[Immune Regulation by TNF Receptor-associated Factor 5]

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.

Molecular characterization of grass carp interleukin-6 receptor and the agonistic activity of its soluble form in head kidney leucocytes

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.

The biology and medical implications of interleukin-6

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.

Novel path to IL-6 trans-signaling through thrombin-induced soluble IL-6 receptor release by platelets

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.

Role of IL-6 in asthma and other inflammatory pulmonary diseases

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.

IL-6-mediated Th17 differentiation through RORγt is essential for the initiation of experimental autoimmune myocarditis

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.

Nonreceptor tyrosine kinase BMX maintains self-renewal and tumorigenic potential of glioblastoma stem cells by activating STAT3

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.

Interleukin 6 mediates myocardial fibrosis, concentric hypertrophy, and diastolic dysfunction in rats

Although there is a correlation between hypertension and levels of interleukin (IL) 6, the exact role this cytokine plays in myocardial remodeling is unknown. This is complicated by the variable tissue and circulating levels of IL-6 reported in numerous experimental models of hypertension. Accordingly, we explored the hypothesis that elevated levels of IL-6 mediate adverse myocardial remodeling. To this end, adult male Sprague-Dawley rats were infused with IL-6 (2.5 microg . kg(-1) . h(-1), IP) for 7 days via osmotic minipump and compared with vehicle-infused, aged-matched controls. Left ventricular function was evaluated using a blood-perfused isolated heart preparation. Myocardial interstitial collagen volume fraction and isolated cardiomyocyte size were also assessed. Isolated adult cardiac fibroblast experiments were performed to determine the importance of the soluble IL-6 receptor in mediating cardiac fibrosis. IL-6 infusions in vivo resulted in concentric left ventricular hypertrophy, increased ventricular stiffness, a marked increase in collagen volume fraction (6.2% versus 1.7%; P<0.001), and proportional increases in cardiomyocyte width and length, all independent of blood pressure. The soluble IL-6 receptor in combination with IL-6 was found to be essential to producing increased collagen concentration by isolated cardiac fibroblasts and also played a role in mediating a phenotypic conversion to myofibroblasts. These novel observations demonstrate that IL-6 induces a myocardial phenotype almost identical to that of the hypertensive heart, identifying IL-6 as potentially important in this remodeling process.

Establishment and characterization of an androgen receptor-dependent, androgen-independent human prostate cancer cell line, LNCaP-CS10

BACKGROUND

Hormone refractoriness is a lethal event for advanced prostate cancer patients, but the mechanisms of the disease are not well elucidated, especially for the so-called "outlaw" pathways of androgen receptor (AR)-dependent, androgen-independent hormone-refractory prostate cancer.

METHODS

Androgen-dependent prostate cancer LNCaP cells were treated with bicalutamide under an androgen-depleted condition to obtain refractory cells. In the obtained cell line, LNCaP-CS10, we analyzed the effects of androgen and bicalutamide on cell growth and prostate-specific antigen (PSA) production. In addition, AR gene mutation, AR expression levels, and AR subcellular localizations were analyzed.

RESULTS

In LNCaP-CS10, cell growth and PSA production were found under an androgen-depleted condition and were induced by both R1881 and bicalutamide. Knocking down AR by siRNAs did suppress the growth and PSA production of LNCaP-CS10 cells in the androgen-depleted condition. In comparison to LNCaP, amplification or additional new mutations were not found in the AR genes, but AR nuclear translocation induced by bicalutamide was identified in the LNCaP-CS10 cells. The growth and PSA production of xenografted LNCaP-CS10 tumors, which secrete PSA not only in non-castrated SCID mice but also in castrated SCID mice, were not inhibited by bicalutamide.

CONCLUSIONS

We have generated a bicalutamide-resistant and androgen-independent prostate cancer cell line, LNCaP-CS10, with outlaw activation both in vitro and in vivo. The LNCaP-CS10 cell line is beneficial for elucidating outlaw pathway mechanisms and evaluating the efficacy of new therapeutics for hormone-refractory prostate cancer.

Interleukin-6 trans-signalling differentially regulates proliferation, migration, adhesion and maspin expression in human prostate cancer cells

Interleukin-6 (IL-6) is suggested to have a pathogenic role in the progression of prostate cancer (PC), therefore representing an attractive target for new therapies. However, due to the pleiotropy of this cytokine, targeting IL-6 results in different and unpredictable responses. In order to better understand the mechanisms underlying the different responses to the cytokine, we focused our attention on IL-6 receptors (IL-6Rs) that represent the first element in the cascade of cytokine-activated signalling pathways. IL-6 signal transduction may indeed occur through the membrane IL-6R (classical signalling) and/or through the less studied soluble IL-6R (sIL-6R; IL-6 trans-signalling (IL-6TS)). We provide the first evidence how responses to IL-6 may depend on the different content of IL-6Rs in PC. In particular, the studies of (3)H-thymidine incorporation and exploitation of different approaches (i.e. activation or inhibition of IL-6TS in sIL-6R-negative and -positive cell lines and transfection of IL-6R siRNA) allowed us to demonstrate that IL-6TS specifically accounts for an anti-proliferative effect of the cytokine in three PC cell lines that are known to respond differently to IL-6. Additionally, by applying migration-, scratch- and adhesion assays, we show that IL-6TS increases motility and migration and decreases adhesion of prostate cells facilitating thereby processes that determine metastasis initiation and spread. Finally, by western analyses, we uncovered an IL-6- and sIL-6R-dependent downregulation of the tumour suppressor maspin. Collectively, these data suggest that selective targeting of IL-6TS might allow to refine the currently available experimental anti-IL-6 therapies against PC.

Loss of CD4+ T cell IL-6R expression during inflammation underlines a role for IL-6 trans signaling in the local maintenance of Th17 cells

IL-6 responses are classically orchestrated via a membrane-bound IL-6R (CD126) alpha subunit (classical IL-6R signaling) or through a soluble form of this cognate receptor (IL-6 trans signaling). Appraisal of IL-6R expression on human and mouse T cells emphasized that IL-6R expression is closely linked with that of CCR7 and CD62L. In this regard, infiltrating effector T cells from clinical and experimental peritonitis episodes lose IL-6R expression, and anti-CD3/CD28 Ab costimulation of peripheral T cells in vitro leads to a downregulation in IL-6R expression. Consequently, IL-6 signaling through membrane-bound IL-6R seems to be limited to naive or central memory T cell populations. Loss of IL-6R expression by activated T cells further suggests that these effector cells might still retain IL-6 responsiveness via IL-6 trans signaling. Using IL-6R-deficient mice and recombinant tools that modulate the capacity of IL-6 to signal via its soluble receptor, we report that local control of IL-6 trans signaling regulates the effector characteristics of the T cell infiltrate and promotes the maintenance of IL-17A-secreting CD4(+) T cells. Therefore, we concluded that classical IL-6R signaling in naive or central memory CD4(+) T cells is required to steer their effector characteristics, whereas local regulation of soluble IL-6R activity might serve to maintain the cytokine profile of the Th cell infiltrate. Therefore, the activation status of a T cell population is linked with an alteration in IL-6 responsiveness.

