世界生命科学前沿动态周报（三十七）

（12.20-12.31/2010）
美宝国际集团:陶国新 
---2010再生科学年度进展 

 　　本次动态包括以下内容：耐力锻炼使心肌细胞增殖的机理；癌症干细胞基因表达高癌症治疗结果差；无需标记实时观察活组织中分子运动；果蝇激活生殖细胞遗传基因来产生肿瘤；癌细胞自我毁灭与自我保护的信号分子；微小RNA表达模式的整体图谱区分干细胞类别。以及2010各期中出现过的比较突出的几项再生科学进展的小结。

1. 耐力锻炼使心肌细胞增殖的机理
【摘要】
人们都知道锻炼身体可以促进新陈代谢，有益于心血管健康，但此前科学家对运动究竟如何影响心脏却所知甚少。美国哈佛大学医学院的研究人员日前报告说，他们首次从分子水平发现运动有益心脏健康的机理，这一发现将有助于开发出治疗心血管疾病的新疗法。研究人员通过小鼠实验发现，经常运动可以使小鼠体内的C/EBPβ转录因子水平显著下降，其结果会促进小鼠心脏肌肉细胞增殖，有益于心脏生长。此外，研究人员还发现，体内C/EBPβ水平较低的小鼠对心力衰竭具有抵抗能力。研究人员表示，这项研究对心脏肌肉再生的潜力有了深入理解。参与研究的哈佛大学医学院教授安东尼·罗森茨魏希表示，通过这项研究可以开发出针对那些无法运动的心脏病患者的疗法。这项研究成果发表在新一期美国《细胞》杂志上。（来源：新华社）

【点评】
　　该研究所发现的心肌增殖机理同样有助于理解非药物方式实现组织再生的机制并促进此类自然再生方法的推广。

【原文摘录】Cell, Volume 143, Issue 7, 1072-1083, 23 December 2010
C/EBPβ Controls Exercise-Induced Cardiac Growth and Protects against Pathological Cardiac Remodeling
Pontus Boström, Nina Mann, Jun Wu, et al.
The heart has the ability to grow in size in response to exercise, but little is known about the transcriptional mechanisms underlying physiological hypertrophy. Adult cardiomyocytes have also recently been proven to hold the potential for proliferation, a process that could be of great importance for regenerative medicine. Using a unique RT-PCR-based screen against all transcriptional components, we showed that C/EBPβ was downregulated with exercise, whereas the expression of CITED4 was increased. Reduction of C/EBPβ in vitro and in vivo resulted in a phenocopy of endurance exercise with cardiomyocyte hypertrophy and proliferation. This proliferation was mediated, at least in part, by the increased CITED4. Importantly, mice with reduced cardiac C/EBPβ levels displayed substantial resistance to cardiac failure upon pressure overload. These data indicate that C/EBPβ represses cardiomyocyte growth and proliferation in the adult mammalian heart and that reduction in C/EBPβ is a central signal in physiologic hypertrophy and proliferation.

