Nonredundant protective properties of FPR2/ALX in polymicrobial murine sepsis

Effect of esketamine pretreatment on acute sepsis-associated encephalopathy

PURPOSE

Esketamine, the S(+) enantiomer of ketamine, exhibits good anesthetic efficacy and controllability; however, its potential clinical applications, particularly in sepsis-associated encephalopathy (SAE), remain underexplored. SAE involves the development of diffuse brain dysfunction after sepsis, leading to markedly increased sepsis-related disability and mortality. In this study, we investigated the effects of esketamine pretreatment on acute SAE.

METHODS

Mice were randomly divided into four groups: control (C, n = 22), acute SAE (L, n = 22), esketamine pretreatment + acute SAE (EL, n = 22), and nuclear factor erythroid 2-related factor 2 (Nrf2) inhibitor (ML385) + esketamine pretreatment + acute SAE (N + EL, n = 22). Acute SAE was established using intraperitoneal (i.p.) injection of lipopolysaccharide (LPS; 10 mg/kg), while controls received equal amounts of saline. The EL group received daily i.p. injections of esketamine (10 mg/kg) for 5 consecutive days, followed by LPS on day 6. The N + EL group received i.p. injections of ML385 (30 mg/kg) 1 h before esketamine pretreatment. The remainder of treatment followed the same protocol as the EL group. Behavioral tests were performed 24 h post-LPS injection, and whole blood and brain tissues were collected for further analysis.

RESULTS

Esketamine improved sepsis symptoms, 7-day survival, and spatial cognitive impairment, without altering locomotor activity. Moreover, esketamine reversed the LPS-induced increase in serum S100 calcium-binding protein β and neuron-specific enolase levels and reduced hippocampal neuroinflammation, oxidative stress, and neuronal apoptosis in the EL group. However, these neuroprotective effects of esketamine were reversed by ML385.

CONCLUSION

The results of our study suggest that esketamine pretreatment mitigates acute SAE, highlighting the involvement of the Nrf2/heme oxygenase-1 pathway in mediating its neuroprotective effects.

The Annexin-A1 mimetic RTP-026 promotes acute cardioprotection through modulation of immune cell activation

AIMS

The cardio-protective and immuno-regulatory properties of RTP-026, a synthetic peptide that spans the Annexin-A1 (AnxA1) N-terminal region, were tested in rat acute myocardial infarction.

METHODS AND RESULTS

In vitro, selective activation of formyl-peptide receptor type 2 (FPR2) by RTP-026 occurred with apparent EC50 in the 10-30 nM range. With human primary cells, RTP-026 counteracted extension of neutrophil life-span and augmented phagocytosis of fluorescent E.coli by blood myeloid cells. An in vivo model of rat acute infarction was used to quantify tissue injury and phenotype immune cells in myocardium and blood. The rat left anterior descending coronary artery was occluded and then reopened for 2-hour or 24-hour reperfusion. For the 2-hour reperfusion protocol, RTP-026 (25-500 µg/kg; given i.v. at the start of reperfusion) significantly reduced infarct size by ∼50 %, with maximal efficacy at 50 µg/kg. Analyses of cardiac immune cells showed that RTP-026 reduced neutrophil and classical monocyte recruitment to the damaged heart. In the blood, RTP-026 (50 µg/kg) attenuated activation of neutrophils and monocytes monitored through CD62L and CD54 expression. Modulation of vascular inflammation by RTP-026 was demonstrated by reduction in plasma levels of mediators like TNF-α, IL-1β, KC, PGE2 and PGF2α⊡ For the 24-hour reperfusion protocol, RTP-026 (30 µg/kg given i.v. at 0, 3 and 6 h reperfusion) reduced necrotic myocardium by ∼40 %.

CONCLUSIONS

RTP-026 modulate immune cell responses and decreases infarct size of the heart in preclinical settings. Tempering over-exuberant immune cell activation by RTP-026 is a suitable approach to translate the biology of AnxA1 for therapeutic purposes.

Stimulation of the Pro-Resolving Receptor Fpr2 Reverses Inflammatory Microglial Activity by Suppressing NFκB Activity

Neuroinflammation driven primarily by microglia directly contributes to neuronal death in many neurodegenerative diseases. Classical anti-inflammatory approaches aim to suppress pro-inflammatory mediator production, but exploitation of inflammatory resolution may also be of benefit. A key driver of peripheral inflammatory resolution, formyl peptide receptor 2 (Fpr2), is expressed by microglia, but its therapeutic potential in neurodegeneration remains unclear. Here, we studied whether targeting of Fpr2 could reverse inflammatory microglial activation induced by the potent bacterial inflammogen lipopolysaccharide (LPS). Exposure of murine primary or immortalised BV2 microglia to LPS triggered pro-inflammatory phenotypic change and activation of ROS production, effects significantly attenuated by subsequent treatment with the Fpr2 agonist C43. Mechanistic studies showed C43 to act through p38 MAPK phosphorylation and reduction of LPS-induced NFκB nuclear translocation via prevention of IκBα degradation. Here, we provide proof-of-concept data highlighting Fpr2 as a potential target for control of microglial pro-inflammatory activity, suggesting that it may be a promising therapeutic target for the treatment of neuroinflammatory disease.

Maresin1 prevents sepsis-induced acute liver injury by suppressing NF-κB/Stat3/MAPK pathways, mitigating inflammation

Aims

The treatment of sepsis remains challenging and the liver is a non-neglectful target of sepsis-induced injury. Uncontrolled inflammatory responses exert a central role in the pathophysiological process of sepsis-induced acute liver injury (SI-ALI). Maresin1 (MaR1) is a derivative of omega-3 docosahexaenoic acid (DHA), which has been shown to have anti-inflammatory effects and is effective in a variety of sepsis-related diseases. This study aimed to determine the effect of MaR1 on cecal ligation and puncture (CLP)-caused SI-ALI and explore its possible mechanisms.

Main methods

Mice were subjected to CLP, and then intravenously injected via tail vein with low-dose MaR1 (0.5 ng, 200 μL) or high-dose MaR1 (1 ng, 200 μL) or sterile normal saline (NS) (200 μL) 1 h later. Then, the survival rate, body weight change, liver function, bacterial load, neutrophil infiltration, and inflammatory cytokines were detected.

Results

MaR1 significantly increased the 7-day survival rate and reduced the bacterial load in peritoneal lavage fluid and blood in a dose-dependent manner in mice with SI-ALI. Treatment with MaR1 could also restore the function of the liver in septic mice. Besides, MaR1 exerted anti-inflammatory effects by decreasing the expression of pro-inflammatory molecules (TNF-α, IL-6 and IL-1β), bacterial load, and neutrophil infiltration and increasing the expression of anti-inflammatory molecules (IL-10).

Significance

Our experimental results showed that MaR1 alleviated liver injury induced by sepsis. This work highlighted a potential clinic use of MaR1 in treating acute inflammation of SI-ALI, but also provided new insight into the underlying molecular mechanism.

Transcriptome sequencing and experiments reveal the effect of formyl peptide receptor 2 on liver homeostasis

BACKGROUND

Formyl peptide receptor 2 (Fpr2) is an important receptor in host resistance to bacterial infections. In previous studies, we found that the liver of Fpr2-/- mice is the most severely damaged target organ in bloodstream infections, although the reason for this is unclear.

AIM

To investigate the role of Fpr2 in liver homeostasis and host resistance to bacterial infections.