Interleukin-6: an autocrine regulator of the mouse cumulus cell-oocyte complex expansion process

Ovulation has long been regarded as a process resembling an inflammatory response. Recent studies indicate that genes associated with innate immune responses were also expressed during the ovulation process. Because the innate immune genes are induced in cumulus cell oocyte complexes (COCs) later than the inflammation-associated genes, we hypothesize that COC expansion is dependent on specific sequential changes in cumulus cells. Because IL-6 is a potent mediator of immune responses, we sought to determine what factors regulate the induction of Il6 mRNA in COCs and what impact IL-6 alone would have on COC expansion. We found that the levels of Il6 mRNA increased dramatically during COC expansion, both in vivo and in vitro. Moreover, IL-6, together with its soluble receptor (IL-6SR), could bypass the need for either amphiregulin and/or prostaglandin E2 to induce the expansion of COCs. This ability of IL-6/IL-6SR to induce COC expansion was blocked by the inhibitors to p38MAPK, MAPK kinase 1/2, and Janus kinase. More importantly, when COCs were in vitro maturated in the presence of IL-6, they had a significantly higher embryo transfer rate than the ones without IL-6 and comparable with in vivo matured oocytes. IL-6/IL-6SR activated multiple signaling pathways (Janus kinase/signal transducer and activator of transcription, ERK1/2, p38MAPK, and AKT) and progressively induced genes known to impact COC expansion, genes related to inflammation and immune responses, and some transcription factors. Collectively, these data indicate that IL-6 alone can act as a potent autocrine regulator of ovarian cumulus cell function, COC expansion, and oocyte competence.

Regulation of Th17 cell differentiation and EAE induction by MAP3K NIK

Th17 cells play an important role in mediating autoimmune diseases, but the molecular mechanism underlying Th17 differentiation is incompletely understood. We show here that NF-kappaB-inducing kinase (NIK), which is known to regulate B-cell maturation and lymphoid organogenesis, is important for the induction of Th17 cells. NIK-deficient naive CD4 T cells are attenuated in the differentiation to Th17 cells, although they are competent in committing to the other effector lineages. Consistently, NIK knockout mice are resistant to experimental autoimmune encephalomyelitis, a disease model that involves the function of Th17 cells. This phenotype was also detected in Rag2 knockout mice reconstituted with NIK-deficient T cells, confirming a T-cell intrinsic defect. We further show that NIK mediates synergistic activation of STAT3 by T-cell receptor and IL-6 receptor signals. NIK deficiency attenuates activation of STAT3 and induction of STAT3 target genes involved in Th17-commitment program. These findings establish NIK as an important signaling factor that regulates Th17 differentiation and experimental autoimmune encephalitis induction.

Transgenic mouse models

The development of peritoneal dialysis has been paralleled by a growing interest in establishing suitable experimental models to better understand the functional and structural processes operating in the peritoneal membrane. Thus far, most investigations have been performed in rat and rabbit models, with mechanistic insights essentially based on intervention studies using pharmacological agents, blocking antibodies, or transient expression systems. Since the body size of a species is no longer a limiting factor in the performance of in vivo studies related to peritoneal dialysis, it has been considered that mice, particularly once they have been genetically modified, could provide an attractive tool to investigate the molecular mechanisms operating in the peritoneal membrane. The purpose of this review is to illustrate how investigators in peritoneal dialysis research, catching up with other fields of biomedical research, are increasingly taking advantage of mouse models to provide direct evidence of basic mechanisms involved in the major complications of peritoneal dialysis.

Inflammation may modulate IL-6 and C-reactive protein gene expression in the adipose tissue: the role of IL-6 cell membrane receptor

Only few studies have been addressed to the presence and regulation of C-reactive protein (CRP) gene expression in different districts of adipose tissue, and no study has investigated the role of adipose tissue in presence of inflammation. Therefore, the aim of this study was to investigate the inflammatory involvement of either adipose tissue or adipose cells (adipocytes and stromal cells, respectively) in patients with chronic inflammatory disease, focusing on regional adipose tissue CRP gene expression. Eighteen patients with inflammatory disease and 14 healthy controls were enrolled. All subjects underwent specific surgical procedures. Inflamed and noninflamed patients provided samples of subcutaneous and/or omental adipose tissue. All samples were analyzed by RT-PCR and real-time PCR for specific gene expression. In addition, both adipocytes and stromal cells were studied by real-time PCR and immunoprecipitation to evaluate either gene or protein expression of CRP. Our results (real-time PCR) demonstrated a higher gene expression of CRP, IL-6, and both IL-6 membrane receptors in subcutaneous samples of inflamed patients than in healthy controls. Furthermore, in omental fragments of inflamed patients, an enhanced mRNA abundance of the same genes, compared with subcutaneous, was observed. The results obtained at cellular level did not provide evidence of any difference between adipocytes and stromal cell CRP gene expression, whereas immunoprecipitation demonstrated the presence of CRP in inflamed subjects. These results provide first-time evidence of the involvement of adipose tissue in the course of chronic inflammatory diseases, with a different degree of participation of the different adipose tissue districts.

Il-6 signaling in inflammatory bowel disease: pathophysiological role and clinical relevance

Crohn's disease (CD) and ulcerative colitis (UC) are chronic inflammatory bowel diseases (IBDs) occurring in the gut of genetically susceptible individuals independent of a specific pathogen. The interaction between antigen-presenting cells and the local bacterial flora contributes to an uncontrolled activation of mucosal CD4+ T lymphocytes with the consecutive release of proinflammatory cytokines such as tumor necrosis factor (TNF), interleukin (IL)-6, IL-12, IL-23, IL-27, and also IL-17, which is attributed to a specific, differentiated CD4+ lineage called Th17 (TH-IL17, THi). Recent data suggest that IL-6 contributes to Th17 differentiation. However, to clarify the importance of Th17 cells in IBD further data are needed. So far, CD has been attributed to a Th1-mediated disease, whereas UC exhibits a modified Th2 cytokine response. In both diseases CD4+ T cells at the site of inflammation are critically dependent on antiapoptotic IL-6 signaling. Thereby, IL-6 induces the transcription factor STAT-3 via transsignaling (activation of a cell lacking membrane-bound IL-6 receptor via soluble IL-6 receptor). STAT-3 itself induces the antiapoptotic factors bcl-2 and bcl-xL, thus resulting in T-cell resistance against apoptosis. This vicious circle of T-cell accumulation, mediated by apoptosis resistance, finally leading to chronic inflammation, can be blocked by anti-IL-6 receptor antibodies. This review highlights the role of IL-6 in IBD immunopathogenesis and its clinical relevance in IBD therapy and diagnostics.

