Publications by authors named "Ryan E Temel"

41 Publications

The Prorenin Receptor and its Soluble Form Contribute to Lipid Homeostasis.

Am J Physiol Endocrinol Metab 2021 Jan 18. Epub 2021 Jan 18.

Department of Pharmacology and Nutritional Sciences, University of Kentucky, United States.

Obesity is associated with alterations in hepatic lipid metabolism. We previously identified the prorenin receptor (PRR) as a potential contributor to liver steatosis. Therefore, we aimed to determine the relative contribution of PRR and its soluble form, sPRR, to lipid homeostasis. PRR-floxed male mice were treated with an adeno-associated virus with thyroxine-binding globulin promoter driven Cre to delete specifically PRR in hepatocytes (Liver PRR KO mice). Hepatic PRR deletion did not change the body weight but increased liver weights. Liver PRR KO mice exhibited higher plasma cholesterol levels and lower hepatic LDLR protein than control mice. Surprisingly, hepatic PRR deletion elevated hepatic cholesterol, and up-regulated hepatic SREBP2 and HMG CoA-R genes. In addition, the plasma levels of sPRR were significantly higher in Liver PRR KO mice compared with controls. In vitro studies in Hep-G2 cells demonstrated that sPRR treatment up-regulated SREBP2 suggesting that sPRR could contribute to hepatic cholesterol biosynthesis. Interestingly, PRR and total sPRR were elevated in the adipose tissue of Liver PRR KO mice suggesting that adipose tissue could contribute to the circulating pool of sPRR. Overall, this work supports previous works and open new area of investigation concerning the function of sPRR in lipid metabolism and adipose tissue - liver crosstalk.
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http://dx.doi.org/10.1152/ajpendo.00135.2020DOI Listing
January 2021

Stigmasterol stimulates transintestinal cholesterol excretion independent of liver X receptor activation in the small intestine.

J Nutr Biochem 2020 02 9;76:108263. Epub 2019 Nov 9.

Department of Pharmaceutical Sciences, College of Pharmacy; Saha Cardiovascular Research Center; Barnstable Brown Diabetes and Obesity Center. Electronic address:

Despite advances in healthcare, cardiovascular disease (CVD) remains the leading cause of death in the United States. Elevated levels of plasma cholesterol are highly predictive of CVD and stroke and are the principal driver of atherosclerosis. Unfortunately, current cholesterol lowering agents, such as statins, are not known to reverse atherosclerotic disease once it has been established. In preclinical models, agonists of nuclear receptor, LXR, have been shown to reduce and reverse atherosclerosis. Phytosterols are bioactive non-cholesterol sterols that act as LXR agonists and regulate cholesterol metabolism and transport. We hypothesized that stigmasterol would act as an LXR agonist and alter intestinal cholesterol secretion to promote cholesterol elimination. Mice were fed a control diet, or a diet supplemented with stigmasterol (0.3% w/w) or T0901317 (0.015% w/w), a known LXR agonist. In this experiment we analyzed the sterol content of bile, intestinal perfusate, plasma, and feces. Additionally, the liver and small intestine were analyzed for relative levels of transcripts known to be regulated by LXR. We observed that T0901317 robustly promoted cholesterol elimination and acted as a strong LXR agonist. Stigmasterol promoted transintestinal cholesterol secretion through an LXR-independent pathway.
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http://dx.doi.org/10.1016/j.jnutbio.2019.108263DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7199294PMC
February 2020

Simultaneous Determination of Biliary and Intestinal Cholesterol Secretion Reveals That CETP (Cholesteryl Ester Transfer Protein) Alters Elimination Route in Mice.

Arterioscler Thromb Vasc Biol 2019 10 29;39(10):1986-1995. Epub 2019 Aug 29.

From the Graduate Center for Nutritional Sciences (J.L., R.E.T., D.R.v.d.W., G.A.G.), University of Kentucky, Lexington.

Objective: Determine the impact of CETP (cholesteryl ester transfer protein) on the route of cholesterol elimination in mice. Approach and Results: We adapted our protocol for biliary cholesterol secretion with published methods for measuring transintestinal cholesterol elimination. Bile was diverted and biliary lipid secretion maintained by infusion of bile acid. The proximal small bowel was perfused with bile acid micelles. In high-fat, high-cholesterol-fed mice, the presence of a CETP transgene increased biliary cholesterol secretion at the expense of transintestinal cholesterol elimination. The increase in biliary cholesterol secretion was not associated with increases in hepatic SR-BI (scavenger receptor BI) or ABCG5 (ATP-binding cassette G5) ABCG8. The decline in intestinal cholesterol secretion was associated with an increase in intestinal Niemann-Pick disease, type C1, gene-like 1 mRNA. Finally, we followed the delivery of HDL (high-density lipoprotein) or LDL (low-density lipoprotein) cholesteryl esters (CE) from plasma to bile and intestinal perfusates. HDL-CE favored the biliary pathway. Following high-fat feeding, the presence of CETP directed HDL-CE away from the bile and towards the intestine. The presence of CETP increased LDL-CE delivery to bile, whereas the appearance of LDL-CE in intestinal perfusate was near the lower limit of detection.

Conclusions: Biliary and intestinal cholesterol secretion can be simultaneously measured in mice and used as a model to examine factors that alter cholesterol elimination. Plasma factors, such as CETP, alter the route of cholesterol elimination from the body. Intestinal and biliary cholesterol secretion rates are independent of transhepatic or transintestinal delivery of HDL-CE, whereas LDL-CE was eliminated almost exclusively in the hepatobiliary pathway.
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http://dx.doi.org/10.1161/ATVBAHA.119.312952DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6761010PMC
October 2019

The long noncoding RNA CHROME regulates cholesterol homeostasis in primate.

Nat Metab 2019 01 3;1(1):98-110. Epub 2018 Dec 3.

