Precipitation of Soluble Uric Acid Is Necessary for In Vitro Activation of the NLRP3 Inflammasome in Primary Human Monocytes.

OBJECTIVE: To investigate the effects of soluble uric acid (UA) on expression and activation of the NOD-like receptor (NLR) pyrin domain containing protein 3 (NLRP3) inflammasome in human monocytes to elucidate the role of hyperuricemia in the pathogenesis of gout. METHODS: Primary human monocytes and the THP-1 human monocyte cell line were used to determine the effects of short- and longterm exposure to UA on activation of the NLRP3 inflammasome and subsequent interleukin 1ß (IL-1ß) secretion by ELISA and cell-based assays. Expression of key NLRP3 components in monocytes from patients with a history of gout were analyzed by quantitative PCR. RESULTS: Precipitation of UA was required for activation of the NLRP3 inflammasome and subsequent release of IL-1ß in human monocytes. Neither monosodium urate (MSU) crystals nor soluble UA had any effect on activation of the transcription factor, nuclear factor-κB. Prolonged exposure of monocytes to soluble UA did not alter these responses. However, both MSU crystals and soluble UA did result in a 2-fold increase in reactive oxygen species. Patients with gout (n = 15) had significantly elevated serum UA concentrations compared to healthy individuals (n = 16), yet secretion of IL-1ß and expression of NLRP3 inflammasome components in monocytes isolated from these patients were not different from those of healthy controls. CONCLUSION: Despite reports indicating that soluble UA can prime and activate the NLRP3 inflammasome in human peripheral blood mononuclear cells, precipitation of soluble UA into MSU crystals is essential for in vitro NLRP3 signaling in primary human monocytes.

Secretion of IL-1ß From Monocytes in Gout Is Redox Independent.

The pro-inflammatory cytokine interleukin-1ß (IL-1ß) plays important roles in immunity but is also implicated in autoimmune disease. The most well-established mechanism of IL-1ß secretion is via activation of the NOD-like receptor family pyrin domain containing-3 (NLRP3) inflammasome which requires an initial priming signal followed by an activating signal. However, the precise mechanism by which the inflammasome is activated remains unclear. The role of reactive oxygen species (ROS) in this process is contradictory, with some studies suggesting that ROS are crucial while others describe opposite effects. In this study, we evaluated the effects of oxidative stress on IL-1ß secretion. Gout is a disease driven solely by IL-1ß secretion in response to monosodium urate (MSU) crystals which form during periods of hyperuricemia and thus presents an opportunity to study factors contributing to IL-1ß secretion. Sera and monocytes were isolated from patients with gout to determine whether differences in antioxidant status could explain the susceptibility of these individuals to gout attacks. In addition, sera and monocytes were collected from patients with chronic kidney disease (CKD) for comparison as this condition is associated with high levels of oxidative stress and disturbances in serum uric acid levels. There were differences in some aspects of antioxidant defenses in gout patients and these were mainly due to higher serum uric acid. Monocytes from gout patients were more responsive to priming, but not activation, of the NLRP3 inflammasome. However, expression of the components of the NLRP3 inflammasome were unaffected by priming or activation of the inflammasome, nor were these expression levels differentially regulated in gout patients. Inhibition of ROS by N-Acetyl Cysteine inhibited TLR2-induced priming of the NLRP3 inflammasome, but had no effect on MSU-induced activation. Together these findings demonstrate that oxidative stress only affects priming of the NLRP3 inflammasome but does not influence activation.

Engineering of TIMP-3 as a LAP-fusion protein for targeting to sites of inflammation.

Tissue inhibitor of metalloproteinase (TIMP)-3 is a natural inhibitor of a range of enzymes that degrade connective tissue and are involved in the pathogenesis of conditions such as arthritis and cancer. We describe here the engineering of TIMP-3 using a novel drug-delivery system known as the 'LAP technology'. This involves creating therapeutic proteins in fusion with the latency-associated peptide (LAP) from the cytokine TGF-? to generate proteins that are biologically inactive until cleavage of the LAP to release the therapy. LAP-TIMP-3 was successfully expressed in mammalian cells and the presence of the LAP resulted in a 14-fold increase in the quantity of recombinant TIMP-3 produced. LAP-TIMP-3 was latent until release from the LAP by treatment with matrix metalloproteinase when it could inhibit proteases of the adamalysins and adamalysins with thrombospondin motifs families, but not matrix metalloproteinases, indicating that this version of TIMP-3 is a more specific inhibitor than the native protein. There was sufficient protease activity in synovial fluid from human joints with osteoarthritis to release TIMP-3 from the LAP fusion. These results demonstrate the potential for development of TIMP-3 as a novel therapy for conditions where upregulation of catabolic enzymes are part of the pathology.

Pattern recognition receptors as potential therapeutic targets in inflammatory rheumatic disease.

