The innate immune response during liver inflammation and metabolic disease

Hepatocellular carcinoma is accelerated by NASH involving M2 macrophage polarization mediated by hif-1induced IL-10

Obesity-related inflammation promotes cancer development. Tissue resident macrophages affect tumor progression and the tumor micro-environment favors polarization into alternatively activated macrophages (M2) that facilitate tumor invasiveness. Here, we dissected the role of western diet-induced NASH in inducing macrophage polarization in a carcinogen initiated model of hepatocellular carcinoma (HCC). Adult C57BL/6 male mice received diethyl nitrosamine (DEN) followed by 24 weeks of high fat-high cholesterol-high sugar diet (HF-HC-HSD). We assessed liver MRI and histology, serum ALT, AFP, liver triglycerides, and cytokines. Macrophage polarization was determined by IL-12/TNFα (M1) and CD163/CD206 (M2) expression using flow cytometry. Role of hif-1α-induced IL-10 was dissected in hepatocyte specific hif-1αKO and hif-1αdPA (over-expression) mice. The western diet-induced features of NASH and accelerated HCC development after carcinogen exposure. Liver fibrosis and serum AFP were significantly increased in DEN + HF-HC-HSD mice compared to controls. Western diet resulted in macrophage (F4/80⁺CD11b⁺) infiltration to liver and DEN + HF-HC-HSD mice showed preferential increase in M2 macrophages. Isolated hepatocytes from western diet fed mice showed significant upregulation of the hypoxia-inducible transcription factor, hif-1α, and livers from hif-1α over-expressing mice had increased proportion of M2 macrophages. Primary hepatocytes from wild-type mice treated with DEN and palmitic acid in vitro showed activation of hif-1α and induction of IL-10, a M2 polarizing cytokine. IL-10 neutralization in hepatocyte-derived culture supernatant prevented M2 macrophage polarization and silencing hif-1α in macrophages blocked their M2 polarization. Therefore, our data demonstrate that NASH accelerates HCC progression via upregulation of hif-1α mediated IL-10 polarizing M2 macrophages.

Tissue resident macrophages: Key players in the pathogenesis of type 2 diabetes and its complications

There is increasing evidence showing that chronic inflammation is an important pathogenic mediator of the development of type 2 diabetes (T2D). It is now generally accepted that tissue-resident macrophages play a major role in regulation of tissue inflammation. T2D-associated inflammation is characterized by an increased abundance of macrophages in different tissues along with production of inflammatory cytokines. The complexity of macrophage phenotypes has been reported from different human tissues. Macrophages exhibit a phenotypic range that is intermediate between two extremes, M1 (pro-inflammatory) and M2 (anti-inflammatory). Cytokines and chemokines produced by macrophages generate local and systemic inflammation and this condition leads to pancreatic β-cell dysfunction and insulin resistance in liver, adipose and skeletal muscle tissues. Data from human and animal studies also suggest that macrophages contribute to T2D complications such as nephropathy, neuropathy, retinopathy and cardiovascular diseases through cell-cell interactions and the release of pro-inflammatory cytokines, chemokines, and proteases to induce inflammatory cell recruitment, cell apoptosis, angiogenesis, and matrix protein remodeling. In this review we focus on the functions of macrophages and the importance of these cells in the pathogenesis of T2D. In addition, the contribution of macrophages to diabetes complications such as nephropathy, neuropathy, retinopathy and cardiovascular diseases is discussed.

Liver innate immune cells and insulin resistance: the multiple facets of Kupffer cells

Obesity, which affects 600 million adults worldwide, is a major risk factor for type 2 diabetes (T2D) and insulin resistance. Current therapies for these metabolic disorders include weight management by lifestyle intervention or bariatric surgery and pharmacological treatment with the aim of regulating blood glucose. Probably because of their short-term effectiveness, these therapies have not been able to stop the rapidly rising prevalence of T2D over the past decades, highlighting an urgent need to develop new therapeutic strategies. The role of immune cells, such as macrophages, in insulin resistance has been extensively studied. Major advances have been made to elucidate the role of adipose tissue macrophages in these pathogeneses. Recently, anti-inflammatory drugs have been suggested as an alternative treatment for T2D, and clinical trials of these agents are currently ongoing. In addition, results of previous clinical trials using antibodies against inflammatory cytokines, which showed modest effects, are now being rigorously re-evaluated. However, it is still unclear how liver macrophages [termed Kupffer cells (KCs)], which constitute the major source of macrophages in the body, contribute to the development of insulin resistance. In this review, we will discuss the present understanding of the role of liver immune cells in the development of insulin resistance. We will particularly focus on KCs, which could represent an attractive target for the treatment of metabolic diseases.

