IL-17A mediates inflammatory and tissue remodelling events in early human tendinopathy.

Neal L Millar,Lindsay A N Crowe,Abigail L Campbell,Marina Frleta-Gilchrist,George A C Murrell,George A C Murrell,George A C Murrell,Shauna C Kerr,Brian P Rooney,Michael Mclean,Iain B Mcinnes,Moeed Akbar,Umberto G Fazzi,William J Leach,James H Reilly

doi:10.1038/srep27149

Abstract

Increasingly, inflammatory mediators are considered crucial to the onset and perpetuation of tendinopathy. We sought evidence of interleukin 17A (IL-17A) expression in early human tendinopathy and thereafter, explored mechanisms whereby IL-17A mediated inflammation and tissue remodeling in human tenocytes. Torn supraspinatus tendon (established pathology) and matched intact subscapularis tendon (representing ‘early pathology’) along with control biopsies were collected from patients undergoing shoulder surgery. Markers of inflammation and IL-17A were quantified by RT-PCR and immunohistochemistry. Human tendon cells were derived from hamstring tendon obtained during ACL reconstruction. In vitro effects of IL-17A upon tenocytes were measured using RT-PCR, multiplex cytokine assays, apoptotic proteomic profiling, immunohistochemistry and annexin V FACS staining. Increased expression of IL-17A was detected in ‘early tendinopathy’ compared to both matched samples and non-matched control samples (p < 0.01) by RT-PCR and immunostaining. Double immunofluoresence staining revealed IL-17A expression in leukocyte subsets including mast cells, macrophages and T cells. IL-17A treated tenocytes exhibited increased production of proinflammatory cytokines (p < 0.001), altered matrix regulation (p < 0.01) with increased Collagen type III and increased expression of several apoptosis related factors. We propose IL-17A as an inflammatory mediator within the early tendinopathy processes thus providing novel therapeutic approaches in the management of tendon disorders.

Highlights

Tear Size Number of cases Mean age in years(range) Mean duration of symptoms in months Mean number of steroid injections
CD4 cells were limited in number throughout the samples and we identified no co-expression of IL-17A, presumably reflecting this low sample size
The majority of IL-17A+ cells double-stained with MCT, suggesting that mast cells represent a lineage in which IL-17A protein expression is enriched in human tendinopathy (Figs 1C and 2A,C)

Summary

Introduction

Tear Size Number of cases Mean age in years(range) Mean duration of symptoms in months (range) Mean number of steroid injections. IL-17A exerts various biological activities that could promote tissue destruction and degeneration during inflammation It induces the production, often in a synergistic manner, of cytokines, including IL-1, IL-6, TNF-α, chemokines, inducible NO synthase, and matrix metalloproteinases (MMPs) by fibroblasts, macrophages, and endothelial cells[21]. A recent transcriptomic analysis has highlighted increased expression of IL-17F in human tendinopathy biopsies[26] Based on these observations and the plausible biological profile exhibited by IL-17A, we hypothesized that IL-17A may play a role in tendinopathy. We previously suggested that matched subscapularis tendon from patients with full thickness rotator cuff tears may be a model of early human tendinopathy based on histological appearances and significantly increased levels of cytokines and apoptotic markers in these tissues[27]. The purpose of this study was to formally assess the expression of IL-17A within this model and thereafter explore the mechanistic activities of IL-17A on inflammation, apoptosis and matrix production in tenocytes in vitro

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Conclusion