FPR1 is the plague receptor on host immune cells.

The causative agent of plague, Yersinia pestis, uses a type III secretion system to selectively destroy immune cells in humans, thus enabling Y. pestis to reproduce in the bloodstream and be transmitted to new hosts through fleabites. The host factors that are responsible for the selective destruction of immune cells by plague bacteria are unknown. Here we show that LcrV, the needle cap protein of the Y. pestis type III secretion system, binds to the N-formylpeptide receptor (FPR1) on human immune cells to promote the translocation of bacterial effectors. Plague infection in mice is characterized by high mortality; however, Fpr1-deficient mice have increased survival and antibody responses that are protective against plague. We identified FPR1R190W as a candidate resistance allele in humans that protects neutrophils from destruction by the Y. pestis type III secretion system. Thus, FPR1 is a plague receptor on immune cells in both humans and mice, and its absence or mutation provides protection against Y. pestis. Furthermore, plague selection of FPR1 alleles appears to have shaped human immune responses towards other infectious diseases and malignant neoplasms.

Interferon-ß regulates proresolving lipids to promote the resolution of acute airway inflammation.

Aberrant immune responses, including hyperresponsiveness to Toll-like receptor (TLR) ligands, underlie acute respiratory distress syndrome (ARDS). Type I interferons confer antiviral activities and could also regulate the inflammatory response, whereas little is known about their actions to resolve aberrant inflammation. Here we report that interferon-ß (IFN-ß) exerts partially overlapping, but also cooperative actions with aspirin-triggered 15-epi-lipoxin A4 (15-epi-LXA4) and 17-epi-resolvin D1 to counter TLR9-generated cues to regulate neutrophil apoptosis and phagocytosis in human neutrophils. In mice, TLR9 activation impairs bacterial clearance, prolongs Escherichia coli-evoked lung injury, and suppresses production of IFN-ß and the proresolving lipid mediators 15-epi-LXA4 and resolvin D1 (RvD1) in the lung. Neutralization of endogenous IFN-ß delays pulmonary clearance of E. coli and aggravates mucosal injury. Conversely, treatment of mice with IFN-ß accelerates clearance of bacteria, restores neutrophil phagocytosis, promotes neutrophil apoptosis and efferocytosis, and accelerates resolution of airway inflammation with concomitant increases in 15-epi-LXA4 and RvD1 production in the lungs. Pharmacological blockade of the lipoxin receptor ALX/FPR2 partially prevents IFN-ß-mediated resolution. These findings point to a pivotal role of IFN-ß in orchestrating timely resolution of neutrophil and TLR9 activation-driven airway inflammation and uncover an IFN-ß-initiated resolution program, activation of an ALX/FPR2-centered, proresolving lipids-mediated circuit, for ARDS.

Release of immunomodulatory peptides at bacterial membrane interfaces as a novel strategy to fight microorganisms.

Cationic and amphiphilic peptides can be used as homing devices to accumulate conjugated antibiotics to bacteria-enriched sites and promote efficient microbial killing. However, just as important as tackling bacterial infections, is the modulation of the immune response in this complex microenvironment. In the present report, we designed a peptide chimaera called Chim2, formed by a membrane-active module, an enzyme hydrolysis site and a formyl peptide receptor 2 (FPR2) agonist. This molecule was designed to adsorb onto bacterial membranes, promote their lysis, and upon hydrolysis by local enzymes, release the FPR2 agonist sequence for activation and recruitment of immune cells. We synthesized the isolated peptide modules of Chim2 and characterized their biological activities independently and as a single polypeptide chain. We conducted antimicrobial assays, along with other tests aiming at the analyses of the cellular and immunological responses. In addition, assays using vesicles as models of eukaryotic and prokaryotic membranes were conducted and solution structures of Chim2 were generated by 1H NMR. Chim2 is antimicrobial, adsorbs preferentially to negatively charged vesicles while adopting an α-helix structure and exposes its disorganized tail to the solvent, which facilitates hydrolysis by tryptase-like enzymes, allowing the release of the FPR2 agonist fragment. This fragment was shown to induce accumulation of the cellular activation marker, lipid bodies, in mouse macrophages and the release of immunomodulatory interleukins. In conclusion, these data demonstrate that peptides with antimicrobial and immunomodulatory activities can be considered for further development as drugs.

