Soluble gp130 is the natural inhibitor of soluble interleukin-6 receptor transsignaling responses

IL-6 blockade in the management of non-infectious uveitis

Several pathogenetic studies have paved the way for a newer more rational therapeutic approach to non-infectious uveitis, and treatment of different forms of immune-driven uveitis has drastically evolved in recent years after the advent of biotechnological drugs. Tumor necrosis factor-α targeted therapies, the first-line recommended biologics in uveitis, have certainly led to remarkable results in patients with non-infectious uveitis. Nevertheless, the decision-making process turns out to be extremely difficult in anti-tumor necrosis factor or multidrug-resistant cases. Interleukin (IL)-6 holds a critical role in the pathogenic pathways of uveitis, due to its extended and protean range of effects. On this background, manipulation of IL-6 inflammatory cascade has unraveled encouraging outcomes. For instance, rising evidence has been achieved regarding the successful use of tocilizumab, the humanized monoclonal antibody targeted against the IL-6 receptor, in treating uveitis related to juvenile idiopathic arthritis or Behçet's disease. Similar findings have also been reported for uveitis associated with systemic disorders, such as rheumatoid arthritis or multicentric Castleman disease, but also for idiopathic uveitis, the rare birdshot chorioretinopathy, and even in cases complicated by macular edema. This work provides a digest of all current experiences and evidences concerning IL-6 blockade, as suggested by the medical literature, proving its potential role in the management of non-infectious uveitis.

Over-expressing the soluble gp130-Fc does not ameliorate methionine and choline deficient diet-induced non alcoholic steatohepatitis in mice

Non-alcoholic steatohepatitis (NASH) is a liver disease with the potential to lead to cirrhosis and hepatocellular carcinoma. Interleukin-6 (IL-6) has been implicated in the pathogenesis of NASH, with the so-called IL-6 ‘trans-signaling’ cascade being responsible for the pro-inflammatory actions of this cytokine. We aimed to block IL-6 ‘trans-signaling’, using a transgenic mouse that overexpresses human soluble glycoprotein130 (sgp130Fc Tg mice) fed a commonly used dietary model of inducing NASH (methionine and choline deficient-diet; MCD diet) and hypothesized that markers of NASH would be ameliorated in such mice. Sgp130Fc Tg and littermate control mice were fed a MCD or control diet for 4 weeks. The MCD diet induced many hallmarks of NASH including hepatomegaly, steatosis, and liver inflammation. However, in contrast with other mouse models and, indeed, human NASH, the MCD diet model did not increase the mRNA or protein expression of IL-6. Not surprisingly, therefore, markers of MCD diet-induced NASH were unaffected by sgp130Fc transgenic expression. While the MCD diet model induces many pathophysiological markers of NASH, it does not induce increased IL-6 expression in the liver, a key hallmark of human NASH. We, therefore, caution the use of the MCD diet as a viable mouse model of NASH.

C1q/TNF-Related Protein 3 (CTRP3) Function and Regulation

As the largest endocrine organ, adipose tissue secretes many bioactive molecules that circulate in blood, collectively termed adipokines. Efforts to identify such metabolic regulators have led to the discovery of a family of secreted proteins, designated as C1q tumor necrosis factor (TNF)-related proteins (CTRPs). The CTRP proteins, adiponectin, TNF-alpha, as well as other proteins with the distinct C1q domain are collectively grouped together as the C1q/TNF superfamily. Reflecting profound biological potency, the initial characterization of these adipose tissue-derived CTRP factors finds wide-ranging effects upon metabolism, inflammation, and survival-signaling in multiple tissue types. CTRP3 (also known as CORS26, cartducin, or cartonectin) is a unique member of this adipokine family. In this review we provide a comprehensive overview of the research concerning the expression, regulation, and physiological function of CTRP3. © 2017 American Physiological Society. Compr Physiol 7:863-878, 2017.

Profile of sarilumab and its potential in the treatment of rheumatoid arthritis

In recent years the use of biotechnological agents has drastically revolutionized the therapeutic approach and the progression of rheumatoid arthritis (RA). In particular, interleukin-6 (IL-6) has been demonstrated as a pivotal cytokine in the pathogenesis of the disease by contributing to both the innate and the adaptive immune system perturbation, and to the production of acute-phase proteins involved in the systemic expression of the disorder. The first marketed IL-6 blocker was tocilizumab, a humanized anti-IL-6 receptor (anti-IL-6R) monoclonal antibody. The successful use of tocilizumab in RA has encouraged the development of other biologic agents specifically targeting the IL-6 pathway, either directed against IL-6 cytokine (sirukumab, olokizumab, and clazakizumab) or IL-6 receptor (sarilumab). One Phase II and six Phase III randomized controlled trials demonstrated a broad efficacy of sarilumab across all RA patient subtypes, ranging from methotrexate (MTX) to tumor necrosis factor inhibitor insufficient responders. In particular, sarilumab as monotherapy demonstrated a clear head-to-head superiority over adalimumab in MTX-intolerant subjects. In addition, compared with tocilizumab, sarilumab showed a similar safety profile with significantly higher affinity and longer half-life, responsible for a reduction of the frequency of administration (every other week instead weekly). All these aspects may be important in defining the strategy for positioning sarilumab in the treatment algorithm of RA. Indeed, observational data coming from post-marketing real-life studies may provide crucial additional information for better understanding the role of sarilumab in the management of the disease. This review summarizes both the biological role of IL-6 in RA and the clinical data available on sarilumab as an alternative therapeutic option in RA patients.

SorLA in Interleukin-6 Signaling and Turnover

Interleukin-6 (IL-6) is a multifunctional cytokine with important functions in various physiologic processes. Mice lacking IL-6 exhibit multiple phenotypic abnormalities, such as an inadequate immune and acute-phase response, and elevated levels of circulating IL-6 have been found to accompany several pathological conditions. IL-6 binds the nonsignaling IL-6 receptor (IL-6R), which is expressed as a transmembrane, as well as a secreted circulating protein, before it engages homodimeric gp130 for signaling. Complex formation between IL-6 and the membrane-bound IL-6 receptor gives rise to classic cis signaling, whereas complex formation between IL-6 and the soluble IL-6R results in trans signaling. Here, we report that the endocytic receptor SorLA targets IL-6 and IL-6R. We present evidence that SorLA mediates efficient cellular uptake of both IL-6 and the circulating IL-6R in astrocytes. We further show that SorLA interacts with the membrane-bound IL-6R at the cell surface and thereby downregulates IL-6 cis signaling. Finally, we find that the SorLA ectodomain, released from the cell membrane upon enzymatic cleavage of full-length SorLA, may act as an IL-6 carrier protein that stabilizes IL-6 and its capacity for trans signaling.

IL-6 Improves Energy and Glucose Homeostasis in Obesity via Enhanced Central IL-6 trans-Signaling

Interleukin (IL)-6 engages similar signaling mechanisms to leptin. Here, we find that central application of IL-6 in mice suppresses feeding and improves glucose tolerance. In contrast to leptin, whose action is attenuated in obesity, the ability of IL-6 to suppress feeding is enhanced in obese mice. IL-6 suppresses feeding in the absence of neuronal IL-6-receptor (IL-6R) expression in hypothalamic or all forebrain neurons of mice. Conversely, obese mice exhibit increased soluble IL-6R levels in the cerebrospinal fluid. Blocking IL-6 trans-signaling in the CNS abrogates the ability of IL-6 to suppress feeding. Furthermore, gp130 expression is enhanced in the paraventricular nucleus of the hypothalamus (PVH) of obese mice, and deletion of gp130 in the PVH attenuates the beneficial central IL-6 effects on metabolism. Collectively, these experiments indicate that IL-6 trans-signaling is enhanced in the CNS of obese mice, allowing IL-6 to exert its beneficial metabolic effects even under conditions of leptin resistance.

