NF-kappaB, IkappaB, and IRAK control glutamate receptor density at the Drosophila NMJ

NF-kappaB signaling has been implicated in neurodegenerative disease, epilepsy, and neuronal plasticity. However, the cellular and molecular activity of NF-kappaB signaling within the nervous system remains to be clearly defined. Here, we show that the NF-kappaB and IkappaB homologs Dorsal and Cactus surround postsynaptic glutamate receptor (GluR) clusters at the Drosophila NMJ. We then show that mutations in dorsal, cactus, and IRAK/pelle kinase specifically impair GluR levels, assayed immunohistochemically and electrophysiologically, without affecting NMJ growth, the size of the postsynaptic density, or homeostatic plasticity. Additional genetic experiments support the conclusion that cactus functions in concert with, rather than in opposition to, dorsal and pelle in this process. Finally, we provide evidence that Dorsal and Cactus act posttranscriptionally, outside the nucleus, to control GluR density. Based upon our data we speculate that Dorsal, Cactus, and Pelle could function together, locally at the postsynaptic density, to specify GluR levels.

Selective predisposition to bacterial infections in IRAK-4-deficient children: IRAK-4-dependent TLRs are otherwise redundant in protective immunity

Human interleukin (IL) 1 receptor–associated kinase 4 (IRAK-4) deficiency is a recently discovered primary immunodeficiency that impairs Toll/IL-1R immunity, except for the Toll-like receptor (TLR) 3– and TLR4–interferon (IFN)-a/b pathways. The clinical and immunological phenotype remains largely unknown. We diagnosed up to 28 patients with IRAK-4 deficiency, tested blood TLR responses for individual leukocyte subsets, and TLR responses for multiple cytokines. The patients' peripheral blood mononuclear cells (PBMCs) did not induce the 11 non-IFN cytokines tested upon activation with TLR agonists other than the nonspecific TLR3 agonist poly(I:C). The patients' individual cell subsets from both myeloid (granulocytes, monocytes, monocyte-derived dendritic cells [MDDCs], myeloid DCs [MDCs], and plasmacytoid DCs) and lymphoid (B, T, and NK cells) lineages did not respond to the TLR agonists that stimulated control cells, with the exception of residual responses to poly(I:C) and lipopolysaccharide in MDCs and MDDCs. Most patients (22 out of 28; 79%) suffered from invasive pneumococcal disease, which was often recurrent (13 out of 22; 59%). Other infections were rare, with the exception of severe staphylococcal disease (9 out of 28; 32%). Almost half of the patients died (12 out of 28; 43%). No death and no invasive infection occurred in patients older than 8 and 14 yr, respectively. The IRAK-4–dependent TLRs and IL-1Rs are therefore vital for childhood immunity to pyogenic bacteria, particularly Streptococcus pneumoniae. Conversely, IRAK-4–dependent human TLRs appear to play a redundant role in protective immunity to most infections, at most limited to childhood immunity to some pyogenic bacteria.

Impact of hepatic vein deprivation on liver regeneration and function after major hepatectomy

BACKGROUND AND AIMS

In extended liver resections, the preservation of vascular and biliary structures of the entire remnant liver is of paramount importance. The impact of venous outflow impairment and its consequences for liver regeneration and function are still a matter of debate.

MATERIALS AND METHODS

Rats (n = 75) were subjected to a 90% partial hepatectomy (PH), to a 70% liver resection with narrowing of the hepatic outflow of an additional 20% parenchyma (70%+ PH) or to an anatomic 70% PH. Postoperatively hepatocyte proliferation (Ki-67), liver function and survival were assessed. Gene expression analysis for markers of regeneration was determined by in-house complementary (DNA) arrays and quantitative real-time polymerase chain reaction (RT-PCR).

RESULTS

Ninety percent PH led to a greater regenerative response as shown Ki-67 compared to animals with a 70%+PH (p < 0.05). However, liver function was equally impaired in both groups. Rats with 70% PH showed a greater proliferation index with less hepatic injury and better liver function. While mortality was 0% in the group of 70% PH, rats with 90% PH and 70+PH had a reduced survival of 75% (p < 0.05)

CONCLUSION

Venous outflow obstruction leads to an impairment of liver regeneration and liver function. In cases with critically small liver remnants, restoration of an adequate venous outflow may be mandatory.

