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

IL-6 exhibits both cis- and trans-signaling in osteocytes and osteoblasts, but only trans-signaling promotes bone formation and osteoclastogenesis

Interleukin 6 (IL-6) supports development of bone-resorbing osteoclasts by acting early in the osteoblast lineage via membrane-bound (cis) or soluble (trans) receptors. Here, we investigated how IL-6 signals and modifies gene expression in differentiated osteoblasts and osteocytes and determined whether these activities can promote bone formation or support osteoclastogenesis. Moreover, we used a genetically altered mouse with circulating levels of the pharmacological IL-6 trans-signaling inhibitor sgp130-Fc to determine whether IL-6 trans-signaling is required for normal bone growth and remodeling. We found that IL-6 increases suppressor of cytokine signaling 3 (Socs3) and CCAAT enhancer-binding protein δ (Cebpd) mRNA levels and promotes signal transducer and activator of transcription 3 (STAT3) phosphorylation by both cis- and trans-signaling in cultured osteocytes. In contrast, RANKL (Tnfsf11) mRNA levels were elevated only by trans-signaling. Furthermore, we observed soluble IL-6 receptor release and ADAM metallopeptidase domain 17 (ADAM17) sheddase expression by osteocytes. Despite the observation that IL-6 cis-signaling occurs, IL-6 stimulated bone formation in vivo only via trans-signaling. Although IL-6 stimulated RANKL (Tnfsf11) mRNA in osteocytes, these cells did not support osteoclast formation in response to IL-6 alone; binucleated TRAP+ cells formed, and only in response to trans-signaling. Finally, pharmacological, sgp130-Fc-mediated inhibition of IL-6 trans-signaling did not impair bone growth or remodeling unless mice had circulating sgp130-Fc levels > 10 μg/ml. At those levels, osteopenia and impaired bone growth occurred, reducing bone strength. We conclude that high sgp130-Fc levels may have detrimental off-target effects on the skeleton.

Elevated plasma interleukin 6 predicts poor response in patients treated with sunitinib for metastatic clear cell renal cell carcinoma

INTRODUCTION

Clear cell renal cell carcinoma (ccRCC) is the most common type among renal cell carcinomas, and anti-angiogenic treatment is currently first line therapy in metastatic ccRCC (mccRCC). Response rates and duration of response show considerable variation, and adverse events have major influence on patient's quality of life. The need for predictive biomarkers to select those patients most likely to respond to receptor tyrosine kinase inhibitors (rTKI) upfront is urgent. We investigated the predictive value of plasma interleukin-6 (pIL6), interleukin-6 receptor α (pIL6Rα) and interleukin 6 signal transducer (pIL6ST) in mccRCC patients treated with sunitinib.

MATERIAL AND METHODS

Forty-six patients with metastatic or non-resectable ccRCC treated with sunitinib were included. Full blood samples were collected at baseline before start of sunitinib and after every second cycle of treatment during the study time. pIL6, pIL6R and pIL6ST at baseline and week 12 samples were analysed by ELISA. The predictive potential of the candidate markers was assessed by correlation with response rates (RECIST). In addition, progression free survival (PFS) and overall survival (OS) were analysed.

RESULTS

Low pIL6 at baseline was significantly associated with improved response to sunitinib (Fisher's exact test, p < 0.01). Furthermore, low pIL6 at baseline was significantly associated with improved PFS (log rank, p = 0.04). In addition, patients with a decrease in concentration of pIL6R between baseline and week 12 showed significantly improved PFS (log rank, p = 0.04) and patients with high pIL6ST at baseline showed significantly improved OS (log rank, p = 0.03).

CONCLUSION

Low pIL6 at baseline in mccRCC patients treated with sunitinib predicts improved treatment response, and might represent a candidate predictive marker.

The role of the interleukin (IL)-6/IL-6 receptor axis in cancer

Interleukin-6 (IL-6) is a pleiotropic cytokine that activates a classic signalling pathway upon binding to its membrane-bound receptor (IL-6R). Alternatively, IL-6 may 'trans-signal' in a manner that is facilitated by its binding to a soluble derivative of the IL-6 receptor (sIL-6R). Resultant signal transduction is, respectively, driven by the association of IL-6/IL-6R or IL-6/sIL-6R complex with the membrane-associated signal transducer, gp130 (Glycoprotein 130). Distinct JAK (Janus tyrosine kinase)/STAT (signal transducers and activators of transcription) and other signalling pathways are activated as a consequence. Of translational relevance, overexpression of IL-6 has been documented in several neoplastic disorders, including but not limited to colorectal, ovarian and breast cancer and several haematological malignancies. This review attempts to summarise our current understanding of the role of IL-6 in cancer development. In short, these studies have shown important roles for IL-6 signalling in tumour cell growth and survival, angiogenesis, immunomodulation of the tumour microenvironment, stromal cell activation, and ultimate disease progression. Given this background, we also consider the potential for therapeutic targeting of this system in cancer.

Soluble gp130 prevents interleukin-6 and interleukin-11 cluster signaling but not intracellular autocrine responses

Interleukin-6 (IL-6) is a proinflammatory cytokine of the IL-6 family, members of which signal through a complex of a cytokine-specific receptor and the signal-transducing subunit gp130. The interaction of IL-6 with the membrane-bound IL-6 receptor (IL-6R) and gp130 stimulates “classic signaling,” whereas the binding of IL-6 and a soluble version of the IL-6R to gp130 stimulates “trans-signaling.” Alternatively, “cluster signaling” occurs when membrane-bound IL-6:IL-6R complexes on transmitter cells activate gp130 receptors on neighboring receiver cells. The soluble form of gp130 (sgp130) is a selective trans-signaling inhibitor, but it does not affect classic signaling. We demonstrated that the interaction of soluble gp130 with natural and synthetic membrane-bound IL-6:IL-6R complexes inhibited IL-6 cluster signaling. Similarly, IL-11 cluster signaling through the IL-11R to gp130 was also inhibited by soluble gp130. However, autocrine classic and trans-signaling was not inhibited by extracellular inhibitors such as sgp130 or gp130 antibodies. Together, our results suggest that autocrine IL-6 signaling may occur intracellularly.

IL-6: a cytokine at the crossroads of autoimmunity

IL-6 is implicated in the development and progression of autoimmune diseases in part by influencing CD4 T cell lineage and regulation. Elevated IL-6 levels drive inflammation in a wide range of autoimmune diseases, some of which are also characterized by enhanced T cell responses to IL-6. Notably, the impact of IL-6 on inflammation is contextual in nature and dependent on the cell type, cytokine milieu and tissue. Targeting the IL-6/IL-6R axis in humans has been shown to successfully ameliorate a subset of autoimmune conditions. In this review, we discuss recent studies investigating how IL-6 regulates the CD4 T cell response in the context of autoimmune disease and highlight how blocking different aspects of the IL-6 pathway is advantageous in the treatment of disease.