Department of Medicine, Leon H. Charney Division of Cardiology, New York University School of Medicine, New York, New York, USA.

The human genome encodes thousands of long non-coding RNAs (lncRNAs), the majority of which are poorly conserved and uncharacterized. Here we identify a primate-specific lncRNA (), elevated in the plasma and atherosclerotic plaques of individuals with coronary artery disease, that regulates cellular and systemic cholesterol homeostasis. LncRNA expression is influenced by dietary and cellular cholesterol via the sterol-activated liver X receptor transcription factors, which control genes mediating responses to cholesterol overload. Using gain- and loss-of-function approaches, we show that promotes cholesterol efflux and HDL biogenesis by curbing the actions of a set of functionally related microRNAs that repress genes in those pathways. knockdown in human hepatocytes and macrophages increases levels of miR-27b, miR-33a, miR-33b and miR-128, thereby reducing expression of their overlapping target gene networks and associated biologic functions. In particular, cells lacking show reduced expression of ABCA1, which regulates cholesterol efflux and nascent HDL particle formation. Collectively, our findings identify as a central component of the non-coding RNA circuitry controlling cholesterol homeostasis in humans.
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http://dx.doi.org/10.1038/s42255-018-0004-9DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6691505PMC
January 2019

XX sex chromosome complement promotes atherosclerosis in mice.

Nat Commun 2019 06 14;10(1):2631. Epub 2019 Jun 14.

Department of Pharmacology and Nutritional Sciences, University of Kentucky, Lexington, 40536, KY, USA.

Men and women differ in circulating lipids and coronary artery disease (CAD). While sex hormones such as estrogens decrease CAD risk, hormone replacement therapy increases risk. Biological sex is determined by sex hormones and chromosomes, but effects of sex chromosomes on circulating lipids and atherosclerosis are unknown. Here, we use mouse models to separate effects of sex chromosomes and hormones on atherosclerosis, circulating lipids and intestinal fat metabolism. We assess atherosclerosis in multiple models and experimental paradigms that distinguish effects of sex chromosomes, and male or female gonads. Pro-atherogenic lipids and atherosclerosis are greater in XX than XY mice, indicating a primary effect of sex chromosomes. Small intestine expression of enzymes involved in lipid absorption and chylomicron assembly are greater in XX male and female mice with higher intestinal lipids. Together, our results show that an XX sex chromosome complement promotes the bioavailability of dietary fat to accelerate atherosclerosis.
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http://dx.doi.org/10.1038/s41467-019-10462-zDOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6643208PMC
June 2019

Efficacy and safety assessment of a TRAF6-targeted nanoimmunotherapy in atherosclerotic mice and non-human primates.

Nat Biomed Eng 2018 05 16;2(5):279-292. Epub 2018 Apr 16.

Translational and Molecular Imaging Institute, Icahn School of Medicine at Mount Sinai, New York, NY, USA.

Macrophage accumulation in atherosclerosis is directly linked to the destabilization and rupture of plaque, causing acute atherothrombotic events. Circulating monocytes enter the plaque and differentiate into macrophages, where they are activated by CD4 T lymphocytes through CD40-CD40 ligand signalling. Here, we report the development and multiparametric evaluation of a nanoimmunotherapy that moderates CD40-CD40 ligand signalling in monocytes and macrophages by blocking the interaction between CD40 and tumour necrosis factor receptor-associated factor 6 (TRAF6). We evaluated the biodistribution characteristics of the nanoimmunotherapy in apolipoprotein E-deficient (Apoe) mice and in non-human primates by in vivo positron-emission tomography imaging. In Apoe mice, a 1-week nanoimmunotherapy treatment regimen achieved significant anti-inflammatory effects, which was due to the impaired migration capacity of monocytes, as established by a transcriptome analysis. The rapid reduction of plaque inflammation by the TRAF6-targeted nanoimmunotherapy and its favourable toxicity profiles in both mice and non-human primates highlights the translational potential of this strategy for the treatment of atherosclerosis.
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http://dx.doi.org/10.1038/s41551-018-0221-2DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6447057PMC
May 2018

microRNA-146a-5p association with the cardiometabolic disease risk factor TMAO.

Physiol Genomics 2019 02 11;51(2):59-71. Epub 2019 Jan 11.

US Department of Agriculture, Agricultural Research Service Western Human Nutrition Research Center, Obesity and Metabolism Unit, Davis, California.

Trimethylamine-N-oxide (TMAO), a microbial choline metabolism byproduct that is processed in the liver and excreted into circulation, is associated with increased atherosclerotic lesion formation and cardiovascular disease risk. Genetic regulators of TMAO levels are largely unknown. In the present study, we used 288 mice from a genetically heterogeneous mouse population [Diversity Outbred (DO)] to determine hepatic microRNA associations with TMAO in the context of an atherogenic diet. We also validated findings in two additional animal models of atherosclerosis: liver-specific insulin receptor knockout mice fed a chow diet (LIRKO) and African green monkeys fed high-fat/high-cholesterol diet. Small RNA-sequencing analysis in DO mice, LIRKO mice, and African green monkeys identified only one hepatic microRNA (miR-146a-5p) that is aberrantly expressed across all three models. Moreover, miR-146a-5p levels are associated with circulating TMAO after atherogenic diet in each of these models. We also performed high-resolution genetic mapping and identified a novel quantitative trait locus on Chromosome 12 for TMAO levels. This interval includes two genes, Numb and Dlst, which are inversely correlated with both miR-146a and TMAO and are predicted targets of miR-146a. Both of these genes have been validated as direct targets of miR-146a, though in other cellular contexts. This is the first report to our knowledge of a link between miR-146 and TMAO. Our findings suggest that miR-146-5p, as well as one or more genes at the Chromosome 12 QTL (possibly Numb or Dlst), is strongly linked to TMAO levels and likely involved in the control of atherosclerosis.
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http://dx.doi.org/10.1152/physiolgenomics.00079.2018DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6397334PMC
February 2019

ABCG5 and ABCG8: more than a defense against xenosterols.

