Severe impairment of interleukin-1 and Toll-like receptor signalling in mice lacking IRAK-4

IRAK4 mediates colitis-induced tumorigenesis and chemoresistance in colorectal cancer

Aberrant activation of the NF-κB transcription factors underlies chemoresistance in various cancer types, including colorectal cancer (CRC). Targeting the activating mechanisms, particularly with inhibitors to the upstream IκB kinase (IKK) complex, is a promising strategy to augment the effect of chemotherapy. However, clinical success has been limited, largely because of low specificity and toxicities of tested compounds. In solid cancers, the IKKs are driven predominantly by the Toll-like receptor (TLR)/IL-1 receptor family members, which signal through the IL-1 receptor-associated kinases (IRAKs), with isoform 4 (IRAK4) being the most critical. The pathogenic role and therapeutic value of IRAK4 in CRC have not been investigated. We found that IRAK4 inhibition significantly abrogates colitis-induced neoplasm in APCMin/+ mice, and bone marrow transplant experiments showed an essential role of IRAK4 in immune cells during neoplastic progression. Chemotherapy significantly enhances IRAK4 and NF-κB activity in CRC cells through upregulating TLR9 expression, which can in turn be suppressed by IRAK4 and IKK inhibitors, suggesting a feed-forward pathway that protects CRC cells from chemotherapy. Lastly, increased tumor phospho-IRAK4 staining or IRAK4 mRNA expression is associated with significantly worse survival in CRC patients. Our results support targeting IRAK4 to improve the effects of chemotherapy and outcomes in CRC.

Protective Effects of Oridonin on Acute Liver Injury via Impeding Posttranslational Modifications of Interleukin-1 Receptor-Associated Kinase 4 (IRAK4) in the Toll-Like Receptor 4 (TLR4) Signaling Pathway

OBJECTIVE

Recent researches have demonstrated that inflammation-related diseases are effectively regulated by posttranslational modifications (PTMs) including phosphorylation and acetylation. Our previous study found a new acetyltransferase inhibitor, oridonin, which had a protective effect on acute liver injury (ALI). In the present study, we further investigated its protective mechanism against D-galactosamine (D-Gal) combined with lipopolysaccharide- (LPS-) induced ALI in mice.

METHODS

Intraperitoneal injections of LPS (40 μg/mouse)/D-Gal (5 mg/mouse) were given to the mice, and the experimental group was pretreated with intraperitoneal injection of oridonin (0.2 mg/mouse). To elucidate the protective mechanism of oridonin, we collected liver specimens and used RNA-sequencing (RNA-Seq) analysis. We focused on the genes that were upregulated by LPS/D-Gal and downregulated after pretreatment with oridonin. The downregulated genes examined by Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis were further verified by real-time polymerase chain reaction (PCR) and western blot.

RESULTS

GO analysis showed that genes that were downregulated after pretreatment with oridonin were extremely concentrated in immune response, chemotaxis, and inflammatory response. Real-time PCR confirmed that the expression of these genes was upregulated by LPS/D-Gal induction and reduced after treatment with oridonin, which was consistent with RNA-Seq results. KEGG pathway analysis showed a significantly enriched downregulated gene that was present in the Toll-like receptor (TLR) 4 signaling cascade. Our results manifested that phosphorylation levels of upstream signaling molecules in the TLR4 signaling cascade, including extracellular signal-regulated kinase (ERK), P38, and IκB, were significantly inhibited by oridonin. Furthermore, LPS/D-Gal stimulation triggered posttranslational modifications of related gene loci in the TLR4 signaling pathway, including phosphorylation of IL-1 receptor-associated kinase 4 (IRAK4 T345/S346) and acetylation of IRAK4 (K34). However, after treatment with oridonin, the modification pattern of IRAK4 expression stimulated by LPS/D-Gal was suggestively attenuated.

CONCLUSION

Our study revealed that the protective effects of oridonin on LPS/D-Gal-induced ALI mediated by inhibition of the PTMs of IRAK4, including phosphorylation of T345/S346 and acetylation of K34.

Toll-Like Receptors and Relevant Emerging Therapeutics with Reference to Delivery Methods

The built-in innate immunity in the human body combats various diseases and their causative agents. One of the components of this system is Toll-like receptors (TLRs), which recognize structurally conserved molecules derived from microbes and/or endogenous molecules. Nonetheless, under certain conditions, these TLRs become hypofunctional or hyperfunctional, thus leading to a disease-like condition because their normal activity is compromised. In this regard, various small-molecule drugs and recombinant therapeutic proteins have been developed to treat the relevant diseases, such as rheumatoid arthritis, psoriatic arthritis, Crohn’s disease, systemic lupus erythematosus, and allergy. Some drugs for these diseases have been clinically approved; however, their efficacy can be enhanced by conventional or targeted drug delivery systems. Certain delivery vehicles such as liposomes, hydrogels, nanoparticles, dendrimers, or cyclodextrins can be employed to enhance the targeted drug delivery. This review summarizes the TLR signaling pathway, associated diseases and their treatments, and the ways to efficiently deliver the drugs to a target site.

Interleukin-1/-33 Signaling Pathways as Therapeutic Targets for Endometriosis

Endometriosis is an estrogen-dependent disease with symptoms of dysmenorrhea, chronic pain, and infertility that affects 6–10% of women of reproductive age. Medical or surgical therapy, such as administration of an anti-gonadotropin or ovarian cystectomy, provide effective pain relief. However, neither therapy can be used for patients wishing to become pregnant. Despite the high morbidity, the pathogenesis of endometriosis has not been well-elucidated. Several inflammatory cytokines are reported to participate in the onset of endometriosis. Here, we examined the role of interleukin (IL)-1/IL-33 signaling in the development of endometriosis using a mouse model of endometriosis. Endometriotic lesion volume was significantly reduced in Il33^−/− and Il1r1^−/− mice, and almost completely suppressed in Myd88^−/− mice. Mice intraperitoneally administered with an antibody against IL-1 receptor 1 (IL-1R1) or IL-33 developed limited endometriotic lesions. Oral administration of an inhibitor against IL-1R-associated kinase 4 (IRAK4), a downstream signal molecule of MyD88, also suppressed lesion formation. Furthermore, even after the development of cystic lesions the IRAK4 inhibitor prevented the enlargement of lesions. These treatments all significantly reduced cellular proliferation, shown by decreased Ki-67 expression. These results reveal that IL-1/IL-1R1, IL-33/IL-33R and associated downstream signaling molecules are involved in the pathogenesis of endometriosis, and may provide novel therapeutic targets for endometriosis.

Bacterial Translocation and Host Immune Activation in Chronic Hepatitis C Infection

Hepatitis C virus (HCV) infects 71 million individuals, and barriers to treatment remain. Bacterial translocation is a complication of chronic HCV infection, and this study evaluated circulating microbial components including lipopolysaccharide, peptidoglycan, and β-D-glucan in addition to their pattern recognition receptors and degree of hepatic macrophage uptake. The findings suggest that regulation of serum peptidoglycan and β-D-glucan differs from that of lipopolysaccharide. Additionally, macrophage activation in the liver may be better reflected by the degree of macrophage uptake than by circulating levels of microbial markers. These findings allow for a greater understanding of bacterial translocation and host immune activation during HCV infection.

