Distinct signaling cascades elicited by different formyl peptide receptor 2 (FPR2) agonists

Pro-Resolving Mediator Annexin A1 Regulates Intracellular Ca2+ and Mucin Secretion in Cultured Goblet Cells Suggesting a New Use in Inflammatory Conjunctival Diseases

The amount of mucin secreted by conjunctival goblet cells is regulated to ensure the optimal level for protection of the ocular surface. Under physiological conditions lipid specialized pro-resolving mediators (SPM) are essential for maintaining tissue homeostasis including the conjunctiva. The protein Annexin A1 (AnxA1) can act as an SPM. We used cultured rat conjunctival goblet cells to determine if AnxA1 stimulates an increase in intracellular [Ca²⁺] ([Ca²⁺]_i) and mucin secretion and to identify the signaling pathways. The increase in [Ca²⁺]_i was determined using fura2/AM and mucin secretion was measured using an enzyme-linked lectin assay. AnxA1 stimulated an increase in [Ca²⁺]_i and mucin secretion that was blocked by the cell-permeant Ca²⁺ chelator BAPTA/AM and the ALX/FPR2 receptor inhibitor BOC2. AnxA1 increased [Ca²⁺]_i to a similar extent as the SPMs lipoxin A₄ and Resolvin (Rv) D1 and histamine. The AnxA1 increase in [Ca²⁺]_i and mucin secretion were inhibited by blocking the phospholipase C (PLC) pathway including PLC, the IP₃ receptor, the Ca²⁺/ATPase that causes the intracellular Ca²⁺ stores to empty, and blockade of Ca²⁺ influx. Inhibition of protein kinase C (PKC) and Ca²⁺/calmodulin-dependent protein kinase also decreased the AnxA1-stimulated increase in [Ca²⁺]_i and mucin secretion. In contrast inhibitors of ERK 1/2, phospholipase A₂ (PLA₂), and phospholipase D (PLD) did not alter AnxA1-stimulated increase in [Ca²⁺]_i, but did inhibit mucin secretion. Activation of protein kinase A did not decrease either the AnxA1-stimulated rise in [Ca²⁺]_i or secretion. We conclude that in health, AnxA1 contributes to the mucin layer of the tear film and ocular surface homeostasis by activating the PLC signaling pathway to increase [Ca²⁺]_i and stimulate mucin secretion and ERK1/2, PLA₂, and PLD to stimulate mucin secretion from conjunctival goblet cells.

The Role of Formyl Peptide Receptors in Permanent and Low-Grade Inflammation: Helicobacter pylori Infection as a Model

Formyl peptide receptors (FPRs) are cell surface pattern recognition receptors (PRRs), belonging to the chemoattractant G protein-coupled receptors (GPCRs) family. They play a key role in the innate immune system, regulating both the initiation and the resolution of the inflammatory response. FPRs were originally identified as receptors with high binding affinity for bacteria or mitochondria N-formylated peptides. However, they can also bind a variety of structurally different ligands. Among FPRs, formyl peptide receptor-like 1 (FPRL1) is the most versatile, recognizing N-formyl peptides, non-formylated peptides, and synthetic molecules. In addition, according to the ligand nature, FPRL1 can mediate either pro- or anti-inflammatory responses. Hp(2-20), a Helicobacter pylori-derived, non-formylated peptide, is a potent FPRL1 agonist, participating in Helicobacter pylori-induced gastric inflammation, thus contributing to the related site or not-site specific diseases. The aim of this review is to provide insights into the role of FPRs in H. pylori-associated chronic inflammation, which suggests this receptor as potential target to mitigate both microbial and sterile inflammatory diseases.

Regulation of Inflammation and Oxidative Stress by Formyl Peptide Receptors in Cardiovascular Disease Progression

G protein-coupled receptors (GPCRs) are the most important regulators of cardiac function and are commonly targeted for medical therapeutics. Formyl-Peptide Receptors (FPRs) are members of the GPCR superfamily and play an emerging role in cardiovascular pathologies. FPRs can modulate oxidative stress through nicotinamide adenine dinucleotide phosphate (NADPH) oxidase-dependent reactive oxygen species (ROS) production whose dysregulation has been observed in different cardiovascular diseases. Therefore, many studies are focused on identifying molecular mechanisms of the regulation of ROS production. FPR1, FPR2 and FPR3 belong to the FPRs family and their stimulation triggers phosphorylation of intracellular signaling molecules and nonsignaling proteins that are required for NADPH oxidase activation. Some FPR agonists trigger inflammatory processes, while other ligands activate proresolving or anti-inflammatory pathways, depending on the nature of the ligands. In general, bacterial and mitochondrial formylated peptides activate a proinflammatory cell response through FPR1, while Annexin A1 and Lipoxin A4 are anti-inflammatory FPR2 ligands. FPR2 can also trigger a proinflammatory pathway and the switch between FPR2-mediated pro- and anti-inflammatory cell responses depends on conformational changes of the receptor upon ligand binding. Here we describe the detrimental or beneficial effects of the main FPR agonists and their potential role as new therapeutic and diagnostic targets in the progression of cardiovascular diseases.

Identification of FPR3 as a Unique Biomarker for Targeted Therapy in the Immune Microenvironment of Breast Cancer

Although research into immunotherapy is growing, its use in the treatment of breast cancer remains limited. Thus, identification and evaluation of prognostic biomarkers of tissue microenvironments will reveal new immune-based therapeutic strategies for breast cancer. Using an in silico bioinformatic approach, we investigated the tumor microenvironmental and genetic factors related to breast cancer. We calculated the Immune score, Stromal score, Estimate score, Tumor purity, TMB (Tumor mutation burden), and MATH (Mutant-allele tumor heterogeneity) of Breast cancer patients from the Cancer Genome Atlas (TCGA) using the ESTIMATE algorithm and Maftools. Significant correlations between Immune/Stromal scores with breast cancer subtypes and tumor stages were established. Importantly, we found that the Immune score, but not the Stromal score, was significantly related to the patient's prognosis. Weighted correlation network analysis (WGCNA) identified a pattern of gene function associated with Immune score, and that almost all of these genes (388 genes) are significantly upregulated in the higher Immune score group. Protein-protein interaction (PPI) network analysis revealed the enrichment of immune checkpoint genes, predicting a good prognosis for breast cancer. Among all the upregulated genes, FPR3, a G protein-coupled receptor essential for neutrophil activation, is the sole factor that predicts poor prognosis. Gene set enrichment analysis analysis showed FRP3 upregulation synergizes with the activation of many pathways involved in carcinogenesis. In summary, this study identified FPR3 as a key immune-related biomarker predicting a poor prognosis for breast cancer, revealing it as a promising intervention target for immunotherapy.

Club Cell Protein 16 Attenuates CD16brightCD62dim Immunosuppressive Neutrophils in Damaged Tissue upon Posttraumatic Sepsis-Induced Lung Injury

Background

Recently, identification of immunosuppressive polymorphonuclear leukocytes (PMNL) that were traditionally described as proinflammatory cells emerged in the field of posttraumatic immunity. To understand their local and remote distribution after trauma, PMNL-subsets and the impact of immunomodulatory Club Cell protein (CC)16 that correlates with pulmonary complications were assessed.

Methods

C57BL/6N mice were divided into three groups, receiving isolated blunt chest trauma (TxT), undergoing TxT followed by cecal ligation and puncture (CLP, TxT + CLP) after 24 h, or sham undergoing analgosedation (n = 18/group). Further, each group was subdivided into three groups receiving either no treatment (ctrl) or intratracheal neutralization of CC16 by application of anti-CC16-antibody or application of an unspecific IgG control antibody (n = 6/group). Treatment was set at the time point after TxT. Analyses followed 6 h post-CLP. PMNL were characterized via expression of CD11b, CD16, CD45, CD62L, and Ly6G by flow cytometry in bone marrow (BM), blood, spleen, lung, liver, and bronchoalveolar and peritoneal lavage fluid (BALF and PL). Apoptosis was assessed by activated (cleaved) caspase-3. Results from untreated ctrl and IgG-treated mice were statistically comparable between all corresponding sham, TxT, and TxT + CLP groups.

Results

Immature (CD16^dimCD62L^bright) PMNL increased significantly in BM, circulation, and spleen after TxT vs. sham and were significantly attenuated in the lungs, BALF, PL, and liver. Classical-shaped (CD16^brightCD62L^bright) PMNL increased after TxT vs. sham in peripheral tissue and were significantly attenuated in circulation, proposing a trauma-induced migration of mature or peripheral differentiation of circulating immature PMNL. Immunosuppressive (CD16^brightCD62L^dim) PMNL decreased significantly in the lungs and spleen, while they systemically increased after TxT vs. sham. CLP in the TxT + CLP group reduced immunosuppressive PMNL in PL and increased their circulatory rate vs. isolated TxT, showing local reduction in affected tissue and their increase in nonaffected tissue. CC16 neutralization enhanced the fraction of immunosuppressive PMNL following TxT vs. sham and decreased caspase-3 in the lungs post-CLP in the TxT + CLP group, while apoptotic cells in the liver diminished post-TxT. Posttraumatic CC16 neutralization promotes the subset of immunosuppressive PMNL and antagonizes their posttraumatic distribution.