Inhibition of interleukin-6 trans-signaling prevents inflammation and endothelial barrier disruption in retinal endothelial cells

Vascular inflammation plays a critical role in the pathogenesis of diabetic retinopathy. Recently, Interleukin-6 (IL-6) trans-signaling via soluble IL-6 receptor (sIL-6R) has emerged as a prominent regulator of inflammation in endothelial cells. This study was designed to test the hypothesis that selective inhibition of the IL-6 trans-signaling pathway will attenuate inflammation and subsequent barrier disruption in retinal endothelial cells. Human retinal endothelial cells (HRECs) were exposed to IL-6 and sIL-6R to induce IL-6 trans-signaling and the commercially available compound sgp130Fc (soluble gp-130 fused chimera) was used to selectively inhibit IL-6 trans-signaling. IL-6 trans-signaling activation caused a significant increase in STAT3 phosphorylation, expression of adhesion molecules, ROS production and apoptosis in HRECs whereas a significant decrease in mitochondrial membrane potential and NO production was observed in IL-6 trans-signaling activated cells. These changes were not observed in cells pre-treated with sgp130Fc. IL-6 trans-signaling activation was sufficient to cause barrier disruption in endothelial monolayers and pre-treatment of HRECs with sgp130Fc, maintained endothelial barrier function similar to that of untreated cells. Thus, in conclusion, these results indicate that IL-6 trans-signaling is an important mediator of inflammation, apoptosis and barrier disruptive effects in the retinal endothelial cells and inhibition of the IL-6 trans-signaling pathway using sgp130-Fc attenuates vascular inflammation and endothelial barrier disruption.

Control of Listeria monocytogenes infection requires classical IL-6 signaling in myeloid cells

IL-6 is required for the response of mice against Listeria monocytogenes. Control of infection depends on classical IL-6 signaling via membrane IL-6Rα, but IL-6 target cells and protective mechanisms remain unclear. We used mice with IL-6Rα-deficiency in T cells (Il6rafl/fl×CD4cre) or myeloid cells (Il6rafl/fl×LysMcre) to define the role of these cells in IL-6-mediated protection. Abrogation of IL-6Rα in T cells did not interfere with bacteria control and induction of TH1 and CD8+ T-cell responses. IL-6Rα-deficiency in myeloid cells caused significant defects in listeria control. This defect was not associated with reduced recruitment of granulocytes and inflammatory monocytes, and both cell populations were activated and not impaired in cytokine production. However, IL-6Rα-deficient inflammatory monocytes displayed diminished expression of IL-4Rα and of CD38, a protein required for phagocytosis and innate control of listeria. In vitro studies revealed that IL-4 and IL-6 cooperated in induction of CD38. In listeria-infected mice, phagocytic activity of inflammatory monocytes correlated with CD38 expression levels on cells and inflammatory monocytes of Il6rafl/fl×LysMcre mice were significantly impaired in phagocytosis. In conclusion, we demonstrate that inhibition of classical IL-6 signaling in myeloid cells causes alterations in differentiation and function of these cells, which subsequently prevent effective control of L. monocytogenes.

Sarilumab: patient-reported outcomes in rheumatoid arthritis

In the last few decades, strategies for the management of rheumatoid arthritis (RA) have been increasingly oriented toward more comprehensive control of the disease, taking into account even RA extra-articular manifestations, comorbidities, and the patient’s perception about the disease. The need for improving the shared decision-making process suggested by European League Against Rheumatism recommendations is leading to an increasing interest in the role of patient-reported outcomes (PROs) beside the usual more objective criteria for defining clinical response based on disease-activity composite indices. Measurement of such PROs as pain or fatigue may be significantly influenced by mood disorders often complicating RA, the pathogenesis of which is deeply interconnected with phlogistic processes mediated by proinflammatory cytokines. IL6 is a pleiotropic mediator involved in neuroendocrine and neuropsychological processes, besides its well known effects on immune, cardiovascular, and metabolic systems. Therefore, there is a growing body of evidence about the efficacy of IL6 blockade in PRO improvement in RA patients. Sarilumab is a monoclonal antibody binding both soluble and membrane-bound IL6Rα, inhibiting the IL6-mediated signaling pathway with favorable efficacy and safety profile. This review analyzes the importance of PROs in strategies for the management of RA and the pathogenic mechanisms linking IL6 with the patient’s perception of the disease. Moreover, the main findings from sarilumab randomized controlled trials are summarized in detail, emphasizing the potential role of this IL6 blocker in the holistic treatment of RA.

Soluble interleukin-27 receptor alpha is a valuable prognostic biomarker for acute graft-versus-host disease after allogeneic haematopoietic stem cell transplantation

Acute graft-versus-host disease (aGVHD) is a major life-threatening complication after allogeneic haematopoietic stem cell transplantation. Interleukin-27 receptor alpha (IL-27Rα) is a co-receptor of IL-27, an inflammatory cytokine that possesses extensive immunological functions. It has been reported that IL-27Rα can exist in its soluble form (sIL-27Rα) in human serum and can function as a natural IL-27 antagonist. In this study, we examined serum sIL-27Rα levels and evaluated their prognostic value in aGVHD. A total of 152 subjects were prospectively recruited and separated into the training group (n = 72) and the validation group (n = 80). Serum sIL-27Rα at neutrophil engraftment was measured by ELISA. In the training set, a cut-off value of sIL-27Rα = 59.40 ng/ml was identified to predict grade II–IV aGVHD (AUC = 0.735, 95% CI 0.618–0.853, P = 0.001). Cumulative incidences of grade II–IV aGVHD (P = 0.004), relapse rate (P = 0.008), and non-relapse mortality (P = 0.008) in patients with low serum sIL-27Rα (≥59.40 ng/ml) were significantly higher than those of patients with high serum sIL-27Rα (<59.40 ng/ml). Multivariate analysis confirmed that low sIL-27Rα level (HR = 2.83 95% CI 1.29–6.19, P < 0.01) was an independent risk factor for predicting grade II-IV aGVHD. In addition, serum sIL-27Rα was positively correlated with IL-27 (R = 0.27, P = 0.029), IL-10 (R = 0.37, P = 0.0015) and HGF (R = 0.27, P = 0.0208), but was negatively correlated with TNFR1 (R = −0.365, P = 0.0022) and ST2 (R = −0.334, P = 0.0041), elafin (R = −0.29, P = 0.0117), and REG3α (R = −0.417, P = 0.0003). More importantly, the threshold value of sIL-27Rα was then validated in an independent cohort of 80 patients (AUC = 0.790, 95% CI 0.688–0.892, P < 0.001). Taken together, our findings suggested that serum sIL-27Rα at neutrophil engraftment maybe a valuable prognostic biomarker in predicting the incidence of moderate-to-severe aGVHD.

Putative biomarkers of vedolizumab resistance and underlying inflammatory pathways involved in IBD

Objectives

Characterise the circulating inflammatory cytokine pattern among patients failing consecutive anti-tumour necrosis factor (anti-TNF) and anti-integrin treatments to identify predictors of response.

Methods

A retrospective single-centre cohort study of 28 patients with inflammatory bowel disease (IBD) receiving anti-integrin therapy (vedolizumab) subsequent to the failure of anti-TNF treatment was conducted. Blood samples were obtained immediately prior to initiation of vedolizumab therapy, and the response to treatment was evaluated after completion of the 14-week induction regimen. Multiplex ELISA was applied to quantify 47 preselected plasma proteins based on their putative involvement in the inflammatory process in IBD.

