Institution: The University of Oxford
Investigators: Professor Andrew Carr, Dr Philippa Hulley, Ms Hannah Cornell
Stream: PhD
Topic: Upper Limbs (Shoulder)
Status: Live
Previous studies carried out by this group and others have identified chondroplasia in biopsies taken from rotator cuff tendon tears. The frequency of occurance of this metaplasia increases as the tear size increases suggesting disease progression. The project aims to both determine the sequence of events in chondrocytic transformation and to investigate three potentially chondrogenic paradigms in vitro.
The United Kingdom Rotator Cuff trial (UKUFF) is a multi-centre study co-ordinated from the Nuffield Orthopaedic Centre. Biopsies from the full spectrum of tear sizes are being collected providing a cross-sectional disease model. They will be analysed by histology and immunohistochemistry for the appearance of markers of chondroplasia including the presence of rounded cells lying within lacunae, vimentin intermediate filaments, Sox9, collagen II and a matrix which stains positively with toludine blue.
Cultured normal human hamstring tenocytes will provide an in vitro model with which to determine the chondrogenic potential of three different peturbations in the natural environment to which rotator cuff tenocytes are subject to upon tendon rupture. Namely, actin cytoskeletal disruption/cell shape change, hypoxia and compression.
The extracellular matrix (ECM) of the tendon is profoundly altered in degenerate samples. Tenocytes are intimately associated with their ECM via integrins. These receptors have the capacity to recruit second messengers which can signal through small GTPases such as RhoA resulting in downstream effects including actin cytoskeletal rearrangement and altered gene expression. The pro-chondrogenic effects of actin depolymerising agents such as cytochalasin D are well documented in chondrocytes. Recent work has identified RhoA and its downstream effector ROCK as playing a key role in chondrogenesis. Additionally, statins, inhibitors of protein prenylation which disturb the intracellular location of small GTPases, upregulate markers of the chondrocytic phenotype. Statins and various inhibitors of the cytoskeleton and the RhoA/ROCK pathway will be used in the in vitro model to determine if alterations in these pathways could be responsible for the progression of chondroplasia in the tendon.
In contrast to avascular cartilage, tendon is well vascularised with tenocytes adapted for aerobic respiration. Upon tendon rupture, the blood supply to the affected area is compromised, suggesting localised hypoxia. In chondrocytes, hypoxia upregulates expression of Sox9, the 'master regulator' of chondrogenesis, and results in upregulation of genes of the chondrocytic phenotype including COL2A1 and AGN. It also upregulates the expression of the transcriptional repressors DEC1 and DEC2 which appear to prevent differentiation to alternative phenotypes. Work by our group indicates that degenerate supraspinatus tendon is subject to hypoxia and that tenocytes upregulate classical hypoxic response genes when subjected to low oxygen tension. Human hamstring tenocytes will be subjected to varying oxygen concentrations to determine if hypoxia affects the levels of tenocytic or chondrocytic markers.
Compression appears to play a role in the development of non-pathological fibrocartilage at so-called 'wrap-around regions', where bone surfaces exert local pressure on tendon. Some researchers believe the supraspinatus tendon to be subject to compression from the acromion and/or enthesophytes. The physical location of rotator cuff tears and the lack of signs of friction at tear sites make this hypothesis unlikely. Nevertheless, if there is sufficient time, the effect of compression on the expression of chondrocytic and tenocytic markers will be determined.
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