Cross-talk between TGF-beta/SMAD and integrin signaling pathways in regulating hypertrophy of mesenchymal stem cell chondrogenesis under deferral dynamic compression

The molecular mechanisms of mechanotransduction in regulating mesenchymal stem cell (MSC) chondrogenesis are not fully understood and represent an area of growing investigation. In this study, human MSC was subjected to chondrogenic differentiation in chitosan-coated poly l-lactide-co-ɛ-caprolactone scaffolds under free swelling or deferral dynamic compression conditions. The effect of deferral dynamic compression to MSC chondrogenesis and late stage hypertrophy development was investigated, and the involvement of TGF-β/SMAD pathway and integrin β1 signaling was analyzed. Deferral dynamic compression enhanced cartilage formation and suppressed chondrocyte hypertrophy. Differential cell morphology and cytoskeletal organization were induced under dynamic compression, together with the activation of TGF-β/Activin/Nodal and suppression of the BMP/GDP signaling. This was accompanied by the repression of integrin/FAK/ERK signaling in the non-hypertrophic cells when compared to the free swelling samples. Inhibition studies blocking TGF-β/Activin/Nodal signaling heightened hypertrophy, activate BMP/SMAD1/5/8 and integrin signaling, while inhibition of integrin-ECM interaction suppressed hypertrophy and activate TGF-β/SMAD2/3 in the free-swelling samples. This study demonstrates the roles of TGF-β/SMAD and integrin signaling, and suggests cross-talk between these two signaling pathways, in regulating the compression-driven hypertrophy development.