Results

Anti-TNF and vedolizumab non-responders (n=20) had significantly higher levels of circulating interleukin (IL)-6 than anti-TNF non-responders with subsequent response to vedolizumab (n=8): median 9.5 pg/mL versus 5.9 pg/mL, p<0.05. Following stratification by diagnosis, patients with Crohn's disease who failed vedolizumab therapy (n=7) had higher soluble CD40 ligand (sCD40L) than responders (n=4): 153.0 pg/mL versus 45.5 pg/mL, p<0.01; sensitivity 100% (95% CI 59% to 100%), specificity 100% (95% CI 40% to 100%). Osteocalcin was higher among patients with ulcerative colitis responding to vedolizumab (n=4) compared with those not responding (n=13): 4219 pg/mL versus 2823 pg/mL, p=0.01; sensitivity 85% (95% CI 55% to 98%), specificity 100% (95% CI 40% to 100%).

Conclusions

Patients with IBD failing vedolizumab induction and anti-TNF therapy have persistent IL-6 pathway activity, which could be a potential alternative treatment target. sCD40L, osteocalcin and the IL-6 pathway activity might be predictors for response to vedolizumab.

Interleukin-6 trans-signaling contributes to chronic hypoxia-induced pulmonary hypertension

Interleukin-6 (IL-6) is a pleotropic cytokine that signals through the membrane-bound IL-6 receptor (mIL-6R) to induce anti-inflammatory (“classic-signaling”) responses. This cytokine also binds to the soluble IL-6R (sIL-6R) to promote inflammation (“trans-signaling”). mIL-6R expression is restricted to hepatocytes and immune cells. Activated T cells release sIL-6R into adjacent tissues to induce trans-signaling. These cellular actions require the ubiquitously expressed membrane receptor gp130. Reports show that IL-6 is produced by pulmonary arterial smooth muscle cells (PASMCs) exposed to hypoxia in culture as well as the medial layer of the pulmonary arteries in mice exposed to chronic hypoxia (CH), and IL-6 knockout mice are protected from CH-induced pulmonary hypertension (PH). IL-6 has the potential to contribute to a broad array of downstream effects, such as cell growth and migration. CH-induced PH is associated with increased proliferation and migration of PASMCs to previously non-muscularized vessels of the lung. We tested the hypothesis that IL-6 trans-signaling contributes to CH-induced PH and arterial remodeling. Plasma levels of sgp130 were significantly decreased in mice exposed to CH (380 mmHg) for five days compared to normoxic control mice (630 mmHg), while sIL-6R levels were unchanged. Consistent with our hypothesis, mice that received the IL-6 trans-signaling-specific inhibitor sgp130Fc, a fusion protein of the soluble extracellular portion of gp130 with the constant portion of the mouse IgG1 antibody, showed attenuation of CH-induced increases in right ventricular systolic pressure, right ventricular and pulmonary arterial remodeling as compared to vehicle (saline)-treated control mice. In addition, PASMCs cultured in the presence of IL-6 and sIL-6R showed enhanced migration but not proliferation compared to those treated with IL-6 or sIL-6R alone or in the presence of sgp130Fc. These results indicate that IL-6 trans-signaling contributes to pulmonary arterial cell migration and CH-induced PH.

Interleukin-6: designing specific therapeutics for a complex cytokine

Interleukin-6 (IL-6) is a pivotal cytokine with a diverse repertoire of physiological functions that include regulation of immune cell proliferation and differentiation. Dysregulation of IL-6 signalling is associated with inflammatory and lymphoproliferative disorders such as rheumatoid arthritis and Castleman disease, and several classes of therapeutics have been developed that target components of the IL-6 signalling pathway. So far, monoclonal antibodies against IL-6 or IL-6 receptor (IL-6R) and Janus kinases (JAK) inhibitors have been successfully developed for the treatment of autoimmune diseases such as rheumatoid arthritis. However, clinical trials of agents targeting IL-6 signalling have also raised questions about the diseases and patient populations for which such agents have an appropriate benefit-risk profile. Knowledge from clinical trials and advances in our understanding of the complexities of IL-6 signalling, including the potential to target an IL-6 trans-signalling pathway, are now indicating novel opportunities for therapeutic intervention. In this Review, we overview the roles of IL-6 in health and disease and analyse progress with several approaches of inhibiting IL-6-signalling, with the aim of illuminating when and how to apply IL-6 blockade.

Pharmacological inhibition of IL-6 trans-signaling improves compromised fracture healing after severe trauma

Patients with multiple injuries frequently suffer bone fractures and are at high risk to develop fracture healing complications. Because of its key role both in systemic posttraumatic inflammation and fracture healing, the pleiotropic cytokine interleukin-6 (IL-6) may be involved in the pathomechanisms of trauma-induced compromised fracture healing. IL-6 signals are transmitted by two different mechanisms: classic signaling via the membrane-bound receptor (mIL-6R) and trans-signaling via its soluble form (sIL-6R). Herein, we investigated whether IL-6 classic and trans-signaling play different roles in bone regeneration after severe injury. Twelve-week-old C57BL/6J mice underwent combined femur osteotomy and thoracic trauma. To study the function of IL-6, either an anti-IL-6 antibody, which inhibits both IL-6 classic and trans-signaling, or a soluble glycoprotein 130 fusion protein (sgp130Fc), which selectively blocks trans-signaling, were injected 30 min and 48 h after surgery. Bone healing was assessed using cytokine analyses, flow cytometry, histology, micro-computed tomography, and biomechanical testing. Selective inhibition of IL-6 trans-signaling significantly improved the fracture healing outcome after combined injury, as confirmed by accelerated cartilage-to-bone transformation, enhanced bony bridging of the fracture gap and improved mechanical callus properties. In contrast, global IL-6 inhibition did not affect compromised fracture healing. These data suggest that classic signaling may mediate beneficial effects on bone repair after severe injury. Selective inhibition of IL-6 trans-signaling might have therapeutic potential to treat fracture healing complications in patients with concomitant injuries.

Soluble glycoprotein 130 is inversely related to severity of coronary atherosclerosis

PURPOSE

Recent studies indicate that the effects of interleukin 6 (IL-6) realized via soluble IL-6 receptor (sIL-6R) facilitate the development of various pathological processes. Soluble gp130 (sgp130) is a naturally occurring inhibitor of signal transduction via this pathway. In this study, we assessed the relationship between circulating levels of IL-6, sIL-6R and sgp130 and severity of coronary atherosclerosis in patients with stable coronary artery disease (CAD).

METHODS

Plasma levels of IL-6, sIL-6R and sgp130 were measured in patients with atherosclerotic coronary lesions (n = 128, group 1) and with intact coronary arteries (n = 48, group 2). The severity of coronary atherosclerosis was evaluated by the number of affected arteries and by Gensini Score index.

RESULTS

Circulating IL-6 levels in group 1 were significantly higher than those in group 2. The levels of sIL-6R did not differ considerably in both the groups. The levels of sgp130 in group 1 were significantly lower than in group 2. A negative correlation has been revealed between sgp130 levels and the number of affected coronary arteries and Gensini Score index.

CONCLUSIONS

Serum concentration of sgp130 in patients with stable CAD is inversely related to severity of coronary damage. Low sgp130 level may serve as an additional indicator of coronary atherosclerosis severity.

