The effect of aging related structural changes in tendons on the development of tendinopathies and the capacity to respond to therapeutic exercise

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Tendinopathies and tendon injuries are major clinical topics, especially in sports medicine and as a disease of the elderly. The proposed study utilizes a well established in-vivo rat model of early onset tendinopathy to identify structural, compositional and biomechanical proteins that contribute to the resistance and repair of fatigue damage accumulation in consideration of different age groups.AIM I of this project will be to asses the structure and composition associated with the extent of accumulation of fatigue damage. To complete this aim, patellar tendons of young and old rats will fatigue loaded with two different protocols of cyclic tensile force and measured concerning their biomechanical properties. Second harmonic generation imaging will be used to quantify the level of structural damage. After a healing period of 2 weeks tendons will be harvested and examined for differences in key proteins using immunohistochemistry. AIM II will be to determine the effect of exercise regarding the same parameters between young and old animals. 2 weeks after fatigue loading the one subgroups will be exposed to physical training and the other subgroups will be kept on cage-active level. Results will provide new insight not only into the effect of age on effectiveness of physical training on tendinopathy, but also on the structural and compositional factors that contribute to tendon remodeling.A second part of the study (AIM III) will address the validation of sonoelastography as a method for application in rat patellar tendons. Sonoelastography is a non-invasive imaging tool that measures elasticity of soft tissue in real-time. The capacity to apply sonoelastography in this model will allow for a more rigorous assessment and investigation of this technique in controlled animal studies. For validation, animals in Aim I will be scanned during the hole project for determination of correlations between sonoelastographic measures and induced damage and biomechanical measures. Sonoelastography will be performed using two current technologies (Strain elastography and Share-wave elastography). To assess the utility of sonoelastography as a guide for therapeutics, sonoelastography methods also will be applied to fatigue damaged tendons in animals undergoing exercise and cage-active animals during the healing period (animals in Aim II).