IL-17 signaling accelerates the progression of nonalcoholic fatty liver disease in mice

Interleukin-17A exacerbates high-fat diet-induced hepatic steatosis by inhibiting fatty acid β-oxidation

There is a growing body of evidence that the interleukin-17A (IL-17A) signaling pathway contributes to the pathogenesis of nonalcoholic fatty liver disease (NAFLD). However, the mechanism by which IL-17A signaling induces hepatocyte injury is unclear. The aim of the present study was to investigate the significance of the IL-17A axis in NAFLD and to explore the role of IL-17A in high-fat diet (HFD)-induced NAFLD in C57BL/6 mice and oleic acid (OA)-induced lipid accumulation in hepatocytes. Firstly, Consistent upregulation of IL-17A was observed in the HFD-induced steatosis mice but not the normal chow-fed control mice. Administration of IL-17A impaired liver function, aggravated hepatic lipid accumulation by inhibiting fatty acid oxidation in the HFD mice. Conversely, inhibition of IL-17A using an anti-IL-17A monoclonal antibody (mAb) significantly attenuated HFD-induced liver injury. Furthermore, IL-17A accelerated hepatic steatosis through activation of the JNK-PPARα pathway in the HFD mice and OA-preloaded hepatocytes.

CONCLUSION

The present study demonstrated that a high fat diet induces IL-17A expression, which exacerbates the progression of NAFLD by inhibiting fatty acid β-oxidation and promoting the accumulation of triglycerides (TG).

The microbiota maintain homeostasis of liver-resident γδT-17 cells in a lipid antigen/CD1d-dependent manner

The microbiota control regional immunity using mechanisms such as inducing IL-17A-producing γδ T (γδT-17) cells in various tissues. However, little is known regarding hepatic γδT cells that are constantly stimulated by gut commensal microbes. Here we show hepatic γδT cells are liver-resident cells and predominant producers of IL-17A. The microbiota sustain hepatic γδT-17 cell homeostasis, including activation, survival and proliferation. The global commensal quantity affects the number of liver-resident γδT-17 cells; indeed, E. coli alone can generate γδT-17 cells in a dose-dependent manner. Liver-resident γδT-17 cell homeostasis depends on hepatocyte-expressed CD1d, that present lipid antigen, but not Toll-like receptors or IL-1/IL-23 receptor signalling. Supplementing mice in vivo or loading hepatocytes in vitro with exogenous commensal lipid antigens augments the hepatic γδT-17 cell number. Moreover, the microbiota accelerate nonalcoholic fatty liver disease through hepatic γδT-17 cells. Thus, our work describes a unique liver-resident γδT-17 cell subset maintained by gut commensal microbes through CD1d/lipid antigens.

γδ T cells are major producers of IL-17A in response to microbial infection. Here the authors show that a high load of commensal microbes can maintain homeostasis of IL-17A⁺ γδ T cells in the liver via CD1d antigen presentation, with implications for liver diseases.

MicroRNA-26a-interleukin (IL)-6-IL-17 axis regulates the development of non-alcoholic fatty liver disease in a murine model

Non-alcoholic fatty liver disease (NAFLD) is a hepatic presentation of obesity and metabolic syndrome. MicroRNA 26a (Mir-26a) has been reported to play functions in cellular differentiation, cell growth, cell apoptosis and metastasis. A recent paper indicated that Mir-26a regulated insulin sensitivity and metabolism of glucose and lipids. However, the role of Mir-26a in NAFLD still needs to be investigated further. In our current study, vectors encoding pre-Mir-26a (LV-26a) and an empty lentiviral vector (LV-Con) delivered approximately 2 × 10⁷ transforming units of recombinant lentivirus were injected into mice through the tail vein. LV-26a-infected mice were protected from glucose dysmetabolism and showed markedly decreased total liver weight, hepatic triglyceride deposition and serum alanine transaminase (ALT) concentration when compared with LV-Con-treated mice. LV-26a-treated mice also exhibited decreased infiltration of immune cells in the liver - something attributed to reduce infiltration of T cell receptor (TCR)-γδ⁺ , granulocyte-differentiation antigen-1 (Gr-1)⁺ cells and CD11b⁺ cells. Next, we found that Mir-26a inhibited the expression of interleukin (IL)-17 and IL-6 in vivo and in vitro. Furthermore, the decreased expression of IL-17 in the liver tissue induced by Mir-26a was abrogated completely by IL-6 overexpression. The decreased total liver weight, hepatic triglyceride deposition and serum ALT concentration induced by Mir-26a was also abrogated completely by IL-6 over-expression. In conclusion, the Mir-26a-IL-6-IL-17 axis regulates the development of NAFLD in a murine model.

Immune Imbalances in Non-Alcoholic Fatty Liver Disease: From General Biomarkers and Neutrophils to Interleukin-17 Axis Activation and New Therapeutic Targets

Non-alcoholic fatty liver disease (NAFLD) is an increasing problem worldwide and is associated with negative outcomes such as cirrhosis, hepatocellular carcinoma, insulin resistance, diabetes, and cardiovascular events. Current evidence shows that the immune response has an important participation driving the initiation, maintenance, and progression of the disease. So, various immune imbalances, from cellular to cytokines levels, have been studied, either for better compression of the disease pathophysiology or as biomarkers for severity assessment and outcome prediction. In this article, we performed a thorough review of studies that evaluated the role of inflammatory/immune imbalances in the NAFLD. At the cellular level, we gave special focus on the imbalance between neutrophils and lymphocytes counts (the neutrophil-to-lymphocyte ratio), and that which occurs between T helper 17 (Th17) and regulatory T cells as emerging biomarkers. By extension, we reviewed the reflection of these imbalances at the molecular level through pro-inflammatory cytokines including those involved in Th17 differentiation (IL-6, IL-21, IL-23, and transforming growth factor-beta), and those released by Th17 cells (IL-17A, IL-17F, IL-21, and IL-22). We gave particular attention to the role of IL-17, either produced by Th17 cells or neutrophils, in fibrogenesis and steatohepatitis. Finally, we reviewed the potential of these pathways as new therapeutic targets in NAFLD.

Oxidative Stress and Liver Cancer: Etiology and Therapeutic Targets

Accumulating evidence has indicated that oxidative stress (OS) is associated with the development of hepatocellular carcinoma (HCC). However, the mechanisms remain largely unknown. Normally, OS occurs when the body receives any danger signal-from either an internal or external source-and further induces DNA oxidative damage and abnormal protein expression, placing the body into a state of vulnerability to the development of various diseases such as cancer. There are many factors involved in liver carcinogenesis, including hepatitis B virus (HBV) and hepatitis C virus (HCV) infection, alcohol abuse, and nonalcoholic fatty liver disease (NAFLD). The relationship between OS and HCC has recently been attracting increasing attention. Therefore, elucidation of the impact of OS on the development of liver carcinogenesis is very important for the prevention and treatment of liver cancer. This review focuses mainly on the relationship between OS and the development of HCC from the perspective of cellular and molecular mechanisms and the etiology and therapeutic targets of HCC.