Mediators and Patterns of Muscle Loss in Chronic Systemic Inflammation

Besides its primary function in locomotion, skeletal muscle (SKM), which represents up to half of human's weight, also plays a fundamental homeostatic role. Through the secretion of soluble peptides, or myokines, SKM interacts with major organs involved in metabolic processes. In turn, metabolic cues from these organs are received by muscle cells, which adapt their response accordingly. This is done through an intricate intracellular signaling network characterized by the cross-talking between anabolic and catabolic pathways. A fine regulation of the network is required to protect the organism from an excessive energy expenditure. Systemic inflammation evokes a catabolic reaction in SKM known as sarcopenia. In turn this response comprises several mechanisms, which vary depending on the nature of the insult and its magnitude. In this regard, aging, chronic inflammatory systemic diseases, osteoarthritis and idiopathic inflammatory myopathies can lead to muscle loss. Interestingly, sarcopenia may persist despite remission of chronic inflammation, an issue which warrants further research. The Janus kinase/signal transducer and activator of transcription (JAK/STAT) system stands as a major participant in muscle loss during systemic inflammation, while it is also a well-recognized orchestrator of muscle cell turnover. Herein we summarize current knowledge about models of sarcopenia, their triggers and major mediators and their effect on both protein and cell growth yields. Also, the dual action of the JAK/STAT pathway in muscle mass changes is discussed. We highlight the need to unravel the precise contribution of this system to sarcopenia in order to design targeted therapeutic strategies.

Update of sarilumb to treat rheumatoid arthritis based on randomized clinical trials: a systematic review

INTRODUCTION

Sarilumab is a human monoclonal antibody against Interleukin 6 α (IL-6α) receptor. Compared to tocilizumab, another IL-6 α receptor antibody, sarilumab has a different structure and higher affinity. Areas covered: In a systematic literature review, we examined all sarilumab randomized clinical trials (RCTs) in rheumatoid arthritis. The 6 reviewed RCTs included patients who were inadequate MTX, DMARD and/or TNFi responders. Sarilumab 150-200 mg every 2 weeks improved RA signs, symptoms, function and decreased radiological progression up to 52 weeks. The most common adverse events were infections and neutropenia, the latter of which will require careful observation in future trials. Examination of the effect of sero-positivity, disease duration, presence of erosions, use of previous biologic and comparisons to other biologics etc are still needed to complete understanding of this drug's profile. Long term studies, too, will be needed to assess long term tolerability Expert commentary: Results support the use of sarilumab to treat RA patients with inadequate response to MTX, other DMARDs and TNFis, although further studies are needed to fully assess its toxicity and understand the specific place of sarilumab in the RA armamentarium.

Plasma cytokine and angiogenic factors associated with prognosis and therapeutic response to sunitinib vs everolimus in advanced non-clear cell renal cell carcinoma

No biomarkers are available to predict relative clinical benefit from targeted therapies in patients with non-clear cell renal cell carcinoma (nccRCC). To identify candidate predictive markers, we investigated a set of cytokines and angiogenic factors (CAFs) in previously untreated patients with nccRCC participating in the phase II ESPN trial comparing first-line sunitinib to everolimus. Pre-treatment concentrations of 30 CAFs were measured in plasma from 37 patients treated with everolimus (n=16) or sunitinib (n=21), and associated with progression-free (PFS) and overall survival (OS) after adjusting for potential confounders. High (>median) concentrations of soluble glycoprotein 130 (sgp130) were predictive of a longer PFS with sunitinib compared with everolimus (HR = 0.30; 95% CI: 0.11-0.85; P = 0.024). Significantly shorter PFS was noted, independently of treatment arm, in patients with high (>median) levels of IL-8 (HR = 3.13; 95% CI: 1.41-6.92), IL-13 (HR = 3.36; 95% CI: 1.49-7.58), and soluble tumor necrosis factor receptor II (HR = 2.21; 95% CI: 1.04-4.72). High IL-8 levels were also associated with significantly shorter OS (HR = 3.55; 95% CI: 1.55-8.14). Thus, using CAF profiling we identified candidate prognostic and predictive circulating biomarkers that can be used to inform therapeutic decisions in nccRCC.

Targeting the IL-6/JAK/STAT3 signalling axis in cancer

The IL-6/JAK/STAT3 pathway is aberrantly hyperactivated in many types of cancer, and such hyperactivation is generally associated with a poor clinical prognosis. In the tumour microenvironment, IL-6/JAK/STAT3 signalling acts to drive the proliferation, survival, invasiveness, and metastasis of tumour cells, while strongly suppressing the antitumour immune response. Thus, treatments that target the IL-6/JAK/STAT3 pathway in patients with cancer are poised to provide therapeutic benefit by directly inhibiting tumour cell growth and by stimulating antitumour immunity. Agents targeting IL-6, the IL-6 receptor, or JAKs have already received FDA approval for the treatment of inflammatory conditions or myeloproliferative neoplasms and for the management of certain adverse effects of chimeric antigen receptor T cells, and are being further evaluated in patients with haematopoietic malignancies and in those with solid tumours. Novel inhibitors of the IL-6/JAK/STAT3 pathway, including STAT3-selective inhibitors, are currently in development. Herein, we review the role of IL-6/JAK/STAT3 signalling in the tumour microenvironment and the status of preclinical and clinical investigations of agents targeting this pathway. We also discuss the potential of combining IL-6/JAK/STAT3 inhibitors with currently approved therapeutic agents directed against immune-checkpoint inhibitors.

Compounds of IL-6 Receptor Complex during Acute Lung Injury

Soluble receptor of IL-6 (sIL-6R) and antagonist of the receptor complex, soluble glycoprotein 130 (sgp130) mediate opposite effects during inflammation. We measured the levels of these cytokines and their ratio in rat blood on the model of acute lung injury. The injury was modeled by the intratracheal administration of LPS. The levels of sgp130 and sIL-6R increased during the inflammatory process in the injured lungs. The sgp130/sIL-6R ratio increased or decreased depending on the intensity of the inflammatory process. sgp130/sIL-6R ratio might reflect the intensity of inflammation during lung injury.

The balance of interleukin (IL)-6, IL-6·soluble IL-6 receptor (sIL-6R), and IL-6·sIL-6R·sgp130 complexes allows simultaneous classic and trans-signaling

Interleukin (IL-)6 is the major pro-inflammatory cytokine within the IL-6 family. IL-6 signals via glycoprotein 130 (gp130) and the membrane-bound or soluble IL-6 receptor (IL-6R), referred to as classic or trans-signaling, respectively. Whereas inflammation triggers IL-6 expression, eventually rising to nanogram/ml serum levels, soluble IL-6R (sIL-6R) and soluble gp130 (sgp130) are constitutively present in the upper nanogram/ml range. Calculations based on intermolecular affinities have suggested that systemic IL-6 is immediately trapped in IL-6·sIL-6R and IL-6·sIL-6R·sgp130 complexes, indicating that sIL-6R and sgp130 constitute a buffer system that increases the serum half-life of IL-6 or restricts systemic IL-6 signaling. However, this scenario has not been experimentally validated. Here, we quantified IL-6·sIL-6R and IL-6·sIL-6R·sgp130 complexes over a wide concentration range. The amounts of IL-6 used in this study reflect concentrations found during active inflammatory events. Our results indicated that most IL-6 is free and not complexed with sIL-6R or sgp130, indicating that the level of endogenous sgp130 in the bloodstream is not sufficient to block IL-6 trans-signaling via sIL-6R. Importantly, addition of the single-domain antibody VHH6, which specifically stabilizes IL-6·sIL-6R complexes but did not bind to IL-6 or sIL-6R alone, drove free IL-6 into IL-6·sIL-6R complexes and boosted trans-signaling but not classic signaling, demonstrating that endogenous sIL-6R has at least the potential to form complexes with IL-6. Our findings indicate that even though high concentrations of sIL-6R and sgp130 are present in human serum, the relative ratio of free IL-6 to IL-6·sIL-6R allows for simultaneous classic and trans-signaling.

