Sterol O-Acyltransferase 2-Driven Cholesterol Esterification Opposes Liver X Receptor-Stimulated Fecal Neutral Sterol Loss.

Statin drugs have proven a successful and relatively safe therapy for the treatment of atherosclerotic cardiovascular disease (CVD). However, even with the substantial low-density lipoprotein (LDL) cholesterol lowering achieved with statin treatment, CVD remains the top cause of death in developed countries. Selective inhibitors of the cholesterol esterifying enzyme sterol-O acyltransferase 2 (SOAT2) hold great promise as effective CVD therapeutics. In mouse models, previous work has demonstrated that either antisense oligonucleotide (ASO) or small molecule inhibitors of SOAT2 can effectively reduce CVD progression, and even promote regression of established CVD. Although it is well known that SOAT2-driven cholesterol esterification can alter both the packaging and retention of atherogenic apoB-containing lipoproteins, here we set out to determine whether SOAT2-driven cholesterol esterification can also impact basal and liver X receptor (LXR)-stimulated fecal neutral sterol loss. These studies demonstrate that SOAT2 is a negative regulator of LXR-stimulated fecal neutral sterol loss in mice.

Targeted Knockdown of Hepatic SOAT2 With Antisense Oligonucleotides Stabilizes Atherosclerotic Plaque in ApoB100-only LDLr-/- Mice.

OBJECTIVE: To test the hypothesis that the attenuation of cholesterol oleate packaging into apoB-containing lipoproteins will arrest progression of pre-existing atherosclerotic lesions. APPROACH AND RESULTS: Atherosclerosis was induced in apoB-100 only, LDLr(-/-) mice by feeding a diet enriched in cis-monounsaturated fatty acids for 24 weeks. A subset of mice was then euthanized to quantify the extent of atherosclerosis. The remaining mice were continued on the same diet (controls) or assigned to the following treatments for 16 weeks: (1) a diet enriched in n-3 polyunsaturated fatty acids, (2) the cis-monounsaturated fatty acid diet plus biweekly injections of an antisense oligonucleotide specific to hepatic sterol-O-acyltransferase 2 (SOAT2); or (3) the cis-monounsaturated fatty acid diet and biweekly injections of a nontargeting hepatic antisense oligonucleotide. Extent of atherosclerotic lesions in the aorta was monitored morphometrically in vivo with magnetic resonance imaging and ex vivo histologically and immunochemically. Hepatic knockdown of SOAT2 via antisense oligonucleotide treatment arrested lesion growth and stabilized lesions. CONCLUSIONS: Hepatic knockdown of SOAT2 in apoB100-only, LDLr(-/-) mice resulted in remodeling of aortic atherosclerotic lesions into a stable phenotype, suggesting SOAT2 is a viable target for the treatment of atherosclerosis.

Cholesterol esters (CE) derived from hepatic sterol O-acyltransferase 2 (SOAT2) are associated with more atherosclerosis than CE from intestinal SOAT2.

RATIONALE: Cholesterol esters (CE), especially cholesterol oleate, generated by hepatic and intestinal sterol O-acyltransferase 2 (SOAT2) play a critical role in cholesterol homeostasis. However, it is unknown whether the contribution of intestine-derived CE from SOAT2 would have similar effects in promoting atherosclerosis progression as for liver-derived CE. OBJECTIVE: To test whether, in low-density lipoprotein receptor null (LDLr(-/-)) mice, the conditional knockout of intestinal SOAT2 (SOAT2(SI-/SI-)) or hepatic SOAT2 (SOAT2(L-/L-)) would equally limit atherosclerosis development compared with the global deletion of SOAT2 (SOAT2(-/-)). METHODS AND RESULTS: SOAT2 conditional knockout mice were bred with LDLr(-/-) mice creating LDLr(-/-) mice with each of the specific SOAT2 gene deletions. All mice then were fed an atherogenic diet for 16 weeks. SOAT2(SI-/SI-)LDLr(-/-) and SOAT2(-/-)LDLr(-/-) mice had significantly lower levels of intestinal cholesterol absorption, more fecal sterol excretion, and lower biliary cholesterol levels. Analysis of plasma LDL showed that all mice with SOAT2 gene deletions had LDL CE with reduced percentages of cholesterol palmitate and cholesterol oleate. Each of the LDLr(-/-) mice with SOAT2 gene deletions had lower accumulations of total cholesterol and CE in the liver compared with control mice. Finally, aortic atherosclerosis development was significantly lower in all mice with global or tissue-restricted SOAT2 gene deletions. Nevertheless, SOAT2(-/-)LDLr(-/-) and SOAT2(L-/L-)LDLr(-/-) mice had less aortic CE accumulation and smaller aortic lesions than SOAT2(SI-/SI-)LDLr(-/-) mice. CONCLUSIONS: SOAT2-derived CE from both the intestine and liver significantly contribute to the development of atherosclerosis, although the CE from the hepatic enzyme appeared to promote more atherosclerosis development.