Th17 involvement in nonalcoholic fatty liver disease progression to non-alcoholic steatohepatitis

The nonalcoholic fatty liver disease (NAFLD) is the hepatic manifestation of the metabolic syndrome. NAFLD encompasses a wide histological spectrum ranging from benign simple steatosis to non-alcoholic steatohepatitis (NASH). Sustained inflammation in the liver is critical in this process. Hepatic macrophages, including liver resident macropaghes (Kupffer cells), monocytes infiltrating the injured liver, as well as specific lymphocytes subsets play a pivotal role in the initiation and perpetuation of the inflammatory response, with a major deleterious impact on the progression of fatty liver to fibrosis. During the last years, Th17 cells have been involved in the development of inflammation not only in liver but also in other organs, such as adipose tissue or lung. Differentiation of a naïve T cell into a Th17 cell leads to pro-inflammatory cytokine and chemokine production with subsequent myeloid cell recruitment to the inflamed tissue. Th17 response can be mitigated by T regulatory cells that secrete anti-inflammatory cytokines. Both T cell subsets need TGF-β for their differentiation and a characteristic plasticity in their phenotype may render them new therapeutic targets. In this review, we discuss the role of the Th17 pathway in NAFLD progression to NASH and to liver fibrosis analyzing different animal models of liver injury and human studies.

Psoriatic inflammation causes hepatic inflammation with concomitant dysregulation in hepatic metabolism via IL-17A/IL-17 receptor signaling in a murine model

Psoriatic inflammation has been shown to be associated with cardiovascular dysfunction and systemic inflammation. Recently, psoriasis has also been linked to hepatic disorders, however underlying mechanism connecting the two are unknown. IL-17A being a central pro-inflammatory cytokine in the pathogenesis of psoriasis may be involved in hepatic inflammation through its receptor and downward signaling; however so far no study has investigated IL-17A related signaling in the liver during psoriasis in a murine model. Therefore, this study explored psoriasis-induced hepatic inflammation and concurrent metabolic changes. Mice were applied topically imiquimod (IMQ) to develop psoriatic inflammation. Additionally mice were also treated either with IL-17A or anti-IL17A antibody to explore the role of IL-17 related signaling in liver. Mice were then assessed for hepatic inflammation through assessment of inflammatory/oxidative stress markers (IL-17RC, NFκB, IL-6, MCP-1, IL-1β, GM-CSF, ICAM-1, iNOS, lipid peroxides and myeloperoxidase activity) as well as hepatic injury (alanine aminotransferase, aspartate aminotransferase and alkaline phosphatase) and protein/lipid metabolic biomarkers (total proteins, albumin, total bilirubin, triglycerides, HDL cholesterol, and total cholesterol). IMQ treatment led to hepatic inflammation as evidenced by increased pro-inflammatory cytokines and oxidative stress with concomitant dysregulation in hepatic protein/lipid metabolism. Treatment with IL-17A further aggravated, whereas treatment with anti-IL17A antibody ameliorated IMQ-induced changes in hepatic injury/inflammation and protein/lipid metabolism. Our study shows for the first time that psoriatic inflammation leads to hepatic inflammation which results in dysregulated protein/lipid metabolism through IL-17RC/NFκB signaling. This could result in increased risk of cardiovascular dysfunction in patients with psoriasis.

Pathogenesis of Nonalcoholic Steatohepatitis: Interactions between Liver Parenchymal and Nonparenchymal Cells

Nonalcoholic fatty liver disease (NAFLD) is the most common type of chronic liver disease in the Western countries, affecting up to 25% of the general population and becoming a major health concern in both adults and children. NAFLD encompasses the entire spectrum of fatty liver disease in individuals without significant alcohol consumption, ranging from nonalcoholic fatty liver (NAFL) to nonalcoholic steatohepatitis (NASH) and cirrhosis. NASH is a manifestation of the metabolic syndrome and hepatic disorders with the presence of steatosis, hepatocyte injury (ballooning), inflammation, and, in some patients, progressive fibrosis leading to cirrhosis. The pathogenesis of NASH is a complex process and implicates cell interactions between liver parenchymal and nonparenchymal cells as well as crosstalk between various immune cell populations in liver. Lipotoxicity appears to be the central driver of hepatic cellular injury via oxidative stress and endoplasmic reticulum (ER) stress. This review focuses on the contributions of hepatocytes and nonparenchymal cells to NASH, assessing their potential applications to the development of novel therapeutic agents. Currently, there are limited pharmacological treatments for NASH; therefore, an increased understanding of NASH pathogenesis is pertinent to improve disease interventions in the future.

Interleukin-17 as a factor linking the pathogenesis of psoriasis with metabolic disorders

Psoriasis is a systemic disease with numerous concomitant metabolic disorders. Apparently, T-helper 17 lymphocytes and interleukin (IL)-17 constitute an important element linking those disorders. The role of IL-17 has been confirmed by numerous studies, although it remains not completely understood, and the study results are controversial. Based on the studies performed so far, it is assumed that IL-17 contributes to development of atherosclerosis by means of: stimulation of production of proinflammatory compounds; induction of apoptosis of endothelial cells and heart muscle cells; stimulation of von Willebrand factor production; and induction of the matrix metalloproteinase-9 (atherosclerotic plaque rupture). On the other hand, IL-17 may exert protective activity due to inhibition of proatherogenic interferon-γ and vascular cell adhesion molecule-1, and production of type I collagen by smooth muscle cells. The role of IL-17 in the pathogenesis of obesity is as important as other proinflammatory cytokines. On the other hand, its deficiency increases diet-induced obesity and accelerates adipose tissue accumulation. Although the role of IL-17A in the pathogenesis of metabolic disorders in humans remains controversial, introduction of anti-IL-17A treatments brings hope that development of metabolic disorders in patients with psoriasis may be inhibited.

Modulation of ambient temperature promotes inflammation and initiates atherosclerosis in wild type C57BL/6 mice

Objectives

Obesity and obesity-associated inflammation is central to a variety of end-organ sequelae including atherosclerosis, a leading cause of death worldwide. Although mouse models have provided important insights into the immunopathogenesis of various diseases, modeling atherosclerosis in mice has proven difficult. Specifically, wild-type (WT) mice are resistant to developing atherosclerosis, while commonly used genetically modified mouse models of atherosclerosis are poor mimics of human disease. The lack of a physiologically relevant experimental model of atherosclerosis has hindered the understanding of mechanisms regulating disease development and progression as well as the development of translational therapies. Recent evidence suggests that housing mice within their thermoneutral zone profoundly alters murine physiology, including both metabolic and immune processes. We hypothesized that thermoneutral housing would allow for augmentation of atherosclerosis induction and progression in mice.

Methods

ApoE^−/− and WT mice were housed at either standard (T_S) or thermoneutral (T_N) temperatures and fed either a chow or obesogenic “Western” diet. Analysis included quantification of (i) obesity and obesity-associated downstream sequelae, (ii) the development and progression of atherosclerosis, and (iii) inflammatory gene expression pathways related to atherosclerosis.

Results

Housing mice at T_N, in combination with an obesogenic “Western” diet, profoundly augmented obesity development, exacerbated atherosclerosis in ApoE^−/− mice, and initiated atherosclerosis development in WT mice. This increased disease burden was associated with altered lipid profiles, including cholesterol levels and fractions, and increased aortic plaque size. In addition to the mild induction of atherosclerosis, we similarly observed increased levels of aortic and white adipose tissue inflammation and increased circulating immune cell expression of pathways related to adverse cardiovascular outcome.

