Influence of cyclic mechanical strain and heat of human tendon fibroblasts on HSP-72

Heat shock protein 72 (HSP-72) is a member of a superfamily of different proteins that are synthesized as a cytoprotective response following cellular stress. Mechanical strain is an important component in ligament and tendon healing. Up to the present point of time, the influence of mechanical strain on the expression of HSP-72 is unknown. Tendon fibroblasts from the patellar tendons of nine individuals were isolated and amplified in vitro. First, the effect of 15 or 60 min of heat exposition was studied immunohistochemically and by Western blotting. In a second experiment, the effects of 15 and 60 min of cyclic longitudinal stretching were investigated. Samples were taken after 2, 4 and 8 h. The heat exposition experiments indicate that HSP-72 accumulates in the nucleus and that there is a transient upregulation. This effect is more prominent after 60 min of heat exposure. The same reaction was found after stretching stimulation, however, to a lesser extent. There was a transient up regulation of HSP-72 after short-term stretching and a biphasic increase after 60 min of stretching. Upregulation of HSP-72 by heat and mechanical stress is a response in human fibroblasts which involves a nuclear translocation. The response differs with regard to the time points beyond 2 h after the application of either stress.