Therapeutic effects of 1,25-dihydroxyvitamin D3 on diabetes-induced liver complications in a rat model

It has been suggested that 1,25-dihydroxyvitamin D3 (vitamin D) plays a protective role against inflammation and insulin resistance (IR) in type 2 diabetes mellitus (T2DM). The present study investigate the hypothesis that vitamin D may exert beneficial effects on the liver in a rat model of T2DM by regulating the expression of inflammation-related cytokines and ameliorating IR induced by inflammation. Normal control group rats were fed a basic diet (NC). Experimental rats received a high-fat diet for 8 weeks and were then injected with streptozotocin (STZ) to induce T2DM. Half of the T2DM model rats received vitamin D (0.03 µg/kg/day) for 8 weeks (vitamin D-treated group; VD; n=11), while the other (T2DM group; DM; n=10) and NC group received an equivalent quantity of peanut oil. Following sacrifice, fasting plasma glucose (FPG) and fasting insulin (FINS) were recorded and homeostasis model assessment of IR (HOMA-IR) was calculated. Liver histopathology was examined using hematoxylin and eosin staining. The levels of the inflammatory cytokines C-Jun N-terminal kinase, C-Jun, tumor necrosis factor-α and interleukin-1β were measured using immunohistology, quantitative polymerase chain reaction and western blot analyses. The results revealed that treatment with vitamin D markedly alleviated the pathological alterations of liver and reduced the expression of inflammatory cytokines at the protein and mRNA levels. Furthermore, decreased levels of FPG, HOMA-IR and increased FINS were detected. In conclusion, the results of the present study indicate that vitamin D has therapeutic effects on diabetes-induced liver complications in T2DM model rats, which may involve the modulation of the inflammatory response, attenuating the crosstalk' between inflammation and IR and ameliorating hyperglycemic state.

The Anti-inflammatory Effect of the CXCR4 Antagonist-N15P Peptide and Its Modulation on Inflammation-Associated Mediators in LPS-Induced PBMC

Inflammation was the important pathological process of many disease developments, but current therapeutic means for inflammatory diseases are not satisfactory. Chemokines and their receptors represent valuable targets for anti-inflammatory drug discovery. The N15P polypeptide (sequence: LGASWHRPDKCCLGY) is independently developed by our research group, it is a new CXCR4 antagonist drug derived from viral macrophage inflammatory protein-II (vMIP-II). This study aims to clarify the anti-inflammatory potency of N15P polypeptide on the lipopolysaccharide (LPS)-induced inflammation in vitro. In this study, we evaluated the anti-inflammatory effects of N15P polypeptide by the LPS-induced peripheral blood mononuclear cell (PBMC) model and measured the level of inflammatory factors (tumor necrosis factor alpha (TNF-α), IL-6, IL-8, nuclear factor kappaB (NF-κB), cyclooxygenase-2 (COX-2), Toll-like receptor 4 (TLR4), MyD88, phosphoinositide 3-kinase (PI3K), and Akt). The messenger RNA (mRNA) expressions of inflammatory factors were analyzed by real-time PCR (RT-PCR) microarray analysis, and the production of inflammatory factors was measured further by enzyme-linked immunosorbent assay (ELISA) and Western blot. The results showed that the expression of inflammatory factors (TNF-α, IL-6, IL-8, NF-κB, COX-2, TLR4, MyD88, PI3K, and Akt) was downregulated by N15P peptide, suggesting that N15P peptide has a strong inhibitory effect on the inflammatory responses induced by LPS.

Angiotensin-converting enzyme inhibitor prevents oxidative stress, inflammation, and fibrosis in carbon tetrachloride-treated rat liver

Hepatic fibrosis is a common feature of chronic liver injury, and the involvement of angiotensin II in such process has been studied earlier. We hypothesized that anti-angiotensin II agents may be effective in preventing hepatic fibrosis. In this study, Long Evans female rats were used and divided into four groups such as Group-I, Control; Group-II, Control + ramipril; Group-III, CCl4; and Group-IV, CCl4 + ramipril. Group II and IV are treated with ramipril for 14 d. At the end of treatment, the livers were removed, and the level of hepatic marker enzymes (aspartate aminotransferase, Alanine aminotransferase, and alkaline phosphatase), nitric oxide, advanced protein oxidation product , catalase activity, and lipid peroxidation were determined. The degree of fibrosis was evaluated through histopathological staining with Sirius red and trichrome milligan staining. Carbon-tetrachloride (CCl4) administration in rats developed hepatic dysfunction and raised the hepatic marker enzymes activities significantly. CCl4 administration in rats also produced oxidative stress, inflammation, and fibrosis in liver. Furthermore, angiotensinogen-inhibitor ramipril normalized the hepatic enzymes activities and improved the antioxidant enzyme catalase activity. Moreover, ramipril treatment ameliorated lipid peroxidation and hepatic inflammation in CCl4-treated rats. Ramipril treatment also significantly reduced hepatic fibrosis in CCl4-administered rats. In conclusion, our investigation suggests that the antifibrotic effect of ramipril may be attributed to inhibition of angiotensin-II mediated oxidative stress and inflammation in liver CCl4-administered rats.

