吉林大学学报(医学版)  2018, Vol. 44 Issue (05): 919-923

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于雷, 唐庚, 方芳, 李鑫, 龚守良, 王志成, 王剑锋
YU Lei, TANG Geng, FANG Fang, LI Xin, GONG Shouliang, WANG Zhicheng, WANG Jianfeng
低剂量辐射诱导小鼠睾丸细胞中IRE1α和XBP1 mRNA及其蛋白的表达
Expressions of IRE1α and XBP1 mRNA and proteins in mouse testis cells induced by low dose ionizing radiation
吉林大学学报(医学版), 2018, 44(05): 919-923
Journal of Jilin University (Medicine Edition), 2018, 44(05): 919-923
10.13481/j.1671-587x.20180506

文章历史

收稿日期: 2017-10-20
低剂量辐射诱导小鼠睾丸细胞中IRE1α和XBP1 mRNA及其蛋白的表达
于雷1 , 唐庚2 , 方芳2 , 李鑫2 , 龚守良2 , 王志成2 , 王剑锋3     
1. 吉林大学第二医院放疗科, 吉林 长春 130041;
2. 吉林大学公共卫生学院卫生部放射生物学重点实验室, 吉林 长春 130021;
3. 吉林大学中日联谊医院放疗科, 吉林 长春 130033
[摘要]: 目的: 检测小鼠睾丸细胞中肌醇需求酶1α(IRE1α)和X盒结合蛋白1(XBP1)mRNA和蛋白的表达,探讨IRE1-XBP1通路激活在低剂量辐射(LDR)诱导小鼠睾丸细胞内质网应激中的作用。方法: 50只健康雄性ICR小鼠,随机分为10组,经75 mGy X射线全身照射后不同时间(0、3、6、12和24h)及不同剂量(0、50、75、100和200 mGy)X射线照射后12 h处死,分别采用实时定量PCR法和Western blotting法检测小鼠睾丸细胞中IRE1α、Total-XBP1(T-XBP1)和Spliced-XBP1(S-XBP1)mRNA表达水平及蛋白表达强度。结果: 75 mGy X射线照射后0~24 h,小鼠睾丸细胞中IRE1α、T-XBP1和S-XBP1 mRNA(除了3 h时T-XBP1和S-XBP1 mRNA)表达水平均随时间延长而升高,并在6 h时达到峰值,而后逐渐降低;与0 h组比较,6、12和24 h组IRE1α mRNA、6和12 h组T-XBP1 mRNA及S-XBP1 mRNA表达水平均明显升高(P < 0.05或P < 0.01)。与0 h组比较,不同时间组IRE1α和S-XBP1蛋白表达强度升高,6和12 h组IRE1α蛋白表达强度升高最明显,24 h组S-XBP1蛋白表达强度升高最明显,而T-XBP1蛋白表达强度稍有降低。0~200 mGy照射后12 h,小鼠睾丸细胞中IRE1α、T-XBP1和S-XBP1 mRNA表达水平升高,75 mGyX射线照射后升高达峰值后逐渐降低,甚至降至0 mGy以下;与0 mGy组比较,75和200 mGy组小鼠睾丸细胞中IRE1α、75 mGy组小鼠睾丸细胞中T-XBP1和S-XBP1mRNA表达水平明显升高(P < 0.05或P < 0.01)。与0 mGy组比较,75 mGy组IRE1α和S-XBP1蛋白表达强度升高,75和200 mGy组小鼠睾丸细胞中S-XBP1蛋白表达强度升高最明显,而T-XBP1蛋白表达强度无明显变化。结论: LDR可诱导小鼠睾丸细胞中IRE1α和S-XBP1 mRNA表达水平和蛋白表达强度增加,从而激活内质网应激中的IRE1-XBP1信号通路。
关键词: 低剂量辐射    睾丸    内质网应激    肌醇需求酶1α    X盒结合蛋白1    
Expressions of IRE1α and XBP1 mRNA and proteins in mouse testis cells induced by low dose ionizing radiation
YU Lei1, TANG Geng2, FANG Fang2, LI Xin2, GONG Shouliang2, WANG Zhicheng2, WANG Jianfeng3     
1. Department of Radiotherapy, Second Hospital, Jilin University, Changchun 130041, China;
2. Key Laboratory of Radiobiology, Ministry of Health, School of Public Health, Jilin University, Changchun 130021, China;
3. Department of Radiotherapy, China-Japan Union Hospital, Jilin University, Changchun 130033, China
[Abstract]: Objective: To detect the expressions of inositol-requiring enzyme-1α(IRE1α) and X box-binding protein-1(XBP1) mRNA and proteins in mouse testis cells, and to explore the role of IRE1-XBP1 pathway activation in the endoplasmic reticulum stress induced by low dose radiation(LDR) in the mouse testis cells. Methods: A total of 50 heatly male ICR mice were randomly divided into 10 groups.After the mice were irradiated with 75 mGy X-ray in whole body at different time (0, 3, 6, 12, and 24 h) or with different doses(0, 50, 75, 100, and 200 mGy) of X-ray for12 h, the expression levels of IRE1α, T-XBP1 and S-XBP1 mRNA and proteins were measured by real-time quantitative PCR and Western blotting method, respectively. Results: The expression levels of IRE1α, T-XBP1 and S-XBP1 mRNA (except T-XBP1 and S-XBP1 mRNA at 3 h after irradiation) in the testis cells of the mice after irradiated with 75 mGy X-ray for 0-24 h were increased with the time prolongation, and reached to the maximum value at 6 h after irradiation, then were gradually decreased.Compared with 0 h group, the expression levels of IRE1α mRNA(6, 12, and 24 h after irradiation), T-XBP1 mRNA and S-XBP1 mRNA(6 and 12 h after irradiation) were significantly increased (P < 0.05 or P < 0.01); the expression intensities of IRE1α and S-XBP1 proteins were increased; the expression intensities of IRE1α (6 and 12 h after irradiation)and S-XBP1(24 h after irradiation) proteins were increased most significantly, but the expression intensity of T-XBP1 protein was slightly decreased. The expression levels of IRE1α, T-XBP1 and S-XBP1 mRNA in the testis cells of the mice after irradiated with 0-200 mGy for 12 h were increased, and reached to the maximum values after 75 mGy irradiation, then they were gradually decreased, even below 0 mGy. Compared with 0 mGy group, the expression levels of IRE1α mRNA in the testis cells of the mice in 75 and 200 mGy groups and the expression levels of T-XBP1 mRNA and S-XBP1 mRNA in 75 mGy group were significantly increased (P < 0.05 or P < 0.01); the expression intensities of IRE1α protein in 75 mGy group and S-XBP1 protein in 75 and 200 mGy groups were increased mostly, while the expression intensity of T-XBP1 protein had no obvious change. Conclusion: LDR can induce the increase of IRE1α and S-XBP1 mRNAs and proteins, and activate the IRE1-XBP1 pathway in endoplasmic reticulum stress.
Key words: low dose radiation     testis     endoplasmic reticulum stress     inositol-requiring enzyme 1α     X-box binding protein 1    

