Mechanostimulation changes the catabolic phenotype of human dedifferentiated osteoarthritic chondrocytes

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Abstract
Purpose: The treatment of cartilage defects with matrix‐embedded autologous chondrocytes is a promising method to support the repair process and to foster reconstitution of full functionality of the joint.Methods: Human osteoarthritic chondrocytes were harvest from nine different patients (mean ± SD age 68 ± 8 years) who underwent total knee replacement. The chondrocytes were embedded after a precultivation phase into a collagen I hydrogel. Mid‐term intermitted mechanostimulation on matrix‐embedded dedifferentiated human osteoarthritic chondrocytes was performed by intermittently applying a cyclic sinusoid compression regime for 4 days (cycles of 1 h of sinusoidal stimulation (1 Hz) and 4 h of break; maximum compression 2.5 %). Stimulated (Flex) and non‐stimulated (No Flex) cell matrix constructs were analysed concerning the expression of genes involved in tissue metabolism, the content of sulphated glycosaminoglycans (sGAG) and the morphology of the chondrocytes.Results: Gene expression analysis showed a high significant increase in collagen type II expression (p < 0.001), a significant increase in aggrecan expression (p < 0.04) and a high significant decrease in MMP‐13 expression (p < 0.001) under stimulation condition compared with unstimulated controls. No significant changes were found in the gene expression rate of MMP‐3. This positive effect of the mechanostimulation was confirmed by the analyses of sGAG. Mechanically stimulated cell–matrix constructs had nearly tripled sGAG content than the non‐stimulated control (p < 0.002). In addition, histological examination showed that morphology of chondrocytes was altered from a spindle‐shaped to a chondrocyte‐characteristic rounded phenotype.Conclusion: Mid‐term intermitted mechanical stimulation in vitro has the potential to improve the cell quality of cell matrix constructs prepared from dedifferentiated osteoarthritic chondrocytes. This observation may extend the inclusion criteria for matrix‐assisted autologous chondrocyte implantation (MACI) and confirms the importance of moderate dynamic compression in clinical rehabilitation after MACI.

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