3-O-Formyl-20R,21-epoxyresibufogenin suppresses IL-6–type cytokine actions by targeting the glycoprotein 130 subunit: Potential clinical implications

BACKGROUND

The multifunctional inflammatory cytokine IL-6 regulates the acute phase reaction and plays central roles in the pathogenesis of chronic inflammatory disorders.

OBJECTIVES

Two small chemical compounds, 3-O-formyl-20R,21-epoxyresibufogenin (TB-2-081) and 3-O-formyl-20S,21-epoxyresibufogenin (TB-2-082), known isolates from the Chinese toad skin extract drug Ch'an Su, were synthesized and tested on the IL-6-induced hepatic acute-phase reaction.

METHODS

HepG2 cells or rat primary hepatocytes were incubated with the compounds, and the effects on IL-6-induced expression of acute-phase molecules were tested.

RESULTS

TB-2-081, and to a lesser extent TB-2-082, suppressed IL-6-induced alpha1-antichymotrypsin (AACT) mRNA expression in HepG2 cells, whereas TB-2-081 failed to influence the mRNA expression of the TNF-alpha-induced mRNA expression of the methionine adenosyltransferase 2A gene in these cells. TB-2-081 suppressed IL-6-induced mRNA expression of alpha1-acid glycoprotein, alpha2-macroglobulin, and beta-fibrinogen in and secretion of the C-reactive protein by rat primary hepatocytes. TB-2-081 shifted the IL-6 dose-response curve of the AACT mRNA expression right and downward and inhibited IL-6-induced phosphorylation of signal transducer and activator of transcription 3. In addition to IL-6, TB-2-081 inhibited IL-11-stimulated and oncostatin M-stimulated AACT mRNA expression independently of the IL-6 receptor subunit. The soluble glycoprotein 130, but not the soluble IL-6 receptor, antagonized TB-2-081-induced suppression of IL-6-stimulated AACT mRNA expression.

CONCLUSION

TB-2-081 inhibits IL-6-type cytokine action by attenuating the function of the common receptor subunit glycoprotein 130.

CLINICAL IMPLICATIONS

This class of compounds may be beneficial for the treatment of diseases in which excessive circulation/production/action of IL-6-type cytokines play pathologic roles.

[Effect of Notch ligand Delta-1 on the differentiation and maturation of erythroid progenitors in humans]

OBJECTIVE

To explore the biological effect of Notch ligand Delta-1 (Notch L delta-1) on the sIL-6R during the differentiation of erythroid hematopoiesis.

METHODS

Mononuclear cells (MNCs) was isolated from the normal cord blood using Ficoll graduation solution. MNCs were enriched for CD34(+) CD38(-) cells by CD34 immunomagnetic beads and a FACS Vantage. CD34(+) CD38(-) cells was cultured for 7 days in the presence of SCF, Flt3L, TPO and IL-3 (4GFs). The cultured cells was detected for the expression of IL-6R and GPA. The subsequently enriched CD36(+) erythroid progenitors were sorted for cells with IL-6R(+) and IL-6R(-) using FACS Vantage. The CD36(+) GPA(-) IL-6R(-) cells were respectively cultured in the 4GFs, 4GFs + IL-6 or 4GFs + FP6 containing medium in the presence or absence of Notch L delta-1 for 14 days and CD36(+) GPA high red cells were counted.

RESULTS

IL-6R cells accounted for 95% of CD36(+) GPA(+) cells. The CD36(+) GPA(-) cells was clearly divided into IL-6R(+) (46%) and IL-6R(-) (54%) subpopulations, the IL-6R(+) cell subpopulation formed only a few GM colonies (2.1 +/- 1.8) and a greater number of BFU-E colonies were generated from the IL-6R(-) subpopulation (58.2 +/- 18.1) (P < 0.05). The number of CD36(+) GPA high cell was (1.400 +/- 0.180) x 10(6) in the presence of FP6, lower than that [(2.460 +/- 0.190) x 10(6)] in the presence of FP6 + Notch L delta-1 (P < 0.05).

CONCLUSION

Notch L delta-1 enhances the sIL-6R-mediated effects of IL-6 on the generation of erythroid cells.

The IL-6/sIL-6R complex as a novel target for therapeutic approaches

IL-6 plays a pivotal role in immune responses and certain oncologic conditions. The intense investigation of its biological activity and function led to the discovery of two different IL-6-driven signalling pathways. Binding to the membrane-bound IL-6 receptor (mIL-6R, CD126) causes the recruitment of two gp130 co-receptor molecules (CD130) and the activation of intracellular signalling cascades via gp130. Although this classical pathway is mainly limited to hepatocytes, neutrophils, monocytes/macrophages and certain other leukocyte populations, which express IL-6R on their surface, an alternative mechanism has also been described. Proteolytic cleavage of the mIL-6R protein or translation from alternatively spliced mRNA leads to the generation of a soluble form of the IL-6R (sIL-6R), which is likewise able to bind to IL-6. The resulting IL-6/sIL-6R complex is also capable of binding to gp130 and inducing intracellular signalling. Through this so-called 'trans-signalling' mechanism, IL-6 is able to stimulate cells that lack an endogenous mIL-6R. High levels of IL-6 and sIL-6R have been reported in several chronic inflammatory and autoimmune diseases as well as in cancer. Preclinical animal disease models have provided strong evidence that specific blockade of IL-6-regulated signalling pathways represents a promising approach for the therapy of these diseases. An optimised variant of the recently described fusion protein sgp30Fc is now heading towards its clinical evaluation.

Essential role of IL-6 signaling pathway in keloid pathogenesis

Cytokines are pleiotropic substances that are known to participate in inflammatory and immune responses as well as cell differentiation and proliferation. Interleukin-6 (IL-6) is a key cytokine with pro-inflammatory function. Wound healing is a complex cascade of physiologic events comprising inflammation, proliferation and remodeling, and proceeds with the integrated actions of different cells, cytokines, and the extracellular matrix. Aberrant wound healing results in keloid formation which causes disfigured appearance, discomfort, psychological stress, and patient frustration. In this review, the role of IL-6 signaling pathway in the pathogenesis of keloid is assessed and its potential as a therapeutic target is addressed. The existing data suggest that IL-6 mediated inflammation is a key player and may be considered as a common causative factor for development of keloid. Furthermore, in a recent comprehensive study, we confirmed the functional role of IL-6 signaling in keloid pathogenesis. Accordingly, inhibitory strategies of IL-6 signaling pathway by targeting the IL-6 receptors, its downstream effecters, or other molecules influencing this pathway appear to have considerable potential as new therapeutic or preventive challenges for keloid. Hopefully, several IL-6 blocking agents including a humanized antibody to IL-6 receptor have been developed and successfully used in clinical trials of inflammatory diseases. It is likely that these agents may prove worthy in the treatment or prevention of keloid as well. Future in-depth exploration of such challenges will shed light on their efficacy and safety for clinical application in keloid.

