Cardiology
Abstract
A new member of the lipase gene family, initially termed endothelial lipase (gene nomenclature, LIPG; protein, EL), is expressed in a variety of different tissues, suggesting a general role in lipid metabolism. To assess the hypothesis that EL plays a physiological role in lipoprotein metabolism in vivo, we have used gene targeting of the native murine locus and transgenic introduction of the human LIPG locus in mice to modulate the level of EL expression. Evaluation of these alleles in a C57Bl/6 background revealed an inverse relationship between HDL cholesterol level and EL expression. Fasting plasma HDL cholesterol was increased by 57% in LIPG–/– mice and 25% in LIPG+/– mice and was decreased by 19% in LIPG transgenic mice as compared with syngeneic controls. Detailed analysis of lipoprotein particle composition indicated that this increase was due primarily to an increased number of HDL particles. Phospholipase assays indicated that EL is a primary contributor to phospholipase activity in mouse. These data indicate that expression levels of this novel lipase have a significant effect on lipoprotein metabolism.
Authors
Tatsuro Ishida, Sungshin Choi, Ramendra K. Kundu, Ken-ichi Hirata, Edward M. Rubin, Allen D. Cooper, Thomas Quertermous
Abstract
Lipoprotein lipase is the principal enzyme that hydrolyzes circulating triglycerides and liberates free fatty acids that can be used as energy by cardiac muscle. Although lipoprotein lipase is expressed by and is found on the surface of cardiomyocytes, its transfer to the luminal surface of endothelial cells is thought to be required for lipoprotein lipase actions. To study whether nontransferable lipoprotein lipase has physiological actions, we placed an α-myosin heavy-chain promoter upstream of a human lipoprotein lipase minigene construct with a glycosylphosphatidylinositol anchoring sequence on the carboxyl terminal region. Hearts of transgenic mice expressed the altered lipoprotein lipase, and the protein localized to the surface of cardiomyocytes. Hearts, but not postheparin plasma, of these mice contained human lipoprotein lipase activity. More lipid accumulated in hearts expressing the transgene; the myocytes were enlarged and exhibited abnormal architecture. Hearts of transgenic mice were dilated, and left ventricular systolic function was impaired. Thus, lipoprotein lipase expressed on the surface of cardiomyocytes can increase lipid uptake and produce cardiomyopathy.
Authors
Hiroaki Yagyu, Guangping Chen, Masayoshi Yokoyama, Kumiko Hirata, Ayanna Augustus, Yuko Kako, Toru Seo, Yunying Hu, E. Peer Lutz, Martin Merkel, André Bensadoun, Shunichi Homma, Ira J. Goldberg
Abstract
Restrictive cardiomyopathy (RCM) is an uncommon heart muscle disorder characterized by impaired filling of the ventricles with reduced volume in the presence of normal or near normal wall thickness and systolic function. The disease may be associated with systemic disease but is most often idiopathic. We recognized a large family in which individuals were affected by either idiopathic RCM or hypertrophic cardiomyopathy (HCM). Linkage analysis to selected sarcomeric contractile protein genes identified cardiac troponin I (TNNI3) as the likely disease gene. Subsequent mutation analysis revealed a novel missense mutation, which cosegregated with the disease in the family (lod score: 4.8). To determine if idiopathic RCM is part of the clinical expression of TNNI3 mutations, genetic investigations of the gene were performed in an additional nine unrelated RCM patients with restrictive filling patterns, bi-atrial dilatation, normal systolic function, and normal wall thickness. TNNI3 mutations were identified in six of these nine RCM patients. Two of the mutations identified in young individuals were de novo mutations. All mutations appeared in conserved and functionally important domains of the gene.
Authors
Jens Mogensen, Toru Kubo, Mauricio Duque, William Uribe, Anthony Shaw, Ross Murphy, Juan R. Gimeno, Perry Elliott, William J. McKenna
Abstract
Cholesterol-loaded macrophage foam cells are a central component of atherosclerotic lesions. ABCA1, the defective molecule in Tangier disease, mediates the efflux of phospholipids and cholesterol from cells to apoA-I, reversing foam cell formation. In ABCA1, we identified a sequence rich in proline, glutamic acid, serine, and threonine (PEST sequence) that enhances the degradation of ABCA1 by calpain protease and thereby controls the cell surface concentration and cholesterol efflux activity of ABCA1. In an apparent positive feedback loop, apoA-I binds ABCA1, promotes lipid efflux, inhibits calpain degradation, and leads to increased levels of ABCA1. ApoA-I infusion also increases ABCA1 in vivo. These studies reveal a novel mode of regulation of ABCA1 by PEST sequence–mediated calpain proteolysis that appears to be reversed by apolipoprotein-mediated phospholipid efflux. Inhibition of ABCA1 degradation by calpain could represent a novel therapeutic approach to increasing macrophage cholesterol efflux and decreasing atherosclerosis.
Authors
Nan Wang, Wengen Chen, Patrick Linsel-Nitschke, Laurent O. Martinez, Birgit Agerholm-Larsen, David L. Silver, Alan R. Tall
Abstract
Research Article
Authors
Emily R. Eden, Dilipkumar D. Patel, Xi-Ming Sun, Jemima J. Burden, Michael Themis, Matthew Edwards, Philip Lee, Clare Neuwirth, Rossitza P. Naoumova, Anne K. Soutar
Abstract
Research Article
Authors
Colleen E. Clancy, Michihiro Tateyama, Robert S. Kass
Abstract
Research Article
Authors
Gregory A. Graf, Wei-Ping Li, Robert D. Gerard, Ingrid Gelissen, Ann White, Jonathan C. Cohen, Helen H. Hobbs
Abstract
Research Article
Authors
Liqing Yu, Jia Li-Hawkins, Robert E. Hammer, Knut E. Berge, Jay D. Horton, Jonathan C. Cohen, Helen H. Hobbs
Abstract
Research Article
Authors
Roshni R. Singaraja, Catherine Fievet, Graciela Castro, Erick R. James, Nathalie Hennuyer, Susanne M. Clee, Nagat Bissada, Jonathan C. Choy, Jean-Charles Fruchart, Bruce M. McManus, Bart Staels, Michael R. Hayden
Copyright © 2019 American Society for Clinical Investigation
ISSN: 0021-9738 (print), 1558-8238 (online)