Interleukin-15-mediated inflammation promotes non-alcoholic fatty liver disease

Interleukin-15 (IL-15) is essential for the homeostasis of lymphoid cells particularly memory CD8(+) T cells and NK cells. These cells are abundant in the liver, and are implicated in obesity-associated pathogenic processes. Here we characterized obesity-associated metabolic and cellular changes in the liver of mice lacking IL-15 or IL-15Rα. High fat diet-induced accumulation of lipids was diminished in the livers of mice deficient for IL-15 or IL-15Rα. Expression of enzymes involved in the transport of lipids in the liver showed modest differences. More strikingly, the liver tissues of IL15-KO and IL15Rα-KO mice showed decreased expression of chemokines CCl2, CCL5 and CXCL10 and reduced infiltration of mononuclear cells. In vitro, IL-15 stimulation induced chemokine gene expression in wildtype hepatocytes, but not in IL15Rα-deficient hepatocytes. Our results show that IL-15 is implicated in the high fat diet-induced lipid accumulation and inflammation in the liver, leading to fatty liver disease.

CX3CR1 is a gatekeeper for intestinal barrier integrity in mice: Limiting steatohepatitis by maintaining intestinal homeostasis

Nonalcoholic fatty liver disease is seen as the hepatic manifestation of the metabolic syndrome and represents the most common liver disease in Western societies. The G protein-coupled chemokine receptor CX3CR1 plays a central role in several metabolic syndrome-related disease manifestations and is involved in maintaining intestinal homeostasis. Because diet-induced intestinal dysbiosis is a driver for nonalcoholic fatty liver disease, we hypothesized that CX3CR1 may influence the development of steatohepatitis. In two independent models of diet-induced steatohepatitis (high-fat diet and methionine/choline-deficient diet), CX3CR1 protected mice from excessive hepatic steatosis and inflammation, as well as systemic glucose intolerance. Lack of Cx3cr1 expression was associated with significantly altered intestinal microbiota composition, which was linked to an impaired intestinal barrier. Concomitantly, endotoxin levels in portal serum and inflammatory macrophages in liver were increased in Cx3cr1-/- mice, indicating an increased inflammatory response. Depletion of intestinal microbiota by administration of broad-spectrum antibiotics suppressed the number of infiltrating macrophages and promoted macrophage polarization in liver. Consequently, antibiotic-treated mice demonstrated a marked improvement of steatohepatitis.

CONCLUSION

Microbiota-mediated activation of the innate immune responses through CX3CR1 is crucial for controlling steatohepatitis progression, which recognizes CX3CR1 as an essential gatekeeper in this scenario.

Targeting Kupffer cells in non-alcoholic fatty liver disease/non-alcoholic steatohepatitis: Why and how?

Mechanisms for non-alcoholic steatohepatitis (NASH) development are under investigation in an era of increased prevalence of obesity and metabolic syndrome. Previous findings have pointed to the role of adipose tissue, adipose tissue macrophages and their secretory products in the development of a chronic inflammatory status inducing insulin resistance and a higher risk of liver steatosis called non-alcoholic fatty liver disease. The activation of resident macrophages [Kupffer cells (KC)] and the recruitment of blood derived monocytes/macrophages into the diseased liver have now been identified as key elements for disease initiation and progression. Those cells could be activated through gut flora modifications and an altered gut barrier function but also through the internalization of toxic lipid compounds in adjacent hepatocytes or in KC themselves. Due to the role of activated KC in insulin resistance, fibrosis development and inflammation amplification, they became a target in clinical trials. A shift towards an anti-inflammatory KC phenotype through peroxisome proliferator activator-receptorδ agonists, an inhibition of macrophage recruitment through anti-C-C chemokine receptor 2 action and a specific blocking of internalization of toxic lipoxidation or glycation compounds into KC by galectin-3 receptor inhibitors are now under investigation in human NASH.

Animal Models Correlating Immune Cells for the Development of NAFLD/NASH

This review mainly elaborates on the animal models available for understanding the pathogenesis of the second hit of non-alcoholic fatty liver disease (NAFLD) involving immune system. This is known to be a step forward from simple steatosis caused during the first hit, which leads to the stage of inflammation followed by more serious liver conditions like non-alcoholic steatohepatitis (NASH) and cirrhosis. Immune-deficient animal models serve as an important tool for understanding the role of a specific cell type or a cytokine in the progression of NAFLD. These animal models can be used in combination with the already available animal models of NAFLD, including dietary models, as well as genetically modified mouse models. Advancements in molecular biological techniques enabled researchers to produce several new animal models for the study of NAFLD, including knockin, generalized knockout, and tissue-specific knockout mice. Development of NASH/NAFLD in various animal models having compromised immune system is discussed in this review.