Quantification of Dynamic Protein Interactions and Phosphorylation in LPS Signaling Pathway by SWATH-MS

Lipopolysaccharide (LPS)-induced macrophage activation is a prototype of innate immune response. Although key effector proteins in LPS signaling pathway have been revealed, the map of dynamic protein interactions and phosphorylation as well as the stoichiometry of protein complexes are lacking. Here we present a dynamic map of protein interactions and phosphorylation in MyD88, TRAF6 and NEMO complexes obtained by SWATH-MS. The comprehensive MS measurement leads to quantification of up to about 3,000 proteins across about 21-40 IP samples. We detected and quantified almost all known interactors of MyD88, TRAF6 and NEMO. By analyzing these quantitative data, we uncovered differential recruitment of IRAK family proteins to LPS-induced signaling complexes and determined the stoichiometry of the Myddosome complex. In addition, quantitative phosphoproteomics analysis identified a number of unreported high-confidence phosphosites on the key proteins in LPS signaling pathway. Collectively, data of dynamic protein interactions and phosphorylation presented by this study could be a resource for further study of the LPS signaling pathway.

Sea bass (Lateolabrax maculatus) accelerates wound healing: A transition from inflammation to proliferation

ETHNOPHARMACOLOGICAL RELEVANCE

Sea bass (Lateolabrax maculatus) has been used for dietary therapy practice for wound healing of puerperal or surgery patients in China. Traditional Chinese medicinal books also documented that sea bass can be used to manage inflammation-associated conditions such as wound, miscarriage and cough. Some studies also proved that dietary supplement with fish benefited for treating many inflammatory - associated conditions, such as cardiovascular disease, ulcerative colitis and hyperlipidemia. However, the studies on the pharmacological mechanisms of wound healing efficacy of sea bass remain lack of investigation.

AIM OF THE STUDY

The aim of this study is to investigate the molecular mechanisms of sea bass on wound healing efficacy. Establishing a further justification for clinical application of aqueous extract of sea bass (ASB) in treating wound healing.

MATERIALS AND METHODS

Transition from inflammation to proliferation phase treated as the critical step in wound repair which were investigated via in vitro and in vivo study. A series of inflammatory mediators associated with wound healing and proliferation effects of fibroblasts upon treatments were studied via Western blotting, enzyme-linked immunosorbent assay (ELISA), real time reverse transcription-polymerase chain reaction (RT-PCR) and scratch assay. The cutaneous wound model was applied on skin wound healing study to observe the healing process in C57BL/6 mice upon ASB treatments. Hematological parameters and tumor necrosis factor-α (TNF-α) secretions in serum were determined. Histopathological examinations were conducted by hematoxylin and eosin (H&E) staining and Masson staining. Immunofluorescence were performed to identify infiltrating neutrophils (MPO) and α-smooth muscle actin (α-SMA).

RESULTS

Results showed that ASB significantly reduced the production of inflammatory mediators cyclooxygenase-2 (COX-2), nitrite oxide (NO) production and TNF-α. The phosphorylation and nuclear protein levels of transcription factor nuclear factor-κB (NF-ĸB) in toll-like receptor 4 (TLR4) signaling were decreased by ASB treatment as well. Wound closure rate and cyclin D1 expression level of fibroblasts were significantly increased by ASB treatments. Moreover, cutaneous wound model in C57BL/6 mice presented many similarities in appearance to the process of wound healing.

CONCLUSIONS

The in vitro study demonstrated an inhibitory effect of ASB on the inflammatory mediators regulated by TLR4 signaling pathways, providing evidence that ASB treatment potentially accelerate the wound healing through migration and proliferation enhancement. Additionally, the in vivo study suggested that ASB treatment has a potential in accelerating the proliferation phase of wound healing via well-organized abundant collagen deposition, angiogenesis and re-epithelialization in wounds. The present findings can be treated as a pharmacological basis for the folk use of sea bass and further studies in biological and medical fields.

Interleukin-1 receptor-associated kinase 4 (IRAK4) inhibitors: an updated patent review (2016-2018)

INTRODUCTION

Interleukin-1 receptor-associated kinase 4 (IRAK4) is the most upstream kinase in Toll/Interleukin-1 receptor (TIR) signaling. Human and rodent genetics support the role of IRAK4 in immune function and the involvement of IRAK4-dependent signaling in certain cancers is hypothesized. The accumulating evidence has motivated the discovery of IRAK4 inhibitors that could be used therapeutically.

AREAS COVERED

This review summarizes patents published in 2016-2018 claiming IRAK4 inhibitors. Representative analogues from each patent are presented with a focus on compounds that have been profiled in cellular and in vivo assays.

EXPERT OPINION

The last three years have seen an increased number of IRAK4 inhibitors with which to assess the therapeutic potential of the target. At least 5 companies are believed to have advanced to the clinic. Pfizer is in phase II for rheumatoid arthritis (RA). The outcomes of these studies should inform on the therapeutic potential in autoimmune disease and cancer.

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.

Discovery of potent IRAK-4 inhibitors as potential anti-inflammatory and anticancer agents using structure-based exploration of IRAK-4 pharmacophoric space coupled with QSAR analyses

Interleukin-1 Receptor-Associated Kinase 4 (IRAK-4) has an important role in immunity, inflammation, and malignancy. The significant role of IRAK-4 makes it an interesting target for the discovery and development of potent small molecule inhibitors. In the current study, multiple linear regression -based QSAR analyses coupled with structure-based pharmacophoric exploration was applied to reveal the structural and physiochemical properties required for IRAK-4 inhibition. Manually built pharmacophoric models were initially validated with receiver operating characteristic curve, and best-ranked models were subsequently integrated in QSAR analysis along with other physiochemical descriptors. The pharmacophore model, selected using the statistically optimum QSAR equation, was implied as a 3D-search filter to mine the National Cancer Institute database for novel IRAK-4 inhibitors. Whereas the associated QSAR model prioritized the bioactivities of captured hits for in vitro evaluation. Experimental validation identified several potent IRAK-4 inhibitors of novel structural scaffolds. The most potent captured hit exhibited an IC₅₀ value of 157 nM.

