Pathways include promoting the activity of SIRT1, a member of the sirtuin family of NAD-dependent deacetylases [14]. Our previous study also demonstrated that resveratrol, which is a SIRT1 activator, could exert anti-aging effects by increasing telomerase reverse transcriptase (TERT) through elevating NAMPT and intracellular NAD+ levels [15]. Overexpression of NAMPT has been shown to increase SIRT1 activity [12]. Age-related reduction of NAMPT has also been linked to increased adipogenesis [13]. Although these observations provided the correlation of Nampt to the lineage fate determination of mesenchymal stem cells (MSCs), the molecular mechanism by which Nampt regulates osteogenic differentiation in bone marrow stromal cells has not been elucidated. In this study, we tested osteoblast formation in differentiated bone marrow stromal cells isolated from both Nampt wild-type (Nampt+/+) and Nampt heterozygous (Nampt+/-) mice. Our results indicated that in differentiated bone marrow stromal cells isolated from heterozygous mice, the osteogenic differentiation was lower than those derived from wild-type mice. Further investigation in osteoblasts identified that in Nampt-deficient cells, or in Nampt activity-inhibited cells, osteoblast differentiation was inhibited. Additional investigations also suggested that age-related Nampt reduction could inhibit Runx2 transcriptional activity and expression, and consequently decreased osteogenesis in bone marrow stromal cells. The murine fibroblast C3H/10T1/2 Clone 8 (Z-DEVD-FMKMedChemExpress Z-DEVD-FMK CCL-226TM) and preosteoblastic MC3T3-E1 Subclone 24 (CRL2595TM) were obtained from the American Type Culture Collection (ATCC? Manassas, VA, USA). The cells were cultured in Modified Eagle’s Medium alpha (-MEM, Catalog#: A10490, Life Tech., Grand Island, NY, USA) supplemented with 10 fetal bovine serum (Catalog#: S11150, Atlanta Biologicals, Flowery Branch, GA, USA), and 1 of penicillin/streptomycin (Catalog#: 15140-122, Life tech.) at 37 in a humidified 5 CO2 atmosphere. For osteoblast differentiation, cells were cultured in osteoblast medium (OBM), including -MEM mediumCell and mouse bone marrow stromal cell culturesupplemented with 10 FBS, 10 mM -glycerophosphate (Catalog#: 251291, Sigma, St Louis, MO, USA), 50 /mL ascorbic acid (Catalog#: A5960, Sigma) and 0.1 dexamethasone (Catalog#: D4902, Sigma) for the indicated days with medium changes twice a week. Mouse bone marrow stromal cells were obtained from 6- to 8-week-old male C57BL/6 wild-type Nampt+/+ and Nampt+/- mice generated as described previously [16]. Briefly, mice were euthanized using 4 isofluorane in CO2, and the bones were excised aseptically from the hind limbs. External soft tissue was discarded, and the bones were place in a-MEM supplemented with 1 penicillin/streptomycin. Both ends of the femur and tibia were clipped. An 18-gauge PubMed ID:http://www.ncbi.nlm.nih.gov/pubmed/27465830 needle was inserted into the diaphysis at one end, and bone marrow was flushed out from the other end to a 50-mL Falcon tube by culture medium. After centrifugation at 1000 rpm for 5 min, the cell pellet was collected and diluted in 15 mL of culture medium and cultured in a 75-cm flask. Non adherent cells were removed after 24 h, and the remaining cells were passaged after reaching 80 confluence. For osteoblast differentiation, cells were cultured in OBM for 2 weeks, with medium changes twice per week. All mouse experiments were conducted in accordance with NIH guidelines and were approved by the University of Missouri Kansas C.