Toll-like receptor-4 (TLR4) signaling augments chemokine-induced neutrophil migration by modulating cell surface expression of chemokine receptors

Chemerin attracts neutrophil reverse migration by interacting with C-C motif chemokine receptor-like 2

Neutrophil reverse migration (rM) is a recently identified phenomenon in which neutrophils migrate away from the inflammatory site back into the vasculature following initial infiltration, which involved in the resolution of loci inflammatory response or dissemination of inflammation. Present study was aimed to explore the mechanisms in neutrophil rM. By scRNA-seq on the white blood cells in acute lung injury model, we found rM-ed neutrophils exhibited increased gene expression of C-C motif chemokine receptor-like 2 (Ccrl2), an atypical chemokine receptor. Furthermore, an air pouch model was established to directly track rM-ed neutrophils in vivo. Air pouches were generated by 3 ml filtered sterile air injected subcutaneously for 3 days, and then LPS (2 mg/kg) was injected into the pouches to mimic the inflammatory state. For the rM-ed neutrophil tracking system, cell tracker CMFDA were injected into the air pouch to stain the inflammatory loci cells, and after 6 h, stained cells in blood were regarded as the rM-ed neutrophil. Based on this tracking system, we confirmed that rM-ed neutrophils showed increased CCRL2. We also found that the concentrations of the CCRL2 ligand chemerin in plasma was increased in the late stage. Neutralizing chemerin decreased the rM-ed neutrophil ratio in the blood. These results suggest that circulating chemerin attracts neutrophils to leave inflammatory sites by interacting with CCRL2, which might involve in the dissemination of inflammation.

Toll-like receptor 4 in pancreatic damage and immune infiltration in acute pancreatitis

Acute pancreatitis is a complex inflammatory disease resulting in extreme pain and can result in significant morbidity and mortality. It can be caused by several factors ranging from genetics, alcohol use, gall stones, and ductal obstruction caused by calcification or neutrophil extracellular traps. Acute pancreatitis is also characterized by immune cell infiltration of neutrophils and M1 macrophages. Toll-like receptor 4 (TLR4) is a pattern recognition receptor that has been noted to respond to endogenous ligands such as high mobility group box 1 (HMGB1) protein and or exogenous ligands such as lipopolysaccharide both of which can be present during the progression of acute pancreatitis. This receptor can be found on a variety of cell types from endothelial cells to resident and infiltrating immune cells leading to production of pro-inflammatory cytokines as well as immune cell activation and maturation resulting in the furthering of pancreatic damage during acute pancreatitis. In this review we will address the various mechanisms mediated by TLR4 in the advancement of acute pancreatitis and how targeting this receptor could lead to improved outcomes for patients suffering from this condition.

DANGER Signals Activate G -Protein Receptor Kinases Suppressing Neutrophil Function and Predisposing to Infection After Tissue Trauma

OBJECTIVE

Injured tissue predisposes the subject to local and systemic infection. We studied injury-induced immune dysfunction seeking novel means to reverse such predisposition.

BACKGROUND

Injury mobilizes primitive "DANGER signals" [danger-associated molecular patterns (DAMPs)] activating innate immunocyte (neutrophils, PMN) signaling and function. Mitochondrial formyl peptides activate G -protein coupled receptors (GPCR) like formyl peptide receptor-1. Mitochondrial DNA and heme activate toll-like receptors (TLR9 and TLR2/4). GPCR kinases (GRKs) can regulate GPCR activation.

METHODS

We studied human and mouse PMN signaling elicited by mitochondrial DAMPs (GPCR surface expression; protein phosphorylation, or acetylation; Ca 2+ flux) and antimicrobial functions [cytoskeletal reorganization, chemotaxis (CTX), phagocytosis, bacterial killing] in cellular systems and clinical injury samples. Predicted rescue therapies were assessed in cell systems and mouse injury-dependent pneumonia models.

RESULTS

Mitochondrial formyl peptides activate GRK2, internalizing GPCRs and suppressing CTX. Mitochondrial DNA suppresses CTX, phagocytosis, and killing through TLR9 through a novel noncanonical mechanism that lacks GPCR endocytosis. Heme also activates GRK2. GRK2 inhibitors like paroxetine restore functions. GRK2 activation through TLR9 prevented actin reorganization, implicating histone deacetylases (HDACs). Actin polymerization, CTX, bacterial phagocytosis, and killing were also rescued, therefore, by the HDAC inhibitor valproate. Trauma repository PMN showed GRK2 activation and cortactin deacetylation, which varied with severity and was most marked in patients developing infections. Either GRK2 or HDAC inhibition prevented loss of mouse lung bacterial clearance, but only the combination rescued clearance when given postinjury.

CONCLUSIONS

Tissue injury-derived DAMPs suppress antimicrobial immunity through canonical GRK2 activation and a novel TLR-activated GRK2-pathway impairing cytoskeletal organization. Simultaneous GRK2/HDAC inhibition rescues susceptibility to infection after tissue injury.

Sustained induction of IP-10 by MRP8/14 via the IFNβ-IRF7 axis in macrophages exaggerates lung injury in endotoxemic mice

Background

As a damage-associated molecular pattern, the myeloid-related protein 8/14 (MRP8/14) heterodimer mediates various inflammatory diseases, such as sepsis. However, how MRP8/14 promotes lung injury by regulating the inflammatory response during endotoxemia remains largely unknown. This study aims at illuminating the pathological functions of MRP8/14 in endotoxemia.

Methods

An endotoxemic model was prepared with wild-type and myeloid cell-specific Mrp8 deletion (Mrp8ΔMC) mice for evaluating plasma cytokine levels. Lung injury was evaluated by hematoxylin and eosin (H&E) staining, injury scoring and wet-to-dry weight (W/D) ratio. The dynamic profile of interferon γ (IFNγ)-inducible protein 10 (IP-10) mRNA expression induced by macrophage MRP8/14 was determined by quantitative real-time polymerase chain reaction (qPCR). Immunoblotting was used to evaluate the increase in IP-10 level induced by activation of the JAK-STAT signaling pathway. Luciferase reporter assay was performed to detect the involvement of IRF7 in Ip-10 gene transcription. In vivo air pouch experiments were performed to determine the biological function of IP-10 induced by MRP8/14.

Results

Experiments with Mrp8ΔMC mice showed that MRP8/14 promoted the production of cytokines, including IP-10, in the bronchoalveolar lavage fluid (BALF) and lung injury in endotoxic mice. The result of qPCR showed sustained expression of Ip-10 mRNA in macrophages after treatment with MRP8/14 for 12 h. Neutralization experiments showed that the MRP8/14-induced Ip-10 expression in RAW264.7 cells was mediated by extracellular IFNβ. Western blotting with phosphorylation-specific antibodies showed that the JAK1/TYK2-STAT1 signaling pathway was activated in MRP8/14-treated RAW264.7 cells, leading to the upregulation of Ip-10 gene expression. IRF7 was further identified as a downstream regulator of the JAK-STAT pathway that mediated Ip-10 gene expression in macrophages treated with MRP8/14. In vivo air pouch experiments confirmed that the IFNβ-JAK1/TYK2-STAT1-IRF7 pathway was required for chemokine (C-X-C motif) receptor 3 (CXCR3)+ T lymphocyte migration, which promoted lung injury in the context of endotoxemia.

Conclusions

In summary, our study demonstrates that MRP8/14 induces sustained production of IP-10 via the IFNβ-JAK1/TYK2-STAT1-IRF7 pathway to attract CXCR3+ T lymphocytes into lung tissues and ultimately results in lung injury by an excessive inflammatory response in the context of endotoxemia.

METTL3-mediated m6A mRNA methylation regulates neutrophil activation through targeting TLR4 signaling

N6-methyladenosine (m6A) modification accounts for the most prevalent mRNA internal modification and has emerged as a widespread regulatory mechanism in multiple physiological processes. We address a role of methyltransferase-like protein 3 (METTL3) in neutrophil activation. METTL3 controls neutrophil release from bone marrow to circulation through surface expression of CXC chemokine receptor 2 (CXCR2) in a Toll-like receptor 4 (TLR4) signaling-dependent manner in lipopolysaccharide (LPS)-induced endotoxemia. We show that the mRNA of TLR4 is modified by m6A, exhibiting increased translation and slowed degradation simultaneously, leading to elevated protein levels of TLR4, which eventually promotes the TLR4 signaling activation of neutrophil. The reduced expression of TLR4 lowers cytokine secretion in METTL3-deleted neutrophils upon LPS stimulation through TLR4/Myd88/nuclear factor κB (NF-κB) signaling. Collectively, these data demonstrate that METTL3 modulation of TLR4 expression is a critical determinant of neutrophil activation in endotoxemia.