Interleukin-6 Signaling Pathway and Its Role in Kidney Disease: An Update

Interleukin-6 (IL-6) is a pleiotropic cytokine that not only regulates the immune and inflammatory response but also affects hematopoiesis, metabolism, and organ development. IL-6 can simultaneously elicit distinct or even contradictory physiopathological processes, which is likely discriminated by the cascades of signaling pathway, termed classic and trans-signaling. Besides playing several important physiological roles, dysregulated IL-6 has been demonstrated to underlie a number of autoimmune and inflammatory diseases, metabolic abnormalities, and malignancies. This review provides an overview of basic concept of IL-6 signaling pathway as well as the interplay between IL-6 and renal-resident cells, including podocytes, mesangial cells, endothelial cells, and tubular epithelial cells. Additionally, we summarize the roles of IL-6 in several renal diseases, such as IgA nephropathy, lupus nephritis, diabetic nephropathy, acute kidney injury, and chronic kidney disease.

IL-6 signaling in diabetic nephropathy: From pathophysiology to therapeutic perspectives

Diabetic nephropathy (DN) is a leading cause of chronic kidney disease (CKD). Interleukin-6 (IL-6) signaling participates in inflammation responses central to the progression of DN. Current evidence suggests that these IL-6 responses are mediated via gp130-STAT3 dependent mechanisms which, on one hand, trigger globally the transition from innate to adaptive immune response, and on the other hand act locally for tissue remodeling and immune cell infiltration. In diabetic conditions the role of IL-6 is not well elucidated. Both IL-6 classical signaling pathway via receptor IL-6R (IL-6R) and IL-6 trans-signaling pathway via soluble IL-6R (sIL-6R) were shown to participate in the pathogenesis and progression of DN, and IL-6 appears to influence renal cells also in an autocrine manner. To date, evidence is limited. The goal of this review is to provide an overview of our current understanding on the role of IL-6 signaling in DN and to delineate challenges for future research. Putative sequential events related to IL-6 secretion by different cell populations in diabetic conditions are outlined. Further, we discuss potential applications of anti-IL-6 therapy in the context of DN.

Soluble IL6R Expressed by Myeloid Cells Reduces Tumor-Specific Th1 Differentiation and Drives Tumor Progression

IL6 produced by tumor cells promotes their survival, conferring a poor prognosis in patients with cancer. IL6 also contributes to immunosuppression of CD4⁺ T cell-mediated antitumor effects. In this study, we focused on the impact of IL6 trans-signaling mediated by soluble IL6 receptors (sIL6R) expressed in tumor-bearing hosts. Higher levels of sIL6R circulating in blood were observed in tumor-bearing mice, whereas the systemic increase of sIL6R was not prominent in tumor-bearing mice with myeloid cell-specific conditional deletion of IL6R even when tumor cells produced sIL6R. Abundant sIL6R was released by CD11b⁺ cells from tumor-bearing mice but not tumor-free mice. Notably, IL6-mediated defects in Th1 differentiation, T-cell helper activity for tumor-specific CD8⁺ T cells, and downstream antitumor effects were rescued by myeloid-specific deletion of sIL6R. Expression of the T-cell transcription factor c-Maf was upregulated in CD4⁺ T cells primed in tumor-bearing mice in an IL6-dependent manner. Investigations with c-Maf loss-of-function T cells revealed that c-Maf activity was responsible for IL6/sIL6R-induced Th1 suppression and defective T-cell-mediated antitumor responses. In patients with cancer, myeloid cell-derived sIL6R was also possibly associated with Th1 suppression and c-Maf expression. Our results argued that increased expression of sIL6R from myeloid cells and subsequent c-Maf induction were adverse events for counteracting tumor-specific Th1 generation. Overall, this work provides a mechanistic rationale for sIL6R targeting to improve the efficacy of T-cell-mediated cancer immunotherapy. Cancer Res; 77(9); 2279-91. ©2017 AACR.

Interleukin-6 "Trans-Signaling" and Ischemic Vascular Disease: The Important Role of Soluble gp130

Inflammation plays a major role in the onset of cardiovascular disease (CVD). Interleukine-6 (IL-6) is a multifunctional cytokine involved both in the beneficial acute inflammatory response and in the detrimental chronic low-grade systemic inflammation. Large genetic human studies, using Mendelian randomization approaches, have clearly showed that IL-6 pathway is causally involved in the onset of myocardial infarction. At the same time, IL-6 pathway is divided into two arms: classic signaling (effective in hepatocytes and leukocytes) and trans-signaling (with ubiquitous activity). Trans-signaling is known to be inhibited by the circulating soluble glycoprotein 130 (sgp130). In animal and in vitro models, trans-signaling inhibition with sgp130 antibody clearly shows a beneficial effect on inflammatory disease and atherosclerosis. Conversely, epidemiological data report inconsistent results between sgp130 levels and CV risk factors as well as CV outcome. We have reviewed the literature to understand the role of sgp130 and to find the evidence in favor of or against a possible clinical application of sgp130 treatment in the prevention of cardiovascular disease.

Trans-signaling of interleukin-6 (IL-6) is mediated by the soluble IL-6 receptor, but not by soluble CD5

IL-6 exerts its pleiotropic activities on its target cells via the IL-6 alpha-receptor (IL-6R), which is expressed on a limited number of cell types. IL-6 can further signal via soluble forms of its receptor (sIL-6R), a process that has been termed trans-signaling. Recently, CD5 was described as an alternative alpha-receptor for IL-6 on B cells leading to the phosphorylation of the transcription factor STAT3 via the signal-transducing β-receptor gp130 in a Jak2-dependent manner. In this study, we sought to investigate whether IL-6 was also able to signal via soluble CD5 (sCD5) analogous to IL-6 trans-signaling. We show that IL-6 indeed binds to sCD5, but that this does not lead to the activation of signal transduction or cell proliferation. Furthermore, sCD5 did also not interfere with IL-6 classic signaling, suggesting that the affinity between the two proteins was too weak to provoke a biological effect. Thus, trans-signaling of IL-6 can only occur via sIL-6R, but not sCD5.

