Persistent stromal fibroblast activation is present in chronic tendinopathy

Stephanie G Dakin,Christopher D Buckley,Kim Wheway,Robert Hedley,Bridget Watkins,Andrew J Carr,Mohammad Hussein Al-Mossawi,Fernando O Martinez

doi:10.1186/s13075-016-1218-4

Abstract

BackgroundGrowing evidence supports a key role for inflammation in the onset and progression of tendinopathy. However, the effect of the inflammatory infiltrate on tendon cells is poorly understood.MethodsWe investigated stromal fibroblast activation signatures in tissues and cells from patients with tendinopathy. Diseased tendons were collected from well-phenotyped patient cohorts with supraspinatus tendinopathy before and after sub-acromial decompression treatment. Healthy tendons were collected from patients undergoing shoulder stabilisation or anterior cruciate ligament repair. Stromal fibroblast activation markers including podoplanin (PDPN), CD106 (VCAM-1) and CD248 were investigated by immunostaining, flow cytometry and RT-qPCR.ResultsPDPN, CD248 and CD106 were increased in diseased compared to healthy tendon tissues. This stromal fibroblast activation signature persisted in tendon biopsies in patients at 2–4 years post treatment. PDPN, CD248 and CD106 were increased in diseased compared to healthy tendon cells. IL-1β treatment induced PDPN and CD106 but not CD248. IL-1β treatment induced NF-κB target genes in healthy cells, which gradually declined following replacement with cytokine-free medium, whilst PDPN and CD106 remained above pre-stimulated levels. IL-1β-treated diseased cells had more profound induction of PDPN and CD106 and sustained expression of IL6 and IL8 mRNA compared to IL-1β-treated healthy cells.ConclusionsWe conclude that stromal fibroblast activation markers are increased and persist in diseased compared to healthy tendon tissues and cells. Diseased tendon cells have distinct stromal fibroblast populations. IL-1β treatment induced persistent stromal fibroblast activation which was more profound in diseased cells. Persistent stromal fibroblast activation may be implicated in the development of chronic inflammation and recurrent tendinopathy. Targeting this stromal fibroblast activation signature is a potential therapeutic strategy.

Highlights

Growing evidence supports a key role for inflammation in the onset and progression of tendinopathy
As IL-1β induces nuclear factor kappa beta (NF-κB) target genes known to be highly expressed in early-stage tendinopathy [8], we further investigated if IL-1β treatment of cultured tendon cells induces persistent stromal fibroblast activation, and if this response differs between healthy and diseased cells
Diseased supraspinatus tendons had significantly increased PDPN, CD248 and CD106 mRNA compared to healthy subscapularis tendons (Fig. 1a) (p = 0.001, p = 0.003 and p = 0.0007, respectively)

Summary

Introduction

Growing evidence supports a key role for inflammation in the onset and progression of tendinopathy. Soft-tissue pathologic conditions such as tendinopathy are a common cause of pain and loss of function and an important and increasing component of health expenditure in ageing societies [2]. Diseased tendons heal by forming a repair scar; the normal architecture, composition, and tissue function are not Recent work highlights the complex activation states of immune cells including macrophages populating diseased human shoulder tendons [8]. Investigation of inflammation activation pathways in cultured stromal cells from diseased human tendons has revealed that. Non-myeloid/ non-lymphoid populations such as resident stromal fibroblasts are known to play a prominent role in the generation and maintenance of chronic synovial inflammation [9, 10]. Phenotypic alterations in RA synovial fibroblasts play an important role in the switch from resolving to persistent disease [11, 12]

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Discussion

Conclusion