CD13 restricts TLR4 endocytic signal transduction in inflammation

TLRs1-10 Protein Expression in Circulating Human White Blood Cells during Bacterial and COVID-19 Infections

INTRODUCTION

Toll-like receptors play crucial roles in the sepsis-induced systemic inflammatory response. Septic shock mortality correlates with overexpression of neutrophilic TLR2 and TLR9, while the role of TLR4 overexpression remains a debate. In addition, TLRs are involved in the pathogenesis of viral infections such as COVID-19, where the single-stranded RNA of SARS-CoV-2 is recognized by TLR7 and TLR8, and the spike protein activates TLR4.

METHODS

In this study, we conducted a comprehensive analysis of TLRs 1-10 expressions in white blood cells from 71 patients with bacterial and viral infections. Patients were divided into 4 groups based on disease type and severity (sepsis, septic shock, moderate, and severe COVID-19) and compared to 7 healthy volunteers.

RESULTS

We observed a significant reduction in the expression of TLR4 and its co-receptor CD14 in septic shock neutrophils compared to the control group (p < 0.001). Severe COVID-19 patients exhibited a significant increase in TLR3 and TLR7 levels in neutrophils compared to controls (p < 0.05). Septic shock patients also showed a similar increase in TLR7 in neutrophils along with elevated intermediate monocytes (CD14+CD16+) compared to the control group (p < 0.005 and p < 0.001, respectively). However, TLR expression remained unchanged in lymphocytes.

CONCLUSION

This study provides further insights into the mechanisms of TLR activation in various infectious conditions. Additional analysis is needed to assess their correlation with patient outcome and to evaluate the impact of TLR-pathway modulation during septic shock and severe COVID-19.

The Implant-Induced Foreign Body Response Is Limited by CD13-Dependent Regulation of Ubiquitination of Fusogenic Proteins

Implanted medical devices, from artificial heart valves and arthroscopic joints to implantable sensors, often induce a foreign body response (FBR), a form of chronic inflammation resulting from the inflammatory reaction to a persistent foreign stimulus. The FBR is characterized by a subset of multinucleated giant cells (MGCs) formed by macrophage fusion, the foreign body giant cells (FBGCs), accompanied by inflammatory cytokines, matrix deposition, and eventually deleterious fibrotic implant encapsulation. Despite efforts to improve biocompatibility, implant-induced FBR persists, compromising the utility of devices and making efforts to control the FBR imperative for long-term function. Controlling macrophage fusion in FBGC formation presents a logical target to prevent implant failure, but the actual contribution of FBGCs to FBR-induced damage is controversial. CD13 is a molecular scaffold, and in vitro induction of CD13KO bone marrow progenitors generates many more MGCs than the wild type, suggesting that CD13 regulates macrophage fusion. In the mesh implant model of FBR, CD13KO mice produced significantly more peri-implant FBGCs with enhanced TGF-β expression and increased collagen deposition versus the wild type. Prior to fusion, increased protrusion and microprotrusion formation accompanies hyperfusion in the absence of CD13. Expression of fusogenic proteins driving cell-cell fusion was aberrantly sustained at high levels in CD13KO MGCs, which we show is due to a novel CD13 function, to our knowledge, regulating ubiquitin/proteasomal protein degradation. We propose CD13 as a physiologic brake limiting aberrant macrophage fusion and the FBR, and it may be a novel therapeutic target to improve the success of implanted medical devices. Furthermore, our data directly implicate FBGCs in the detrimental fibrosis that characterizes the FBR.

Shifts in intestinal microbiota and improvement of sheep immune response to resist Salmonella infection using Toll-like receptor 4 (TLR4) overexpression

Introduction

Toll-like receptor 4 (TLR4) identifies Gram-negative bacteria or their products and plays a crucial role in host defense against invading pathogens. In the intestine, TLR4 recognizes bacterial ligands and interacts with the immune system. Although TLR4 signaling is a vital component of the innate immune system, the influence of TLR4 overexpression on innate immune response and its impact on the composition of the intestinal microbiota is unknown.

Methods

Here, we obtained macrophages from sheep peripheral blood to examine phagocytosis and clearance of Salmonella Typhimurium (S. Typhimurium) in macrophages. Meanwhile, we characterized the complex microbiota inhabiting the stools of TLR4 transgenic (TG) sheep and wild-type (WT) sheep using 16S ribosomal RNA (rRNA) deep sequencing.

Results

The results showed that TLR4 overexpression promoted the secretion of more early cytokines by activating downstream signaling pathways after stimulation by S. Typhimurium. Furthermore, diversity analysis demonstrated TLR4 overexpression increased microbial community diversity and regulated the composition of intestinal microbiota. More importantly, TLR4 overexpression adjusted the gut microbiota composition and maintained intestinal health by reducing the ratio of Firmicutes/Bacteroidetes and inflammation and oxidative stress-producing bacteria (Ruminococcaceae, Christensenellaceae) and upregulating the abundance of Bacteroidetes population and short-chain fatty acid (SCFA)-producing bacteria, including Prevotellaceae. These dominant bacterial genera changed by TLR4 overexpression revealed a close correlation with the metabolic pathways of TG sheep.

Discussion

Taken together, our findings suggested that TLR4 overexpression can counteract S. Typhimurium invasion as well as resist intestinal inflammation in sheep by regulating intestinal microbiota composition and enhancing anti-inflammatory metabolites.

Macrophage-derived exosomal aminopeptidase N aggravates sepsis-induced acute lung injury by regulating necroptosis of lung epithelial cell

Sepsis-induced acute lung injury (ALI) is a serious sepsis complication and the prevailing cause of death. Circulating plasma exosomes might exert a key role in regulating intercellular communication between immunological and structural cells, as well as contributing to sepsis-related organ damage. However, the molecular mechanisms by which exosome-mediated intercellular signaling exacerbate ALI in septic infection remains undefined. Therefore, we investigated the effect of macrophage-derived exosomal APN/CD13 on the induction of epithelial cell necrosis. Exosomal APN/CD13 levels in the plasma of septic mice and patients with septic ALI were found to be higher. Furthermore, increased plasma exosomal APN/CD13 levels were associated with the severity of ALI and fatality in sepsis patients. We found remarkably high expression of APN/CD13 in exosomes secreted by LPS-stimulated macrophages. Moreover, c-Myc directly induced APN/CD13 expression and was packed into exosomes. Finally, exosomal APN/CD13 from macrophages regulated necroptosis of lung epithelial cells by binding to the cell surface receptor TLR4 to induce ROS generation, mitochondrial dysfunction and NF-κB activation. These results demonstrate that macrophage-secreted exosomal APN/CD13 can trigger epithelial cell necroptosis in an APN/CD13-dependent manner, which provides insight into the mechanism of epithelial cell functional disorder in sepsis-induced ALI.

Necroptosis of lung epithelial cells is regulated by aminopeptidase N levels in circulating plasma exosomes in patients and mice with sepsis-induced acute lung injury.