Metabolic Response of Human Osteoarthritic Cartilage to Biochemically Characterized Collagen Hydrolysates

The most frequent disease of the locomotor system is osteoarthritis (OA), which, as a chronic joint disease, might benefit more from nutrition than acute illnesses. Collagen hydrolysates (CHs) are peptidic mixtures that are often used as nutraceuticals for OA. Three CHs were characterized biochemically and pharmacologically. Our biophysical (MALDI-TOF-MS, NMR, AFM) and fluorescence assays revealed marked differences between CHs of fish (Peptan^® F 5000, Peptan^® F 2000) and porcine (Mobiforte^®) origin with respect to the total number of peptides and common peptides between them. Using a novel dual radiolabeling procedure, no CH modulated collagen biosynthesis in human knee cartilage explants. Peptan^® F 2000 enhanced the activities of the aggrecanase ADMATS4 and ADMATS5 in vitro without loss of proteoglycan from cartilage explants; the opposite effect was observed with Mobiforte^®. Interleukin (IL)-6, matrix metalloproteinase (MMP)-1, -3 and -13 levels were elevated in explants that were treated with Mobiforte^® and Peptan^® F 5000, but not with Peptan^® F 2000. In conclusion, the heterogeneous peptide composition and disparate pharmacological effects between CHs suggest that the effect of a CH preparation cannot be extrapolated to other formulations. Thus, the declaration of a CH as a safe and effective nutraceutical requires a thorough examination of its pleiotropic effects.

Microglial production of TNF-alpha is a key element of sustained fear memory

The proinflammatory cytokine productions in the brain are altered in a process of fear memory formation, indicating a possibility that altered microglial function may contribute to fear memory formation. We aimed to investigate whether and how microglial function contributes to fear memory formation. Expression levels of M1- and M2-type microglial marker molecules in microglia isolated from each conditioned mice group were assessed by real-time PCR and immunohistochemistry. Levels of tumor necrosis factor (TNF)-α, but not of other proinflammatory cytokines produced by M1-type microglia, increased in microglia from mice representing retention of fear memory, and returned to basal levels in microglia from mice representing extinction of fear memory. Administration of inhibitors of TNF-α production facilitated extinction of fear memory. On the other hand, expression levels of M2-type microglia-specific cell adhesion molecules, CD206 and CD209, were decreased in microglia from mice representing retention of fear memory, and returned to basal levels in microglia from mice representing extinction of fear memory. Our findings indicate that microglial TNF-α is a key element of sustained fear memory and suggest that TNF-α inhibitors can be candidate molecules for mitigating posttraumatic reactions caused by persistent fear memory.

Mechanisms of immunomodulation by mammalian and viral decoy receptors: insights from structures

Immune responses are regulated by effector cytokines and chemokines that signal through cell surface receptors. Mammalian decoy receptors - which are typically soluble or inactive versions of cell surface receptors or soluble protein modules termed binding proteins - modulate and antagonize signalling by canonical effector-receptor complexes. Viruses have developed a diverse array of molecular decoys to evade host immune responses; these include viral homologues of host cytokines, chemokines and chemokine receptors; variants of host receptors with new functions; and novel decoy receptors that do not have host counterparts. Over the past decade, the number of known mammalian and viral decoy receptors has increased considerably, yet a comprehensive curation of the corresponding structure-mechanism relationships has not been carried out. In this Review, we provide a comprehensive resource on this topic with a view to better understanding the roles and evolutionary relationships of mammalian and viral decoy receptors, and the opportunities for leveraging their therapeutic potential.

Trans-presentation of IL-6 by dendritic cells is required for the priming of pathogenic TH17 cells

The cellular sources of interleukin-6 (IL-6) that are relevant for the differentiation of T_H17 cells remain unclear. Here, we used a novel strategy of IL-6 conditional deletion of distinct IL-6-producing cell types to show that Sirpα⁺ dendritic cells (DC) were essential for the generation of pathogenic T_H17 cells. During the process of cognate interaction, Sirpα⁺ DCs trans-presented IL-6 to T cells using their own IL-6Rα. While ambient IL-6 was sufficient to suppress the induction of the transcription factor Foxp3 in T cells, IL-6 trans-presentation by DC-bound IL-6Rα (here defined as IL-6 cluster signaling) was required to prevent premature induction of IFN-γ in T cells and to generate pathogenic T_H17 cells in vivo. These findings will guide therapeutic approaches for T_H17-mediated autoimmune diseases.

Classic IL-6R signalling is dispensable for intestinal epithelial proliferation and repair

Inflammatory bowel disease is characterized by disturbed cytokine signalling in the mucosa. Inhibition of the proinflammatory interleukin (IL)-6 pathway is a promising new therapeutic strategy, but safety concerns arise as IL-6 signalling also contributes to epithelial repair of the intestinal mucosa. To which extent IL-6 classic or trans-signalling contributes to intestinal repair remains elusive. We tested the influence of IL-6 classic signalling on intestinal repair and proliferation. Whereas IL-6 induced STAT3 phosphorylation in the colonic cancer cell lines, primary non-malignant intestinal organoids did not respond to IL-6 classic signalling. Mice deficient in intestinal IL-6R (IL-6R^ΔIEC mice) did not display increased susceptibility to acute dextran sulfate sodium (DSS)-induced colitis. In the azoxymethane DSS model IL-6R^ΔIEC mice were not protected from inflammation-induced carcinogenesis but showed comparable tumor load to wild-type mice. These data indicate that classic signalling is not the major pathway to transduce IL-6 stimuli into the intestinal epithelium.

IL-6 Trans-Signaling Links Inflammation with Angiogenesis in the Peritoneal Membrane

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.

Exploration of early-life candidate biomarkers for childhood asthma using antibody arrays

BACKGROUND

Proteomic approaches identifying biomarkers have been applied to asthma to only a very limited extent.

METHODS

With an antibody array (RayBiotech, Norcross, GA, USA), the relative intensity and rank differences of 444 proteins were compared in 24 plasma samples obtained at age 3, 11 from children with and 12 without asthma diagnoses at ages 5 and 9. Protein candidates identified by antibody array were quantitated by ELISA in an enlarged sample. Proteins found to differentiate children with and without asthma were also examined for association with known Year 1 asthma risk factors, eczema, and wheeze.

RESULTS

In the antibody array, four proteins had rank differences between asthma and non-asthma groups (FDR <0.1). By ELISA, mean log (±s.e.m.) erythropoietin (EPO) level (IU/l) was lower (0.750 ± 0.048 vs. 0.898 ± 0.035; p = 0.006) and mean (±s.e.m.) soluble GP130 (sGP130) level (ng/ml) was higher in the asthma vs. the non-asthma group (302 ± 13 vs. 270 ± 8; p = 0.041). The other 2 array proteins (galactin-3 and eotaxin-3) did not differ by ELISA by asthma. EPO related to the asthma risk factor, first year eczema, whereas sGP130 related to first year wheeze.

CONCLUSIONS

Through two independent assessments, age 3 plasma levels of EPO and sGP130 were found related to childhood asthma.

Circulating Soluble IL-6R but Not ADAM17 Activation Drives Mononuclear Cell Migration in Tissue Inflammation

Neutrophil and mononuclear cell infiltration during inflammatory processes is highly regulated. The first cells at the site of infection or inflammation are neutrophils, followed by mononuclear cells. IL-6 plays an important role during inflammatory states. It has been shown in several models that the soluble form of IL-6R (sIL-6R) is involved in the recruitment of mononuclear cells by a mechanism called IL-6 trans-signaling. It had been speculated that sIL-6R was generated at the site of inflammation by shedding from neutrophils via activation of the metalloprotease ADAM17. Attempts to genetically delete the floxed ADAM17 gene selectively in myeloid cells infiltrating an air pouch cavity upon injection of carrageenan failed because in transgenic mice, LysM^cre did not lead to appreciable loss of the ADAM17 protein in these cells. We therefore used ADAM17 hypomorphic mice, which only express ∼5% of ADAM17 wild-type levels in all tissues and show virtually no shedding of all tested ADAM17 substrates, to clarify the role of ADAM17 during local inflammation in the murine air pouch model. In the present study, we demonstrate that although IL-6 and the trans-signaling mechanism is mandatory for cellular infiltration in this model, it is not ADAM17-mediated shedding of IL-6R within the pouch that orchestrates this inflammatory process. Instead, we demonstrate that sIL-6R is infiltrating from the circulation in an ADAM17-independent process. Our data suggest that this infiltrating sIL-6R, which is needed for IL-6 trans-signaling, is involved in the controlled resolution of an acute inflammatory episode.