Renoprotective effect of isoliquiritigenin on cisplatin-induced acute kidney injury through inhibition of FPR2 in macrophage.

Acute kidney injury (AKI) is a serious complication in critically ill patients. Accumulating evidences indicated that macrophages play an important pro-inflammatory role in AKI and isoliquiritigenin (ISL) can inhibit macrophagic inflammation, but its role in AKI and the underlying mechanism are unknown. The present study aims to investigate the renoprotective effect of ISL on AKI and the role of Formyl peptide receptors 2 (FPR2) in this process. In this study, cisplatin-induced AKI model and lipopolysaccharide-induced macrophage inflammatory model were employed to perform the in vivo and in vitro experiments. The results showed that ISL strongly relieved kidney injury and inhibited renal inflammation in vivo and suppress macrophagic inflammatory response in vitro. Importantly, it was found that FPR2 was significantly upregulated compared to the control group in AKI and LPS-induced macrophage, whereas it was strongly suppressed by ISL. Interestingly, overexpression of FPR2 with transfection of pcDNA3.1-FPR2 effectively reversed the anti-inflammatory effect of ISL in macrophage, suggesting that FPR2 may be the potential target for ISL to prevent inflammation and improve kidney injury of AKI. Take together, these findings indicated that ISL improved cisplantin-induced kidney injury by inhibiting FPR2 involved macrophagic inflammation, which may provide a potential therapeutic option for AKI.

Suppression of FPR2 expression inhibits inflammation in preeclampsia by improving the biological functions of trophoblast via NF-κB pathway.

PURPOSE: The dysfunction of trophoblast during inflammation plays an important role in PE. Formyl peptide receptor 2 (FPR2) plays crucial roles in the development of inflammation-associated disease. This present study aimed to explore the effect of FPR2 on a trophoblast cellular model of preeclampsia. METHODS: The expression of FPR2 in placenta was detected by immunohistochemical staining and western blotting. Transfection of siRNA was used to knockdown FPR2 in HTR-8/SVneo cells. Inflammatory cytokines were detected by ELISA. CCK8, Transwell, wound healing, FACS and tube formation assays were performed to observe the abilities of cell proliferation, migration, invasion, apoptosis and angiogenesis. Western blotting was implemented to clarify that NF-κB signaling pathway was downstream of FPR2. RESULTS: The expression levels of FPR2 were higher in placental tissues of patients with PE. Knockdown of FPR2 expression by siFPR2 or inhibition of its activity by WRW4 decreased the release of proinflammatory cytokines in HTR8/SVneo cells treated with LPS. Knockdown of FPR2 expression or inhibition of its activity further reversed the LPS-induced attenuation of the proliferation, migration, invasion and angiogenesis and increase in apoptosis in HTR8/SVneo cells. Moreover, the NF-κB signaling pathway was activated in both placental tissues of patients with PE and LPS-treated HTR8/SVneo cells. However, the activation was attenuated when FPR2 was knocked down or inhibited. CONCLUSION: Suppression of FPR2 expression alleviated the effects of inflammation induced by LPS on trophoblasts via the NF-κB signaling pathway, which provided a novel and potential strategy for the treatment of PE.

Electroacupuncture decreases inflammatory pain through a pro-resolving mechanism involving the peripheral annexin A1-formyl peptide receptor 2/ALX-opioid receptor pathway.

