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脑胶质瘤在治疗上主要采用手术加术后放射治疗,而部分不能手术或者拒绝手术的患者,单纯放疗可能是唯一的治疗方法。但是目前的治疗效果令人不甚满意,治疗失败的主要原因为局部肿瘤未控和复发。有研究表明,脑胶质瘤是干细胞疾病,干细胞的放射抵抗可能是治疗失败的根源[1-2]。因此,研究脑胶质瘤干细胞的放射敏感性及其可能的原因显得尤为重要。为此,本研究选用人脑胶质瘤细胞系U87,采用免疫流式分选技术,分选出人脑胶质瘤干细胞,在研究放射敏感性的基础上进一步研究DNA双链断裂的损伤修复。
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本实验中,由于U87单细胞悬液中加入了藻红蛋白标记的CD133抗体,经过流式细胞仪分选后,得到细胞膜表面有CD133表达的细胞(CD133+细胞)和无CD133表达的细胞(CD133-细胞),见图 1。
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U87细胞系在假照射条件下,CD133+和CD133-细胞的克隆形成率分别为5.33%和1.50%,前者显著高于后者(t=3.66,P < 0.01);4 Gy照射后,CD133+细胞的克隆形成率为4.50%,与假照射组相比差异无统计学意义(t=0.71,P > 0.05),CD133-细胞的克隆形成率为0.33%,与假照射组相比明显下降(t=2.91,P < 0.05)。实验结果表明,CD133+细胞的放射敏感性显著低于CD133-细胞。
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采用中性单细胞凝胶电泳实验初步研究分选后的干细胞及非干细胞在0 Gy和4 Gy照射后0.5、6、24 h的DNA双链断裂情况。DNA双链断裂水平通过尾力矩表示。实验中发现,假照射条件下,CD133+和CD133-细胞的DNA双链断裂程度差异无统计学意义(t=1.67,P > 0.05);4 Gy照射后0.5 h,两种细胞的DNA双链断裂程度均明显增加,但损伤程度差异无统计学意义(t=1.44,P > 0.05);4 Gy照射后6、24 h,CD133+细胞的DNA双链断裂程度与CD133-细胞相比均有下降(t=5.31和8.09,P < 0.01),其中,CD133-细胞在照射后24 h的DNA双链断裂程度接近假照射时水平(t=1.56,P > 0.05),而CD133+细胞的DNA双链断裂程度进一步减小,至24 h时已经远远低于假照射时的水平(t=16.28,P < 0.01)。实验结果表明,CD133+和CD133-细胞在4 Gy照射后的DNA损伤均有一定程度的修复,而前者的修复能力远远高于后者(表 1,图 2)。
细胞 样本数 假照射 照后0.5h 照后6h 照后24h CD133- 150 1.52±0.14 5.36±0.26 2.31±0.14 1.91±0.22 CD133+ 150 1.26±0.07 4.99±0.04 1.23±0.15 0.17±0.02 表 1 CD133+和CD133-脑胶质瘤U87细胞在4 Gy X射线照射后不同时间DNA尾力矩的测定结果(
)$\bar x \pm s$ 实验中进一步采用γ-H2AX作为辐射后DNA双链断裂损伤的观察指标。实验结果发现,假照射条件下,CD133+和CD133-细胞均有γ-H2AX灶的低水平表达(t=0.28,P > 0.05);4 Gy照射后0.5 h,CD133+和CD133-细胞的γ-H2AX灶表达水平显著上升(t=16.37和12.48,P < 0.01),而两者间差异无统计学意义(t=0.12,P > 0.05),且在照射后6 h两种细胞的γ-H2AX灶的表达仍维持在较高的水平,但两者间差异仍无统计学意义(t=0.99,P > 0.05);照射后24 h,两种细胞的γ-H2AX灶的表达水平明显下降(t=8.64和5.02,P < 0.01),且CD133+细胞的下降程度明显大于CD133-细胞(t=4.99,P < 0.01)。这种结果可能与CD133+细胞的修复能力远高于CD133-细胞有关(表 2,图 3)。
细胞 样本数 假照射 照后0.5h 照后6h 照后24h CD133+ 100 11.76±2.78 74.09±2.60 60.52±9.30 41.39±2.75 CD133- 100 10.39±3.99 74.59±3.25 70.36±3.48 56.82±1.42 表中,γ-H2AX:磷酸化组蛋白H2AX。 表 2 CD133+和CD133-脑胶质瘤U87细胞在4 Gy X射线照射后不同时间γ-H2AX灶的表达率(
)$\bar x \pm s$ -