Due to interleukin-6 type cytokine redundancy only glycoprotein 130 receptor blockade efficiently inhibits myeloma growth

Interleukin-6 has an important role in the pathophysiology of multiple myeloma where it supports the growth and survival of the malignant plasma cells in the bone marrow. It belongs to a family of cytokines which use the glycoprotein 130 chain for signal transduction, such as oncostatin M or leukemia inhibitory factor. Targeting interleukin-6 in plasma cell diseases is currently evaluated in clinical trials with monoclonal antibodies. Here, efforts were made to elucidate the contribution of interleukin-6 and glycoprotein 130 signaling in malignant plasma cell growth in vivo In the xenograft severe combined immune deficiency model employing our interleukin-6-dependent plasma cell line INA-6, the lack of human interleukin-6 induced autocrine interleukin-6 production and a proliferative response to other cytokines of the glycoprotein 130 family. Herein, mice were treated with monoclonal antibodies against human interleukin-6 (elsilimomab/B-E8), the interleukin-6 receptor (B-R6), and with an antibody blocking glycoprotein 130 (B-R3). While treatment of mice with interleukin-6 and interleukin-6 receptor antibodies resulted in a modest delay in tumor growth, the development of plasmacytomas was completely prevented with the anti-glycoprotein 130 antibody. Importantly, complete inhibition was also achieved using F(ab')2-fragments of monoclonal antibody B-R3. Tumors harbor activated signal transducer and activator of transcription 3, and in vitro, the antibody inhibited leukemia inhibitory factor stimulated signal transducer and activator of transcription 3 phosphorylation and cell growth, while being less effective against interleukin-6. In conclusion, the growth of INA-6 plasmacytomas in vivo under interleukin-6 withdrawal remains strictly dependent on glycoprotein 130, and other glycoprotein 130 cytokines may substitute for interleukin-6. Antibodies against glycoprotein 130 are able to overcome this redundancy and should be explored for a possible therapeutic window.

Inhibition of IL-6 trans-signaling in the brain increases sociability in the BTBR mouse model of autism

Autism is a severe neurodevelopmental disorder with a large population prevalence, characterized by abnormal reciprocal social interactions, communication deficits, and repetitive behaviors with restricted interests. The BTBR T(+)Itpr3(tf) (BTBR) mice have emerged as strong candidates to serve as models of a range of autism-relevant behaviors. Increasing evidences suggest that interleukin (IL)-6, one of the most important neuroimmune factors, was involved in the pathophysiology of autism. It is of great importance to further investigate whether therapeutic interventions in autism can be achieved through the manipulation of IL-6. Our previous studies showed that IL-6 elevation in the brain could mediate autistic-like behaviors, possibly through the imbalances of neural circuitry and impairments of synaptic plasticity. In this study, we evaluate whether inhibiting IL-6 signaling in the brain is sufficient to modulate the autism-like behaviors on the BTBR mice. The results showed that chronic infusion of an analog of the endogenous IL-6 trans-signaling blocker sgp130Fc protein increased the sociability in BTBR mice. Furthermore, no change was observed in the number of excitatory synapse, level of synaptic proteins, density of dentitic spine and postsynaptic density in BTBR cortices after inhibiting IL-6 trans-signaling. However, inhibition of IL-6 trans-signaling increased the evoked glutamate release in synaptoneurosomes from the cerebral cortex of BTBR mice. Our findings suggest that inhibition of excessive production of IL-6 may have selective therapeutic efficacy in treating abnormal social behaviors in autism.

Generation of Soluble Interleukin-11 and Interleukin-6 Receptors: A Crucial Function for Proteases during Inflammation

The cytokines interleukin-11 (IL-11) and IL-6 are important proteins with well-defined pro- and anti-inflammatory functions. They activate intracellular signaling cascades through a homodimer of the ubiquitously expressed signal-transducing β-receptor glycoprotein 130 (gp130). Specificity is gained through the cell- and tissue-specific expression of the nonsignaling IL-11 and IL-6 α-receptors (IL-11R and IL-6R), which determine the responsiveness of the cell to these two cytokines. IL-6 is a rare example, where its soluble receptor (sIL-6R) has agonistic properties, so that the IL-6/sIL-6R complex is able to activate cells that are usually not responsive to IL-6 alone (trans-signaling). Recent evidence suggests that IL-11 can signal via a similar trans-signaling mechanism. In this review, we highlight similarities and differences in the functions of IL-11 and IL-6. We summarize current knowledge about the generation of the sIL-6R and sIL-11R by different proteases and discuss possible roles during inflammatory processes. Finally, we focus on the selective and/or combined inhibition of IL-6 and IL-11 signaling and how this might translate into the clinics.

Circulating Levels of IL-6 Receptor and gp130 and Long-Term Clinical Outcomes in ST-Elevation Myocardial Infarction

BACKGROUND

Reports on soluble interleukin-6 (IL-6) receptor (sIL-6R) and glycoprotein 130 (sgp130) in ST-elevation myocardial infarction (STEMI) are few and include a small number of patients. The aim of this study was to investigate the possible association between levels of these biomarkers in the acute phase of STEMI and future cardiovascular events.

METHODS AND RESULTS

Circulating IL-6, sgp130, sIL-6R, and C-reactive protein (CRP) were measured in 989 STEMI patients during 2007-2011, and cardiovascular events were recorded during follow-up. The primary endpoint was composite of all-cause mortality, myocardial infarction, stroke, unscheduled revascularization, or rehospitalization for heart failure. Cox regression models were used to estimate hazard ratios (HRs) for cardiovascular events in relation to biomarker levels. Median levels of sIL-6R, sgp130, IL-6, and CRP measured 24 hours (median) after symptom onset were 39.2 ng/mL, 240 ng/mL, 18.8 pg/mL, and 13.7 mg/L, respectively. During a median follow-up time of 4.6 years, 200 patients (20.2%) experienced a primary endpoint, and 82 patients (8.3%) died. Patients with sIL-6R levels in the upper quartile (>47.7 ng/mL) had significantly higher risk of future adverse events (primary endpoint) and mortality compared to patients with lower levels (adjusted HR, 1.54 [1.08, 2.21]; P=0.02 and 1.81 [1.04, 3.18]; P=0.04, respectively). Neither IL-6 nor sgp130 levels were related to future events, but patients with CRP levels in the upper quartile (>31.5 mg/L) had higher risk of death.

CONCLUSION

High levels of sIL-6R were associated with future cardiovascular events and mortality in STEMI patients, suggesting an important role of the IL-6 signaling system.

