The mechanisms that promote an inflammatory environment and accelerated atherosclerosis in diabetes are poorly understood. We show that macrophages isolated from two different mouse models of type 1 diabetes exhibit an inflammatory phenotype. This inflammatory phenotype associates with increased expression of long-chain acyl-CoA synthetase 1 (ACSL1), an enzyme that catalyzes the thioesterification of fatty acids. Monocytes from humans and mice with type 1 diabetes also exhibit increased ACSL1. Furthermore, myeloid-selective deletion of ACSL1 protects monocytes and macrophages from the inflammatory effects of diabetes. Strikingly, myeloid-selective deletion of ACSL1 also prevents accelerated atherosclerosis in diabetic mice without affecting lesions in nondiabetic mice. Our observations indicate that ACSL1 plays a critical role by promoting the inflammatory phenotype of macrophages associated with type 1 diabetes; they also raise the possibilities that diabetic atherosclerosis has an etiology that is, at least in part, distinct from the etiology of nondiabetic vascular disease and that this difference is because of increased monocyte and macrophage ACSL1 expression.
Type 1 diabetes mellitus (T1DM) increases the risk of atherosclerotic cardiovascular disease (CVD) in humans by poorly understood mechanisms. Using mouse models of T1DM-accelerated atherosclerosis, we found that relative insulin deficiency, rather than hyperglycemia, elevated levels of apolipoprotein C3 (APOC3), an apolipoprotein that prevents clearance of triglyceride-rich lipoproteins (TRLs) and their remnants. We then showed that serum APOC3 levels predict incident CVD events in subjects with T1DM in the Coronary Artery Calcification in Type 1 Diabetes (CACTI) study. To explore underlying mechanisms, we examined the impact of Apoc3 antisense oligonucleotides (ASOs) on lipoprotein metabolism and atherosclerosis in a mouse model of T1DM. Apoc3 ASO treatment abolished the increased hepatic expression of Apoc3 in diabetic mice, resulting in lower levels of TRLs, without improving glycemic control. APOC3 suppression also prevented arterial accumulation of APOC3-containing lipoprotein particles, macrophage foam cell formation, and accelerated atherosclerosis in diabetic mice. Our observations demonstrate that relative insulin deficiency increases APOC3 and that this results in elevated levels of TRLs and accelerated atherosclerosis in a mouse model of T1DM. Because serum levels of APOC3 predicted incident CVD events in the CACTI study, inhibition of APOC3 might reduce CVD risk in patients with T1DM.
Cardiovascular disease, largely because of disruption of atherosclerotic lesions, accounts for the majority of deaths in people with type 1 diabetes. Recent mouse models have provided insights into the accelerated atherosclerotic lesion initiation in diabetes, but it is unknown whether diabetes directly worsens more clinically relevant advanced lesions. We therefore used an LDL receptordeficient mouse model, in which type 1 diabetes can be induced at will, to investigate the effects of diabetes on preexisting lesions. Advanced lesions were induced by feeding mice a high-fat diet for 16 weeks before induction of diabetes. Diabetes, independently of lesion size, increased intraplaque hemorrhage and plaque disruption in the brachiocephalic artery of mice fed low-fat or high-fat diets for an additional 14 weeks. Hyperglycemia was not sufficient to induce plaque disruption. Furthermore, diabetes resulted in increased accumulation of monocytic cells positive for S100A9, a proinflammatory biomarker for cardiovascular events, and for a macrophage marker protein, without increasing lesion macrophage content. S100A9 immunoreactivity correlated with intraplaque hemorrhage. Aggressive lowering primarily of triglyceride-rich lipoproteins prevented both plaque disruption and the increased S100A9 in diabetic atherosclerotic lesions. Conversely, oleate promoted macrophage differentiation into an S100A9-positive population in vitro, thereby mimicking the effects of diabetes. Thus, diabetes increases plaque disruption, independently of effects on plaque initiation, through a mechanism that requires triglyceride-rich lipoproteins and is associated with an increased accumulation of S100A9-positive monocytic cells. These findings indicate an important link between diabetes, plaque disruption, and the innate immune system. intraplaque hemorrhage ͉ macrophage ͉ S100A9
SUMMARY Inflammatory activation of myeloid cells is accompanied by increased glycolysis, which is required for the surge in cytokine production. Although in vitro studies suggest that increased macrophage glucose metabolism is sufficient for cytokine induction, the pro-inflammatory effects of increased myeloid cell glucose flux in vivo and the impact on atherosclerosis, a major complication of diabetes, are unknown. We therefore tested the hypothesis that increased glucose uptake in myeloid cells stimulates cytokine production and atherosclerosis. Overexpression of the glucose transporter GLUT1 in myeloid cells caused increased glycolysis and flux through the pentose phosphate pathway, but did not induce cytokines. Moreover, myeloid cell-specific overexpression of GLUT1 in LDL receptor-deficient mice was ineffective in promoting atherosclerosis. Thus, increased glucose flux is insufficient for inflammatory myeloid cell activation and atherogenesis. If glucose promotes atherosclerosis by increasing cellular glucose flux, myeloid cells do not appear to be the key targets.