Conclusions

In sum, our novel data in WT C57Bl/6 mice suggest that modulation of a single environmental variable, temperature, dramatically alters mouse physiology, metabolism, and inflammation, allowing for an improved mouse model of atherosclerosis. Thus, thermoneutral housing of mice shows promise in yielding a better understanding of the cellular and molecular pathways underlying the pathogenesis of diverse diseases.

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Thermoneutral housing augments atherosclerosis in ApoE^−/− and WT mice.

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Thermoneutral housing increases serum LDL levels in obese WT mice.

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Thermoneutral housing increases inflammatory potential in lean and obese mice.

IL-17 Axis Driven Inflammation in Non-Alcoholic Fatty Liver Disease Progression

Obesity is a primary risk factor for the development of non-alcoholic fatty liver disease (NAFLD). NAFLD, the most common chronic liver disease in the world, represents a spectrum of disorders that range from steatosis (NAFL) to steatohepatitis (NASH) to cirrhosis. It is anticipated that NAFLD will soon surpass chronic hepatitis C infection as the leading cause for needing liver transplantation. Despite its clinical and public health significance no specific therapies are available. Although the etiology of NAFLD is multifactorial and remains largely enigmatic, it is well accepted that inflammation is a central component of NAFLD pathogenesis. Despite the significance, critical immune mediators, loci of immune activation, the immune signaling pathways and the mechanism(s) underlying disease progression remain incompletely understood. Recent findings have focused on the role of Interleukin 17 (IL-17) family of proinflammatory cytokines in obesity and pathogenesis of obesity-associated sequelae. Notably, obesity favors a Th17 bias and is associated with increased IL-17A expression in both humans and mice. Further, in mice, IL-17 axis has been implicated in regulation of both obesity and NAFLD pathogenesis. However, despite these recent advances several important questions require further evaluation including: the relevant cellular source of IL-17A production; the critical IL- 17RA-expressing cell type; the critical liver infiltrating immune cells; and the underlying cellular effector mechanisms. Addressing these questions may aid in the identification and development of novel therapeutic targets for prevention of inflammation- driven NAFLD progression.

Metabolic Inflammation-Associated IL-17A Causes Non-alcoholic Steatohepatitis and Hepatocellular Carcinoma

Obesity increases hepatocellular carcinoma (HCC) risks via unknown mediators. We report that hepatic unconventional prefoldin RPB5 interactor (URI) couples nutrient surpluses to inflammation and non-alcoholic steatohepatitis (NASH), a common cause of HCC. URI-induced DNA damage in hepatocytes triggers inflammation via T helper 17 (Th17) lymphocytes and interleukin 17A (IL-17A). This induces white adipose tissue neutrophil infiltration mediating insulin resistance (IR) and fatty acid release, stored in liver as triglycerides, causing NASH. NASH and subsequently HCC are prevented by pharmacological suppression of Th17 cell differentiation, IL-17A blocking antibodies, and genetic ablation of the IL-17A receptor in myeloid cells. Human hepatitis, fatty liver, and viral hepatitis-associated HCC exhibit increased IL-17A correlating positively with steatosis. IL-17A blockers may prevent IR, NASH, and HCC in high-risk patients.

P(URI)fying Novel Drivers of NASH and HCC: A Feedforward Loop of IL17A via White Adipose Tissue

How obesity and metabolic syndrome trigger non-alcoholic steatohepatitis (NASH) and hepatocellular carcinoma (HCC) remains elusive. In this issue, Gomes and colleagues describe that nutrient surplus induces hepatic URI expression, triggering genotoxicity and IL17A expression, thus leading to insulin resistance, NASH, and HCC. IL17A signaling blockers might become a readily translatable therapy.

Relationship between leptin concentration and body fat with peripheral blood mononuclear cells cytokines among obese and overweight adults

BACKGROUND

Overweight and obesity has been suggested to be well correlated with altered levels of pro-inflammatory cytokines.

AIM

The purpose of this study is to assess the relationship of body fat mass (BFM), body fat percentage (BFP) and leptin levels with peripheral blood mononuclear cells (PBMCs) cytokines among obese and overweight adults.

METHODS

Eighty-two overweight and obese individuals were divided into two BMI-category groups (BMI <30 and BMI ≥30 kg/m²) in this study. Balanced blocked randomization was used based on their sex and BMI ranges. Fasting blood samples, PBMCs cytokines, leptin and anthropometric indices were measured and PBMCs were cultured.

RESULTS

Mean of leptin concentrations were 23.14 ± 4.07 and 28.25 ± 4.35 pg/ml among individuals with BMI <30 and BMI ≥30 kg/m², respectively. The mean values of anthropometric measurements (all P < 0.001), the concentrations of TNF-α (P = 0.028) and IFN-γ (P = 0.029) were significantly higher among obese individuals. BFP had a significant positive correlation with leptin (P < 0.001, r = 0.445) and TGF-β (P = 0.03, r = 0.243). BFM has significant positive correlation with leptin (P < 0.001, r = 0.521). Leptin had a positive significant correlation with IFN-γ (p = 0.03, r = 0.251).

CONCLUSIONS

Regarding these results, we proved that BFP, BFM and leptin levels have significant correlations with some PBMC cytokines. Focusing on such strategies may lead to promises for alleviating obesity and its co-morbidities.

The role of immune cells in metabolism-related liver inflammation and development of non-alcoholic steatohepatitis (NASH)

The low grade inflammatory state present in obesity promotes the progression of Non-Alcoholic Fatty Liver Disease (NAFLD). In Non-Alcoholic Steatohepatitis (NASH), augmented hepatic steatosis is accompanied by aberrant intrahepatic inflammation and exacerbated hepatocellular injury. NASH is an important disorder and can lead to fibrosis, cirrhosis and even neoplasia. The pathology of NASH involves a complex network of mechanisms, including increased infiltration of different subsets of immune cells, such as monocytes, T-lymphocytes and neutrophils, to the liver, as well as activation and in situ expansion of liver resident cells such as Kupffer cells or stellate cells. In this review, we summarize recent advances regarding understanding the role of the various cells of the innate and adaptive immunity in NASH development and progression, and discuss possible future therapeutic options and tools to interfere with disease progression.

Regulation of Inflammation by IL-17A and IL-17F Modulates Non-Alcoholic Fatty Liver Disease Pathogenesis

Non-alcoholic fatty liver disease (NAFLD) has become the most common chronic liver disease worldwide. While it is well-accepted that inflammation is central to NAFLD pathogenesis, the immune pathway(s) orchestrating disease progression are poorly defined. Notably, IL-17RA signaling, via IL-17A, plays an important role in obesity-driven NAFLD pathogenesis. However, the role of the IL-17F, another IL-17RA ligand, in NAFLD pathogenesis has not been examined. Further, the cell types expressing IL-17RA and producing IL-17RA ligands in the pathogenesis of NAFLD have not been defined. Here, IL-17RA-/-, IL-17A-/-, IL-17F-/- and wild-type (WT) mice were fed either standard chow diet or methionine and choline deficient diet (MCDD)--a diet known to induce steatosis and hepatic inflammation through beta-oxidation dysfunction--and hepatic inflammation and NAFLD progression were subsequently quantified. MCDD feeding augmented hepatic IL-17RA expression and significantly increased hepatic infiltration of macrophages and IL-17A and IL-17F producing CD4+ and CD8+ T cells in WT mice. In contrast, IL-17RA-/-, IL-17A-/-, and IL-17F-/- mice, despite increased steatosis, exhibited significant protection from hepatocellular damage compared to WT controls. Protection from hepatocellular damage correlated with decreased levels of hepatic T-cell and macrophage infiltration and decreased expression of inflammatory mediators associated with NAFLD. In sum, our results indicate that the IL-17 axis also plays a role in a MCDD-induced model of NAFLD pathogenesis. Further, we show for the first time that IL-17F, and not only IL-17A, plays an important role in NAFLD driven inflammation.