Interleukin-6: an emerging regulator of pathological pain

Interleukin-6 is an inflammatory cytokine with wide-ranging biological effects. It has been widely demonstrated that neuroinflammation plays a critical role in the development of pathological pain. Recently, various pathological pain models have shown elevated expression levels of interleukin-6 and its receptor in the spinal cord and dorsal root ganglia. Additionally, the administration of interleukin-6 could cause mechanical allodynia and thermal hyperalgesia, and an intrathecal injection of anti-interleukin-6 neutralizing antibody alleviated these pain-related behaviors. These studies indicated a pivotal role of interleukin-6 in pathological pain. In this review, we summarize the recent progress in understanding the roles and mechanisms of interleukin-6 in mediating pathological pain associated with bone cancer, peripheral nerve injury, spinal cord injury, chemotherapy-induced peripheral neuropathy, complete Freund’s adjuvant injection, and carrageenan injection. Understanding and regulating interleukin-6 could be an interesting lead to novel therapeutic strategies for pathological pain.

IL-6 pathway in the liver: From physiopathology to therapy

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.

Different Soluble Forms of the Interleukin-6 Family Signal Transducer gp130 Fine-tune the Blockade of Interleukin-6 Trans-signaling

Soluble forms of the IL-6 receptor (sIL-6R) bind to the cytokine IL-6 with similar affinity as the membrane-bound IL-6R. IL-6·sIL-6R complexes initiate IL-6 trans-signaling via activation of the ubiquitously expressed membrane-bound β-receptor glycoprotein 130 (gp130). Inhibition of IL-6 trans-signaling has been shown to be favorable in numerous inflammatory diseases. Furthermore, different soluble forms of gp130 (sgp130) exist that, together with the sIL-6R, are thought to form a buffer for IL-6 in the blood. However, a functional role for the different sgp130 forms has not been described to date. Here we demonstrate that the metalloproteases ADAM10 and ADAM17 can produce sgp130 by ectodomain shedding of gp130, even though this mechanism only accounts for a minor proportion of sgp130 in the circulation. We further show that full-length sgp130 and the shorter forms sgp130-rheumatoid arthritis-associated peptide (RAPS) and sgp130-E10 are differentially expressed in a cell type- specific manner. Remarkably, full-length sgp130 is expressed by monocytes, but this expression is completely lost during differentiation into macrophages in vitro Using genetically engineered murine pre-B cells that secrete different forms of sgp130, we found that these secreted sgp130 proteins are able to prevent trans-signaling-driven cell proliferation of the secreting cells, whereas conditioned supernatant from these cells failed to block IL-6 trans-signaling in other cells. Thus, our data suggest that the different sgp130 forms are released from cells into their immediate surroundings and appear to form cell-associated gradients to modulate their own susceptibility for IL-6 trans-signaling.

IL-6 in diabetes and cardiovascular complications

IL-6 is a pleiotropic cytokine that participates in normal functions of the immune system, haematopoiesis, metabolism, as well as in the pathogenesis of metabolic and cardiovascular diseases. Both pro- and anti-inflammatory roles of IL-6 have been described, which are distinguished by different cascades of signalling transduction, namely classic and trans-signalling. The present review summarizes the basic principles of IL-6 signalling and discusses its roles in diabetes and associated cardiovascular complications, with emphasis on the different outcomes mediated by the two modes of IL-6 signalling and the value of developing therapeutic strategies to specifically target the deleterious trans-signalling of IL-6.

Inflammatory transcription factors as activation markers and functional readouts in immune-to-brain communication

Immune-to-brain communication pathways involve humoral mediators, including cytokines, central modulation by neuronal afferents and immune cell trafficking to the brain. During systemic inflammation these pathways contribute to mediating brain-controlled sickness symptoms including fever. Experimentally, activation of these signaling pathways can be mimicked and studied when injecting animals with pathogen associated molecular patterns (PAMPS). One central component of the brain inflammatory response, which leads, for example, to fever induction, is transcriptional activation of brain cells via cytokines and PAMPS. We and others have studied the spatiotemporal activation and the physiological significance of transcription factors for the induction of inflammation within the brain and the manifestation of fever. Evidence has revealed a role of nuclear factor (NF)κB in the initiation, signal transducer and activator of transcription (STAT)3 in the maintenance and NF-interleukin (IL)6 in the maintenance or even termination of brain-inflammation and fever. Moreover, psychological stressors, such as exposure to a novel environment, leads to increased body core temperature and genomic NF-IL6-activation, suggesting a potential use of NF-IL6-immunohistochemistry as a multimodal brain cell activation marker and a role for NF-IL6 for differential brain activity. In addition, the nutritional status, as reflected by circulating levels of the cytokine-like hormone leptin, influence immune-to-brain communication and age-dependent changes in LPS-induced fever. Overall, transcription factors remain therapeutically important targets for the treatment of brain-inflammation and fever induction during infectious/non-infectious inflammatory and psychological stress. However, the exact physiological role and significance of these transcription factors requires to be further investigated.

Heat stress, gastrointestinal permeability and interleukin-6 signaling - Implications for exercise performance and fatigue

Exercise in heat stress exacerbates performance decrements compared to normothermic environments. It has been documented that the performance decrements are associated with reduced efferent drive from the central nervous system (CNS), however, specific factors that contribute to the decrements are not completely understood. During exertional heat stress, blood flow is preferentially distributed away from the intestinal area to supply the muscles and brain with oxygen. Consequently, the gastrointestinal barrier becomes increasingly permeable, resulting in the release of lipopolysaccharides (LPS, endotoxin) into the circulation. LPS leakage stimulates an acute-phase inflammatory response, including the release of interleukin (IL)-6 in response to an increasingly endotoxic environment. If LPS translocation is too great, heat shock, neurological dysfunction, or death may ensue. IL-6 acts initially in a pro-inflammatory manner during endotoxemia, but can attenuate the response through signaling the hypothalamic pituitary adrenal (HPA)-axis. Likewise, IL-6 is believed to be a thermoregulatory sensor in the gut during the febrile response, hence highlighting its role in periphery – to – brain communication. Recently, IL-6 has been implicated in signaling the CNS and influencing perceptions of fatigue and performance during exercise. Therefore, due to the cascade of events that occur during exertional heat stress, it is possible that the release of LPS and exacerbated response of IL-6 contributes to CNS modulation during exertional heat stress. The purpose of this review is to evaluate previous literature and discuss the potential role for IL-6 during exertional heat stress to modulate performance in favor of whole body preservation.

Recombinant soluble gp130 protein reduces DEN-induced primary hepatocellular carcinoma in mice

IL-6 (interleukin 6) plays an important role in the development and growth of hepatocellular carcinoma (HCC) via both classic signaling and trans-signaling pathways. Soluble gp130 (sgp130) is known to be a natural inhibitor of the trans-signaling pathway. In the present study, our goal was to investigate whether recombinant sgp130 could suppress the initiation and progression of HCC in mouse models. Our results demonstrate that sgp130 induced an apoptosis of HepG2 cells and inhibited the clonogenicity of HepG2 in vitro. Moreover, the IL-6 trans-signaling pathway is significantly suppressed by sgp130 as reflected by the decrease in the level of STAT3 phosphorylation and other inflammatory factors both in vitro and in vivo. In the DEN-induced HCC mouse model, intravenous injection of sgp130 attenuated hepatic fibrosis at 16 weeks and reduced the initiation and progression of primary HCC at 36 weeks. Furthermore, our results also demonstrate that intravenous administration of sgp130 significantly suppressed the growth and metastasis of xenograft human HCC in NOD/SCID mice.