Plasma fatty acid composition in French-Canadian children with non-alcoholic fatty liver disease: Effect of n-3 PUFA supplementation

Non-alcoholic fatty liver disease (NAFLD) represents one of the most common causes of liver disease worldwide. As the NAFLD pathogenesis is associated with diet and lifestyle, the aims of the present work are to assess fatty acid (FA) composition in NAFLD young French-Canadian, to determine whether treatment with n-3 FA improves the plasma FA profile, and to define the time on the effectiveness of n-3 FA supplementation. Baseline characteristics of the NAFLD subjects show increased, anthropometric and biochemical parameters. Their plasma FA composition is characterized by a percent increase in total n-6 FA and a high proportion of saturated and total monounsaturated FA, as well as a decrease in Δ5 and increase in Δ6 desaturases. In conclusion, our results document for the first time the composition of plasma FAs in NAFLD young French Canadian and the efficacy of 3-month supplementation to improve the proportion of n-3 FA in their plasma.

Host Responses and Regulation by NFκB Signaling in the Liver and Liver Epithelial Cells Infected with A Novel Tick-borne Bunyavirus

Infection in humans by severe fever with thrombocytopenia syndrome virus (SFTSV), a novel bunyavirus transmitted by ticks, is often associated with pronounced liver damage, especially in fatal cases. Little has been known, however, about how liver cells respond to SFTSV and how the response is regulated. In this study we report that proinflammatory cytokines were induced in liver tissues of C57/BL6 mice infected with SFTSV, which may cause tissue necrosis in mice. Human liver epithelial cells were susceptible to SFTSV and antiviral interferon (IFN) and IFN-inducible proteins were induced upon infection. We observed that infection of liver epithelial cells led to significant increases in proinflammatory cytokines and chemokines, including IL-6, RANTES, IP-10, and MIP-3a, which were regulated by NFκB signaling, and the activation of NFκB signaling during infection promoted viral replication in liver epithelial cells. Viral nonstructural protein NSs was inhibitory to the induction of IFN-β, but interestingly, NFκB activation was enhanced in the presence of NSs. Therefore, NSs plays dual roles in the suppression of antiviral IFN-β induction as well as the promotion of proinflammatory responses. Our findings provide the first evidence for elucidating host responses and regulation in liver epithelial cells infected by an emerging bunyavirus.

Protective effect of galangin in Concanavalin A-induced hepatitis in mice

Galangin is an active pharmacological ingredient from propolis and Alpinia officinarum Hance, and has been reported to have anti-inflammatory and antioxidative properties. The present study aims to reveal the effect of galangin on Concanavalin A (ConA)-induced hepatitis (CIH), a well-established animal model of immune-mediated liver injury, and to clarify the related mechanism. C57BL/6 mice were pretreated with galangin followed by ConA challenge. Results indicated that galangin inhibited ConA-induced liver damage. Mice pretreated with galangin showed more reduction of liver damage when compared with control mice pretreated with vehicle solution. In galangin-pretreated mice with induced CIH, increases in serum levels of several inflammatory cytokines, including tumor necrosis factor-α, interferon-γ, and interleukin-12 were dramatically attenuated, and chemokines and adhesion molecules like interferon inducible protein-10, macrophage inflammatory protein-1α, and inter-cellular adhesion molecule-1 messenger RNA expressions in liver were decreased. Moreover, CIH mice pretreated with galangin showed less leukocyte infiltration and T-cell activation in the liver. Further, the mechanism of the anti-inflammatory effects of galangin may be attributed to its modulation of crucial inflammatory signaling pathways, including nuclear factor kappa B and interferon-gamma/signal transducer and activator of transcription 1. Collectively, these findings suggest the preventive and therapeutic potential of galangin in immune-mediated liver injury in vivo.

How Inflammation Impinges on NAFLD: A Role for Kupffer Cells

Nonalcoholic fatty liver disease (NAFLD) is rapidly becoming the most prevalent cause of liver disease worldwide and afflicts adults and children as currently associated with obesity and insulin resistance. Even though lately some advances have been made to elucidate the mechanism and causes of the disease much remains unknown about NAFLD. The aim of this paper is to discuss the present knowledge regarding the pathogenesis of the disease aiming at the initial steps of NAFLD development, when inflammation impinges on fat liver deposition. At this stage, the Kupffer cells attain a prominent role. This knowledge becomes subsequently relevant for the development of future diagnostic, prevention, and therapeutic options for the management of NAFLD.