The pro-resolving mechanism is a recently described endogenous process that controls inflammation. The present study evaluated components of this mechanism, including annexin 1 (ANXA1) and the formyl peptide receptor 2/ALX (FPR2/ALX) receptor, in the antihyperalgesic effect induced by electroacupuncture (EA) in an animal model of persistent peripheral inflammation. Male Swiss mice underwent intraplantar (i.pl.) injection with complete Freund's adjuvant (CFA). Mechanical hyperalgesia was assessed with von Frey monofilaments. Animals were treated with EA (2-10 Hz, ST36-SP6) or subcutaneous BML-111 injection (FPR2/ALX agonist) for 5 consecutive days. In a separate set of experiments, on the first and fifth days after CFA injection, animals received i.pl. WRW4 (FPR2/ALX antagonist) or naloxone (non-selective opioid receptor antagonist) before EA or BML-111 injection. Paw protein levels of FPR2/ALX and ANXA1 were evaluated on the second day after CFA injection by western blotting technique. EA and BML-111 reduced mechanical hyperalgesia. I.pl. naloxone or WRW4 prevented the antihyperalgesic effect induced by either EA or BML-111. EA increased ANXA1 but did not alter FPR2/ALX receptor levels in the paw. Furthermore, i.pl. pretreatment with WRW4 prevented the increase of ANXA1 levels induced by EA. This work demonstrates that the EA antihyperalgesic effect on inflammatory pain involves the ANXA1/FPR2/ALX pro-resolution pathway. This effect appears to be triggered by the activation of FPR2/ALX receptors and crosstalk communication with the opioid system.

FPR2-based anti-inflammatory and anti-lipogenesis activities of novel meroterpenoid dimers from Ganoderma.

Four pairs of novel meroterpenoid dimers, (±)-applandimeric acids A-D (1-4) with an unprecedented spiro[furo[3,2-b]benzofuran-3,2'-indene] core were isolated from the fruiting bodies of Ganoderma applanatum. Their planar structures were unambiguously determined via extensive spectroscopic analysis. Their relative and absolute configurations were confirmed through calculated internuclear distance, coupling constant, 13C NMR with DP4 + analysis and electronic circular dichroism (ECD). Furthermore, the molecular docking-based method was used to evaluate their interaction with formyl peptide receptor 2 (FPR2) associated with inflammation. Interestingly, (±)-applandimeric acid D (4) can bond with FPR2 by some key hydrogen bonds. Furthermore, an in vitro bioassay verified that 4 can inhibit the expression of FPR2 with IC50 value of 7.93 µM. In addition, compared to the positive control LiCl (20 mM), 4 showed comparable anti-lipogenesis activity at the concentration of 20 µM. Meanwhile, 4 can suppress the protein levels of peroxisome proliferators-activated receptor-γ (PPAR-γ), CCAAT/enhancer-binding protein-ß (C/EBP-ß), adipocyte fatty acid-binding protein 4 (FABP4), and fatty acid synthase (FAS) through activating AMP-activated protein kinase (AMPK) signaling pathway. Thus, our findings indicate that compound 4 could be a lead compound to treat obesity and obesity-related diseases by inhibiting lipid accumulation in adipocyte and alleviating inflammation.

Formyl-Peptide Receptor Activation Enhances Phagocytosis of Community-Acquired Methicillin-Resistant Staphylococcus aureus.

BACKGROUND: Formyl-peptide receptors (FPRs) are important pattern recognition receptors that sense specific bacterial peptides. Formyl-peptide receptors are highly expressed on neutrophils and monocytes, and their activation promotes the migration of phagocytes to sites of infection. It is currently unknown whether FPRs may also influence subsequent processes such as bacterial phagocytosis and killing. Staphylococcus aureus, especially highly pathogenic community-acquired methicillin-resistant S aureus strains, release high amounts of FPR2 ligands, the phenol-soluble modulins. METHODS: We demonstrate that FPR activation leads to upregulation of complement receptors 1 and 3 as well as FCγ receptor I on neutrophils and, consequently, increased opsonic phagocytosis of S aureus and other pathogens. RESULTS: Increased phagocytosis promotes killing of S aureus and interleukin-8 release by neutrophils. CONCLUSIONS: We show here for the first time that FPRs govern opsonic phagocytosis. Manipulation of FPR2 activation could open new therapeutic opportunities against bacterial pathogens.

Inhibition of formyl peptide receptors improves the outcome in a mouse model of Alzheimer disease.

