Molecular and cellular regulation of toll-like receptor-4 activity induced by lipopolysaccharide ligands

RHBDL4-triggered downregulation of COPII adaptor protein TMED7 suppresses TLR4-mediated inflammatory signaling

The toll-like receptor 4 (TLR4) is a central regulator of innate immunity that primarily recognizes bacterial lipopolysaccharide cell wall constituents to trigger cytokine secretion. We identify the intramembrane protease RHBDL4 as a negative regulator of TLR4 signaling. We show that RHBDL4 triggers degradation of TLR4's trafficking factor TMED7. This counteracts TLR4 transport to the cell surface. Notably, TLR4 activation mediates transcriptional upregulation of RHBDL4 thereby inducing a negative feedback loop to reduce TLR4 trafficking to the plasma membrane. This secretory cargo tuning mechanism prevents the over-activation of TLR4-dependent signaling in an in vitro Mycobacterium tuberculosis macrophage infection model and consequently alleviates septic shock in a mouse model. A hypomorphic RHBDL4 mutation linked to Kawasaki syndrome, an ill-defined inflammatory disorder in children, further supports the pathophysiological relevance of our findings. In this work, we identify an RHBDL4-mediated axis that acts as a rheostat to prevent over-activation of the TLR4 pathway.

Decreased toll-like receptor 4 and CD11b/CD18 expression on peripheral monocytes of hypertensive patients correlates with a lesser extent of endothelial damage: a preliminary study

BACKGROUND

Low-grade chronic inflammation is recognized to contribute to the physiopathology of arterial hypertension. Therefore, this study aimed to assess the pro-inflammatory phenotype of peripheral monocytes of hypertensive patients by analyzing Toll-like receptor 4 (TLR4) and CD11b/CD18 surface expression. In the second part, the influence of phenotypic alterations of monocytes on the endothelial status reflected by circulating endothelial cells (CECs) was evaluated.

PATIENTS

The study included 60 patients with arterial hypertension, who were divided into two subgroups based on the disease severity according to the applicable criteria. The mild hypertension and resistant hypertension groups included 30 patients each. The control group consisted of 33 normotensive volunteers matched for age and sex.

RESULTS

Both in the entire group of patients and individual subgroups, reduced surface expression of TLR4 and CD11b/CD18 was found compared to normotensive volunteers. A reduced percentage of monocytes with the CD14 + TLR4 + immunophenotype was correlated with a lower MFI level of CD18 and CD11b in the entire group of patients and after division only in the mild hypertension group. Reduced surface expression of TLR4 in hypertensive patients correlated with a lower number of CECs. This relationship was not observed in the resistant hypertension group; instead, an independent effect of reduced CD11b/CD18 expression on the reduction of CEC number was demonstrated.

CONCLUSION

Our preliminary study showed for the first time that hypertension of varying severity is accompanied by phenotypic changes in monocytes, manifested by reduced surface expression of both TLR4 and CD11b/CD18. These phenotypic changes were associated with a reduced degree of endothelial injury. Our study opens a new, unexplored area of research on the protective features of peripheral monocytes in hypertension.

Protective Role of MAVS Signaling for Murine Lipopolysaccharide-Induced Acute Kidney Injury

Despite treatment advances, acute kidney injury (AKI)-related mortality rates are still high in hospitalized adults, often due to sepsis. Sepsis and AKI could synergistically worsen the outcomes of critically ill patients. TLR4 signaling and mitochondrial antiviral signaling protein (MAVS) signaling are innate immune responses essential in kidney diseases, but their involvement in sepsis-associated AKI (SA-AKI) remains unclear. We studied the role of MAVS in kidney injury related to the TLR4 signaling pathway using a murine LPS-induced AKI model in wild-type and MAVS-knockout mice. We confirmed the importance of M1 macrophage in SA-AKI through in vivo assessment of inflammatory responses. The TLR4 signaling pathway was upregulated in activated bone marrow-derived macrophages, in which MAVS helped maintain the LPS-suppressed TLR4 mRNA level. MAVS regulated redox homeostasis via NADPH oxidase Nox2 and mitochondrial reverse electron transport in macrophages to alleviate the TLR4 signaling response to LPS. Hypoxia-inducible factor 1α (HIF-1α) and AP-1 were key regulators of TLR4 transcription and connected MAVS-dependent reactive oxygen species signaling with the TLR4 pathway. Inhibition of succinate dehydrogenase could partly reduce inflammation in LPS-treated bone marrow-derived macrophages without MAVS. These findings highlight the renoprotective role of MAVS in LPS-induced AKI by regulating reactive oxygen species generation-related genes and maintaining redox balance. Controlling redox homeostasis through MAVS signaling may be a promising therapy for SA-AKI.

Trimetazidine alleviates paclitaxel-induced peripheral neuropathy through modulation of TLR4/p38/NFκB and klotho protein expression

Chemotherapy-induced peripheral neuropathy is a common adverse effect associated with a number of chemotherapeutic agents including paclitaxel (PTX) which is commonly used in a wide range of solid tumors. Development of PTX-induced peripheral neuropathy (PIPN) during cancer treatment requires dose reduction which limits its clinical benefits. This study is conducted to investigate the role of toll like receptor-4 (TLR4) and p38 signaling and Klotho protein expression in PIPN and the role of Trimetazidine (TMZ) in this pathway. Sixty-four male Swiss albino mice were divided into 4 groups (n = 16); Group (1) injected intraperitoneally (IP) with ethanol/tween 80/saline for 8 successive days. Group (2) received TMZ (5 mg/kg, IP, day) for 8 successive days. Group (3) treated with 4 doses of PTX (4.5 mg/kg, IP) every other day over a period of 8 days. Group (4) received a combination of TMZ as group 2 and PTX as group 3. The Effect of TMZ on the antitumor activity of PTX was studied in another set of mice-bearing Solid Ehrlich Carcinoma (SEC) that was similarly divided as the above-mentioned set. TMZ mitigated tactile allodynia, thermal hypoalgesia, numbness and fine motor dyscoordination associated with PTX in Swiss mice. The results of the current study show that the neuroprotective effect of TMZ can be attributed to inhibition of TLR4/p38 signaling which also includes a reduction in matrix metalloproteinase-9 (MMP9) protein levels as well as the proinflammatory interleukin-1β (IL-1β) and preserving the levels of the anti-inflammatory IL-10. Moreover, the current study is the first to demonstrate that PTX reduces the neuronal levels of klotho protein and showed its modulation via cotreatment with TMZ. In addition, this study showed that TMZ neither alter the growth of SEC nor the antitumor activity of PTX. In conclusion, we suggest that (1) Inhibition of Klotho protein and upregulation of TLR4/p38 signals in nerve tissues may contribute to PIPN. (2) TMZ attenuates PIPN by modulating TLR4/p38 and Klotho protein expression in without interfering with its antitumor activity.

Luteolin Protects Cardiomyocytes Cells against Lipopolysaccharide-Induced Apoptosis and Inflammatory Damage by Modulating Nlrp3

PURPOSE

In this article, we aimed to investigate the influences of luteolin on inflammatory injury to cardiomyocytes induced by lipopolysaccharide (LPS).

MATERIALS AND METHODS

H9c2 cells were pretreated with different concentrations of luteolin (10, 20, and 50 µM) for 12 h and then stimulated with 10 µg/mL LPS or no LPS for 6 h. Cell viability was detected by CCK-8 assay. Cell apoptosis was determined by flow cytometry. QRT-PCR and Western blotting were utilized to examine mRNA and protein levels. ELISA was used to determine the levels of monocyte chemoattractant protein-1, tumor necrosis factor-alpha, interleukin (IL)-6, IL-1β, and IL-18 in cell supernatants among different groups of H9c2 cells. Immunofluorescence was applied to evaluate reactive oxygen species formation in H9c2 cells. M-mode images of echocardiography, the ejection fraction test, fractional shortening test, end-systolic volume test, and end-diastolic volume test of mouse heart function were obtained by ultrasonic electrocardiogram.