Innate Immune Signaling and Its Role in Metabolic and Cardiovascular Diseases

The innate immune system is an evolutionarily conserved system that senses and defends against infection and irritation. Innate immune signaling is a complex cascade that quickly recognizes infectious threats through multiple germline-encoded cell surface or cytoplasmic receptors and transmits signals for the deployment of proper countermeasures through adaptors, kinases, and transcription factors, resulting in the production of cytokines. As the first response of the innate immune system to pathogenic signals, inflammatory responses must be rapid and specific to establish a physical barrier against the spread of infection and must subsequently be terminated once the pathogens have been cleared. Long-lasting and low-grade chronic inflammation is a distinguishing feature of type 2 diabetes and cardiovascular diseases, which are currently major public health problems. Cardiometabolic stress-induced inflammatory responses activate innate immune signaling, which directly contributes to the development of cardiometabolic diseases. Additionally, although the innate immune elements are highly conserved in higher-order jawed vertebrates, lower-grade jawless vertebrates lack several transcription factors and inflammatory cytokine genes downstream of the Toll-like receptors (TLRs) and retinoic acid-inducible gene-I (RIG-I)-like receptors (RLRs) pathways, suggesting that innate immune signaling components may additionally function in an immune-independent way. Notably, recent studies from our group and others have revealed that innate immune signaling can function as a vital regulator of cardiometabolic homeostasis independent of its immune function. Therefore, further investigation of innate immune signaling in cardiometabolic systems may facilitate the discovery of new strategies to manage the initiation and progression of cardiometabolic disorders, leading to better treatments for these diseases. In this review, we summarize the current progress in innate immune signaling studies and the regulatory function of innate immunity in cardiometabolic diseases. Notably, we highlight the immune-independent effects of innate immune signaling components on the development of cardiometabolic disorders.

N-terminal domain of EcC1INH in Epinephelus coioides can antagonize the LPS-stimulated inflammatory response

Complement 1 inhibitor (C1INH) serving as a multifunctional factor can participate in the regulation of complement cascades and attenuate the activation of various proteases. In this study, we obtained EcC1INH cDNA and the tissue-specific analysis indicate that the highest expression level of EcC1INH mRNA was detected in liver. Moreover, Vibrio alginolyticus challenge can significantly increase EcC1INH mRNA expression in liver and kidney. N-terminal domain of EcC1INH could decrease LPS binding activity to cell surface, while loss of positively charged residues (PCRs) Arg21, His22, Lys50, Arg61 in N-terminal domain of EcC1INH can significantly reduce its interaction with LPS. Furthermore, LPS injection experiment indicated that the binding of EcC1INH N-terminal domain to LPS can antagonize LPS-induced inflammatory signaling pathway and attenuate the production of proinflammatory cytokines in vivo, indicating that EcC1INH was involved in negative regulation of inflammatory response.

A novel interleukin-1 receptor-associated kinase-4 from thick shell mussel Mytilus coruscus is involved in inflammatory response

Interleukin-1 receptor-associated kinase-4 (IRAK4) is considered as the most upstream kinase of IRAKs and plays a vital role in Toll-like receptor/Interleukin-1 receptor (TLR/IL-1R) signal transduction. In the present study, IRAK4 from thick shell mussel Mytilus coruscus (McIRAK4) was identified and characterized. McIRAK4 showed the most similarity to its counterparts in bivalves. The conserved death domain (DD) and catalytic domain of serine/threonine kinases (STKc) were predicted in all examined IRAK4s. McIRAK4 transcripts were constitutively expressed in all examined tissues with the higher expression level in immune related tissues, and were significantly induced in haemocytes upon lipopolysaccharide (LPS) and polyinosinic-polycytidylic acid (poly I:C) challenge. Further, the expression of McIRAK4 was obviously repressed by dsRNA mediated RNA interference (RNAi), meanwhile the proinflammatory cytokines TNF-alpha and IL17 were down-regulated while the antiinflammatory cytokine TGF-β was up-regulated. Additionally, McIRAK4 showed a global cytoplasmic localization in HEK293T cells through fluorescence microscopy. These results collectively indicated that McIRAK4 is one member of IRAK4 subfamily and might play the potential signal transducer role in inflammatory response. The present study provides supplement for TLR-mediated signaling pathway triggered by pathogenic invasions in thick shell mussel, and contributes to the clarification of the innate immune response in molluscs.

Targeting the immunity protein kinases for immuno-oncology

With the rise of immuno-oncology, small-molecule modulators targeting immune system and inflammatory processes are becoming a research hotspot. This work mainly focuses on key kinases acting as central nodes in immune signaling pathways. Although over thirty small-molecule kinase inhibitors have been approved by FDA for the treatment of various cancers, only a few are associated with immuno-oncology. With the going deep of the research work, more and more immunity protein kinase inhibitors are approved for clinical trials to treat solid tumors and hematologic malignancies by FDA, which remain good prospects. Meanwhile, in-depth understanding of biological function of immunity protein kinases in immune system is pushing the field forward. This article focuses on the development of safe and effective small-molecule immunity protein kinase inhibitors and further work needs to keep the promises of these inhibitors for patients' welfare.

LncRNA HOTAIR regulates lipopolysaccharide-induced cytokine expression and inflammatory response in macrophages

Long noncoding RNAs (lncRNAs) are emerging as major regulators of a variety of cell signaling processes. Many lncRNAs are expressed in immune cells and appear to play critical roles in the regulation of immune response. Here, we have investigated the potential role of a well-known lncRNA, HOTAIR, in inflammatory and immune response. Our studies demonstrate that HOTAIR expression is induced in immune cells (macrophages) upon treatment with lipopolysaccharide (LPS). Knockdown of HOTAIR reduces NF-κB-mediated inflammatory gene and cytokine expression in macrophages. Inhibition of NF-κB resulted in down-regulation of LPS-induced expression of HOTAIR as well as IL-6 and iNOS expression. We further demonstrated that HOTAIR regulates activation of NF-κB and its target genes (IL-6 and iNOS) expression via facilitating the degradation of IκBα. HOTAIR knockdown reduces the expression of NF-κB target gene expression via inhibiting the recruitment of NF-κB and associated cofactors at the target gene promoters. Taken together, our findings suggest that HOTAIR is a critical player in NF-κB activation in macrophages suggesting its potential functions in inflammatory and immune response.

Understanding early TLR signaling through the Myddosome

TLRs are expressed on the plasma and endosomal membranes of innate immune cells acting as sensors of foreign and inherent danger signals that threaten the host. Upon activation, TLRs facilitate the assembly of large intracellular oligomeric signaling complexes, termed Myddosomes, which initiate key signal transduction pathways to elicit critical inflammatory immune responses. The formation of the Myddosome is integral for TLR signaling; however, the molecular mechanisms controlling its formation, disassembly, and the subsequent proximal signaling events remain to be clearly defined. In this review, we present a brief overview of TLR signal transduction pathways, summarize the current understanding of the Myddosome and the proteins that comprise its structure, including MyD88 and members of the IL-1 receptor-associated kinase (IRAK) family. Finally, we will discuss recent advances and open questions regarding early TLR signaling in the context of the Myddosome complex.