2. 癌症干细胞基因表达高癌症治疗结果差
【摘要】  
　　据美国物理学家组织网12月22日（北京时间）报道，斯坦福大学研究人员通过对白血病干细胞的基因表达方式研究发现，癌症干细胞基因表达水平更高的病人比表达水平低的病人预后效果要差很多，该发现首次通过临床数据证明了癌症干细胞概念。医疗人员可据此预测群体病人的治疗结果，并帮助开发新的临床疗法。研究发表在12月22日的《美国医学会杂志》（JAMA）上。几年前提出的癌症干细胞概念认为，某些癌症起源于一小撮自我更新能力很强的细胞，这一小撮细胞即是癌症干细胞。这些癌症干细胞能不断补充生成新的癌症细胞，癌症要彻底治疗，必须清除这些干细胞。癌症干细胞对抗治疗已经在一些固状肿瘤和血癌的动物模型中得到验证，虽然有大量实验室证据支持，但至今还缺乏临床证据。论文合著者、斯坦福癌症中心医务部艾什·埃里沙德和同事拉文达·马杰提今年9月曾在实验室小鼠中，对非霍奇森淋巴瘤癌症干细胞表面发现的蛋白质CD47研究发现，CD47是癌症干细胞的“保护伞”，有了它，很多药物对这些细胞无效。CD47在其他几种癌症干细胞中也存在。马杰提认为这些动物实验中发现的证据在人体中也应该存在。他们用两种能识别白血病干细胞的表面标记，从7个白血病患者的肿瘤样本中分离出这些白血病干细胞，将肿瘤干细胞和其他肿瘤细胞的基因表达方式进行了对比，结果有52%的基因表达不同。癌症干细胞基因表达方式和正常的血液干细胞很相似，不仅能自我更新，还能像正常干细胞在需要时候才分裂。为了逃避那些针对迅速分裂细胞的传统治疗方法，它会选择少量分裂，潜伏着，等待机会“东山再起”。
　　研究人员还对来自1000多位急性骨髓白血病病人的4组肿瘤样本进行了对比研究，发现在“癌症干细胞基因高表达”和“治疗结果差”之间存在很强的相关性。在一组德国样本中，高表达病人3年内死亡的绝对风险高达78%，而低表达病人仅为57%。同样，无病生存率、某个时期再度恶化可能性、对抗初次治疗顽固性等指标也如此。论文第一作者、斯坦福大学癌症系统生物学中心安德鲁·简托斯表示，白血病干细胞的信号越强，病人寿命越短，病情恶化得越快，治疗效果就更差。目前，研究小组正在继续研究数据，以最终从各种结合抗体疗法中确定哪些疗法对癌症干细胞高表达基因信号的病人最有效。（来源：科技日报 发布时间：2010-12-23 10:20:47）

【点评】
　　该研究发现了白血病干细胞基因的高表达与急性粒细胞白血病的治疗效果差之间有独立的相关性，但是并没有证明癌症干细胞是肿瘤发生的起因。

【原文摘录】 JAMA. 2010;304(24):2706-2715. doi: 10.1001/jama.2010.1862
Association of a Leukemic Stem Cell Gene Expression Signature With Clinical Outcomes in Acute Myeloid Leukemia
Andrew J. Gentles, Sylvia K. Plevritis, Ravindra Majeti, Ash A. Alizadeh
Abstract
Context In many cancers, specific subpopulations of cells appear to be uniquely capable of initiating and maintaining tumors. The strongest support for this cancer stem cell model comes from transplantation assays in immunodeficient mice, which indicate that human acute myeloid leukemia (AML) is driven by self-renewing leukemic stem cells (LSCs). This model has significant implications for the development of novel therapies, but its clinical relevance has yet to be determined.
Objective To identify an LSC gene expression signature and test its association with clinical outcomes in AML.
Design, Setting, and Patients Retrospective study of global gene expression (microarray) profiles of LSC-enriched subpopulations from primary AML and normal patient samples, which were obtained at a US medical center between April 2005 and July 2007, and validation data sets of global transcriptional profiles of AML tumors from 4 independent cohorts (n = 1047).
Main Outcome Measures Identification of genes discriminating LSC-enriched populations from other subpopulations in AML tumors; and association of LSC-specific genes with overall, event-free, and relapse-free survival and with therapeutic response.
Results Expression levels of 52 genes distinguished LSC-enriched populations from other subpopulations in cell-sorted AML samples. An LSC score summarizing expression of these genes in bulk primary AML tumor samples was associated with clinical outcomes in the 4 independent patient cohorts. High LSC scores were associated with worse overall, event-free, and relapse-free survival among patients with either normal karyotypes or chromosomal abnormalities. For the largest cohort of patients with normal karyotypes (n = 163), the LSC score was significantly associated with overall survival as a continuous variable (hazard ratio [HR], 1.15; 95% confidence interval [CI], 1.08-1.22; log-likelihood P <.001). The absolute risk of death by 3 years was 57% (95% CI, 43%-67%) for the low LSC score group compared with 78% (95% CI, 66%-86%) for the high LSC score group (HR, 1.9 [95% CI, 1.3-2.7]; log-rank P = .002). In another cohort with available data on event-free survival for 70 patients with normal karyotypes, the risk of an event by 3 years was 48% (95% CI, 27%-63%) in the low LSC score group vs 81% (95% CI, 60%-91% ) in the high LSC score group (HR, 2.4 [95% CI, 1.3-4.5]; log-rank P = .006). In multivariate Cox regression including age, mutations in FLT3 and NPM1, and cytogenetic abnormalities, the HRs for LSC score in the 3 cohorts with data on all variables were 1.07 (95% CI, 1.01-1.13; P = .02), 1.10 (95% CI, 1.03-1.17; P = .005), and 1.17 (95% CI, 1.05-1.30; P = .005).
Conclusion High expression of an LSC gene signature is independently associated with adverse outcomes in patients with AML.

