Abstract
目的
研究垂体肿瘤转化基因(PTTG1)在系统性硬化症(SSc)中的表达及其对成纤维细胞的作用。
方法
收集皮肤活检组织,其中SSc患者组21例,正常组22例。分别应用实时荧光定量聚合酶链式反应法(Real-time PCR)检测皮肤组织中PTTG1基因表达水平;应用免疫组化方法检测皮肤组织中PTTG1蛋白表达水平;应用小干扰RNA(siRNA)降低成纤维细胞中PTTG1基因表达,通过Real-time PCR方法检测细胞中PTTG1及与细胞纤维化密切相关的几个基因α-SMA、COL1A1、COL1A2、COL3A1的表达变化;通过细胞实时增殖检测系统检测细胞增殖。
结果
与正常对照相比,SSc患者皮肤组织中PTTG1的表达水平明显升高,差异具有统计学意义(P < 0.05);与正常对照相比,SSc患者皮肤组织中阳性细胞增多,PTTG1蛋白表达明显升高;原代皮肤成纤维细胞中PTTG1表达水平和α-SMA、COL1A1、COL1A2、COL3A1均存在正相关,差异具有统计学意义(R2= 0.8192,P < 0.05;R2=0.6398,P < 0.05;R2=0.316,P < 0.05;R2=0.3723,P < 0.05);同时,原代皮肤成纤维细胞中PTTG1干扰后,细胞增殖被显著抑制,纤维化相关基因(COL1A1、COL1A2、PAI-1)表达下降,胶原蛋白的基因表达降低。
结论
SSc患者中存在PTTG1过度表达,干扰PTTG1可降低成纤维细胞活性,提示PTTG1与SSc纤维化程度密切相关。
Keywords: 垂体肿瘤转化基因, 系统性硬化症, 纤维化, 细胞增殖, 成纤维细胞
Abstract
Objective
To investigate the expression of tumor-transforming gene-1 (PTTG1) in systemic sclerosis (SSc) and its role in fibrosis.
Methods
Skin biopsy samples were collected from 21 patients with SSc and 22 patients with healthy skin for detecting the mRNA and protein expressions of PTTG1 using real-time PCR (RT-PCR) and immunohistochemistry, respectively. In cultured primary human dermal fibroblasts, PTTG1 expression was knocked down via RNA interference (siRNA), and the mRNA expression levels of PTTG1 and the fibrosis-related genes α-SMA, COL1A1, COL1A2, and COL3A1 were detected using RT-PCR; the proliferation of the cells was assessed using a real-time cell proliferation detection system.
Results
Compared with those in normal skin samples, the mRNA and protein expressions of PTTG1 increased significantly in the skin tissue of patients with SSc (P < 0.05). In cultured primary skin fibroblasts, the expression of PTTG1 mRNA was positively correlated with those of α-SMA (R2=0.8192, P < 0.05), COL1A1 (R2=0.6398, P < 0.05), COL1A2 (R2=0.316, P < 0.05) and COL3A1 mRNAs (R2=0.3727, P < 0.05). Interference of PTTG1 expression significantly inhibited the cell proliferation, obviously lowered the expressions of fibrosis-related genes, and down-regulated the expression of collagen in the fibroblasts.
Conclusion
PTTG1 is highly expressed in skin tissues of patients with SSc, and PTTG1 knockdown can reduce the activity of the dermal fibroblasts, suggesting a close correlation of PTTG1 with fibrosis in SSc.
