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.

Background-S100A9 is constitutively expressed in neutrophils, dendritic cells, and monocytes; is associated with acute and chronic inflammatory conditions; and is implicated in obesity and cardiovascular disease in humans. Most of the constitutively secreted S100A9 is derived from myeloid cells. A recent report demonstrated that mice deficient in S100A9 exhibit reduced atherosclerosis compared with controls and suggested that this effect was due in large part to loss of S100A9 in bone marrow-derived cells. Methods and Results-To directly investigate the role of bone marrow-derived S100A9 in atherosclerosis and insulin resistance in mice, low-density lipoprotein receptor-deficient, S100A9-deficient bone marrow chimeras were generated. Neither atherosclerosis nor insulin resistance was reduced in S100A9-deficient chimeras fed a diet rich in fat and carbohydrates. To investigate the reason for this lack of effect, myeloid cells were isolated from the peritoneal cavity or bone marrow. S100A9-deficient neutrophils exhibited a reduced secretion of cytokines in response to toll-like receptor-4 stimulation. In striking contrast, S100A9-deficient dendritic cells showed an exacerbated release of cytokines after toll-like receptor stimulation. Macrophages rapidly lost S100A9 expression during maturation; hence, S100A9 deficiency did not affect the inflammatory status of macrophages. Conclusions-S100A9 differentially modifies phenotypic states of neutrophils, macrophages, and dendritic cells. The effect of S100A9 deficiency on atherosclerosis and other inflammatory diseases is therefore predicted to depend on the relative contribution of these cell types at different stages of disease progression. Furthermore, S100A9 expression in nonmyeloid cells is likely to contribute to atherosclerosis. (Circulation. 2011;123:1216-1226.)Key Words: atherosclerosis Ⅲ immunology Ⅲ macrophage Ⅲ S100 proteins S 100A9 and its binding partner, S100A8, are members of the S100 family of proteins and are promising novel markers of cardiovascular risk in humans. 1 Recent studies on mice demonstrate that S100A8/A9 promote atherosclerosis. 2 Thus, S100A9 appears to be both a marker and a mediator of atherosclerosis. Furthermore, circulating levels of S100A8/A9 are increased in a number of autoimmune and proinflammatory states, including type 1 diabetes mellitus 3,4 and obesity, 5 characterized by increased cardiovascular risk. Studies on S100A9-deficient mice suggest that S100A8/A9 have proinflammatory actions, eg, in sepsis 6,7 and pancreatitis. 8 Clinical Perspective on p 1226S100A8/A9 are abundantly and constitutively expressed in neutrophils and monocytes. Expression of S100A8/A9 is lost during differentiation of monocytes into macrophages, 9 yet some expression is sustained in dendritic cells (DCs). 10 S100A8/A9 promote migration of neutrophils through increased CD11b expression. 11 The effects of S100A9 deficiency in neutrophils might be due to the combined loss of S100A8 and S100A9 because S100A9-deficient neutrophils express S100A8 mRNA...

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

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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.

Loss-of-function mutations in the transcription factor CREB3L3 (CREBH) associate with severe hypertriglyceridemia in humans. CREBH is believed to lower plasma triglycerides by augmenting the action of lipoprotein lipase (LPL). However, by using a mouse model of type 1 diabetes mellitus (T1DM), we found that greater liver expression of active CREBH normalized both elevated plasma triglycerides and cholesterol.Residual triglyceride-rich lipoprotein (TRL) remnants were enriched in apolipoprotein E (APOE) and impoverished in APOC3, an apolipoprotein composition indicative of increased hepatic clearance. The underlying mechanism was independent of LPL as CREBH reduced both triglycerides and cholesterol in LPL-deficient mice. Instead, APOE was critical for CREBH's ability to lower circulating remnant lipoproteins because it failed to reduce TRL cholesterol in Apoe -/mice. Importantly, humans with CREB3L3 loss-of-function mutations exhibited increased levels of remnant lipoproteins that were deprived of APOE. Recent evidence suggests that impaired clearance of TRL remnants promotes cardiovascular disease in patients with T1DM. Consistently, we found that hepatic expression of CREBH prevented the progression of diabetes-accelerated atherosclerosis. Our results support the proposal that CREBH acts through an APOEdependent pathway to increase hepatic clearance of remnant lipoproteins. They also implicate elevated levels of remnants in the pathogenesis of atherosclerosis in T1DM.

We have developed an inducible and reversible hepatic LDLR knockdown mouse model of atherosclerosis regression. Although cholesterol reduction decreased early en face lesions in the aortic arches, macrophage area was reduced in both early and late lesions within the aortic sinus after reversal of hypercholesterolemia. Our model circumvents many of the challenges associated with current mouse models of regression. The use of this technology will potentially expedite studies of atherosclerosis and regression without use of mice with genetic defects in lipid metabolism.