Local Activation of Interleukin 6 Signaling Is Associated With Arteriovenous Fistula Stenosis in Hemodialysis Patients

BACKGROUND

Vascular access failure is the main cause of morbidity in hemodialysis patients. Stenosis of the arteriovenous fistula (AVF) is similar histologically to atherosclerosis. Recent studies showed that interleukin 6 (IL-6) has a key role in the pathogenesis of atherosclerosis by binding 2 specific receptors, gp80 and gp130. When activated, gp130 interacts with a tyrosine kinase, Janus kinase (JAK2), which then activates a transcription factor, signal transducers and activators of transcription (STAT3), directly turning on several proinflammatory genes. The aim of this study is to evaluate gp130 expression and JAK2/STAT3 activation within stenotic AVFs.

METHODS

44 patients undergoing surgery for AVF creation were enrolled; 10 of them had AVF failure with histologically proven AVF stenosis (wall-lumen ratio > 1). A venous fragment of the AVFs was collected during creation and revision of the vascular access. gp130 and gp80 expression, as well as JAK/STAT activation, were evaluated by means of confocal microscopy. Peripheral-blood mononuclear cells were isolated at the time of AVF creation and revision.

RESULTS

gp130 protein expression, barely detectable in native AVFs, was strikingly increased within the venous branch of stenotic AVFs. The signaling subunit of the IL-6 receptor broadly colocalized with gp80, the IL-6-binding subunit. gp130-expressing cells were mainly CD34(+), suggesting that this receptor is expressed primarily by neovasculature endothelial cells. At the same time, a significant increase in phosphorylation of JAK2/STAT3 was observed in endothelial cells of stenotic AVFs. Interestingly, peripheral-blood mononuclear cells isolated at the time of AVF failure presented strikingly greater IL-6 expression compared with dialysis age-matched controls.

CONCLUSION

IL-6 receptor activation may have a role in the pathogenesis of AVF failure in hemodialysis patients and may represent a potential therapeutic target in this setting.

Anti-interleukin-6 receptor antibody therapy in rheumatic diseases

In the treatment of rheumatic diseases such as rheumatoid arthritis (RA) or systemic onset juvenile idiopathic arthritis (soJIA), new therapies targeting pro-inflammatory cytokines have been developed. IL-6 is a pleiotropic cytokine with a wide range of biological activities including a pro-inflammatory mediator activity. Overproduction of IL-6 has been reported to be pathologically involved in the rheumatic diseases and, therefore, blockade of IL-6 actions may improve the disease. Tocilizumab, a humanized monoclonal antibody against human interleukin-6 receptor (IL-6R), inhibits IL-6 binding to IL-6R and specifically interferes with IL-6 actions. Castleman's disease is an atypical lymphoproliferative disorder caused by the overproduction of IL-6. Tocilizumab therapy improves immunological and hematological abnormalities as well as systemic inflammatory symptoms including wasting. This translational study also confirmed the pathological significance of IL-6 in the disease. RA is a representative autoimmune inflammatory disease characterized by bone and cartilage destruction in multiple joints. Since IL-6 also plays pathological roles in RA, tocilizumab therapy has been introduced to the patients with refractory disease and has shown a strong therapeutic effect. Besides Castleman's disease and RA, tocilizumab has been shown to be effective for patients with soJIA and Crohn's disease. Tocilizumab treatment is generally well tolerated and safe. Therefore, tocilizumab can be a promising therapeutic agent for the rheumatic diseases in which IL-6 overproduction is pathologically involved.

Interleukin-6--a key mediator of systemic and local symptoms in rheumatoid arthritis

Interleukin-6 (IL-6) is a pleiotropic cytokine, present at elevated levels in patients with rheumatoid arthritis (RA). Il-6 signaling involves both a specific IL-6 receptor (IL-6R) and a ubiquitous signal-transducing protein, gp130 that is also utilized by other members of the IL-6 family. Il-6 signaling occurs by two mechanisms. Conventional signaling involves the binding of IL-6 to transmembrane IL-6R on cells expressing this receptor. In contrast, trans-signaling involves binding between the complex of soluble IL-6R/IL-6 and membrane-bound gp130. Trans-signaling allows IL-6 to affect cells that do not express IL-6R, including many synovial cells. The biological activities of IL-6 contribute to both systemic and local RA symptoms. Il-6 is a strong inducer of the acute-phase response, which can result in fever, secondary amyloidosis, anemia, and elevations in acute-phase proteins, such as C-reactive protein (CRP). The ability of IL-6 to induce B-cell differentiation may lead to the formation of rheumatoid factor and other autoantibodies. In joints, IL-6 promotes osteoclast activation and induces the release of matrix metalloproteinases, thus contributing to joint damage. In patients with RA, IL-6 levels correlate with markers of disease activity and clinical symptoms, and animal studies support the concept that this cytokine plays a role in the development of inflammatory arthritis. Clinical trials with tocilizumab, a humanized monoclonal antibody to soluble IL-6R, have shown that blocking IL-6 signaling reduces RA symptoms and markers of disease activity. Current evidence thus strongly supports the association between IL-6 and RA symptoms and suggests that IL-6 blockade will be a useful therapeutic strategy for patients with this disease.

Interleukin-6 trans-signaling in inflammatory bowel disease

The pathogenesis of inflammatory bowel disease (IBD) is complex, involving a wide range of molecules including cytokines. Recent investigations support the important role of an interleukin-6 (IL-6) signaling pathway in the development of IBD. However, the molecular mechanisms of this pathway in the intestine remain incompletely understood. The circulating and intestinal levels of IL-6 as well as soluble IL-6 receptor (sIL-6R) are increased in patients with IBD. It is remarkable that the mucosal T cells of IBD patients are extremely resistant to apoptosis and that a large fraction of these cells express membrane-bound gp130 but not IL-6R. The accumulated evidence strongly supports the hypothesis that the development and perpetuation of IBD relies on the increased formation of IL-6/sIL-6R complexes interacting with membrane-bound gp130 on T cells via trans-signaling. These studies suggest that IL-6 trans-signaling may play a role in the development of IBD; they therefore imply the possibility of a selective therapeutic strategy to target this signaling.

