Receptor tyrosine kinase ligands and inflammatory cytokines cooperatively suppress the fibrogenic activity in temporomandibular-joint-derived fibroblast-like synoviocytes via mitogen-activated protein kinase kinase/extracellular signal-regulated kinase.

Osteoarthritis (OA)-related fibrosis is a possible cause of temporomandibular joint (TMJ) stiffness. However, the molecular mechanisms underlying the fibrogenic activity in fibroblast-like synoviocytes (FLSs) remain to be clarified. The present study examined the effects of receptor tyrosine kinase (RTK) ligands, such as fibroblast growth factor (FGF)-1 and epidermal growth factor (EGF), on myofibroblastic differentiation of the FLS cell line FLS1, which is derived from the mouse TMJ. The present study revealed that both FGF-1 and EGF dose-dependently suppressed the expression of the myofibroblast (MF) markers, including α-smooth muscle actin (α-SMA) and type I collagen, in FLS1 cells. Additionally, both FGF-1 and EGF activated extracellular signal-regulated kinase (ERK) in FLS1 cells. In addition, the mitogen-activated protein kinase (MAPK)/ERK kinase (MEK) inhibitor U0126 abrogated the FGF-1- and EGF-mediated suppression of MF marker expression. On the other hand, inflammatory cytokines, such as interleukin-1ß and tumor necrosis factor-α, also suppressed the expression of MF markers in FLS1 cells. Importantly, U0126 abrogated the inflammatory cytokine-mediated suppression of MF marker expression. Interestingly, RTK ligands and inflammatory cytokines additively suppressed the expression of type I collagen. These results suggested that RTK ligands and inflammatory cytokines cooperatively inhibited the fibrogenic activity in FLSs derived from the TMJ in a MEK/ERK-dependent manner. The present findings partially clarify the molecular mechanisms underlying the development of OA-related fibrosis in the TMJ and may aid in identifying therapeutic targets for this condition. Additionally, FGF-1 and EGF could be therapeutically utilized to prevent OA-related fibrosis around the inflammatory TMJ.

ROCK/actin/MRTF signaling promotes the fibrogenic phenotype of fibroblast-like synoviocytes derived from the temporomandibular joint.

Malocclusion caused by abnormal jaw development or muscle overuse during mastication results in abnormal mechanical stress to the tissues surrounding the temporomandibular joint (TMJ). Excessive mechanical stress against soft and hard tissues around the TMJ is involved in the pathogenesis of inflammatory diseases, including osteoarthritis (OA). OA-related fibrosis is a possible cause of joint stiffness in OA. However, cellular and molecular mechanisms underlying fibrosis around the TMJ remain to be clarified. Here, we established a cell line of fibroblast­like synoviocytes (FLSs) derived from the mouse TMJ. Then, we examined whether the Rho­associated coiled­coil forming kinase (ROCK)/actin/myocardin-related transcription factor (MRTF) gene regulatory axis positively regulates the myofibroblast (MF) differentiation status of FLSs. We found that i) FLSs extensively expressed the MF markers α­smooth muscle actin (α­SMA) and type I collagen; and ii) an inhibitor against the actin­polymerizing agent ROCK, Y­27632; iii) an actin-depolymerizing agent cytochalasin B; iv) an inhibitor of the MRTF/serum response factor­regulated transcription, CCG­100602, clearly suppressed the mRNA levels of α­SMA and type I collagen in FLSs; and v) an MF differentiation attenuator fibroblast growth factor­1 suppressed filamentous actin formation and clearly suppressed the mRNA levels of α-SMA and type I collagen in FLSs. These results strongly suggest that the ROCK/actin/MRTF axis promotes the fibrogenic activity of synoviocytes around the TMJ. Our findings partially clarify the molecular mechanisms underlying the emergence of TMJ­OA and may aid in identifying drug targets for treating this condition at the molecular level.

EGF positively regulates the proliferation and migration, and negatively regulates the myofibroblast differentiation of periodontal ligament-derived endothelial progenitor cells through MEK/ERK- and JNK-dependent signals.

BACKGROUND/AIMS: Remodeling of fibrous and vascular tissues in the periodontal ligament (PDL) around the tooth root was observed during tooth movement by orthodontic force application. We previously demonstrated that a single cell-derived culture (SCDC) of primarily cultured PDL fibroblasts, called SCDC2, has an endothelial progenitor cell (EPC)-like character and can form endothelial cell (EC) marker-positive blood vessel-like structures. However, the types of molecular mechanisms that control the in vivo kinetic properties and the differentiation of the PDL-derived EPC-like cells into myofibroblasts (MFs), which are known to expand fibrous tissues, require clarification. METHODS: Using specific mitogen activated protein kinase (MAPK) inhibitors, we examined how epidermal growth factor (EGF)-mediated MAPK signals affected the proliferation, migration, and MF differentiation of these cells. RESULTS: EGF induced SCDC2 cell proliferation in MAPK/extracellular signal-regulated kinase (ERK) kinase (MEK)- and c-Jun N-terminal kinase (JNK)-dependent manners. In addition, EGF suppressed the expression of MF differentiation markers in these cells in a MEK/ERK-dependent manner, and, moreover, stimulated the cell migration in a MEK/ERK-dependent manner. CONCLUSION: EGF regulates fibrous tissue remodeling in PDLs through MEK/ERK- and JNK-mediated signals by affecting the proliferation, migration, and MF differentiation of the PDL-derived EPC-like cells.