The Protective Role of CD44 and microRNA-146a in Tendinopathy: A Signaling Axis Targets Apoptosis

Objective Tendinopathy refers to the clinical condition characterized by pain in a tendon accompanied by significant dysfunction, with preference given to pathological terms such as tendinitis and tendinosis. It is influenced by multiple factors, including chronic inflammation, senescence, and apoptosis. CD44 serves as a principal cell-surface receptor for hyaluronan (HA), a constituent of the extracellular matrix. Previous studies have shown that inhibition of the CD44 signaling pathway induces apoptosis, inflammation, and expression of matrix metalloproteinases in tendinopathic tenocytes. Furthermore, microRNA-146a (miR-146a) blocks interleukin-1β (IL)-1β-induced senescence in tendinopathic tenocytes. Therefore, the aim of this study is to investigate the signaling axis between CD44 and miR-146a in tendinopathic tenocytes and tendons, which may finely regulate apoptosis. Methods Overexpression of CD44 and miR-146a in rat primary tendinopathic tenocytes and tendons were achieved through lentiviral vector-mediated transfer of CD44 cDNA (LVCD44) and precursor miR-146a (LVmiR-146a). TUNEL staining was performed to evaluate apoptosis. Additionally, LY294002, a PI3K/AKT inhibitor, and OX-50, an antagonizing antibody that blocks CD44 activity, in situ hybridization (ISH), and immunohistochemistry were used to examine the CD44-AKT-miR-146a signaling axis targeting Smad4 in tendinopathic tenocytes and tendons. Results Tendinopathic tenocyte transfectants overexpressing CD44 and miR-146a exhibited lower apoptotic cell numbers compared to transfectants treated with control vectors. Furthermore, the CD44-AKT-miR-146a signaling axis was shown to alleviate apoptosis in IL-1β-stimulated tendinopathic tenocytes and rat collagenase-induced Achilles tendons by inhibiting Smad4 expression. Conclusions We demonstrate that overexpression of CD44 and miR-146a protects tendinopathic tenocytes and tendons from apoptosis through the AKT/miR-146a/Smad4 signaling pathway.