The role of G protein-coupled receptor in neutrophil dysfunction during sepsis-induced acute respiratory distress syndrome

Sepsis is defined as a life-threatening dysfunction due to a dysregulated host response to infection. It is a common and complex syndrome and is the leading cause of death in intensive care units. The lungs are most vulnerable to the challenge of sepsis, and the incidence of respiratory dysfunction has been reported to be up to 70%, in which neutrophils play a major role. Neutrophils are the first line of defense against infection, and they are regarded as the most responsive cells in sepsis. Normally, neutrophils recognize chemokines including the bacterial product N-formyl-methionyl-leucyl-phenylalanine (fMLP), complement 5a (C5a), and lipid molecules Leukotriene B4 (LTB4) and C-X-C motif chemokine ligand 8 (CXCL8), and enter the site of infection through mobilization, rolling, adhesion, migration, and chemotaxis. However, numerous studies have confirmed that despite the high levels of chemokines in septic patients and mice at the site of infection, the neutrophils cannot migrate to the proper target location, but instead they accumulate in the lungs, releasing histones, DNA, and proteases that mediate tissue damage and induce acute respiratory distress syndrome (ARDS). This is closely related to impaired neutrophil migration in sepsis, but the mechanism involved is still unclear. Many studies have shown that chemokine receptor dysregulation is an important cause of impaired neutrophil migration, and the vast majority of these chemokine receptors belong to the G protein-coupled receptors (GPCRs). In this review, we summarize the signaling pathways by which neutrophil GPCR regulates chemotaxis and the mechanisms by which abnormal GPCR function in sepsis leads to impaired neutrophil chemotaxis, which can further cause ARDS. Several potential targets for intervention are proposed to improve neutrophil chemotaxis, and we hope that this review may provide insights for clinical practitioners.

Antimicrobial peptides could antagonize uncontrolled inflammation via Toll-like 4 receptor

Antimicrobial peptides are part of the organism's defense system. They are multifunctional molecules capable of modulating the host's immune system and recognizing molecules present in pathogens such as lipopolysaccharides (LPSs). LPSs are recognized by molecular patterns associated with pathogens known as Toll-like receptors (TLRs) that protect the organism from pathological microorganisms. TLR4 is responsible for LPS recognition, thus inducing an innate immune response. TLR4 hyperstimulation induces the uncontrolled inflammatory process that is observed in many illnesses, including neurodegenerative, autoimmune and psoriasis). Molecules that act on TLR4 can antagonize the exacerbated inflammatory process. In this context, antimicrobial peptides (AMPs) are promising molecules capable of mediating toll-like receptor signaling. Therefore, here we address the AMPs studied so far with the aim of inhibiting the intense inflammatory process. In addition, we aim to explore some of the interactions between exogenous AMPs and TLR4.

KIAA1199 drives immune suppression to promote colorectal cancer liver metastasis by modulating neutrophil infiltration

BACKGROUND AND AIMS

Metastasis is the primary cause of cancer mortality, and colorectal cancer (CRC) frequently metastasizes to the liver. Our previous studies demonstrated the critical role of KIAA1199 in tumor invasion and metastasis in CRC. In the present study, we described an immune regulatory effect of KIAA1199 that creates a permissive environment for metastasis.

APPROACH AND RESULTS

Flow cytometry was used to examine the effects of KIAA1199 on the infiltration of tumor immune cells. Neutrophils and T cells were isolated, stimulated, and/or cultured for in vitro function assays. In the patients with CRC, high expression levels of KIAA1199 were associated with an increased neutrophil infiltration into the liver. This result was further validated in mouse metastasis models. The increased influx of neutrophils contributed to the KIAA1199-driven CRC liver metastasis. Mechanistically, KIAA1199 activated the TGFβ signaling pathway by interacting with the TGFBR1/2 to stimulate CXCL1 and CXCL3 production, thereby driving the aggregation of immunosuppressive neutrophils. Genetic blockade or pharmacologic inhibition of KIAA1199 restored tumor immune infiltration, impeded tumor progression, and potentiated response to immune checkpoint blockade (ICB).

CONCLUSIONS

These findings indicated that KIAA1199 could facilitate the liver infiltration of immunosuppressive neutrophils via the TGFβ-chemokine (C-X-C motif) ligand (CXCL)3/1-CXCR2 axis, which might be clinically targeted for the treatment of hepatic metastasis.

Flightless I Negatively Regulates Macrophage Surface TLR4, Delays Early Inflammation, and Impedes Wound Healing

TLR4 plays a pivotal role in orchestrating inflammation and tissue repair. Its expression has finally been balanced to initiate the early, robust immune response necessary for efficient repair without excessively amplifying and prolonging inflammation, which impairs healing. Studies show Flightless I (Flii) is an immunomodulator that negatively regulates macrophage TLR4 signalling. Using macrophages from Flii^+/−, WT, and Flii^Tg/Tg mice, we have shown that elevated Flii reduces early TLR4 surface expression, delaying and reducing subsequent TNF secretions. In contrast, reduced Flii increases surface TLR4, leading to an earlier robust TNF peak. In Flii^+/− mice, TLR4 levels peak earlier during wound repair, and overall healing is accelerated. Fewer neutrophils, monocytes and macrophages are recruited to Flii^+/− wounds, leading to fewer TNF-positive macrophages, alongside an early peak and a robust shift to M2 anti-inflammatory, reparative Ym1⁺ and IL-10⁺ macrophages. Importantly, in diabetic mice, high Flii levels are found in plasma and unwounded skin, with further increases observed in their wounds, which have impaired healing. Lowering Flii in diabetic mice results in an earlier shift to M2 macrophages and improved healing. Overall, this suggests Flii regulation of TLR4 reduces early inflammation and decreases the M2 macrophage phenotype, leading to impaired healing.

Spatial barcoding-enabled highly multiplexed immunoassay with digital microfluidics

Digital microfluidics (DMF), facilitating independent manipulation of microliter samples, provides an ideal platform for immunoassay detection; however, suffering limited multiplexity. To address the need, herein we described a digital microfluidics (DMF) platform that realizes spatial barcoding on the Teflon-coated indium tin oxide (ITO) glass side to fulfill highly multiplexed immunoassay (10+) with low-volume samples (∼4 μL) in parallel, representing the highest multiplexing recorded to date for DMF-actuated immunoassay. Planar-based spatial immobilization of multiple capture antibodies was realized on a Teflon-coated ITO glass side, which was then used as the top plate of the DMF device. Droplets containing analytes, secondary antibodies, and fluorescent signaling reporters with low volume, which were electrically manipulated by our DMF control system, were shuttled sequentially along the working electrodes to complete the immuno-reaction. Evaluation of platform performance with recombinant proteins showed excellent sensitivity and reproducibility. To test the feasibility of our platform in analyzing multiplex biomarkers of the immune response, we used lipopolysaccharide-stimulated macrophages as a model system for protein secretion dynamics studies. As a result, temporal profiling of pro-inflammatory cytokine secretion dynamics was obtained. The spatial barcoding strategy presented here is easy-to-operate to enable a more comprehensive evaluation of protein abundance from biological samples, paving the way for new opportunities to realize multiplexity-associated applications with the DMF platform.

Regulation of TLR10 Expression and Its Role in Chemotaxis of Human Neutrophils

Toll-like receptors are innate immune receptors that play a critical role in pathogen-associated molecular pattern recognition. TLR10 was recently identified and very limited data are available on its expression, mechanisms that regulate its expression, and its role in primary immune cells. To study the expression pattern of TLR10 in primary immune cells, we examined TLR10 protein expression in naive and Escherichia coli lipopolysaccharide (LPS)-activated human neutrophils. Human neutrophils challenged with LPS showed a decrease in total and surface TLR10 expression at 90 min. TLR10 in LPS-activated neutrophils colocalized with flotallin-1, a lipid raft marker, and EEA-1, an early endosomal marker, to suggest its endocytosis. There was increased colocalization of TLR10 with TLR4 at LPS 60 min followed by decrease at later LPS treatment times. Treatment with TLR4 neutralizing antibody decreased cytoplasmic localization of TLR10 in LPS-treated neutrophils. Reactive oxygen species (ROS) depletion and neutralization of p65 subunit of NF-κB in LPS-treated neutrophils decreased TLR10 expression. Live cell imaging of LPS-activated neutrophils showed TLR10 translocation in the leading edge and TLR10 knockdown in neutrophils reduced their fMLP-induced chemotaxis and the number of neutrophils with pseudopodia but without affecting the expression of key proteins of actin nucleation process, ARP-3 and Diap1. Taken together, our findings show that neutrophil activation alters TLR10 expression through ROS production and NF-κB regulation, and TLR10 knockdown reduced neutrophil chemotaxis.