Identification of Toll-like receptor signaling inhibitors based on selective activation of hierarchically acting signaling proteins

Toll-like receptors (TLRs) recognize various pathogen- and host tissue-derived molecules and initiate inflammatory immune responses. Exaggerated or prolonged TLR activation, however, can lead to etiologically diverse diseases, such as bacterial sepsis, metabolic and autoimmune diseases, or stroke. Despite the apparent medical need, no small-molecule drugs against TLR pathways are clinically available. This may be because of the complex signaling mechanisms of TLRs, which are governed by a series of protein-protein interactions initiated by Toll/interleukin-1 receptor homology domains (TIR) found in TLRs and the cytoplasmic adaptor proteins TIRAP and MyD88. Oligomerization of TLRs with MyD88 or TIRAP leads to the recruitment of members of the IRAK family of kinases and the E3 ubiquitin ligase TRAF6. We developed a phenotypic drug screening system based on the inducible homodimerization of either TIRAP, MyD88, or TRAF6, that ranked hits according to their hierarchy of action. From a bioactive compound library, we identified methyl-piperidino-pyrazole (MPP) as a TLR-specific inhibitor. Structure-activity relationship analysis, quantitative proteomics, protein-protein interaction assays, and cellular thermal shift assays suggested that MPP targets the TIR domain of MyD88. Chemical evolution of the original MPP scaffold generated compounds with selectivity for distinct TLRs that interfered with specific TIR interactions. Administration of an MPP analog to mice protected them from TLR4-dependent inflammation. These results validate this phenotypic screening approach and suggest that the MPP scaffold could serve as a starting point for the development of anti-inflammatory drugs.

Targeting toll-like receptor 4 signalling pathways: can therapeutics pay the toll for hypertension?

The immune system plays a prominent role in the initiation and maintenance of hypertension. The innate immune system, via toll-like receptors (TLRs), identifies distinct signatures of invading microbes and damage-associated molecular patterns and triggers a chain of downstream signalling cascades, leading to secretion of pro-inflammatory cytokines and shaping the adaptive immune response. Over the past decade, a dysfunctional TLR-mediated response, particularly via TLR4, has been suggested to support a chronic inflammatory state in hypertension, inducing deleterious local and systemic effects in host cells and tissues and contributing to disease progression. While the underlying mechanisms triggering TLR4 need further research, evidence suggests that sustained elevations in BP disrupt homeostasis, releasing endogenous TLR4 ligands in hypertension. In this review, we discuss the emerging role of TLR4 in the pathogenesis of hypertension and whether targeting this receptor and its signalling pathways could offer a therapeutic strategy for management of this multifaceted disease. LINKED ARTICLES: This article is part of a themed section on Immune Targets in Hypertension. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v176.12/issuetoc.

Interleukin-1 receptor-associated kinase 4 (IRAK4) plays a dual role in myddosome formation and Toll-like receptor signaling

Toll-like receptors (TLRs) form part of the host innate immune system, in which they act as sensors of microbial and endogenous danger signals. Upon TLR activation, the intracellular Toll/interleukin-1 receptor domains of TLR dimers initiate oligomerization of a multiprotein signaling platform comprising myeloid differentiation primary response 88 (MyD88) and members of the interleukin-1 receptor–associated kinase (IRAK) family. Formation of this myddosome complex initiates signal transduction pathways, leading to the activation of transcription factors and the production of inflammatory cytokines. To date, little is known about the assembly and disassembly of the myddosome and about the mechanisms by which these complexes mediate multiple downstream signaling pathways. Here, we isolated myddosome complexes from whole-cell lysates of TLR-activated primary mouse macrophages and from IRAK reporter macrophages to examine the kinetics of myddosome assembly and disassembly. Using a selective inhibitor of IRAK4's kinase activity, we found that whereas TLR cytokine responses were ablated, myddosome formation was stabilized in the absence of IRAK4's kinase activity. Of note, IRAK4 inhibition had only a minimal effect on NF-κB and mitogen-activated protein kinase (MAPK) signaling. In summary, our results indicate that IRAK4 has a critical scaffold function in myddosome formation and that its kinase activity is dispensable for myddosome assembly and activation of the NF-κB and MAPK pathways but is essential for MyD88-dependent production of inflammatory cytokines. Our findings suggest that the scaffold function of IRAK4 may be an attractive target for treating inflammatory and autoimmune diseases.

Aluminum trichloride-induced hippocampal inflammatory lesions are associated with IL-1β-activated IL-1 signaling pathway in developing rats

Aluminum (Al) is a recognized environmental pollutant that causes neuroinflammatory lesions, leading to neurodegenerative diseases. Interleukin-1 (IL-1) signaling pathway is responsible for regulating inflammatory lesions. However, it remains unclear whether IL-1 signaling pathway is involved in neuroinflammatory lesions induced by Al exposure. In the present study, one hundred and twenty Wistar rats were orally exposed to 0, 50, 150 and 450 mg/kg BW/d aluminum trichloride (AlCl₃) for 90 days, respectively. We found that AlCl₃ exposure increased hippocampal Al concentration, reduced hippocampus coefficient, impaired cognitive ability, deteriorated microstructure of hippocampal CA1 and CA3 regions, increased reactive oxygen species (ROS) level, activated astrocytes and microglia, increased pro-inflammatory cytokines contents and mRNA expressions, and decreased anti-inflammatory cytokines contents and mRNA expressions in the hippocampus. These results indicated that AlCl₃ induced the hippocampal inflammatory lesion (HIL). Moreover, AlCl₃ exposure increased the mRNA and protein expression of IL-1 signaling pathway core components in the hippocampus, demonstrating that AlCl₃ activated IL-1 signaling pathway. Furthermore, the correlation between interleukin-1β (IL-1β) content and HIL and activation of the IL-1 signaling pathway was analyzed. Results showed that IL-1β content was positively correlated with pro-inflammatory cytokines contents and mRNA expressions and activation of IL-1 signaling pathway, and was negatively correlated with hippocampus coefficient, anti-inflammatory cytokines contents and mRNA expressions, and the number of hippocampal neurons. The above results demonstrate that AlCl₃-induced HIL is associated with IL-1 signaling pathway, in which IL-1β is a link.

Protective effect of hydroxysafflor yellow A against acute kidney injury via the TLR4/NF-κB signaling pathway

This study aimed to evaluate the protective effect of hydroxysafflor yellow A (HSYA) on ischemia/reperfusion (I/R)-induced acute kidney injury via the TLR4/NF-κB pathway, both in vitro and in vivo. Rats were subjected to removal of the right kidney and I/R injury to the left kidney. Rats subjected to renal I/R injury were treated with HSYA at 0.5 h prior to I/R injury. Renal function, histopathological analysis, and cells apoptosis were measured in vivo. In vitro, proximal renal tubular cells (HK-2) were subjected to hypoxia/reoxygenation (H/R). Apoptotic cell death and inflammatory cytokines, Toll-like receptor 4 (TLR4), and nuclear factor (NF)-κB expression were determined. Treatment of I/R rats with HSYA markedly reduced the levels of serum creatinine and blood urea nitrogen, attenuated renal cell apoptosis, alleviated changes in renal tissue morphology, and reduced IL-1β, TNF-α, and caspase-3 release. In vitro, HSYA effectively decreased NF-κB p65 and inflammatory cytokines, such as IL-1β, TNF-α, and IL-6. Thus, HSYA can protect renal function from I/R injury by ameliorating acute kidney injury and partly by promoting tubular cell survival via the TLR4/NF-κB pathway. These results suggest that HSYA can be used to prevent I/R-induced acute kidney injury.

