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世界生命科学前沿动态周报（十）
（05.24--05.30 / 2010）
美宝国际集团:陶国新
本周动态包括以下内容：新型DNA抗癌疫苗; 首次发现可发育成卵的干细胞; 脂肪干细胞分化为心肌细胞; CD95 促进肿瘤生长；核糖核酸干扰可抑制癌症活跃基因；人体干细胞成功造出人工牙齿。
1. 新型DNA抗癌疫苗
【摘要】新华网 发布时间：2010-5-25 16:44:42
瑞典卡罗林斯卡医学院日前发表公告说，该机构研究人员研制出一种可抑制恶性肿瘤生长的新型DNA（脱氧核糖核酸）疫苗，实验显示这种疫苗无副作用。当恶性肿瘤超过几个毫米时，需要形成新的血管为肿瘤提供营养和氧气。因此，阻止血管的生长是治疗恶性肿瘤的思路之一。蛋白质DLL4是形成血管的必要成分，如果能抑制肿瘤细胞中的DLL4蛋白质，将使新血管失去功能，从而大大减缓肿瘤的生长速度。
研究人员据此研制出了这种DNA疫苗。经对患有乳腺癌的小白鼠进行试验，证明接种疫苗的小白鼠体内产生了可抑制DLL4蛋白质的抗体，阻止了体内乳腺肿瘤的生长，而且没有引起任何不良反应，也未影响小白鼠的伤口愈合。研究人员皮耶特拉斯称，选择乳腺癌作为试验目标是因为乳腺肿瘤带有大量的DLL4蛋白质。研究人员希望能将这种疫苗用于乳腺癌的术后治疗，防止肿瘤复发。
【点评】 点评：小鼠通过接种DNA疫苗，产生抗体抑制恶性肿瘤新生血管必需的DLL4蛋白质，从而阻止肿瘤生长。该疫苗对于减缓肿瘤生长和防止肿瘤复发可能有作用，但是由于不能直接作用于肿瘤细胞，还不可能根除癌症。
【原文摘录】Oncogene , (24 May 2010) | doi:10.1038/onc.2010.176
Therapeutic efficacy of a DNA vaccine targeting the endothelial tip cell antigen delta-like 4 in mammary carcinoma
BK Haller, A Bråve, E Wallgard, P Roswall, VG Sunkari, U Mattson, D Hallengärd, S-B Catrina, M Hellström och K Pietras
The Notch ligand delta-like ligand 4 (DLL4) is an essential component expressed by endothelial tip cells during angiogenic sprouting. We have described a conceptually novel therapeutic strategy for targeting tumor angiogenesis and endothelial tip cells based on DNA vaccination against DLL4. Immunization with DLL4-encoding plasmid DNA by in vivo electroporation severely retarded the growth of orthotopically implanted mammary carcinomas in mice by induction of a nonproductive angiogenic response. Mechanistically, vaccination brought about a break in tolerance against the self-antigen, DLL4, as evidenced by the production of inhibitory and inherently therapeutic antibodies against mouse DLL4. Importantly, no evidence for a delayed wound healing response, or for toxicity associated with pharmacological blockade of DLL4 signaling, was noted in mice immunized with the DLL4 vaccine. We have thus developed a well-tolerated DNA vaccination strategy targeting the endothelial tip cells and the antigen DLL4 with proven therapeutic efficacy in mouse models of mammary carcinoma; a disease that has been reported to dramatically induce the expression of DLL4. Conceivably, induction of immunity toward principal mediators of pathological angiogenesis could provide protection against recurrent malignant disease in the adjuvant setting.