METHODS

Transcriptome sequencing was performed on the livers of Fpr2-/- and wild-type (WT) mice. Differentially expressed genes (DEGs) were identified in the Fpr2-/- and WT mice, and the biological functions of DEGs were analyzed by Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) en-richment analysis. Quantitative real time-polymerase chain reaction (qRT-PCR) and western blot (WB) analyses were used to further validate the expression levels of differential genes. Cell counting kit-8 assay was employed to investigate cell survival. The cell cycle detection kit was used to measure the distribution of cell cycles. The Luminex assay was used to analyze cytokine levels in the liver. The serum biochemical indices and the number of neutrophils in the liver were measured, and hepatic histopathological analysis was performed.

RESULTS

Compared with the WT group, 445 DEGs, including 325 upregulated genes and 120 downregulated genes, were identified in the liver of Fpr2-/- mice. The enrichment analysis using GO and KEGG showed that these DEGs were mainly related to cell cycle. The qRT-PCR analysis confirmed that several key genes (CycA, CycB1, Cdc20, Cdc25c, and Cdk1) involved in the cell cycle had significant changes. The WB analysis confirmed a decrease in the expression of CDK1 protein. WRW4 (an antagonist of Fpr2) could inhibit the proliferation of HepG2 cells in a concentration dependent manner, with an increase in the number of cells in the G0/G1 phase, and a decrease in the number of cells in the S phase. Serum alanine aminotransferase levels increased in Fpr2-/- mice. The Luminex assay measurements showed that interleukin (IL)-10 and chemokine (C-X-C motif) ligand (CXCL)-1 levels were significantly reduced in the liver of Fpr2-/- mice. There was no difference in the number of neutrophils, serum C-reactive protein levels, and liver pathology between WT and Fpr2-/- mice.

CONCLUSION

Fpr2 participates in the regulation of cell cycle and cell proliferation, and affects the expression of IL-10 and CXCL-1, thus playing an important protective role in maintaining liver homeostasis.

Developmental and homeostatic signaling transmitted by the G-protein coupled receptor FPR2

Formyl peptide receptor 2 (FPR2) and its mouse counterpart Fpr2 are the members of the G protein-coupled receptor (GPCR) family. FPR2 is the only member of the FPRs that interacts with ligands from different sources. FPR2 is expressed in myeloid cells as well as epithelial cells, endothelial cells, neurons, and hepatocytes. During the past years, some unusual properties of FPR2 have attracted intense attention because FPR2 appears to possess dual functions by activating or inhibiting intracellular signal pathways based on the nature, concentration of the ligands, and the temporal and spatial settings of the microenvironment in vivo, the cell types it interacts with. Therefore, FPR2 controls an abundant array of developmental and homeostatic signaling cascades, in addition to its "classical" capacity to mediate the migration of hematopoietic and non-hematopoietic cells including malignant cells. In this review, we summarize recent development in FPR2 research, particularly in its role in diseases, therefore helping to establish FPR2 as a potential target for therapeutic intervention.

Fpr2-/- Mice Developed Exacerbated Alcohol-Associated Liver Disease

Alcohol-associated liver disease (ALD) is the most common chronic liver disease and carries a significant healthcare burden. ALD has no long-term treatment options aside from abstinence, and the mechanisms that contribute to its pathogenesis are not fully understood. This study aimed to investigate the role of formyl peptide receptor 2 (FPR2), a receptor for immunomodulatory signals, in the pathogenesis of ALD. WT and Fpr2-/- mice were exposed to chronic-binge ethanol administration and subsequently assessed for liver injury, inflammation, and markers of regeneration. The differentiation capacity of liver macrophages and the oxidative burst activity of neutrophils were also examined. Compared to WT, Fpr2-/- mice developed more severe liver injury and inflammation and had compromised liver regeneration in response to ethanol administration. Fpr2-/- mice had fewer hepatic monocyte-derived restorative macrophages, and neutrophils isolated from Fpr2-/- mice had diminished oxidative burst capacity. Fpr2-/- MoMF differentiation was restored when co-cultured with WT neutrophils. Loss of FPR2 led to exacerbated liver damage via multiple mechanisms, including abnormal immune responses, indicating the crucial role of FPR2 in ALD pathogenesis.

Formyl Peptide Receptor Type 2 Deficiency in Myeloid Cells Amplifies Sepsis-Induced Cardiac Dysfunction

Using a global formyl peptide receptor (Fpr) 2 knockout mouse colony, we have reported the modulatory properties of this pro-resolving receptor in polymicrobial sepsis. Herein, we have used a humanized FPR2 (hFPR2) mouse colony, bearing an intact or a selective receptor deficiency in myeloid cells to dwell on the cellular mechanisms. hFPR2 mice and myeloid cell-specific hFPR2 KO (KO) mice were subjected to cecal ligation and puncture (CLP)-induced polymicrobial sepsis. Compared with hFPR2 mice, CLP caused exacerbated cardiac dysfunction (assessed by echocardiography), worsened clinical outcome, and impaired bacterial clearance in KO mice. This pathological scenario was paralleled by increased recruitment of pro-inflammatory monocytes and reduced M2-like macrophages within the KO hearts. In peritoneal exudates of KO mice, we quantified increased neutrophil and MHC II+ macrophage numbers but decreased monocyte/macrophage and MHC II- macrophage recruitment. hFPR2 upregulation was absent in myeloid cells, and local production of lipoxin A4 was reduced in septic KO mice. Administration of the FPR2 agonist annexin A1 (AnxA1) improved cardiac function in hFPR2 septic mice but had limited beneficial effects in KO mice, in which the FPR2 ligand failed to polarize macrophages toward an MHC II- phenotype. In conclusion, FPR2 deficiency in myeloid cells exacerbates cardiac dysfunction and worsens clinical outcome in polymicrobial sepsis. The improvement of cardiac function and the host immune response by AnxA1 is more effective in hFPR2-competent septic mice.

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

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

Deletion of macrophage Gpr101 disrupts their phenotype and function dysregulating host immune responses in sterile and infectious inflammation

We recently found that the G protein coupled receptor GPR101 mediates the phagocyte-directed pro-resolving activities of RvD5_{n-3 DPA} (n-3 docosapentaenoic acid-derived Resolvin D5). Herein, we investigated the endogenous role of this pro-resolving receptor in modulating macrophage biology using a novel mouse line where the expression of Gpr101 was conditionally deleted in macrophages (Mac^Gpr101KO). Peritoneal macrophages obtained from naïve Mac^Gpr101KO mice displayed a marked shift in the expression of phenotypic and activation markers, including the Interleukin (IL)-10 and IL-23 receptors. Loss of Gpr101 on macrophages was also associated with a significant disruption in their cellular metabolism and a decreased ability to migrate towards the chemoattractant Mcp-1. The alterations in macrophage phenotype observed in Gpr101 deficient macrophages were maintained following inflammatory challenge. This was linked with an increased inflammatory response in the Gpr101 deficient animals and a reduced ability of phagocytes, including macrophages, to clear bacteria. Loss of Gpr101 on macrophages disrupted host pro-resolving responses to zymosan challenge with Mac^Gpr101KO mice exhibiting significantly higher neutrophil numbers and a delay in the resolution interval when compared with control mice. These observations were linked with a marked dysregulation in peritoneal lipid mediator concentrations in Gpr101 deficient mice, with a downregulation of pro-resolving mediators including MaR2_{n-3 DPA}, Resolvin (Rv) D3 and RvE3. Together these findings identify Gpr101 as a novel regulator of both macrophage phenotype and function, modulating key biological activities in both limiting the propagation of inflammation and expediting its resolution.