Keywords: tumor-transforming gene-1, systemic sclerosis, fibrosis, cell proliferation, fibroblasts
系统性硬化症(SSc)又称为硬皮病,是一种以皮肤和内脏器官纤维化为主要特征的慢性自身免疫性疾病,其主要特征是出现弥漫性或者局限性的皮肤增厚和纤维化[1-2]。SSc的发病率在世界范围内为2.3~22.8/100万人年,患病率存在性别差异,男女发生率之比约为1:4[3-4]。SSc虽然发病率较低,但经常累及一个或者多个内脏器官,加之疾病的发展变化较快,导致生存率较低,与肿瘤相当[5-8]。SSc病因复杂,发病机制不明确,缺乏针对SSc的有效治疗方案。
已有研究认为,SSc是在遗传因素及环境因素等原因诱发下发生,表现为微血管内皮发生病变,免疫系统过度活化,细胞外基质(ECM)过度沉积,导致患者心、肺、肾、消化道等末端器官过度病理性纤维化,最终死于内脏器官衰竭[9-12]。ECM的主要组成成分为胶原蛋白,包括胶原纤维Ⅰ、Ⅲ、Ⅳ和Ⅵ,此外还包含蛋白多糖、金属蛋白酶组织抑制剂-1(TIMP-1)、TIMP-2等[13-14]。人体合成胶原蛋白的最主要细胞是肌成纤维细胞,肌成纤维细胞在转化生长因子(TGF-β)、结缔组织生长因子(CTGF)等细胞因子影响下由成纤维细胞活化产生[15-17]。肌成纤维细胞分泌细胞外基质蛋白(包括胶原、纤粘连蛋白等),细胞外基质成分在结缔组织中的持续合成和累积导致纤维化的发生[18],故肌成纤维细胞的活性及数量在很大程度上决定组织器官纤维化的进程。本课题组前期对SSc患者皮肤成纤维细胞体外培养发现,与正常人皮肤成纤维细胞相比,SSc患者皮肤成纤维细胞产生更多的胶原蛋白及TGF-β等促纤维化因子[19]。明确相关基因在成纤维细胞活化及纤维化发生、发展中的作用,对于揭示SSc发病机制、探寻有效的治疗方案具有重要意义。
垂体肿瘤转化基因1(PTTG1)是一种参与细胞周期调节的多功能蛋白,可诱导细胞转化、参与细胞修复及基因表达调控。目前已知PTTG在胚胎发育、细胞增殖与分化、细胞周期调节、免疫、病毒感染等一系列生理活动中具有重要的调控作用[20-21]。研究表明PTTG1不仅可作为胃癌、肾上腺皮质癌的标志物[22-23],同时可作为银屑病、脂溢性角化病和皮肤肿瘤等与细胞周期调节相关的增生性皮肤疾病的标记物[24],本课题组前期研究发现丹酚酸B(SAB)可抑制成纤维细胞活化、抑制博来霉素诱导的硬皮病小鼠纤维化,具有抗硬皮病纤维化的作用。此外,本团队通过RNA-seq筛选及Real-time PCR验证发现,SAB可降低硬皮病成纤维细胞中PTTG1基因表达。上述结果提示,PTTG1可能在硬皮病纤维化以及药物抗纤维化中发挥重要作用[25-26]。但PTTG1在硬皮病及纤维化中的作用及机制尚未阐明。因此,本研究通过对PTTG1在SSc患者中的表达水平进行检测,观察PTTG1对成纤维细胞增殖及纤维化相关基因表达的影响,以期对PTTG1在成纤维细胞活化继而引发SSc皮肤纤维化过程中的具体作用进行评估,为SSc的发病机制研究提供基础材料。
1. 资料和方法
1.1. 材料
选取2009年1月~2015年12月在复旦大学附属华山医院皮肤科就诊的硬皮病患者21例,所选患者均符合美国风湿病学会制定的SSc评判标准,采样部位为患病部位,主要为四肢和腹部;同期选择22例无自身免疫性疾病及其他任何皮肤疾病病史的正常人的皮肤组织作为正常对照,正常人均来源于该医院的外伤等手术患者,选取采样部位为手术切除部位边缘部分,且与SSc患者采样部位对应。入组志愿者均签署由医院伦理委员会批准的患者知情同意书。本实验经复旦大学生命科学学院伦理审查委员会审批同意。原代皮肤成纤维细胞为本实验室前期皮肤活检组织中培养所得。
1.2. 主要仪器及试剂
4 ℃冷冻离心机(5415R);0.2~1.5、1~20、20~100、100~1000 μL移液器(Eppendorf);Milli-Q纯水仪;PTTG1抗体;高通量组织研磨仪(上海万柏);ND-1000 NanoDrop紫外分光光度计(Thermo Scientific);Prism 7900 Detector System;RNA逆转录试剂(High Capacity cDNA Reverse Transcription Kit)(Applied Biosystems);0~10、10~200、100~1000 μL枪头;1.5 mL EP管(Axygen);MCO-18AIC CO2细胞培养箱(三洋);细胞培养板(Thermo