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Current evidences indicate that both inflammation and oxidative stress contribute to the pathogenesis of sepsis-associated skeletal muscle atrophy. However, the interaction between inflammation and oxidative stress has not been completely understood in sepsis-associated skeletal muscle atrophy. Here in the present study, a murine model of sepsis has been established by cecal ligation and puncture (CLP) with wild-type and interleukin- (IL-) 6 knockout (KO) mice. Our results suggested that IL-6 KO largely attenuated skeletal muscle atrophy as reflected by reduced protein degradation, increased cross-sectional area (CSA) of myofibers, and improved muscle contractile function (all P < 0.05). In addition, we observed that IL-6 KO promoted the expression of peroxisome proliferator-activated receptor γ coactivator-1alpha (PGC-1 α ) and inhibited CLP-induced mitochondrial reactive oxygen species (ROS) production in skeletal muscles (all P < 0.05). However, the knockdown of PGC-1 α abolished the protective effects of IL-6 KO in CLP-induced skeletal muscle atrophy and reversed the changes in mitochondrial ROS production (all P < 0.05). Ex vivo experiments found that exogenous IL-6 inhibited PGC-1 α expression, promoted mitochondrial ROS production, and induced proteolysis in C2C12 cells (all P < 0.05). Together, these results suggested that IL-6 deficiency attenuated skeletal muscle atrophy by inhibiting mitochondrial ROS production through the upregulation of PGC-1 α expression in septic mice., Competing Interests: The authors declare no competing interests., (Copyright © 2022 Bo Yang et al.)

Traumatic injury to the brain is one of the leading causes of injury-related death or disability. Brain response to injury is orchestrated by cytokines, such as interleukin (IL)-6, but the full repertoire of responses involved is not well known. We here report the results obtained with microarrays in wild-type and IL-6 knockout mice subjected to a cryolesion of the somatosensorial cortex and killed at 0, 1, 4, 8 and 16 days post-lesion. Overall gene expression was analyzed by using Affymetrix genechips/oligonucleotide arrays with∼12 400 probe sets corresponding to∼10 000 different murine genes (MG_U74Av2). A robust, conventional statistical method (two-wayanova) was employed to select the genes significantly affected. An orderly pattern of gene responses was clearly detected, with genes being up- or down-regulated at specific timings consistent with the processes involved in the initial tissue injury and later regeneration of the parenchyma. IL-6 deficiency showed a dramatic effect in the expression of many genes, especially in the 1 day post-lesion timing, which presumably underlies the poor capacity of IL-6 knockout mice to cope with brain damage. The results highlight the importance of IL-6 controlling the response of the brain to injury as well as the suitability of microarrays for identifying specific targets worthy of further study. [ABSTRACT FROM AUTHOR]

Interleukin-6 (IL-6) can reportedly centrally affect the thermogenesis of brown fat. However, whether the peripheral IL-6 signaling regulates beiging of white fat remains largely unknown. In vitro experiments indicated IL-6-KO-derived white adipocytes exhibited lower thermogenic gene expression compared to the WT, associating with reduced phosphorylation of STAT3 at Tyr705. Mechanistically, exogenous IL-6 application increased the p-STAT3 Tyr705 level, thus the phosphorylated STAT3 bound to the promoter regions, and enhanced the transcription of Pparγ and Ucp1. The protein interaction of PGC-1α with PPARγ was increased by IL-6, which also contributed to stimulate Ucp1 expression. In vivo experiments demonstrated that IL-6 KO decreased the beiging potential of white fat with suppressed STAT3 Tyr705 phosphorylation. Accordingly, IL-6-KO mature mice were associated with disrupted glucose homeostasis and accelerated hepatic steatosis. Collectively, we identified a novel function of peripheral IL-6/STAT3 signaling which is essential for beiging of white fat, such ensuring fat and glucose homeostasis., (Copyright © 2021 Elsevier B.V. All rights reserved.)

Interleukin 6 (IL-6) is a pleiotropic cytokine that is elevated in inflammatory bowel disease. However, the role of IL-6 deficiency in colitis is not well-defined. Some IL-6 and IL-6 receptor antagonists are associated with severe gastrointestinal immune adverse effects, but the mechanisms of the effects are not clear. This study aimed to investigate the effect of IL-6 in ulcerative colitis in Il6 -/- mice. Results indicated that physiological deficiency of IL-6 promoted the development of colitis. Moreover, IL-6 deficiency significantly increased the mRNA levels of monocytes chemokine Ccl2 and its receptor Ccr2 in colon tissues. Similarly, the percentage of Ly6C high monocytes and neutrophils were increased in the colon of Il6 -/- mice. Intestinal crypts more strongly increased the migration of Il6 -/- macrophages than wild-type ones. Moreover, Il6 -/- macrophages promoted the migration of neutrophils. Most importantly, RS102895, an antagonist of CCR2, diminished chemotaxis of macrophages and inhibited colitis in Il6 -/- mice. Collectively, these results indicate that Il6 -/- macrophages migrate to inflamed colon tissues and recruit neutrophils, thereby promoting the effect of Il6 -/- on colitis. This study expands our understanding on the effect of IL-6 deficiency in colitis and the development of gastrointestinal immune adverse effects., (Copyright © 2021 Elsevier B.V. All rights reserved.)

Clinical observation and ex vivo studies have established a strong association between inflammation and postoperative atrial fibrillation (POAF). However, it is unclear whether the inflammatory phenotype is causally linked to this event or is an epiphenomenon, and it is not known which inflammatory meditators may increase susceptibility to POAF. The limitations of available animal models of spontaneous POAF (sPOAF) makes it difficult to select an experimental system. Here, we provide experimental and clinical evidence for mechanistic involvement of interleukin-6 (IL-6) in sPOAF., Phase I: We established a mouse model of cardiac surgery with nonpaced sPOAF. IL-6 knockout mice were protected from sPOAF compared with wild-type mice., Phase Ii: At 48 hours after surgery, the heart was separated into 6 regions and cultured. IL-6 was expressed in all regions, with highest abundance in the left atrium (LA). In PHASE III, we demonstrated that IL-6 in the LA elicited early profibrotic properties in atria via the pSTAT3/STAT3 signaling pathway and contributed to sPOAF., Phase Iv: In a translational prospective clinical study, we demonstrated that humans with POAF had a higher IL-6 concentration in pericardial drainage (PD). This study provides preliminary evidence of a causal relationship between IL-6 and POAF in a novel nonpaced sPOAF mouse model. IL-6 is a crucial prerequisite for eliciting profibrotic properties in cardiac myocytes via the pSTAT3 pathway during the early postoperative period, leading to an increased susceptibility to POAF. Measuring IL-6 in PD could be a new noninvasive biomarker for the clinical prediction of POAF., (Copyright © 2021. Published by Elsevier Inc.)

Several cytokines have been reported to participate in spermatogenesis, including interleukin-6 (IL6). However, not many studies have been conducted on the loss of Il6 on the male reproductive tract. Nonetheless, there is considerable knowledge regarding the pathological and physiological role of IL6 on spermatogenesis. In this way, this study evaluated the impact of Il6 deficiency on mice testicles in the absence of infection or inflammation. We showed that Il6 deficiency increases daily sperm production, the number of spermatids, and the testicular testosterone and dihydrotestosterone levels. Besides that, mice with a deleted Il6 (IL6KO) showed increased testicular SOCS3 levels, with no changes in pJAK/JAK and pSTAT3/STAT3 ratios. It is worth noting that the aforementioned pathway is not the only pathway to up-regulate SOCS3, nor is it the only SOCS3 target, thus proposing that the increase of SOCS3 in the testis occurs independently of the JAK-STAT signaling in IL6KO mice. Therefore, we suggest that the lack of Il6 drives androgenic production by increasing SOCS3 in the testis, thus leading to an increase in spermatogenesis.

Interleukin-6 (IL-6) is associated with pathological cardiac hypertrophy and can be dramatically increased in serum after an acute strenuous exercise session. However, IL-6 is also associated with the increased production and release of anti-inflammatory cytokines and the inhibition of tumor necrosis factor-alpha (TNF-α) after chronic moderate exercise. To elucidate the relevance of IL-6 in inflammatory and hypertrophic signaling in the heart in response to an acute strenuous exercise session, we combined transcriptome analysis using the BXD mice database and exercised IL-6 knockout mice (IL-6KO). Bioinformatic analysis demonstrated that low or high-levels of Il6 mRNA in the heart did not change the inflammation- and hypertrophy-related genes in BXD mice strains. On the other hand, bioinformatic analysis revealed a strong positive correlation between Il6 gene expression in skeletal muscle with inflammation-related genes in cardiac tissue in several BXD mouse strains, suggesting that skeletal muscle-derived IL-6 could alter the heart's intracellular signals, particularly the inflammatory signaling. As expected, an acute strenuous exercise session increased IL-6 levels in wild-type, but not in IL-6KO mice. Despite not showing morphofunctional differences in the heart at rest, the IL-6KO group presented a reduction in physical performance and attenuated IL-6, TNF-α, and IL-1beta kinetics in serum, as well as lower p38MAPK phosphorylation, Ampkalpha expression, and higher Acta1 and Tnf gene expressions in the left ventricle in the basal condition. In response to strenuous exercise, IL-6 ablation was linked to a reduction in the pro-inflammatory response and higher activation of classical physiological cardiac hypertrophy proteins., (Copyright © 2021 Elsevier Ltd. All rights reserved.)

