Dall 2019 J Biol Chem
|Dall M, Trammell SAJ, Asping M, Hassing AS, Agerholm M, Vienberg SG, Gillum MP, Larsen S, Treebak JT (2019) Mitochondrial function in liver cells is resistant to perturbations in NAD+ salvage capacity. J Biol Chem 294:13304-26.|
Abstract: Supplementation with nicotinamide adenine dinucleotide (NAD+) precursors such as nicotinamide riboside (NR) has been shown to enhance mitochondrial function in the liver and prevent hepatic lipid accumulation in high-fat diet (HFD)-fed rodents. Hepatocyte-specific knockout of the NAD+-synthesizing enzyme nicotinamide phosphoribosyltransferase (NAMPT) reduces liver NAD+ levels, but the metabolic phenotype of Nampt-deficient hepatocytes in mice is unknown. Here, we assessed Nampt's role in maintaining mitochondrial and metabolic functions in the mouse liver. Using the Cre-LoxP system, we generated hepatocyte-specific Nampt knockout (HNKO) mice, having a 50% reduction of liver NAD+ levels. We screened the HNKO mice for signs of metabolic dysfunction following 60% HFD feeding for 20 weeks +/- NR supplementation and found that NR increases hepatic NAD+ levels without affecting fat mass or glucose tolerance in HNKO or WT animals. High-resolution respirometry revealed that NR supplementation of the HNKO mice did not increase state III respiration, which was observed in WT mice following NR supplementation. Mitochondrial oxygen consumption and fatty-acid oxidation was unaltered in primary HNKO hepatocytes. Mitochondria isolated from whole HNKO livers had only a 20% reduction in NAD+, suggesting that the mitochondrial NAD+ pool is less affected by HNKO than the whole-tissue pool. When stimulated with tryptophan in the presence of 15N-glutamine, HNKO hepatocytes had a higher 15N-NAD+ enrichment than WT hepatocytes, indicating that HNKO mice compensate through de novo NAD+ synthesis. We conclude that NAMPT-deficient hepatocytes can maintain substantial NAD+ levels and that the Nampt knockout has only minor consequences for mitochondrial function in the mouse liver.
Published under license by The American Society for Biochemistry and Molecular Biology, Inc.
• Keywords: NAD biosynthesis, NAMPT, Fatty acid metabolism, Hepatocyte, Mitochondrial metabolism, Nicotinamide adenine dinucleotide (NAD), Respiration, Tryptophan metabolism • Bioblast editor: Plangger M • O2k-Network Lab: DK Copenhagen Larsen S
Labels: MiParea: Respiration, Genetic knockout;overexpression, Exercise physiology;nutrition;life style
Organism: Mouse Tissue;cell: Liver Preparation: Intact cells
Coupling state: LEAK, OXPHOS, ET Pathway: F, N, S HRR: Oxygraph-2k