MyD88, IRAK1 and TRAF6 knockdown in human chondrocytes inhibits interleukin-1-induced matrix metalloproteinase-13 gene expression and promoter activity by impairing MAP kinase activation

Interleukin-1 (IL-1) is the major prototypic proinflammatory cytokine that stimulates degradation of cartilage in arthritis by inducing prominent collagen II-degrading matrix metalloproteinase-13 (MMP-13). Nothing is known about the involvement of adaptor proteins, MyD88, IRAK1 and TRAF6 in MMP-13 regulation. Here we investigated for the first time the role of these proteins in IL-1-regulated MMP-13 expression in chondrocytes. MyD88 homodimerization inhibitory peptide diminished the expression of MMP-13 gene, promoter activity, phosphorylation of mitogen-activated protein kinases (MAPKs), c-Jun and activating protein 1 (AP-1) activity. Knockdown of MyD88, IRAK1 and TRAF6 by RNA interference (RNAi) drastically down-regulated the expression of IL-1-induced MMP-13 mRNA and protein levels and MMP-13 promoter-driven luciferase activity. Non-specific control siRNA had no effect. Mechanisms of MMP-13 inhibition involved reduced phosphorylation of ERK, p38, JNK and c-Jun as well as AP-1 transcription factor binding activity. The genetic evidence presented here demonstrates that MyD88, IRAK1 and TRAF6 proteins are crucial early mediators for the IL-1-induced MMP-13 regulation through MAPK pathways and AP-1 activity. These proteins could constitute important therapeutic targets for arthritis-associated cartilage loss by MMP-13.

Inflammatory responses associated with acute coronary syndrome up-regulate IRAK-M and induce endotoxin tolerance in circulating monocytes

Acute coronary syndrome (ACS) groups different cardiac diseases whose development is associated with inflammation. Here we have analyzed the levels of inflammatory cytokines and of members of the TLR/IRAK pathway including IRAK-M in monocytes from ACS patients classified as either UA (unstable angina), STEMI (ST-elevation myocardial infarction) or NSTEMI (non-ST-elevation myocardial infarction). Circulating monocytes from all patients, but not from healthy individuals, showed high levels of pro-inflammatory cytokines, TNF-alpha and IL-6, as well as of IRAK-M and IL-10. TLR4 was also up-regulated, but IRAK-1, IRAK-4 and MyD88 levels were similar in patients and controls. Further, we investigated the consequences of cytokines/IRAK-M expression on the innate immune response to endotoxin. Ex vivo responses to LPS were markedly attenuated in patient monocytes compared to controls. Control monocytes cultured for 6 h in supplemented medium (10% serum from ACS patients) expressed IRAK-M, and LPS stimulation failed to induce TNF-alpha and IL-6 in these cultures. Pre-incubation of the serum with a blocking anti-TNF-alpha antibody reduced this endotoxin tolerance effect, suggesting that TNF-alpha controls this phenomenon, at least partially. We show for the first time that inflammatory responses associated with ACS induce an unresponsiveness state to endotoxin challenge in circulating monocytes, which correlates with expression of IRAK-M, TLR4 and IL-10. The magnitude of this response varies according to the clinical condition (UA, STEMI or NSTEMI), and is regulated by TNF-alpha.

The X-files of inflammation: cellular mosaicism of X-linked polymorphic genes and the female advantage in the host response to injury and infection

Females as compared with males display better general health status, longevity, and improved clinical course after injury and infection. It is generally believed that the female advantage is associated with the effects of sex hormones. This review argues that the sex benefit of females during the host response is associated with polymorphism of X-linked genes and cellular mosaicism for X-linked parental alleles. Cells from females carry both parental X chromosomes (maternal, Xm; or paternal, Xp), whereas males carry only one (Xm). Because of dosage compensation and random X inactivation, half of the cells from females express either Xm or Xp. Therefore, females are cellular mosaics for their X-linked polymorphic genes. This cellular mosaicism in females represents a more adaptive and balanced cellular machinery that is advantageous during the innate immune response. Several genes encoding key metabolic and regulatory proteins reside on the X chromosome, including members of the apoptotic cascade, hormone homeostasis, glucose metabolic enzymes, superoxide-producing machinery, and the toll-like receptor/nuclear factor kappaB/c-Jun N-terminal kinase signaling pathway. Polymorphic forms of these X-linked proteins are likely to manifest in phenotypic differences in the mosaic cell populations in females and may contribute to sex-related differences in the host response to injury and infection. The unique inheritance pattern of X-linked polymorphisms and their potential confounding effects in clinical trials are also discussed; furthermore, we present potential biomarkers for studying mosaic cell populations of innate immunity.

