世界生命科學前沿動態(tài)周報（七十七）

（5.27-6.2/2012）
美寶國際集團:陶國新 

　　主要內容：胎盤干細胞多能性的治療學潛力；脂肪組織間充質干細胞的機械力學性質反映其分化潛能；免疫抑制受體維持正常成體干細胞的干細胞性質；血漿蛋白的纖溶酶原可能治療慢性糖尿病創(chuàng)傷；新發(fā)現(xiàn)有望改變狼瘡和哮喘的研究方向；新的干細胞培養(yǎng)技術可穩(wěn)定的大量生產(chǎn)心肌細胞。

　　焦點動態(tài)：胎盤干細胞多能性的治療學潛力；血漿蛋白的纖溶酶原可能治療慢性糖尿病創(chuàng)傷。

1. 胎盤干細胞多能性的治療學潛力

【動態(tài)】美國科學家的研究最近發(fā)現(xiàn)能夠從人體胎盤絨毛膜大量收集胎盤干細胞，這些干細胞有很重要的治療性能。絨毛膜是胞衣的一部分，通常在產(chǎn)后被丟棄，但是它里面含有源于胚胎的多能干細胞，這些干細胞能夠分化成不同類型的人體細胞。相對于胚胎干細胞，來自胎盤的干細胞常被視為“成體”干細胞。但相對于成體干細胞，胎盤干細胞只有9個月大，并且不需要重編程就已具有多能性。人體絨毛膜間充質干細胞能夠復制超過100代而端粒長度保持不變，同時還不激活端粒酶活性。這些細胞高度表達胚胎干細胞的標志物OCT-4, NANOG, SSEA-3, 和TRA-1–60，在體外能夠分化成為所有三個胚層的組織。該研究表明胎盤干細胞比骨髓移植的治療潛力更大更廣，它們不僅能夠分化成許多不同類型的細胞，還能夠生產(chǎn)生長因子幫助組織修復。在老鼠中移植的胎盤干細胞能夠與不同類型的組織融為一體，與胚胎多能干細胞相比，在老鼠身上胎盤干細胞不形成腫瘤樣結構。從新鮮或冷凍的人體胎盤都能夠分離出功能性的胎盤干細胞，這意味著如果每個人的胎盤在出生時儲存起來而不是丟掉，那么將來有治療需要時就可以從中獲取胎盤干細胞。

【點評】 相比于胚胎干細胞和誘導多能干細胞，胎盤干細胞在倫理方面和安全有效方面都是更好的選擇，只是如何能真正轉化為一種臨床治療手段還需要很多的研究。

【參考論文】
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. 脂肪組織間充質干細胞的機械力學性質反映其分化潛能
【動態(tài)】 組織工程學家能夠利用來自脂肪的間充質干細胞（ASC）制造軟骨，骨組織或更多脂肪。最好用的細胞是那些已經(jīng)像是要變成期望細胞的細胞。盡管ASC因其免疫原性和多能性方面的特點而成為非常吸引人的干細胞源，但必須先得用表面標志物從其他細胞中純化出來才能實際使用，這是關鍵一步，也被證明是很困難的一步。美國科學家最近的研究用原子力顯微鏡檢測未分化ASC的彈性和粘性，并將這類“機械生物標志”與其譜系特異的分化產(chǎn)物相關聯(lián)，發(fā)現(xiàn)來自脂肪的成體干細胞的硬度、粘度和其他機械性質能夠預測它們會變成哪種細胞。這一發(fā)現(xiàn)會有助于從眾多組織樣品中篩選出需要的細胞，富集組織特異性的細胞和大大提高再生組織的質量。

【點評】 干細胞的物理性質能夠反映出它的分化潛能，或者說其物理性質能夠決定它分化成哪種細胞。這為篩選特定的細胞群提供了明確的標準，有助于促進干細胞定向分化的研究以及轉化應用的開發(fā)。

【參考論文】
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. 免疫抑制受體維持正常成體干細胞的干細胞性質
【動態(tài)】中美日科學家的聯(lián)合研究發(fā)現(xiàn)一種免疫系統(tǒng)的受體在保持干細胞不分化和幫助血癌細胞生長方面起到意外的關鍵作用。癌細胞快速增殖部分是因為它們不能分化成成熟細胞，能夠誘導分化的藥物可用于癌癥治療。新的研究在癌細胞上鑒定出了一種抑制分化的蛋白受體，名為傳統(tǒng)免疫抑制受體，作用是維持正常成體干細胞的干細胞性質，在白血病的發(fā)生中有重要作用。這類受體蛋白家族的研究或許會開拓一個整合免疫學與干細胞和癌癥的新研究領域。該研究發(fā)現(xiàn)人體免疫抑制受體LILRB2和老鼠細胞表面相應的受體能夠結合數(shù)種促血管新生蛋白因子，其中兩種與受體LILRB2結合緊密，對細胞產(chǎn)生抑制作用。在干細胞這種抑制使其保持在干細胞狀態(tài)，維持分化成成熟細胞的能力，而不是耗盡能量分化為成熟細胞。
【點評】 該研究發(fā)現(xiàn)的抑制性受體因其維持正常成體干細胞的干細胞性質的功能而將免疫，干細胞，和癌細胞聯(lián)系在一起，對于在整個有機體背景下研究干細胞和癌癥可能會有意外的促進作用。