Functional implications of the IL-6 signaling pathway in keloid pathogenesis

The molecular mechanism(s) behind keloid pathogenesis remains unclear. Previously by global gene expression analysis of keloid fibroblasts (KFs), we implicated the IL-6 signaling pathway in keloid pathogenesis. Here, we determine a functional role of IL-6 signaling in keloid scars. Primary cultures of KFs and surrounding nonlesional fibroblasts (NFs) were subjected to induction or inhibition of IL-6 or its specific receptor IL-6 receptor alpha (IL-6R alpha) and detection of their effects on extracellular matrix gene expression. The levels of gp130 and several downstream targets in IL-6 signaling were also examined. IL-6 secretion was significantly higher in KFs than NFs. Addition of IL-6 peptide to NFs culture or inhibition of IL-6 or its receptor IL-6R alpha by their corresponding antibodies in KFs culture revealed a dose-dependent increase or decrease in collagen type I alpha 2 and fibronectin 1 mRNAs, respectively. Induction of IL-6 by IL-1beta peptide and stimulation by IL-6 peptide in NFs, or inhibition of IL-6 or IL-6R alpha in KFs cultures demonstrated a dose-dependent increase or decrease in procollagen I synthesis, respectively. The mRNA and protein expressions of gp130 and several downstream targets in IL-6 signaling (JAK1, STAT3, RAF1, and ELK1) were upregulated in KFs versus NFs. Our results indicate that IL-6 signaling may play an integral role in keloid pathogenesis and provide clues for development of IL-6 receptor blocking strategies for therapy or prophylaxis of keloid scars.

Regulation of pre-B cell colony-enhancing factor by STAT-3-dependent interleukin-6 trans-signaling: implications in the pathogenesis of rheumatoid arthritis

OBJECTIVE

To determine whether interleukin-6 (IL-6) trans-signaling directs the expression of pre-B cell colony-enhancing factor (PBEF) in vitro and in vivo.

METHODS

Complementary DNA from rheumatoid arthritis (RA) synovial fibroblasts treated with IL-6 and soluble IL-6 receptor (sIL-6R) was used to probe a cytokine microarray. PBEF regulation by the IL-6-related cytokines, IL-6, sIL-6R, oncostatin M (OSM), IL-11, and leukemia inhibitory factor (LIF) was determined by reverse transcription-polymerase chain reaction analysis. IL-6-mediated STAT-3 regulation of PBEF was determined using a cell-permeable STAT-3 inhibitor peptide. Antigen-induced arthritis (AIA) was induced in wild-type (IL-6(+/+)) and IL-6-deficient (IL-6(-/-)) mice. PBEF and STAT were detected by immunohistochemistry, immunoblotting, and electrophoretic mobility shift assay. Synovial levels of PBEF were quantified by enzyme immunoassay.

RESULTS

IL-6 trans-signaling regulated PBEF in a STAT-3-dependent manner. In addition, PBEF was regulated by the IL-6-related cytokine OSM, but not IL-11 or LIF. Flow cytometric analysis of the IL-6-related cognate receptors suggested that OSM regulates PBEF via its OSM receptor beta and not its LIF receptor. The involvement of PBEF in arthritis progression was confirmed in vivo, where induction of AIA resulted in a 4-fold increase in the synovial expression of PBEF. In contrast, little or no change was observed in IL-6(-/-) mice, in which the inflammatory infiltrate was markedly reduced and synovial STAT-1/3 activity was also impaired. Analysis of human RA synovial tissue confirmed that PBEF immunolocalized in apical synovial membrane cells, endothelial cells, adipocytes, and lymphoid aggregates. Synovial fluid levels of PBEF were significantly higher in RA patients than in osteoarthritis patients.

CONCLUSION

Experiments presented herein demonstrate that PBEF is regulated via IL-6 trans-signaling and the IL-6-related cytokine OSM. PBEF is also actively expressed during arthritis. Although these data confirm an involvement of PBEF in disease progression, the consequence of its action remains to be determined.

Signal transduction by human herpesvirus 8 viral interleukin-6 (vIL-6) is modulated by the nonsignaling gp80 subunit of the IL-6 receptor complex and is distinct from signaling induced by human IL-6

Human herpesvirus 8 (HHV-8) viral interleukin-6 (vIL-6) mediates signaling through the gp130 signal transducer but unlike human IL-6 (hIL-6) does not require the nonsignaling gp80 alpha subunit of the IL-6 receptor complex. By utilizing a gp80-refractory vIL-6 variant, vIL-6(R189L), we found that signal transduction, as measured by STAT1 and STAT3 activation and gp130 tyrosine phosphorylation in gp80+/gp130+ HEK293T cells, was modulated by gp80. Furthermore, the signaling and BAF-130 cell growth-promoting activities of vIL-6 and hIL-6 could be distinguished, and exogenous addition of soluble gp80 enhanced cell growth supported by vIL-6. Our findings demonstrate that gp80 can modulate vIL-6 activity and that vIL-6 and hIL-6 signaling are not directly equivalent.

IL-6 protects enterocytes from hypoxia-induced apoptosis by induction of bcl-2 mRNA and reduction of fas mRNA

Interleukin-6 (IL-6) has been shown to rescue enterocytes from hypoxia-induced apoptosis when given orally following hemorrhagic shock. In vitro models using an intestinal epithelial cell line (IEC-6) cultured with lipopolysaccharide (LPS) under low O2 conditions, to mimic intestinal conditions, show that these cells also undergo apoptosis, which can be reduced by subsequent culture with IL-6. To examine further the mechanisms of rescue, we cultured normal rat intestinal epithelial cells (IEC-6) under both normoxic and hypoxic conditions and analyzed their responses to LPS and IL-6. We showed that IEC-6 expressed IL-6 receptor on its surface. Further, IEC-6 cells could be rescued from hypoxia-induced apoptosis by co-culture with IL-6. RNase protection assay (RPA) examination revealed that under hypoxic conditions, IEC-6 cells that were resistant to apoptosis showed reduced fas expression and increased bcl-2 expression after co-culture with LPS+IL-6.

Signalling and survival pathways in multiple myeloma

The main factors that govern the pathophysiology and malignant growth of multiple myeloma (MM) are genetic defects within the tumour and the interaction between myeloma cells and the bone marrow microenvironment (BMM). This interaction leads to the activation of signalling pathways that promote the expansion of the malignant clone and stimulate neoangiogenesis and osteoclastogenesis. For many years, the cytokine interleukin-6 (IL-6) was considered a central growth factor and was thus believed to play a pivitol role in the pathogenesis of MM. However, increasing numbers of cytokines, chemokines and cell-to-cell contacts provided by the BMM have since been found to support MM cells. It has consistently been demonstrated that oncogenic mutations as well as the BMM stimulate IL-6-independent signalling pathways that protect MM cells from apoptosis. Consequently, multiple targeting of a complex signalling network rather than inhibition of a single pathway or growth factor is required to effectively induce myeloma cell death. Because the tumour suppressor p53 is rarely mutated in MM, non-genotoxic activation of the p53-dependent death pathway could be another attractive therapeutic strategy for this disease. Even though a number of promising new drugs are currently being tested in MM, a comprehensive knowledge of the signalling and survival pathways should pinpoint additional molecular targets and lead to the development of novel and hopefully more effective treatment strategies.