The balance between IL-17 and IL-22 produced by liver-infiltrating T-helper cells critically controls NASH development in mice

The mechanisms responsible for the evolution of steatosis towards NASH (non-alcoholic steatohepatitis) and fibrosis are not completely defined. In the present study we evaluated the role of CD4(+) T-helper (Th) cells in this process. We analysed the infiltration of different subsets of CD4(+) Th cells in C57BL/6 mice fed on a MCD (methionine choline-deficient) diet, which is a model reproducing all phases of human NASH progression. There was an increase in Th17 cells at the beginning of NASH development and at the NASH-fibrosis transition, whereas levels of Th22 cells peaked between the first and the second expansion of Th17 cells. An increase in the production of IL (interleukin)-6, TNFα (tumour necrosis factor α), TGFβ (transforming growth factor β) and CCL20 (CC chemokine ligand 20) accompanied the changes in Th17/Th22 cells. Livers of IL-17(-/-) mice were protected from NASH development and characterized by an extensive infiltration of Th22 cells. In vitro, IL-17 exacerbated the JNK (c-Jun N-terminal kinase)-dependent mouse hepatocyte lipotoxicity induced by palmitate. IL-22 prevented lipotoxicity through PI3K (phosphoinositide 3-kinase)-mediated inhibition of JNK, but did not play a protective role in the presence of IL-17, which up-regulated the PI3K/Akt inhibitor PTEN (phosphatase and tensin homologue deleted on chromosome 10). Consistently, livers of IL-17(-/-) mice fed on the MCD diet displayed decreased activation of JNK, reduced expression of PTEN and increased phosphorylation of Akt compared with livers of wild-type mice. Hepatic infiltration of Th17 cells is critical for NASH initiation and development of fibrosis in mice, and reflects an infiltration of Th22 cells. Th22 cells are protective in NASH, but only in the absence of IL-17. These data strongly support the potentiality of clinical applications of IL-17 inhibitors that can prevent NASH by both abolishing the lipotoxic action of IL-17 and allowing IL-22-mediated protection.

PTPRO-mediated autophagy prevents hepatosteatosis and tumorigenesis

Autophagy plays a critical role in the progression of nonalcoholic steatohepatitis (NASH) and hepatocellular carcinoma (HCC). Protein tyrosine phosphatase receptor type O (PTPRO) was recently identified as a tumor suppressor, but little is known about its role in NASH. Here, we investigated the role of PTPRO-dependent autophagy in insulin resistance, lipid metabolism, and hepatocarcinogenesis. Wild-type (WT) and ptpro^−/− mice were fed a high-fat diet (HFD) for another 16 weeks after diethylnitrosamine (DEN) injection to induce NASH. Ptpro^−/− mice exhibited severe liver injury, insulin resistance, hepatosteatosis and autophagy deficiency compared with WT littermates. PTPRO deletion also promoted the induction of lipogenic target genes and decreases in β-oxidation-related genes. Increased activation of AKT and accumulation of cytoplasmic p53 was detected in ptpro^−/− mice, which in combination repressed autophagy. Intriguingly, hyperinsulinemia involving AKT activation was also exacerbated in HFD-fed mice due to PTPRO deletion. Activation of AKT induced stabilization of the MDMX/MDM2 heterocomplex, thus promoting p53 accumulation in the cytoplasm. Inhibition of AKT restored autophagy and p53 accumulation in hepatocytes, indicating that AKT acts upstream of p53. Due to hyperinsulinemia and autophagy deficiency, a HFD could aggravate steatohepatitis in ptpro^−/− mice. Importantly, the expression of PTPRO was much decreased in human steatohepatitis, which was associated with increased p62 accumulation. Together, these data indicate that PTPRO regulates insulin and lipid metabolism via the PI3K/Akt/MDM4/MDM2/P53 axis by affecting autophagy.

Immune Cells and Metabolism

Low-grade inflammation in the obese AT (AT) and the liver is a critical player in the development of obesity-related metabolic dysregulation, including insulin resistance, type 2 diabetes and non-alcoholic steatohepatitis (NASH). Myeloid as well as lymphoid cells infiltrate the AT and the liver and expand within these metabolic organs as a result of excessive nutrient intake, thereby exacerbating tissue inflammation. Macrophages are the paramount cell population in the field of metabolism-related inflammation; as obesity progresses, a switch takes place within the AT environment from an M2-alternatively activated macrophage state to an M1-inflammatory macrophage-dominated milieu. M1-polarized macrophages secrete inflammatory cytokines like TNF in the obese AT; such cytokines contribute to insulin resistance in adipocytes. Besides macrophages, also CD8+ T cells promote inflammation in the AT and the liver and thereby the deterioration of the metabolic balance in adipocytes and hepatocytes. Other cells of the innate immunity, such as neutrophils or mast cells, interfere with metabolic homeostasis as well. On the other hand, eosinophils or T-regulatory cells, the number of which in the AT decreases in the course of obesity, function to maintain metabolic balance by ameliorating inflammatory processes. In addition, eosinophils and M2-polarized macrophages may contribute to "beige" adipogenesis under lean conditions; beige adipocytes are located predominantly in the subcutaneous AT and have thermogenic and optimal energy-dispensing properties like brown adipocytes. This chapter will summarize the different aspects of the regulation of homeostasis of metabolic tissues by immune cells.

Role of interleukin 17 in fatty liver disease and other liver diseases

Fatty liver disease is a lipid metabolism disorder in the liver, with a variety of etiologies which result in the accumulation of fat in the liver. The pathogenesis of fatty liver disease is still unclear and symptomatic treatment is the main method. In recent years, the incidence of fatty liver disease in China is increasing year by year, and the age of onset becomes younger. Recent studies suggest that interleukin 17 (IL-17) is involved not only in the pathogenesis of various diseases, such as autoimmune diseases, inflammatory diseases, and malignant tumors, but also in fatty liver and other liver diseases through inducing insulin resistance, activating some important pathways in the liver, mediating some inflammatory factors and so on. This paper will review the role of IL-17 in fatty liver disease and other liver diseases.