Scientific);DM1L倒置显微镜(Leica);PCR仪(Veriti 96 well Thermal cycler)(ABI)细胞实时分析检测系统(xCELLigence)系统(Roche);10 x PBS(上海双螺旋);Trizol,DEPC(sigma);RNase Zap(Ambion);氯仿、异丙醇、无水乙醇(上海试剂);DNase free水;丙烯酰胺/双丙烯酰胺;硫酸铵(APS);20% Tween20(上海生工);SYBR Premix ExTaq(Takara);DMEM;胎牛血清;0.25% EDTA-Trypsin(Gibco);Lipofectamine RNAiMAX(Invitrogen);siPTTG1(上海吉玛制药技术);Sircol assay试剂盒(Biocolor);多功能酶标仪(Bio-Rad)。
1.3. 方法
1.3.1. 皮肤组织免疫组织化学染色
采用免疫组化方法检测SSc患者与正常人皮肤组织切片中PTTG1蛋白表达水平。具体方法为:组织切片经过二甲苯、无水乙醇和95%乙醇等试剂脱水,将修复盒盛满柠檬酸抗原修复缓冲液(pH 6.0,99.0 ℃,20 min),将组织切片放入,于微波炉内进行抗原修复。中火至沸后断电间隔10 min中低火至沸,此过程中应防止缓冲液过度蒸发,切勿干片。自然冷却后将玻片置于PBS(pH=7.4)中在脱色摇床上晃动洗涤3次,5 min/次。采用3 %的过氧化氢阻断内源性过氧化物酶(10 min),水洗及PBS溶液冲洗。切片稍甩干后在圈内滴加3% BSA均匀覆盖组织,室温封闭30 min。轻轻甩掉封闭液,在切片上滴加PBS按一定比例配好的一抗(按1:500稀释),切片平放于湿盒内4 ℃孵育过夜。玻片置于PBS(pH=7.4)中在脱色摇床上晃动洗涤3次,5 min/次。切片稍甩干后在圈内滴加与一抗相应种属的二抗覆盖组织,避光室温孵育50 min。PBS洗3次,5 min/次;DAB显色,苏木精复染,各级梯度酒精脱水,二甲苯透明,中性树脂封片。切片于尼康倒置荧光显微镜下观察并采集图像。
1.3.2. 细胞培养
原代皮肤成纤维细胞培养采用含10%胎牛血清(FBS)的DMEM培养基,于37 ℃、5% CO2的培养箱中进行培养。
1.3.3. 总RNA提取
(1)组织:称取10~20 mg组织,加入300 μL Buffer RBC(使用前检查是否加入β-巯基乙醇),用组织匀浆器将组织破碎均匀。加入与Buffer RBC等体积的异丙醇,涡旋振荡15 s,把吸附柱装好,转移上述的液体(包括沉淀)于吸附柱中。1000 r/min离心1 min。将废液倒掉,把吸附柱装回套管,加入500 μL Buffer RW1(使用前检查是否加入无水乙醇),1000 r/min离心1 min,弃掉废液。把柱子装回,加入50 μLDNase Ⅰ mix(48 μLBuffer DNase + 2 μLDNase Ⅰ),室温放置8 min。加入500 μLBuffer RW1(已用无水乙醇稀释)至柱子上。1000 r/min离心1 min。倒弃废液,装回套管,加入500 μL Buffer RW2至柱子上,1000 r/min离心1 min。重复上述步骤1次。倒弃废液,把柱子装回套管,12 000 r/min离心5 min。而后将柱子装在新的无菌1.5 mL离心管中。加入30 μLBuffer RE至柱子的膜中央。放置3 min,12 000 r/min离心1 min,得到RNA溶液,短期保存4 ℃,长期保存-80 ℃。
使用NanDrop 2000超微量分光光度计检测样品RNA的浓度和纯度。
1.3.4. 实时定量PCR(Real-time PCR)检测基因表达水平
(1)反转录:按TakaRa公司反转录试剂盒说明书(NO. RR047A)操作。去除基因组DNA:按表 1成分于冰上配制反应混合液,为了保证反应液配制的准确性,进行各项反应时,应先按反应数+2的量配制Master Mix,然后再分装到每个反应管中,最后加入RNA样品(使用500 ng左右的Total RNA)。混匀,于42 ℃反应2 min,后置于冰上进行后续的反转录。在冰上配制反应液。按表 2成分配置反转录反应体系,分装10 μL到每个反应管中。轻柔混匀后立即进行反转录反应;(2)Real-time PCR:按照SYBR Premix ExTaq(Takara)说明书所述的步骤配制10 μL Real-time PCR反应体系,反应体系如表 3所示,反应程序如表 4所示,引物序列如表 5所示。使用ABI7500 System检测,用相对定量的方法进行统计分析。
1.