Effect of BuShen JiangZhi Recipe on Atherosclerosis in ApoE-/- Mice by Regulating the Expression of Anpep via mmu_circRNA_22187

The BuShen JiangZhi (BSJZ) recipe is a Chinese medicine compound with the effect of tonifying the kidney, replenishing essence, and lowering blood fat to unblock vessels. The purpose of this study is to explore whether the mechanism of BSJZ for effective intervention in the treatment of AS is related to mmu_circRNA_22187 and aminopeptidase N (Anpep). ApoE^−/− mice were induced by a high-fat diet to replicate the AS model. 24 ApoE^−/− mice were randomly divided into model group (group M), BSJZ group (group BS), and 12 C57BL/6 mice of the same genetic background and same weeks of age as the normal control group (group C). Mice in the BS group were given an aqueous solution of BSJZ by gavage, while mice in groups C and M were given the same volume of distilled water. HE and Oil Red O staining were used to detect the pathomorphology and lipid accumulation of mouse aortic sinus. Arraystar version 2.0 mouse circRNA chip was used to scan with Agilent Scanner G2505C, and the differential circRNAs expression profile of mice aorta was obtained. Scatter plot, volcano plot, and cluster map, respectively, visualized the differentially expressed circRNAs, as well as the types of circRNAs and the chromosomes' distribution, screened and compared the differentially expressed circRNAs intersection between groups by Venny software, and then combined ceRNA bioinformatics analysis to construct a ceRNA network. The results showed that BSJZ could significantly reduce the area of AS plaque and lipid accumulation in the aortic sinus of ApoE^−/− mice induced by a high-fat diet. The bioinformatics analysis showed that mmu_circRNA_22187 may be a key circRNA of BSJZ intervention in the treatment of AS. Compared with group C, the expressions of Anpep mRNA and protein were upregulated in group M. After the intervention of BSJZ, the expressions of Anpep mRNA and protein were downregulated. Therefore, BSJZ could effectively treat AS which might be related to the regulation of mmu_circRNA_22187 and Anpep.

CD13 orients the apical-basal polarity axis necessary for lumen formation

Polarized epithelial cells can organize into complex structures with a characteristic central lumen. Lumen formation requires that cells coordinately orient their polarity axis so that the basolateral domain is on the outside and apical domain inside epithelial structures. Here we show that the transmembrane aminopeptidase, CD13, is a key determinant of epithelial polarity orientation. CD13 localizes to the apical membrane and associates with an apical complex with Par6. CD13-deficient cells display inverted polarity in which apical proteins are retained on the outer cell periphery and fail to accumulate at an intercellular apical initiation site. Here we show that CD13 is required to couple apical protein cargo to Rab11-endosomes and for capture of endosomes at the apical initiation site. This role in polarity utilizes the short intracellular domain but is independent of CD13 peptidase activity.

Involvement of Toll-Like Receptor 4 in Decreased Vasopressor Response Following Trauma/Hemorrhagic Shock

OBJECTIVES:

Refractory vascular failure due to the inability of vascular smooth muscle to respond to vasoconstrictors such as phenylephrine is a final common pathway for severe circulatory shock of any cause, including trauma/hemorrhagic shock. Increased inflammation, Toll-like receptor 4 activation, and decreased response of the alpha-1 adrenergic receptors which control vascular tone have been reported in trauma/hemorrhagic shock.

HYPOTHESIS:

In trauma/hemorrhagic shock, Toll-like receptor 4 activation contributes to vascular failure via decreased bioavailability of adrenergic receptors.

DESIGN AND MEASUREMENTS:

Trauma/hemorrhagic shock was induced in Wistar rats (laparotomy combined with mean arterial pressure at 40 mm Hg for 90 min followed by 2 hr resuscitation with Lactated Ringers solution). To inhibit Toll-like receptor 4, resatorvid (TAK-242) and resveratrol were used, and plasma was collected. Smooth muscle cells were incubated with lipopolysaccharide (10 ng/mL) or plasma. Inflammatory cytokines were screened using dot-blot. Toll-like receptor 4 and nuclear factor κB activation and cellular localization of the alpha-1 adrenergic receptor were measured by immunofluorescence imaging and Western blot analysis. Clustered regularly interspaced short palindromic repeats/Cas9 was used to knock out Toll-like receptor 4, and calcium influx following stimulation with phenylephrine was recorded.

MAIN RESULTS:

Trauma/hemorrhagic shock caused a decreased response to phenylephrine, whereas Toll-like receptor 4 inhibition improved blood pressure. Trauma/hemorrhagic shock plasma activated the Toll-like receptor 4/nuclear factor κB pathway in smooth muscle cells. Double labeling of Toll-like receptor 4 and the alpha-1 adrenergic receptor showed that these receptors are colocalized on the cell membrane. Activation of Toll-like receptor 4 caused cointernalization of both receptors. Calcium influx was impaired in cells incubated with trauma/hemorrhagic shock plasma but restored when Toll-like receptor 4 was knocked out or inhibited.

CONCLUSIONS:

Activation of the Toll-like receptor 4 desensitizes vascular smooth muscle cells to vasopressors in experimental trauma/hemorrhagic shock by reducing the levels of membrane alpha-1 adrenergic receptor.

CD13 is a critical regulator of cell-cell fusion in osteoclastogenesis

The transmembrane aminopeptidase CD13 is highly expressed in cells of the myeloid lineage, regulates dynamin-dependent receptor endocytosis and recycling and is a necessary component of actin cytoskeletal organization. Here, we show that CD13-deficient mice present a low bone density phenotype with increased numbers of osteoclasts per bone surface, but display a normal distribution of osteoclast progenitor populations in the bone marrow and periphery. In addition, the bone formation and mineral apposition rates are similar between genotypes, indicating a defect in osteoclast-specific function in vivo. Lack of CD13 led to exaggerated in vitro osteoclastogenesis as indicated by significantly enhanced fusion of bone marrow-derived multinucleated osteoclasts in the presence of M-CSF and RANKL, resulting in abnormally large cells containing remarkably high numbers of nuclei. Mechanistically, while expression levels of the fusion-regulatory proteins dynamin and DC-STAMP1 must be downregulated for fusion to proceed, these are aberrantly sustained at high levels even in CD13-deficient mature multi-nucleated osteoclasts. Further, the stability of fusion-promoting proteins is maintained in the absence of CD13, implicating CD13 in protein turnover mechanisms. Together, we conclude that CD13 may regulate cell–cell fusion by controlling the expression and localization of key fusion regulatory proteins that are critical for osteoclast fusion.

Overexpression of Toll-like receptor 4 contributes to the internalization and elimination of Escherichia coli in sheep by enhancing caveolae-dependent endocytosis

BACKGROUND

Gram-negative bacterial infections have a major economic impact on both the livestock industry and public health. Toll-like receptor 4 (TLR4) plays a crucial role in host defence against Gram-negative bacteria. Exploring the defence mechanism regulated by TLR4 may provide new targets for treatment of inflammation and control of bacterial infections. In a previous study, we generated transgenic sheep overexpressing TLR4 by microinjection to improve disease resistance. The defence mechanism through which TLR4 overexpression protected these sheep against pathogens is still not fully understood.

RESULTS

In the present study, we used Escherichia coli to infect monocytes isolated from peripheral blood of the animal model. The overexpression of TLR4 strongly enhanced the percentage of endocytosis and capacity of elimination in monocytes during the early stages of infection. This phenomenon was mainly due to overexpression of TLR4 promoting caveolae-mediated endocytosis. Pretreatment of the transgenic sheep monocytes with inhibitors of TLR4, Src signalling, or the caveolae-mediated endocytosis pathway reduced the internalization of bacteria, weakened the ability of the monocytes to eliminate the bacteria, and increased the pH of the endosomes.

CONCLUSION

Together, our results reveal the effects of TLR4 on the control of E. coli infection in the innate immunity of sheep and provide crucial evidence of the caveolae-mediated endocytosis pathway required for host resistance to invading bacteria in a large animal model, providing theoretical support for breeding disease resistance in the future. Furthermore, Src and caveolin 1 (CAV1) could be potentially valuable targets for the control of infectious diseases.