The role of interleukin-6 signaling in nervous tissue

The cytokine interleukin-6 (IL-6) plays a critical role in the pathogenesis of inflammatory disorders and in the physiological homeostasis of neural tissue. Profound neuropathological changes, such as multiple sclerosis (MS), Parkinson's and Alzheimer's disease are associated with increased IL-6 expression in brain. Increased nocturnal concentrations of serum IL-6 are found in patients with impaired sleep whereas IL-6-deficient mice spend more time in rapid eye movement sleep associated with dreaming. IL-6 is crucial in the differentiation of oligodendrocytes, regeneration of peripheral nerves and acts as a neurotrophic factor. It exerts its cellular effects through two distinct pathways which include the anti-inflammatory pathway involving the membrane-bound IL-6 receptor (IL-6R) expressed on selective cells, including microglia, in a process known as classical signaling that is also critical for bacterial defense. In classical signaling binding of IL-6 to the membrane-bound IL-6R activates the β-receptor glycoprotein 130 (gp130) and subsequent down-stream signaling. The alternative, rather pro-inflammatory pathway, shown to mediate neurodegeneration in mice, termed trans-signaling, depends on a soluble form of the IL-6R that is capable of binding IL-6 to stimulate a response on distal cells that express gp130. A naturally occurring soluble form of gp130 (sgp130) has been identified that can specifically bind and neutralize the IL-6R/IL-6 complex. Thus, trans-signaling is blocked but classical signaling is completely unaffected. A modified, recombinant dimerized version of sgp130 (sgp130Fc) has successfully been used to block inflammatory processes in mice and may also be used in the clarification of IL-6 trans-signaling in neurological diseases.

IL6 Trans-signaling Promotes KRAS-Driven Lung Carcinogenesis

Oncogenic KRAS mutations occur frequently in lung adenocarcinoma. The signaling pathways activated by IL6 promote Kras-driven lung tumorigenesis, but the basis for this cooperation is uncertain. In this study, we used the gp130(F/F) (Il6st) knock-in mouse model to examine the pathogenic contribution of hyperactivation of the STAT3 arm of IL6 signaling on KRAS-driven lung tumorigenesis. Malignant growths in the gp130(F/F):Kras(G12D) model displayed features of atypical adenomatous hyperplasia, adenocarcinoma in situ, and invasive adenocarcinoma throughout the lung, as compared with parental Kras(G12D) mice, where STAT3 was not hyperactivated. Among IL6 family cytokines, only IL6 was upregulated in the lung. Accordingly, normalization of pulmonary STAT3 activity, by genetic ablation of either Il6 or Stat3, suppressed the extent of lung cancer in the model. Mechanistic investigations revealed elevation in the lung of soluble IL6 receptor (sIL6R), the key driver of IL6 trans-signaling, and blocking this mechanism via interventions with an anti-IL6R antibody or the inhibitor sgp130Fc ameliorated lung cancer pathogenesis. Clinically, expression of IL6 and sIL6R was increased significantly in human specimens of lung adenocarcinoma or patient serum. Our results offer a preclinical rationale to clinically evaluate IL6 trans-signaling as a therapeutic target for the treatment of KRAS-driven lung adenocarcinoma.

Proteolytic Cleavage Governs Interleukin-11 Trans-signaling

Interleukin (IL)-11 has been shown to be a crucial factor for intestinal tumorigenesis, lung carcinomas, and asthma. IL-11 is thought to exclusively mediate its biological functions through cell-type-specific expression of the membrane-bound IL-11 receptor (IL-11R). Here, we show that the metalloprotease ADAM10, but not ADAM17, can release the IL-11R ectodomain. Chimeric proteins of the IL-11R and the IL-6 receptor (IL-6R) revealed that a small juxtamembrane portion is responsible for this substrate specificity of ADAM17. Furthermore, we show that the serine proteases neutrophil elastase and proteinase 3 can also cleave the IL-11R. The resulting soluble IL-11R (sIL-11R) is biologically active and binds IL-11 to activate cells. This IL-11 trans-signaling pathway can be inhibited specifically by the anti-inflammatory therapeutic compound sgp130Fc. In conclusion, proteolysis of the IL-11R represents a molecular switch that controls the IL-11 trans-signaling pathway and widens the number of cells that can be activated by IL-11.

Immunoinflammatory diseases of the central nervous system - the tale of two cytokines

Cytokines are potent mediators of cellular communication that have crucial roles in the regulation of innate and adaptive immunoinflammatory responses. Clear evidence has emerged in recent years that the dysregulated production of cytokines may in itself be causative in the pathogenesis of certain immunoinflammatory disorders. Here we review current evidence for the involvement of two different cytokines, IFN-α and IL-6, as principal mediators of specific immunoinflammatory disorders of the CNS. IFN-α belongs to the type I IFN family and is causally linked to the development of inflammatory encephalopathy exemplified by the genetic disorder, Aicardi-Goutières syndrome. IL-6 belongs to the gp130 family of cytokines and is causally linked to a number of immunoinflammatory disorders of the CNS including neuromyelitis optica, idiopathic transverse myelitis and genetically linked autoinflammatory neurological disease. In addition to clinical evidence, experimental studies, particularly in genetically engineered mouse models with astrocyte-targeted, CNS-restricted production of IFN-α or IL-6 replicate many of the cardinal neuropathological features of these human cytokine-linked immunoinflammatory neurological disorders giving crucial evidence for a direct causative role of these cytokines and providing further rationale for the therapeutic targeting of these cytokines in neurological diseases where indicated.

A soluble form of the interleukin-6 family signal transducer gp130 is dimerized via a C-terminal disulfide bridge resulting from alternative mRNA splicing

Interleukin-6 (IL-6) signaling can be divided into classic signaling (via the membrane-bound IL-6 receptor, IL-6R) and trans-signaling (via the soluble IL-6R, sIL-6R), and both modes of signaling activate cells via a homodimer of the ubiquitously expressed β-receptor glycoprotein 130 (gp130). IL-6 trans-signaling is responsible for most of the pro-inflammatory activities of IL-6 and plays a role in many inflammatory diseases including inflammation-driven cancers. IL-6 trans-signaling can be selectively inhibited by soluble forms of gp130. To date, three forms of sgp130 (full-length sgp130, sgp130-RAPS and sgp130-E10) with different molecular weight have been described, which originate from alternative splicing or alternative polyadenylation of the gp130 mRNA. All these proteins are capable of blocking signaling of the IL-6/sIL-6R complex, albeit with different efficacy. The full length form of sgp130 comprises the domains D1 to D6 and a short unique C-terminus which arises from alternative splicing. In the present study, we analyze the role of a unique cysteine residue (Cys-628) within this C-terminus, which is contained neither in the membrane-bound gp130 nor in the two other sgp130 forms. Full-length sgp130 can form a disulfide-linked dimer via this cysteine residue. These natural sgp130 dimers are absent under reducing conditions or in a sgp130 C628A mutant. Although the disulfide-dimerized sgp130 represents only a small fraction of the total amount of sgp130 and, thus, may appear to be dispensable for the global inhibitory activities of sgp130 in the circulation, it may represent a further possibility to modulate gradients of sgp130 with different properties depending on the local redox potential in a cell- or tissue-dependent manner.