去除基因组DNA反应体系
Reaction system for genomic DNA removal
Reagents | Volume (μL) |
5*gDNA Eraser Buffer | 2.0 |
gDNA Eraser | 1.0 |
Total RNA | 500 |
RNase Free H2O | Up to 10 |
2.
反转录反应体系
Reaction system of RT-PCR
Reagents | Volume (μL) |
Reaction mixture form step1 | 10.0 |
Prime script RT enzyme mix 1 | 1.0 |
RT primer mix | 1.0 |
5 x prime script buffer 2 (for real time) | 4.0 |
RNase Free dH2O | 4.0 |
Total | 20.0 |
3.
Real-time PCR反应体系
Reaction system of real-time PCR
Reagents | Volume (μL) |
SYBR premix Ex TaqrM (x2) | 5.0 |
Primers (2 g·mol/L) 0.2 μL | 1.0 |
ROX reference dye (x50) 1.0 μL | 0.2 |
RNase inhibitor | 1.0 |
cDNA | 3.8 |
4.
Real-time PCR反应程序
Reaction program of Real-time PCR
Step | Temperature (℃) | Time | Repeats |
1 | 50 | 2 min | 1 |
2 | 95 | 10 min | 1 |
3 | 95 | 15 s | 40 |
3 | 60 | 1 min | 40 |
4 | 95 | 15 s | 1 |
4 | 60 | 15 s | 1 |
4 | 95 | 15 s | 1 |
5.
引物序列(5'到3')
Sequences of primers (Form 5' to 3')
Gene name | Forward primer | Reversed primer |
GAPDH | GAAGGTGAAGGTCGGAGTC | GAAGATGGTGATGGGATTTC |
PTTG1 | ACTGTCTGATGAGTGCCAGC | AGCTAAACAGCGGAACAGTCA |
a-SMA | GAGCGTGGCTATTCCTTCGT | GCCCATCAGGCAACTCGTAA |
COL1A1 | CATCTGGTGGTGAGACTTGC | TCCTGGTTTCTCCTTTGG |
COL1A2 | AAGGTCATGCTGGTCTTGCT | GACCCTGTTCACCTTTTCCA |
COL3A1 | GTCCCAGCGGTTCTCCA | CCCCGTGCTCCAGTGAT |
CTGF | GGAAATGCTGCGAGGAGTGG | GGCTCTAATCATAGTTGGGTCTGG |
1.3.5. 细胞转染
将原代皮肤成纤维细胞以2.0×105/mL的密度接种于六孔板中,将铺满2/3生长良好的细胞分为阴性对照siRNA(NC组)及转染siPTTG1(siPTTG1组),做好标记。转染前,把六孔板内换成新鲜的细胞培养液。培养液的体积约为2 mL。把LipoFiter脂质体转染试剂轻轻混匀。对于待转染的六孔板中1个孔的细胞,取一只洁净无菌离心管,加4 µg质粒DNA及适量DMEM溶液,用枪轻轻吹打混匀,终体积250 µL。取1只洁净无菌的离心管加入238 µL DMEM溶液,再加入12 µL LipoFiter用枪轻轻吹打混匀,终体积250 µL,室温放置5 min。将前两步中的DNA溶液于LipoFiter溶液混匀,孵育20 min后把500 µL的混合物全部加入六孔板的1个孔内,随后轻轻八字摇摆混匀。细胞培养箱培养6 h后,除去含有LipoFiter-DNA的培养液,每孔加入2 mL新鲜培养液继续培养。24 h后在荧光显微镜下观察转染效率。再24 h后提取细胞RNA。
1.3.6. 细胞增殖检测