Formylpeptide receptor 2: Nomenclature, structure, signalling and translational perspectives: IUPHAR review 35

We discuss the fascinating pharmacology of formylpeptide receptor 2 (FPR2; often referred to as FPR2/ALX since it binds lipoxin A₄ ). Initially identified as a low-affinity 'relative' of FPR1, FPR2 presents complex and diverse biology. For instance, it is activated by several classes of agonists (from peptides to proteins and lipid mediators) and displays diverse expression patterns on myeloid cells as well as epithelial cells and endothelial cells, to name a few. Over the last decade, the pharmacology of FPR2 has progressed from being considered a weak chemotactic receptor to a master-regulator of the resolution of inflammation, the second phase of the acute inflammatory response. We propose that exploitation of the biology of FPR2 offers innovative ways to rectify chronic inflammatory states and represents a viable avenue to develop novel therapies. Recent elucidation of FPR2 structure will facilitate development of the anti-inflammatory and pro-resolving drugs of next decade.

Identification of PIK3CG as a hub in septic myocardial injury using network pharmacology and weighted gene co-expression network analysis

Sepsis causes multiple organ injuries, among which the heart is one most severely damaged organ. Melatonin (MEL) alleviates septic myocardial injury, although a systematic and comprehensive approach is still lacking to understand the precise protective machinery of MEL. This study aimed to examine the underlying mechanisms of MEL on improvement of septic myocardial injury at a systematic level. This study integrated three analytic modalities including database investigations, RNA-seq analysis, and weighted gene co-expression network analysis (WCGNA), in order to acquire a set of genes associated with the pathogenesis of sepsis. The Drugbank database was employed to predict genes that may serve as pharmacological targets for MEL-elicited benefits, if any. A pharmacological protein-protein interaction network was subsequently constructed, and 66 hub genes were captured which were enriched in a variety of immune response pathways. Notably, PIK3CG, one of the hub genes, displayed high topological characteristic values, strongly suggesting its promise as a novel target for MEL-evoked treatment of septic myocardial injury. Importantly, molecular docking simulation experiments as well as in vitro and in vivo studies supported an essential role for PIK3CG in MEL-elicited effect on septic myocardial injury. This study systematically clarified the mechanisms of MEL intervention in septic myocardial injury involved multiple targets and multiple pathways. Moreover, PIK3CG-governed signaling cascade plays an important role in the etiology of sepsis and septic myocardial injury. Findings from our study provide valuable information on novel intervention targets for the management of septic myocardial injury. More importantly, this study has indicated the utility of combining a series of techniques for disease target discovery and exploration of possible drug targets, which should shed some light on elucidation of experimental and clinical drug action mechanisms systematically.

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

Acute respiratory distress syndrome is characterized by aberrant inflammatory responses, including polymorphonuclear neutrophil granulocyte dysfunction and hyperactive Toll-like receptor signaling. Timely resolution of bacterial infections depends on efficient removal of neutrophils from the inflamed tissue. Here we show that the antiviral cytokine interferon-β is essential for the resolution of neutrophil-driven airway inflammation by countering Toll-like receptor 9–mediated suppression of phagocytosis, neutrophil apoptosis, and uptake by macrophages. We also report that the beneficial effects of interferon-β are, in part, mediated by production of proresolving lipid mediators, such as 15-epi-lipoxin A₄ and resolvin D1, which act through the lipoxin receptor ALX/FPR2. These findings uncover an interferon-β–initiated ALX/FPR2-centered resolution program as a potential target for facilitating the resolution of 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-β (IFN-β) 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-β and the proresolving lipid mediators 15-epi-LXA₄ and resolvin D1 (RvD1) in the lung. Neutralization of endogenous IFN-β delays pulmonary clearance of E. coli and aggravates mucosal injury. Conversely, treatment of mice with IFN-β 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-β–mediated resolution. These findings point to a pivotal role of IFN-β in orchestrating timely resolution of neutrophil and TLR9 activation–driven airway inflammation and uncover an IFN-β–initiated resolution program, activation of an ALX/FPR2-centered, proresolving lipids-mediated circuit, for ARDS.

Impact of High-Molecular-Weight Hyaluronic Acid on Gene Expression in Rabbit Achilles Tenocytes In Vitro

(1) Background: Surgical tendon repair often leads to adhesion formation, leading to joint stiffness and a reduced range of motion. Tubular implants set around sutured tendons might help to reduce peritendinous adhesions. The lubricant hyaluronic acid (HA) is a viable option for optimizing such tubes with the goal of further enhancing the anti-adhesive effect. As the implant degrades over time and diffusion is presumed, the impact of HA on tendon cells is important to know. (2) Methods: A culture medium of rabbit Achilles tenocytes was supplemented with high-molecular-weight (HMW) HA and the growth curves of the cells were assessed. Additionally, after 3, 7 and 14 days, the gene expression of several markers was analyzed for matrix assembly, tendon differentiation, fibrosis, proliferation, matrix remodeling, pro-inflammation and resolution. (3) Results: The addition of HA decreased matrix marker genes, downregulated the fibrosis marker α-SMA for a short time and slightly increased the matrix-remodeling gene MMP-2. Of the pro-inflammatory marker genes, only IL-6 was significantly upregulated. IL-6 has to be kept in check, although IL-6 is also needed for a proper initial inflammation and efficient resolution. (4) Conclusions: The observed effects in vitro support the intended anti-adhesion effect and therefore, the use of HMW HA is promising as a biodegradable implant for tendon repair.

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

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

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.

Pro-resolving therapies as potential adjunct treatment for infectious diseases: Evidence from studies with annexin A1 and angiotensin-(1-7)

Infectious diseases, once believed to be an eradicable public health threat, still represent a leading cause of death worldwide. Environmental and social changes continuously favor the emergence of new pathogens and rapid dissemination around the world. The limited availability of anti-viral therapies and increased antibiotic resistance has made the therapeutic management of infectious disease a major challenge. Inflammation is a primordial defense to protect the host against invading microorganisms. However, dysfunctional inflammatory responses contribute to disease severity and mortality during infections. In recent years, a few studies have examined the relevance of resolution of inflammation in the context of infections. Inflammation resolution is an active integrated process transduced by several pro-resolving mediators, including Annexin A1 and Angiotensin-(1-7). Here, we examine some of the cellular and molecular circuits triggered by pro-resolving molecules and that may be beneficial in the context of infectious diseases.

Atherosclerosis is a major human killer and non-resolving inflammation is a prime suspect

The resolution of inflammation (or inflammation-resolution) is an active and highly coordinated process. Inflammation-resolution is governed by several endogenous factors, and specialized pro-resolving mediators (SPMs) are one such class of molecules that have robust biological function. Non-resolving inflammation is associated with a variety of human diseases, including atherosclerosis. Moreover, non-resolving inflammation is a hallmark of ageing, an inevitable process associated with increased risk for cardiovascular disease. Uncovering mechanisms as to why inflammation-resolution is impaired in ageing and in disease and identifying useful biomarkers for non-resolving inflammation are unmet needs. Recent work has pointed to a critical role for balanced ratios of SPMs and pro-inflammatory lipids (i.e. leucotrienes and/or specific prostaglandins) as a key determinant of timely inflammation resolution. This review will focus on the accumulating findings that support the role of non-resolving inflammation and imbalanced pro-resolving and pro-inflammatory mediators in atherosclerosis. We aim to provide insight as to why these imbalances occur, the importance of ageing in disease progression, and how haematopoietic function impacts inflammation-resolution and atherosclerosis. We highlight open questions regarding therapeutic strategies and mechanisms of disease to provide a framework for future studies that aim to tackle this important human disease.