The pattern recognition receptors of the innate immune system are part of the first line of defence against pathogens. However, they also have the ability to respond to danger signals that are frequently elevated during tissue damage and at sites of inflammation. Inadvertent activation of pattern recognition receptors has been proposed to contribute to the pathogenesis of many conditions including inflammatory rheumatic diseases. Prolonged inflammation most often results in pain and damage to tissues. In particular, the Toll-like receptors and nucleotide-binding oligomerisation domain-like receptors that form inflammasomes have been postulated as key contributors to the inflammation observed in rheumatoid arthritis, osteoarthritis, gout and systemic lupus erythematosus. As such, there is increasing interest in targeting these receptors for therapeutic treatment in the clinic. Here the role of pattern recognition receptors in the pathogenesis of these diseases is discussed, with an update on the development of interventions to modulate the activity of these potential therapeutic targets.

Increased disulphide dimer formation of latent associated peptide fusions of TGF-ß by addition of L-cystine.

The development of novel protein therapeutics relies on the ability to express appreciable amounts of correctly folded recombinant proteins. Latent IFN-ß is engineered using the latency-associated peptide (LAP) of transforming growth factor ß1 (TGF-ß1) to maintain IFN-ß in a biologically inactive form until such time as it is released at sites of inflammation by matrix metalloproteinase activity (see Adams et al., 2003). CHO cells cultured in suspension were used for expression of latent IFN-ß to allow medium scale transient transfection. However, the recombinant protein expressed in this system consisted of a mixture of properly linked disulphide dimers and monomers. The ratio of dimer:monomer produced could be significantly altered towards increased dimer production by the addition of L-cystine to the CHO culture medium. The total yield of latent IFN-ß was increased by co-transfection of plasmid coding for the simian virus (SV) 40 large T antigen to the plasmid with the SV40 origin of replication expressing latent IFN-ß DNA. These results provide valuable new insights for developing protocols to produce substantial quantities of latent cytokine dimers in CHO cells in suspension.

Inactivation of the complement anaphylatoxin C5a by secreted products of parasitic nematodes.

Given the importance of the complement anaphylatoxins in cellular recruitment during infection, the ability of secreted products from larval stages of Brugia malayi and Trichinella spiralis to influence C5a-mediated chemotaxis of human peripheral blood granulocytes in vitro was examined. Secreted products from B. malayi microfilariae almost completely abolished chemotaxis. This inhibition was blocked by phenylmethylsulphonyl fluoride, indicating the presence of a serine protease, which was subsequently shown to cleave C5a. In contrast, secreted products from T. spiralis infective larvae showed modest inhibition of C5a-mediated granulocyte chemotaxis, and this was blocked by potato carboxypeptidase inhibitor, an inhibitor of several metallocarboxypeptidases. Adult and larval stages of both parasites were demonstrated to secrete carboxypeptidases which cleaved hippuryl-L-lysine and hippuryl-L-arginine, and the T. spiralis enzyme was partially characterised. The data are discussed with reference to inflammation in parasitic nematode infection.

Pasteurellaceae ComE1 proteins combine the properties of fibronectin adhesins and DNA binding competence proteins.

A novel fibronectin-binding protein from Pasteurella multocida (PM1665) that binds to the fibronectin type III(9-10) modules via two helix-hairpin-helix motifs has recently been described [1]. This protein shares homology with competence-related DNA-binding and uptake proteins (ComEA and ComE) from Gram-positive and Gram-negative bacteria. Here, we show that recombinant PM1665 (now designated ComE1) also binds to DNA through the same helix-hairpin-helix motifs required for fibronectin-binding. This binding to DNA is non sequence-specific and is confined to double-stranded DNA. We have cloned and expressed ComE1 proteins from five members of the Pasteurellaceae in order to further investigate the function(s) of these proteins. When expressed as recombinant GST-fusion proteins, all of the homologues bound both to fibronectin and to double-stranded DNA. Inactivation of the gene encoding the ComE1 homologue in Actinobacillus pleuropneumoniae indicates major roles for these proteins in at least two processes: natural transformation, and binding of bacteria to fibronectin.

Novel adhesin from Pasteurella multocida that binds to the integrin-binding fibronectin FnIII9-10 repeats.

Phage display screening with fragmented genomic DNA from the animal pathogen Pasteurella multocida has identified a gene encoding a putative fibronectin binding protein (19). Homologues of this gene (PM1665) are found in all other sequenced members of the Pasteurellaceae. Gene PM1665 has been cloned, and the protein has been expressed. Recombinant PM1665 protein binds to both soluble and immobilized fibronectin and is unique in that it interacts with the integrin-binding fibronectin type III (FnIII) repeats FnIII(9-10) and not, as is the case for almost all other fibronectin adhesins, to the N-terminal type I repeats. Surface plasmon resonance analysis revealed a complex binding mechanism with a K(D) (equilibrium dissociation constant) of 150 nM +/- 70 nM. Bioinformatics analysis suggests that the PM1665 protein contains two helix-hairpin-helix (HhH) motifs, and truncation mutation studies have identified the binding site in the protein as a combination of these two HhH motifs in conjunction with a conserved amino acid motif, VNINTA. We have shown that the PM1665 protein is on the cell surface and that binding of P. multocida to fibronectin is almost completely inhibited by anti-PM1665 antiserum. These results support the hypothesis that the PM1665 protein is a member of a new family of fibronectin binding adhesins that are important in the adhesion of P. multocida to fibronectin.