Interleukin-6 trans-signalling in chronic inflammation and cancer

Interleukin-6 (IL-6) is a cytokine, which plays an important role in many chronic inflammatory diseases. IL-6 belongs to a family of 10 cytokines, which all act via receptor complexes containing the cytokine receptor subunit gp130. On cells, IL-6 first binds to a specific membrane-bound IL-6R and the complex of IL-6 and IL-6R interacts with gp130 leading to signal initiation. Whereas gp130 is widely expressed throughout the body, the IL-6R is only found on some cells including hepatocytes and some leucocytes. A soluble form of the IL-6R is an agonist capable of transmitting signals through interaction with the gp130 protein. In vivo, the IL-6/soluble IL-6R complex stimulates several types of target cells, which are unresponsive to IL-6 alone, as they do not express the membrane-bound IL-6R. We have named this process trans-signalling. We provided evidence that a soluble form of the IL-6 family signalling receptor subunit gp130 is the natural inhibitor of IL-6 trans-signalling responses. We showed that in chronic inflammatory diseases such as inflammatory bowel disease, peritonitis, rheumatoid arthritis, asthma as well as in colon cancer, IL-6 trans-signalling is critically involved in the maintenance of the disease state. Moreover, in all these animal models, the progression of the disease can be interrupted by specifically interfering with IL-6 trans-signalling using recombinant-soluble gp130Fc protein. The pathophysiologic mechanisms by which the IL-6/soluble IL-6R complex perpetuates the inflammatory state are discussed.

Interleukin-6 and its receptor: from bench to bedside

Interleukin-6 (IL-6) is an inflammatory cytokine with a well-documented role in inflammation and cancer. The cytokine binds to a membrane bound IL-6 receptor (IL-6R) and this complex associates with two molecules of the signal transducing protein gp130 thereby initiating intracellular signaling. While gp130 is present on most if not all cells of the body, the IL-6R is only present on some cells, mainly hepatocytes and several leukocytes. Cells, which only express gp130 and no IL-6R are refractory to IL-6 signals. We have shown earlier that the IL-6R can exist as a soluble protein generated by limited proteolysis of the membrane bound receptor or by translation from an alternatively spliced mRNA. This soluble IL-6R (sIL-6R) can bind the ligand IL-6 and the soluble complex of sIL-6R and IL-6 can bind to gp130 on cells which lack the membrane bound IL-6R and trigger gp130 signaling. We have named this process 'trans-signaling'. We will review data, which clearly show that IL-6 uses classical signaling via the membrane bound receptor and trans-signaling via the soluble receptor in various physiological and pathophysiological situations. Furthermore, we have developed designer cytokines, which can specifically enhance or inhibit IL-6 trans-signaling. These designer cytokines have been shown to be extremely useful to in therapeutic applications ranging from the long-term culture of stem cells and enhancing liver regeneration up to the blockade of chronic inflammation and cancer.

Anti-interleukin-6 receptor antibody therapy -From Bedside to Bench-

Recent progress in immunology, utilizing molecular biology techniques, has elucidated the molecular mechanism of immune system. In the treatment of autoimmune diseases, molecular targeting therapies utilizing biologics such as monoclonal antibodies are now available. However, exact causes of the most autoimmune diseases are not known and there remain many issues which should be resolved. Interleukin-6 (IL-6) is a cytokine which regulates immune response and inflammation. Deregulated overproduction of IL-6 is involved in the immune-inflammatory diseases such as Castleman's disease and rheumatoid arthritis. A humanized anti-IL-6 receptor antibody tocilizumab has been proven to be therapeutically effective for the diseases. Simultaneously, we have learned new biological activities from the translational research. In this review, a study from bedside to bench is to be discussed.

Modeling and simulation with Hybrid Functional Petri Nets of the role of interleukin-6 in human early haematopoiesis

The regulation of human haematopoiesis is a complex biological system with numerous interdependent processes. In vivo Haematopoietic Stem Cells (HSCs) self-renew so as to maintain a constant pool of these cells. It would be very interesting to maintain these cells in vitro, in view of their therapeutical importance. Unfortunately, there is currently no known process to activate HSCs self-renewal in vitro. Since the difficulties related to in vitro experiments, modeling and simulating this process is indispensable. Moreover, the complexity of haematopoiesis makes it necessary to integrate various functionalities: both discrete and continuous models as well as consumption and production of resources. We thus focus on the use of Hybrid Functional Petri Nets, which offer a number of features and flexibility. We begin by modeling and simulating the role of a specific cytokine, interleukin-6, in the regulation of early haematopoiesis. Results obtained in silico lead to the disappearence of HSCs, which is in agreement with in vitro results.

Directing transition from innate to acquired immunity: defining a role for IL-6

Appropriate control of leukocyte recruitment and activation is a fundamental requirement for competent host defense and resolving inflammation. A pivotal event that defines the successful outcome of any inflammatory event is the transition from innate to acquired immunity. In IL-6 deficiency, this process appears defective, and a series of in vivo studies have documented important roles for IL-6 in both the resolution of innate immunity and the development of acquired immune responses. Within this review, particular attention will be given to the regulatory properties of the soluble IL-6 receptor and how its activity may affect chronic disease progression.

Interleukin-6: An osteotropic factor influencing bone formation?

Interleukin (IL)-6 has long been considered as an osteoresorptive factor. However, recent data indicate that IL-6 could influence bone formation in conditions of increased bone turnover. In this paper, the effects of IL-6 and its soluble receptor on osteoblast proliferation, differentiation and apoptosis are readdressed. A brief summary of IL-6 signaling after binding to its receptor is provided and hypotheses concerning IL-6 and the central control of bone formation are also highlighted.

Bacterial induction of TNF-alpha converting enzyme expression and IL-6 receptor alpha shedding regulates airway inflammatory signaling

Airway epithelial cells have a major role in initiating inflammation in response to bacterial pathogens. Through the immediate induction of CXCL8 and cytokine expression, polymorphonuclear cells are mobilized and activated to eradicate the infecting organisms. However, the influx of polymorphonuclear cells and the effects of their toxic exoproducts impede respiratory function. We postulated that respiratory epithelial cells must also participate in the regulation of their own proinflammatory signaling. Both Staphylococcus aureus and Pseudomonas aeruginosa were found to potently activate IL-6 expression immediately upon contact with epithelial cells, and by 1 h induced TNF-alpha converting enzyme (TACE) transcription. By 4 h of bacterial exposure, TACE colocalized with IL-6Ralpha on the apical surface of airway cells, and by 24 h, soluble IL-6Ralpha accumulated in the cell culture supernatant. Epithelial IL-6 and soluble IL-6Ralpha were shown to participate in trans-signaling, interacting with membrane-associated gp130 to activate CCL-2 expression and inhibit additional CXCL8 production. Thus, bacteria are physiological activators of TACE expression, which provides a mechanism to regulate inflammatory signaling that is initiated by airway epithelial cells.