IRAK4 activity controls immune responses to intracellular bacteria Listeria monocytogenes and Mycobacterium smegmatis

IL-1 receptor-associated kinase (IRAK) 4 is a central enzyme of the TLR pathways. This study tested the hypothesis that IRAK4 kinase activity is prerequisite for regulating innate immunity during infections with intracellular bacteria. To this end, we analyzed responses of macrophages obtained from mice expressing wild-type (WT) IRAK4 or its kinase-inactive K213M mutant (IRAK4^KI ) upon infection with intracellular bacteria Listeria monocytogenes or Mycobacterium smegmatis. In contrast to robust induction of cytokines by macrophages expressing kinase-sufficient IRAK4, IRAK4^KI macrophages expressed decreased TNF-α, IL-6, IL-1β, and C-C motif chemokine ligand 5 upon infection with L. monocytogenes or M. smegmatis. Bacterial infection of IRAK4^KI macrophages led to attenuated activation of IRAK1, MAPKs and NF-κB, impaired induction of inducible NO synthase mRNA and secretion of NO, but resulted in elevated microbial burdens. Compared with WT animals, systemic infection of IRAK4^KI mice with M. smegmatis or L. monocytogenes resulted in decreased levels of serum IL-6 and CXCL-1 but increased bacterial burdens in the spleen and liver. Thus, a loss of IRAK4 kinase activity underlies deficient cytokine and microbicidal responses during infection with intracellular bacteria L. monocytogenes or M. smegmatis via impaired activation of IRAK1, MAPKs, and NF-κB but increases bacterial burdens, correlating with decreased induction of NO.

An Integrative Framework Reveals Signaling-to-Transcription Events in Toll-like Receptor Signaling

Building an integrated view of cellular responses to environmental cues remains a fundamental challenge due to the complexity of intracellular networks in mammalian cells. Here, we introduce an integrative biochemical and genetic framework to dissect signal transduction events using multiple data types and, in particular, to unify signaling and transcriptional networks. Using the Toll-like receptor (TLR) system as a model cellular response, we generate multifaceted datasets on physical, enzymatic, and functional interactions and integrate these data to reveal biochemical paths that connect TLR4 signaling to transcription. We define the roles of proximal TLR4 kinases, identify and functionally test two dozen candidate regulators, and demonstrate a role for Ap1ar (encoding the Gadkin protein) and its binding partner, Picalm, potentially linking vesicle transport with pro-inflammatory responses. Our study thus demonstrates how deciphering dynamic cellular responses by integrating datasets on various regulatory layers defines key components and higher-order logic underlying signaling-to-transcription pathways.

Tumor-Stroma IL1β-IRAK4 Feedforward Circuitry Drives Tumor Fibrosis, Chemoresistance, and Poor Prognosis in Pancreatic Cancer

Targeting the desmoplastic stroma of pancreatic ductal adenocarcinoma (PDAC) holds promise to augment the effect of chemotherapy, but success in the clinic has thus far been limited. Preclinical mouse models suggest that near-depletion of cancer-associated fibroblasts (CAF) carries a risk of accelerating PDAC progression, underscoring the need to concurrently target key signaling mechanisms that drive the malignant attributes of both CAF and PDAC cells. We previously reported that inhibition of IL1 receptor-associated kinase 4 (IRAK4) suppresses NFκB activity and promotes response to chemotherapy in PDAC cells. In this study, we report that CAF in PDAC tumors robustly express activated IRAK4 and NFκB. IRAK4 expression in CAF promoted NFκB activity, drove tumor fibrosis, and supported PDAC cell proliferation, survival, and chemoresistance. Cytokine array analysis of CAF and microarray analysis of PDAC cells identified IL1β as a key cytokine that activated IRAK4 in CAF. Targeting IRAK4 or IL1β rendered PDAC tumors less fibrotic and more sensitive to gemcitabine. In clinical specimens of human PDAC, high stromal IL1β expression associated strongly with poor overall survival. Together, our studies establish a tumor-stroma IL1β-IRAK4 feedforward signal that can be therapeutically disrupted to increase chemotherapeutic efficacy in PDAC.Significance: Targeting the IL1β-IRAK4 signaling pathway potentiates the effect of chemotherapy in pancreatic cancer. Cancer Res; 78(7); 1700-12. ©2018 AACR.

Modulating inflammation through the negative regulation of NF-κB signaling

Immune system activation is essential to thwart the invasion of pathogens and respond appropriately to tissue damage. However, uncontrolled inflammation can result in extensive collateral damage underlying a diverse range of auto-inflammatory, hyper-inflammatory, and neoplastic diseases. The NF-κB signaling pathway lies at the heart of the immune system and functions as a master regulator of gene transcription. Thus, this signaling cascade is heavily targeted by mechanisms designed to attenuate overzealous inflammation and promote resolution. Mechanisms associated with the negative regulation of NF-κB signaling are currently under intense investigation and have yet to be fully elucidated. Here, we provide an overview of mechanisms that negatively regulate NF-κB signaling through either attenuation of signal transduction, inhibition of posttranscriptional signaling, or interference with posttranslational modifications of key pathway components. While the regulators discussed for each group are far from comprehensive, they exemplify common mechanistic approaches that inhibit this critical biochemical signaling cascade. Despite their diversity, a commonality among these regulators is their selection of specific targets at key inflection points in the pathway, such as TNF-receptor-associated factor family members or essential kinases. A better understanding of these negative regulatory mechanisms will be essential to gain greater insight related to the maintenance of immune system homeostasis and inflammation resolution. These processes are vital elements of disease pathology and have important implications for targeted therapeutic strategies.

Cloning, expression pattern and functional characterization of interleukin-1 receptor-associated kinase 4, an important mediator of the Toll-like receptor signaling pathway, from Artemia sinica

As a crucial component of Toll-like receptor (TLR)/interleukin-1 receptor (IL-1R) signaling pathways, IL-1R--associated kinase 4 (IRAK-4) plays a central role in innate immunity and embryonic development. Herein, we have characterized the full length cDNA of IRAK4 from Artemia sinica. Molecular characterization revealed that the sequence includes a 2550 bp open reading frame, encoding a predicted protein of 849 amino acids. The predicted protein contains a death domain in the N-terminus and two serine/threonine/tyrosine protein kinasedomains. Bioinformatics analysis showed that it belonged to a new member of the IRAK-4 family. The expression of AsIRAK-4 was researched in various stages during embryonic development by several molecular biology methods including real time PCR, Western blotting and immunohistochemistry. The results showed that AsIRAK-4 was constitutively expressed at all developmental stages from embryo to adult, and it was mainly expressed in the head and thorax at the early stages and on the surface of the alimentary canal at later stages. The highest expression level was at the 0 h, 15 h and 5 d stages of A. sinica. While challenged by Gram-positive and Gram-negative bacteria, AsIRAK-4 was remarkably upregulated with the rising concentration of bacteria. Our research revealed that AsIRAK-4 plays a vital role in growth, development and innate immunity of A. sinica.

