LIGHT/TNFSR14 can regulate hepatic lipase expression by hepatocytes independent of T cells and Kupffer cells

Dendrimer-Based N-Acetyl Cysteine Maternal Therapy Ameliorates Placental Inflammation via Maintenance of M1/M2 Macrophage Recruitment

Intrauterine inflammation (IUI) is the primary cause of spontaneous preterm birth and predisposes neonates to long-term sequelae, including adverse neurological outcomes. N-acetyl-L-cysteine (NAC) is the amino acid L-cysteine derivative and a precursor to the antioxidant glutathione (GSH). NAC is commonly used clinically as an antioxidant with anti-inflammatory properties. Poor bioavailability and high protein binding of NAC necessitates the use of high doses resulting in side effects including nausea, vomiting, and gastric disruptions. Therefore, dendrimer-based therapy can specifically target the drug to the cells involved in inflammation, reducing side effects with efficacy at much lower doses than the free drug. Towards development of the new therapies for the treatment of maternal inflammation, we successfully administered dendrimer-based N-Acetyl Cysteine (DNAC) in an animal model of IUI to reduce preterm birth and perinatal inflammatory response. This study explored the associated immune mechanisms of DNAC treatment on placental macrophages following IUI, especially on M1/M2 type macrophage polarization. Our results demonstrated that intraperitoneal maternal DNAC administration significantly reduced the pro-inflammatory cytokine mRNA of Il1β and Nos2, and decreased CD45⁺ leukocyte infiltration in the placenta following IUI. Furthermore, we found that DNAC altered placental immune profile by stimulating macrophages to change to the M2 phenotype while decreasing the M1 phenotype, thus suppressing the inflammatory responses in the placenta. Our study provides evidence for DNAC therapy to alleviate IUI via the maintenance of macrophage M1/M2 imbalance in the placenta.

HVEM structures and mutants reveal distinct functions of binding to LIGHT and BTLA/CD160

HVEM is a TNF (tumor necrosis factor) receptor contributing to a broad range of immune functions involving diverse cell types. It interacts with a TNF ligand, LIGHT, and immunoglobulin (Ig) superfamily members BTLA and CD160. Assessing the functional impact of HVEM binding to specific ligands in different settings has been complicated by the multiple interactions of HVEM and HVEM binding partners. To dissect the molecular basis for multiple functions, we determined crystal structures that reveal the distinct HVEM surfaces that engage LIGHT or BTLA/CD160, including the human HVEM-LIGHT-CD160 ternary complex, with HVEM interacting simultaneously with both binding partners. Based on these structures, we generated mouse HVEM mutants that selectively recognized either the TNF or Ig ligands in vitro. Knockin mice expressing these muteins maintain expression of all the proteins in the HVEM network, yet they demonstrate selective functions for LIGHT in the clearance of bacteria in the intestine and for the Ig ligands in the amelioration of liver inflammation.

Metabolic activation and colitis pathogenesis is prevented by lymphotoxin β receptor expression in neutrophils

Inflammatory bowel disease is characterized by an exacerbated intestinal immune response, but the critical mechanisms regulating immune activation remain incompletely understood. We previously reported that the TNF-superfamily molecule TNFSF14 (LIGHT) is required for preventing severe disease in mouse models of colitis. In addition, deletion of lymphotoxin beta receptor (LTβR), which binds LIGHT, also led to aggravated colitis pathogenesis. Here, we aimed to determine the cell type(s) requiring LTβR and the mechanism critical for exacerbation of colitis. Specific deletion of LTβR in neutrophils (LTβRΔN), but not in several other cell types, was sufficient to induce aggravated colitis and colonic neutrophil accumulation. Mechanistically, RNA-Seq analysis revealed LIGHT-induced suppression of cellular metabolism, and mitochondrial function, that was dependent on LTβR. Functional studies confirmed increased mitochondrial mass and activity, associated with excessive mitochondrial ROS production and elevated glycolysis at steady-state and during colitis. Targeting these metabolic changes rescued exacerbated disease severity. Our results demonstrate that LIGHT signals to LTβR on neutrophils to suppress metabolic activation and thereby prevents exacerbated immune pathogenesis during colitis.

Genetic inactivation of the LIGHT (TNFSF14) cytokine in mice restores glucose homeostasis and diminishes hepatic steatosis

AIMS/HYPOTHESIS

Non-alcoholic fatty liver disease (NAFLD) is frequently associated with type 2 diabetes mellitus. Progression of NAFLD is mediated, among other things, by activation of inflammatory pathways. In the present study, the role of the proinflammatory cytokine LIGHT (TNFSF14) was explored in NAFLD and type 2 diabetes mellitus in mice deficient for the cytokine.

