Theaflavin reduces Achilles tendon heterotopic ossification in mice through the TGF-β/Smad signaling pathway

Heterotopic ossification (HO) affects millions of people worldwide. TGF-β/Smad signaling pathway plays an essential role in HO of the Achilles tendon. Recent studies have found that Theaflavin can regulate the TGF-β/Smad signaling pathway, suggesting Theaflavin may have a positive effect on HO. In this study, we aimed to study the effects of Theaflavin on preventing endochondral differentiation of Tendon-derived stem cells (TDSCs) and the HO process after in the achilles tendon injury model. Here, we investigated the role of Theaflavin in a mouse model of Achilles tendon heterotopic ossification. In addition, we use TDSCs to explore the molecular mechanism of Theaflavin affecting HO. Our data showed that Theaflavin can inhibit HO of the Achilles tendon and significantly reduce the volume of mature bone tissues. SOX9 and RUNX2 were decreased significantly after Theaflavin administration. Experiments showed Theaflavin inhibited TGF-β/Smad signaling pathway during chondrogenic differentiation and osteogenic differentiation of TDSCs. Surface Plasmon Resonance Assay and Molecular docking simulation showed that a direct molecular interaction between Theaflavin and TβRI (a membrane receptor of TGF-βs). Meanwhile, Cellular Thermal Shift Assay showed Theaflavin bonded and thermally stabilized TβRI significantly. Moreover, WB and IHC displayed Theaflavin also exhibited inhibitory effects on TβRI phosphorylation. In summary, Our findings demonstrated that Theaflavin inhibited HO by down-regulating the TGF-β/Smad signal pathway, and this effect may attributed to Theaflavin binded directly to TβRI and prevented its phosphorylation.