新的组织工程种子细胞--内皮祖细胞

内皮祖细胞作为一种在血管领域的干细胞在组织工程中有着广阔的应用前景.内皮祖细胞取材方便,参与新生血管的形成,具有成熟内皮细胞相似的特性.因此,内皮祖细胞可能是组织工程血管、血管植入物再内皮化以及构建组织工程器官血管网络的种子细胞的理想来源.简单介绍了内皮祖细胞的来源、特性以及体外扩增技术,并对其在组织工程中应用的研究进展做一回顾.     

新的组织工程种子细胞——内皮祖细胞

内皮祖细胞作为一种在血管领域的干细胞在组织工程中有着广阔的应用前景。内皮祖细胞取材方便，参与新生血管的形成，具有成熟内皮细胞相似的特性。因此，内皮祖细胞可能是组织工程血管、血管植入物再内皮化以及构建组织工程器官血管网络的种子细胞的理想来源。简单介绍了内皮祖细胞的来源、特性以及体外扩增技术，并对其在组织工程中应用的研究进展做一回顾。     

内皮祖细胞在血管新生及血管组织工程化过程中的生物学意义

内皮祖细胞(EPCs)是能分化为成熟血管内皮细胞的祖细胞,参与了出生后的血管再生和受损内皮的修复过程。近年来围绕以EPCs作为种子细胞来促进血管新生、维持内皮功能完整并构建组织工程化血管方面展开了许多研究。本文就这方面的进展作一综述。     

人血中内皮祖细胞研究现状

人循环血液中存在内皮祖细胞，可以分化成内皮细胞和／或平滑肌细胞并促进血管新生。目前，确定内皮祖细胞还没有一个统一的标准，相对认可为内皮祖细胞的是CD34、AC133和FLK-1等标志阳性细胞。其来源于骨髓，可通过内皮特异性标志VEGFR-2、Ⅷ因子来鉴定，可用密度梯度离心法分离单核细胞，或用免疫磁珠吸附分离法或两种方法结合应用分离出目标细胞，可分化为内皮细胞、平滑肌细胞，用于治疗心肌梗死、肢体缺血、基因载体和组织工程血管重建，本文对此进行了综述。     

先天性心脏病患儿骨髓单核细胞分离培养内皮祖细胞的实验研究

目的探索自先天性心脏病患儿骨髓单核细胞中分离培养内皮祖细胞的方法，期望为儿童组织工程血管、补片或带瓣管道的制备找到新的种子细胞来源。方法采集先天性心脏病患儿骨髓，梯度密度离心法分离单核细胞，内皮细胞培养液EGM-2培养，种植于提前包埋了纤维连接蛋白的培养皿进行体外扩增，取48h后贴壁细胞，应用免疫组织化学和免疫荧光技术鉴定内皮细胞系列标志：CD34、CD31、FLK-1、ve-Cadherin和Ⅷ因子。结果经过梯度密度离心和贴壁法选择的细胞表达内皮细胞特异性抗原：CD34、CD31、FLK-1、ve—Cadherin和Ⅷ因子。培养至第5代细胞形态基本相似，细胞总数可以达到10^8以上。结论自先天性心脏病患儿骨髓单核细胞中可以分离培养出内皮祖细胞并能体外扩增，可以作为先天性心脏病患儿构建组织工程血管的种子细胞来源。     

兔骨髓内皮祖细胞在组织工程血管构建中的实验研究

建立体外分离、培养及鉴定兔骨髓血内皮祖细胞(endothelial progenitor cell,EPCs)的方法,并探讨其在血管组织工程构建过程中的功能。采用密度梯度离心法分离单个核细胞,经培养鉴定为EPCs后作为种子细胞接种于人纤维连接蛋白包被(FN)的组织工程血管支架上,加入血管内皮生长因子(VEGF)、碱性成纤维细胞生长因子(bFGF)进行体外诱导培养,同时设置未包被纤维连接蛋白及未添加血管内皮生长因子(VEGF)、碱性成纤维细胞生长因子(bFGF)的培养方法作为对照组,体外培养10 d后,对构建的组织工程血管进行鉴定分析。分离培养的骨髓单个核细胞呈典型的"铺路石样"外观。经免疫荧光检测、细胞吞噬功能鉴定为内皮祖细胞;种植细胞10 d后结果显示:加入纤维连接蛋白和血管内皮生长因子的血管支架可见细胞种植密度明显高于对照组,扫描电子显微镜观察到,血管内腔面较为完整的覆盖内皮细胞。HE染色显示:内皮细胞在血管支架上成活并较为均匀;免疫组化结果显示分化为成熟血管内皮细胞并表达VEGFR-2、vWF、CD34。兔骨髓单个核细胞体外培养可以诱导分化为内皮祖细胞,血管内皮生长因子(VEGF)、碱性成纤维细胞生长因子(bFGF)和纤维连接蛋白(FN)的组合更有利于内皮祖细胞在血管支架上增殖和分化,为人工血管制备创造了条件。     