METHODS

Light-deficient (Light^-/-) mice and WT controls were fed a regular chow diet (RCD) or a high-fat high-cholesterol diet (HFHCD) for 16 weeks. The expression of LIGHT and its receptors, herpes virus entry mediator (HVEM) and lymphotoxin β receptor (LTβR), was investigated in both dietary regimens. Glucose tolerance, insulin sensitivity, non-alcoholic fatty liver (NAFL), systemic and tissue inflammation, and metabolic gene expression were explored in Light^-/- and WT mice fed an RCD and an HFHCD. The effect of Light deficiency was also evaluated in hepatic tissue and in inflammation in HFHCD-fed Irs2^+/- mice with impaired insulin signalling.

RESULTS

Light deficiency did not have an effect on metabolism, in NAFL or in tissue and systemic inflammation, in RCD-fed WT mice. HVEM and LTβR were markedly increased in livers of HFHCD-fed WT mice compared with RCD-fed WT controls. In WT mice under HFHCD, Light deficiency improved glucose tolerance and insulin sensitivity. Non-alcoholic fatty liver disease activity (NAS) score, hepatic CD3⁺ T lymphocytes and F4/80⁺ macrophages were decreased in HFHCD-fed Light^-/- mice compared with HFHCD-fed WT controls. Consistent with a potential role of adipose tissue in hepatic homeostasis, Light^-/- mice exhibited augmented anti-inflammatory F4/80⁺CD206⁺ adipose tissue macrophages and reduced proinflammatory F4/80⁺CD11c⁺ adipose tissue macrophages. Moreover, adipose tissue explants from Light^-/- mice showed diminished secretion of monocyte chemoattractant protein 1 (MCP1), TNF-α and IL-17 cytokines. Circulating Light^-/- leucocytes consistently displayed augmented levels of the patrolling Ly6C^low monocytes, decreased Th9 T cell subset and diminished plasma TNF-α and IL-6 levels. Similarly, Light deficiency in Irs2^+/- mice, which display impaired insulin signalling, also reduced NAFL as well as systemic and adipose tissue inflammation. Analysis of hepatic gene expression in Light^-/- mouse livers showed reduced levels of Zbtb16, the transcription factor essential for natural killer T (NKT) cell function, and two genes related to NAFLD and fibrosis, Klf6 and Tlr4.

CONCLUSIONS/INTERPRETATION

These results indicate that Light deficiency in HFHCD improves hepatic glucose tolerance, and reduces hepatic inflammation and NAFL. This is accompanied by decreased systemic inflammation and adipose tissue cytokine secretion and by changes in the expression of key genes such as Klf6 and Tlr4 involved in NAFLD. These results suggest that therapies to block LIGHT-dependent signalling might be useful to restore hepatic homeostasis and to restrain NAFLD.

T Cells in Atherosclerosis in Ldlr-/- and Apoe-/- Mice

Atherosclerosis is the underlying basis for most cardiovascular diseases. It is a chronic inflammation affecting the arterial intima and is promoted by hypercholesterolemia. Cells of both the innate and adaptive immune systems contribute to this inflammation with macrophages and T cells being the most abundant immune cells in the atherosclerotic plaques. In this review, we discuss the studies that examined the role of T cells and T cell subsets in Apoe-/- and Ldlr-/- murine models of atherosclerosis. While there is a general consensus that Th1 cells are pro-atherogenic and regulatory T cells are atheroprotective, the role of other subsets is more ambiguous. In addition, the results in the two models of atherosclerosis do not always yield similar results. Additional studies in the two murine models using cell specific gene manipulations are needed.

Hepatic lipase inactivation decreases atherosclerosis in insulin resistance by reducing LIGHT/Lymphotoxin β-Receptor pathway

Coexistence of insulin resistance (IR) and metabolic syndrome (MetS) increases the risk of cardiovascular disease (CVD). Genetic studies in diabetes have linked Hepatic Lipase (HL) to an enhanced risk of CVD while others indicate a role of HL in inflammatory cells. Thus, we explored the role of HL on atherosclerosis and inflammation in a mouse model of MetS/IR, (apoE-/-Irs2+/- mice) and in patients with MetS and IR. HL-deficiency in apoE-/-Irs2+/- mice reduced atheroma size, plaque vulnerability, leukocyte infiltration and macrophage proliferation. Compared with apoE-/-Irs2+/-HL+/+ mice, MCP1, TNFa and IL6 plasma levels, pro-inflammatory Ly6Chi monocytes and activated(CD69+)-T lymphocytes were also decreased in apoE-/-Irs2+/-HL-/- mice. The LIGHT (Tumour necrosis factor ligand superfamily member 14, TNFSF14)/ Lymphotoxin β-Receptor(LTβ-R) pathway, which is involved in T-cell and macrophage activation, was diminished in plasma and in apoE-/-Irs2+/-HL-/- mouse atheromas. Treatment of apoE-/-Irs2+/-HL-/- mice with LIGHT increased the number of Ly6Chi-monocytes and lesion size. Acutely LIGHT-treated apoE-/- mice displayed enhanced proliferating Ly6Chi-monocytes and increased activation of the mitogen-activated protein kinase p38, suggesting that LIGHT/LTβ-R axis might promote atherogenesis by increasing proinflammatory monocytes and proliferation. Notably, MetS-IR subjects with increased atherosclerosis displayed up-regulation of the LIGHT/LTβ-R axis, enhanced inflammatory monocytes and augmented HL mRNA expression in circulating leukocytes. Thus, HL-deficiency decreases atherosclerosis in MetS/IR states by reducing inflammation and macrophage proliferation which are partly attributed to reduced LIGHT/LTβ-R pathway. These studies identify the LIGHT/LTβ-R axis as a main pathway in atherosclerosis and suggest that its inactivation might ameliorate inflammation and macrophage proliferation associated with atherosclerosis burden in MetS/IR.