Acute sterol o-acyltransferase 2 (SOAT2) knockdown rapidly mobilizes hepatic cholesterol for fecal excretion.

The primary risk factor for atherosclerotic cardiovascular disease is LDL cholesterol, which can be reduced by increasing cholesterol excretion from the body. Fecal cholesterol excretion can be driven by a hepatobiliary as well as a non-biliary pathway known as transintestinal cholesterol efflux (TICE). We previously showed that chronic knockdown of the hepatic cholesterol esterifying enzyme sterol O-acyltransferase 2 (SOAT2) increased fecal cholesterol loss via TICE. To elucidate the initial events that stimulate TICE, C57Bl/6 mice were fed a high cholesterol diet to induce hepatic cholesterol accumulation and were then treated for 1 or 2 weeks with an antisense oligonucleotide targeting SOAT2. Within 2 weeks of hepatic SOAT2 knockdown (SOAT2HKD), the concentration of cholesteryl ester in the liver was reduced by 70% without a reciprocal increase in hepatic free cholesterol. The rapid mobilization of hepatic cholesterol stores resulted in a ∼ 2-fold increase in fecal neutral sterol loss but no change in biliary cholesterol concentration. Acute SOAT2HKD increased plasma cholesterol carried primarily in lipoproteins enriched in apoB and apoE. Collectively, our data suggest that acutely reducing SOAT2 causes hepatic cholesterol to be swiftly mobilized and packaged onto nascent lipoproteins that feed cholesterol into the TICE pathway for fecal excretion.

Myeloid cell-specific ATP-binding cassette transporter A1 deletion has minimal impact on atherogenesis in atherogenic diet-fed low-density lipoprotein receptor knockout mice.

OBJECTIVE: Transplantation studies suggest that bone marrow cell ATP-binding cassette transporter A1 protects against atherosclerosis development. However, the in vivo effect of macrophage ATP-binding cassette transporter A1 expression on atherogenesis is not fully understood because bone marrow contains other leukocytes and hematopoietic stem and progenitor cells. Myeloid-specific ATP-binding cassette transporter A1 knockout mice in the low-density lipoprotein (LDL) receptor knockout C57BL/6 background were developed to address this question. APPROACH AND RESULTS: Chow-fed myeloid-specific ATP-binding cassette transporter A1 knockout/LDL receptor knockout (double knockout [DKO]) versus LDL receptor knockout (single knockout [SKO]) mice had similar plasma lipid concentrations, but atherogenic diet (AD)-fed DKO mice had reduced plasma very-LDL (VLDL)/LDL concentrations resulting from decreased hepatic VLDL triglyceride secretion. Resident peritoneal macrophages from AD-fed DKO versus SKO mice had significantly higher cholesterol content but similar proinflammatory gene expression. Atherosclerosis extent was similar between genotypes after 10 to 16 weeks of AD but increased modestly in DKO mice by 24 weeks of AD. Lesional macrophage content was similar, likely because of the higher monocyte flux through aortic root lesions in DKO versus SKO mice. After transplantation of DKO or SKO bone marrow into SKO mice and 16 weeks of AD feeding, atherosclerosis extent was similar and plasma apolipoprotein B lipoproteins were reduced in mice receiving DKO bone marrow. When differences in plasma VLDL/LDL concentrations were minimized by maintaining mice on chow for 24 weeks, DKO mice had modest, but significantly more, atherosclerosis compared with SKO mice. CONCLUSIONS: Myeloid cell ATP-binding cassette transporter A1 increases hepatic VLDL triglyceride secretion and plasma VLDL/LDL concentrations in AD-fed LDL receptor knockout mice, offsetting its atheroprotective role in decreasing macrophage cholesterol content, resulting in a minimal increase in atherosclerosis.

