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The tumor necrosis factor receptor (TNFR)-associated factor (TRAF) family of molecules are intracellular adaptors that regulate cellular signaling through members of the TNFR and Toll-like receptor superfamily. Mammals have seven TRAF molecules numbered sequentially from TRAF1 to TRAF7. Although TRAF5 was identified as a potential regulator of TNFR superfamily members, the in vivo function of TRAF5 has not yet been fully elucidated. We identified an unconventional role of TRAF5 in interleukin-6 (IL-6) receptor signaling involving CD4 + T cells. Moreover, TRAF5 binds to the signal-transducing glycoprotein 130 (gp130) receptor for IL-6 and inhibits the activity of the janus kinase (JAK)-signal transducer and activator of transcription (STAT) signaling pathway. In addition, Traf5-deficient CD4 + T cells exhibit significantly enhanced IL-6-driven differentiation of T helper 17 (Th17) cells, which exacerbates neuroinflammation in experimental autoimmune encephalomyelitis. Furthermore, TRAF5 demonstrates a similar activity to gp130 for IL-27, another cytokine of the IL-6 family. Additionally, Traf5-deficient CD4 + T cells display significantly increased IL-27-mediated differentiation of Th1 cells, which increases footpad swelling in delayed-type hypersensitivity response. Thus, TRAF5 functions as a negative regulator of gp130 in CD4 + T cells. This review aimed to explain how TRAF5 controls the differentiation of CD4 + T cells and discuss how the expression of TRAF5 in T cells and other cell types can influence the development and progression of autoimmune and inflammatory diseases.

Epithelial-mesenchymal transition (EMT)/mesenchymal-epithelial transition (MET) processes are proposed to be a driving force of cancer metastasis. By studying metastasis in bone marrow-derived mesenchymal stem cell (BM-MSC)-driven lung cancer models, microarray time-series data analysis by systems biology approaches revealed BM-MSC-induced signaling triggers early dissemination of CD133 + /CD83 + cancer stem cells (CSCs) from primary sites shortly after STAT3 activation but promotes proliferation towards secondary sites. The switch from migration to proliferation was regulated by BM-MSC-secreted LIF and activated LIFR/p-ERK/pS727-STAT3 signaling to promote early disseminated cancer cells MET and premetastatic niche formation. Then, tumor-tropic BM-MSCs circulated to primary sites and triggered CD151 + /CD38 + cells acquiring EMT-associated CSC properties through IL6R/pY705-STAT3 signaling to promote tumor initiation and were also attracted by and migrated towards the premetastatic niche. In summary, STAT3 phosphorylation at tyrosine 705 and serine 727 differentially regulates the EMT-MET switch within the distinct molecular subtypes of CSCs to complete the metastatic process.

Interleukin-6 (IL-6) is a cytokine implicated in proinflammatory as well as regenerative processes and acts via receptor complexes consisting of the ubiquitously expressed, signal-transducing receptor gp130 and the IL-6 receptor (IL-6R). The IL-6R is expressed only on hepatocytes and subsets of leukocytes, where it mediates specificity of the receptor complex to IL-6 as the subunit gp130 is shared with all other members of the IL-6 cytokine family such as IL-11 or IL-27. The amount of IL-6R at the cell surface thus determines the responsiveness of the cell to the cytokine and might therefore be decisive in the development of inflammatory disorders. However, how the expression levels of IL-6R and gp130 at the cell surface are controlled is largely unknown. Here, we show that IL-6R and gp130 are constitutively internalized independent of IL-6. This process depends on dynamin and clathrin and is temporally controlled by motifs within the intracellular region of gp130 and IL-6R. IL-6 binding and internalization of the receptors is a prerequisite for activation of the Jak/STAT signaling cascade. Targeting of gp130, but not of the IL-6R, to the lysosome for degradation depends on stimulation with IL-6. Furthermore, we show that after internalization and activation of signaling, both the IL-6R and gp130 are recycled back to the cell surface, a process that is enhanced by IL-6. These data reveal an important function of IL-6 beyond the pure activation of signaling., Competing Interests: Conflict of interest The authors declare that they have no conflicts of interest with the contents of this article., (Copyright © 2021 The Authors. Published by Elsevier Inc. All rights reserved.)

Biochemically, interleukin-6 belongs to the class of four-helical cytokines. The cytokine can be synthesised and secreted by many cells. It acts via a cell surface-expressed interleukin-6 receptor, which is not signalling competent. This receptor, when complexed with interleukin-6, associates with the signalling receptor glycoprotein 130 kDa (gp130), which becomes dimerised and initiates intracellular signalling via the Janus kinase/signal transducer and activator of transcription and rat sarcoma proto oncogene/mitogen-activated protein kinase/phosphoinositide-3 kinase pathways. Physiologically, interleukin-6 is involved in the regulation of haematopoiesis and the coordination of the innate and acquired immune systems. Additionally, interleukin-6 plays an important role in the regulation of metabolism, in neural development and survival, and in the development and maintenance of various cancers. Although interleukin-6 is mostly regarded as a pro-inflammatory cytokine, there are numerous examples of protective and regenerative functions of this cytokine. This review will explain the molecular mechanisms of the, in part opposing, activities of the cytokine interleukin-6., Competing Interests: Competing interests: Stefan Rose-John has acted as a consultant and speaker for AbbVie, Amgen, Janssen, Chugai, Roche, Genentech Roche, Pfizer, Eli Lilly, and Sanofi. He also declares that he is an inventor on patents owned by CONARIS Research Institute, which develops the sgp130Fc protein (olamkicept), and he has stock ownership in CONARIS.No competing interests were disclosed.No competing interests were disclosed.No competing interests were disclosed., (Copyright: © 2020 Rose-John S.)

COVID-19 is viral respiratory infection with frequently fatal lung complications in the elderly or in people with serious comorbidities. Lung destruction appears to be associated with a cytokine storm related to an increased level of interleukin-6 (IL6). Therapeutic targeting of the interleukin-6 signaling pathway can attenuate such a cytokine storm and can be beneficial for patients with COVID-19 in danger of pulmonary failure. This article demonstrates the importance of IL6 in progression of disease and the possibility of inhibition of IL6 signaling in COVID-19 therapy., (Copyright© 2020, International Institute of Anticancer Research (Dr. George J. Delinasios), All rights reserved.)

Interleukin-6 (IL-6) is critically involved in liver regeneration after partial hepatectomy (PHX). Previous reports suggest that IL-6 trans-signaling through the soluble IL-6/IL-6R complex is involved in this process. However, the long-term contribution of IL-6 trans-signaling for liver regeneration after PHX is unknown. PHX-induced generation of the soluble IL-6R by ADAM (a disintegrin and metallo) proteases enables IL-6 trans-signaling, in which IL-6 forms an agonistic complex with the soluble IL-6 receptor (sIL-6R) to activate all cells expressing the signal-transducing receptor chain glycoprotein 130 (gp130). In contrast, without activation of ADAM proteases, IL-6 in complex with membrane-bound IL-6R and gp130 activates classic signaling. Here, we describe the generation of IL-6 trans-signaling mice, which exhibit boosted IL-6 trans-signaling and abrogated classic signaling by genetic conversion of all membrane-bound IL-6R into sIL-6R proteins phenocopying hyperactivation of ADAM-mediated shedding of IL-6R as single substrate. Importantly, although IL-6R deficient mice were strongly affected by PHX, survival and regeneration of IL-6 trans-signaling mice was indistinguishable from control mice, demonstrating that IL-6 trans-signaling fully compensates for disabled classic signaling in liver regeneration after PHX. Moreover, we monitored the long-term consequences of global IL-6 signaling inhibition versus IL-6 trans-signaling selective blockade after PHX by IL-6 monoclonal antibodies and soluble glycoprotein 130 as fragment crystallizable fusion, respectively. Both global IL-6 blockade and selective inhibition of IL-6 trans-signaling results in a strong decrease of overall survival after PHX, accompanied by decreased signal transducer and activator of transcription 3 phosphorylation and proliferation of hepatocytes. Mechanistically, IL-6 trans-signaling induces hepatocyte growth factor production by hepatic stellate cells. Conclusion: IL-6 trans-signaling, but not classic signaling, controls liver regeneration following PHX., (© 2019 by the American Association for the Study of Liver Diseases.)

