The de novo synthesis of fatty acids occurs in two distinct cellular compartments. Palmitate (C16:0) is synthesized in the cytoplasm by acetyI-CoA carboxylasel and fatty acid synthase. The vast majority of palmitate synthesized is then elongated to longer chain fatty acids in the endoplasmic reticulum via four sequential reactions: condensation, reduction, dehydration, and a final reduction to form the elongated fatty acyI-CoA. The objectives of this application are to identify and characterize the function of three enzymes involved in microsomal fatty acid elongation. First, we will investigate the in vivo function of the long chain fatty acyl elongase (LCE), the initial condensing enzyme required for the elongation of long chain fatty acids in vitro. We will use LCE knockout mice to determine whether LCE is required for the elongation of palmitate in vivo and whether its activity is required for normal lipid homeostasis in liver. Additional studies will determine whether the lack of LCE activity attenuates or prevents the development of obesity and diabetes in mice. Second, we have identified a novel condensing enzyme, designated ELOVL7. Unlike other condensing enzymes, ELOVL7 is not expressed in liver, but is highly expressed in intestine. We will determine the fatty acid substrate specificity of ELOVL7, and characterize the biologic function of ELOVL7 in intestine using knockout mice. Preliminary data suggests that ELOVL7 elongates long chain saturated and monounsaturated fatty acids. Therefore, we will determine whether ELOVL7 is required for the normal synthesis of lipids that have long chain saturated fatty acid moieties, such as ceramide and sphingolipids. Third, we will identify and characterize the microsomal 3-hydroxystearoyI-CoA dehydratase. This enzyme catalyzes the third reaction in microsomal fatty acid elongation, and is the only unidentified enzyme in this pathway. Studies, both in vitro and in vivo, will focus on characterizing the activity and regulation of this enzyme. The studies proposed in this application will provide a comprehensive characterization of three mammalian microsomal fatty acid elongation enzymes and will determine whether enzymes involved in microsomal fatty acid elongation are potential targets for treating common diseases such as hypertriglyceridemia, obesity, and insulin-resistant diabetes.

Agency
National Institute of Health (NIH)
Institute
National Heart, Lung, and Blood Institute (NHLBI)
Type
Research Project (R01)
Project #
5R01HL038049-18
Application #
7076824
Study Section
Special Emphasis Panel (ZRG1-EMNR-C (06))
Program Officer
Ershow, Abby
Project Start
1987-04-01
Project End
2008-06-30
Budget Start
2006-07-01
Budget End
2007-06-30
Support Year
18
Fiscal Year
2006
Total Cost
$304,668
Indirect Cost
Name
University of Texas Sw Medical Center Dallas
Department
Internal Medicine/Medicine
Type
Schools of Medicine
DUNS #
800771545
City
Dallas
State
TX
Country
United States
Zip Code
75390
Kim, Chai-Wan; Moon, Young-Ah; Park, Sahng Wook et al. (2010) Induced polymerization of mammalian acetyl-CoA carboxylase by MIG12 provides a tertiary level of regulation of fatty acid synthesis. Proc Natl Acad Sci U S A 107:9626-31
McNutt, Markey C; Kwon, Hyock Joo; Chen, Chiyuan et al. (2009) Antagonism of secreted PCSK9 increases low density lipoprotein receptor expression in HepG2 cells. J Biol Chem 284:10561-70
Moon, Young-Ah; Hammer, Robert E; Horton, Jay D (2009) Deletion of ELOVL5 leads to fatty liver through activation of SREBP-1c in mice. J Lipid Res 50:412-23
Kwon, Hyock Joo; Lagace, Thomas A; McNutt, Markey C et al. (2008) Molecular basis for LDL receptor recognition by PCSK9. Proc Natl Acad Sci U S A 105:1820-5
Grefhorst, Aldo; McNutt, Markey C; Lagace, Thomas A et al. (2008) Plasma PCSK9 preferentially reduces liver LDL receptors in mice. J Lipid Res 49:1303-11
Lagace, Thomas A; Curtis, David E; Garuti, Rita et al. (2006) Secreted PCSK9 decreases the number of LDL receptors in hepatocytes and in livers of parabiotic mice. J Clin Invest 116:2995-3005
Rashid, Shirya; Curtis, David E; Garuti, Rita et al. (2005) Decreased plasma cholesterol and hypersensitivity to statins in mice lacking Pcsk9. Proc Natl Acad Sci U S A 102:5374-9
Park, Sahng Wook; Moon, Young-Ah; Horton, Jay D (2004) Post-transcriptional regulation of low density lipoprotein receptor protein by proprotein convertase subtilisin/kexin type 9a in mouse liver. J Biol Chem 279:50630-8
Browning, Jeffrey D; Horton, Jay D (2004) Molecular mediators of hepatic steatosis and liver injury. J Clin Invest 114:147-52
Moon, Young-Ah; Horton, Jay D (2003) Identification of two mammalian reductases involved in the two-carbon fatty acyl elongation cascade. J Biol Chem 278:7335-43

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