STAT3 targets the regulatory regions of gluconeogenic genes in vivo

Early transcriptional effects of inflammatory cytokines reveal highly redundant cytokine networks

Inflammatory cytokines are fundamental mediators of the organismal response to injury, infection, or other harmful stimuli. To elucidate the early and mostly direct transcriptional signatures of inflammatory cytokines, we profiled all immunologic cell types by RNAseq after systemic exposure to IL1β, IL6, and TNFα. Our results revealed a significant overlap in the responses, with broad divergence between myeloid and lymphoid cells, but with very few cell-type-specific responses. Pathway and motif analysis identified several main controllers (NF-κB, IRF8, and PU.1), but the largest portion of the response appears to be mediated by MYC, which was also implicated in the response to γc cytokines. Indeed, inflammatory and γc cytokines elicited surprisingly similar responses (∼50% overlap in NK cells). Significant overlap with interferon-induced responses was observed, paradoxically in lymphoid but not myeloid cell types. These results point to a highly redundant cytokine network, with intertwined effects between disparate cytokines and cell types.

Hepatic gluconeogenesis and PDK3 upregulation drive cancer cachexia in flies and mice

Cachexia, a severe wasting syndrome characterized by tumour-induced metabolic dysregulation, is a leading cause of death in people with cancer, yet its underlying mechanisms remain poorly understood. Here we show that a longitudinal full-body single-nuclei-resolution transcriptome analysis in a Drosophila model of cancer cachexia captures interorgan dysregulations. Our study reveals that the tumour-secreted interleukin-like cytokine Upd3 induces fat-body expression of Pepck1 and Pdk, key regulators of gluconeogenesis, disrupting glucose metabolism and contributing to cachexia. Similarly, in mouse cancer cachexia models, we observe IL-6-JAK-STAT-signalling-mediated induction of Pck1 and Pdk3 expression in the liver. Increased expression of these genes in fly, mouse, and human correlates with poor prognosis, and hepatic expression of Pdk3 emerges as a previously unknown mechanism contributing to metabolic dysfunction in cancer cachexia. This study highlights the conserved nature of tumour-induced metabolic disruptions and identifies potential therapeutic targets to mitigate cachexia in people with cancer.

A strategic review of STAT3 signaling inhibition by phytochemicals for cancer prevention and treatment: Advances and insights

Cancer remains a significant global health concern. The dysregulation of signaling networks in tumor cells greatly affects their functions. This review intends to explore phytochemicals possessing potent anticancer properties that specifically target the STAT3 signaling pathway, elucidating strategies and emphasizing their potential as promising candidates for cancer therapy. The review comprehensively examines various STAT3 inhibitors designed to disrupt the signaling cascade, including those targeting upstream activation, SH2 domain phosphorylation, DNA binding domain (DBD), N-terminal domain (NTD), nuclear translocation, and enhancing endogenous STAT3 negative regulators. A literature review was conducted to identify phytochemicals with anticancer activity targeting the STAT3 signaling pathway. Popular research databases such as Google Scholar, PubMed, Science Direct, Scopus, Web of Science, and ResearchGate were searched from the years 1989 - 2023 based on the keywords "Cancer", "STAT3", "Phytochemicals", "Phytochemicals targeting STAT3 signaling", "upstream activation of STAT3", "SH2 domain of STAT3", "DBD of STAT3", "NTD of STAT3, "endogenous negative regulators of STAT3", or "nuclear translocation of STAT3", and their combinations. A total of 264 relevant studies were selected and analyzed based on the mechanisms of action and the efficacy of the phytocompounds. The majority of the discussed phytochemicals primarily focus on inhibiting upstream activation of STAT3. Additionally, flavonoid and terpenoid compounds exhibit multifaceted effects by targeting one or more checkpoints within the STAT3 pathway. Analysis reveals that phytochemicals targeting upstream activation predominantly belong to the classes of flavonoids and terpenoids, which hold significant promise as effective anticancer therapeutics. Future research in this field can be directed towards exploring and developing these scrutinized classes of phytochemicals to achieve desired therapeutic outcomes in cancer treatment.

Dibutyl phthalate adsorbed on multi-walled carbon nanotubes can aggravate liver injury in mice via the Jak2/STAT3 pathway

Phthalic acid esters (PAEs) and carbon nanotubes (CNTs) are common environmental pollutants and may degrade differently with different resulting biotoxicity, when present together. This study investigated the toxicological effects of singular or combined exposure to dibutyl phthalate (DBP) and multi-walled carbon nanotubes (MWCNTs) in KM mice. Results indicated that combined exposure led to slower weight gain and an increased leukocyte count in the blood, as well as liver tissue lesions and downregulation of organ coefficients. Additionally, alanine aminotransferase (ALT) and aspartate aminotransferase (AST) were elevated in the liver, and glucose, pyruvate, triglyceride (TG), and total cholesterol (T-CHO) were significantly reduced, suggesting compromised liver function. Furthermore, mRNA levels of genes related to hepatic glucose and lipid metabolism were significantly altered. These findings suggest that combined exposure to DBP and MWCNTs can have severe impacts on liver function in mice, highlighting the importance of considering interactions between multiple contaminants in environmental risk assessments.

Metabolic Enzymes in Viral Infection and Host Innate Immunity

Metabolic enzymes are central players for cell metabolism and cell proliferation. These enzymes perform distinct functions in various cellular processes, such as cell metabolism and immune defense. Because viral infections inevitably trigger host immune activation, viruses have evolved diverse strategies to blunt or exploit the host immune response to enable viral replication. Meanwhile, viruses hijack key cellular metabolic enzymes to reprogram metabolism, which generates the necessary biomolecules for viral replication. An emerging theme arising from the metabolic studies of viral infection is that metabolic enzymes are key players of immune response and, conversely, immune components regulate cellular metabolism, revealing unexpected communication between these two fundamental processes that are otherwise disjointed. This review aims to summarize our present comprehension of the involvement of metabolic enzymes in viral infections and host immunity and to provide insights for potential antiviral therapy targeting metabolic enzymes.

Insights into the mechanism of growth and fat deposition by feeding different levels of lipid provided by transcriptome analysis of swamp eel (Monopterus albus, Zuiew 1793) liver

Lipid is an important source of energy in fish feeds, and the appropriate fat content can improve the efficiency of protein utilization. However, excessive lipid content in the feed can lead to abnormal fat deposition in fish, which has a negative effect on the growth of fish. Therefore, the effects of feed lipid levels on swamp eel were studied. Essential functional genes were screened using transcriptomics. We divided 840 fish into seven groups (four replicates). A mixture of fish and soybean oils (1:4), 0%, 2%, 4%, 6%, 8%, 10%, and 12% was added to the basic feed were named groups one to seven (L1-L7), respectively. Isonitrogenous diets were fed swamp eel for 10 weeks. Growth performance, visceral index, nutritional components, and biochemical indexes were measured and analyzed. Livers of the 0%, 6%, and 12% groups were subjected to transcriptome sequencing analysis. The results of our study showed that: the suitable lipid level for the growth of swamp eel was 7.03%; the crude fat content of whole fish, liver, intestine, muscle, and skin increased with the increase of lipid level, with some significant difference, and excess fat was deposited in skin tissue; triglyceride, total cholesterol, and free fatty acid contents increased with the increase of feed lipid level. High-density lipoprotein levels in the L3 and L4 groups were higher than in the other groups. Blood glucose concentrations in the L5, L6, and L7 groups increased; the liver tissue structure was damaged when the lipid level was too high. two-hundred-and-twenty-eight differentially expressed genes were found. Several critical pathways regulating glucose metabolism and energy balance (e.g., glycerolipid metabolism, glycolysis synthesis, degradation of ketone bodies, and Janus Kinase/Signal Transducer and Activator of Transcription signaling pathway) were enriched in swamp eel compared with the Kyoto Encyclopedia of Genes and Genomes (KEGG) database. Suitable lipid levels (7.03%) can promote the growth of swamp eel, and excessive lipid levels can cause elevated blood lipids and lead to liver cell damage. Regulatory mechanisms may involve multiple metabolic pathways for glucose and lipid metabolism in eels. This study provides new insights to explain the mechanism of fat deposition due to high levels of lipid and provides a basis for the production of efficient and environmentally friendly feed for swamp eel.