BACKGROUND: An important hallmark of Alzheimer's disease (AD) is the increase of Aß1-42 burden and its accumulation to senile plaques, leading the reactive gliosis and neurodegeneration. The modulation of glia cell function represents an attractive therapeutic strategy, but is currently limited by an incomplete understanding of its relevance for AD. The chemotactic G-protein coupled formyl peptide receptor (FPR), which is known to modulate Aß1-42 uptake and signal transduction, might be one candidate molecule regulating glia function in AD. Here, we investigate whether the modulation of FPR exerts beneficial effects in an AD preclinical model. METHODS: To address this question, APP/PS1 double-transgenic AD mice were treated for 20 weeks with either the pro-inflammatory FPR agonist fMLF, the FPR1/2 antagonist Boc2 or the anti-inflammatory FPR2 agonist Ac2-26. Spatial learning and memory were evaluated using a Morris water maze test. Immunohistological staining, gene expression studies, and flow cytometry analyses were performed to study neuronal loss, gliosis, and Aß-load in the hippocampus and cortex, respectively. RESULTS: FPR antagonism by Boc2-treatment significantly improved spatial memory performance, reduced neuronal pathology, induced the expression of homeostatic growth factors, and ameliorated microglia, but not astrocyte, reactivity. Furthermore, the elevated levels of amyloid plaques in the hippocampus were reduced by Boc2-treatment, presumably by an induction of amyloid degradation. CONCLUSIONS: We suggest that the modulation of FPR signaling cascades might be considered as a promising therapeutic approach for alleviating the cognitive deficits associated with early AD. Additional studies are now needed to address the downstream effectors as well as the safety profile of Boc2.

Formyl Peptide Receptor-1 Blockade Prevents Receptor Regulation by Mitochondrial Danger-Associated Molecular Patterns and Preserves Neutrophil Function After Trauma.

OBJECTIVES: Trauma predisposes to systemic sterile inflammation (systemic inflammatory response syndrome) as well as infection, but the mechanisms linking injury to infection are poorly understood. Mitochondrial debris contains formyl peptides. These bind formyl peptide receptor-1, trafficking neutrophils to wounds, initiating systemic inflammatory response syndrome, and wound healing. Bacterial formyl peptides, however, also attract neutrophils via formyl peptide receptor-1. Thus, mitochondrial formyl peptides might suppress neutrophils antimicrobial function. Also, formyl peptide receptor-1 blockade used to mitigate systemic inflammatory response syndrome might predispose to sepsis. We examined how mitochondrial formyl peptides impact neutrophils functions contributing to antimicrobial responses and how formyl peptide receptor-1 antagonists affect those functions. DESIGN: Prospective study of human and murine neutrophils and clinical cohort analysis. SETTING: University research laboratory and level 1 trauma center. PATIENTS: Trauma patients, volunteer controls. ANIMAL SUBJECTS: C57Bl/6, formyl peptide receptor-1, and formyl peptide receptor-2 knockout mice. INTERVENTIONS: Human and murine neutrophils functions were activated with autologous mitochondrial debris, mitochondrial formyl peptides, or bacterial formyl peptides followed by chemokines or leukotrienes. The experiments were repeated using formyl peptide receptor-1 antagonist cyclosporin H, "designer" human formyl peptide receptor-1 antagonists (POL7178 and POL7200), or anti-formyl peptide receptor-1 antibodies. Mouse injury/lung infection model was used to evaluate effect of formyl peptide receptor-1 inhibition. MEASUREMENTS AND MAIN RESULTS: Human neutrophils cytosolic calcium, chemotaxis, reactive oxygen species production, and phagocytosis were studied before and after exposure to mitochondrial debris, mitochondrial formyl peptides, and bacterial formyl peptides. Mitochondrial formyl peptide and bacterial formyl peptides had similar effects on neutrophils. Responses to chemokines and leukotrienes were suppressed by prior exposure to formyl peptides. POL7200 and POL7178 were specific antagonists of human formyl peptide receptor-1 and more effective than cyclosporin H or anti-formyl peptide receptor-1 antibodies. Formyl peptides inhibited mouse neutrophils responses to chemokines only if formyl peptide receptor-1 was present. Formyl peptide receptor-1 blockade did not inhibit neutrophils bacterial phagocytosis or reactive oxygen species production. Cyclosporin H increased bacterial clearance in lungs after injury. CONCLUSIONS: Formyl peptides both activate and desensitize neutrophils. Formyl peptide receptor-1 blockade prevents desensitization, potentially both diminishing systemic inflammatory response syndrome and protecting the host against secondary infection after tissue trauma or primary infection.

