Tetramethylpyrazine induces differentiation of human umbilical cord-derived mesenchymal stem cells into neuron-like cells in vitro

The present study evaluated the ability and optimal concentration of tetramethylpyrazine (TMP) to induce human umbilical cord-derived mesenchymal stem cells (hUMSCs) to differentiate into neuron-like cells in vitro. Human umbilical cords from full-term caesarean section patients were used to obtain hUMSCs by collagenase digestion after removal of the umbilical artery and vein. The surface antigen expression profile of cultured hUMSCs was monitored by flow cytometry. After amplification, cells of the 5th passage were divided into experimental groups A–C treated with TMP at 4.67, 2.34 and 1.17 mg/ml, respectively, in low glucose-Dulbecco's Modified Eagle's Medium (L-DMEM) (induction medium), while group D (control) was exposed to L-DMEM culture medium only. Differentiation of hUMSCs into neuron-like cells and morphological changes were observed every 0.5 h with an inverted phase contrast microscope for 6 h. After the 6-h induction period, proportions of cells expressing neuronal markers neuron-specific enolase (NSE), neurofilament protein (NF-H) and glial fibrillary acidic protein (GFAP) were detected by immunohistochemistry. The optimal concentration of TMP was selected on the basis of neuron-like cell positive rate. Western blotting and RT-polymerase chain reaction were applied to detect the expression of NSE, NF-H, and GFAP of the group of optimal concentration in each point-in-time. Results showed that most primary cells were adherent 12 h after seeding and first appeared as diamond or polygon shapes. Thereafter, they gradually grew into long spindle-shaped cells and finally in a radiating or swirling pattern. The cells maintained a strong proliferative capacity after continuous passage. Flow cytometry analysis of cultured hUMSCs at the 3rd, 5th and 10th passages expressed CD73, CD90 and CD105, but not CD11b, CD19, CD34, CD45 or human leukocyte antigen-DR. After 6 h of TMP treatment, typical neuron-like cells with many protrusions connected into a net-like pattern were observed in all experimental groups. These neuron-like cells were positive for NSE and NF-H, but negative for GFAP. Among the tested treatment groups, group A with TMP at 4.67 mg/ml had the highest expression of NSE and NF-H. By contrast, no change was found after induction in the control group. The mRNA expression of cells expressing neuronal markers as well as GAPDH was observed, with the relative NSE transcript levels of 0, 1.303±0.031, 1.558±0.025, 1.927±0.019 and 2.415±0.033 after 0, 1, 2, 4 and 6 h of treatment, respectively; the mRNA expression of NH-F was 0, 1.429±0.025, 1.551±0.024, 1.930±0.042 and 1.398±0.014 after 0, 1, 2, 4 and 6 h of treatment, respectively. There was no expression of GFAP before or after induction and all the groups showed high expression of GAPDH at each time point. Protein expression was also observed on cells expressing neuronal markers as well as GAPDH at each time point. The protein expression of NSE was 0, 0.717±0.097, 0.919±0.056, 1.097±0.143 and 1.157±0.055 in proper order; the protein expression of NH-F was 0, 0.780±0.103, 0.973±0.150, 1.053±0.107 and 0.753±0.094 in proper order. There was no expression of GFAP before or after induction, and all the groups showed high expression of GAPDH at each tested time point. Our results demonstrated that TMP can induce hUMSCs to differentiate into neuron-like cells effectively with the optimal concentration of 4.67 mg/ml. After induction, the NSE and NF-H of the neuron-like cells were positive, but the GFAP-2 was negative.