Fak silencing impairs osteogenic differentiation of bone mesenchymal stem cells induced by uniaxial mechanical stretch.

Mechanical stretch plays a key role in promoting proliferation and differentiation of bone marrow mesenchymal stem cells (BMSCs) in distraction osteogenesis (DO). A better understanding of how the extracellular biomechanical stimulation is transferred to intracellular signal expression will benefit DO. Focal adhesion kinase (FAK) is a key factor in integrin signaling pathway. However, little is known about the effect of integrin-FAK signaling during the process of stretch induced osteogenic differentiation of BMSCs. A specific short hairpin RNAs (shRNAs) lentiviral expression vector was used to silence Fak gene and a well-established in vitro uniaxial dynamic stretching device was applied to stimulate DO. Fak silencing was confirmed by fluorescence microscopy and the detection of Fak mRNA and FAK, p-FAK protein expression. Alkaline phosphatase (ALP) activity, expression of osteogenic differentiation markers - runt-related transcription factor 2 (RUNX2/ Runx2) and alkaline phosphatase (Alp) together with integrin upstream signal transduction molecules integrin beta-1 (ITGB1/ Itgb1) and downstream signal transduction molecules integrin-linked kinase (ILK) were detected after the stretch. The results showed that mechanical stretch in control groups significantly induced the osteogenic differentiation of BMSCs with increased ALP activity, expression of RUNX2/ Runx2 and Alp , together with upregulated ITGB1/ Itgb1 and ILK, which all vanished in Fak silencing group. Silencing of the Fak gene inhibited the osteogenic differentiation of rat BMSCs induced by in vitro mechanical stretch through integrin signaling pathway. [ABSTRACT FROM AUTHOR]