Interleukin-6-induced activation of signal transducer and activator of transcription-3 in ruptured rotator cuff tendon

The aim of this study was to examine interleukin-6 production and the activation of signal transducer and activator of transcription-3 (STAT3) in ruptured rotator cuff tendon. Specimens of ruptured rotator cuff tendons were analysed using real-time reverse transcriptase polymerase chain reaction, Western blotting and immunohistochemistry. Specimens of co-existing inflammatory subacromial synovia were examined for comparison. The level of interleukin-6 messenger RNA was increased in ruptured rotator cuff tendon as well as in subacromial synovium. Western blot analysis showed constitutive production of activated, phosphorylated STAT3 in ruptured rotator cuff tendon and co-existing subacromial synovium. Immunohistochemical examination detected cells producing interleukin-6, interleukin-6 receptor and phosphorylated STAT3 in ruptured rotator cuff tendon, mainly in proliferative vessels and, to a lesser extent, in tendon fibroblasts around the vessels. This study demonstrates that activation of STAT3 induced by interleukin-6 is promoted mainly by proliferative vessels in ruptured rotator cuff tendon.