Study On The Effect Of Mechanical Load On The Reconstruction Of Tissue Engineering Cartilage

Mechanical load is a well known factor which plays important role in cartilage tissue engineering. This study investigated the effect of mechanical load in articular cartilage tissue engineering with chondrocytes and BMSCs as cell resources.We investigated the effect of mechanical load on the gene expression of PRG4, HAS 1, and HAS2, and on the protein release of PRG4 and HA of chondrocytes from different zones of bovine knee joint cartilage. The results indicate that mechanical load can modulate the phenotype of the chondrocyte subpopulations in order to adapt to their specific environment. The interaction between different zone subpopulations may have an important meaning for regulation of HA synthesis. It is conceivable that with the use of cells from a heterogeneous population, an optimized mechanical and chemical environment may direct the composites top layer cells toward the phenotype of superficial zone chondrocytes. This means the zonal organization of articular cartilage and a functional cartilage synovial interface could be restored in engineered cartilage. This may be significant for tissue engineering approaches where generally heterogeneous cell populations are used.Because of the limited number, complicated and invasive harvest method of chondrocytes. we investigated the effect of mechanical load in cartilage tissue engineering with BMSCs as cell resource. To establish a culture system for chondrogenesis of hBMSCs in vitro, we investigated the capability of fibrin-polyurethane composites to support chondrogenesis of hBMSCs. GAG/DNA measurement, Real-time PCR, histology, and immunohistochemistry were used to compare scaffold culture and pellet culture. Under the optimal seeding density (5×106 cells/scaffold), cells in scaffold culture had comparable chondrocytic protein synthesis GAG/DNA value, higher chondrocytic marker genes COL2 and AGG mRNA level, and lower osteoblastic marker genes Sp7, ALP, and BSP2 mRNA level compared with pellets. Besides, fibrin-polyurethane composites can serve as a template for neo-tissue accumulation, and this system can be used for further investigations in combination with mechanical load to further modulate chondrogenesis of BMSCs.We investigated the effect of mechanical load on hBMSCs differentiation under different exogenous TGF-β1 concentrations. The role of TGF-P signaling pathway in this process was also studied by adding TGF-βtype I receptor inhibitor LY364947. The results demonstrated that mechanical load can stimulate chondrogenesis of hBMSCs cultured in fibrin-polyurethane composites, however, it is only observable under low concentrations of TGF-P and in the presence of dexamethasone. Because TGF-P itself can induce chondrogenesis, the effect of mechanical load is diminished under high exogenous TGF-P concentration. Mechanical load induces chondrogenesis through TGF-P pathway and this can be blocked using a specific inhibitor of TGF-P type I receptor.Human BMSCs seeded fibrin-polyurethane composites were subjected to cyclic dynamic compression and surface shear with different frequency and amplitude to investigate the response of hBMSCs under different mechanical environment. The results indicate that chondrogenesis of hBMSCs was modulated by frequency and amplitude of mechanical load. Within the selected range of load, higher load frequency and higher compression amplitude are superior for chondrogenesis and inhibition of hypertrophy. This suggests that for cartilage tissue engineering using BMSCs, it may be important to apply an appropriate magnitude of mechanical load.A retinoic acid receptorβinhibitor LE135 was combined with mechanical load to modulate chondrogenesis of hBMSCs. In both pellect culture and scaffold culture, LE135 inhibited the chondrogenic response induced by exogenous TGF-βor mechanical load created endogenous TGF-β, while the osteogenic response was not affected.