Reduction of VLDL secretion decreases cholesterol excretion in niemann-pick C1-like 1 hepatic transgenic mice.

An effective way to reduce LDL cholesterol, the primary risk factor of atherosclerotic cardiovascular disease, is to increase cholesterol excretion from the body. Our group and others have recently found that cholesterol excretion can be facilitated by both hepatobiliary and transintestinal pathways. However, the lipoprotein that moves cholesterol through the plasma to the small intestine for transintestinal cholesterol efflux (TICE) is unknown. To test the hypothesis that hepatic very low-density lipoproteins (VLDL) support TICE, antisense oligonucleotides (ASO) were used to knockdown hepatic expression of microsomal triglyceride transfer protein (MTP), which is necessary for VLDL assembly. While maintained on a high cholesterol diet, Niemann-Pick C1-like 1 hepatic transgenic (L1Tg) mice, which predominantly excrete cholesterol via TICE, and wild type (WT) littermates were treated with control ASO or MTP ASO. In both WT and L1Tg mice, MTP ASO decreased VLDL triglyceride (TG) and cholesterol secretion. Regardless of treatment, L1Tg mice had reduced biliary cholesterol compared to WT mice. However, only L1Tg mice treated with MTP ASO had reduced fecal cholesterol excretion. Based upon these findings, we conclude that VLDL or a byproduct such as LDL can move cholesterol from the liver to the small intestine for TICE.

Liver ABCA1 deletion in LDLrKO mice does not impair macrophage reverse cholesterol transport or exacerbate atherogenesis.

OBJECTIVE: Hepatic ATP binding cassette transporter A1 (ABCA1) expression is critical for maintaining plasma high-density lipoprotein (HDL) concentrations, but its role in macrophage reverse cholesterol transport and atherosclerosis is not fully understood. We investigated atherosclerosis development and reverse cholesterol transport in hepatocyte-specific ABCA1 knockout (HSKO) mice in the low-density lipoprotein (LDL) receptor KO (LDLrKO) C57BL/6 background. APPROACH AND RESULTS: Male and female LDLrKO and HSKO/LDLrKO mice were switched from chow at 8 weeks of age to an atherogenic diet (10% palm oil, 0.2% cholesterol) for 16 weeks. Chow-fed HSKO/LDLrKO mice had HDL concentrations 10% to 20% of LDLrKO mice, but similar very low-density lipoprotein and LDL concentrations. Surprisingly, HSKO/LDLrKO mice fed the atherogenic diet had significantly lower (40% to 60%) very low-density lipoprotein, LDL, and HDL concentrations (50%) compared with LDLrKO mice. Aortic surface lesion area and cholesterol content were similar for both genotypes of mice, but aortic root intimal area was significantly lower (20% to 40%) in HSKO/LDLrKO mice. Although macrophage (3)H-cholesterol efflux to apoB lipoprotein-depleted plasma was 24% lower for atherogenic diet-fed HSKO/LDLrKO versus LDLrKO mice, variation in percentage efflux among individual mice was <2-fold compared with a 10-fold variation in plasma HDL concentrations, suggesting that HDL levels, per se, were not the primary determinant of plasma efflux capacity. In vivo reverse cholesterol transport, resident peritoneal macrophage sterol content, biliary lipid composition, and fecal cholesterol mass were similar between both genotypes of mice. CONCLUSIONS: The markedly reduced plasma HDL pool in HSKO/LDLrKO mice is sufficient to maintain macrophage reverse cholesterol transport, which, along with reduced plasma very low-density lipoprotein and LDL concentrations, prevented the expected increase in atherosclerosis.

LDL particle core enrichment in cholesteryl oleate increases proteoglycan binding and promotes atherosclerosis.

