世界生命科学前沿动态周报（六十一）

（10.10-10.16/2011）
美宝国际集团:陶国新 

　　主要内容：快速高效的将体细胞重组为干细胞；微小RNA-101是有效的细胞自噬抑制剂；用分子感受器原位定量显示细胞脂质；运动能够防治偏头痛；在伤后肺部修复中环支气管平滑肌细胞构建气管上皮干细胞微环境；在胰腺β细胞中PDGF信号控制年龄依赖性增殖。

　　焦点动态：在伤后肺部修复中环支气管平滑肌细胞构建气管上皮干细胞微环境

1.快速高效的将体细胞重组为干细胞

【动态】
通过表达四种转录因子Oct4, Sox2, Klf4, 和 c-Myc，体细胞能够重组成诱导多能干细胞（iPSCs）。中美英三国科学家的联合研究发现了可以将重组效率提高100倍的的方法。他们发现通过表达维甲酸受体（RARs）或通过维甲酸激动剂增强维甲酸信号能够极大的促进细胞重组，但是用RAR-α阴性形式抑制维甲酸信号会完全阻断细胞重组。与上述四种转录因子同时表达RAR-γ和Lrh-1(肝受体同源物-1)能够大大加速细胞重组，通过这种方法老鼠胚胎成纤维细胞重组成基态的诱导多能干细胞仅仅需要4天。该发现说明RARs介导的信号在重组中有关键作用以及RAR-γ和Lrh-1之间的协同作用指导细胞向基态多能性方向重组。

【点评】
该发现大大提高了体细胞重组为干细胞的效率和速度，使干细胞的获得变得容易，对于深入研究干细胞的生命规律会有很大帮助。       

【参考论文】
Proceedings of the National Academy of Sciences, 2011; DOI: 10.1073/pnas.1100893108
Rapid and efficient reprogramming of somatic cells to induced pluripotent stem cells by retinoic acid receptor gamma and liver receptor homolog.
Wang et al.
Somatic cells can be reprogrammed to induced pluripotent stem cells (iPSCs) by expressing four transcription factors: Oct4, Sox2, Klf4, and c-Myc. Here we report that enhancing RA signaling by expressing RA receptors (RARs) or by RA agonists profoundly promoted reprogramming, but inhibiting it using a RAR-α dominant-negative form completely blocked it. Coexpressing Rarg (RAR-γ) and Lrh-1 (liver receptor homologue 1; Nr5a2) with the four factors greatly accelerated reprogramming so that reprogramming of mouse embryonic fibroblast cells to ground-state iPSCs requires only 4 d induction of these six factors. The six-factor combination readily reprogrammed primary human neonatal and adult fibroblast cells to exogenous factor-independent iPSCs, which resembled ground-state mouse ES cells in growth properties, gene expression, and signaling dependency. Our findings demonstrate that signaling through RARs has critical roles in molecular reprogramming and that the synergistic interaction between Rarg and Lrh1 directs reprogramming toward ground-state pluripotency. The human iPSCs described here should facilitate functional analysis of the human genome.

2. 微小RNA-101是有效的细胞自噬抑制剂

【动态】
自噬是一种进化上保守的细胞自消化机制，把蛋白和细胞器送到溶酶体来降解。在包括癌症在内的许多人体疾病中牵涉到这一过程存在的缺陷。为了进一步阐明自噬的调节机制，丹麦科学家对在乳腺癌细胞中调节自噬流的微小RNA（miRNA）进行了功能筛选，鉴定出肿瘤抑制性miRNA, miR-101,是依托伯苷和雷帕霉素诱导的基础自噬的有效抑制剂。通过转录组分析，他们确定了三个miR-101的新靶点，STMN1, RAB5A 和 ATG4D，通过siRNA静默这些基因，能够模拟过多表达miR-101产生的表型，显示了这些基因在自噬调节中的重要性。特别是，过表达STMN1能够部分拯救细胞于miR-101介导的自噬抑制，揭示了该靶点的重要功能。最后，他们的研究还显示miR-101介导的自噬抑制能够使乳腺癌细胞对4-羟基他莫西芬（4-OHT）引起的细胞死亡更敏感。总而言之，这些研究结果在两个非常重要的快速发展的研究领域间建立了新的联系，提出了miR-101作为关键的自噬调节子的新作用。

