gms | German Medical Science

Objectives: Mechanical signals are important homeostatic factors in articular cartilage and chondrocytes can remodel the extracellular matrix to meet the functional demands of loading. Aim was to identify mechano-regulated genes and candidate pathways in human chondrocytes in response to a single anabolic loading episode and characterization of time evolution and re-inducibility of the response.

Methods: Osteochondral constructs were prepared from chondrocyte-seeded collagen-scaffolds connected to beta-tricalcium-phosphate. The constructs were pre-cultured for 35 days in chondrogenic medium and subjected to dynamic compression (25% strain, 1 Hz, 9x10 minutes over 3h). The mechano-response was analysed by micro array profiling and proteoglycan synthesis was determined by 35S-sulfate-incorporation over 24 hours. Protein alterations were determined by Western blot analysis.

Results and Conclusion: Cell viability and hardness of constructs were not affected by dynamic compression while proteoglycan synthesis was significantly stimulated (1.45-fold, p=0.016). According to micro array analysis, 115 genes were significantly regulated, of which 114 were up-regulated, 48 of them > two-fold. AP-1-relevant transcription factors FOSB and FOS strongly increased in line with elevated ERK1/2-phosphorylation and rising MAP3K4 expression. Expression of proteoglycan-synthesizing enzymes CHSY1 and GALNT4 was load-responsive as were factors associated with the MAPK-, TGF-beta-, calcium-, retinoic-acid-, Wnt- and Notch-signaling pathway. SOX9, BMP4 and BMP6 levels rose significantly also after multiple loading episodes at daily intervals even at the 14th cycle with no indication for desensitation. Canonical pSmad2/3 and pSmad1/5/9-signalling was apparently unaltered.

In this study, novel genes are associated with mechanoregulation in chondrocytes and raising SOX9 protein levels with anabolic loading. Apparantly, more pathways than so far anticipated form a complex network of stimulators and feedback-regulators defining the mechano-response. Knowledge on time evolution of mechanosensitive indicators responding to anabolic loading is crucial to maximize cartilage matrix-deposition for the generation of high-level, functional cartilage replacement tissue.