RESULTS

Luteolin could alleviate inflammatory damage and inflammatory factor expression among LPS-induced H9c2 cells. Additionally, we found that luteolin decreased LPS-stimulated inflammatory damage in H9c2 cells by down-regulating NOD-like receptor family pyrin domain containing 3 (Nlrp3). Luteolin also improved myocardial function in mice treated with LPS and reduced myocardial relaxation. Luteolin reversed myocardial histological abnormalities in mice and reduced inflammation and cardiomyocyte apoptosis. Additionally, luteolin inhibited oxidative stress-mediated myocardial and systemic tissue damage in mice. Finally, luteolin reduced LPS-induced inflammatory damage in mouse cardiomyocytes by down-regulating Nlrp3.

CONCLUSION

We found that luteolin could reduce inflammatory damage to cardiomyocytes induced by LPS by down-regulating Nlrp3.

K48/K63-linked polyubiquitination of ATG9A by TRAF6 E3 ligase regulates oxidative stress-induced autophagy

Excessive generation and accumulation of highly reactive oxidizing molecules causes oxidative stress and oxidative damage to cellular components. Accumulating evidence indicates that autophagy diminishes oxidative damage in cells and maintains redox homeostasis by degrading and recycling intracellular damaged components. Here, we show that TRAF6 E3 ubiquitin ligase and A20 deubiquitinase coordinate to regulate ATG9A ubiquitination and autophagy activation in cells responding to oxidative stress. The ROS-dependent TRAF6-mediated non-proteolytic, K48/63-linked ubiquitination of ATG9A enhances its association with Beclin 1 and the assembly of VPS34-UVRAG complex, thereby stimulating autophagy. Notably, expression of the ATG9A ubiquitination mutants impairs ROS-induced VPS34 activation and autophagy. We further find that lipopolysaccharide (LPS)-induced ROS production also stimulates TRAF6-mediated ATG9A ubiquitination. Ablation of ATG9A causes aberrant TLR4 endosomal trafficking and decreases IRF-3 phosphorylation in LPS-stimulated macrophages. Our findings provide important insights into how K48/K63-linked ubiquitination of ATG9A contributes to the regulation of oxidative stress-induced autophagy.

Surfactant protein A enhances the degradation of LPS-induced TLR4 in primary alveolar macrophages involving Rab7, β-arrestin2, and mTORC1

Respiratory infections by Gram-negative bacteria are a major cause of global morbidity and mortality. Alveolar macrophages (AMs) play a central role in maintaining lung immune homeostasis and host defense by sensing pathogens via pattern recognition receptors (PRR). The PRR Toll-like receptor (TLR) 4 is a key sensor of lipopolysaccharide (LPS) from Gram-negative bacteria. Pulmonary surfactant is the natural microenvironment of AMs. Surfactant protein A (SP-A), a multifunctional host defense collectin, controls LPS-induced pro-inflammatory immune responses at the organismal and cellular level via distinct mechanisms. We found that SP-A post-transcriptionally restricts LPS-induced TLR4 protein expression in primary AMs from healthy humans, rats, wild-type and SP-A^-/- mice by further decreasing cycloheximide-reduced TLR4 protein translation and enhances the co-localization of TLR4 with the late endosome/lysosome. Both effects as well as the SP-A-mediated inhibition of LPS-induced TNFα release are counteracted by pharmacological inhibition of the small GTPase Rab7. SP-A-enhanced Rab7 expression requires β-arrestin2 and, in β-arrestin2^-/- AMs and after intratracheal LPS challenge of β-arrestin2^-/- mice, SP-A fails to enhance TLR4/lysosome co-localization and degradation of LPS-induced TLR4. In SP-A^-/- mice, TLR4 levels are increased after pulmonary LPS challenge. SP-A-induced activation of mechanistic target of rapamycin complex 1 (mTORC1) kinase requires β-arrestin2 and is critically involved in degradation of LPS-induced TLR4. The data suggest that SP-A post-translationally limits LPS-induced TLR4 expression in primary AMs by lysosomal degradation comprising Rab7, β-arrestin2, and mTORC1. This study may indicate a potential role of SP-A-based therapeutic interventions in unrestricted TLR4-driven immune responses to lower respiratory tract infections caused by Gram-negative bacteria.

Targeting Gut–Liver Axis for Treatment of Liver Fibrosis and Portal Hypertension

Antifibrotic therapies for the treatment of liver fibrosis represent an unconquered area of drug development. The significant involvement of the gut microbiota as a driving force in a multitude of liver disease, be it pathogenesis or fibrotic progression, suggest that targeting the gut–liver axis, relevant signaling pathways, and/or manipulation of the gut’s commensal microbial composition and its metabolites may offer opportunities for biomarker discovery, novel therapies and personalized medicine development. Here, we review potential links between bacterial translocation and deficits of host-microbiome compartmentalization and liver fibrosis that occur in settings of advanced chronic liver disease. We discuss established and emerging therapeutic strategies, translated from our current knowledge of the gut–liver axis, targeted at restoring intestinal eubiosis, ameliorating hepatic fibrosis and rising portal hypertension that characterize and define the course of decompensated cirrhosis.

Terminal uridyltransferase 7 regulates TLR4-triggered inflammation by controlling Regnase-1 mRNA uridylation and degradation

Different levels of regulatory mechanisms, including posttranscriptional regulation, are needed to elaborately regulate inflammatory responses to prevent harmful effects. Terminal uridyltransferase 7 (TUT7) controls RNA stability by adding uridines to its 3′ ends, but its function in innate immune response remains obscure. Here we reveal that TLR4 activation induces TUT7, which in turn selectively regulates the production of a subset of cytokines, including Interleukin 6 (IL-6). TUT7 regulates IL-6 expression by controlling ribonuclease Regnase-1 mRNA (encoded by Zc3h12a gene) stability. Mechanistically, TLR4 activation causes TUT7 to bind directly to the stem-loop structure on Zc3h12a 3′-UTR, thereby promotes Zc3h12a uridylation and degradation. Zc3h12a from LPS-treated TUT7-sufficient macrophages possesses increased oligo-uridylated ends with shorter poly(A) tails, whereas oligo-uridylated Zc3h12a is significantly reduced in Tut7^-/- cells after TLR4 activation. Together, our findings reveal the functional role of TUT7 in sculpting TLR4-driven responses by modulating mRNA stability of a selected set of inflammatory mediators.

Terminal uridyltransferase 7 (TUT7) adds U-tails on diverse RNAs to promote degradation. Here the authors show that TUT7 is induced upon LPS treatment in macrophages and promotes decay of Regnase-1, thereby regulating the expression of a subset of cytokines, including IL-6.

Fatty acid-binding protein 4 silencing protects against lipopolysaccharide-induced cardiomyocyte hypertrophy and apoptosis by inhibiting the Toll-like receptor 4-nuclear factor-κB pathway

Objective

To explore the effects and potential mechanisms of fatty acid-binding protein 4 (FABP4) in a lipopolysaccharide (LPS)-induced in vitro septic cardiomyopathy model.

Methods

Rat cardiomyocyte H9c2 cells were transfected with small interfering RNA (siRNA) against FABP4 (siFABP4), then induced with LPS. The following parameters were measured: cell viability, lactate dehydrogenase release, cardiac hypertrophy and related marker expression, apoptosis, inflammatory cytokine release and expression, and the activation of Toll-like receptor 4 (TLR4) and nuclear factor-κB (NF-κB) pathways.

Results

LPS increased the mRNA and protein expression of FABP4 in H9c2 cells. FABP4 silencing by siFABP4 significantly inhibited LPS-induced cardiac hypertrophy and reduced the mRNA expression of the myocardial hypertrophy markers atrial natriuretic peptide and brain natriuretic peptide. siFABP4 also attenuated LPS-induced increase in TUNEL-positive apoptotic cells, caspase-3 and caspase-9 activities, and the release and expression of proinflammatory cytokines. Mechanistically, we found that FABP4 silencing inhibited the mRNA and protein expression of TLR4 and suppressed the NF-kappa B signaling pathway, as evidenced by reduced nuclear NF-κB p65 and increased cytoplasmic I-κBα expression in LPS-stimulated H9c2 cells.

Conclusion

FABP4 silencing reduces LPS-induced cardiomyocyte hypertrophy and apoptosis by down-regulating the TLR4/NF-κB axis.