3. 无需标记实时观察活组织中分子运动
【摘要】  
　　美国哈佛大学科学家将受激拉曼散射（SRS）显微镜和核磁共振成像（MRI）技术结合，研制出一种最新的生物医学成像设备，极大拓展了SRS显微镜的视野。其速度之快精度之高，如同“视频”，足以使科学家直接目睹分子在活组织中的运动。研究论文发表在最新一期《科学》杂志上。“此前，SRS显微镜每分钟只能拍摄一幅画面，用于活的动物或人体就太慢了。”哈佛大学化学与化学生物学教授谢晓亮说，“我们大大提高了采集数据的速度，使拍摄达到了视频速率。”研究小组还用这种新型SRS显微镜追踪药物在皮肤下的移动，其能清晰显示出药物实时吸收情况。如与内镜检查术结合，还能一层一层观察组织的三维结构。新型SRS显微镜的工作原理是探测原子之间化学键的内在震动，由于融合了MRI技术，在透视深度上更适合拍摄体内器官和其他大目标，既可广泛用于拍摄器官和组织结构的静态图像，也能在亚细胞水平以流动画面观察细胞中的蛋白质、脂质和水。
　　同多种常用的观察生物分子的技术相比，新型SRS显微镜优势明显。它能采集分析照射生物样本的近30%激光，比传统SRS显微镜高出30倍；并且不需要插入荧光标记，避免了绿色荧光标记蛋白质扰乱生物路径或压住较小生物分子的问题。此外，传统的红外显微镜空间分辨率太低，并需要给样本脱水；自然的拉曼显微镜需要很高的激光能量，整体耗时很长，在活样本中的应用受到限制；相干反斯托克拉曼散射显微镜在拍摄除了脂质以外的大多数分子时对比度不够，而新型SRS显微镜都能突破这些局限。研究人员表示，新型SRS显微镜在医疗领域的应用前景广阔。比如，手术之前必须将样本送检以用于组织分析，这个过程大约要花20分钟，其间病人需要等在手术台上，而新技术可提供实时扫描透视，有助于加速外科手术，清除肿瘤和其他损伤。谢晓亮说：“这一项目开始于11年前，核磁共振技术花了30多年才用于临床，我们期望这种SRS显微镜尽早应用于医院。”来源：科技日报 常丽君

【点评】
　　该项技术将会极大的促进生理生化尤其是新陈代谢的研究，如能成熟地运用于人体，对于人体生理学及医学研究将有巨大的帮助。

【原文摘录】 Science Vol. 330 no. 6009 pp. 1368-1370 DOI: 10.1126/science.1197236
Video-Rate Molecular Imaging in Vivo with Stimulated Raman Scattering
Brian G. Saar1,Christian W. Freudiger, Jay Reichman, et al.
Optical imaging in vivo with molecular specificity is important in biomedicine because of its high spatial resolution and sensitivity compared with magnetic resonance imaging. Stimulated Raman scattering (SRS) microscopy allows highly sensitive optical imaging based on vibrational spectroscopy without adding toxic or perturbative labels. However, SRS imaging in living animals and humans has not been feasible because light cannot be collected through thick tissues, and motion-blur arises from slow imaging based on backscattered light. In this work, we enable in vivo SRS imaging by substantially enhancing the collection of the backscattered signal and increasing the imaging speed by three orders of magnitude to video rate. This approach allows label-free in vivo imaging of water, lipid, and protein in skin and mapping of penetration pathways of topically applied drugs in mice and humans.