Nonalcoholic fatty liver disease

Nonalcoholic fatty liver disease (NAFLD) is a disorder characterized by excess accumulation of fat in hepatocytes (nonalcoholic fatty liver (NAFL)); in up to 40% of individuals, there are additional findings of portal and lobular inflammation and hepatocyte injury (which characterize nonalcoholic steatohepatitis (NASH)). A subset of patients will develop progressive fibrosis, which can progress to cirrhosis. Hepatocellular carcinoma and cardiovascular complications are life-threatening co-morbidities of both NAFL and NASH. NAFLD is closely associated with insulin resistance; obesity and metabolic syndrome are common underlying factors. As a consequence, the prevalence of NAFLD is estimated to be 10-40% in adults worldwide, and it is the most common liver disease in children and adolescents in developed countries. Mechanistic insights into fat accumulation, subsequent hepatocyte injury, the role of the immune system and fibrosis as well as the role of the gut microbiota are unfolding. Furthermore, genetic and epigenetic factors might explain the considerable interindividual variation in disease phenotype, severity and progression. To date, no effective medical interventions exist that completely reverse the disease other than lifestyle changes, dietary alterations and, possibly, bariatric surgery. However, several strategies that target pathophysiological processes such as an oversupply of fatty acids to the liver, cell injury and inflammation are currently under investigation. Diagnosis of NAFLD can be established by imaging, but detection of the lesions of NASH still depend on the gold-standard but invasive liver biopsy. Several non-invasive strategies are being evaluated to replace or complement biopsies, especially for follow-up monitoring.

Pathophysiology and Mechanisms of Nonalcoholic Fatty Liver Disease

Nonalcoholic fatty liver disease (NAFLD) encompasses a spectrum of liver disorders characterized by abnormal hepatic fat accumulation, inflammation, and hepatocyte dysfunction. Importantly, it is also closely linked to obesity and the metabolic syndrome. NAFLD predisposes susceptible individuals to cirrhosis, hepatocellular carcinoma, and cardiovascular disease. Although the precise signals remain poorly understood, NAFLD pathogenesis likely involves actions of the different hepatic cell types and multiple extrahepatic signals. The complexity of this disease has been a major impediment to the development of appropriate metrics of its progression and effective therapies. Recent clinical data place increasing importance on identifying fibrosis, as it is a strong indicator of hepatic disease-related mortality. Preclinical modeling of the fibrotic process remains challenging, particularly in the contexts of obesity and the metabolic syndrome. Future studies are needed to define the molecular pathways determining the natural progression of NAFLD, including key determinants of fibrosis and disease-related outcomes. This review covers the evolving concepts of NAFLD from both human and animal studies. We discuss recent clinical and diagnostic methods assessing NAFLD diagnosis, progression, and outcomes; compare the features of genetic and dietary animal models of NAFLD; and highlight pharmacological approaches for disease treatment.

Progression from Nonalcoholic Fatty Liver to Nonalcoholic Steatohepatitis Is Marked by a Higher Frequency of Th17 Cells in the Liver and an Increased Th17/Resting Regulatory T Cell Ratio in Peripheral Blood and in the Liver

Nonalcoholic fatty liver disease is increasing in prevalence. It can be subdivided into nonalcoholic fatty liver (NAFL) and nonalcoholic steatohepatitis (NASH). Five to twenty percent of cases progress from NAFL to NASH. Increased hepatic Th17 cells and IL-17 expression were observed in NASH mice and patients, respectively. We analyzed CD4(+) effector T cells and regulatory T cells (Tregs) from peripheral blood and livers of NAFL and NASH patients. A total of 51 NAFL patients, 30 NASH patients, 31 nonalcoholic fatty liver disease patients (without histology), and 43 healthy controls were included. FACS analysis was performed on PBMCs and intrahepatic lymphocytes. Compared with healthy controls, a lower frequency of resting Tregs (rTregs; CD4(+)CD45RA(+)CD25(++)) and higher frequencies of IFN-γ(+) and/or IL-4(+) cells were detected among CD4(+) T cells of peripheral blood in NASH, and to a lesser degree in NAFL. In hepatic tissue, NAFL to NASH progression was marked by an increase in IL-17(+) cells among intrahepatic CD4(+) T cells. To define immunological parameters in peripheral blood to distinguish NAFL from NASH, we calculated different ratios. Th17/rTreg and Th2/rTreg ratios were significantly increased in NASH versus NAFL. The relevance of our findings for NASH pathogenesis was highlighted by the normalization of all of the changes 1 y after bariatric surgery. In conclusion, our data indicate that NAFL patients show changes in their immune cell profile compared with healthy controls. NAFL to NASH progression is marked by an increased frequency of IL-17(+) cells among intrahepatic CD4(+) T cells and higher Th17/rTreg and Th2/rTreg ratios in peripheral blood.

IL-25 or IL-17E Protects against High-Fat Diet-Induced Hepatic Steatosis in Mice Dependent upon IL-13 Activation of STAT6

IL-25 or IL-17E is a member of IL-17 cytokine family and has immune-modulating activities. The role of IL-25 in maintaining lipid metabolic homeostasis remains unknown. We investigated the effects of exogenous IL-25 or deficiency of IL-25 on hepatic lipid accumulation. IL-25 expression was examined in paraffin-embedded tissue sections of liver from patients or in the livers from mice. Mouse model of steatosis was induced by feeding a high-fat diet (HFD). Extent of steatosis as well as expression of cytokines, key enzymes for lipid metabolic pathways, markers for Kupffer cells/macrophages, and lipid droplet (LD) proteins, were analyzed. Our results show that hepatic steatosis in mice was accompanied by increased LD proteins, but decreased IL-25 in the liver. Decreased hepatic IL-25 was also observed in patients with fatty liver. Administration of IL-25 to HFD-fed wild-type mice led to a significant improvement in hepatic steatosis. This effect was associated with increased expression of IL-13, development of alternatively activated Kupffer cells/macrophages, and decreased expression of LD proteins in the liver. In contrast, administration of IL-25 to HFD-fed mice deficient in STAT6 or IL-13 had no effects. In addition, stimulation of primary hepatocytes with IL-13, but not IL-25, resulted in downregulation of LD proteins. Finally, mice deficient in IL-25 had exacerbated hepatic lipid accumulation when fed the HFD. These data demonstrate that dysregulated IL-25 expression contributes to lipid accumulation, whereas exogenous IL-25 protects against hepatic steatosis through IL-13 activation of STAT6. IL-25 and IL-13 are potential therapeutic agents for hepatic steatosis and associated pathologies.

Effect of Clematis polysaccharide on serum IL-17 and TNF-α levels and hepatic pathological changes in rats with non-alcoholic steatohepatitis

AIM: To investigate the effect of Clematis polysaccharide on serum levels of interleukin-17 (IL-17) and tumor necrosis factor alpha (TNF-α) and hepatic pathological changes in rats with non-alcoholic steatohepatitis (NASH), and to analyze the correlation between serum levels of IL-17 and TNF-α.

METHODS: A rat model of NASH was established by feeding SD rats a high-fat diet. The levels of fasting IL-17 and TNF-α were tested, and the liver fatty degeneration grade and liver inflammation grade were assessed for NASH model rats, NASH rats treated with Clematis polysaccharide, NASH rats treated with polyene phosphatidylcholine, and normal rats. The differences in fasting IL-17 and TNF-α levels and hepatic pathological changes among all groups were compared, and the correlation between serum levels of IL-17 and TNF-α was analyzed.