Conclusion

Since CC16 affects both the distribution of PMNL subsets and apoptosis in tissues after trauma, it may constitute as a novel target to beneficially shape the posttraumatic tissue microenvironment and homeostasis to improving outcomes.

Pro-Resolving FPR2 Agonists Regulate NADPH Oxidase-Dependent Phosphorylation of HSP27, OSR1, and MARCKS and Activation of the Respective Upstream Kinases

Background: Formyl peptide receptor 2 (FPR2) is involved in the pathogenesis of chronic inflammatory diseases, being activated either by pro-resolving or proinflammatory ligands. FPR2-associated signal transduction pathways result in phosphorylation of several proteins and in NADPH oxidase activation. We, herein, investigated molecular mechanisms underlying phosphorylation of heat shock protein 27 (HSP27), oxidative stress responsive kinase 1 (OSR1), and myristolated alanine-rich C-kinase substrate (MARCKS) elicited by the pro-resolving FPR2 agonists WKYMVm and annexin A1 (ANXA1). Methods: CaLu-6 cells or p22phox^Crispr/Cas9 double nickase CaLu-6 cells were incubated for 5 min with WKYMVm or ANXA1, in the presence or absence of NADPH oxidase inhibitors. Phosphorylation at specific serine residues of HSP27, OSR1, and MARCKS, as well as the respective upstream kinases activated by FPR2 stimulation was analysed. Results: Blockade of NADPH oxidase functions prevents WKYMVm- and ANXA1-induced HSP-27(Ser82), OSR1(Ser339) and MARCKS(Ser170) phosphorylation. Moreover, NADPH oxidase inhibitors prevent WKYMVm- and ANXA1-dependent activation of p38MAPK, PI3K and PKCδ, the kinases upstream to HSP-27, OSR1 and MARCKS, respectively. The same results were obtained in p22phox^Crispr/Cas9 cells. Conclusions: FPR2 shows an immunomodulatory role by regulating proinflammatory and anti-inflammatory activities and NADPH oxidase is a key regulator of inflammatory pathways. The activation of NADPH oxidase-dependent pro-resolving downstream signals suggests that FPR2 signalling and NADPH oxidase could represent novel targets for inflammation therapeutic intervention.

N-Formylated Peptide Induces Increased Expression of Both Formyl Peptide Receptor 2 (Fpr2) and Toll-Like Receptor 9 (TLR9) in Schwannoma Cells-An In Vitro Model for Early Inflammatory Profiling of Schwann Cells

Following nerve injury, disintegrated axonal mitochondria distal to the injury site release mitochondrial formylated peptides and DNA that can induce activation and inflammatory profiling of Schwann cells via formyl peptide receptor 2 (Fpr2) and toll-like receptor 9 (TLR9), respectively. We studied RT4 schwannoma cells to investigate the regulation of Fpr2 and TLR9 after stimulation with fMLF as a prototypical formylated peptide. RT4 cells were treated with fMLF at various concentrations and times with and without pretreatment with inhibitors (chloroquine for activated TLR9, PBP10 for Fpr2). Western blots of Fpr2, TLR9, p-p38, p-NFκB, and IL-6 were compared in relation to inflammatory profiling of RT4 cells and chemokine receptors (CCR2, CXCR4) as potential co-receptors of Fpr2. fMLF stimulation upregulated Fpr2 in RT4 cells at low concentrations (10 nM and 100 nM) but higher concentrations were required (10 µM and 50 µM) when the cells were pretreated with an activated TLR9 inhibitor. Moreover, the higher concentrations of fMLF could modulate TLR9 and inflammatory markers. Upregulation of Fpr2 triggered by 10 nM and 100 nM fMLF coincided with higher levels of chemokine receptors (CCR2, CXCR4) and PKCβ. Treating RT4 cells with fMLF, as an in vitro model of Schwann cells, uncovered Schwann cells’ complex responses to molecular patterns of release from injured axonal mitochondria.

The G-Protein Coupled Formyl Peptide Receptors and Their Role in the Progression of Digestive Tract Cancer

Chronic inflammation is a causative factor of many cancers, although it originally acts as a protective host response to the loss of tissue homeostasis. Many inflammatory conditions predispose susceptible cells, most of which are of epithelial origin, to neoplastic transformation. There is a close correlation between digestive tract (DT) cancer and chronic inflammation, such as esophageal adenocarcinoma associated with Barrett’s esophagus, helicobacter pylori infection as the cause of stomach cancer, hepatitis leading to liver cirrhosis and subsequent cancer, and colon cancer linking to inflammatory bowel diseases and schistosomiasis. A prominent feature of malignant transformation of DT tract epithelial cells is their adoption of somatic gene mutations resulting in abnormal expression of proteins that endow the cells with unlimited proliferation as well as increased motility and invasive capabilities. Many of these events are mediated by Gi-protein coupled chemoattractant receptors (GPCRs) including formyl peptide receptors (FPRs in human, Fprs in mice). In this article, we review the current understanding of FPRs (Fprs) and their function in DT cancer types as well as their potential as therapeutic targets.

The formyl peptide receptor agonist Ac2-26 alleviates neuroinflammation in a mouse model of pneumococcal meningitis

Background

Bacterial meningitis is still a cause of severe neurological disability. The brain is protected from penetrating pathogens by the blood-brain barrier and the innate immune system. The invading pathogens are recognized by pattern recognition receptors including the G-protein-coupled formyl peptide receptors (FPRs), which are expressed by immune cells of the central nervous system. FPRs show a broad spectrum of ligands, including pro- and anti-inflammatory ones. Here, we investigated the effects of the annexin A1 mimetic peptide Ac2-26 in a mouse model of pneumococcal meningitis.

Methods

Wildtype (WT) and Fpr1- and Fpr2-deficient mice were intrathecally infected with Streptococcus pneumoniae D39 (type 2). Subsequently, the different mice groups were treated by intraperitoneal injections of Ac2-26 (1 mg/kg body weight) 2, 8, and 24 h post-infection. The extent of inflammation was analyzed in various brain regions by means of immunohistochemistry and real-time reverse transcription polymerase chain reaction (RT-PCR) 30 h post-infection.

Results

Ac2-26-treated WT mice showed less severe neutrophil infiltration, paralleled by a reduced induction of pro-inflammatory glial cell responses in the hippocampal formation and cortex. While meningitis was ameliorated in Ac2-26-treated Fpr1-deficient mice, this protective effect was not observed in Fpr2-deficient mice. Irrespective of Ac2-26 treatment, inflammation was more severe in Fpr2-deficient compared to Fpr1-deficient mice.

Conclusions

In summary, this study demonstrates anti-inflammatory properties of Ac2-26 in a model of bacterial meningitis, which are mediated via FPR2, but not FPR1. Ac2-26 and other FPR2 modulators might be promising targets for the development of novel therapies for Streptococcus pneumoniae-induced meningitis.

WKYMVm ameliorates acute lung injury via neutrophil antimicrobial peptide derived STAT1/IRF1 pathway

Formyl peptide receptors (FPRs) are mainly expressed on leucocytes and sense microbe-associated molecular pattern (MAMP) molecules, thereby regulating leukocyte chemotaxis and activation. The formyl peptide receptor 2 (FPR2) selective agonist WKYMVm (Trp-Lys-Met-Val-D-Met) has shown potent pro-angiogenic, anti-inflammatory, and anti-apoptotic properties. In this study, we investigated whether WKYMVm exhibits bactericidal activity during neutrophil accumulation in acute lung injury (ALI) in mice and determined its cellular signaling pathways in HL-60 neutrophil-like cells. A daily intraperitoneal treatment of ALI mice with WKYMVm (2.5- and 5 mg/kg/d) daily over four days decreased the levels of proinflammatory cytokines TNF-α, IL-6, and IL-1β, while it increased the MPO and NO release by differentiated HL-60 neutrophil-like cells. The IRF1 level and STAT1 phosphorylation at S727 were increased in the lungs of mice with ALI treated with WKYMVm. Lung histology induced by ALI was unaffected by treatment with WKYMVm. In vitro, WKYMVm increased MPO, NO, and SOD activity, as well as IRF1 and STAT1 phosphorylation at Ser727. Taken together, our data suggest therapeutic potential of WKYMVm, via FPR2-dependent regulation of STAT1/IRF1, in ALI.

