Cyclic stretch induces decorin expression via yes-associated protein in tenocytes: A possible mechanism for hyperplasia in masticatory muscle tendon-aponeurosis hyperplasia

Abstract Objective Masticatory muscle tendon-aponeurosis hyperplasia (MMTAH) is a disease which exhibits limiting mouth opening caused by hyperplasia of the tendon and aponeurosis of bilateral masticatory muscles. Although it is unclear whether hyperplasticity of tendons in MMTAH is due to cyclic stretch, we hypothesize that cyclic stretch is the main cause of force on MMTAH. In this study, we examined decorin expression in the masticatory muscle tendon of MMTAH patients. We also examined decorin (Dcn) expression of tenocytes on which stretch forces are loaded to explore whether stretch forces affect yes-associated protein (YAP) signaling and whether Dcn expression is regulated by YAP. Methods Quantitative reverse-transcription polymerase chain reaction, immunoblot analysis and immunohistochemistry were performed in tendons of patients having MMTAH. Mechanical loading experiment for TT-D6 tendon fibroblastic cells using RNA interference technique was conducted. Results We found that Dcn expression is increased in tendons of MMTAH patients. We also showed that cyclic stretch force increases decorin expression in TT-D6 tendon fibroblastic cells and that Dcn expression is regulated via YAP in TT-D6 tendon fibroblastic cells acted upon by cyclic stretch. Conclusions Our results, for the first time, demonstrated that cyclic stretch induces decorin expression via YAP in tenocytes and Dcn is upregulated in tendons of MMTAH, suggesting that tendons of MMTAH were subjected to cyclic stretch conditions.