2020 Volume 45 Issue 1 Pages 46-57
Osteoarthritis( OA)-related fibrosis is a plausible cause of temporomandibular joint( TMJ) stiffness. We previously demonstrated that receptor tyrosine kinase( RTK) ligands, fibroblast growth factor( FGF)-1, and epidermal growth factor( EGF), suppressed fibrogenic activity in a fibroblast-like synoviocytes( FLS) cell line, FLS1, derived from mouse TMJ. However, the molecular mechanisms underlying the suppression of fibrogenic activity in FLS1 cells by RTK ligands remained to be clarified.
In particular, in inflamed TMJ, it remained unclear how extracellular adenosine 5′-triphosphate( eATP), which is a danger associated molecular pattern( DAMP), affected the RTK-ligand-induced suppression of fibrogenic activity in FLS1 cells. Here, we found that FLS1 cells vigorously expressed the purinergic receptors, P2X3, P2X7, P2Y2, P2Y4, P2Y12, and P2Y13. We found that ATP significantly decreased the expression of the fibrogenic marker, alpha-smooth muscle actin( α-SMA), in FLS1 cells. In addition, ATP strengthened the RTK-ligand-induced suppression of α-SMA expression. Since ATP typically binds to P2X3, P2X7, P2Y2, P2Y4, and P2Y13, and to determine which purinergic receptor mediates the suppressive effects of ATP on the fibrogenic marker expression, we examined the effects of P2Y12 and P2Y13 agonist, adenosine 5 ′-diphosphate( ADP), and P2Y2 and P2Y4 agonist, uridine 5 ′-triphosphate( UTP), and ligand-induced suppression of α-SMA expression. Importantly, P2X3 antagonist, RO-3, and P2X7 antagonists, A-438079 and A-804598, did not reverse the ATP-induced suppressive effects on the α-SMA expression. Taken together, these results strongly suggested that eATP strengthened the RTK-ligandinduced suppression of fibrogenic activity in FLSs possibly through P2Y2, P2Y4, or P2Y13.
Our findings partially clarify the molecular mechanisms underlying the development of OA-related fibrosis in TMJ and may aid in identifying therapeutic targets for this condition. In addition, FGF-1 and EGF could be utilized as drugs to prevent OA-related fibrosis around inflammatory TMJ.