Objective: To determine molecular events in the regulation of messenger RNA (mRNA) of cartilage matrix molecules and proteases by mechanical stimulation of chondrocytes from normal human articular cartilage and to ascertain whether similar regulatory systems are present in chondrocytes from osteoarthritic (OA) cartilage.
Methods: Chondrocytes extracted from macroscopically and microscopically normal and OA cartilage were mechanically stimulated in the presence or absence of GRGDSP or GRADSP oligopeptides, neutralizing interleukin-4 (IL-4) antibodies, gadolinium, or apamin. The relative levels of mRNA for aggrecan, tenascin, matrix metalloproteinase 1 (MMP-1), MMP-3, and tissue inhibitor of metalloproteinases 1 (TIMP-1) were determined by semiquantitative reverse transcription-polymerase chain reaction at several time points up to 24 hours poststimulation, using GAPDH as a control.
Results: Normal chondrocytes showed an increase in aggrecan mRNA and a decrease in MMP-3 mRNA within 1 hour following stimulation, with a return to baseline levels within 24 hours. These changes were blocked by GRGDSP, IL-4 antibodies, and gadolinium, but were unaffected by apamin. In contrast, chondrocytes isolated from OA cartilage showed no change in aggrecan or MMP-3 mRNA levels following mechanical stimulation. The mRNA levels of tenascin, MMP-1, and TIMP-1 were unaltered in mechanically stimulated normal and OA chondrocytes.
Conclusion: Mechanical stimulation of human articular chondrocytes in vitro results in increased levels of aggrecan mRNA and decreased levels of MMP-3 mRNA. The transduction process involves integrins, stretch-activated ion channels, and IL-4. This chondroprotective response is absent in chondrocytes from OA cartilage. Abnormalities of mechanotransduction leading to aberrant chondrocyte activity in diseased articular cartilage may be important in the progression of OA.