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Nicotinamide N-methyltransferase knockdown protects against diet-induced obesity
Daniel Kraus1, Qin Yang1, Dong Kong2
11] Division of Endocrinology, Diabetes, and Metabolism, Department of Medicine, Beth Israel Deaconess Medical Center and Harvard Medical School, 330 Brookline Avenue, Boston, Massachusetts 02215, USA [2] [3] Division of Nephrology, Department of Internal Medicine I, Würzburg University Hospital, Oberdürrbacher Straße 6, 97080 Würzburg, Germany (D.K.); Department of Medicine, Physiology and Biophysics, Center for Diabetes Research and Treatment, and Center for Epigenetics and Metabolism, University of California, Irvine, California 92697, USA (Q.Y.); Research Programs Unit, Molecular Neurology, Biomedicum Helsinki, University of Helsinki, 00290, Helsinki, Finland (E.P.); Department of Biochemistry and Molecular Biology, Faculty of Medicine, Dalhousie Medicine New Brunswick, Dalhousie University, Saint John, New Brunswick E2L4L5, USA (T.C.P.); Department of Endocrinology, Key Laboratory of Endocrinology of Ministry of Health, Peking Union Medical College Hospital, Chinese Academy of Medical Sciences and Peking Union Medical College, Beijing 100730, China (F.G.); School of Pharmacy, University of Eastern Finland, P.O. Box 1627, FI-70211 Kuopio, Finland (L.A.).
None:
In obesity and type 2 diabetes, Glut4 glucose transporter expression is decreased selectively in adipocytes. Adipose-specific knockout or overexpression of Glut4 alters systemic insulin sensitivity. Here we show, using DNA array analyses, that nicotinamide N-methyltransferase (Nnmt) is the most strongly reciprocally regulated gene when comparing gene expression in white adipose tissue (WAT) from adipose-specific Glut4-knockout or adipose-specific Glut4-overexpressing mice with their respective controls. NNMT methylates nicotinamide (vitamin B3) using S-adenosylmethionine (SAM) as a methyl donor. Nicotinamide is a precursor of NAD(+), an important cofactor linking cellular redox states with energy metabolism. SAM provides propylamine for polyamine biosynthesis and donates a methyl group for histone methylation. Polyamine flux including synthesis, catabolism and excretion, is controlled by the rate-limiting enzymes ornithine decarboxylase (ODC) and spermidine-spermine N(1)-acetyltransferase (SSAT; encoded by Sat1) and by polyamine oxidase (PAO), and has a major role in energy metabolism. We report that NNMT expression is increased in WAT and liver of obese and diabetic mice. Nnmt knockdown in WAT and liver protects against diet-induced obesity by augmenting cellular energy expenditure. NNMT inhibition increases adipose SAM and NAD(+) levels and upregulates ODC and SSAT activity as well as expression, owing to the effects of NNMT on histone H3 lysine 4 methylation in adipose tissue. Direct evidence for increased polyamine flux resulting from NNMT inhibition includes elevated urinary excretion and adipocyte secretion of diacetylspermine, a product of polyamine metabolism. NNMT inhibition in adipocytes increases oxygen consumption in an ODC-, SSAT- and PAO-dependent manner. Thus, NNMT is a novel regulator of histone methylation, polyamine flux and NAD(+)-dependent SIRT1 signalling, and is a unique and attractive target for treating obesity and type 2 diabetes.
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