Primate innate immune responses to bacterial and viral pathogens reveals an evolutionary trade-off between strength and specificity

Humans and our close evolutionary relatives respond differently to a large number of infections. Such differences are thought to result, at least in part, from interspecies differences in immune function. Here, we report on the whole-genome expression of blood leukocytes from four primate species responding to bacterial and viral stimulation. We show that apes mount a markedly stronger early transcriptional response to both viral and bacterial stimulation when compared to African and Asian monkeys. In addition, our findings suggest that apes activate a broader array of defense molecules that may be beneficial for early pathogen killing at the potential cost of increased energy expenditure and tissue damage. Our results provide insight into the evolution of immune responses in primates.

Despite their close genetic relatedness, apes and African and Asian monkeys (AAMs) differ in their susceptibility to severe bacterial and viral infections that are important causes of human disease. Such differences between humans and other primates are thought to be a result, at least in part, of interspecies differences in immune response to infection. However, because of the lack of comparative functional data across species, it remains unclear in what ways the immune systems of humans and other primates differ. Here, we report the whole-genome transcriptomic responses of ape species (human and chimpanzee) and AAMs (rhesus macaque and baboon) to bacterial and viral stimulation. We find stark differences in the responsiveness of these groups, with apes mounting a markedly stronger early transcriptional response to both viral and bacterial stimulation, altering the transcription of ∼40% more genes than AAMs. Additionally, we find that genes involved in the regulation of inflammatory and interferon responses show the most divergent early transcriptional responses across primates and that this divergence is attenuated over time. Finally, we find that relative to AAMs, apes engage a much less specific immune response to different classes of pathogens during the early hours of infection, up-regulating genes typical of anti-viral and anti-bacterial responses regardless of the nature of the stimulus. Overall, these findings suggest apes exhibit increased sensitivity to bacterial and viral immune stimulation, activating a broader array of defense molecules that may be beneficial for early pathogen killing at the potential cost of increased energy expenditure and tissue damage.

Coronavirus Receptors as Immune Modulators

The Coronaviridae family includes the seven known human coronaviruses (CoV) that cause mild to moderate respiratory infections (HCoV-229E, HCoV-NL63, HCoV-OC43, HCoV-HKU1) as well as severe illness and death (MERS-CoV, SARS-CoV, SARS-CoV-2). Severe infections induce hyperinflammatory responses that are often intensified by host adaptive immune pathways to profoundly advance disease severity. Proinflammatory responses are triggered by CoV entry mediated by host cell surface receptors. Interestingly, five of the seven strains use three cell surface metallopeptidases (CD13, CD26, and ACE2) as receptors, whereas the others employ O-acetylated-sialic acid (a key feature of metallopeptidases) for entry. Why CoV evolved to use peptidases as their receptors is unknown, but the peptidase activities of the receptors are dispensable, suggesting the virus uses/benefits from other functions of these molecules. Indeed, these receptors participate in the immune modulatory pathways that contribute to the pathological hyperinflammatory response. This review will focus on the role of CoV receptors in modulating immune responses.

CD13: A Key Player in Multidrug Resistance in Cancer Chemotherapy

Cancer is one of the most serious diseases that are harmful to human health. Systemic chemotherapy is an optimal therapeutic strategy for the treatment of cancer, but great difficulty has been encountered in its administration in the form of multidrug resistance (MDR). As an enzyme on the outer cell surface, CD13 is documented to be involved in the MDR development of tumor cells. In this review, we will focus on the role of CD13 in MDR generation based on the current evidence.

Anticoagulant and signaling functions of antithrombin

Antithrombin (AT) is a major plasma glycoprotein of the serpin superfamily that regulates the proteolytic activity of the procoagulant proteases of both intrinsic and extrinsic pathways. Two important structural features that participate in the regulatory function of AT include a mobile reactive center loop that binds to active site of coagulation proteases, trapping them in the form of inactive covalent complexes, and a basic D-helix that binds to therapeutic heparins and heparan sulfate proteoglycans (HSPGs) on vascular endothelial cells. The binding of D-helix of AT by therapeutic heparins promotes the reactivity of the serpin with coagulation proteases by several orders of magnitude by both a conformational activation of the serpin and a template (bridging) mechanism. In addition to its essential anticoagulant function, AT elicits a potent anti-inflammatory signaling response when it binds to distinct vascular endothelial cell HSPGs, thereby inducing prostacyclin synthesis. Syndecans-4 has been found as a specific membrane-bound HSPG receptor on endothelial cells that relays the signaling effect of AT to the relevant second messenger molecules in the signal transduction pathways inside the cell. However, following cleavage by coagulation proteases and/or by spontaneous conversion to a latent form, AT loses both its anti-inflammatory activity and high-affinity interaction with heparin and HSPGs. Interestingly, these low-affinity heparin conformers of AT elicit potent proapoptotic and antiangiogenic activities by also binding to specific HSPGs by unknown mechanisms. This review article will summarize current knowledge about mechanisms through which different conformers of AT exert their serine protease inhibitory and intracellular signaling functions in these biological pathways.

TLR4 and CD14 trafficking and its influence on LPS-induced pro-inflammatory signaling

Toll-like receptor (TLR) 4 belongs to the TLR family of receptors inducing pro-inflammatory responses to invading pathogens. TLR4 is activated by lipopolysaccharide (LPS, endotoxin) of Gram-negative bacteria and sequentially triggers two signaling cascades: the first one involving TIRAP and MyD88 adaptor proteins is induced in the plasma membrane, whereas the second engaging adaptor proteins TRAM and TRIF begins in early endosomes after endocytosis of the receptor. The LPS-induced internalization of TLR4 and hence also the activation of the TRIF-dependent pathway is governed by a GPI-anchored protein, CD14. The endocytosis of TLR4 terminates the MyD88-dependent signaling, while the following endosome maturation and lysosomal degradation of TLR4 determine the duration and magnitude of the TRIF-dependent one. Alternatively, TLR4 may return to the plasma membrane, which process is still poorly understood. Therefore, the course of the LPS-induced pro-inflammatory responses depends strictly on the rates of TLR4 endocytosis and trafficking through the endo-lysosomal compartment. Notably, prolonged activation of TLR4 is linked with several hereditary human diseases, neurodegeneration and also with autoimmune diseases and cancer. Recent studies have provided ample data on the role of diverse proteins regulating the functions of early, late, and recycling endosomes in the TLR4-induced inflammation caused by LPS or phagocytosis of E. coli. In this review, we focus on the mechanisms of the internalization and intracellular trafficking of TLR4 and CD14, and also of LPS, in immune cells and discuss how dysregulation of the endo-lysosomal compartment contributes to the development of diverse human diseases.

CD13/Aminopeptidase N Is a Potential Therapeutic Target for Inflammatory Disorders

CD13/aminopeptidase N is a widely expressed ectoenzyme with multiple functions. As an enzyme, CD13 regulates activities of numerous cytokines by cleaving their N-terminals and is involved in Ag processing by trimming the peptides bound to MHC class II. Independent of its enzymatic activity, cell membrane CD13 functions by cross-linking-induced signal transduction, regulation of receptor recycling, enhancement of FcγR-mediated phagocytosis, and acting as a receptor for cytokines. Moreover, soluble CD13 has multiple proinflammatory roles mediated by binding to G-protein-coupled receptors. CD13 not only modulates development and activities of immune-related cells, but also regulates functions of inflammatory mediators. Therefore, CD13 is important in the pathogenesis of various inflammatory disorders. Inhibitors of CD13 have shown impressive anti-inflammatory effects, but none of them has yet been used for clinical therapy of human inflammatory diseases. We reevaluate CD13's regulatory role in inflammation and suggest that CD13 could be a potential therapeutic target for inflammatory disorders.

