Heat shock protein and apoptosis in supraspinatus tendinopathy

Heat shock proteins (HSPs) are often upregulated following oxidative and other forms of stress. Based on reports of excessive apoptosis in torn supraspinatus tendon and mechanically loaded tendon cells, we hypothesized heat shock proteins may be present in rodent and human models of tendinopathy due to their central role in caspase dependent apoptotic cell signaling. We used a running rat supraspinatus tendinopathy overuse model with custom microarrays to investigate the process at a genetic level. Additionally torn supraspinatus tendon and matched intact subscapularis tendon samples were collected from patients undergoing arthroscopic shoulder surgery. Control samples of subscapularis tendon were collected from 10 patients undergoing arthroscopic stabilization surgery and evaluated using semiquantative RT-PCR and immunohistochemistry. We identified substantial upregulation of heat shock proteins and apoptotic genes in the rodent model. We further confirmed increased levels of heat shock protein and apoptotic regulatory genes in human supraspinatus and subscapularis tendon. This finding suggests heat shock proteins play a role in the cascade of stress-activated programmed cell death and degeneration in tendinopathy and may provide a novel target in preventing tendinopathies.