Membrane-bound toll-like receptors are overexpressed in peripheral blood and synovial fluid mononuclear cells of enthesitis-related arthritis category of juvenile idiopathic arthritis (JIA–ERA) patients and lead to secretion of inflammatory mediators

Structural feature of TRAFs, their related human diseases and therapeutic intervention

Several studies have been conducted over the years to unravel the structural information on the receptors that bind to tumor necrosis factor receptor-associated factor (TRAF) and the driving forces for the TRAF/receptor complex. In addition, studies have also been performed to highlight the influence of TRAF malfunctioning and mutations on the development of human disease. However, a holistic study that systematically summarizes the available information and the existing clinical trends towards development of the TRAF-targeting drugs has not been conducted to date. Herein, I reviewed existing research that focused on the structural information of various receptors recognized by the different members of the TRAF family. I also reviewed studies on the different human diseases that occur due to TRAF malfunctioning or mutations as well as the clinical trials undertaken to treat TRAF-associated diseases.

TRAF molecules in inflammation and inflammatory diseases

Purpose of Review

This review presents an overview of the current knowledge of TRAF molecules in inflammation with an emphasis on available human evidence and direct in vivo evidence of mouse models that demonstrate the contribution of TRAF molecules in the pathogenesis of inflammatory diseases.

Recent Findings

The tumor necrosis factor receptor (TNF-R)-associated factor (TRAF) family of cytoplasmic proteins was initially identified as signaling adaptors that bind directly to the intracellular domains of receptors of the TNF-R superfamily. It is now appreciated that TRAF molecules are widely employed in signaling by a variety of adaptive and innate immune receptors as well as cytokine receptors. TRAF-dependent signaling pathways typically lead to the activation of nuclear factor-κBs (NF-κBs), mitogen-activated protein kinases (MAPKs), or interferon-regulatory factors (IRFs). Most of these signaling pathways have been linked to inflammation, and therefore TRAF molecules were expected to regulate inflammation and inflammatory responses since their discovery in 1990s. However, direct in vivo evidence of TRAFs in inflammation and especially in inflammatory diseases had been lacking for many years, partly due to the difficulty imposed by early lethality of TRAF2^-/-, TRAF3^-/-, and TRAF6^-/- mice. With the creation of conditional knockout and lineage-specific transgenic mice of different TRAF molecules, our understanding about TRAFs in inflammation and inflammatory responses has rapidly advanced during the past decade.

Summary

Increasing evidence indicates that TRAF molecules are versatile and indispensable regulators of inflammation and inflammatory responses and that aberrant expression or function of TRAFs contributes to the pathogenesis of inflammatory diseases.

Gut microbiome in children with enthesitis-related arthritis in a developing country and the effect of probiotic administration

In Asia, enthesitis-related arthritis (ERA) is the most frequent category of juvenile idiopathic arthritis. ERA has a strong association with human leucocyte antigen (HLA)-B27 and subclinical gut inflammation. In an HLA-B27 transgenic rat model, the presence of Bacteroides bacteria in the gut appears to cause spondyloarthropathy (SpA). Thus, we studied gut microbiota in children with ERA. Stool specimens from 33 patients with ERA and 14 age-matched healthy controls were studied; none had any gastrointestinal symptom, or had received a drug known to affect gut motility or microbiota in the preceding 6 weeks. From each specimen, a cDNA library for the V3 region of bacterial 16S rRNA was subjected to high-throughput, massively parallel sequencing. Relationship of the specimens was studied using principal co-ordinate analysis (PCoA), and abundances of various bacterial taxa and alpha diversity were compared between groups. In eight patients, a repeat faecal specimen was studied after 12 weeks of probiotic therapy. The 55 specimens yielded a median (range) of 397 315 (102 093-1 502 380) high-quality reads each. In PCoA, gut microbiota from ERA showed a wider dispersion than those from controls. In patients, families Bacteroidaceae and Enterobacteriaceae were more abundant and Prevotellaceae were less abundant than in controls. Also, genera Bacteroides, Entercoccus and Klebsiella were over-represented and genus Prevotella was under-represented in ERA patients. Probiotic therapy led to a non-significant increase in Prevotellaceae. Patients with ERA have a dysbiosis in the gut, with increased abundance of Bacteroides and reduction of Prevotella. Probiotic supplementation in a subset of patients did not reverse these changes significantly.