RESULTS: Compared with the model group, NASH rats treated with Clematis polysaccharide had milder liver fatty degeneration and liver inflammation (P < 0.05 for both) and lower serum levels of IL-17 and TNF-α (P < 0.01 for both). Compared with the polyene phosphatidylcholine group, NASH rats treated with Clematis polysaccharide had a similar liver fatty degeneration grade and liver inflammation grade, and similar serum IL-17 and TNF-α levels (P > 0.05 for all).

CONCLUSION: Clematis polysaccharide is effective in NASH rats, its therapeutic effect is equivalent to that of polyene phosphatidylcholine, and the underlying mechanism may be associated with reducing serum IL-17 and TNF-α levels, and improving hepatic pathological change.

Type 2 immunity-dependent reduction of segmented filamentous bacteria in mice infected with the helminthic parasite Nippostrongylus brasiliensis

BACKGROUND

Dynamic interactions between the host and gastrointestinal microbiota play an important role for local and systemic immune homeostasis. Helminthic parasites modulate the host immune response, resulting in protection against autoimmune disease but also increased susceptibility to pathogen infection. The underlying mechanisms remain largely unknown.

RESULTS

We showed that the type 2 immune response to enteric Nippostrongylus brasiliensis infection in mice was associated with altered intestinal mucin and AMP expression and shifts in microbiota composition. Most strikingly, infection reduced concentrations of intestinal segmented filamentous bacteria (SFB), known inducers of T helper 17 cells, and IL-17-associated gene expression. Infected mice deficient in IL-13 or STAT6 did not reduce SFB or IL-17, and exogenous IL-25 replicated the effects of parasite infection in wild type mice.

CONCLUSIONS

Our data show that parasite infection acts through host type 2 immunity to reduce intestinal SFB and expression of IL-17, providing an example of a microbiota-dependent immune modulation by parasites.

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.

IL-6 and ICOS Antagonize Bim and Promote Regulatory T Cell Accrual with Age

Regulatory T cells (Tregs), a subset of CD4(+) T cells, dramatically accumulate with age in humans and mice and contribute to age-related immune suppression. Recently, we showed that a majority of accumulating Tregs in aged mice expressed low levels of CD25, and their accrual is associated with declining levels of IL-2 in aged mice. In this study, we further investigated the origin of CD25(lo) Tregs in aged mice. First, aged Tregs had high expression of neuropilin-1 and Helios, and had a broad Vβ repertoire. Next, we analyzed the gene expression profile of Tregs, naive T cells, and memory T cells in aged mice. We found that the gene expression profile of aged CD25(lo) Tregs were more related to young CD25(lo) Tregs than to either naive or memory T cells. Further, the gene expression profile of aged Tregs was consistent with recently described "effector" Tregs (eTregs). Additional analysis revealed that nearly all Tregs in aged mice were of an effector phenotype (CD44(hi)CD62L(lo)) and could be further characterized by high levels of ICOS and CD69. ICOS contributed to Treg maintenance in aged mice, because in vivo Ab blockade of ICOSL led to a loss of eTregs, and this loss was rescued in Bim-deficient mice. Further, serum levels of IL-6 increased with age and contributed to elevated expression of ICOS on aged Tregs. Finally, Treg accrual was significantly blunted in aged IL-6-deficient mice. Together, our data show a role for IL-6 in promoting eTreg accrual with age likely through maintenance of ICOS expression.

Subcutaneous fat transplantation alleviates diet-induced glucose intolerance and inflammation in mice

AIMS/HYPOTHESIS

Adipose tissue (AT) distribution is a major determinant of mortality and morbidity in obesity. In mice, intra-abdominal transplantation of subcutaneous AT (SAT) protects against glucose intolerance and insulin resistance (IR), but the underlying mechanisms are not well understood.

METHODS

We investigated changes in adipokines, tissue-specific glucose uptake, gene expression and systemic inflammation in male C57BL6/J mice implanted intra-abdominally with either inguinal SAT or epididymal visceral AT (VAT) and fed a high-fat diet (HFD) for up to 17 weeks.

RESULTS

Glucose tolerance was improved in mice receiving SAT after 6 weeks, and this was not attributable to differences in adiposity, tissue-specific glucose uptake, or plasma leptin or adiponectin concentrations. Instead, SAT transplantation prevented HFD-induced hepatic triacylglycerol accumulation and normalised the expression of hepatic gluconeogenic enzymes. Grafted fat displayed a significant increase in glucose uptake and unexpectedly, an induction of skeletal muscle-specific gene expression. Mice receiving subcutaneous fat also displayed a marked reduction in the plasma concentrations of several proinflammatory cytokines (TNF-α, IL-17, IL-12p70, monocyte chemoattractant protein-1 [MCP-1] and macrophage inflammatory protein-1β [ΜIP-1β]), compared with sham-operated mice. Plasma IL-17 and MIP-1β concentrations were reduced from as early as 4 weeks after transplantation, and differences in plasma TNF-α and IL-17 concentrations predicted glucose tolerance and insulinaemia in the entire cohort of mice (n = 40). In contrast, mice receiving visceral fat transplants were glucose intolerant, with increased hepatic triacylglycerol content and elevated plasma IL-6 concentrations.

CONCLUSIONS/INTERPRETATION

Intra-abdominal transplantation of subcutaneous fat reverses HFD-induced glucose intolerance, hepatic triacylglycerol accumulation and systemic inflammation in mice.

Are obesity-related insulin resistance and type 2 diabetes autoimmune diseases?

Obesity and associated insulin resistance predispose individuals to develop chronic metabolic diseases, such as type 2 diabetes and cardiovascular disease. Although these disorders affect a significant proportion of the global population, the underlying mechanisms of disease remain poorly understood. The discovery of elevated tumor necrosis factor-α in adipose tissue as an inducer of obesity-associated insulin resistance marked a new era of understanding that a subclinical inflammatory process underlies the insulin resistance and metabolic dysfunction that precedes type 2 diabetes. Advances in the field identified components of both the innate and adaptive immune response as key players in regulating such inflammatory processes. As antigen specificity is a hallmark of an adaptive immune response, its role in modulating the chronic inflammation that accompanies obesity and type 2 diabetes begs the question of whether insulin resistance and type 2 diabetes can have autoimmune components. In this Perspective, we summarize current data that pertain to the activation and perpetuation of adaptive immune responses during obesity and discuss key missing links and potential mechanisms for obesity-related insulin resistance and type 2 diabetes to be considered as potential autoimmune diseases.

