Dynamic Compression Stimulates Proteoglycan Synthesis by Mesenchymal Stem Cells in the Absence of Chondrogenic Cytokines

The objective of this study was to evaluate the effect of dynamic compression on mesenchymal stem cell (MSC) chondrogenesis. Dynamic compression was applied to agarose hydrogels seeded with bone marrow-derived adult equine MSCs. In the absence of the chondrogenic cytokine transforming growth factor beta (TGF beta), dynamic compression applied for 12 h per day led to significantly greater proteoglycan synthesis than in unloaded TGF beta-free cultures, although at a rate that was approximately 20% to 35% of unloaded TGF beta cultures. These data suggest that the emergence of aggrecan dominated a chondrogenic response to loading as increases in proteoglycan synthesis. Cross-sectional analyses were conducted to subjectively identify potential spatial distributions of heterogeneous differentiation. In loaded samples, cell viability and metachromatic staining was low near the porous compression platen interface but increased with depth, reaching levels in the lower portion of the hydrogel that resembled unloaded TGF beta cultures. These results suggest that the combination of high hydrostatic pressure and low dynamic strain and fluid flow had a stronger effect on chondrogenesis than did low hydrostatic pressure coupled with high dynamic strain and fluid flow. Next, the 12-h per day loading protocol was applied in the presence of TGF beta. Biosynthesis in loaded cultures was less than in unloaded TGF beta samples. Taken together, these data suggest that the duration of loading necessary to stimulate mechanoinduction of MSCs may not be optimal for neo-tissue accumulation in the presence of chondrogenic cytokines.