Interleukin-6/soluble interleukin-6 receptor complex reduces infarct size via inhibiting myocardial apoptosis

Apoptosis of cardiomyocytes plays an important role in reperfusion injury following myocardial infarction. Conversely, interleukin-6 (IL-6)--a potent cytokine--inhibits myeloma cell apoptosis by activating GP130 through the IL-6 receptor (IL-6R). We hypothesized that the IL-6/soluble IL-6R complex can inhibit myocardial apoptosis, and limit infarct size in reperfused acute myocardial infarction. Anesthetized rats were randomly divided into five groups: sham, coronary occlusion and reperfusion rats administered IL-6/soluble IL-6R complex, IL-6 alone, soluble IL-6R (sIL-6R) alone, or a control vehicle. Rats were subjected to 30 min occlusion of the left coronary artery followed by 3 h reperfusion. After reperfusion, the hearts were excised. For detection and quantification of apoptosis, gel electrophoresis of extracted genomic DNA and TUNEL method of paraffin sections were performed. The percentage of the infarct area was measured using tetrazolium chloride staining. The cardiomyocyte apoptosis analysis revealed that apoptosis in the reperfused myocardium was inhibited only in the complex group. Furthermore, the percentage of the infarct area out of the area at risk was remarkably reduced in the complex group (23.8+/-1.8%), compared with that in the vehicle (37.9+/-3.7%), the IL-6 (40.7+/-1.0%), or the sIL-6R (37.5+/-2.4%) groups (P=0.0002). No significant differences were observed among the vehicle, IL-6, and sIL-6R groups. The IL-6/soluble IL-6 receptor complex inhibits cardiomyocyte apoptosis in reperfused acute myocardial infarction. It possibly reduces irreversible reperfusion injury.

GP130/OSMR is the only LIF/IL-6 family receptor complex to promote osteoblast differentiation of calvaria progenitors

Leukemia inhibitory factor (LIF) and its receptor (LIFR) are "twins" of Oncostatin M (OSM) and OSMR, respectively, likely having arisen through gene duplications. We compared their effects in a bone nodule-forming model of in vitro osteogenesis, rat calvaria (RC) cell cultures. Using a dominant-negative LIF mutant (hLIF-05), we showed that in RC cell cultures mouse OSM (mOSM) activates exclusively glycoprotein 130 (gp130)/OSMR. In treatments starting at early nodule formation stage, LIF, mOSM, IL-11, and IL-6 + sIL-6R inhibit bone nodule formation, that is, osteoprogenitor differentiation. Treatment with mOSM, and no other cytokine of the family, in early cultures (day 1-3 or 1-4) increases bone colony numbers. hLIF-05 also dose dependently stimulates bone nodule formation, confirming the inhibitory action of gp130/LIFR on osteogenesis. In pulse treatments at successive stages of bone nodule formation and maturation, LIF blocks osteocalcin (OCN) expression by differentiated osteoblasts, but has no effect on bone sialoprotein (BSP) expression. Mouse OSM inhibits OCN and BSP expression in preconfluent cultures with no or progressively reduced effects at later stages, reflecting the disruption of early nodules, possibly due to the strong apoptotic action of mOSM in RC cell cultures. In summary, LIFR and OSMR display differential effects on differentiation and phenotypic expression of osteogenic cells, most likely through different signal transduction pathways. In particular, gp130/OSMR is the only receptor complex of the family to stimulate osteoprogenitor differentiation in the RC cell culture model.

All-trans-retinoic acid inhibits the development of mesangial proliferative glomerulonephritis in interleukin-6 transgenic mice

All-trans-retinoic acid (ATRA), a vitamin A derivative, was reported to suppress the interleukin-6 (IL-6) production and to downregulate the IL-6 receptor (IL-6R) and/or its signal transducer glycoprotein 130. We investigated the in vivo antinephritic effect of ATRA on IL-6 transgenic mice which had developed mesangial proliferative glomerulonephritis (PGN) as well as its in vitro inhibitory effect on the proliferation of rat mesangial cells. In vivo experiments on IL-6 transgenic mice showed that ATRA administration suppressed proteinuria and hematuria and reduced the IL-6 concentrations; furthermore, histological examination demonstrated that it improved PGN. In vitro experiments using rat mesangial cells demonstrated that ATRA inhibited cell growth in a dose-dependent manner within a range from 10(-4) to 10(-6) M. This inhibition by ATRA was partially counteracted by the addition of IL-6. RT-PCR assay results showed that ATRA also reduced IL-6R, but not the glycoprotein 130 expression in mesangial cells. These findings indicate that, by blocking of the IL-6 function, ATRA may be therapeutically effective in PGN.

Inhibition of T cell apoptosis in the aqueous humor of patients with uveitis by IL-6/soluble IL-6 receptor trans-signaling

A fundamental mechanism of immune privilege in the eye is the induction of T lymphocyte apoptosis. Intraocular inflammation in uveitis implies compromise of immune privilege. This study sought to determine whether apoptosis of T cells is actively inhibited in patients with uveitis and by what pathways this may occur. Apoptotic lymphocytes were found to be absent from aqueous humor (AqH) of virtually all patients with recent-onset uveitis. However, T cells removed from the eye were highly susceptible to both spontaneous and Fas ligand-induced apoptosis in vitro. AqH from patients with uveitis had no modulatory effect on Fas ligand-induced apoptosis, but strongly suppressed survival factor deprivation-induced apoptosis. In contrast, noninflammatory AqH from patients undergoing cataract surgery had no modulatory effects on apoptosis at all. These data suggest that triggering of the Fas pathway is diminished in uveitis, and also that homeostatic resolution through survival factor deprivation-induced apoptosis is inhibited by factors present in AqH. The most widely recognized pathways, common gamma-chain cytokines and type I IFNs, did not contribute to AqH-mediated T cell survival. High levels of both IL-6 and soluble IL-6R were found in AqH. IL-6 alone did not induce T cell survival, because IL-6R expression on T cells in AqH was too low to facilitate signaling. However, combinations of IL-6 and soluble IL-6R were highly effective inhibitors of T cell apoptosis, suggesting that the trans-signaling pathway is likely to be a key mediator of T cell apoptosis inhibition mediated by uveitis AqH.

