世界生命科学前沿动态周报（七十七）

（5.27-6.2/2012）
美宝国际集团:陶国新 

　　主要内容：胎盘干细胞多能性的治疗学潜力；脂肪组织间充质干细胞的机械力学性质反映其分化潜能；免疫抑制受体维持正常成体干细胞的干细胞性质；血浆蛋白的纤溶酶原可能治疗慢性糖尿病创伤；新发现有望改变狼疮和哮喘的研究方向；新的干细胞培养技术可稳定的大量生产心肌细胞。

　　焦点动态：胎盘干细胞多能性的治疗学潜力；血浆蛋白的纤溶酶原可能治疗慢性糖尿病创伤。

1. 胎盘干细胞多能性的治疗学潜力

【动态】美国科学家的研究最近发现能够从人体胎盘绒毛膜大量收集胎盘干细胞，这些干细胞有很重要的治疗性能。绒毛膜是胞衣的一部分，通常在产后被丢弃，但是它里面含有源于胚胎的多能干细胞，这些干细胞能够分化成不同类型的人体细胞。相对于胚胎干细胞，来自胎盘的干细胞常被视为“成体”干细胞。但相对于成体干细胞，胎盘干细胞只有9个月大，并且不需要重编程就已具有多能性。人体绒毛膜间充质干细胞能够复制超过100代而端粒长度保持不变，同时还不激活端粒酶活性。这些细胞高度表达胚胎干细胞的标志物OCT-4, NANOG, SSEA-3, 和TRA-1–60，在体外能够分化成为所有三个胚层的组织。该研究表明胎盘干细胞比骨髓移植的治疗潜力更大更广，它们不仅能够分化成许多不同类型的细胞，还能够生产生长因子帮助组织修复。在老鼠中移植的胎盘干细胞能够与不同类型的组织融为一体，与胚胎多能干细胞相比，在老鼠身上胎盘干细胞不形成肿瘤样结构。从新鲜或冷冻的人体胎盘都能够分离出功能性的胎盘干细胞，这意味着如果每个人的胎盘在出生时储存起来而不是丢掉，那么将来有治疗需要时就可以从中获取胎盘干细胞。

【点评】 相比于胚胎干细胞和诱导多能干细胞，胎盘干细胞在伦理方面和安全有效方面都是更好的选择，只是如何能真正转化为一种临床治疗手段还需要很多的研究。

【参考论文】
Stem Cells Trans Med, May 8, 2012 DOI:10.5966/sctm.2011-0021
Multipotent Stromal Stem Cells from Human Placenta Demonstrate High Therapeutic Potential
Igor Nazarov, Jae W. Lee, Eric Soupene, et al.
We describe human chorionic mesenchymal stem cell (hCMSC) lines obtained from the chorion of human term placenta with high therapeutic potential in human organ pathology. hCMSCs propagated for more than 100 doublings without a decrease in telomere length and with no telomerase activity. Cells were highly positive for the embryonic stem cell markers OCT-4, NANOG, SSEA-3, and TRA-1–60. In vitro, cells could be differentiated into neuron-like cells (ectoderm), adipocytes, osteoblasts, endothelial-like cells (mesoderm), and hepatocytes (endoderm)—derivatives of all three germ layers. hCMSCs effectively facilitated repair of injured epithelium as demonstrated in an ex vivo-perfused human lung preparation injured by Escherichia coli endotoxin and in in vitro human lung epithelial cultures. We conclude that the chorion of human term placenta is an abundant source of multipotent stem cells that are promising candidates for cell-based therapies.

