The Role of IL-6 in Neurodegenerative Disorders

"Neurodegenerative disorder" is an umbrella term for a group of fatal progressive neurological illnesses characterized by neuronal loss and inflammation. Interleukin-6 (IL-6), a pleiotropic cytokine, significantly affects the activities of nerve cells and plays a pivotal role in neuroinflammation. Furthermore, as high levels of IL-6 have been frequently observed in association with several neurodegenerative disorders, it may potentially be used as a biomarker for the progression and prognosis of these diseases. This review summarizes the production and function of IL-6 as well as its downstream signaling pathways. Moreover, we make a comprehensive review on the roles of IL-6 in neurodegenerative disorders and its potential clinical application.

Targeting IL-6 trans-signalling: past, present and future prospects

Interleukin-6 (IL-6) is a key immunomodulatory cytokine that affects the pathogenesis of diverse diseases, including autoimmune diseases, chronic inflammatory conditions and cancer. Classical IL-6 signalling involves the binding of IL-6 to the membrane-bound IL-6 receptor α-subunit (hereafter termed 'mIL-6R') and glycoprotein 130 (gp130) signal-transducing subunit. By contrast, in IL-6 trans-signalling, complexes of IL-6 and the soluble form of IL-6 receptor (sIL-6R) signal via membrane-bound gp130. A third mode of IL-6 signalling - known as cluster signalling - involves preformed complexes of membrane-bound IL-6-mIL-6R on one cell activating gp130 subunits on target cells. Antibodies and small molecules have been developed that block all three forms of IL-6 signalling, but in the past decade, IL-6 trans-signalling has emerged as the predominant pathway by which IL-6 promotes disease pathogenesis. The first selective inhibitor of IL-6 trans-signalling, sgp130, has shown therapeutic potential in various preclinical models of disease and olamkicept, a sgp130Fc variant, had promising results in phase II clinical studies for inflammatory bowel disease. Technological developments have already led to next-generation sgp130 variants with increased affinity and selectivity towards IL-6 trans-signalling, along with indirect strategies to block IL-6 trans-signalling. Here, we summarize our current understanding of the biological outcomes of IL-6-mediated signalling and the potential for targeting this pathway in the clinic.

Raft platforms highly enriched in cholesterol: major scaffolds for IL-6 signalling assembly with implications in inflammation and cancer

Interleukin-6 (IL-6) is a pleiotropic cytokine with complex and major roles in inflammation, which could be linked to the different ways IL-6 signals at the plasma membrane. In this issue of FEBS Journal, Woo and co-workers present evidence for the involvement of Eps15 homology domain-containing protein 1 (EHD1)-mediated lipid raft platforms, highly enriched in cholesterol, in the IL-6 signalling pathway. Because of the strong connection between IL-6, inflammation and cancer, one implication of this report is that agents or approaches targeting cholesterol-rich raft platforms may assist the development of novel strategies to treat inflammatory and malignant diseases. Comment on: https://doi.org/10.1111/febs.16458.

The hormetic and hermetic role of IL-6

Interleukin-6 is a pleiotropic cytokine regulating different tissues and organs in diverse and sometimes discrepant ways. The dual and sometime hermetic nature of IL-6 action has been highlighted in several contexts and can be explained by the concept of hormesis, in which beneficial or toxic effects can be induced by the same molecule depending on the intensity, persistence, and nature of the stimulation. According with hormesis, a low and/or controlled IL-6 release is associated with anti-inflammatory, antioxidant, and pro-myogenic actions, whereas increased systemic levels of IL-6 can induce pro-inflammatory, pro-oxidant and pro-fibrotic responses. However, many aspects regarding the multifaceted action of IL-6 and the complex nature of its signal transduction remains to be fully elucidated. In this review we collect mechanistic insight into the molecular networks contributing to normal or pathologic changes during advancing age and in chronic diseases. We point out the involvement of IL-6 deregulation in aging-related diseases, dissecting the hormetic action of this key mediator in different tissues, with a special focus on skeletal muscle. Since IL-6 can act as an enhancer of detrimental factor associated with both aging and pathologic conditions, such as chronic inflammation and oxidative stress, this cytokine could represent a "Gerokine", a determinant of the switch from physiologic aging to age-related diseases.

