Contribution of SATB2 to the stronger osteogenic potential of bone marrow stromal cells from craniofacial bones

Previous studies have shown that craniofacial bone marrow stromal cells (BMSCs) have a strong osteogenic potential. However, the mechanism by which BMSCs of various embryonic origins develop diverse osteogenic potentials remains unclear. To investigate the mechanisms regulating osteoblast differentiation in two different types of BMSCs, we compared the temporal and spatial mRNA and protein expression patterns of Satb2 and its downstream gene Hoxa2 by using real-time polymerase chain reaction, Western blotting and fluorescent immunostaining in mandible BMSCs (M-BMSCs) and tibia BMSCs (T-BMSCs) undergoing osteoblast differentiation. Higher levels of alkaline phosphatase, greater calcium accumulation and earlier expression of Runx2 were observed in osteogenic-induced M-BMSCs compared with T-BMSCs. Low levels of Satb2 were detected in both types of uninduced BMSCs but the majority of SATB2 was located in the nuclei of M-BMSCs. Notably, Satb2 was expressed earlier in M-BMSCs and Hoxa2, a downstream target of Satb2, was not expressed in uninduced M-BMSCs or during osteoblast differentiation, just as during embryonic mandible development. In contrast, Hoxa2 was reactivated in T-BMSCs during osteoblast differentiation. Based on these results, we conclude that SATB2 plays a different role during osteoblast differentiation of M-BMSCs and T-BMSCs. The earlier activation of Satb2 expression in M-BMSCs compared with T-BMSCs might explain the stronger osteogenic potential of M-BMSCs.