with expression of AnxA1 during the resolving phase of inflammation. Neutralization of AnxA1 with antiserum or blockade of its receptor with BOC-1 (nonselective) or WRW₄ (selective) prevented the spontaneous resolution of gout. There was greater neutrophil infiltration after challenge with MSU crystals in AnxA1 knockout mice (AnxA1^-/- ) and delayed resolution associated to decreased neutrophil apoptosis and efferocytosis. Pretreatment of mice with AnxA1-active N-terminal peptide (Ac_2-26 ) decreased neutrophil influx, IL-1β, and CXCL1 production in periarticular joint. Posttreatment with Ac_2-26 decreased neutrophil accumulation, IL-1β, and hypernociception, and improved the articular histopathological score. Importantly, the therapeutic effects of Ac_2-26 were associated with increased neutrophils apoptosis and shortened resolution intervals. In conclusion, AnxA1 plays a crucial role in the context of acute gouty inflammation by promoting timely resolution of inflammation.

Ocular diseases: immunological and molecular mechanisms

Many factors, such as environmental, microbial and endogenous stress, antigen localization, can trigger the immunological events that affect the ending of the diverse spectrum of ocular disorders. Significant advances in understanding of immunological and molecular mechanisms have been researched to improve the diagnosis and therapy for patients with ocular inflammatory diseases. Some kinds of ocular diseases are inadequately responsive to current medications; therefore, immunotherapy may be a potential choice as an alternative or adjunctive treatment, even in the prophylactic setting. This article first provides an overview of the immunological and molecular mechanisms concerning several typical and common ocular diseases; second, the functions of immunological roles in some of systemic autoimmunity will be discussed; third, we will provide a summary of the mechanisms that dictate immune cell trafficking to ocular local microenvironment in response to inflammation.

Annexin A1 and the Resolution of Inflammation: Modulation of Neutrophil Recruitment, Apoptosis, and Clearance

Neutrophils (also named polymorphonuclear leukocytes or PMN) are essential components of the immune system, rapidly recruited to sites of inflammation, providing the first line of defense against invading pathogens. Since neutrophils can also cause tissue damage, their fine-tuned regulation at the inflammatory site is required for proper resolution of inflammation. Annexin A1 (AnxA1), also known as lipocortin-1, is an endogenous glucocorticoid-regulated protein, which is able to counterregulate the inflammatory events restoring homeostasis. AnxA1 and its mimetic peptides inhibit neutrophil tissue accumulation by reducing leukocyte infiltration and activating neutrophil apoptosis. AnxA1 also promotes monocyte recruitment and clearance of apoptotic leukocytes by macrophages. More recently, some evidence has suggested the ability of AnxA1 to induce macrophage reprogramming toward a resolving phenotype, resulting in reduced production of proinflammatory cytokines and increased release of immunosuppressive and proresolving molecules. The combination of these mechanisms results in an effective resolution of inflammation, pointing to AnxA1 as a promising tool for the development of new therapeutic strategies to treat inflammatory diseases.