Human cathelicidin antimicrobial peptide LL-37 promotes lymphangiogenesis in lymphatic endothelial cells through the ERK and Akt signaling pathways.

LL-37, the only member of the cathelicidin family of cationic antimicrobial peptides in humans has been shown to exhibit a wide variety of biological actions in addition to its antimicrobial activity. However, the lymphangiogenic effect of LL-37 has not been elucidated yet. In this study, we examined the effects of LL-37 on lymphangiogenesis and evaluated the underlying molecular mechanisms. LL-37 treatment significantly increased the migration and tube-like formation of human dermal lymphatic microvascular endothelial cells (HDLECs) and promoted the expression of lymphangiogenic factor in HDLECs. Treatment with LL-37 increased phosphorylation of ERK and Akt proteins in HDLECs, and pretreatment with ERK and Akt inhibitors significantly blocked the LL-37-induced HDLEC migration and tube-like formation. Furthermore, to investigate the involvement of formyl peptide receptor-like 1 (FPRL1) signaling in LL-37-induced lymphangiogenesis, HDLECs were treated with an FPRL1 antagonist. Pretreatment with the FPRL1 antagonist inhibited LL-37-induced phosphorylation of ERK and Akt proteins and attenuated LL-37-induced HDLEC migration and tube-like formation. These data indicated that LL-37 induces lymphangiogenesis in lymphatic endothelial cells via FPRL1, and the activation of the ERK and Akt-dependent signaling pathways.

Ongoing Lung Inflammation and Disease Progression in Mice after Smoking Cessation: Beneficial Effects of Formyl-Peptide Receptor Blockade.

The most important risk factor for chronic obstructive pulmonary disease (COPD) is cigarette smoking. Until now, smoking cessation (SC) is the only treatment effective in slowing down the progression of the disease. However, in many cases SC may only relieve the airflow obstruction and inflammatory response. Consequently, a persistent lung inflammation in ex-smokers is associated with progressive deterioration of respiratory functions. This is an increasingly important clinical problem whose mechanistic basis remains poorly understood. Available therapies do not adequately suppress inflammation and are not able to stop the vicious cycle that is at the basis of persistent inflammation. In addition, in mice after SC an ongoing inflammation and progressive lung deterioration is observed. After 4 months of smoke exposure mice show mild emphysematous changes. Lung inflammation is still present after SC, and emphysema progresses during the next 6-month period of observation. Destruction of alveolar walls is associated with airways remodeling (goblet cell metaplasia and peribronchiolar fibrosis). Modulation of formyl-peptide receptor signaling with antagonists mitigates inflammation and prevents deterioration of lung structures. This study suggests an important role for N-formylated peptides in the progression and exacerbation of COPD. Modulating formyl-peptide receptor signal should be explored as a potential new therapy for COPD.

Intravital Imaging of Neutrophil Recruitment Reveals the Efficacy of FPR1 Blockade in Hepatic Ischemia-Reperfusion Injury.

Neutrophils are considered responsible for the pathophysiological changes resulting from hepatic ischemia-reperfusion (I/R) injury, which is a complication of trauma, shock, liver resection, and transplantation. Recently, evidence is accumulating that formyl-peptide receptor (FPR) signaling constitutes an important danger signal that guides neutrophils to sites of inflammation. This study aimed to investigate dynamic neutrophil recruitment using two-photon laser-scanning microscopy (TPLSM) in response to FPR1 blockade during hepatic I/R. LysM-eGFP mice were subjected to partial warm hepatic I/R. They were pretreated with an FPR1 antagonist, cyclosporine H (CsH), or formyl peptide, fMLF. Liver was imaged after hepatic laser irradiation or I/R using the TPLSM technique. CsH treatment alleviated hepatic I/R injury, as evidenced by decreased serum transaminase levels, reduced hepatocyte necrosis/apoptosis, and diminished inflammatory cytokine, chemokine, and oxidative stress. In contrast, systemic administration of fMLF showed few effects. Time-lapse TPLSM showed that FPR1 blockade inhibited the accumulation of neutrophils in the necrotic area induced by laser irradiation in vivo. In the CsH-treated I/R group, the number and crawling velocity of neutrophils in the nonperfused area were lower than those in the control group. Meanwhile, FPR1 blockade did not affect monocyte/macrophage recruitment. Hepatic I/R promoted the retention of neutrophils and their active behavior in the spleen, whereas CsH treatment prevented their changes. Intravital TPLSM revealed that formyl-peptide-FPR1 signaling is responsible for regulating neutrophil chemotaxis to allow migration into the necrotic area in hepatic I/R. Our findings suggest effective approaches for elucidating the mechanisms of immune cell responses in hepatic I/R.