Toll-like receptor 4 (TLR4) antagonists as potential therapeutics for intestinal inflammation

Gastrointestinal inflammation is a hallmark of highly prevalent disorders, including cancer treatment-induced mucositis and ulcerative colitis. These disorders cause debilitating symptoms, have a significant impact on quality of life, and are poorly managed. The activation of toll-like receptor 4 (TLR4) has been proposed to have a major influence on the inflammatory signalling pathways of the intestinal tract. Inhibition of TLR4 has been postulated as an effective way to treat intestinal inflammation. However, there are a limited number of studies looking into the potential of TLR4 antagonism as a therapeutic approach for intestinal inflammation. This review surveyed available literature and reported on the in vitro, ex vivo and in vivo effects of TLR4 antagonism on different models of intestinal inflammation. Of the studies reviewed, evidence suggests that there is indeed potential for TLR4 antagonists to treat inflammation, although only a limited number of studies have investigated treating intestinal inflammation with TLR4 antagonists directly. These results warrant further research into the effect of TLR4 antagonists in the intestinal tract.

Toll-like receptor 4 gene polymorphisms rs4986790 and rs4986791 and age-related macular degeneration susceptibility: a meta-analysis

Background: Several studies have investigated two single nucleotide polymorphisms (SNPs) (rs4986790 and rs4986791) of toll-like receptor 4 (TLR4) and age-related macular degeneration (AMD) susceptibility. However, their results varied. Here, we performed a systematic review and meta-analysis to investigate the association between these two SNPs and AMD susceptibility.Materials and Methods: We searched the PubMed and Web of Science databases for articles indexed up to July 20, 2019. Studies investigating the association between TLR4 polymorphisms rs4986790 (Asp299Gly) and rs4986791 (Thr399Ile) and AMD susceptibility were included in this systematic review. The results of the included studies were pooled with allele contrast, recessive, dominant and overdominant models. The quality of the included studies was assessed using the Newcastle-Ottawa Scale. Egger's test was used to evaluate publication bias.Results: Six studies with 9 cohorts were included in this systematic review and meta-analysis. The recessive and overdominant models showed that rs4986790 was significantly associated with AMD susceptibility, with odds ratios (ORs) of 0.73 and 1.41, respectively. By contrast, rs4986791 was not associated with AMD susceptibility. No publication bias was observed for either rs4986791 or rs4986790.Conclusion: The current evidence supports the hypothesis that rs4986790 but not rs4986791 is associated with AMD susceptibility.

Circular RNA TUBD1 Acts as the miR-146a-5p Sponge to Affect the Viability and Pro-Inflammatory Cytokine Production of LX-2 Cells through the TLR4 Pathway

The functions and molecular mechanism of circRNAs in the development of radiation-induced liver disease (RILD) remain largely unknown. The goal of this study was to explore the expression and potential role of a new circular RNA, named circTUBD1, in irradiated and lipopolysaccharide (LPS)-stimulated human hepatic stellate cell (HSC) line LX-2 cells. The expression of circTUBD1 was significantly upregulated in irradiated and LPS-stimulated LX-2 cells compared to non-treated LX-2 cells. To explore the functions of circTUBD1, small interfering RNAs targeting circTUBD1 were designed. Silencing circTUBD1 inhibited proliferation, promoted apoptosis of LX-2 cells, and significantly decreased the expression level of pro-inflammatory cytokines, including IL-1β, IL-6 and TNF-α in irradiated and LPS-stimulated LX-2 cells. Mechanistic analysis suggested that circTUBD1 acted as the miR-146a-5p sponge to affect pro-inflammatory cytokine production through regulating expression of Toll-like receptor 4 (TLR4), interleukin receptor-associated kinase 1 (IRAK1), tumor necrosis factor receptor-associated factor-6 (TRAF6), and phosphorylation of nuclear factor-kappa B (pNF-κB) in irradiated and LPS-stimulated LX-2 cells. To our knowledge, this is the first study to show that circTUBD1 acts as a miR-146a-5p sponge to affect the viability and pro-inflammatory cytokine production of LX-2 cells through the TLR4 pathway, suggesting that circTUBD1 is a potential target for RILD therapy.

FC-99 reduces macrophage tenascin-C expression by upregulating miRNA-494 in arthritis

The excessive production of inflammatory mediators by inflammatory cells contributes to the pathogenesis of rheumatoid arthritis. Tenascin-C (TN-C) is expressed in rheumatoid joint, and is associated with levels of inflammatory mediators. FC-99 (N1-[(4-methoxy)methyl]-4-methyl-1,2-Benzenediamine), a novel 1,2-benzenediamine derivative, was previously reported to block the prolonged expression of key rheumatoid arthritis inflammatory cytokines and relieve zymosan-induced joint inflammation. However, the specific mechanism is unknown. This study aimed to examine the effects of FC-99 on TN-C expression and inflammation and investigate its possible molecular mechanism. The results showed that FC-99 treatment reduced the high expression of TN-C in ankle joints of arthritis mice. Besides, FC-99 reduced the increased number of macrophages in arthritis mice, while did not change the number of synovioblasts. Concomitantly, expression of TN-C in synovial fibroblasts exhibited no difference between control and ZIA groups, and was not apparently altered following FC-99 treatment, while FC-99 decreased TN-C expression in macrophages both in vivo and in vitro. Meanwhile, TargetScan and luciferase assays indicated that TN-C was negatively regulated by miR-494. Transfection assay further demonstrated that FC-99 inhibited TN-C by targeting miR-494. Furthermore, the reduction of miR-494 mimic on expression of TN-C was associated with NF-κB pathway. Similarly, the down-regulation of FC-99 on TN-C was considerably decreased when NF-κB pathway was inhibited. These results indicated that FC-99 relieved macrophages inflammation via the miR-494/TN-C/NF-κB pathway, finally leading to the relief of inflammation in arthritis. The findings suggested that FC-99 might be a potential therapeutic candidate for the treatment of rheumatoid arthritis.

PC1/3 KD Macrophages Exhibit Resistance to the Inhibitory Effect of IL-10 and a Higher TLR4 Activation Rate, Leading to an Anti-Tumoral Phenotype

During tumorigenesis, macrophages are recruited by tumors and orientated towards a pro-tumoral phenotype. One of the main anti-tumoral immunotherapy consists of their re-polarization in an anti-tumoral phenotype. We have demonstrated that the inhibition of proprotein convertase 1/3 combined with TLR4 activation in macrophages is a promising strategy. These macrophages display pro-inflammatory and anti-tumoral phenotypes. A hallmark is a stronger activation of the pro-inflammatory NFKB pathway. We believe that this can be explained by a modification of TLR4 expression at the cell surface or MYD88 cleavage since it exhibits a potential cleavage site for proprotein convertases. We tested these hypotheses through immunofluorescence and Western blot experiments. A proteomics study was also performed to test the sensitivity of these macrophages to IL-10. We demonstrated that these macrophages treated with LPS showed a quicker re-expression of TLR4 at the cell surface. The level of MYD88 was also higher when TLR4 was internalized. Moreover, these macrophages were resistant to the pro-tumoral effect of IL-10 and still produced pro-inflammatory factors. This established that the sensitivity to anti-inflammatory molecules and the length of TLR4 desensitization were reduced in these macrophages. Therefore, during antitumoral immunotherapy, a repeated stimulation of TLR4 may reactivate PC1/3 inhibited macrophages even in an anti-inflammatory environment.

Ethanol Exposure Induces Microglia Activation and Neuroinflammation through TLR4 Activation and SENP6 Modulation in the Adolescent Rat Hippocampus

The ethanol-induced toll-like receptor 4 (TLR4) signal activation of microglia and neuroinflammation are observed in both adolescent and adult rat brains, but the regulatory mechanisms of some TLR4 signaling-related factors in this process are still unclear. SUMO-specific protease 6 (SENP6) inhibits neuroinflammation by dampening nuclear factor kappa-B (NF-κB) activation via the de-SUMOylation of NF kappa-B essential modulator (NEMO). This study investigates the effects of long-term ethanol consumption on neuroinflammation in the hippocampus of adolescent rats and the regulatory roles of TLR4 and SENP6. Twenty-one days of ethanol exposure in adolescent rats were used to develop an animal model. The number of microglia, microglial activation, and the expression of TLR4 in the hippocampus of adolescent rats were examined by immunoreactivity. The levels of TLR4, activation of NF-κB including IkB-α and p-NF-κB-p65, and SENP6 were measured by western blotting. Proinflammatory cytokines including TNF-α, IL-1β, and IL-6 were measured by enzyme-linked immunosorbent assay. The NF-κB activation and proinflammatory cytokines released in overexpressed SENP6 and siRNA targeting SENP6 microglial cells after treatment with ethanol were estimated in vitro. This study found that alcohol exposure increased the number of activated microglia and the levels of p-NF-κB-p65 and proinflammatory cytokines, while it decreased the SENP6 level in wild-type rats, but not in TLR4 knockout rats. The ethanol-induced increases of p-NF-κB-p65, TNF-α, and IL-1β were dampened by overxpression of SENP6 and enhanced in SENP6-siRNA microglia. Our data suggest that ethanol exposure during adolescence induces the microglia-mediated neuroinflammation via TLR4 activation, and SENP6 plays an essential role in dampening NF-κB activation and neuroinflammation.