Several studies in humans and animals suggest that LDL particle core enrichment in cholesteryl oleate (CO) is associated with increased atherosclerosis. Diet enrichment with MUFAs enhances LDL CO content. Steroyl O-acyltransferase 2 (SOAT2) is the enzyme that catalyzes the synthesis of much of the CO found in LDL, and gene deletion of SOAT2 minimizes CO in LDL and protects against atherosclerosis. The purpose of this study was to test the hypothesis that the increased atherosclerosis associated with LDL core enrichment in CO results from an increased affinity of the LDL particle for arterial proteoglycans. ApoB-100-only Ldlr(-/-) mice with and without Soat2 gene deletions were fed diets enriched in either cis-MUFA or n-3 PUFA, and LDL particles were isolated. LDL:proteogylcan binding was measured using surface plasmon resonance. Particles with higher CO content consistently bound with higher affinity to human biglycan and the amount of binding was shown to be proportional to the extent of atherosclerosis of the LDL donor mice. The data strongly support the thesis that atherosclerosis was induced through enhanced proteoglycan binding of LDL resulting from LDL core CO enrichment.

Intestinal SR-BI does not impact cholesterol absorption or transintestinal cholesterol efflux in mice.

Reverse cholesterol transport (RCT) can proceed through the classic hepatobiliary route or through the nonbiliary transintestinal cholesterol efflux (TICE) pathway. Scavenger receptor class B type I (SR-BI) plays a critical role in the classic hepatobiliary route of RCT. However, the role of SR-BI in TICE has not been studied. To examine the role of intestinal SR-BI in TICE, sterol balance was measured in control mice and mice transgenically overexpressing SR-BI in the proximal small intestine (SR-BI(hApoCIII-ApoAIV-Tg)). SR-BI(hApoCIII-ApoAIV-Tg) mice had significantly lower plasma cholesterol levels compared with wild-type controls, yet SR-BI(hApoCIII-ApoAIV-Tg) mice had normal fractional cholesterol absorption and fecal neutral sterol excretion. Both in the absence or presence of ezetimibe, intestinal SR-BI overexpression had no impact on the amount of cholesterol excreted in the feces. To specifically study effects of intestinal SR-BI on TICE we crossed SR-BI(hApoCIII-ApoAIV-Tg) mice into a mouse model that preferentially utilized the TICE pathway for RCT (Niemann-Pick C1-like 1 liver transgenic), and likewise found no alterations in cholesterol absorption or fecal sterol excretion. Finally, mice lacking SR-BI in all tissues also exhibited normal cholesterol absorption and fecal cholesterol disposal. Collectively, these results suggest that SR-BI is not rate limiting for intestinal cholesterol absorption or for fecal neutral sterol loss through the TICE pathway.

Cholesteryl esters associated with acyl-CoA:cholesterol acyltransferase predict coronary artery disease in patients with symptoms of acute coronary syndrome.

OBJECTIVES: Identifying the likelihood of a patient having coronary artery disease (CAD) at the time of emergency department (ED) presentation with chest pain could reduce the need for stress testing or coronary imaging after myocardial infarction (MI) has been excluded. The authors aimed to determine if a novel cardiac biomarker consisting of plasma cholesteryl ester (CE) levels typically derived from the activity of the enzyme acyl-CoA:cholesterol acyltransferase (ACAT2) are predictive of CAD in a clinical model. METHODS: A single-center prospective cohort design enrolled participants with symptoms of acute coronary syndrome (ACS) undergoing coronary computed tomography angiography (CCTA) or invasive angiography. Plasma samples were analyzed for CE composition with mass spectrometry. The primary endpoint was any CAD determined at angiography. Multivariable logistic regression analyses were used to estimate the relationship between the sum of the plasma concentrations from cholesteryl palmitoleate (16:1) and cholesteryl oleate (18:1) (defined as ACAT2-CE) and the presence of CAD. The added value of ACAT2-CE to the model was analyzed comparing the C-statistics and integrated discrimination improvement (IDI). RESULTS: The study cohort was composed of 113 participants with a mean (± standard deviation [SD]) age of 49 (±11.7) years, 59% had CAD at angiography, and 23% had an MI within 30 days. The median (interquartile range [IQR]) plasma concentration of ACAT2-CE was 938 µmol/L (IQR = 758 to 1,099 µmol/L) in patients with CAD and 824 µmol/L (IQR = 683 to 998 µmol/L) in patients without CAD (p = 0.03). When considered with age, sex, and the number of conventional CAD risk factors, ACAT2-CE levels were associated with a 6.5% increased odds of having CAD per 10 µmol/L increase in concentration. The addition of ACAT2-CE significantly improved the C-statistic (0.89 vs. 0.95, p = 0.0035) and IDI (0.15, p < 0.001) compared to the reduced model. In the subgroup of low-risk observation unit patients, the CE model had superior discrimination compared to the Diamond-Forrester classification (IDI = 0.403, p < 0.001). CONCLUSIONS: Plasma levels of ACAT2-CE have strong potential to predict a patient's likelihood of having CAD when considered in a clinical model but not when used alone. In turn, a clinical model containing ACAT2-CE could reduce the need for cardiac imaging after the exclusion of MI.

