(A) Schematic illustrating NAD+ consumption by
sirtuins and PARPs and the salvage of NAD+ from NAM via NAMPT and
NMNAT enzymes. (B and C) Correlation of
Nampt (B) and Nmnat3 (C) transcripts from
42 strains of genetically diverse BXD mice with various measurements of muscle
mass, as a percentage of body weight. CD, chow diet. (D)
Correlation of Nampt transcript expression in the BXD strains
with transcript expression for regulators of mitochondrial transcription and for
genes encoding the components of the mitochondria. (E) A factor
loading plot (biplot) showing the correlation of transcripts for
mitochondrial-related genes (Tfam, Hspd1, Atp5h, and
Tomm70a), utrophin (Utr),
dystrophin-associated glycoproteins (Dag1, Sgcb, and
Sgcd), muscle growth–related genes
(Maged1 and Il6), and genes involved in
the pathology of mdx mice (Tgfb1, Tnf, Mstn,
Il1b, and Redd2) with NAD+ synthesis
transcripts (Nampt, Nmnat1, and Nrk1) in the
BXD mouse strains. Angles more than 90° between gene vectors represent
negative correlation (an angle of 180° indicates perfect negative
correlation). (F) These transcripts were then plotted in a circular
schematic using Pearson’s r ≥
|0.2| in BXD strains showing negative (red) and positive (green)
correlations. The expression of transcripts related to NAD+
(G) consumption or (H) biosynthesis shows an
enrichment signature of PARP genes and of the
NNMT gene in human DMD skeletal muscle data sets
(n = 5 per group) (24, 25). CON, control.