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Abstract
Background Increasingly, inflammatory mediators are considered crucial to the onset and perpetuation of tendinopathy.1 We have previously reported increased expression of key cytokines in human and rodent models of tendinopathy.2 Interleukin-17 is the founding member of a group of cytokines called the IL-17 family and induces the production of IL-1, IL-6, TNF-α, inducible NO synthase, matrix metalloproteinases (MMPs), and chemokines by fibroblasts, macrophages, and endothelial cells.3
Objectives To seek evidence of interleukin 17 (IL-17) expression in early human tendinopathy and thereafter, to explore mechanisms whereby IL-17 may regulate apoptosis, inflammatory mediators and matrix regulation in human tenocytes.
Methods Fifteen torn supraspinatus tendon (established pathology) and matched intact subscapularis tendon (representing ‘early pathology’) biopsies were collected from patients undergoing arthroscopic shoulder surgery. Control samples of subscapularis tendon were collected from 10 patients undergoing arthroscopic stabilisation surgery. Human tendon-derived primary cells were derived from hamstring tendon tissue obtained during hamstring tendon ACL reconstruction. The Human mast cells were generated from CD133+ cells from buffy coat preparations. Markers of inflammation and IL-17 were quantified by immunohistochemical methods. The impact of IL-17 upon tenocyte biology in vitro was measured using quantitative RT-PCR, multiplex cytokine assays, apoptotic proteomic profiling, immunohistochemistry and annexin V FACS staining.
Results Increased expression of IL-17A was detected in subscapularis tendon samples compared to both matched from samples and non-matched control samples (p < 0.01). Double immunofluoresence staining revealed several IL-17A expressing lineages, but particularly mast cells were the predominant source of IL-17A in biopsy samples.
IL-17 treated tenocytes exhibited increased production of proinflammatory cytokines (p < 0.001), altered matrix regulation (p < 0.01) with increased production of Collagen type III and increased expression of several apoptosis is related factors to thereby promote tenocyte apoptosis. Cytokine stimulation with IL-1β and Il-23 resulted in significant (p < 0.01) production of IL-17A from human derived mast cells in vitro.
(A) IL-17A mRNA levels in control torn and early tendinopathic tendon. (B) Mast cell positive /IL-17A positive cells in tendon biopsies. (C) IF images of mast cell tryptase, IL-17A and merger images (×40)
Conclusion IL-17 promotes expression of proinflammatory cytokines, key apoptotic mediators and drives matrix changes toward a collagen type III phenotype. We propose that IL-17 is a central inflammatory mediator driving the early tendinopathy processes which may offer novel therapeutic approaches in the management of tendon disorders.
References
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