Tissue-specific knockouts of ACAT2 reveal that intestinal depletion is sufficient to prevent diet-induced cholesterol accumulation in the liver and blood.

Acyl-CoA:cholesterol acyltransferase 2 (ACAT2) generates cholesterol esters (CE) for packaging into newly synthesized lipoproteins and thus is a major determinant of blood cholesterol levels. ACAT2 is expressed exclusively in the small intestine and liver, but the relative contributions of ACAT2 expression in these tissues to systemic cholesterol metabolism is unknown. We investigated whether CE derived from the intestine or liver would differentially affect hepatic and plasma cholesterol homeostasis. We generated liver-specific (ACAT2(L-/L-)) and intestine-specific (ACAT2(SI-/SI-)) ACAT2 knockout mice and studied dietary cholesterol-induced hepatic lipid accumulation and hypercholesterolemia. ACAT2(SI-/SI-) mice, in contrast to ACAT2(L-/L-) mice, had blunted cholesterol absorption. However, specific deletion of ACAT2 in the intestine generated essentially a phenocopy of the conditional knockout of ACAT2 in the liver, with reduced levels of plasma very low-density lipoprotein and hepatic CE, yet hepatic-free cholesterol does not build up after high cholesterol intake. ACAT2(L-/L-) and ACAT2(SI-/SI-) mice were equally protected from diet-induced hepatic CE accumulation and hypercholesterolemia. These results suggest that inhibition of intestinal or hepatic ACAT2 improves atherogenic hyperlipidemia and limits hepatic CE accumulation in mice and that depletion of intestinal ACAT2 is sufficient for most of the beneficial effects on cholesterol metabolism. Inhibitors of ACAT2 targeting either tissue likely would be beneficial for atheroprotection.

Echium oil reduces atherosclerosis in apoB100-only LDLrKO mice.

INTRODUCTION: The anti-atherogenic and hypotriglyceridemic properties of fish oil are attributed to its enrichment in eicosapentaenoic acid (EPA; 20:5, n-3) and docosahexaenoic acid (DHA; 22:6, n-3). Echium oil contains stearidonic acid (SDA; 18:4, n-3), which is metabolized to EPA in humans and mice, resulting in decreased plasma triglycerides. OBJECTIVE: We used apoB100 only, LDLrKO mice to investigate whether echium oil reduces atherosclerosis. METHODS: Mice were fed palm, echium, or fish oil-containing diets for 16 weeks and plasma lipids, lipoproteins, and atherosclerosis were measured. RESULTS: Compared to palm oil, echium oil feeding resulted in significantly less plasma triglyceride and cholesterol levels, and atherosclerosis, comparable to that of fish oil. CONCLUSION: This is the first report that echium oil is anti-atherogenic, suggesting that it may be a botanical alternative to fish oil for atheroprotection.

Endogenous synthesis of n-3 polyunsaturated fatty acids in Fat-1 mice is associated with increased mammary gland and liver syndecan-1.