Galectin-3 Ablation Enhances Liver Steatosis, but Attenuates Inflammation and IL-33-Dependent Fibrosis in Obesogenic Mouse Model of Nonalcoholic Steatohepatitis

The importance of Galectin-3 (Gal-3) in obesity-associated liver pathology is incompletely defined. To dissect the role of Gal-3 in fibrotic nonalcoholic steatohepatitis (NASH), Gal-3-deficient (LGALS3(-/-)) and wild-type (LGALS3(+/+)) C57Bl/6 mice were placed on an obesogenic high fat diet (HFD, 60% kcal fat) or standard chow diet for 12 and 24 wks. Compared to WT mice, HFD-fed LGALS3(-/-) mice developed, in addition to increased visceral adiposity and diabetes, marked liver steatosis, which was accompanied with higher expression of hepatic PPAR-γ, Cd36, Abca-1 and FAS. However, as opposed to LGALS3(-/-) mice, hepatocellular damage, inflammation and fibrosis were more extensive in WT mice which had an elevated number of mature myeloid dendritic cells, proinflammatory CD11b(+)Ly6C(hi) monocytes/macrophages in liver, peripheral blood and bone marrow, and increased hepatic CCL2, F4/80, CD11c, TLR4, CD14, NLRP3 inflammasome, IL-1β and NADPH-oxidase enzymes mRNA expression. Thus, obesity-driven greater steatosis was uncoupled with attenuated fibrotic NASH in Gal-3-deficient mice. HFD-fed WT mice had a higher number of hepatocytes that strongly expressed IL-33 and hepatic CD11b(+)IL-13(+) cells, increased levels of IL-33 and IL-13 and up-regulated IL-33, ST2 and IL-13 mRNA in liver compared with LGALS3(-/-) mice. IL-33 failed to induce ST2 upregulation and IL-13 production by LGALS3(-/-) peritoneal macrophages in vitro. Administration of IL-33 in vivo enhanced liver fibrosis in HFD-fed mice in both genotypes, albeit to a significantly lower extent in LGALS3(-/-) mice, which was associated with less numerous hepatic IL-13-expressing CD11b(+) cells. The present study provides evidence of a novel role for Gal-3 in regulating IL-33-dependent liver fibrosis.

Xenobiotic and Endobiotic Mediated Interactions Between the Cytochrome P450 System and the Inflammatory Response in the Liver

The liver is a unique organ in the body as it has significant roles in both metabolism and innate immune clearance. Hepatocytes in the liver carry a nearly complete complement of drug metabolizing enzymes, including numerous cytochrome P450s. While a majority of these enzymes effectively detoxify xenobiotics, or metabolize endobiotics, a subportion of these reactions result in accumulation of metabolites that can cause either direct liver injury or indirect liver injury through activation of inflammation. The liver also contains multiple populations of innate immune cells including the resident macrophages (Kupffer cells), a relatively large number of natural killer cells, and blood-derived neutrophils. While these cells are primarily responsible for clearance of pathogens, activation of these immune cells can result in significant tissue injury during periods of inflammation. When activated chronically, these inflammatory bouts can lead to fibrosis, cirrhosis, cancer, or death. This chapter will focus on interactions between how the liver processes xenobiotic and endobiotic compounds through the cytochrome P450 system, and how these processes can result in a response from the innate immune cells of the liver. A number of different clinically relevant diseases, as well as experimental models, are currently available to study mechanisms related to the interplay of innate immunity and cytochrome P450-mediated metabolism. A major focus of the chapter will be to evaluate currently understood mechanisms in the context of these diseases, as a way of outlining mechanisms that dictate the interactions between the P450 system and innate immunity.

Control of oxidative stress in hepatocellular carcinoma: Helpful or harmful?

Oxidative stress is becoming recognized as a key factor in the progression of chronic liver disease (CLD) and hepatocarcinogenesis. The metabolically important liver is a major reservoir of mitochondria that serve as sources of reactive oxygen species, which are apparently responsible for the initiation of necroinflammation. As a result, CLD could be a major inducer of oxidative stress. Chronic hepatitis C is a powerful generator of oxidative stress, causing a high rate of hepatocarcinogenesis among patients with cirrhosis. Non-alcoholic steatohepatitis is also associated with oxidative stress although its hepatocarcinogenic potential is lower than that of chronic hepatitis C. Analyses of serum markers and histological findings have shown that hepatocellular carcinoma correlates with oxidative stress and experimental data indicate that oxidative stress increases the likelihood of developing hepatocarcinogenesis. However, the results of antioxidant therapy have not been favorable. Physiological oxidative stress is a necessary biological response, and thus adequate control of oxidative stress and a balance between oxidative and anti-oxidative responses is important. Several agents including metformin and L-carnitine can reportedly control mechanistic oxidative stress. This study reviews the importance of oxidative stress in hepatocarcinogenesis and of control strategies for the optimal survival of patients with CLD and hepatocellular carcinoma.

Immunoregulation by lipids during the development of non-alcoholic steatohepatitis

Non-alcoholic fatty liver disease (NAFLD) represents the most common liver disorder in western countries and it is commonly associated with obesity and progression of the metabolic syndrome. Comprehending a wide spectrum of pathologic features, it is currently well recognized that a key point for the integrity of hepatocyte functionality in NAFLD is the progression from simple steatosis to non-alcoholic steatohepatitis (NASH). Indeed, activation of the innate immune system in response to hepatic metabolic stresses represents a central process that determines the evolution and the reversibility of liver damage. Despite of the burden of studies published in recent years, it is still intriguingly unclear how accumulation of lipids in hepatocytes triggers the activation of the inflammatory response leading to the recruitment of infiltrating cells of extra-hepatic origins. In this review we offer a general view on recent advances pointing out how different classes of lipids are able to specifically affect hepatocytes functionality and survival, thus differently influencing the organization of the hepatic immune response. On the other hand, we gathered recent studies intending to illustrate the basic mechanisms through which several non-parenchymal hepatic and extra-hepatic cell populations get activated in response to lipids. Finally, we indicate latter findings proposing how the immune system majorly contributes to the progression of NASH.

Lymphocyte roles in metabolic dysfunction: of men and mice

Type 2 diabetes (T2D) is a metabolic disease associated with obesity-related insulin resistance (IR) and chronic inflammation. Animal studies indicate that IR can be caused and/or exacerbated by systemic and/or tissue-specific alterations in lymphocyte differentiation and function. Human studies also indicate that obesity-associated inflammation promotes IR. Nevertheless, clinical trials with anti-inflammatory therapies have yielded modest impacts on established T2D. Unlike mouse models, where obesity is predominantly associated with IR, 20-25% of obese humans are metabolically healthy with high insulin sensitivity. The uncoupling of obesity from IR in humans but not in animal models advocates for a more comprehensive understanding of mediators and mechanisms of human obesity-promoted IR, and better integration of knowledge from human studies into animal experiments to efficiently pursue T2D prevention and treatment.

Trypanosoma cruzi infection is a potent risk factor for non-alcoholic steatohepatitis enhancing local and systemic inflammation associated with strong oxidative stress and metabolic disorders

BACKGROUND

The immune mechanisms underlying experimental non-alcoholic steatohepatitis (NASH), and more interestingly, the effect of T. cruzi chronic infection on the pathogenesis of this metabolic disorder are not completely understood.