Changes of lipoxin levels during pregnancy and the monthly-cycle, condition the normal course of pregnancy or pathology

OBJECTIVE AND DESIGN

The purpose of the review was to gather information on the role and possibilities of using lipoxin in the treatment of infertility and maintaining a normal pregnancy. Ovulation, menstruation, embryo implantation, and childbirth are reactions representing short-term inflammatory events involving lipoxin activities. Lipoxin A4 (LXA4) is an arachidonic acid metabolite, and in cooperation with its positional isomer lipoxin B4 (LXB4), it is a major lipoxin in mammals. Biosynthesis process occurs in two stages: in the first step, the donor cell releases the eicosanoid intermediate; secondarily, the acceptor cell gets and converts the intermediate product into LXA4 (leukocyte/platelet interaction).

RESULTS

Generating lipoxin synthesis may also be triggered by salicylic acid, which acetylates cyclooxygenase-2. Lipoxin A4 and its analogues are considered as specialized pro-resolving mediators. LXA4 is an important component for a proper menstrual cycle, embryo implantation, pregnancy, and delivery. Its level in the luteal phase is high, while in the follicular phase, it decreases, which coincides with an increase in estradiol concentration with which it competes for the receptor. LXA4 inhibits the progression of endometriosis. However, during the peri-implantation period, before pregnancy is confirmed clinically, high levels of LXA4 can contribute to early pregnancy loss and may cause miscarriage. After implantation, insufficient LXA4 levels contribute to incorrect maternal vessel remodeling; decreased, shallow trophoblastic invasion; and the immuno-energetic abnormality of the placenta, which negatively affects fetal growth and the maintenance of pregnancy. Moreover, the level of LXA4 increases in the final stages of pregnancy, allowing vessel remodeling and placental separation.

METHODS

The review evaluates the literature published in the PubMed and Embase database up to 31 December 2019. The passwords were checked on terms: lipoxin and pregnancy with combined endometriosis, menstrual cycle, implantation, pre-eclampsia, fetal growth restriction, and preterm labor.

CONCLUSIONS

Although no human studies have been performed so far, the cell and animal model study results suggest that LXA4 will be used in obstetrics and gynecology soon.

Resolvin D1 and D2 inhibit tumour growth and inflammation via modulating macrophage polarization

Plastic polarization of macrophage is involved in tumorigenesis. M1-polarized macrophage mediates rapid inflammation, entity clearance and may also cause inflammation-induced mutagenesis. M2-polarized macrophage inhibits rapid inflammation but can promote tumour aggravation. ω-3 long-chain polyunsaturated fatty acid (PUFA)-derived metabolites show a strong anti-inflammatory effect because they can skew macrophage polarization from M1 to M2. However, their role in tumour promotive M2 macrophage is still unknown. Resolvin D1 and D2 (RvD1 and RvD2) are docosahexaenoic acid (DHA)-derived docosanoids converted by 15-lipoxygenase then 5-lipoxygenase successively. We found that although dietary DHA can inhibit prostate cancer in vivo, neither DHA (10 μmol/L) nor RvD (100 nmol/L) can directly inhibit the proliferation of prostate cancer cells in vitro. Unexpectedly, in a cancer cell-macrophage co-culture system, both DHA and RvD significantly inhibited cancer cell proliferation. RvD1 and RvD2 inhibited tumour-associated macrophage (TAM or M2d) polarization. Meanwhile, RvD1 and RvD2 also exhibited anti-inflammatory effects by inhibiting LPS-interferon (IFN)-γ-induced M1 polarization as well as promoting interleukin-4 (IL-4)-mediated M2a polarization. These differential polarization processes were mediated, at least in part, by protein kinase A. These results suggest that regulation of macrophage polarization using RvDs may be a potential therapeutic approach in the management of prostate cancer.

Phosphorylation Sites in Protein Kinases and Phosphatases Regulated by Formyl Peptide Receptor 2 Signaling

FPR1, FPR2, and FPR3 are members of Formyl Peptides Receptors (FPRs) family belonging to the GPCR superfamily. FPR2 is a low affinity receptor for formyl peptides and it is considered the most promiscuous member of this family. Intracellular signaling cascades triggered by FPRs include the activation of different protein kinases and phosphatase, as well as tyrosine kinase receptors transactivation. Protein kinases and phosphatases act coordinately and any impairment of their activation or regulation represents one of the most common causes of several human diseases. Several phospho-sites has been identified in protein kinases and phosphatases, whose role may be to expand the repertoire of molecular mechanisms of regulation or may be necessary for fine-tuning of switch properties. We previously performed a phospho-proteomic analysis in FPR2-stimulated cells that revealed, among other things, not yet identified phospho-sites on six protein kinases and one protein phosphatase. Herein, we discuss on the selective phosphorylation of Serine/Threonine-protein kinase N2, Serine/Threonine-protein kinase PRP4 homolog, Serine/Threonine-protein kinase MARK2, Serine/Threonine-protein kinase PAK4, Serine/Threonine-protein kinase 10, Dual specificity mitogen-activated protein kinase kinase 2, and Protein phosphatase 1 regulatory subunit 14A, triggered by FPR2 stimulation. We also describe the putative FPR2-dependent signaling cascades upstream to these specific phospho-sites.

Discovery of BMS-986235/LAR-1219: A Potent Formyl Peptide Receptor 2 (FPR2) Selective Agonist for the Prevention of Heart Failure

Formyl peptide receptor 2 (FPR2) agonists can stimulate resolution of inflammation and may have utility for treatment of diseases caused by chronic inflammation, including heart failure. We report the discovery of a potent and selective FPR2 agonist and its evaluation in a mouse heart failure model. A simple linear urea with moderate agonist activity served as the starting point for optimization. Introduction of a pyrrolidinone core accessed a rigid conformation that produced potent FPR2 and FPR1 agonists. Optimization of lactam substituents led to the discovery of the FPR2 selective agonist 13c, BMS-986235/LAR-1219. In cellular assays 13c inhibited neutrophil chemotaxis and stimulated macrophage phagocytosis, key end points to promote resolution of inflammation. Cardiac structure and functional improvements were observed in a mouse heart failure model following treatment with BMS-986235/LAR-1219.

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 Aβ1-42 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 Aβ1-42 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.

Decreased Placental FPR2 in Early Pregnancies That Later Developed Small-For-Gestation Age: A Potential Role of FPR2 in the Regulation of Epithelial-Mesenchymal Transition

We reported earlier that an anti-inflammatory small peptide receptor-formyl peptide receptor-2 (FPR2) was significantly decreased in placentas from third trimester pregnancies complicated with fetal growth restriction (FGR), compared to placentas from uncomplicated control pregnancies, suggesting FPR2 may play a role in the development of FGR. The aim of this study is to investigate whether the actions of FPR2 alters placental growth process in humans. Accordingly, using small-for-gestation age (SGA) as a proxy for FGR, we hypothesize that FPR2 expression is decreased in first-trimester placentas of women who later manifest FGR, and contributes to aberrant trophoblast function and the development of FGR. Chorionic villus sampling (CVS) tissues were collected at 10–12 weeks gestation in 70 patients with singleton fetuses; surplus tissue was used. Real-time PCR and immunoassays were performed to quantitate FPR2 gene and protein expression. Silencing of FPR2 was performed in two independent, trophoblast-derived cell lines, HTR-8/SVneo and JEG-3 to investigate the functional consequences of FPR2 gene downregulation. FPR2 mRNA relative to 18S rRNA was significantly decreased in placentae from SGA-pregnancies (n = 28) compared with controls (n = 52) (p < 0.0001). Placental FPR2 protein was significantly decreased in SGA compared with control (n = 10 in each group, p < 0.05). Proliferative, migratory and invasive potential of the human placental-derived cell lines, HTR-8/SVneo and JEG-3 were significantly reduced in siFPR2 treated cells compared with siCONT control groups. Down-stream signaling molecules, STAT5B and SOCS3 were identified as target genes of FPR2 action in the trophoblast-derived cell lines and in SGA and control chorionic villous tissues. FPR2 is a novel regulator of key molecular pathways and functions in placental development, and its decreased expression in women destined to develop FGR reinforces a placental origin of SGA/FGR, and that it contributes to causing the development of SGA/FGR.

Structural basis of ligand binding modes at the human formyl peptide receptor 2

The human formyl peptide receptor 2 (FPR2) plays a crucial role in host defense and inflammation, and has been considered as a drug target for chronic inflammatory diseases. A variety of peptides with different structures and origins have been characterized as FPR2 ligands. However, the ligand-binding modes of FPR2 remain elusive, thereby limiting the development of potential drugs. Here we report the crystal structure of FPR2 bound to the potent peptide agonist WKYMVm at 2.8 Å resolution. The structure adopts an active conformation and exhibits a deep ligand-binding pocket. Combined with mutagenesis, ligand binding and signaling studies, key interactions between the agonist and FPR2 that govern ligand recognition and receptor activation are identified. Furthermore, molecular docking and functional assays reveal key factors that may define binding affinity and agonist potency of formyl peptides. These findings deepen our understanding about ligand recognition and selectivity mechanisms of the formyl peptide receptor family.