Neutrophils: Amoeboid Migration and Swarming Dynamics in Tissues

Neutrophils are key cells of our innate immune response with essential roles for eliminating bacteria and fungi from tissues. They are also the prototype of an amoeboid migrating leukocyte. As one of the first blood-recruited immune cell types during inflammation and infection, these cells can invade almost any tissue compartment. Once in the tissue, neutrophils undergo rapid shape changes and migrate at speeds higher than most other immune cells. They move in a substrate-independent manner in interstitial spaces and do not follow predetermined tissue paths. Instead, neutrophil navigation is largely shaped by the chemokine and chemoattractant milieu around them. This highlights the decisive role of attractant-sensing G-protein coupled receptors (GPCRs) and downstream molecular pathways for controlling amoeboid neutrophil movement in tissues. A diverse repertoire of cell-surface expressed GPCRs makes neutrophils the perfect sentinel cell type to sense and detect danger-associated signals released from wounds, inflamed interstitium, dying cells, complement factors or directly from tissue-invading microbes. Moreover, neutrophils release attractants themselves, which allows communication and coordination between individual cells of a neutrophil population. GPCR-mediated positive feedback mechanisms were shown to underlie neutrophil swarming, a population response that amplifies the recruitment of amoeboid migrating neutrophils to sites of tissue injury and infection. Here we discuss recent findings and current concepts that counteract excessive neutrophil accumulation and swarm formation. In particular, we will focus on negative feedback control mechanisms that terminate neutrophil swarming to maintain the delicate balance between tissue surveillance, host protection and tissue destruction.

GRK2 regulates group 2 innate lymphoid cell mobilization in sepsis

BACKGROUND

Sepsis induces group 2 innate lymphoid cell (ILC2) expansion in the lung. However, the origin of these lung-recruited ILC2 and the mechanism of ILC2 expansion are unclear. This study aims to determine the origin of lung-recruited ILC2 and its underlying mechanism in sepsis.

METHODS

Sepsis was induced by cecal ligation and puncture (CLP) model in wild-type, IL-33-deficient and ST2-deficient mice. The frequency, cell number and C-X-C chemokine receptor 4 (CXCR4) expression of ILC2 in bone marrow (BM), blood and lung were measured by flow cytometry. In the in vitro studies, purified ILC2 progenitor (ILC2p) were challenged with IL-33 or G protein-coupled receptor kinase 2 (GRK2) inhibitor, the CXCR4 expression and GRK2 activity were detected by confocal microscopy or flow cytometry.

RESULTS

We show that IL-33 acts through its receptor, ST2, on BM ILC2p to induce GRK2 expression and subsequent downregulation of cell surface expression of CXCR4, which results in decreasing retention of ILC2p in the BM and promoting expansion of ILC2 in the lung. Importantly, we demonstrate that reduced IL-33 level in aging mice contributes to impaired ILC2 mobilization from BM and accumulation in the lung following sepsis.

CONCLUSION

This study identifies a novel pathway in regulating ILC2p mobilization and expansion during sepsis and indicates BM as the main source of ILC2 in the lung following sepsis.

GRK5 Deficiency Causes Mild Cognitive Impairment due to Alzheimer's Disease

Prevention of Alzheimer's disease (AD) is a high priority mission while searching for a disease modifying therapy for AD, a devastating major public health crisis. Clinical observations have identified a prodromal stage of AD for which the patients have mild cognitive impairment (MCI) though do not yet meet AD diagnostic criteria. As an identifiable transitional stage before the onset of AD, MCI should become the high priority target for AD prevention, assuming successful prevention of MCI and/or its conversion to AD also prevents the subsequent AD. By pulling this string, one demonstrated cause of amnestic MCI appears to be the deficiency of G protein-coupled receptor-5 (GRK5). The most compelling evidence is that GRK5 knockout (GRK5KO) mice naturally develop into aMCI during aging. Moreover, GRK5 deficiency was reported to occur during prodromal stage of AD in CRND8 transgenic mice. When a GRK5KO mouse was crossbred with Tg2576 Swedish amyloid precursor protein transgenic mouse, the resulted double transgenic GAP mice displayed exaggerated behavioral and pathological changes across the spectrum of AD pathogenesis. Therefore, the GRK5 deficiency possesses unique features and advantage to serve as a prophylactic therapeutic target for MCI due to AD.

Exosomal miR-30d-5p of neutrophils induces M1 macrophage polarization and primes macrophage pyroptosis in sepsis-related acute lung injury

BACKGROUND

Polymorphonuclear neutrophils (PMNs) play an important role in sepsis-related acute lung injury (ALI). Accumulating evidence suggests PMN-derived exosomes as a new subcellular entity acting as a fundamental link between PMN-driven inflammation and tissue damage. However, the role of PMN-derived exosomes in sepsis-related ALI and the underlying mechanisms remains unclear.

METHODS

Tumor necrosis factor-α (TNF-α), a key regulator of innate immunity in sepsis-related ALI, was used to stimulate PMNs from healthy C57BL/6J mice in vitro. Exosomes isolated from the supernatant were injected to C57BL/6J wild-type mice intraperitoneally (i.p.) and then examined for lung inflammation, macrophage (Mϕ) polarization and pyroptosis. In vitro co-culture system was applied where the mouse Raw264.7 macrophages or bone marrow-derived macrophages (BMDMs) were co-cultured with PMN-derived exosomes to further confirm the results of in vivo animal study and explore the potential mechanisms involved.

RESULTS

Exosomes released by TNF-α-stimulated PMNs (TNF-Exo) promoted M1 macrophage activation after in vivo i.p. injection or in vitro co-culture. In addition, TNF-Exo primed macrophage for pyroptosis by upregulating NOD-like receptor 3 (NLRP3) inflammasome expression through nuclear factor κB (NF-κB) signaling pathway. Mechanistic studies demonstrated that miR-30d-5p mediated the function of TNF-Exo by targeting suppressor of cytokine signaling (SOCS-1) and sirtuin 1 (SIRT1) in macrophages. Furthermore, intravenous administration of miR-30d-5p inhibitors significantly decreased TNF-Exo or cecal ligation and puncture (CLP)-induced M1 macrophage activation and macrophage death in the lung, as well as the histological lesions.

CONCLUSIONS

The present study demonstrated that exosomal miR-30d-5p from PMNs contributed to sepsis-related ALI by inducing M1 macrophage polarization and priming macrophage pyroptosis through activating NF-κB signaling. These findings suggest a novel mechanism of PMN-Mϕ interaction in sepsis-related ALI, which may provide new therapeutic strategies in sepsis patients.

Clec4e-Receptor Signaling in Myocardial Repair After Ischemia-Reperfusion Injury

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The role of the CLEC4E during myocardial healing after ischemia-reperfusion injury is unknown.

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CLEC4E deletion is associated with reduced cardiac injury, inflammation, and left ventricular structural and functional remodeling.

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CLEC4E is a promising target to modulate myocardial inflammation and enhance repair after ischemia-reperfusion injury.

The bacterial C-type lectin domain family 4 member E (CLEC4E) has an important role in sterile inflammation, but its role in myocardial repair is unknown. Using complementary approaches in porcine, murine, and human samples, we show that CLEC4E expression levels in the myocardium and in blood correlate with the extent of myocardial injury and left ventricular (LV) functional impairment. CLEC4E expression is markedly increased in the vasculature, cardiac myocytes, and infiltrating leukocytes in the ischemic heart. Loss of Clec4e signaling is associated with reduced acute cardiac injury, neutrophil infiltration, and infarct size. Reduced myocardial injury in Clec4e^–/– translates into significantly improved LV structural and functional remodeling at 4 weeks’ follow-up. The early transcriptome of LV tissue from Clec4e^–/– mice versus wild-type mice reveals significant upregulation of transcripts involved in myocardial metabolism, radical scavenging, angiogenesis, and extracellular matrix organization. Therefore, targeting CLEC4E in the early phase of ischemia-reperfusion injury is a promising therapeutic strategy to modulate myocardial inflammation and enhance repair after ischemia-reperfusion injury.

Neutrophils self-limit swarming to contain bacterial growth in vivo

Neutrophils communicate with each other to form swarms in infected organs. Coordination of this population response is critical for the elimination of bacteria and fungi. Using transgenic mice, we found that neutrophils have evolved an intrinsic mechanism to self-limit swarming and avoid uncontrolled aggregation during inflammation. G protein-coupled receptor (GPCR) desensitization acts as a negative feedback control to stop migration of neutrophils when they sense high concentrations of self-secreted attractants that initially amplify swarming. Interference with this process allows neutrophils to scan larger tissue areas for microbes. Unexpectedly, this does not benefit bacterial clearance as containment of proliferating bacteria by neutrophil clusters becomes impeded. Our data reveal how autosignaling stops self-organized swarming behavior and how the finely tuned balance of neutrophil chemotaxis and arrest counteracts bacterial escape.