De-regulation of common housekeeping genes in hepatocellular carcinoma

Background

Tumorigenesis is associated with changes in gene expression and involves many pathways. Dysregulated genes include "housekeeping" genes that are often used for normalization for quantitative real-time RT-PCR (qPCR), which may lead to unreliable results. This study assessed eight stages of hepatitis C virus (HCV) induced hepatocellular carcinoma (HCC) to search for appropriate genes for normalization.

Results

Gene expression profiles using microarrays revealed differential expression of most "housekeeping" genes during the course of HCV-HCC, including glyceraldehyde-3-phosphate dehydrogenase (GAPDH) and beta-actin (ACTB), genes frequently used for normalization. QPCR reactions confirmed the regulation of these genes. Using them for normalization had strong effects on the extent of differential expressed genes, leading to misinterpretation of the results.

Conclusion

As shown here in the case of HCV-induced HCC, the most constantly expressed gene is the arginine/serine-rich splicing factor 4 (SFRS4). The utilization of at least two genes for normalization is robust and advantageous, because they can compensate for slight differences of their expression when not co-regulated. The combination of ribosomal protein large 41 (RPL41) and SFRS4 used for normalization led to very similar results as SFRS4 alone and is a very good choice for reference in this disease as shown on four differentially expressed genes.

Induction of Human Monocyte Interleukin (IL)-8 by Fibrinogen through the Toll-Like Receptor Pathway

Fibrinogen, in addition to its role in coagulation, is also an acute phase protein of inflammation. Treatment of adherent human monocytes with fibrinogen increases IL-8, IL-6, and TNF-alpha, but has no effect on MCP-1, IFN-beta, or IP-10. Treatment of monocytes with fibrinogen and C5a doubles IL-8 and IL-6 production, compared to fibrinogen alone. The increase in cytokine production was accompanied by a transient increase in IL-8 mRNA and increased NF-kappaB activity. Monocytes from an IRAK-4- and two NEMO-deficient patients had 80% reduced IL-8 responses to fibrinogen. Moreover, responses to fibrinogen were blocked with anti-CD14 antibody (MY4), a subunit of the LPS receptor. The data indicate that fibrinogen alone and fibrinogen plus C5a are potent inducers of cytokine production in monocytes, and that signaling by fibrinogen is mediated through the TLR-4 pathway.

Association of interleukin-1 receptor-associated kinase M (IRAK-M) and inflammatory bowel diseases

OBJECTIVE

Inflammatory bowel diseases (IBD) have a complex genetic background. The interleukin receptor associated kinase-M (IRAK-M) is a NF-kappaB-mediated, negative regulator of Toll-like receptor (TLR) signaling. A functional mutation in a negative regulator might induce impaired endotoxin tolerance and increased inflammatory responses. IRAK-M is situated on chromosome 12q14, a susceptibility locus for IBD, which makes it a good candidate gene. The objective of the study was to analyze a large cohort of IBD patients for the association between IBD and IRAK-M.

MATERIAL AND METHODS

A total of 542 patients with IBD (309 Crohn's disease (CD), 233 ulcerative colitis (UC)) and 305 controls were studied. Two single nucleotide polymorphisms (V147I and V270I) and six microsatellite markers were evaluated using association analysis and the haplotype sharing statistic. Results were stratified for CARD15 mutations R702W, G908R and 1007fsinsC.

RESULTS

No significant differences in IRAK-M allele frequencies were observed between IBD, UC, CD or subgroups of CD or UC and controls. Five out of 36 UC patients (13.9%) with an IBD-associated CARD15 mutation were carriers versus 2/167 (1.2%) in non-carriers (OR 13.1, 95% CI 1.0-164.5). No interaction was observed for CD.

CONCLUSIONS

No evidence was found to suggest an association between IBD, CD, UC or subsets of CD and UC and IRAK-M. However, an interaction was found between IRAK-M and CARD15 in UC patients. In CARD15 mutant patients, the production of IRAK-M upon stimulation might be impaired. Further studies are needed to determine whether an impaired negative regulation of the TLR-signaling pathway might be partly responsible for the development of IBD.

Cerebellar gene expression profiles of mouse models for Rett syndrome reveal novel MeCP2 targets

Background

MeCP2, methyl-CpG-binding protein 2, binds to methylated cytosines at CpG dinucleotides, as well as to unmethylated DNA, and affects chromatin condensation. MECP2 mutations in females lead to Rett syndrome, a neurological disorder characterized by developmental stagnation and regression, loss of purposeful hand movements and speech, stereotypic hand movements, deceleration of brain growth, autonomic dysfunction and seizures. Most mutations occur de novo during spermatogenesis. Located at Xq28, MECP2 is subject to X inactivation, and affected females are mosaic. Rare hemizygous males suffer from a severe congenital encephalopathy.

