Conclusions
For the first time, these results revealed a vital role of TGF-β1 in cell-cell communication in chondrocytes via gap junction formation. We describe the regulatory mechanism, the involvement of TGF-β type I receptor and the nuclear translocation of Smad3/4.
Methods
qPCR and mRNA microarray were used to verify the expression of genes in the TGF-β and connexin families in cartilage and chondrocytes. A scrape loading/dye transfer assay was performed to explore GJIC. Western blot analysis was used to detect connexin43 (Cx43) and Smad signalling components. Immunofluorescence staining was performed to characterize protein distribution.
Results
The TGF-β1 mRNA was the highest expressed member of the TGFβ super family in cartilage. TGF-β1 promoted functional GJIC through increased expression of Cx43. TGF-β1-mediated GJIC required the participation of TGF-β type I receptor. TGF-β1 activated Smad3 and Smad4 signalling to facilitate their nuclear translocation. The Smad3 and Smad4 signalling proteins bound to the promoter of Gja1 and thus initiated Cx43 gene expression. Conclusions: For the first time, these results revealed a vital role of TGF-β1 in cell-cell communication in chondrocytes via gap junction formation. We describe the regulatory mechanism, the involvement of TGF-β type I receptor and the nuclear translocation of Smad3/4.