Mechanical stimulation promotes osteogenic and chondrogenic differentiation of synovial mesenchymal stem cells through BMP-2

Mounting evidences have been shown that mesenchymal stem cells are present in various tissues including synovium. Given that environmental factors could have impacts on the differentiation of stem cells in vivo, we elucidated that whether mechanical stimulation may influence the process. In this study, we investigated the effect of cyclic mechanical stimulation on the osteogenic and chondrogenic differentiation of synovial mesenchymal stem cells (SMSCs) and its correlation with BMP-2. Cyclic mechanical stimulation was applied to SMSCs isolated from bilateral hip, knee joints and unilateral ankle joint of rabbits. SMSCs were grouped into two classifications: treated with mechanical stimulation (MS group) and without mechanical stimulation (no MS group). The mechanical stimulation was a cyclic tensile and compression: the amplitude and frequency of strain was 8%, 0.33 Hz and the peak of cyclic stress was 2.35 kilopascals (kPa) (1 kPa = 1.0 × 103 N/m2). The osteogenic and chondrogenic differentiation of SMSCs was determined by detecting expressions of osteogenesis markers (ALP and Cbfa1) and chondrogenesis markers (Sox9 and Col2a1). qRT-PCR and western blot showed that mechanical stimulation up-regulated expressions of osteogenesis markers (ALP and Cbfa1) and chondrogenesis markers (Sox9 and Col2a1) of SMSCs, respectively. In addition, BMP-2 was increased in SMSCs treated with mechanical stimulation during osteogenic and chondrogenic differentiation, and knockdown of BMP-2 leaded to the reversed result of the expression of osteogenesis markers and chondrogenesis markers. To conclude, our study confirm that repetitive mechanical stimulation increased the expression of BMP-2, and promoted osteogenic and chondrogenic differentiation of SMSCs.