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Gastroenterology. 2018 Jan;154(1):224-237. doi: 10.1053/j.gastro.2017.09.010. Epub 2017 Sep 18.

Deficiency of the Mitochondrial NAD Kinase Causes Stress-Induced Hepatic Steatosis in Mice.

Author information

1
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. Electronic address: kzhang@med.wayne.edu.
2
Center for Molecular Medicine and Genetics, Wayne State University School of Medicine, Detroit, Michigan.
3
College of Pharmacy and Health Sciences, Wayne State University, Detroit, Michigan.
4
Department of Molecular and Integrative Physiology, University of Michigan Medical School, Ann Arbor, Michigan.
5
Department of Oncology, Wayne State University School of Medicine, Detroit, Michigan.
6
Department of Internal Medicine, University of Michigan Medical School, Ann Arbor, Michigan.
7
Department of Genetics and Genomic Sciences, Icahn Institute for Genomics and Multiscale Biology, Icahn School of Medicine at Mount Sinai, New York, New York.
8
Center for Molecular Medicine and Genetics, Wayne State University School of Medicine, Detroit, Michigan. Electronic address: rzhang@med.wayne.edu.

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.

KEYWORDS:

CREBH; Liver Injury; Mouse Model; PPARα; Steatohepatitis

PMID:
28923496
PMCID:
PMC5742027
DOI:
10.1053/j.gastro.2017.09.010
[Indexed for MEDLINE]
Free PMC Article

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