The purpose of this study was to investigate the effect of biaxial tensile strain on the osteogenic differentiation of rat bone marrow mesenchymal stem cells (rBMSCs) in vitro. The rBMSCs were isolated from tibia and femur of 4 weeks-old Sprague-Dawley (SD) rats. The rBMSCs were cultured in DMEM-LG complete culture medium and grew to subconfluence in the cell culture device for loading tensile strain. The biaxial tensile strain was applied to the rBMSCs for periods of 2, 4 and 6 hours every day, respectively, lasting 3 days. The amplitude of biaxial tensile strain applied to the rBMSCs were 1%, 2% and 5% respectively, at a frequency of 1 Hz. Unstrained rBMSCs were used as blank control (control group). The rBMSCs cultured with DMEM-LG complete culture medium containing 100 nmol/L β-Estradiol (E2) were used as positive control. The mRNA expression of alkaline phosphatase (ALP), collagen typeⅠ (ColⅠ), Runt-related transcription factor 2 (Runx2) and osteocalcin (OCN) was examined with real-time quantitative PCR and the protein expression of ALP, ColⅠ, Runx2 and OCN was detected with Western blot method. The results showed as follws: (1) The mRNA and protein expression of the ALP, ColⅠ, Runx2, OCN were significantly higher in rBMSCs of the E2 group than those in the control group (P＜0.05). (2) The mRNA and protein expression level of the ALP, Runx2 were higher markedly in the 1% tensile strain groups than those in the control group (P＜0.05), but lower than those in the E2 group (P＜0.05). (3) The mRNA and protein expression level of the ALP, ColⅠ, Runx2, OCN were significantly higher in the 2% tensile strain groups than those in the control group (P＜0.05), and the mRNA and protein expression level of ColⅠ and Runx2 in the group applied with 2% amplitude of tensile strain for 4 h/d was significantly higher than those in E2 group (P＜0.05). (4) The mRNA and protein expression level of the ALP, ColⅠ, Runx2 were significantly higher in the groups applied with 5% amplitude of tensile strain for 2 h/d or for 4 h/d than those in the control group (P＜0.05). In our study, E2 and mechanical stimulation played an important role in the regulation of differentiation of rBMSCs into osteoblasts, and the manner applied with the 2% amplitude of tensile strain for 4 h/d, lasting 3 days was an optimal stimulus for up-regulating the mRNA and protein expression of ALP, ColⅠ, Runx2, OCN of rBMSCs.
Bone marrow-derived mesenchymal stem cells (BMSCs) for repairing damaged heart tissue are a new kind of important treatment options because of their potential to differentiate into cardiomyocytes. We in this experiment investigated the effect of different electrical stimulation time on the expression of myocardial specificity gene and protein in rat bone marrow mesenchymal stem cells (rBMSCs) in vitro. The rBMSCs of second or third generation were randomly divided into three groups, i.e. electrical stimulation (ES) group, 5-Azacytidine (5-Aza) group and the control group. The rBMSCs in the ES groups with complete medium were exposed to 2 V, 2 Hz, 5 ms electrical stimulation for 0.5 h, 2 h, 4 h, and 6 h respectively every day for 10 days. Those in the 5-Aza group were induced by 5-Aza (10 μmol/L) for 24 h, and then cultured with complete medium for 10 days. Those in the control group were only cultured with complete medium, without any treatment, for 10 days. The rBMSCs' morphological feature in each group was observed with inverted phase microscope. The mRNA expression of myocyte-specific enhancer factor 2C (MEF-2C) and connexin 43 (Cx43) were examined with Real-Time quantitative PCR and the protein expression of MEF-2C, Cx43 were detected with Western Blot method. The results showed that the mRNA expression level of the MEF-2C, Cx43 and the protein expression level of MEF-2C, Cx43 were significantly higher in the ES group and 5-Aza group than those in the relative control group (P < 0.05). It suggests that electrical stimulation could play a part of role in the induction of the rBMSCs to differentiate into the cariomyocyte-like cells in vitro and the effectiveness of the electrical stimulation with 2 h/d had the best in our experiement. But the mechanism how electrical stimulation promotes the differentiation of rBMSC into cardiomyocyte is still unclear.