J Lipid Res 2018 07 4;59(7):1103-1113. Epub 2018 May 4.

Department of Pharmacology and Nutritional Sciences, University of Kentucky, Lexington, KY 40536

The elucidation of the molecular basis of the rare disease, sitosterolemia, has revolutionized our mechanistic understanding of how dietary sterols are excreted and how cholesterol is eliminated from the body. Two proteins, ABCG5 and ABCG8, encoded by the sitosterolemia locus, work as obligate dimers to pump sterols out of hepatocytes and enterocytes. ABCG5/ABCG8 are key in regulating whole-body sterol trafficking, by eliminating sterols via the biliary tree as well as the intestinal tract. Importantly, these transporters keep xenosterols from accumulating in the body. The sitosterolemia locus has been genetically associated with lipid levels and downstream atherosclerotic disease, as well as formation of gallstones and the risk of gallbladder cancer. While polymorphic variants raise or lower the risks of these phenotypes, loss of function of this locus leads to more dramatic phenotypes, such as premature atherosclerosis, platelet dysfunction, and thrombocytopenia, and, perhaps, increased endocrine disruption and liver dysfunction. Whether small amounts of xenosterol exposure over a lifetime cause pathology in normal humans with polymorphic variants at the sitosterolemia locus remains largely unexplored. The purpose of this review will be to summarize the current state of knowledge, but also highlight key conceptual and mechanistic issues that remain to be explored.
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http://dx.doi.org/10.1194/jlr.R084244DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6027916PMC
July 2018

Targeting hepatic heparin-binding EGF-like growth factor (HB-EGF) induces anti-hyperlipidemia leading to reduction of angiotensin II-induced aneurysm development.

PLoS One 2017 9;12(8):e0182566. Epub 2017 Aug 9.

Saha Cardiovascular Research Center at the University of Kentucky College of Medicine, Lexington, Kentucky, United States of America.

Objective: The upregulated expression of heparin binding EGF-like growth factor (HB-EGF) in the vessel and circulation is associated with risk of cardiovascular disease. In this study, we tested the effects of HB-EGF targeting using HB-EGF-specific antisense oligonucleotide (ASO) on the development of aortic aneurysm in a mouse aneurysm model.

Approach And Results: Low-density lipoprotein receptor (LDLR) deficient mice (male, 16 weeks of age) were injected with control and HB-EGF ASOs for 10 weeks. To induce aneurysm, the mice were fed a high fat diet (22% fat, 0.2% cholesterol; w/w) at 5 week point of ASO administration and infused with angiotensin II (AngII, 1,000ng/kg/min) for the last 4 weeks of ASO administration. We confirmed that the HB-EGF ASO administration significantly downregulated HB-EGF expression in multiple tissues including the liver. Importantly, the HB-EGF ASO administration significantly suppressed development of aortic aneurysms including thoracic and abdominal types. Interestingly, the HB-EGF ASO administration induced a remarkable anti-hyperlipidemic effect by suppressing very low density lipoprotein (VLDL) level in the blood. Mechanistically, the HB-EGF targeting suppressed hepatic VLDL secretion rate without changing heparin-releasable plasma triglyceride (TG) hydrolytic activity or fecal neutral cholesterol excretion rate.

Conclusion: This result suggested that the HB-EGF targeting induced protection against aneurysm development through anti-hyperlipidemic effects. Suppression of hepatic VLDL production process appears to be a key mechanism for the anti-hyperlipidemic effects by the HB-EGF targeting.
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http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0182566PLOS
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5549937PMC
October 2017

Paradoxical Suppression of Atherosclerosis in the Absence of microRNA-146a.

Circ Res 2017 Aug 21;121(4):354-367. Epub 2017 Jun 21.

From the Toronto General Hospital Research Institute, University Health Network, Ontario, Canada (H.S.C, R.B., A.L., Z.C., E.A.S., N.K., S.A.M., M.H., M.I.C., C.S.R., J.E.F.); Department of Laboratory Medicine and Pathobiology, University of Toronto, Ontario, Canada (H.S.C, R.B., A.L., Z.C., E.A.S., N.K., S.A.M., M.H., M.I.C., C.S.R., J.E.F.); Heart and Stroke Richard Lewar Centre of Excellence in Cardiovascular Research, Toronto, Ontario, Canada (H.S.C, R.B., A.L., Z.C., E.A.S., N.K., M.H., M.I.C., C.S.R., J.E.F.); Institute for Cardiovascular Prevention, Ludwig-Maximilians-University Munich, Germany (M.N.-J., A.S.); INSERM, Unit 970, Paris Cardiovascular Research Center-PARCC, France (A.H., C.M.B.); University of Ottawa Heart Institute, Ontario, Canada (M.-A.N., M.G., K.J.R.); and Pharmacology and Nutritional Sciences, University of Kentucky, Lexington (L.C., T.L., R.E.T.).

Rationale: Inflammation is a key contributor to atherosclerosis. MicroRNA-146a (miR-146a) has been identified as a critical brake on proinflammatory nuclear factor κ light chain enhancer of activated B cells signaling in several cell types, including endothelial cells and bone marrow (BM)-derived cells. Importantly, miR-146a expression is elevated in human atherosclerotic plaques, and polymorphisms in the precursor have been associated with risk of coronary artery disease.

Objective: To define the role of endogenous miR-146a during atherogenesis.