Generation of Innate Immune Reporter Cells Using Retroviral Transduction

Innate immune cells are notoriously difficult to transfect; however, retroviruses can be used to stably integrate genes of interest into the host genome of primary or immortalized immune cells resulting in the generation of reporter cells. Here, we provide a detailed protocol covering the production of retroviruses, retroviral infection of innate immune target cells (including isolation and differentiation of murine bone marrow cells to macrophages), and several methods for enrichment of positively transduced cells.

Macrophage-Bacteria Interactions-A Lipid-Centric Relationship

Macrophages are professional phagocytes at the front line of immune defenses against foreign bodies and microbial pathogens. Various bacteria, which are responsible for deadly diseases including tuberculosis and salmonellosis, are capable of hijacking this important immune cell type and thrive intracellularly, either in the cytoplasm or in specialized vacuoles. Tight regulation of cellular metabolism is critical in shaping the macrophage polarization states and immune functions. Lipids, besides being the bulk component of biological membranes, serve as energy sources as well as signaling molecules during infection and inflammation. With the advent of systems-scale analyses of genes, transcripts, proteins, and metabolites, in combination with classical biology, it is increasingly evident that macrophages undergo extensive lipid remodeling during activation and infection. Each bacterium species has evolved its own tactics to manipulate host metabolism toward its own advantage. Furthermore, modulation of host lipid metabolism affects disease susceptibility and outcome of infections, highlighting the critical roles of lipids in infectious diseases. Here, we will review the emerging roles of lipids in the complex host-pathogen relationship and discuss recent methodologies employed to probe these versatile metabolites during the infection process. An improved understanding of the lipid-centric nature of infections can lead to the identification of the Achilles' heel of the pathogens and host-directed targets for therapeutic interventions. Currently, lipid-moderating drugs are clinically available for a range of non-communicable diseases, which we anticipate can potentially be tapped into for various infections.

MicroRNA sequence analysis identifies microRNAs associated with peri-implantitis in dogs

Peri-implantitis, which is characterized by dense inflammatory infiltrates and increased osteoclast activity, can lead to alveolar bone destruction and implantation failure. miRNAs participate in the regulation of various inflammatory diseases, such as periodontitis and osteoporosis. Therefore, the present study aimed to investigate the differential expression of miRNAs in canine peri-implantitis and to explore the functions of their target genes. An miRNA sequence analysis was used to identify differentially expressed miRNAs in peri-implantitis. Under the criteria of a fold-change >1.5 and P<0.01, 8 up-regulated and 30 down-regulated miRNAs were selected for predictions of target genes and their biological functions. Based on the results of Gene Ontology (GO) and KEGG pathway analyses, these miRNAs may fine-tune the inflammatory process in peri-implantitis through an intricate mechanism. The results of quantitative real-time PCR (qRT-PCR) revealed that let-7g, miR-27a, and miR-145 may play important roles in peri-implantitis and are worth further investigation. The results of the present study provide insights into the potential biological effects of the differentially expressed miRNAs, and specific enrichment of target genes involved in the mitogen-activated protein kinase (MAPK) signaling pathway was observed. These findings highlight the intricate and specific roles of miRNAs in inflammation and osteoclastogenesis, both of which are key aspects of peri-implantitis, and thus may contribute to future investigations of the etiology, underlying mechanism, and treatment of peri-implantitis.

The IL-1β signalling pathway and its role in regulating pro-inflammatory and pro-labour mediators in human primary myometrial cells

Interleukin (IL)-1β plays a central role in the processes of human labour and delivery. The adaptor proteins involved in the IL-1β signalling pathway in human myometrium are not known. This study sought to determine the role of the adaptor proteins myeloid differentiation primary response 88 (MyD88), tumour necrosis factor receptor-associated factor 6 (TRAF6), IL-1 receptor-associated kinase 4 (IRAK4) and transforming growth factor beta-activated kinase 1 (TAK1) in IL-1β-induced formation of pro-inflammatory and pro-labour mediators in human myometrium. Human primary myometrial cells were transfected with siRNA against MyD88 (siMYD88), TRAF6 (siTRAF6), IRAK4 (siIRAK4) or TAK1 (siTAK1), treated with IL-1β, and assayed for the mRNA expression and or secretion of pro-inflammatory and pro-labour mediators. Transfection of primary myometrial cells with siMYD88, siTRAF6, siIRAK4 and siTAK1 significantly decreased IL-1β-induced IL-1α, IL-6, growth-regulated alpha protein (GRO-α), IL-8, monocyte chemoattractant protein (MCP)-1, intercellular adhesion molecule (ICAM)-1 and cyclooxygenase (COX)-2 mRNA expression and release of IL-6, GRO-α, IL-8, MCP-1, ICAM-1 and prostaglandin PGF_2α. The expression and secretion of the extracellular matrix remodelling enzyme matrix metalloproteinase (MMP)-9 was significantly lower with siMYD88 and siTRAF6. Finally, IL-1β-induced nuclear factor κB (NF-κB) transcriptional activity was significantly attenuated by transfection with siMyD88, siTRAF6 and siIRAK4; there was no effect of siTAK1 transfection on NF-κB transcriptional activity. Collectively, these findings suggest that MyD88, TRAF6, IRAK4 and TAK1 are involved in IL-1β signalling in human myometrium. Further studies are required to determine if inhibition of these proteins can prevent preterm birth.

Inulin-Type Fructans Modulates Pancreatic-Gut Innate Immune Responses and Gut Barrier Integrity during Experimental Acute Pancreatitis in a Chain Length-Dependent Manner

Acute pancreatitis (AP) is a common abdominal inflammatory disorder and one of the leading causes of hospital admission for gastrointestinal disorders. No specific pharmacological or nutritional therapy is available but highly needed. Inulin-type fructans (ITFs) are capable of modifying gut immune and barrier homeostasis in a chemistry-dependent manner and hence potentially applicable for managing AP, but their efficacy in AP has not been demonstrated yet. The current study aimed to examine and compare modulatory effects of ITFs with different degrees of fermentability on pancreatic-gut immunity and barrier function during experimentally induced AP in mice. BALB/c mice were fed short (I)- or long (IV)-chain ITFs supplemented diets for up to 3 days before AP induction by caerulein. Attenuating effects on AP development were stronger with ITF IV than with ITF I. We found that long-chain ITF IV attenuated the severity of AP, as evidenced by reduced serum amylase levels, lipase levels, pancreatic myeloperoxidase activity, pancreatic edema, and histological examination demonstrating reduced pancreatic damage. Short-chain ITF I demonstrated only partial protective effects. Both ITF IV and ITF I modulated AP-associated systemic cytokine levels. ITF IV but not ITF I restored AP-associated intestinal barrier dysfunction by upregulating colonic tight junction modulatory proteins, antimicrobial peptides, and improved general colonic histology. Additionally, differential modulatory effects of ITF IV and ITF I were observed on pancreatic and gut immunity: ITF IV supplementation prevented innate immune cell infiltration in the pancreas and colon and tissue cytokine production. Similar effects were only observed in the gut with ITF I and not in the pancreas. Lastly, ITF IV but not ITF I downregulated AP-triggered upregulation of IL-1 receptor-associated kinase 4 (IRAK-4) and phosphor-c-Jun N-terminal kinase (p-JNK), and a net decrease of phosphor-nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB) p65 (p-NF-κB p65) nuclear translocation and activation in the pancreas. Our findings demonstrate a clear chain length-dependent effect of inulin on AP. The attenuating effects are caused by modulating effects of long-chain inulin on the pancreatic-gut immunity via the pancreatic IRAK-4/p-JNK/p-NF-κBp65 signaling pathway and on prevention of disruption of the gut barrier.

