Mechanical load modulates chondrogenesis of human mesenchymal stem cells through the TGF-β pathway

This study investigated the effect of mechanical load on human mesenchymal stem cell (hMSC) differentiation under different exogenous transforming growth factor-β1 (TGF-β(1)) concentrations (0, 1 or 10 ng/ml).The role of the TGF-β signalling pathway in this process was also studied. Human MSCs were seeded into fibrin-biodegradable polyurethane scaffolds at a cell density of 5 × 10(6) cells per scaffold and stimulated using our bioreactor. One hour of surface motion superimposed on cyclic compression was applied once a day over seven consecutive days. Scaffolds were analysed for gene expression, DNA content and glycosaminoglycan amount. Addition of TGF-β(1) in the culture medium was sufficient to induce chondrogenesis of hMSCs. Depending on the TGF-β(1) concentration of the culture medium, mechanical load stimulated chondrogenesis of hMSCs compared to the unloaded scaffolds, with a much stronger effect on gene expression at lower TGF-β(1) concentrations. With TGF-β(1) absent in the culture medium, mechanical load stimulated gene transcripts and protein synthesis of TGF-β(1) and TGF-β(3). TGF-β type I receptor inhibitor LY364947 blocked the up-regulation on TGF-β(1) and TGF-β(3) production stimulated by mechanical load, and also blocked the chondrogenesis of hMSCs. Taken together, these findings suggest that mechanical load promotes chondrogenesis of hMSCs through TGF-β pathway by up-regulating TGF-β gene expression and protein synthesis.