Methods And Results: Paradoxically, (low-density lipoprotein receptor null) mice deficient in develop less atherosclerosis, despite having highly elevated levels of circulating proinflammatory cytokines. In contrast, cytokine levels are normalized in mice receiving wild-type BM transplantation, and these mice have enhanced endothelial cell activation and elevated atherosclerotic plaque burden compared with mice receiving wild-type BM, demonstrating the atheroprotective role of miR-146a in the endothelium. We find that deficiency of in BM-derived cells precipitates defects in hematopoietic stem cell function, contributing to extramedullary hematopoiesis, splenomegaly, BM failure, and decreased levels of circulating proatherogenic cells in mice fed an atherogenic diet. These hematopoietic phenotypes seem to be driven by unrestrained inflammatory signaling that leads to the expansion and eventual exhaustion of hematopoietic cells, and this occurs in the face of lower levels of circulating low-density lipoprotein cholesterol in mice lacking in BM-derived cells. Furthermore, we identify sortilin-1(), a known regulator of circulating low-density lipoprotein levels in humans, as a novel target of miR-146a.

Conclusions: Our study reveals that miR-146a regulates cholesterol metabolism and tempers chronic inflammatory responses to atherogenic diet by restraining proinflammatory signaling in endothelial cells and BM-derived cells.
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http://dx.doi.org/10.1161/CIRCRESAHA.116.310529DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5542783PMC
August 2017

Para-bile-osis Establishes a Role for Nonbiliary Macrophage to Feces Reverse Cholesterol Transport.

Arterioscler Thromb Vasc Biol 2017 05;37(5):738-739

From the Department of Cellular and Molecular Medicine, Cleveland Clinic Lerner Research Institute, OH (J.M.B.); Saha Cardiovascular Research Center, University of Kentucky, Lexington (R.E.T.); and Department of Pharmaceutical Sciences, University of Kentucky, Lexington (G.A.G.).

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http://dx.doi.org/10.1161/ATVBAHA.117.309224DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5546086PMC
May 2017

miRNA Targeting of Oxysterol-Binding Protein-Like 6 Regulates Cholesterol Trafficking and Efflux.

Arterioscler Thromb Vasc Biol 2016 05 3;36(5):942-951. Epub 2016 Mar 3.

Marc and Ruti Bell Vascular Biology and Disease Program, Leon H. Charney Division of Cardiology, Department of Medicine, New York University School of Medicine, New York, NY 10016.

Objective: Cholesterol homeostasis is fundamental to human health and is, thus, tightly regulated. MicroRNAs exert potent effects on biological pathways, including cholesterol metabolism, by repressing genes with related functions. We reasoned that this mode of pathway regulation could be exploited to identify novel genes involved in cholesterol homeostasis.

Approach And Results: Here, we identify oxysterol-binding protein-like 6 (OSBPL6) as a novel target of 2 miRNA hubs regulating cholesterol homeostasis: miR-33 and miR-27b. Characterization of OSBPL6 revealed that it is transcriptionally regulated in macrophages and hepatocytes by liver X receptor and in response to cholesterol loading and in mice and nonhuman primates by Western diet feeding. OSBPL6 encodes the OSBPL-related protein 6 (ORP6), which contains dual membrane- and endoplasmic reticulum-targeting motifs. Subcellular localization studies showed that ORP6 is associated with the endolysosomal network and endoplasmic reticulum, suggesting a role for ORP6 in cholesterol trafficking between these compartments. Accordingly, knockdown of OSBPL6 results in aberrant clustering of endosomes and promotes the accumulation of free cholesterol in these structures, resulting in reduced cholesterol esterification at the endoplasmic reticulum. Conversely, ORP6 overexpression enhances cholesterol trafficking and efflux in macrophages and hepatocytes. Moreover, we show that hepatic expression of OSBPL6 is positively correlated with plasma levels of high-density lipoprotein cholesterol in a cohort of 200 healthy individuals, whereas its expression is reduced in human atherosclerotic plaques.

Conclusions: These studies identify ORP6 as a novel regulator of cholesterol trafficking that is part of the miR-33 and miR-27b target gene networks that contribute to the maintenance of cholesterol homeostasis.
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http://dx.doi.org/10.1161/ATVBAHA.116.307282DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4850101PMC
May 2016

A new model of reverse cholesterol transport: enTICEing strategies to stimulate intestinal cholesterol excretion.

Trends Pharmacol Sci 2015 Jul 27;36(7):440-51. Epub 2015 Apr 27.

Department of Cellular and Molecular Medicine, Cleveland Clinic Lerner Research Institute, Cleveland, OH 44195, USA. Electronic address:

Cardiovascular disease (CVD) remains the largest cause of mortality in most developed countries. Although recent failed clinical trials and Mendelian randomization studies have called into question the high-density lipoprotein (HDL) hypothesis, it remains well accepted that stimulating the process of reverse cholesterol transport (RCT) can prevent or even regress atherosclerosis. The prevailing model for RCT is that cholesterol from the artery wall must be delivered to the liver where it is secreted into bile before leaving the body through fecal excretion. However, many studies have demonstrated that RCT can proceed through a non-biliary pathway known as transintestinal cholesterol excretion (TICE). The goal of this review is to discuss the current state of knowledge of the TICE pathway, with emphasis on points of therapeutic intervention.
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http://dx.doi.org/10.1016/j.tips.2015.04.002DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4485953PMC
July 2015

The TMAO-Generating Enzyme Flavin Monooxygenase 3 Is a Central Regulator of Cholesterol Balance.

Cell Rep 2015 Jan 15;10(3):326-338. Epub 2015 Jan 15.

