The p38-Mediated Rapid Down-Regulation of Cell Surface gp130 Expression Impairs Interleukin-6 Signaling in the Synovial Fluid of Juvenile Idiopathic Arthritis Patients

Deoxynivalenol hijacks the pathway of Janus kinase 2/signal transducers and activators of transcription 3 (JAK2/STAT-3) to drive caspase-3-mediated apoptosis in intestinal porcine epithelial cells

Deoxynivalenol (DON) can easily injure the intestinal tract, which represents the first barrier against food contaminants. The intestinal toxicity induced by DON was mainly focused on mitogen-activated protein kinase (MAPK) activation, however, the underlying mechanisms by which DON triggers apoptosis by other pathways remain poorly understood. In this study, the Janus kinase 2/signal transducers and activators of transcription 3 (JAK2/STAT-3) pathway was proposed to regulate the intrinsic apoptosis induced by DON and thoroughly investigated in intestinal porcine epithelial cells (IPEC-J2). First, DON was found to be able to efficiently inhibit cell viability and increase the release of lactate dehydrogenase. It could also enhance the activity of the cleaved caspase-3 in a time-dependent manner, accompanied by a loss of mitochondrial membrane potential and an up-regulation of the apoptosis rate. Then, the expression of genes associated with inflammation and apoptosis were investigated. DON increased the expression of IL-6, IL-1β, TNF-α, SOCS3 and Bax, but decreased the expression of Bcl-2 and Bcl-xL. Moreover, we discovered that DON robustly inhibited STAT-3 activity together with the down-regulation of JAK2, Bcl-2 and Bcl-xL, paralleling the increase in p38 phosphorylation. Furthermore, a pharmacological activation of JAK2/STAT-3 alleviated DON induced-apoptosis. Concurrent with the apoptotic pathway, during the initial exposure to DON (first 4 h), a survival pathway involving phosphorylated Erk1/2, Akt, and FoxO1 was also observed. Thus, apoptosis induced by DON was Janus faced: although the survival pathway was activated, the DON-induced apoptotic JAK2/STAT-3/caspase-3 pathway dominated, leading to an imbalance in cell homeostasis. This study provides a novel avenue to comprehensively reveal the pathological mechanisms of DON-induced intestinal disorders, which is promising for future applications to other contaminants in food and feed.

IL-6 and its role in IgA nephropathy development

IL-6 is considered one of the well characterized cytokines exhibiting homeostatic, pro- and anti-inflammatory activities, depending on the receptor variant and the induced intracellular cis- or trans-signaling responses. IL-6-activated pathways are involved in the regulation of cell proliferation, survival, differentiation, and cell metabolism changes. Deviations in IL-6 levels or abnormal response to IL-6 signaling are associated with several autoimmune diseases including IgA nephropathy (IgAN), one of most frequent primary glomerulonephritis worldwide. IgAN is associated with increased plasma concentration of IL-6 and increased plasma concentration of aberrantly galactosylated IgA1 immunoglobulin (Gd-IgA1). Gd-IgA1 is specifically recognized by autoantibodies, leading to the formation of circulating immune complexes (CIC) with nephritogenic potential, since CIC deposited in the glomerular mesangium induce mesangial cells proliferation and glomerular injury. Infection of the upper respiratory or digestive tract enhances IL-6 production and in IgAN patients is often followed by the macroscopic hematuria. This review recapitulates general aspects of IL-6 signaling and summarizes experimental evidences about IL-6 involvement in the etiopathogenesis of IgA nephropathy through the production of Gd-IgA1 and regulation of mesangial cell proliferation.

miR-23a contributes to T cellular redox metabolism in juvenile idiopathic oligoarthritis

OBJECTIVE

Juvenile idiopathic arthritis (JIA) is a chronic inflammatory disease of unknown origin. The regulation of inflammatory processes involves multiple cellular steps including mRNA transcription and translation. Different miRNAs tightly control these processes. We aimed to determine the roles of specific miRNAs within JIA pathogenesis.

METHODS

We performed a global miRNA expression analysis in parallel in cells from the arthritic joint and peripheral blood of oligoarticular JIA patients and healthy controls. QRT-PCR analysis was used to verify expression of miRNA in T cells. Ex vivo experiments and flow cytometric analyses were used to analyze proliferation and redox metabolism.

RESULTS

Global miRNA expression analysis demonstrated a different composition of miRNA expression at the site of inflammation compared with peripheral blood. Bioinformatic analysis of predicted miRNA target genes suggest a huge overrepresentation of genes involved in metabolic and oxidative stress pathways in the inflamed joint. Despite enhanced ROS levels within the local inflammatory milieu, JIA T cells are hyperproliferative and reveal an overexpression of miR-23a, which is an inhibitor of PPIF, the regulator of mitochondrial ROS escape. Mitochondrial ROS escape is diminished in JIA T cells resulting in their prolonged survival.

