FIGURE 1.

Overexpression of NAMPT increases NAD concentration in muscle. A, proportion of Cre-recombined genomes in total genomic DNA of quadriceps muscle from mice carrying MCK-Cre in addition to one (NC) or two (NNC) copies of the Nampt transgene as compared with littermates carrying the same number of copies but lacking MCK-Cre (n = 4–9 per group). B, mRNA expression in quadriceps of NAD salvage pathway enzymes measured by quantitative RT-PCR: total nicotinamide phosphoribosyltransferase (Nampt), 3′-untranslated region of endogenous Nampt transcript (Nampt3UTR), nicotinamide mononucleotide adenylyltransferases (NMNAT1–3), and nicotinamide N-methyltransferase (NNMT) (n = 3–6 per group). A Western blot (C) and quantification (D) of NAMPT protein in gastrocnemius muscle (Gas) and heart of each genotype (n = 3 per group) are shown. E, NAD content of quadriceps muscle (n = 4–11 per group). F, representative histological sections of extensor digitorum longus (EDL) and soleus muscles stained with H&E or antibody against myosin heavy chain I (MyHCI). Scale bars represent 50 μm. NAD content in whole hearts (G) and heart weight (H) normalized to tibia length (n = 8–9 per group) are shown. I, NAD content of quadriceps muscle from 15-month-old mice supplied with 400 mg/kg/day NAM in the drinking water for 2 weeks. Error bars represent S.E. *, p < 0.05; **, p < 0.01; ***, p < 0.001 by Student's t test (D and G) or one-way analysis of variance with Bonferroni's multiple comparisons test (B and E). Mice were aged 5–10 months and fed a standard diet unless otherwise noted.