Garcinia Multiflora Inhibits FPR1-Mediated Neutrophil Activation and Protects Against Acute Lung Injury.

BACKGROUND/AIMS: Formyl peptide receptors (FPRs) recognize different endogenous and exogenous molecular stimuli and mediate neutrophil activation. Dysregulation of excessive neutrophil activation and the resulting immune responses can induce acute lung injury (ALI) in the host. Accordingly, one promising approach to the treatment of neutrophil-dominated inflammatory diseases involves therapeutic FPR1 inhibition. METHODS: We extracted a potent FPR1 antagonist from Garcinia multiflora Champ. (GMC). The inhibitory effects of GMC on superoxide anion release and elastase degranulation from activated human neutrophils were determined with spectrophotometric analysis. Reactive oxygen species (ROS) production and the FPR1 binding ability of neutrophils were assayed by flow cytometry. Signaling transduction mediated by GMC in response to chemoattractants was assessed with a calcium influx assay and western blotting. A lipopolysaccharide (LPS)-induced ALI mouse model was used to determine the therapeutic effects of GMC in vivo. RESULTS: GMC significantly reduced superoxide anion release, the reactive oxidants derived therefrom, and elastase degranulation mediated through selective, competitive FPR1 blocking in N-formyl-L-methionyl-L-leucyl-L-phenylalanine (fMLF)-stimulated human neutrophils. In cell-free systems, GMC was unable to scavenge superoxide anions or suppress elastase activity. GMC produced a right shift in fMLF-activated concentration-response curves and was confirmed to be a competitive FPR1 antagonist. GMC binds to FPR1 not only in neutrophils, but also FPR1 in neutrophil-like THP-1 and hFPR1-transfected HEK293 cells. Furthermore, the mobilization of calcium and phosphorylation of mitogen-activated protein kinases and Akt, which are involved in FPR1-mediated downstream signaling, was competitively blocked by GMC. In an in vivo study, GMC significantly reduced pulmonary edema, neutrophil infiltration, and alveolar damage in LPS-induced ALI mice. CONCLUSION: Our findings demonstrate that GMC is a natural competitive FPR1 inhibitor, which makes it a possible anti-inflammatory treatment option for patients critically inflicted with FPR1-mediated neutrophilic lung damage.

Resolvin D1 promotes corneal epithelial wound healing and restoration of mechanical sensation in diabetic mice.

Purpose: To investigate the effect and mechanism of proresolving lipid mediator resolvin D1 (RvD1) on the corneal epithelium and the restoration of mechanical sensation in diabetic mice. Methods: Type 1 diabetes was induced in mice with intraperitoneal streptozocin injections. The healthy and diabetic mice underwent removal of the central corneal epithelium, and then 100 ng/ml RvD1 or its formyl peptide receptor 2 (FPR2) antagonist WRW4 was used to treat the diabetic mice. Regeneration of the corneal epithelium and nerves was observed with sodium fluorescein staining and whole-mount anti-ß3-tubulin fluorescence staining. The inflammatory response level was measured with hematoxylin and eosin staining (inflammatory cell infiltration), enzyme-linked immunosorbent assay (tumor necrosis factor alpha and interleukin-1 beta content), myeloperoxidase activity, and fluorescence staining (macrophage content). The reactive oxygen species (ROS) and glutathione (GSH) levels were examined with incubation with fluorescent probes, and oxidative stress-related protein expression levels were evaluated with fluorescence staining and western blotting. Results: Topical application of RvD1 promoted regeneration of the corneal epithelium in diabetic mice, accompanied by the reactivation of signaling and inflammation resolution related to regeneration of the epithelium. Furthermore, RvD1 directly attenuated the accumulation of ROS and nicotinamide adenine dinucleotide phosphate oxidase 2/4 expression, while RvD1 enhanced GSH synthesis and reactivated the Nrf2-ARE signaling pathway that was impaired in the corneal epithelium in the diabetic mice. More interestingly, topical application of RvD1 promoted regeneration of corneal nerves and completely restored impaired mechanical sensitivity of the cornea in diabetic mice. In addition, the promotion of corneal epithelial wound healing by RvD1 in diabetic mice was abolished by its FPR2 antagonist WRW4. Conclusions: Topical application of RvD1 promotes corneal epithelial wound healing and the restoration of mechanical sensation in diabetic mice, which may be related to the lipid mediator's regulation of inflammation resolution, the reactivation of regenerative signaling in the epithelium, and the attenuation of oxidative stress.