Neutrophil Homeostasis and Emergency Granulopoiesis: The Example of Systemic Juvenile Idiopathic Arthritis

Neutrophils are key pathogen exterminators of the innate immune system endowed with oxidative and non-oxidative defense mechanisms. More recently, a more complex role for neutrophils as decision shaping cells that instruct other leukocytes to fine-tune innate and adaptive immune responses has come into view. Under homeostatic conditions, neutrophils are short-lived cells that are continuously released from the bone marrow. Their development starts with undifferentiated hematopoietic stem cells that pass through different immature subtypes to eventually become fully equipped, mature neutrophils capable of launching fast and robust immune responses. During severe (systemic) inflammation, there is an increased need for neutrophils. The hematopoietic system rapidly adapts to this increased demand by switching from steady-state blood cell production to emergency granulopoiesis. During emergency granulopoiesis, the de novo production of neutrophils by the bone marrow and at extramedullary sites is augmented, while additional mature neutrophils are rapidly released from the marginated pools. Although neutrophils are indispensable for host protection against microorganisms, excessive activation causes tissue damage in neutrophil-rich diseases. Therefore, tight regulation of neutrophil homeostasis is imperative. In this review, we discuss the kinetics of neutrophil ontogenesis in homeostatic conditions and during emergency myelopoiesis and provide an overview of the different molecular players involved in this regulation. We substantiate this review with the example of an autoinflammatory disease, i.e. systemic juvenile idiopathic arthritis.

Characterizing the Neutrophilic Inflammation in Chronic Rhinosinusitis With Nasal Polyps

The mechanisms underlying neutrophilic inflammation in chronic rhinosinusitis with nasal polyps (CRSwNP) remain poorly investigated. This study aimed to examine the factors that contribute to tissue neutrophilia in CRSwNP. The numbers of neutrophils and active caspase-3-positive apoptotic neutrophils in sinonasal tissues were assessed via immunofluorescence staining. The 95th percentile of tissue neutrophil numbers in control subjects was selected as a cut-off to define neutrophil-high (Neu-high) or neutrophil-low (Neu-low) nasal polyps (NPs). The levels of 34 inflammatory mediators in sinonasal tissues were analyzed using Bio-Plex assay. Purified human peripheral blood neutrophils were incubated with nasal tissue homogenates, and the apoptotic neutrophils were assessed via flow cytometry. The cut-off for Neu-high NPs was >10 myeloperoxidase positive cells/high-power field. Compared with Neu-low NPs, Neu-high NPs had higher tissue levels of IL-1β, IL-1Ra, IL-6, IL-8, G-CSF, MCP-1, and MIP-1α, but lower levels of IL-5, IL-13, IgE, and eosinophils. Principal component and multiple correspondence analyses revealed mixed type 1, type 2, and type 3 endotypes for Neu-low NPs, and predominant type 1 and type 3 endotypes for Neu-high NPs. Neu-high NPs had lower percentages of apoptotic neutrophils than Neu-low NPs. The numbers of neutrophils and the percentages of apoptotic neutrophils correlated with G-CSF and IL-6 levels in the NPs. Tissue homogenates from Neu-high NPs, but not those from Neu-low NPs, suppressed neutrophil apoptosis in vitro, which was reversed by anti-G-CSF treatment. Tissue neutrophil numbers were associated with difficult-to-treat disease in patients with CRSwNP after surgery. We propose that G-CSF promotes neutrophilic inflammation by inhibiting neutrophil apoptosis in CRSwNP.

Local and systemic effects of interleukin-6 (IL-6) in inflammation and cancer

Interleukin-6 (IL-6) is an inflammatory cytokine, the level of which is highly elevated in most, if not all, inflammatory states. IL-6 triggers cell type-specific responses and acts on target cells via a specific interleukin-6 receptor (IL-6R), which, together with IL-6, binds to and induces the dimerization of a second receptor subunit, gp130. IL-6 also binds to soluble IL-6R, and this complex interacts with gp130, regardless of IL-6R expression. This allows cells that do not express IL-6R and would be otherwise insensitive to IL-6 to respond to it. We have generated a constitutively active version of gp130 by forced leucine-zipper-mediated dimerization, named L-gp130. Once inserted into the Rosa26 locus of mice, L-gp130 can be activated in a cell-autonomous manner by crossing these mice with any Cre-recombinase transgenic mouse strain. Activation of gp130 in hepatocytes produced liver-specific effects such as the induction of acute-phase proteins, but it also had profound systemic effects on the immune system. Such local and systemic effects of interleukin-6 will be reviewed.