Long chain n-3 PUFA have been shown to have chemopreventive properties against breast cancer through various mechanisms. One pathway, studied in human breast cancer cell lines, involves upregulation of the proteoglycan, syndecan-1 (SDC-1) by n-3 PUFA-enriched LDL. Using Fat-1 mice that are able to convert n-6 to n-3 PUFA, we tested whether SDC-1 level in vivo is elevated in mammary glands due to endogenously synthesized rather than LDL-derived n-3 PUFA. Female Fat-1 and wild type (wt) mice were fed an n-6 PUFA- enriched diet for 7 weeks. Fatty acid analysis of plasma lipoproteins showed that total n-6 PUFA reflected dietary intake similarly in both genotypes (VLDL, 36.2±2.2 and 40.9±3.9; LDL, 49.0±3.3 and 48.1±2.0; HDL, 54.6±1.2 and 58.2±1.3, mean ± SEM percent of total fatty acids for Fat-1 and wt animals respectively). Lipoprotein percent n-3 PUFA was also similar between groups. However, phospholipids and triglycerides extracted from mammary and liver tissues demonstrated significantly higher n-3 PUFA and a corresponding decrease in the ratio n-6/n-3 PUFA in Fat-1 compared to wt mice. This was accompanied by higher SDC-1 in mammary glands and livers of Fat-1 mice, thus demonstrating that endogenously synthesized n-3 PUFA may upregulate SDC-1 in the presence of high dietary n-6 PUFA.

CGI-58 knockdown in mice causes hepatic steatosis but prevents diet-induced obesity and glucose intolerance.

Mutations of Comparative Gene Identification-58 (CGI-58) in humans cause triglyceride (TG) accumulation in multiple tissues. Mice genetically lacking CGI-58 die shortly after birth due to a skin barrier defect. To study the role of CGI-58 in integrated lipid and energy metabolism, we utilized antisense oligonucleotides (ASOs) to inhibit CGI-58 expression in adult mice. Treatment with two distinct CGI-58-targeting ASOs resulted in ∼80-95% knockdown of CGI-58 protein expression in both liver and white adipose tissue. In chow-fed mice, ASO-mediated depletion of CGI-58 did not alter weight gain, plasma TG, or plasma glucose, yet raised hepatic TG levels ∼4-fold. When challenged with a high-fat diet (HFD), CGI-58 ASO-treated mice were protected against diet-induced obesity, but their hepatic contents of TG, diacylglycerols, and ceramides were all elevated, and intriguingly, their hepatic phosphatidylglycerol content was increased by 10-fold. These hepatic lipid alterations were associated with significant decreases in hepatic TG hydrolase activity, hepatic lipoprotein-TG secretion, and plasma concentrations of ketones, nonesterified fatty acids, and insulin. Additionally, HFD-fed CGI-58 ASO-treated mice were more glucose tolerant and insulin sensitive. Collectively, this work demonstrates that CGI-58 plays a critical role in limiting hepatic steatosis and maintaining hepatic glycerophospholipid homeostasis and has unmasked an unexpected role for CGI-58 in promoting HFD-induced obesity and insulin resistance.

Macrophage ABCA1 reduces MyD88-dependent Toll-like receptor trafficking to lipid rafts by reduction of lipid raft cholesterol.

We previously showed that macrophages from macrophage-specific ATP-binding cassette transporter A1 (ABCA1) knockout (Abca1(-M/-M)) mice had an enhanced proinflammatory response to the Toll-like receptor (TLR) 4 agonist, lipopolysaccharide (LPS), compared with wild-type (WT) mice. In the present study, we demonstrate a direct association between free cholesterol (FC), lipid raft content, and hyper-responsiveness of macrophages to LPS in WT mice. Abca1(-M/-M) macrophages were also hyper-responsive to specific agonists to TLR2, TLR7, and TLR9, but not TLR3, compared with WT macrophages. We hypothesized that ABCA1 regulates macrophage responsiveness to TLR agonists by modulation of lipid raft cholesterol and TLR mobilization to lipid rafts. We demonstrated that Abca1(-M/-M) vs. WT macrophages contained 23% more FC in isolated lipid rafts. Further, mass spectrometric analysis suggested raft phospholipid composition was unchanged. Although cell surface expression of TLR4 was similar between Abca1(-M/-M) and WT macrophages, significantly more TLR4 was distributed in membrane lipid rafts in Abca1(-M/-M) macrophages. Abca1(-M/-M) macrophages also exhibited increased trafficking of the predominantly intracellular TLR9 into lipid rafts in response to TLR9-specific agonist (CpG). Collectively, our data suggest that macrophage ABCA1 dampens inflammation by reducing MyD88-dependent TLRs trafficking to lipid rafts by selective reduction of FC content in lipid rafts.