Obesity, a chronic low-grade inflammatory state, not only promotes bone loss, but also accelerates cell senescence. However, little is known about the mechanisms that link obesity, bone loss, and cell senescence. Interleukin-6 (IL-6), a pivotal inflammatory mediator increased during obesity, is a candidate for promoting cell senescence and an important part of senescence-associated secretory phenotype (SASP). Here, wild type (WT) and (IL-6 KO) mice were fed with high-fat diet (HFD) for 12 weeks. The results showed IL-6 KO mice gain less weight on HFD than WT mice. HFD induced trabecular bone loss, enhanced expansion of bone marrow adipose tissue (BMAT), increased adipogenesis in bone marrow (BM), and reduced the bone formation in WT mice, but it failed to do so in IL-6 KO mice. Furthermore, IL-6 KO inhibited HFD-induced clone formation of bone marrow cells (BMCs), and expression of senescence markers (p53 and p21). IL-6 antibody inhibited the activation of STAT3 and the senescence of bone mesenchymal stem cells (BMSCs) from WT mice in vitro , while rescued IL-6 induced senescence of BMSCs from IL-6 KO mice through the STAT3/p53/p21 pathway. In summary, our data demonstrated that IL-6 KO may maintain the balance between osteogenesis and adipogenesis in BM, and restrain senescence of BMSCs in HFD-induced bone loss., Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2021 Li, Lu, Xie, Chen, Tian, Liang, Li, Zhang, Liu and Yu.)

Chronic inflammation (CI) in older adults is associated with reduced health span and life span. Interleukin-6 (IL-6) is one CI marker that is strongly associated with adverse health outcomes and mortality in aging. We have previously characterized a mouse model of frailty and chronic inflammatory pathway activation (IL-10tm/tm, IL-10 KO) that demonstrates the upregulation of numerous proinflammatory cytokines, including IL-6. We sought to identify a more specific role for IL-6 within the context of CI and aging and developed a mouse with targeted deletion of both IL-10 and IL-6 (IL-10tm/tm/IL-6tm/tm, DKO). Phenotypic characteristics, cytokine measurements, cardiac myocardial oxygen consumption, physical function, and survival were measured in DKO mice and compared to age- and gender-matched IL-10 KO and wild-type mice. Our findings demonstrate that selective knockdown of IL-6 in a frail mouse with CI resulted in the reversal of some of the CI-associated changes. We observed increased protective mitochondrial-associated lipid metabolites, decreased cardiac oxaloacetic acid, improved myocardial oxidative metabolism, and better short-term functional performance in DKO mice. However, the DKO mice also demonstrated higher mortality. This work shows the pleiotropic effects of IL-6 on aging and frailty., (© The Author(s) 2020. Published by Oxford University Press on behalf of The Gerontological Society of America. All rights reserved. For permissions, please e-mail: journals.permissions@oup.com.)

Several interleukins (ILs) have been shown to be involved in aging, but the effects of IL-6 on aging-related cardiac dysfunction remain unknown. In this study, the expression and sources of cardiac IL-6 in aging hearts were investigated for the first time. The results showed that cardiac IL-6 expression in mice gradually increased with age, and the expression at 16 months, 20 months and 25 months was higher than that at 3 months. In addition, cardiac macrophages (Møs) were shown to be the main sources of IL-6 in aging mice. IL-6 knockout (KO) significantly alleviated cardiac dysfunction, increased M2 macrophage (Mø2) differentiation, reduced M1 macrophage (Mø1) differentiation and protected against cardiomyocyte apoptosis in aging mice. IL-6 KO also reversed the stimulatory effect of doxorubicin (DOX) treatment on Mø1s and the inhibitory effect of DOX treatment on Mø2s in vitro . Furthermore, the mRNA expression of both aging markers and apoptosis-related markers was markedly inhibited by IL-6 KO. Our results suggest that aging can be significantly reversed by IL-6 KO and that the mechanisms of this effect are related to alleviation of Mø1/Mø2 imbalance and protection against apoptosis in cardiomyocytes.

Background: Interleukin-6 (IL-6) is a pleiotropic cytokine that controls numerous physiological processes both in basal and neuroinflammatory conditions, including the inflammatory response to experimental autoimmune encephalomyelitis (EAE). IL-6 is produced by multiple peripheral and central cells, and until now, the putative roles of IL-6 from different cell types have been evaluated through conditional cell-specific IL-6 knockout mice. Nevertheless, these mice probably undergo compensatory responses of IL-6 from other cells, which makes it difficult to assess the role of each source of IL-6., Methods: To give some insight into this problem, we have produced a novel mouse model: a conditional reversible IL-6 KO mouse (IL6-DIO-KO). By using double-inverted, open-reading-frame (DIO) technology, we created a mouse line with the loss of Il6 expression in all cells that can be restored by the action of Cre recombinase. Since microglia are one of the most important sources and targets of IL-6 into the central nervous system, we have recovered microglial Il6 expression in IL6-DIO-KO mice through breeding to Cx3cr1-CreER mice and subsequent injection of tamoxifen (TAM) when mice were 10-16 weeks old. Then, they were immunized with myelin oligodendrocyte glycoprotein 35-55 peptide (MOG 35-55 ) 7 weeks after TAM treatment to induce EAE. Clinical symptoms and demyelination, CD3 infiltration, and gliosis in the spinal cord were evaluated., Results: IL6-DIO-KO mice were resistant to EAE, validating the new model. Restoration of microglial Il6 was sufficient to develop a mild version of EAE-related clinical symptoms and neuropathology., Conclusions: IL6-DIO-KO mouse is an excellent model to understand in detail the role of specific cellular sources of IL-6 within a recovery-of-function paradigm in EAE.

Purpose: Interleukin-6 (IL-6) is elevated in intraocular fluid from eyes with proliferative vitreoretinopathy (PVR), but the exact role of the cytokine is still unclear. We investigated the function and mechanism of IL-6 in retinal pigment epithelium (RPE) cell biology in vitro and in a mouse model in vivo., Methods: After treatment with various concentrations of IL-6, RPE cell proliferation was assessed with cell counting kit-8 (CCK-8) assay, and epithelial-mesenchymal transition (EMT) markers were evaluated using western blotting and immunofluorescent staining. The activation of JAK1/STAT3 signaling was determined with western blotting. Moreover, the effects of blockade of IL-6/JAK1/STAT3 signaling were investigated using pharmacological inhibitor S3I-201. For in vivo studies, the PVR model was induced with intravitreal injection of dispase/collagenase in wild-type and IL-6 knockout mice. The severity of PVR was evaluated with histological analysis. The expression of IL-6, gp130, and EMT markers was assessed with quantitative real-time PCR and western blotting., Results: IL-6 statistically significantly induced RPE cell proliferation and EMT in a dose-dependent manner in vitro , which was accompanied by rapid phosphorylation of JAK1 and STAT3. Blockade of the IL-6/JAK1/STAT3 pathway with S3I-201 apparently inhibited RPE proliferation and EMT. Furthermore, IL-6 and gp130 overexpression, and JAK1/STAT3 signaling hyperactivation were detected in the retinas of the wild-type mice at 1, 3, and 7 days after dispase/collagenase injection. Finally, we confirmed that IL-6 deficiency markedly alleviated mouse PVR development via inhibiting EMT., Conclusions: These findings indicate that IL-6 promotes PVR by inducing RPE proliferation and EMT via the JAK1/STAT3 signaling pathway. We provided new evidence that therapeutic strategies to block IL-6 may be beneficial for PVR., (Copyright © 2020 Molecular Vision.)

Huntington's disease (HD) is an incurable neurodegenerative disorder caused by CAG trinucleotide expansions in the huntingtin gene. Markers of both systemic and CNS immune activation and inflammation have been widely noted in HD and mouse models of HD. In particular, elevation of the pro-inflammatory cytokine interleukin-6 (IL-6) is the earliest reported marker of immune activation in HD, and this elevation has been suggested to contribute to HD pathogenesis. To test the hypothesis that IL-6 deficiency would be protective against the effects of mutant huntingtin, we generated R6/2 HD model mice that lacked IL-6. Contrary to our prediction, IL-6 deficiency exacerbated HD-model associated behavioral phenotypes. Single nuclear RNA Sequencing (snRNA-seq) analysis of striatal cell types revealed that IL-6 deficiency led to the dysregulation of various genes associated with synaptic function, as well as the BDNF receptor Ntrk2. These data suggest that IL-6 deficiency exacerbates the effects of mutant huntingtin through dysregulation of genes of known relevance to HD pathobiology in striatal neurons, and further suggest that modulation of IL-6 to a level that promotes proper regulation of genes associated with synaptic function may hold promise as an HD therapeutic target.