IL-6 signalling pathways and the development of type 2 diabetes

Interleukin 6 (IL-6), a multifunctional cytokine, has been implicated in the pathophysiology of type 2 diabetes (T2D). The elevated circulating level of IL-6 is an independent predictor of T2D and is considered to be involved in the development of inflammation, insulin resistance and β-cell dysfunction. On the other hand, an increasing number of evidence suggests that IL-6 has an anti-inflammatory role and improves glucose metabolism. The complex signal transduction mechanism of IL-6 may help explain the pleiotropic nature of the cytokine. IL-6 acts via two distinct signalling pathways called classic signalling and trans-signalling. While both signalling modes lead to activation of the same receptor subunit, their final biological effects are completely different. The aim of this review is to summarize our current knowledge about the role of IL-6 in the development of T2D. We will also discuss the importance of specific blockade of IL-6 trans-signalling rather than inhibiting both signalling pathways as a therapeutic strategy for the treatment of T2D and its associated macrovascular complications.

ADAM17 is required for EGF-R-induced intestinal tumors via IL-6 trans-signaling

Schmidt et al. show that loss of the membrane-bound metalloprotease ADAM17 led to impaired intestinal cancer development in the murine APC^min/+ model, which also depended on IL-6 trans-signaling via the soluble IL-6R and could be blocked by the specific IL-6 trans-signaling inhibitor sgp130Fc.

Colorectal cancer is treated with antibodies blocking epidermal growth factor receptor (EGF-R), but therapeutic success is limited. EGF-R is stimulated by soluble ligands, which are derived from transmembrane precursors by ADAM17-mediated proteolytic cleavage. In mouse intestinal cancer models in the absence of ADAM17, tumorigenesis was almost completely inhibited, and the few remaining tumors were of low-grade dysplasia. RNA sequencing analysis demonstrated down-regulation of STAT3 and Wnt pathway components. Because EGF-R on myeloid cells, but not on intestinal epithelial cells, is required for intestinal cancer and because IL-6 is induced via EGF-R stimulation, we analyzed the role of IL-6 signaling. Tumor formation was equally impaired in IL-6^−/− mice and sgp130Fc transgenic mice, in which only trans-signaling via soluble IL-6R is abrogated. ADAM17 is needed for EGF-R–mediated induction of IL-6 synthesis, which via IL-6 trans-signaling induces β-catenin–dependent tumorigenesis. Our data reveal the possibility of a novel strategy for treatment of colorectal cancer that could circumvent intrinsic and acquired resistance to EGF-R blockade.

Interleukin (IL)-6 Inhibits IL-27- and IL-30-Mediated Inflammatory Responses in Human Monocytes

Interleukin (IL)-30, the IL-27p28 subunit of the heterodimeric cytokine IL-27, acts as an antagonist of IL-27 and IL-6 signaling in murine cells via glycoprotein 130 (gp130) receptor and additional binding partners. Thus far, functions of IL-30 have not been fully elucidated in human cells. We demonstrate that like IL-27, IL-30 upregulated TLR4 expression to enhance lipopolysaccharide-induced TNF-α production in human monocytes; however, these IL-30-mediated activities did not reach the same levels of cytokine induction compared to IL-27. Interestingly, IL-30- and IL-27-mediated interferon-γ-induced protein 10 (IP-10) production required WSX-1 engagement and signal transducer and activator of transcription (STAT) 3 phosphorylation; furthermore, IL-30 induced STAT phosphorylation after 16 h, whereas IL-27 induced STAT phosphorylation within 30 min. This prompted us to examine if a secondary mediator was required for IL-30-induced pro-inflammatory functions, and hence we examined IL-6-related molecules. Combined with inhibition of soluble IL-6 receptor α (sIL-6Rα) and data showing that IL-6 inhibited IL-30/IL-27-induced IP-10 expression, we demonstrate a role for sIL-6Rα and gp130 in IL-30-mediated activity in human cells.

Interleukin-6 Family Cytokines

The interleukin (IL)-6 family cytokines is a group of cytokines consisting of IL-6, IL-11, ciliary neurotrophic factor (CNTF), leukemia inhibitory factor (LIF), oncostatin M (OSM), cardiotrophin 1 (CT-1), cardiotrophin-like cytokine (CLC), and IL-27. They are grouped into one family because the receptor complex of each cytokine contains two (IL-6 and IL-11) or one molecule (all others cytokines) of the signaling receptor subunit gp130. IL-6 family cytokines have overlapping but also distinct biologic activities and are involved among others in the regulation of the hepatic acute phase reaction, in B-cell stimulation, in the regulation of the balance between regulatory and effector T cells, in metabolic regulation, and in many neural functions. Blockade of IL-6 family cytokines has been shown to be beneficial in autoimmune diseases, but bacterial infections and metabolic side effects have been observed. Recent advances in cytokine blockade might help to minimize such side effects during therapeutic blockade.

Proteins of TNF-α and IL6 Pathways Are Elevated in Serum of Type-1 Diabetes Patients with Microalbuminuria

Soluble cytokine receptors may play an important role in development of microalbuminuria (MA) in type-1 diabetes (T1D). In this study, we measured 12 soluble receptors and ligands from TNF-α/IL6/IL2 pathways in T1D patients with MA (n = 89) and T1D patients without MA (n = 483) participating in the PAGODA study. Twelve proteins in the sera from T1D patients with and without MA were measured using multiplex Luminex assays. Ten serum proteins (sTNFR1, sTNFR2, sIL2Rα, MMP2, sgp130, sVCAM1, sIL6R, SAA, CRP, and sICAM1) were significantly elevated in T1D patients with MA. After adjusting for age, duration of diabetes, and sex in logistic regression, association remained significant for seven proteins. MA is associated with increasing concentrations of all 10 proteins, with the strongest associations observed for sTNFR1 (OR = 108.3, P < 10⁻³²) and sTNFR2 (OR = 65.5, P < 10⁻³⁷), followed by sIL2Rα (OR = 12.9, P < 10⁻¹³), MMP2 (OR = 5.5, P < 10⁻⁶), sgp130 (OR = 5.2, P < 10⁻³), sIL6R (OR = 4.6, P < 10⁻⁴), and sVCAM1 (OR = 3.3, P < 10⁻⁴). We developed a risk score system based on the combined odds ratios associated with each quintile for each protein. The risk scores cluster MA patients into three subsets, each associated with distinct risk for MA attributable to proteins in the TNF-α/IL6 pathway (mean OR = 1, 13.5, and 126.3 for the three subsets, respectively). Our results suggest that the TNF-α/IL6 pathway is overactive in approximately 40% of the MA patients and moderately elevated in the middle 40% of the MA patients. Our results suggest the existence of distinct subsets of MA patients identifiable by their serum protein profiles.