CONCLUSION

Our data suggest that miRNA dependent mitochondrial ROS shuttling might be a mechanism that contributes to T cell regulation in JIA at the site of inflammation.

Interleukin-6 in juvenile idiopathic arthritis

Juvenile idiopathic arthritis (JIA) is a chronic childhood arthritis. Its pathogenesis is very complicated, with the involvement of not only immune cells but various types of parenchymal cells, and is affected by both genetic and environmental predispositions. The clinical spectrum from inflammation to related conditions is largely mediated by cytokines including interleukin (IL)-6. Fluctuations in IL-6 and its related molecules can modulate the pathogenesis and the clinical presentation positively or negatively. The recent clinical impact of IL-6 blockade on JIA has begun a therapeutic paradigm shift. This review describes the characteristics of JIA, mainly focused on IL-6 with the current therapeutic perspective.

Modulation of the IL-6-Signaling Pathway in Liver Cells by miRNAs Targeting gp130, JAK1, and/or STAT3

Interleukin-6 (IL-6)-type cytokines share the common receptor glycoprotein 130 (gp130), which activates a signaling cascade involving Janus kinases (JAKs) and signal transducer and activator of transcription (STAT) transcription factors. IL-6 and/or its signaling pathway is often deregulated in diseases, such as chronic liver diseases and cancer. Thus, the identification of compounds inhibiting this pathway is of interest for future targeted therapies. We established novel cellular screening systems based on a STAT-responsive reporter gene (Cypridina luciferase). Of a library containing 538 microRNA (miRNA) mimics, several miRNAs affected hyper-IL-6-induced luciferase activities. When focusing on candidate miRNAs specifically targeting 3′ UTRs of signaling molecules of this pathway, we identified, e.g., miR-3677-5p as a novel miRNA affecting protein expression of both STAT3 and JAK1, whereas miR-16-1-3p, miR-4473, and miR-520f-3p reduced gp130 surface expression. Interestingly, combination treatment with 2 or 3 miRNAs targeting gp130 or different signaling molecules of the pathway did not increase the inhibitory effects on phospho-STAT3 levels and STAT3 target gene expression compared to treatment with single mimics. Taken together, we identified a set of miRNAs of potential therapeutic value for cancer and inflammatory diseases, which directly target the expression of molecules within the IL-6-signaling pathway and can dampen inflammatory signal transduction.

Use of Laplacian Heat Diffusion Algorithm to Infer Novel Genes With Functions Related to Uveitis

Uveitis is the inflammation of the uvea and is a serious eye disease that can cause blindness for middle-aged and young people. However, the pathogenesis of this disease has not been fully uncovered and thus renders difficulties in designing effective treatments. Completely identifying the genes related to this disease can help improve and accelerate the comprehension of uveitis. In this study, a new computational method was developed to infer potential related genes based on validated ones. We employed a large protein–protein interaction network reported in STRING, in which Laplacian heat diffusion algorithm was applied using validated genes as seed nodes. Except for the validated ones, all genes in the network were filtered by three tests, namely, permutation, association, and function tests, which evaluated the genes based on their specialties and associations to uveitis. Results indicated that 59 inferred genes were accessed, several of which were confirmed to be highly related to uveitis by literature review. In addition, the inferred genes were compared with those reported in a previous study, indicating that our reported genes are necessary supplements.

Tocilizumab Contributes to the Inflammatory Status of Mature Dendritic Cells through Interleukin-6 Receptor Subunits Modulation

Tocilizumab, a humanized anti-IL-6 receptor α (IL-6Rα) is widely used in the treatment of a panel of pathologies such as adult and juvenile rheumatoid arthritis (RA) and the systemic form of juvenile idiopathic arthritis in children. Its indications are expected to be largely extended to other inflammatory diseases in close future. Dendritic cells (DCs) appear to be deeply involved in the immunopathology of these diseases, yet the effects of tocilizumab on these cells were poorly studied. In this study, we explored the effect of tocilizumab on the regulation of IL-6R subunits [gp130, soluble form of IL-6Rα (sIL-6Rα), and mIL-6Rα] in human monocyte-derived DCs. Human DCs were derived from CD14⁺ monocytes purified with beads with IL-4 and granulocyte macrophage colony-stimulating factor. Ex vivo cultures of DCs were performed in the presence of tocilizumab. Using lipopolysaccharide (LPS) maturation of DCs, we demonstrated that tocilizumab did not inhibit IL-6 secretion, enhanced mIL-6Rα expression, and largely increased sIL-6Rα secretion. MAPK modulated STAT3 phosphorylation and surface expression of IL-6Rα in LPS-DCs. Tocilizumab had no impact on STAT3 phosphorylation in LPS-DCs while both LPS and IL-6 increased its activation. Tocilizumab modulated the regulation of IL-6R subunits leading to an inflammatory status of DCs and a massive secretion of IL-6Rα. Our results demonstrate that DCs acquire a pro-inflammatory profile following tocilizumab treatment, becoming a major source of IL-6 trans-signaling activation that might explain the poor clinical benefit in some RA patients.