2011年日本福岛核电站泄漏事件后,辐射高本底环境是否影响人类健康再次引起广泛关注,其焦点是致癌问题。低剂量辐射(low dose radiation,LDR)的生物效应区别于高剂量诱导的损伤,但LDR诱导的效应仍不确定[1-2]。LDR诱导的损伤效应主要依据是线性无阈模型(linear no threhold, LNT),任何剂量的电离辐射都有致癌的可能性[3-4]。但也有学者[5-6]认为:LDR可诱导适应性反应和兴奋性效应。睾丸是辐射敏感的器官,极低剂量就能引起睾丸生精细胞凋亡[7-8],并且具有一定的剂量和时程-效应规律性。前期研究[9]显示:LDR能够诱导小鼠睾丸生精细胞内质网应激的发生,并且启动了凋亡信号通路。肌醇需求酶1(inositol-requiring enzyme-1, IRE1)是一种定位在内质网膜的具有激酶和核酸内切酶活性的双功能酶,可以被内质网应激激活,从而激活多条下游信号通路,其中X盒结合蛋白1(X box-binding protein-1, XBP1)是最早发现并且最受关注[10],是重要的内质网应激信号调节通路。本实验旨在通过检测LDR后小鼠睾丸细胞中肌醇需求酶1α(inositol-requiring enzyme-1α, IRE1α)、Total-XBP1(T-XBP1)、spliced XBP1(S-XBP1)mRNA及蛋白的表达,阐明IRE1-XBP1通路的激活在LDR诱导小鼠睾丸内质网应激信号调控中的作用。

