The effects of repetitive cyclic biaxial strain to proliferation and apoptosis of human tendon fibroblasts

Introduction: The treatment of tendon injuries with a well dosed repetitive strain might have a positive effect on the healing of such injuries. There might be an adaption of the cells to the strain, which results in processes that lead to a better regeneration of the damaged tissue. Therefore, we measured the proliferation and apoptosis rate of repetitive strained in vitro fibroblasts. Methods: Human tendon fibroblasts received from patient isolates were cultered on silicon dishes within the scope of the passages 3 to 6. The repetitive biaxial strain took place 15 and 30 minutes with an interval of 4 hours. The strain parameters had an amplitude of 5% and a frequency of IHz. The experiments were aborted after 0 minutes, 6, 12 and 24 hours. The proliferation rate was detected by the incorporation of BrdU and the apoptosis rate by an annexinFACS-staining. Results: The repetitive strain reseulted in a continuous activation of proliferation in tendon fibroblasts. Within 24 hours after strain the proliferation rate increased up to 50% above the basic level of unstressed controls. The apoptosis rate showed a biphasic progress/development with an increase of 40% above the basic level after 24 hours. Discussion: Repetitive cyclic biaxial strain leads to an increase of proliferation as well as apoptosis rate. This might result in a faster/better wound healing of tendon injuries because of the faster replacement of damaged cells by new tissue. These results are important biological data for the rehabilitation of tendon injuries in patients.