When Innate Immunity Meets Angiogenesis-The Role of Toll-Like Receptors in Endothelial Cells and Pulmonary Hypertension

Toll-like receptors serve a central role in innate immunity, but they can also modulate cell function in various non-immune cell types including endothelial cells. Endothelial cells are necessary for the organized function of the vascular system, and part of their fundamental role is also the regulation of immune function and inflammation. In this review, we summarize the current knowledge of how Toll-like receptors contribute to the immune and non-immune functions of the endothelial cells.

Can aminopeptidase N determined in the meconium be a candidate for biomarker of fetal intrauterine environment?

AIM

To investigate possible association of aminopeptidase N/CD13 with other parameters of possible homeostatic mechanisms in meconium for potential use in identifying intrauterine environmental stress factors during fetal and perinatal life.

METHODS

Aminopeptidase N/CD13 (APN/CD13), calprotectin (CAL), myeloperoxidase (MPO), ceruloplasmin (CER), lactoferrin (LF) and interleukin-8 (IL-8) were determined using ELISA kits in 115 meconium samples collected from 30 healthy full term neonates.

RESULTS

Significant correlations were established between meconium APN/CD13 [μg/g] (mean ± SD, median, range: 2.88 ± 9.90, 0.94, 0.09-91.54) and MPO (r = 0.77, p = .0000), CER (r = 0.48, p = .0000), LF (r = 0.26, p = .005), IL-8 (r = 0.44, p = .00012) but no correlation of APN/CD13 vs CAL (r = 0.15, p > .05). With increased APN/CD13 concentrations there were increases (p < .05) in concentrations of MPO, CER, LF and L-8.

CONCLUSIONS

Meconium APN/CD13 demonstrates characteristic associations with other proteins involved in the regulation of metabolic processes. The panel of APN/CD13, MPO, CER and LF may be candidate biomarker for disorders developing in utero which may have impact on health in later life.

Phosphorylated Heat Shock Protein 27 Inhibits Lipopolysaccharide-Induced Inflammation in Thp1 Cells by Promoting TLR4 Endocytosis, Ubiquitination, and Degradation

The aims of this study were to investigate the effect of Hsp27 on LPS-induced inflammation and identify the precise mechanisms about how Hsp27 regulates LPS-induced TLR4 signaling in Thp1 cells. Thp1 cells were transfected with Flag-Hsp27 or pcDNA3.1, and then treated with LPS for indicated time. TNF-α, IL-1β, and IL-6 were determined by ELISA. The protein levels of Hsp27, p-Hsp27 (Ser15, Ser78, and Ser82), and TLR4 were measured by Western blotting. In vitro study showed that over-expression of Hsp27 downregulated the release of TNF-α, IL-1β, and IL-6 and suppressed the activation of TLR4 signals after stimulated by LPS. The location of TLR4 and RAB5 was detected by confocal microscopy. Immunoprecipitation was used to determine the ubiquitination and degradation of TLR4 and interaction between Hsp27 and TLR4. Results showed that Hsp27 could promote TLR4 endocytosis and ubiquitination and degradation. Further research revealed that Hsp27 was phosphorylated after LPS, only phosphorylated Hsp27 can interact with TLR4 and inhibit the activation of TLR4 signaling, which was demonstrated by inhibition of Hsp27 phosphorylation with inhibitors or transfection of Hsp27 mutants into Thp1 cells. Phosphorylated Hsp27 reduced the release of TNF-α, IL-1β, and IL-6, and suppressed the activation of TLR4 signaling by promoting TLR4 endocytosis, ubiquitination, and degradation.

The Emerging Role of Rab5 in Membrane Receptor Trafficking and Signaling Pathways

Ras analog in brain (Rab) proteins are small guanosine triphosphatases (GTPases) that belong to the Ras-like GTPase superfamily, and they can regulate vesicle trafficking. Rab proteins alternate between an activated (GTP-bound) state and an inactivated (GDP-bound) state. Early endosome marker Rab5 GTPase, a key member of the Rab family, plays a crucial role in endocytosis and membrane transport. The activated-state Rab5 recruits its effectors and regulates the internalization and trafficking of membrane receptors by regulating vesicle fusion and receptor sorting in the early endosomes. In this review, we summarize the role of small Rab GTPases Rab5 in membrane receptor trafficking and the activation of signaling pathways, such as Ras/MAPK and PI3K/Akt, which ultimately affect cell growth, apoptosis, tumorigenesis, and tumor development. This review may provide some insights for our future research and novel therapeutic targets for diseases.

Therapeutic effect and mechanism of action of quercetin in a rat model of osteoarthritis

Objective

To study the therapeutic effect and mechanism of action of quercetin in a rat model of osteoarthritis (OA).

Methods

The OA rat model was established by intra-articular injection of papain. Changes in knee diameter, toe volume and histopathology were measured. Levels of interleukin (IL)-β and tumor necrosis factor (TNF)-α were assessed by ELISA. Relative expression of Toll-like receptor (TLR)-4 and nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB) was evaluated by western blotting.

Results

Compared with rats treated with papain alone, changes in knee diameter, toe volume and Makin' s score were less apparent in OA rats treated with quercetin. Levels of serum IL-1β and TNF-α were also reduced in quercetin-treated OA rats. Expression of TLR-4 and NF-κB was significantly suppressed in a dose-dependent manner in quercetin-treated OA rats.

Conclusion

Quercetin exhibited a therapeutic effect in OA rats, which may be related to inhibition of IL-1β and TNF-α production via the TLR-4/NF-κB pathway.

CD13 regulation of membrane recycling: implications for cancer dissemination

Membrane recycling is critical to numerous cell functions and its dysregulation contributes to cancer and metastasis. We established that activation of the transmembrane molecule aminopeptidase N (ANPEP, also known as CD13) tethers the IQ motif containing, guanosine triphosphate hydrolase activating protein 1 (IQGAP1) scaffolding protein at the plasma membrane, thus stimulating the recycling regulator ADP-ribosylation factor 6 (ARF6) to ensure proper recycling of β1-integrin and other membrane components impacting cell attachment.

Multiple exposures to poultry barn air and lipopolysaccharide synergistically increase the pulmonary expression of TLR-4 and IL-1β

Objective

Poultry farm workers are exposed to barn air and suffer from various respiratory disorders. Due to frequent prevalence of endotoxin in the farm settings workers can get co‐exposed to barn air and endotoxin. The study was aimed to explore the pulmonary damage following long‐term multiple exposures to poultry barn air with or without endotoxin.

Methods

We studied the pulmonary expression of Toll‐like receptor 4 (TLR4) and Interleukin‐1β (IL‐1β) by exposing Swiss albino mice to poultry barn air for 6 days (Monday‐Saturday) in a week for 5 and 10 weeks. At the end of exposure, animals were challenged with lipopolysaccharide (LPS) or normal saline solution @80 μg/mouse intranasally. Histopathology, bronchoalveolar lavage (BAL) fluid and blood analysis were used to characterize lung damage. mRNA and protein expression of TLR4 and IL‐1β were evaluated using quantitative polymerase chain reaction (qPCR) and immunohistochemistry, respectively.

Results

Histopathology along with TLC and DLC of blood and BAL fluid revealed lung damage following multiple exposures and damage was severe in combination with LPS. Exposures altered mRNA and protein expression of TLR‐4 and IL‐1β and the expression was more marked following 30 days of exposure. Further LPS co‐challenge showed a synergistic effect on the expression of TLR4 and IL‐1β.

Conclusions

The data suggest that long‐term exposures with or without LPS caused lung damage and altered the pulmonary expression of TLR4 and IL‐1β.