Mouse Bone Marrow Sca-1+ CD44+ Mesenchymal Stem Cells Kill Avirulent Mycobacteria but Not Mycobacterium tuberculosis through Modulation of Cathelicidin Expression via the p38 Mitogen-Activated Protein Kinase-Dependent Pathway

Mycobacterium tuberculosis primarily infects lung macrophages. However, a recent study showed that M. tuberculosis also infects and persists in a dormant form inside bone marrow mesenchymal stem cells (BM-MSCs) even after successful antibiotic therapy. However, the mechanism(s) by which M. tuberculosis survives in BM-MSCs is still not known. Like macrophages, BM-MSCs do not contain a well-defined endocytic pathway, which is known to play a central role in the clearance of internalized mycobacteria. Here, we studied the fate of virulent and avirulent mycobacteria in Sca-1⁺ CD44⁺ BM-MSCs. We found that BM-MSCs were able to kill avirulent Mycobacterium smegmatis and Mycobacterium bovis BCG but not the pathogenic species M. tuberculosis Further mechanistic studies revealed that pathogenic M. tuberculosis dampens the antibacterial response of BM-MSCs by downregulating the expression of the cationic antimicrobial peptide cathelicidin. In contrast, avirulent mycobacteria were effectively killed by inducing the Toll-like receptor 2/4 (TLR2/4) pathway-dependent expression of cathelicidin, while small interfering RNA (siRNA)-mediated cathelicidin silencing increased the survival of M. bovis BCG in BM-MSCs. We also showed that M. bovis BCG infection caused increased expression levels of MyD88, phospho-interleukin-1 receptor-associated kinase 4 (pIRAK-4), and the p38 mitogen-activated protein kinase (MAPK) signaling pathway. Further downstream investigations demonstrated that IRAK-4-p38 activation increased the nuclear translocation of NF-κB, which subsequently induced the expression of cathelicidin and the cytokine interleukin-1β (IL-1β), resulting in the decreased survival of M. bovis BCG. On the other hand, inhibition of TLR2/4, pIRAK-4, p38, and NF-κB nuclear translocation decreased cathelicidin and IL-1β expression levels and therefore increased the survival of avirulent mycobacteria. This is the first report that demonstrates that virulent mycobacteria manipulate the TLR2/4-MyD88-IRAK-4-p38-NF-κB-Camp-IL-1β pathway to survive inside bone marrow stem cells.

IRAK4 kinase activity controls Toll-like receptor-induced inflammation through the transcription factor IRF5 in primary human monocytes

Interleukin-1 receptor-associated kinase 4 (IRAK4) plays a critical role in innate immune signaling by Toll-like receptors (TLRs), and loss of IRAK4 activity in mice and humans increases susceptibility to bacterial infections and causes defects in TLR and IL1 ligand sensing. However, the mechanism by which IRAK4 activity regulates the production of downstream inflammatory cytokines is unclear. Using transcriptomic and biochemical analyses of human monocytes treated with a highly potent and selective inhibitor of IRAK4, we show that IRAK4 kinase activity controls the activation of interferon regulatory factor 5 (IRF5), a transcription factor implicated in the pathogenesis of multiple autoimmune diseases. Following TLR7/8 stimulation by its agonist R848, chemical inhibition of IRAK4 abolished IRF5 translocation to the nucleus and thus prevented IRF5 binding to and activation of the promoters of inflammatory cytokines in human monocytes. We also found that IKKβ, an upstream IRF5 activator, is phosphorylated in response to the agonist-induced TLR signaling. Of note, IRAK4 inhibition blocked IKKβ phosphorylation but did not block the nuclear translocation of NFκB, which was surprising, given the canonical role of IKKβ in phosphorylating IκB to allow NFκB activation. Moreover, pharmacological inhibition of either IKKβ or the serine/threonine protein kinase TAK1 in monocytes blocked TLR-induced cytokine production and IRF5 translocation to the nucleus, but not nuclear translocation of NFκB. Taken together, our data suggest a mechanism by which IRAK4 activity regulates TAK1 and IKKβ activation, leading to the nuclear translocation of IRF5 and induction of inflammatory cytokines in human monocytes.

MicroRNA-93 inhibits inflammatory responses and cell apoptosis after cerebral ischemia reperfusion by targeting interleukin-1 receptor-associated kinase 4

The present study aimed to investigate changes in the expression of interleukin (IL)-1 receptor-associated kinase 4 (IRAK4) and microRNA (miRNA or miR)-93 in mice with cerebral ischemia reperfusion (CIR) injury, as well as the association and regulatory mechanism between IRAK4 and miR-93. The CIR mouse model was constructed and mouse microglia BV2 cells were transfected with miR-93 mimic or miR-93 inhibitor. Quantitative polymerase chain reaction was used to measure the expression of mRNA and miR-93. Western blotting was performed to determine protein expression. Enzyme-linked immunosorbent assays were performed to measure the concentrations pro-inflammatory factors. The expression of miR-93 in CIR mice brains was significantly reduced, while Ago-miR-93 (a type of miRNA analog) increased its expression. Ago-miR-93 alleviated neurological deficits and reduced cerebral infarction volume in the mice. Furthermore, Ago-miR-93 inhibited inflammatory responses following CIR. Ago-miR-93 decreased the rate of cell apoptosis following CIR. In addition, miR-93 downregulated IRAK4 protein expression, but did not alter its mRNA expression levels in BV2 cells. miR-93 expression reduced the expression of pro-inflammatory factors in BV2 cells. Ago-miR-93 inhibited IRAK4 expression in the brain tissues of CIR mice. The present study demonstrated that miR-93 inhibits inflammatory responses and cell apoptosis following CIR by targeting the IRAK4 signaling pathway.

How neutrophils kill fungi

Neutrophils play a critical role in the prevention of invasive fungal infections. Whereas mouse studies have demonstrated the role of various neutrophil pathogen recognition receptors (PRRs), signal transduction pathways, and cytotoxicity in the murine antifungal immune response, much less is known about the killing of fungi by human neutrophils. Recently, novel primary immunodeficiencies have been identified in patients with a susceptibility to fungal infections. These human 'knock-out' neutrophils expand our knowledge to understand the role of PRRs and signaling in human fungal killing. From the studies with these patients it is becoming clear that neutrophils employ fundamentally distinct mechanisms to kill Candida albicans or Aspergillus fumigatus.