Signaling pathways and intervention for therapy of type 2 diabetes mellitus

Type 2 diabetes mellitus (T2DM) represents one of the fastest growing epidemic metabolic disorders worldwide and is a strong contributor for a broad range of comorbidities, including vascular, visual, neurological, kidney, and liver diseases. Moreover, recent data suggest a mutual interplay between T2DM and Corona Virus Disease 2019 (COVID-19). T2DM is characterized by insulin resistance (IR) and pancreatic β cell dysfunction. Pioneering discoveries throughout the past few decades have established notable links between signaling pathways and T2DM pathogenesis and therapy. Importantly, a number of signaling pathways substantially control the advancement of core pathological changes in T2DM, including IR and β cell dysfunction, as well as additional pathogenic disturbances. Accordingly, an improved understanding of these signaling pathways sheds light on tractable targets and strategies for developing and repurposing critical therapies to treat T2DM and its complications. In this review, we provide a brief overview of the history of T2DM and signaling pathways, and offer a systematic update on the role and mechanism of key signaling pathways underlying the onset, development, and progression of T2DM. In this content, we also summarize current therapeutic drugs/agents associated with signaling pathways for the treatment of T2DM and its complications, and discuss some implications and directions to the future of this field.

Tumor Cytokine-Induced Hepatic Gluconeogenesis Contributes to Cancer Cachexia: Insights from Full Body Single Nuclei Sequencing

A primary cause of death in cancer patients is cachexia, a wasting syndrome attributed to tumor-induced metabolic dysregulation. Despite the major impact of cachexia on the treatment, quality of life, and survival of cancer patients, relatively little is known about the underlying pathogenic mechanisms. Hyperglycemia detected in glucose tolerance test is one of the earliest metabolic abnormalities observed in cancer patients; however, the pathogenesis by which tumors influence blood sugar levels remains poorly understood. Here, utilizing a Drosophila model, we demonstrate that the tumor secreted interleukin-like cytokine Upd3 induces fat body expression of Pepck1 and Pdk, two key regulatory enzymes of gluconeogenesis, contributing to hyperglycemia. Our data further indicate a conserved regulation of these genes by IL-6/JAK-STAT signaling in mouse models. Importantly, in both fly and mouse cancer cachexia models, elevated gluconeogenesis gene levels are associated with poor prognosis. Altogether, our study uncovers a conserved role of Upd3/IL-6/JAK-STAT signaling in inducing tumor-associated hyperglycemia, which provides insights into the pathogenesis of IL-6 signaling in cancer cachexia.

Correlation between improved leptin signaling and cognitive function post bariatric surgery

Determining whether changes in leptin signaling plays a role in the improvement of cognitive function post-bariatric surgery may aid in the understanding and development of novel therapeutic approaches targeting cognitive dysfunction through the greater understanding of processes connecting obesity and brain health. Several studies have explored the effects of cognition post bariatric surgery, and others have studied leptin and its changes post surgery. However the amalgamation of the effects of leptin signaling in relation to cognition post bariatric surgery have yet to be considered as key tools in the understanding of cognitive dysfunction in obese subjects with leptin resistance or insensitivity. This review serves to highlight the potential correlations, to further elucidate the effect of improved leptin signaling on cognition post bariatric surgery, and to propose a direct cause for the improvement of cognitive function via the amelioration of the leptin Janus kinase/Signal transducer and activator of transcription (JAK/STAT) signaling pathway as a result of the reversal of inflammatory processes involved in diseased individuals.

Adipose tissue macrophages in remote modulation of hepatic glucose production

Hepatic glucose production (HGP) is fine-regulated via glycogenolysis or gluconeogenesis to maintain physiological concentration of blood glucose during fasting-feeding cycle. Aberrant HGP leads to hyperglycemia in obesity-associated diabetes. Adipose tissue cooperates with the liver to regulate glycolipid metabolism. During these processes, adipose tissue macrophages (ATMs) change their profiles with various physio-pathological settings, producing diverse effects on HGP. Here, we briefly review the distinct phenotypes of ATMs under different nutrition states including feeding, fasting or overnutrition, and detail their effects on HGP. We discuss several pathways by which ATMs regulate hepatic gluconeogenesis or glycogenolysis, leading to favorable or unfavorable metabolic consequences. Furthermore, we summarize emerging therapeutic targets to correct metabolic disorders in morbid obesity or diabetes based on ATM-HGP axis. This review puts forward the importance and flexibility of ATMs in regulating HGP, proposing ATM-based HGP modulation as a potential therapeutic approach for obesity-associated metabolic dysfunction.

Pcyt2 deficiency causes age-dependant development of nonalcoholic steatohepatitis and insulin resistance that could be attenuated with phosphoethanolamine

The mechanisms of NASH development in the context of age and genetics are not fully elucidated. This study investigates the age-dependent liver defects during NASH development in mice with heterozygous deletion of Pcyt2 (Pcyt2^+/−), the rate limiting enzyme in phosphatidylethanolamine (PE) synthesis. Further, the therapeutic potential of Pcyt2 substrate, phosphoethanolamine (PEtn), is examined. Pcyt2^+/− were investigated at 2 and 6–8 months (mo) of age and in addition, 6-mo old Pcyt2^+/− with developed NASH were supplemented with PEtn for 8 weeks and glucose and fatty acid metabolism, insulin signaling, and inflammation were examined. Heterozygous ablation of Pcyt2 causes changes in liver metabolic regulators from young age, prior to the development of liver disease which does not occur until adulthood. Only older Pcyt2^+/− experiences perturbed glucose and fatty acid metabolism. Older Pcyt2^+/− liver develops NASH characterized by increased glucose production, accumulation of TAG and glycogen, and increased inflammation. Supplementation with PEtn reverses Pcyt2^+/− steatosis, inflammation, and other aspects of NASH, showing that was directly caused by Pcyt2 deficiency. Pcyt2 deficiency is a novel mechanism of metabolic dysregulation due to reduced membrane ethanolamine phospholipid synthesis, and the metabolite PEtn offers therapeutic potential for NASH reversion.

Epigenetic regulation of epithelial dectin-1 through an IL-33-STAT3 axis in allergic disease

Allergic diseases arise in susceptible individuals in part because of decrements in protective pathways. The mechanism by which these anti-inflammatory molecules become repressed remains unclear. We have previously reported that epithelial dectin-1 prevents aberrant type 2 responses and is downregulated in the epithelium of allergic patients. Here, we report that dectin-1 is constitutively expressed by the respiratory epithelium in humans and that IL-33 specifically acts as a repressor of dectin-1. Mechanistically, this occurs via IL-33-dependent STAT3 activation and the subsequent repression of the dectin-1 gene, CLEC7A. We have identified a novel enhancer region upstream of the proximal promoter of CLEC7A that is only accessible in epithelial cells, but not in hematopoietic cells. Epigenetic repression of CLEC7A through this newly identified locus, downstream of an aberrant IL-33-STAT3 axis, occurs in the epithelium of allergic individuals. Collectively, our data identify a mechanism of epigenetic fine-tuning of dectin-1 expression in epithelial cells that may participate in allergenicity.