4.  果蝇激活生殖细胞遗传基因来产生肿瘤
【摘要】  
　　巴塞罗那的 科学家近日在Science上报道他们发现了果蝇幼虫利用生殖细胞的遗传程序来催生脑部肿瘤。关闭涉及到的相关基因就会保持健康的大脑，这是首次发现关闭这些相关基因可以使果蝇脑部肿瘤消失。说明这些生殖细胞的遗传基因对于此类肿瘤的发生有关键作用。此前十年积累的数据显示某些肿瘤如黑色素瘤和某些类癌的癌细胞会激活生殖细胞的遗传基因。

【点评】
　　这项研究说明癌基因并不一定是癌症发生的原因，生殖基因的激活也可能引发癌症。基因激活的生理调控是否正常是很重要的。

【原文摘录】 Science, December 23, 2010 DOI: 10.1126/science.1195481
Ectopic expression of germline genes drives malignant brain tumor growth in Drosophila.
Janic A, Mendizabal L, Llamazares S, Rossell D, Gonzalez C.
Model organisms such as the fruit fly Drosophila melanogaster can help to elucidate the molecular basis of complex diseases such as cancer. Mutations in the Drosophila gene lethal (3) malignant brain tumor cause malignant growth in the larval brain. Here we show that l(3)mbt tumors exhibited a soma-to-germline transformation through the ectopic expression of genes normally required for germline stemness, fitness, or longevity. Orthologs of some of these genes were also expressed in human somatic tumors. In addition, inactivation of any of the germline genes nanos, vasa, piwi, or aubergine suppressed l(3)mbt malignant growth. Our results demonstrate that germline traits are necessary for tumor growth in this Drosophila model and suggest that inactivation of germline genes might have tumor-suppressing effects in other species.

5.  癌细胞自我毁灭与自我保护的信号分子
【摘要】
　　斯坦福大学医学院的研究人员发现许多癌细胞自身带有自我毁灭的种子--细胞表面一种名为钙网素的蛋白—能召集循环系统的巨噬细胞来吞食消化他们。而绝大多数癌细胞没有被毁灭是因为他们同时表达另一种信号蛋白CD47对抗钙网素的作用。

【点评】
　　CD47与钙网素的作用及二者平衡的调节会促进癌症免疫疗法的发展。

【原文摘录】 Sci Transl Med 22 December 2010: Vol. 2, Issue 63, p. 63ra94
Calreticulin Is the Dominant Pro-Phagocytic Signal on Multiple Human Cancers and Is Counterbalanced by CD47
M. P. Chao, S. Jaiswal, R. Weissman-Tsukamoto, et al.
Under normal physiological conditions, cellular homeostasis is partly regulated by a balance of pro- and anti-phagocytic signals. CD47, which prevents cancer cell phagocytosis by the innate immune system, is highly expressed on several human cancers including acute myeloid leukemia, non-Hodgkin’s lymphoma, and bladder cancer. Blocking CD47 with a monoclonal antibody results in phagocytosis of cancer cells and leads to in vivo tumor elimination, yet normal cells remain mostly unaffected. Thus, we postulated that cancer cells must also display a potent pro-phagocytic signal. Here, we identified calreticulin as a pro-phagocytic signal that was highly expressed on the surface of several human cancers, but was minimally expressed on most normal cells. Increased CD47 expression correlated with high amounts of calreticulin on cancer cells and was necessary for protection from calreticulin-mediated phagocytosis. Blocking the interaction of target cell calreticulin with its receptor, low-density lipoprotein receptor–related protein, on phagocytic cells prevented anti-CD47 antibody–mediated phagocytosis. Furthermore, increased calreticulin expression was an adverse prognostic factor in diverse tumors including neuroblastoma, bladder cancer, and non-Hodgkin’s lymphoma. These findings identify calreticulin as the dominant pro-phagocytic signal on several human cancers, provide an explanation for the selective targeting of tumor cells by anti-CD47 antibody, and highlight the balance between pro- and anti-phagocytic signals in the immune evasion of cancer.