METHODOLOGY/PRINCIPAL FINDINGS

We evaluated immunological parameters in male C57BL/6 wild type and TLR4 deficient mice fed with a standard, low fat diet, LFD (3% fat) as control group, or a medium fat diet, MFD (14% fat) in order to induce NASH, or mice infected intraperitoneally with 100 blood-derived trypomastigotes of Tulahuen strain and also fed with LFD (I+LFD) or MFD (I+MFD) for 24 weeks. We demonstrated that MFD by itself was able to induce NASH in WT mice and that parasitic infection induced marked metabolic changes with reduction of body weight and steatosis revealed by histological studies. The I+MFD group also improved insulin resistance, demonstrated by homeostasis model assessment of insulin resistance (HOMA-IR) analysis; although parasitic infection increased the triglycerides and cholesterol plasma levels. In addition, hepatic M1 inflammatory macrophages and cytotoxic T cells showed intracellular inflammatory cytokines which were associated with high levels of IL6, IFNγ and IL17 plasmatic cytokines and CCL2 chemokine. These findings correlated with an increase in hepatic parasite load in I+MFD group demonstrated by qPCR assays. The recruitment of hepatic B lymphocytes, NK and dendritic cells was enhanced by MFD, and it was intensified by parasitic infection. These results were TLR4 signaling dependent. Flow cytometry and confocal microscopy analysis demonstrated that the reactive oxygen species and peroxinitrites produced by liver inflammatory leukocytes of MFD group were also exacerbated by parasitic infection in our NASH model.

CONCLUSIONS

We highlight that a medium fat diet by itself is able to induce steatohepatitis. Our results also suggest a synergic effect between damage associated with molecular patterns generated during NASH and parasitic infection, revealing an intense cross-talk between metabolically active tissues, such as the liver, and the immune system. Thus, T. cruzi infection must be considered as an additional risk factor since exacerbates the inflammation and accelerates the development of hepatic injury.

Thermoneutral housing is a critical factor for immune function and diet-induced obesity in C57BL/6 nude mice

OBJECTIVES

Obesity-related cancers represent public health burdens of the first order. Nevertheless, suitable mouse models to unravel molecular mechanisms linking obesity to human cancer are still not available. One translational model is the immunocompromised Foxn1 (winged-helix/forkead transcription factor) nude mouse transplanted with human tumor xenografts. However, most xenograft studies are conducted in nude mice on an in-bred BALB/c background that entails protection from diet-induced obesity. To overcome such resistance to obesity and its sequelae, we here propose the dual strategy of utilizing Foxn1 nude mice on a C57BL/6 background and housing them at their thermoneutral zone.

METHODS

C57BL/6 nude and corresponding wild-type mice, housed at 23 or 33 °C, were subjected to either low-fat diet or high-fat diet (HFD). Energy expenditure, locomotor activity, body core temperature, respiratory quotient as well as food and water intake were analyzed using indirect calorimetry. Immune function at different housing temperatures was assessed by using an in vivo cytokine capture assay.

RESULTS

Our data clearly demonstrate that conventional housing protects C57BL/6 nude mice from HFD-induced obesity, potentially via increased energy expenditure. In contrast, HFD-fed C57BL/6 nude mice housed at thermoneutral conditions develop adiposity, increased hepatic triglyceride accumulation, adipose tissue inflammation and glucose intolerance. Moreover, increased circulating levels of lipopolysaccharide-driven cytokines suggest a greatly enhanced immune response in C57BL/6 nude mice housed at thermoneutrality.

CONCLUSION

Our data reveals mild cold stress as a major modulator for energy and body weight homeostasis as well as immune function in C57BL/6 nude mice. Adjusting housing temperatures to the thermoneutral zone may ultimately be key to successfully study growth and progression of human tumors in a diet-induced obese environment.

Induction of IL-17A Precedes Development of Airway Hyperresponsiveness during Diet-Induced Obesity and Correlates with Complement Factor D

Obesity is a risk factor for the development of asthma. Obese mice exhibit innate airway hyperresponsiveness (AHR), a characteristic feature of asthma, and IL-17A is required for development of AHR in obese mice. The purpose of this study was to examine the temporal association between the onset of AHR and changes in IL-17A during the development of obesity by high-fat feeding in mice. At weaning, C57BL/6J mice were placed either on mouse chow or on a high-fat diet (HFD) and examined 9, 12, 15, 18, or 24 weeks later. Airway responsiveness to aerosolized methacholine (assessed via the forced oscillation technique) was greater in mice fed HFD versus chow for 24 weeks but not at earlier time points. Bronchoalveolar lavage and serum IL-17A were not affected by either the type or duration of diet, but increased pulmonary IL17a mRNA abundance was observed in HFD versus chow fed mice after both 18 and 24 weeks. Flow cytometry also confirmed an increase in IL-17A(+) γδ T cells and IL-17A(+) CD4(+) T (Th17) cells in lungs of HFD versus chow fed mice. Pulmonary expression of Cfd (complement factor D, adipsin), a gene whose expression can be reduced by IL-17A, decreased after both 18 and 24 weeks in HFD versus chow fed mice. Furthermore, pulmonary Cfd mRNA abundance correlated with elevations in pulmonary Il17a mRNA expression and with AHR. Serum levels of TNFα, MIP-1α, and MIP-1β, and classical markers of systemic inflammation of obesity were significantly greater in HFD than chow fed mice after 24 weeks, but not earlier. In conclusion, our data indicate that pulmonary rather than systemic IL-17A is important for obesity-related AHR and suggest that changes in pulmonary Cfd expression contribute to these effects of IL-17A. Further, the observation that increases in Il17a preceded the development of AHR by several weeks suggests that IL-17A interacts with other factors to promote AHR. The observation that the onset of the systemic inflammation of obesity coincided temporally with the development of AHR suggest that systemic inflammation may be one of these factors.

Molecular mechanisms and new treatment strategies for non-alcoholic steatohepatitis (NASH)

Non-alcoholic steatohepatitis (NASH) is a severe form of non-alcoholic fatty liver disease (NAFLD), in which most patients exhibit non-progressive, non-alcoholic fatty liver (NAFL) attributable to simple steatosis. Multiple hits, including genetic differences, fat accumulation, insulin resistance and intestinal microbiota changes, account for the progression of NASH. NAFLD is strongly associated with obesity, which induces adipokine secretion, endoplasmic reticulum (ER) and oxidative stress at the cellular level, which in turn induces hepatic steatosis, inflammation and fibrosis. Among these factors, gut microbiota are acknowledged as having an important role in initiating this multifactorial disease. Oxidative stress is considered to be a key contributor in the progression from NAFL to NASH. Macrophage infiltration is apparent in NAFL and NASH, while T-cell infiltration is apparent in NASH. Although several clinical trials have shown that antioxidative therapy with vitamin E can effectively control hepatitis pathology in the short term, the long-term effects remain obscure and have often proved to be ineffective in many other diseases. Several long-term antioxidant protocols have failed to reduce mortality. New treatment modalities that incorporate current understanding of NAFLD molecular pathogenesis must be considered.

Mechanisms of Liver Injury in Non-Alcoholic Steatohepatitis

Non-alcoholic steatohepatitis (NASH) is a disorder marked by alterations in hepatic lipid homeostasis as well as liver injury in the form of cell death, inflammation and fibrosis. Research into the pathophysiology of NASH is dynamic. New concepts from the fields of cell biology, microbiology, immunology and genetics are being tested for their applicability to NASH; discoveries in each of these areas are enriching our understanding of this complex disease. This review summarizes how recent developments from the bench and bedside are merging with more traditional concepts to reshape our view of NASH pathogenesis. Highlights include human studies that emphasize the role of de novo lipogenesis in NASH and experimental work uncovering a role for the inflammasome in NASH. Genetic predispositions to NASH are being clarified, and intestinal microbiome is emerging as a determinant of fatty liver. These unique ideas are now taking their place within an integrated picture of NASH pathogenesis.