New insights into IL-6 family cytokines in metabolism, hepatology and gastroenterology

IL-6 family cytokines are defined by the common use of the signal-transducing receptor chain glycoprotein 130 (gp130). Increasing evidence indicates that these cytokines are essential in the regulation of metabolic homeostasis as well as in the pathophysiology of multiple gastrointestinal and liver disorders, thus making them attractive therapeutic targets. Over the past few years, therapies modulating gp130 signalling have grown exponentially in several clinical settings including obesity, cancer and inflammatory bowel disease. A newly engineered gp130 cytokine, IC7Fc, has shown promising preclinical results for the treatment of type 2 diabetes, obesity and liver steatosis. Moreover, drugs that modulate gp130 signalling have shown promise in refractory inflammatory bowel disease in clinical trials. A deeper understanding of the main roles of the IL-6 family of cytokines during homeostatic and pathological conditions, their signalling pathways, sources of production and target cells will be crucial to the development of improved treatments. Here, we review the current state of the role of these cytokines in hepatology and gastroenterology and discuss the progress achieved in translating therapeutics targeting gp130 signalling into clinical practice.

Function and proteolytic generation of the soluble interleukin-6 receptor in health and disease

The pleiotropic cytokine interleukin-6 (IL-6) is involved in numerous physiological and pathophysiological functions that include development, immune cell differentiation, inflammation and cancer. IL-6 can signal via the membrane-bound IL-6 receptor (IL-6R, classic signaling) or via soluble forms of the IL-6R (sIL-6R, trans-signaling). Both modes of signaling induce the formation of a homodimer of the signal transducing β-receptor glycoprotein 130 (gp130) and the activation of several intracellular signaling cascades, e.g. the Jak/STAT pathway. Intriguingly, only IL-6 trans-signaling is required for the pro-inflammatory properties of IL-6, while regenerative and anti-inflammatory functions are mediated via classic signaling. The sIL-6R is generated by different molecular mechanisms, including alternative mRNA splicing, proteolysis of the membrane-bound IL-6R and the release of extracellular vesicles. In this review, we give an in-depth overview on these molecular mechanisms with a special emphasize on IL-6R cleavage by the metalloprotease ADAM17 and other proteases. We discuss the biological functions of the sIL-6R and highlight attempts to selectively block IL-6 trans-signaling in pre-clinical animal models as well as in clinical studies in patients with inflammatory bowel disease.

Role of IL-6 in the commitment of T cell subsets

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IL-6 is a non-redundant differentiation factor for Th17 cells and Tfh cells.

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The induction of ROR-γt⁺ Treg cells in the lamina propria depends on IL-6.

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Generation of distinct T helper cell subsets might depend on different IL-6 signaling modalities.

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IL-6-directed therapies must consider the disease-relevant IL-6 signaling modality.

IL-6 gained much attention with the discovery that this cytokine is a non-redundant differentiation factor for Th17 cells and T follicular helper cells. Adaptive immune responses to fungi and extracellular bacteria are impaired in the absence of IL-6. IL-6 is also required for the induction of ROR-γt⁺ Treg cells, which are gatekeepers of homeostasis in the gut lamina propria in the presence of commensal bacteria. Conversely, severe immunopathology in T cell-mediated autoimmunity is mediated by Th17 cells that rely on IL-6 for their generation and maintenance. Recently, it has been discovered that the differentiation of these distinct T helper cell subsets may be linked to distinct signaling modalities of IL-6. Here, we summarize the current knowledge on the mode of action of IL-6 in the differentiation and maintenance of T cell subsets and propose that a context-dependent understanding of the impact of IL-6 on T cell subsets might inform rational IL-6-directed interventions in autoimmunity and chronic inflammation.

Endosomes as Signaling Platforms for IL-6 Family Cytokine Receptors

Interleukin-6 (IL-6) is the name-giving cytokine of a family of eleven members, including IL-6, CNTF, LIF, and IL-27. IL-6 was first recognized as a B-cell stimulating factor but we now know that the cytokine plays a pivotal role in the orchestration of inflammatory processes as well as in inflammation associated cancer. Moreover, IL-6 is involved in metabolic regulation and it has been shown to be involved in major neural activities such as neuroprotection, which can help to repair and to reduce brain damage. Receptor complexes of all members formed at the plasma membrane contain one or two molecules of the signaling receptor subunit GP130 and the mechanisms of signal transduction are well understood. IL-6 type cytokines can also signal from endomembranes, in particular the endosome, and situations have been reported in which endocytosis of receptor complexes are a prerequisite of intracellular signaling. Moreover, pathogenic GP130 variants were shown to interfere with spatial activation of downstream signals. We here summarize the molecular mechanisms underlying spatial regulation of IL-6 family cytokine signaling and discuss its relevance for pathogenic processes.

