Cholesterol, the most important sterol in mammals, helps maintain plasma membrane fluidity and is a precursor of bile acids, oxysterols, and steroid hormones. Cholesterol in the body is obtained from the diet or can be de novo synthetized. Cholesterol homeostasis is mainly regulated by the liver, where cholesterol is packed in lipoproteins for transport through a tightly regulated process. Changes in circulating lipoprotein cholesterol levels lead to atherosclerosis development, which is initiated by an accumulation of modified lipoproteins in the subendothelial space; this induces significant changes in immune cell differentiation and function. Beyond lesions, cholesterol levels also play important roles in immune cells such as monocyte priming, neutrophil activation, hematopoietic stem cell mobilization, and enhanced T cell production. In addition, changes in cholesterol intracellular metabolic enzymes or transporters in immune cells affect their signaling and phenotype differentiation, which can impact on atherosclerosis development. In this review, we describe the main regulatory pathways and mechanisms of cholesterol metabolism and how these affect immune cell generation, proliferation, activation, and signaling in the context of atherosclerosis.

Our findings establish a direct link between p19(ARF), plaque apoptosis, and atherosclerosis, and suggest that human genetic variants associated to diminished CDKN2A expression may accelerate atherosclerosis by limiting plaque apoptosis.

Lixisenatide decreases atheroma plaque size and instability in Apoe Irs2 mice by reprogramming macrophages towards an M2 phenotype, which leads to reduced inflammation. This study identifies a critical role for this drug in macrophage polarisation inside plaques and provides experimental evidence supporting a novel mechanism of action for GLP-1 analogues in the reduction of cardiovascular risk associated with insulin resistance.

IR increases plaque vulnerability by augmenting the CX3CL1/CX3CR1 axis, which is mechanistically linked to reduced VSMC survival. Thus, modulation of IRS2-dependent signalling emerges as a potential therapeutic strategy to promote VSMC survival and atheroma plaque stability and to reduce inflammatory mediators in IR-MetS.

Objective-The mechanisms underlying accelerated atherosclerosis in metabolic syndrome (MetS) patients remain poorly defined. In the mouse, complete disruption of insulin receptor substrate-2 (Irs2) causes insulin resistance, MetS-like manifestations, and accelerates atherosclerosis. Here, we performed human, mouse, and cell culture studies to gain insight into the contribution of defective Irs2 signaling to MetS-associated alterations. Methods and Results-In circulating leukocytes from insulin-resistant MetS patients, Irs2 and Akt2 mRNA levels inversely correlate with plasma insulin levels and HOMA index and are reduced compared to insulin-sensitive MetS patients. Notably, a moderate reduction in Irs2 expression in fat-fed apolipoprotein E-null mice lacking one allele of Irs2 (apoE Ϫ/Ϫ Irs2 ϩ/Ϫ ) accelerates atherosclerosis compared to apoE-null controls, without affecting plaque composition. Partial Irs2 inactivation also increases CD36 and SRA scavenger receptor expression and modified LDL uptake in macrophages, diminishes Akt2 and Ras expression in aorta, and enhances expression of the proatherogenic cytokine MCP1 in aorta and primary vascular smooth muscle cells (VSMCs) and macrophages. T he metabolic syndrome (MetS) is defined by the presence of at least 3 of the following abnormalities: abdominal obesity, glucose intolerance, hypertension, low HDL-cholesterol levels, or hypertriglyceridemia. 1,2 Patients with MetS and type-2 diabetes mellitus (T2DM) have 2 to 5 times higher risk of atherosclerosis, a chronic inflammatory disease that results from interactions between modified lipoproteins and cells of the arterial wall, including endothelial, immune, and vascular smooth muscle cells (VSMCs). [3][4][5] Among the different cardiovascular risk factors that precipitate atherosclerosis and associated cardiovascular disease (CVD), T2DM and MetS are becoming the most relevant given that the prevalence of these metabolic diseases is expected to increase by 165% in the next 40 years, representing the health plague of the 21st century. 2 Importantly, the incidence of CVD increases when T2DM and the MetS coexist. 1,2 Population aging and acquisition of sedentary lifestyle patterns (eg, obesity and physical inactivity) are major driving forces behind these metabolic diseases. A number of alterations in endothelial cells, VSMCs, and platelets have been identified which may accelerate atherosclerosis, plaque instability, and thrombus formation in T2DM/MetS patients, however the underlying mechanisms remain ill defined. 2,6,7 Many MetS patients display insulin resistance (IR), which seems to play a pivotal role in the development of both atherogenic dyslipidemia and T2DM. 1 Therefore, IR is an attractive target for prevention of CVD. However, whether IR management per se might reduce CVD risk remains unknown.On binding to the insulin receptor (INS-R), insulin exerts its action through insulin-receptor substrate proteins (IRS1-4). 8 Studies in genetically-modified mice have highlighted a major role of IRS2 in ␤-cell funct...

In vivo metabolic tests are highly valuable to determine whether atherosclerosis progression in mouse models is accompanied by carbohydrate metabolism alterations such as glucose intolerance and insulin resistance. In this chapter, we describe protocols to perform in the mouse glucose and insulin tolerance tests, two metabolic assays which evaluate the glucose tolerance and the insulin sensitivity, respectively.

SummaryRecent genome-wide association studies have linked type-2 diabetes mellitus to a genomic region in chromosome 9p21 near the Ink4/Arf locus, which encodes tumor suppressors that are up-regulated in a variety of mammalian organs during aging. However, it is unclear whether the susceptibility to type-2 diabetes is associated with altered expression of the Ink4/Arf locus. In the present study, we investigated the role of Ink4/Arf in age-dependent alterations of insulin and glucose homeostasis using Super-Ink4/Arf mice which bear an extra copy of the entire Ink4/Arf locus. We find that, in contrast to age-matched wild-type controls, Super-Ink4/Arf mice do not develop glucose intolerance with aging. Insulin tolerance tests demonstrated increased insulin sensitivity in Super-Ink4/Arf compared with wild-type mice, which was accompanied by higher activation of the insulin receptor substrate (IRS)-PI3K-AKT pathway in liver, skeletal muscle and heart. Glucose uptake studies in Super-Ink4/Arf mice showed a tendency toward increased 18 F-fluorodeoxyglucose uptake in skeletal muscle compared with wild-type mice (P = 0.079). Furthermore, a positive correlation between glucose uptake and baseline glucose levels was observed in Super-Ink4/ Arf mice (P < 0.008) but not in wild-type mice. Our studies reveal a protective role of the Ink4/Arf locus against the development of age-dependent insulin resistance and glucose intolerance.

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.