2. 首次发现可发育成卵的干细胞
【摘要】新华网 2010-5-25 9:39:40
日本一个研究小组日前发现，在雌鳉鱼的卵巢内存在可发育成鳉鱼卵的干细胞。有关成果已经刊登在最新一期的美国《科学》杂志网络版上。这一成果是日本自然科学研究机构基础生物学研究所的研究人员获得的。基础生物学研究所日前发表公告说，在脊椎动物中，已经发现雄性的精巢中存在发育成精子的干细胞，但是在卵巢中发现会发育成卵的干细胞则属世界首次。研究小组对雌性鳉鱼进行基因操作，使其卵巢内的卵发出红光，结果发现了很多即将发育为卵的细胞。利用绿色荧光蛋白质给这些细胞做上标记以后，研究人员发现许多新形成的卵也会发出绿色荧光，这说明这些细胞的确发育成了卵，因此这些细胞就是干细胞。
【点评】 点评：世界首次在脊椎动物卵巢中发现会发育成卵的干细胞。由于没有直接证据显示成体脊椎动物卵巢中有生殖干细胞，这些发育成卵的干细胞很可能是从卵巢中的体细胞原位转变的。
【原文摘录】Science DOI: 10.1126/science.1185473
Identification of Germline Stem Cells in the Ovary of the Teleost Medaka
Shuhei Nakamura,1 Kayo Kobayashi,1 Toshiya Nishimura,1,2 Shin-ichi Higashijima,3,4 Minoru Tanaka1,2,*
Germline stem cells continually produce sperm in vertebrate testes, whereas there is no direct evidence showing that germline stem cells are present in adult vertebrate ovaries. Using transgenic methods and clonal analysis, we identified germline stem cells that supported oogenesis and the production of offspring in the ovaries of adult medaka fish. Early-stage germ cells were localized in clusters along interwoven threadlike cords of sox9b-expressing somatic cells (termed "germinal cradles") where the germ cells developed. Germline stem cells gave rise to germ cells that divided to produce cysts, which then underwent cell death or separated to form follicles. Our results provide insight into germline stem cell biology of medaka and provide a model system for studying vertebrate stem cell niches.
3. 脂肪干细胞分化为心肌细胞
【摘要】西班牙研究人员首次从人类脂肪组织中分离出成熟的干细胞，让这些细胞暂时暴露于人类的心房细胞中，随后再对这些细胞重新进行培养。经过12天的培养，这些细胞向着心肌细胞的表型方向分化，这可以通过以下方面得到证明：这些细胞从形态上发生了改变，表现为带有纤维纹和分枝的双核细胞；免疫荧光检查发现，它们带有心脏特有的标记；RT - PCR检测证明，这些细胞存在心肌基因；它们有逆转录表达。这样，这些干细胞获得了一个心脏的表型。未来可通过这项技术从患者身上直接提取细胞来再生心肌细胞。但是医生们表示，目前这项研究还处于初期阶段，要用于治疗还有很长一段时间。
【点评】 点评：干细胞分化的决定受到其所处生理环境的调控，这类调控也决定了其在体外培养时的分化方向。
【原文摘录】Cytotherapy DOI: 10.3109/14653240903548202
Human cardiac tissue induces transdifferentiation of adult stem cells towards cardiomyocytes
Background aims. The goal was to induce the transdifferentiation (or conversion) of human adipose-derived stem cells to cardiomyocytes using an intracellular extract obtained from adult human heart tissue. Methods. Human adult stem cells from lipoaspirates were transiently permeabilized, exposed to human atrial extracts and allowed to recover in culture. Results. After 21 days, the cells acquired a cardiomyocyte phenotype, as demonstrated by morphologic changes (appearance of binucleate, striated cells and branching fibers), immunofluorescence detection of cardiac-specific markers (connexin-43, sarcomeric α-actinin, cardiac troponin I and T, and desmin) and the presence of cardiomyocyte-related genes analyzed by reverse transcription–polymerase chain reaction (cardiac myosin light chain 1, α-cardiac actin, cardiac troponin T and cardiac β-myosin). Conclusions. We have demonstrated for the first time that adult cardiomyocytes obtained from human donors retain the capacity to induce cardiomyocyte differentiation of mesenchymal stromal cells. The use of autologous extracts for reprogramming adult stem cells may have potential therapeutic implications for treating heart disease.