Immune Relevant and Immune Deficient Mice: Options and Opportunities in Translational Research

In 1989 ILAR published a list and description of immunodeficient rodents used in research. Since then, advances in understanding of molecular mechanisms; recognition of genetic, epigenetic microbial, and other influences on immunity; and capabilities in manipulating genomes and microbiomes have increased options and opportunities for selecting mice and designing studies to answer important mechanistic and therapeutic questions. Despite numerous scientific breakthroughs that have benefitted from research in mice, there is debate about the relevance and predictive or translational value of research in mice. Reproducibility of results obtained from mice and other research models also is a well-publicized concern. This review summarizes resources to inform the selection and use of immune relevant mouse strains and stocks, aiming to improve the utility, validity, and reproducibility of research in mice. Immune sufficient genetic variations, immune relevant spontaneous mutations, immunodeficient and autoimmune phenotypes, and selected induced conditions are emphasized.

Elevated Heterozygosity in Adults Relative to Juveniles Provides Evidence of Viability Selection on Eagles and Falcons

Viability selection yields adult populations that are more genetically variable than those of juveniles, producing a positive correlation between heterozygosity and survival. Viability selection could be the result of decreased heterozygosity across many loci in inbred individuals and a subsequent decrease in survivorship resulting from the expression of the deleterious alleles. Alternatively, locus-specific differences in genetic variability between adults and juveniles may be driven by forms of balancing selection, including heterozygote advantage, frequency-dependent selection, or selection across temporal and spatial scales. We use a pooled-sequencing approach to compare genome-wide and locus-specific genetic variability between 74 golden eagle (Aquila chrysaetos), 62 imperial eagle (Aquila heliaca), and 69 prairie falcon (Falco mexicanus) juveniles and adults. Although genome-wide genetic variability is comparable between juvenile and adult golden eagles and prairie falcons, imperial eagle adults are significantly more heterozygous than juveniles. This evidence of viability selection may stem from a relatively smaller imperial eagle effective population size and potentially greater genetic load. We additionally identify ~2000 single-nucleotide polymorphisms across the 3 species with extreme differences in heterozygosity between juveniles and adults. Many of these markers are associated with genes implicated in immune function or olfaction. These loci represent potential targets for studies of how heterozygote advantage, frequency-dependent selection, and selection over spatial and temporal scales influence survivorship in avian species. Overall, our genome-wide data extend previous studies that used allozyme or microsatellite markers and indicate that viability selection may be a more common evolutionary phenomenon than often appreciated.

Syntaxin 11 regulates the stimulus-dependent transport of Toll-like receptor 4 to the plasma membrane by cooperating with SNAP-23 in macrophages

Syntaxin 11 (stx11) is a soluble N-ethylmaleimide–sensitive factor attachment protein receptor (SNARE) that is selectively expressed in immune cells; however, its precise role in macrophages is unclear. We showed that stx11 knockdown reduces the phagocytosis of Escherichia coli in interferon-γ–activated macrophages. stx11 knockdown decreased Toll-like receptor 4 (TLR4) localization on the plasma membrane without affecting total expression. Plasma membrane–localized TLR4 was primarily endocytosed within 1 h by lipopolysaccharide (LPS) stimulation and gradually relocalized 4 h after removal of LPS. This relocalization was significantly impaired by stx11 knockdown. The lack of TLR4 transport to the plasma membrane is presumably related to TLR4 degradation in acidic endosomal organelles. Additionally, an immunoprecipitation experiment suggested that stx11 interacts with SNAP-23, a plasma membrane–localized SNARE protein, whose depletion also inhibits TLR4 replenishment in LPS-stimulated cells. Using an intramolecular Förster resonance energy transfer (FRET) probe for SNAP-23, we showed that the high FRET efficiency caused by LPS stimulation is reduced by stx11 knockdown. These findings suggest that stx11 regulates the stimulus-dependent transport of TLR4 to the plasma membrane by cooperating with SNAP-23 in macrophages. Our results clarify the regulatory mechanisms underlying intracellular transport of TLR4 and have implications for microbial pathogenesis and immune responses.

TRAF3-interacting JNK-activating modulator promotes inflammation by stimulating translocation of Toll-like receptor 4 to lipid rafts

Toll-like receptors (TLRs) are key players of the innate immune system and contribute to inflammation and pathogen clearance. Although TLRs have been extensively studied, it remains unclear how exactly bacterial lipopolysaccharide (LPS)-induced conformational changes of the extracellular domain of the TLRs trigger the dimerization of their intracellular domain across the plasma membrane and thereby stimulate downstream signaling. Here, using LPS-stimulated THP-1-derived macrophages and murine macrophages along with immunoblotting and immunofluorescence and quantitative analyses, we report that in response to inflammatory stimuli, the coiled-coil protein TRAF3-interacting JNK-activating modulator (T3JAM) associates with TLR4, promotes its translocation to lipid rafts, and thereby enhances macrophage-mediated inflammation. T3JAM overexpression increased and T3JAM depletion decreased TLR4 signaling through both the MyD88-dependent pathway and TLR4 endocytosis. Importantly, deletion or mutation of T3JAM to disrupt its coiled-coil-mediated homoassociation abrogated TLR4 recruitment to lipid rafts. Consistently, T3JAM depletion in mice dampened TLR4 signaling and alleviated LPS-induced inflammatory damage. Collectively, our findings reveal an additional molecular mechanism by which TLR4 activity is regulated and suggest that T3JAM may function as a molecular clamp to "tighten up" TLR4 and facilitate its translocation to lipid rafts.

TLR4-interacting SPA4 peptide improves host defense and alleviates tissue injury in a mouse model of Pseudomonas aeruginosa lung infection

Interaction between surfactant protein-A (SP-A) and toll-like receptor (TLR)4 plays a critical role in host defense. In this work, we studied the host defense function of SPA4 peptide (amino acids GDFRYSDGTPVNYTNWYRGE), derived from the TLR4-interacting region of SP-A, against Pseudomonas aeruginosa. We determined the binding of SPA4 peptide to live bacteria, and its direct antibacterial activity against P. aeruginosa. Pro-phagocytic and anti-inflammatory effects were investigated in JAWS II dendritic cells and primary alveolar macrophages. The biological relevance of SPA4 peptide was evaluated in a mouse model of acute lung infection induced by intratracheal challenge with P. aeruginosa. Our results demonstrate that the SPA4 peptide does not interact with or kill P. aeruginosa when cultured outside the host. The SPA4 peptide treatment induces the uptake and localization of bacteria in the phagolysosomes of immune cells. At the same time, the secreted amounts of TNF-α are significantly reduced in cell-free supernatants of SPA4 peptide-treated cells. In cells overexpressing TLR4, the TLR4-induced phagocytic response is maintained, but the levels of TLR4-stimulated TNF-α are reduced. Furthermore, our results demonstrate that the therapeutic administration of SPA4 peptide reduces bacterial burden, inflammatory cytokines and chemokines, intracellular signaling, and lactate levels, and alleviates lung edema and tissue damage in P. aeruginosa-infected mice. Together, our results suggest that the treatment with SPA4 peptide can help control the bacterial burden, inflammation, and tissue injury in a P. aeruginosa lung infection model.

MicroRNA-regulated pathways of flow-stimulated angiogenesis and vascular remodeling in vivo

BACKGROUND

Vascular shear stress promotes endothelial cell sprouting in vitro. The impact of hemodynamic forces on microRNA (miRNA) and gene expression within growing vascular networks in vivo, however, remain poorly investigated. Arteriovenous (AV) shunts are an established model for induction of neoangiogenesis in vivo and can serve as a tool for analysis of hemodynamic effects on miRNA and gene expression profiles over time.