Postoperative adhesion formation often ruins the quality of life or is an obstacle to illnesses with curative operation such as cancer. Previously we demonstrated that interferon-γ-promoted fibrin deposition drove postoperative adhesion formation. However, its underlying cellular and molecular mechanisms remain poorly understood. We found that myofibroblasts of the adhesion predominantly expressed signature molecules of mesothelial cells that line the serosa. Microarray analysis revealed IL-6 as a key underlying player, supported by elevated IL-6 levels in the peritoneal fluid of post-laparotomy human subjects. Injured serosa of cecum-cauterized mice also exhibited induction of Il6, which was followed by Tnf, concomitant with rapid accumulation of neutrophils, substantial population of which expressed TGF-β1, a master regulator of fibrosis. Besides, neutrophil-ablated mice showed reduction in induction of the adhesion, suggesting that TGF-β1 + neutrophils triggered the adhesion. Human neutrophils expressed TGFB1 in response to TNF-α and TNF in response to IL-6. Moreover, anti-IL-6 receptor monoclonal antibody abrogated neutrophil recruitment and adhesion formation. Thus, IL-6 signaling represents a potential target for the prevention of postoperative adhesions.

IL-17 has been implicated in the pathogenesis of multiple sclerosis (MS). Here, we show that blockade of IL-17A, but not IL-17F, attenuated experimental autoimmune encephalomyelitis (EAE). We further show that IL-17A levels were elevated in the CSF of relapsing-remitting MS (RRMS) patients and that they correlated with the CSF/serum albumin quotient (Qalb), a measure of blood-brain barrier (BBB) dysfunction. We then demonstrated that the combination of IL-17A and IL-6 reduced the expression of tight junction (TJ)-associated genes and disrupted monolayer integrity in the BBB cell line hCMEC/D3. However, unlike IL-17A, IL-6 in the CSF from RRMS patients did not correlate with Qalb. These data highlight the potential importance of targeting IL-17A in preserving BBB integrity in RRMS., (Copyright © 2019 The Authors. Published by Elsevier B.V. All rights reserved.)

Since the molecular cloning of interleukin-6 (IL-6) in 1986, many other cytokines have been found to share the same signal transducer, gp130, in their receptor complexes. Thus, the IL-6 family of cytokines now consists of ten members. Although some of the family members' functions are redundant as a result of the expression of gp130, there are also functional distinctions between members. The mechanisms that determine functional redundancies and distinctions are not completely understood. Yet, research has clarified the role of IL-6 family cytokines in autoimmune diseases and has led to effective therapies that target them. Here, we review the IL-6 family of cytokines in autoimmune diseases, with a particular focus on the prototypical member IL-6, from the viewpoints of their structure, signaling, and biological features and discuss possible mechanisms of their functional pleiotropy., (Copyright © 2019 Elsevier Inc. All rights reserved.)

The cytokine IL-6 controls the survival, proliferation and effector characteristics of lymphocytes through activation of the transcription factors STAT1 and STAT3. While STAT3 activity is an ever-present feature of IL-6 signaling in CD4 + T cells, prior activation via the T cell antigen receptor limits IL-6's control of STAT1 in effector and memory populations. Here we found that phosphorylation of STAT1 in response to IL-6 was regulated by the tyrosine phosphatases PTPN2 and PTPN22 expressed in response to the activation of naïve CD4 + T cells. Transcriptomics and chromatin immunoprecipitation-sequencing (ChIP-seq) of IL-6 responses in naïve and effector memory CD4 + T cells showed how the suppression of STAT1 activation shaped the functional identity and effector characteristics of memory CD4 + T cells. Thus, tyrosine phosphatases induced by the activation of naïve T cells determine the way activated or memory CD4 + T cells sense and interpret cytokine signals.

Interleukin (IL)-6 receptor (IL-6R) can specifically bind to IL-6 and the complex subsequently recruits a transmembrane signal transducer, gp130, to trigger the intracellular signal transduction. IL-6R exists in two forms, a transmembrane IL-6R and a soluble IL-6R (sIL-6R), leading to different signal transduction mechanisms as classic signaling and trans-signaling, respectively. There is now a general consensus that these two modes of signal transduction can mediate anti-inflammatory and pro-inflammatory activities of IL-6. The study on Il-6r is limited although Il-6 has been well studied in teleost. In the present study, a cDNA encoding grass carp Il-6r (gcIl-6r) was isolated. An in-silico analysis showed that gcIl-6r shared the same functional domains and conserved gene synteny at its loci with mouse homologue, and its amino acid sequence was conserved in fish species. A tissue distribution assay demonstrated that gcil6r mRNA was expressed with high levels in immune tissues including spleen and head kidney, and its expression was induced by LPS and Poly I:C in grass carp head kidney leucocytes (HKLs). An in vitro binding assay showed that recombinant soluble gcIl-6r (rgcsIl-6r) could specifically bind to recombinant gcIl-6 (rgcIl-6) protein. Moreover, rgcIl-6 stimulated suppressor of cytokine signaling 3 (socs3)'s mRNA expression in grass carp HKLs and it combined with rgcsIl-6r increased socs3 mRNA expression in CIK cells with gp130 but without Il-6r expression. In HKLs, rgcIl-6 stimulated the mRNA levels of both pro-inflammatory (tnfa and il1b) and anti-inflammatory (il10) cytokines, and rgcsIl-6r could augment these stimulatory effects of gcIl-6. Taken these data together, gcsIl-6r can mediate the immuno-regulatory functions of gcIl-6 and has an agonistic property in these actions of Il-6 in grass carp., (Copyright © 2018 Elsevier Ltd. All rights reserved.)

Objective: Juvenile ischemic osteonecrosis (JIO) of the femoral head is one of the most serious hip disorders causing a permanent deformity of the femoral head in childhood. We recently reported that interleukin 6 (IL6) is predominantly increased in the hip synovial fluid of patients with JIO and that articular chondrocytes are primary source of IL6. This study investigated whether an inhibition of IL6 receptor improves cartilage preservation and bone healing in JIO., Method: A small animal model (i.e., 6-week-old mouse) of JIO was treated with either saline or tocilizumab, an IL6 receptor blocker, for 6 weeks., Results: TUNEL-positive chondrocytes in the articular cartilage were reduced by the tocilizumab treatment, concomitant with the increase in cartilage matrix. The levels of a cartilage anabolic marker Sox9 was significantly increased in the articular cartilage of mice treated with tocilizumab. Micro-CT assessment showed tocilizumab treatment significantly increased trabecular epiphyseal bone volume (P = 0.001, n = 10), thickness (P = 0.007) and number (P = 0.014) and decreased bone separation (P = 0.002) and its deformity (P = 0.003). A bone formation marker, BMP2, and an angiogenic marker, vascular endothelial growth factor (VEGF), were both significantly increased by tocilizumab treatment under hypoxia using human chondrocytes while the bone resorption marker, RANKL/OPG ratio, was reduced., Conclusion: Tocilizumab treatment following ischemic osteonecrosis has cartilage anabolic effect and increases bone volume in JIO mouse model. The findings lead to a possible application of tocilizumab for preclinical study using a large animal model of JIO and a clinical trial to validate this treatment., (Copyright © 2018 Osteoarthritis Research Society International. Published by Elsevier Ltd. All rights reserved.)

