Effects of overexpression of basic helix–loop–helix transcription factor Dec1 on osteogenic and adipogenic differentiation of mesenchymal stem cells

We recently reported that forced expression of basic helix–loop–helix transcription factor Dec1 accelerated chondrogenic differentiation of mesenchymal stem cells (MSC) in pellet cultures (Shen, M., Yoshida, E., Yan, W., Kawamoto, T., Suardita, K., Koyano, Y., Fujimoto, K., Noshiro, M., Kato, Y., 2002. Basic helix–loop–helix protein DEC1 promotes chondrocyte differentiation at the early and terminal stages. J. Biol. Chem. 277, 50112–50120). Since MSC have multilineage differentiation potential, we investigated the roles of Dec1 in osteogenic and adipogenic differentiation of human bone marrow-derived MSC. After osteogenic induction of MSC in medium containing dexamethasone, β-glycerophosphate, and ascorbic acid, Dec1 expression gradually increased from day 5 to day 14, while expression levels of Dec1 mRNA markedly decreased on days 3 and 7 after adipogenic induction. Infection with adenovirus expressing Dec1 raised mRNA levels of several bone characteristic molecules such as osteopontin, PTH receptor, and alkaline phosphatase, even in the absence of the osteogenic induction medium, although it had little effect on Runx2 expression or calcification. In the osteogenic induction medium, Dec1 overexpression enhanced the expression of osteopontin and alkaline phosphatase and induced matrix calcification. Knockdown of Dec1 with siRNA suppressed the expression of osteoblastic phenotype by the induced MSC. Using MSC cultures, we also confirmed that forced expression of Dec1 suppressed adipogenic differentiation. These findings suggest that Dec1 modulates osteogenic differentiation of MSC by inducing the expression of several, but not all, bone-related genes.