METHODS

AV shunts were microsurgically created in rats and explanted on postoperative days 5, 10 and 15. Neoangiogenesis was confirmed by histologic analysis and micro-computed tomography. MiRNA and gene expression profiles were determined in tissue specimens from AV shunts by microarray analysis and quantitative real-time polymerase chain reaction and compared with sham-operated veins by bioinformatics analysis. Changes in protein expression within AV shunt endothelial cells were determined by immunohistochemistry.

RESULTS

Samples from AV shunts exhibited a strong overexpression of proangiogenic cytokines, oxygenation-associated genes (HIF1A, HMOX1), and angiopoetic growth factors. Significant inverse correlations of the expressions of miR-223-3p, miR-130b-3p, miR-19b-3p, miR-449a-5p, and miR-511-3p which were up-regulated in AV shunts, and miR-27b-3p, miR-10b-5p, let-7b-5p, and let-7c-5p, which were down-regulated in AV shunts, with their predicted interacting targets C-X-C chemokine receptor 2 (CXCR2), interleukin-1 alpha (IL1A), ephrin receptor kinase 2 (EPHA2), synaptojanin-2 binding protein (SYNJ2BP), forkhead box C1 (FOXC1) were present. CXCL2 and IL1A overexpression in AV shunt endothelium was confirmed at the protein level by immunohistochemistry.

CONCLUSIONS

Our data indicate that flow-stimulated angiogenesis is determined by an upregulation of cytokines, oxygenation associated genes and miRNA-dependent regulation of FOXC1, EPHA2 and SYNJ2BP.

The GTPase Rab1 Is Required for NLRP3 Inflammasome Activation and Inflammatory Lung Injury

Uncontrolled inflammatory response during sepsis predominantly contributes to the development of multiorgan failure and lethality. However, the cellular and molecular mechanisms for excessive production and release of proinflammatory cytokines are not clearly defined. In this study, we show the crucial role of the GTPase Ras-related protein in brain (Rab)1a in regulating the nucleotide binding domain-like receptor family, pyrin domain containing 3 (NLRP3) inflammasome activation and lung inflammatory injury. Expression of dominant negative Rab1 N124I plasmid in bone marrow-derived macrophages prevented the release of IL-1β and IL-18, NLRP3 inflammasome activation, production of pro-IL-1β and pro-IL-18, and attenuated TLR4 surface expression and NF-кB activation induced by bacterial LPS and ATP compared with control cells. In alveolar macrophage-depleted mice challenged with cecal ligation and puncture, pulmonary transplantation of Rab1a-inactivated macrophages by expression of Rab1 N124I plasmid dramatically reduced the release of IL-1β and IL-18, neutrophil count in bronchoalveolar lavage fluid, and inflammatory lung injury. Rab1a activity was elevated in alveolar macrophages from septic patients and positively associated with severity of sepsis and respiratory dysfunction. Thus, inhibition of Rab1a activity in macrophages resulting in the suppression of NLRP3 inflammasome activation may be a promising target for the treatment of patients with sepsis.

TLR4-MyD88 pathway promotes the imbalanced activation of NLRP3/NLRP6 via caspase-8 stimulation after alkali burn injury

Alkali burn (AB) is one of the most serious ocular traumas in the world, characterized by extreme ocular surface disorders, critical secondary dry eye and irreversible vision loss. The exact mechanisms involved are unknown. Innate immunity, including the involvement of Toll-like receptors (TLRs) and NOD-like receptors (NLRs), is believed to participate in the pathogenesis of the epithelia, but the exact mechanisms by which TLRs transduce signals to NLRs and downstream molecules to initiate innate immunity remain poorly defined. In this present study, we used murine models of AB and AB concomitant desiccating stress (DS) to investigate the potential functions and mechanisms of TLR4 in regulating NLRP3 and NLRP6 during AB injury and secondary dry eye. We demonstrated that AB injury induced activation of the TLR4-MyD88 pathway, leading to imbalanced NLRP3 and NLRP6 via the activation of caspase-8 signaling. DS worsened ocular surface disorders post-AB injury by magnifying this phenomenon. Caspase-8 signaling promoted NLRP3 upregulation via the nuclear factor (NF)-κB pathway, while NLRP6 suppressed NF-κB activation. Our findings also revealed that TLR4-MyD88 knockout can alleviate AB-induced or DS-worsened ocular surface disorders, shedding light on the potential therapeutic strategies in the future for AB injury. Taken together, our findings demonstrate that AB promotes the TLR4-MyD88-caspase-8 axis to cause imbalanced NLRP3/NLRP6, and DS exacerbates ocular surface damage via magnifying this imbalance.

Klotho preservation by Rhein promotes toll-like receptor 4 proteolysis and attenuates lipopolysaccharide-induced acute kidney injury

Renal anti-aging protein Klotho exhibits impressive properties of anti-inflammation and renal protection, however is suppressed early after renal injury, making Klotho restoration an attractive strategy of treating renal inflammatory disorders. Here, we reported that Klotho is enriched in macrophages and Klotho preservation by Rhein, an anthraquinone derived from medicinal plant rhubarb, attenuates lipopolysaccharide (LPS)-induced acute inflammation essentially via promoting toll-like receptor 4 (TLR4) degradation. LPS-induced pro-inflammatory NF-κB signaling and cytokine expressions coincided with Klotho repression and toll-like receptor 4 (TLR4) elevation in macrophages, renal epithelial cells, and acutely- inflamed kidney. Intriguingly, Rhein treatment effectively corrected the inverted alterations of Klotho and TLR4 and mitigated the TLR4 downstream inflammatory response in a Klotho restoration and TLR4 repression-dependent manner. Klotho inducibly associated with TLR4 after LPS stimulation and suppressed TLR4 protein abundance mainly via a proteolytic process sensitive to the inhibition of Klotho's putative β-glucuronidase activity. Consistently, Klotho knockdown by RNA interferences largely diminished the anti-inflammatory and renal protective effects of Rhein in a mouse model of acute kidney injury incurred by LPS. Thus, Klotho suppression of TLR4 via deglycosylation negatively controls TLR-associated inflammatory signaling and the endogenous Klotho preservation by Rhein or possibly other natural or synthetic compounds possesses promising potentials in the clinical treatment of renal inflammatory disorders.

KEY MESSAGES

• Klotho is highly expressed in macrophages and repressed by LPS in vitro and in vivo. • Klotho inhibits LPS-induced TLR4 accumulation and the downstream signaling. • Klotho decreases TLR4 via a deglycosylation-associated proteolytic process. • Rhein effectively prevents acute inflammation-incurred Klotho suppression. • Rhein reversal of Klotho attenuates LPS-induced acute inflammation and kidney injury.

Comparative evaluation of cell- and serum-derived exosomes to deliver immune stimulators to lymph nodes

To determine whether exosomes are efficient carriers for immune stimulating molecules into lymph nodes, comparative studies of exosomes (EXOs) derived from different origins (cells and serums) in terms of physicochemical properties and delivery efficiency were performed. Serum-derived EXOs were of a preferable size and generated higher yields than RAW264.7 cell-derived exosomes (RAW-EXO). In particular, fetal bovine serum-derived exosomes (bo-EXO), with a size below 50 nm, were delivered not only to surface zones (subcapsular sinus (SCS) macrophage zone) but also to inner paracortex zones (T cell zone) of lymph nodes, which allowed an efficient delivery of immune stimulating molecules to antigen presenting cells and T cells. The encapsulation of immune stimulating biomolecules (monophosphoryl lipid A (MPLA) and CpG oligodeoxynucleotides (CpG ODN)) within EXOs greatly increased intracellular delivery to macrophages via phagocytic pathways, which induced higher TNF-α and IL-6 secretion than free MPLA and free CpG ODN. MPLA-incorporated exosomes activated and differentiated T cells after subcutaneous injection, which elevated cytokine IFN-γ and TNF-α induction for CD3⁺ T cells. Taken together, bo-EXOs might serve as efficient carrier systems of immune stimulators to lymph nodes for desired immune responses.