Suppressor of cytokine signalling-2 controls hepatic gluconeogenesis and hyperglycemia by modulating JAK2/STAT5 signalling pathway

Hepatic gluconeogenesis plays a crucial role in maintaining blood glucose homeostasis in mammals. Globe knockout of suppressor of cytokine signalling-2 (SOCS2), a feedback inhibitor of cytokine signalling, has been shown resistant to high-fat-diet (HFD)-induced hepatic steatosis with impaired glucose tolerance in mice. However, the underlying mechanism of SOCS2 regulates hepatic glucose homeostasis still undefined. In the present study, we demonstrated that the hepatic SOCS2 expression is markedly reduced in fasted C57BL/6 J mice or db/db mice. Moreover, hepatic SOCS2 expression levels are induced by metformin treatment. Ablation of SOCS2 attenuates suppressing effects of metformin on gluconeogenesis in hepatocytes. Gain- and loss-of-function studies indicated that SOCS2 regulates hepatic gluconeogenic genes expression and glucose output by mediating JAK2/STAT5 signalling pathway in db/db mice. Mechanistically, we observed that SOCS2 inactivates STAT5 by attenuating the interaction between JAK2 and STAT5, which in turn reduces hepatic gluconeogenesis. The present study reveals a critical role of SOCS2 in regulating hepatic gluconeogenesis. The inhibitory effect of metformin on gluconeogenesis is mediated, at least in part, by upregulating SOCS2 and therefore reducing hepatic gluconeogenic genes expression. SOCS2 may represent a new therapeutic target for the treatment of diabetes.

Blood glucose regulation in context of infection

The immune and endocrine systems collectively control homeostasis in the body. The endocrine system ensures that values of essential factors and nutrients such as glucose, electrolytes and vitamins are maintained within threshold values. The immune system resolves local disruptions in tissue homeostasis, caused by pathogens or malfunctioning cells. The immediate goals of these two systems do not always align. The immune system benefits from optimal access to nutrients for itself and restriction of nutrient availability to all other organs to limit pathogen replication. The endocrine system aims to ensure optimal nutrient access for all organs, limited only by the nutrients stores that the body has available. The actual state of homeostatic parameters such as blood glucose levels represents a careful balance based on regulatory signals from the immune and endocrine systems. This state is not static but continuously adjusted in response to changes in the current metabolic needs of the body, the amount of resources it has available and the level of threats it encounters. This balance is maintained by the ability of the immune and endocrine systems to interact and co-regulate systemic metabolism. In context of metabolic disease, this system is disrupted, which impairs functionality of both systems. The failure of the endocrine system to retain levels of nutrients such as glucose within threshold values impairs functionality of the immune system. In addition, metabolic stress of organs in context of obesity is perceived by the immune system as a disruption in local homeostasis, which it tries to resolve by the excretion of factors which further disrupt normal metabolic control. In this chapter, we will discuss how the immune and endocrine systems interact under homeostatic conditions and during infection with a focus on blood glucose regulation. In addition, we will discuss how this system fails in the context of metabolic disease.

Hepatic transcriptional responses to fasting and feeding

Mammals undergo regular cycles of fasting and feeding that engage dynamic transcriptional responses in metabolic tissues. Here we review advances in our understanding of the gene regulatory networks that contribute to hepatic responses to fasting and feeding. The advent of sequencing and -omics techniques have begun to facilitate a holistic understanding of the transcriptional landscape and its plasticity. We highlight transcription factors, their cofactors, and the pathways that they impact. We also discuss physiological factors that impinge on these responses, including circadian rhythms and sex differences. Finally, we review how dietary modifications modulate hepatic gene expression programs.

FGF21 is required for the metabolic benefits of IKKε/TBK1 inhibition

The protein kinases IKKε and TBK1 are activated in liver and fat in mouse models of obesity. We have previously demonstrated that treatment with the IKKε/TBK1 inhibitor amlexanox produces weight loss and relieves insulin resistance in obese animals and patients. While amlexanox treatment caused a transient reduction in food intake, long-term weight loss was attributable to increased energy expenditure via FGF21-dependent beiging of white adipose tissue (WAT). Amlexanox increased FGF21 synthesis and secretion in several tissues. Interestingly, although hepatic secretion determined circulating levels, it was dispensable for regulating energy expenditure. In contrast, adipocyte-secreted FGF21 may have acted as an autocrine factor that led to adipose tissue browning and weight loss in obese mice. Moreover, increased energy expenditure was an important determinant of improved insulin sensitivity by amlexanox. Conversely, the immediate reductions in fasting blood glucose observed with acute amlexanox treatment were mediated by the suppression of hepatic glucose production via activation of STAT3 by adipocyte-secreted IL-6. These findings demonstrate that amlexanox improved metabolic health via FGF21 action in adipocytes to increase energy expenditure via WAT beiging and that adipocyte-derived IL-6 has an endocrine role in decreasing gluconeogenesis via hepatic STAT3 activation, thereby producing a coordinated improvement in metabolic parameters.

Metabolic Codependencies in the Tumor Microenvironment

Metabolic reprogramming enables cancer cell growth, proliferation, and survival. This reprogramming is driven by the combined actions of oncogenic alterations in cancer cells and host cell factors acting on cancer cells in the tumor microenvironment. Cancer cell-intrinsic mechanisms activate signal transduction components that either directly enhance metabolic enzyme activity or upregulate transcription factors that in turn increase expression of metabolic regulators. Extrinsic signaling mechanisms involve host-derived factors that further promote and amplify metabolic reprogramming in cancer cells. This review describes intrinsic and extrinsic mechanisms driving cancer metabolism in the tumor microenvironment and how such mechanisms may be targeted therapeutically. SIGNIFICANCE: Cancer cell metabolic reprogramming is a consequence of the converging signals originating from both intrinsic and extrinsic factors. Intrinsic signaling maintains the baseline metabolic state, whereas extrinsic signals fine-tune the metabolic processes based on the availability of metabolites and the requirements of the cells. Therefore, successful targeting of metabolic pathways will require a nuanced approach based on the cancer's genotype, tumor microenvironment composition, and tissue location.

Etiology of lactic acidosis in malaria

Lactic acidosis and hyperlactatemia are common metabolic disturbances in patients with severe malaria. Lactic acidosis causes physiological adverse effects, which can aggravate the outcome of malaria. Despite its clear association with mortality in malaria patients, the etiology of lactic acidosis is not completely understood. In this review, the possible contributors to lactic acidosis and hyperlactatemia in patients with malaria are discussed. Both increased lactate production and impaired lactate clearance may play a role in the pathogenesis of lactic acidosis. The increased lactate production is caused by several factors, including the metabolism of intraerythrocytic Plasmodium parasites, aerobic glycolysis by activated immune cells, and an increase in anaerobic glycolysis in hypoxic cells and tissues as a consequence of parasite sequestration and anemia. Impaired hepatic and renal lactate clearance, caused by underlying liver and kidney disease, might further aggravate hyperlactatemia. Multiple factors thus participate in the etiology of lactic acidosis in malaria, and further investigations are required to fully understand their relative contributions and the consequences of this major metabolic disturbance.

