TMF suppresses chondrocyte hypertrophy in osteoarthritic cartilage by mediating the FOXO3a/BMPER pathway

Osteoarthritis (OA) is a disease of the joints, characterized by chronic inflammation, cartilage destruction and extracellular matrix (ECM) remodeling. Aberrant chondrocyte hypertrophy promotes cartilage destruction and OA development. Collagen X, the biomarker of chondrocyte hypertrophy, is upregulated by runt-related transcription factor 2 (Runx2), which is mediated by the bone morphogenetic protein 4 (BMP4)/Smad1 signaling pathway. BMP binding endothelial regulator (BMPER), a secreted glycoprotein, acts as an agonist of BMP4. 5,7,3',4'-tetramethoxyflavone (TMF) is a natural flavonoid derived from Murraya exotica L. Results of our previous study demonstrated that TMF exhibits chondroprotective effects against OA development through the activation of Forkhead box protein O3a (FOXO3a) expression. However, whether TMF suppresses chondrocyte hypertrophy through activation of FOXO3a expression and inhibition of BMPER/BMP4/Smad1 signaling remains unknown. Results of the present study revealed that TMF inhibited collagen X and Runx2 expression, inhibited BMPER/BMP4/Smad1 signaling, and activated FOXO3a expression; thus, protecting against chondrocyte hypertrophy and OA development. However, BMPER overexpression and FOXO3a knockdown impacted the protective effects of TMF. Thus, TMF inhibited chondrocyte hypertrophy in OA cartilage through mediating the FOXO3a/BMPER signaling pathway.