Expression of Siglec-E Alters the Proteome of Lipopolysaccharide (LPS)-Activated Macrophages but Does Not Affect LPS-Driven Cytokine Production or Toll-Like Receptor 4 Endocytosis

Siglec-E is a murine CD33-related siglec that functions as an inhibitory receptor and is expressed mainly on neutrophils and macrophage populations. Recent studies have suggested that siglec-E is an important negative regulator of lipopolysaccharide (LPS)-toll-like receptor 4 (TLR4) signaling and one report (1) claimed that siglec-E is required for TLR4 endocytosis following uptake of Escherichia coli by macrophages and dendritic cells (DCs). Our attempts to reproduce these observations using cells from wild-type (WT) and siglec-E-deficient mice were unsuccessful. We used a variety of assays to determine if siglec-E expressed by different macrophage populations can regulate TLR4 signaling in response to LPS, but found no consistent differences in cytokine secretion in vitro and in vivo, comparing three different strains of siglec-E-deficient mice with matched WT controls. No evidence was found that the siglec-E deficiency was compensated by expression of siglecs-F and -G, the other murine inhibitory CD33-related siglecs. Quantitative proteomics was used as an unbiased approach and provided additional evidence that siglec-E does not suppress inflammatory TLR4 signaling. Interestingly, proteomics revealed a siglec-E-dependent alteration in macrophage protein composition that could be relevant to functional responses in host defense. In support of this, siglec-E-deficient mice exhibited enhanced growth of Salmonella enterica serovar Typhimurium in the liver following intravenous infection, but macrophages lacking siglec-E did not show altered uptake or killing of bacteria in vitro. Using various cell types including bone marrow-derived DCs (BMDCs), splenic DCs, and macrophages from WT and siglec-E-deficient mice, we showed that siglec-E is not required for TLR4 endocytosis following E. coli uptake or LPS challenge. We failed to see expression of siglec-E by BMDC even after LPS-induced maturation, but confirmed previous studies that splenic DCs express low levels of siglec-E. Taken together, our findings do not support a major role of siglec-E in regulation of TLR4 signaling functions or TLR4 endocytosis in macrophages or DCs. Instead, they reveal that induction of siglec-E by LPS can modulate the phenotype of macrophages, the functional significance of which is currently unclear.

The impact of hypoxic conditions on apoptosis and Toll-like receptor 4 expression in polymorphonuclear neutrophils

Many patients are admitted to the emergency department due to trauma. Trauma patients suffer from hypoxia due to massive hemorrhage, respiratory failure, and hypovolemic shock. Further damage is caused by reduced immune function and over-expression of inflammatory response. We conducted an experiment to determine the effects of hyperoxia and hypoxia on apoptosis and expression of Toll-like receptor 4 (TLR4) in polymorphonuclear neutrophils (PMNs). Initially, the PMNs were placed in normoxic and hypoxic conditions, and these PMNs were divided into two groups as stimulated or not stimulated with lipopolysaccharide (LPS). Levels of apoptosis and TLR4 expression were measured under normoxic, hypoxic, and hyperoxic conditions. Apoptosis decreased in the hypoxic group than in the normoxic group. With LPS stimulation, apoptosis was decreased in all three treatment groups and even more reduced in the hypoxic group. TLR4 expression increased in all three treatment groups with LPS stimulation, increased further in the hypoxic group, and to a lesser degree in the hyperoxic group. Unlike the cells exposed to hypoxic conditions, the cells exposed to the hyperoxic condition reacted similarly to the cells in the control (normoxic) group. Therefore, the inflammatory reactions can be stronger in the hypoxic group than in the other two groups.

Anti-inflammatory Effect of Discretamine, a Protoberberine Alkaloid Isolated from Duguetia moricandiana

Discretamine is a tetrahydroprotoberberine alkaloid isolated from Duguetia moricandiana (Annonaceae). In the present study, anti-inflammatory ability of discretamine in a lipopolysaccharide (LPS) stimulated macrophages model was investigated. LPS-induced NO production was reduced by discretamine treatment (100 and 200 μg/mL) around 50%. Furthermore, discretamine (50, 100, and 200 μg/mL) treatment down-regulated pivotal inflammatory cytokines levels, such as IL-6 (74.1, 76.6, and 75.1%, respectively), IL1-β (89.4, 87.4, and 71.8%, respectively), and TNF-α (61, 45.2, and 52.6%, respectively) levels. Also, discretamine did not reduce peritoneal macrophage viability. Besides that, in vivo carrageenan-induced paw edema experiments were also carried out. Discretamine treatment (5, 10, and 20 mg/kg) reduced paw edema up to 6h. Taken together, these data demonstrated that discretamine exerted its anti-inflammatory effect by down-regulation the levels of TNF-α, IL-6, and IL1-β, and by inhibition of NO release.

Association of TLR4 gene polymorphisms with childhood Henoch-Schönlein purpura in a Chinese population

Recent studies demonstrated that aberrant activation of Toll-like receptor (TLR) 4 was involved in the pathogenesis of Henoch-Schönlein purpura (HSP). In this study, we evaluated the association between TLR4 gene polymorphisms and the risk of childhood HSP in a Chinese population. A total of 175 HSP patients and 186 controls were recruited in this case-control study. Three single-nucleotide polymorphisms of the TLR4 gene (rs1927914, rs10759932 and rs1927907) were genotyped using the matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) and Sequenom MassARRAY system. Our results revealed that a significantly reduced risk for HSP was associated with the G allele (OR = 0.71; p = 0.023) and G/G genotype (OR = 0.49; p = 0.021) of rs1927914. We also showed that rs1927914 variant decreased the risk of HSP in recessive inheritance model (OR = 0.55; p = 0.035, G/G vs A/A + A/G). In addition, we observed that a significantly decreased frequency of the haplotype GTC (rs1927914-rs10759932-rs1927907) in HSP patients compared with controls (OR = 0.56; p = 0.028). Our data suggested that TLR 4 rs1927914 polymorphism was associated with the decreased susceptibility to HSP in the Chinese children.

Tmbim1 is a multivesicular body regulator that protects against non-alcoholic fatty liver disease in mice and monkeys by targeting the lysosomal degradation of Tlr4

Non-alcoholic steatohepatitis (NASH) is an increasingly prevalent liver pathology that can progress from non-alcoholic fatty liver disease (NAFLD), and it is a leading cause of cirrhosis and hepatocellular carcinoma. There is currently no pharmacological therapy for NASH. Defective lysosome-mediated protein degradation is a key process that underlies steatohepatitis and a well-recognized drug target in a variety of diseases; however, whether it can serve as a therapeutic target for NAFLD and NASH remains unknown. Here we report that transmembrane BAX inhibitor motif-containing 1 (TMBIM1) is an effective suppressor of steatohepatitis and a previously unknown regulator of the multivesicular body (MVB)-lysosomal pathway. Tmbim1 expression in hepatocytes substantially inhibited high-fat diet-induced insulin resistance, hepatic steatosis and inflammation in mice. Mechanistically, Tmbim1 promoted the lysosomal degradation of toll-like receptor 4 by cooperating with the ESCRT endosomal sorting complex to facilitate MVB formation, and the ubiquitination of Tmbim1 by the E3 ubiquitin ligase Nedd4l was required for this process. We also found that overexpression of Tmbim1 in the liver effectively inhibited a severe form of NAFLD in mice and NASH progression in monkeys. Taken together, these findings could lead to the development of promising strategies to treat NASH by targeting MVB regulators to properly orchestrate the lysosome-mediated protein degradation of key mediators of the disease.

The Contribution of Immune Infiltrates to Ototoxicity and Cochlear Hair Cell Loss

Cells of the immune system have been shown to infiltrate the cochlea after acoustic trauma or ototoxic drug treatment; however, the contribution of the immune system to hair cell loss in the inner ear is incompletely understood. Most studies have concentrated on the immediate innate response to hair cell damage using CD45 as a broad marker for all immune cells. More recent studies have used RNA sequencing, GeneChip arrays and quantitative PCR to analyze gene expression in the entire cochlea after auditory trauma, leading to a better understanding of the chemokines and cytokines that attract immune cells to the cochlea. Immune suppression by blocking cytokines or immune receptors has been proven to suppress hair cell damage. However, it is now understood that not all immune cells are detrimental to the cochlea. CX3CR1+ resident macrophages protect hair cells from damage mediated by infiltrating immune cells. Systemically, the immune response is associated with both protection and pathology, and it has been implicated in the regeneration of certain tissues after injury. This review focuses on the studies of immune cells in various models of hearing loss and highlights the steps that can be taken to elucidate the connection between the immune response and hearing loss. The interplay between the immune system and tissues that were previously thought to be immune privileged, such as the cochlea, is an emerging research field, to which additional studies of the immune component of the cochlear response to injury will make an important contribution.