Interleukin-6 receptor inhibitor tocilizumab ameliorates periodontal inflammation in patients with rheumatoid arthritis and periodontitis as well as tumor necrosis factor inhibitors

Interleukin-6 (IL-6) may play a pathological role in rheumatoid arthritis (RA) and periodontitis. Although the efficacy of medication with IL-6 receptor inhibitor, tocilizumab (TCZ), has been demonstrated in the treatment of RA, very little is known about whether TCZ therapy affects periodontitis. The aim of the present study is to compare periodontal condition in patients with RA and periodontitis before and after TCZ therapy. The study participants consisted of 20 patients with RA and periodontitis who were treated with TCZ and 40 patients with RA and periodontitis who received medication with tumor necrosis factor inhibitor (TNFI). Clinical periodontal and rheumatologic assessments and serum biochemical measurements using enzyme-linked immunosorbent assays were performed at baseline and 3 and 6 months later. TCZ and TNFI therapies significantly reduced periodontal inflammation that was determined by gingival index, bleeding on probing, and probing depth (p < 0.017), although plaque levels were comparable before and after the therapies. Both therapies also significantly decreased disease activity score including 28 joints using C-reactive protein (CRP), number of tender and swollen joints, and serum levels of anti-cyclic citrullinated peptide antibodies, rheumatoid factor, CRP, and matrix metalloproteinase-3 (p < 0.017). Additionally, a significant decrease was observed in periodontal clinical attachment level after TCZ therapy (p < 0.017), but not after TNFI therapy. TCZ therapy significantly decreased serum levels of TNF-α, total immunoglobulin G, and serum amyloid A (p < 0.017), although serum levels of IL-6 and soluble IL-6R were significantly increased (p < 0.017). These results suggest a beneficial effect of TCZ therapy on levels of periodontal inflammation in patients with RA and periodontitis, which might be related to decrease in serum inflammatory mediators.

Pulmonary instillation of MWCNT increases lung permeability, decreases gp130 expression in the lungs, and initiates cardiovascular IL-6 transsignaling

Pulmonary instillation of multiwalled carbon nanotubes (MWCNT) has the potential to promote cardiovascular derangements, but the mechanisms responsible are currently unclear. We hypothesized that exposure to MWCNT would result in increased epithelial barrier permeability by 24 h postexposure and initiate a signaling process involving IL-6/gp130 transsignaling in peripheral vascular tissue. To test this hypothesis we assessed the impact of 1 and 10 μg/cm(2) MWCNT on transepithelial electrical resistance (TEER) and expression of barrier proteins and cell activation in vitro using normal human bronchial epithelial primary cells. Parallel studies using male Sprague-Dawley rats instilled with 100 μg MWCNT measured bronchoalveolar lavage (BAL) differential cell counts, BAL fluid total protein, and lung water-to-tissue weight ratios 24 h postexposure and quantified serum concentrations of IL-6, soluble IL-6r, and soluble gp130. Aortic sections were examined immunohistochemically for gp130 expression, and gp130 mRNA/protein expression was evaluated in rat lung, heart, and aortic tissue homogenates. Our in vitro findings indicate that 10 μg/cm(2) MWCNT decreased the development of TEER and zonula occludens-1 expression relative to the vehicle. In rats MWCNT instillation increased BAL protein, lung water, and induced pulmonary eosinophilia. Serum concentrations of soluble gp130 decreased, aortic endothelial expression of gp130 increased, and expression of gp130 in the lung was downregulated in the MWCNT-exposed group. We propose that pulmonary exposure to MWCNT can manifest as a reduced epithelial barrier and activator of vascular gp130-associated transsignaling that may promote susceptibility to cardiovascular derangements.

ADAM17 controls IL-6 signaling by cleavage of the murine IL-6Rα from the cell surface of leukocytes during inflammatory responses

The cytokine IL-6 is part of a regulatory signaling network that controls immune responses. IL-6 binds either to the membrane-bound IL-6 receptor-α (classic signaling) or to the soluble IL-6 receptor-α (trans-signaling) to initiate signal transduction via gp130 activation. Because classic and trans-signaling of IL-6 fulfill different tasks during immune responses, controlled shedding of the membrane-bound IL-6 receptor-α from the surface of immune cells can be considered a central regulator of IL-6 function. The results from cell culture-based experiments have implicated both a disintegrin and metalloprotease 10 and a disintegrin and metalloprotease 17 in IL-6 receptor-α shedding. However, the nature of the protease mediating IL-6 receptor-α release in vivo is not yet known. We used hypomorphic a disintegrin and metalloprotease 17 mice and conditional a disintegrin and metalloprotease 10 knock-out mice to identify the natural protease of the murine IL-6 receptor-α. Circulating homeostatic soluble IL-6 receptor-α levels are not dependent on a disintegrin and metalloprotease 10 or 17 activity. However, during Listeria monocytogenes infection, IL-6 receptor-α cleavage by the α-secretase a disintegrin and metalloprotease 17 is rapidly induced from the surface of different leukocyte populations. In contrast, CD4-Cre-driven a disintegrin and metalloprotease 10 deletion in T cells did not influence IL-6 receptor-α shedding from these cells after L. monocytogenes infection. A disintegrin and metalloprotease 17 was also required for IL-6 receptor-α ectodomain cleavage and release during endotoxemia. These results demonstrate a novel physiologic role for a disintegrin and metalloprotease 17 in regulating murine IL-6 signals during inflammatory processes.

Peripheral and central blockade of interleukin-6 trans-signaling differentially affects sleep architecture

The immune system is known to essentially contribute to the regulation of sleep. Whereas research in this regard focused on the pro-inflammatory cytokines interleukin-1 and tumor necrosis factor, the role of interleukin-6 (IL-6) in sleep regulation has been less intensely studied, probably due to the so far seemingly ambiguous results. Yet, this picture might simply reflect that the effects of IL-6 are conveyed via two different pathways (with possibly different actions), i.e., in addition to the 'classical' signaling pathway via the membrane bound IL-6 receptor (IL-6R), IL-6 stimulates cells through the alternative 'trans-signaling' pathway via the soluble IL-6R. Here, we concentrated on the contributions of the trans-signaling pathway to sleep regulation. To characterize this contribution, we compared the effect of blocking IL-6 trans-signaling (by the soluble gp130Fc fusion protein) in the brain versus body periphery. Thus, we compared sleep in transgenic mice expressing the soluble gp130Fc protein only in the brain (GFAP mice) or in the body periphery (PEPCK mice), and in wild type mice (WT) during a 24-h period of undisturbed conditions and during 18 h following a 6-h period of sleep deprivation. Compared with WT mice, PEPCK mice displayed less sleep, particularly during the late light phase, and this was accompanied by decreases in slow wave sleep (SWS) and rapid eye movement (REM) sleep. Following sleep deprivation PEPCK mice primarily recovered REM sleep rather than SWS. GFAP mice showed a slight decrease in REM sleep in combination with a profound and persistent increase in EEG theta activity. In conclusion, peripheral and central nervous IL-6 trans-signaling differentially influences brain activity. Peripheral IL-6 trans-signaling appears to more profoundly contribute to sleep regulation, mainly by supporting SWS.