应用xCELLigence系统对细胞增殖进行实时定量检测。实验分为NC组和siPTTG1组,每组3个重复,具体步骤如下:在16孔E-plate板中每孔加入50 µL新鲜完全培养基,将滴定板装入仪器,按说明书操作设好相应程序,检测接触是否良好并消除背景误差。对细胞计数,取下E-plate板,每孔加50 µL细胞液,调整至每孔最终细胞数为10 000个。保持仪器原有设定程序,将加完细胞培养液的E-plate板放回仪器,启动程序运行,至生长曲线的CI值接近1.0时,取下E-plate板,吸去孔中的旧培养基,siPTTG1组转染siPTTG1,NC组转染NC作为对照放入仪器中进行检测。实验结果用RTCA software进行分析。
1.3.7. Sircol assay
采用Sircol assay方法检测体外培养的硬皮病患者皮肤成纤维细胞胶原含量。12孔板上接种原代培养的硬皮病患者皮肤成纤维细胞,培养36 h后分组:对照组,siPTTG1处理组,每组3个复孔。培养48 h,收集上清液,各加入胶原分离与浓缩试剂100 μL,混匀后4 ℃下放置约24 h,离心弃上清。取Sircol assay染料500 μL在每个EP管中加入。胶原蛋白溶液20 μL、sircol染料1 mL,旋转摇床上混匀30 min后离心,弃尽上清,各添加750 μL冰浴的酸-盐洗涤试剂,离心后弃尽上清,各管加250 μL碱性试剂释放染料混匀,转移200 μL样本至96孔板中;用酶标仪检测吸光值(A555 nm)为零,利用标准曲线算得各个样本的胶原含量。
1.3.8. 数据处理
实验结果以数据和图表表示,测定值以均数±标准差表示。使用GraphPad Prism 7软件进行统计学处理,组间比较采用单因素方差分析,组内两两比较采用LSD法,以P < 0.05为差异有统计学意义。
2. 结果
2.1. SSc患者皮肤组织中PTTG1表达升高
SSc患者皮肤组织中PTTG1基因表达水平较正常对照组上升0.43倍,具有统计学意义(P < 0.05,图 1)。SSc患者皮肤组织中PTTG1基因表达水平升高,提示PTTG1可能与纤维化密切相关。进一步通过免疫组化检测表明,在SSc患者皮肤组织成纤维细胞中阳性细胞增多,PTTG1蛋白表达升高(图 2)。
1.
人皮肤组织中PTTG1的基因表达水平
Expression levels of PTTG1 mRNA in human skin tissue. *P < 0.05.
2.
人皮肤组织中PTTG1蛋白表达水平
Protein expression of PTTG1 in human skin tissue. A, B: Immunohistochemistry (Original magnitication: A, ×100; B, ×400); C: Relative positive cells. *P < 0.05.
2.2. 干扰PTTG1表达可抑制原代皮肤成纤维细胞增殖
为分析PTTG1在SSc纤维化发展中的作用,利用xCELLigence系统对原代皮肤成纤维细胞干扰PTTG1后的增殖情况进行实时定量检测。结果发现原代皮肤成纤维细胞干扰PTTG1,细胞增殖被抑制(图 3)。
3.
干扰PTTG1对原代皮肤成纤维细胞增殖的影响
Effect of PTTG1 interference on proliferation of cultured primary human dermal fibroblasts.
2.3. 干扰PTTG1可降低纤维化相关基因及胶原蛋白的表达
SSc患者及正常对照组的原代皮肤成纤维细胞中PTTG1基因表达水平与胶原蛋白基因α-SMA、COL1A1、COL1A2、COL3A1的表达水平呈正相关,且具有统计学意义(R2=0.8192,P < 0.05;R2=0.6398,P < 0.05;R2=0.316,P < 0.05;R2=0.3723,P < 0.05,图 4)。为进一步探究PTTG1对成纤维细胞活性的影响,本研究利用RNA干扰方法降低原代皮肤成纤维细胞中PTTG1的基因表达。干扰PTTG1能够降低成纤维细胞中纤维化相关基因的表达,其中胶原基因COL1A1、COL1A2、PAI-1的差异具有统计学意义(P < 0.05,图 5)。进一步通过Sircol assay检测对照组及干扰组细胞上清中胶原蛋白含量,发现干扰PTTG1后,PTTG1蛋白表达水平显著降低,能够显著降低成纤维细胞中胶原蛋白的表达(P < 0.05,图 6)。
4.