Pathophysiological and pharmacological relevance of TLR4 in peripheral immune cells after stroke

Stroke is a very common disease being the leading cause of death and disability worldwide. The immune response subsequent to an ischemic stroke is a crucial factor in its physiopathology and outcome. This response is not limited to the injury site. In fact, the immune response to the ischemic process mobilizes mainly circulating cells which upon activation will be recruited to the injury site. When a stroke occurs, molecules that are usually retained inside the cell bodies are released into the extracellular space by uncontrolled cell death. These molecules can bind to the Toll-like receptor 4 (TLR4) in circulating immune cells which are then activated, eliciting, although not exclusively, the inflammatory response to the stroke. In this review, we present an up-to-date summary of the role of the different peripheral immune cells in stroke as well as the role of TLR4 in the function of each cell type in ischemia. Also, we summarize the different antagonists developed against TLR4 and their potential as a pharmacological tool for stroke treatment.

Lipopolysaccharides increase the risk of colorectal cancer recurrence and metastasis due to the induction of neutrophil extracellular traps after curative resection

BACKGROUND

Intra-abdominal infection after curative surgery for colorectal cancer is a serious complication associated with an increased risk of recurrence. Lipopolysaccharides (LPS)-an essential component of the cell wall of Gram-negative bacteria-were found to exert a protumorigenic effect by stimulating the inflammatory pathology and formation of neutrophil extracellular traps (NETs). This study was conducted to test whether LPS-induced formation of NETs promotes the development of cancer and metastasis.

METHODS

The clinical characteristics, incidence of relapse, and serum myeloperoxidase-DNA complexes of 40 patients with infection and 40 patients without infection after curative surgery were analyzed. The effects of LPS on the induction of NETs were evaluated in a mouse model of colorectal cancer and liver metastasis. The toll-like receptor 9 (TLR9)-a DNA receptor-was knocked down to assess its effect on the mitogen-activated protein kinase pathway and activities implicated in the formation of NETs.

RESULTS

Analysis of the clinical data obtained from these patients showed the significant relation of the formation of NETs and incidence of metastasis and survival rates. Subsequent in vitro experiments revealed an increased level of citrullinated-histone H3 and myeloperoxidase-DNA in LPS-injected mice with colorectal cancer. In the mimic metastatic model, injection of LPS enhanced the metastatic capacity, which was then attenuated by DNase I. This suggested that the formation of NETs was activated by LPS. Injection of TLR9-knockdown HCT116 cells in mice, followed by induction through LPS, mitigated the level of citrullinated-histone H3 and myeloperoxidase-DNA. This finding implied that the formation of NETs was suppressed.

CONCLUSION

These findings shed light on the mechanism underlying the relationship between the elevated rate of colorectal cancer recurrence in patients who underwent surgery and the incidence of infection. This mechanism involves the protumorigenic activities of LPS-induced formation of NETs. The NETs which could be mediated by the TLR9 and the mitogen-activated protein kinase signaling pathway.

Immunomodulation by epigenome alterations in Mycobacterium tuberculosis infection

Mycobacterium tuberculosis (MTB) has co-evolved with humans for decades and developed several mechanisms to evade host immunity. It can efficiently alter the host epigenome, thus playing a major role in immunomodulation by either activating or suppressing genes responsible for mounting an immune response against the pathogen. Epigenetic modifications such as DNA methylation and chromatin remodelling regulate gene expression and influence several cellular processes. The involvement of epigenetic factors in disease onset and development had been overlooked upon in comparison to genetic mutations. It is now believed that assessment of epigenetic changes hold great potential in diagnosis, prevention and treatment strategies for a wide range of diseases. In this review, we unravel the principles of epigenetics and the numerous ways by which MTB re-shapes the host epigenetic landscape as a strategy to overpower the host immune system for its survival and persistence.

MicroLet-7b Regulates Neutrophil Function and Dampens Neutrophilic Inflammation by Suppressing the Canonical TLR4/NF-κB Pathway

Sepsis is a heterogeneous syndrome caused by a dysregulated host response during the process of infection. Neutrophils are involved in the development of sepsis due to their essential role in host defense. COVID-19 is a viral sepsis. Disfunction of neutrophils in sepsis has been described in previous studies, however, little is known about the role of microRNA-let-7b (miR-let-7b), toll-like receptor 4 (TLR4), and nuclear factor kappa B (NF-κB) activity in neutrophils and how they participate in the development of sepsis. In this study, we investigated the regulatory pathway of miR-let-7b/TLR4/NF-κB in neutrophils. We also explored the downstream cytokines released by neutrophils following miR-let-7b treatment and its therapeutic effects in cecal ligation and puncture (CLP)-induced septic mice. Six-to-eight-week-old male C57BL/6 mice underwent CLP following treatment with miR-let-7b agomir. Survival (n=10), changes in liver and lungs histopathology (n=4), circulating neutrophil counts (n=4), the liver-body weight ratio (n=4–7), and the lung wet-to-dry ratio (n=5–6) were recorded. We found that overexpression of miR-let-7b could significantly down-regulate the expression of human-derived neutrophilic TLR4 at a post-transcriptional level, a decreased level of proinflammatory factors including interleukin-6 (IL-6), IL-8, tumor necrosis factor α (TNF-α), and an upregulation of anti-inflammatory factor IL-10 in vitro. After miR-let-7b agomir treatment in vivo, neutrophil recruitment was inhibited and thus the injuries of liver and lungs in CLP-induced septic mice were alleviated (p=0.01 and p=0.04, respectively), less weight loss was reduced, and survival in septic mice was also significantly improved (p=0.013). Our study suggested that miR-let-7b could be a potential target of sepsis.

Single-Cell Secretion Analysis in the Engineered Tumor Microenvironment Reveals Differential Modulation of Macrophage Immune Responses

It is increasingly recognized that the cellular microenvironment plays critical roles in regulating the fate and physiology of cells. Despite recent advancements in single-cell analysis technologies, engineering and integration of the microenvironment for single-cell analysis platforms remain limited. Here, we report a single-cell cytokine secretion analysis platform that integrated both the three-dimensional cell culture and the primary oral squamous cell carcinoma tumor cell co-culture to provide both physical and physiological cues for single cells to be analyzed. We apply the platform to investigate the immune responses of human macrophages stimulated with the ligand of toll-like receptor 4 lipopolysaccharide. Notably, we observe the differential modulation effect in cytokine secretions by the tumor microenvironment, in which antitumor cytokine TNF-a secretion was attenuated, and protumor cytokine IL-6 would increase. The differential modulation effect is conserved from cell line-derived macrophages to primary macrophages derived from healthy donors. Immunofluorescence staining further reveals that ∼50% of macrophage cells could be polarized from M1 to the M2 phenotype within 12 h in the engineered tumor microenvironment. This work demonstrates the significance of the cell microenvironment toward single-cell analysis, which could help to evaluate how immune cells will respond in the complex microenvironment more accurately.

Outer Membrane Structural Defects in Salmonella enterica Serovar Typhimurium Affect Neutrophil Chemokinesis but Not Chemotaxis

Neutrophils, the first line of defense against pathogens, are critical in the host response to acute and chronic infections. In Gram-negative pathogens, the bacterial outer membrane (OM) is a key mediator of pathogen detection; nonetheless, the effects of variations in its molecular structure on the neutrophil migratory response to bacteria remain largely unknown. Here, we developed a quantitative microfluidic assay that precludes physical contact between bacteria and neutrophils while maintaining chemical communication, thus allowing investigation of both transient and steady-state responses of neutrophils to a library of Salmonella enterica serovar Typhimurium OM-related mutants at single-cell resolution. Using single-cell quantitative metrics, we found that transient neutrophil chemokinesis is highly gradated based upon OM structure, while transient and steady-state chemotaxis responses differ little between mutants. Based on our finding of a lack of correlation between chemokinesis and chemotaxis, we define "stimulation score" as a metric that comprehensively describes the neutrophil response to pathogens. Complemented with a killing assay, our results provide insight into how OM modifications affect neutrophil recruitment and pathogen survival. Altogether, our platform enables the discovery of transient and steady-state migratory responses and provides a new path for quantitative interrogation of cell decision-making processes in a variety of host-pathogen interactions.IMPORTANCE Our findings provide insights into the previously unexplored effects of Salmonella envelope defects on fundamental innate immune cell behavior, which advance the knowledge in pathogen-host cell biology and potentially inspire the rational design of attenuated strains for vaccines or immunotherapeutic strains for cancer therapy. Furthermore, the microfluidic assay platform and analytical tools reported herein enable high-throughput, sensitive, and quantitative screening of microbial strains' immunogenicity in vitro This approach could be particularly beneficial for rapid in vitro screening of engineered microbial strains (e.g., vaccine candidates) as the quantitative ranking of the overall strength of the neutrophil response, reported by "stimulation score," agrees with in vivo cytokine response trends reported in the literature.