A human antithrombin isoform dampens inflammatory responses and protects from organ damage during bacterial infection

Severe infectious diseases are often characterized by an overwhelming and unbalanced systemic immune response to microbial infections. Human antithrombin (hAT) is a crucial coagulation inhibitor with anti-inflammatory activities. Here we identify three hAT-binding proteins (CD13, CD300f and LRP-1) on human monocytes that are involved in blocking the activity of nuclear factor-κB. We found that the modulating effect is primarily restricted to the less abundant β-isoform (hβAT) of hAT that lacks N-glycosylation at position 135. Individuals with a mutation at this position have increased production of hβAT and analysis of their blood, which was stimulated ex vivo with lipopolysaccharide, showed a decreased inflammatory response. Similar findings were recorded when heterozygotic mice expressing hAT or hβAT were challenged with lipopolysaccharide or infected with Escherichia coli bacteria. Our results finally demonstrate that in a lethal E. coli infection model, survival rates increased when mice were treated with hβAT one hour and five hours after infection. The treatment also resulted in a reduction of the inflammatory response and less severe organ damage.

CD13 deficiency leads to increased oxidative stress and larger atherosclerotic lesions

BACKGROUND AND AIMS

Atherosclerosis is an inflammatory cardiovascular disorder characterized by accumulation of lipid-loaded macrophages in the intima. Prolonged accumulation leads to apoptosis of macrophages and eventually to progression of lesion development. Prevention of macrophage accumulation within the intima has been shown to reduce lesion formation. Since CD13 mediates trafficking of macrophages to sites of injury and repair, we tested the role of CD13 in atherosclerosis.

METHODS

CD13+/+Ldlr-/- and CD13-/-Ldlr-/- (low density lipoprotein receptor) mice were fed basal or high fat diet (HFD) for 9, 12 and 15 weeks. Mice were euthanized and aortic roots along with innominate arteries were analyzed for atherosclerotic lesions. Cellular mechanisms were determined in vitro using CD13+/+ and CD13-/- bone marrow derived macrophages (BMDMs) incubated with highly oxidized low-density lipoprotein (oxLDL).

RESULTS

At the 9 and 12 week time points, no differences were observed in the average lesion size, but at the 15 week time point, CD13-/-Ldlr-/- mice had larger lesions with exaggerated necrotic areas. CD13+/+ and CD13-/- macrophages endocytosed similar amounts of oxLDL, but CD13-/- macrophages generated higher amounts of oxidative stressors in comparison to CD13+/+ macrophages. This increased oxidative stress was due to increased nitric oxide production in oxLDL treated CD13-/- macrophages. Accumulated oxidative stress subsequently led to accelerated apoptosis and enhanced necrosis of oxLDL treated CD13-/- macrophages.

CONCLUSIONS

Contrary to our prediction, CD13 deficiency led to larger atherosclerotic lesions with increased areas of necrosis. Mechanistically, CD13 deficiency led to increased nitric oxide production and consequently, greater oxidative stress.

CD13 tethers the IQGAP1-ARF6-EFA6 complex to the plasma membrane to promote ARF6 activation, β1 integrin recycling, and cell migration

Cell attachment to the extracellular matrix (ECM) requires a balance between integrin internalization and recycling to the surface that is mediated by numerous proteins, emphasizing the complexity of these processes. Upon ligand binding in various cells, the β1 integrin is internalized, traffics to early endosomes, and is returned to the plasma membrane through recycling endosomes. This trafficking process depends on the cyclical activation and inactivation of small guanosine triphosphatases (GTPases) by their specific guanine exchange factors (GEFs) and their GTPase-activating proteins (GAPs). In this study, we found that the cell surface antigen CD13, a multifunctional transmembrane molecule that regulates cell-cell adhesion and receptor-mediated endocytosis, also promoted cell migration and colocalized with β1 integrin at sites of cell adhesion and at the leading edge. A lack of CD13 resulted in aberrant trafficking of internalized β1 integrin to late endosomes and its ultimate degradation. Our data indicate that CD13 promoted ARF6 GTPase activity by positioning the ARF6-GEF EFA6 at the cell membrane. In migrating cells, a complex containing phosphorylated CD13, IQGAP1, GTP-bound (active) ARF6, and EFA6 at the leading edge promoted the ARF6 GTPase cycling and cell migration. Together, our findings uncover a role for CD13 in the fundamental cellular processes of receptor recycling, regulation of small GTPase activities, cell-ECM interactions, and cell migration.

Below the surface: The inner lives of TLR4 and TLR9

TLRs are a class of pattern recognition receptors (PRRs) that detect invading microbes by recognizing pathogen-associated molecular patterns (PAMPs). Upon PAMP engagement, TLRs activate a signaling cascade that leads to the production of inflammatory mediators. The localization of TLRs, either on the plasma membrane or in the endolysosomal compartment, has been considered to be a fundamental aspect to determine to which ligands the receptors bind, and which transduction pathways are induced. However, new observations have challenged this view by identifying complex trafficking events that occur upon TLR-ligand binding. These findings have highlighted the central role that endocytosis and receptor trafficking play in the regulation of the innate immune response. Here, we review the TLR4 and TLR9 transduction pathways and the importance of their different subcellular localization during the inflammatory response. Finally, we discuss the implications of TLR9 subcellular localization in autoimmunity.

Leukadherin-1-Mediated Activation of CD11b Inhibits LPS-Induced Pro-inflammatory Response in Macrophages and Protects Mice Against Endotoxic Shock by Blocking LPS-TLR4 Interaction

Dysregulation of macrophage has been demonstrated to contribute to aberrant immune responses and inflammatory diseases. CD11b, expressed on macrophages, plays a critical role in regulating pathogen recognition, phagocytosis, and cell survival. In the present study, we explored the effect of leukadherin-1 (LA1), an agonist of CD11b, on regulating LPS-induced pro-inflammatory response in macrophages and endotoxic shock. Intriguingly, we found that LA1 could significantly reduce mortalities of mice and alleviated pathological injury of liver and lung in endotoxic shock. In vivo studies showed that LA1-induced activation of CD11b significantly inhibited the LPS-induced pro-inflammatory response in macrophages of mice. Moreover, LA1-induced activation of CD11b significantly inhibited LPS/IFN-γ-induced pro-inflammatory response in macrophages by inhibiting MAPKs and NF-κB signaling pathways in vitro. Furthermore, the mice injected with LA1-treated BMDMs showed fewer pathological lesions than those injected with vehicle-treated BMDMs in endotoxic shock. In addition, we found that activation of TLR4 by LPS could endocytose CD11b and activation of CD11b by LA1 could endocytose TLR4 in vitro and in vivo, subsequently blocking the binding of LPS with TLR4. Based on these findings, we concluded that LA1-induced activation of CD11b negatively regulates LPS-induced pro-inflammatory response in macrophages and subsequently protects mice from endotoxin shock by partially blocking LPS-TLR4 interaction. Our study provides a new insight into the role of CD11b in the pathogenesis of inflammatory diseases.