1 材料与方法 1.1 实验动物和照射处理方法

50只健康雄性ICR小鼠,体质量(18±2)g,由吉林大学白求恩医学部实验动物中心提供,动物合格证号:SXCK(吉)203-00007,随机分为10组,每组5只。时程-效应实验为75 mGy照射后0、3、6、12和24 h处死动物,剂量-效应实验为0、50、75、100和200 mGy照射后12 h处死动物。应用国产固定式X射线深部治疗机(XSZ-220/20X型,丹东市康嘉仪器设备有限公司)进行全身照射,电压180 kV,电流15 mA,剂量率为12.5 mGy·min-1

1.2 主要试剂和仪器

TRIzol(美国Invitrogen公司),焦碳酸二乙酯(DEPC, 上海生工生物公司),反转录试剂盒(加拿大MBI Fermentas公司),IRE1α、T-XBP1、S-XBP1和GAPDH引物及real time PCR试剂盒(大连宝生物公司),ECL发光试剂盒, IRE1α、T-XBP1、S-XBP1(兔抗鼠多克隆)和GAPDH(山羊抗鼠多克隆)一抗(美国Santa Cruz公司),辣根过氧化酶标记的抗兔及抗山羊二抗(北京中杉金桥公司),其他试剂为国产分析纯;PCR仪(美国Perkin-Elmer公司),Mx3000P real time PCR仪(美国Stratagene公司),Mini-PROTEAN 3 Dodeca微型电泳槽(美国Bio-Rad公司)。

1.3 实时定量PCR法检测小鼠睾丸细胞中IRE1α、T-XBP1和S-XBP1 mRNA表达水平

IRE1α引物:5′-CATGAGGAACAAGAAGCACCACTA-3′(上游序列),5′-TCGCTGTGTGAAGTACTGAATGAA-3′(下游序列);T-XBP1引物:5′-TGGGCATTCTGGACAAGTT-3′(上游序列),5′-GAAAGGGAGGCTGGTAAGG-3′(下游序列);S-XBP1引物:5′-CTGAGTCCGAATCAGGTGCAG-3′(上游序列),5′-GTCCTAGGGAAGATGTTCTGG-3′(下游序列);GAPDH引物:5′-AAATGGTGAAGGTCGGTGTG-3′ (上游序列),5′- TGAAGGGGT-CGTTGATGG-3′(下游序列)。用TRIzol试剂提取各组睾丸细胞中总RNA后,采用反转录试剂盒合成互补DNA(cDNA),MX3000P real time PCR系统进行PCR扩增并分析。每组随机选择5只小鼠左侧睾丸样本,每个样本设3个复孔。每个样本的mRNA表达水平用各自内参照GAPDH表达水平进行标准化,以目的mRNA与GAPDH mRNA比值为该基因的相对表达水平,同时将对照组目的mRNA相对表达水平设定为1[8]

1.4 Western blotting法检测小鼠睾丸细胞中IRE1α、T-XBP1和S-XBP1蛋白表达强度

将上述5只小鼠右侧睾丸组织提取总蛋白并进行蛋白定量。每个样品取20 μg上样,SDS聚丙烯酰胺凝胶电泳时,浓缩胶采用60 V恒压,分离胶采用90 V恒压。蛋白转移至硝酸纤维膜上,膜经新鲜配制的封闭液(1×TBS,5%脱脂奶粉,0.05% Tween-20)常温封闭1 h,加入按一定比例稀释后的IRE1α、T-XBP1、S-XBP1和GAPDH一抗,4℃过夜,用含0.05% Tween 20的TBST洗涤2次,每次15 min,加入按一定比例稀释的辣根过氧化物酶(HRP)标记的二抗,37℃震荡孵育1 h;用ECL发光试剂盒进行发光,X射线片曝光显影,照相后进行分析,结果以条带灰度值表示蛋白表达强度。实验重复3次。

1.5 统计学分析

采用SPSS24.0统计软件进行统计学分析。小鼠睾丸细胞中IRE1α、T-XBP1和S-XBP1mRNA表达水平以x±s表示,组间比较采用单因素方差分析。以P < 0.05为差异有统计学意义。

