The effects of high magnitude cyclic tensile load on cartilage matrix metabolism in cultured chondrocytes

摘要

Excessive mechanical load is though to be responsible for the onset of osteoarthrosis (OA), but the mechanisms of cartilage destruction caused by mechanical loads remain unknown. In this study we applied a high magnitude cyclic tensile load to cultured chondrocytes using a Flexercell strain unit, which produces a change in cell morphology from a polygonal to spindle-like shape, and examined the protein level of cartilage matrices and the gene expression of matrix metalloproteinases (MMPs), tissue inhibitors of matrix metalloproteinases (TIMPs) and proinflammatory cytokines such as IL-1#beta# and TNF-#alpha#. Toluidine blue staining , type II collagen immunostaining, and assay of the incorporation of [~(35)S]sulfate into proteoglycans revealed a decrease in the level of cartilage-specific matrixes in chondrocyte cultures subjected to high magnitude cyclic tensile load. PCR-Southern blot analysis showed that the high magnitude cyclic tensile load increase the mRNA level of MMP-1, MMP-3, MMP-9, IL-1#beta#, TNF-#alpha# and TIMP-1 in the cultured chondrocytes, while the mRNA level of MMP-2 and TIMP-2 was unchanged. Moreover, the induction of MMP-1, MMP-3 and MMP-9 mRNA expression was observed in the presence of cycloheximide, and inhibitor of protein synthesis. These findings suggest that excessive mechanical load directly changes the metabolism of cartilage by reducing the matrix components and causing a quantitative imbalance between MMPs and TIMPs.