摘要目的：探讨超顺磁性氧化铁(SPIO)及绿色荧光蛋白(GFP)双标的骨髓间充质干细胞（BMSCs）向类神经元样分化的生物学活性及MRI信号强度(SI)变化特点。方法将GFP-BMSCs体外标记不同浓度SPIO(A~D组铁浓度分别为25、50、75、100μg/ml, E组未标SPIO为对照组)，普鲁士蓝染色检测各组SPIO标记率，原子分光光度计测量铁含量，CCK8实验检测细胞增殖率，PCR检测细胞周期；A~E组均将1×108个细胞置试管内行MR T2*WI、磁敏感加权成像（SWI），测量2个序列图像SI变化并进行比较，找出最佳成像浓度组与E组共同诱导类神经元样分化，72 h行茜素红、骨钙素及尼氏、神经元特异性核蛋白（NeuN）染色、神经丝蛋白200染色，实时定量PCR检测β-Ⅲ微管蛋白(tub3)、巢蛋白(Nestin)、神经元特异性烯醇化酶(NSE)、微管相关蛋白2（MAP-2)、突触结合蛋白(Syt1)RNA表达量，比较两组细胞染色阳性率及RNA表达量，最终采用SWI分析SI差异。多组间比较用单因素方差分析，多组间两两比较用LSD-t检验；两组均数比较采用独立样本t检验。结果 A~D组SPIO标记率为100%，A~E组细胞内铁含量分别为(14.36±7.61)、(21.73±3.42)、(30.54±8.73)、(33.65±9.62)、(2.31±0.32) pg/cell，A~D组均较E组高(F=3.852，P=0.003)，C组与D组间差异无统计学意义(P=0.267)；CCK8实验A值D组最小(3.18±0.46)；A~E组SI变化SWI序列均较T2*WI序列低，差异均有统计学意义。SWI序列SI变化C组（145.89±14.31）与D组（127.37±12.21）差异无统计学意义(P=0.064)，其余各组两两比较差异均有统计学意义(P值均<0.01)。C组SWI和T2*WI SI衰减百分率分别为48.15%、69.34%。C、E 2组诱导向类神经元样分化，非神经元细胞比例、尼氏染色细胞阳性率比较差异均无统计学意义(P值均>0.05)。tub3、Nestin、NSE均较未诱导分化前表达量明显增高(P值均<0.01)，C组诱导分化前、后SWI序列成像SI差异无统计学意义(t=1.26, P=0.236)。结论 SPIO、GFP双标未影响BMSCs的生物学活性，可诱导分化为类神经元样细胞，且随着细胞内SPIO浓度的升高MR信号降低，SWI序列最敏感，诱导前后SWI信号强度未见变化。

abstractsObjective To explore the biological activities and the MR imaging signal intensities (SIs) characteristics of differentiations of neural-like cells induced by superparamagnetic iron oxide (SPIO) <br> and green fluorescent protein (GFP) double-labeled bone marrow-derived mesenchymal stem cells (BMSCs) in vitro. Methods GFP-BMSCs were labeled with different concentrations of SPIO in vitro (the concentration of the A, B, C and D group was 25, 50, 75 and 100 ug/ml, respectively;the E group without labels of SPIO served as the control group). The Prussian blue stainings were used to detect the labeling rates of SPIO. The iron contents of cells were measured by atomic absorption spectrometer. The CCK8 experiments were used to detect the cell proliferation rates. The cell cycles were detect by PCR. Each of the A-E groups had a test tube with 1 × 108 cells. All test tubes underwent T2* weighted imaging (T2*WI) and susceptibility weighted imaging (SWI) in a MR imaging scanner. The optimal group was defined by comparing the measurements of SIs between T2*WI and SWI. The optimal group and the E group together induced the differentiations of osteogenesis and neural-like cells. The stainings of alizarin red, osteocalcin and Nissl, NeuN, and NF-200 were performed at 72 hours. Real-time quantitative PCR was used to detect the expression levels of RNA in tub3, nestin, NSE, MAP-2 and Syt1. The positive staining rates and the expression levels of RNA were compared between the two groups. Finally, SWI was used to analyse the changes of SIs. One-way analysis of variance (ANOVA) was used to the multi-group comparison. Using least significant difference (LSD) test to analyse the comparisons between the multi-groups. Results The labeling rates of the A-D groups were 100%. The iron contents of cells in the A-E groups were (14.36 ± 7.61), (21.73±3.42), (30.54±8.73), (33.65±9.62), and (2.31±0.32) pg/cell, respectively. The iron contents of cells in the A-D groups were significantly higher than those in the E group ( F=3.852, P=0.003). There was no significant difference between the C and D groups (P=0.267). In all groups, the D group had the lowest OD value in the CCK-8 experiments (3.18 ± 0.46). In the A-E groups, the changes of SIs in SWI were significantly lower than those in T*2 WI. There was no significant difference in SIs of SWI between the C group (145.89±14.31) and the D group (127.37±12.21). Except the comparison between the group C and D, the comparisons between all the groups had significant differences (P<0.001). The percentages of SI attenuations in SWI and T*2 WI were 48.15% and 69.34%, respectively. The proportions of non-neurons cells and the positive rates of Nissl's stainings in group C and E had no significant differences (P>0.05). The expression levels of tub3, nestin and NSE were significantly higher before than after induced differentiations (P<0.01). SIs of SWI had no significant difference between before and after induced differentiations in the C group (t=1.26, P=0.236). Conclusions SPIO and GFP double-labeled BMSCs can induce neural-like cells without influencing biologic activities. MR SIs are decreased by the increase of SPIO concentrations in cells. SWI was the most sensitive sequence. The SIs of SWI has no differnce between before and after induced differentiations.