【參考論文】
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. 血漿蛋白的纖溶酶原可能治療慢性糖尿病創(chuàng)傷
【動態(tài)】盡管創(chuàng)傷愈合的研究已有數(shù)十年，對于慢性創(chuàng)傷特別是糖尿病創(chuàng)傷依然缺乏有效的生物制劑用于治療。瑞典科學家的最新研究報道了血漿蛋白的纖溶酶原（plg）是增強老鼠創(chuàng)傷愈合的關鍵調節(jié)分子。纖溶酶原是眾所周知的血漿蛋白，產(chǎn)于肝臟，遍布全身體液中。他們發(fā)現(xiàn)在創(chuàng)傷處及其周圍纖溶酶原濃度大大升高，并且是啟動愈合必須的炎癥反應的重要信號。但在糖尿病創(chuàng)傷纖溶酶原濃度沒有同樣的升高，這可能是糖尿病創(chuàng)傷難以愈合的原因。給糖尿病老鼠和大鼠的創(chuàng)傷周邊注射纖溶酶原后愈合過程馬上啟動了并最終完全愈合。在愈合過程早期，plg結合在炎癥細胞上運至傷口處，使局部plg水平增加，誘生細胞活素和細胞內信號以及增強早期炎癥反應。整體給與更多的plg不僅促進了野生型老鼠的急性燒傷的愈合，也促進了糖尿病老鼠模型的慢性糖尿病創(chuàng)傷的愈合。其結果意味著使用血漿蛋白的纖溶酶原可能會是治療多種創(chuàng)傷尤其是像糖尿病創(chuàng)傷這種慢性創(chuàng)傷的新治療策略。經(jīng)過幾年成功的試驗室研究后，該蛋白已準備進行臨床測試。

【點評】 由于纖溶酶原是機體自身生產(chǎn)的血漿蛋白，對機體自身幾乎沒有免疫原性。如果在老鼠試驗中發(fā)現(xiàn)的促進糖尿病創(chuàng)傷愈合的能夠在人體臨床實驗重現(xiàn)，那么通過培養(yǎng)和使用纖溶酶原治療慢性糖尿病創(chuàng)傷不失為一種安全有效的選擇。

【參考論文】
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. 新發(fā)現(xiàn)有望改變狼瘡和哮喘的研究方向
【動態(tài)】美國科學家發(fā)現(xiàn)免疫系統(tǒng)的新機理揭示以前從未考慮過的藥物種類有望治療狼瘡和哮喘等過敏性自身免疫疾病。根據(jù)目前的疾病模型，吞噬入侵異物片斷的樹突細胞首先必須在淋巴結內的副皮質區(qū)（或T細胞區(qū)）內遇到T淋巴細胞，才能使淋巴細胞克隆擴增隨后進攻入侵的異物。但美國科學家新的研究發(fā)現(xiàn)盡管在流感病毒感染中免疫反應如此進行，但在其他情況并不總是以這種方式進行。例如，當身體感染寄生蟲后，樹突細胞是在T細胞區(qū)之外B細胞相關信號的控制下在B淋巴細胞附近與T細胞聯(lián)系。鑒于哮喘和狼瘡等疾病的發(fā)作是由于免疫系統(tǒng)錯誤的增強了機體通常用于抵抗寄生蟲的相同類型的T細胞免疫反應，該研究發(fā)現(xiàn)的B淋巴細胞控制觸發(fā)此類反應的T細胞/樹突細胞的相互作用具有重要的實際應用價值。幾種已有的打斷B細胞信號的試驗性藥物現(xiàn)在有理由看看是否能夠成為潛在治療T細胞引起的疾病。
【點評】 該研究為哮喘和狼瘡等自身免疫疾病開拓了一條新的研究思路，雖然看上去很合理，但這條路能否奏效還需要更多的研究和臨床測試。

【參考論文】
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. 新的干細胞培養(yǎng)技術可穩(wěn)定的大量生產(chǎn)心肌細胞
【動態(tài)】條新的研究思路，雖然看上去很合理，但這條路能否奏效還需要更多的研究和臨床測試。美國科學家最近報道了一種通過小分子化合物簡單操控一種關鍵發(fā)育途徑將人體干細胞，包括胚胎干細胞和誘導多能干細胞，轉化為心肌細胞的方法，是替代血清和生長因子的穩(wěn)定，廉價，并且更強力高效的途徑，能在最終細胞群中可靠的獲得超過80% 的心肌細胞，而其他方法只能獲得30% 還有較大的披間差異。

【點評】 這種新的培養(yǎng)方法使用完全明確的小分子化合物取代生長因子，短暫的打開和關閉一種重要的信號途徑來協(xié)調細胞的復雜發(fā)育過程。小分子的穩(wěn)定性使培養(yǎng)更可重復，小分子的經(jīng)濟性使該方法花費更少。對于更穩(wěn)定的獲得更多的心肌細胞，這種方法是一種大的進步。

【參考論文】
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.