Department of Cellular and Molecular Medicine, Cleveland Clinic Lerner Research Institute, Cleveland, OH 44195, USA. Electronic address:

Circulating levels of the gut microbe-derived metabolite trimethylamine-N-oxide (TMAO) have recently been linked to cardiovascular disease (CVD) risk. Here, we performed transcriptional profiling in mouse models of altered reverse cholesterol transport (RCT) and serendipitously identified the TMAO-generating enzyme flavin monooxygenase 3 (FMO3) as a powerful modifier of cholesterol metabolism and RCT. Knockdown of FMO3 in cholesterol-fed mice alters biliary lipid secretion, blunts intestinal cholesterol absorption, and limits the production of hepatic oxysterols and cholesteryl esters. Furthermore, FMO3 knockdown stimulates basal and liver X receptor (LXR)-stimulated macrophage RCT, thereby improving cholesterol balance. Conversely, FMO3 knockdown exacerbates hepatic endoplasmic reticulum (ER) stress and inflammation in part by decreasing hepatic oxysterol levels and subsequent LXR activation. FMO3 is thus identified as a central integrator of hepatic cholesterol and triacylglycerol metabolism, inflammation, and ER stress. These studies suggest that the gut microbiota-driven TMA/FMO3/TMAO pathway is a key regulator of lipid metabolism and inflammation.
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http://dx.doi.org/10.1016/j.celrep.2014.12.036DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4501903PMC
January 2015

BMP7 drives human adipogenic stem cells into metabolically active beige adipocytes.

Lipids 2015 Feb 23;50(2):111-20. Epub 2014 Dec 23.

Department of Nutrition and Health Sciences, University of Nebraska, 316G Ruth Leverton Hall, Lincoln, NE, 68583, USA.

Adult humans have a substantial amount of inducible-brown (or beige) fat, which is associated with increased energy expenditure and reduced weight gain via thermogenesis. Despite the identification of key regulators of beige adipogenesis, impacts of dietary factors on adaptive thermogenesis are largely unknown, partly due to a lack of validated human cell models. Bone morphogenetic protein 7 (BMP7) is known to promote brown adipogenesis in rodent and human progenitor cells. However, controversy still surrounds the cellular identity in BMP7-mediated transition of white to brown adipocytes. The aim of this study was to confirm BMP7-derived human adipocytes as a relevant in vitro model of human beige adipocyte by verifying the cellular lineage and metabolic activity. In this study, we hypothesized that pre-exposure of the stromal vascular (SV) fraction of primary human adipogenic precursor cells (hASC) to BMP7 would convert metabolically active brown adipocytes. Our results showed that exposure of hASC to human BMP7 was associated with significant escalation of (1) UCP1 gene expression, a signature gene of brown adipocytes, (2) beige specific marker gene expression (i.e., CD137 and TMEM26), (3) glucose and fatty acid uptake, and (4) basal and cAMP-stimulated oxygen consumption rate compared to white adipocyte control. Taken together, we demonstrated that BMP7 mediates conversion of hASC into metabolically active beige adipocytes. By confirming the cellular identity and metabolic activity, this BMP7-induced human beige adipocytes from hASC should aid in the discovery and assessment of bioactive molecules to promote adaptive thermogenesis.
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http://dx.doi.org/10.1007/s11745-014-3981-9DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4306630PMC
February 2015

The LXR-Idol axis differentially regulates plasma LDL levels in primates and mice.

Cell Metab 2014 Nov 4;20(5):910-918. Epub 2014 Nov 4.

Howard Hughes Medical Institute, University of California, Los Angeles, Los Angeles, CA 90095, USA; Department of Pathology and Laboratory Medicine, University of California, Los Angeles, Los Angeles, CA 90095, USA. Electronic address:

The LXR-regulated E3 ubiquitin ligase IDOL controls LDLR receptor stability independent of SREBP and PCSK9, but its relevance to plasma lipid levels is unknown. Here we demonstrate that the effects of the LXR-IDOL axis are both tissue and species specific. In mice, LXR agonist induces Idol transcript levels in peripheral tissues but not in liver, and does not change plasma LDL levels. Accordingly, Idol-deficient mice exhibit elevated LDLR protein levels in peripheral tissues, but not in the liver. By contrast, LXR activation in cynomolgus monkeys induces hepatic IDOL expression, reduces LDLR protein levels, and raises plasma LDL levels. Knockdown of IDOL in monkeys with an antisense oligonucleotide blunts the effect of LXR agonist on LDL levels. These results implicate IDOL as a modulator of plasma lipid levels in primates and support further investigation into IDOL inhibition as a potential strategy for LDL lowering in humans.
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http://dx.doi.org/10.1016/j.cmet.2014.10.001DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4261644PMC
November 2014

Cholesterol and lipoprotein metabolism: Early Career Committee contribution.

Arterioscler Thromb Vasc Biol 2014 Sep;34(9):1791-4

From the Department of Medicine, Cardiovascular Institute, Perelman School of Medicine, University of Pennsylvania, Philadelphia (H.Z.); Department of Pharmacology and Nutritional Sciences, Saha Cardiovascular Research Center, University of Kentucky, Lexington (R.E.T.); and Department of Medicine, Montreal Heart Institute, Université de Montréal, Montreal, Quebec, Canada (C.M.).

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http://dx.doi.org/10.1161/ATVBAHA.114.304267DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4142559PMC
September 2014

Transmembrane protein 55B is a novel regulator of cellular cholesterol metabolism.

Arterioscler Thromb Vasc Biol 2014 Sep 17;34(9):1917-23. Epub 2014 Jul 17.

From the Children's Hospital Oakland Research Institute, CA (M.W.M., F.B., D.N., E.T., K.S., R.M.K.); Institute of Human Genetics, University of Heidelberg, Heidelberg, Germany (J.S., H.R.); Sage Bionetworks, Seattle, WA (L.M.M.); Section on Lipid Sciences, Department of Pathology, Wake Forest University Health Sciences, Winston-Salem, NC (L.L.R., R.E.T.); and Molecular Medicine Partnership Unit (MMPU), Heidelberg, Germany (C.S., H.R.).