Methods

To identify the pathways mis-regulated by MeCP2 deficiency, microarray-based global gene expression studies were carried out in cerebellum of Mecp2 mutant mice. We compared transcript levels in mutant/wildtype male sibs of two different MeCP2-deficient mouse models at 2, 4 and 8 weeks of age. Increased transcript levels were evaluated by real-time quantitative RT-PCR. Chromatin immunoprecipitation assays were used to document in vivo MeCP2 binding to promoter regions of candidate target genes.

Results

Of several hundred genes with altered expression levels in the mutants, twice as many were increased than decreased, and only 27 were differentially expressed at more than one time point. The number of misregulated genes was 30% lower in mice with the exon 3 deletion (Mecp2^tm1.1Jae) than in mice with the larger deletion (Mecp2^tm1.1Bird). Between the mutants, few genes overlapped at each time point. Real-time quantitative RT-PCR assays validated increased transcript levels for four genes: Irak1, interleukin-1 receptor-associated kinase 1; Fxyd1, phospholemman, associated with Na, K-ATPase;Reln, encoding an extracellular signaling molecule essential for neuronal lamination and synaptic plasticity; and Gtl2/Meg3, an imprinted maternally expressed non-translated RNA that serves as a host gene for C/D box snoRNAs and microRNAs. Chromatin immunoprecipitation assays documented in vivo MeCP2 binding to promoter regions of Fxyd1, Reln, and Gtl2.

Conclusion

Transcriptional profiling of cerebellum failed to detect significant global changes in Mecp2-mutant mice. Increased transcript levels of Irak1, Fxyd1, Reln, and Gtl2 may contribute to the neuronal dysfunction in MeCP2-deficient mice and individuals with Rett syndrome. Our data provide testable hypotheses for future studies of the regulatory or signaling pathways that these genes act on.

IRAK-M is involved in the pathogenesis of early-onset persistent asthma

Asthma is a multifactorial disease influenced by genetic and environmental factors. In the past decade, several loci and >100 genes have been found to be associated with the disease in at least one population. Among these loci, region 12q13-24 has been implicated in asthma etiology in multiple populations, suggesting that it harbors one or more asthma susceptibility genes. We performed linkage and association analyses by transmission/disequilibrium test and case-control analysis in the candidate region 12q13-24, using the Sardinian founder population, in which limited heterogeneity of pathogenetic alleles for monogenic and complex disorders as well as of environmental conditions should facilitate the study of multifactorial traits. We analyzed our cohort, using a cutoff age of 13 years at asthma onset, and detected significant linkage to a portion of 12q13-24. We identified IRAK-M as the gene contributing to the linkage and showed that it is associated with early-onset persistent asthma. We defined protective and predisposing SNP haplotypes and replicated associations in an outbred Italian population. Sequence analysis in patients found mutations, including inactivating lesions, in the IRAK-M coding region. Immunohistochemistry of lung biopsies showed that IRAK-M is highly expressed in epithelial cells. We report that IRAK-M is involved in the pathogenesis of early-onset persistent asthma. IRAK-M, a negative regulator of the Toll-like receptor/IL-1R pathways, is a master regulator of NF- kappa B and inflammation. Our data suggest a mechanistic link between hyperactivation of the innate immune system and chronic airway inflammation and indicate IRAK-M as a potential target for therapeutic intervention against asthma.

Essential role of IRAK-4 protein and its kinase activity in Toll-like receptor-mediated immune responses but not in TCR signaling

Interleukin-1 receptor-associated kinase 4 (IRAK-4) was reported to be essential for the Toll-like receptor (TLR)- and T cell receptor (TCR)-mediated signaling leading to the activation of nuclear factor kappaB (NF-kappaB). However, the importance of kinase activity of IRAK family members is unclear. In this study, we investigated the functional role of IRAK-4 activity in vivo by generating mice carrying a knockin mutation (KK213AA) that abrogates its kinase activity. IRAK-4(KN/KN) mice were highly resistant to TLR-induced shock response. The cytokine production in response to TLR ligands was severely impaired in IRAK-4(KN/KN) as well as IRAK-4(-/-) macrophages. The IRAK-4 activity was essential for the activation of signaling pathways leading to mitogen-activated protein kinases. TLR-induced IRAK-4/IRAK-1-dependent and -independent pathways were involved in early induction of NF-kappaB-regulated genes in response to TLR ligands such as tumor necrosis factor alpha and IkappaBzeta. In contrast to a previous paper (Suzuki, N., S. Suzuki, D.G. Millar, M. Unno, H. Hara, T. Calzascia, S. Yamasaki, T. Yokosuka, N.J. Chen, A.R. Elford, et al. 2006. Science. 311:1927-1932), the TCR signaling was not impaired in IRAK-4(-/-) and IRAK-4(KN/KN) mice. Thus, the kinase activity of IRAK-4 is essential for the regulation of TLR-mediated innate immune responses.

