oblasts. Resveratrol inhibits nicotinamide-induced downregulation of Sirt-1 during osteogenic differentiation of MSCs in vitro To investigate the possible mechanism for dedifferentiation of MSCs to adipocytes during osteogenesis, we investigated the effect of resveratrol on the expression of Sirt-1. As shown in Sirt-1 blocks adipogenesis by repressing PPAR-c activity and NCoR involvement in this process The PP-242 manufacturer nuclear receptor PPAR-c is known to regulate adipogenesis. It has also been shown that the nuclear 21278085” receptor co-repressor, NCoR, binds to known PPAR-c sites of promoters of adipogenic genes in differentiated 3T3-L1 adipocytes. To test whether Sirt-1 is a PPAR-c co-repressor by means of NCoR, we pretreated the MSCs with resveratrol followed by stimulation with nicotinamide in high-density cultures, and 1828859 co-immunoprecipitation assays. As shown in Expression of Sirt-1 in MSCs before and after osteoblastic differentiation in vitro The NAD-dependent protein deacetylase Sirt-1 has been shown to attenuate development of adipocytes from pre-adipocytes through inhibition of PPAR-c activity. Next, we wanted to evaluate whether phytochemicals known to regulate the activity of Sirt-1 could influence the formation of MSCs during osteoblast differentiation in vitro. First, we could demonstrate the expression of Sirt-1 in the MSCs derived from fat tissue. Whole cell lysate from MSCs in monolayer cultures treated with osteogenic induction medium for 0, 7, 14 and 21 days were analyzed by western blot with anti-Sirt-1 antibody. Sirt-1 was expressed in the MSCs before and after induction of osteoblastic differentiation. Resveratrol blocks nicotinamide-induced inhibition of the association of Sirt-1 proteins with the early osteogenic transcription factor Runx2 in MSC highdensity cultures Resveratrol Promotes Osteogenesis of MSCs antibodies, the samples were probed by immunoblotting with antiRunx2. The results indicated that Runx2 was co-immunoprecipitated by anti-Sirt-1 antiserum but not by pre-immune serum in high-density cultures. This interaction of Sirt-1 with Runx2 was decreased with as little as 10 mM nicotinamide and indicates that the expression and association of Runx2 with Sirt-1 is concentration-dependent. Taken together, these results indicate that during osteogenesis resveratrol activates Sirt-1 and induces Sirt-Runx2 complex formation, which 
activates the osteogenic pathway. Effect of resveratrol on nicotinamide-induced acetylation of Runx2 in MSC high-density cultures Resveratrol has been shown to activate Sirt-1 deacetylase activity. The fact that the stimulation of Sirt-1 protein correlated with the expression of Runx2 and in addition, that both proteins interact together, suggests that Runx2 might be a substrate for Sirt-1 deacetylation. As shown in Fig. 6B, nicotinamide treatment strongly induced Runx2 lysine acetylation in a time dependent manner in high-density cultures. To examine the functional impact of Sirt-1 regulation of nicotinamide-mediated acetylation of Runx2, we pre-treated MSCs with resveratrol and then co-treated them with nicotinamide during osteogenesis in high-density cultures for the indicated time periods. Interestingly, the nicotinamide-induced acetylation of Runx2 markedly decreased by pre-treatment with resveratrol, suggesting, at least in part, a significant reduction in nicotinamide-induced Runx2 acetylation by Sirt-1 activity. To determine whether resveratrol is able to block the nicotinamide-induced acetylatio
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