LXR signaling pathways link cholesterol metabolism with risk for prediabetes and diabetes.

BACKGROUNDPreclinical studies suggest that cholesterol accumulation leads to insulin resistance. We previously reported that alterations in a monocyte cholesterol metabolism transcriptional network (CMTN) - suggestive of cellular cholesterol accumulation - were cross-sectionally associated with obesity and type 2 diabetes (T2D). Here, we sought to determine whether the CMTN alterations independently predict incident prediabetes/T2D risk, and correlate with cellular cholesterol accumulation.

Targeted Deletion of Hepatocyte Abca1 Increases Plasma HDL (High-Density Lipoprotein) Reverse Cholesterol Transport via the LDL (Low-Density Lipoprotein) Receptor.

Objective: The role of hepatocyte Abca1 (ATP binding cassette transporter A1) in trafficking hepatic free cholesterol (FC) into plasma versus bile for reverse cholesterol transport (RCT) is poorly understood. We hypothesized that hepatocyte Abca1 recycles plasma HDL-C (high-density lipoprotein cholesterol) taken up by the liver back into plasma, maintaining the plasma HDL-C pool, and decreasing HDL-mediated RCT into feces. Approach and Results: Chow-fed hepatocyte-specific Abca1 knockout (HSKO) and control mice were injected with human HDL radiolabeled with I-tyramine cellobiose (I-TC; protein) and H-cholesteryl oleate (H-CO).

Feeding of tobacco blend or nicotine induced weight loss associated with decreased adipocyte size and increased physical activity in male mice.

Although epidemiological data and results from rodent studies support an inverse relationship between nicotine consumption and body weight, the molecular mechanisms are poorly understood. CD-1 mice were fed a basal diet or a basal diet containing low or high dose smokeless tobacco blend or high dose nicotine tartrate for 14 weeks. High dose tobacco blend and nicotine tartrate diets vs.

Targeted Deletion of Adipocyte Abca1 (ATP-Binding Cassette Transporter A1) Impairs Diet-Induced Obesity.

Objective: Adipose tissue cholesterol increases with adipocyte triglyceride content and size during development of obesity. However, how adipocyte cholesterol affects adipocyte function is poorly understood. The aim of this study was to evaluate the role of the cellular cholesterol exporter, Abca1 (ATP-binding cassette transporter A1), on adipose tissue function during diet-induced obesity.

In vivo activation of leukocyte GPR120/FFAR4 by PUFAs has minimal impact on atherosclerosis in LDL receptor knockout mice.

G protein-coupled receptor (GPR)120/FFA receptor (FFAR)4 (GPR120/FFAR4) activation by n-3 PUFAs attenuates inflammation, but its impact on atherosclerosis is unknown. We determined whether in vivo activation of leukocyte GPR120/FFAR4 by n-3 versus n-6 PUFAs is atheroprotective. Leukocyte GPR120/FFAR4 WT or KO mice in the LDL receptor KO background were generated by bone marrow transplantation.

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.

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(-/-)).

The serine hydrolase ABHD6 Is a critical regulator of the metabolic syndrome.

The serine hydrolase α/β hydrolase domain 6 (ABHD6) has recently been implicated as a key lipase for the endocannabinoid 2-arachidonylglycerol (2-AG) in the brain. However, the biochemical and physiological function for ABHD6 outside of the central nervous system has not been established. To address this, we utilized targeted antisense oligonucleotides (ASOs) to selectively knock down ABHD6 in peripheral tissues in order to identify in vivo substrates and understand ABHD6's role in energy metabolism.

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.

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.

Phytosterol feeding causes toxicity in ABCG5/G8 knockout mice.

Plant sterols, or phytosterols, are very similar in structure to cholesterol and are abundant in typical diets. The reason for poor absorption of plant sterols by the body is still unknown. Mutations in the ABC transporters G5 and G8 are known to cause an accumulation of plant sterols in blood and tissues (sitosterolemia).

Scavenger receptor class B type I is a plasma membrane cholesterol sensor.

Rationale: Signal initiation by the high-density lipoprotein (HDL) receptor scavenger receptor class B, type I (SR-BI), which is important to actions of HDL on endothelium and other processes, requires cholesterol efflux and the C-terminal transmembrane domain. The C-terminal transmembrane domain uniquely interacts with plasma membrane (PM) cholesterol.