NETosis as a Pathogenic Factor for Heart Failure

Heart failure threatens the lives of patients and reduces their quality of life. Heart failure, especially heart failure with preserved ejection fraction, is closely related to systemic and local cardiac persistent chronic low-grade aseptic inflammation, microvascular damage characterized by endothelial dysfunction, oxidative stress, myocardial remodeling, and fibrosis. However, the initiation and development of persistent chronic low-grade aseptic inflammation is unexplored. Oxidative stress-mediated neutrophil extracellular traps (NETs) are the main immune defense mechanism against external bacterial infections. Furthermore, NETs play important roles in noninfectious diseases. After the onset of myocardial infarction, atrial fibrillation, or myocarditis, neutrophils infiltrate the damaged tissue and aggravate inflammation. In tissue injury, damage-related molecular patterns (DAMPs) may induce pattern recognition receptors (PRRs) to cause NETs, but whether NETs are directly involved in the pathogenesis and development of heart failure and the mechanism is still unclear. In this review, we analyzed the markers of heart failure and heart failure-related diseases and comorbidities, such as mitochondrial DNA, high mobility box group box 1, fibronectin extra domain A, and galectin-3, to explore their role in inducing NETs and to investigate the mechanism of PRRs, such as Toll-like receptors, receptor for advanced glycation end products, cGAS-STING, and C-X-C motif chemokine receptor 2, in activating NETosis. Furthermore, we discussed oxidative stress, especially the possibility that imbalance of thiol redox and MPO-derived HOCl promotes the production of 2-chlorofatty acid and induces NETosis, and analyzed the possibility of NETs triggering coronary microvascular thrombosis. In some heart diseases, the deletion or blocking of neutrophil-specific myeloperoxidase and peptidylarginine deiminase 4 has shown effectiveness. According to the results of current pharmacological studies, MPO and PAD4 inhibitors are effective at least for myocardial infarction, atherosclerosis, and certain autoimmune diseases, whose deterioration can lead to heart failure. This is essential for understanding NETosis as a therapeutic factor of heart failure and the related new pathophysiology and therapeutics of heart failure.

Bistable Mathematical Model of Neutrophil Migratory Patterns After LPS-Induced Epigenetic Reprogramming

The highly controlled migration of neutrophils toward the site of an infection can be altered when they are trained with lipopolysaccharides (LPS), with high dose LPS enhancing neutrophil migratory pattern toward the bacterial derived source signal and super-low dose LPS inducing either migration toward an intermediary signal or dysregulation and oscillatory movement. Empirical studies that use microfluidic chemotaxis-chip devices with two opposing chemoattractants showed differential neutrophil migration after challenge with different LPS doses. The epigenetic alterations responsible for changes in neutrophil migratory behavior are unknown. We developed two mathematical models that evaluate the mechanistic interactions responsible for neutrophil migratory decision-making when exposed to competing chemoattractants and challenged with LPS. The first model, which considers the interactions between the receptor densities of two competing chemoattractants, their kinases, and LPS, displayed bistability between high and low ratios of primary to intermediary chemoattractant receptor densities. In particular, at equilibrium, we observe equal receptor densities for low LPS (< 15ng/mL); and dominance of receptors for the primary chemoattractant for high LPS (> 15ng/mL). The second model, which included additional interactions with an extracellular signal-regulated kinase in both phosphorylated and non-phosphorylated forms, has an additional dynamic outcome, oscillatory dynamics for both receptors, as seen in the data. In particular, it found equal receptor densities in the absence of oscillation for super-low and high LPS challenge (< 0.4 and 1.1 376 ng/mL). Predicting the mechanisms and the type of external LPS challenge responsible for neutrophils migration toward pro-inflammatory chemoattractants, migration toward pro-tolerant chemoattractants, or oscillatory movement is necessary knowledge in designing interventions against immune diseases, such as sepsis.

The lectin-like domain of thrombomodulin is a drug candidate for both prophylaxis and treatment of liver ischemia and reperfusion injury in mice

Ischemia and reperfusion injury (IRI) can occur in any tissue or organ. With respect to liver transplantation, the liver grafts from donors by definition experience transient ischemia and subsequent blood reflow. IRI is a problem not only in organ transplantation but also in cases of thrombosis or circulatory disorders such as mesenteric ischemia, myocardial, or cerebral infarction. We have reported that recombinant human soluble thrombomodulin (rTM), which is currently used in Japan to treat disseminated intravascular coagulation (DIC), has a protective effect and suppresses liver IRI in mice. However, rTM may not be fully safe to use in humans because of its inherent anticoagulant activity. In the present study, we used a mouse liver IRI model to explore the possibility that the isolated lectin-like domain of rTM (rTMD1), which has no anticoagulant activity, could be effective as a therapeutic modality for IRI. Our results indicated that rTMD1 could suppress ischemia and reperfusion-induced liver damage in a dose-dependent manner without concern of associated hemorrhage. Surprisingly, rTMD1 suppressed the liver damage even after IR insult had occurred. Taken together, we conclude that rTMD1 may be a candidate drug for prevention of and therapy for human liver IRI without the possible risk of hemorrhage.

Cell-Cell Interaction Mechanisms in Acute Lung Injury

ABSTRACT

Acute lung injury (ALI) and acute respiratory distress syndrome (ARDS) are caused by an exaggerated inflammatory response arising from a wide variety of pulmonary and systemic insults. Lung tissue is composed of a variety of cell populations, including parenchymal and immune cells. Emerging evidence has revealed that multiple cell populations in the lung work in concert to regulate lung inflammation in response to both direct and indirect stimulations. To date, the question of how different types of pulmonary cells communicate with each other and subsequently regulate or modulate inflammatory cascades remains to be fully addressed. In this review, we provide an overview of current advancements in understanding the role of cell-cell interaction in the development of ALI and depict molecular mechanisms by which cell-cell interactions regulate lung inflammation, focusing on inter-cellular activities and signaling pathways that point to possible therapeutic opportunities for ALI/ARDS.

Identification and Characterization of Zebrafish Tlr4 Coreceptor Md-2

The zebrafish (Danio rerio) is a powerful model organism for studies of the innate immune system. One apparent difference between human and zebrafish innate immunity is the cellular machinery for LPS sensing. In amniotes, the protein complex formed by TLR4 and myeloid differentiation factor 2 (Tlr4/Md-2) recognizes the bacterial molecule LPS and triggers an inflammatory response. It is believed that zebrafish have neither Md-2 nor Tlr4; Md-2 has not been identified outside of amniotes, whereas the zebrafish tlr4 genes appear to be paralogs, not orthologs, of amniote TLR4s We revisited these conclusions. We identified a zebrafish gene encoding Md-2, ly96 Using single-cell RNA sequencing, we found that ly96 is transcribed in cells that also transcribe genes diagnostic for innate immune cells, including the zebrafish tlr4-like genes. In larval zebrafish, ly96 is expressed in a small number of macrophage-like cells. In a functional assay, zebrafish Md-2 and Tlr4ba form a complex that activates NF-κB signaling in response to LPS. In larval zebrafish ly96 loss-of-function mutations perturbed LPS-induced cytokine production but gave little protection against LPS toxicity. Finally, by analyzing the genomic context of tlr4 genes in 11 jawed vertebrates, we found that tlr4 arose prior to the divergence of teleosts and tetrapods. Thus, an LPS-sensitive Tlr4/Md-2 complex is likely an ancestral feature shared by mammals and zebrafish, rather than a de novo invention on the tetrapod lineage. We hypothesize that zebrafish retain an ancestral, low-sensitivity Tlr4/Md-2 complex that confers LPS responsiveness to a specific subset of innate immune cells.

Toll-Like Receptors in Acute Kidney Injury

Acute kidney injury (AKI) is an important health problem, affecting 13.3 million individuals/year. It is associated with increased mortality, mainly in low- and middle-income countries, where renal replacement therapy is limited. Moreover, survivors show adverse long-term outcomes, including increased risk of developing recurrent AKI bouts, cardiovascular events, and chronic kidney disease. However, there are no specific treatments to decrease the adverse consequences of AKI. Epidemiological and preclinical studies show the pathological role of inflammation in AKI, not only at the acute phase but also in the progression to chronic kidney disease. Toll-like receptors (TLRs) are key regulators of the inflammatory response and have been associated to many cellular processes activated during AKI. For that reason, a number of anti-inflammatory agents targeting TLRs have been analyzed in preclinical studies to decrease renal damage during AKI. In this review, we updated recent knowledge about the role of TLRs, mainly TLR4, in the initiation and development of AKI as well as novel compounds targeting these molecules to diminish kidney injury associated to this pathological condition.

