TAZ is Associated with Poor Osteoblast Differentiation of Mesenchymal Stem Cells Under Simulated Microgravity

Background: Exposure to microgravity (MG) leads to many varieties of physiological alterations, including bone loss. Most studies concur that the impaired osteoblast differentiation of mesenchymal stem cells (MSCs) plays an important role in this bone loss. However, the detailed signaling mechanisms underlying the MG-induced bone loss remain to be further clarified. Materials and Methods: We utilized a rotary cell culture system (RCCS) to study the role of transcriptional coactivator with PDZ-binding motif (TAZ) in simulated MG. Cells were obtained from the calvarial bone of 5-d old Balb/c mice littermates. The phenotype of the MSCs was confirmed by positive expression of Sca-1 and CD29, and negative for CD45. MSCs were cultured in osteo-induction medium in order to promote differentiation towards osteoblasts (OSTs). Results: Upon exposure to MG for 7 days, the abundance of Runx2 was significantly reduced to 0.33 and 0.2-fold in MSCs and OSTs, respectively. In contrast, PPARγ2 was significantly enhanced to 3.8 and 3.0-fold in response to MG in MSCs and OSTs, respectively. TAZ mRNA is decreased to 0.22- and 0.08-fold as compared to normal gravity (NG) in both MSCs and OSTs, respectively. Similarly, the TAZ protein level was also significantly decreased to 0.4-fold in MSCs and to 0.2-fold in OSTs. Moreover, we showed that MG indeed disrupted the interaction of TAZ and Runx2, which disturbed osteoblast-related gene expression. Conclusions: We show for the first time that the TAZ is associated with MG-induced impairment of osteoblast differentiation. Our results also suggest that TAZ plays an important role in MG-induced bone loss.