Leukadherin-1-Mediated Activation of CD11b Inhibits LPS-Induced Pro-inflammatory Response in Macrophages and Protects Mice Against Endotoxic Shock by Blocking LPS-TLR4 Interaction

Dysregulation of macrophage has been demonstrated to contribute to aberrant immune responses and inflammatory diseases. CD11b, expressed on macrophages, plays a critical role in regulating pathogen recognition, phagocytosis, and cell survival. In the present study, we explored the effect of leukadherin-1 (LA1), an agonist of CD11b, on regulating LPS-induced pro-inflammatory response in macrophages and endotoxic shock. Intriguingly, we found that LA1 could significantly reduce mortalities of mice and alleviated pathological injury of liver and lung in endotoxic shock. In vivo studies showed that LA1-induced activation of CD11b significantly inhibited the LPS-induced pro-inflammatory response in macrophages of mice. Moreover, LA1-induced activation of CD11b significantly inhibited LPS/IFN-γ-induced pro-inflammatory response in macrophages by inhibiting MAPKs and NF-κB signaling pathways in vitro. Furthermore, the mice injected with LA1-treated BMDMs showed fewer pathological lesions than those injected with vehicle-treated BMDMs in endotoxic shock. In addition, we found that activation of TLR4 by LPS could endocytose CD11b and activation of CD11b by LA1 could endocytose TLR4 in vitro and in vivo, subsequently blocking the binding of LPS with TLR4. Based on these findings, we concluded that LA1-induced activation of CD11b negatively regulates LPS-induced pro-inflammatory response in macrophages and subsequently protects mice from endotoxin shock by partially blocking LPS-TLR4 interaction. Our study provides a new insight into the role of CD11b in the pathogenesis of inflammatory diseases.

Gene expression profiles alteration after infection of virus, bacteria, and parasite in the Olive flounder (Paralichthys olivaceus)

Olive flounder (Paralichthys olivaceus) is one of economically valuable fish species in the East Asia. In comparison with its economic importance, available genomic information of the olive flounder is very limited. The mass mortality caused by variety of pathogens (virus, bacteria and parasites) is main problem in aquaculture industry, including in olive flounder culture. In this study, we carried out transcriptome analysis using the olive flounder gill tissues after infection of three types of pathogens (Virus; Viral hemorrhagic septicemia virus, Bacteria; Streptococcus parauberis, and Parasite; Miamiensis avidus), respectively. As a result, we identified total 12,415 differentially expressed genes (DEG) from viral infection, 1,754 from bacterial infection, and 795 from parasite infection, respectively. To investigate the effects of pathogenic infection on immune response, we analyzed Gene ontology (GO) enrichment analysis with DEGs and sorted immune-related GO terms per three pathogen groups. Especially, we verified various GO terms, and genes in these terms showed down-regulated expression pattern. In addition, we identified 67 common genes (10 up-regulated and 57 down-regulated) present in three pathogen infection groups. Our goals are to provide plenty of genomic knowledge about olive flounder transcripts for further research and report genes, which were changed in their expression after specific pathogen infection.

Combined deficiency of SLAMF8 and SLAMF9 prevents endotoxin-induced liver inflammation by downregulating TLR4 expression on macrophages

Classical signaling lymphocyte activating molecule (SLAM) family receptors are abundant within many types of immune cells, whereas the nonclassical SLAM family receptors SLAMF8 and SLAMF9, which uniquely lack cytoplasmic signaling motifs, are highly expressed by myeloid cells. Due to the potential redundancy, whether these two receptors regulate macrophage function remains largely unknown. Here, we show that SLAMF8 and SLAMF9 co-regulate macrophage-mediated liver inflammation. To overcome the redundancy, we generated mice that simultaneously lacked SLAMF8 and SLAMF9 using CRISPR-Cas9 technology. Although macrophage differentiation was not altered by the combined deficiency of SLAMF8 and SLAMF9, the loss of these two receptors significantly protected against lipopolysaccharide (LPS)-induced liver injury. SLAMF8 and SLAMF9 double-deficient mice had a prolonged survival rate and less infiltration of inflammatory cells. The depletion of macrophages using clodronate liposomes abolished the effects of SLAMF8 and SLAMF9 deficiencies on LPS-induced liver injury, which demonstrates that these receptors are required for macrophage activation following LPS challenge. Moreover, the deficiency of SLAMF8 and SLAMF9 suppressed the secretion of inflammatory cytokines by downregulating the expression of Toll-like receptor-4 (TLR4), a receptor that specifically binds LPS, which led to decreased mitogen-activated protein kinases (MAPK) signaling activation. Notably, combined injections of truncated extracellular SLAMF8 and SLAMF9 proteins significantly alleviated LPS-induced liver injury. Thus, our findings provide insights into the role of SLAMF8 and SLAMF9 in endotoxin-induced liver injury and suggest that SLAMF8 and SLAMF9 are potential therapeutic targets for acute hepatic injury.

Overexpression of Toll-like receptor 4 enhances LPS-induced inflammatory response and inhibits Salmonella Typhimurium growth in ovine macrophages

The Toll-like receptor 4 (TLR4) plays a crucial role in innate inflammatory responses, as it recognizes gram-negative bacteria (or their products) and contributes greatly to host defense against invading pathogens. Though TLR4 overexpressing transgenic sheep, resistant to certain diseases related with gram-negative bacteria, had been bred in our previous research, the effects of overexpression of TLR4 on innate immune response remained unclear. In this study, TLR4 overexpressing ovine macrophages were obtained from peripheral blood, and it was found that the overexpression of TLR4 initially promoted the production of proinflammatory cytokines TNFα and IL-6 by activating TLR4-mediated IRAK4-dependent NF-κB and MAPK (JNK and ERK1/2) signaling following LPS stimulation. However, this effect was later impaired due to increased internalization of TLR4 into endosomal compartment of the macrophages. Then the overexpression of TLR4 triggered TBK1-dependent interferon-regulatory factor-3 (IRF-3) expression, which in turn led to the induction of IFN-β and IFN-inducible genes (i.e.IP10, IRG1 and GARG16). Understandably, an increased IFN-β level facilitated phosphorylation of STAT1 to induce expression of innate antiviral genes Mx1 and ISG15, suggesting that TLR4 overexpressing macrophages were equipped better against viral infection. Correspondingly, the bacterial burden in these macrophages, after infection with live S. Typhimurium, was decreased significantly. In summary, the results indicated that overexpression of TLR4 could enhance innate inflammatory responses, initiate the innate antiviral immunity, and control effectively S. Typhimurium growth in ovine macrophages.

The innate immune response to ischemic injury: a multiscale modeling perspective

Background

Cell death as a result of ischemic injury triggers powerful mechanisms regulated by germline-encoded Pattern Recognition Receptors (PRRs) with shared specificity that recognize invading pathogens and endogenous ligands released from dying cells, and as such are essential to human health. Alternatively, dysregulation of these mechanisms contributes to extreme inflammation, deleterious tissue damage and impaired healing in various diseases. The Toll-like receptors (TLRs) are a prototypical family of PRRs that may be powerful anti-inflammatory targets if agents can be designed that antagonize their harmful effects while preserving host defense functions. This requires an understanding of the complex interactions and consequences of targeting the TLR-mediated pathways as well as technologies to analyze and interpret these, which will then allow the simulation of perturbations targeting specific pathway components, predict potential outcomes and identify safe and effective therapeutic targets.

Results

We constructed a multiscale mathematical model that spans the tissue and intracellular scales, and captures the consequences of targeting various regulatory components of injury-induced TLR4 signal transduction on potential pro-inflammatory or pro-healing outcomes. We applied known interactions to simulate how inactivation of specific regulatory nodes affects dynamics in the context of injury and to predict phenotypes of potential therapeutic interventions. We propose rules to link model behavior to qualitative estimates of pro-inflammatory signal activation, macrophage infiltration, production of reactive oxygen species and resolution. We tested the validity of the model by assessing its ability to reproduce published data not used in its construction.

Conclusions

These studies will enable us to form a conceptual framework focusing on TLR4-mediated ischemic repair to assess potential molecular targets that can be utilized therapeutically to improve efficacy and safety in treating ischemic/inflammatory injury.