原代皮肤成纤维细胞中PTTG1与纤维化相关基因α-SMA、COL1A1、COL1A2、COL3A1的表达水平及相关性
Correlation of PTTG1 expression with the mRNA expression levels of α-SMA (A), COL1A1 (B), COL1A2 (C) and COL3A1 (D).
5.
干扰PTTG1对纤维化相关基因的影响
Effect of PTTG1 interference on fibrosis-related genes in primary dermal fibroblasts. *P < 0.05; **P < 0.01.
6.
干扰PTTG1对胶原蛋白表达的影响
Effect of PTTG1 interference on protein expression of collagen in primary dermal fibroblasts. *P < 0.05.
3. 讨论
PTTG1在肿瘤的发生、发展中扮演着重要角色,而且在细胞的有丝分裂、细胞转化、修复以及基因调控机制等过程中均发挥重要作用[27]。然而,PTTG1在SSc纤维化中的作用及机制目前未见报道,本研究拟检测SSc患者临床样本中PTTG1的表达情况,并通过体外细胞实验研究PTTG1对成纤维细胞的影响,旨在探寻PTTG1在SSc皮肤纤维化中的作用。
本研究显示,与正常人相比PTTG1在SSc患者皮肤组织中的表达显著升高,提示它可能在SSc的发展中具有重要作用。Tomasek等[28]发现,α-平滑肌肌动蛋白(α-SMA)是鉴定肌成纤维细胞最可靠的特异性指标物。因此本研究进一步发现,在原代皮肤成纤维细胞中,PTTG1和α-SMA的基因表达水平呈显著正相关关系,这进一步验证了PTTG1与纤维化相关。此外,本研究还发现在原代皮肤成纤维细胞中,PTTG1和胶原基因COL1A1、COL1A2、COL3A1的基因表达水平也呈显著正相关关系,综合这些结果说明PTTG1与纤维化密切相关。基于临床样本检测结果,本研究进一步通过细胞实验证实了PTTG1对成纤维细胞活性的影响。
Ⅰ型胶原是细胞外基质的主要成分,也是导致SSc纤维化的细胞外基质中最主要的成分,而胶原的合成和降解与成纤维细胞的数量和活性密切相关[29-30]。胶原蛋白中Ⅰ型胶原主要分布于皮肤、肌腱等与纤维化密切相关的组织,由基因COL1A1、COL1A2表达[31]。本研究通过干扰PTTG1降低成纤维细胞中纤维化相关基因的表达,其中胶原基因COL1A1、COL1A2、PAI-1的表达相应降低,这说明干扰PTTG1可抑制纤维化相关基因及胶原蛋白的表达,提示PTTG1可能通过促进成纤维细胞活化,加速胶原的合成,在SSc中纤维化进程中发挥重要作用。
本研究首先发现PTTG1在SSc患者皮肤组织中的表达显著高于正常人,而且PTTG1的表达与α-SMA、COL1A1、COL1A2、COL3A1均显著正相关,证实PTTG1与SSc纤维化有密切关系。进一步的体外细胞实验结果显示,干扰PTTG1可显著抑制成纤维细胞的增殖,降低纤维化相关基因表达。多项研究表明,在SSc的纤维化过程中,多种蛋白参与了成纤维细胞活化,这些蛋白通过不同信号通路发挥作用,促进胶原等细胞外基质过度合成沉积。本研究首次明确了PTTG1可通过增加成纤维细胞的活性,促进胶原的合成,在SSc纤维化中发挥重要作用,有利于进一步揭示SSc的发病机制。因此探明PTTG1的具体作用机制对于揭示SSc的发病机制具有重要作用,通过更深入的研究探明其作为临床诊断SSc的关键标志物、作为治疗的干预靶点、设计针对PTTG1表达降低的治疗药物的可行性,以期为SSc的治疗提供新思路。
Biography
杨安桥,在读硕士研究生,E-mail: 17210700136@fudan.edu.cn
Funding Statement
国家自然科学基金(81703117,81770066)
Supported by National Natural Science Foundation of China (81703117, 81770066)
Contributor Information
杨 安桥 (Anqiao YANG), Email: 17210700136@fudan.edu.cn.
刘 庆梅 (Qingmei LIU), Email: liuqing.mei@163.com.
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