Many studies have reported that an electromagnetic field can promote osteogenic differentiation of mesenchymal stem cells. However, experimental results have differed depending on the experimental and environmental conditions. Optimization of electromagnetic field conditions in a single, identified system can compensate for these differences. Here we demonstrated that specific electromagnetic field conditions (that is, frequency and magnetic flux density) significantly regulate osteogenic differentiation of adipose-derived stem cells (ASCs) in vitro. Before inducing osteogenic differentiation, we determined ASC stemness and confirmed that the electromagnetic field was uniform at the solenoid coil center. Then, we selected positive (30/45 Hz, 1 mT) and negative (7.5 Hz, 1 mT) osteogenic differentiation conditions by quantifying alkaline phosphate (ALP) mRNA expression. Osteogenic marker (for example, runt-related transcription factor 2) expression was higher in the 30/45 Hz condition and lower in the 7.5 Hz condition as compared with the nonstimulated group. Both positive and negative regulation of ALP activity and mineralized nodule formation supported these responses. Our data indicate that the effects of the electromagnetic fields on osteogenic differentiation differ depending on the electromagnetic field conditions. This study provides a framework for future work on controlling stem cell differentiation.

BACKGROUND AND PURPOSEThe transcriptional co-activator with PDZ-binding motif (TAZ) is characterized as a transcriptional modulator of mesenchymal stem cell differentiation into osteoblasts and adipocytes. Moreover, increased TAZ activity in the nucleus enhances osteoblast differentiation and suppresses adipocyte development by interacting with runt-related transcription factor 2 (RUNX2) and PPARg, respectively. Therefore, it would be of interest to identify low MW compounds that modulate nuclear TAZ activity. EXPERIMENTAL APPROACHHigh-throughput screening was performed using a library of low MW compounds in order to identify TAZ modulators that enhance nuclear TAZ localization. The effects and molecular mechanisms of a TAZ modulator have been characterized in osteoblast and adipocyte differentiation. KEY RESULTSWe identified 2-butyl-5-methyl-6-(pyridine-3-yl)-3-[2′-(1H-tetrazole-5-yl)-biphenyl-4-ylmethyl]-3H-imidazo [4,5-b]pyridine] (TM-25659) as a TAZ modulator. TM-25659 enhanced nuclear TAZ localization in a dose-dependent manner and attenuated PPARg-mediated adipocyte differentiation by facilitating PPARg suppression activity of TAZ. In addition, TAZ-induced RUNX2 activity activation was further increased in osteoblasts, causing increased osteoblast differentiation. Accordingly, TM-25659 suppressed bone loss in vivo and decreased weight gain in an obesity model. After oral administration, TM-25659 had a favourable pharmacokinetic profile. CONCLUSION AND IMPLICATIONSTM-25659 stimulated nuclear TAZ localization and thus caused TAZ to suppress PPARg-dependent adipogenesis and enhance RUNX2-induced osteoblast differentiation in vitro and in vivo. Our data suggest that TM-25659 could be beneficial in the control of obesity and bone loss.

In this study, we found that, in the selected range, 1.5 MHz was the most effective frequency for inducing the osteogenic differentiation of hASCs.

We investigated whether transplantation of three-dimensional cell masses (3DCM) of human adipose-derived stromal cells (hASCs) cultured on a basic fibroblast growth factor-immobilized substrate improved hind limb functional recovery by stimulating angiogenesis in an immune-competent rat ischemic limb model. In vitro experiments confirmed that cells within 3DCMs differentiate toward the endothelial lineage one day after culture in normal medium. The therapeutic effect of 3DCMs was evaluated by transplanting hASCs, phosphate-buffered saline alone, and the 3DCM into rat ischemic hind limbs. Blood flow was enhanced in the ischemic hind limb in the 3DCM-injected group compared with the other groups. The ratio of human nuclear antigen (HNA) and hVEGF-positive cells was significantly higher in the 3DCM-injected group compared to hASC-injected group. Human VEGF was observed in most HNA-positive cells. Many hCD31 and hSMA-positive cells were observed in vessel-like structures in the 3DCM-injected group. The 3DCM transplantation improved cell retention and angiogenic effects compared with ASC transplantation. These findings suggest that transplantation of 3DCMs may be an effective stem cell therapy for hind limb ischemia.