A phase 3 double-blind study of the addition of tocilizumab vs placebo to cyclosporin/methotrexate GVHD prophylaxis

We determined the efficacy of tocilizumab (TCZ) in preventing grade 2-4 acute graft-versus-host disease (aGVHD) in patients with acute leukemia or myelodysplasia undergoing matched sibling donor (MSD) or volunteer unrelated donor (VUD) allogeneic stem cell transplantation after myeloablative or reduced-intensity conditioning across 5 Australian centers. A total of 145 patients (50 MSD, 95 VUD) were randomly assigned to placebo or TCZ on day -1. All patients received T-cell-replete peripheral blood stem cell grafts and graft-versus-host disease (GVHD) prophylaxis with cyclosporin/methotrexate. A planned substudy analyzed the VUD cohort. With a median follow-up of 746 days, the incidence of grade 2-4 aGVHD at day 100 for the entire cohort was 36% for placebo vs 27% for TCZ (hazard ratio [HR], 0.69; 95% confidence interval [CI], 0.38-1.26; P = .23) and 45% vs 32% (HR, 0.61; 95% CI, 0.31-1.22; P = .16) for the VUD subgroup. The incidence of grade 2-4 aGVHD at day 180 for the entire cohort was 40% for placebo vs 29% for TCZ (HR, 0.68; 95% CI, 0.38-1.22; P = .19) and 48% vs 32% (HR, 0.59; 95% CI, 0.30-1.16; P = .13) for the VUD subgroup. Reductions in aGVHD were predominantly in grade 2 disease. For the entire cohort, transplant-related mortality occurred in 8% vs 11% of placebo-treated vs TCZ-treated patients, respectively (P = .56), and overall survival was 79% vs 71% (P = .27). Median day to neutrophil and platelet engraftment was delayed by 2 to 3 days in TCZ-treated patients, whereas liver toxicity and infectious complications were similar between groups. In this phase 3 randomized double-blind trial, TCZ showed nonsignificant trends toward reduced incidence of grade 2-4 aGVHD in recipients from HLA-matched VUDs but no improvements in long term-survival.

Interleukin-6 controls recycling and degradation, but not internalization of its receptors

Interleukin-6 (IL-6) is a cytokine implicated in proinflammatory as well as regenerative processes and acts via receptor complexes consisting of the ubiquitously expressed, signal-transducing receptor gp130 and the IL-6 receptor (IL-6R). The IL-6R is expressed only on hepatocytes and subsets of leukocytes, where it mediates specificity of the receptor complex to IL-6 as the subunit gp130 is shared with all other members of the IL-6 cytokine family such as IL-11 or IL-27. The amount of IL-6R at the cell surface thus determines the responsiveness of the cell to the cytokine and might therefore be decisive in the development of inflammatory disorders. However, how the expression levels of IL-6R and gp130 at the cell surface are controlled is largely unknown. Here, we show that IL-6R and gp130 are constitutively internalized independent of IL-6. This process depends on dynamin and clathrin and is temporally controlled by motifs within the intracellular region of gp130 and IL-6R. IL-6 binding and internalization of the receptors is a prerequisite for activation of the Jak/STAT signaling cascade. Targeting of gp130, but not of the IL-6R, to the lysosome for degradation depends on stimulation with IL-6. Furthermore, we show that after internalization and activation of signaling, both the IL-6R and gp130 are recycled back to the cell surface, a process that is enhanced by IL-6. These data reveal an important function of IL-6 beyond the pure activation of signaling.