Despite remarkable improvements in cancer treatment approaches, breast cancer is still the main cause of cancer-related death in women. Its principal cause is the resistance of the cancer cells against conventional anticancer therapeutics, mainly in advanced disease stages. It has been shown that chronic inflammation in the tumor microenvironment facilitates tumor growth and induces resistance toward chemo- and radiotherapy. Overexpression of interleukin-6 (IL-6) cytokine in the tumor microenvironment has been demonstrated in numerous tumors including breast cancer. Tumor cells and tumor-associated fibroblasts are the major sources of IL-6 secretion in the tumor microenvironment. Several studies have demonstrated the immunopathogenic function of IL-6 and its signaling in the tumor growth, metastasis, and therapeutic resistance in the breast cancer. Therefore, it seems that targeting IL-6 and/or its receptor in combination with other potent anticancer therapies may be a potent therapeutic approach for breast cancer therapy., (Copyright © 2018 Elsevier Masson SAS. All rights reserved.)

Aim: To characterize the potential of human periodontal ligament fibroblasts (HPLF) to synthesize CRP and Th-related cytokines in response to IL-6 in periodontal health and apical inflammation., Methodology: Primary HPLF stimulated with IL-6, soluble(s) IL-6 receptor (R) and controls were assayed for CRP, Th1, Th2, Th17 and Treg-related cytokines by quantitative real-time PCR and ELISA, respectively. IL-6R mRNA expression and its soluble protein levels were screened in HPLF cultures, and ex vivo samples of healthy periodontal ligaments (n = 5) and apical lesions (n = 13). Data were analysed with ANOVA or unpaired t-test., Results: 0.5 ng mL -1 IL-6 plus 1 ng mL -1 of its soluble receptor (sIL-6R) for 24 h was effective in inducing CRP production. IL-6 alone had a mild dose-dependent effect; co-stimulation with sIL-6R significantly enhanced this effect, whereas it was completely abolished by the addition of IL-6R blocking antibody (P < 0.05). Similarly, higher mRNA expression and protein levels of Th1, Th17 and partially Treg-related cytokines were found for IL-6 combined with its soluble receptor versus the nonstimulated group and IL-6R antibody (P < 0.05). IL-6R mRNA expression was slightly induced by IL-6 compared to THP-1 cells, but sILR-6 protein could not be detected in HPLF. High sIL-6R levels were detected in apical lesions and were immunolocalized to mononuclear inflammatory cells and proliferating epithelium., Conclusion: IL-6 trans-signalling induced Th1 and Th17-related cytokines and represents an extra-hepatic mechanism for PCR synthesis in human periodontal ligament fibroblasts, contributing to explain the bone-destructive phenotype of apical lesions and eventually its systemic complications., (© 2017 International Endodontic Journal. Published by John Wiley & Sons Ltd.)

IL-6 is a pleiotropic cytokine involved in many biological functions that affect tissues beyond the immune system and the vasculature. This multifunctional cytokine exerts its actions via the classic signalling pathway when it binds to the transmembrane IL-6 receptor (IL-6R) or via the trans-signalling pathway upon binding to the soluble form of IL-6R (sIL-6R). In general, classic IL-6 signalling is responsible for the anti-inflammatory properties of IL-6, whereas trans-signalling is responsible for the pro-inflammatory actions of IL-6. As a result, dysregulation of the IL-6 axis can lead to the onset or development of several disease states, particularly autoimmune and inflammatory disorders, including RA and GCA. This pathological role of IL-6 means that pharmacologic modulation of the IL-6 axis is a rational therapeutic approach; however, multiple predictable, but often underappreciated, effects on tissues and organs beyond the blood vessels may also occur.

Interleukin-6 is a cytokine synthesized by many cells in the human body. IL-6 binds to a membrane bound IL-6R, which is only present on hepatocytes, some epithelial cells and some leukocytes. The complex of IL-6 and IL-6R binds to the ubiquitously expressed receptor subunit gp130, which forms a homodimer and thereby initiates intracellular signaling via the JAK/STAT and the MAPK pathways. IL-6R expressing cells can cleave the receptor protein to generate a soluble IL-6R (sIL-6R), which can still bind IL-6 and can associate with gp130 and induce signaling even on cells, which do not express IL-6R. This paradigm has been called IL-6 trans-signaling whereas signaling via the membrane bound IL-6R is referred to as classic signaling. We have generated several molecular tools to differentiate between IL-6 classic- and trans-signaling and to analyze the consequence of cellular IL-6 signaling in vivo.

Interleukin-6 (IL-6) is a pleiotropic cytokine with neuroprotective properties. Still, the therapeutic potential of IL-6 after experimental stroke has not yet been investigated in a clinically relevant way. Here, we investigated the therapeutic use of intravenously administered IL-6 and the soluble IL-6 receptor (sIL-6R) alone or in combination, early after permanent middle cerebral artery occlusion (pMCAo) in mice. IL-6 did not affect the infarct volume in C57BL/6 mice, at neither 24 nor 72h after pMCAo but reduced the infarct volume in IL-6 knockout mice at 24h after pMCAo. Assessment of post-stroke behavior showed an improved grip strength after a single IL-6 injection and also improved rotarod endurance after two injections, in C57BL/6 mice at 24h. An improved grip strength and a better preservation of sensory functions was also observed in IL-6 treated IL-6 knockout mice 24h after pMCAo. Co-administration of IL-6 and sIL-6R increased the infarct volume, the number of infiltrating polymorphonuclear leukocytes and impaired the rotarod endurance of C57BL/6 mice 24h after pMCAo. IL-6 administration to naïve C57BL/6 mice lead after 45min to increased plasma-levels of CXCL1 and IL-10, whereas IL-6 administration to C57BL/6 mice lead to a reduction in the ischemia-induced increase in IL-6 and CXCL1 at both mRNA and protein level in brain, and of IL-6 and CXCL1 in serum. We also investigated the expression of IL-6 and IL-6R after pMCAo and found that cortical neurons upregulated IL-6 mRNA and protein, and upregulated IL-6R after pMCAo. In conclusion, the results show a complex but potentially beneficial effect of intravenously administered IL-6 in experimental stroke., (Copyright © 2017 Elsevier Inc. All rights reserved.)

Vascular endothelial growth factor (VEGF) is implicated in the peritoneal membrane remodeling that limits ultrafiltration in patients on peritoneal dialysis (PD). Although the exact mechanism of VEGF induction in PD is unclear, VEGF concentrations in drained dialysate correlate with IL-6 levels, suggesting a link between these cytokines. Human peritoneal mesothelial cells (HPMCs), the main source of IL-6 and VEGF in the peritoneum, do not bear the cognate IL-6 receptor and are thus unable to respond to classic IL-6 receptor signaling. Here, we investigated whether VEGF release by HPMCs is controlled by IL-6 in combination with its soluble receptor (IL-6 trans-signaling). Although treatment with either IL-6 or soluble IL-6 receptor (sIL-6R) alone had no effect on VEGF production, stimulation of HPMCs with IL-6 in combination with sIL-6R promoted VEGF expression and secretion through a transcriptional mechanism involving STAT3 and SP4. Conditioned medium from HPMCs cultured with IL-6 and sIL-6R promoted angiogenic endothelial tube formation, which could be blocked by silencing SP4. In vivo , induction of peritoneal inflammation in wild-type and IL-6-deficient mice showed IL-6 involvement in the control of Sp4 and Vegf expression and new vessel formation, confirming the role of IL-6 trans-signaling in these processes. Taken together, these findings identify a novel mechanism linking IL-6 trans-signaling and angiogenesis in the peritoneal membrane., (Copyright © 2017 by the American Society of Nephrology.)