Interleukin-6 and Interferon-α Signaling via JAK1-STAT Differentially Regulate Oncolytic versus Cytoprotective Antiviral States

Malignancy-induced alterations to cytokine signaling in tumor cells differentially regulate their interactions with the immune system and oncolytic viruses. The abundance of inflammatory cytokines in the tumor microenvironment suggests that such signaling plays key roles in tumor development and therapy efficacy. The JAK-STAT axis transduces signals of interleukin-6 (IL-6) and interferons (IFNs), mediates antiviral responses, and is frequently altered in prostate cancer (PCa) cells. However, how activation of JAK-STAT signaling with different cytokines regulates interactions between oncolytic viruses and PCa cells is not known. Here, we employ LNCaP PCa cells, expressing (or not) JAK1, activated (or not) with IFNs (α or γ) or IL-6, and infected with RNA viruses of different oncolytic potential (EHDV-TAU, hMPV-GFP, or HIV-GFP) to address this matter. We show that in JAK1-expressing cells, IL-6 sensitized PCa cells to viral cell death in the presence or absence of productive infection, with dependence on virus employed. Contrastingly, IFNα induced a cytoprotective antiviral state. Biochemical and genetic (knockout) analyses revealed dependency of antiviral state or cytoprotection on STAT1 or STAT2 activation, respectively. In IL-6-treated cells, STAT3 expression was required for anti-proliferative signaling. Quantitative proteomics (SILAC) revealed a core repertoire of antiviral IFN-stimulated genes, induced by IL-6 or IFNs. Oncolysis in the absence of productive infection, induced by IL-6, correlated with reduction in regulators of cell cycle and metabolism. These results call for matching the viral features of the oncolytic agent, the malignancy-induced genetic-epigenetic alterations to JAK/STAT signaling and the cytokine composition of the tumor microenvironment for efficient oncolytic virotherapy.

The EGFR-ADAM17 Axis in Chronic Obstructive Pulmonary Disease and Cystic Fibrosis Lung Pathology

Chronic obstructive pulmonary disease (COPD) and cystic fibrosis (CF) share molecular mechanisms that cause the pathological symptoms they have in common. Here, we review evidence suggesting that hyperactivity of the EGFR/ADAM17 axis plays a role in the development of chronic lung disease in both CF and COPD. The ubiquitous transmembrane protease A disintegrin and metalloprotease 17 (ADAM17) forms a functional unit with the EGF receptor (EGFR), in a feedback loop interaction labeled the ADAM17/EGFR axis. In airway epithelial cells, ADAM17 sheds multiple soluble signaling proteins by proteolysis, including EGFR ligands such as amphiregulin (AREG), and proinflammatory mediators such as the interleukin 6 coreceptor (IL-6R). This activity can be enhanced by injury, toxins, and receptor-mediated external triggers. In addition to intracellular kinases, the extracellular glutathione-dependent redox potential controls ADAM17 shedding. Thus, the epithelial ADAM17/EGFR axis serves as a receptor of incoming luminal stress signals, relaying these to neighboring and underlying cells, which plays an important role in the resolution of lung injury and inflammation. We review evidence that congenital CFTR deficiency in CF and reduced CFTR activity in chronic COPD may cause enhanced ADAM17/EGFR signaling through a defect in glutathione secretion. In future studies, these complex interactions and the options for pharmaceutical interventions will be further investigated.

Dissecting Interleukin-6 Classic- and Trans-Signaling in Inflammation and Cancer

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

Mesenchymal Stem Cells Secretory Responses: Senescence Messaging Secretome and Immunomodulation Perspective

Mesenchymal stem/stromal cells (MSC) have been tested in a significant number of clinical trials, where they exhibit regenerative and repair properties directly through their differentiation into the cells of the mesenchymal origin or by modulation of the tissue/organ microenvironment. Despite various clinical effects upon transplantation, the functional properties of these cells in natural settings and their role in tissue regeneration in vivo is not yet fully understood. The omnipresence of MSC throughout vascularized organs equates to a reservoir of potentially therapeutic regenerative depots throughout the body. However, these reservoirs could be subjected to cellular senescence. In this review, we will discuss current progress and challenges in the understanding of different biological pathways leading to senescence. We set out to highlight the seemingly paradoxical property of cellular senescence: its beneficial role in the development and tissue repair and detrimental impact of this process on tissue homeostasis in aging and disease. Taking into account the lessons from the different cell systems, this review elucidates how autocrine and paracrine properties of senescent MSC might impose an additional layer of complexity on the regulation of the immune system in development and disease. New findings that have emerged in the last few years could shed light on sometimes seemingly controversial results obtained from MSC therapeutic applications.

Split2 Protein-Ligation Generates Active IL-6-Type Hyper-Cytokines from Inactive Precursors

Trans-signaling of the major pro- and anti-inflammatory cytokines Interleukin (IL)-6 and IL-11 has the unique feature to virtually activate all cells of the body and is critically involved in chronic inflammation and regeneration. Hyper-IL-6 and Hyper-IL-11 are single chain designer trans-signaling cytokines, in which the cytokine and soluble receptor units are trapped in one complex via a flexible peptide linker. Albeit, Hyper-cytokines are essential tools to study trans-signaling in vitro and in vivo, the superior potency of these designer cytokines are accompanied by undesirable stress responses. To enable tailor-made generation of Hyper-cytokines, we developed inactive split-cytokine-precursors adapted for posttranslational reassembly by split-intein mediated protein trans-splicing (PTS). We identified cutting sites within IL-6 (E¹³⁴/S¹³⁵) and IL-11 (G¹¹⁶/S¹¹⁷) and obtained inactive split-Hyper-IL-6 and split-Hyper-IL-11 cytokine precursors. After fusion with split-inteins, PTS resulted in reconstitution of active Hyper-cytokines, which were efficiently secreted from transfected cells. Our strategy comprises the development of a background-free cytokine signaling system from reversibly inactivated precursor cytokines.

Potential therapeutic implications of IL-6/IL-6R/gp130-targeting agents in breast cancer

Interleukin-6 (IL-6) is a pleiotropic cytokine with known multiple functions in immune regulation, inflammation, and oncogenesis. Binding of IL-6 to the IL-6 receptor (IL-6R) induces homodimerization and recruitment of glycoprotein 130 (gp130), which leads to activation of downstream signaling. Emerging evidence suggests that high levels of IL-6 are correlated with poor prognosis in breast cancer patients. IL-6 appears to play a critical role in the growth and metastasis of breast cancer cells, renewal of breast cancer stem cells (BCSCs), and drug resistance of BCSCs, making anti-IL-6/IL-6R/gp130 therapies promising options for the treatment and prevention of breast cancers. However, preclinical and clinical studies of the applications of anti-IL-6/IL-6R/gp130 therapy in breast cancers are limited. In this review, we summarize the structures, preclinical and clinical studies, mechanisms of action of chemical and biological blockers that directly bind to IL-6, IL-6R, or gp130, and the potential clinical applications of these pharmacological agents as breast cancer therapies.