Objective: Interindividual variation in pathways affecting cellular cholesterol metabolism can influence levels of plasma cholesterol, a well-established risk factor for cardiovascular disease. Inherent variation among immortalized lymphoblastoid cell lines from different donors can be leveraged to discover novel genes that modulate cellular cholesterol metabolism. The objective of this study was to identify novel genes that regulate cholesterol metabolism by testing for evidence of correlated gene expression with cellular levels of 3-hydroxy-3-methylglutaryl-CoA reductase (HMGCR) mRNA, a marker for cellular cholesterol homeostasis, in a large panel of lymphoblastoid cell lines.

Approach And Results: Expression array profiling was performed on 480 lymphoblastoid cell lines established from participants of the Cholesterol and Pharmacogenetics (CAP) statin clinical trial, and transcripts were tested for evidence of correlated expression with HMGCR as a marker of intracellular cholesterol homeostasis. Of these, transmembrane protein 55b (TMEM55B) showed the strongest correlation (r=0.29; P=4.0E-08) of all genes not previously implicated in cholesterol metabolism and was found to be sterol regulated. TMEM55B knockdown in human hepatoma cell lines promoted the decay rate of the low-density lipoprotein receptor, reduced cell surface low-density lipoprotein receptor protein, impaired low-density lipoprotein uptake, and reduced intracellular cholesterol.

Conclusions: Here, we report identification of TMEM55B as a novel regulator of cellular cholesterol metabolism through the combination of gene expression profiling and functional studies. The findings highlight the value of an integrated genomic approach for identifying genes that influence cholesterol homeostasis.
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http://dx.doi.org/10.1161/ATVBAHA.113.302806DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4141484PMC
September 2014

Dietary cholesterol promotes adipocyte hypertrophy and adipose tissue inflammation in visceral, but not in subcutaneous, fat in monkeys.

Arterioscler Thromb Vasc Biol 2014 Sep 26;34(9):1880-7. Epub 2014 Jun 26.

From the Department of Pathology, Sections on Lipid Sciences (S.C., H.C., S.M.M., A.L.M., R.E.T., J.S.P.) and Comparative Medicine (K.K.), and Department of Biochemistry (J.S.P.), Wake Forest School of Medicine, Winston-Salem, NC; Department of Nutrition and Health Sciences, University of Nebraska, Lincoln (S.C.); Department of Food Science and Human Nutrition, University of Florida, Gainesville (S.C., J.-H.H.); and Department of Pathology and Laboratory Medicine, Howard Hughes Medical Institute, University of California, Los Angeles (C.H., P.T.).

Objective: Excessive caloric intake is associated with obesity and adipose tissue dysfunction. However, the role of dietary cholesterol in this process is unknown. The aim of this study was to determine whether increasing dietary cholesterol intake alters adipose tissue cholesterol content, adipocyte size, and endocrine function in nonhuman primates.

Approach And Results: Age-matched, male African Green monkeys (n=5 per group) were assigned to 1 of 3 diets containing 0.002 (low [Lo]), 0.2 (medium [Med]), or 0.4 (high [Hi]) mg cholesterol/kcal. After 10 weeks of diet feeding, animals were euthanized for adipose tissue, liver, and plasma collection. With increasing dietary cholesterol, free cholesterol (FC) content and adipocyte size increased in a stepwise manner in visceral, but not in subcutaneous fat, with a significant association between visceral adipocyte size and FC content (r(2)=0.298; n=15; P=0.035). In visceral fat, dietary cholesterol intake was associated with (1) increased proinflammatory gene expression and macrophage recruitment, (2) decreased expression of genes involved in cholesterol biosynthesis and lipoprotein uptake, and (3) increased expression of proteins involved in FC efflux.

Conclusions: Increasing dietary cholesterol selectively increases visceral fat adipocyte size, FC and macrophage content, and proinflammatory gene expression in nonhuman primates. Visceral fat cells seem to compensate for increased dietary cholesterol by limiting cholesterol uptake/synthesis and increasing FC efflux pathways.
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http://dx.doi.org/10.1161/ATVBAHA.114.303896DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4140949PMC
September 2014

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

PLoS One 2014 5;9(6):e98953. Epub 2014 Jun 5.

Department of Pathology, Section on Lipid Sciences, Wake Forest University School of Medicine, Winston-Salem, North Carolina, United States of America; Saha Cardiovascular Research Center, University of Kentucky, Lexington, Kentucky, United States of America.

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.
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http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0098953PLOS
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4047063PMC
July 2015

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

PLoS One 2014 3;9(1):e84418. Epub 2014 Jan 3.

Department of Pathology, Section on Lipid Sciences, Wake Forest University School of Medicine, Winston-Salem, North Carolina, United States of America ; Saha Cardiovascular Research Center, University of Kentucky, Lexington, Kentucky, United States of America.

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.
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http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0084418PLOS
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3880293PMC
September 2014

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

J Lipid Res 2013 Jun 5;54(6):1567-77. Epub 2013 Apr 5.

Department of Pathology, Section on Lipid Sciences, Wake Forest School of Medicine, Winston-Salem, NC, USA.

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.
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http://dx.doi.org/10.1194/jlr.M034454DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3646458PMC
June 2013

Phytosterol feeding causes toxicity in ABCG5/G8 knockout mice.

Am J Pathol 2013 Apr 1;182(4):1131-8. Epub 2013 Feb 1.

Section on Lipid Sciences, Department of Pathology, Wake Forest University School of Medicine, Winston-Salem, North Carolina 27157, USA.

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). To determine the significance of phytosterol exclusion from the body, we fed wild-type and ABCG5/G8 knockout mice a diet enriched with plant sterols. The high-phytosterol diet was extremely toxic to the ABCG5/G8 knockout mice but had no adverse effects on wild-type mice. ABCG5/G8 knockout mice died prematurely and developed a phenotype that included high levels of plant sterols in many tissues, liver abnormalities, and severe cardiac lesions. This study is the first to report such toxic effects of phytosterol accumulation in ABCG5/G8 knockout mice. We believe these new data support the conclusion that plant sterols are excluded from the body because they are toxic when present at high levels.
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http://dx.doi.org/10.1016/j.ajpath.2012.12.014DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3620394PMC
April 2013

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

Circ Res 2013 Jan 28;112(1):140-51. Epub 2012 Sep 28.