Effect of lipopolysaccharide and polyinosinic:polycytidylic acid in a murine model of nasal polyp

Several factors, including bacterial and viral infections, have been associated with rhinosinusitis and nasal tissue remodelling that may result in nasal polyp formation. However, the potential role of bacterial or viral stimuli triggering polyp development is unclear. Here, we used lipopolysaccharide (LPS) and polyinosinic:polycytidylic acid [poly(I:C)] in a murine model of allergic rhinosinusitis to compare different effects of bacterial- and virus-derived stimuli in the pathogenesis of nasal polyp formation. Briefly, BALB/c mice were sensitised and challenged with ovalbumin and staphylococcal enterotoxin, with or without LPS or poly(I:C), and the consequent histopathological profiles, cytokines, and systemic humoral responses were studied. While no significant differences in polyp formations and epithelial disruptions were observed among the experimental groups, the local cell recruitment patterns slightly differed in animals that received either LPS or poly(I:C). Additionally, the local immune environments generated by LPS or poly(I:C) stimulation varied. LPS stimulation induced a marked Th1/Th17 response and predominantly neutrophilic nasal polyp formations, whereas poly(I:C) induced a Th2-skewed environment in neutrophilic nasal polyp development. Overall, our findings show that both cell recruitment patterns and local immune environments induced by these two stimuli differ, which may have implications in the physiopathology of rhinosinusitis with nasal polyp.

Going, Toll-like receptors in skin inflammation and inflammatory diseases

The Indian Ayurvedic physicians knew the concept of inflammation dating back to 1500 BC. The continuous progress in the immunology of inflammation has explained its undiscovered mechanisms. For example, the discovery of Toll-like receptor 4 (TLR4) in humans (1997) has revolutionized the field of infection biology and innate immunity. The laboratory mice have shown twelve TLRs and express TLR10 (CD290) as a disrupted pseudogene, and humans have ten functional TLRs. Now, it is well established that TLRs play a significant role in different infectious and inflammatory diseases. Skin inflammation and other associated inflammatory diseases, including atopic dermatitis (AD), acne vulgaris, and psoriasis, along with many skin cancers are major health problems all over the world. The continuous development in the immunopathogenesis of inflammatory skin diseases has opened the window of opportunity for TLRs in studying their role. Hence, the manuscript explores the role of different TLRs in the pathogenesis of skin inflammation and associated inflammatory diseases. The article starts with the concept of inflammation, its origin, and the impact of TLRs discovery on infection and inflammation biology. The subsequent section describes the burden of skin-associated inflammatory diseases worldwide and the effect of the geographical habitat of people affecting it. The third section explains skin as an immune organ and explains the expression of different TLRs on different skin cells, including keratinocytes, Langerhans cells (LCs), skin fibroblasts, and melanocytes. The fourth section describes the impact of TLRs on these cells in different skin-inflammatory conditions, including acne vulgaris, AD, psoriasis, and skin cancers. The article also discusses the use of different TLR-based therapeutic approaches as specific to these inflammatory skin diseases.

The G Protein-Coupled Receptor Kinases (GRKs) in Chemokine Receptor-Mediated Immune Cell Migration: From Molecular Cues to Physiopathology

Although G protein-coupled receptor kinases (GRKs) have long been known to regulate G protein-coupled receptor (GPCR) desensitization, their more recently characterized functions as scaffolds and signalling adapters underscore that this small family of proteins governs a larger array of physiological functions than originally suspected. This review explores how GRKs contribute to the complex signalling networks involved in the migration of immune cells along chemokine gradients sensed by cell surface GPCRs. We outline emerging evidence indicating that the coordinated docking of several GRKs on an active chemokine receptor determines a specific receptor phosphorylation barcode that will translate into distinct signalling and migration outcomes. The guidance cues for neutrophil migration are emphasized based on several alterations affecting GRKs or GPCRs reported to be involved in pathological conditions.

Pinocembrin relieves lipopolysaccharide and bleomycin induced lung inflammation via inhibiting TLR4-NF-κB-NLRP3 inflammasome signaling pathway

Inflammation is a defense response of the body to stimuli. Lung injury caused by external stimuli can stimulate inflammatory cells to accumulate at the site of injury and secrete cytokines. Pinocembrin is a flavonoid with anti-inflammatory effects. Based on previous studies, we further explored the anti-inflammatory mechanisms of pinocembrin in vitro and in vivo. In vitro studies indicated that pinocembrin inhibited lipopolysaccharide (LPS)-stimulated inflammatory response in macrophages. In vivo studies also showed that pinocembrin could reduce LPS and bleomycin (BLM) induced lung inflammatory response in mice. Further mechanistic studies indicated that pinocembrin could regulate the TLR4-NF-κB signaling pathway and suppressed the activation and assembly of NLRP3 inflammasomes. In summary, pinocembrin could relieve pulmonary inflammatory response induced by LPS and BLM mainly via inhibiting TLR4-NF-κB-NLRP3 inflammasome axis. These results contribute to the understanding of the anti-inflammatory mechanisms of pinocembrin and serve as reference for future research on pinocembrin.

GRK2 levels in myeloid cells modulate adipose-liver crosstalk in high fat diet-induced obesity

Macrophages are key effector cells in obesity-associated inflammation. G protein-coupled receptor kinase 2 (GRK2) is highly expressed in different immune cell types. Using LysM-GRK2+/- mice, we uncover that a reduction of GRK2 levels in myeloid cells prevents the development of glucose intolerance and hyperglycemia after a high fat diet (HFD) through modulation of the macrophage pro-inflammatory profile. Low levels of myeloid GRK2 confer protection against hepatic insulin resistance, steatosis and inflammation. In adipose tissue, pro-inflammatory cytokines are reduced and insulin signaling is preserved. Macrophages from LysM-GRK2+/- mice secrete less pro-inflammatory cytokines when stimulated with lipopolysaccharide (LPS) and their conditioned media has a reduced pathological influence in cultured adipocytes or naïve bone marrow-derived macrophages. Our data indicate that reducing GRK2 levels in myeloid cells, by attenuating pro-inflammatory features of macrophages, has a relevant impact in adipose-liver crosstalk, thus preventing high fat diet-induced metabolic alterations.

Influence of Genetic Variance on Biomarker Levels After Occupational Exposure to 1,6-Hexamethylene Diisocyanate Monomer and 1,6-Hexamethylene Diisocyanate Isocyanurate

We evaluated the impact of genetic variance on biomarker levels in a population of workers in the automotive repair and refinishing industry who were exposed to respiratory sensitizers 1,6-hexamethylene diisocyanate (HDI) monomer and one of its trimers, HDI isocyanurate. The exposures and respective urine and plasma biomarkers 1,6-diaminohexane (HDA) and trisaminohexyl isocyanurate (TAHI) were measured in 33 workers; and genome-wide microarrays (Affymetrix 6.0) were used to genotype the workers' single-nucleotide polymorphisms (SNPs). Linear mixed model analyses have indicated that interindividual variations in both inhalation and skin exposures influenced these biomarker levels. Using exposure values as covariates and a false discovery rate < 0.10 to assess statistical significance, we observed that seven SNPs were associated with HDA in plasma, five were associated with HDA in urine, none reached significance for TAHI in plasma, and eight were associated with TAHI levels in urine. The different genotypes for the 20 significant SNPs accounted for 4- to 16-fold changes observed in biomarker levels. Associated gene functions include transcription regulation, calcium ion transport, vascular morphogenesis, and transforming growth factor beta signaling pathway, which may impact toxicokinetics indirectly by altering inflammation levels. Additionally, in an expanded analysis using a minor allele cutoff of 0.05 instead of 0.10, there were biomarker-associated SNPs within three genes that have been associated with isocyanate-induced asthma: ALK, DOCK2, and LHPP. We demonstrate that genetic variance impacts the biomarker levels in workers exposed to HDI monomer and HDI isocyanurate and that genetics can be used to refine exposure predictions in small cohorts when quantitative personal exposure and biomarker measurements are included in the models.

Nintedanib Reduces Neutrophil Chemotaxis via Activating GRK2 in Bleomycin-Induced Pulmonary Fibrosis

Neutrophils are involved in the alveolitis of idiopathic pulmonary fibrosis (IPF). However, their pathogenic mechanisms are still poorly understood. Nintedanib has antifibrotic and anti-inflammatory activity in IPF. This study aimed to investigate the regulatory mechanism of nintedanib on neutrophil chemotaxis in bleomycin (BLM)-induced pulmonary fibrosis. Nintedanib was administered via oral gavage to male C57BL/6 mice 24 h after a bleomycin intratracheal injection (1.5 U/kg). Lung histopathological findings, the expression of cytokines, and the regulatory signaling pathways of neutrophil chemotaxis were analyzed. The effect of nintedanib was also investigated in a mouse model with adoptive neutrophil transfer in vivo. Nintedanib significantly decreased the histopathological changes and neutrophil recruitment in BLM-induced pulmonary fibrosis. Nintedanib mediated a downregulation of chemokine (C-X-C motif) receptor 2 (CXCR2) and very late antigen 4 (VLA-4) expression, as well as an upregulation of G protein-coupled receptor kinase 2 (GRK2) activity in peripheral blood neutrophils in BLM-induced pulmonary fibrosis. Nintedanib also decreased the activation of endothelial cells by the decreased expression of vascular cell adhesion molecule 1 (VCAM-1). The effect of nintedanib on regulating neutrophil chemotaxis was also confirmed by a mouse model with adoptive neutrophil transfer in vivo. In conclusion, nintedanib reduces neutrophil chemotaxis and endothelial cell activation to regulate the severity of BLM-induced pulmonary fibrosis. These effects are associated with an enhancement of GRK2 activity and a reduction in CXCR2 and VLA-4 expression on neutrophils and a decrease in VCAM-1 expression on endothelial cells.

