FGF2-Regulated Osteogenic Differentiation of Human Bone Marrow Stromal Cells

Introduction: Fibroblast growth factor 2 (FGF2) plays a crucial role in regulating the osteogenic differentiation of progenitor cells. However, the process by which this occurs is not yet fully understood. In this study, we aimed to investigate whether FGF2 stimulates the osteogenesis of precursor cells through the yes-associated protein (YAP) and large tumor suppressor kinases 1/2 (LATS1/2). Methods: Human bone marrow stromal cells (hBMSCs) were cultured in osteogenic medium supplemented with FGF2 at concentrations of 2 ng/mL, 10 ng/mL, and 50 ng/mL for 2, 7, or 21 days. Alizarin red staining was performed to identify mineralization after 21 days of culture. RT-qPCR was conducted to detect the mRNA expression of Yap, Lats1, Lats2, Runx2, Bglap, and β-Actin. Immunofluorescence staining was carried out to detect the protein expression of YAP and LATS1/2. Data was analyzed with a p-value set at 0.05. Results: Mineralization was most significant at 10 ng/ml of FGF2 for 7 days and increased with concentrations of FGF2 from 0 ng/ml to 10 ng/ml for 7 days (p < 0.05) but decreased at the high concentration of 50 ng/ml for 2 days (p < 0.05). mRNA expression of Yap, Runx2, and Bglap increased in concordance with the increasing mineralization levels, but Lats1/2 mRNA decreased. mRNA expression levels were dose-dependent when FGF2 was added for 7 days (p < 0.05) and time-dependent when FGF2 concentration was at 10 ng/ml (p < 0.05). At the protein level, YAP increased while LATS1/2 decreased, indicating that LATS1/2 decreased, and YAP increased at higher mineralization levels when hBMSCs were cultured with 10 ng/ml of FGF2 for 7 days. Discussion: Consistent with our results, prior research has also indicated that lower concentrations of FGF2 enhance cell proliferation, thereby increasing the cell population for later osteogenic differentiation. However, excessive expansion can negatively affect differentiation. The mechanism of FGF2 regulation in stem cell osteogenic differentiation needs more exploration. Conclusion: Optimal concentrations and durations of FGF2 are critical for the osteogenic differentiation of hBMSCs. Moreover, it has been observed that mineralization correlates well with increasing YAP and decreasing LATS1/2 during osteogenic differentiation.