Molecular characterization of Pacific oyster (Crassostrea gigas) IRAK4 gene and its role in MyD88-dependent pathway

Interleukin-1 receptor-associated kinases (IRAKs) play important roles in MyD88-dependent TLR signaling, the crucial innate immune pathway in molluscs. In this study, we examined the full-length IRAK4 genetic sequence in the Pacific oyster (Crassostrea gigas) by molecular cloning. Phylogenetic analysis revealed that CgIRAK4 is most closely related to Mytilus edulis, and forms a clade with other molluscs. CgIRAK4 transcripts are widely expressed in all tissues, with the highest expression observed in the hemocytes and gill. Moreover, CgIRAK4 is significantly upregulated after Oyster herpesvirus-1 microvariant (OsHV-1 μvar), Vibrio alginolyticus, and poly I:C challenge. Yeast two-hybrid and co-immunoprecipitation assays reveal that the CgIRAK4 death domain is necessary to mediate interaction between CgIRAK4 and two CgMyD88 isoforms. In addition, CgIRAK4 overexpression cannot induce NF-κB transcriptional activity, but blocks that induced by CgMyD88 in HEK293T cells. These findings elucidate the mechanisms of MyD88-dependent TLR signaling in molluscs, and the differences in IRAK-mediated pathway activation between invertebrates and vertebrates.

Toll-like receptor 2 dominance over Toll-like receptor 4 in stressful conditions for its detrimental role in the heart

It has been suggested that Toll-like receptor (TLR)4 promotes IL-10-mediated cardiac cell survival, whereas another receptor, TLR2, from the same family, is detrimental. Here, we examined the interactive role of these two innate signaling molecules under stressful conditions, including IL-10 knockout (IL-10−/−) mice, global ischemia-reperfusion (I/R) injury in rat hearts, and in vitro short hairpin RNA experimental models in the presence or absence of IL-10 (10 ng/ml). Circulating and myocardial levels of TNF-α as well as apoptosis and fibrosis were higher in IL-10−/− mice. The increase in TLR2 in IL-10−/− hearts indicated its negative regulation by IL-10. Ex vivo I/R also caused a marked upregulation of TLR2 and TNF-α as well as apoptotic and fibrotic signals. However, a 40-min reperfusion with IL-10 triggered an increase in TLR4 expression and improved recovery of cardiac function. The increase in IL-1 receptor-associated kinase (IRAK)-M and IRAK-2 activity during I/R injury suggested their role in TLR2 signaling. In vitro inhibition of TLR4 activity as a consequence of RNA inhibition-mediated suppression of myeloid differentiation gene (MyD)88 suggested MyD88-dependent activation of TLR4. The inclusion of IL-10 during reperfusion also downregulated the expression of IRAK-2, TNF-α receptor-associated factor 1-interacting protein (TRAIP) and apoptotic signals, caspase-3, and the Bax-to-Bcl-xL ratio. IL-10 reduced the TNF-α receptor-associated increase in TRAIP-induced apoptosis during I/R injury, which led to an increase in IL-1β to mitigate transforming growth factor-β receptor type I-mediated fibrosis. The IL-10 mitigation of these changes suggests that the stimulation through TLR4 signaling promotes IRAK-4 and phosphorylates IRAK-1 instead of IRAK-2 and may be an important therapeutic approach in restoring heart health in stress.

NEW & NOTEWORTHY Under stress conditions such as downregulation of the IL-10 gene or ischemia-reperfusion injury, Toll-like receptor (TLR)4 and IL-1 receptor-associated kinase (IRAK)-1 activation is suppressed, along with the upregulation of TLR-2 and IRAK-2, resulting in fibrosis and apoptosis. It is suggested that IL-10 helps to maintain heart function during stress via myeloid differentiation gene 88/IRAK-4/IRAK-1-dependent TLR4 signaling.

Micro RNA-146a But Not IRAK1 is Associated with Rheumatoid Arthritis in the Tunisian Population

BACKGROUND

Rheumatoid arthritis (RA) is characterized by the production of an array of proinflammatory cytokines through the nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB) signaling pathway. Interleukin-1 receptor (IL-1R) and Toll-like receptors contain a common cytoplasmic motif the Toll/IL-1R (TIR) homology domain. This motif is required for NF-κB activation. IL-1R-associated kinase 1 (IRAK1) is a key adapter molecule recruited during the signaling cascade of the TIR. Its gene expression is regulated by the micro-RNA (miR)-146a.

OBJECTIVE

We investigated the role of IRAK1 single-nucleotide polymorphism (SNP) rs3027898 (IRAK1 rs3027898) and miR-146a SNP rs2910164 (miR-146a rs2910164) in Tunisian patients with RA and their association with C reactive protein (CRP), rheumatoid factor (RF), anticyclic citrullinated peptide (anti-CCP) antibodies, and erosion.

PATIENTS AND METHODS

In a cohort of 172 adult RA patients and 224 matched controls, IRAK1 rs3027898 genotyping was determined by mutagenically separated polymerase chain reaction (MS-PCR) with newly designed primers, and miR-146a rs2910164 genotyping was determined by fragment length polymorphism PCR-restriction (RFLP-PCR).

RESULTS

The IRAK1 rs3027898 A allele was detected in 67% of RA patients and 70% of controls indicating that it is not associated with RA in codominant, dominant, or recessive models even after stratification by age and gender. The miR-146a rs2910164 G allele was detected in 76% of RA patients and 68% of controls, thus the C allele confers some protection based on a dominant model [CC+GC (odds ratio (95% confidence interval) = 0.6 (0.3-0.9), p = 0.03)]. No association with CRP, RF, anti-CCP, or erosion was found for either SNPs.

CONCLUSION

The IRAK1 rs3027898 was not associated with RA, whereas C allele of miR-146a rs2910164 was found to be protective. Functional studies are required to investigate the exact role of miR-146a rs2910164 during RA.

Cloning and functional characterization of IRAK4 in large yellow croaker (Larimichthys crocea) that associates with MyD88 but impairs NF-κB activation

As crucial signaling transducer in Toll-like receptor (TLR) and interleukin (IL)-1 receptor (IL-1R) signaling pathway, IL-1R-associated kinase 4 (IRAK4) mediates downstream signaling cascades and plays important roles in innate and adaptive immune responses. In the present study, an IRAK4 orthologue was characterized from large yellow croaker (Larimichthys crocea), named Lc-IRAK4, with a conservative N-terminal death domain and a C-terminal protein kinase domain. The genome of Lc-IRAK4 is structured into eleven exons and ten introns. Expression analysis indicated that Lc-IRAK4 was widely expressed in tested tissues, with the highest level in liver and weakest in muscle. Additionally, in the spleen, liver tissues and blood, it could be induced by poly I:C and LPS stimulation, but not be induced by Vibrio parahemolyticus infection. Fluorescence microscopy assays revealed that Lc-IRAK4 localized in the cytoplasm in HEK 293T cells. It was also determined that Lc-IRAK4 could interact with MyD88, whereas MyD88-mediated NF-κB activation was significantly impaired when co-transfected the two in HEK 293T cells. These findings collectively indicated that although Lc-IRAK4 was evolutionarily conserved in vertebrates, the exact function especially the signaling transduction mediated by IRAK4 in fish immune response was different from that in mammals, which impaired MyD88-mediated NF-κB activation.