Mechanical strain induces osteogenic differentiation: Cbfa1 and Ets-1 expression in stretched rat mesenchymal stem cells

Distraction osteogenesis is an active process of bone regeneration under controlled mechanical stimulation. Osteogenic differentiation of mesenchymal stem cells (MSCs) is essential for bone formation during this process. Cbfa1 and Ets-1 (core binding factor alpha 1 and v-ets erythroblastosis virus E26 oncogene homolog 1) are transcription factors that play important roles in the differentiation of MSCs to osteoblasts. In order to mimic a single activation of a clinical distraction device, a short period of cyclic mechanical strain (40 min and 2000 microstrains) was applied to rat MSCs. Cellular proliferation and alkaline phosphatase (ALP) activity were examined. The mRNA expression of Cbfa1 and Ets-1, as well as ALP, a specific osteoblast marker, was detected using real-time quantitative reverse transcription polymerase chain reaction. The results showed that mechanical strain can promote MSC proliferation, increase ALP activity and up-regulate the expression of Cbfa1 and Ets-1. A significant increase in Ets-1 expression was detected immediately after mechanical stimulation, but Cbfa1 expression was elevated later. The temporal expression pattern of ALP coincided perfectly with that of Cbfa1. Mechanical strain may act as a stimulator to induce differentiation of mesenchymal stem cells into osteoblasts, which is vital for bone formation in distraction osteogenesis.