The study of gp130/the inflammatory factors regulating osteoclast differentiation in rheumatoid arthritis

Rheumatoid arthritis (RA) is a chronic immune disease characterized by synovitis and bone destruction. The osteoclasts play a critical role in pathologic bone loss during inflammatory arthritis. In this paper, we report that Interleukin (IL)-6, IL-6Rα/gp130, IL-11, IL-27, and Matrix Metallo Proteinases (MMP)-9 expression results in serum of the RA group were significantly higher than that of the control group. The gp130 positive cells in peripheral blood mononuclear cell (PBMC) and osteoclast-like cells (OLC) which had been induced with receptor activator of nuclear factor κB ligand (RANKL) in RA group were also higher than that in the control group. In addition, after OLC in RA group is cultured with anti-gp130 Monoclonal antibody (McAb), the IL-6 and MMP-9 expression in osteoclast supernatant insignificantly decreased. Meanwhile, the expression results of Tartrate Resistant Acid Phosphatase (TRAP)-positive cells and osteoclasts were also decreased significantly. Our study suggests that regulating gp130 receptor can be used to control the differentiation and formation of osteoclasts, which provides a new clinical strategy for RA patients in the future.

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The concentration of IL-6, IL-11, IL-27 and the ratio of IL-6Rα to gp130 in RA patients were significantly higher than the control group.

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After inducing with RANKL, gp130, IL-6 and MMP-9 and the TRAP-positive osteoclasts in PBMC from RA increased.

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IL-6 and MMP-9 in PBMC and osteoclasts in RA patients decreased after treatment with anti-gp130 McAb

Blood Leukocyte Signaling Pathways as Predictors of Severity of Acute Pancreatitis

OBJECTIVES

Clinical practice lacks biomarkers to predict the severity of acute pancreatitis (AP). We studied if intracellular signaling of circulating leukocytes could predict persistent organ dysfunction (OD) and secondary infections in AP.

METHODS

A venous blood sample was taken from 174 patients with AP 72 hours or less from onset of symptoms and 31 healthy controls. Phosphorylation levels (p) of appropriately stimulated signal transducer and activator of transcription 1 (STAT1), STAT6, nuclear factor-κB (NF-κB), Akt, and nonstimulated STAT3 in monocytes, neutrophils, and lymphocytes was measured using phosphospecific flow cytometry.

RESULTS

The patients showed higher pSTAT3 and lower pSTAT1, pSTAT6, pNF-κB, and pAkt than healthy controls. pSTAT3 in all leukocyte subtypes studied increased, and pSTAT1 in monocytes and T cells decreased in an AP severity-wise manner. In patients without OD at sampling, high pSTAT3 in monocytes and T lymphocytes were associated with development of persistent OD. In patients with OD, low interleukin-4-stimulated pSTAT6 in monocytes and neutrophils and Escherichia coli-stimulated pNF-κB in neutrophils predicted OD persistence. High pSTAT3 in monocytes, CD8+ T cells, and neutrophils; low pSTAT1 in monocytes and T cells; and low pNF-κB in lymphocytes predicted secondary infections.

CONCLUSIONS

Leukocyte STAT3, STAT1, STAT6, and NF-κΒ phosphorylations are potential predictors of AP severity.

In-silico analysis of myeloid cells across the animal kingdom reveals neutrophil evolution by colony-stimulating factors

Neutrophils constitute the largest population of phagocytic granulocytes in the blood of mammals. The development and function of neutrophils and monocytes is primarily governed by the granulocyte colony-stimulating factor receptor family (CSF3R/CSF3) and macrophage colony-stimulating factor receptor family (CSF1R/IL34/CSF1) respectively. Using various techniques this study considered how the emergence of receptor:ligand pairings shaped the distribution of blood myeloid cell populations. Comparative gene analysis supported the ancestral pairings of CSF1R/IL34 and CSF3R/CSF3, and the emergence of CSF1 later in lineages after the advent of Jawed/Jawless fish. Further analysis suggested that the emergence of CSF3 lead to reorganisation of granulocyte distribution between amphibian and early reptiles. However, the advent of endothermy likely contributed to the dominance of the neutrophil/heterophil in modern-day mammals and birds. In summary, we show that the emergence of CSF3R/CSF3 was a key factor in the subsequent evolution of the modern-day mammalian neutrophil.

IL-6 -572C>G and CARD8 304T>A Genetic Polymorphisms are Associated with the Absolute Neutrophil Count in Patients with Hematological Malignancies Under Chemotherapy: An Application of Multilevel Models to a Preliminary Pharmacogenetic Study

Purpose

Neutropenia is a common event in patients undergoing cytotoxic chemotherapy for the treatment of a hematological malignancy. Some polymorphisms, as IL-6 -572C>G (rs1800796), IL-1β -31 G>A (rs1143627), and CARD8 304T>A (rs2043211), in genes related to the inflammatory process, could affect the level of absolute neutrophil count (ANC) after chemotherapy. Since an efficient inflammatory process enhances neutrophil survival, we hypothesize that these polymorphisms are associated with ANC.

