TGF-β1 Enhances the Expression of α-Smooth Muscle Actin in Cultured Human Pulpal Fibroblasts: Immunochemical and Ultrastructural Analyses

Transforming growth factor-beta 1 (TGF-β1) has been related to induce the expression of α-smooth muscle actin (α-SMA) in fibroblasts during repair. Because pulpal fibroblasts seem to be somewhat different from other fibroblasts, the present study investigated in vitro whether TGF-β1 enhances the expression of α-SMA in human pulpal fibroblasts. TGF-β1 was added in doses between 5-10 ng/mL to cultures of both dental pulp and gingival human fibroblasts. The expression of α-SMA was analyzed by immunofluorescence and Western blotting, whereas the ultrastructure was evaluated by electron microscopy. In addition, the expression of tenascin, osteonectin, and vimentin was also investigated. Both cell types were immunoreactive for α-SMA even without TGF-β1. When TGF-β1 was added to cell cultures, the expression of α-SMA increased dramatically in pulpal fibroblasts, independent of the concentration used. It was confirmed by the Western blotting analysis. Ultrastructure revealed myofilaments and indented nuclei in both fibroblasts treated with TGF-β1. Tenascin and osteonectin were only immunolabeled in pulpal fibroblasts treated or not with TGF-β1. Both fibroblast types were positive for vimentin. The present findings showed that TGF-β1 up-regulated the expression of α-SMA, thus inducing pulpal fibroblasts to acquire the myofibroblast phenotype.