A critical role for IRAK4 kinase activity in Toll-like receptor-mediated innate immunity

IRAK4 is a member of IL-1 receptor (IL-1R)–associated kinase (IRAK) family and has been shown to play an essential role in Toll-like receptor (TLR)–mediated signaling. We recently generated IRAK4 kinase-inactive knock-in mice to examine the role of kinase activity of IRAK4 in TLR-mediated signaling pathways. The IRAK4 kinase–inactive knock-in mice were completely resistant to lipopolysaccharide (LPS)- and CpG-induced shock, due to impaired TLR-mediated induction of proinflammatory cytokines and chemokines. Although inactivation of IRAK4 kinase activity did not affect the levels of TLR/IL-1R–mediated nuclear factor κB activation, a reduction of LPS-, R848-, and IL-1–mediated mRNA stability contributed to the reduced cytokine and chemokine production in bone marrow–derived macrophages from IRAK4 kinase–inactive knock-in mice. Both TLR7- and TLR9-mediated type I interferon production was abolished in plasmacytoid dendritic cells isolated from IRAK4 knock-in mice. In addition, influenza virus–induced production of interferons in plasmacytoid DCs was also dependent on IRAK4 kinase activity. Collectively, our results indicate that IRAK4 kinase activity plays a critical role in TLR-dependent immune responses.

Neutrophil Elastase Up-Regulates Cathepsin B and Matrix Metalloprotease-2 Expression

Neutrophil elastase (NE) activity is increased in many diseases. Other families of proteases, including cathepsins and matrix metalloproteases (MMPs), are also present at elevated levels in similar disease conditions. We postulated that NE could induce expression of cathepsins and MMPs in human macrophages. NE exposure resulted in macrophages, producing significantly greater amounts of cathepsin B and latent and active MMP-2. Cathepsin B and MMP-2 activities were decreased in Pseudomonas-infected NE knockout mice compared with wild-type littermates. We also demonstrate that NE can activate NF-kappaB in macrophages, and inhibition of NF-kappaB resulted in a reduction of NE-induced cathepsin B and MMP-2. Also, inhibition of TLR-4 or transfection of macrophages with dominant-negative IL-1R-associated kinase-1 resulted in a reduction of NE-induced cathepsin B and MMP-2. This study describes for the first time a novel hierarchy among proteases whereby a serine protease up-regulates expression of MMPs and cathepsins. This has important implications for therapeutic intervention in protease-mediated diseases.

Role of IRAK4 and IRF3 in the control of intracellular infection withChlamydia pneumoniae

TLR signal transduction involves a MyD88-mediated pathway, which leads to recruitment of the IL-1 receptor (IL-1R)-associated kinase 4 (IRAK4) and Toll/IL-1R translation initiation region domain-containing adaptor-inducing IFN-beta-mediated pathway, resulting in the activation of IFN regulatory factor (IRF)3. Both pathways can lead to expression of IFN-beta. TLR-dependent and -independent signals converge in the TNF receptor-associated factor 6 (TRAF6) adaptor, which mediates the activation of NF-kappaBeta. Infection of murine bone marrow-derived macrophages (BMM) with Chlamydia pneumoniae induces IFN-alpha/beta- and NF-kappaBeta-dependent expression of IFN-gamma, which in turn, will control bacterial growth. The role of IRAK4 and IRF3 in the regulation of IFN-alpha/beta expression and NF-kappaBeta activation was studied in C. pneumoniae-infected BMM. We found that levels of IFN-alpha, IFN-beta, and IFN-gamma mRNA were reduced in infected IRAK4(-/-) BMM compared with wild-type (WT) controls. BMM also showed an IRAK4-dependent growth control of C. pneumoniae. No increased IRF3 activation was detected in C. pneumoniae-infected BMM. Similar numbers of intracellular bacteria, IFN-alpha, and IFN-gamma mRNA titers were observed in C. pneumoniae-infected IRF3(-/-) BMM. On the contrary, IFN-beta(-/-) BMM showed lower IFN-alpha and IFN-gamma mRNA levels and higher bacterial titers compared with WT controls. C. pneumoniae infection-induced activation of NF-kappaBeta and expression of proinflammatory cytokines were shown to be TRAF6-dependent but did not require IRAK4 or IRF3. Thus, our data indicate that IRAK4, but not IRF3, controls C. pneumoniae-induced IFN-alpha and IFN-gamma secretion and bacterial growth. IRAK4 and IRF3 are redundant for infection-induced NF-kappaB activation, which is regulated by TRAF6.