Pathogenic Inflammation and Its Therapeutic Targeting in Systemic Lupus Erythematosus

Systemic lupus erythematosus (SLE, lupus) is a highly complex and heterogeneous autoimmune disease that most often afflicts women in their child-bearing years. It is characterized by circulating self-reactive antibodies that deposit in tissues, including skin, kidneys, and brain, and the ensuing inflammatory response can lead to irreparable tissue damage. Over many years, clinical trials in SLE have focused on agents that control B- and T-lymphocyte activation, and, with the single exception of an agent known as belimumab which targets the B-cell survival factor BAFF, they have been disappointing. At present, standard therapy for SLE with mild disease is the agent hydroxychloroquine. During disease flares, steroids are often used, while the more severe manifestations with major organ involvement warrant potent, broad-spectrum immunosuppression with cyclophosphamide or mycophenolate. Current treatments have severe and dose-limiting toxicities and thus a more specific therapy targeting a causative factor or signaling pathway would be greatly beneficial in SLE treatment. Moreover, the ability to control inflammation alongside B-cell activation may be a superior approach for disease control. There has been a recent focus on the innate immune system and associated inflammation, which has uncovered key players in driving the pathogenesis of SLE. Delineating some of these intricate inflammatory mechanisms has been possible with studies using spontaneous mouse mutants and genetically engineered mice. These strains, to varying degrees, exhibit hallmarks of the human disease and therefore have been utilized to model human SLE and to test new drugs. Developing a better understanding of the initiation and perpetuation of disease in SLE may uncover suitable novel targets for therapeutic intervention. Here, we discuss the involvement of inflammation in SLE disease pathogenesis, with a focus on several key proinflammatory cytokines and myeloid growth factors, and review the known outcomes or the potential for targeting these factors in SLE.

The soluble interleukin-6 receptor and related proteins

Interleukin-6 is a cytokine involved in the regulation of the immune system and the central nervous system. Interleukin-6 binds to an interleukin-6 receptor, and then associates with a dimer of the ubiquitously expressed gp130 receptor subunit, which initiates intracellular signaling. The interleukin-6 receptor is found in a soluble form, which is generated by proteolytic cleavage and also to a minor extent by translation from an alternatively spliced mRNA. The complex of interleukin-6 bound to the interleukin-6 receptor can stimulate cells, which only express gp130. Such cells are not responsive to interleukin-6 alone. We have for the first time identified the molecular basis of pro-and anti-inflammatory properties of interleukin-6 and we have defined the generation of the soluble IL-6R as a crucial point in the regulation between these two properties. Furthermore, we have deduced a therapeutic principle, which enables us to exclusively block the pro-inflammatory activities of this important cytokine.

Anti-interleukin-6 therapy through application of a monogenic protein inhibitor via gene delivery

Anti-cytokine therapies have substantially improved the treatment of inflammatory and autoimmune diseases. Cytokine-targeting drugs are usually biologics such as antibodies or other engineered proteins. Production of biologics, however, is complex and intricate and therefore expensive which might limit therapeutic application. To overcome this limitation we developed a strategy that involves the design of an optimized, monogenic cytokine inhibitor and the protein producing capacity of the host. Here, we engineered and characterized a receptor fusion protein, mIL-6-RFP-Fc, for the inhibition of interleukin-6 (IL-6), a well-established target in anti-cytokine therapy. Upon application in mice mIL-6-RFP-Fc inhibited IL-6-induced activation of the transcription factor STAT3 and ERK1/2 kinases in liver and kidney. mIL-6-RFP-Fc is encoded by a single gene and therefore most relevant for gene transfer approaches. Gene transfer through hydrodynamic plasmid delivery in mice resulted in hepatic production and secretion of mIL-6-RFP-Fc into the blood in considerable amounts, blocked hepatic acute phase protein synthesis and improved kidney function in an ischemia and reperfusion injury model. Our study establishes receptor fusion proteins as promising agents in anti-cytokine therapies through gene therapeutic approaches for future targeted and cost-effective treatments. The strategy described here is applicable for many cytokines involved in inflammatory and other diseases.

Novel Insights into Interleukin 6 (IL-6) Cis- and Trans-signaling Pathways by Differentially Manipulating the Assembly of the IL-6 Signaling Complex

The IL-6 signaling complex is described as a hexamer, formed by the association of two IL-6·IL-6 receptor (IL-6R)·gp130 trimers, with gp130 being the signal transducer inducing cis- and trans-mediated signaling via a membrane-bound or soluble form of the IL-6R, respectively. 25F10 is an anti-mouse IL-6R mAb that binds to both membrane-bound IL-6R and soluble IL-6R with the unique property of specifically inhibiting trans-mediated signaling events. In this study, epitope mapping revealed that 25F10 interacts at site IIb of IL-6R but allows the binding of IL-6 to the IL-6R and the recruitment of gp130, forming a trimer complex. Binding of 25F10 to IL-6R prevented the formation of the hexameric complex obligate for trans-mediated signaling, suggesting that the cis- and trans-modes of IL-6 signaling adopt different mechanisms for receptor complex assembly. To study this phenomenon also in the human system, we developed NI-1201, a mAb that targets, in the human IL-6R sequence, the epitope recognized by 25F10 for mice. Interestingly, NI-1201, however, did not selectively inhibit human IL-6 trans-signaling, although both mAbs produced beneficial outcomes in conditions of exacerbated IL-6 as compared with a site I-directed mAb. These findings shed light on the complexity of IL-6 signaling. First, triggering cis- versus trans-mediated IL-6 signaling occurs via distinctive mechanisms for receptor complex assembly in mice. Second, the formation of the receptor complex leading to cis- and trans-signaling biology in mice and humans is different, and this should be taken into account when developing strategies to inhibit IL-6 clinically.

First trimester interleukin-6 levels help to predict adverse pregnancy outcomes in both thyroid autoantibody positive and negative patients

AIM

The aim of the present study is to compare pregnancy outcomes among patients with and without thyroid antibodies and/or subclinical hypothyroidism and investigate whether there is an association between first trimester maternal plasma interleukin-6 (IL-6) levels and adverse pregnancy outcomes.

METHODS

A case-control study was carried out including 83 pregnant women (40 thyroid antibody positive and 43 healthy controls). The predictive value of first trimester maternal plasma IL-6 levels on adverse pregnancy outcomes were investigated. The optimal cut-off points of IL-6 for determining maternal and fetal outcomes were evaluated by receiver operating characteristic analyses.

RESULTS

Compared with the control, median IL-6 levels were significantly higher in thyroid antibody positive pregnancies (median 1.58 vs 1.63 pg/mL; P = 0.047). IL-6 levels were found to be significantly higher in women who had suffered a miscarriage (P = 0.002), preterm delivery (P < 0.001), intrauterine growth restriction (P = 0.047), preterm premature rupture of membranes (P = 0.043) and overall prenatal complications (P < 0.001). A statistically significant negative correlation between gestational week at birth and IL-6 levels was also determined among all participants involved in the study (r = -0.385, P < 0.001).

CONCLUSION

IL-6 levels are significantly increased in thyroid antibody positive patients and predictive for future adverse outcomes, irrespective of thyroid autoimmunity. Increased first trimester IL-6 levels independently predict adverse pregnancy outcomes, regardless of subclinical hypothyroidism.