Modulation of TLR3/TLR4 inflammatory signaling by the GABAB receptor agonist baclofen in glia and immune cells: relevance to therapeutic effects in multiple sclerosis

The GABAB receptor agonist, baclofen, is used to treat muscle tightness and cramping caused by spasticity in a number of disorders including multiple sclerosis (MS), but its precise mechanism of action is unknown. Neuroinflammation drives the central pathology in MS and is mediated by both immunoreactive glial cells and invading lymphocytes. Furthermore, a body of data indicates that the Toll-like receptor (TLR) family of innate immune receptors is implicated in MS progression. In the present study we investigated whether modulation of GABAB receptors using baclofen can exert anti-inflammatory effects by targeting TLR3 and(or) TLR4-induced inflammatory signaling in murine glial cells and human peripheral blood mononuclear cells (PBMCs) isolated from healthy control individuals and patients with the relapse-remitting (RR) form of MS. TLR3 and TLR4 stimulation promoted the nuclear sequestration of NF-κB and pro-inflammatory cytokine expression in murine glia, while TLR4, but not TLR3, promoted pro-inflammatory cytokine expression in PBMCs isolated from both healthy donors and RR-MS patients. Importantly, this effect was exacerbated in RR-MS patient immune cells. We present further evidence that baclofen dose-dependently attenuated TLR3- and TLR4-induced inflammatory signaling in primary glial cells. Pre-exposure of PBMCs isolated from healthy donors to baclofen attenuated TLR4-induced TNF-α expression, but did not affect TLR4-induced TNF-α expression in RR-MS patient PBMCs. Interestingly, mRNA expression of the GABAB receptor was reduced in PBMCs from RR-MS donors when compared to healthy controls, an effect that might contribute to the differential sensitivity to baclofen seen in healthy and RR-MS patient cells. Overall these findings indicate that baclofen differentially regulates TLR3 and TLR4 signaling in glia and immune cells, and offers insight on the role of baclofen in the treatment of neuroinflammatory disease states including MS.

Juvenile idiopathic arthritis and physical activity: possible inflammatory and immune modulation and tracks for interventions in young populations

Juvenile idiopathic arthritis (JIA) is a chronic inflammatory disease characterized by persistent joint inflammation that manifests as joint pain and swelling and limited range of joint motion. In healthy subjects, the literature reports that physical activity has an anti-inflammatory effect. In JIA patients, exercise could be used as a therapeutic tool to counteract disease-related inflammation and thereby improve clinical symptoms, although transient flare of pain could be the price to pay. Indeed, in patients with a chronic inflammatory disease, physical activity is prone to exacerbate underlying inflammatory stress. Physical activity improves quality of life and symptoms in JIA patients, but the mechanisms of action remain unclear. This review focuses on the mechanisms underlying exercise-induced immune and hormonal changes. Data on the impact of acute and chronic physical activities on the secretion of hormones and other molecules such as miRNA or peptides involved in the inflammatory process in JIA was compiled and summarized, and the key role of the biological effect of muscle-derived interleukin 6 in the exercise-induced modulation of pro/anti-inflammatory balance is addressed. We also go on to review the effect of training and type of exercise on cytokine response. This review highlights the beneficial effect of physical exercise in children with JIA and potential effect of exercise on the balance between pro- and anti-inflammatory response.

TLR4 endogenous ligand MRP8/14 level in enthesitis-related arthritis and its association with disease activity and TLR4 expression

OBJECTIVE

Enthesitis-related arthritis (ERA) is an inflammatory disease of childhood that lacks autoantibodies. Overexpression of surface-expressed Toll-like receptors (TLRs) has been found in ERA. Myeloid-related proteins (MRPs) 8 and 14 are calcium binding proteins that act as an endogenous ligand of TLR4. MRP8/14 levels are elevated in patients with systemic-onset arthritis. Thus we studied the role of MRP8/14 in ERA.

METHODS

The study enrolled patients with ERA. Plasma and SF levels of MRP8/14 were measured by ELISA and TLR4 expression on peripheral blood and SF monocytes was measured by two-colour flow cytometry. Control plasma samples were collected from 48 blood bank donors.

RESULTS

Of the 69 patients, 67 were male, with a mean age of 15.2 (s.d. 2.7) years and a disease duration of 5 (s.d. 3) years. Median plasma levels of MRP8/14 were higher in patients (10 862.3 ng/ml) than controls (4426.1 ng/ml, P < 0.0001). Patients with active disease (11 669.5 ng/ml) had higher levels as compared with inactive disease (4421.8 ng/ml, P < 0.0001). Plasma MRP8/14 levels decreased on follow-up after 3 months only in patients who responded to treatment (P = 0.012). MRP8/14 levels were negatively correlated with the frequency of CD14(+)TLR4(+) cells (r = -0.372, P = 0.02). MRP8/14 levels were higher in SF as compared with plasma (15 858.45 ng/ml, P = 0.024). The frequency of CD14(+)TLR4(+) cells was higher in SF as compared with peripheral blood.

CONCLUSION

MRP8/14 levels are increased in the plasma of ERA patients and are higher in those with active disease and the levels decrease in patients who respond to treatment, suggesting that it may be a good biomarker during follow-up.