Patients and Methods

We carried out a prospective cohort study in two hospitals in Santiago, Chile. The patients included were adults diagnosed with acute myeloblastic leukemia, acute lymphoblastic leukemia, or non-Hodgkin's lymphoma, undergoing cytotoxic chemotherapy. We use a multilevel linear regression model to test our hypothesis. The best model was selected using the Akaike's information criterion (AIC).

Results

We analyzed 1726 hemograms and ANCs from 172 hospitalizations from 32 patients. The results show that CC and CG genotypes of IL-6 -572 C>G polymorphism are associated with higher ANCs compared with the GG genotype (Ln (ANC) ~ 0.81 IC95% 0.02-1.55). Similarly, TT and AT genotypes of CARD8 304T>A polymorphism were related to higher ANCs compared with AA (Ln (ANC) ~ 0.95 IC95% 0.02-1.82). IL-1β genetic polymorphism had no statistically significant association with ANC.

Conclusion

IL-6 rs1800796 -572C>G and CARD8 rs2043211 304T>A polymorphisms are associated with the absolute neutrophil count in patients undergoing cytotoxic chemotherapy for treatment of hematological malignancies. Our findings might be useful to improve the safety of chemotherapy through predictive ANC models.

Proteomic analysis of synovial fluid from rheumatic arthritis and spondyloarthritis patients

Background

The aetiologies and pathogeneses of the joint diseases rheumatoid arthritis (RA) and spondyloarthritis (SpA) are still not fully elucidated. To increase our understanding of the molecular pathogenesis, we analysed the protein composition of synovial fluid (SF) from rheumatoid arthritis (RA) and spondyloarthritis (SpA) patients.

Methods

Fifty-six synovial fluid samples (RA, n = 32; SpA, n = 24) were digested with trypsin, and the resulting peptides were separated by liquid chromatography and analysed by tandem mass spectrometry. Additionally, the concentration of cell-free DNA (cfDNA) in the synovial fluid was measured, and plasma C-reactive protein (CRP) was determined.

Results

Three hundred thirty five proteins were identified within the SF. The more abundant proteins seen in RA SF were inflammatory proteins, including proteins originating from neutrophil granulocytes, while SpA SF had less inflammatory proteins and a higher concentration of haptoglobin. The concentration of cell-free DNA in the SF increased together with proteins that may have originated from neutrophils. Plasma CRP levels in both RA and SpA, correlated to other acute phase reactants.

Conclusions

The proteomic results underline that neutrophils are central in the RA pathology but not in SpA, and even though inhibitors of neutrophils (migration, proteinase inhibitors) were present in the SF it was not sufficient to interrupt the disease process.

Cutting Edge: IL-6-Driven Immune Dysregulation Is Strictly Dependent on IL-6R α-Chain Expression

IL-6 binds to the IL-6R α-chain (IL-6Rα) and signals via the signal transducer gp130. Recently, IL-6 was found to also bind to the cell surface glycoprotein CD5, which would then engage gp130 in the absence of IL-6Rα. However, the biological relevance of this alternative pathway is under debate. In this study, we developed a mouse model, in which murine IL-6 is overexpressed in a CD11c-Cre-dependent manner. Transgenic mice developed a lethal immune dysregulation syndrome with increased numbers of Ly-6G⁺ neutrophils and Ly-6C^hi monocytes/macrophages. IL-6 overexpression promoted activation of CD4⁺ T cells while suppressing CD5⁺ B-1a cell development. However, additional ablation of IL-6Rα protected IL-6-overexpressing mice from IL-6-triggered inflammation and fully phenocopied IL-6Rα-deficient mice without IL-6 overexpression. Mechanistically, IL-6Rα deficiency completely prevented downstream activation of STAT3 in response to IL-6. Altogether, our data clarify that IL-6Rα is the only biologically relevant receptor for IL-6 in mice.