Cell-intrinsic sphingosine kinase 2 promotes macrophage polarization and renal inflammation in response to unilateral ureteral obstruction

Sphingosine Kinase-2 (Sphk2) is responsible for the production of the bioactive lipid Sphingosine-1 Phosphate, a key regulator of tissue repair. Here we address the in vivo significance of Sphingosine Kinase -2 in renal inflammation/fibrosis in response to unilateral ureteral obstruction using both genetic and pharmacological strategies. Obstructed kidneys of Sphk2^-/- mice showed reduced renal damage and diminished levels of the renal injury markers TGFβ₁ and αSMA when compared to wild type controls. We found a consistently significant increase in anti-inflammatory (M2) macrophages in obstructed Sphk2^-/- kidneys by flow cytometry and a decrease in mRNA levels of the inflammatory cytokines, MCP1, TNFα, CXCL1 and ILβ₁, suggesting an anti-inflammatory bias in the absence of Sphk2. Indeed, metabolic profiling showed that the pro-inflammatory glycolytic pathway is largely inactive in Sphk2^-/- bone marrow-derived macrophages. Furthermore, treatment with the M2-promoting cytokines IL-4 or IL-13 demonstrated that macrophages lacking Sphk2 polarized more efficiently to the M2 phenotype than wild type cells. Bone marrow transplant studies indicated that expression of Sphk2^-/- on either the hematopoietic or parenchymal cells did not fully rescue the pro-healing phenotype, confirming that both infiltrating M2-macrophages and the kidney microenvironment contribute to the damaging Sphk2 effects. Importantly, obstructed kidneys from mice treated with an Sphk2 inhibitor recapitulated findings in the genetic model. These results demonstrate that reducing Sphk2 activity by genetic or pharmacological manipulation markedly decreases inflammatory and fibrotic responses to obstruction, resulting in diminished renal injury and supporting Sphk2 as a novel driver of the pro-inflammatory macrophage phenotype.

The Effects of Agaricus blazei Murill Polysaccharides on Cadmium-Induced Apoptosis and the TLR4 Signaling Pathway of Peripheral Blood Lymphocytes in Chicken

In this study, we investigated the effects of Agaricus blazei Murill polysaccharides (ABP) on cadmium (Cd)-induced apoptosis and the TLR4 signaling pathway of chicken peripheral blood lymphocytes (PBLs). Seven-day-old healthy chickens were randomly divided into four groups, and each group contained 20 males. The cadmium-supplemented diet group (Cd group) was fed daily with full feed that contained 140 mg cadmium chloride (CdCl₂)/kg and 0.2 mL saline. The A. blazei Murill polysaccharide diet group (ABP group) was fed daily with full feed with 0.2 mL ABP solution (30 mg/mL) by oral gavage. The cadmium-supplemented plus A. blazei Murill polysaccharide diet group (Cd + ABP group) was fed daily with full feed containing 140 mg CdCl₂/kg and 0.2 mL ABP solution (30 mg/mL) by gavage. The control group was fed daily with full feed with 0.2 mL saline per day. We measured the apoptosis rate and messenger RNA (mRNA) levels of apoptosis genes (caspase-3, Bax, and Bcl-2), the mRNA levels of TLR4 and TLR4 signaling pathway-related factors (MyD88, TRIF, NF-κB, and IRF3), the TLR4 protein expression, and the concentrations of inflammatory cytokines (IL-1β, IL-6, and TNF-α) in chicken PBLs. The results showed that the PBL apoptosis rate was significantly increased, the mRNA levels of caspase-3 and Bax were significantly increased, while that of Bcl-2 was significantly reduced. The Bax/Bcl-2 ratio was significantly increased in the Cd group at 20, 40, and 60 days after treatment compared with that in the control group. After treatment with ABP, the above changes were clearly suppressed. At the same time, ABP reduced the concentrations of IL-1β, IL-6, and TNF-α induced by Cd. We also found that ABP inhibited the TLR4 mRNA level and protein expression and inhibited the mRNA levels of MyD88, TRIF, NF-κB, and IRF3. The results demonstrated that Cd could induce apoptosis, activate the TLR4 signaling pathway, and induce the expression of inflammatory cytokines in chicken PBLs, and that the administration of ABP clearly inhibited Cd-induced effects on chicken PBLs.

LYRM03, an ubenimex derivative, attenuates LPS-induced acute lung injury in mice by suppressing the TLR4 signaling pathway

Toll-like receptor 4 (TLR4)-mediated signaling plays a critical role in sepsis-induced acute lung injury (ALI). LYRM03 (3-amino-2-hydroxy-4-phenyl-valyl-isoleucine) is a novel derivative of ubenimex, a widely used antineoplastic medicine. We previously found that LYRM03 has anti-inflammatory effects in cecal ligation puncture mouse model. In this study we determined whether LYRM03 attenuated LPS-induced ALI in mice. LPS-induced ALI mouse model was established by challenging the mice with intratracheal injection of LPS (5 mg/kg), which was subsequently treated with LYRM03 (10 mg/kg, ip). LYRM03 administration significantly alleviated LPS-induced lung edema, inflammatory cell (neutrophils and macrophages) infiltration and myeloperoxidase (MPO) activity, decreased pro-inflammatory and chemotactic cytokine (TNF-α, IL-6, IL-1β, MIP-2) generation and reduced iNOS and COX-2 expression in the lung tissues. In cultured mouse alveolar macrophages in vitro, pretreatment with LYRM03 (100 μmol/L) suppressed LPS-induced macrophage activation by reducing Myd88 expression, increasing IκB stability and inhibiting p38 phosphorylation. These results suggest that LYRM03 effectively attenuates LPS-induced ALI by inhibiting the expression of pro-inflammatory mediators and Myd88-dependent TLR4 signaling pathways in alveolar macrophages. LYRM03 may serve as a potential treatment for sepsis-mediated lung injuries.

Early innate immune responses to bacterial LPS

A mammalian receptor for bacterial lipopolysaccharide (LPS), Toll-like receptor 4 (TLR4), plays a beneficial role in controlling bacterial infections, but is also a main driver of aberrant inflammation in lethal sepsis. As a result, investigation of TLR4 signaling has been a major area of research. Despite this focus, our understanding of the mechanisms that regulate TLR4 activities remains primitive. Nowhere is our knowledge of TLR4 biology more lacking than at the receptor-proximal level, where many factors act in concert to regulate LPS signaling. Several recent studies have begun filling these gaps in our knowledge. In this review, we discuss the importance of these receptor proximal activities in the spatiotemporal regulation of TLR4 signaling, and suggest interesting areas for future research.

A mucin-like peptide from Fasciola hepatica instructs dendritic cells with parasite specific Th1-polarizing activity

Fasciolosis is a trematode zoonosis of interest in public health and cattle production. We report here the immunostimulatory effect of a 66 mer mucin-like peptide from Fasciola hepatica (Fhmuc), which synergizes with lipopolysaccharide (LPS) to promote dendritic cell (DC) maturation, endowing these cells with Th1-polarizing capacity. Exposure of DCs to Fhmuc in presence of LPS induced enhanced secretion of pro-inflammatory cytokines and expression of co-stimulatory molecules by DCs, promoting their T cell stimulatory capacity and selectively augmenting IFN-γ secretion by allogeneic T cells. Furthermore, exposure of DCs to Fhmuc augmented LPS-induced Toll-like receptor (TLR) 4 expression on the cell surface. Finally, Fhmuc-conditioned DCs induced parasite specific-adaptive immunity with increased levels of IFN-γ secreted by splenocytes from vaccinated animals, and higher parasite-specific IgG antibodies. However, Fhmuc-treated DC conferred modest protection against F. hepatica infection highlighting the potent immuno-regulatory capacity of the parasite. In summary, this work highlights the capacity of a mucin-derived peptide from F. hepatica to enhance LPS-maturation of DCs and induce parasite-specific immune responses with potential implications in vaccination and therapeutic strategies.