Interferon-γ is a master checkpoint regulator of cytokine-induced differentiation

Cytokines are protein mediators that are known to be involved in many biological processes, including cell growth, survival, inflammation, and development. To study their regulation, we generated a library of 209 different cytokines. This was used in a combinatorial format to study the effects of cytokines on each other, with particular reference to the control of differentiation. This study showed that IFN-γ is a master checkpoint regulator for many cytokines. It operates via an autocrine mechanism to elevate STAT1 and induce internalization of gp130, a common component of many heterodimeric cytokine receptors. This targeting of a receptor subunit that is common to all members of an otherwise diverse family solves the problem of how a master regulator can control so many diverse receptors. When one adds an autocrine mechanism, fine control at the level of individual cells is achieved.

Endocytosis of pro-inflammatory cytokine receptors and its relevance for signal transduction

The pro-inflammatory cytokines tumor necrosis factor (TNF), interleukin-1 (IL-1) and interleukin-6 (IL-6) are key players of the innate and adaptive immunity. Their activity needs to be tightly controlled to allow the initiation of an appropriate immune response as defense mechanism against pathogens or tissue injury. Excessive or sustained signaling of either of these cytokines leads to severe diseases, including rheumatoid arthritis, inflammatory bowel diseases (Crohn's disease, ulcerative colitis), steatohepatitis, periodic fevers and even cancer. Studies carried out in the last 30 years have emphasized that an elaborate control system for each of these cytokines exists. Here, we summarize what is currently known about the involvement of receptor endocytosis in the regulation of these pro-inflammatory cytokines' signaling cascades. Particularly in the last few years it was shown that this cellular process is far more than a mere feedback mechanism to clear cytokines from the circulation and to shut off their signal transduction.

β-arrestin 2 attenuates cardiac dysfunction in polymicrobial sepsis through gp130 and p38

Sepsis is an exaggerated systemic inflammatory response to persistent bacteria infection with high morbidity and mortality rate clinically. β-arrestin 2 modulates cell survival and cell death in different systems. However, the effect of β-arrestin 2 on sepsis-induced cardiac dysfunction is not yet known. Here, we show that β-arrestin 2 overexpression significantly enhances animal survival following cecal ligation and puncture (CLP)-induced sepsis. Importantly, overexpression of β-arrestin 2 in mice prevents CLP-induced cardiac dysfunction. Also, β-arrestin 2 overexpression dramatically attenuates CLP-induced myocardial gp130 and p38 mitogen-activated protein kinase (MAPK) phosphorylation levels following CLP. Therefore, β-arrestin 2 prevents CLP-induced cardiac dysfunction through gp130 and p38. These results suggest that modulation of β-arrestin 2 might provide a novel therapeutic approach to prevent cardiac dysfunction in patients with sepsis.

Interleukin-6 and its receptors: a highly regulated and dynamic system

Interleukin-6 (IL-6) is a multifunctional cytokine with well-defined pro- and anti-inflammatory properties. Although only small amounts in the picogram range can be detected in healthy humans, IL-6 expression is highly and transiently up-regulated in nearly all pathophysiological states. IL-6 induces intracellular signaling pathways after binding to its membrane-bound receptor (IL-6R), which is only expressed on hepatocytes and certain subpopulations of leukocytes (classic signaling). Transduction of the signal is mediated by the membrane-bound β-receptor glycoprotein 130 (gp130). In a second pathway, named trans-signaling, IL-6 binds to soluble forms of the IL-6R (sIL-6R), and this agonistic IL-6/sIL-6R complexes can in principle activate all cells due to the uniform expression of gp130. Importantly, several soluble forms of gp130 (sgp130) are found in the human blood, which are considered to be the natural inhibitors of IL-6 trans-signaling. Most pro-inflammatory roles of IL-6 have been attributed to the trans-signaling pathway, whereas anti-inflammatory and regenerative signaling, including the anti-bacterial acute phase response of the liver, is mediated by IL-6 classic signaling. In this simplistic view, only a minority of cell types expresses the IL-6R and is therefore responsive for IL-6 classic signaling, whereas gp130 is ubiquitously expressed throughout the human body. However, several reports point towards a much more complex situation. A plethora of factors, including proteases, cytokines, chemical drugs, and intracellular signaling pathways, are able to modulate the cellular expression of the membrane-bound and soluble forms of IL-6R and gp130. In this review, we summarize current knowledge of regulatory mechanisms that control and regulate the dynamic expression of IL-6 and its two receptors.