Tendon Degeneration Is Not Mediated by Regulation of Toll-Like Receptors 2 and 4 in Human Tenocytes

We hypothesized that expression of Toll-like receptors (TLRs) 2 and 4 by tenocytes is involved in the catabolic processes of tendon degeneration. We investigated TLR2 and TLR4 expression by tenocytes in healthy and tendinotic Achilles tendons. We also investigated whether TLR2 and TLR4 could be upregulated in tendon explants using proinflammatory cytokines interleukin and tumor necrosis factor alphpa (TNF alpha). Peroperatively harvested healthy (n = 5) and tendinotic (n = 13) Achilles tendon samples were examined by real-time RT-PCR and immunohistochemical staining for TLR2 and TLR4. In addition, the catabolic process in tendinopathy was analyzed by real-time RT-PCR for matrix metalloproteinases MMP1, MMP3, MMP9, and MMP13. Furthermore, healthy, tendon explants were Cultured in the presence of 20 ng/ml IL-1 beta (n = 10) or 10 ng/mL TNF alpha (n = 8) fer 4, 24, 48, and 72 h before analysis of TLR and MMP expression levels. Although mRNA levels for both TLR2 and TLR4 were detected in healthy and tendinotic Achilles tendons, we could not confirm expression of these receptors by immunohistochemical staining in either healthy or tendinotic tendon samples. Both receptors did not show significant transcriptional regulation in tendinopathy, although AMN was downregulated and MMP9 was upregulated in tendinopathy. In tendon explant Cultures TLR2 mRNA was upregulated by TNF alpha (p < 0.05) and IL-1 beta (not significant). TLR4 gene expression was not altered by addition of IL-1 beta or TNF alpha. Tendon tissue can be stimulated to increase TLR2 gene expression by addition of catabolic factors TNF alpha or IL-1 beta. However, the catabolic processes in Achilles tendinopathy cannot be attributed to regulation of TLR2 and TLR4 by tenocytes. (C) 2009 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 27:1043-1047, 2009