The role of prostanoids in the development and progression of tendon degeneration and as therapeutic targets

Tendon injuries are highly prevalent in both horses and humans and lead to high morbidity due to protracted and poorly functional repair. These injuries are characterised by sub-clinical degenerative changes within the tendon extracellular matrix (ECM) suggesting preventative strategies may have a role in reducing such tendon degeneration. The injuries are usually sports-related and are increasing in frequency due to increased sporting activity within an ever increasing ageing population. Hence, there is a large patient population that would benefit from both a successful therapeutic and preventative strategy. The purpose of the work is to target the molecular mechanisms that activate the metalloproteinase mediated degeneration of tendon based on recent findings. Our studies have supported the hypothesis that after skeletal maturity, exercise and ageing of tendon results in a net degradation of the ECM because of reduced responsiveness of tenocytes to growth factors and in cell numbers and intercellular gap junction communication. The multiplicity of these effects makes the strategy of re-activation of the resident cells an impractical approach to prevention. We have therefore concentrated on investigating mechanisms involved in degradation. We demonstrated [1] that repetitive loading induces a cell-mediated loss of tendon strength that is age-related and is prevented with chemical inhibition of MMPs. Increased MMP expression in two different models of tendon loading in vitro and after exercise in vivo in humans support our findings. Furthermore, pilot experiments suggest that repair tissue formed after injury is more susceptible to cyclical-load driven proteolysis, helping to explain the high incidence of re-injuries. The prostanoid PGE2 is also up-regulated by mechanical load [2] and causes tendon degeneration [3], implicating PGE2 as a possible key mediator of increased MMP production and degradation. The aim of this project is therefore to determine the role of PGE2 in modulating effects of mechanical loading in our in vitro system [1] by analysis of changes in the ECM, cell metabolism, and PGE2 and MMP synthesis and activation. The work will also evaluate the effect of COX inhibitors and the commonly used oral nutraceuticals (glucosamine, chondroitin sulphate and polysulphated glycosaminoglycans, suggested to act via a PGE2 mechanism [4]) as potential beneficial agents on intrinsic tendon healing. A further aim is to investigate the integration and function of mesenchymal stem cells (MSCs) implanted into mechanically loaded devitalised tendon explants [5]. We have used MSCs clinically to improve healing with some evidence of improved clinical outcome. However, the exact mechanism whereby these cells contribute to healing is unclear, nor their role in the production and activation of MMPs within reparative tissues. This work will provide further information on the molecular mechanisms behind tendon degeneration and the action of therapeutically implanted mesenchymal stem cells and on the use of adjunctive therapeutic agents for both the treatment of patients post injury and for the prevention of tendon degeneration in at risk individuals. This work will address the hypotheses that PGE2 increases MMP activity and the loss of strength of tendon associated with cyclical load and that this can be prevented by commercially available glucosamine, chondrotin sulphate and polysulphated glycosaminoglycans. As part of their training (see relevant sections) the student will develop and test this hypothesis through specific aims and experimental objectives. References: 1 Dudhia J, et al (2007) Ageing Cell 6:547-6 2 Devkota et al (2007) J. Orthop Res. 25: 1078-1086 3 Khan M, et al (2005) 15:27-33 4 Frean S, Lees P (2000) Am J Vet Res. 61:499-5 5 Richardson LE (2007) The role of extracellular matrix on mesenchymal stem cell differentiation. PhD thesis, University of London