Our earlier studies demonstrated slower age-related memory decline in IL-6-deficient than in control mice. Therefore, in the present study we evaluated the effect of IL-6 deficiency and aging on expression of p53, connected with accumulation of age-related cellular damages, in hippocampus of 4- and 24-month-old IL-6-deficient C57BL/6J (IL-6KO) and wild type control (WT) mice. The accumulation of p53 protein in hippocampus of aged IL-6KO mice was significantly lower than in aged WT ones, while p53 mRNA level was significantly higher in IL-6-deficient mice, what indicates that the effect was independent on p53 transcription. Presence of few apoptotic cells in hippocampal dentate gyrus and lack of changes in levels of pro-apoptotic Bax, antiapoptotic Bcl-2, as well as in p21 protein in aged animals of both genotypes, points to low transcriptional activity of p53, especially in aged WT mice. Because the amount of p53 protein did not correlate with the level of Mdm2 protein, its main negative regulator, other than Mdm2-dependent mechanism was involved in p53 build-up. Significantly higher mRNA levels of autophagy-associated genes: Pten, Tsc2, and Dram1 in IL-6KO mice, in conjunction with significantly lower amount of Bcl-2 protein in 4-month-old IL-6KO mice, suggests that lack of IL-6/STAT3/Bcl-2 signaling could account for better autophagy performance in these mice, preventing excessive accumulation of proteins. Taken together, attenuated p53 protein build-up, absence of enhanced apoptosis, and transcriptional up-regulation of autophagy-associated genes imply that IL-6 deficiency may protect hippocampus from age-related accumulation of cellular damages.

Sustained T cell receptor (TCR) stimulation is required for maintaining germinal center T follicular helper (GC-T FH ) cells. Paradoxically, TCR activation induces interleukin-2 receptor (IL-2R) expression and IL-2 production, thereby initiating a feedback loop of IL-2 signaling that normally inhibits T FH cells. It is unclear how GC-T FH cells can receive prolonged TCR signaling without succumbing to the detrimental effects of IL-2. Using an influenza infection model, we show here that GC-T FH cells secreted large amounts of IL-2 but responded poorly to it. To maintain their IL-2 hyporesponsiveness, GC-T FH cells required intrinsic IL-6 signaling. Mechanistically, we found that IL-6 inhibited up-regulation of IL-2Rβ (CD122) by preventing association of STAT5 with the Il2rb locus, thus allowing GC-T FH cells to receive sustained TCR signaling and produce IL-2 without initiating a TCR/IL-2 inhibitory feedback loop. Collectively, our results identify a regulatory mechanism that controls the generation of GC-T FH cells., (Copyright © 2019 The Authors, some rights reserved; exclusive licensee American Association for the Advancement of Science. No claim to original U.S. Government Works.)

Serotonin (5-HT) signaling pathways are thought to be involved in colorectal tumorigenesis (CRT), but the role of 5-HT synthesis in the early steps of this process is presently unknown. In this study, we used carcinogen treatment in the tryptophan hydroxylase 1 knockout (Tph1KO) and transgenic (Tph1 fl/fl Villin Cre ) mouse models defective in 5-HT synthesis to investigate the early mutagenic events associated with CRT. Our observations of the colonic crypt post-treatment followed a timeline designed to understand how disruption of 5-HT synthesis affects the initial steps leading to CRT. We found Tph1KO mice had decreased development of both allograft tumors and colitis-related CRT. Interestingly, carcinogenic exposure alone induced multiple colon tumors and increased cyclooxygenase-2 (Ptgs2) expression in Tph1KO mice. Deletion of interleukin 6 (Il6) in Tph1KO mice confirmed that inflammation was a part of the process. 5-HT deficiency increased colonic DNA damage but inhibited genetic repair of specific carcinogen-related damage, leading to CRT-related inflammatory reactions and dysplasia. To validate a secondary effect of 5-HT deficiency on another DNA repair pathway, we exposed Tph1KO mice to ionizing radiation and found an increase in DNA damage associated with reduced levels of ataxia telangiectasia and Rad3 related (Atr) gene expression in colonocytes. Restoring 5-HT levels with 5-hydroxytryptophan treatment decreased levels of DNA damage and increased Atr expression. Analysis of Tph1 fl/fl Villin Cre mice with intestine-specific loss of 5-HT synthesis confirmed that DNA repair was tissue specific. In this study, we report a novel protective role for 5-HT synthesis that promotes DNA repair activity during the early stages of colorectal carcinogenesis. © 2019 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd., (© 2019 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.)

To assess the potential role of IL-6 in sciatic nerve injury-induced activation of a pro-regenerative state in remote dorsal root ganglia (DRG) neurons, we compared protein levels of SCG-10 and activated STAT3, as well as axon regeneration in IL-6 knockout (IL-6ko) mice and their wild-type (WT) counterparts. Unilateral sciatic nerve compression and transection upregulated SCG-10 protein levels and activated STAT3 in DRG neurons not only in lumbar but also in cervical segments of WT mice. A pro-regenerative state induced by prior sciatic nerve lesion in cervical DRG neurons of WT mice was also shown by testing for axon regeneration in crushed ulnar nerve. DRG neurons from IL-6ko mice also displayed bilaterally increased levels of SCG-10 and STAT3 in both lumbar and cervical segments after sciatic nerve lesions. However, levels of SCG-10 protein in lumbar and cervical DRG of IL-6ko mice were significantly lower than those of their WT counterparts. Sciatic nerve injury induced a lower level of SCG-10 in cervical DRG of IL-6ko than WT mice, and this correlates with significantly shorter regeneration of axons distal to the crushed ulnar nerve. These results suggest that IL-6 contributes, at the very least, to initiation of the neuronal regeneration program in remote DRG neurons after unilateral sciatic nerve injury.

Chronic peripheral elevation of interleukin 6 (IL-6) in humans is associated with cognitive deficits. 4- and 24-month-old IL-6-deficient C57BL/6J (IL-6KO) and reference wild-type (WT) mice were tested in an object recognition test. Discrimination ratios and recognition indexes were significantly lower in 4-month-old IL-6KO and in 24-month-old WT mice vs 4-month-old WT animals. Their discrimination ratios had negative values and recognition indexes were below 50% indicating inability to differentiate the novel from the familiar object after 1-hour delay. In 24-month-old IL-6KO mice recognition index reached 53.17% indicating that their recognition memory was not worsened with age in comparison with younger IL-6-deficient animals. Results of holeboard and elevated plus maze indicated that this effect was memory specific. Inborn IL-6 deficiency attenuated recognition memory in 4-month-old mice and did not altered recognition memory in aged animals. IL-6 signalling may constitute a target for development of the protection against memory disturbances connected with IL-6 overexpression.

Interleukin-6 (IL-6) is a pleiotropic cytokine with roles in immunity, tissue regeneration, and metabolism. Rapid production of IL-6 contributes to host defense during infection and tissue injury, but excessive synthesis of IL-6 and dysregulation of IL-6 receptor signaling is involved in disease pathology. Therapeutic agents targeting the IL-6 axis are effective in rheumatoid arthritis, and applications are being extended to other settings of acute and chronic inflammation. Recent studies reveal that selective blockade of different modes of IL-6 receptor signaling has different outcomes on disease pathology, suggesting novel strategies for therapeutic intervention. However, some inflammatory diseases do not seem to respond to IL-6 blockade. Here, we review the current state of IL-6-targeting approaches in the clinic and discuss how to apply the growing understanding of the immunobiology of IL-6 to clinical decisions., (Copyright © 2019 Elsevier Inc. All rights reserved.)

Objective: To investigate the effect of interleukin-6 (IL-6) gene knockout on apoptosis of myocardial cells in mice with Coxsackievirus B3 (CVB3)-induced dilated cardiomyopathy (DCM) and its potential mechanism, so as to provide certain references for the clinical prevention and treatment of DCM., Materials and Methods: A total of 40 male C57 mice were randomly divided into Sham group (n=20) and DCM group (n=20) using a random number table. Another 20 mice with IL-6 gene knockout were enrolled into DCM+IL-6 KO group (n=20). The DCM model was established via CVB3 repeated incremental infection. After 9 months, the heart weight/body weight (HW/BW) ratio of mice in each group was detected. The ejection fraction [EF (%)] and fraction shortening [FS (%)] of mice in each group were detected via two-dimensional ultrasonography. The cross-sectional area and pathological changes in myocardial cells in the heart in each group were determined using hematoxylin-eosin (HE) staining. The collagen content in myocardial tissues in each group was detected via Masson staining and picrosirius red (PSR) staining, and the expressions of Collagen I and Collagen III in myocardial tissues in each group were detected via immunohistochemistry. In addition, the myocardial apoptosis in myocardial tissues in each group was detected via terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling (TUNEL) staining. Finally, the protein expression levels of B-cell lymphoma-2 (Bcl-2), Bcl-2 associated X protein (Bax), phosphorylated signal transducer and activator of transcription 3 (p-STAT3), and total STAT3 (t-STAT3) were detected via Western blotting., Results: The expression of IL-6 messenger ribonucleic acids (mRNAs) in myocardial tissues in DCM group was significantly increased compared with that in Sham group (p<0.05). After IL-6 knockout, the HW/BW ratio of DCM mice significantly declined (p<0.05), and the cross-sectional area of myocardial cells was significantly reduced (p<0.05). According to the results of echocardiography, the cardiac function of mice in DCM+IL-6 KO group was significantly superior to that in DCM group, manifested as the significant increase in FS (%) and EF (%) (p<0.05). The results of Masson staining, PSR staining, and immunohistochemical staining showed that IL-6 knockout could reduce the collagen content and Collagen I and Collagen III expressions in myocardial tissues of DCM mice (p<0.05). Furthermore, it was found via TUNEL staining that the number of apoptotic myocardial cells in DCM+IL-6 KO group was markedly smaller than that in DCM group (p<0.05). At the same time, the Bax/Bcl-2 ratio in myocardial tissues in DCM+IL-6 KO group was lower (p<0.05). Finally, the results of Western blotting revealed that DCM+IL-6 KO group had a lower phosphorylation level of STAT3 than DCM group (p<0.05)., Conclusions: Inhibiting IL-6 gene may improve the DCM-induced myocardial remodeling through reducing myocardial apoptosis.