The association between innate immunity gene (IRAK1) and C-reactive protein in the Diabetes Heart Study

Evidence suggests that interleukin-1 receptor-associated kinase-1 (IRAK1), fundamental in the toll-like receptor pathway (TLR), may play a more specific role in atherosclerosis.

METHODS

Caucasian women (N=529) and men (N=467) from the Diabetes Heart Study (DHS) were genotyped at four loci within the IRAK1 gene located on the X chromosome. Generalized estimating equations (GEE1) were used to evaluate association with C-reactive protein (CRP) for both single SNP and haplotype analyses.

RESULTS

For each SNP genotyped, Caucasian women carrying one or two copies of the variant allele had greater CRP concentrations than those carrying the common genotype in both crude and adjusted models. There were 2 major haplotypes, CTTT (82%) and its complement TCCG (13%). The presence of the TCCG haplotype was associated with greater CRP concentrations in Caucasian women (p=0.0004) and this relationship was maintained after adjustment for age, BMI, smoking, diabetes, and cholesterol-lowering therapy (p=0.003). There was no association between CRP and IRAK1 SNPs in Caucasian men.

CONCLUSION

Variation in the IRAK1 gene is associated with CRP concentration in Caucasian women in DHS. Further studies are needed to reproduce the current finding and to understand the biological relationship between IRAK1 and inflammation related to atherosclerosis.

Toll-like receptor 2 ligand mediates the upregulation of angiogenic factor, vascular endothelial growth factor and interleukin-8/CXCL8 in human rheumatoid synovial fibroblasts

Rheumatoid arthritis (RA) is characterized by infiltrations of inflammatory cells accompanied by neovascularization in the joint. We hypothesized that cell activation via the toll-like receptor (TLR) may be involved in the induction of angiogenic molecules, which are relevant to the pathogenesis of RA. RA fibroblast like synoviocytes (FLS) were stimulated with TLR-2 ligand bacterial peptidoglycan (PGN), TLR-4 ligand lipopolysaccharide (LPS) and various cytokines. Vascular endothelial growth factor (VEGF) and IL-8 were measured by ELISA in culture supernatants; mRNA levels were assessed by RT-PCR and real time PCR. The levels of TLR-2, VEGF and IL-8 were analyzed by dual immunohistochemistry in RA synovium and compared with osteoarthritis (OA). Regulation of MyD88, IRAK4, IRAK1, IRAK-M and TRAF-6 mRNA expression levels by PGN were analyzed by RT-PCR. Phosphorylation of I kappa B alpha was evaluated by western blotting. Levels of VEGF and IL-8 were upregulated in culture supernatants of RA FLS stimulated with PGN, similar to the levels of IL-1beta and IL-17 stimulation. Neutralization of TLR-2 with a blocking monoclonal antibody significantly reduced both VEGF and IL-8 levels (P<0.05), which reflected the functional relevance of TLR-2 activation to the induction of VEGF and IL-8 production. Downstream intracellular signaling following TLR-2 stimulation involved MyD88-IRAK-4-TRAF-6 pathways, resulting in NF-kappaB activation. Thus, TLR-2 activation in RA FLS by microbial constituents could be involved in the induction of VEGF and IL-8 and thereby promote inflammation either directly or via angiogenesis. This possibly contributes to the perpetuation of synovitis in patients with RA.

The death domain of IRAK-1: an oligomerization domain mediating interactions with MyD88, Tollip, IRAK-1, and IRAK-4

Ligand binding in the Toll-like/interleukin-1 receptor family results in the recruitment of an intracellular signaling complex. IRAK-1, which is centrally involved in this complex, is able to homo-oligomerize and to bind to Tollip and the adapters MyD88 and IRAK-4. The interactions of IRAK-1 with MyD88 or Tollip are mediated by the N-terminal part of IRAK-1, containing the death domain with the highly conserved threonine at position 66 (T66). Mutation of this amino acid into alanine or aspartic acid stabilized binding to MyD88, Tollip, and IRAK-4, allowing the definitive experimental proof, that all these interactions are mediated by the death domain of IRAK-1. Homo-oligomerization of IRAK-1, which is mediated by the death domain too, is not affected by mutation of T66. Finally, mutation of IRAK-1 at T66 not only allowed stable binding to the signaling adapters, but also enhanced its signaling capacity.