Purpose of Review: This article updates on the concept that muscle-derived cytokines (myokines) play important roles in muscle health and disease., Recent Findings: Interleukin-6 (IL-6) is released from normal skeletal muscle in response to exercise, mediating both anti-inflammatory responses and metabolic adaptations, actions contradictory to the prevailing view that IL-6 is a proinflammatory cytokine that is inducing and propagating disease. The anti-inflammatory effects of IL-6 result from its trans-membrane signalling capability, via membrane-bound receptors, whereas its proinflammatory effects result instead from signalling via the soluble IL-6 receptor and gp130. IL-15 is elevated following exercise, promoting muscle fibre hypertrophy in some circumstances, while inducing fibre apoptosis in others. This functional divergence appears because of variations in expression of IL-15 receptor isoforms. Decorin, a recently described myokine, is also elevated following exercise in normal muscle, and promotes muscle fibre hypertrophy by competitively binding to, and thus inhibiting, myostatin, a negative regulator of muscle protein synthesis. Exercise-induced myostatin downregulation thus promotes muscle fibre growth, prompting recent trials of a biological myostatin inhibitor in inclusion body myositis., Summary: Myokines appear to exert diverse beneficial effects, though their mechanistic roles in myositis and other myopathologies remain poorly understood.

Background: IL-6 is an inflammatory cytokine that controls effector T cell responses but the mechanisms by which it controls allogeneic immune responses and vascular rejection that leads to transplant arteriosclerosis (TA) are poorly understood., Methods: We have examined the mechanism by which IL-6 contributes to the pathogenesis of vascular rejection and TA using a murine aortic interposition model of vascular rejection., Results: The absence of IL-6 production from artery graft cells reduced the development of vascular rejection and arteriosclerotic thickening. There was no apparent effect of donor-derived IL-6 on endothelial cell integrity or on the intimal accumulation of smooth muscle cells, macrophages, and anti-donor antibodies. However, reduced vascular pathology in IL-6 artery grafts was accompanied by a significant reduction in the accumulation of CD4 and CD8 T cells. Further, the absence of graft-derived IL-6 resulted in a significant decrease in the activation and proliferation of alloreactive CD4 and CD8 T cells after transplantation as well as in a marked increase in cell death of effector T cells. Alloreactive effector T cells that expanded in the absence of IL-6 were also more susceptible to Fas-mediated activation-induced cell death in vitro. Finally, systemic neutralization of IL-6R did not reduce arteriosclerotic thickening but reduced endothelial integrity in allograft arteries, indicating differential effects of specific elimination of IL-6 in graft cells and systemic IL-6 neutralization., Conclusions: Donor-derived IL-6 amplifies the expansion of allogeneic T cell responses that cause vascular rejection and TA by increasing T cell proliferation and preventing Fas-mediated T cell death.

Interleukin-6 (IL-6) signaling network has been implicated in oncogenic transformations making it attractive target for the discovery of novel cancer therapeutics. In this study, potent antiproliferative and apoptotic effect of diacerein were observed against breast cancer. In vitro apoptosis was induced by this drug in breast cancer cells as verified by increased sub-G1 population, LIVE/DEAD assay, cell cytotoxicity and presence of terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL)-positive cells, as well as downregulation of antiapoptotic proteins Bcl-2 and Bcl-xL and upregulation of apoptotic protein Bax. In addition, apoptosis induction was found to be caspase dependent. Further molecular investigations indicated that diacerein instigated apoptosis was associated with inhibition of IL-6/IL-6R autocrine signaling axis. Suppression of STAT3, MAPK and Akt pathways were also observed as a consequence of diacerein-mediated upstream inhibition of IL-6/IL-6R. Fluorescence study and western blot analysis revealed cytosolic accumulation of STAT3 in diacerein-treated cells. The docking study showed diacerein/IL-6R interaction that was further validated by competitive binding assay and isothermal titration calorimetry. Most interestingly, it was found that diacerein considerably suppressed tumor growth in MDA-MB-231 xenograft model. The in vivo antitumor effect was correlated with decreased proliferation (Ki-67), increased apoptosis (TUNEL) and inhibition of IL-6/IL-6R-mediated STAT3, MAPK and Akt pathway in tumor remnants. Taken together, diacerein offered a novel blueprint for cancer therapy by hampering IL-6/IL-6R/STAT3/MAPK/Akt network.

Interleukin 6 (IL-6) is a pleiotropic four-helix-bundle cytokine that exerts multiple functions in the body. In the liver, IL-6 is an important inducer of the acute phase response and infection defense. IL-6 is furthermore crucial for hepatocyte homeostasis and is a potent hepatocyte mitogen. It is not only implicated in liver regeneration, but also in metabolic function of the liver. However, persistent activation of the IL-6 signaling pathway is detrimental to the liver and might ultimately result in the development of liver tumors. On target cells IL-6 can bind to the signal transducing subunit gp130 either in complex with the membrane-bound or with the soluble IL-6 receptor to induce intracellular signaling. In this review we describe how these different pathways are involved in the physiology and pathophyiology of the liver. We furthermore discuss how IL-6 pathways can be selectively inhibited and therapeutically exploited for the treatment of liver pathologies., (Copyright © 2016 European Association for the Study of the Liver. Published by Elsevier B.V. All rights reserved.)

Head and neck cancer patients treated by radiation commonly suffer from a devastating side effect known as dry-mouth syndrome, which results from the irreversible loss of salivary gland function via mechanisms that are not completely understood. In this study, we used a mouse model of radiation-induced salivary hypofunction to investigate the outcomes of DNA damage in the head and neck region. We demonstrate that the loss of salivary function was closely accompanied by cellular senescence, as evidenced by a persistent DNA damage response (γH2AX and 53BP1) and the expression of senescence-associated markers (SA-βgal, p19ARF, and DcR2) and secretory phenotype (SASP) factors (PAI-1 and IL6). Notably, profound apoptosis or necrosis was not observed in irradiated regions. Signs of cellular senescence were also apparent in irradiated salivary glands surgically resected from human patients who underwent radiotherapy. Importantly, using IL6 knockout mice, we found that sustained expression of IL6 in the salivary gland long after initiation of radiation-induced DNA damage was required for both senescence and hypofunction. Additionally, we demonstrate that IL6 pretreatment prevented both senescence and salivary gland hypofunction via a mechanism involving enhanced DNA damage repair. Collectively, these results indicate that cellular senescence is a fundamental mechanism driving radiation-induced damage in the salivary gland and suggest that IL6 pretreatment may represent a promising therapeutic strategy to preserve salivary gland function in head and neck cancer patients undergoing radiotherapy., (©2016 American Association for Cancer Research.)