Lipopeptide Pepducins as Therapeutic Agents

Pepducins are lipidated peptides that target the intracellular loops of G protein-coupled receptors (GPCRs) in order to modulate transmembrane signaling to internally located effectors. With a wide array of potential activities ranging from partial, biased, or full agonism to antagonism, pepducins represent a versatile class of compounds that can be used to potentially treat diverse human diseases or be employed as novel tools to probe complex mechanisms of receptor activation and signaling in cells and in animals. Here, we describe a number of different pepducins including an advanced compound, PZ-128, that has successfully progressed through phase 2 clinical trials in cardiac patients demonstrating safety and efficacy in suppressing myonecrosis and arterial thrombosis.

Comprehensive analysis of mRNAs, lncRNAs and circRNAs in the early phase of microglial activation

Sepsis-associated encephalopathy (SAE) is a common complication of sepsis that may seriously affect the prognosis and quality of life of patients with sepsis. Microglial activation is vital to the neuroinflammation and the pathology of SAE. In the present study, in vitro cultured BV-2 microglial cells stimulated with lipopolysaccharide (LPS) were employed as a model of microglia activation. The altered profiles of long noncoding (lnc)RNAs, circular (circ)RNAs and mRNAs in BV-2 cells after 4 h of LPS exposure were arrayed by using the Agilent competing endogenous (ce)RNA Microarray Chip. Using fold change >2 and P<0.05 as the cutoff criteria, 1,135 mRNAs and 2,488 lncRNAs were determined to be upregulated and 630 mRNAs and 744 lncRNAs to be downregulated. The number of differentially expressed circRNAs was lower, with 140 upregulated and 123 downregulated. Gene Ontology and Kyoto Encyclopedia of Genes and Genomes analysis of DE mRNAs suggested that inflammatory responses, as well as lipid metabolism, were involved in microglial activation. Furthermore, analyses of ceRNA networks of the lncRNA-miRNA-mRNA or circRNA-miRNA-mRNA interrelations were performed. The present study revealed a multitude of novel candidate mRNAs, lncRNAs and circRNAs involved in microglial activation, which may improve the current knowledge on neuroinflammation and provide potential therapeutic targets for SAE.

Therapeutic potential of pro-resolving mediators in diabetic kidney disease

Renal microvascular disease associated with diabetes [Diabetic kidney disease - DKD] is the leading cause of chronic kidney disease. In DKD, glomerular basement membrane thickening, mesangial expansion, endothelial dysfunction, podocyte cell loss and renal tubule injury contribute to progressive glomerulosclerosis and tubulointerstitial fibrosis. Chronic inflammation is recognized as a major pathogenic mechanism for DKD, with resident and circulating immune cells interacting with local kidney cell populations to provoke an inflammatory response. The onset of inflammation is driven by the release of well described proinflammatory mediators, and this is typically followed by a resolution phase. Inflammation resolution is achieved through the bioactions of endogenous specialized pro-resolving lipid mediators (SPMs). As our understanding of SPMs advances 'resolution pharmacology' based approaches using these molecules are being explored in DKD.

ATRvD1 Attenuates Renal Tubulointerstitial Injury Induced by Albumin Overload in Sepsis-Surviving Mice

Novel strategies for the prevention and treatment of sepsis-associated acute kidney injury and its long-term outcomes have been required and remain a challenge in critical care medicine. Therapeutic strategies using lipid mediators, such as aspirin-triggered resolvin D1 (ATRvD1), can contribute to the resolution of acute and chronic inflammation. In this study, we examined the potential effect of ATRvD1 on long-term kidney dysfunction after severe sepsis. Fifteen days after cecal ligation and puncture (CLP), sepsis-surviving BALB/c mice were subjected to a tubulointerstitial injury through intraperitoneal injections of bovine serum albumin (BSA) for 7 days, called the subclinical acute kidney injury (subAKI) animal model. ATRvD1 treatment was performed right before BSA injections. On day 22 after CLP, the urinary protein/creatinine ratio (UPC), histologic parameters, fibrosis, cellular infiltration, apoptosis, inflammatory markers levels, and mRNA expression were determined. ATRvD1 treatment mitigated tubulointerstitial injury by reducing proteinuria excretion, the UPC ratio, the glomerular cell number, and extracellular matrix deposition. Pro-fibrotic markers, such as transforming growth factor β (TGFβ), type 3 collagen, and metalloproteinase (MMP)-3 and -9 were reduced after ATRvD1 administration. Post-septic mice treated with ATRvD1 were protected from the recruitment of IBA1⁺ cells. The interleukin-1β (IL-1β) levels were increased in the subAKI animal model, being attenuated by ATRvD1. Tumor necrosis factor-α (TNF-α), IL-10, and IL-4 mRNA expression were increased in the kidney of BSA-challenged post-septic mice, and it was also reduced after ATRvD1. These results suggest that ATRvD1 protects the kidney against a second insult such as BSA-induced tubulointerstitial injury and fibrosis by suppressing inflammatory and pro-fibrotic mediators in renal dysfunction after sepsis.

Therapeutic Potential of Annexins in Sepsis and COVID-19

Sepsis is a continuing problem in modern healthcare, with a relatively high prevalence, and a significant mortality rate worldwide. Currently, no specific anti-sepsis treatment exists despite decades of research on developing potential therapies. Annexins are molecules that show efficacy in preclinical models of sepsis but have not been investigated as a potential therapy in patients with sepsis. Human annexins play important roles in cell membrane dynamics, as well as mediation of systemic effects. Most notably, annexins are highly involved in anti-inflammatory processes, adaptive immunity, modulation of coagulation and fibrinolysis, as well as protective shielding of cells from phagocytosis. These discoveries led to the development of analogous peptides which mimic their physiological function, and investigation into the potential of using the annexins and their analogous peptides as therapeutic agents in conditions where inflammation and coagulation play a large role in the pathophysiology. In numerous studies, treatment with recombinant human annexins and annexin analogue peptides have consistently found positive outcomes in animal models of sepsis, myocardial infarction, and ischemia reperfusion injury. Annexins A1 and A5 improve organ function and reduce mortality in animal sepsis models, inhibit inflammatory processes, reduce inflammatory mediator release, and protect against ischemic injury. The mechanisms of action and demonstrated efficacy of annexins in animal models support development of annexins and their analogues for the treatment of sepsis. The effects of annexin A5 on inflammation and platelet activation may be particularly beneficial in disease caused by SARS-CoV-2 infection. Safety and efficacy of recombinant human annexin A5 are currently being studied in clinical trials in sepsis and severe COVID-19 patients.

Subgingival Microbiome and Specialized Pro-Resolving Lipid Mediator Pathway Profiles Are Correlated in Periodontal Inflammation

Failure of resolution pathways in periodontitis is reflected in levels of specialized pro-resolving lipid mediators (SPMs) and SPM pathway markers but their relationship with the subgingival microbiome is unclear. This study aimed to analyze and integrate lipid mediator level, SPM receptor gene expression and subgingival microbiome data in subjects with periodontitis vs. healthy controls. The study included 13 periodontally healthy and 15 periodontitis subjects that were evaluated prior to or after non-surgical periodontal therapy. Samples of gingival tissue and subgingival plaque were collected prior to and 8 weeks after non-surgical treatment; only once in the healthy group. Metabololipidomic analysis was performed to measure levels of SPMs and other relevant lipid mediators in gingiva. qRT-PCR assessed relative gene expression (2-ΔΔCT) of known SPM receptors. 16S rRNA sequencing evaluated the relative abundance of bacterial species in subgingival plaque. Correlations between lipid mediator levels, receptor gene expression and bacterial abundance were analyzed using the Data Integration Analysis for Biomarker discovery using Latent cOmponents (DIABLO) and Sparse Partial Least Squares (SPLS) methods. Profiles of lipid mediators, receptor genes and the subgingival microbiome were distinct in the three groups. The strongest correlation existed between lipid mediator profile and subgingival microbiome profile. Multiple lipid mediators and bacterial species were highly correlated (correlation coefficient ≥0.6) in different periodontal conditions. Comparing individual correlated lipid mediators and bacterial species in periodontitis before treatment to healthy controls revealed that one bacterial species, Corynebacterium durum, and five lipid mediators, 5(S)6(R)-DiHETE, 15(S)-HEPE, 7-HDHA, 13-HDHA and 14-HDHA, were identified in both conditions. Comparing individual correlated lipid mediators and bacterial species in periodontitis before treatment to after treatment revealed that one bacterial species, Anaeroglobus geminatus, and four lipid mediators, 5(S)12(S)-DiHETE, RvD1, Maresin 1 and LTB4, were identified in both conditions. Four Selenomonas species were highly correlated with RvD1, RvE3, 5(S)12(S)-DiHETE and proinflammatory mediators in the periodontitis after treatment group. Profiles of lipid mediators, receptor gene and subgingival microbiome are associated with periodontal inflammation and correlated with each other, suggesting inflammation mediated by lipid mediators influences microbial composition in periodontitis. The role of correlated individual lipid mediators and bacterial species in periodontal inflammation have to be further studied.