IRAK-4 mutation (Q293X): rapid detection and characterization of defective post-transcriptional TLR/IL-1R responses in human myeloid and non-myeloid cells

Innate immunodeficiency has recently been reported as resulting from the Q293X IRAK-4 mutation with consequent defective TLR/IL-1R signaling. In this study we report a method for the rapid allele-specific detection of this mutation and demonstrate both cell type specificity and ligand specificity in defective IL-1R-associated kinase (IRAK)-4-deficient cellular responses, indicating differential roles for this protein in human PBMCs and primary dermal fibroblasts and in LPS, IL-1beta, and TNF-alpha signaling. We demonstrate transcriptional and post-transcriptional defects despite NF-kappaB signaling and intact MyD88-independent signaling and propose that dysfunctional complex 1 (IRAK1/TRAF6/TAK1) signaling, as a consequence of IRAK-4 deficiency, generates specific defects in MAPK activation that could underpin this patient's innate immunodeficiency. These studies demonstrate the importance of studying primary human cells bearing a clinically relevant mutation; they underscore the complexity of innate immune signaling and illuminate novel roles for IRAK-4 and the fundamental importance of accessory proinflammatory signaling to normal human innate immune responses and immunodeficiencies.

Solving the IRAK-4 enigma: application of kinase-dead knock-in mice

Interleukin-1 receptor-associated kinase (IRAK-4) is an essential component of the signal transduction complex downstream of the interleukin (IL)-1- and Toll-like receptors. Though regarded as the first kinase in the signaling cascade, the role of IRAK-4 kinase activity versus its scaffold function has been controversial. In order to investigate the role of IRAK-4 kinase function in vivo, we generated "knock-in" mice where the wild-type IRAK-4 gene is replaced with a mutant gene encoding kinase-deficient IRAK-4 protein (IRAK-4 KD). IRAK-4 kinase is rendered inactive by mutating the conserved lysine residues in the ATP pocket essential for coordinating ATP. Analyses of embryonic fibroblasts and macrophages obtained from IRAK-4 KD mice demonstrated lack of cellular responsiveness to stimulation with IL-1beta or Toll-like receptor 4 (TLR4) and TLR7 agonists. IRAK-4 KD cells were severely impaired in NF-kappaB, JNK, and p38 activation in response to IL-1beta or TLR7 ligand. In addition, activation of JNK and p38 was affected in lipopolysaccharide (LPS)-stimulated IRAK-4 KD macrophages. As a consequence, IL-1 receptor/TLR4/TLR7-mediated production of cytokines and chemokines was largely absent in these cells. Additionally, microarray analysis identified IL-1beta response genes and revealed that the induction of IL-1beta-responsive mRNAs is largely ablated in IRAK-4 KD cells. In summary, our results suggest that IRAK-4 kinase activity plays a critical role in IL-1R-, TLR4-, and TLR7-mediated induction of inflammatory responses.

Global correlation of genome and transcriptome changes in classical Hodgkin lymphoma

To identify genes involved in the pathogenesis of classical Hodgkin lymphoma (cHL), we performed serial analysis of gene expression (SAGE) and array-based comparative genomic hybridization (aCGH). Comparison of SAGE libraries of cHL cell lines L428 and L1236 with that of germinal centre B cells revealed consistent overexpression of only 14 genes. In contrast, 141 genes were downregulated in both cHL cell lines, including many B cell and HLA genes. aCGH revealed gain of 2p, 7p, 9p, 11q and Xq and loss of 4q and 11q. Eighteen percent of the differentially expressed genes mapped to regions with loss or gain and a good correlation was observed between underexpression and loss or overexpression and gain of DNA. Remarkably, gain of 2p and 9p did not correlate with increased expression of the proposed target genes c-REL and JAK2. Downregulation of many genes within the HLA region also did not correlate with loss of DNA. FSCN1 and IRAK1 mapping at genomic loci (7p and Xq) that frequently showed gain were overexpressed in cHL cell lines and might be involved in the pathogenesis of cHL.

