Synergistic actions of insulin-sensitive and Sirt1-mediated pathways in the differentiation of mouse embryonic stem cells to osteoblast.

Murine embryonic stem cells (mESCs) have the potential to differentiate into almost any type of cell, and hence, represent a useful biological resource for tissue engineering. The differentiation of mESCs into osteoblasts in vitro is usually dampened by simultaneous differentiation of adipocytes. Insulin exerts a profound effect on bone development through increased differentiation of osteoblasts and concurrent formation of adipocytes. Comparatively, Sirt1, which plays a crucial role in osteoblast differentiation, has been reported to down regulate adipocyte formation during osteoblast differentiation. This study analyzed the combined effects of insulin and Sirt1 on the differentiation of osteoblasts. Osteoblast differentiation was quantified by estimating the accumulation of mineralized matrix and expression of osteogenic genes. The present data show that the simultaneous action of the insulin and Sirt1-mediated pathways increased the efficiency of osteoblast differentiation. When the cells were tested for ALP activity and Alizarin red staining, there was a respective increase of ~180% and ~166% (P<0.05) compared to the control. Furthermore, the mRNA expression patterns of osteoprotegerin, osterix, runx2, and osteopontin were increased by 3.6, 2.3, 1.8, and 1.7-fold, respectively, with a concomitant decrease in the mRNA expression levels of adipocyte marker genes. Interestingly, blocking the effects of both Sirt1 and insulin resulted in decreased osteoblastogenesis (60%) and subsequent increased adipocyte differentiation (195%) (P<0.05). Moreover, immunoblotting analysis demonstrated that this activation was via an Akt-dependent pathway. In conclusion, the present data suggests an enhanced process of osteoblast differentiation that can be exploited further to improve mESC differentiation.