2 结果 2.1 75 mGy X射线照射后不同时间小鼠睾丸细胞中IRE1α、T-XBP1和S-XBP1mRNA表达水平和蛋白表达强度

除3 h组小鼠睾丸细胞中T-XBP1和S-XBP1 mRNA表达水平降低外,其他各时间组IRE1α、T-XBP1和S-XBP1 mRNA表达水平均随时间延长而升高,并在6 h达到峰值,而后逐渐降低。与0 h组比较,6、12和24 h组小鼠睾丸细胞中IRE1αmRNA表达水平及6和12 h组T-XBP1、S-XBP1mRNA表达水平均明显升高(P < 0.05或P < 0.01);与0 h组比较,不同时间组IRE1α和S-XBP1蛋白表达强度增加,6和12 h组IRE1α蛋白表达强度及24 h组S-XBP1蛋白表达强度最高,而T-XBP1蛋白表达强度稍有降低。见表 1图 1

表 1 75 mGy X射线照射后不同时间各组小鼠睾丸细胞中IRE1α、T-XBP1和S-XBP1mRNA表达水平 Table 1 Expression levels of IRE1α, T-XBP1 and S-XBP1 mRNA in mouse testis cells at different time after 75 mGy irradiationin various groups
(n=5, x±s)
Group IRE1α mRNA T- XBP1 mRNA S-XBP1 mRNA
0 h 1 1 1
3 h 1.37±0.33 0.69±0.21 0.63±0.32
6 h 3.75±0.58* 2.37±0.20** 2.14±0.29*
12 h 3.13±0.36** 2.37±0.72* 1.58±0.16*
24 h 1.54±0.10** 2.18±0.17 0.91±0.10
*P < 0.05,** P < 0.01 vs 0 h group.
Lane 1:0 h group; Lane 2:3 h group; Lane 3:6 h group; Lane 4:12 h group; Lane 5:24 h group. 图 1 Western blotting法检测75 mGy X射线照射后不同时间各组小鼠睾丸细胞中IRE1α、T-XBP1和S-XBP1蛋白表达电泳图 Figure 1 Electrophoregram of expressions of IRE1α, T-XBP1 and S-XBP1proteins in mouse testis cells at different time after 75 mGy X-ray irradiation in various groups detected by Western blotting method
2.2 不同剂量X射线照射后小鼠睾丸细胞中IRE1α、T-XBP1和S-XBP1 mRNA表达水平和蛋白表达强度

0~200 mGy X射线全身照射后12 h,随照射剂量的增加,各组小鼠睾丸细胞中IRE1α、T-XBP1和S-XBP1 mRNA表达水平升高,75 mGy组升高达峰值后逐渐降低,甚至降至0 mGy组以下。与0 mGy组比较,75和200 mGy组小鼠睾丸细胞中IRE1αmRNA表达水平、75 mGy组T-XBP1和S-XBP1mRNA表达水平明显升高(P < 0.05或P < 0.01)。与0 h组比较,各剂量组小鼠睾丸细胞中IRE1α和S-XBP1蛋白表达强度升高,75 mGy组IRE1α蛋白表达强度、75和200 mGy组S-XBP1蛋白表达强度升高最明显,而T-XBP1蛋白表达强度无明显变化。见表 2图 2

表 2 不同剂量X射线照射后12 h各组小鼠睾丸细胞中IRE1α、T-XBP1和S-XBP1 mRNA表达水平 Table 2 Expression levels of IRE1α, T-XBP1 and S-XBP1 mRNA in mouse testis cells 12 h after irradiation with different doses of X-ray in various groups
(n=5, x±s)
Group IRE1α mRNA T-XBP1 mRNA S-XBP1 mRNA
0 mGy 1 1 1
50 mGy 1.34±0.11 1.42±0.46 1.39±0.27
75 mGy 3.13±0.36** 2.37±0.72* 1.58±0.16*
100 mGy 1.08±0.43 0.64±0.29 0.58±0.28
200 mGy 1.12±0.07* 0.85±0.36 0.83±0.40
*P < 0.05,** P < 0.01 vs 0 mGy group.
Lane 1:0 mGy group; Lane 2:50 mGy group; Lane 3:75 mGy group; Lane 4:100 mGy group; Lane 5:200 mGy group. 图 2 Western blotting法检测不同剂量X射线照射后12 h各组小鼠睾丸细胞中IRE1α、T-XBP1和S-XBP1蛋白表达电泳图 Figure 2 Electrophoregram of expressions of IRE1α, T-XBP1 and S-XBP1 proteins in mouse testis cells 12 h after different doses of X-ray irradiation in various groups detected by Western blotting method
3 讨论