Interleukin-1 (IL-1)-induced TAK1-dependent Versus MEKK3-dependent NFkappaB activation pathways bifurcate at IL-1 receptor-associated kinase modification

Interleukin-1 (IL-1) receptor-associated kinase (IRAK) is phosphorylated after it is recruited to the receptor, subsequently ubiquitinated, and eventually degraded upon IL-1 stimulation. Although a point mutation changing lysine 134 to arginine (K134R) in IRAK abolished IL-1-induced IRAK ubiquitination and degradation, mutations of serines and threonines adjacent to lysine 134 to alanines ((S/T)A (131-144)) reduced IL-1-induced IRAK phosphorylation and abolished IRAK ubiquitination. Through the study of these IRAK modification mutants, we uncovered two parallel IL-1-mediated signaling pathways for NFkappaB activation, TAK1-dependent and MEKK3-dependent, respectively. These two pathways bifurcate at the level of IRAK modification. The TAK1-dependent pathway leads to IKKalpha/beta phosphorylation and IKKbeta activation, resulting in classical NFkappaB activation through IkappaBalpha phosphorylation and degradation. The TAK1-independent MEKK3-dependent pathway involves IKKgamma phosphorylation and IKKalpha activation, resulting in NFkappaB activation through IkappaBalpha phosphorylation and subsequent dissociation from NFkappaB but without IkappaBalpha degradation. These results provide significant insight to our further understanding of NFkappaB activation pathways.

Toll-like receptors are part of the innate immune defense system of sponges (demospongiae: Porifera)

During evolution and with the emergence of multicellular animals, the need arose to ward off foreign organisms that threaten the integrity of the animal body. Among many different receptors that participate in the recognition of microbial invaders, toll-like receptors (TLRs) play an essential role in mediating the innate immune response. After binding distinct microbial components, TLRs activate intracellular signaling cascades that result in an induced expression of diverse antimicrobial molecules. Because sponges (phylum Porifera) are filter feeders, they are abundantly exposed to microorganisms that represent a potential threat. Here, we describe the identification, cloning, and deduced protein sequence from 3 major elements of the poriferan innate response (to bacterial lipopeptides): the TLR, the IL-1 receptor-associated kinase-4-like protein (IRAK-4l), and a novel effector caspase from the demosponge Suberites domuncula. Each molecule shares significant sequence similarity with its homologues in higher Metazoa. Sequence homologies were found in particular within the family-specific domains toll/interleukin-1 receptor/resistance (TLR family), Ser/Thr/Tyr kinase domain (IRAK family), and CASc (caspase family). In addition, in situ hybridization and immunohistological analyses revealed an abundance of SDTLR (TLR) transcripts in epithelial layers of the sponge surface (exopinacoderm and endopinacoderm). Furthermore, it is shown that both SDTLR and SDIRAK-4 like (IRAK) are expressed constitutively, regardless of treatment with synthetic triacyl lipopeptide Pam(3)Cys-Ser-(Lys)(4). In contrast, SDCASL (caspase) expression is highly Pam(3)Cys-Ser-(Lys)(4) inducible. However, blocking of the lipopeptide with recombinant TLR prior to its application completely prevented the induced expression of this poriferan caspase. These results underscore that the phylogenetically oldest extant metazoan phylum is provided already with the signaling pathways of the antimicrobial host-defense system of Metazoa.

Glycine blunts transplantative liver ischemia-reperfusion injury by downregulating interleukin 1 receptor associated kinase-4

AIM

To determine whether glycine could downregulate interleukin 1 receptor associated kinase-4 (IRAK-4) expression to interfere with lipopolysaccharides (LPS) signal transduction and blunt transplantative liver ischemia-reperfusion injury (I/RI).

METHODS

SD rats were randomly divided into two groups: donor animals of the glycine group (n=40) were given glycine (1.5 mL; 300 mmol/L, iv) 1 h before harvest, and the control group were treated with 1.5 mL physiological saline (n= 40). Orthotopic liver transplantation was then performed according to the Kamada technique. Ten animals in each group were followed up for 7 d after surgery to assess survival. The remaining animals in each group were divided into 3 subgroups (n=10) at 1h, 2 h and 6 h after portal vein reperfusion. Levels of LPS, serum aspartate aminotransferase (AST), alanine aminotransferase (ALT) and total bilirubin in portal circulation, as well as IRAK-4 and TNF-alpha expression, NF-kappaB transcriptional activity and morphological study of liver tissues were analyzed.

RESULTS

Reperfusion resulted in a significant elevation of LPS concentrations in each group persisting to the end of our study. However, glycine, which led to improved survival rate and liver function, significantly alleviated liver parenchyma cell damage by downregulating IRAK-4, TNF-alpha expression and NF-kappaB transcriptional activity compared with the control group.

CONCLUSION

Glycine can attenuate hepatic I/RI by downregulating IRAK-4 to interfere with LPS signal transduction.