Interleukin-13 ameliorates postischemic hepatic gluconeogenesis and hyperglycemia in rat model of stroke

Hyperglycemia is a well-known indicator of stroke prognosis, and one-third of nondiabetic patients develop postischemic hyperglycemia during the acute phase of stroke; this is related to relatively poor prognosis, high mortality, and impaired neurological recovery. Interleukin-13 (IL-13), a member of the Th2 cytokine family, is involved in both the regulation of immune response and glucose metabolism. Thus, we investigated the mechanism of postischemic hyperglycemia and the role of IL-13 by using a permanent middle cerebral artery occlusion (MCAO) rat model. Our results indicated that postischemic hyperglycemia was accompanied with hyperinsulinemia and increased HOMA-IR, elevated hepatic gluconeogenesis, and suppressed insulin signaling. A shift towards inflammatory response was evident with results of elevated proinflammatory cytokines and increased expression of negative regulatory proteins, suggesting an ongoing vicious cycle of inflammatory-induced insulin-resistant hyperglycemia. IL-13 treatment counteracted the proinflammatory states and abolished the vicious cycle through enhancing STAT6 and STAT3, which mediated the immune and metabolic pathways respectively; these effects resolved the formerly described pathological changes of postischemic hyperglycemia and reduced infarction size in the MCAO rats. Our findings demonstrated the importance of Th1-Th2 balance in the peripheral glucose metabolism affected by acute ischemic stroke, which provides a new perspective for the prevention and control of postischemic hyperglycemia.

Metabolic Role of PTEN in Insulin Signaling and Resistance

Phosphatase and tensin homolog (PTEN) is most prominently known for its function in tumorigenesis. However, a metabolic role of PTEN is emerging as a result of its altered expression in type 2 diabetes (T2D), which results in impaired insulin signaling and promotion of insulin resistance during the pathogenesis of T2D. PTEN functions in regulating insulin signaling across different organs have been identified. Through the use of a variety of models, such as tissue-specific knockout (KO) mice and in vitro cell cultures, PTEN's role in regulating insulin action has been elucidated across many cell types. Herein, we will review the recent advancements in the understanding of PTEN's metabolic functions in each of the tissues and cell types that contribute to regulating systemic insulin sensitivity and discuss how PTEN may represent a promising therapeutic strategy for treatment or prevention of T2D.

TRIM14 Is a Key Regulator of the Type I IFN Response during Mycobacterium tuberculosis Infection

Tripartite motif-containing proteins (TRIMs) play a variety of recently described roles in innate immunity. Although many TRIMs regulate type I IFN expression following cytosolic nucleic acid sensing of viruses, their contribution to innate immune signaling and gene expression during bacterial infection remains largely unknown. Because Mycobacterium tuberculosis is an activator of cGAS-dependent cytosolic DNA sensing, we set out to investigate a role for TRIM proteins in regulating macrophage responses to M. tuberculosis In this study, we demonstrate that TRIM14, a noncanonical TRIM that lacks an E3 ubiquitin ligase RING domain, is a critical negative regulator of the type I IFN response in Mus musculus macrophages. We show that TRIM14 interacts with both cGAS and TBK1 and that macrophages lacking TRIM14 dramatically hyperinduce IFN stimulated gene (ISG) expression following M. tuberculosis infection, cytosolic nucleic acid transfection, and IFN-β treatment. Consistent with a defect in resolution of the type I IFN response, Trim14 knockout macrophages have more phospho-Ser754 STAT3 relative to phospho-Ser727 and fail to upregulate the STAT3 target Socs3, which is required to turn off IFNAR signaling. These data support a model whereby TRIM14 acts as a scaffold between TBK1 and STAT3 to promote phosphorylation of STAT3 at Ser727 and resolve ISG expression. Remarkably, Trim14 knockout macrophages hyperinduce expression of antimicrobial genes like Nos2 and are significantly better than control cells at limiting M. tuberculosis replication. Collectively, these data reveal an unappreciated role for TRIM14 in resolving type I IFN responses and controlling M. tuberculosis infection.

Targeting Janus Kinases and Signal Transducer and Activator of Transcription 3 to Treat Inflammation, Fibrosis, and Cancer: Rationale, Progress, and Caution

Before it was molecularly cloned in 1994, acute-phase response factor or signal transducer and activator of transcription (STAT)3 was the focus of intense research into understanding the mammalian response to injury, particularly the acute-phase response. Although known to be essential for liver production of acute-phase reactant proteins, many of which augment innate immune responses, molecular cloning of acute-phase response factor or STAT3 and the research this enabled helped establish the central function of Janus kinase (JAK) family members in cytokine signaling and identified a multitude of cytokines and peptide hormones, beyond interleukin-6 and its family members, that activate JAKs and STAT3, as well as numerous new programs that their activation drives. Many, like the acute-phase response, are adaptive, whereas several are maladaptive and lead to chronic inflammation and adverse consequences, such as cachexia, fibrosis, organ dysfunction, and cancer. Molecular cloning of STAT3 also enabled the identification of other noncanonical roles for STAT3 in normal physiology, including its contribution to the function of the electron transport chain and oxidative phosphorylation, its basal and stress-related adaptive functions in mitochondria, its function as a scaffold in inflammation-enhanced platelet activation, and its contributions to endothelial permeability and calcium efflux from endoplasmic reticulum. In this review, we will summarize the molecular and cellular biology of JAK/STAT3 signaling and its functions under basal and stress conditions, which are adaptive, and then review maladaptive JAK/STAT3 signaling in animals and humans that lead to disease, as well as recent attempts to modulate them to treat these diseases. In addition, we will discuss how consideration of the noncanonical and stress-related functions of STAT3 cannot be ignored in efforts to target the canonical functions of STAT3, if the goal is to develop drugs that are not only effective but safe. SIGNIFICANCE STATEMENT: Key biological functions of Janus kinase (JAK)/signal transducer and activator of transcription (STAT)3 signaling can be delineated into two broad categories: those essential for normal cell and organ development and those activated in response to stress that are adaptive. Persistent or dysregulated JAK/STAT3 signaling, however, is maladaptive and contributes to many diseases, including diseases characterized by chronic inflammation and fibrosis, and cancer. A comprehensive understanding of JAK/STAT3 signaling in normal development, and in adaptive and maladaptive responses to stress, is essential for the continued development of safe and effective therapies that target this signaling pathway.

High-saturated-fat diet-induced obesity causes hepatic interleukin-6 resistance via endoplasmic reticulum stress

The relationship between liver interleukin-6 (IL-6) resistance following high-fat diet (HFD)-induced obesity and glucose intolerance is unclear. The purpose of this study was to assess the temporal development of hepatic IL-6 resistance and the role of endoplasmic reticulum (ER) stress in this process. We hypothesized that HFD would rapidly induce hepatic IL-6 resistance through a mechanism involving ER stress. Male C57BL/6N mice consumed chow or a HFD (60%) derived from lard (saturated) or olive oil (monounsaturated) for 4 days or 7 weeks before being injected intraperitoneally with IL-6 (6 ng·kg^-1). Glucose, insulin, and pyruvate tolerance tests were used as proxies for systemic glucose metabolism and hepatic glucose production, respectively. Primary mouse hepatocytes were incubated with palmitate (saturated) and oleate (unsaturated) overnight, then treated with 20 ng/ml IL-6. ER stress was induced via tunicamycin or prevented by sodium phenylbutyrate (PBA). Seven weeks of a saturated, but not monounsaturated, HFD reduced hepatic IL-6 signaling in conjunction with hepatic ER stress. Palmitate directly impaired IL-6 signaling in hepatocytes along with inducing ER stress. Pharmacologically induced ER stress caused hepatic IL-6 resistance, whereas PBA reversed HFD-induced IL-6 resistance. Chronic HFD-induced obesity is associated with hepatic IL-6 resistance due to saturated FA-induced ER stress.

Essential Roles for the Non-Canonical IκB Kinases in Linking Inflammation to Cancer, Obesity, and Diabetes

Non-canonical IκB kinases (IKKs) TBK1 and IKKε have essential roles as regulators of innate immunity and cancer. Recent work has also implicated these kinases in distinctively controlling glucose homeostasis and repressing adaptive thermogenic and mitochondrial biogenic response upon obesity-induced inflammation. Additionally, TBK1 and IKKε regulate pancreatic β-cell regeneration. In this review, we summarize current data on the functions and molecular mechanisms of TBK1 and IKKε in orchestrating inflammation to cancer, obesity, and diabetes.