Formyl peptide receptors (FPRs) are GPCRs that play important roles in transducing chemotactic signals in phagocytes and mediating host-defense and inflammatory responses. Here the authors present the 2.8 Å crystal structure of human FPR2 in complex with the peptide agonist WKYMVm and in combination with molecular docking, ligand-binding and signalling assays provide further insights into the binding modes of FPR2 to both non-formyl and formyl peptides.

Formyl peptide receptor 2 orchestrates mucosal protection against Citrobacter rodentium infection

Citrobacter rodentium is an attaching and effacing intestinal murine pathogen which shares similar virulence strategies with the human pathogens enteropathogenic- and enterohemorrhagic Escherichia coli to infect their host. C. rodentium is spontaneously cleared by healthy wild-type (WT) mice whereas mice lacking Muc2 or specific immune regulatory genes demonstrate an impaired ability to combat the pathogen. Here we demonstrate that apical formyl peptide receptor 2 (Fpr2) expression increases in colonic epithelial cells during C. rodentium infection. Using a conventional inoculum dose of C. rodentium, both WT and Fpr2^−/− mice were infected and displayed similar signs of disease, although Fpr2^−/− mice recovered more slowly than WT mice. However, Fpr2^−/− mice exhibited increased susceptibility to C. rodentium colonization in response to low dose infection: 100% of the Fpr2^−/− and 30% of the WT mice became colonized and Fpr2^−/− mice developed more severe colitis and more C. rodentium were in contact with the colonic epithelial cells. In line with the larger amount of C. rodentium detected in the spleen in Fpr2^−/− mice, more C. rodentium and enteropathogenic Escherichia coli translocated across an in vitro mucosal surface to the basolateral compartment following FPR2 inhibitor treatment. Fpr2^−/− mice also lacked the striated inner mucus layer that was present in WT mice. Fpr2^−/− mice had decreased mucus production and different mucin O-glycosylation in the colon compared to WT mice, which may contribute to their defect inner mucus layer. Thus, Fpr2 contributes to protection against infection and influence mucus production, secretion and organization.

Formyl Peptide Receptor 2 Deficiency Improves Cognition and Attenuates Tau Hyperphosphorylation and Astrogliosis in a Mouse Model of Alzheimer's Disease

Alzheimer's disease (AD) is characterized by progressive loss of memory and other cognitive functions. Accumulation of amyloid-β (Aβ) and hyperphosphorylated tau are two major neuropathological features of AD. Formyl peptide receptor 2 (FPR2), contributing to innate immunity and inflammation, has been implicated in the uptake and clearance of Aβ. It remains unclear whether FPR2 affects cognition and tau phosphorylation. The effects of FPR2 in cognition and tau phosphorylation were examined using FPR2 knock-out (Fpr2-/-) mice receiving intracerebroventricular (ICV) injection of streptozotocin (STZ). The general behaviors and cognitive functions were evaluated using rotarod, open field test, and Morris water maze test. The alteration in tau hyperphosphorylation and activation of astrocytes were determined by using western blotting and/or immunofluorescence staining. ICV injection of STZ impaired spatial learning and memory of mice in Morris water maze. FPR2 deficiency improved spatial learning and memory of ICV-STZ mice. In the hippocampus and cortex of ICV-STZ mice, a marked increase was observed in tau phosphorylation at Ser199, Thr205, and Ser396 compared with ICV-saline control mice. However, FPR2 deficiency attenuated the hyperphosphorylation of tau at Ser199 and Ser396. In addition, the expression of GFAP was significantly increased in hippocampus and cortex of ICV-STZ mice. FPR2 deletion reduced the increase of GFAP expression induced by ICV injection of STZ. These results indicate that FPR2 deficiency is associate with improved cognition, reduced tau hyperphosphorylation, and activation of astrocytes in the mouse AD model tested. FPR2 may be a potential target in AD prevention and therapy.

Structure of formylpeptide receptor 2-Gi complex reveals insights into ligand recognition and signaling

Formylpeptide receptors (FPRs) as G protein-coupled receptors (GPCRs) can recognize formylpeptides derived from pathogens or host cells to function in host defense and cell clearance. In addition, FPRs, especially FPR2, can also recognize other ligands with a large chemical diversity generated at different stages of inflammation to either promote or resolve inflammation in order to maintain a balanced inflammatory response. The mechanism underlying promiscuous ligand recognition and activation of FPRs is not clear. Here we report a cryo-EM structure of FPR2-Gi signaling complex with a peptide agonist. The structure reveals a widely open extracellular region with an amphiphilic environment for ligand binding. Together with computational docking and simulation, the structure suggests a molecular basis for the recognition of formylpeptides and a potential mechanism of receptor activation, and reveals conserved and divergent features in Gi coupling. Our results provide a basis for understanding the molecular mechanism of the functional promiscuity of FPRs.

Inhibition of IRF4 in dendritic cells by PRR-independent and -dependent signals inhibit Th2 and promote Th17 responses

Cyclic AMP (cAMP) is involved in many biological processes but little is known regarding its role in shaping immunity. Here we show that cAMP-PKA-CREB signaling (a pattern recognition receptor [PRR]-independent mechanism) regulates conventional type-2 Dendritic Cells (cDC2s) in mice and reprograms their Th17-inducing properties via repression of IRF4 and KLF4, transcription factors essential for cDC2-mediated Th2 induction. In mice, genetic loss of IRF4 phenocopies the effects of cAMP on Th17 induction and restoration of IRF4 prevents the cAMP effect. Moreover, curdlan, a PRR-dependent microbial product, activates CREB and represses IRF4 and KLF4, resulting in a pro-Th17 phenotype of cDC2s. These in vitro and in vivo results define a novel signaling pathway by which cDC2s display plasticity and provide a new molecular basis for the classification of novel cDC2 and cDC17 subsets. The findings also reveal that repressing IRF4 and KLF4 pathway can be harnessed for immuno-regulation.

Fair-Weather Friends: Evidence of Lipoxin Dysregulation in Neurodegeneration

Lipoxins (LXs) are autacoids, specialized proresolving lipid mediators (SPMs) acting locally in a paracrine or autocrine fashion. They belong to a complex superfamily of dietary small polyunsaturated fatty acid (PUFA)-metabolites, which direct potent cellular responses to resolve inflammation and restore tissue homeostasis. Together, these SPM activities have been intensely studied in systemic inflammation and acute injury or infection, but less is known about LX signaling and activities in the central nervous system. LXs are derived from arachidonic acid, an omega-6 PUFA. In addition to well-established roles in systemic inflammation resolution, they have increasingly become implicated in regulating neuroinflammatory and neurodegenerative processes. In particular, chronic inflammation plays a central role in Alzheimer's disease (AD) etiology, and dysregulated LX production and activities have been reported in a variety of AD rodent models and clinical tissue samples, yet with complex and sometimes conflicting results. In addition, reduced LX production following retinal injury has been reported recently by the authors, and an intriguing direct neuronal activity promoting survival and homeostasis in retinal and cortical neurons is demonstrated. Here, the authors review and clarify this growing literature and suggest new research directions to further elaborate the role of lipoxins in neurodegeneration.

NOX2-Dependent Reactive Oxygen Species Regulate Formyl-Peptide Receptor 1-Mediated TrkA Transactivation in SH-SY5Y Cells

Several enzymes are capable of producing reactive oxygen species (ROS), but only NADPH oxidases (NOX) generate ROS as their primary and sole function. In the central nervous system, NOX2 is the major source of ROS, which play important roles in signalling and functions. NOX2 activation requires p47^phox phosphorylation and membrane translocation of cytosolic subunits. We demonstrate that SH-SY5Y cells express p47^phox and that the stimulation of Formyl-Peptide Receptor 1 (FPR1) by N-fMLP induces p47^phox phosphorylation and NOX-dependent superoxide generation. FPR1 is a member of the G protein-coupled receptor (GPCR) family and is able to transphosphorylate several tyrosine kinase receptors (RTKs). This mechanism requires ROS as signalling intermediates and is necessary to share information within the cell. We show that N-fMLP stimulation induces the phosphorylation of cytosolic Y490, Y751, and Y785 residues of the neurotrophin receptor TrkA. These phosphotyrosines provide docking sites for signalling molecules which, in turn, activate Ras/MAPK, PI3K/Akt, and PLC-γ1/PKC intracellular cascades. N-fMLP-induced ROS generation plays a critical role in FPR1-mediated TrkA transactivation. In fact, the blockade of NOX2 functions prevents Y490, Y751, and Y785 phosphorylation, as well as the triggering of downstream signalling cascades. Moreover, we observed that FPR1 stimulation by N-fMLP also improves proliferation, cellular migration, and neurite outgrowth of SH-SY5Y cells.