4. CD95 促进肿瘤生长
【摘要】CD95 原来一直被认为是凋亡受体蛋白，通过诱导细胞凋亡来调节组织内稳态，是癌细胞杀手。现在发现，自相矛盾的是，癌细胞的正常生长也离不开它。没有它，小鼠的卵巢癌和肝癌发病率和肿瘤体积都降低了。
【点评】 点评：发现CD95 受体蛋白在癌症发展中有促进作用，在癌症治疗中应该抑制其活性而非原来认为的增强其活性。
【原文摘录】Nature 465, 492–496 (27 May 2010) doi:10.1038/nature09075
CD95 promotes tumour growth
Lina Chen, Sun-Mi Park, Alexei V. Tumanov, Annika Hau, Kenjiro Sawada, Christine Feig, Jerrold R. Turner, Yang-Xin Fu, Iris L. Romero, Ernst Lengyel & Marcus E. Peter
CD95 (also called Fas and APO-1) is a prototypical death receptor that regulates tissue homeostasis mainly in the immune system through the induction of apoptosis1, 2, 3. During cancer progression CD95 is frequently downregulated or cells are rendered apoptosis resistant4, 5, raising the possibility that loss of CD95 is part of a mechanism for tumour evasion. However, complete loss of CD95 is rarely seen in human cancers4 and many cancer cells express large quantities of CD95 and are highly sensitive to CD95-mediated apoptosis in vitro. Furthermore, cancer patients frequently have elevated levels of the physiological ligand for CD95, CD95L6. These data raise the possibility that CD95 could actually promote the growth of tumours through its non-apoptotic activities7. Here we show that cancer cells in general, regardless of their CD95 apoptosis sensitivity, depend on constitutive activity of CD95, stimulated by cancer-produced CD95L, for optimal growth. Consistently, loss of CD95 in mouse models of ovarian cancer and liver cancer reduces cancer incidence as well as the size of the tumours. The tumorigenic activity of CD95 is mediated by a pathway involving JNK and Jun. These results demonstrate that CD95 has a growth-promoting role during tumorigenesis and indicate that efforts to inhibit its activity rather than to enhance it should be considered during cancer therapy.
5. 核糖核酸干扰可抑制癌症活跃基因
【摘要】2010年05月29日 09:15:13 来源： 科技日报
加拿大麦吉尔大学生物化学系研究人员发现，与核糖核酸相结合的一种蛋白质片断能够控制基因的正常表达，其中包括那些在癌症中活跃的基因。专家认为，这是癌症研究工作的一项重要突破，可立即将其应用到实验室的研究工作中，并且使目前各国科学家广泛开展的癌症个性化治疗工作向前推进了一大步。相关研究成果发表在5月26日《自然》杂志网络版上。人类细胞需要在合适的时间生产出适度数量的正常蛋白以维持其健康。细胞对蛋白生产进行有效控制时，所采用的重要手段之一就是依靠“核糖核酸干扰”。“核糖核酸干扰”是基因静默的一种形式，即小片段核糖核酸（又称微核糖核酸）与它们的遗传密码结合，以阻断特殊蛋白的生产。然而，不是核糖核酸的任何片段都能够按此方式行事。
麦吉尔大学的哈桑·拉贾尔博士与同事合作，使用结构生物学揭开了Argonaute蛋白中的一小段，即“核糖核酸干扰”的关键分子如何能够选择正确的微核糖核酸的奥秘。研究人员发现，“核糖核酸干扰”可以促使Argonaute蛋白增加基因静默。拉贾尔博士认为，“核糖核酸干扰”可以作为可行的治疗方法，来抑制那些在癌症等疾病中显得特别活跃的特殊基因。他表示现在已经掌握了修改微核糖核酸的方法，可以使其更具效力，并有希望基于此开发出治疗药物。研究人员认为，该发现要进入实际治疗还需时日，但它为有目的地控制那些非正常蛋白的生产提供了有效方法。麦吉尔大学生化系主任汤姆斯博士认为，医学界一直期盼有朝一日可以结束依靠化疗方法治疗癌症，而该项发现朝着癌症患者个性化基因治疗方向迈出了重要的一步。（记者杜华斌）
【点评】 点评：核糖核酸干扰（RNAi）是可行的抑制那些在癌症等疾病中特别活跃的特殊基因的方法，但只是临时关闭这类基因而不能消除导致其特别活跃的因素，很难根除癌症。
【原文摘录】Nature advance online publication 26 May 2010 | doi:10.1038/nature09039
Structural basis for 5′-nucleotide base-specific recognition of guide RNA by human AGO2
Filipp Frank1,2,3, Nahum Sonenberg1,2 & Bhushan Nagar1,3