Acute administration of IL-6 improves indices of hepatic glucose and insulin homeostasis in lean and obese mice

Obesity can lead to impairments in hepatic glucose and insulin homeostasis, and although exercise is an effective treatment, the molecular targets remain incompletely understood. As IL-6 is an exercise-inducible cytokine, we aimed to identify whether IL-6 itself influences hepatic glucose and insulin homeostasis and whether this response differs during obesity. In vivo, male mice were fed a low-fat diet (LFD; 10% kcal) or a high-fat diet (HFD; 60% kcal) for 7 wk, which induced obesity and hepatic lipid accumulation. LFD- and HFD-fed mice were injected with IL-6 (400 ng, 75 min) or PBS and then with insulin (1 U/kg; ~15 min) or saline, at which point livers were collected. In both LFD- and HFD-fed mice, IL-6 decreased blood glucose and mRNA expression of gluconeogenic genes alongside increased phosphorylation of AKT in comparison to PBS controls, and this occurred without changes in circulating insulin. To determine whether this effect of IL-6 was directly on the liver, we completed in vitro isolated primary hepatocyte experiments from chow-fed mice and cultured with or without exposure to free fatty acid (250 μm palmitate and 250 μm oleate, 24 h) to induce lipid accumulation. In both control and free fatty acid-treated hepatocytes, IL-6 (20 ng/ml, 75 min) slightly attenuated insulin-stimulated (10 nM; ~15 min) AKT phosphorylation. Together, these data suggest that IL-6 may lead to improvements in indices of hepatic glucose and insulin homeostasis in vivo; however, this is likely due to an indirect effect on the hepatocyte. NEW & NOTEWORTHY In this study, we used lean and obese mice and found that a single injection of IL-6 improved glucose tolerance, decreased hepatic gluconeogenic gene expression, and increased hepatic phosphorylation of AKT. In primary hepatocytes cultured under control and lipid-laden conditions, IL-6 had a mild, but deleterious, effect on phosphorylation of AKT. Our results show that the beneficial effects of IL-6 on glucose and insulin homeostasis, in vivo, are maintained in obesity.

Interleukin-6 derived from cutaneous deficiency of stearoyl-CoA desaturase- 1 may mediate metabolic organ crosstalk among skin, adipose tissue and liver

Stearoyl-CoA desaturase 1 (SCD1), a lipogenic enzyme that adds a double bond at the delta 9 position of stearate (C18: 0) and palmitate (C16: 0), has been proven to be important in the development of obesity. Mice with skin-specific deficiency of SCD1 (SKO) display increased whole-body energy expenditure, which is protective against adiposity from a high-fat diet because it improves glucose clearance, insulin sensitivity, and hepatic steatosis. Of note, these mice also display elevated levels of the "pro-inflammatory" plasma interleukin-6 (IL-6). In whole skin of SKO mice, IL-6 mRNA levels are increased, and protein expression is evident in hair follicle cells and in keratinocytes. Recently, the well-known role of IL-6 in causing white adipose tissue lipolysis has been linked to indirectly activating the gluconeogenic enzyme pyruvate carboxylase 1 in the liver, thereby increasing hepatic glucose production. In this study, we suggest that skin-derived IL-6 leads to white adipose tissue lipolysis, which contributes to the lean phenotype of SKO mice without the incidence of meta-inflammation that is associated with IL-6 signaling.

Inhibition of SphK2 Stimulated Hepatic Gluconeogenesis Associated with Dephosphorylation and Deacetylation of STAT3

BACKGROUND

Sphingosine kinase (SphK) is considered as a potential target for developing novel therapeutics of cancer and other diseases including diabetes. As the major SphK isoform in the liver, much less is known the role of SphK2 involved in regulating hepatic glucose metabolism.

METHOD

In this study, RNA interference, real time RT-PCR, western blot and immunoprecipitation method was used to investigate the regulation of SphK2 in hepatic glucose metabolism.

RESULTS

Both siRNA and SphK2 inhibitor ABC294640 stimulated expression of gluconeogenetic gene PEPCK and G6Pase but not enzymes of hepatic glycogenolysis, glycolysis and glycogen synthesis. Inhibition of SphK2 also prevented insulin repressed PEPCK and G6Pase expression as well as glucose production levels. Furtherly, inhibition of SphK2 inactivated STAT3 by decreasing both phosphorylation on Tyr705 and acetylation on lysine residue, and led to stimulation of PEPCK and G6Pase expression. Inhibition of SphK2 also prevented IL-6 dependent activation of STAT3 and suppression of PEPCK and G6pase expression both in vitro and in vivo.

CONCLUSION

Our study suggests that SphK2 participates in hepatic glucose metabolism related to activation of STAT3.

STAT3: The art of multi-tasking of metabolic and immune functions in obesity

Signal transducer and activator of transcription 3 (STAT3) is a transcription factor that has recently attracted increased attention. Accumulating studies have demonstrated that STAT3 plays an important role in various diseases, such as cancer and ischemic injury. In light of the distinctive effects of STAT3 on the regulation of metabolism and immune responses, we present the elaborate network of STAT3 in obesity. In this review, we first introduce the general background of STAT3, including a discussion regarding the STAT family and the characterization and regulation of STAT3. Then, we describe the STAT3 signaling network and its pathophysiological roles in lipid and glucose metabolism and immune function. Finally, we highlight the research progress regarding STAT3 in obesity. The information presented here may be useful for the design of future studies and may highlight the potential of STAT3 as a future therapeutic target for obesity.

JAK/STAT - Emerging Players in Metabolism

The Janus kinase (JAK)/signal transducer and activator of transcription (STAT) pathway is crucial for transducing signals from a variety of metabolically relevant hormones and cytokines including growth hormone, leptin, erythropoietin, IL4, IL6 and IFNγ. A growing body of evidence suggests that this pathway is dysregulated in the context of obesity and metabolic disease. Recent development of animal models has been instrumental in identifying the role of JAK/STAT signaling in the peripheral metabolic organs including adipose, liver, muscle, pancreas, and the immune system. In this review we summarize current knowledge about the function of JAK/STAT proteins in the regulation of metabolism, and highlight new potential therapeutic targets for the treatment of obesity and diabetes.

Hypothalamic POMC expression is required for peripheral insulin action on hepatic gluconeogenesis through regulating STAT3 in sepsis rats

Liver injury and dysregulated glucose homoeostasis are common manifestations during sepsis. Although plenty of studies reported insulin could protect against multiple organ injuries caused by critical infections among patients, little was known about the precise mechanism. We investigated whether liver inflammatory pathway and central neuropeptides were involved in the process. In sepsis rats, hepatic IKK/NF‐κB pathway and STAT3 were strongly activated, along with reduced body weight, blood glucose and suppressed hepatic gluconeogenesis (GNG). Peripheral insulin administration efficiently attenuated liver dysfunction and glucose metabolic disorders by suppressing hypothalamic anorexigenic neuropeptide proopiomelanocortin (POMC) expression, hepatic NF‐κB pathway and STAT3 phosphorylation. Furthermore, knockdown of hypothalamic POMC significantly diminished protective effect of insulin on hepatic GNG and insulin‐induced STAT3 inactivation, but not inflammation or IKK/NF‐κB pathway. These results suggest that hepatic IKK/NF‐κB pathway mediates the anti‐inflammatory effect of insulin in septic rats, and peripheral insulin treatment may improve hepatic GNG by inhibiting STAT3 phosphorylation dependent on hypothalamic POMC expression.