The search for effective therapeutic strategies for irritable bowel syndrome (IBS) is hampered by an incomplete understanding of its underlying pathophysiology. Stress and altered plasma cytokine profiles indicative of immune activation are characteristic of the disorder. The neuromodulatory effects of interleukin-6 (IL-6) and corticotropin-releasing factor receptor (CRFR) 1 in visceral pain and stress-induced defecation in the Wistar Kyoto (WKY) rat model of IBS were investigated. Sprague Dawley and WKY rats were administered anti-IL-6 receptor antibodies (xIL-6R, 0.5 mg kg(-1) i.p) with or without the CRFR1 antagonist antalarmin (10 mg kg(-1) i.p). Post-intervention, the pain threshold to colorectal distension and stress-induced faecal output were compared and changes in colonic mucosal protein expression were investigated. The neuro-stimulatory effects of IBS plasma on the myenteric plexus is mediated by IL-6, IL-8 and CRF. The stimulatory effects of these soluble factors on myenteric neuron excitability and colonic contractility were additive. Moreover, inhibition of IL-6 and CRF1 receptors in vivo in the WKY IBS rat model normalized stress-induced defecation (P < 0.01) and visceral pain sensitivity (P < 0.001) with associated changes in protein expression of the tight junction proteins occludin and claudin 2, the visceral pain-associated T-type calcium channel CaV3.2 and intracellular signalling molecules STAT3, SOCS3 and ERK1/2. These studies demonstrate the additive effects of immune and stress factors on myenteric neuronal excitability. Moreover, combined targeting of peripheral IL-6 and CRF1 receptors is effective in alleviating IBS-like symptoms in the WKY rat. Thus, crosstalk between stress and immune factors during IBS flares may underlie symptom exacerbation., (© 2014 The Authors. The Journal of Physiology © 2014 The Physiological Society.)

Introduction: Increased IL-6 and soluble IL-6 receptor (sIL-6R) levels in depressed patients was first shown over 20 years ago. The pro-inflammatory effects of IL-6 are predominantly mediated by IL-6 trans-signalling via the sIL-6R, whereas IL-6R membrane signalling has anti-inflammatory effects., Areas Covered: We review data on IL-6 and sIL-6R in inflammation, depression, animal models of depression and the effects of different classes of antidepressants. The biological context for IL-6 trans-signalling as a pathogenic factor in depression involves its role in the acute phase response, disorders in zinc and the erythron, hypothalamic-pituitary-adrenal axis activation, induction of the tryptophan catabolite pathway, oxidative stress, bacterial translocation, transition towards sensitisation, autoimmune processes and neuroprogression and the multicausal aetiology of depression, considering that psychosocial stressors and comorbid immune-inflammatory diseases are associated with the onset of depression., Expert Opinion: The homeostatic functions of IL-6 imply that ubiquitous IL-6 inhibitors, for example, tocilizumab, may not be the optimal treatment target in depression. A more promising target may be to increase soluble glycoprotein 130 (sgp130) inhibition of IL-6 trans-signalling, while allowing the maintenance of IL-6R membrane signalling. Future research should delineate the effects of treatments with sgp130Fc in combination with antidepressants in various animal models of chronic depression.

Cytokines are soluble mediators, which aid cell-to-cell communication in immune responses, and interleukin-6 (IL-6) is a prototypical cytokine featuring redundant and pleiotropic activity. The complete elucidation of the IL-6-mediated signal transduction system has provided a molecular basis for the characteristic features of cytokines. When tissue damage or inflammation due to infections or injuries occurs, IL-6 synthesis is promptly induced, contributing to the host defense through the stimulation of acute-phase immune reactions and hematopoiesis. The production of IL-6 is terminated when tissue homeostasis is restored. The synthesis of IL-6 is tightly regulated transcriptionally and posttranscriptionally. However, the dysregulated continual synthesis of IL-6 has been implicated in the development of various diseases, including autoimmune and chronic inflammatory diseases and cancers. Clinical trials using the humanized anti-IL-6 receptor monoclonal antibody tocilizumab have demonstrated the efficacy of IL-6 blockade for the treatment of refractory inflammatory diseases, such as rheumatoid arthritis, systemic juvenile idiopathic arthritis, and Castleman disease. Moreover, favorable results from the off-label use of tocilizumab strongly suggest that it may be applicable for the treatment of other refractory immune-mediated diseases, including cancer. Therefore, the mechanisms for the dysregulated synthesis of IL-6 need to be elucidated to understand the pathogenesis of the resultant diseases and to facilitate the development of effective therapeutic strategies.

Interleukin (IL)-6 is a multifunctional cytokine with a critical role in inflammatory, immunoregulatory and haemopoietic responses. Its receptor consists of an ubiquitously expressed membrane transducing element (gp130) and of the specific element IL-6R-alpha (gp80), present only on hepatocytes and some leukocyte subsets. IL-6R-alpha also exists as soluble protein (sIL-6R) that, in the presence of IL-6, forms a complex able to bind gp130 and, thanks to the mechanism called trans-signaling, transduces IL-6 effect through tyrosine phosphorylation and activation of the signal transducer and transcription activator (STAT)-3. The aim of this study was to analyze the bidirectional relationships between platelet aggregation and IL-6-dependent effects. While platelets do not produce IL-6, we found that resting platelets express gp130, but not gp80, on their membranes. Upon activation by thrombin or calcium ionophore A23187, but not by ADP, the IL-6R-alpha is released in soluble form, while cangrelor, the specific inhibitor of P2Y12 receptor, can partially inhibit sIL-6R release. This sIL-6R is biologically active and, in the presence of IL-6, can trigger IL-6 trans-signaling, inducing an autocrine activation loop (as measured by an increase in gp80 and gp130 content) and STAT3 phosphorylation. On the other hand, IL-6 trans-signaling has no effect on platelet degranulation or aggregation by itself, nor on thrombin-induced platelet aggregation. Our data add an important piece to the puzzle of thrombosis and inflammation: in the presence of IL-6, which can be produced by stressed endothelial cells, the platelet-derived IL-6 trans-signaling could be crucial for the evolution of inflammation within a damaged vessel.

Objective: To report first experiences with interleukin 6 receptor inhibition in therapy-resistant neuromyelitis optica (NMO)., Design: Retrospective case series., Setting: Neurology department at a tertiary referral center., Patients: Patients with an aggressive course of NMO switched to tocilizumab after failure of anti-CD20 therapy., Main Outcome Measures: Annualized relapse rate and disability progression measured by the Expanded Disability Status Scale., Results: We report 3 female patients with a median age of 39 years (range, 26-40 years) and aquaporin 4-positive NMO. All patients had been treated with different immunosuppressive and immunomodulating agents, followed by 1 to 3 cycles of rituximab. Despite complete CD20-cell depletion during rituximab therapy, the median annualized relapse rate was 3.0 (range, 2.3-3.0) and the median Expanded Disability Status Scale score increased from 5.0 (range, 4.5-7.0) to 6.5 (range, 5.0-7.0). After the switch to tocilizumab (median duration of therapy, 18 months), the median annualized relapse rate decreased to 0.6 (range, 0-1.3). A total of 2 relapses occurred; however, they were mild and there were no changes in clinical disability., Conclusions: Interleukin 6 receptor-blocking therapy can be effective in therapy-resistant cases of NMO. Larger controlled studies are needed to confirm the efficacy of tocilizumab.

The Janus kinases (JAKs) are involved in multiple signaling networks relevant to inflammatory diseases, and inhibition of one or more members of this class may modulate disease activity or progression. We optimized a new inhibitor scaffold, 3-amido-5-cyclopropylpyrrolopyrazines, to a potent example with reasonable kinome selectivity, including selectivity for JAK3 versus JAK1, and good biopharmaceutical properties. Evaluation of this analogue in cellular and in vivo models confirmed functional selectivity for modulation of a JAK3/JAK1-dependent IL-2 stimulated pathway over a JAK1/JAK2/Tyk2-dependent IL-6 stimulated pathway.