Background/aims: Interleukin-6 (IL-6) is a major cytokine controlling body weight and metabolism, at least in part through actions in the central nervous system (CNS) from local sources., Methods: We herewith report results obtained in conditional IL-6 KO mice for brain cells (Il6ΔGfap and Il6ΔSyn)., Results: The reporter RiboTag mouse line demonstrated specific astrocytic expression of GFAP-dependent Cre in the hypothalamus but not in other brain areas, whereas that of synapsin 1-dependent Cre was specific for neurons. Feeding a high-fat diet (HFD) or a control diet showed that Il6ΔGfap and Il6ΔSyn mice were more prone and resistant, respectively, to HFD-induced obesity. Energy intake was not altered in HFD experiments, but it was reduced in Il6ΔSyn male mice following a 24-h fast. HFD increased circulating insulin, leptin, and cholesterol levels, decreased triglycerides, and caused impaired responses to the insulin and glucose tolerance tests. In Il6ΔGfap mice, the only significant difference observed was an increase in insulin levels of females, whereas in Il6ΔSyn mice the effects of HFD were decreased. Hypothalamic Agrp expression was significantly decreased by HFD, further decreased in Il6ΔGfap, and increased in Il6ΔSyn female mice. Hypothalamic Il-6 mRNA levels were not decreased in Il6ΔSyn mice and even increased in Il6ΔGfapmale mice. Microarray analysis of hypothalamic RNA showed that female Il6ΔGfap mice had increased interferon-related pathways and affected processes in behavior, modulation of chemical synaptic transmission, learning, and memory., Conclusion: The present results demonstrate that brain production of IL-6 regulates body weight in the context of caloric excess and that the cellular source is critical., (© 2019 S. Karger AG, Basel.)

Significance of interleukin 6 (IL-6) deficiency in cognitive processes was evaluated in 4- and 24-month-old C57BL/6J IL-6-deficient (IL-6 KO) and control (WT) mice in Morris water maze (MWM), holeboard test (HB) and elevated plus maze (EPM). During 3-day learning escape latency time (ELT) was longer in IL-6 KO than in WT mice, however their swimming was slower, floating longer, and path length did not differ. The comparison of ELT and the distance traveled between the first and the third learning day within each group revealed significant decrease of ELT in all groups with the highest difference in 4-month-old WT mice, and significant decrease of distance traveled only in both groups of WT mice. In a single probe trial, performed 24 h after the last learning session, there were no major differences in the absolute values of ELT, but ELT turned out to be significantly shorter in both IL-6 KO groups, when it was compared to the ELT on the last learning day, indicating on better memory retrieval. In HB test only significant increase in number of rearings in aged WT mice, and in EPM significant prolongation of open arm time and higher number of open arm entries in 4-month-old IL-6 KO mice were observed. Results of HB and EPM tests showed that alterations of learning and reference memory observed in MWM were specific to cognition. Attenuation of learning ability in young adult IL-6-deficient mice assessed in MWM suggests that physiological level of IL-6 is involved in mechanisms engaged in proper memory formation, and it may also indicate on the importance of IL-6 signaling in brain development. Maintained on similar level in both 4- and 24-month-old IL-6 KO mice learning ability and its attenuation in 24-month-old vs 4-month-old WT mice indicates on slower age-related memory decline in mice not expressing IL-6. Better performance of IL-6 KO mice in the probe trial points to their reference memory improvement and may also indicate that IL-6 plays a role in mechanism responsible for cognitive flexibility., (Copyright © 2018 Elsevier Inc. All rights reserved.)

Legg-Calvé-Perthes disease (LCPD) is a childhood form of ischemic osteonecrosis of the femoral head which can produce a permanent femoral head deformity and early osteoarthritis. The femoral head deformity results from increased bone resorption and decreased bone formation during repair and remodeling of the necrotic femoral head. A recent study showed that a pro-inflammatory cytokine, interleukin-6 (IL-6), is significantly elevated in the synovial fluid of patients with LCPD. We hypothesized that IL-6 elevation decreases bone formation during the repair process following ischemic osteonecrosis and that IL-6 depletion will increase new bone formation. To test this hypothesis, we surgically induced ischemic osteonecrosis in the wild-type (n = 29) and IL-6 knockout (KO) mice (n = 25). The animals were assessed at 48 h, 2 weeks and 4 weeks following the induction of ischemic osteonecrosis using histologic, histomorphometric and micro-CT methods. IL-6 immunohistochemistry showed high expression of IL-6 in the osteonecrotic side of the wild-type mice at 48 h and 4 weeks following ischemic osteonecrosis, but not in the IL-6 KO mice. We also confirmed an undetectable level of IL-6 expression in the primary osteoblasts of the IL-6 KO mice compared to the readily detectable level in the wild-type mice. Furthermore, we confirmed that IL-6 deletion did not affect the extent of bone necrosis in the IL-6 KO mice compared to the wild-type mice by performing histologic and terminal deoxynucleotidyl transferase mediated dUTP nick-end labeling (TUNEL) assessments at 2 weeks following the induction of ischemia. Both groups had the same extent of ischemic osteonecrosis and absence of repair at 2 weeks. At 4 weeks, the necrotic epiphyses showed a significant increase in the extent of revascularization in the IL-6 KO mice compared to the wild-type mice (p = 0.001). In addition, a significantly greater recovery of the hematopoietic bone marrow was observed in the osteonecrotic side of the IL-6 KO mice compared to the wild-type mice (p < 0.01). Vascular endothelial growth factor (VEGF) immunohistochemistry showed regionally increased staining in the areas of repair in the osteonecrosis side of IL-6 KO mice compared to the wild-type mice at 4 weeks following ischemic osteonecrosis. Micro-CT assessment of the wild-type mice at 4 weeks showed a significant decrease in the percent bone volume (p < 0.01) in the osteonecrotic side compared to the control side. In contrast, IL-6 KO mice showed significantly increased bone volume in the osteonecrotic side compared to the osteonecrotic side of WT mice (p < 0.001). No significant difference in the bone volume percentage was found between the control side of the wild-type and the IL-6 KO mice. Histomorphometric analysis at 4 weeks revealed increased osteoblast number/bone surface (p < 0.001), bone formation rate (BFR) (p = 0.0001), and mineral apposition rate (MAR) (p < 0.0001) in the osteonecrotic side of the IL-6 KO mice compared to the wild-type mice. The number of osteoclast/bone surface was also increased in the IL-6 KO mice compared to the wild-type mice (p < 0.0001). No significant difference was observed between the control side of the wild-type and IL-6 KO mice with regards to the number of osteoblast or osteoclast/bone surface, BFR, and MAR. We next obtained primary osteoblasts from IL-6 KO mice and showed they expressed a significantly higher level of RANKL/OPG than wild-type mice (p = 0.001) in hypoxia culture condition. Taken together, the findings indicate that IL-6 deletion stimulates revascularization and new bone formation following ischemic osteonecrosis. This study provides new evidence that therapeutic strategies to block IL-6 may be beneficial for bone healing following ischemic osteonecrosis., (Copyright © 2018 Elsevier Inc. All rights reserved.)

Neisseria musculi , isolated from the oral cavity of wild-caught mice, does not colonize most inbred mouse strains. N. musculi does weakly (50%) colonize C57BL/6J (B6) mice but readily colonizes CAST/EiJ (CAST) mice. In this study, we examined whether differences in the CAST and B6 host response could elucidate mechanisms governing N. musculi colonization. In vivo stimulation of B6 or CAST splenocytes with wild type (WT) Neisseria or Escherichia coli LPS showed that CAST mice had a blunted inflammatory response, producing significantly lower levels of IL-6 than B6 mice. The use of specific genetic knockouts highlighted a need for an intact innate immune system to prevent colonization. B6-RAG-1 -/- mice were colonized at a similar rate as WT B6 mice, whereas B6-MyD88 -/- and TLR4 -/- mice were readily colonized like CAST (100%) mice. Sequence analysis revealed a unique point mutation in TLR4 in CAST mice. However, crosses to TLR4 -/- mice and analysis of recombinant inbred Collaborative Cross mice showed that TLR4 from CAST mice was not sufficient to allow Neisseria colonization. In vitro stimulation of B6 bone marrow-derived macrophages or splenocytes with WT Neisseria yielded low levels of IL-6 compared with LPS stimulation. Surprisingly, UV-inactivated Neisseria induced high levels of IL-6, suggesting suppression of IL-6 production is an active bacterial process. Consistent with a critical role for IL-6 in preventing colonization, mice deficient for the IL-6 receptor were efficiently colonized, indicating host IL-6 production plays a critical role in determining host colonization susceptibility., (Copyright © 2018 The Authors.)