【点评】
miR-101对细胞尤其是乳腺癌细胞自噬的调节的研究，对于解决癌细胞对部分抗癌药物的抗药性开启了一条新路。

【参考论文】
The EMBO Journal, 2011; DOI: 10.1038/emboj.2011.331
microRNA-101 is a potent inhibitor of autophagy
Lisa B Frankel, Jiayu Wen, Michael Lees, et al.
Autophagy is an evolutionarily conserved mechanism of cellular self-digestion in which proteins and organelles are degraded through delivery to lysosomes. Defects in this process are implicated in numerous human diseases including cancer. To further elucidate regulatory mechanisms of autophagy, we performed a functional screen in search of microRNAs (miRNAs), which regulate the autophagic flux in breast cancer cells. In this study, we identified the tumour suppressive miRNA, miR-101, as a potent inhibitor of basal, etoposide- and rapamycin-induced autophagy. Through transcriptome profiling, we identified three novel miR-101 targets, STMN1, RAB5A and ATG4D. siRNA-mediated depletion of these genes phenocopied the effect of miR-101 overexpression, demonstrating their importance in autophagy regulation. Importantly, overexpression of STMN1 could partially rescue cells from miR-101-mediated inhibition of autophagy, indicating a functional importance for this target. Finally, we show that miR-101-mediated inhibition of autophagy can sensitize breast cancer cells to 4-hydroxytamoxifen (4-OHT)-mediated cell death. Collectively, these data establish a novel link between two highly important and rapidly growing research fields and present a new role for miR-101 as a key regulator of autophagy.

3.  用分子感受器原位定量显示细胞脂质

【动态】
膜脂是动态的分子，在细胞信号传导和调节中起重要作用，但目前还缺少在活细胞中定量追踪膜脂分子的原位显像技术。美国科学家最近报道了一种新的化学方法用环境敏感性荧光团标记的工程蛋白作为感受器定量显像膜脂分子。这种感受器能够在哺乳动物细胞中进行强力和敏感的显影。在免疫细胞中的应用揭示了触发吞噬作用必须的PtdIns(4,5)P2（一种关键的信号脂分子）浓度阈值。这一策略普遍适用于细胞脂类分子的原位定量。

【点评】
原位定量显示特定分子的技术使得我们能够深入了解一些重要的生物分子的数量和浓度水平与特定生物事件的关系，从而能更准确地把握事件的发生过程和机理。

【参考论文】
Nature Chemistry, 2011; DOI: 10.1038/nchem.1163
In situ quantitative imaging of cellular lipids using molecular sensors
Youngdae Yoon, Park J. Lee, Svetlana Kurilova, Wonhwa Cho.
Membrane lipids are dynamic molecules that play important roles in cell signalling and regulation, but an in situ imaging method for quantitatively tracking lipids in living cells is lacking at present. Here, we report a new chemical method of quantitative lipid imaging using sensors engineered by labelling proteins with an environmentally sensitive fluorophore. A prototype sensor for phosphatidylinositol-4,5-bisphosphate (PtdIns(4,5)P2)—a key signalling lipid in diverse cellular processes—was generated by covalently attaching a single 2-dimethylamino-6-acyl-naphthalene group to the N-terminal α-helix of the engineered epsin1 ENTH domain, a protein that selectively binds PtdIns(4,5)P2. The sensor allows robust and sensitive in situ quantitative imaging in mammalian cells, providing new insight into the spatiotemporal dynamics and fluctuation of this key signalling lipid. Application of the sensor to immune cells reveals the presence of a local threshold PtdIns(4,5)P2 concentration required for triggering phagocytosis. This sensor strategy is generally applicable to in situ quantification of other cellular lipids.

4.  运动能够防治偏头痛

【动态】
瑞典科学家最近报道了运动防治偏头痛的第一个确凿的科学证据。在一项涉及91例成年偏头痛患者的随机对照临床试验中，1/3人在理疗师监督下每周运动3次，每次40分钟；另外1/3做放松活动；最后1/3服用药物Topiramate（妥泰）。研究持续3个月，其间对患者的偏头痛状态、生活质量、身体活动水平和氧气摄入量都进行评估。主要的效果参数是相对于基线水平，治疗最后一个月偏头痛发作频率的平均减少量。结果显示三组偏头痛次数都减少了，有意思的是，三组间预防和减少偏头痛的效果没有差异，意味着运动和放松、服药对于防治偏头痛有相同作用，可以作为不能或不愿服药时的选择。

【点评】
该研究提供了比较充分的科学依据证明对于偏头痛，运动的确能够起到和药物一样的防治效果。

【参考论文】
Cephalalgia, 2011; DOI: 10.1177/0333102411419681
Exercise as migraine prophylaxis: A randomized study using relaxation and topiramate as controls
E. Varkey, A. Cider, J. Carlsson, M. Linde.