同源重组是哺乳动物DNA双链断裂重要的修复方式,Rad51荧光灶被认为是同源重组修复的标志[4]。本研究中CD133+和CD133-细胞在假照射时的Rad51灶表达率差异无统计学意义(t=2.41,P > 0.05);4 Gy照射后0.5 h内就能检测到Rad51灶的高表达(t=36.65和32.80,P < 0.01),而这两种细胞之间的表达率差异无统计学意义(t=1.12,P > 0.05);照射后6 h,CD133+细胞Rad51灶的表达率与照射后0.5 h相比仍维持在较高水平(t=1.91,P > 0.05),而CD133-细胞则下降(t=20.64,P < 0.01),两种细胞之间的表达率差异有统计学意义(t=22.88,P < 0.01);照射后24 h,CD133+细胞Rad51灶的表达率与CD133-细胞相比差异有统计学意义(t=12.43,P < 0.01),而CD133+细胞的Rad51灶的表达率与照射后6 h相比无明显变化(t=0.47,P > 0.05),即照射后6~24 h,CD133+细胞的Rad51灶的表达率未见明显变化,CD133-细胞的Rad51灶的表达率与照射后6 h相比继续降低(t=2.86,P < 0.05)。这一结果表明CD133+和CD133-细胞在辐照初期均有修复,但随着时间的增加,CD133+细胞在24 h内仍能保持在较高的修复水平,而CD133-细胞的修复能力持续下降(表 3,图 4)。
细胞 样本数 假照射 照后0.5h 照后6h 照后24h CD133+ 100 24.48±0.43 72.72±2.98 69.54±1.11 68.29±2.43 CD133- 100 22.56±0.67 68.61±2.13 37.93±0.83 33.14±1.46 表中,Rad51:一种同源重组修复蛋白。 表 3 CD133+和CD133-脑胶质瘤U87细胞在4 Gy X射线照射后不同时间Rad51灶的表达率(
)$\bar x \pm s$
CD133+ U87人脑胶质瘤干细胞放射敏感性和DNA双链断裂损伤修复的实验研究
CD133 positive U87 glioma stem cell radiosensitivity and DNA double-strand break repair
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摘要:
目的 探讨CD133+ U87人脑胶质瘤干细胞放射敏感性及DNA双链断裂损伤修复的情况。 方法 选择人脑胶质瘤U87细胞系,采用免疫流式分选技术分选出CD133+、CD133-细胞;采用克隆形成实验研究细胞的放射敏感性;采用中性单细胞凝胶电泳实验检测4 Gy X射线垂直照射后不同时间点的DNA双链断裂;采用间接免疫荧光技术检测不同时间点磷酸化组蛋白H2AX(γ-H2AX)荧光灶、Rad51(一种同源重组修复蛋白)荧光灶的表达。 结果 假照射条件下,CD133+细胞克隆的形成率明显高于CD133-细胞(t=3.66,P < 0.01);CD133+细胞经4 Gy照射后的克隆形成率无明显变化(t=0.71,P > 0.05),而CD133-细胞经4 Gy照射后的克隆形成率下降(t=2.91,P < 0.05)。4 Gy照射后0.5 h,CD133+、CD133-细胞间尾力矩差异无统计学意义(t=1.44,P > 0.05),照射后6、24 h,CD133+细胞尾力距下降程度大于CD133-细胞(t=5.31和8.09,P < 0.01);照射后0.5、6 h,CD133+、CD133-细胞间γ-H2AX灶的表达率差异均无统计学意义(t=0.12和0.99,P > 0.05),照射后24 h,CD133+细胞的γ-H2AX灶的表达率下降程度大于CD133-细胞(t=4.99,P < 0.01);照射后0.5 h,CD133+、CD133-细胞间Rad51灶的表达率差异无统计学意义(t=1.12,P > 0.05),照射后6、24 h,CD133-细胞的Rad51灶的表达率与CD133+细胞相比明显下降(t=22.88和12.43,P < 0.01),而CD133+细胞无明显变化。 结论 CD133+ U87人脑胶质瘤干细胞具有放射抵抗性,可能与其照射后DNA双链的断裂修复能力较高有关。 Abstract:Objective To explore the radiosensitivity and DNA double-strand break repair of CD133+ U87 glioma stem cell. Methods CD133+ and CD133- cells were isolated from glioma U87 cell lines by flow cytometry sorter system. After irradiated vertically by 4 Gy X-rays, the radiosensitivity of cells was determined by clonogenic assay. The radiation-induced DNA double-strand break repair of CD133+ and CD133- cells was determined by the neutral comet assay, and the expression of phosphorylated histone H2AX (γ-H2AX) and Rad51 foci were measured by immunofluorescence. Results The clone forming rate of CD133+ cells was higher than CD133- cells (t=3.66, P < 0.01) with