Supplementary Material to this article is available at www.thrombosis-online.com.

LTβR signalling preferentially accelerates oncogenic AKT-initiated liver tumours

OBJECTIVES

The relative contributions of inflammatory signalling and sequential oncogenic dysregulation driving liver cancer pathogenesis remain incompletely understood. Lymphotoxin-β receptor (LTβR) signalling is critically involved in hepatitis and liver tumorigenesis. Therefore, we explored the interdependence of inflammatory lymphotoxin signalling and specific oncogenic pathways in the progression of hepatic cancer.

DESIGN

Pathologically distinct liver tumours were initiated by hydrodynamic transfection of oncogenic V-Akt Murine Thymoma Viral Oncogene Homolog 1 (AKT)/β-catenin or AKT/Notch expressing plasmids. To investigate the relationship of LTβR signalling and specific oncogenic pathways, LTβR antagonist (LTβR-Fc) or agonist (anti-LTβR) were administered post oncogene transfection. Initiated livers/tumours were investigated for changes in oncogene expression, tumour proliferation, progression, latency and pathology. Moreover, specific LTβR-mediated molecular events were investigated in human liver cancer cell lines and through transcriptional analyses of samples from patients with intrahepatic cholangiocarcinoma (ICC).

RESULTS

AKT/β-catenin-transfected livers displayed increased expression of LTβ and LTβR, with antagonism of LTβR signalling reducing tumour progression and enhancing survival. Conversely, enforced LTβR-activation of AKT/β-catenin-initiated tumours induced robust increases in proliferation and progression of hepatic tumour phenotypes in an AKT-dependent manner. LTβR-activation also rapidly accelerated ICC progression initiated by AKT/Notch, but not Notch alone. Moreover, LTβR-accelerated development coincides with increases of Notch, Hes1, c-MYC, pAKT and β-catenin. We further demonstrate LTβR signalling in human liver cancer cell lines to be a regulator of Notch, pAKTser473 and β-catenin. Transcriptome analysis of samples from patients with ICC links increased LTβR network expression with poor patient survival, increased Notch1 expression and Notch and AKT/PI3K signalling.

CONCLUSIONS

Our findings link LTβR and oncogenic AKT signalling in the development of ICC.

Regulation of hepatic lipase activity by sphingomyelin in plasma lipoproteins

Hepatic lipase (HL) is an important enzyme in the clearance of triacylglycerol (TAG) from the circulation, and has been proposed to have pro-atherogenic as well as anti-atherogenic properties. It hydrolyzes both phospholipids and TAG of lipoproteins, and its activity is negatively correlated with HDL levels. Although it is known that HL acts preferentially on HDL lipids, the basis for this specificity is not known, since it does not require any specific apoprotein for activity. In this study, we tested the hypothesis that sphingomyelin (SM), whose concentration is much higher in VLDL and LDL compared to HDL, is an inhibitor of HL, and that this could explain the lipoprotein specificity of the enzyme. The results presented show that the depletion of SM from normal lipoproteins activated the HL roughly in proportion to their SM content. SM depletion stimulated the hydrolysis of both phosphatidylcholine (PC) and TAG, although the PC hydrolysis was stimulated more. In the native lipoproteins, HL showed specificity for PC species containing polyunsaturated fatty acids at sn-2 position, and produced more unsaturated lyso PC species. The enzyme also showed preferential hydrolysis of certain TAG species over others. SM depletion affected the specificity of the enzyme towards PC and TAG species modestly. These results show that SM is a physiological inhibitor of HL activity in lipoproteins and that the specificity of the enzyme towards HDL is at least partly due to its low SM content.

The mutual interplay of lipid metabolism and the cells of the immune system in relation to atherosclerosis

Atherosclerosis is a chronic inflammation in the arterial wall involving cells of the innate and adaptive immune system that is promoted by hyperlipidemia. In addition, the immune system can influence lipids and lipoprotein levels and cellular lipid homeostasis can influence the level and function of the immune cells. We will review the effects of manipulation of adaptive immune cells and immune cell products on lipids and lipoproteins, focusing mainly on studies performed in murine models of atherosclerosis. We also review how lipoproteins and cellular lipid levels, particularly cholesterol levels, influence the function of cells of the innate and adaptive immune systems. The overriding theme is that these interactions are driven by the need to provide the energy and membrane components for cell proliferation and migration, membrane expansion and other functions that are so important in the functioning of the immune cells.