Review on Toll-Like Receptor Activation in Myasthenia Gravis: Application to the Development of New Experimental Models

Abnormal toll-like receptor (TLR) activation and uncontrolled resolution of inflammation are suspected to play a key role in the development of autoimmune diseases. Acquired myasthenia gravis (MG) is an invalidating neuromuscular disease leading to muscle weaknesses. MG is mainly mediated by anti-acetylcholine receptor (AChR) autoantibodies, and thymic hyperplasia characterized by ectopic germinal centers is a common feature in MG. An abnormal expression of certain TLRs is observed in the thymus of MG patients associated with the overexpression of interferon (IFN)-β, the orchestrator of thymic changes in MG. Experimental models have been developed for numerous autoimmune diseases. These models are induced by animal immunization with a purified antigen solubilized in complete Freund's adjuvant (CFA) containing heat-inactivated mycobacterium tuberculosis (MTB). Sensitization against the antigen is mainly due to the activation of TLR signaling pathways by the pathogen motifs displayed by MTB, and attempts have been made to substitute the use of CFA by TLR agonists. AChR emulsified in CFA is used to induce the classical experimental autoimmune MG model (EAMG). However, the TLR4 activator lipopolysaccharide (LPS) has proved to be efficient to replace MTB and induce a sensitization against purified AChR. Poly(I:C), the well-known TLR3 agonist, is also able by itself to induce MG symptoms in mice associated with early thymic changes as observed in human MG. In this review, we discuss the abnormal expression of TLRs in MG patients and we describe the use of TLR agonists to induce EAMG in comparison with other autoimmune experimental models.

The helminth product, ES-62 modulates dendritic cell responses by inducing the selective autophagolysosomal degradation of TLR-transducers, as exemplified by PKCδ

We have previously shown that ES-62, a phosphorylcholine (PC)-containing glycoprotein secreted by the parasitic filarial nematode Acanthocheilonema viteae targets dendritic cell (DC) responses, specifically by suppressing TLR4 signalling to inhibit Th1/Th17-driven inflammation. We have now investigated the molecular mechanisms underpinning such immunomodulation and show here that ES-62-mediated downregulation of protein kinase C-δ (PKC-δ), a TLR4-associated signalling mediator required for full activation of LPS-driven pro-inflammatory responses, is associated with induction of a low level of autophagic flux, as evidenced by upregulation and trafficking of p62 and LC3 and their consequent autophagolysosomal degradation. By contrast, the classical TLR4 ligand LPS, strongly upregulates p62 and LC3 expression but under such canonical TLR4 signalling this upregulation appears to reflect a block in autophagic flux, with these elements predominantly degraded in a proteasomal manner. These data are consistent with autophagic flux acting to homeostatically suppress proinflammatory DC responses and indeed, blocking of PKC-δ degradation by the autophagolysosomal inhibitors, E64d plus pepstatin A, results in abrogation of the ES-62-mediated suppression of LPS-driven release of IL-6, IL-12p70 and TNF-α by DCs. Thus, by harnessing this homeostatic regulatory mechanism, ES-62 can protect against aberrant inflammation, either to promote parasite survival or serendipitously, exhibit therapeutic potential in inflammatory disease.

Elevated levels of serum MRP8/14 in ankylosing spondylitis: associated with peripheral arthritis and active disease

Monocytes of patients with ankylosing spondylitis (AS) have toll-like receptor 4 (TLR4) overexpression on their monocytes. Myeloid-related protein (MRP) 8/14 protein complexes are calcium-binding proteins, which act as endogenous ligands to TLR4. Thus, we studied the levels of MRP8/14 in adult AS patients. MRP8/14 levels were assessed in 99 adult AS patients satisfying Assessments in Ankylosing Spondylitis International Society 2010 criteria and 71 healthy controls by ELISA. Patient disease parameters like patient and physician global assessment, Bath Ankylosing Spondylitis Disease Activity Index (BASDAI), swollen and tender joint count, entheseal count by Maastricht enthesitis index, erythrocyte sedimentation rate (ESR), and C-reactive protein (CRP) were also recorded. Levels were reassessed in 23 patients after 2-5 months of treatment with NSAIDs. All values are in median (IQR). The serum MRP8/14 levels in patients [34.1 (17.94-264.58) μg/ml] were significantly higher than in healthy controls [4.94 (IQR 3.01-8.32) μg/ml (p < 0.0001)]. Patients with peripheral arthritis (n = 50) had higher levels than those with pure axial disease (n = 49) [40.63 (IQR 28.41-73.15) μg/ml vs. 23.72 (11.04-61.55) μg/ml; p = 0.012]. Levels of MRP8/14 correlated with AS Disease Activity Score (DAS)-CRP (r = 0.23, 95%CI = 0.038-0.422, p = 0.02) and CRP (r = 0.28, 95%CI = 0.081-0.45, p = 0.01), and the correlation was better in early disease [≤5 years disease duration; r = 0.40, p = 0.007 and r = 0.57, p = <0.0001, respectively]. Baseline levels were higher in treatment responders than in non-responders [51.17 vs. 32.22 μg/ml; p = 0.02]. Change in MRP8/14 levels correlated with change in BASDAI and ASDAS-CRP (r = 0.489, p = 0.018 and r = 0·498, p = 0.016, respectively). MRP8/14 levels may be used as a biomarker for activity, peripheral arthritis, and response to therapy.

IL-22 is rapidly induced by Pathogen Recognition Receptors Stimulation in Bone-Marrow-derived Dendritic Cells in the Absence of IL-23

In vertebrates, microorganisms are recognized by pathogen recognition receptors (PRRs). Exposure of immune cells to the ligands of these receptors activates intracellular signaling cascades that rapidly induce the expression of a variety of genes. Within these genes, the cytokines family plays a crucial function because of its role in adaptive immunity induction and in tissue-specific functional regulation, such as tissue repair and tissue homeostasis during steady state conditions. Within the myeloid compartment, dendritic cells (DCs) release a variety of inflammatory cytokines in response to microbes. In this study, we show that BMDCs release IL-22 directly upon PRRs activation without the need of IL-23 signaling as reported for other IL22-producing cells. Moreover, we demonstrate that cytokine IL-22 is rapidly released in a cell-specific manner as macrophages are not able to produce IL-22 through the same PRRs system. In addition, we characterize the intracellular signaling cascade required for IL-22 release in BMDCs. Myd88, MEK1/2, NFkb and AhR, but not p38, NFAT, and RORgt, were found to be involved in IL-22 regulation in DCs. Our study suggests that BMDCs possess a unique intracellular molecular plasticity which, once activated, directs different BMDCs functions in a cell-specific manner.

p24 family proteins: key players in the regulation of trafficking along the secretory pathway

p24 family proteins have been known for a long time, but their functions have remained elusive. However, they are emerging as essential regulators of protein trafficking along the secretory pathway, influencing the composition, structure, and function of different organelles in the pathway, especially the ER and the Golgi apparatus. In addition, they appear to modulate the transport of specific cargos, including GPI-anchored proteins, G-protein-coupled receptors, or K/HDEL ligands. As a consequence, they have been shown to play specific roles in signaling, development, insulin secretion, and the pathogenesis of Alzheimer's disease. The search of new putative ligands may open the way to discover new functions for this fascinating family of proteins.