Epigenetic mechanisms contribute to the expression of immune related genes in the livers of dairy cows fed a high concentrate diet

Purpose

Epigenetic modifications critically regulate the expression of immune-related genes in response to inflammatory stimuli. It has been extensively reported that a high concentrate (HC) diet can trigger systemic inflammation in dairy cows, yet it is unclear whether epigenetic regulation is involved in the expression of immune genes in the livers of dairy cows. This study aimed to investigate the impact of epigenetic modifications on the expression of immune-related genes.

Experimental Design

In eight mid-lactating cows, we installed a rumen cannula and catheters of the portal and hepatic veins. Cows were randomly assigned to either the treatment group fed a high concentrate (HC) diet (60% concentrate + 40% forage, n = 4) or a control group fed a low concentrate (LC) diet (40% concentrate + 60% forage, n = 4).

Results

After 10 weeks of feeding, the rumen pH was reduced, and levels of lipopolysaccharide (LPS) in the rumen, and portal and hepatic veins were notably increased in the HC group compared with the LC group. The expression levels of detected immune response-related genes, including Toll-like receptor 4 (TLR4), cytokines, chemokines, and acute phase proteins, were significantly up-regulated in the livers of cows fed a HC diet. Chromatin loosening at the promoter region of four candidate immune-related genes (TLR4, LPS-binding protein, haptoglobin, and serum amyloid A3) was elicited, and was strongly correlated with enhanced expression of these genes in the HC group. Demethylation at the promoter region of all four candidate immune-related genes was accompanied by chromatin decompaction.

Conclusion

After HC diet feeding, LPS derived from the digestive tract translocated to the liver via the portal vein, enhancing hepatic immune gene expression. The up-regulation of these immune genes was mediated by epigenetic mechanisms, which involve chromatin remodeling and DNA methylation. Our findings suggest that modulating epigenetic mechanisms could provide novel ways to treat systemic inflammatory responses elicited by the feeding of a HC diet.

AMP-kinase pathway is involved in tumor necrosis factor alpha-induced lipid accumulation in human hepatoma cells

AIM

It is well known that lipid accumulation and inflammation are two important steps in pathogenesis and progress of nonalcoholic fatty liver disease (NAFLD). However, fewer studies have explored the direct relationship between lipid accumulation and inflammation in early NAFLD. Tumor necrosis factor alpha (TNF-α) is one of the classical inflammatory cytokines. AMP-activated protein kinase (AMPK) is known as a critical regulator of energy homeostasis in metabolic processes. This study aims to investigate the role of TNF-α on lipid deposition of HepG2 cells and examine the modification of AMPK pathway.

MAIN METHODS

TNF-α was added in HepG2 cells and lipid accumulation was analyzed by Oil Red O staining and quantitative test of triglyceride (TG). The expressions of phosphorylated AMPK and its pathway (including mTOR and SREBP-1) were determined. Furthermore, an AMPK agonist (metformin or AICAR) or antagonist (compound C) was co-administrated with TNF-α in HepG2 cells to investigate its effect on TNF-α induced lipid deposition.

KEY FINDINGS

A significant increment of TG content in HepG2 cells was observed after TNF-α treatment. Meanwhile, substantially suppressed AMPK and ACC phosphorylation, enhanced mTOR and p70S6K phosphorylation, and increased protein expression of FAS and SREBP-1 were found. Co-treatment with metformin or AICAR decreased the TNF-α-induced intracellular TG, accompanied by significantly enhanced AMPK and ACC phosphorylation, suppressed mTOR and p70S6K phosphorylation, and reduced SREBP-1 and FAS expressions. On the contrary, while co-incubated with compound C, AMPK and ACC phosphorylation were suppressed and the inhibitory effect of metformin on HepG2 cell lipid deposition was also attenuated.

SIGNIFICANCE

Our results suggest that TNF-α directly induces lipid accumulation in HepG2 cells, at least in part, through the inhibition of AMPK/mTOR/SREBP-1 pathway.

Tributyltin chloride leads to adiposity and impairs metabolic functions in the rat liver and pancreas

Tributyltin chloride (TBT) is an environmental contaminant used in antifouling paints of boats. Endocrine disruptor effects of TBT are well established in animal models. However, the adverse effects on metabolism are less well understood. The toxicity of TBT in the white adipose tissue (WAT), liver and pancreas of female rats were assessed. Animals were divided into control and TBT (0.1 μg/kg/day) groups. TBT induced an increase in the body weight of the rats by the 15th day of oral exposure. The weight gain was associated with high parametrial (PR) and retroperitoneal (RP) WAT weights. TBT-treatment increased the adiposity, inflammation and expression of ERα and PPARγ proteins in both RP and PR WAT. In 3T3-L1 cells, estrogen treatment reduced lipid droplets accumulation, however increased the ERα protein expression. In contrast, TBT-treatment increased the lipid accumulation and reduced the ERα expression. WAT metabolic changes led to hepatic inflammation, lipid accumulation, increase of PPARγ and reduction of ERα protein expression. Accordingly, there were increases in the glucose tolerance and insulin sensitivity tests with increases in the number of pancreatic islets and insulin levels. These findings suggest that TBT leads to adiposity in WAT specifically, impairing the metabolic functions of the liver and pancreas.