MicroRNAs (miRNAs) mediate post-transcriptional gene regulation through association with Argonaute proteins (AGOs)1. Crystal structures of archaeal and bacterial homologues of AGOs have shown that the MID (middle) domain mediates the interaction with the phosphorylated 5′ end of the miRNA guide strand and this interaction is thought to be independent of the identity of the 5′ nucleotide in these systems2,3. However, analysis of the known sequences of eukaryotic miRNAs and co-immunoprecipitation experiments indicate that there is a clear bias for U or A at the 5′ position4,5,6,7. Here we report the crystal structure of a MID domain from a eukaryotic AGO protein, human AGO2. The structure, in complex with nucleoside monophosphates (AMP, CMP, GMP, and UMP) mimicking the 5′ end of miRNAs, shows that there are specific contacts made between the base of UMP or AMP and a rigid loop in the MID domain. Notably, the structure of the loop discriminates against CMP and GMP and dissociation constants calculated from NMR titration experiments confirm these results, showing that AMP (0.26 mM) and UMP (0.12 mM) bind with up to 30-fold higher affinity than either CMP (3.6 mM) or GMP (3.3 mM). This study provides structural evidence for nucleotide-specific interactions in the MID domain of eukaryotic AGO proteins and explains the observed preference for U or A at the 5′ end of miRNAs.
6. 人体干细胞成功造出人工牙齿
【摘要】网易探索2010-5-28 5:18:39
哥伦比亚大学医学中心5月25日宣布牙齿再生技术获得新突破，研究人员成功在动物口腔内进行了牙齿再生实验，这意味着未来人们就可将该技术应用于临床实验领域。
杰瑞米·毛（Jeremy Mao）博士负责带领哥伦比亚大学医学中心组织工程学及再生药物实验室的研究人员从事该课题的研究，他们找到一种新的技术，只需在患者口腔内植入一个托架，并将患者体内的干细胞引导至需要牙齿再生的地方，就可以实现真正意义上的“牙齿再生”。用于植入患者口腔的托架将全部采用天然材料制成，并将被放置在失去牙齿的牙洞内。在生长的过程中，该托架将与其周围的牙洞组织逐渐融合，甚至还会令牙周韧带及齿槽骨再生。而这些正是传统种牙方法所无法带来的。
【点评】 点评：干细胞分化的决定受到其所处生理环境的调控，在没有移植细胞的情况下，在牙齿托架和再生诱导物的作用下，体内细胞迁移过来再生新牙齿。
【原文摘录】Journal of Dental Research, May 2010; vol. 0: pp. 0022034510370803v1.
Anatomically Shaped Tooth and Periodontal Regeneration by Cell Homing
K. Kim, C.H. Lee, B.K. Kim, and J.J. Mao
Tooth regeneration by cell delivery encounters translational hurdles. We hypothesized that anatomically correct teeth can regenerate in scaffolds without cell transplantation. Novel, anatomically shaped human molar scaffolds and rat incisor scaffolds were fabricated by 3D bioprinting from a hybrid of poly--caprolactone and hydroxyapatite with 200-μm-diameter interconnecting microchannels. In each of 22 rats, an incisor scaffold was implanted orthotopically following mandibular incisor extraction, whereas a human molar scaffold was implanted ectopically into the dorsum. Stromal-derived factor-1 (SDF1) and bone morphogenetic protein-7 (BMP7) were delivered in scaffold microchannels. After 9 weeks, a putative periodontal ligament and new bone regenerated at the interface of rat incisor scaffold with native alveolar bone. SDF1 and BMP7 delivery not only recruited significantly more endogenous cells, but also elaborated greater angiogenesis than growthfactor-free control scaffolds. Regeneration of tooth-like structures and periodontal integration by cell homing provide an alternative to cell delivery, and may accelerate clinical applications.