no radiation. The clone forming rate of CD133+ cells irradiated by 4 Gy X-rays has no significant changes compared to that of the non-irradiation cells(t=0.71, P > 0.05), but for CD133- cells, it decreased compared to non-irradiation cells(t=2.91, P < 0.05). The tailmoment between CD133+ cells and CD133- cells had no difference at 0.5 h after irradiation (t=1.44, P > 0.05); the tailmoment of CD133+ cells was lower than CD133- cells at 6 and 24 h after irradiation, respectively(t=5.31 and 8.09, P < 0.01). There was no significant difference in the expression of γ-H2AX foci between CD133+ and CD133- cells at 0.5 and 6 h after irradiation(t=0.12 and 0.99, P > 0.05), γ-H2AX foci of CD133+ cells was significantly decreased compared to CD133- cells at 24 h after irradiation(t=4.99, P < 0.01). For Rad 51 foci, there was no difference between CD133+ and CD133- cells at 0.5 h after irradiation(t=1.12, P > 0.05). The expression of Rad 51 foci of CD133- cells was decreased compared to that of CD133+ cells at 6 and 24 h after irradiation, respectively (t=22.88 and 12.43, P < 0.01). And the expression of Rad51 foci of CD133+ cells had no significant changes at 6-24 h after irradiation. Conclusions Glioma stem cells is more radioresistive than glioma non-stem cells. The probable mechanism is that the DNA double-strand break repair capacity of glioma stem cells is more powerful than non-stem cells. -
Key words:
- Glioma /
- Stem cells /
- Radiation tolerance /
- DNA repair /
- Histones /
- Rad51 recombinase
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表 1 CD133+和CD133-脑胶质瘤U87细胞在4 Gy X射线照射后不同时间DNA尾力矩的测定结果(
)$\bar x \pm s$ 细胞 样本数 假照射 照后0.5h 照后6h 照后24h CD133- 150 1.52±0.14 5.36±0.26 2.31±0.14 1.91±0.22 CD133+ 150 1.26±0.07 4.99±0.04 1.23±0.15 0.17±0.02 表 2 CD133+和CD133-脑胶质瘤U87细胞在4 Gy X射线照射后不同时间γ-H2AX灶的表达率(
)$\bar x \pm s$ 细胞 样本数 假照射 照后0.5h 照后6h 照后24h CD133+ 100 11.76±2.78 74.09±2.60 60.52±9.30 41.39±2.75 CD133- 100 10.39±3.99 74.59±3.25 70.36±3.48 56.82±1.42 表中,γ-H2AX:磷酸化组蛋白H2AX。 表 3 CD133+和CD133-脑胶质瘤U87细胞在4 Gy X射线照射后不同时间Rad51灶的表达率(
)$\bar x \pm s$ 细胞 样本数 假照射 照后0.5h 照后6h 照后24h CD133+ 100 24.48±0.43 72.72±2.98 69.54±1.11 68.29±2.43 CD133- 100 22.56±0.67 68.61±2.13 37.93±0.83 33.14±1.46 表中,Rad51:一种同源重组修复蛋白。 -
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