Cellular and Oxidative Mechanisms Associated with Interleukin-6 Signaling in the Vasculature

Reactive oxygen species, particularly superoxide, promote endothelial dysfunction and alterations in vascular structure. It is increasingly recognized that inflammatory cytokines, such as interleukin-6 (IL-6), contribute to endothelial dysfunction and vascular hypertrophy and fibrosis. IL-6 is increased in a number of cardiovascular diseases, including hypertension. IL-6 is also associated with a higher incidence of future cardiovascular events and all-cause mortality. Both immune and vascular cells produce IL-6 in response to a number of stimuli, such as angiotensin II. The vasculature is responsive to IL-6 produced from vascular and non-vascular sources via classical IL-6 signaling involving a membrane-bound IL-6 receptor (IL-6R) and membrane-bound gp130 via Jak/STAT as well as SHP2-dependent signaling pathways. IL-6 signaling is unique because it can also occur via a soluble IL-6 receptor (sIL-6R) which allows for IL-6 signaling in tissues that do not normally express IL-6R through a process referred to as IL-6 trans-signaling. IL-6 signaling mediates a vast array of effects in the vascular wall, including endothelial activation, vascular permeability, immune cell recruitment, endothelial dysfunction, as well as vascular hypertrophy and fibrosis. Many of the effects of IL-6 on vascular function and structure are representative of loss or reductions in nitric oxide (NO) bioavailability. IL-6 has direct effects on endothelial nitric oxide synthase activity and expression as well as increasing vascular superoxide, which rapidly inactivates NO thereby limiting NO bioavailability. The goal of this review is to highlight both the cellular and oxidative mechanisms associated with IL-6-signaling in the vascular wall in general, in hypertension, and in response to angiotensin II.

Neuroinflammation, cortical activity, and fatiguing behaviour during self-paced exercise

The present study aimed to identify whether or not the release of interleukin (IL)-6 and soluble (s) IL-6 receptor (R) is associated with fatiguing behaviour and changes in cortical activity during self-paced exercise. Relationships between the IL-6 and its soluble receptors, total work, reductions in power output, and changes in slow, alpha (α) and fast, beta (β) brain waves during self-paced exercise were evaluated. Different intensities and environments were used to manipulate the release of IL-6, whereby seven active males cycled for 60 min in heat stress (HS) or thermoneutral (TN) environments at a clamped rating of perceived exertion (RPE) equating to low intensity (RPE = 12) or high intensity (RPE = 16). IL-6 and sIL-6R were positively associated with total work, but not with reductions in power output. There was greater α activity in high-intensity conditions, which was associated with the reduction in power output. Both high-intensity conditions appeared to have greater β activity, and there was a positive correlation between β activity and total work and β activity and sIL-6R. We conclude that IL-6 and sIL-6R may contribute to perturbations in cortical activity and are associated with total work output, but reductions in power output are likely influenced greater by other internal and external factors.

Inflammation: Treatment Progress and Limitations

There is an increasing understanding on the etiology of chronic immune-mediated inflammatory diseases such as inflammatory bowel disease (IBD), psoriasis, or rheumatoid arthritis. Large consortia contributed to the elucidation of the genetics, for instance, of IBD identifying a number of genes involved in innate mucosal defense and immune tolerance (most prominent, e.g., NOD2) and other related processes. For a number of such diseases, common genetic susceptibility loci were identified, suggesting overlapping immune response pathways, although there is no causality of single genetic traits.² In particular, the elucidation of main triggers of inflammation like tumor necrosis factor alpha (TNFα), integrins, specific cytokines like interleukin (IL)-6 or IL-23 launched the successful development of new pharmacological approaches, leading to a tremendous improvement of therapeutic outcomes.

The classic signalling and trans-signalling of interleukin-6 are both injurious in podocyte under high glucose exposure

Interleukin‐6 (IL‐6) is a multifunctional cytokine that employs IL‐6 classic and trans‐signalling pathways, and these two signal channels execute different or even opposite effects in certain diseases. As a cardinal event of diabetic kidney disease (DKD), whether the podocyte abnormalities are associated with IL‐6 signalling, especially classic or trans‐signalling respectively, remains unclear. In this study, we identified that the circulatory IL‐6, soluble IL‐6R (sIL‐6R) and soluble glycoprotein 130 (sgp130) levels are elevated in patients with DKD. The expressions of membrane‐bound IL‐6R (mIL‐6R), sIL‐6R and gp130 are enhanced in kidney cortex of diabetic mice accompanying with activated STAT3 by tyrosine 705 residue phosphorylation, while not serine 727. Above data infer both classic signalling and trans‐signalling of IL‐6 are activated during DKD. In cultured podocyte, high glucose (HG) up‐regulates the expression of mIL‐6R and gp130, as well as STAT3 tyrosine 705 phosphorylation, in a time‐dependent manner. Entirely blocking IL‐6 signalling by gp130 shRNA, gp130 or IL‐6 neutralizing antibodies attenuates HG‐induced podocyte injury. Interestingly, either inhibiting IL‐6 classic signalling by mIL‐6R shRNA or suppressing its trans‐signalling using sgp130 protein dramatically alleviates HG‐induced podocyte injury, suggesting both IL‐6 classic signalling and trans‐signalling play a detrimental role in HG‐induced podocyte injury. Additionally, activation of IL‐6 classic or trans‐signalling aggravates podocyte damage in vitro. In summary, our observations demonstrate that the activation of either IL‐6 classic or trans‐signalling advances podocyte harming under hyperglycaemia. Thus, suppressing IL‐6 classic and trans‐signalling simultaneously may be more beneficial in podocyte protection and presents a novel therapeutic target for DKD.

The balance between Treg and TH17 cells: CD11b and interleukin-6

One of the gold standards for animal models of rheumatoid arthritis is the murine collagen-induced arthritis model. Native type II collagen together with CFA is injected into susceptible mouse strains. Unfortunately, only mice with H-2^q or H-2^r MHC haplotypes are susceptible, making the widely used C57BL/6 mouse strain, which carries the H-2^b haplotype, resistant against the disease. In this issue of the European Journal of Immunology, Stevanin et al. [Eur. J. Immunol. 2017. 47: 637-645] now convincingly show that although WT C57BL/6 mice are resistant to collagen-induced arthritis, mice with a homozygous deletion of CD11b on the same genetic background are fully susceptible in this important animal model of rheumatoid arthritis. They clearly demonstrate that the injection of type II collagen together with CFA leads to early onset of the disease with high incidence and with sustained severity. The authors further characterize this disease with an increase of leukocyte infiltration and enhanced TH₁₇ differentiation.