Department of Pediatrics, University of Texas Southwestern Medical Center, 5323 Harry Hines Blvd, Dallas, TX 75390, USA.

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. We tested the hypotheses that the interaction is required for SR-BI signaling, and that it enables SR-BI to serve as a PM cholesterol sensor.

Methods And Results: In studies performed in COS-M6 cells, mutation of a highly conserved C-terminal transmembrane domain glutamine to alanine (SR-BI-Q445A) decreased PM cholesterol interaction with the receptor by 71% without altering HDL binding or cholesterol uptake or efflux, and it yielded a receptor incapable of HDL-induced signaling. Signaling prompted by cholesterol efflux to methyl-β-cyclodextrin also was prevented, indicating that PM cholesterol interaction with the receptor enables it to serve as a PM cholesterol sensor. Using SR-BI-Q445A, we further demonstrated that PM cholesterol sensing by SR-BI does not influence SR-BI-mediated reverse cholesterol transport to the liver in mice. However, the PM cholesterol sensing does underlie apolipoprotein B intracellular trafficking in response to postprandial micelles or methyl-β-cyclodextrin in cultured enterocytes, and it is required for HDL activation of endothelial NO synthase and migration in cultured endothelial cells and HDL-induced angiogenesis in vivo.

Conclusions: Through interaction with PM cholesterol, SR-BI serves as a PM cholesterol sensor, and the resulting intracellular signaling governs processes in both enterocytes and endothelial cells.
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http://dx.doi.org/10.1161/CIRCRESAHA.112.280081DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3564583PMC
January 2013

Hypercholesterolemia increases supraspinatus tendon stiffness and elastic modulus across multiple species.

J Shoulder Elbow Surg 2013 May 13;22(5):681-6. Epub 2012 Sep 13.

McKay Orthopaedic Research Laboratory, University of Pennsylvania, Philadelphia, PA 19104, USA.

Background: More than one-quarter of Americans have hypercholesterolemia and/or are being treated with cholesterol-lowering medications. Given the systemic nature of hypercholesterolemia and remaining questions regarding its effect on tendons at a local level, we sought to assess the utility of small versus large animal model systems for translational studies by exploring the effect of hypercholesterolemia on supraspinatus tendon elastic mechanical properties in mice, rats, and monkeys. We hypothesized that stiffness and elastic modulus would be increased in tendons across species due to hypercholesterolemia.

Materials And Methods: Supraspinatus tendons from normal (control) and high-cholesterol (HC) mice, rats, and monkeys were used in this study. After dissection, tendons were geometrically measured and tensile tested with tissue strain measured optically.

Results: Overall, HC animals had significantly altered plasma lipid profiles. Biomechanical testing showed a significant increase in stiffness compared with control in HC mice and rats, as well as a nonsignificant trend for HC monkeys. Elastic modulus was also significantly increased in HC mice and monkeys, with HC rats showing a trend.

Conclusions: The consistency of our findings across species and between small and large animals, combined with the fact that the aged mice were exposed to lifelong hypercholesterolemia (compared with rats and nonhuman primates, which were fed HC diets), suggests that these increased properties may be inherent to the effect of hypercholesterolemia on supraspinatus tendon rather than due to an effect of cumulative exposure time to the effects of HC. Further investigation is needed to confirm this concept.
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http://dx.doi.org/10.1016/j.jse.2012.07.008DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3525802PMC
May 2013

Biliary and nonbiliary contributions to reverse cholesterol transport.

Curr Opin Lipidol 2012 Apr;23(2):85-90

Department of Pathology-Section on Lipid Sciences, Wake Forest University School of Medicine, Winston-Salem, North Carolina 27157-1040, USA.

Purpose Of Review: The process of reverse cholesterol transport (RCT) is critical for disposal of excess cholesterol from the body. Although it is generally accepted that RCT requires biliary secretion, recent studies show that RCT persists in genetic or surgical models of biliary insufficiency. Discovery of this nonbiliary pathway has opened new possibilities of targeting the intestine as an inducible cholesterol excretory organ. In this review we highlight the relative contribution and therapeutic potential for both biliary and nonbiliary components of RCT.

Recent Findings: Recently, the proximal small intestine has gained attention for its underappreciated ability to secrete cholesterol in a process called transintestinal cholesterol efflux (TICE). Although this intestinal pathway for RCT is quantitatively less important than the biliary route under normal physiological conditions, TICE is highly inducible, providing a novel therapeutic opportunity for treatment of atherosclerotic cardiovascular disease (ASCVD). In fact, recent studies show that intestine-specific activation of RCT protects against ASCVD in mice.

Summary: It is well known that the small intestine plays a gatekeeper role in the maintenance of cholesterol balance. Through integrated regulation of cholesterol absorption and TICE, the small intestine is a key target for new therapies against ASCVD.
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http://dx.doi.org/10.1097/MOL.0b013e3283508c21DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3711548PMC
April 2012

Monocyte tissue factor-dependent activation of coagulation in hypercholesterolemic mice and monkeys is inhibited by simvastatin.

J Clin Invest 2012 Feb 3;122(2):558-68. Epub 2012 Jan 3.

Department of Medicine, Division of Hematology and Oncology, McAllister Heart Institute, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina, USA.