Toll-like receptors: exploring their potential connection with post-operative infectious complications and cancer recurrence

Cancer is the leading cause of death in North America. Despite modern advances in cancer therapy, many patients will ultimately develop cancer metastasis resulting in mortality. Surgery to resect early stage solid malignancies remains the cornerstone of cancer treatment. However, surgery places patients at risk of developing post-operative infectious complications that are linked to earlier cancer metastatic recurrence and cancer mortality. Toll-like receptors (TLRs) are evolutionarily-conserved sentinel receptors of the innate immune system that are activated by microbial products present during infection, leading to activation of innate immunity. Numerous types of solid cancer cells also express TLRs, with their activation augmenting their ability to metastasize. Similarly, healthy host-tissue TLRs activated during infection induce a prometastatic environment in the host. Cancer cells additionally secrete TLR activating ligands that activate both cancer TLRs and host TLRs to promote metastasis. Consequently, TLRs are an attractive therapeutic candidate to target infection-induced cancer metastasis and progression.

Concepts of GPCR-controlled navigation in the immune system

G‐protein–coupled receptor (GPCR) signaling is essential for the spatiotemporal control of leukocyte dynamics during immune responses. For efficient navigation through mammalian tissues, most leukocyte types express more than one GPCR on their surface and sense a wide range of chemokines and chemoattractants, leading to basic forms of leukocyte movement (chemokinesis, haptokinesis, chemotaxis, haptotaxis, and chemorepulsion). How leukocytes integrate multiple GPCR signals and make directional decisions in lymphoid and inflamed tissues is still subject of intense research. Many of our concepts on GPCR‐controlled leukocyte navigation in the presence of multiple GPCR signals derive from in vitro chemotaxis studies and lower vertebrates. In this review, we refer to these concepts and critically contemplate their relevance for the directional movement of several leukocyte subsets (neutrophils, T cells, and dendritic cells) in the complexity of mouse tissues. We discuss how leukocyte navigation can be regulated at the level of only a single GPCR (surface expression, competitive antagonism, oligomerization, homologous desensitization, and receptor internalization) or multiple GPCRs (synergy, hierarchical and non‐hierarchical competition, sequential signaling, heterologous desensitization, and agonist scavenging). In particular, we will highlight recent advances in understanding GPCR‐controlled leukocyte navigation by intravital microscopy of immune cells in mice.

Neutrophil trafficking on-a-chip: an in vitro, organotypic model for investigating neutrophil priming, extravasation, and migration with spatiotemporal control

Neutrophil trafficking is essential for a strong and productive immune response to infection and injury. During acute inflammation, signals from resident immune cells, fibroblasts, and the endothelium help to prime, attract, and activate circulating neutrophils at sites of inflammation. Due to current limitations with in vitro and animal models, our understanding of these events is incomplete. In this paper, we describe a microfluidic technology which incorporates a lumen-based vascular component with a high degree of spatiotemporal control to facilitate the study of neutrophil trafficking using primary human cells. The improved spatiotemporal control allows functional selection of neutrophils based on their migratory capacity. We use this technology to investigate neutrophil-endothelial interactions and find that these interactions are necessary for robust neutrophil chemotaxis to interleukin-8 (IL-8) and priming of the neutrophils. In agreement with previous studies, we observed that transendothelial migration (TEM) is required for neutrophils to enter a primed phenotypic state. TEM neutrophils not only produce a significantly higher amount of reactive oxygen species (ROS) when treated with PMA, but also upregulate genes involved in ROS production (CYBB, NCF1, NFKB1, NFKBIA), cell adhesion (CEACAM-8, ITGAM), and chemokine receptors (CXCR2, TNFRSF1A). These results suggest that neutrophil-endothelial interactions are crucial to neutrophil chemotaxis and ROS generation.

G protein-coupled receptor kinase 2 (GRK2) as a multifunctional signaling hub

Accumulating evidence indicates that G protein-coupled receptor kinase 2 (GRK2) is a versatile protein that acts as a signaling hub by modulating G protein-coupled receptor (GPCR) signaling and also via phosphorylation or scaffolding interactions with an extensive number of non-GPCR cellular partners. GRK2 multifunctionality arises from its multidomain structure and from complex mechanisms of regulation of its expression levels, activity, and localization within the cell, what allows the precise spatio-temporal shaping of GRK2 targets. A better understanding of the GRK2 interactome and its modulation mechanisms is helping to identify the GRK2-interacting proteins and its substrates involved in the participation of this kinase in different cellular processes and pathophysiological contexts.

TLR4 mediates upregulation and sensitization of TRPV1 in primary afferent neurons in 2,4,6-trinitrobenzene sulfate-induced colitis

Elevated excitability of primary afferent neurons underlies chronic pain in patients with functional or inflammatory bowel diseases. Recent studies have established an essential role for an enhanced transient receptor potential vanilloid subtype 1 (TRPV1) signaling in mediating peripheral hyperalgesia in inflammatory conditions. Since colocalization of Toll-like receptor 4 (TLR4) and TRPV1 has been observed in primary afferents including the trigeminal sensory neurons and the dorsal root ganglion neurons, we test the hypothesis that TLR4 might regulate the expression and function of TRPV1 in primary afferent neurons in 2,4,6-trinitrobenzene sulfate (TNBS)-induced colitis using the TLR4-deficient and the wild-type C57 mice. Despite having a higher disease activity index following administration of 2,4,6-trinitrobenzene sulfate, the TLR4-deficient mice showed less inflammatory infiltration in the colon than the wild-type mice. Increased expression of TLR4 and TRPV1 as well as increased density of capsaicin-induced TRPV1 current was observed in L4–S2 dorsal root ganglion neurons of the wild-type colitis mice till two weeks post 2,4,6-trinitrobenzene sulfate treatment. In comparison, the TLR4-deficient colitis mice had lower TRPV1 expression and TRPV1 current density in dorsal root ganglion neurons with lower abdominal withdrawal response scores during noxious colonic distensions. In the wild type but not in the TLR4-deficient dorsal root ganglion neurons, acute administration of the TLR4 agonist lipopolysaccharide increased the capsaicin-evoked TRPV1 current. In addition, we found that the canonical signaling downstream of TLR4 was activated in 2,4,6-trinitrobenzene sulfate-induced colitis in the wild type but not in the TLR4-deficient mice. These results indicate that TLR4 may play a major role in regulation of TRPV1 signaling and peripheral hyperalgesia in inflammatory conditions.

Complement-Dependent Mechanisms and Interventions in Periodontal Disease

Periodontitis is a prevalent inflammatory disease that leads to the destruction of the tooth-supporting tissues. Current therapies are not effective for all patients and this oral disease continues to be a significant public health and economic burden. Central to periodontal disease pathogenesis is a reciprocally reinforced interplay between microbial dysbiosis and destructive inflammation, suggesting the potential relevance of host-modulation therapies. This review summarizes and discusses clinical observations and pre-clinical intervention studies that collectively suggest that complement is hyperactivated in periodontitis and that its inhibition provides a therapeutic benefit. Specifically, interception of the complement cascade at its central component, C3, using a locally administered small peptidic compound (Cp40/AMY-101) protected non-human primates from induced or naturally occurring periodontitis. These studies indicate that C3-targeted intervention merits investigation as an adjunctive treatment of periodontal disease in humans.

GRK5 - A Functional Bridge Between Cardiovascular and Neurodegenerative Disorders

Complex aging-triggered disorders are multifactorial programs that comprise a myriad of alterations in interconnected protein networks over a broad range of tissues. It is evident that rather than being randomly organized events, pathophysiologies that possess a strong aging component such as cardiovascular diseases (hypertensions, atherosclerosis, and vascular stiffening) and neurodegenerative conditions (dementia, Alzheimer's disease, mild cognitive impairment, Parkinson's disease), in essence represent a subtly modified version of the intricate molecular programs already in place for normal aging. To control such multidimensional activities there are layers of trophic protein control across these networks mediated by so-called "keystone" proteins. We propose that these "keystones" coordinate and interconnect multiple signaling pathways to control whole somatic activities such as aging-related disease etiology. Given its ability to control multiple receptor sensitivities and its broad protein-protein interactomic nature, we propose that G protein coupled receptor kinase 5 (GRK5) represents one of these key network controllers. Considerable data has emerged, suggesting that GRK5 acts as a bridging factor, allowing signaling regulation in pathophysiological settings to control the connectivity between both the cardiovascular and neurophysiological complications of aging.

