Continuous cyclic mechanical tension inhibited Runx2 expression in mesenchymal stem cells through RhoA-ERK1/2 pathway

Tensile load is known to regulate the osteogenesis of mesenchymal stem cells (MSCs) and osteogenic progenitors; therefore it is widely used in clinical treatment and tissue engineering. Meanwhile, in vitro, both published studies and our lab data demonstrate that the application of intermittent tensile loading which stimulates cells several minutes or hours each day for several days has promoted the osteogenic differentiation of MSCs. Whereas, for clinic trails, it is important to know accurately how and how long mechanical tension should be applied. Hence, it is necessary to investigate different kinds of mechanical tension on osteogenesis of MSCs. Until now, during the osteogenesis, there has been no research on the effect of continuous cyclic mechanical tension (CCMT) which provides continuous stimulation throughout the study period. We firstly figure out CCMT inhibiting the expression of osteogenic genes such as key transcription factor Runx2. It is known that RhoA regulates cell differentiation in response to mechanical stimuli. MAPK signaling acts as a downstream effector of RhoA. So, we ask in MSCs, if CCMT regulates the osteogenic master gene Runx2 through RhoA-ERK1/2 pathway. And then, we find out there is a decrease in RhoA activity after CCMT stimulation. Pre-treatment of CCMT-loaded MSCs with LPA, a RhoA activator, restores ALP activity and significantly rescues Runx2 expression, while pre-treatment with C3 toxin, a RhoA inhibitor, further decreases the activity of ALP and down-regulates the expression of Runx2. Following results indicate that the inhibition of Runx2 expression after CCMT stimulation is mediated by RhoA-ERK1/2 pathway.