y represses PPAR-c by the involvement of NCoR, we pre-treated the cells with resveratrol and co-treated with nicotinamide in highdensity cultures. We found that PPAR-c, NCoR and Sirt-1 were in a common complex, but in the presence of 1 mM resveratrol and 1 and 10 mM nicotinamide the amount of NCoR and Sirt-1 increased and the amount of PPAR-c decreased. In contrast, in the presence of 1 mM resveratrol and 100 mM nicotinamide, the amount of Sirt-1 and NCoR decreased and the amount PPAR-c increased in these experiments. It has also been reported that Sirt-1 indirectly influences the transcriptional Lysine vasopressin activity of the nuclear receptor PPAR-c by docking the NCoR and SMRT to PPAR-c. The co-repressor protein, NCoR does not have an enzymatic activity, but it can activate the catalytic activity of histone deacetylases for deacetylation of histone proteins. These data indicate that Sirt-1 interacts with the nuclear receptor co-repressor NCoR suggesting that Sirt-1, at least in part represses PPAR-c activity by involving the co-activators. However, it should be considered that while resveratrol is known to activate Sirt-1, it has also other additional target proteins in the cells, thus it cannot be the only effect of Sirt-1. Resveratrol’s enhancement of osteogenesis was, at least in part regulated by Runx2 with additional contributions by Sirt-1. Resveratrol increases alkaline phosphatase activity in osteoblastic cells an effect that is blocked by tamoxifen, an estrogen antagonist, suggesting that some of resveratrol’s stimulatory actions may be mediated through the estrogen receptor. Gehm et al. have reported that resveratrol acts as a phytoestrogen and decreases osteoporosis. Moreover, resveratrol is one of the most potent Sirt-1 activators; through binding to a special binding site it induces a conformational change in Sirt-1, lowering the Km for both the acetylated substrate and NAD, thus resulting in increased enzymatic activity. Sirt-1 facilitates the differentiation of MSCs to osteoblasts by directly regulating factors such as Runx2 and by modulation of nuclear receptor co-repressor NCoR and PPAR-c. It is known that the nuclear protein deacetylase Sirt-1 belongs ” to class III of histone deacetylases, resulting in transcriptional silencing. Thus, Sirt-1 participates in the regulation of genome architecture and gene expression. These results suggest that Runx2 and Sirt-1 directly interact together and that Runx2 might be a substrate for Sirt-1 deacetylation. Furthermore, our data demonstrate that nicotinamide treatment induced Runx2 acetylation and this was decreased and attenuated in the pretreatment cultures with resveratrol, suggesting that Sirt-1 activity is increased in these cultures. This data suggest that resveratrol suppresses nicotinamide-induced Runx2 acetylation 9528756 through Sirt1 activation and at the same time through inhibition of NCoR/ PPAR-c complex. Our study suggests that nicotinamide induces Runx2 acetylation in MSCs during osteogenesis in vitro. Runx2 acetylation was reversed by resveratrol, resulting in the suppression of nicotinamide-induced PPAR-c transcriptional activity including adipogenesis. Resveratrol activates the deacetylase Sirt-1, but it can also inhibit a number of other signaling pathways. Therefore, we used a specific gene knockdown approach to investigate whether the ability of resveratrol to reverse Runx2 acetylation operates via Sirt-1. Knockdown of Sirt-1 protein levels inhibited the effects of resveratrol, su