Inflammation is a crucial driving force in the development of gastric cancers (GCs). Accordingly, persistent activation of STAT3, a transcription factor pivotal in regulating both inflammation and oncogenesis, is often detected in GC, although its mechanism remains elusive. Suppressor of cytokine signaling-1 (SOCS-1) is a negative regulator of proinflammatory cytokine signaling and SOCS-1 gene methylation is frequently detected in various cancers including GC. However, the significance of SOCS-1 methylation in GC cells remains unexplored. Our study is undertaken to evaluate the role of SOCS-1 in GC cell proliferation and its effect on signaling pathways in GC cells. Among five GC cell lines, SOCS-1 gene was methylated in all cell lines and constitutive STAT3 phosphorylation with elevated endogenous IL-6 production was detected in two cell lines (NUGC-3 and AGS). Unexpectedly, anti-IL-6R antibody inhibited neither cell proliferation nor STAT3 phosphorylation in NUGC-3 and AGS. In contrast, enforced SOCS-1 expression by adenoviral vector (AdSOCS-1) markedly suppressed STAT3 phosphorylation and proliferation of NUGC-3 and AGS cells in vitro. Interestingly, the antiproliferative effect of SOCS-1 was attributable not only to the inhibition of STAT3 but also to that of p38 MAPK activity, and chemical inhibitors of JAK/STAT and p38 MAPK signaling effectively suppressed proliferation of these GC cells. Furthermore, treatment with AdSOCS-1 in vivo significantly suppressed GC proliferation in a xenograft model. These results suggest that SOCS-1 gene methylation is a critical step in the development of GC, and enforced expression of SOCS-1 may represent a novel therapeutic approach for the treatment of GC., (Copyright © 2011 UICC.)

The biological hypothesis that the astrocyte-secreted cytokine, interleukin-6 (IL6), stimulates differentiation of adult rat hippocampal progenitor cells (AHPCs) is considered from a mathematical perspective. The proposed mathematical model includes two different mechanisms for stimulation and is based on mass-action kinetics. Both biological mechanisms involve sequential binding, with one pathway solely utilizing surface receptors while the other pathway also involves soluble receptors. Choosing biologically-reasonable values for parameters, simulations of the mathematical model show good agreement with experimental results. A global sensitivity analysis is also conducted to determine both the most influential and non-influential parameters on cellular differentiation, providing additional insights into the biological mechanisms., (Copyright © 2012 Elsevier Inc. All rights reserved.)

Interleukin-6 is a classic pro-inflammatory cytokine needed to mount an effective immune response. It is secreted by a wide array of cell types, however, its target cells are more restricted, due to the fact that very few cells, except lymphocytes and hepatocytes, express the functional membrane IL-6 receptor. This therefore limits the amount of cells that can respond to IL-6. Transsignalling, the shedding of the membrane bound form of the IL-6 receptor (sIL-6R) into the local microenvironment, greatly increases the range of cells that can respond e.g. as part of a wound healing response necessary to restore the homeostatic balance. Therefore, tight regulation of IL-6 signalling must occur to stop an inappropriate wound healing response occurring. This review focusses on the role of IL-6 in inflammation and fibrosing conditions, with a particular emphasis on systemic sclerosis (SSc), a chronic autoimmune disease in which a classical hallmark of fibrosis occurs. This fibrosis, in particular the skin and internal organs, leads to contractures and internal organ failure respectively with potential fatal consequences. In this review we will discuss the biology of IL-6 in the context of fibrosing conditions such as SSc and argue why molecular targeting of IL-6 is a promising therapeutic target., (Copyright © 2012. Published by Elsevier Ltd.)

Interleukin (IL)-6-type cytokines are critically involved in health and disease. The duration and strength of IL-6-type cytokine-mediated signaling is tightly regulated to avoid overshooting activities. Here, molecular mechanisms of inter-familiar cytokine cross-talk are reviewed which regulate dynamics and strength of IL-6 signal transduction. Both plasticity and cytokine cross-talk are significantly involved in pro- and anti-inflammatory/regenerative properties of IL-6-type cytokines. Furthermore, we focus on IL-6-type cytokine/cytokine receptor plasticity and cross-talk exemplified by the recently identified composite cytokines IL-30/IL-6R and IL-35, the first inter-familiar IL-6/IL-12 family member. The complete understanding of the intra- and extracellular cytokine networks will aid to develop novel tailor-made therapeutic strategies with reduced side effects., (Copyright © 2012 Elsevier Ltd. All rights reserved.)

Astrocytes have an important role in the regulation of inflammation within the central nervous system (CNS). In neuroinflammatory conditions such as multiple sclerosis, numerous cytokines and chemokines are elevated including IL-6, IL-17, and CCL20. IL-17 enhances IL-6 signaling and subsequent IL-6 expression in astrocytes. CCL20 is a CC motif chemokine that functions as a chemoattractant to facilitate the recruitment of CCR6-expressing cells, including Th17 cells. In this study, we examined the role of IL-6 and IL-17 on CCL20 production in primary murine astrocytes. IL-6 in combination with the IL-6 soluble receptor (sIL-6R) stimulated CCL20 expression in part through STAT3 activation, whereas IL-17 alone had no effect. However, the combination of IL-6, sIL-6R, and IL-17 led to a robust increase in CCL20 production. IL-17 increased the activation-associated phosphorylation of NF-κB, and inhibition of the NF-κB pathway significantly inhibited the enhancement of CCL20 expression by IL-17. In addition, chromatin immunoprecipitation revealed that stimulation of primary astrocytes with IL-6 plus the sIL-6R induced STAT3 binding to the CCL20 promoter. Combined stimulation with IL-6, sIL-6R, and IL-17 increased the recruitment of phosphorylated NF-κB to the CCL20 promoter, increased binding of coactivators such as p300 and CBP, and enhanced H3 and H4 histone acetylation, consistent with a transcriptionally active gene. The astrocyte-produced CCL20 increased T cell migration as determined by transwell migration assay. Collectively, these results suggest that astrocytes, in response to IL-6, sIL-6R, and IL-17, may shift chemokine production to that favoring T cell recruitment to the CNS., (Copyright © 2012 Wiley Periodicals, Inc.)

Interleukin-6 (IL-6) is a cytokine with many activities. It has functions in the regulation of the immune system and the nervous system. Furthermore, IL-6 is involved in liver regeneration and in the metabolic control of the body. On target cells, IL-6 binds to an 80 kDa IL-6 receptor (IL-6R). The complex of IL-6 and IL-6R associates with a second protein, gp130, which thereupon dimerizes and initiates intracellular signaling. Whereas gp130 is expressed on all cells, IL-6R is only present on few cells in the body including hepatocytes and some leukocytes. Cells, which do not express IL-6R cannot respond to the cytokine, since gp130 alone has no measurable affinity for IL-6. Interestingly, a soluble form of IL-6R (sIL-6R) comprising the extracellular portion of the receptor can bind IL-6 with a similar affinity as the membrane bound IL-6R. The complex of IL-6 and sIL-6R can bind to gp130 on cells, which do not express the IL-6R, and which are unresponsive to IL-6. This process has been called trans-signaling. Here I will review published evidence that IL-6 trans-signaling is pro-inflammatory whereas classic IL-6 signaling via the membrane bound IL-6R is needed for regenerative or anti-inflammatory activities of the cytokine. Furthermore, the detailed knowledge of IL-6 biology has important consequences for therapeutic strategies aimed at the blockade of the cytokine IL-6.