6. 微小RNA表达模式的整体图谱区分干细胞类别
【摘要】
　　干细胞生物学在全世界引发人们对其可以最终修复身体部位的巨大期望。尽管很多科学家认为这是可行的，但是必须克服很多障碍，包括令人担忧的在修复器官时引发癌症的潜在风险。而近日报道的加州大学的一项关于多能性干细胞的微小RNA表达模式的研究或许对此有所帮助。他们分析很多种多能性干细胞的微小RNA表达模式，发现所有的多能性干细胞微小RNA表达模式并不相同，但不是因细胞来源而异，而是具有不同的p53 体系状态。微小RNA表达模式的整体图谱能够告诉你这是何种细胞，何种癌症，是否干细胞等信息。

【点评】
　　微小RNA表达模式的整体图谱研究也许会有助于研究人体潜能再生细胞的定位和属性。

【原文摘录】 Cell Stem Cell, Volume 7, Issue 6, 671-681, 3 December 2010
MicroRNA Profiling Reveals Two Distinct p53-Related Human Pluripotent Stem Cell States
Pierre Neveu, Min Jeong Kye, Shuping Qi, et al.
Highlights
miRNA profiles distinguish two categories of human pluripotent stem cells
The p53 network status distinguishes pluripotent cells independently of their origin
p53-targeting miRNAs change the classification status of iPSCs
A 2D representation of miRNA profiles tracks differentiation and reprogramming
Summary
Reprogramming methodologies have provided multiple routes for achieving pluripotency. However, pluripotency is generally considered to be an almost singular state, with subtle differences described between induced pluripotent stem cells (iPSCs) and embryonic stem cells (ESCs). We profiled miRNA expression levels across 49 human cell lines, including ESCs, iPSCs, differentiated cells, and cancer cell lines. We found that the resulting miRNA profiles divided the iPSCs and hESCs examined into two distinct categories irrespective of the cell line origin. The miRNAs that defined these two pluripotency categories also distinguished cancer cells from differentiated cells. Transcriptome analysis suggested that several gene sets related to p53 distinguished these categories, and overexpression of the p53-targeting miRNAs miR-92 and miR-141 in iPSCs was sufficient to change their classification status. Thus, our results suggest a subdivision of pluripotent stem cell states that is independent of their origin but related to p53 network status.

7. 2010再生科学年度进展
　　根据与人体再生复原科学的相关程度，本年度登载的以下动态作为2010再生科学年度进展：

1.人体多能干细胞体外定向分化形成肠组织；
2.老鼠实验表明修复端粒可以逆转衰老；
3.蝾螈重生肢体和器官的独特酶；
4.生长因子TGF-β2和BMP4可使成熟细胞转化为成人干细胞；
5.生命复杂性的产生可能必须先有线粒体出现；
6.黄芩汤可减轻肠癌患者化疗损伤；
7.细胞生长调控依靠细胞质核传输；
8.洞螈长寿研究或解开衰老之谜；
9.脂肪可用作细胞内在pH感受器；
10.发现上皮组织中神秘免疫细胞的功能和机理；
11.细胞归巢法使兔滑膜关节面再生；
12.控制细胞分化的力学因素；
13.关键基因控制哺乳动物组织再生；
14.细胞运动的集体调控控制胚胎的生长；
15.首次发现可发育成卵的干细胞;
16.精子形成过程中的细胞在一定时期内可以变回干细胞；
17.“活体生物反应器”“原位”培养再生新器官；
18.发现斑马鱼造血干细胞生成机理。