随着核电和核技术应用越来越广泛,由此产生的辐射对人体健康的影响也日渐增加,尤其是LDR所引发的问题已经成为放射医学领域的研究热点。过去20多年来,LDR的生物学效应特别是导致生殖及遗传效应引起诸多研究者的关注。睾丸组织是辐射敏感器官,睾丸细胞群主要包括精原细胞、精母细胞、精子细胞和精子,以及Lydig和Sertoli细胞;其中,精原细胞及精母细胞对辐射敏感,而精子细胞和精子以及Lydig和Sertoli细胞则表现为辐射抵抗。因此,LDR诱导睾丸细胞的凋亡以精原细胞和精母细胞为主,很少涉及到精子细胞和精子以及Lydig和Sertoli细胞,这一点本研究前期的相关研究已经证实[7]。睾丸组织是辐射敏感器官,低至100 mGy的单次剂量照射损伤分裂中的精原细胞,导致生精障碍[11-12]。在放射治疗中睾丸组织分次照射生精小管损伤也会增加,主要可能是由于干细胞的重复激活导致的,对于生精上皮来说,多种低程度的遗传损伤甚至比高程度的损伤更严重[13]。因此,研究LDR对睾丸生殖损伤则有望提出相应的新理论和新机制。

内质网是真核细胞中蛋白质合成、折叠和分泌的重要细胞器,内质网内环境的稳定是实现内质网功能的基本条件, 因此内质网具有极强的内稳态体系。在氧化应激、缺氧和电离辐射等条件下,内质网内未折叠和错误折叠的蛋白明显增多,超出了内质网处理能力时,细胞会激活相关的信号级联反应来应对条件的变化,并恢复内质网良好的环境,这种情况被称为内质网应激,当应激发生程度较低时则细胞可以正常分裂,恢复生命;而当应激过载时则激活下游凋亡通路信号分子,诱导细胞凋亡。参与内质网应激的信号调控的3个重要的跨膜蛋白分别为:双链RNA依赖的蛋白激酶样内质网激酶(PKR-like ER kinase,PERK)、活化转录因子6(activating transcription factor-6,ATF6)和IRE1,均可与下游相应的分子构成独立的或互为网状的信号通路。IRE1被激活后能够切割下游XBP1 mRNA(T-XBP1)形成切割体mRNA(S-XBP1),进而导致该通路的激活[14-18]。本课题组前期研究显示:LDR能够诱导睾丸细胞发生内质网应激,并且激活了PERK-CHOP凋亡通路[8],但是内质网应激能否激活ATF6和IRE1通路尚不明确。本实验通过检测75 mGy照射后0~24 h和0~200 mGy照射后12 h各组小鼠睾丸细胞中IRE1α、T-XBP1和S-XBP1 mRNA表达水平及蛋白表达强度变化来判断发生内质网应激的可能,结果显示:75 mGy照射后0~24 h,随着时间延长,小鼠睾丸细胞中IRE1α mRNA表达水平及蛋白表达强度逐渐增加,分别在6和/或12 h达到峰值而后降低;T-XBP1和S-XBP1与IRE1α mRNA表达时程变化趋势相似,S-XBP1蛋白随时间延长逐渐增加,但是在照射后24 h表达最高,而T-XBP1蛋白表达有降低趋势但不明显;0~200 mGy照射后12 h,随着剂量的增加,小鼠睾丸细胞中IRE1α、T-XBP1和S-XBP1 mRNA表达水平的变化趋势基本一致,即75 mGy照射后其表达水平最高,而后逐渐减低甚至降至0 mGy组水平以下。IRE1α和S-XBP1蛋白表达强度分别在75和200 mGy照射后达最强,而T-XBP1蛋白表达强度无明显的变化。本研究结果表明:LDR能够诱导小鼠睾丸细胞中IRE1α mRNA表达水平及蛋白表达强度增加,进而切割T-XBP1 mRNA形成S-XBP1 mRNA。理论上T-XBP1 mRNA被切割后其表达减少,但是其表达也随着时间延长而增加,可能与辐射后时间不同有关[19-20]。本研究结果提示:LDR能够诱导小鼠睾丸细胞IRE1-XBP1内质网应激通路的激活。本结果为研究LDR诱导睾丸细胞凋亡机制提供了必要的补充,为电离辐射防护政策和法规的制订提供了实验数据。

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