Phosphoproteomic analysis sheds light on intracellular signaling cascades triggered by Formyl-Peptide Receptor 2

Formyl peptide receptors (FPRs) belong to the family of seven transmembrane Gi-protein coupled receptors (GPCR). FPR2 is considered the most promiscuous member of this family since it recognizes a wide variety of ligands. It plays a crucial role in several physio-pathological processes and different studies highlighted the correlation between its expression and the higher propensity to invasion and metastasis of some cancers. FPR2 stimulation by its synthetic agonist WKYMVm triggers multiple phosphorylations of intracellular signaling molecules, such as ERKs, PKC, PKB, p38MAPK, PI3K, PLC, and of non-signaling proteins, such as p47^phox and p67^phox which are involved in NADPH oxidase-dependent ROS generation. Biological effects of FPR2 stimulation include intracellular Ca²⁺ mobilization, cellular proliferation and migration, and wound healing. A systematic analysis of the phosphoproteome in FPR2-stimulated cells has not been yet reported. Herein, we describe a large-scale phosphoproteomic study in WKYMVm-stimulated CaLu-6 cells. By using high resolution MS/MS we identified 290 differentially phosphorylated proteins and 53 unique phosphopeptides mapping on 40 proteins. Phosphorylations on five selected phospho-proteins were further validated by western blotting, confirming their dependence on FPR2 stimulation. Interconnection between some of the signalling readout identified was also evaluated. Furthermore, we show that FPR2 stimulation with two anti-inflammatory agonists induces the phosphorylation of selected differentially phosphorylated proteins, suggesting their role in the resolution of inflammation. These data provide a promising resource for further studies on new signaling networks triggered by FPR2 and on novel molecular drug targets for human diseases.

Formyl Peptide Receptor 2 Activation Ameliorates Dermal Fibrosis and Inflammation in Bleomycin-Induced Scleroderma

Systemic sclerosis is a profibrotic autoimmune disease mediated by the dysregulation of extracellular matrix synthesis. Formyl peptide receptor 2 (Fpr2) is a G protein-coupled receptor that modulates inflammation and host defense by regulating the activation of inflammatory cells, such as macrophages. However, the role of Fpr2 in the development and therapy of scleroderma is still unclear. The present study was conducted to investigate the effects of Fpr2 activation in the treatment of scleroderma fibrosis. We found that intradermal administration of WKYMVm, an Fpr2-specific agonist, alleviated bleomycin-induced scleroderma fibrosis in mice and decreased dermal thickness in scleroderma skin. WKYMVm-treated scleroderma skin tissues displayed reduced numbers of myofibroblasts expressing α-smooth muscle actin, Vimentin, and phosphorylated SMAD3. WKYMVm treatment attenuated macrophage infiltration in scleroderma skin and reduced the number of M2 macrophages. The therapeutic effects of WKYMVm in scleroderma-associated fibrosis and inflammation were completely abrogated in Fpr2 knockout mice. Moreover, WKYMVm treatment reduced the serum levels of inflammatory cytokines, such as tumor necrosis factor-α, and interferon-γ, in the scleroderma model of wild-type mice but not in Fpr2 knockout mice. These results suggest that WKYMVm-induced activation of Fpr2 leads to alleviation of fibrosis by stimulating immune resolution in systemic sclerosis.

Inhibition of FPR2 impaired leukocytes recruitment and elicited non-resolving inflammation in acute heart failure

Lifestyle or age-related risk factors over-activate the inflammation that triggers acute heart failure (HF)-related mortality following myocardial infarction (MI). Post-MI activated leukocytes express formyl peptide receptor 2 (FPR2) that is essential for inflammation-resolution and in cardiac healing. However, the role of FPR2 in acute HF is incomplete and remain of interest. Here, we aimed to determine whether pharmacological inhibition of FPR2 perturb leukocyte trafficking in acute HF. Male C57BL/6 (8-12 weeks) mice were subjected to acute HF (MI-d1) using permanent coronary artery ligation that develops irreversible acute and chronic heart failure. FPR2 antagonist WRW4 (1 μg/kg/day) was subcutaneously injected 3 h post-MI maintaining saline-injected MI-controls. Leukocytes were quantitated using flow cytometry, and acute decompensated HF was confirmed using echocardiography and histology. FPR2 inhibition decreased the expression of FPR2 in the LV and spleen tissues. Administration of WRW4 inhibitor to mice primed immature and inactive neutrophils infiltration Ly6G^int and intensified the Ccl2 expression compared to MI-control in the infarcted LV post-MI. Leukocyte profiling revealed an overall decrease in monocytes (23.3 ± 2%) in WRW4-injected mice compared with MI-control (49.1 ± 2%) in infarcted LV. FPR2 inhibition increased F4/80⁺/Ly6C^hi pro-inflammatory macrophages (14.8 ± 2%) compared with MI-control (10 ± 1%) with increased transcripts of pro-inflammatory markers TNF-α and IL-1β, and decreased Arg-1 expression in the infarcted LV compared to MI-controls is suggestive of the impaired acute inflammatory response. Inhibition of FPR2 using WRW4 also disturbed splenocardiac leukocytes recruitment by priming immature neutrophils leading to the onset of incomplete resolution signaling in acute decompensated HF post-MI.

The formyl peptide receptor agonist FPRa14 induces differentiation of Neuro2a mouse neuroblastoma cells into multiple distinct morphologies which can be specifically inhibited with FPR antagonists and FPR knockdown using siRNA

The N-formyl peptide receptors (FPRs) have been identified within neuronal tissues and may serve as yet undetermined functions within the nervous system. The FPRs have been implicated in the progression and invasiveness of neuroblastoma and other cancers. In this study the effects of the synthetic FPR agonist FPRa14, FPR antagonists and FPR knockdown using siRNA on mouse neuroblastoma neuro2a (N2a) cell differentiation plus toxicity were examined. The FPRa14 (1-10μM) was found to induce a significant dose-dependent differentiation response in mouse neuroblastoma N2a cells. Interestingly, three distinct differentiated morphologies were observed, with two non-archetypal forms observed at the higher FPRa14 concentrations. These three forms were also observed in the human neuroblastoma cell-lines IMR-32 and SH-SY5Y when exposed to 100μM FPRa14. In N2a cells combined knockdown of FPR1 and FPR2 using siRNA inhibited the differentiation response to FPRa14, suggesting involvement of both receptor subtypes. Pre-incubating N2a cultures with the FPR1 antagonists Boc-MLF and cyclosporin H significantly reduced FPRa14-induced differentiation to near baseline levels. Meanwhile, the FPR2 antagonist WRW4 had no significant effect on FPRa14-induced N2a differentiation. These results suggest that the N2a differentiation response observed has an FPR1-dependent component. Toxicity of FPRa14 was only observed at higher concentrations. All three antagonists used blocked FPRa14-induced toxicity, whilst only siRNA knockdown of FPR2 reduced toxicity. This suggests that the toxicity and differentiation involve different mechanisms. The demonstration of neuronal differentiation mediated via FPRs in this study represents a significant finding and suggests a role for FPRs in the CNS. This finding could potentially lead to novel therapies for a range of neurological conditions including neuroblastoma, Alzheimer's disease, Parkinson's disease and neuropathic pain. Furthermore, this could represent a potential avenue for neuronal regeneration therapies.

Fpr2 Deficiency Alleviates Diet-Induced Insulin Resistance Through Reducing Body Weight Gain and Inhibiting Inflammation Mediated by Macrophage Chemotaxis and M1 Polarization

Obesity and related inflammation are critical for the pathogenesis of insulin resistance, but the underlying mechanisms are not fully understood. Formyl peptide receptor 2 (FPR2) plays important roles in host immune responses and inflammation-related diseases. We found that Fpr2 expression was elevated in the white adipose tissue of high-fat diet (HFD)-induced obese mice and db/db mice. The systemic deletion of Fpr2 alleviated HFD-induced obesity, insulin resistance, hyperglycemia, hyperlipidemia, and hepatic steatosis. Furthermore, Fpr2 deletion in HFD-fed mice elevated body temperature, reduced fat mass, and inhibited inflammation by reducing macrophage infiltration and M1 polarization in metabolic tissues. Bone marrow transplantations between wild-type and Fpr2^-/- mice and myeloid-specific Fpr2 deletion demonstrated that Fpr2-expressing myeloid cells exacerbated HFD-induced obesity, insulin resistance, glucose/lipid metabolic disturbances, and inflammation. Mechanistic studies revealed that Fpr2 deletion in HFD-fed mice enhanced energy expenditure probably through increasing thermogenesis in skeletal muscle; serum amyloid A3 and other factors secreted by adipocytes induced macrophage chemotaxis via Fpr2; and Fpr2 deletion suppressed macrophage chemotaxis and lipopolysaccharide-, palmitate-, and interferon-γ-induced macrophage M1 polarization through blocking their signals. Altogether, our studies demonstrate that myeloid Fpr2 plays critical roles in obesity and related metabolic disorders via regulating muscle energy expenditure, macrophage chemotaxis, and M1 polarization.