兔骨髓内皮祖细胞在组织工程血管构建中的实验研究

建立体外分离、培养及鉴定兔骨髓血内皮祖细胞（endothelial progenitor cell,EPCs）的方法,并探讨其在血管组织工程构建过程中的功能。采用密度梯度离心法分离单个核细胞,经培养鉴定为EPCs后作为种子细胞接种于人纤维连接蛋白包被（FN）的组织工程血管支架上,加入血管内皮生长因子（VEGF）、碱性成纤维细胞生长因子（bFGF）进行体外诱导培养,同时设置未包被纤维连接蛋白及未添加血管内皮生长因子（VEGF）、碱性成纤维细胞生长因子（bFGF）的培养方法作为对照组,体外培养10 d后,对构建的组织工程血管进行鉴定分析。分离培养的骨髓单个核细胞呈典型的＂铺路石样＂外观。经免疫荧光检测、细胞吞噬功能鉴定为内皮祖细胞;种植细胞10 d后结果显示：加入纤维连接蛋白和血管内皮生长因子的血管支架可见细胞种植密度明显高于对照组,扫描电子显微镜观察到,血管内腔面较为完整的覆盖内皮细胞。HE染色显示：内皮细胞在血管支架上成活并较为均匀;免疫组化结果显示分化为成熟血管内皮细胞并表达VEGFR-2、vWF、CD34。兔骨髓单个核细胞体外培养可以诱导分化为内皮祖细胞,血管内皮生长因子（VEGF）、碱性成纤维细胞生长因子（bFGF）和纤维连接蛋白（FN）的组合更有利于内皮祖细胞在血管支架上增殖和分化,为人工血管制备创造了条件。     

内皮祖细胞的动员、归巢和分化

内皮祖细胞是内皮细胞的前体细胞 ,在某些生理、病理状态下可随血流至相应组织 ,分化为内皮细胞 ,并进一步形成血管。内皮祖细胞不仅参与胚胎发育的血管发生 ,而且在成人机体的血管新生中起重要的作用。研究内皮祖细胞的生物学特性、动员、归巢及分化机制将为临床治疗缺血性疾病、创伤修复及抑制肿瘤生长提供理论依据。     

不同细胞浓度种植于脱细胞血管基质上的细胞生长方式*☆

背景：对于组织工程血管而言,如何在平滑肌细胞层上成功获得致密的内皮细胞层是最为关键的。 目的：探索不同细胞种植浓度对构建全生物化组织工程血管的影响。 方法：先将不同浓度(5×105,5×107 L-1)猪血管平滑肌细胞种植在猪脱细胞血管基质上,培养3 d后再将不同浓度(5×105,5×107 L-1)内皮祖细胞接种在平滑肌细胞-血管基质复合体上,构建片状全生物化组织工程材料。 结果与结论：高浓度与低浓度平滑肌细胞在脱细胞血管基质上的细胞生长曲线相似,并且种植在孔板上和在脱细胞基质上的生长曲线亦相似,但低浓度组增殖较慢,覆盖率较低。细胞覆盖率由高到低的顺序为：高浓度内皮祖细胞+含高浓度平滑肌细胞的脱细胞基质>高浓度内皮祖细胞+含低浓度平滑肌细胞的脱细胞基质>低浓度内皮祖细胞+含高浓度平滑肌细胞的脱细胞基质>低浓度内皮祖细胞+含低浓度平滑肌细胞的脱细胞基质,且高浓度内皮祖细胞在脱细胞基质上可形成较为致密的细胞层,呈现出铺路石样生长方式。说明提高细胞接种浓度有利于其在材料表面快速形成致密的细胞层。     

内皮祖细胞的来源及应用

内皮祖细胞（endothelial progenitor cells，EPC）是能自我更新、增殖分化为内皮细胞的多能干细胞，具有迟发性高增殖潜能及定向归巢特性。EPC细胞表面既存在造血干细胞表面标志，如CD34、CDl33，又存在内皮细胞表面标志VEG—FR-2，它可以摄取乙酰化低密度脂蛋白，具有yon Willebrand因子，在体外培养中具有特异的形态特征。它与血管新生、心血管组织工程内皮化等关系密切，在基础研究、肢体缺血性疾病及心血管疾病等领域有关EPC的研究非常活跃，从而为治疗缺血性疾病、血管组织工程及肿瘤治疗提供了新的思路和手段。     