2. 脂肪组织间充质干细胞的机械力学性质反映其分化潜能
【动态】 组织工程学家能够利用来自脂肪的间充质干细胞（ASC）制造软骨，骨组织或更多脂肪。最好用的细胞是那些已经像是要变成期望细胞的细胞。尽管ASC因其免疫原性和多能性方面的特点而成为非常吸引人的干细胞源，但必须先得用表面标志物从其他细胞中纯化出来才能实际使用，这是关键一步，也被证明是很困难的一步。美国科学家最近的研究用原子力显微镜检测未分化ASC的弹性和粘性，并将这类“机械生物标志”与其谱系特异的分化产物相关联，发现来自脂肪的成体干细胞的硬度、粘度和其他机械性质能够预测它们会变成哪种细胞。这一发现会有助于从众多组织样品中筛选出需要的细胞，富集组织特异性的细胞和大大提高再生组织的质量。

【点评】 干细胞的物理性质能够反映出它的分化潜能，或者说其物理性质能够决定它分化成哪种细胞。这为筛选特定的细胞群提供了明确的标准，有助于促进干细胞定向分化的研究以及转化应用的开发。

【参考论文】
PNAS, 2012 DOI:10.1073/pnas.1120349109
Cellular mechanical properties reflect the differentiation potential of adipose-derived mesenchymal stem cells
Rafael D. González-Cruz, Vera C. Fonseca, and Eric M. Darling.  
The mechanical properties of adipose-derived stem cell (ASC) clones correlate with their ability to produce tissue-specific metabolites, a finding that has dramatic implications for cell-based regenerative therapies. Autologous ASCs are an attractive cell source due to their immunogenicity and multipotent characteristics. However, for practical applications ASCs must first be purified from other cell types, a critical step which has proven difficult using surface-marker approaches. Alternative enrichment strategies identifying broad categories of tissue-specific cells are necessary for translational applications. One possibility developed in our lab uses single-cell mechanical properties as predictive biomarkers of ASC clonal differentiation capability. Elastic and viscoelastic properties of undifferentiated ASCs were tested via atomic force microscopy and correlated with lineage-specific metabolite production. Cell sorting simulations based on these “mechanical biomarkers” indicated they were predictive of differentiation capability and could be used to enrich for tissue-specific cells, which if implemented could dramatically improve the quality of regenerated tissues.

3. 免疫抑制受体维持正常成体干细胞的干细胞性质
【动态】中美日科学家的联合研究发现一种免疫系统的受体在保持干细胞不分化和帮助血癌细胞生长方面起到意外的关键作用。癌细胞快速增殖部分是因为它们不能分化成成熟细胞，能够诱导分化的药物可用于癌症治疗。新的研究在癌细胞上鉴定出了一种抑制分化的蛋白受体，名为传统免疫抑制受体，作用是维持正常成体干细胞的干细胞性质，在白血病的发生中有重要作用。这类受体蛋白家族的研究或许会开拓一个整合免疫学与干细胞和癌症的新研究领域。该研究发现人体免疫抑制受体LILRB2和老鼠细胞表面相应的受体能够结合数种促血管新生蛋白因子，其中两种与受体LILRB2结合紧密，对细胞产生抑制作用。在干细胞这种抑制使其保持在干细胞状态，维持分化成成熟细胞的能力，而不是耗尽能量分化为成熟细胞。
【点评】 该研究发现的抑制性受体因其维持正常成体干细胞的干细胞性质的功能而将免疫，干细胞，和癌细胞联系在一起，对于在整个有机体背景下研究干细胞和癌症可能会有意外的促进作用。

【参考论文】
Nature, 2012; 485 (7400): 656 DOI:10.1038/nature11095
Inhibitory receptors bind ANGPTLs and support blood stem cells and leukaemia development
Junke Zheng, Masato Umikawa, Changhao Cui, et al.
How environmental cues regulate adult stem cell and cancer cell activity through surface receptors is poorly understood. Angiopoietin-like proteins (ANGPTLs), a family of seven secreted glycoproteins, are known to support the activity of haematopoietic stem cells (HSCs) in vitro and in vivo. ANGPTLs also have important roles in lipid metabolism, angiogenesis and inflammation, but were considered ‘orphan ligands’ because no receptors were identified. Here we show that the immune-inhibitory receptor human leukocyte immunoglobulin-like receptor B2 (LILRB2) and its mouse orthologue paired immunoglobulin-like receptor (PIRB) are receptors for several ANGPTLs. LILRB2 and PIRB are expressed on human and mouse HSCs, respectively, and the binding of ANGPTLs to these receptors supported ex vivo expansion of HSCs. In mouse transplantation acute myeloid leukaemia models, a deficiency in intracellular signalling of PIRB resulted in increased differentiation of leukaemia cells, revealing that PIRB supports leukaemia development. Our study indicates an unexpected functional significance of classical immune-inhibitory receptors in maintenance of stemness of normal adult stem cells and in support of cancer development.