Annexin-A1: Therapeutic Potential in Microvascular Disease

Annexin-A1 (ANXA1) was first discovered in the early 1980's as a protein, which mediates (some of the) anti-inflammatory effects of glucocorticoids. Subsequently, the role of ANXA1 in inflammation has been extensively studied. The biology of ANXA1 is complex and it has many different roles in both health and disease. Its effects as a potent endogenous anti-inflammatory mediator are well-described in both acute and chronic inflammation and its role in activating the pro-resolution phase receptor, FPR2, has been described and is now being exploited for therapeutic benefit. In the present mini review, we will endeavor to give an overview of ANXA1 biology in relation to inflammation and functions that mediate pro-resolution that are independent of glucocorticoid induction. We will focus on the role of ANXA1 in diseases with a large inflammatory component focusing on diabetes and microvascular disease. Finally, we will explore the possibility of exploiting ANXA1 as a novel therapeutic target in diabetes and the treatment of microvascular disease.

Klebsiella pneumoniae ST258 Negatively Regulates the Oxidative Burst in Human Neutrophils

The epidemic clone of Klebsiella pneumoniae (Kpn), sequence type 258 (ST258), carbapenamase producer (KPC), commonly infects hospitalized patients that are left with scarce therapeutic option since carbapenems are last resort antibiotics for life-threatening bacterial infections. To improve prevention and treatment, we should better understand the biology of Kpn KPC ST258 infections. Our hypothesis was that Kpn KPC ST258 evade the first line of defense of innate immunity, the polymorphonuclear neutrophil (PMN), by decreasing its functional response. Therefore, our aim was to evaluate how the ST258 Kpn clone affects PMN responses, focusing on the respiratory burst, compared to another opportunistic pathogen, Escherichia coli (Eco). We found that Kpn KPC ST258 was unable to trigger bactericidal responses as reactive oxygen species (ROS) generation and NETosis, compared to the high induction observed with Eco, but both bacterial strains were similarly phagocytized and cause increases in cell size and CD11b expression. The absence of ROS induction was also observed with other Kpn ST258 strains negative for KPC. These results reflect certain selectivity in terms of the functions that are triggered in PMN by Kpn, which seems to evade specifically those responses critical for bacterial survival. In this sense, bactericidal mechanisms evasion was associated with a higher survival of Kpn KPC ST258 compared to Eco. To investigate the mechanisms and molecules involved in ROS inhibition, we used bacterial extracts (BE) and found that BE were able to inhibit ROS generation triggered by the well-known ROS inducer, fMLP. A sequence of experiments led us to elucidate that the polysaccharide part of LPS was responsible for this inhibition, whereas lipid A mediated the other responses that were not affected by bacteria, such as cell size increase and CD11b up-regulation. In conclusion, we unraveled a mechanism of immune evasion of Kpn KPC ST258, which may contribute to design more effective strategies for the treatment of these multi-resistant bacterial infections.

Dynamic changes and clinical significance of LXA4 in the perioperative period of cardiopulmonary bypass

Dynamic changes in lipoxin A₄ (LXA₄) in child patients with congenital heart disease (CHD), in the perioperative period of cardiopulmonary bypass (CPB) were studied. Peripheral blood was collected from 16 child patients (CPB group) before operation (Tc), after operation (T0), at 1 day after operation (T1), at 3 days after operation (T3), and at 7 days after operation (T7); and from 17 children with no CHD (control group). The level of LXA₄ in peripheral blood was detected via enzyme-linked immunosorbent assay (ELISA). Clinical data of the child patients were collected. The white blood cell (WBC) count, the proportion of neutrophils (N%) and high-sensitivity C-reactive protein (hs-CRP) levels were also detected, followed by statistical analysis. The plasma LXA₄ levels in CPB group at Tc were significantly lower compared to that in the control group (P<0.01). In CPB group, the level of LXA₄ showed an increasing trend at T0, WBC and hs-CRP were transiently increased at T0 and increased most significantly at T1. N% was obviously increased at T0 compared to that at Tc and was still significantly higher at T7 compared to that at Tc. The CPB time and aortic clamping time were positively correlated with the time in the Pediatric Intensive Care Unit (PICU), the application time of ventilator, and the hs-CRP level at T0. The LXA₄ level at each time-point had no correlation with other indexes. In conclusion, the inflammatory response after CPB increases the synthesis of LXA₄ with an anti-inflammatory effect, but LXA₄ cannot be used as a sensitive index for monitoring inflammation.

Formyl peptide receptor-2 is decreased in foetal growth restriction and contributes to placental dysfunction

STUDY QUESTION

What is the association between placental formyl peptide receptor 2 (FPR2) and trophoblast and endothelial functions in pregnancies affected by foetal growth restriction (FGR)?

SUMMARY ANSWER

Reduced FPR2 placental expression in idiopathic FGR results in significantly altered trophoblast differentiation and endothelial function in vitro.

WHAT IS KNOWN ALREADY

FGR is associated with placental insufficiency, where defective trophoblast and endothelial functions contribute to reduced feto-placental growth.

STUDY DESIGN, SIZE, DURATION

The expression of FPR2 in placental tissues from human pregnancies complicated with FGR was compared to that in gestation-matched uncomplicated control pregnancies (n = 25 from each group). Fpr2 expression was also determined in placental tissues obtained from a murine model of FGR (n = 4). The functional role of FPR2 in primary trophoblasts and endothelial cells in vitro was assessed in diverse assays in a time-dependent manner.

PARTICIPANTS/MATERIALS, SETTING, METHODS

Placentae from third-trimester pregnancies complicated by idiopathic FGR (n = 25) and those from gestation-matched pregnancies with appropriately grown infants as controls (n = 25) were collected at gestation 27-40 weeks. Placental tissues were also collected from a spontaneous CBA/CaH × DBA/2 J murine model of FGR. Placental FPR2/Fpr2 mRNA expression was determined by real-time PCR, while protein expression was examined by immunoblotting and immunohistochemistry. siRNA transfection was used to silence FPR2 expression in primary trophoblasts and in human umbilical vein endothelial cells (HUVEC), and the quantitation of cytokines, chemokines and apoptosis was performed following a cDNA array analyses. Functional effects of trophoblast differentiation were measured using HCGB/β-hCG and syncytin-2 expression as well as markers of apoptosis, tumour protein 53 (TP53), caspase 8, B cell lymphoma 2 (BCL2) and BCL associated X (BAX). Endothelial function was assessed by proliferation, network formation and permeability assays.

MAIN RESULTS AND THE ROLE OF CHANCE

Placental FPR2/Fpr2 expression was significantly decreased in FGR placentae (n = 25, P < 0.05) as well as in murine FGR placentae compared to controls (n = 4, P < 0.05). FPR2 siRNA (siFPR2) in term trophoblasts significantly increased differentiation markers, HCGB and syncytin-2; cytokines, interleukin (IL)-6, CXCL8; and apoptotic markers, TP53, caspase 8 and BAX, but significantly reduced the expression of the chemokines CXCL12 and its receptors CXCR4 and CXCR7; CXCL16 and its receptor, CXCR6; and cytokine, IL-10, compared with control siRNA (siCONT). Treatment of HUVECs with siFPR2 significantly reduced proliferation and endothelial tube formation, but significantly increased permeability of HUVECs.

LARGE SCALE DATA

N/A.

LIMITATIONS, REASONS FOR CAUTION

Reduced expression of placental FPR2/Fpr2 was observed in the third trimester at delivery after development of FGR, suggesting that FPR2 is associated with FGR pregnancies. However, there is a possibility that the decreased placental FPR2 observed in FGR may be a consequence rather than a cause of FGR, although our in vitro functional analyses using primary trophoblasts and endothelial cells suggest that FPR2 may have a direct or indirect regulatory role on trophoblast differentiation and endothelial function in FGR.

WIDER IMPLICATIONS OF THE FINDINGS

This is the first study linking placental FPR2 expression with changes in the trophoblast and endothelial functions that may explain the placental insufficiency observed in FGR.

STUDY FUNDING/COMPETING INTERESTS

P.M. and P.R.E. received funding from the Australian Institute of Musculoskeletal Science, Western Health, St. Albans, Victoria 3021, Australia. M.L. is supported by a Career Development Fellowship from the National Health and Medical Research Council (NHMRC; Grant no. 1047025). Monash Health is supported by the Victorian Government's Operational Infrastructure Support Programme. The authors declare that there is no conflict of interest in publishing this work.