Formyl peptide receptor 2, as an important target for ligands triggering the inflammatory response regulation: a link to brain pathology

Formyl peptide receptors (FPRs) belong to the family of seven-transmembrane G protein-coupled receptors. Among them, FPR2 is a low affinity receptor for N-formyl peptides and is considered the most promiscuous member of FPRs. FPR2 is able to recognize a broad variety of endogenous or exogenous ligands, ranging from lipid to proteins and peptides, including non-formylated peptides. Due to this property FPR2 has the ability to modulate both pro- and anti-inflammatory response, depending on the nature of the bound agonist and on the different recognition sites of the receptor. Thus, FPR2 takes part not only in the proinflammatory response but also in the resolution of inflammation (RoI) processes. Recent data have indicated that the malfunction of RoI may be the background for some central nervous system (CNS) disorders. Therefore, much interest is focused on endogenous molecules called specialized pro-resolving mediators (SPMs), as well as on new synthetic FPR2 agonists, which kick-start the resolution of inflammation (RoI) and modulate its course. Here, we shed some light on the general characteristics of the FPR family in humans and in the experimental animals. Moreover, we present a guide to understanding the "double faced" action of FPR2 activation in the context of immune-related diseases of the CNS.

Cardiac Dysfunction in Rheumatoid Arthritis: The Role of Inflammation

Rheumatoid arthritis is a chronic, systemic inflammatory disease that carries an increased risk of mortality due to cardiovascular disease. The link between inflammation and atherosclerotic disease is clear; however, recent evidence suggests that inflammation may also play a role in the development of nonischemic heart disease in rheumatoid arthritis (RA) patients. We consider here the link between inflammation and cardiovascular disease in the RA community with a focus on heart failure with preserved ejection fraction. The effect of current anti-inflammatory therapeutics, used to treat RA patients, on cardiovascular disease are discussed as well as whether targeting resolution of inflammation might offer an alternative strategy for tempering inflammation and subsequent inflammation-driven comorbidities in RA.

Exploiting formyl peptide receptor 2 to promote microglial resolution: a new approach to Alzheimer's disease treatment

Alzheimer's disease and dementia are among the most significant current healthcare challenges given the rapidly growing elderly population, and the almost total lack of effective therapeutic interventions. Alzheimer's disease pathology has long been considered in terms of accumulation of amyloid beta and hyperphosphorylated tau, but the importance of neuroinflammation in driving disease has taken greater precedence over the last 15-20 years. Inflammatory activation of the primary brain immune cells, the microglia, has been implicated in Alzheimer's pathogenesis through genetic, preclinical, imaging and postmortem human studies, and strategies to regulate microglial activity may hold great promise for disease modification. Neuroinflammation is necessary for defence of the brain against pathogen invasion or damage but is normally self-limiting due to the engagement of endogenous pro-resolving circuitry that terminates inflammatory activity, a process that appears to fail in Alzheimer's disease. Here, we discuss the potential for a major regulator and promoter of resolution, the receptor FPR2, to restrain pro-inflammatory microglial activity, and propose that it may serve as a valuable target for therapeutic investigation in Alzheimer's disease.

Recent advances in the design and development of formyl peptide receptor 2 (FPR2/ALX) agonists as pro-resolving agents with diverse therapeutic potential

Under physiological conditions the initiation, duration and amplitude of inflammatory responses are tightly regulated to ensure the restoration of homeostasis. The resolution of inflammation in these circumstances is dictated by responses to endogenously generated mediators. Mimicry of such mediators underpins the principle of promoting the resolution of inflammation in treating inflammatory pathologies. The formyl peptide receptor 2 (FPR2/ALX) is a G-protein coupled receptor known to play a crucial role in maintaining host defence and orchestrating the inflammatory process. FPR2/ALX can be activated by a wide range of distinct agonists, including lipids, proteins, peptides, and an array of synthetic small molecule agonists. The focus of this review is to provide a comprehensive overview of recent progress made in the development of FPR2/ALX agonists which promote resolution and tissue regeneration.

Pro-resolving lipid mediators: regulators of inflammation, metabolism and kidney function

Obesity, diabetes mellitus, hypertension and cardiovascular disease are risk factors for chronic kidney disease (CKD) and kidney failure. Chronic, low-grade inflammation is recognized as a major pathogenic mechanism that underlies the association between CKD and obesity, impaired glucose tolerance, insulin resistance and diabetes, through interaction between resident and/or circulating immune cells with parenchymal cells. Thus, considerable interest exists in approaches that target inflammation as a strategy to manage CKD. The initial phase of the inflammatory response to injury or metabolic dysfunction reflects the release of pro-inflammatory mediators including peptides, lipids and cytokines, and the recruitment of leukocytes. In self-limiting inflammation, the evolving inflammatory response is coupled to distinct processes that promote the resolution of inflammation and restore homeostasis. The discovery of endogenously generated lipid mediators - specialized pro-resolving lipid mediators and branched fatty acid esters of hydroxy fatty acids - which promote the resolution of inflammation and attenuate the microvascular and macrovascular complications of obesity and diabetes mellitus highlights novel opportunities for potential therapeutic intervention through the targeting of pro-resolution, rather than anti-inflammatory pathways.

Exploiting the pro-resolving actions of glucocorticoid-induced proteins Annexin A1 and GILZ in infectious diseases

For decades, glucocorticoids (GC) have been used to treat several inflammatory conditions, including chronic and autoimmune diseases, due to their potent anti-inflammatory properties. In the context of infectious diseases, the use of GCs may be effective as adjuvant to antibiotic therapy by controlling excessive inflammatory responses resulting in better outcome in some cases. However, the use of GCs has been associated with a vast number of side effects, including increased probability of immunosuppression and consequent risk of opportunistic infection. Glucocorticoid-induced leucine zipper (GILZ) and Annexin A1 (AnxA1) are GC-induced proteins intrinsically involved with the anti-inflammatory functions of GCs without the associated adverse metabolic effects. Recent studies have shown that these GC-proteins exhibit pro-resolving effects. An essential characteristic of pro-resolving molecules is their ability to coordinate the resolution of inflammation and promote host defense in most experimental models of infection. Although the role of GILZ and AnxA1 in the context of infectious diseases remain to be better explored, herein we provide an overview of the emerging functions of these GC-proteins obtained from pre-clinical models of infectious diseases.