Objective: The molecular basis and functional significance of SR-BI interaction with PM cholesterol are unknown.

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.

ACAT2 and ABCG5/G8 are both required for efficient cholesterol absorption in mice: evidence from thoracic lymph duct cannulation.

The metabolic fate of newly absorbed cholesterol and phytosterol is orchestrated through adenosine triphosphate-binding cassette transporter G5 and G8 heterodimer (G5G8), and acyl CoA:cholesterol acyltransferase 2 (ACAT2). We hypothesized that intestinal G5G8 limits sterol absorption by reducing substrate availability for ACAT2 esterification and have attempted to define the roles of these two factors using gene deletion studies in mice. Male ACAT2(-/-), G5G8(-/-), ACAT2(-/-)G5G8(-/-) (DKO), and wild-type (WT) control mice were fed a diet with 20% of energy as palm oil and 0.

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.

Cholesterol esterification by ACAT2 is essential for efficient intestinal cholesterol absorption: evidence from thoracic lymph duct cannulation.

The hypothesis tested in this study was that cholesterol esterification by ACAT2 would increase cholesterol absorption efficiency by providing cholesteryl ester (CE) for incorporation into chylomicrons. The assumption was that absorption would be proportional to Acat2 gene dosage. Male ACAT2⁺/⁺, ACAT2⁺/⁻, and ACAT2⁻/⁻ mice were fed a diet containing 20% of energy as palm oil with 0.

Adipose tissue ATP binding cassette transporter A1 contributes to high-density lipoprotein biogenesis in vivo.

Background: Adipose tissue (AT) is the body's largest free cholesterol reservoir and abundantly expresses ATP binding cassette transporter A1 (ABCA1), a key cholesterol transporter for high-density lipoprotein (HDL) biogenesis. However, the extent to which AT ABCA1 expression contributes to HDL biogenesis in vivo is unknown.

Methods And Results: Adipocyte-specific ABCA1 knockout mice (ABCA1(-A/-A)) were generated by crossing ABCA1(floxed) mice with aP2Cre transgenic mice.

Non-contrasted computed tomography for the accurate measurement of liver steatosis in obese patients.

Background: Hepatic macrosteatosis (HMS) is prevalent among high BMI patients, but a lack of validation of non-invasive measures of liver fat hampers non-alcoholic liver disease (NAFLD) investigation in general. Recent work suggests BMI adjusted, non-contrasted computed tomography (nc-CT) attenuation data (Hounsfield units) reflects liver fat accumulation in a normal weight population. However, this and other CT-based HMS studies have only approximated macrosteatosis (%) histologically, but have not validated findings with chemical liver triglyceride (TG) concentrations (mg/gram protein).

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.

Biliary sterol secretion is not required for macrophage reverse cholesterol transport.

Recent evidence suggests that the intestine may play a direct facilitative role in reverse cholesterol transport (RCT), independent of hepatobiliary secretion. In order to understand the nonbiliary pathway for RCT, we created both genetic and surgical models of biliary cholesterol insufficiency. To genetically inhibit biliary cholesterol secretion, we generated mice in which Niemann-Pick C1-Like 1 (NPC1L1) was overexpressed in the liver.

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.

Targeted deletion of hepatocyte ABCA1 leads to very low density lipoprotein triglyceride overproduction and low density lipoprotein hypercatabolism.

Loss of ABCA1 activity in Tangier disease (TD) is associated with abnormal apoB lipoprotein (Lp) metabolism in addition to the complete absence of high density lipoprotein (HDL). We used hepatocyte-specific ABCA1 knock-out (HSKO) mice to test the hypothesis that hepatic ABCA1 plays dual roles in regulating Lp metabolism and nascent HDL formation. HSKO mice recapitulated the TD lipid phenotype with postprandial hypertriglyceridemia, markedly decreased LDL, and near absence of HDL.

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.

Inhibition of stearoyl-coenzyme A desaturase 1 dissociates insulin resistance and obesity from atherosclerosis.

Background: Stearoyl-coenzyme A desaturase 1 (SCD1) is a well-known enhancer of the metabolic syndrome. The purpose of the present study was to investigate the role of SCD1 in lipoprotein metabolism and atherosclerosis progression.

Methods And Results: Antisense oligonucleotides were used to inhibit SCD1 in a mouse model of hyperlipidemia and atherosclerosis (LDLr(-/-)Apob(100/100)).