Neonatal and fetal exposure to trans-fatty acids retards early growth and adiposity while adversely affecting glucose in mice.

Industrially produced trans-fatty acids (TFAs) consumed in Western diets are incorporated into maternal and fetal tissues and are passed linearly to offspring via breast milk. We hypothesized that TFA exposure in utero and during lactation in infants would promote obesity and poor glycemic control as compared with unmodified fatty acids. We further hypothesized that in utero exposure alone may program for these outcomes in adulthood. To test this hypothesis, we fed female C57/BL6 mice identical Western diets that differed only in cis- or trans-isomers of C18:1 and then aimed to determine whether maternal transfer of TFAs through pregnancy and lactation alters growth, body composition, and glucose metabolism. Mice were unexposed, exposed during pregnancy, during lactation, or throughout pregnancy and lactation to TFA. Body weight and composition (by computed tomography) and glucose metabolism were assessed at weaning and adulthood. Trans-fatty acid exposure through breast milk caused significant early growth retardation (P < .001) and higher fasting glucose (P = .01), but insulin sensitivity was not different. Elevated plasma insulin-like growth factor-1 in mice consuming TFA-enriched milk (P = .02) may contribute to later catch-up growth and leanness and preserved peripheral insulin sensitivity observed in these mice. Mice exposed to TFA in utero underwent rapid early neonatal growth with TFA-free breast milk and had significantly impaired insulin sensitivity (P < .05) and greater abdominal fat (P = .01). We conclude that very early catch-up growth resulted in impaired peripheral insulin sensitivity in this model of diet-related fetal and neonatal programming. Trans-fatty acid surprisingly retarded growth and adiposity while still adversely affecting glucose metabolism.

Dyslipidemia induces opposing effects on intrapulmonary and extrapulmonary host defense through divergent TLR response phenotypes.

Dyslipidemia influences innate immune responses in the bloodstream, but whether and how pulmonary innate immunity is sensitive to circulating lipoproteins is largely unknown. To define whether dyslipidemia impacts responses to bacteria in the airspace and, if so, whether differently from its effects in other tissues, airspace, bloodstream, and i.p. responses to LPS and Klebsiella pneumoniae were investigated using murine models of dyslipidemia. Dyslipidemia reduced neutrophil (PMN) recruitment to the airspace in response to LPS and K. pneumoniae by impairing both chemokine induction in the airspace and PMN chemotaxis, thereby compromising pulmonary bacterial clearance. Paradoxically, bacteria were cleared more effectively from the bloodstream during dyslipidemia. This enhanced systemic response was due, at least in part, to basal circulating neutrophilia and basal TLR4/MyD88-dependent serum cytokine induction and enhanced serum cytokine responses to systemically administered TLR ligands. Dyslipidemia did not globally impair PMN transvascular trafficking to, and host defense within all loci, because neutrophilia, cytokine induction, and bacterial clearance were enhanced within the infected peritoneum. Peritoneal macrophages from dyslipidemic animals were primed for more robust TLR responses, reflecting increased lipid rafts and increased TLR4 expression, whereas macrophages from the airspace, in which cholesterol was maintained constant during dyslipidemia, had normal responses and rafts. Dyslipidemia thus imparts opposing effects upon intra- and extrapulmonary host defense by inducing tissue-divergent TLR response phenotypes and dysregulating airspace/blood compartmental levels of PMNs and cytokines. We propose that the airspace is a "privileged" site, thereby uniquely sensitive to dyslipidemia.

Inhibition of acyl-coenzyme A:cholesterol acyltransferase 2 (ACAT2) prevents dietary cholesterol-associated steatosis by enhancing hepatic triglyceride mobilization.