Formyl peptide receptor type 2 agonists to kick-start resolution pharmacology

One way to develop innovative approaches for the treatment of chronic diseases is to exploit the biology of the resolution of inflammation. With this terminology, we identify the integrated and complex network of mediators and pathways that ensure a timely and spatially regulated inflammatory response. Pro-resolving mediators act on specific receptors. This provides an opportunity for developing a new arm of pharmacology we have termed "resolution pharmacology." Here we present the reasoning behind the need to develop new medicines based on resolution and use a prototype GPCR as an example. Understanding how the formyl peptide receptor type 2 (FPR2) operates in a cell-specific manner can guide the development of agonists as new therapeutics that could be of benefit as a therapy or co-therapy for several diseases that affect our society. FPR2 agonists would be among the first drugs to establish "resolution pharmacology" as the pharmacological approach for the third decade of the millennium.

RvE1 Attenuates Polymicrobial Sepsis-Induced Cardiac Dysfunction and Enhances Bacterial Clearance

The development of cardiac dysfunction caused by microbial infection predicts high mortality in sepsis patients. Specialized pro-resolving mediators (SPMs) mediate resolution of inflammation in many inflammatory diseases, and are differentially expressed in plasma of sepsis patients. Here, we investigated whether the levels of SPMs are altered in the murine septic heart following polymicrobial sepsis-induced cardiac dysfunction. Ten weeks-old male C57BL/6 mice were subjected to polymicrobial sepsis induced by cecal ligation and puncture (CLP), which is a clinically relevant sepsis model receiving analgesics, antibiotics, and fluid resuscitation. CLP caused a significant systolic dysfunction assessed by echocardiography. The hearts were subjected to LC-MS/MS based lipid mediator profiling. Many SPMs were significantly reduced in septic hearts, among which RvE1 had a ~93-fold reduction. Treatment of CLP mice with synthetic RvE1 (1 μg/mouse i.v.) at 1 h after CLP increased peritoneal macrophages number, particularly MHC II^- macrophages. RvE1 reduced pro-inflammatory gene expression (interleukin-1β, interleukin-6, and CCL2) in lipopolysaccharide-stimulated bone marrow-derived macrophages (BMDMs) in vitro. RvE1 attenuated cardiac dysfunction in septic mice and increased cardiac phosphorylated Akt; decreased cardiac phosphorylated IκB kinase α/β, nuclear translocation of the NF-κB subunit p65, extracellular signal-regulated kinase 1/2, and c-Jun amino-terminal kinases 1/2. Most notably, RvE1 treatment reduced peritoneal bacterial load and promoted phagocytosis activity of BMDMs. In conclusion, cardiac SPMs, particularly RvE1, are substantially reduced in mice with polymicrobial sepsis. Delayed therapeutic administration of RvE1 to mice with polymicrobial sepsis attenuates the cardiac dysfunction through modulating immuno-inflammatory responses. In addition to the above effects, the ability to enhance bacterial clearance makes RvE1 an ideal therapeutic to reduce the sequalae of polymicrobial sepsis.

Lipoxin A4 impairs effective bacterial control and potentiates joint inflammation and damage caused by Staphylococcus aureus infection

Staphylococcus aureus is the main cause of septic arthritis in humans, a disease associated with high morbidity and mortality. Inflammation triggered in response to infection is fundamental to control bacterial growth but may cause permanent tissue damage. Here, we evaluated the role of Lipoxin A₄ (LXA₄ ) in S aureus-induced arthritis in mice. Septic arthritis was induced by S aureus injection into tibiofemoral joints. At different time points, we evaluated cell recruitment and bacterial load in the joint, the production of pro-inflammatory molecules, and LXA₄ in inflamed tissue and analyzed joint damage and dysfunction. LXA₄ was investigated using genetically modified mice or by pharmacological blockade of its synthesis and receptor. CD11c⁺ cells were evaluated in lymph nodes by confocal microscopy and flow cytometry and dendritic cell chemotaxis using the Boyden chamber. Absence or pharmacological blockade of 5-lipoxygenase (5-LO) reduced joint inflammation and dysfunction and was associated with better control of infection at 4 to 7 days after the infection. There was an increase in LXA₄ in joints of S aureus-infected mice and administration of LXA₄ reversed the phenotype in 5-LO^-/- mice. Blockade or absence of the LXA₄ receptor FPR2 has a phenotype similar to 5-LO^-/- mice. Mechanistically, LXA₄ appeared to control migration and function of dendritic cells, cells shown to be crucial for adequate protective responses in the model. Thus, after the first days of infection when symptoms become evident therapies that inhibit LXA₄ synthesis or action could be useful for treatment of S aureus-induced arthritis.

Harnessing inflammation resolving-based therapeutic agents to treat pulmonary viral infections: What can the future offer to COVID-19?

Inflammation is generally accepted as a component of the host defence system and a protective response in the context of infectious diseases. However, altered inflammatory responses can contribute to disease in infected individuals. Many endogenous mediators that drive the resolution of inflammation are now known. Overall, mediators of resolution tend to decrease inflammatory responses and provide normal or greater ability of the host to deal with infection. In the lung, it seems that pro‐resolution molecules, or strategies that promote their increase, tend to suppress inflammation and lung injury and facilitate control of bacterial or viral burden. Here, we argue that the demonstrated anti‐inflammatory, pro‐resolving, anti‐thrombogenic and anti‐microbial effects of such endogenous mediators of resolution may be useful in the treatment of the late stages of the disease in patients with COVID‐19.

Bioinformatics-Based Study to Investigate Potential Differentially Expressed Genes and miRNAs in Pediatric Sepsis

BACKGROUND Sepsis is an extremely common health issue with a considerable mortality rate in children. Our understanding about the pathogenic mechanisms of sepsis is limited. The aim of this study was to identify the differential expression genes (DEGs) in pediatric sepsis through comprehensive analysis, and to provide specific insights for the clinical sepsis therapies in children. MATERIAL AND METHODS Three pediatric gene expression profiles (GSE25504, GSE26378, GSE26440) were downloaded from the Gene Expression Omnibus (GEO) database. The difference expression genes (DEGs) between pediatric sepsis and normal control group were screened with the GEO2R online tool. The Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway enrichment analyses of the DEGs were performed. Cytoscape with CytoHubba were used to identify the hub genes. Finally, NetworkAnalyst was used to construct the targeted microRNAs (miRNAs) of the hub genes. RESULTS Totally, 160 overlapping upward genes and 61 downward genes were identified. In addition, 5 KEGG pathways, including hematopoietic cell lineage, Staphylococcus aureus infection, starch and sucrose metabolism, osteoclast differentiation, and tumor necrosis factor (TNF) signaling pathway, were significantly enriched using a database for labeling, visualization, and synthetic discovery. In combination with the results of the protein-protein interaction (PPI) network and CytoHubba, 9 hub genes including ITGAM, TLR8, IL1ß, MMP9, MPO, FPR2, ELANE, SPI1, and C3AR1 were selected. Combined with DEG-miRNAs visualization, 5 miRNAs, including has-miR-204-5p, has-miR-211-5p, has-miR-590-5p, and has-miR-21-5p, were predicted as possibly the key miRNAs. CONCLUSIONS Our findings will contribute to identification of potential biomarkers and novel strategies for pediatric sepsis treatment.