Our aim was to investigate the role of interleukin-6 (IL-6) in myocardial regeneration from mice after cardiac injury. The newborn mice were divided into the following 4 groups (16 in each group): sham group, model group, IL-6-/- group (IL-6 knockout) and IL-6 group (IL-6 overexpression). Electrocardiography was performed on all mice and found higher LVEDD, LVESD and IVST and lower LVEF and LVFS in the IL-6 group compared with the sham group. Using HE staining, severe myocardial injury combined with infarction and fibrosis were observed in the IL-6-/- group, while the damaged myocardial tissue was repaired to some extent in the IL-6 group. The expression of IL-6 in the IL-6 group were significantly up-regulated. BrdU immunofluorescence found that the IL-6-/- group had the least number of BrdU positive cells, while the IL-6 group had more BrdU positive cells than the model group and the IL-6-/- group. Expressions of IL-6, cyclinD1 and Bcl-2 in the IL-6 group were up-regulated compared with other groups. In conclusion, IL-6 overexpression could enhance cardiomyocyte proliferation and relevant protein expression in mice myocardium, thus promoting cardiac regeneration., (Copyright © 2018 Elsevier Masson SAS. All rights reserved.)

IL-6 has a wide range of biological activities that includes anti- and pro-inflammatory aspects. In this study, we investigated the role of IL-6 in immune responses to the rodent filarial nematode Litomosoides sigmodontis, a model for human filarial infections. IL-6 -/- mice had a significantly increased worm burden after natural infection compared with wild type controls at early time points p.i. Given that the worm burden in IL-6 -/- mice was already increased at the time point the infective larvae reached the pleural cavity, immune responses that may facilitate the migration from the site of infection (skin) via the lymphatics to the pleural cavity were analysed. Increased vascular permeability may facilitate larval migration, but blocking of histamine receptors had no effect on worm burden and vascular permeability was similar between IL-6 -/- mice and wild type controls. In contrast, blocking mast cell degranulation reduced the worm burden in IL-6 -/- mice partially, suggesting that release of mast cell-derived mediators improves larval migration to some degree. Protective immune responses within the skin were involved, as bypassing the skin barrier by inoculating infective L3s subcutaneously resulted in a comparable worm recovery in both mouse strains. Analysis of the cellular composition by flow cytometry and PCR array in the skin after exposure to filarial extract or L3s, respectively, indicate that the absence of IL-6 results in a delayed recruitment of neutrophils and macrophages to the site of initial infection. These results demonstrate that IL-6 is essentially involved in protective immune responses within the skin that impair migration of infective L3s., (Copyright © 2018 Australian Society for Parasitology. Published by Elsevier Ltd. All rights reserved.)

Acute liver failure (ALF) is associated with high mortality, and a poor understanding of the underlying pathophysiology has resulted in a lack of effective treatments so far. Here, using an amatoxin-induced rhesus monkey model of ALF, we panoramically revealed the cellular and molecular events that lead to the development of ALF. The challenged monkeys with toxins underwent a typical course of ALF including severe hepatic injury, systemic inflammation and eventual death. Adaptive immune was not noticeably disturbed throughout the progress of ALF. A systematic examination of serum factors and cytokines revealed that IL-6 increase was the most rapid and drastic. Interestingly, we found that IL-6 was mainly produced by circulating monocytes. Furthermore, ablation of monocyte-derived IL-6 in mice decreased liver injury and systemic inflammation following chemical injection. Our findings reveal a critical role of circulating monocytes in initiating and accelerating ALF, indicating a potential therapeutic target in clinical treatment for ALF., (© 2018 The Authors. Journal of Cellular and Molecular Medicine published by John Wiley & Sons Ltd and Foundation for Cellular and Molecular Medicine.)

BACKGROUND Limited efficacy of immune checkpoint blockades was observed in clinical trials in colorectal (CRC) patients, especially in the microsatellite-stable patients. Interleukin-6 (IL-6) is critical in modeling immune responses in cancers. However, the effects of targeting IL-6 in combination with immune checkpoint blockades is unknown in CRC. MATERIAL AND METHODS In the present study, we investigated the profile of IL-6 expression in tumor tissues of CRC patient and we established CRC mouse models with various IL-6 expression levels using CT26 cells and MC38 cells. Effects of anti-IL-6 and anti-PD-L1 combination treatment were tested in these models. RESULTS A total of 105 CRC patients were included in this study, with 41 (39%) females and 64 (61%) males. Sixty patients showed IL-6 high expression and 45 patients showed IL-6 low expression. The patients with IL-6 high expression tended to have shorter survival (median survival time of 25.5 months) than the patients with IL-6 low expression (median survival time of 46 months, P value=0.013). In the CRC mouse models, tumors with IL-6 overexpression tended to grow faster than the tumors with IL-6 knockout. The numbers of CD8+ T cells and CD4+ T cells were decreased in IL-6 overexpressed tumors. On the contrary, myeloid-derived suppressor cells and regulatory/suppressor T cells were more numerous in tumors with IL-6 overexpression. PD-L1 expression was upregulated in the tumors with IL-6 overexpression. Importantly, an IL-6 blockade reversed the anti-PD-L1 resistance and prolonged tumor-bearing mouse survival. CONCLUSIONS Our study indicates that IL-6 induces strong immunosuppression in the CRC microenvironment by recruiting immunosuppression cells and impairing T cell infiltration. Inhibition of IL-6 enhanced the efficacy of anti-PD-L1 in CRC, providing a novel strategy to overcome anti-PD-L1 resistance in CRC.

Systemic sclerosis (SSc) is an autoimmune disease characterized by skin and lung fibrosis. More than 90% of patients with SSc are positive for autoantibodies. In addition, serum B cell activating factor (BAFF) level is correlated with SSc severity and activity. Thus, B cells are considered to play a pathogenic role in SSc. However, there are two opposing subsets: regulatory B cells (Bregs) and effector B cells (Beffs). Interleukin-10 (IL-10)-producing Bregs negatively regulate the immune response, while IL-6-producing Beffs positively regulate it. Therefore, a protocol that selectively depletes Beffs would represent a potent therapy for SSc. The aims of this study were to investigate the roles of Bregs and Beffs in SSc and to provide a scientific basis for developing a new treatment strategy targeting B cells. A bleomycin-induced scleroderma model was induced in mice with a B cell-specific deficiency in IL-6 or IL-10. We also examined whether BAFF regulates cytokine-producing B cells and its effects on the scleroderma model. IL-6-producing Beffs increased in number and infiltrated the inflamed skin in the scleroderma model. The skin and lung fibrosis was attenuated in B cell-specific IL-6-deficient mice, whereas B cell-specific IL-10-deficient mice showed more severe fibrosis. In addition, BAFF increased Beffs but suppressed Bregs. Furthermore, BAFF antagonist attenuated skin and lung fibrosis in the scleroderma model with reduction of Beffs but not of Bregs. The current study indicates that Beffs play a pathogenic role in the scleroderma model, while Bregs play a protective role. BAFF inhibition is a potential therapeutic strategy for SSc via alteration of B cell balance.

Immunoglobulin A (IgA) nephropathy (IgAN), the most common glomerulonephritis worldwide, is characterized by IgA depositions in the kidney. Deficiency of CD37, a leukocyte-specific tetraspanin, leads to spontaneous development of renal pathology resembling IgAN. However, the underlying molecular mechanism has not been resolved. Here we found that CD37 expression on B cells of patients with IgAN was significantly decreased compared to B cells of healthy donors. Circulating interleukin (IL)-6 levels, but not tumor necrosis factor-α or IL-10, were elevated in Cd37 -/- mice compared to wild-type mice after lipopolysaccharide treatment. Cd37 -/- mice displayed increased glomerular neutrophil influx, immune complex deposition, and worse renal function. To evaluate the role of IL-6 in the pathogenesis of accelerated renal pathology in Cd37 -/- mice, we generated Cd37xIl6 double-knockout mice. These double-knockout and Il6 -/- mice displayed no glomerular IgA deposition and were protected from exacerbated renal failure following lipopolysaccharide treatment. Moreover, kidneys of Cd37 -/- mice showed more mesangial proliferation, endothelial cell activation, podocyte activation, and segmental podocyte foot process effacement compared to the double-knockout mice, emphasizing that IL-6 mediates renal pathology in Cd37 -/- mice. Thus, our study indicates that CD37 may protect against IgA nephropathy by inhibition of the IL-6 pathway., (Copyright © 2018 International Society of Nephrology. Published by Elsevier Inc. All rights reserved.)

The significance of interleukin 6 (IL-6) in long-term reference memory was tested in the Morris water maze (MWM) in 4-month-old C57BL/6J IL-6-deficient (IL-6 KO) and control mice. Three-day learning measured by escape latency time to find the hidden platform was comparable in both genotypes. In a single probe trial performed 7 days later, without the platform, latency to the platform site and path length to the target place were significantly shorter (p < 0.05 and p < 0.02, respectively), and platform-site crossovers more frequent (p < 0.05) in IL-6 KO mice. The swimming speed in IL-6 KO mice was significantly lower during learning (p = 0.0025) but not in the probe trial. Lack of differences between genotypes in a hole-board and in an elevated plus maze indicates that the observed effects were memory specific. The facilitatory effect of IL-6 deficiency on long-term reference memory in MWM indicates that IL-6 plays a role in consolidation process.