Acyl-CoA:cholesterol O-acyl transferase 2 (ACAT2) promotes cholesterol absorption by the intestine and the secretion of cholesteryl ester-enriched very low density lipoproteins by the liver. Paradoxically, mice lacking ACAT2 also exhibit mild hypertriglyceridemia. The present study addresses the unexpected role of ACAT2 in regulation of hepatic triglyceride (TG) metabolism. Mouse models of either complete genetic deficiency or pharmacological inhibition of ACAT2 were fed low fat diets containing various amounts of cholesterol to induce hepatic steatosis. Mice genetically lacking ACAT2 in both the intestine and the liver were dramatically protected against hepatic neutral lipid (TG and cholesteryl ester) accumulation, with the greatest differences occurring in situations where dietary cholesterol was elevated. Further studies demonstrated that liver-specific depletion of ACAT2 with antisense oligonucleotides prevents dietary cholesterol-associated hepatic steatosis both in an inbred mouse model of non-alcoholic fatty liver disease (SJL/J) and in a humanized hyperlipidemic mouse model (LDLr(-/-), apoB(100/100)). All mouse models of diminished ACAT2 function showed lowered hepatic triglyceride concentrations and higher plasma triglycerides secondary to increased hepatic secretion of TG into nascent very low density lipoproteins. This work demonstrates that inhibition of hepatic ACAT2 can prevent dietary cholesterol-driven hepatic steatosis in mice. These data provide the first evidence to suggest that ACAT2-specific inhibitors may hold unexpected therapeutic potential to treat both atherosclerosis and non-alcoholic fatty liver disease.

Dietary n-3 LCPUFA from fish oil but not alpha-linolenic acid-derived LCPUFA confers atheroprotection in mice.

The atheroprotective potential of n-3 alpha-linolenic acid (ALA) has not yet been fully determined, even in murine models of atherosclerosis. We tested whether ALA-derived, n-3 long chain polyunsaturated fatty acids (LCPUFA) could offer atheroprotection in a dose-dependent manner. Apolipoprotein B (ApoB)100/100LDLr-/- mice were fed with diets containing two levels of ALA from flaxseed oil for 16 weeks. Fish oil- and cis-monounsaturated-fat-enriched diets were used as positive and negative controls, respectively. The mice fed cis-monounsaturated fat and ALA-enriched diets exhibited equivalent plasma total cholesterol (TPC) and LDL-cholesterol (LDL-c) levels; only mice fed the fish-oil diet had lower TPC and LDL-c concentrations. Plasma LDL-CE fatty acid composition analysis showed that ALA-enriched diets lowered the percentage of atherogenic cholesteryl oleate compared with cis-monounsaturated-fat diet (44% versus 55.6%) but not as efficiently as the fish-oil diet (32.4%). Although both ALA and fish-oil diets equally enriched hepatic phospholipids with eicosapentaenoic acid (EPA) and ALA-enriched diets lowered hepatic cholesteryl ester (CE) levels compared with cis-monounsaturated-fat diet, only fish oil strongly protected from atherosclerosis. These outcomes indicate that dietary n-3 LCPUFA from fish oil and n-3 LCPUFA (mostly EPA) synthesized endogenously from ALA were not equally atheroprotective in these mice.

Combined therapy of dietary fish oil and stearoyl-CoA desaturase 1 inhibition prevents the metabolic syndrome and atherosclerosis.

BACKGROUND: Stearoyl-CoA desaturase 1 (SCD1) is a critical regulator of energy metabolism and inflammation. We have previously reported that inhibition of SCD1 in hyperlipidemic mice fed a saturated fatty acid (SFA)-enriched diet prevented development of the metabolic syndrome, yet surprisingly promoted severe atherosclerosis. In this study we tested whether dietary fish oil supplementation could prevent the accelerated atherosclerosis caused by SCD1 inhibition. METHODS AND RESULTS: LDLr(-/-), ApoB(100/100) mice were fed diets enriched in saturated fat or fish oil in conjunction with antisense oligonucleotide (ASO) treatment to inhibit SCD1. As previously reported, in SFA-fed mice, SCD1 inhibition dramatically protected against development of the metabolic syndrome, yet promoted atherosclerosis. In contrast, in mice fed fish oil, SCD1 inhibition did not result in augmented macrophage inflammatory response or severe atherosclerosis. In fact, the combined therapy of dietary fish oil and SCD1 ASO treatment effectively prevented both the metabolic syndrome and atherosclerosis. CONCLUSIONS: SCD1 ASO treatment in conjunction with dietary fish oil supplementation is an effective combination therapy to comprehensively combat the metabolic syndrome and atherosclerosis in mice.