Involvement of Spinal IL-6 Trans-Signaling in the Induction of Hyperexcitability of Deep Dorsal Horn Neurons by Spinal Tumor Necrosis Factor-Alpha

During peripheral inflammation, both spinal TNF-α and IL-6 are released within the spinal cord and support the generation of inflammation-evoked spinal hyperexcitability. However, whether spinal TNF-α and IL-6 act independently in parallel or in a functionally dependent manner has not been investigated. In extracellular recordings from mechanonociceptive deep dorsal horn neurons of normal rats in vivo, we found that spinal application of TNF-α increased spinal neuronal responses to mechanical stimulation of knee and ankle joints. This effect was significantly attenuated by either sgp130, which blocks IL-6 trans-signaling mediated by IL-6 and its soluble receptor IL-6R (sIL-6R); by an antibody to the IL-6 receptor; or by minocycline, which inhibits the microglia. IL-6 was localized in neurons of the spinal cord and, upon peripheral noxious stimulation in the presence of spinal TNF-α, IL-6 was released spinally. Furthermore, TNF-α recruited microglial cells to provide sIL-6R, which can form complexes with IL-6. Spinal application of IL-6 plus sIL-6R, but not of IL-6 alone, enhanced spinal hyperexcitability similar to TNF-α and the inhibition of TNF-α-induced hyperexcitability by minocycline was overcome by coadministration of sIL-6R, showing that sIL-6R is required. Neither minocycline nor the TNF-α-neutralizing compound etanercept inhibited the induction of hyperexcitability by IL-6 plus sIL-6R. Together, these data show that the induction of hyperexcitability of nociceptive deep dorsal horn neurons by TNF-α largely depends on the formation of IL-6/sIL-6R complexes that are downstream of TNF-α and requires the interactions of neurons and microglia orchestrated by TNF-α.

SIGNIFICANCE STATEMENT

Both spinal TNF-α and IL-6 induce a state of spinal hyperexcitability. We present the novel finding that the full effect of TNF-α on the development of spinal hyperexcitability depends on IL-6 trans-signaling acting downstream of TNF-α. IL-6 trans-signaling requires the formation of complexes of IL-6 and soluble IL-6 receptor. Spinal TNF-α furthers the release of IL-6 from neurons in the spinal cord during peripheral noxious stimulation and recruits microglial cells to provide soluble IL-6 receptor, which can form complexes with IL-6. Therefore, a specific interaction between neurons and microglia is required for the full development of TNF-α-induced hyperexcitability of nociceptive deep horsal horn neurons.

Interleukin-6 as a Multifunctional Regulator: Inflammation, Immune Response, and Fibrosis

Interleukin 6 (IL-6) is a 184-amino acid protein cytokine that is produced by many types of cells and is expressed during states of cellular stress, such as inflammation, infection, wound sites, and cancer. IL-6 levels may increase several thousand-fold in these states and may help to coordinate the response to dysregulation of tissue homeostasis. IL-6 acts through a membrane-bound IL-6 receptor (mIL-6R), which, together with a second receptor, glycoprotein 130 (gp130), leads to the initiation of intracellular signaling (classic signaling). Given that IL-6R is expressed on only a few types of cells, though all cells express gp130, direct stimulation by IL-6 is limited to cells that express mIL-6R. However, IL-6R is also produced as a soluble, secreted protein that, together with IL-6, can stimulate all gp130-expressing cells by a process termed IL-6 trans-signaling. IL-6 trans-signaling can be blocked without affecting IL-6 classic signaling through mIL-6R. IL-6 has major effects on the adaptive and innate immune system and on mesenchymal and stromal responses during inflammation. It promotes the development of pathogenic T-helper 17 T cells and the maturation of B lymphocytes. Many innate immune cells, neutrophils, and monocytes/macrophages produce and respond to IL-6, resulting in autocrine feedback loops that amplify inflammation. IL-6 has been implicated in the pathogenesis of fibrotic diseases in which IL-6 trans-signaling has been shown to stimulate the proliferation of fibroblasts and the release of procollagen and fibronectin.

Interleukin-6 signaling in patients with chronic heart failure treated with cardiac resynchronization therapy

INTRODUCTION

Increased expression of interleukin-6 (IL-6) has been described in left ventricular dysfunction in the course of chronic heart failure. Cardiac resynchronization therapy (CRT) is a unique treatment method that may reverse the course of chronic heart failure (CHF) with reduced ejection fraction (HF-REF). We aimed to evaluate the IL-6 system, including soluble IL-6 receptor (sIL-6R) and soluble glycoprotein 130 (sgp130), in HF-REF patients, with particular emphasis on CRT effects.

MATERIAL AND METHODS

The study enrolled 88 stable HF-REF patients (63.6 ±11.1 years, 12 females, EF < 35%) and 35 comorbidity-matched controls (63.5 ±9.8 years, 7 females). Forty-five HF-REF patients underwent CRT device implantation and were followed up after 6 months. Serum concentrations of IL-6, sIL-6R and sgp130 were determined using ELISA kits.

RESULTS

The HF-REF patients had higher IL-6 (median: 2.6, IQR: 1.6-3.8 vs. 2.1, IQR: 1.4-3.1 pg/ml, p = 0.03) and lower sIL-6R concentrations compared to controls (median: 51, IQR: 36-64 vs. 53. IQR 44-76 ng/ml, p = 0.008). There was no significant difference between sgp130 concentrations. In the HF-REF group IL-6 correlated negatively with EF (r = -0.5, p = 0.001) and positively with BNP (r = 0.5, p = 0.008) and CRP concentrations (r = 0.4, p = 0.02). Patients who presented a positive response after CRT showed a smaller change of sIL-6R concentration compared to nonresponders (ΔsIL-6R: -0.2 ±7.1 vs. 7 ±14 ng/ml; p = 0.04).

CONCLUSIONS

HF-REF patients present higher IL-6 and lower sIL-6R levels. IL-6 concentration reflects their clinical status. CRT-related improvement of patients' functional status is associated with a smaller change of sIL-6R concentration in time.

Therapeutic Targeting of the IL-6 Trans-Signaling/Mechanistic Target of Rapamycin Complex 1 Axis in Pulmonary Emphysema

RATIONALE

The potent immunomodulatory cytokine IL-6 is consistently up-regulated in human lungs with emphysema and in mouse emphysema models; however, the mechanisms by which IL-6 promotes emphysema remain obscure. IL-6 signals using two distinct modes: classical signaling via its membrane-bound IL-6 receptor (IL-6R), and trans-signaling via a naturally occurring soluble IL-6R.

OBJECTIVES

To identify whether IL-6 trans-signaling and/or classical signaling contribute to the pathogenesis of emphysema.

METHODS

We used the gp130^F/F genetic mouse model for spontaneous emphysema and cigarette smoke-induced emphysema models. Emphysema in mice was quantified by various methods including in vivo lung function and stereology, and terminal deoxynucleotidyl transferase dUTP nick end labeling assay was used to assess alveolar cell apoptosis. In mouse and human lung tissues, the expression level and location of IL-6 signaling-related genes and proteins were measured, and the levels of IL-6 and related proteins in sera from emphysematous mice and patients were also assessed.

MEASUREMENTS AND MAIN RESULTS

Lung tissues from patients with emphysema, and from spontaneous and cigarette smoke-induced emphysema mouse models, were characterized by excessive production of soluble IL-6R. Genetic blockade of IL-6 trans-signaling in emphysema mouse models and therapy with the IL-6 trans-signaling antagonist sgp130Fc ameliorated emphysema by suppressing augmented alveolar type II cell apoptosis. Furthermore, IL-6 trans-signaling-driven emphysematous changes in the lung correlated with mechanistic target of rapamycin complex 1 hyperactivation, and treatment of emphysema mouse models with the mechanistic target of rapamycin complex 1 inhibitor rapamycin attenuated emphysematous changes.

CONCLUSIONS

Collectively, our data reveal that specific targeting of IL-6 trans-signaling may represent a novel treatment strategy for emphysema.