Detrimental Role of miRNA-144-3p in Intracerebral Hemorrhage Induced Secondary Brain Injury is Mediated by Formyl Peptide Receptor 2 Downregulation Both In Vivo and In Vitro

Although microRNA-144-3p (miRNA-144-3p) has been shown to suppress tumor proliferation and invasion, its function in intracerebral hemorrhage (ICH)-induced secondary brain injury (SBI) remains unclear. Thus, this study was designed to investigate the role of miRNA-144-3p in ICH. To accomplish this, we used adult male Sprague-Dawley rats to establish an in vivo ICH model by injecting autologous blood, while cultured primary rat cortical neurons were exposed to oxyhemoglobin (OxyHb) to mimic ICH in vitro. To examine the role of miRNA-144-3p in ICH-induced SBI, we used an miRNA-144-3p mimic and inhibitor both in vivo and in vitro. Following ICH induction, we found miRNA-144-3p expression to increase. Additionally, we predicted the formyl peptide receptor 2 (FPR2) to be a potential miRNA-144-3p target, which we validated experimentally, with FPR2 expression downregulated when miRNA-144-3p was upregulated. Furthermore, elevated miRNA-144-3p levels aggravated brain edema and neurobehavioral disorders and induced neuronal apoptosis via the downregulation of FPR2 both in vivo and in vitro. We suspected that these beneficial effects provided by FPR2 were associated with the PI3K/AKT pathway. We validated this finding by overexpressing FPR2 while inhibiting PI3K/AKT in vitro and in vivo. In conclusion, miRNA-144-3p aggravated ICH-induced SBI by targeting and downregulating FPR2, thereby contributing to neurological dysfunction and neural apoptosis via PI3K/AKT pathway activation. These findings suggest that inhibiting miRNA-144-3p may offer an effective approach to attenuating brain damage incurred after ICH and a potential therapy to improve ICH-induced SBI.

A long-lived peptide-conjugated iridium(iii) complex as a luminescent probe and inhibitor of the cell migration mediator, formyl peptide receptor 2

Formyl peptide receptors play important biological and therapeutic roles in wound repair and inflammatory diseases. In this work, we present a luminescent iridium(iii) complex (6) conjugated with the peptide agonist WKYMVm as a luminescent formyl peptide receptor 2 (FPR2) imaging probe in living cells. Complex 6 displayed ideal cell imaging characteristics, high photostability and low cytotoxicity. Competition assays with a known FPR2 antagonist, WRW4, and siRNA knockdown experiments both revealed that complex 6 selectively targeted FPR2 in living HUVEC cells. Moreover, complex 6 regulated FPR2 signalling in HUVEC cells as shown using a mechanical scratch assay. Finally, complex 6 reduced epithelial cell migration capacity and inhibited lipoxin A4 (LXA4)-triggered cell migration in HUVEC cells, demonstrating the ability of this complex to inhibit FPR2 in living cells. To our knowledge, this is the first long-lived probe for imaging FPR2 in living cells.

Staphylococcal superantigen-like protein 13 activates neutrophils via formyl peptide receptor 2

Staphylococcal superantigen-like (SSL) proteins, one of the major virulence factor families produced by Staphylococcus aureus, were previously demonstrated to be immune evasion molecules that interfere with a variety of innate immune defences. However, in contrast to characterised SSLs, which inhibit immune functions, we show that SSL13 is a strong activator of neutrophils via the formyl peptide receptor 2 (FPR2). Moreover, our data show that SSL13 acts as a chemoattractant and induces degranulation and oxidative burst in neutrophils. As with many other staphylococcal immune evasion proteins, SSL13 shows a high degree of human specificity. SSL13 is not able to efficiently activate mouse neutrophils, hampering in vivo experiments. In conclusion, SSL13 is a neutrophil chemoattractant and activator that acts via FPR2. Therefore, SSL13 is a unique SSL member that does not belong to the immune evasion class but is a pathogen alarming molecule. Our study provides a new concept of SSLs; SSLs not only inhibit host immune processes but also recruit human neutrophils to the site of infection. This new insight allows us to better understand complex interactions between host and S. aureus pathological processes.

Pro-resolving lipid mediators: Agents of anti-ageing?

Inflammation is an essential response to injury and its timely and adequate resolution permits tissue repair and avoidance of chronic inflammation. Ageing is associated with increased inflammation, sub-optimal resolution and these act as drivers for a number of ageing-associated pathologies. We describe the role played by specialised proresolving lipid mediators (SPMs) in the resolution of inflammation and how insufficient levels of these mediators, or compromised responsiveness may play a role in the pathogenesis of many ageing-associated pathologies, e.g. Alzheimer's Disease, atherosclerosis, obesity, diabetes and kidney disease. Detailed examination of the resolution phase of inflammation highlights the potential to harness these lipid mediators and or mimetics of their bioactions, in particular, their synthetic analogues to promote effective resolution of inflammation, without compromising the host immune system.

Beyond sepsis: Staphylococcus epidermidis is an underestimated but significant contributor to neonatal morbidity

Staphylococcus epidermidis accounts for the majority of cases of neonatal sepsis. Moreover, it has been demonstrated to be associated with neonatal morbidities, such as bronchopulmonary dysplasia (BPD), white matter injury (WMI), necrotizing enterocolitis (NEC) and retinopathy of prematurity (ROP), which affect short-term and long-term neonatal outcome. Imbalanced inflammation has been considered to be a major underlying mechanism of each entity. Conventionally regarded as a harmless commensal on human skin, S. epidermidis has received less attention than its more virulent relative Staphylococcus aureus. Particularities of neonatal innate immunity and nosocomial environmental factors, however, may contribute to the emergence of S. epidermidis as a significant nosocomial pathogen. Neonatal host response to S. epidermidis sepsis has not been fully elucidated. Evidence is emerging regarding the implication of S. epidermidis sepsis in the pathogenesis of neonatal inflammatory diseases. This review focuses on the interplay among S. epidermidis, neonatal innate immunity and inflammation-driven organ injury.

Biased Ligands of G Protein-Coupled Receptors (GPCRs): Structure-Functional Selectivity Relationships (SFSRs) and Therapeutic Potential

G protein-coupled receptors (GPCRs) signal through both G-protein-dependent and G-protein-independent pathways, and β-arrestin recruitment is the most recognized one of the latter. Biased ligands selective for either pathway are expected to regulate biological functions of GPCRs in a more precise way, therefore providing new drug molecules with superior efficacy and/or reduced side effects. During the past decade, biased ligands have been discovered and developed for many GPCRs, such as the μ opioid receptor, the angiotensin II receptor type 1, the dopamine D₂ receptor, and many others. In this Perspective, recent advances in this field are reviewed by discussing the structure-functional selectivity relationships (SFSRs) of GPCR biased ligands and the therapeutic potential of these molecules. Further understanding of the biological functions associated with each signaling pathway and structural basis for biased signaling will facilitate future drug design in this field.

[Effect of lipoxin A4 on the expression of Toll-like receptor 4 and TNF receptor-associated factor 6 in the liver of obese rats with sepsis]

OBJECTIVE

To study the protective effect of lipoxin A4 (LXA4) against sepsis induced by lipopolysaccharide (LPS) in rats with obesity and its effect on the expression of Toll-like receptor 4 (TLR4) and TNF receptor-associated factor 6 (TRAF6) in the liver.

METHODS

A total of 60 male Sprague-Dawley rats aged three weeks were randomly divided into a normal group and an obesity group, with 30 rats in each group. A rat model of obesity was established by high-fat diet. Each of the two groups was further randomly divided into control group, sepsis group, and LXA4 group, and 8 rats were selected from each group. The rats in the control, sepsis, and LXA4 groups were treated with intraperitoneal injection of normal saline, LPS, and LXA4+LPS respectively. Twelve hours later, blood samples were collected from the heart and liver tissue samples were also collected. ELISA was used to measure the serum levels of interleukin-6 (IL-6) and tumor necrosis factor-α (TNF-α). Western blot was used to measure the protein expression of TLR4 and TRAF6 in liver tissue. Quantitative real-time PCR was used to measure the mRNA expression of TLR4 and TRAF6.

RESULTS

After being fed with high-fat diet for 6 weeks, the obesity group had significantly higher average weight and Lee's index than the normal group (P<0.05). Compared with the normal group, the obesity group had significant increases in the serum levels of IL-6 and TNF-α (P<0.05). In the normal group or the obesity group, the sepsis subgroup had significant increases in the serum levels of IL-6 and TNF-α compared with the control subgroup (P<0.05), while the LXA4 subgroup had significant reductions in the two indices compared with the sepsis subgroup (P<0.05). Compared with the normal group, the obesity group had significant increases in the protein and mRNA expression of TLR4 and TRAF6 (P<0.05). In the normal group or the obesity group, the sepsis subgroup had significant increases in the protein and mRNA expression of TLR4 and TRAF6 compared with the control subgroup (P<0.05). Compared with the sepsis subgroup, the LXA4 subgroup had significant reductions in the protein and mRNA expression of TLR4 and TRAF6 (P<0.05).