Feeding a high-grain diet reduces the percentage of LPS clearance and enhances immune gene expression in goat liver

Background

The effects of feeding a high-grain (HG) diet on lipopolysaccharide (LPS) clearance and innate immune defence responses in the liver remain unclear. Therefore, we conducted the present study in which twelve female goats were randomly assigned to either a treatment group fed a HG diet (60% grain, n = 6) or a control group fed a low grain diet (LG; 40% grain, n = 6) for 6 weeks. Catheters were installed in the mesenteric, portal and hepatic veins, as well as one femoral artery of the goats, for determining blood flow and net clearance rate of LPS in the liver. Plasma and tissue samples were collected in the week 6 for analyzing pro-inflammatory cytokines, acute phase protein and biochemical parameters, as well as expression of genes involved in immune response.

Result

HG diet feeding increased blood flow and LPS concentration in the portal vein, hepatic vein and artery. Hepatic net LPS clearance showed that HG diet feeding elevated the rate of hepatic LPS clearance, but decreased the percentage of removed LPS accounting for the total entry of LPS into the liver. Our results demonstrated that the feeding of HG diet increased plasma concentrations of pro-inflammatory cytokines and acute phase proteins and triggered a systemic inflammatory response. In addition, peripheral blood plasma concentrations of alanine aminotransferase, alkaline phosphatase and total bilirubin were increased in the HG group compared to the LG group. This indicated that the impairment of hepatocytes occurred after 6 weeks of HG diet feeding. The expression of genes involved in immune response and Toll-like receptor (TLR)4 protein in the liver was up-regulated in the HG group compared to the LG group, indicating that increased entry of LPS enhanced hepatic immune defence responses and contributed to hepatic inflammatory responses.

Conclusion

These results provide insight into the capacity of the liver to clear LPS. The increased entry of LPS into liver enhanced hepatic immune defence responses, thereby elevated the rate of LPS clearance. However, the reduction of the percentage of hepatic LPS clearance could be due to the formation of hepatocyte lesion during HG diet feeding.

Innate immune signaling and gut-liver interactions in non-alcoholic fatty liver disease

Non-alcoholic fatty liver disease (NAFLD) is the hepatic manifestation of the metabolic syndrome and covers a disease spectrum ranging from steatosis to inflammation, fibrosis, cirrhosis and hepatocellular carcinoma (HCC). The innate immune response in the liver plays an important role during NAFLD progression. In addition, changes in the intestinal microbial balance and bacterial translocation can further affect disease progression. Immune cells in the liver recognize cell damage or pathogen invasion with intracellular or surface-expressed pattern recognition receptors (PRRs), subsequently initiating signaling cascades that trigger the release of factors promoting the inflammatory response during NAFLD progression. Therefore, mechanisms by which cells of the immune system are activated and recruited into the liver and how these cells cause injury and stress are important for understanding the inflammatory response during NAFLD.

Haematopoietic cell-derived Jnk1 is crucial for chronic inflammation and carcinogenesis in an experimental model of liver injury

BACKGROUND & AIMS

Chronic liver injury triggers complications such as liver fibrosis and hepatocellular carcinoma (HCC), which are associated with alterations in distinct signalling pathways. Of particular interest is the interaction between mechanisms controlled by IKKγ/NEMO, the regulatory IKK subunit, and Jnk activation for directing cell death and survival. In the present study, we aimed to define the relevance of Jnk in hepatocyte-specific NEMO knockout mice (NEMO(Δhepa)), a genetic model of chronic inflammatory liver injury.

METHODS

We generated Jnk1(-/-)/NEMO(Δhepa) and Jnk2(-/-)/NEMO(Δhepa) mice by crossing NEMO(Δhepa) mice with Jnk1 and Jnk2 global deficient animals, respectively, and examined the progression of chronic liver disease. Moreover, we investigated the expression of Jnk during acute liver injury, evaluated the role of Jnk1 in bone marrow-derived cells, and analysed the expression of NEMO and p-JNK in human diseased-livers.

RESULTS

Deletion of Jnk1 significantly aggravated the progression of liver disease, exacerbating apoptosis, compensatory proliferation and carcinogenesis in NEMO(Δhepa) mice. Conversely, Jnk2(-/-)/NEMO(Δhepa) displayed hepatic inflammation. By using bone marrow transfer, we observed that Jnk1 in haematopoietic cells had an impact on the progression of chronic liver disease in NEMO(Δhepa) livers. These findings are of clinical relevance since NEMO expression was downregulated in hepatocytes of patients with HCC whereas NEMO and p-JNK were expressed in a large amount of infiltrating cells.