We examined the effects of tumor necrosis factor-α (TNFα) and interleukin-6 (IL6) gene knockout in preserving the bone loss induced by ovariectomy (OVX) and the mechanisms involved in bone metabolism. Twenty female wild-type (WT), TNFα -knockout (TNFα -/- ) or IL6- knockout (IL6 -/- ) mice aged 12 weeks were sham-operated (SHAM) or subjected to OVX and killed after 4 weeks. Bone mass and skeletal microarchitecture were determined using micro-CT. Bone marrow stromal cells (BMSCs) from all three groups (WT, TNFα -/- and IL6 -/- ) were induced to differentiate into osteoblasts or osteoclasts and treated with 17-β-estradiol. Bone metabolism was assessed by histological analysis, serum analyses and qRT-PCR. OVX successfully induced a high turnover in all mice, but a repair effect was observed in TNFα -/- and IL6 -/- mice. The ratio of femoral trabecular bone volume to tissue volume, trabecular number and trabecular thickness were significantly decreased in WT mice subjected to OVX, but increased in TNFα -/- mice (1.62, 1.34, 0.27-fold respectively; P  < 0.01) and IL6 -/- mice (1.34, 0.80, 0.22-fold respectively; P  < 0.01). Furthermore, we observed a 29.6% increase in the trabecular number in TNFα -/- mice when compared to the IL6 -/- mice. Both, TNFα -/- and IL6 -/- BMSCs exhibited decreased numbers of TRAP-positive cells and an increase in ALP-positive cells, with or without E2 treatment ( P  < 0.05). While the knockout of TNFα or IL6 significantly upregulated mRNA expressions of osteoblast-related genes ( Runx2 and Col1a1 ) and downregulated osteoclast-related mRNA for TRAP , MMP9 and CTSK in vivo and in vitro , TNFα knockout appeared to have roles beyond IL6 knockout in upregulating Col1a1 mRNA expression and downregulating mRNA expressions of WNT-related genes ( DKK1 and Sost ) and TNF-related activation-induced genes ( TRAF6 ). TNFα seemed to be more potentially invasive in inhibiting bone formation and enhancing TRAF6-mediated osteoclastogenesis than IL6, implying that the regulatory mechanisms of TNFα and IL6 in bone metabolism may be different., (© 2018 Society for Endocrinology.)

Arginase-1 (Arg-1)-expressing M2-like macrophages are associated with Th2-skewed immune responses, allergic airway pathology, ectopic B16 melanoma cancer growth in murine models, and can be induced by Oncostatin M (OSM) transient overexpression in vivo. Here, we compare OSM to the gp130-cytokine IL-6 in mediating macrophage polarization, and find that IL-6 overexpression alone (Ad vector, AdIL-6) did not induce Arg-1 protein in mouse lungs at day 7, nor ectopic melanoma tumor growth at day 14, in contrast to overexpression of OSM (AdOSM). AdOSM elevated levels of IL-4, IL-5 and IL-13 in bronchoalveolar lavage fluid, whereas AdIL-6 did not. Bone marrow-derived macrophages respond with Arg-1 enzymatic activity to M2 stimuli (IL-4/IL-13), which was further elevated in combination with IL-6 stimulation; however, OSM or LIF had no detectable activity in vitro. Arg-1 mRNA expression induced by AdOSM was attenuated in IL-6-/- and STAT6-/- mice, suggesting requirements for both IL-6 and IL-4/IL-13 signaling in vivo. Ectopic B16 tumor burden was also reduced in IL-6-/- mice. Thus, OSM induces Arg-1+ macrophage accumulation indirectly through elevation of Th2 cytokines and IL-6 in vivo, whereas IL-6 acts directly on macrophages but requires a Th2 microenvironment, demonstrating distinct roles for OSM and IL-6 in M2 macrophage polarization., (© 2017 Australasian Society for Immunology Inc.)

Olanzapine is a widely prescribed antipsychotic drug. While effective in reducing psychoses, treatment with olanzapine causes rapid increases in blood glucose. We wanted to determine if a single bout of exercise, immediately prior to treatment, would attenuate the olanzapine-induced rise in blood glucose and if this occurred in an IL-6 dependent manner. We found that exhaustive, but not moderate exercise, immediately prior to treatment, prevented olanzapine-induced hyperglycemia and this occurred in parallel with increases in serum IL-6. To determine if IL-6 was involved in the mechanisms through which exhaustive exercise protected against olanzapine-induced hyperglycemia several additional experiments were completed. Treatment with IL-6 (3 ng/g bw, IP) alone did not protect against olanzapine-induced increases in blood glucose. The protective effects of exhaustive exercise against olanzapine-induced increases in blood glucose were intact in whole body IL-6 knockout mice. Similarly, treating mice with an IL-6 neutralizing antibody prior to exhaustive exercise did not negate the protective effect of exercise against olanzapine-induced hyperglycemia. Our findings provide evidence that a single bout of exhaustive exercise protects against acute olanzapine-induced hyperglycemia and that IL-6 is neither sufficient, nor required for exercise to protect against increases in blood glucose with olanzapine treatment.

Objective: Obesity is associated with metabolic disorder and chronic inflammation that plays a crucial role in cardiovascular diseases. IL-6 is involved in regulating obesity-related lipid metabolism and inflammation. In this study, we sought to determine the role of IL-6 in high-fat diet (HFD)-induced cardiomyopathy and explore the signaling pathway., Methods: Female, 5-week-old IL-6 knockout (KO) and littermate mice were fed a normal diet (ND, 10% fat) or HFD (45% fat) for 14 weeks. At the end of treatment, cardiac function was assessed by echocardiography. Adipose tissues and plasma were collected for further measurement. Immunohistology of CD68 was performed to detect inflammation in the heart. Masson's trichrome staining and Oil Red O staining was applied to evaluated cardiac fibrosis and lipid accumulation. Real-time PCR and Western immunoblotting analyses on heart tissue were used to explore the underlying mechanism., Results: IL-6 KO mice displayed increased insulin resistance compared to WT mice at baseline. When fed HFD, IL-6 KO mice showed decreased gains in body weight and fat mass, increased insulin resistance relative to IL-6 KO mice feed ND. Furthermore, IL-6 KO mice developed cardiac dysfunction during HFD-induced obesity. Histological analysis suggested increased lipid accumulation, fibrosis and inflammation without affecting cardiac morphology during HFD treatment in the heart of IL-6 KO mice. Finally, IL-6 deficiency increased the phosphorylation of AMPK and ACC in the heart during HFD-induced obesity., Conclusion: Our results suggest that IL-6 contributes to limit lipid metabolic disorder, cardiac hypertrophy, fibrosis, inflammation and myocardium lipotoxicity during HFD-induced obesity., (Copyright © 2017 Elsevier B.V. All rights reserved.)

Aging is related to gradual increase of interleukin 6 (IL-6) plasma level that affects peroxisome proliferator-activated receptor (PPAR) expression. We evaluated age-related changes in cardiac expression of PPARα, its coactivator PGC-1α, and selected downstream proteins in mice with systemic IL-6 knockout (IL6KO). Male C57BL6/J wild-type (WT) and IL6KO mice were used at the age of 16-20 weeks (young) and 24-30 months (senescent). Echocardiography and electron microscopy were applied to assess the function and ultrastructure of the heart. Western blotting and quantitative real-time PCR were used to estimate protein and mRNA levels of selected genes. PPARα expression in the myocardium of young IL6KO animals is lower and remains unchanged with aging, whereas in WT mice it declines with age and in both senescent groups it is equal. We observed aging-related upregulation of PGC-1α and less pronounced decline of Sirt3 in IL6KO animals; the level of cytochrome C was significantly decreased in IL6KO group only, suggesting disturbed mitochondrial function, which was not sufficient to evoke obvious changes in cardiac performance and function assessed by echocardiography. IL-6 and aging are involved in regulation of PPARα and PGC-1α expression and may influence the mitochondrial function.

Ginseng (Panax ginseng), an herbal medicine, has been used to prevent neurodegenerative disorders. Ginsenosides (e.g., Re, Rb1, or Rg1) were obtained from Korean mountain cultivated ginseng. The anticonvulsant activity of ginsenoside Re (20 mg/kg/day × 3) against trimethyltin (TMT) insult was the most pronounced out of ginsenosides (e.g., Re, Rb1, and Rg1). Re itself did not significantly alter tumor necrosis factor-α (TNF-α), interferon-ϒ (IFN-ϒ), and interleukin-1β (IL-1β) expression, however, it significantly increases the interleukin-6 (IL-6) expression. In addition, Re attenuated the TMT-induced decreases in IL-6 protein level. Therefore, IL-6 knockout (-/-) mice were employed to investigate whether Re requires IL-6-dependent neuroprotective activity against TMT toxicity. Re significantly attenuated TMT-induced lipid peroxidation, protein peroxidation, and reactive oxygen species in the hippocampus. Re-mediated antioxidant effects were more pronounced in IL-6 (-/-) mice than in WT mice. Consistently, TMT-induced increase in c-Fos-immunoreactivity (c-Fos-IR), TUNEL-positive cells, and nuclear chromatin clumping in the dentate gyrus of the hippocampus were significantly attenuated by Re. Furthermore, Re attenuated TMT-induced proapoptotic changes. Protective potentials by Re were comparable to those by recombinant IL-6 protein (rIL-6) against TMT-insult in IL-6 (-/-) mice. Moreover, treatment with a phosphoinositol 3-kinase (PI3K) inhibitor, LY294002 (1.6 µg, i.c.v) counteracted the protective potential mediated by Re or rIL-6 against TMT insult. The results suggest that ginsenoside Re requires IL-6-dependent PI3K/Akt signaling for its protective potential against TMT-induced neurotoxicity.

