Osteoclastogenesis accompanying early osteoblastic differentiation of BMSCs promoted by mechanical stretch.

Mechanical stress plays a crucial role in bone formation and absorption. In previous studies, we verified the osteoblastogenesis of bone mesenchymal stem cells (BMSCs) affected by intermittent traction stretch. However, little is known about the osteoclastogenesis process under mechanical stimulation and its underlying association with osteoblastogenesis. In the present study, we investigated the osteoclastogenesis of BMSCs under this special mechanical stress. BMSCs were subjected to 10% elongation for 1-7 days using a Flexcell Strain Unit and then the mRNA levels of osteoclastic genes were examined. The results indicated time-dependent varying of mRNA levels of the receptor activator of nuclear factor-κB ligand (RANKL) and osteoprotegerin (OPG) in BMSCs at different stretching time points. The ratio of RANKL/OPG increased at the early stage of mechanical stimulation (5 days) and decreased to a low level at a later stage (7 days). Findings of this study may help to understand the correlations between osteoblastogenesis and osteoclasteogenesis when mechanical stretch induces the osteoblastic differentiation of BMSCs.