Time course of signaling profiles of blood leukocytes in acute pancreatitis and sepsis

Activation of intracellular signaling pathways in circulating leukocytes represents an early step in systemic immune-inflammatory response occurring e.g. in acute pancreatitis (AP) and sepsis. Previously, we found aberrations in the phosphorylation of leukocyte signaling proteins in patients with sepsis or AP (measured <48 h from hospital admission) resembling each other and associating with AP severity. Of these patients, those with sepsis or severe AP complicated by persistent organ dysfunction (OD+, n = 17) and patients with moderately severe AP (OD-, n = 6) were followed up in this study by measuring the phosphorylations at two additional time points (2-4 and 5-8 days after the initial sample) using phosphospecific whole blood flow cytometry. Twenty-eighty healthy subjects served as controls (HC). Constitutive STAT3 phosphorylation (pSTAT3) declined in monocytes and neutrophils of OD-/OD + and in lymphocytes of OD + and remained higher in OD- than HC. Monocytes of OD-/OD + showed low pSTAT3 and pSTAT1 levels in response to IL-6 through follow-up. Monocyte pNF-κB levels in response to TNF, LPS and E. coli in OD+, to E. coli in OD-, and lymphocyte pNF-κB levels in response to TNF in OD- increased during follow-up but remained lower than in HC, and neutrophil pNF-κB levels in response to TNF declined in OD-. Phorbol myristate acetate + Ca²⁺ ionophore-stimulated pERK1/2 decreased in neutrophils of OD-/OD+. To conclude, in patients with moderately severe or severe AP or sepsis, improvement and molecular events contributing to OD can be assessed at the level of blood leukocyte signaling.

IL-6 dysregulation originates in dendritic cells and mediates graft-versus-host disease via classical signaling

Graft-versus-host disease (GVHD) after allogeneic stem cell transplantation (alloSCT) is characterized by interleukin-6 (IL-6) dysregulation. IL-6 can mediate effects via various pathways, including classical, trans, and cluster signaling. Given the recent availability of agents that differentially inhibit these discrete signaling cascades, understanding the source and signaling and cellular targets of this cytokine is paramount to inform the design of clinical studies. Here we demonstrate that IL-6 secretion from recipient dendritic cells (DCs) initiates the systemic dysregulation of this cytokine. Inhibition of DC-driven classical signaling after targeted IL-6 receptor (IL-6R) deletion in T cells eliminated pathogenic donor Th17/Th22 cell differentiation and resulted in long-term survival. After engraftment, donor DCs assume the same role, maintaining classical IL-6 signaling-dependent GVHD responses. Surprisingly, cluster signaling was not active after transplantation, whereas inhibition of trans signaling with soluble gp130Fc promoted severe, chronic cutaneous GVHD. The latter was a result of exaggerated polyfunctional Th22-cell expansion that was reversed by IL-22 deletion or IL-6R inhibition. Importantly, inhibition of IL-6 classical signaling did not impair the graft-versus-leukemia effect. Together, these data highlight IL-6 classical signaling and downstream Th17/Th22 differentiation as important therapeutic targets after alloSCT.

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

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

Deficiency of Socs3 leads to brain-targeted EAE via enhanced neutrophil activation and ROS production

Dysregulation of the JAK/STAT signaling pathway is associated with Multiple Sclerosis (MS) and its mouse model, Experimental Autoimmune Encephalomyelitis (EAE). Suppressors Of Cytokine Signaling (SOCS) negatively regulate the JAK/STAT pathway. We previously reported a severe, brain-targeted, atypical form of EAE in mice lacking Socs3 in myeloid cells (Socs3ΔLysM), which is associated with cerebellar neutrophil infiltration. There is emerging evidence that neutrophils are detrimental in the pathology of MS/EAE, however, their exact function is unclear. Here we demonstrate that neutrophils from the cerebellum of Socs3ΔLysM mice show a hyper-activated phenotype with excessive production of reactive oxygen species (ROS) at the peak of EAE. Neutralization of ROS in vivo delayed the onset and reduced severity of atypical EAE. Mechanistically, Socs3-deficient neutrophils exhibit enhanced STAT3 activation, a hyper-activated phenotype in response to G-CSF, and upon G-CSF priming, increased ROS production. Neutralization of G-CSF in vivo significantly reduced the incidence and severity of the atypical EAE phenotype. Overall, our work elucidates that hypersensitivity of G-CSF/STAT3 signaling in Socs3ΔLysM mice leads to atypical EAE by enhanced neutrophil activation and increased oxidative stress, which may explain the detrimental role of G-CSF in MS patients.