Bacitracin promotes osteogenic differentiation of human bone marrow mesenchymal stem cells by stimulating the bone morphogenetic protein-2/Smad axis

Bacitracin, a widely used metallopeptide antibiotic, has been reported to be locally used in treating wounds without systemic adverse reactions. Our preliminary study showed that bacitracin might enhance the osteogenic differentiation of human bone marrow mesenchymal stem cells (HBMSCs). The present study investigated whether bacitracin affects the osteogenic differentiation of HBMSCs and the molecular mechanisms involved. The proliferation of HBMSCs in the presence of bacitracin was examined using a cell counting kit-8 (CCK-8) assay. The effects of bacitracin on the cell cycle and apoptosis of HBMSCs were observed using flow cytometry assay. Staining and quantitative assays for alkaline phosphatase (ALP) staining, collagen deposition (Sirius Red), and mineralization (Alizarin Red) were used to study osteogenic differentiation of HBMSCs. The expression of osteogenic differentiation markers was detected using quantitative reverse transcription polymerase chain reaction (RT-qPCR) analyses. The activation of related signaling pathways was examined using a luciferase reporter assay and western blotting. Bacitracin treatment increased osteogenic differentiation of HBMSCs without cytotoxicity and did not adversely affect cell cycle progression or apoptosis. The luciferase reporter assay showed that bacitracin activated the transcription of bone morphogenetic protein-2 (BMP2) gene, a key gene in the BMP2/Smad signaling axis. Western blotting indicated that this axis was markedly activated by bacitracin stimulation of osteogenesis. Moreover, the activation of Smad phosphorylation and osteogenic differentiation by bacitracin was inhibited by a transforming growth factor (TGF)-beta/Smad inhibitor (LDN-193189 HCl) and small interfering RNA (siRNA) gene silencing (si-BMP2). In conclusion, our results suggest that bacitracin can promote osteogenesis of HBMSCs by activating the BMP2/Smad signaling axis.