The Annexin A1 Receptor FPR2 Regulates the Endosomal Export of Influenza Virus.

The Formyl Peptide Receptor 2 (FPR2) is a novel promising target for the treatment of influenza. During viral infection, FPR2 is activated by annexinA1, which is present in the envelope of influenza viruses; this activation promotes virus replication. Here, we investigated whether blockage of FPR2 would affect the genome trafficking of influenza virus. We found that, upon infection and cell treatment with the specific FPR2 antagonist WRW4 or the anti-FPR2 monoclonal antibody, FN-1D6-AI, influenza viruses were blocked into endosomes. This effect was independent on the strain and was observed for H1N1 and H3N2 viruses. In addition, blocking FPR2signaling in alveolar lung A549 epithelial cells with the monoclonal anti-FPR2 antibody significantly inhibited virus replication. Altogether, these results show that FPR2signaling interferes with the endosomal trafficking of influenza viruses and provides, for the first time, the proof of concept that monoclonal antibodies directed against FPR2 inhibit virus replication. Antibodies-based therapeutics have emerged as attractive reagents in infectious diseases. Thus, this study suggests that the use of anti-FPR2 antibodies against influenza hold great promise for the future.

Human Mesenchymal Stem (Stromal) Cells Promote the Resolution of Acute Lung Injury in Part through Lipoxin A4.

Previous studies demonstrated that bone marrow-derived mesenchymal stem (stromal) cells (MSCs) reduce the severity of acute lung injury in animal models and in an ex vivo perfused human lung model. However, the mechanisms by which MSCs reduce lung injury are not well understood. In the present study, we tested the hypothesis that human MSCs promote the resolution of acute lung injury in part through the effects of a specialized proresolving mediator lipoxin A4 (LXA4). Human alveolar epithelial type II cells and MSCs expressed biosynthetic enzymes and receptors for LXA4. Coculture of human MSCs with alveolar epithelial type II cells in the presence of cytomix significantly increased the production of LXA4 by 117%. The adoptive transfer of MSCs after the onset of LPS-induced acute lung injury (ALI) in mice led to improved survival (48 h), and blocking the LXA4 receptor with WRW4, a LXA4 receptor antagonist, significantly reversed the protective effect of MSCs on both survival and the accumulation of pulmonary edema. LXA4 alone improved survival in mice, and it also significantly decreased the production of TNF-α and MIP-2 in bronchoalveolar lavage fluid. In summary, these experiments demonstrated two novel findings: human MSCs promote the resolution of lung injury in mice in part through the proresolving lipid mediator LXA4, and LXA4 itself should be considered as a therapeutic for acute respiratory distress syndrome.

Lipoxin Signaling in Murine Lung Host Responses to Cryptococcus neoformans Infection.

