Objective. To determine differences in the metabolism of proteoglycans and the gene expression of proteinases and their inhibitors between patellar tendons exhibiting chronic overuse tendinopathy and normal patellar tendons in humans.Methods. Rates of loss and synthesis of proteoglycans were determined. Radiolabeled and total proteoglycans retained in and lost from the tissue were analyzed by fluorography and Western blotting. Levels of messenger RNA for matrix metalloproteinase 1 (MMP-1), MMP-2, MMP-3, MMP-9, MMP-13, ADAMTS-1, ADAMTS-4, ADAMTS-5, tissue inhibitor of metalloproteinases 1 (TIMP-1), TIMP-2, TIMP-3, and TIMP-4 were determined in fresh tissue.Results. The rate of loss of 35 S-labeled proteoglycans was greater in abnormal tendons, as was the rate of synthesis of proteoglycans. Fluorography and Western blotting revealed the presence of greater amounts of large proteoglycans (aggrecan and versican) in abnormal tendons, and these proteoglycans were rapidly lost from the matrix of abnormal tendons. There was no significant difference in the expression of ADAMTS-1, ADAMTS-4, ADAMTS-5, MMP-1, MMP-2, MMP-3, MMP-13, TIMP-2, TIMP-3, or TIMP-4. There was a significant increase in the expression of MMP-9 and TIMP-1 in abnormal tendons.Conclusion. Our findings suggest that a change in the proteoglycan content of the extracellular matrix in abnormal tendons results from the altered metabolism of the cells, reflected in the enhanced synthesis of the large proteoglycans aggrecan and versican, and does not appear to result from changes at the level of gene expression.

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Expansion of the extracellular matrix is a prominent but poorly characterized feature of tendinosis. The present study aimed to characterize the extent and distribution of the large aggregating proteoglycan versican in patients with patellar tendinosis. We obtained tendon from tendinopathy patients undergoing debridement of the patellar tendon and from controls undergoing intramedullary tibial nailing. Versican content was investigated by Western blotting and immunohistochemistry. Microvessel thickness and density were determined using computerassisted image analysis. Markers for smooth muscle (α-SMA), endothelial cells (CD31) and proliferating cells (Ki67) were examined immunohistochemically. Western blot analysis and immunohistochemical staining revealed elevated versican content in the proximal patellar tendon of tendinosis patients (p=0.042). Versican content was enriched in regions of fibrocartilage metaplasia and fibroblast proliferation, as well as in the perivascular matrix of proliferating microvessels and within the media and intima of arterioles. Microvessel density was higher in tendinosis tissue compared to control tissue. Versican deposition is a prominent feature of patellar tendinosis. Because this molecule is not only a component of normal fibrocartilagenous matrices, but is also implicated in a variety of soft tissue pathologies, future studies should further detail both pathological and adaptive roles of versican in tendons.

Introduction A predominant feature of tendinopathy is a change in the appearance and organisation of the extracellular matrix including greater amounts of the large aggregating proteoglycans, aggrecan and versican. We have shown that in patellar tendinopathy these large proteoglycans are also rapidly degraded so that mainly fragments remain in the tissue. 1 This catabolism of large proteoglycans is likely to be mediated by a number of matrix-degrading proteinases such as the matrix metalloproteinases (MMPs) and the aggrecanases (ADAMTSs).The aim of this work was to investigate whether in patellar tendinopathy there is a change in the gene expression of the matrix proteinases involved in proteoglycan catabolism including the MMPs and ADAMTSs, as well as their inhibitors, the tissue inhibitor of metalloproteinases (TIMPs). Methods Total mRNA isolated from ∼100mg tissue samples of normal (n=9) and pathologic (n=12) tendon was assayed by relative quantitative RT-PCR for MMP (-1, -2, -3, -9, and -13), ADAMTS (-1, -4, -5), and TIMP (-1, -2, -3, and -4), and normalised to GAPDH. Results Expression of mRNA for MMP-9 and TIMP-1 was significantly up-regulated in pathologic tendons ( p=0.019 and p=0.013, respectively). A trend toward a down-regulation of expression of MMP-3 was observed in pathologic tendons (p=0.06). There were no significant changes in ADAMTS-1, -4, or -5 gene expressions. Discussion These results suggest that the elevated expression of MMP-9 and TIMP-1 genes is likely to reflect the changes in collagen metabolism in pathologic tendons. However, these results also suggest that the proteolysis of proteoglycans in the pathologic tendons is not likely to be affected at the gene expression level of proteinases and their inhibitors. These observations are consistent with others, who showed no difference in the expression of ADAMTS-1, -4, and -5 genes between human Achilles tendons with chronic pain and normal tendons. 2 3 Therefore, it is likely that proteoglycan catabolism is elevated by the activation of ADAMTSs and possibly MMPs and not by increased gene expression. This activation may be driven by growth factors and cytokines such as IL-1α, TGF-β and TNF-α, which are shown to be increased in overuse tendinopathy. However, the details of the mechanisms of these regulatory processes warrant further investigation.

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