Transplantation of Endothelial Progenitor Cells: Summary and prospect

Endothelial Progenitor Cells (EPCs) are precursor cells of endothelial cells (ECs), which can differentiate into vascular ECs, protect from endothelial dysfunction and tissue ischemia, and reduce vascular hyperplasia. Due to these functions, EPCs are used as a candidate cell source for transplantation strategies. In recent years, a great progress was achieved in EPCs biology research, and EPCs transplantation has become a research hotspot. At present, transplanted EPCs have been used to treat ischemic diseases due to their powerful vasculogenesis and beneficial paracrine effects. Although EPCs transplantation has been proved to play an important role, the clinical application of EPCs still faces many challenges. This review briefly summarized the basic characteristics of EPCs, the process of EPCs transplantation promoting the healing of ischemic tissue, and the ways to improve the efficiency of EPCs transplantation. In addition, the application of EPCs in neurological improvement, cardiovascular and respiratory diseases and the challenges and problems in clinical application of EPCs were also discussed. In the end, the application of EPCs transplantation in regenerative medicine and tissue engineering was discussed.     

New strategies for in vivo tissue engineering by mimicry of homing factors for self-endothelialisation of blood contacting materials

For years intensive research has been done to endothelialise vascular prostheses with autologous endothelial cells before implantation in patients. However, this procedure is extremely time-, labor- and cost-intensive and can be realized only in very few clinical cases. The discovery of circulating endothelial progenitor cells (EPCs) in 1997 brought new perspectives for the endothelialisation of blood contacting materials. Coating of synthetic graft surfaces with capture molecules for circulating EPCs mimics a pro-homing substrate for fishing out EPCs directly from the bloodstream after implantation. These cells with high proliferation potential can cover the graft with non-thrombogenic endothelium which maintains optimal haemostasis and minimize the risk of restenosis. In this review, different concepts are discussed to capture circulating EPCs on synthetic vascular grafts after implantation. We hypothesize that in vivo self-endothelialisation of blood contacting materials by homing factor-mimetic capture molecules for EPCs may bring revolutionary new perspectives towards future clinical application of stem cell and tissue engineering strategies.     

内皮祖细胞与肿瘤血管新生

血管内皮祖细胞（EPCs）是内皮细胞的前体细胞，特异性表达CD34,CD133和VEGFR-2，具有向血管内皮细胞分化的潜能。EPCs主要位于骨髓和外周血。肿瘤的生长和转移依赖于肿瘤血管新生。肿瘤细胞可合成和释放多种细胞因子，在不同因子的趋化作用下EPCs从骨髓动员至外周血循环，然后迁移和定居到肿瘤组织，经细胞因子诱导分化为成熟内皮细胞，参与肿瘤血管新生。VEGF/VEGFR-2信号途径在EPCs参与的肿瘤血管新生方面起重要作用。     

Potential of baboon endothelial progenitor cells for tissue engineered vascular grafts

Thrombosis and intimal hyperplasia limit the usefulness of small caliber vascular grafts. While some improvements have been reported for grafts seeded with mature endothelial cells (EC), the harvesting of ECs from autologous sources, for example, veins or adipose tissue, remains problematic. More recently, endothelial progenitor cells (EPCs) have been considered a promising source of ECs because EPCs can be readily isolated from whole blood then rapidly expanded in vitro. Additionally, EPCs are increasingly recognized to play important roles in hemostasis, angiogenesis, and arterial injury repair. However, the characterization of EPCs in relevant animal models remains poorly defined. Accordingly, we have characterized the isolation, growth, and functional characteristics of Baboon EPCs (BaEPCs) to evaluate their potential for an autologous cell source for tissue engineered vascular grafts. BaEPCs were successfully cultured from the peripheral blood with an average population doubling time of 1.17 +/- 0.43 days. While the BaEPCs were positive for typical EC markers of vWF, CD31, VE-cadherin, VEGF-R2, Thrombomodulin, and E-selectin, there was reduced eNOS expression. The BaEPCs cell body and actin filaments align in the direction of flow typical of mature ECs. Thus while the lack of eNOS expression is worthy of investigation, EPCs are an attractive cell source for tissue engineered vascular grafts and the baboon model has great potential for continuing evaluations of these cells.     