CONCLUSIONS

A synergistic function of Jnk1 in haematopoietic cells and hepatocytes might be relevant for the development of chronic liver injury. These results elucidate the complex function of Jnk in chronic inflammatory liver disease.

Protein S exacerbates alcoholic hepatitis by stimulating liver natural killer T cells

BACKGROUND

Alcohol consumption is a major cause of liver injury but the mechanisms are not completely understood. Protein S (PS) is an anticoagulant glycoprotein with multiple functions. The role of PS in liver injury is unknown.

OBJECTIVES

This study investigated the role of PS in acute alcoholic hepatitis.

METHODS

A mouse overexpressing human PS (hPS-TG) was generated in which acute hepatitis was induced by intraperitoneal injection of ethanol.

RESULTS

The levels of serum liver enzymes and liver tissue inflammatory cytokines and the degree of hepatic steatosis were significantly increased in hPS-TG mice treated with ethanol compared with ethanol-treated wild type (WT) mice. Cell expansion, activation and inhibition of apoptosis were significantly augmented in natural killer T (NKT) cells from hPS-TG mice compared with WT mice. Liver mononuclear cells from hPS-TG mice express higher levels of inflammatory cytokines than those from WT mice after stimulation with a specific stimulant of NKT cells in vitro. In a co-culture system of hepatocytes and NKT cells, the effects of PS on ethanol-mediated cell injury were suppressed by a CD1d neutralizing antibody. Alcoholic liver injury was significantly improved in mice pre-treated with PS siRNA and anti-protein S antibody compared with control mice. Patients with alcoholic hepatitis showed significantly increased plasma PS levels and enhanced liver expression of PS and CD1d compared with controls.

CONCLUSIONS

The results of this study suggest that PS exacerbates acute alcoholic hepatitis by inhibiting apoptosis of activated NKT cells.

Neurotropin suppresses inflammatory cytokine expression and cell death through suppression of NF-κB and JNK in hepatocytes

Inflammatory response and cell death in hepatocytes are hallmarks of chronic liver disease, and, therefore, can be effective therapeutic targets. Neurotropin® (NTP) is a drug widely used in Japan and China to treat chronic pain. Although NTP has been demonstrated to suppress chronic pain through the descending pain inhibitory system, the action mechanism of NTP remains elusive. We hypothesize that NTP functions to suppress inflammatory pathways, thereby attenuating disease progression. In the present study, we investigated whether NTP suppresses inflammatory signaling and cell death pathways induced by interleukin-1β (IL-1β) and tumor necrosis factor-α (TNFα) in hepatocytes. NTP suppressed nuclear factor-κB (NF-κB) activation induced by IL-1β and TNFα assessed by using hepatocytes isolated from NF-κB-green fluorescent protein (GFP) reporter mice and an NF-κB-luciferase reporter system. The expression of NF-κB target genes, Il6, Nos2, Cxcl1, ccl5 and Cxcl2 induced by IL-1β and TNFα was suppressed after NTP treatment. We also found that NTP suppressed the JNK phosphorylation induced by IL-1β and TNFα. Because JNK activation contributes to hepatocyte death, we determined that NTP treatment suppressed hepatocyte death induced by IL-1β and TNFα in combination with actinomycin D. Taken together, our data demonstrate that NTP attenuates IL-1β and TNFα-mediated inflammatory cytokine expression and cell death in hepatocytes through the suppression of NF-κB and JNK. The results from the present study suggest that NTP may become a preventive or therapeutic strategy for alcoholic and non-alcoholic fatty liver disease in which NF-κB and JNK are thought to take part.

CD4(+)Foxp3(+) Tregs protect against innate immune cell-mediated fulminant hepatitis in mice

Foxp3(+) Tregs play important roles in maintaining homeostasis by suppressing excessive immune responses that result in serious tissue damage; yet, it is largely unknown about the impact of Tregs on innate immune cells in hepatitis models in vivo. In this study, we examined the effect of hepatic Tregs on innate immune-mediated liver injury by using the murine model of polyI:C and d-galactosamine (d-GalN)-induced hepatitis. Administration of polyI:C/d-GalN increased the number of CD4(+)Foxp3(+) Tregs in the liver. Depletion of Tregs leaded to higher levels of proinflammatory cytokine expression and severer liver injury, whereas adoptive transfer of Foxp3(+) Tregs attenuated liver injury in polyI:C/d-GalN-treated mice. In addition, depletion of Tregs leaded to a reduction in TGF-β and IL-10 expression in polyI:C/d-GalN-treated mice. Both of these cytokines were important for suppression of polyI:C/d-GalN-induced liver injury. TGF-β was derived from Tregs. IL-10 was derived from active Kupffer cells, and coincubation of Kupffer cells with Tregs increased IL-10 secretion. Furthermore, TGF-β blockade abrogated Treg-mediated suppression of proinflammatory cytokine production by innate immune cell in vitro.

