Dose-Dependent Effects of TGF-β Inhibition on Osteoblast Differentiation and Wound Healing

TGF-β is a multifunctional pathway that controls significant cellular and physiological processes and several pathological activities. TGF-β-induced signaling can be triggered upon binding to specific receptors to initiate the transcriptional activation of several genes and cellular processes. However, the detailed role of TGF-β signaling in osteoblast differentiation remains to be explicated. SB525334, a selective TGF-βRI inhibitor, was investigated for its effect on the osteoblastic differentiation of human bone marrow MSCs at different concentrations. Alkaline phosphatase (ALP) activity was used to assess osteoblast differentiation marker, while Alizarin red staining was used as a marker for mineralization. Expressions of osteoblast-specific genes were evaluated using real-time PCR. A migration assay was performed to assess the effect of TGF-β on wound healing. Moreover, immunofluorescent staining for SMAD2/3 and SMAD4 was employed to confirm the activation of the TGF-β pathway. The inhibition of TGF-β1 signaling using a high concentration of SB525334 (3 µM) significantly reduced ALP activity and mineralization and downregulated osteoblast-specific genes. However, the opposite effect was reported using a lower concentration (0.03 µM), where osteoblast-associated genes were significantly upregulated, and ALP activity and mineralization were higher. Significant scratch/wound healing was achieved at a lower concentration of SB525334, while a higher concentration of SB525334 resulted in lower healing. Moreover, a low concentration of SB525334 demonstrated nuclear translocation of SMAD 2/3 and 4. Our study confirms that the effect of TGF-β signaling in bone formation and wound healing is dose-dependent, and the use of TGF-β is recommended as a valuable therapeutic approach.