[The IL-6 soluble receptors in hemodialyzed patients]

Pro-inflammatory cytokines, in addition to their role in host defence, can be considered a disease mediator; therefore, a reduction in cytokine synthesis or its effects is becoming a target of many diseases. Interleukin-6 (IL-6) is a pro-inflammatory cytokine that could play a role in several clinical problems related to dialysis treatment. Biological activities of IL-6 could be modulated by two soluble circulating receptors, namely sIL-6R and sgp130. sIL-6R can enhance the inflammatory effects of IL-6 and; therefore, is an "agonistically" acting molecule. On the contrary, sgp130 efficiently binds the IL-6/sIL-6R complex with "antagonistic" effects. In this study we evaluated sgp130 release by peripheral blood mononuclear cells (PBMC) harvested from 10 healthy controls (CON) and 11 end-stage renal disease (ESRD) patients undergoing renal dialysis therapy RDT) with cellulosic hemophan membrane (HD). We also evaluated gp130 gene expression by reverse transcriptase polymerase chain reaction (RT-PCR). gp130 is the membrane bound receptor of IL-6 that could be proteolytically cleaved to generate soluble sgp130. Our results demonstrated that HD. at basal conditions, showed a higher release of sgp130 as compared with CON. We also demonstrated by RT-PCR at basal conditions a higher gene expression of gp130 in HD, as compared with CON. These results took place in the absence of any mitogenic stimulation and suggest that in HD patients an inflammatory subclinical status increases sgp130 release. The results obtained after lipopolysaccharide (LPS) stimulation confirm the role of inflammation on the increased release of sgp130 in HD patients.

The role of interleukin-6 and of its soluble receptors in the biocompatibility of dialysis treatment

Proinflammatory cytokines, in addition to their role in host defence, may be considered mediators of disease; a reduction of cytokine synthesis or effects is, therefore, becoming a target of many diseases. IL-6 is a pro-inflammatory cytokine that may play a role in several clinical problems related to dialysis treatment. An enhanced spontaneous production of IL-6 by Peripheral Blood Mononuclear Cells (PBMC) harvested from ESRD patients dialyzed with a poor biocompatible membrane has been first demonstrated by our group. These results were also obtained in patients undergoing continuous peritoneal dialysis, in absence of peritonitis. We have also demonstrated that IL-6 release was inversely correlated with serum albumin changes. Biological activities of IL-6 may be modulated by two soluble circulating receptors, namely sIL-6R and sgp130. sIL-6R may enhance the inflammatory effects of IL-6 and is, therefore, an "agonistically" acting molecule. We have recently studied sIL-6R production in ESRD patients dialyzed with different membranes; the conclusion was that poor biocompatible membranes, via the sIL-6R, might further increase the inflammatory effects of IL-6. On the contrary, sgp130 can efficiently bind the IL-6/sIL-6R complex with "antagonistic" effects. We have evaluated plasma levels of sgp130 in 18 ESRD patients regularly dialyzed with hemophan membranes (HE) and in 15 patients dialyzed with more biocompatible synthetic membranes (BIO). Our results demonstrate that plasma levels of sgp130 in HE are 33% higher than in both healthy controls and BIO. Circulating levels of sgp130 were correlated positively with C-reactive protein (r: 0.338, p<0.05) and negatively with serum albumin (r: -0.334, p<0.05). These results suggest that higher circulating levels of sgp130 are likely associated with higher IL-6 levels. These higher amounts are probably insufficient to control the activity of IL-6 and may be considered only as a marker of PBMC activation.

IL-6 as an intracrine growth factor for renal carcinoma cell lines

Interleukin-6 (IL-6) is produced at high levels by renal cell carcinoma cell lines. The molecular mechanisms involved in its possible role as an autocrine growth factor were investigated. IL-6 and IL-6 receptor expression was investigated in 8 renal cell carcinoma (RCC) cell lines. The modulation of RCC cell line proliferation by an anti-IL-6 Ab, an IL-6 antisense oligonucleotide (ASON) directed against the second exon of IL-6 and cytokines inhibiting IL-6 production (IL-4 and IL-13) was investigated. All 8 RCC cell lines expressed IL-6 mRNA, produced IL-6 and expressed the soluble and membrane-bound gp130 chain of IL-6 receptor. The gp80 chain of IL-6 receptor was undetectable at the surface of the 8 RCC cell lines tested, while the soluble form of gp80 was detectable in the supernatant of one of these cell lines. The addition of a blocking IL-6 Ab did not inhibit the proliferation of any of the 8 RCC cell lines. In contrast, IL-6 ASON inhibited specifically IL-6 production and the proliferation of all RCC cell lines. Exogenous IL-6 failed to restore RCC cell line proliferation blocked by ASON, indicating that IL-6 acts through an intracrine loop in RCC cell lines. IL-13 and IL-4 inhibited the proliferation of 7 of the 8 cell lines without interfering with IL-6 or IL-6 receptor expression. IL-6 ASON inhibited the proliferation of the 8 RCC cell lines tested additively with IL-4 or IL-13. IL-6 is an intracrine growth factor in renal cell carcinoma cell lines.

Differential regulation of neutrophil-activating chemokines by IL-6 and its soluble receptor isoforms

Interleukin-6 signaling via its soluble receptor (sIL-6R) differentially regulates inflammatory chemokine expression and leukocyte apoptosis to coordinate transition from neutrophil to mononuclear cell infiltration. sIL-6R activities may, however, be influenced in vivo by the occurrence of two sIL-6R isoforms that are released as a consequence of differential mRNA splicing (DS) or proteolytic cleavage (PC) of the cognate IL-6R (termed DS- and PC-sIL-6R). Using human peritoneal mesothelial cells and a murine model of peritoneal inflammation, studies described in this work have compared the ability of both isoforms to regulate neutrophil recruitment. In this respect, DS- and PC-sIL-6R were comparable in their activities; however, these studies emphasized that IL-6 trans signaling differentially controls neutrophil-activating CXC chemokine expression. In vitro, stimulation of mesothelial cells with IL-6 in combination with either DS-sIL-6R or PC-sIL-6R showed no induction of CXC chemokine ligand (CXCL)1 (GRO alpha) and CXCL8 (IL-8), whereas both isoforms enhanced CXCL5 (ENA-78) and CXCL6 (granulocyte chemotactic protein-2) expression. Moreover, when complexed with IL-6, both isoforms specifically inhibited the IL-1 beta-induced secretion of CXCL8. These findings were paralleled in vivo, in which induction of peritoneal inflammation in IL-6-deficient (IL-6(-/-)) mice resulted in enhanced keratinocyte-derived chemokine and macrophage-inflammatory protein-2 (the murine equivalent of CXCL1 and CXCL8) levels, but reduced LPS-induced CXC chemokine (the murine equivalent of CXCL5) expression. Reconstitution of IL-6 signaling in IL-6(-/-) mice with IL-6 and its soluble receptor isoforms corrected this chemokine imbalance and suppressed overall neutrophil infiltration. These data confirm that sIL-6R-mediated signaling primarily limits neutrophil influx; however, induction of CXCL5 and CXCL6 may regulate other neutrophil responses.