Glucagon-like peptide 1 (GLP-1) is a hormone released from enteroendocrine L cells. Although first described as a glucoregulatory incretin hormone, GLP-1 also suppresses inflammation and promotes mucosal integrity. Here, we demonstrate that plasma GLP-1 levels are rapidly increased by lipopolysaccharide (LPS) administration in mice via a Toll-like receptor 4 (TLR4)-dependent mechanism. Experimental manipulation of gut barrier integrity after dextran sodium sulfate treatment, or via ischemia/reperfusion experiments in mice, triggered a rapid rise in circulating GLP-1. This phenomenon was detected prior to measurable changes in inflammatory status and plasma cytokine and LPS levels. In human subjects, LPS administration also induced GLP-1 secretion. Furthermore, GLP-1 levels were rapidly increased following the induction of ischemia in the human intestine. These findings expand traditional concepts of enteroendocrine L cell biology to encompass the sensing of inflammatory stimuli and compromised mucosal integrity, linking glucagon-like peptide secretion to gut inflammation., (Copyright © 2017 The Authors. Published by Elsevier Inc. All rights reserved.)

Conquering immunosuppression in tumor microenvironments is crucial for effective cancer immunotherapy. It is well known that interleukin (IL)-6, a pleiotropic cytokine, is produced in the tumor-bearing state. In the present study, we investigated the precise effects of IL-6 on antitumor immunity and the subsequent tumorigenesis in tumor-bearing hosts. CT26 cells, a murine colon cancer cell line, were intradermally injected into wild-type and IL-6-deficient mice. As a result, we found that tumor growth was decreased significantly in IL-6-deficient mice compared with wild-type mice and the reduction was abrogated by depletion of CD8 + T cells. We further evaluated the immune status of tumor microenvironments and confirmed that mature dendritic cells, helper T cells and cytotoxic T cells were highly accumulated in tumor sites under the IL-6-deficient condition. In addition, higher numbers of interferon (IFN)-γ-producing T cells were present in the tumor tissues of IL-6-deficient mice compared with wild-type mice. Surface expression levels of programmed death-ligand 1 (PD-L1) and MHC class I on CT26 cells were enhanced under the IL-6-deficient condition in vivo and by IFN-γ stimulation in vitro. Finally, we confirmed that in vivo injection of an anti-PD-L1 antibody or a Toll-like receptor 3 ligand, polyinosinic-polycytidylic acid, effectively inhibited tumorigenesis under the IL-6-deficient condition. Based on these findings, we speculate that a lack of IL-6 produced in tumor-bearing host augments induction of antitumor effector T cells and inhibits tumorigenesis in vivo, suggesting that IL-6 signaling may be a promising target for the development of effective cancer immunotherapies., (© 2017 The Authors. Cancer Science published by John Wiley & Sons Australia, Ltd on behalf of Japanese Cancer Association.)

Multiple cytokines, including interleukin 6 (IL-6), IL-11, IL-27, oncostatin M (OSM), and leukemia inhibitory factor (LIF), signal via the common GP130 cytokine receptor subunit. In this study, we describe a patient with a homozygous mutation of IL6ST (encoding GP130 p.N404Y) who presented with recurrent infections, eczema, bronchiectasis, high IgE, eosinophilia, defective B cell memory, and an impaired acute-phase response, as well as skeletal abnormalities including craniosynostosis. The p.N404Y missense substitution is associated with loss of IL-6, IL-11, IL-27, and OSM signaling but a largely intact LIF response. This study identifies a novel immunodeficiency with phenotypic similarities to STAT3 hyper-IgE syndrome caused by loss of function of GP130., (© 2017 Schwerd et al.)

Introduction: Leptin is thought to play an important role in the regulation of the immune system. In patients, leptin is inversely proportional to interleukin-6 (IL-6) levels. Thus, the objective of our study was to evaluate a dose-dependent therapeutic impact of leptin with possible IL-6-dependency on immune actions and outcome in a trauma/sepsis model., Materials and Methods: Sixty-nine wild-type and 63 IL-6 mice were subdivided into three groups: trauma/sepsis group (first hit: femur fracture and hemorrhage; second hit: cecal ligation and puncture 2 days later), trauma group (first hit and laparotomy), sham group (laparotomy only). Each group received vehicle or leptin (2.5 μg/g (leptin1) or 5 μg/g (leptin2)) subcutaneously and was observed for 8 days after induction of the first hit. Mortality, humoral, and cellular immune markers were determined., Results: We revealed a dose-dependent anti-inflammatory effect of exogenous leptin in the sepsis groups and to some extent a pro-inflammatory effect in the sham groups. Leptin administration resulted in a decreased mortality in septic wild-type mice (trauma/sepsis vehicle group: 36.4%, trauma/sepsis leptin1 group: 25%, trauma/sepsis leptin2 group: 0%) and in an increased mortality in septic IL-6 mice (53.8%, 83.4%, 100%). All mice of the trauma groups and sham groups survived. In wild-type trauma/sepsis mice, exogenous leptin led to increased levels of CD4 and CD8 in the spleen, and a less pronounced type IV hypersensitivity (P ≤ 0.039). Furthermore, it decreased the levels of tumor necrosis factor-α and IL-6, not reaching statistical significance., Conclusions: Due to the fact that leptin administration to traumatized and septic mice seems to have a positive effect on their outcome via IL-6 and does not negatively impact their medical condition if applied preventively, leptin might be a therapeutic agent for the prevention, or treatment of sepsis-related detrimental outcome after initial trauma.

The aim of the present work was to further explore the physiological roles of muscle-derived IL-6. Adult-floxed and conditional skeletal muscle IL-6 knock out male and female mice were used to study energy expenditure (indirect calorimetry at rest and during treadmill exercise, and body temperature cycle during the light phase) and energy intake (response to fast/refeeding). We also evaluated the responses to leptin and the activity of the insulin signalling pathway in skeletal muscle and liver by phosphorylation of Akt at Ser 473. The stress response was also studied. Results indicate a relevant role of muscle IL-6 in maintaining energy homeostasis, especially in males. Absence of muscle IL-6 in male mice results in lower core body temperature in the light phase, increased respiratory exchange ratio (RER) both at rest and during exercise, increased expression of TCA cycle marked gene, citrate synthase in muscle, reduced fat storage and decreased body weight and food consumption in response to leptin. In females, muscle IL-6 deficiency increases VO2 and CO2 levels similarly. Also in contrast to males, energy expenditure (EE) measured over 48h reveals a significant elevation in female mice with muscle IL-6 deficiency; moreover, they show a modified response to fasting-refeeding and to restraint stress. The present results contribute to the understanding of the role of muscle IL-6 in male and female mouse metabolism, not only during exercise but also in the basal state and in situations where energy balance is altered.

Interleukin 6 (IL-6) is involved in innate and adaptive immune responses to defend against pathogens. It also participates in the process of influenza infection by affecting viral clearance and immune cell responses. However, whether IL-6 impacts lung repair in influenza pathogenesis remains unclear. Here, we studied the role of IL-6 in acute influenza infection in mice. IL-6-deficient mice infected with influenza virus exhibited higher lethality, lost more body weight and had higher fibroblast accumulation and lower extracellular matrix (ECM) turnover in the lung than their wild-type counterparts. Deficiency in IL-6 enhanced proliferation, migration and survival of lung fibroblasts, as well as increased virus-induced apoptosis of lung epithelial cells. IL-6-deficient lung fibroblasts produced elevated levels of TGF-β, which may contribute to their survival. Furthermore, macrophage recruitment to the lung and phagocytic activities of macrophages during influenza infection were reduced in IL-6-deficient mice. Collectively, our results indicate that IL-6 is crucial for lung repair after influenza-induced lung injury through reducing fibroblast accumulation, promoting epithelial cell survival, increasing macrophage recruitment to the lung and enhancing phagocytosis of viruses by macrophages. This study suggests that IL-6 may be exploited for lung repair during influenza infection.

Basophils are rare, circulating granulocytes proposed to be involved in T helper (T H ) type 2 immunity, mainly through secretion of interleukin (IL)-4. In addition to IL-4, basophils produce IL-6 and tumor necrosis factor (TNF)-α in response to immunoglobulin E (IgE) crosslinking. Differentiation of T H 17 cells requires IL-6 and transforming growth factor (TGF)-β, but whether basophils play a significant role in T H 17 induction is unknown. Here we show a role for basophils in T H 17 cell development by using in vitro T cell differentiation and in vivo T H 17-mediated inflammation models. Bone marrow derived-basophils (BMBs) and splenic basophils produce significant amounts of IL-6 as well as IL-4 following stimulation with IgE crosslink or cholera toxin (CT). In addition, through IL-6 secretion, BMBs cooperate with dendritic cells to promote T H 17 cell differentiation. In the T H 17 lung inflammation model, basophils are recruited to the inflamed lungs following CT challenge, and T H 17 responses are significantly reduced in the absence of basophils or IL-6. Furthermore, reconstitution with wild-type, but not IL-6-deficient, basophils restored CT-mediated lung inflammation. Lastly, basophil-deficient mice showed reduced phenotypes of T H 17-dependent experimental autoimmune encephalomyelitis. Therefore, our results indicate that basophils are an important inducer of T H 17 cell differentiation, which is dependent on IL-6 secretion., Competing Interests: The authors declare no competing financial interests.