The MST3/STK24 kinase mediates impaired fasting blood glucose after a high-fat diet

AIMS/HYPOTHESIS

The identification of mediators in the pathogenesis of type 2 diabetes mellitus is essential for the full understanding of this disease. Protein kinases are especially important because of their potential as pharmacological targets. The goal of this study was to investigate whether mammalian sterile-20 3 (MST3/STK24), a stress-regulated kinase, is involved in metabolic alterations in obesity.

METHODS

Glucose regulation of Mst3 (also known as Stk24)-knockout mice was analysed both in 129;C57 mixed background mice and in C57/BL6J mice fed normally or with a high-fat diet (HFD). This work was complemented with an analysis of the insulin signalling pathway in cultured human liver cells made deficient in MST3 using RNA interference.

RESULTS

MST3 is phosphorylated in the livers of mice subject to an obesity-promoting HFD, and its deficiency lowers the hyperglycaemia, hyperinsulinaemia and insulin resistance that the animals develop with this diet, an effect that is seen even without complete inactivation of the kinase. Lack of MST3 results in activation of the insulin signalling pathway downstream of IRS1, in both cultured liver cells and the liver of animals after HFD. This effect increases the inhibition of forkhead box (FOX)O1, with subsequent downregulation of the expression of gluconeogenic enzymes.

CONCLUSIONS/INTERPRETATION

MST3 inhibits the insulin signalling pathway and is important in the development of insulin resistance and impaired blood glucose levels after an HFD.

Insulin regulation of gluconeogenesis

The coordinated regulation between cellular glucose uptake and endogenous glucose production is indispensable for the maintenance of constant blood glucose concentrations. The liver contributes significantly to this process by altering the levels of hepatic glucose release, through controlling the processes of de novo glucose production (gluconeogenesis) and glycogen breakdown (glycogenolysis). Various nutritional and hormonal stimuli signal to alter hepatic gluconeogenic flux, and suppression of this metabolic pathway during the postprandial state can, to a significant extent, be attributed to insulin. Here, we review some of the molecular mechanisms through which insulin modulates hepatic gluconeogenesis, thus controlling glucose production by the liver to ultimately maintain normoglycemia. Various signaling pathways governed by insulin converge at the level of transcriptional regulation of the key hepatic gluconeogenic genes PCK1 and G6PC, highlighting this as one of the focal mechanisms through which gluconeogenesis is modulated. In individuals with compromised insulin signaling, such as insulin resistance in type 2 diabetes, insulin fails to suppress hepatic gluconeogenesis, even in the fed state; hence, an insight into these insulin-moderated pathways is critical for therapeutic purposes.

Lysophosphatidic acid counteracts glucagon-induced hepatocyte glucose production via STAT3

Hepatic glucose production (HGP) is required to maintain normoglycemia during fasting. Glucagon is the primary hormone responsible for increasing HGP; however, there are many additional hormone and metabolic factors that influence glucagon sensitivity. In this study we report that the bioactive lipid lysophosphatidic acid (LPA) regulates hepatocyte glucose production by antagonizing glucagon-induced expression of the gluconeogenic enzyme phosphoenolpyruvate carboxykinase (PEPCK). Treatment of primary hepatocytes with exogenous LPA blunted glucagon-induced PEPCK expression and glucose production. Similarly, knockout mice lacking the LPA-degrading enzyme phospholipid phosphate phosphatase type 1 (PLPP1) had a 2-fold increase in endogenous LPA levels, reduced PEPCK levels during fasting, and decreased hepatic gluconeogenesis in response to a pyruvate challenge. Mechanistically, LPA antagonized glucagon-mediated inhibition of STAT3, a transcriptional repressor of PEPCK. Importantly, LPA did not blunt glucagon-stimulated glucose production or PEPCK expression in hepatocytes lacking STAT3. These data identify a novel role for PLPP1 activity and hepatocyte LPA levels in glucagon sensitivity via a mechanism involving STAT3.

Hypothalamic Insulin Resistance in Obesity: Effects on Glucose Homeostasis

The central link between obesity and type 2 diabetes is the development of insulin resistance. To date, it is still not clear whether hyperinsulinemia causes insulin resistance, which underlies the pathogenesis of obesity-associated type 2 diabetes, owing to the sophisticated regulatory mechanisms that exist in the periphery and in the brain. In recent years, accumulating evidence has demonstrated the existence of insulin resistance within the hypothalamus. In this review, we have integrated the recent discoveries surrounding both central and peripheral insulin resistance to provide a comprehensive overview of insulin resistance in obesity and the regulation of systemic glucose homeostasis. In particular, this review will discuss how hyperinsulinemia and hyperleptinemia in obesity impair insulin sensitivity in tissues such as the liver, skeletal muscle, adipose tissue, and the brain. In addition, this review highlights insulin transport into the brain, signaling pathways associated with hypothalamic insulin receptor expression in the regulation of hepatic glucose production, and finally the perturbation of systemic glucose homeostasis as a consequence of central insulin resistance. We also suggest future approaches to overcome both central and peripheral insulin resistance to treat obesity and type 2 diabetes.

Angiogenic factor with G patch and FHA domains 1 (Aggf1) promotes hepatic steatosis in mice

Increased uptake of nutrients coupled with reduced activity leads to the development of a host of metabolic disorders in humans. In the present study we examined the role of angiogenic factor with G patch and FHA domains 1 (Aggf1) in the pathogenesis of steatosis, characterized by accumulation of lipids in the liver and consequently hepatic insulin resistance. We report here that Aggf1 expression was up-regulated in the liver in both genetically predisposed and diet-induced mouse model of steatosis. Aggf1 expression was also stimulated by free fatty acids in primary hepatocytes. Over-expression of Aggf1 in mice promoted steatosis. On the contrary, Aggf1 depletion ameliorated steatosis in mice. Mechanistically, Aggf1 activated the expression of gluconeogenesis gene and skewed the insulin signaling pathway to induce insulin resistance. Taken together, our data suggest that Aggf1 plays a role in steatosis in vivo and as such may be a new target in the development of therapeutics solutions against steatosis.

APPL1-mediated activation of STAT3 contributes to inhibitory effect of adiponectin on hepatic gluconeogenesis

Adiponectin has been shown to suppress hepatic gluconeogenesis. However, the signaling pathways underlying its action remain ill-defined. The purpose of this study was to examine the potential role of APPL1 in mediating anti-gluconeogenic ability of adiponectin. Primary hepatocytes were isolated from male C57BL/6 mice. Western blot and RT-PCR were performed to detect protein expression and mRNA level, respectively. The protein-protein association was determined by immunoprecipitation and GST pull-down assay. We found that APPL1 protein levels were negatively associated with expressions of proteins and mRNAs of gluconeogenesis enzymes under stimulation with adiponectin. In addition, adiponectin-stimulated STAT3 phosphorylation and acetylation were positively regulated by APPL1 and negative regulated by SirT1. Pharmacological and genetic inhibition of STAT3 mitigated impact of adiponectin on hepatic gluconeogenesis. Furthermore, adiponectin administration facilitated the binding of APPL1 to SirT1 and suppressed the association of SirT1 with STAT3. Taken together, our study showed that APPL1-SirT1-STAT3 pathway mediated adiponectin signaling in primary hepatocytes. This new finding provides a novel mechanism by which adiponectin suppresses hepatic gluconeogenesis.