Reversal of β-Amyloid-Induced Microglial Toxicity In Vitro by Activation of Fpr2/3

Microglial inflammatory activity is thought to be a major contributor to the pathology of neurodegenerative conditions such as Alzheimer's disease (AD), and strategies to restrain their behaviour are under active investigation. Classically, anti-inflammatory approaches are aimed at suppressing proinflammatory mediator production, but exploitation of inflammatory resolution, the endogenous process whereby an inflammatory reaction is terminated, has not been fully investigated as a therapeutic approach in AD. In this study, we sought to provide proof-of-principle that the major proresolving actor, formyl peptide receptor 2, Fpr2, could be targeted to reverse microglial activation induced by the AD-associated proinflammatory stimulus, oligomeric β-amyloid (oAβ). The immortalised murine microglial cell line BV2 was employed as a model system to investigate the proresolving effects of the Fpr2 ligand QC1 upon oAβ-induced inflammatory, oxidative, and metabolic behaviour. Cytotoxic behaviour of BV2 cells was assessed through the use of cocultures with retinoic acid-differentiated human SH-SY5Y cells. Stimulation of BV2 cells with oAβ at 100 nM did not induce classical inflammatory marker production but did stimulate production of reactive oxygen species (ROS), an effect that could be reversed by subsequent treatment with the Fpr2 ligand QC1. Further investigation revealed that oAβ-induced ROS production was associated with NADPH oxidase activation and a shift in BV2 cell metabolic phenotype, activating the pentose phosphate pathway and NADPH production, changes that were again reversed by QC1 treatment. Microglial oAβ-stimulated ROS production was sufficient to induce apoptosis of bystander SH-SY5Y cells, an effect that could be prevented by QC1 treatment. In this study, we provide proof-of-concept data that indicate exploitation of the proresolving receptor Fpr2 can reverse damaging oAβ-induced microglial activation. Future strategies that are aimed at restraining neuroinflammation in conditions such as AD should examine proresolving actors as a mechanism to harness the brain's endogenous healing pathways and limit neuroinflammatory damage.

Endogenous Specialized Proresolving Mediator Profiles in a Novel Experimental Model of Lymphatic Obstruction and Intestinal Inflammation in African Green Monkeys

Changes in the intestinal lymphatic vascular system, such as lymphatic obstruction, are characteristic features of inflammatory bowel diseases. The lymphatic vasculature forms a conduit to enable resolution of inflammation; this process is driven by specialized endogenous proresolving mediators (SPMs). To evaluate contributions of lymphatic obstruction to intestinal inflammation and to study profiles of SPMs, we generated a novel animal model of lymphatic obstruction using African green monkeys. Follow-up studies were performed at 7, 21, and 61 days. Inflammation was determined by histology. Luminex assays were performed to evaluate chemokine and cytokine levels. In addition, lipid mediator metabololipidomic profiling was performed to identify SPMs. After 7 days, lymphatic obstruction resulted in a localized inflammatory state, paralleled by an increase in inflammatory chemokines and cytokines, which were found to be up-regulated after 7 days but returned to baseline after 21 and 61 days. At the same time, a distinct pattern of SPMs was profiled, with an increase for D-series resolvins, protectins, maresins, and lipoxins at 61 days. These results indicate that intestinal lymphatic obstruction can lead to an acute inflammatory state, accompanied by an increase in proinflammatory mediators, followed by a phase of resolution, paralleled by an increase and decrease of respective SPMs.

The Contribution of Chemoattractant GPCRs, Formylpeptide Receptors, to Inflammation and Cancer

A hallmark of inflammatory responses is leukocyte mobilization, which is mediated by pathogen and host released chemotactic factors that activate Gi-protein-coupled seven-transmembrane receptors (GPCRs) on host cell surface. Formylpeptide receptors (FPRs, Fprs in mice) are members of the chemoattractant GPCR family, shown to be critical in myeloid cell trafficking during infection, inflammation, immune responses, and cancer progression. Accumulating evidence demonstrates that both human FPRs and murine Fprs are involved in a number of patho-physiological processes because of their expression on a wide variety of cell types in addition to myeloid cells. The unique capacity of FPRs (Fprs) to interact with numerous structurally unrelated chemotactic ligands enables these receptors to participate in orchestrated disease initiation, progression, and resolution. One murine Fpr member, Fpr2, and its endogenous agonist peptide, Cathelicidin-related antimicrobial peptide (CRAMP), have been demonstrated as key mediators of colon mucosal homeostasis and protection from inflammation and associated tumorigenesis. Recent availability of genetically engineered mouse models greatly expanded the understanding of the role of FPRs (Fprs) in pathophysiology that places these molecules in the list of potential targets for therapeutic intervention of diseases.

The Annexin A1/FPR2 pathway controls the inflammatory response and bacterial dissemination in experimental pneumococcal pneumonia

Streptococcus pneumoniae is a major cause of community-acquired pneumonia leading to high mortality rates. Inflammation triggered by pneumococcal infection is necessary for bacterial clearance but must be spatially and temporally regulated to prevent further tissue damage and bacterial dissemination. Annexin A1 (AnxA1) mainly acts through Formyl Peptide Receptor 2 (FPR2) inducing the resolution of inflammation. Here, we have evaluated the role of AnxA1 and FPR2 during pneumococcal pneumonia in mice. For that, AnxA1, Fpr2/3 knockout (KO) mice and wild-type (WT) controls were infected intranasally with S pneumoniae. AnxA1 and Fpr2/3 KO mice were highly susceptible to infection, displaying uncontrolled inflammation, increased bacterial dissemination, and pulmonary dysfunction compared to WT animals. Mechanistically, the absence of AnxA1 resulted in the loss of lung barrier integrity and increased neutrophil activation upon S pneumoniae stimulation. Importantly, treatment of WT or AnxA1 KO-infected mice with Ac2-26 decreased inflammation, lung damage, and bacterial burden in the airways by increasing macrophage phagocytosis. Conversely, Ac2-26 peptide was ineffective to afford protection in Fpr2/3 KO mice during infection. Altogether, these findings show that AnxA1, via FPR2, controls inflammation and bacterial dissemination during pneumococcal pneumonia by promoting host defenses, suggesting AnxA1-based peptides as a novel therapeutic strategy to control pneumococcal pneumonia.

Formyl peptide receptor 2 regulates monocyte recruitment to promote intestinal mucosal wound repair

Mucosal wound repair is coordinated by dynamic crosstalk between endogenous and exogenous mediators and specific receptors on epithelial cells and infiltrating immune cells. One class of such receptor-ligand pairs involves formyl peptide receptors (FPRs) that have been shown to influence inflammatory response and repair. Here we explored the role of murine Fpr2/3, an ortholog of human FPR2/receptor for lipoxin A4 (ALX), in orchestrating intestinal mucosal repair. Compared with wild-type (WT) mice, Fpr2/3-/- mice exhibited delayed recovery from acute experimental colitis and perturbed repair after biopsy-induced colonic mucosal injury. Decreased numbers of infiltrating monocytes were observed in healing wounds from Fpr2/3-/- mice compared with WT animals. Bone marrow transplant experiments revealed that Fpr2/3-/- monocytes showed a competitive disadvantage when infiltrating colonic wounds. Moreover, Fpr2/3-/- monocytes were defective in chemotactic responses to the chemokine CC chemokine ligand (CCL)20, which is up-regulated during early phases of inflammation. Analysis of Fpr2/3-/- monocytes revealed altered expression of the CCL20 receptor CC chemokine receptor (CCR)6, suggesting that Fpr2/3 regulates CCL20-CCR6-mediated monocyte chemotaxis to sites of mucosal injury in the gut. These findings demonstrate an important contribution of Fpr2/3 in facilitating monocyte recruitment to sites of mucosal injury to influence wound repair.-Birkl, D., O'Leary, M. N., Quiros, M., Azcutia, V., Schaller, M., Reed, M., Nishio, H., Keeney, J., Neish, A. S., Lukacs, N. W., Parkos, C. A., Nusrat, A. Formyl peptide receptor 2 regulates monocyte recruitment to promote intestinal mucosal wound repair.

