The interaction between β1 integrins and ERK1/2 in osteogenic differentiation of human mesenchymal stem cells under fluid shear stress modelled by a perfusion system

Fluid shear stress (FSS) is an important biomechanical factor regulating the osteogenic differentiation of human mesenchymal stem cells (hMSCs) and is therefore widely used in bone tissue engineering. However, the mechanotransduction of FSS in hMSCs remains largely unknown. As beta 1 integrins are considered to be important mechanoreceptors in other cells, we suspect that beta 1 integrins should also be important for hMSCs to sense the stimulation of FSS. We used a perfusion culture system to produce FSS loading on hMSCs seeded in PLGA three-dimensional (3D) scaffolds and investigated the roles of beta 1 integrins, FAK and ERK1/2 in FSS-induced osteogenic differentiation of hMSCs. Our results showed that FSS not only markedly increased ALP activity and the expression of ALP, OCN, Runx2 and COLI alpha genes but also significantly enhanced the phosphorylation of ERK1/2, Runx2 and FAK. FSS-induced activation of ERK1/2 and FAK was inhibited by blockade of the connection between beta 1 integrins and ECM with RGDS peptide and integrins beta 1 monoclonal antibody. Our study also found that FSS could upregulate the expression level of beta 1 integrins and that this upregulation could be abolished by PD98059. Further investigation indicated that FSS-activated ERK1/2 led to the phosphorylation of I kappa B alpha and NF kappa B p65. The activation of NF kappa B p65 resulted in the upregulation of beta 1 integrin expression. Therefore, it could be inferred that beta 1 integrins should sense the stimulation of FSS and thus activate ERK1/2 through activating of FAK, and FSS-activated ERK1/2 feedback to upregulate the expression of beta 1 integrins through activating NF kappa B. Copyright (c) 2012 John Wiley & Sons, Ltd.