Increased expression of type 1 cannabinoid (CB1) receptor among patients with rotator cuff lesions and shoulder stiffness

Background Shoulder stiffness is a disease manifested by pain, limited range of motion, and functional disability. The inflammatory and fibrosis processes play a substantial role in the pathogenesis of shoulder stiffness. The CB1 receptor has been recognized to mediate the processes of pathologic fibrosis. This study investigated the role of the CB1 pathway in pathogenesis of rotator cuff lesions with shoulder stiffness. Methods All of the patients undergoing repair surgery for rotator cuff lesions were recruited and subcategorized into subjects with and without shoulder stiffness. Reverse transcription-polymerase chain reaction assay was used to evaluate the expression level of CB1 and interleukin 1β (IL-1β) in the subacromial bursae, and enzyme-linked immunosorbent assay was used to measure the concentration of CB1 and IL-1β in the subacromial fluid. Tenocytes treated with CB1 agonists and antagonists were also studied for the relationship of CB1 and the inflammatory cytokine IL-1β. Results The patients with shoulder stiffness had higher messenger RNA (mRNA) expression (P =.040) and immunohistochemistry staining (P <.001) of CB1 in the subacromial bursa and higher CB1 concentration in the subacromial fluid (P =.008). Tenocytes treated with the CB1 agonist WIN 55,212-2 and antagonist AM251 showed increased expression of IL-1β mRNA (P =.049) and suppressed expression of IL-1β mRNA (P =.001), respectively. Discussion The CB1 pathway is involved in the pathogenesis of shoulder stiffness. It may be a promising target for the treatment of rotator cuff lesions with shoulder stiffness.