Disabled-2 is a negative immune regulator of lipopolysaccharide-stimulated Toll-like receptor 4 internalization and signaling

Toll-like receptor 4 (TLR4) plays a pivotal role in the host response to lipopolysaccharide (LPS), a major cell wall component of Gram-negative bacteria. Here, we elucidated whether the endocytic adaptor protein Disabled-2 (Dab2), which is abundantly expressed in macrophages, plays a role in LPS-stimulated TLR4 signaling and trafficking. Molecular analysis and transcriptome profiling of RAW264.7 macrophage-like cells expressing short-hairpin RNA of Dab2 revealed that Dab2 regulated the TLR4/TRIF pathway upon LPS stimulation. Knockdown of Dab2 augmented TRIF-dependent interferon regulatory factor 3 activation and the expression of subsets of inflammatory cytokines and interferon-inducible genes. Dab2 acted as a clathrin sponge and sequestered clathrin from TLR4 in the resting stage of macrophages. Upon LPS stimulation, clathrin was released from Dab2 to facilitate endocytosis of TLR4 for triggering the TRIF-mediated pathway. Dab2 functions as a negative immune regulator of TLR4 endocytosis and signaling, supporting a novel role for a Dab2-associated regulatory circuit in controlling the inflammatory response of macrophages to endotoxin.

Localization, Shedding, Regulation and Function of Aminopeptidase N/CD13 on Fibroblast like Synoviocytes

Aminopeptidase N/CD13 is highly expressed by fibroblast like synoviocytes (FLS) and may play a role in rheumatoid arthritis (RA). CD13 was previously detected in human synovial fluid where it was significantly increased in RA compared to osteoarthritis. In this study we found that CD13 in biological fluids (plasma, synovial fluid, FLS culture supernatant) is present as both a soluble molecule and on extracellular vesicles, including exosomes, as assessed by differential ultracentrifugation and density gradient separation. Having determined CD13 could be released as a soluble molecule from FLS, we examined potential mechanisms by which CD13 might be shed from the FLS membrane. The use of protease inhibitors revealed that CD13 is cleaved from the FLS surface by metalloproteinases. siRNA treatment of FLS revealed one of those proteases to be MMP14. We determined that pro-inflammatory cytokines (TNFα, IFNγ, IL-17) upregulated CD13 mRNA in FLS, which may contribute to the increased CD13 in RA synovium and synovial fluid. Inhibition of CD13 function by either inhibitors of enzymatic activity or anti-CD13 antibodies resulted in decreased growth and diminished migration of FLS. This suggests that CD13 may be involved in the pathogenic hyperplasia of RA FLS. This data expands potential roles for CD13 in the pathogenesis of RA.

Regnase-1 in microglia negatively regulates high mobility group box 1-mediated inflammation and neuronal injury

Extracellular high mobility group box 1 (HMGB1) has been demonstrated to function as a proinflammatory cytokine and induces neuronal injury in response to various pathological stimuli in central nervous system (CNS). However, the regulatory factor involved in HMGB1-mediated inflammatory signaling is largely unclear. Regulatory RNase 1 (Regnase-1) is a potent anti-inflammation enzyme that can degrade a set of mRNAs encoding proinflammatory cytokines. The present study aims to determine the role of Regnase-1 in the regulation of HMGB1-mediated inflammatory injury in CNS. Cultured microglia and rat brain were treated with recombinant HMGB1 to examine the induction of Regnase-1 expression. Moreover, the role of Regnase-1 in modulating the expression of inflammatory cytokines and neuronal injury was then investigated in microglia by specific siRNA knockdown upon HMGB1 treatment. Results showed that HMGB1 could significantly induce the de novo synthesis of Regnase-1 in cultured microglia. Consistently, Regnase-1 was elevated and found to be co-localized with microglia marker in the brain of rat treated with HMGB1. Silencing Regnase-1 in microglia enhanced HMGB1-induced expression of proinflammatory cytokines and exacerbated neuronal toxicity. Collectively, these results suggest that Regnase-1 can be induced by HMGB1 in microglia and negatively regulates HMGB1-mediated neuroinflammation and neuronal toxicity.

CD13/aminopeptidase N is a negative regulator of mast cell activation

Antigen-induced mast cell (MC) activation via cross-linking of IgE-bound high-affinity receptors for IgE (FcεRI) underlies type I allergy and anaphylactic shock. Comprehensive knowledge of FcεRI regulation is thus required. We have identified a functional interaction between FcεRI and CD13 in murine MCs. Antigen-triggered activation of IgE-loaded FcεRI results in cocapping and cointernalization of CD13 and equivalent internalization rates of up to 40%. Cointernalization is not unspecific, because ligand-driven KIT internalization is not accompanied by CD13 internalization. Moreover, antibody-mediated cross-linking of CD13 causes IL-6 production in an FcεRI-dependent manner. These data are indicative of a functional interaction between FcεRI and CD13 on MCs. To determine the role of this interaction, CD13-deficient bone marrow-derived MCs (BMMCs) were analyzed. Intriguingly, antigen stimulation of CD13-deficient BMMCs results in significantly increased degranulation and proinflammatory cytokine production compared to wild-type cells. Furthermore, in a low-dose model of passive systemic anaphylaxis, antigen-dependent decrease in body temperature, reflecting the anaphylactic reaction, is substantially enhanced by the CD13 inhibitor bestatin (-5.9 ± 0.6°C) and by CD13 deficiency (-8.8 ± 0.6°C) in contrast to controls (-1.2 ± 1.97°C). Importantly, bestatin does not aggravate anaphylaxis in CD13-deficient mice. Thus, we have identified CD13 as a novel negative regulator of MC activation in vitro and in vivo-Zotz, J. S., Wölbing, F., Lassnig, C., Kauffmann, M., Schulte, U., Kolb, A., Whitelaw, B., Müller, M., Biedermann, T., Huber, M. CD13/aminopeptidase N is a negative regulator of mast cell activation.

TRAM1 Promotes Microglia M1 Polarization

Microglia, the major immune cells of the central nervous system (CNS), can be driven to adopt M1 and M2 phenotypes. Recently, the distinct functions of M1 and M2 microglia have been intensively studied. M1-activation microglia are pro-inflammatory and may contribute to the development of several CSN disorders, while M2-activation microglia are anti-inflammatory and may promote tissue reconstruction. TRAM1 is a protein involved in translocation of nascent polypeptides and functions as a sorting adaptor of TLR4. Here, we found that TRAM1 plays an important role in microglia M1 polarization. Our results showed that the expression of TRAM1 is highly induced in LPS/interferon (IFN)-γ-stimulated BV2 cells and primary microglia cells. Flag-TRAM1 transfection, but not Flag-GFP used as a control, significantly enhanced M1 polarization by strongly increasing expression of M1 makers, such as IL-6, IL-1β, iNOS, and so on. Silence of TRAM1 effectively inhibited LPS/IFN-γ-induced expression of M1-related genes in BV2 cells. In addition, TRAM1 was found to cooperate with TLR4 to induce an M1 genetic program in Flag-TRAM1-transfected and LPS/IFN-γ-induced BV2 cells. TRAM1 is essential for LPS/IFN-γ induced expressions of adapter molecule (IRAK1, phosphorylation of TBK1, and IRF3) of TLR4. TRAM1 is also essential for phosphorylation of IκB and P65 and for P65-NF-kB translocation to nucleus. Overall, our findings showed that TRAM1 could promote microglia M1 polarization.