Fibrotic matrix induces mesenchymal transformation of epithelial cells in oral submucous fibrosis

Abstract Oral submucous fibrosis (OSF) is a precancerous state of the oral mucosa; however, whether and how the fibrotic matrix of OSF is involved in the malignant transformation of epithelial cells remains unknown. Herein, oral mucosa tissue from patients with OSF, arecoline-induced rat OSF models, and their controls were used to observe the extracellular matrix changes and epithelial-mesenchymal transformation (EMT) in fibrotic lesions, and to explore the effects and mechanism of matrix stiffness on epithelial cell EMT. Compared with the controls, oral mucous tissues from patient exhibited increased number of myofibroblasts, decreased number of blood vessels and increased type I and type III collagen levels, with thicker, less porous, and disorderly arranged fibers. The oral mucous tissues from humans and OSF rats showed increased stiffness compared with the controls, accompanied by increased EMT activities of epithelial cells. Moreover, stiff collagen constructs caused increased EMT and proliferation of epithelial cells compared with soft constructs, and caused increased expression of Piezo1 and YAP. The EMT activities of stiff construct-cultured epithelial cells were significantly increased by exogenous Piezo1 activation, and decreased by YAP inhibition. During ex vivo implantation, the cells in the epithelium of the stiff group showed increased EMT activities and increased levels of Piezo1 and YAP compared with those in the sham and soft groups. We concluded that increased stiffness of the fibrotic matrix in OSF led to increased proliferation and EMT of mucosal epithelial cells, in which the Piezo1-YAP signal transduction is important.