Background: Animal and human studies have shown that nicotinamide phosphoribosyltransferase (NAMPT), the key enzyme of mammalian NAD biosynthesis from nicotinamide, is modified in non-alcoholic fatty liver disease. Here, we investigated the effect of a high fat diet on hepatic NAD metabolism in mice.
Objective and hypotheses: A dysregulation of NAD metabolism is a pathogenic factor for the development of steatohepatitis (NASH).
Method: C57BL/6 mice were either fed a standard chow diet (n=12) or a high fat diet (HFD) (n=12) for 11 weeks. NAD levels were determined by HPLC. NAMPT activity was assessed by measuring the conversion rate of 14C-Nam to 14C-NMN. Protein and mRNA levels were analysed by western blot and qPCR, respectively.
Results: Mice fed a HFD significantly gained weight (39.0±4.2 g vs 29.9±2.5), stored more hepatic triglycerides compared to chow fed animals (2.2-fold) and showed a significantly impaired glucose tolerance. Acetylation status of p53, a Sirt1 target, and phosphorylation status of eIF2α was significantly decreased (−67.4 and −27.9%, respectively) as well as total protein levels of Bax and Caspase3 (−63.1 and −43.0%, respectively), indicating a reduction in proapoptosis signaling in mice fed a HFD compared to control mice. NAMPT mRNA (2.0-fold) and protein levels (2.2-fold), NAMPT activity (1.6-fold) and intracellular NAD concentration (1.6-fold) were significantly higher in HFD compared with control mice, as well as protein levels of the NAD dependent deacetlyase Sirt1 (1.4-fold).
Conclusion: We found increased NAMPT activity, higher NAD levels, and higher Sirt1 activity in HFD mice. This may be an early compensatory mechanism to protect against the excessive supply of lipids.
20 - 22 Sep 2014
European Society for Paediatric Endocrinology