Comparison of transforming growth factor beta expression in healthy and diseased human tendon

Abstract

BackgroundDiseased tendons are characterised by fibrotic scar tissue, which adversely affects tendon structure and function and increases the likelihood of re-injury. The mechanisms and expression profiles of fibrosis in diseased tendon is understudied compared to pulmonary and renal tissues, where transforming growth factor (TGF)β and its associated superfamily are known to be key drivers of fibrosis and modulate extracellular matrix homeostasis. We hypothesised that differential expression of TGFβ superfamily members would exist between samples of human rotator cuff tendons with established disease compared to healthy control tendons.MethodsHealthy and diseased rotator cuff tendons were collected from patients presenting to an orthopaedic referral centre. Diseased tendinopathic (intact) and healthy rotator cuff tendons were collected via ultrasound-guided biopsy and torn tendons were collected during routine surgical debridement. Immunohistochemistry and quantitative real-time polymerase chain reaction were used to investigate the protein and gene expression profiles of TGFβ superfamily members in these healthy and diseased tendons.ResultsTGFβ superfamily members were dysregulated in diseased compared to healthy tendons. Specifically, TGFβ-1, TGFβ receptor (R)1 and TGFβ R2 proteins were reduced (p < 0.01) in diseased compared to healthy tendons. At the mRNA level, TGFβ R1 was significantly reduced in samples of diseased tendons, whereas TGFβ R2 was increased (p < 0.01). BMP-2, BMP-7 and CTGF mRNA remained unchanged with tendon disease.ConclusionsWe propose that downregulation of TGFβ pathways in established tendon disease may be a protective response to limit disease-associated fibrosis. The disruption of the TGFβ axis with disease suggests associated downstream pathways may be important for maintaining healthy tendon homeostasis. The findings from our study suggest that patients with established tendon disease would be unlikely to benefit from therapeutic TGFβ blockade, which has been investigated as a treatment strategy in several animal models. Future studies should investigate the expression profile of fibrotic mediators in earlier stages of tendon disease to improve understanding of the targetable mechanisms underpinning tendon fibrosis.

Profibrotic mediators in tendon disease: a systematic review

“…The expression of TGF-β, BMPs and CTGF was dysregulated at different stages of tendon disease (Table 4); the single study that compared the protein expression of these growth factors between torn, tendinopathic and healthy RC tissues reported a decreased expression of TGF-β and its receptors in the diseased tendon tissues of both chronic tendinopathy and tear [22]. Gene and protein expression of TGF-β and protein expression of BMP2, BMP4 and BMP7 were increased in the six studies that compared tendinopathy and healthy tendon tissues from the patella or the Achilles [23–28].…”

“…The gene expression of BMP4 and BMP6 was suppressed in the calcific area of calcific tendinopathy of the RC [29]. The diagnosis of chronic tendinopathy was made clinically in all seven studies of human disease, with auxiliary imaging methods such as MRI or US [22–28]. The duration of pain was defined as more than 3 and 6 months in one study [28] and in four studies [22, 25–27] respectively, but there was no clear explanation in the other two studies [23, 24].…”

“…The diagnosis of chronic tendinopathy was made clinically in all seven studies of human disease, with auxiliary imaging methods such as MRI or US [22–28]. The duration of pain was defined as more than 3 and 6 months in one study [28] and in four studies [22, 25–27] respectively, but there was no clear explanation in the other two studies [23, 24]. The control tissues were obtained from the same anatomical location except in one study that investigated the gene expression in RC tear compared with the hamstring tendons in patients going under anterior cruciate ligament reconstruction surgery [22].…”

“…The duration of pain was defined as more than 3 and 6 months in one study [28] and in four studies [22, 25–27] respectively, but there was no clear explanation in the other two studies [23, 24]. The control tissues were obtained from the same anatomical location except in one study that investigated the gene expression in RC tear compared with the hamstring tendons in patients going under anterior cruciate ligament reconstruction surgery [22]. In the other studies that utilized the same anatomy, two studies obtained the control tissues from the unaffected area diagnosed by US in the same tendon [25, 27], and one study used cadaveric samples [23].…”

“…One study focused on a particular subtype of tendinopathy, calcific tendinopathy [29]. The two studies that investigated the gene expression of CTGF in RC tendon tear tissues did not show significant differences compared with the healthy tendon tissues [22, 27]. The studies investigating the effect of exercise in human tendons were excluded because the primary objective was to investigate the expression pattern across the spectrum of tendon disease and not to assess the impact of activity in tendons.…”