In vivo use of PRP, but also of PPP to a certain extent, in tendon injuries might accelerate the catabolic demarcation of traumatically injured tendon matrices and promote angiogenesis and formation of a fibrovascular callus. Whether this will also be beneficial for degenerative tendinopathies remains to be elucidated.

Background: Tendinosis lesions show an increase of glycosaminoglycan amount, calcifications, and lipid accumulation. Therefore, altered cellular differentiation might play a role in the etiology of tendinosis. This study investigates whether adolescent human tendon tissue contains a population of cells with intrinsic differentiation potential.

This model can be used to investigate chondrogenic differentiation as a possible target for drug treatment, contributing to the development of more successful mechanism-based treatment opportunities.

Although tendon tissue directly adjacent to an Achilles tendinosis lesion looks macroscopically healthy, histological and biochemical degenerative changes in adjacent tissue are evident, which may have implications for surgical interventions.

The observed disorganisation of the collagen network warrants caution when using ESWT. Exposing noninjured tissue to ESWT should be avoided and it may be advisable to restrict exercise in recently treated patients. However, the induced tissue disorganisation might also be a trigger for repair in chronic tendinopathies.

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 (IL)-1b and tumor necrosis factor alphpa (TNFa). Peroperatively harvested healthy (n ¼ 5) and tendinotic (n ¼ 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-1b (n ¼ 10) or 10 ng/mL TNFa (n ¼ 8) for 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 MMP3 was downregulated and MMP9 was upregulated in tendinopathy. In tendon explant cultures TLR2 mRNA was upregulated by TNFa (p < 0.05) and IL-1b (not significant). TLR4 gene expression was not altered by addition of IL-1b or TNFa. Tendon tissue can be stimulated to increase TLR2 gene expression by addition of catabolic factors TNFa or IL-1b. However, the catabolic processes in Achilles tendinopathy cannot be attributed to regulation of TLR2 and TLR4 by tenocytes. Toll-like receptors (TLRs) are phylogenetically conserved transmembrane receptors belonging to the family of pattern-recognition receptors (PRR). In humans, 11 TLR homologs have been identified thus far, expressed by numerous cell types like monocytes and dendritic cells, 1 and for example by chondrocytes. 2 TLRs detect microbial components, but TLR2 and TLR4 also recognize endogenous ligands like heat-shock proteins, necrotic cells, hyaluronan, and fibronectin. 1 Ligand recognition elicits an immune response with upregulation and activation of proinflammatory cytokines and matrix-metalloproteinases (MMPs). 2 Hence, via endogenous ligand recognition the TLR-mediated catabolic signalling pathways can directly contribute to degradative tissue reactions even in the absence of microbial components. TLRs are implicated in inflammatory and autoimmune diseases, but also in disorders like atherosclerosis and cancer. 3,4 Furthermore they play a role in noninfected rheumatoid arthritis (RA) and in the primarily degenerative joint disease osteoarthritis (OA). [1][2][3]5,6 In degenerative tendinopathies the balance between matrix synthesis and degradation is disturbed, and increased MMP activity as well as an increased percentage of degraded collagen are found. 7-9 An increase in NO synthase expression was found in a sup...

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