Jak3, STAT3, and STAT5 inhibit expression of miR-22, a novel tumor suppressor microRNA, in cutaneous T-Cell lymphoma

Aberrant activation of Janus kinase-3 (Jak3) and its key down-stream effectors, Signal Transducer and Activator of Transcription-3 (STAT3) and STAT5, is a key feature of malignant transformation in cutaneous T-cell lymphoma (CTCL). However, it remains only partially understood how Jak3/STAT activation promotes lymphomagenesis. Recently, non-coding microRNAs (miRNAs) have been implicated in the pathogenesis of this malignancy. Here, we show that (i) malignant T cells display a decreased expression of a tumor suppressor miRNA, miR-22, when compared to non-malignant T cells, (ii) STAT5 binds the promoter of the miR-22 host gene, and (iii) inhibition of Jak3, STAT3, and STAT5 triggers increased expression of pri-miR-22 and miR-22. Curcumin, a nutrient with anti-Jak3 activity and histone deacetylase inhibitors (HDACi) also trigger increased expression of pri-miR-22 and miR-22. Transfection of malignant T cells with recombinant miR-22 inhibits the expression of validated miR-22 targets including NCoA1, a transcriptional co-activator in others cancers, as well as HDAC6, MAX, MYCBP, PTEN, and CDK2, which have all been implicated in CTCL pathogenesis. In conclusion, we provide the first evidence that de-regulated Jak3/STAT3/STAT5 signalling in CTCL cells represses the expression of the gene encoding miR-22, a novel tumor suppressor miRNA.

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

Interleukin 6 (IL-6) is a pleiotropic four-helix-bundle cytokine that exerts multiple functions in the body. In the liver, IL-6 is an important inducer of the acute phase response and infection defense. IL-6 is furthermore crucial for hepatocyte homeostasis and is a potent hepatocyte mitogen. It is not only implicated in liver regeneration, but also in metabolic function of the liver. However, persistent activation of the IL-6 signaling pathway is detrimental to the liver and might ultimately result in the development of liver tumors. On target cells IL-6 can bind to the signal transducing subunit gp130 either in complex with the membrane-bound or with the soluble IL-6 receptor to induce intracellular signaling. In this review we describe how these different pathways are involved in the physiology and pathophyiology of the liver. We furthermore discuss how IL-6 pathways can be selectively inhibited and therapeutically exploited for the treatment of liver pathologies.

The JAK/STAT pathway in obesity and diabetes

Diabetes mellitus are complex, multi-organ metabolic pathologies characterized by hyperglycemia. Emerging evidence shows that the highly conserved and potent JAK/STAT signaling pathway is required for normal homeostasis, and, when dysregulated, contributes to the development of obesity and diabetes. In this review, we analyze the role of JAK/STAT activation in the brain, liver, muscle, fat and pancreas, and how this affects the course of the disease. We also consider the therapeutic implications of targeting the JAK/STAT pathway in treatment of obesity and diabetes.

HIF2α Is an Essential Molecular Brake for Postprandial Hepatic Glucagon Response Independent of Insulin Signaling

Glucagon drives hepatic gluconeogenesis and maintains blood glucose levels during fasting. The mechanism that attenuates glucagon action following refeeding is not understood. The present study demonstrates an increase in perivenous liver hypoxia immediately after feeding, which stabilizes hypoxia-inducible factor 2α (HIF2α) in liver. The transient postprandial increase in hepatic HIF2α attenuates glucagon signaling. Hepatocyte-specific disruption of HIF2α increases postprandial blood glucose and potentiates the glucagon response. Independent of insulin/AKT signaling, activation of hepatic HIF2α resulted in lower blood glucose, improved glucose tolerance, and decreased gluconeogenesis due to blunted hepatic glucagon action. Mechanistically, HIF2α abrogated glucagon-PKA signaling by activating cAMP-phosphodiesterases in a MEK/ERK-dependent manner. Repression of glucagon signaling by HIF2α ameliorated hyperglycemia in streptozotocin-induced diabetes and acute insulin-resistant animal models. This study reveals that HIF2α is essential for the acute postprandial regulation of hepatic glucagon signaling and suggests HIF2α as a potential therapeutic target in the treatment of diabetes.

Central Insulin Action Activates Kupffer Cells by Suppressing Hepatic Vagal Activation via the Nicotinic Alpha 7 Acetylcholine Receptor

Central insulin action activates hepatic IL-6/STAT3 signaling, which suppresses the gene expression of hepatic gluconeogenic enzymes. The vagus nerve plays an important role in this centrally mediated hepatic response; however, the precise mechanism underlying this brain-liver interaction is unclear. Here, we present our findings that the vagus nerve suppresses hepatic IL-6/STAT3 signaling via α7-nicotinic acetylcholine receptors (α7-nAchR) on Kupffer cells, and that central insulin action activates hepatic IL-6/STAT3 signaling by suppressing vagal activity. Indeed, central insulin-mediated hepatic IL-6/STAT3 activation and gluconeogenic gene suppression were impeded in mice with hepatic vagotomy, pharmacological cholinergic blockade, or α7-nAchR deficiency. In high-fat diet-induced obese and insulin-resistant mice, control of the vagus nerve by central insulin action was disturbed, inducing a persistent increase of inflammatory cytokines. These findings suggest that dysregulation of the α7-nAchR-mediated control of Kupffer cells by central insulin action may affect the pathogenesis of chronic hepatic inflammation in obesity.

Central insulin-mediated regulation of hepatic glucose production [Review]

Insulin controls hepatic glucose production (HGP) and maintains glucose homeostasis through the direct action of hepatic insulin receptors, as well as the indirect action of insulin receptors in the central nervous system. Insulin acts on insulin receptors in the hypothalamic arcuate nucleus, activates ATP-sensitive potassium channels in a phosphoinositide 3-kinase (PI3K)-dependent manner, induces hyperpolarization of the hypothalamic neurons, and regulates HGP via the vagus nerve. In the liver, central insulin action augments IL-6 expression in Kupffer cells and activates STAT3 transcription factors in hepatocytes. Activated STAT3 suppresses the gene expression of gluconeogenic enzymes, thereby reducing HGP. It has become evident that nutrients such as glucose, fatty acids, and amino acids act upon the hypothalamus together with insulin, affecting HGP. On the other hand, HGP control by central insulin action is impeded in obesity and impeded by insulin resistance due to disturbance of PI3K signaling and inflammation in the hypothalamus or inhibition of STAT3 signaling in the liver. Although the mechanism of control of hepatic gluconeogenic gene expression by central insulin action is conserved across species, its importance in human glucose metabolism has not been made entirely clear and its elucidation is anticipated in the future.

Nighttime Administration of Nicotine Improves Hepatic Glucose Metabolism via the Hypothalamic Orexin System in Mice

Nicotine is known to affect the metabolism of glucose; however, the underlying mechanism remains unclear. Therefore, we here investigated whether nicotine promoted the central regulation of glucose metabolism, which is closely linked to the circadian system. The oral intake of nicotine in drinking water, which mainly occurred during the nighttime active period, enhanced daily hypothalamic prepro-orexin gene expression and reduced hyperglycemia in type 2 diabetic db/db mice without affecting body weight, body fat content, and serum levels of insulin. Nicotine administered at the active period appears to be responsible for the effect on blood glucose, because nighttime but not daytime injections of nicotine lowered blood glucose levels in db/db mice. The chronic oral treatment with nicotine suppressed the mRNA levels of glucose-6-phosphatase, the rate-limiting enzyme of gluconeogenesis, in the liver of db/db and wild-type control mice. In the pyruvate tolerance test to evaluate hepatic gluconeogenic activity, the oral nicotine treatment moderately suppressed glucose elevations in normal mice and mice lacking dopamine receptors, whereas this effect was abolished in orexin-deficient mice and hepatic parasympathectomized mice. Under high-fat diet conditions, the oral intake of nicotine lowered blood glucose levels at the daytime resting period in wild-type, but not orexin-deficient, mice. These results indicated that the chronic daily administration of nicotine suppressed hepatic gluconeogenesis via the hypothalamic orexin-parasympathetic nervous system. Thus, the results of the present study may provide an insight into novel chronotherapy for type 2 diabetes that targets the central cholinergic and orexinergic systems.