Interleukin-6 (IL-6) is a cytokine originally identified almost 30 years ago as a B-cell differentiation factor, capable of inducing the maturation of B cells into antibody-producing cells. As with many other cytokines, it was soon realized that IL-6 was not a factor only involved in the immune response, but with many critical roles in major physiological systems including the nervous system. IL-6 is now known to participate in neurogenesis (influencing both neurons and glial cells), and in the response of mature neurons and glial cells in normal conditions and following a wide arrange of injury models. In many respects, IL-6 behaves in a neurotrophin-like fashion, and seemingly makes understandable why the cytokine family that it belongs to is known as neuropoietins. Its expression is affected in several of the main brain diseases, and animal models strongly suggest that IL-6 could have a role in the observed neuropathology and that therefore it is a clear target of strategic therapies.

Growing evidence proposes an important role for pro-inflammatory cytokines during tumor development. Several experimental and clinical studies have linked the pleiotropic cytokine interleukin-6 (IL-6) to the pathogenesis of sporadic and inflammation-associated colorectal cancer (CRC). Increased IL-6 expression has been related to advanced stage of disease and decreased survival in CRC patients. According to experimental studies, these effects are mediated through IL-6 trans-signaling promoting tumor cell proliferation and inhibiting apoptosis through gp130 activation on tumor cells with subsequent signaling through Janus kinases (JAKs) and signal transducer and activator of transcription 3 (STAT3). During recent years, several therapeutics targeting the IL-6/STAT3 pathway have been developed and pose a promising strategy for the treatment of CRC. This review discusses the molecular mechanisms and possible therapeutic targets involved in IL-6 signaling in CRC.

The incidence and severity of chronic lung diseases is growing and affects between 100 and 150 million people worldwide and is associated with a significant rate of mortality. Unfortunately, the initial cause that triggers most chronic lung diseases remains unknown and current available therapies only ameliorate, but do not cure the disease. Thus, there is a need for identification of new targets and development of novel therapies especially for those most severely affected. IL-6, like other inflammatory cytokines, has been shown to be elevated in different lung diseases, but it was considered a byproduct of ongoing inflammation in the lung. However, recent studies support a dissociation of IL-6 from inflammation in the lung and suggest that this cytokine plays an active role in pathogenesis of asthma and, in all likelihood, COPD. IL-6 may therefore be a germane target for treatment of these and other chronic lung disease. Here, we provide an overview of the studies in mouse models and human patients that provide support for the involvement of IL-6 in lung diseases.

One of the earliest metastatic events in human ovarian cancer, tumor spread to the omentum, may be influenced by expression of interleukin 6 (IL6) and its cognate receptor (IL6Rα). Previous reports have shown that IL6 and IL6Rα expression is elevated in the serum and ascites of patients with ovarian cancer and that this can influence in vitro processes such as cell survival, proliferation and migration. In this study, overexpression of IL6Rα, and to a lesser extent IL6, enhanced tumor growth on the omentum. Moreover, adherence to plastic and to peritoneal extracellular matrix components was enhanced in tumor cells overexpressing IL6 or IL6Rα. Host production of IL6 and IL6Rα was also sufficient to influence tumor adherence to the omentum. Expression of LY75/CD205/DEC205, a collagen-binding mannose family receptor, was directly influenced by IL6Rα expression. Blocking LY75 with antibody reduced the adherence of tumor cells overexpressing IL6Rα to matrices in vitro and to the omentum. The association between IL6Rα expression and LY75 expression has not been previously reported, and the promotion of cellular adherence is a novel role for LY75. These studies indicate that overexpression of LY75 may be an additional mechanism by which IL6 signaling influences the progression of ovarian cancer, and suggests that blocking LY75 could be a valuable clinical strategy for reducing the early metastasis of ovarian cancer.

Background: Epidemiological studies have suggested periodontitis as a risk factor for ischemic heart disease. High sensitive C-reactive protein (hs-CRP), a predictor of cardiovascular risk, is elevated in periodontitis patients. Therefore, local infection-induced elevation of systemic CRP could account for the relationship between the 2 diseases. However, the underlying mechanism of CRP production in the periodontal tissues has not been fully elucidated. Therefore, the aim of the present study was to clarify the mechanism of CRP production in periodontal tissues., Methods: Gene expression of CRP in gingival biopsies was analysed by quantitative PCR. Human gingival epithelial cells (HGECs), human gingival fibroblasts (HGFBs), and human coronary artery endothelial cells (HCAECs) were characterized for CRP-producing ability by incubating with interleukin (IL)-1β, IL-6, soluble IL-6 receptor (sIL-6R), and Porphyromonas gingivalis strain W83., Results: Gene expression of CRP is significantly elevated in periodontitis lesions compared with gingivitis lesions. HCAECs, but not HGECs and HGFBs, produced CRP in response to IL-6 and IL-1β in the presence of sIL-6R. In contrast to IL-6, the effect of IL-1β on CRP production was indirect via induction of IL-6. IL-1β was produced by HGECs and HGFBs with stimulation of P. gingivalis antigens., Conclusion: These results suggest that CRP induced locally by periodontal infection may play another role in the pathogenesis of periodontal disease, and to a much lesser extent, has the potential to modulate systemic CRP level by extra-hepatic CRP production., (Copyright © 2011 Elsevier Ltd. All rights reserved.)

The cation-chloride cotransporter NKCC1 plays a fundamental role in the central and peripheral nervous systems by setting the value of intracellular chloride concentration. Following peripheral nerve injury, NKCC1 phosphorylation-induced chloride accumulation contributes to neurite regrowth of sensory neurons. However, the molecules and signaling pathways that regulate NKCC1 activity remain to be identified. Functional analysis of cotransporter activity revealed that inhibition of endogenously produced cytokine interleukin-6 (IL-6), with anti-mouse IL-6 antibody or in IL-6⁻/⁻ mice, prevented chloride accumulation in a subset of axotomized neurons. Nerve injury upregulated the transcript and protein levels of IL-6 receptor in myelinated, TrkB-positive sensory neurons of murine lumbar dorsal root ganglia. Expression of phospho-NKCC1 was observed mainly in sensory neurons expressing IL-6 receptor and was absent from IL-6⁻/⁻ dorsal root ganglia. The use of IL-6 receptor blocking-function antibody or soluble IL-6 receptor, together with pharmacological inhibition of Janus kinase, confirmed the role of neuronal IL-6 signaling in chloride accumulation and neurite growth of a subset of axotomized sensory neurons. Cell-specific expression of interleukin-6 receptor under pathophysiological conditions is therefore a cellular response by which IL-6 contributes to nerve regeneration through neuronal NKCC1 phosphorylation and chloride accumulation.