4. 血浆蛋白的纤溶酶原可能治疗慢性糖尿病创伤
【动态】尽管创伤愈合的研究已有数十年，对于慢性创伤特别是糖尿病创伤依然缺乏有效的生物制剂用于治疗。瑞典科学家的最新研究报道了血浆蛋白的纤溶酶原（plg）是增强老鼠创伤愈合的关键调节分子。纤溶酶原是众所周知的血浆蛋白，产于肝脏，遍布全身体液中。他们发现在创伤处及其周围纤溶酶原浓度大大升高，并且是启动愈合必须的炎症反应的重要信号。但在糖尿病创伤纤溶酶原浓度没有同样的升高，这可能是糖尿病创伤难以愈合的原因。给糖尿病老鼠和大鼠的创伤周边注射纤溶酶原后愈合过程马上启动了并最终完全愈合。在愈合过程早期，plg结合在炎症细胞上运至伤口处，使局部plg水平增加，诱生细胞活素和细胞内信号以及增强早期炎症反应。整体给与更多的plg不仅促进了野生型老鼠的急性烧伤的愈合，也促进了糖尿病老鼠模型的慢性糖尿病创伤的愈合。其结果意味着使用血浆蛋白的纤溶酶原可能会是治疗多种创伤尤其是像糖尿病创伤这种慢性创伤的新治疗策略。经过几年成功的试验室研究后，该蛋白已准备进行临床测试。

【点评】 由于纤溶酶原是机体自身生产的血浆蛋白，对机体自身几乎没有免疫原性。如果在老鼠试验中发现的促进糖尿病创伤愈合的能够在人体临床实验重现，那么通过培养和使用纤溶酶原治疗慢性糖尿病创伤不失为一种安全有效的选择。

【参考论文】
Blood, 2012; DOI: 10.1182/blood-2012-01-407825
Plasminogen is a key pro-inflammatory regulator that accelerates the healing of acute and diabetic wounds.
Y. Shen, Y. Guo, P. Mikus, et al.
Despite decades of research on wound healing, effective biologic agents for the treatment of chronic wounds, especially diabetic wounds, are still lacking. In this study, we report that the inert plasma protein plasminogen (plg) acts as a key regulatory molecule that potentiates wound healing in mice. Early in the healing process, plg bound to inflammatory cells is transported to the wound area, where the level of plg is locally increased. This leads to induction of cytokines and intracellular signaling events and to a potentiation of the early inflammatory response. Systemic administration of additional plg not only accelerates the healing of acute burn wounds in wild-type mice but also improves the healing of chronic diabetic wounds in a mouse model of diabetes. Our results suggest that administration of plg may be a novel therapeutic strategy to treat many different types of wounds, especially those that are chronic, such as diabetic wounds.

