Changes in microstructure and gene expression of articular chondrocytes cultured in a tube under mechanical stress

The objective of this study was to clarify the effects of mechanical stress on chondrocytes cultured in a tube. Centrifugal pressure was applied to chondrocytes cultured in a tube for 28 days, and the effect of this stress was evaluated using a molecular biological method.

Articular cartilage was harvested from a rabbit. A cell suspension was then prepared, and transferred in 1 ml aliquots to polypropylene tubes. After 48 h of incubation, centrifugal pressure (6.9 MPa) was applied every 24 h. Changes in morphology, expression of messenger RNA (mRNA) for insulin-like growth factor-I (IGF-I) and type II collagen, cell number, wet weight and protein concentration were evaluated.

Microscopically, formation of chondrocyte clusters was seen in the cultures subjected to stress. Ultrastructurally, collagen fibers were seen to run parallel to the cytoplasmic surface of the stressed chondrocytes. The peak of IGF-I mRNA expression was seen on day 5, whereas type II collagen mRNA expression peaked on day 14. Cell number, wet weight and protein concentration were significantly increased in the stressed cultures.

These results suggest that mechanical stress might affect the arrangement of collagen fibers and the IGF-I activity of chondrocytes cultured in a tube, thus influencing chondrocyte proliferation and increasing the volume of the extracellular matrix. Furthermore, mechanical stress may also affect the metabolism of articular cartilage in vitro.