Metabolic profiling of alternative NAD biosynthetic routes in mouse tissues

PLoS One. 2014 Nov 25;9(11):e113939. doi: 10.1371/journal.pone.0113939. eCollection 2014.

Abstract

NAD plays essential redox and non-redox roles in cell biology. In mammals, its de novo and recycling biosynthetic pathways encompass two independent branches, the "amidated" and "deamidated" routes. Here we focused on the indispensable enzymes gating these two routes, i.e. nicotinamide mononucleotide adenylyltransferase (NMNAT), which in mammals comprises three distinct isozymes, and NAD synthetase (NADS). First, we measured the in vitro activity of the enzymes, and the levels of all their substrates and products in a number of tissues from the C57BL/6 mouse. Second, from these data, we derived in vivo estimates of enzymes'rates and quantitative contributions to NAD homeostasis. The NMNAT activity, mainly represented by nuclear NMNAT1, appears to be high and nonrate-limiting in all examined tissues, except in blood. The NADS activity, however, appears rate-limiting in lung and skeletal muscle, where its undetectable levels parallel a relative accumulation of the enzyme's substrate NaAD (nicotinic acid adenine dinucleotide). In all tissues, the amidated NAD route was predominant, displaying highest rates in liver and kidney, and lowest in blood. In contrast, the minor deamidated route showed higher relative proportions in blood and small intestine, and higher absolute values in liver and small intestine. Such results provide the first comprehensive picture of the balance of the two alternative NAD biosynthetic routes in different mammalian tissues under physiological conditions. This fills a gap in the current knowledge of NAD biosynthesis, and provides a crucial information for the study of NAD metabolism and its role in disease.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Mice
  • Mice, Inbred C57BL
  • NAD / analogs & derivatives
  • NAD / biosynthesis*
  • NAD / metabolism
  • Nicotinamide-Nucleotide Adenylyltransferase / metabolism

Substances

  • NAD
  • nicotinic acid adenine dinucleotide
  • Nicotinamide-Nucleotide Adenylyltransferase

Grant support

This work was funded by grants “Ricerca Scientifica Ateneo – RSA 2010/2012” (to GO and GM) and by a Marie Curie Intra European Fellowship within the 7th European Community Framework Program (to MDS). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.