Aims: Interleukin (IL)-17-producing helper T (Th17) cells have been proposed to participate in the pathogenesis of chronic inflammation, such as autoimmune myocarditis. IL-6 gene ablation confers the resistance to experimental autoimmune myocarditis (EAM). In this study, we have addressed the pathological roles of IL-6 in the regulation of Th17 cells in EAM., Methods and Results: To induce EAM, mice were immunized twice with α-myosin heavy chain peptide. Three weeks after the first injection, the cardiac expression of the Th17-specific transcription factor, retinoic acid receptor-related orphan nuclear receptor (ROR γt), was up-regulated. Consistently, Th17 cells were recruited into EAM hearts, as analysed by flow cytometry. Using the mice with enhanced green fluorescence protein (eGFP) gene knocked-in at RORγt locus (RORγt-eGFP mice), we observed Th17 cell infiltration into inflamed lesions. Pre-treatment with IL-6 receptor (IL-6R)-blocking antibody (anti-IL-6R Ab) inhibited EAM induction in terms of disease severity score (3.5 ± 0.8; IgG vs. 0.5 ± 0.8; anti-IL-6R Ab, n = 6, P< 0.01) and suppressed the myocardial expression of IL-17 and RORγt. In contrast, the administration of anti-IL-6R Ab 7 days after the first immunization failed to show the inhibitory effects, suggesting that IL-6 plays important roles in EAM initiation. Finally, by generating RORγt-eGFP homozygous mice, we revealed that RORγt gene ablation conferred the resistance to EAM induction., Conclusion: IL-6-mediated induction of Th17 cells is critical for the onset of EAM, but not for its progression. IL-6/Th17 signalling could be a promising therapeutic target for the prevention of myocardial inflammation.

Glioblastomas display cellular hierarchies containing tumor-propagating glioblastoma stem cells (GSCs). STAT3 is a critical signaling node in GSC maintenance but molecular mechanisms underlying STAT3 activation in GSCs are poorly defined. Here we demonstrate that the bone marrow X-linked (BMX) nonreceptor tyrosine kinase activates STAT3 signaling to maintain self-renewal and tumorigenic potential of GSCs. BMX is differentially expressed in GSCs relative to nonstem cancer cells and neural progenitors. BMX knockdown potently inhibited STAT3 activation, expression of GSC transcription factors, and growth of GSC-derived intracranial tumors. Constitutively active STAT3 rescued the effects of BMX downregulation, supporting that BMX signals through STAT3 in GSCs. These data demonstrate that BMX represents a GSC therapeutic target and reinforces the importance of STAT3 signaling in stem-like cancer phenotypes., (Copyright © 2011 Elsevier Inc. All rights reserved.)

IL-6 activates various cell types carrying the membrane bound IL-6R (classical IL-6 signaling) as well as IL-6R(-) gp130(+) cells via the soluble IL-6R (IL-6 trans-signaling). IL-6 signaling plays a pivotal role in controlling the differentiation and activation of T lymphocytes by inducing the Jak/STAT-3 and the Ras/Erk/C/EBP pathways. In particular, IL-6 modulates the resistance of T cells against apoptosis, induces activation of T helper cells and controls the balance between regulatory T cells and Th17 cells. Importantly, recent findings suggest that blockade of IL-6 signaling is effective in treating experimental models of autoimmune and chronic inflammatory diseases such as inflammatory bowel diseases, diabetes, multiple sclerosis, asthma and rheumatoid arthritis as well as models of inflammation-associated cancer. Thus, anti-IL-6/anti-IL-6R strategies emerge as promising novel approaches for therapy of inflammatory diseases in humans. In this review article, we discuss the latest findings on the role of IL-6 in experimental models of autoimmunity and cancer, as well as clinical perspectives., (Copyright © 2011 Elsevier Ltd. All rights reserved.)

This study examined how interleukin-6 (IL-6) and soluble IL-6 receptor (sIL-6r) influence osteoclastic differentiation through the function of chondrocytes. Chondrocytes were cultured with or without IL-6 and/or sIL-6r in the presence or absence of NS398, a specific inhibitor of cyclooxygenase (COX)-2, for up to 28 days. Chondrocytes were also cultured with or without IL-6 and sIL-6r for 28 days, and the conditioned medium from cells cultured without IL-6 and sIL-6r was used to induce differentiation of RAW264.7 cells into osteoclast precursors. Osteoclastic differentiation was assessed by tartrate-resistant acid phosphatase (TRAP) staining. Expression of osteoprotegerin (OPG), receptor activator of NF-κB ligand (RANKL), COX-2, and prostaglandin E(2) (PGE(2)) increased in cells exposed to IL-6 and sIL-6r, whereas expression of macrophage colony-stimulating factor (M-CSF) and bone resorption-related enzymes decreased. NS398 blocked the stimulatory/suppressive effects of IL-6 and sIL-6r on the expression of OPG, RANKL, and M-CSF. Fewer TRAP-positive multinucleated cells were detected after treatment with conditioned medium from IL-6- and sIL-6r-treated chondrocytes than after treatment with conditioned medium from untreated chondrocytes. These results suggest that IL-6 and sIL-6r interfere with osteoclast function through the involvement of chondrocytes. Specifically, they appear to suppress the differentiation of osteoclast precursors into osteoclasts by inducing chondrocytic PGE(2) production, which, in turn, increases OPG secretion and decreases M-CSF secretion by chondrocytes.

Classic IL-6 signaling is conditioned by the transmembrane receptor (IL-6R) and homodimerization of gp130. During trans-signaling, IL-6 binds to soluble IL-6R (sIL-6R), enabling activation of cells expressing solely gp130. Soluble gp130 (sgp130) selectively inhibits IL-6 trans-signaling. To characterize amniotic fluid (AF) IL-6 trans-signaling molecules (IL-6, sIL-6R, sgp130) in normal gestations and pregnancies complicated by intra-amniotic inflammation (IAI), we studied 301 women during second trimester (n = 39), third trimester (n = 40), and preterm labor with intact (n = 131, 85 negative IAI and 46 positive IAI) or preterm premature rupture of membranes (PPROM; n = 91, 61 negative IAI and 30 positive IAI). ELISA, Western blotting, and real-time RT-PCR were used to investigate AF, placenta, and amniochorion for protein and mRNA expression of sIL-6R, sgp130, IL-6R, and gp130. Tissues were immunostained for IL-6R, gp130, CD15(+) (polymorphonuclear), and CD3(+) (T cell) inflammatory cells. The ability of sIL-6R and sgp130 to modulate basal and LPS-stimulated release of amniochorion matrix metalloprotease-9 was tested ex vivo. We showed that in physiologic gestations, AF sgp130 decreases toward term. AF IL-6 and sIL-6R were increased in IAI, whereas sgp130 was decreased in PPROM. Our results suggested that fetal membranes are the probable source of AF sIL-6R and sgp130. Immunohistochemistry and RT-PCR revealed increased IL-6R and decreased gp130 expression in amniochorion of women with IAI. Ex vivo, sIL-6R and LPS augmented amniochorion matrix metalloprotease-9 release, whereas sgp130 opposed this effect. We conclude that IL-6 trans-signaling molecules are physiologic constituents of the AF regulated by gestational age and inflammation. PPROM likely involves functional loss of sgp130.

Naturally occurring CD4(+)CD25(+)Foxp3(+) T regulatory cells (nTregs) regulate lung allergic responses through production of IL-10 and TGF-β. nTregs from CD8(-/-) mice failed to suppress lung allergic responses and were characterized by reduced levels of Foxp3, IL-10, and TGF-β, and high levels of IL-6. Administration of anti-IL-6 or anti-IL-6R to wild-type recipients prior to transfer of CD8(-/-) nTregs restored suppression. nTregs from IL-6(-/-) mice were suppressive, but lost this capability if incubated with IL-6 prior to transfer. The importance of CD8 in regulating the production of IL-6 in nTregs was demonstrated by the loss of suppression and increases in IL-6 following transfer of nTregs from wild-type donors depleted of CD8(+) cells. Transfer of nTregs from CD8(-/-) donors reconstituted with CD8(+) T cells was suppressive, and accordingly, IL-6 levels were reduced. These data identify the critical role of CD8-T regulatory cell interactions in regulating the suppressive phenotype of nTregs through control of IL-6 production.