Retinoic acid remodels extracellular matrix (ECM) of cultured human fetal palate mesenchymal cells (hFPMCs) through down-regulation of TGF-β/Smad signaling

• RA dose-dependently inhibited cell proliferation and mRNA and protein levels of ECM components.
• RA increased the ratio of MMP2/TIMP2 mRNA expression.
• RA inhibited TGF-β/Smad pathway.
• Activation of TGF-β/Smad signaling attenuated cellular responses of RA.

The regulation of extracellular matrix (ECM) by retinoic acid (RA) is interesting in light of the fact that the ECM plays an essential role in morphogenesis and palatal shelf elevation. In the current study, we explored the effect of RA overexposure on ECM and the probable mechanisms in cultured human fetal palate mesenchymal cells (hFPMCs). RA dose-dependently inhibited cell proliferation and mRNA and protein levels of ECM components fibronectin, tenascin C and fibrillin-2. Zymography revealed that MMP-2 activity was suppressed by RA. Further analysis revealed that mRNA levels of MMP2 and TIMP2 were decreased, while the MMP2/TIMP2 mRNA ratio was increased, which might facilitate the ECM degradation. Because of the pivotal role of TGF-β/Smad pathway in palatogenesis we therefore checked the effect of RA on TGF-β/Smad signaling. The results indicated RA treatment increased Smad7 expression and decreased the levels of TGF-β1, TGF-β3, TGF-β type II receptor (TβRII) and phosphorylated Smad2 and Smad3. Activation of the Smad pathways by either exogenous TGF-β3 or recombinant adenoviruses for Smad3 attenuated RA-induced inhibition of cell proliferation and ECM components and rescued the RA-altered MMP2/TIMP2 mRNA ratio. In conclusion, these findings suggested that RA overexposure inhibited cell proliferation and disrupted the ECM network through down-regulation of TGF-β/Smad pathway.