5. 新发现有望改变狼疮和哮喘的研究方向
【动态】美国科学家发现免疫系统的新机理揭示以前从未考虑过的药物种类有望治疗狼疮和哮喘等过敏性自身免疫疾病。根据目前的疾病模型，吞噬入侵异物片断的树突细胞首先必须在淋巴结内的副皮质区（或T细胞区）内遇到T淋巴细胞，才能使淋巴细胞克隆扩增随后进攻入侵的异物。但美国科学家新的研究发现尽管在流感病毒感染中免疫反应如此进行，但在其他情况并不总是以这种方式进行。例如，当身体感染寄生虫后，树突细胞是在T细胞区之外B细胞相关信号的控制下在B淋巴细胞附近与T细胞联系。鉴于哮喘和狼疮等疾病的发作是由于免疫系统错误的增强了机体通常用于抵抗寄生虫的相同类型的T细胞免疫反应，该研究发现的B淋巴细胞控制触发此类反应的T细胞/树突细胞的相互作用具有重要的实际应用价值。几种已有的打断B细胞信号的试验性药物现在有理由看看是否能够成为潜在治疗T细胞引起的疾病。
【点评】 该研究为哮喘和狼疮等自身免疫疾病开拓了一条新的研究思路，虽然看上去很合理，但这条路能否奏效还需要更多的研究和临床测试。

【参考论文】
Nature Immunology, 2012; DOI: 10.1038/ni.2309
Regulation of TH2 development by CXCR5 dendritic cells and lymphotoxin-expressing B cells
Beatriz León, André Ballesteros-Tato, Jeffrey L Browning,  et al.
Although cognate encounters between antigen-bearing dendritic cells (DCs) that express the chemokine receptor CCR7 and CCR7+ naive T cells take place in the T cell zone of lymph nodes, it is unknown whether the colocalization of DCs and T cells in the T cell area is required for the generation of effector cells. Here we found that after infection with an intestinal nematode, antigen-bearing DCs and CD4+ T cells upregulated the chemokine receptor CXCR5 and localized together outside the T cell zone by a mechanism dependent on the chemokine CXCL13, B cells and lymphotoxin. Notably, lymphotoxin-expressing B cells, CXCR5-expressing DCs and T cells, and CXCL13 were also necessary for development of interleukin 4 (IL-4)-producing type 2 helper T cells (TH2 cells), which suggests that TH2 differentiation can initiate outside the T cell zone.

6. 新的干细胞培养技术可稳定的大量生产心肌细胞
【动态】条新的研究思路，虽然看上去很合理，但这条路能否奏效还需要更多的研究和临床测试。美国科学家最近报道了一种通过小分子化合物简单操控一种关键发育途径将人体干细胞，包括胚胎干细胞和诱导多能干细胞，转化为心肌细胞的方法，是替代血清和生长因子的稳定，廉价，并且更强力高效的途径，能在最终细胞群中可靠的获得超过80% 的心肌细胞，而其他方法只能获得30% 还有较大的披间差异。

【点评】 这种新的培养方法使用完全明确的小分子化合物取代生长因子，短暂的打开和关闭一种重要的信号途径来协调细胞的复杂发育过程。小分子的稳定性使培养更可重复，小分子的经济性使该方法花费更少。对于更稳定的获得更多的心肌细胞，这种方法是一种大的进步。

【参考论文】
PNAS, May 29, 2012, doi: 10.1073/pnas.1200250109
Robust cardiomyocyte differentiation from human pluripotent stem cells via temporal modulation of canonical Wnt signaling
Xiaojun Lian, Cheston Hsiaoa, Gisela Wilson, et al.

Human pluripotent stem cells (hPSCs) offer the potential to generate large numbers of functional cardiomyocytes from clonal and patient-specific cell sources. Here we show that temporal modulation of Wnt signaling is both essential and sufficient for efficient cardiac induction in hPSCs under defined, growth factor-free conditions. shRNA knockdown of β-catenin during the initial stage of hPSC differentiation fully blocked cardiomyocyte specification, whereas glycogen synthase kinase 3 inhibition at this point enhanced cardiomyocyte generation. Furthermore, sequential treatment of hPSCs with glycogen synthase kinase 3 inhibitors followed by inducible expression of β-catenin shRNA or chemical inhibitors of Wnt signaling produced a high yield of virtually (up to 98%) pure functional human cardiomyocytes from multiple hPSC lines. The robust ability to generate functional cardiomyocytes under defined, growth factor-free conditions solely by genetic or chemically mediated manipulation of a single developmental pathway should facilitate scalable production of cardiac cells suitable for research and regenerative applications.