Human endothelial progenitor cell-seeded hybrid graft: proliferative and antithrombogenic potentials in vitro and fabrication processing

In this article, we show that human endothelial progenitor cells (EPCs) in circulating peripheral blood may be a novel cell source for a cell-incorporated engineered vascular graft. Cultures of human peripheral blood mononuclear cells collected by the density gradient technique developed highly proliferative EPC colonies, which expanded with culture time. The production rates of antiplatelet substances such as endothelial-type nitric oxide synthase and 6-keto-prostaglandin-F(1)-alpha were approximately one-third and approximately one-half of those of mature endothelial cells (ECs), respectively. On the other hand, the tissue-type plasminogen activator production rate of EPCs was almost the same as that of ECs. EPCs were seeded and cultured on a small-diameter compliant graft (inner diameter, 1.5 mm) made of microporous segmented polyurethane film coated with a photo-reactive gelatin layer, and subsequently subjected to hydrodynamic shear stress by ex vivo circulation. EPCs fully covering the graft elongated and aligned themselves with the direction of the flow, resulting in the production of an integrated EPC-engineered graft. These results indicate that EPCs, which have high proliferative potential and high antithrombogenic potential, comparable to those of ECs, are a suitable cell source for cardiovascular tissue engineering.     

内皮祖细胞与雌激素

背景：研究发现雌激素对血管内皮具有明显的保护作用,而内皮祖细胞作为内皮细胞的前体细胞参与内皮的修复。 目的：总结内皮祖细胞生物特点及雌激素对内皮祖细胞作用的研究进展。 方法：应用计算机检索PubMed数据库及CNKI数据库,在标题和摘要中以“内皮祖细胞,雌激素”或“Endothelial progenitor cells,estrogen”为检索词进行检索。选择与内皮祖细胞生物学特点及雌激素对其作用研究相关的文献。 结果与结论：内皮祖细胞存在于骨髓和外周血中,是具有增殖、迁移、黏附能力并分化为血管内皮细胞潜能的原始细胞,可作为未来治疗心血管疾病的重要的靶点。雌激素对内皮祖细胞有保护效应,能增强内皮祖细胞增殖、迁移、黏附等生物活性,同时还能延迟内皮祖细胞衰老、拮抗其凋亡。但雌激素影响内皮祖细胞生物活性的具体靶点及机制尚有待进一步研究。     

Immobilized DNA aptamers used as potent attractors for porcine endothelial precursor cells

Because of their insufficient biocompatibility and high thrombogenicity, small diameter artificial vascular prostheses still do not show a satisfactory patency rate. In vitro endothelialization of artificial grafts before implantation has been established experimentally years ago, but, this procedure is extremely time consuming and expensive. This study deals with the coating of graft surfaces with capture molecules (aptamers) for circulating endothelial progenitor cells (EPCs), mimicking a prohoming substrate to fish out EPCs from the bloodstream after implantation and to create an autologous functional endothelium. Using the SELEX technology, aptamers with a high affinity to EPCs were identified, isolated, and grafted onto polymeric discs using a blood compatible star-PEG coating. A porcine in vitro model that demonstrates the specific adhesion of EPCs and their differentiation into vital endothelial-like cells within 10 days in cell culture is presented. We suggest that the rapid adhesion of EPCs to aptamer-coated implants could be useful to promote endothelial wound healing and to prevent increased neointimal hyperplasia. We hypothesize that future in vivo self-endothelialization of blood contacting implants by homing factor mimetic capture molecules for EPCs may bring revolutionary new perspectives towards clinical applications of stem cell and tissue engineering strategies.     

Composite implantation of mesenchymal stem cells with endothelial progenitor cells enhances tissue-engineered bone formation

For successful tissue engineering, neovascularization of the implanted tissue is critical. Factors generated by endothelial cells are also considered crucial for the process of osteogenesis. The direct effects of supplementing tissue engineered constructs with cultured endothelial progenitor cells (EPCs) for enhancing bone regeneration have not been reported. In this study, we investigated the potential of EPCs to facilitate neovascularization in implants and evaluated their influence on bone regeneration. The influence of EPC soluble factors on osteogenic differentiation of mesenchymal stem cells (MSCs) was tested by adding EPC culture supernatant to MSC culture medium. To evaluate the influence of EPCs on MSC osteogenesis, canine MSCs-derived osteogenic cells and EPCs were seeded independently onto collagen fiber mesh scaffolds and co-transplanted to nude mice subcutaneously. Results from coimplant experiments were compared to implanted cells absent of EPCs 12 weeks after implantation. Factors from the culture supernatant of EPCs did not influence MSC differentiation. Coimplanted EPCs increased neovascularization and the capillary score was 1.6-fold higher as compared to the MSC only group (p < 0.05). Bone area was also greater in the MSC + EPC group (p < 0.05) and the bone thickness was 1.3-fold greater in the MSC + EPC group than the MSC only group (p < 0.05). These results suggest that soluble factors generated by EPCs may not facilitate the osteogenic differentiation of MSCs; however, newly formed vasculature may enhance regeneration of tissue-engineered bone.