CONCLUSION

CD4(+)Foxp3(+) Tregs modify innate immune responses in polyI:C/d-GalN-induced fulminant hepatitis via producing TGF-β and enhancing IL-10 secretion by Kupffer cells.

Inositol pyrophosphates: why so many phosphates?

The inositol pyrophosphates (PP-InsPs) are a specialized group of "energetic" signaling molecules found in yeasts, plants and animals. PP-InsPs boast the most crowded three dimensional phosphate arrays found in Nature; multiple phosphates and diphosphates are crammed around the six-carbon, inositol ring. Yet, phosphate esters are also a major energy currency in cells. So the synthesis of PP-InsPs, and the maintenance of their levels in the face of a high rate of ongoing turnover, all requires significant bioenergetic input. What are the particular properties of PP-InsPs that repay this investment of cellular energy? Potential answers to that question are discussed here, against the backdrop of a recent hypothesis that signaling by PP-InsPs is evolutionarily ancient. The latter idea is extended herein, with the proposal that the primordial origins of PP-InsPs is reflected in the apparent lack of isomeric specificity of certain of their actions. Nevertheless, there are other aspects of signaling by these polyphosphates that are more selective for a particular PP-InsP isomer. Consideration of the nature of both specific and non-specific effects of PP-InsPs can help rationalize why such molecules possess so many phosphates.

Comparative Analysis of Glycogene Expression in Different Mouse Tissues Using RNA-Seq Data

Glycogenes regulate a wide array of biological processes in the development of organisms as well as different diseases such as cancer, primary open-angle glaucoma, and renal dysfunction. The objective of this study was to explore the role of differentially expressed glycogenes (DEGGs) in three major tissues such as brain, muscle, and liver using mouse RNA-seq data, and we identified 579, 501, and 442 DEGGs for brain versus liver (BvL579), brain versus muscle (BvM501), and liver versus muscle (LvM442) groups. DAVID functional analysis suggested inflammatory response, glycosaminoglycan metabolic process, and protein maturation as the enriched biological processes in BvL579, BvM501, and LvM442, respectively. These DEGGs were then used to construct three interaction networks by using GeneMANIA, from which we detected potential hub genes such as PEMT and HPXN (BvL579), IGF2 and NID2 (BvM501), and STAT6 and FLT1 (LvM442), having the highest degree. Additionally, our community analysis results suggest that the significance of immune system related processes in liver, glycosphingolipid metabolic processes in the development of brain, and the processes such as cell proliferation, adhesion, and growth are important for muscle development. Further studies are required to confirm the role of predicted hub genes as well as the significance of biological processes.

Role of innate immune response in non-alcoholic Fatty liver disease: metabolic complications and therapeutic tools

Non-alcoholic fatty liver disease (NAFLD) is currently the most common liver disease worldwide, both in adults and children. It is characterized by an aberrant lipid storage in hepatocytes, named hepatic steatosis. Simple steatosis remains a benign process in most affected patients, while some of them develop superimposed necroinflammatory activity with a non-specific inflammatory infiltrate and a progression to non-alcoholic steatohepatitis with or without fibrosis. Deep similarity and interconnections between innate immune cells and those of liver parenchyma have been highlighted and showed to play a key role in the development of chronic liver disease. The liver can be considered as an “immune organ” because it hosts non-lymphoid cells, such as macrophage Kupffer cells, stellate and dendritic cells, and lymphoid cells. Many of these cells are components of the classic innate immune system, enabling the liver to play a major role in response to pathogens. Although the liver provides a “tolerogenic” environment, aberrant activation of innate immune signaling may trigger “harmful” inflammation that contributes to tissue injury, fibrosis, and carcinogenesis. Pathogen recognition receptors, such as toll-like receptors and nucleotide oligomerization domain-like receptors, are responsible for the recognition of immunogenic signals, and represent the major conduit for sensing hepatic and non-hepatic noxious stimuli. A pivotal role in liver inflammation is also played by cytokines, which can initiate or have a part in immune response, triggering hepatic intracellular signaling pathways. The sum of inflammatory signals and deranged substrate handling induce most of the metabolic alteration traits: insulin resistance, obesity, diabetes, hyperlipidemia, and their compounded combined effects. In this review, we discuss the relevant role of innate immune cell activation in relation to NAFLD, the metabolic complications associated to this pathology, and the possible pharmacological tools.