Rosiglitazone is an insulin-sensitizing agent that has recently been shown to exert beneficial effects on atherosclerosis. In addition to peroxisome proliferator-activated receptor (PPAR)-␥, rosiglitazone can affect other targets, such as directly inhibiting recombinant long-chain acylCoA synthetase (ACSL)-4 activity. Because it is unknown if ACSL4 is expressed in vascular cells involved in atherosclerosis, we investigated the ability of rosiglitazone to inhibit ACSL activity and fatty acid partitioning in human and murine arterial smooth muscle cells (SMCs) and macrophages. Human and murine SMCs and human macrophages expressed Acsl4, and rosiglitazone inhibited Acsl activity in these cells. Furthermore, rosiglitazone acutely inhibited partitioning of fatty acids into phospholipids in human SMCs and inhibited fatty acid partitioning into diacylglycerol and triacylglycerol in human SMCs and macrophages through a PPAR-␥-independent mechanism. Conversely, murine macrophages did not express ACSL4, and rosiglitazone did not inhibit ACSL activity in these cells, nor did it affect acute fatty acid partitioning into cellular lipids. Thus, rosiglitazone inhibits ACSL activity and fatty acid partitioning in human and murine SMCs and in human macrophages through a PPAR-␥-independent mechanism likely to be mediated by ACSL4 inhibition. Therefore, rosiglitazone might alter the biological effects of fatty acids in these cells and in atherosclerosis.
Abstract-It is becoming increasingly clear that suboptimal blood glucose control results in adverse effects on large blood vessels, thereby accelerating atherosclerosis and cardiovascular disease, manifested as myocardial infarction, stroke, and peripheral vascular disease. Cardiovascular disease is accelerated by both type 1 and type 2 diabetes. In type 1 diabetes, hyperglycemia generally occurs in the absence of elevated blood lipid levels, whereas type 2 diabetes is frequently associated with dyslipidemia. In this review article, we discuss hyperglycemia versus hyperlipidemia as culprits in diabetes-accelerated atherosclerosis and cardiovascular disease, with emphasis on studies in mouse models and isolated vascular cells. Recent studies on LDL receptor-deficient mice that are hyperglycemic, but exhibit no marked dyslipidemia compared with nondiabetic controls, show that diabetes in the absence of diabetes-induced hyperlipidemia is associated with an accelerated formation of atherosclerotic lesions, similar to what is seen in fat-fed nondiabetic mice. These effects of diabetes are masked in severely dyslipidemic mice, suggesting that the effects of glucose and lipids on lesion initiation might be mediated by similar mechanisms. Recent evidence from isolated endothelial cells demonstrates that glucose and lipids can induce endothelial dysfunction through similar intracellular mechanisms. Analogous effects of glucose and lipids are also seen in macrophages. Furthermore, glucose exerts many of its cellular effects through lipid mediators. We propose that diabetes without associated dyslipidemia accelerates atherosclerosis by mechanisms that can also be activated by hyperlipidemia. (Circ Res. 2007;100:769-781.)
content is ABCA1, a sterol-induced membrane protein that mediates the transport of excess cholesterol from cells to lipid-poor apolipoprotein (apo)A-I, the major protein component of HDLs ( 1 ). Mutations in human ABCA1 are associated with a severe HDL defi ciency, cholesterol deposition in tissue macrophages, and prevalent cardiovascular disease ( 2 ). Over-expressing ABCA1 in mice signifi cantly decreases atherosclerosis ( 3 ), whereas ablating ABCA1 in stem-cell transferred mouse macrophages increases atherosclerotic lesions ( 4, 5 ). Thus, ABCA1 plays a critical role in protecting against cardiovascular disease.We showed previously that diabetes-associated metabolic factors impair ABCA1 function by destabilizing the protein in vitro . Reactive carbonyl precursors for advance glycation end products (AGEs), which are increased in both types 1 and 2 diabetes ( 6-9 ), acutely and severely suppress ABCA1 cholesterol export activity and reduce ABCA1 protein levels in cultured cells ( 10 ). Unsaturated fatty acids, which can be elevated in poorly controlled type 1 diabetes and are often elevated in type 2 diabetes and the metabolic syndrome ( 11-13 ), increase ABCA1 degradation through a phospholipase D/protein kinase C ␦ signaling pathway that phosphorylates ABCA1 serines ( 14-17 ).These studies raise the possibility that diabetes impairs the ABCA1 cholesterol export pathway in vivo, leading to increased accumulation of cholesterol in arterial macrophages and enhanced atherogenesis (18)(19)(20). In support of this idea are our studies showing that inducing diabetes in cholesterol-fed swine markedly increased atherosclerotic lesion size in association with a dramatic reduction in the level of immunodectable ABCA1 in lesion foam-cell macrophages ( 10 ).Here, we examined the effects of type 1 diabetes on ABCA1 protein and mRNA levels in mouse macrophages and tissues. Results show that inducing diabetes in two different type 1 diabetic mouse models reduced the ABCA1 protein content of peritoneal macrophages and the kidAbstract Accumulation of cholesterol in arterial macrophages may contribute to diabetes-accelerated atherosclerotic cardiovascular disease. The ATP-binding cassette transporter ABCA1 is a cardioprotective membrane protein that mediates cholesterol export from macrophages. Factors elevated in diabetes, such as reactive carbonyls and free fatty acids, destabilize ABCA1 protein in cultured macrophages, raising the possibility that impaired ABCA1 plays an atherogenic role in diabetes. We therefore examined the modulation of ABCA1 in two mouse models of diabetes. We isolated peritoneal macrophages, livers, kidneys, and brains from type 1 non-obese diabetic (NOD) mice and mice made diabetic by viral-induced autoimmune destruction of pancreatic ␤ -cells, and we measured ABCA1 protein and mRNA levels and cholesterol contents. ABCA1 protein levels and cholesterol export activity were reduced by 40-44% ( P < 0.01) in peritoneal macrophages and protein levels by 48% ( P < 0.001) in kidneys in diabetic NOD mice comp...
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