Persistent stromal fibroblast activation is present in chronic tendinopathy

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.

Stroma: the forgotten cells of innate immune memory

“…This may help to explain the capacity of antibodies against widely expressed antigens to drive joint inflammation. Recent research from Oxford University suggested that chronic tendinopathy was due to an initial (and supposedly resolved) insult, which led nonetheless to fibroblasts acquiring a fibrotic and hyper‐responsive phenotype . As remarked above, the altered fibroblast phenotype may be explained in part by differentiation or expansion of a fibroblast subpopulation.…”

“…This will obviously due be partly to the adaptive immune response, but as this review has shown, the effect on other cell types, and so the tissue or even organism as a whole, are not to be dismissed. Didierlaurent and colleagues discussed the effects of repeat lung infection [74], while Dakin et al hypothesized [31] and later confirmed [36] that an acute injury event may prepare tendons for chronic tendinopathy and fibrosis upon a second insult. Such concepts show a clear clinical relevance to repeat challenge of innate cells.…”

“…In 2011, however, gingival fibroblasts were shown to be capable of tolerance, but in a gene‐specific fashion . A recent spate of publications has advanced our understanding further. Sohn et al .…”

“…In 2011, however, gingival fibroblasts were shown to be capable of tolerance, but in a gene-specific fashion [33]. A recent spate of publications [34][35][36][37][38] has advanced our understanding further. Sohn et al displayed inflammatory memory of T cell chemoattractants in fibroblast-like synoviocytes (FLS) derived from patients with rheumatoid arthritis (RA) [39].…”

“…Repeat challenges with LPS induced a refractory state seen only in fibroblasts of certain sites, and only in genes linked to the anti-viral response. Dakin et al showed that tendon fibroblasts from chronic tendinopathy patients mounted stronger inflammatory responses in vitro than those of healthy tendons, thus demonstrating the longevity of innate immune memory in fibroblasts [35,36]. They also discovered that while intracellular signalling diminished over time after removal of stimulus, surface markers of fibroblast activation such as podoplanin (PDPN) and vascular adhesion molecule-1 (VCAM-1) were maintained at high levels.…”