CONCLUSIONS

LXA4 can reduce the serum levels of IL-6 and TNF-α and alleviate inflammatory response. LXA4 can inhibit the expression of TLR4 and TRAF6 in the liver of septic rats, possibly by inhibiting the TLR4 signaling pathway.

Formyl Peptide Receptor 1 Modulates Endothelial Cell Functions by NADPH Oxidase-Dependent VEGFR2 Transactivation

In the vasculature, NADPH oxidase is the main contributor of reactive oxygen species (ROS) which play a key role in endothelial signalling and functions. We demonstrate that ECV304 cells express p47^phox, p67^phox, and p22^phox subunits of NADPH oxidase, as well as formyl peptide receptors 1 and 3 (FPR1/3), which are members of the GPCR family. By RT-PCR, we also detected Flt-1 and Flk-1/KDR in these cells. Stimulation of FPR1 by N-fMLP induces p47^phox phosphorylation, which is the crucial event for NADPH oxidase-dependent superoxide production. Transphosphorylation of RTKs by GPCRs is a biological mechanism through which the information exchange is amplified throughout the cell. ROS act as signalling intermediates in the transactivation mechanism. We show that N-fMLP stimulation induces the phosphorylation of cytosolic Y951, Y996, and Y1175 residues of VEGFR2, which constitute the anchoring sites for signalling molecules. These, in turn, activate PI3K/Akt and PLC-γ1/PKC intracellular pathways. FPR1-induced ROS production plays a critical role in this cross-talk mechanism. In fact, inhibition of FPR1 and/or NADPH oxidase functions prevents VEGFR2 transactivation and the triggering of the downstream signalling cascades. N-fMLP stimulation also ameliorates cellular migration and capillary-like network formation ability of ECV304 cells.

The natural sesquiterpene lactones arglabin, grosheimin, agracin, parthenolide, and estafiatin inhibit T cell receptor (TCR) activation

Inhibition of the T cell receptor (TCR) pathway represents an effective strategy for the treatment of T cell-mediated inflammatory and autoimmune diseases. To identify natural compounds that could inhibit inflammatory T cell responses, we screened 13 sesquiterpene lactones, including achillin, arglabin, argolide, argracin, 3β-hydroxyarhalin, artesin, artemisinin, estafiatin, grosheimin, grossmisin, leucomisine, parthenolide, and taurine, for their ability to modulate activation-induced Ca²⁺ mobilization in Jurkat T cells. Five of the compounds (arglabin, grosheimin, argracin, parthenolide, and estafiatin) inhibited anti-CD3-induced mobilization of intercellular Ca²⁺ ([Ca²⁺]_i) in Jurkat cells, with the most potent being parthenolide and argacin (IC₅₀ = 5.6 and 6.1 μM, respectively). Likewise, phosphorylation of extracellular signal-regulated kinase (ERK) 1/2 in activated Jurkat cells was inhibited by these five compounds, with the most potent being parthenolide and estafiatin (IC₅₀ = 13.8 and 15.4 μM, respectively). These compounds also inhibited ERK1/2 phosphorylation in primary human T cells and depleted intracellular glutathione. In contrast, none of the sesquiterpene lactones inhibited ERK1/2 phosphorylation in HL60 cells transfected with N-formyl peptide receptor 2 (FPR2) and stimulated with the FPR2 peptide agonist WKYMVM, indicating specificity for T cell activation. Estafiatin, a representative sesquiterpene lactone, was also profiled in a cell-based phosphokinase array for 43 kinase phosphorylation sites, as well as in a cell-free competition binding assay for its ability to compete with an active-site directed ligand for 95 different protein kinases. Besides inhibition of ERK1/2 phosphorylation, estafiatin also inhibited phosphorylation of p53, AMPKα1, CREB, and p27 elicited by TCR activation in Jurkat cells, but it did not bind to any of 95 kinases evaluated. These results suggest that arglabin, grosheimin, agracin, parthenolide, and estafiatin can selectively inhibit initial phases of TCR activation and may be natural compounds with previously undescribed immunotherapeutic properties.

Regulation of inflammation by members of the formyl-peptide receptor family

Inflammation is associated with a variety of diseases. The hallmark of inflammation is leukocyte infiltration at disease sites in response to pathogen- or damage-associated chemotactic molecular patterns (PAMPs and MAMPs), which are recognized by a superfamily of seven transmembrane, Gi-protein-coupled receptors (GPCRs) on cell surface. Chemotactic GPCRs are composed of two major subfamilies: the classical GPCRs and chemokine GPCRs. Formyl-peptide receptors (FPRs) belong to the classical chemotactic GPCR subfamily with unique properties that are increasingly appreciated for their expression on diverse host cell types and the capacity to interact with a plethora of chemotactic PAMPs and MAMPs. Three FPRs have been identified in human: FPR1-FPR3, with putative corresponding mouse counterparts. FPR expression was initially described in myeloid cells but subsequently in many non-hematopoietic cells including cancer cells. Accumulating evidence demonstrates that FPRs possess multiple functions in addition to controlling inflammation, and participate in the processes of many pathophysiologic conditions. They are not only critical mediators of myeloid cell trafficking, but are also implicated in tissue repair, angiogenesis and protection against inflammation-associated tumorigenesis. A series recent discoveries have greatly expanded the scope of FPRs in host defense which uncovered the essential participation of FPRs in step-wise trafficking of myeloid cells including neutrophils and dendritic cells (DCs) in host responses to bacterial infection, tissue injury and wound healing. Also of great interest is the FPRs are exploited by malignant cancer cells for their growth, invasion and metastasis. In this article, we review the current understanding of FPRs concerning their expression in a vast array of cell types, their involvement in guiding leukocyte trafficking in pathophysiological conditions, and their capacity to promote the differentiation of immune cells, their participation in tumor-associated inflammation and cancer progression. The close association of FPRs with human diseases and cancer indicates their potential as targets for the development of therapeutics.

CSA13 inhibits colitis-associated intestinal fibrosis via a formyl peptide receptor like-1 mediated HMG-CoA reductase pathway

Many Crohn’s disease (CD) patients develop intestinal strictures, which are difficult to prevent and treat. Cationic steroid antimicrobial 13 (CSA13) shares cationic nature and antimicrobial function with antimicrobial peptide cathelicidin. As many functions of cathelicidin are mediated through formyl peptide receptor-like 1 (FPRL1), we hypothesize that CSA13 mediates anti-fibrogenic effects via FPRL1. Human intestinal biopsies were used in clinical data analysis. Chronic trinitrobenzene sulfonic acid (TNBS) colitis-associated intestinal fibrosis mouse model with the administration of CSA13 was used. Colonic FPRL1 mRNA expression was positively correlated with the histology scores of inflammatory bowel disease patients. In CD patients, colonic FPRL1 mRNA was positively correlated with intestinal stricture. CSA13 administration ameliorated intestinal fibrosis without influencing intestinal microbiota. Inhibition of FPRL1, but not suppression of intestinal microbiota, reversed these protective effects of CSA13. Metabolomic analysis indicated increased fecal mevalonate levels in the TNBS-treated mice, which were reduced by the CSA13 administration. CSA13 inhibited colonic HMG-CoA reductase activity in an FPRL1-dependent manner. Mevalonate reversed the anti-fibrogenic effect of CSA13. The increased colonic FPRL1 expression is associated with severe mucosal disease activity and intestinal stricture. CSA13 inhibits intestinal fibrosis via FPRL1-dependent modulation of HMG-CoA reductase pathway.

Quantification and application of a liquid chromatography-tandem mass spectrometric method for the determination of WKYMVm peptide in rat using solid-phase extraction

A liquid chromatographic-electrospray ionization-time-of-flight/mass spectrometric (LC-ESI-TOF/MS) method was developed and applied for the determination of WKYMVm peptide in rat plasma to support preclinical pharmacokinetics studies. The method consisted of micro-elution solid-phase extraction (SPE) for sample preparation and LC-ESI-TOF/MS in the positive ion mode for analysis. Phenanthroline (10 mg/mL) was added to rat blood immediately for plasma preparation followed by addition of trace amount of 2 m hydrogen chloride to plasma before SPE for stability of WKYMVm peptide. Then sample preparation using micro-elution SPE was performed with verapamil as an internal standard. A quadratic regression (weighted 1/concentration² ), with the equation y = ax²  + bx + c was used to fit calibration curves over the concentration range of 3.02-2200 ng/mL for WKYMVm peptide. The quantification run met the acceptance criteria of ±25% accuracy and precision values. For quality control samples at 15, 165 and 1820 ng/mL from the quantification experiment, the within-run and the between-run accuracy ranged from 92.5 to 123.4% with precision values ≤15.1% for WKYMVm peptide from the nominal values. This novel LC-ESI-TOF/MS method was successfully applied to evaluate the pharmacokinetics of WKYMVm peptide in rat plasma.