Impact of high glucose on metastasis of colon cancer cells

AIM: To investigate the possible mechanism of how glucose promotes invasion and metastasis of colon cancer cells.

METHODS: CT-26 rat colorectal cancer cells were cultured in different concentrations of glucose environments (10, 20, and 30 mmol/L). Wound healing assay and transwell chamber invasion assay were utilized to test the migration and invasion, respectively. In order to understand the role of signal transducer and activator of transcription 3 (STAT3) in the process, STAT3 inhibitors, including Stattic (an STAT3 specific inhibitor) and small interfering RNA targeting STAT3, were used to block STAT3 function to evaluate their impact on CT-26 cell motion. To verify whether STAT3 and matrix metalloproteinase-9 (MMP-9) protein expression is associated with glucose-induced cell movement, Western blot was used to compare the differences in the expression of MMP-9 and STAT3 in cells incubated with and without STAT3 inhibitors in high glucose condition.

RESULTS: In both wound healing and invasion assays, the migration and invasion of CT-26 cells increased gradually with the increase in glucose concentration. However, the glucose-induced migration and invasion were obviously inhibited by STAT3 inhibitors (P < 0.05). Similarly, in Western blot assessment, both MMP-9 and STAT3 expression increased under a high glucose environment and the highest expression was achieved when 30 mmol/L glucose was used. However, in cells treated with 30 mmol/L mannitol, either MMP-9 or STAT3 expression did not increase (P > 0.05). When STAT3 inhibitors were added in the 30 mM glucose group, not only STAT3 but also MMP-9 expression decreased significantly (P < 0.05).

CONCLUSION: Our study provides evidence that glucose can promote both migration and invasion of CT-26 cells, and that the STAT3-induced MMP-9 signal pathway is involved in this process.

Temporal relationship between diet-induced steatosis and onset of insulin/leptin resistance in male Wistar rats

Rats fed with high-fat-high-sucrose (HFHS) diet are known to manifest metabolic syndrome including hyperinsulinemia, hyperleptinemia, hyperglycemia, diabetic dyslipidemia, and hepatic steatosis. The aim of the current study is to determine the temporal relationships between the development of hepatic steatosis and the onset of insulin and leptin resistance in hypothalamus and liver in male Wistar rats (six weeks of age) fed chow or HFHS diet for up to 8 weeks. Fasting plasma glucose, lipids/lipoproteins, insulin and leptin levels were quantified, histopathologic score of hepatic steatosis and inflammation were assessed, and the responses of common checkpoints of insulin and leptin signalling responsible for lipogenesis and gluconeogenesis were analyzed. In addition, acute insulin or leptin administration was performed at different stages of HFHS dieting to determine the responsiveness of the respective signalling pathways. Hyperinsulinemia, hyperglycemia, dyslipidemia, and increased homeostasis model assessment of basal insulin resistance occurred 1-week after HFHS dieting, coinciding with upregulation of suppressor of cytokine signalling 3 in both hypothalamus and liver. However, hepatosteatosis, accompanied with increased expression of sterol regulatory element binding protein 1c and phosphoenolpyruvate carboxykinase, did not manifest until 4- to 8-week after HFHS dieting. Lowered insulin sensitivity (shown by decreased insulin receptor substrate 1 and protein kinase B phosphorylation) occurred approximately 2 weeks prior to leptin resistance (shown by impaired signal transducer and activator of transcription 3 activation) in both the liver and hypothalamus. Acute insulin/leptin administration also demonstrated the impaired insulin or leptin signalling transduction. These data suggest that lowered insulin sensitivity and leptin resistance occurred at least 2-3 weeks earlier than the manifestation of hepatosteatosis in rats fed HFHS diet.

Versatile functions for IL-6 in metabolism and cancer

Owing to its abundance in inflammatory settings, interleukin IL-6 is frequently viewed as a proinflammatory cytokine, with functions that parallel those of tumor necrosis factor (TNF) and IL-1β in the context of inflammation. However, accumulating evidence points to a broader role for IL-6 in a variety of (patho)physiological conditions, including functions related to the resolution of inflammation. We review recent findings on the complex biological functions governed by IL-6 signaling, focusing on its role in inflammation-associated cancer and metabolic disorders such as obesity and type 2 diabetes mellitus (T2DM). We propose that the anti-inflammatory functions of IL-6 may extend to multiple settings and cell types, and suggest that these dimensions should be incorporated in therapeutic approaches to these diseases. Finally, we outline important areas of inquiry towards understanding this pleiotropic cytokine.

A subcutaneous adipose tissue-liver signalling axis controls hepatic gluconeogenesis

The search for effective treatments for obesity and its comorbidities is of prime importance. We previously identified IKK-ε and TBK1 as promising therapeutic targets for the treatment of obesity and associated insulin resistance. Here we show that acute inhibition of IKK-ε and TBK1 with amlexanox treatment increases cAMP levels in subcutaneous adipose depots of obese mice, promoting the synthesis and secretion of the cytokine IL-6 from adipocytes and preadipocytes, but not from macrophages. IL-6, in turn, stimulates the phosphorylation of hepatic Stat3 to suppress expression of genes involved in gluconeogenesis, in the process improving glucose handling in obese mice. Preliminary data in a small cohort of obese patients show a similar association. These data support an important role for a subcutaneous adipose tissue–liver axis in mediating the acute metabolic benefits of amlexanox on glucose metabolism, and point to a new therapeutic pathway for type 2 diabetes.

The drug amlexanox is known to improve obesity-related metabolic dysfunction in mice. Here the authors show that this effect is mediated by interleukin-6 secreted from subcutaneous adipocytes, which then inhibits gluconeogenesis in the liver by phosphorylating the hepatic transcription factor Stat3.

Energy metabolism in the liver

The liver is an essential metabolic organ, and its metabolic function is controlled by insulin and other metabolic hormones. Glucose is converted into pyruvate through glycolysis in the cytoplasm, and pyruvate is subsequently oxidized in the mitochondria to generate ATP through the TCA cycle and oxidative phosphorylation. In the fed state, glycolytic products are used to synthesize fatty acids through de novo lipogenesis. Long-chain fatty acids are incorporated into triacylglycerol, phospholipids, and/or cholesterol esters in hepatocytes. These complex lipids are stored in lipid droplets and membrane structures, or secreted into the circulation as very low-density lipoprotein particles. In the fasted state, the liver secretes glucose through both glycogenolysis and gluconeogenesis. During pronged fasting, hepatic gluconeogenesis is the primary source for endogenous glucose production. Fasting also promotes lipolysis in adipose tissue, resulting in release of nonesterified fatty acids which are converted into ketone bodies in hepatic mitochondria though β-oxidation and ketogenesis. Ketone bodies provide a metabolic fuel for extrahepatic tissues. Liver energy metabolism is tightly regulated by neuronal and hormonal signals. The sympathetic system stimulates, whereas the parasympathetic system suppresses, hepatic gluconeogenesis. Insulin stimulates glycolysis and lipogenesis but suppresses gluconeogenesis, and glucagon counteracts insulin action. Numerous transcription factors and coactivators, including CREB, FOXO1, ChREBP, SREBP, PGC-1α, and CRTC2, control the expression of the enzymes which catalyze key steps of metabolic pathways, thus controlling liver energy metabolism. Aberrant energy metabolism in the liver promotes insulin resistance, diabetes, and nonalcoholic fatty liver diseases.