Aim: Scientific evidence regarding exercise in migraine prophylaxis is required. Therefore this study aimed to evaluate the effects of exercise in migraine prevention.
Methods: In a randomized, controlled trial of adults with migraine, exercising for 40 minutes three times a week was compared to relaxation according to a recorded programme or daily topiramate use, which was slowly increased to the individual’s highest tolerable dose (maximum 200 mg/day). The treatment period lasted for 3 months, and migraine status, quality of life, level of physical activity, and oxygen uptake were evaluated. The primary efficacy variable was the mean reduction of the frequency of migraine attacks during the final month of treatment compared with the baseline.
Results: Ninety-one patients were randomized and included in the intention-to-treat analysis. The primary efficacy variable showed a mean reduction of 0.93 (95% confidence interval (CI) 0.31–1.54) attacks in the exercise group, 0.83 (95% CI 0.22–1.45) attacks in the relaxation group, and 0.97 (95% CI 0.36–1.58) attacks in the topiramate group. No significant difference was observed between the groups (p = 0.95).
Conclusion: Exercise may be an option for the prophylactic treatment of migraine in patients who do not benefit from or do not want to take daily medication.

5.  在伤后肺部修复中环支气管平滑肌细胞构建气管上皮干细胞微环境

【动态】
美国比利时和德国的科学家的一项合作研究最近确定了触发肺部受伤后的修复的细胞和信号分子。老鼠肺部组织受伤诱导气管周围平滑肌细胞分泌纤维母细胞生长因子10（FGF10），后者诱导气管的幸存上皮细胞回归干细胞状态并增殖、修复和重整肺部组织，该修复过程很像肺部形成时的原始发育过程。

【点评】
该研究结果说明机体具有伤后自我修复的能力并且是通过将体细胞激活到干细胞状态再进行类似器官发育的过程修复受损组织。

【参考论文】
Journal of Clinical Investigation, 2011; DOI: 10.1172/JCI58097
Parabronchial smooth muscle constitutes an airway epithelial stem cell niche in the mouse lung after injury
Thomas Volckaert, Erik Dill, Alice Campbell, et al.
During lung development, parabronchial SMC (PSMC) progenitors in the distal mesenchyme secrete fibroblast growth factor 10 (Fgf10), which acts on distal epithelial progenitors to promote their proliferation. β-catenin signaling within PSMC progenitors is essential for their maintenance, proliferation, and expression of Fgf10. Here, we report that this Wnt/Fgf10 embryonic signaling cascade is reactivated in mature PSMCs after naphthalene-induced injury to airway epithelium. Furthermore, we found that this paracrine Fgf10 action was essential for activating surviving variant Clara cells (the cells in the airway epithelium from which replacement epithelial cells originate) located at the bronchoalveolar duct junctions and adjacent to neuroendocrine bodies. After naphthalene injury, PSMCs secreted Fgf10 to activate Notch signaling and induce Snai1 expression in surviving variant Clara cells, which subsequently underwent a transient epithelial to mesenchymal transition to initiate the repair process. Epithelial Snai1 expression was important for regeneration after injury. We have therefore identified PSMCs as a stem cell niche for the variant Clara cells in the lung and established that paracrine Fgf10 signaling from the niche is critical for epithelial repair after naphthalene injury. These findings also have implications for understanding the misregulation of lung repair in asthma and cancer.

6.  在胰腺β细胞中PDGF信号控制年龄依赖性增殖

【动态】
美国科学家最近确定了一个导致人随年龄增长生产胰岛素的细胞的增殖自然减少的关键信号途径。在老鼠和人体内胰腺β细胞的旺盛增殖随年龄增加而减弱，血小板源生长因子受体（Pdgfr）信号控制胰岛的年龄依赖性β细胞增殖。随着变老，β细胞Pdgfr水平和β细胞增强子Ezh2以及β细胞增殖同时减少。

【点评】
该研究发现为增强胰岛β细胞增殖提供了新的研究方向。

【参考论文】
Nature, 2011; DOI: 10.1038/nature10502
PDGF signalling controls age-dependent proliferation in pancreatic β-cells
Hainan Chen, Xueying Gu, Yinghua Liu, et al.  
Determining the signalling pathways that direct tissue expansion is a principal goal of regenerative biology. Vigorous pancreatic β-cell replication in juvenile mice and humans declines with age, and elucidating the basis for this decay may reveal strategies for inducing β-cell expansion, a long-sought goal for diabetes therapy. Here we show that platelet-derived growth factor receptor (Pdgfr) signalling controls age-dependent β-cell proliferation in mouse and human pancreatic islets. With age, declining β-cell Pdgfr levels were accompanied by reductions in β-cell enhancer of zeste homologue 2 (Ezh2) levels and β-cell replication. Conditional inactivation of the Pdgfra gene in β-cells accelerated these changes, preventing mouse neonatal β-cell expansion and adult β-cell regeneration. Targeted human PDGFR-α activation in mouse β-cells stimulated Erk1/2 phosphorylation, leading to Ezh2-dependent expansion of adult β-cells. Adult human islets lack PDGF signalling competence, but exposure of juvenile human islets to PDGF-AA stimulated β-cell proliferation. The discovery of a conserved pathway controlling age-dependent β-cell proliferation indicates new strategies for β-cell expansion