Neutrophil Suppresses Tumor Cell Proliferation via Fas /Fas Ligand Pathway Mediated Cell Cycle Arrested

While neutrophils have dutifully performed their function in injury and infection, the recent works have found that cytotoxicity and/or cytostatic of neutrophils has also been observed in tumor. Till now the molecular players that participate in this neutrophils antitumoral effect remain unclear. In the current study, we find that neutrophils from healthy donors have potent suppression to tumor cell lines by physical contact. Importantly, these suppression activities seem to be cancer cell-specific which is not observed in the normal cells. Further observations show that neutrophils mediated tumor cell lines growth inhibitory effect through early cell cycle arrested. Treatment with an antagonist Fas receptor in A549 cell line or knocking out of the Fas gene in A549 cell line recovers tumor cells cycle and lessen neutrophils anti-tumor effect. The interaction between neutrophils and A549 cell line through Fas ligand /Fas regulates the expression of cell cycle checkpoint proteins, leading to early cell cycle arrest. This phenomenon is also seen in other 3 tumor cell lines. Taken together, our results identified a new role of Fas ligand /Fas interaction in neutrophils antitumoral effect in tumors via arresting cell cycle.

Lung epithelial cell-derived IL-25 negatively regulates LPS-induced exosome release from macrophages

BACKGROUND

Acute lung injury (ALI) is a major component of multiple organ dysfunction syndrome (MODS) following pulmonary and systemic infection. Alveolar macrophages (AMϕ) are at the center of ALI pathogenesis. Emerging evidence has shown that cell-cell interactions in the lungs play an important regulatory role in the development of acute lung inflammation. However, the underneath mechanisms remain poorly addressed. In this study, we explore a novel function of lung epithelial cells (LEPCs) in regulating the release of exosomes from AMϕ following LPS stimulation.

METHODS

For the in vivo experiments, C57BL/6 wildtype (WT) mice were treated with lipopolysaccharide (LPS) (2 mg/kg B.W.) in 0.2 ml of saline via intratracheal aerosol administration. Bronchoalveolar lavage fluid was collected at 0-24 h after LPS treatment, and exosomes derived from AMϕ were measured. For the in vitro studies, LEPCs and bone marrow-derived Mϕ (BMDM) were isolated from WT or TLR4^-/- mice and were then cocultured in the Transwell™ system. After coculture for 0-24 h, the BMDM and supernatant were harvested for the measurement of exosomes and cytokines.

RESULTS

We demonstrate that LPS induces macrophages (Mϕ) to release exosomes, which are then internalized by neighboring Mϕ to promote TNF-α expression. The secreted interleukin (IL)-25 from LEPCs downregulates Rab27a and Rab27b expression in Mϕ, resulting in suppressed exosome release and thereby attenuating exosome-induced TNF-α expression and secretion.

CONCLUSION

These findings reveal a previously unidentified crosstalk pathway between LEPCs and Mϕ that negatively regulates the inflammatory responses of Mϕ to LPS. Modulating IL-25 signaling and targeting exosome release may present a new therapeutic strategy for the treatment of ALI.

Neutrophil extracellular traps promote macrophage pyroptosis in sepsis

In response to infection, polymorphonuclear neutrophils (PMN) are recruited in the infectious sites, and employ three major strategies to fight against the microbes including phagocytosis, degranulation, and neutrophil extracellular traps (NETs). NETs are a meshwork of chromatin fibers mixed with granule-derived antimicrobial peptides and enzymes, which trap and kill the bacteria extracellularly. In this study, by using a mouse sepsis model, we identified a novel mechanism by which NETs induce macrophage (Mϕ) pyroptosis, a caspase-1-dependent regulated cell death. We show that NET-derived HMGB1, acting through RAGE and dynamin-dependent signaling, triggers an intra-Mϕ cascade of molecular events including cathepsin B (CatB) release from the ruptured lysosomes, followed by pyroptosome formation and caspase-1 activation, and subsequent Mϕ pyroptosis. The study further demonstrates that Mϕ pyroptosis augments inflammatory responses following sepsis. These findings shed light on the proinflammatory role of NETs in mediating PMN–Mϕ interaction, which therefore influences the progress of inflammation following infection.

Endotoxin promotes neutrophil hierarchical chemotaxis via the p38-membrane receptor pathway

Neutrophils are the most abundant leukocytes in peripheral blood and play critical a role in bacterial infection, tumor immunity and wound repair. Clarifying the process of neutrophil chemotaxis to target sites of immune activity has been a focus of increased interest within the past decade. In bacterial infectious foci, neutrophils migrate toward the bacterial-derived chemoattractant N-formyl-Met-Leu-Phe (fMLP) and ignore other intermediary chemoattractants to arrive at the area of infection. Using an under agarose chemotaxis assay, we observed that the bacterial fMLP-induced neutrophil chemotaxis signal overrode interleukin 8 (IL-8)- and leukotriene B4 (LTB4)-induced chemotaxis signals. Moreover, in the presence of bacterial lipopolysaccharide (LPS), the fMLP-induced hierarchical chemotaxis signal was enhanced. Further studies revealed that LPS increased the membrane expression of the fMLP receptor, formyl peptide receptor 1 (FPR1). However, expression levels of the membrane receptors for IL-8 and LTB4 were decreased by LPS administration. A human Phospho-mitogen-activated protein kinase (MAPK) proteome array showed that the p38 pathway was significantly activated by LPS stimulation. Moreover, p38 was responsible for the altered expression of neutrophil membrane chemoattractant receptors. Inhibition of neutrophil p38 restored LPS-improved hierarchical chemotaxis. Taken together, these data indicate that endotoxin promotes neutrophil hierarchical chemotaxis via the p38-membrane receptor pathway.

GPCR Kinase (GRK)-2 Is a Key Negative Regulator of Itch: l-Glutamine Attenuates Itch via a Rapid Induction of GRK2 in an ERK-Dependent Way

Many itch mediators activate GPCR and trigger itch via activation of GPCR-mediated signaling pathways. GPCRs are desensitized by GPCR kinases (GRKs). The aim of this study is to explore the role of GRKs in itch response and the link between GRKs and glutamine, an amino acid previously shown to be an itch reliever. Itch responses were evoked by histamine, chloroquine, and dinitrochlorobenzene-induced contact dermatitis (CD). Phosphorylation and protein expression were detected by immunofluorescent staining and Western blotting. GRK2 knockdown using small interfering RNA enhanced itch responses evoked by histamine, chloroquine, and dinitrochlorobenzene-induced CD, whereas GRK2 overexpression using GRK2-expressing adenovirus reduced the itch responses. Glutamine reduced all itch evoked by histamine, chloroquine, and dinitrochlorobenzene-induced CD. Glutamine-mediated inhibition of itch was abolished by GRK2 knockdown. Glutamine application resulted in a rapid and strong expression of GRK2 in not only dinitrochlorobenzene-induced CD (within 10 minutes) but also cultured rat dorsal root ganglion cells, F11 (within 1 minute). ERK inhibitor abrogates glutamine-mediated GRK2 expression and inhibition of itch in dinitrochlorobenzene-induced CD. Our data indicate that GRK2 is a key negative regulator of itch and that glutamine attenuates itch via a rapid induction of GRK2 in an ERK-dependent way.

CCL24 contributes to HCC malignancy via RhoB- VEGFA-VEGFR2 angiogenesis pathway and indicates poor prognosis

CCL24 is one chemotactic factor extensively studied in airway inflammation and colorectal cancer but less studied in hepatocellular carcinoma (HCC) retrospectively. So HCC tissue microarray (TMA) was used to estimate relationship between CCL24 and prognosis, cell experiments were conducted to study its influence for HCC cell biological behavior. CCL24 was injected to nude mice to monitor tumor formation and pulmonary metastasis; qRT-PCR, western blot and Immunohistochemistry were used to explore potential mechanism. CCL24 plays roles in target cells via its downstream CCR3, or it is regulated by Type 2 helper T cells (Th2 cell) factors, so immune related experiments were conducted. Meanwhile, Rho GTPase family have close relation not only with T cell priming, but with neovascularization; CCL24 contributes to neovascularization in age-related macular degeneration via CCR3, so Rho GTPase family, Th2 cell factors, Human Umbilical Vein Endothelial Cells were used to uncover their trafficking. Ultimate validation was confirmed by small interfering RNA. Results showed CCL24 expression was higher in caner tissues than adjacent normal tissues, it could contribute to proliferation, migration, and invasion in HCCs, could accelerate pulmonary metastasis, promote HUVECs tube formation. Th2 cell factors were irrelevant with CCL24 in HCCs; and RhoB, VEGFA, and VEGFR2 correlated with CCL24 in both mRNA and protein level. Downstream RhoB-VEGFA signaling pathway was validated by siRhoB and siVEGFA inhibition. In a word, CCL24 contributes to HCC malignancy via RhoB-VEGFA-VEGFR2 angiogenesis pathway and indicates poor prognosis, which urges us to study further CCL24 effects on diagnosis and potential therapy for HCC.