Radiotherapy is effective in reducing primary tumors, however, it may enhance macrophage infiltration to tumor sites, accelerating tumor progression in several ways. We investigated whether radiation can increase macrophage infiltration into non-small cell lung carcinoma (NSCLC) cells. Analysis of in vitro macrophage (differentiated THP-1 cells) migration to either nonirradiated or irradiated tumor cells showed increased migration to the irradiated tumor cells. Because the IL-6 levels in A549 and H157 cells were significantly increased after irradiation, we then investigated whether this increased IL-6 level contributes to radiation-induced macrophage migration. Radiation-induced macrophage infiltration was reduced when IL-6 was knocked down in tumor cells, indicating a positive IL-6 role in this process. To validate this in vitro result, an orthotopic mouse model was developed using a luciferase-tagged H157siIL-6/scramble control (sc) cell set. After tumors developed, the lungs were irradiated, and infiltration of endogenous macrophages and tail-vein injected fluorescent macrophages to tumor sites was investigated. In both groups, increased macrophage infiltration was observed in H157sc cell-derived xenografts compared to H157siIL-6 cell-derived xenografts, confirming the positive IL-6 role in the radiation-induced macrophage infiltration process. In mechanistic dissection studies, radiation-induced up-regulation of CCL2 and CCL5 by IL-6 was detected, and blocking the action of CCL2/CCL5 molecules significantly reduced the number of migrated macrophages to tumor cells after irradiation. These results demonstrate that targeting the IL-6 signaling or CCL2/CCL5 molecules in combination with conventional radiotherapy potentially blocks undesired radiation-induced macrophage infiltration.

The hypermetabolic stress response after burn contributes to multi-organ failure, sepsis, morbidity, and mortality. The cytokine interleukin 6 (IL-6) has been hypothesized to mediate not only white adipose tissue (WAT) browning in burns, but also other hypermetabolic conditions. In addition to its inflammatory effects, IL-6 also acts as a metabolic mediator that affects metabolic tissues. Therefore, we sought to uncover the origin of circulating IL-6 post burn injury that regulates WAT browning. WAT and sera samples were collected from both adult burn patients admitted to the Ross Tilley Burn Centre at Sunnybrook Hospital and mice subjected to a burn injury. Collected tissues were analyzed for browning markers and metabolic state via histology, gene expression, and resting energy expenditure. Increased WAT browning was observed in burn patients as well as mice subjected to burn injury. Circulating IL-6 levels were significantly elevated post burn injury in mice (<0.05) and in burn patients (<0.05), the latter of which was positively correlated with elevated REE. Genetic loss of whole body IL-6 in mice prevented burn-induced WAT browning. Transplanting IL-6 knockout (KO) mice with bone marrow (BM) from wild-type (WT) mice, recovered the browning phenotype in these mice, as evaluated by increased uncoupling protein 1 (UCP1) expression (<0.05). Conversely, transplanting irradiated WT mice with BM from IL-6 KO mice impaired burn induced browning with no significant expression of UCP1. Together, our findings implicate BM derived IL-6 as the source controlling browning of WAT post burn injury. Thus, targeting IL-6 is a promising target for hypermetabolism in burns., Competing Interests: Authors have no conflicts of interest to declare.

Psoriasis patients are at increased risk of heart attack and stroke and have elevated MRP8/14 levels that predict heart attack. The KC-Tie2 psoriasiform mouse model exhibits elevated MRP8/14 and is prothrombotic. Mrp14 -/- mice, in contrast, are protected from thrombosis, but, surprisingly, KC-Tie2x Mrp14 -/- mice remain prothrombotic. Treating KC-Tie2x Mrp14 -/- mice with anti-IL-23p19 antibodies reversed the skin inflammation, improved thrombosis, and decreased IL-6. In comparison, IL-6 deletion from KC-Tie2 animals improved thrombosis despite sustained skin inflammation, suggesting that thrombosis improvements following IL-23 inhibition occur secondary to IL-6 decreases. Psoriasis patient skin has elevated IL-6 and IL-6 receptor is present in human coronary atheroma, supporting a link between skin and distant vessel disease in patient tissue. Together, these results identify a critical role for skin-derived IL-6 linking skin inflammation with thrombosis, and shows that in the absence of IL-6 the connection between skin inflammation and thrombosis comorbidities is severed., Competing Interests: The authors declare that no conflict of interest exists.

In patients with cancer, the wasting syndrome, cachexia, is associated with caloric deficiency. Here, we describe tumor-induced alterations of the host metabolic response to caloric deficiency that cause intratumoral immune suppression. In pre-cachectic mice with transplanted colorectal cancer or autochthonous pancreatic ductal adenocarcinoma (PDA), we find that IL-6 reduces the hepatic ketogenic potential through suppression of PPARalpha, the transcriptional master regulator of ketogenesis. When these mice are challenged with caloric deficiency, the resulting relative hypoketonemia triggers a marked rise in glucocorticoid levels. Multiple intratumoral immune pathways are suppressed by this hormonal stress response. Moreover, administering corticosterone to elevate plasma corticosterone to a level that is lower than that occurring in cachectic mice abolishes the response of mouse PDA to an immunotherapy that has advanced to clinical trials. Therefore, tumor-induced IL-6 impairs the ketogenic response to reduced caloric intake, resulting in a systemic metabolic stress response that blocks anti-cancer immunotherapy., (Copyright © 2016 The Authors. Published by Elsevier Inc. All rights reserved.)

Background: There have been no previous studies regarding whether combined use of Polymyxin B-immobilized fiber column direct hemoperfusion (PMX-DHP) and continuous hemodiafiltration (CHDF) is helpful in the treatment of preterm infants with systemic inflammatory response syndrome (SIRS) and hypercytokinemia., Methods: A retrospective review was carried out of 18 SIRS infants born at gestational week 24-28. Eight with blood interleukin (IL)-6 ≥ 1000 pg/mL were treated actively with 2 h PMX-DHP followed by 2 h PMX-DHP and CHDF. Ten with IL-6 < 500 pg/mL were treated conventionally (with neither PMX-DHP nor CHDF) and served as controls., Results: Demographic characteristics were similar except for IL-6, arterial-to-alveolar oxygen tension ratio (a/APO 2 ), and number of immature neutrophils between the two groups. Baseline a/APO 2 was significantly lower in infants with than without active treatment (0.44 vs 0.67, respectively, P = 0.002). After 4 h treatment, the IL-6 decreased to < 500 pg/mL in all eight infants, and a/APO 2 improved significantly to 0.62 (P = 0.006). Bronchopulmonary dysplasia occurred in a similar proportion (63%, 5/8 vs 80%, 8/10, respectively), but the number of days on inhaled oxygen (30 vs 47 days, respectively, P = 0.033) and tracheal intubation (36 vs 51 days, respectively, P = 0.040) was significantly lower in infants with than without active treatment. Prevalence of adverse events was similar (13%, 1/8 vs 50%, 5/10 for active vs conventional treatment, respectively)., Conclusion: Active treatment with PMX-DHP and CHDF was helpful in the reduction of days on inhaled oxygen and tracheal intubation in preterm SIRS infants with hypercytokinemia. Further prospective randomized studies are warranted., (© 2016 Japan Pediatric Society.)

During intraocular bacterial infections, the primary innate responders are neutrophils, which may cause bystander damage to the retina or perturb the clarity of the visual axis. We hypothesized that cytokine IL-6 and chemokine CXCL1 contributed to rapid neutrophil recruitment during Bacillus cereus endophthalmitis, a severe form of intraocular infection that is characterized by explosive inflammation and retinal damage that often leads to rapid vision loss. To test this hypothesis, we compared endophthalmitis pathogenesis in C57BL/6J, IL-6 -/- , and CXCL1 -/- mice. Bacterial growth in eyes of CXCL1 -/- , IL-6 -/- , and C67BL/6J mice was similar. Retinal function retention was greater in eyes of IL-6 -/- and CXCL1 -/- mice compared with that of C57BL/6J, despite these eyes having similar bacterial burdens. Neutrophil influx into eyes of CXCL1 -/- mice was reduced to a greater degree compared with that of eyes of IL6 -/- mice. Histology confirmed significantly less inflammation in eyes of CXCL1 -/- mice, but similar degrees of inflammation in IL6 -/- and C57BL/6J eyes. Because inflammation was reduced in eyes of infected CXCL1 -/- mice, we tested the efficacy of anti-CXCL1 in B. cereus endophthalmitis. Retinal function was retained to a greater degree and there was less overall inflammation in eyes treated with anti-CXCL1, which suggested that anti-CXCL1 may have therapeutic efficacy in limiting inflammation during B. cereus endophthalmitis. Taken together, our results indicate that absence of IL-6 did not affect overall pathogenesis of endophthalmitis. In contrast, absence of CXCL1, in CXCL1 -/- mice or after anti-CXCL1 treatment, led to an improved clinical outcome. Our findings suggest a potential benefit in targeting CXCL1 to control inflammation during B. cereus and perhaps other types of intraocular infections., (© Society for Leukocyte Biology.)