Repulsive guidance molecule a blockade exerts the immunoregulatory function in DCs stimulated with ABP and LPS

Repulsive guidance molecule a (RGMa) is an axonal guidance molecule that has recently found to exert function in immune system. This study evaluated the function of RGMa in modulation of dendritic cells (DCs) function stimulated with Achyranthes bidentata polysaccharide (ABP) and lipopolysaccharide (LPS) using a RGMa-neutralizing antibody. Compared with the Control-IgG/ABP and Control-IgG/LPS groups, DCs in the Anti-RGMa/ABP and Anti-RGMa/LPS groups 1) showed small, round cells with a few cell processes and organelles, and many pinocytotic vesicles; 2) had decreased MHC II, CD86, CD80, and CD40 expression; 3) displayed the decreased IL-12p70, IL-1β and TNF-α levels and increased IL-10 secretion; 4) had a high percentage of FITC-dextran uptake; and 5) displayed a reduced ability to drive T cell proliferation and reinforced T cell polarization toward a Th2 cytokine pattern. We conclude that DCs treated with RGMa-neutralizing antibodies present with tolerogenic and immunoregulatory characteristics, which provides new insights into further understanding of the function of RGMa.

Differential behaviour of epicardial adipose tissue-secretomes with high and low orosomucoid levels from patients with cardiovascular disease in H9C2 cells

Epicardial adipose tissue releases orosomucoid (ORM), an acute phase protein with multiple modulatory and protective properties. We aimed to identify the effect of EAT-supernatants according to their ORM levels on H9C2 cells. H9C2 were cultured with EAT-secretomes or ORM protein itself on a Real-Time Cell Analyser. Secretome proteins identification was performed by LC-mass spectrometry according to their ORM levels. Two of them were validated by ELISA in EAT-supernatants from 42 patients. ORM effect on H9C2 and neonatal rat cardiomyocytes apoptosis under hypoxia with or without fatty acid treatment was determined by Annexin-V flow cytometry measurement. Caspase-3 expression levels were determined by western blot in H9C2. Our results showed a differential effect of EAT-secretomes according their ORM levels. Although additional secreted proteins can contribute to their beneficial effects, ORM reduced hypoxia-induced apoptosis through caspase-3 inhibition. Our data showed the cardioprotective role of ORM and suggest that its quantification on EAT secretomes might help us to find new secreted factors with a cardioprotective role.

Chloroquine attenuates LPS-mediated macrophage activation through miR-669n-regulated SENP6 protein translation

Chloroquine (CQ) has been shown to inhibit Toll-like receptor 4 (TLR4)-mediated monocyte and macrophage activation induced by lipopolysaccharide (LPS). However, the underlying mechanisms have not been completely elucidated. Recently, SUMO-specific protease 6 (SENP6) has been reported to suppress LPS-induced activation of macrophages through deSUMOlation of NF-κB essential modifier (NEMO). Here, we studied whether this molecular pathway may also be involved in CQ/LPS model. We found that CQ dose-dependently increased SENP6 protein, but not mRNA, in mouse macrophages, RAW264.7 cells. Overexpression of SENP6 in RAW264.7 cells significantly decreased the LPS-induced release of pro-inflammatory proteins, TNF-α, IL-6 and IFN-γ, while depletion of SENP6 in RAW264.7 cells significantly increased these proteins. Moreover, in LPS-treated RAW264.7 cells, CQ dose-dependently decreased the levels of microRNA-669n (miR-669n), which bound to 3'-UTR of SENP6 mRNA to inhibit its translation. Overexpression of miR-669n decreased SENP6, resulting in increased production of TNF-α, IL-6 and IFN-γ in RAW264.7 cells, while depletion of miR-669n increased SENP6, resulting in decreased production of TNF-α, IL-6 and IFN-γ in RAW264.7 cells. In vivo, delivery of miR-669n plasmids augmented the effects of LPS, while delivery of antisense of miR-669n (as-miR-669n) plasmids abolished the effects of LPS. Taken together, our data demonstrate a previously unappreciated molecular control of LPS-induced macrophage activation by CQ, through miR-669n-regulated SENP6 protein translation.

STK4 regulates TLR pathways and protects against chronic inflammation-related hepatocellular carcinoma

Hepatocellular carcinoma (HCC) is frequently associated with pathogen infection-induced chronic inflammation. Large numbers of innate immune cells are present in HCCs and can influence disease outcome. Here, we demonstrated that the tumor suppressor serine/threonine-protein kinase 4 (STK4) differentially regulates TLR3/4/9-mediated inflammatory responses in macrophages and thereby is protective against chronic inflammation-associated HCC. STK4 dampened TLR4/9-induced proinflammatory cytokine secretion but enhanced TLR3/4-triggered IFN-β production via binding to and phosphorylating IL-1 receptor-associated kinase 1 (IRAK1), leading to IRAK1 degradation. Notably, macrophage-specific Stk4 deletion resulted in chronic inflammation, liver fibrosis, and HCC in mice treated with a combination of diethylnitrosamine (DEN) and CCl4, along with either LPS or E. coli infection. STK4 expression was markedly reduced in macrophages isolated from human HCC patients and was inversely associated with the levels of IRAK1, IL-6, and phospho-p65 or phospho-STAT3. Moreover, serum STK4 levels were specifically decreased in HCC patients with high levels of IL-6. In STK4-deficient mice, treatment with an IRAK1/4 inhibitor after DEN administration reduced serum IL-6 levels and liver tumor numbers to levels similar to those observed in the control mice. Together, our results suggest that STK4 has potential as a diagnostic biomarker and therapeutic target for inflammation-induced HCC.

Methyl 9-Oxo-(10E,12E)-octadecadienoate Isolated from Fomes fomentarius Attenuates Lipopolysaccharide-Induced Inflammatory Response by Blocking Phosphorylation of STAT3 in Murine Macrophages

Fomes fomentarius is a fungus of the Polyporaceae family and is used in traditional oriental therapies. Although the anti-inflammatory activities of this species have been previously reported, the identity of the bioactive compounds responsible for this activity remains unknown. Here, we investigated whether methyl 9-oxo-(10E,12E)-octadecadienoate (FF-8) purified from F. fomentarius exerts anti-inflammatory activity in murine macrophages stimulated with lipopolysaccharide (LPS). FF-8 suppressed secretion of nitric oxide (NO) and prostaglandin E2 through downregulation of inducible NO synthase and cyclooxygenase-2 expression induced by LPS. In addition, pretreatment of cells with FF-8 led to a reduction in levels of secreted inflammatory cytokines such as tumor necrosis factor-α and interleukin-6 in macrophages stimulated with LPS. Conversely, FF-8 did not affect nuclear factor κB, p38, c-Jun NH2-terminal kinase, and extracellular signal-regulated kinase pathways. Instead, FF-8 specifically interfered with signal transducer and activator of transcription 3 (STAT3) phosphorylation induced by LPS. Collectively, this study demonstrated that FF-8 purified from F. fomentarius suppresses inflammatory responses in macrophages stimulated with LPS by inhibiting STAT3 activation. Further studies will be required to elucidate the anti-inflammatory effect of FF-8 in vivo.

Contributions of unique intracellular domains to switchlike biosensing by Toll-like receptor 4

Toll-like receptors (TLRs) mediate immune recognition of both microbial infections and tissue damage. Aberrant TLR signaling promotes disease; thus, understanding the regulation of TLR signaling is of medical relevance. Although downstream mediators of TLR signaling have been identified, the detailed mechanism by which ligand binding-mediated dimerization induces downstream signaling remains poorly understood. Here, we investigate this question for TLR4, which mediates responsiveness to bacterial LPS and drives inflammatory disease. TLR4 exhibits structural and functional features that are unique among TLRs, including responsiveness to a wide variety of ligands. However, the connection between these structural features and the regulation of signaling is not clear. Here, we investigated how the unique intracellular structures of TLR4 contribute to receptor signaling. Key conclusions include the following. 1) The unique intracellular linker of TLR4 is important for achieving LPS-inducible signaling via Toll/IL-1 receptor (TIR) domain-containing adapter-inducing interferon-β (TRIF) but less so for signaling via myeloid differentiation primary response 88 (MyD88). 2) Membrane-bound TLR4 TIR domains were sufficient to induce signaling. However, introducing long, flexible intracellular linkers neither induced constitutive signaling nor ablated LPS-inducible signaling. Thus, the initiation of TLR4 signaling is regulated by a mechanism that does not require tight geometric constraints. Together, these observations necessitate refining the model of TLR4 signal initiation. We hypothesize that TLR4 may interact with an inhibitory partner in the absence of ligand, via both TIR and extracellular domains of TLR4. In this speculative model, ligand binding induces dissociation of the inhibitory partner, triggering spontaneous, switchlike TIR domain homodimerization to initiate downstream signaling.