Hypercholesterolemia is a major risk factor for atherosclerosis. It also is associated with platelet hyperactivity, which increases morbidity and mortality from cardiovascular disease. However, the mechanisms by which hypercholesterolemia produces a procoagulant state remain undefined. Atherosclerosis is associated with accumulation of oxidized lipoproteins within atherosclerotic lesions. Small quantities of oxidized lipoproteins are also present in the circulation of patients with coronary artery disease. We therefore hypothesized that hypercholesterolemia leads to elevated levels of oxidized LDL (oxLDL) in plasma and that this induces expression of the procoagulant protein tissue factor (TF) in monocytes. In support of this hypothesis, we report here that oxLDL induced TF expression in human monocytic cells and monocytes. In addition, patients with familial hypercholesterolemia had elevated levels of plasma microparticle (MP) TF activity. Furthermore, a high-fat diet induced a time-dependent increase in plasma MP TF activity and activation of coagulation in both LDL receptor-deficient mice and African green monkeys. Genetic deficiency of TF in bone marrow cells reduced coagulation in hypercholesterolemic mice, consistent with a major role for monocyte-derived TF in the activation of coagulation. Similarly, a deficiency of either TLR4 or TLR6 reduced levels of MP TF activity. Simvastatin treatment of hypercholesterolemic mice and monkeys reduced oxLDL, monocyte TF expression, MP TF activity, activation of coagulation, and inflammation, without affecting total cholesterol levels. Our results suggest that the prothrombotic state associated with hypercholesterolemia is caused by oxLDL-mediated induction of TF expression in monocytes via engagement of a TLR4/TLR6 complex.
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http://dx.doi.org/10.1172/JCI58969DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3266787PMC
February 2012

Inhibition of miR-33a/b in non-human primates raises plasma HDL and lowers VLDL triglycerides.

Nature 2011 Oct 19;478(7369):404-7. Epub 2011 Oct 19.

Marc and Ruti Bell Vascular Biology and Disease Program, Leon H. Charney Division of Cardiology, Department of Medicine, New York University School of Medicine, New York, New York 10016, USA.

Cardiovascular disease remains the leading cause of mortality in westernized countries, despite optimum medical therapy to reduce the levels of low-density lipoprotein (LDL)-associated cholesterol. The pursuit of novel therapies to target the residual risk has focused on raising the levels of high-density lipoprotein (HDL)-associated cholesterol in order to exploit its atheroprotective effects. MicroRNAs (miRNAs) have emerged as important post-transcriptional regulators of lipid metabolism and are thus a new class of target for therapeutic intervention. MicroRNA-33a and microRNA-33b (miR-33a/b) are intronic miRNAs whose encoding regions are embedded in the sterol-response-element-binding protein genes SREBF2 and SREBF1 (refs 3-5), respectively. These miRNAs repress expression of the cholesterol transporter ABCA1, which is a key regulator of HDL biogenesis. Recent studies in mice suggest that antagonizing miR-33a may be an effective strategy for raising plasma HDL levels and providing protection against atherosclerosis; however, extrapolating these findings to humans is complicated by the fact that mice lack miR-33b, which is present only in the SREBF1 gene of medium and large mammals. Here we show in African green monkeys that systemic delivery of an anti-miRNA oligonucleotide that targets both miR-33a and miR-33b increased hepatic expression of ABCA1 and induced a sustained increase in plasma HDL levels over 12 weeks. Notably, miR-33 antagonism in this non-human primate model also increased the expression of miR-33 target genes involved in fatty acid oxidation (CROT, CPT1A, HADHB and PRKAA1) and reduced the expression of genes involved in fatty acid synthesis (SREBF1, FASN, ACLY and ACACA), resulting in a marked suppression of the plasma levels of very-low-density lipoprotein (VLDL)-associated triglycerides, a finding that has not previously been observed in mice. These data establish, in a model that is highly relevant to humans, that pharmacological inhibition of miR-33a and miR-33b is a promising therapeutic strategy to raise plasma HDL and lower VLDL triglyceride levels for the treatment of dyslipidaemias that increase cardiovascular disease risk.
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http://dx.doi.org/10.1038/nature10486DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3235584PMC
October 2011

Antagonism of miR-33 in mice promotes reverse cholesterol transport and regression of atherosclerosis.

J Clin Invest 2011 Jul 6;121(7):2921-31. Epub 2011 Jun 6.

Marc and Ruti Bell Vascular Biology and Disease Program, Leon H. Charney Division of Cardiology, Department of Medicine, New York University School of Medicine, New York, New York 10016, USA.

Plasma HDL levels have a protective role in atherosclerosis, yet clinical therapies to raise HDL levels have remained elusive. Recent advances in the understanding of lipid metabolism have revealed that miR-33, an intronic microRNA located within the SREBF2 gene, suppresses expression of the cholesterol transporter ABC transporter A1 (ABCA1) and lowers HDL levels. Conversely, mechanisms that inhibit miR-33 increase ABCA1 and circulating HDL levels, suggesting that antagonism of miR-33 may be atheroprotective. As the regression of atherosclerosis is clinically desirable, we assessed the impact of miR-33 inhibition in mice deficient for the LDL receptor (Ldlr-/- mice), with established atherosclerotic plaques. Mice treated with anti-miR33 for 4 weeks showed an increase in circulating HDL levels and enhanced reverse cholesterol transport to the plasma, liver, and feces. Consistent with this, anti-miR33-treated mice showed reductions in plaque size and lipid content, increased markers of plaque stability, and decreased inflammatory gene expression. Notably, in addition to raising ABCA1 levels in the liver, anti-miR33 oligonucleotides directly targeted the plaque macrophages, in which they enhanced ABCA1 expression and cholesterol removal. These studies establish that raising HDL levels by anti-miR33 oligonucleotide treatment promotes reverse cholesterol transport and atherosclerosis regression and suggest that it may be a promising strategy to treat atherosclerotic vascular disease.
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http://dx.doi.org/10.1172/JCI57275DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3223840PMC
July 2011