Lipoxins (LX) are proresolving mediators that augment host defense against bacterial infection. Here, we investigated roles for LX in lung clearance of the fungal pathogen Cryptococcus neoformans (Cne). After intranasal inoculation of 5,000 CFU Cne, C57BL/6 and C.B-17 mice exhibited strain-dependent differences in Cne clearance, immunologic responses, and lipoxin A4 (LXA4) formation and receptor (ALX/FPR2) expression. Compared with C.B-17 mice, C57BL/6 lungs had increased and persistent Cne infection 14 days after inoculation, increased eosinophils, and distinct profiles of inflammatory cytokines. Relative to C.B-17 mice, bronchoalveolar lavage fluid levels of LXA4 were increased before and after infection in C57BL/6. The kinetics for 15-epi-LXA4 production were similar in both strains. Lung basal expression of the LX biosynthetic enzyme Alox12/15 (12/15-lipoxygenase) was increased in C57BL/6 mice and further increased after Cne infection. In contrast, lung basal expression of the LXA4 receptor Alx/Fpr2 was higher in C.B-17 relative to C57BL/6 mice, and after Cne infection, Alx/Fpr2 expression was significantly increased in only C.B-17 mice. Heat-killed Cne initiated lung cell generation of IFN-γ and IL-17 and was further increased in C.B-17 mice by 15-epi-LXA4. A trend toward reduced Cne clearance and IFN-γ production was observed upon in vivo administration of an ALX/FPR2 antagonist. Together, these findings provide the first evidence that alterations in cellular immunity against Cne are associated with differences in LXA4 production and receptor expression, suggesting an important role for ALX/FPR2 signaling in the regulation of pathogen-mediated inflammation and antifungal lung host defense.

Aspirin-triggered 15-epi-lipoxin A4 regulates neutrophil-platelet aggregation and attenuates acute lung injury in mice.

Evidence is emerging that platelets are major contributors to innate immune responses in conditions such as acute lung injury (ALI). Platelets form heterotypic aggregates with neutrophils, and we hypothesized that lipoxin mediators regulate formation of neutrophil-platelet aggregates (NPA) and that NPA significantly contribute to ALI. Lipopolysaccharide (LPS)-induced lung injury was accompanied by platelet sequestration, activation, intra-alveolar accumulation, and NPA formation within both blood and alveolar compartments. Using lung intravital microscopy, we observed the dynamic formation of NPA during physiologic conditions, which sharply increased with ALI. Aspirin (ASA) treatment significantly reduced lung platelet sequestration and activation, NPA formation, and lung injury. ASA treatment increased levels of ASA-triggered lipoxin (ATL; 15-epi-lipoxin A4), and blocking the lipoxin A4 receptor (ALX) with a peptide antagonist (Boc2) or using ALX knockouts (Fpr2/3(-/-)) reversed this protection. LPS increased NPA formation in vitro, which was reduced by ATL, and engagement of ALX by ATL on both neutrophils and platelets was necessary to prevent aggregation. In a model of transfusion-related acute lung injury (TRALI), Boc2 also reversed ASA protection, and treatment with ATL in both LPS and TRALI models protected from ALI. We conclude that ATL regulates neutrophil-platelet aggregation and that platelet-neutrophil interactions are a therapeutic target in lung injury.

The role of formyl peptide receptor 1 (FPR1) in neuroblastoma tumorigenesis.

BACKGROUND: Formyl peptide receptor 1 (FPR1) is a G protein-coupled receptor mainly expressed by the cells of myeloid origin, where it mediates the innate immune response to bacterial formylated peptides. High expression of FPR1 has been detected in various cancers but the function of FPR1 in tumorigenesis is poorly understood. METHODS: Expression of FPR1 in neuroblastoma cell lines and primary tumors was studied using RT-PCR, western blotting, immunofluorescence and immunohistochemistry. Calcium mobilization assays and western blots with phospho-specific antibodies were used to assess the functional activity of FPR1 in neuroblastoma. The tumorigenic capacity of FPR1 was assessed by xenografting of neuroblastoma cells expressing inducible FPR1 shRNA, FPR1 cDNA or control shRNA in nude mice. RESULTS: FPR1 is expressed in neuroblastoma primary tumors and cell lines. High expression of FPR1 corresponds with high-risk disease and poor patient survival. Stimulation of FPR1 in neuroblastoma cells using fMLP, a selective FPR1 agonist, induced intracellular calcium mobilization and activation of MAPK/Erk, PI3K/Akt and P38-MAPK signal transduction pathways that were inhibited by using Cyclosporin H, a selective receptor antagonist for FPR1. shRNA knock-down of FPR1 in neuroblastoma cells conferred a delayed xenograft tumor development in nude mice, whereas an ectopic overexpression of FPR1 promoted augmented tumorigenesis in nude mice. CONCLUSION: Our data demonstrate that FPR1 is involved in neuroblastoma development and could represent a therapy option for the treatment of neuroblastoma.