The nuclear localization of MGF receptor in osteoblasts under mechanical stimulation

Mechano-growth factor (MGF) has emerged as an important mechanosensitive player in bone repair, but understanding of MGF function is hampered by the fact that MGF receptor and the underlying pathways remain unknown. In this study, fluorescein isothiocyanate (FITC)-labeled MGF-Ct24E (FITC-MGF) was used to determine the subcellular localization of MGF receptor in osteoblasts. After the primary osteoblasts were exposed to stretch with the strain at 10 %, and/or loaded with 50 ng/ml exogenous MGF-Ct24E, cells were incubated with the different concentrations of FITC-MGF (0.01, 0.1, and 1 mg/ml) followed by flow cytometry and laser scanning confocal microscope analysis. Our results showed that the fluorescence intensity and cell population internalizing FITC-MGF increased with the concentration of FITC-MGF. And all the cells were labeled with fluorescence at 1 mg/ml. Notably, FITC-MGF had nuclear localization when osteoblasts were exposed to stretch and/or 50 ng/ml MGF-Ct24E added, compared to the evident cytoplasmic localization in the static culture group. The nuclear localization of FITC-MGF in response to mechanical loading was found to associate with high expression of proliferating cell nuclear antigen, suggesting MGF and its receptor could serve as potential messengers that replay information in nuclei to control cell proliferation.