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Zhang K, Kim H, Fu Z, Qiu Y, Yang Z, Wang J, Zhang D, Tong X, Yin L, Li J, Wu J, Qi NR, Houten SM, Zhang R. Deficiency of the Mitochondrial NAD Kinase Causes Stress-Induced Hepatic Steatosis in Mice. Gastroenterology 2018; 154:224-237. [PMID: 28923496 PMCID: PMC5742027 DOI: 10.1053/j.gastro.2017.09.010] [Citation(s) in RCA: 29] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 11/10/2016] [Revised: 08/31/2017] [Accepted: 09/10/2017] [Indexed: 12/13/2022]
Abstract
BACKGROUND & AIMS The mitochondrial nicotinamide adenine dinucleotide (NAD) kinase (NADK2, also called MNADK) catalyzes phosphorylation of NAD to yield NADP. Little is known about the functions of mitochondrial NADP and MNADK in liver physiology and pathology. We investigated the effects of reduced mitochondrial NADP by deleting MNADK in mice. METHODS We generated MNADK knockout (KO) mice on a C57BL/6NTac background; mice with a wild-type Mnadk gene were used as controls. Some mice were placed on an atherogenic high-fat diet (16% fat, 41% carbohydrate, and 1.25% cholesterol supplemented with 0.5% sodium cholate) or given methotrexate intraperitoneally. We measured rates of fatty acid oxidation in primary hepatocytes using radiolabeled palmitate and in mice using indirect calorimetry. We measured levels of reactive oxygen species in mouse livers and primary hepatocytes. Metabolomic analyses were used to quantify serum metabolites, such as amino acids and acylcarnitines. RESULTS The KO mice had metabolic features of MNADK-deficient patients, such as increased serum concentrations of lysine and C10:2 carnitine. When placed on the atherogenic high-fat diet, the KO mice developed features of nonalcoholic fatty liver disease and had increased levels of reactive oxygen species in livers and primary hepatocytes, compared with control mice. During fasting, the KO mice had a defect in fatty acid oxidation. MNADK deficiency reduced the activation of cAMP-responsive element binding protein-hepatocyte specific and peroxisome proliferator-activated receptor alpha, which are transcriptional activators that mediate the fasting response. The activity of mitochondrial sirtuins was reduced in livers of the KO mice. Methotrexate inhibited the catalytic activity of MNADK in hepatocytes and in livers in mice with methotrexate injection. In mice given injections of methotrexate, supplementation of a diet with nicotinamide riboside, an NAD precursor, replenished hepatic NADP and protected the mice from hepatotoxicity, based on markers such as increased level of serum alanine aminotransferase. CONCLUSION MNADK facilitates fatty acid oxidation, counteracts oxidative damage, maintains mitochondrial sirtuin activity, and prevents metabolic stress-induced non-alcoholic fatty liver disease in mice.
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Affiliation(s)
- Kezhong Zhang
- Center for Molecular Medicine and Genetics, Wayne State University School of Medicine, Detroit, Michigan; Department of Microbiology, Immunology and Biochemistry, Wayne State University School of Medicine, Detroit, Michigan.
| | - Hyunbae Kim
- Center for Molecular Medicine and Genetics, Wayne State University School of Medicine, Detroit, MI 48201, USA
| | - Zhiyao Fu
- Center for Molecular Medicine and Genetics, Wayne State University School of Medicine, Detroit, MI 48201, USA
| | - Yining Qiu
- Center for Molecular Medicine and Genetics, Wayne State University School of Medicine, Detroit, MI 48201, USA
| | - Zhao Yang
- Center for Molecular Medicine and Genetics, Wayne State University School of Medicine, Detroit, MI 48201, USA
| | - Jiemei Wang
- College of Pharmacy and Health Sciences, Wayne State University, Detroit, MI 48201, USA
| | - Deqiang Zhang
- Department of Molecular and Integrative Physiology, University of Michigan Medical School, Ann Arbor, MI 48109, USA
| | - Xin Tong
- Department of Molecular and Integrative Physiology, University of Michigan Medical School, Ann Arbor, MI 48109, USA
| | - Lei Yin
- Department of Molecular and Integrative Physiology, University of Michigan Medical School, Ann Arbor, MI 48109, USA
| | - Jing Li
- Department of Oncology, Wayne State University School of Medicine, Detroit, MI 48202, USA
| | - Jianmei Wu
- Department of Oncology, Wayne State University School of Medicine, Detroit, MI 48202, USA
| | - Nathan R. Qi
- Department of Internal Medicine, University of Michigan Medical School, Ann Arbor, MI 48109, USA
| | - Sander M. Houten
- Department of Genetics and Genomic Sciences, Icahn Institute for Genomics and Multiscale Biology, Icahn School of Medicine at Mount Sinai, New York, NY 10029, USA
| | - Ren Zhang
- Center for Molecular Medicine and Genetics, Wayne State University School of Medicine, Detroit, Michigan.
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McGuinness ET, Butler JR. NAD+ kinase--a review. THE INTERNATIONAL JOURNAL OF BIOCHEMISTRY 1985; 17:1-11. [PMID: 2987053 DOI: 10.1016/0020-711x(85)90079-5] [Citation(s) in RCA: 69] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/03/2023]
Abstract
NAD+ kinase catalyzes the only (known) biochemical reaction leading to the production of NADP+ from NAD+. Most evidence indicates it is found in the cytoplasm, but reports of its presence in (other) cell bodies can not be discounted. Viewed as a protein, our knowledge of NADK composition and architecture is rudimentary. Though recognized as a large multimeric protein, no agreement is evident for the molecular weight (Mr = approximately 4-65 X 10(4] of the native protein. Is calmodulin an integral subunit of (some, all) NAD+ kinases (analogous to phosphorylase kinase in skeletal muscle)? Or is it an external modulator? Consensus is evident that a subunit of molecular weight 30-35 X 10(3) is a component of the mammalian and yeast kinase. In one case (rabbit liver) two types of subunits are reported to give rise to oligomers differing in molecular weight and catalytic activities. Viewed as an enzyme it is not known why such a complex aggregate is needed for what might otherwise appear to a routine phosphorylation reaction. Rapid equilibrium random (for pigeon liver and C. utilis preparations) and ping-pong (for A. vinelandii kinase) mechanisms have been proposed for the reaction, with multiple reactant binding sites indicated for the random cases. From the perspective of enzyme modulation, the demonstration that green plant and sea urchin egg kinases are targets for calmodulin regulation by intracellular Ca2+ links NADP+ production in these sources to the multi-level discriminatory control functions inherent to this Ca2+-protein complex. Significant questions arise from the results of various investigators considered in this review. These queries offer fertile ground for the selective design of key experiments directed to a better understanding of NAD+ kinase function and pyridine nucleotide biochemistry.
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