Effects of mechanical stimulation on gene expression of articular chondrocytes in polylayer culture

Mechanical loads are constantly being applied to articular cartilage. However, comparatively few studies have investigated the effects of mechanical stress on the gene expression of chondrocytes. Hence, the objective of the present study was to clarify the effects of mechanical stress on cultured chondrocytes. Articular chondrocytes of rabbits were isolated and placed in minimun essential medium eagle a modification containing 10% fetal bovine serum. The chondrocytes were cultured in polylayer in polypropylene tubes. After 48 hours, centrifugal stress (2.7 MJ) was applied once every 24 hours for 28 consecutive days. The mRNA expression of insulin-like growth factor-I (IGF-I) and cartilage-specific genes (type II collagen and aggrecan) in chondrocytes, cell count, wet tissue mass and protein content were subsequently measured. The results showed that the mRNA expression of the IGF-I gene for the stress groups was significantly greater than that of the control group from days 3 to 5 of incubation, as was the mRNA expression of the type II collagen gene from days 7 to 14 of incubation. However, there were no significant differences in the mRNA expression of the aggrecan gene between the control and stress groups. The cell count for the stress groups was significantly higher from days 7 to 28 of incubation, and the wet tissue mass and protein content were significantly higher from days 14 to 28 of incubation. These findings suggest that one of the mechanisms by which mechanical stress increases the number of cultured chondrocytes and the volume of extracellular matrix is to increase IGF-I expression at the early stage of incubation.