Comparative functional genomic analysis of Pasteurellaceae adhesins using phage display.

The Pasteurellaceae contain a number of important animal pathogens. Although related, the various members of this family cause a diversity of pathology in a wide variety of organ systems. Adhesion is an important virulence factor in bacterial infections. Surprisingly little is known about the adhesins of the Pasteurellaceae. To attempt to identify the genes coding for adhesins to some key components of the hosts extracellular matrix molecules, phage display libraries of fragmented genomic DNA from Haemophilus influenzae, Actinobacillus pleuropneumoniae, Pasteurella multocida and Aggregatibacter actinomycetemcomitans, were prepared in the phage display vector pG8SAET. The libraries were screened against human or porcine fibronectin, serum albumin or a commercial extracellular matrix containing type IV collagen, laminin and heparin sulphate. Four genes encoding putative adhesins were identified. These genes code for: (i) a 34 kDa human serum albumin binding protein from Haemophilus influenzae; (ii) a 12.8 kDa fibronectin-binding protein from Pasteurella multocida; (iii) a 13.7 kDa fibronectin-binding protein from A. actinomycetemcomitans; (iv) a 9.5 kDa serum albumin-binding protein from A. pleuropneumoniae. None of these genes have previously been proposed to code for adhesins. The applications of phage display with whole bacterial genomes to identify genes encoding novel adhesins in this family of bacteria are discussed.

Phage display in the study of infectious diseases.

Microbial infections are dependent on the panoply of interactions between pathogen and host and identifying the molecular basis of such interactions is necessary to understand and control infection. Phage display is a simple functional genomic methodology for screening and identifying protein-ligand interactions and is widely used in epitope mapping, antibody engineering and screening for receptor agonists or antagonists. Phage display is also used widely in various forms, including the use of fragment libraries of whole microbial genomes, to identify peptide-ligand and protein-ligand interactions that are of importance in infection. In particular, this technique has proved successful in identifying microbial adhesins that are vital for colonization.

Immune responses of locusts to challenge with the pathogenic fungus Metarhizium or high doses of laminarin.

Two isolates of Metarhizium anisopliae var acridum were tested for their effects on the locust immune system and for comparison with the effects of challenge by injection with laminarin. Isolate IMI 330189 (referred to hereafter as Met 189) is highly pathogenic whether applied topically as conidia or injected as blastospores. However, isolate ARSEF 728 (referred to hereafter as Met 728) is pathogenic only when injected as blastospores, suggesting that the lack of pathogenicity of topically applied conidia from this isolate is due to a failure to penetrate the insect cuticle and gain access to the haemocoel. After topical application of conidia from Met 189, no activation of prophenoloxidase is detected, but injection of blastospores from Met 189 brings about a transient increase in phenoloxidase activity in the haemolymph in both adult locusts and 5th instar nymphs, although this does not prevent fungal-induced mortality. Co-injection of adipokinetic hormone-I (AKH-I) with blastospores prolongs the activation of prophenoloxidase in the haemolymph of adult locusts, and enhances it in nymphs. It is argued that the lack of activation of prophenoloxidase in nymphs shown previously (Mullen, L., Goldsworthy, G., 2003. Changes in lipophorins are related to the activation of phenoloxidase in the haemolymph of Locusta migratoria in response to injection of immunogens. Insect Biochemistry and Molecular Biology 33, 661-670), reflects differences in the sensitivity of the immune system between adults and nymphs rather than distinct qualitative differences, and this is confirmed in this study by the demonstration that doses of laminarin higher than those used previously (>or=100 microg) do activate the prophenoloxidase cascade in 5th instar nymphs. Nodules are formed in locusts of all ages in response to fungal infection or injection of laminarin, although there is wide variation in the number, size and distribution of nodules formed. During the examination of 5th instar nymphs for nodule formation, a previously unknown phenomenon was observed in which the salivary glands melanise in response to injections of blastospores or high doses of laminarin. In c. 85% of such nymphs, this reaction is so strong that the whole salivary gland is intensely black. Such a response is not observed in the salivary glands of mature adult locusts.

Induced hyperlipaemia and immune challenge in locusts.

Injections of immunogens, such as beta-1,3-glucan or lipopolysaccharide (LPS), bring about a marked hyperlipaemia with associated changes in lipophorins and apolipophorin-III in the haemolymph of Locusta migratoria. These changes are similar to those observed after injection of adipokinetic hormone (AKH). The possibility that endogenous AKH is released as part of the response to these immunogens is investigated using passive immunisation against AKH-I, and measurement of AKH-I titre in the haemolymph after injection of immunogens. The data presented show that, despite the similarity of the changes brought about by the presence of immunogens in the haemolymph to those brought about by AKH, there is no release of endogenous AKH after injection of laminarin or LPS. A direct effect of the immunogens on release of neutral lipids by the fat body cannot be demonstrated in vitro, and the mechanism by which hyperlipaemia is induced during immune challenge remains uncertain.