Lack of resolution sensor drives age-related cardiometabolic and cardiorenal defects and impedes inflammation-resolution in heart failure

Objective

Recently, we observed that the specialized proresolving mediator (SPM) entity resolvin D1 activates lipoxin A₄/formyl peptide receptor 2 (ALX/FPR2), which facilitates cardiac healing and persistent inflammation is a hallmark of impaired cardiac repair in aging. Splenic leukocyte-directed SPMs are essential for the safe clearance of inflammation and cardiac repair after injury; however, the target of SPMs remains undefined in cardiac healing and repair.

Methods

To define the mechanistic basis of ALX/FPR2 as a resolvin D1 target, ALX/FPR2-null mice were examined extensively. The systolic-diastolic heart function was assessed using echocardiography, leukocytes were phenotyped using flow cytometry, and SPMs were quantitated using mass spectrometry. The presence of cardiorenal syndrome was validated using histology and renal markers.

Results

Lack of ALX/FPR2 led to the development of spontaneous obesity and diastolic dysfunction with reduced survival with aging. After cardiac injury, ALX/FPR2^−/− mice showed lower expression of lipoxygenases (−5, −12, −15) and a reduction in SPMs in the infarcted left ventricle and spleen, indicating nonresolving inflammation. Reduced SPM levels in the infarcted heart and spleen are suggestive of impaired cross-talk between the injured heart and splenic leukocytes, which are required for the resolution of inflammation. In contrast, cyclooxygenases (−1 and −2) were over amplified in the infarcted heart. Together, these results suggest interorgan signaling in which the spleen acts as both an SPM biosynthesizer and supplier in acute heart failure. ALX/FPR2 dysfunction magnified obesogenic cardiomyopathy and renal inflammation (↑NGAL, ↑TNF-α, ↑CCL2, ↑IL-1β) with elevated plasma creatinine levels in aging mice. At the cellular level, ALX/FPR2^−/− mice showed impairment of macrophage phagocytic function ex-vivo with expansion of neutrophils after myocardial infarction.

Conclusions

Lack of ALX/FPR2 induced obesity, reduced the life span, amplified leukocyte dysfunction, and facilitated profound interorgan nonresolving inflammation. Our study shows the integrative and indispensable role of ALX/FPR2 in lipid metabolism, cardiac inflammation–resolution processes, obesogenic aging, and renal homeostasis.

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Lack of resolution sensor (ALX/FPR2) led to spontaneous, age-related obesity.

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Absence of ALX/FPR2 triggered obesogenic cardiomyopathy and renal inflammation.

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Deficiency of ALX/FPR2 reduced SPMs in the infarcted heart after cardiac injury.

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ALX/FPR2 dysfunction impaired macrophage function and amplified inflammation.

Preservation of Post-Infarction Cardiac Structure and Function via Long-Term Oral Formyl Peptide Receptor Agonist Treatment

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Myocardial infarction leads to recruitment of monocyte/macrophages to the injured myocardium to drive infarct healing.

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Activation of formyl peptide receptors (FPR1 and FPR2) present on macrophages contributes to key cellular activities that can potentiate wound healing.

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Myocardial infarction was induced in rodents to study the effects of long-term treatment with Compound 43, a small molecule agonist of FPR1 and FPR2.

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Main findings: Compound 43 stimulated proresolution macrophage activities, improved left ventricle and infarct structure, and preserved cardiac function post-myocardial infarction.

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The results suggest that stimulation of proresolution activities of FPRs can favorably alter post-myocardial infarction pathophysiology that leads to heart failure.

Dysregulated inflammation following myocardial infarction (MI) promotes left ventricular (LV) remodeling and loss of function. Targeting inflammation resolution by activating formyl peptide receptors (FPRs) may limit adverse remodeling and progression towards heart failure. This study characterized the cellular and signaling properties of Compound 43 (Cmpd43), a dual FPR1/FPR2 agonist, and examined whether Cmpd43 treatment improves LV and infarct remodeling in rodent MI models. Cmpd43 stimulated FPR1/2-mediated signaling, enhanced proresolution cellular function, and modulated cytokines. Cmpd43 increased LV function and reduced chamber remodeling while increasing proresolution macrophage markers. The findings demonstrate that FPR agonism improves cardiac structure and function post-MI.

Enhanced Neutrophil Immune Homeostasis Due to Deletion of PHLPP

Neutrophils are known to adopt dynamic and distinct functional phenotypes involved in the modulation of inflammation and immune homeostasis. However, inter-cellular signaling mechanisms that govern neutrophil polarization dynamics are not well understood. Employing a novel model of PHLPP deficient mice, we examined how neutrophils deficient in PHLPP may uniquely modulate immune defense and the host response during acute colitis. We found that PHLPP^-/- mice were protected from dextran sodium sulfate (DSS)-induced septic colitis characterized by minimal body weight-loss, alleviated colon tissue destruction and reduced clinical symptoms. PHLPP^-/- neutrophils have enhanced immune homeostasis as compared to WT neutrophils, reflected in enhanced migratory capacity toward chemoattractants, and reduced expression of inflammatory mediators due to elevated phosphorylation of AKT, STAT1, and ERK. Further, adoptive transfer of PHLPP deficient neutrophils to WT mice is sufficient to potently alleviate the severity of DSS-induced colitis. Our data reveal that PHLPP deficient neutrophils can be uniquely reprogrammed to a state conducive to host inflammation resolution. As a consequence, PHLPP^-/- neutrophils can effectively transfer immune homeostasis in mice subjected to acute colitis. Our findings hold significant and novel insights into the mechanisms by which neutrophils can be effectively reprogrammed into a homeostatic state conducive for treating acute injuries such as septic colitis.

Chemotactic Ligands that Activate G-Protein-Coupled Formylpeptide Receptors

Leukocyte infiltration is a hallmark of inflammatory responses. This process depends on the bacterial and host tissue-derived chemotactic factors interacting with G-protein-coupled seven-transmembrane receptors (GPCRs) expressed on the cell surface. Formylpeptide receptors (FPRs in human and Fprs in mice) belong to the family of chemoattractant GPCRs that are critical mediators of myeloid cell trafficking in microbial infection, inflammation, immune responses and cancer progression. Both murine Fprs and human FPRs participate in many patho-physiological processes due to their expression on a variety of cell types in addition to myeloid cells. FPR contribution to numerous pathologies is in part due to its capacity to interact with a plethora of structurally diverse chemotactic ligands. One of the murine Fpr members, Fpr2, and its endogenous agonist peptide, Cathelicidin-related antimicrobial peptide (CRAMP), control normal mouse colon epithelial growth, repair and protection against inflammation-associated tumorigenesis. Recent developments in FPR (Fpr) and ligand studies have greatly expanded the scope of these receptors and ligands in host homeostasis and disease conditions, therefore helping to establish these molecules as potential targets for therapeutic intervention.

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.

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.

Basophil-derived tumor necrosis factor can enhance survival in a sepsis model in mice

Basophils are evolutionarily conserved in vertebrates, despite their small numbers and short lifespan, suggesting that basophils have beneficial roles in maintaining health. However, these roles are not fully defined. Here, we demonstrate that basophil-deficient mice exhibited reduced bacterial clearance, and increased morbidity and mortality, in the cecal ligation and puncture (CLP) model of sepsis. Among the several pro-inflammatory mediators we measured, tumor necrosis factor (TNF) was the only cytokine that was significantly reduced in basophil-deficient mice after CLP. In accordance with that observation, we found that mice with genetic ablation of Tnf in basophils exhibited reduced systemic TNF concentrations during endotoxemia. Moreover, during CLP, mice whose basophils could not produce TNF exhibited reduced neutrophil and macrophage TNF production and effector functions, reduced bacterial clearance, and increased mortality. Taken together, our studies show that basophils can enhance the innate immune response against bacterial infection and help prevent sepsis.