Hypoxia-inducible factor-1α is essential for hypoxia-induced mesenchymal stem cell mobilization into the peripheral blood

Mobilization of mesenchymal stem cells (MSCs) is a promising strategy for tissue repair and regenerative medicine. The establishment of an appropriate animal model and clarification of the underlying mechanisms are beneficial to develop the mobilization regimens for therapeutic use. In this study, we therefore established a rat MSC mobilization model and investigated the related mechanisms, using continuous hypoxia as the mobilizing stimulus. We found that MSCs could be mobilized into peripheral blood of rats exposed to short-term hypoxia (2 days) and the mobilization efficiency increased in a time-dependent manner (2-14 days). Hypoxia-inducible factor-1α (HIF-1α) was upregulated during hypoxic exposure and was expressed continuously in bone marrow. Inhibition of HIF-1α expression by YC-1 remarkably reduced the number of mobilized MSCs, suggesting that HIF-1α is essential for hypoxia-induced MSC mobilization. Further, we investigated the potential role of HIF-1α target genes, vascular endothelial growth factor (VEGF), and stromal cell-derived factor-1α (SDF-1α). VEGF expression was elevated from day 2 to day 7 of hypoxia, stimulating an increase in bone marrow sinusoidal vessels and possibly facilitating the egress of MSCs. SDF-1α protein levels were increased in the peripheral blood of rats during MSC mobilization and promoted the migration of MSCs under hypoxic conditions in vitro. These results suggest that HIF-1α plays a pivotal role in hypoxia-induced MSC mobilization, possibly acting via its downstream genes VEGF and SDF-1α. These data provide a novel insight into the mechanisms responsible for MSC mobilization and may help in the development of clinically useful therapeutic agents.     

长期培养对基质细胞衍生因子1/CXCR4介导间充质干细胞迁移的影响**◆

背景：人外源性的间充质干细胞能特异性地向损伤部位迁移,参与多种组织的损伤修复,然而其定向迁移的机制尚不清楚。 目的：观察基质细胞衍生因子1对骨髓间充质干细胞定向迁移的影响。 方法：体外培养不同个体的骨髓间充质干细胞,培养至第10代,检测细胞衰老状态。RT-PCR和细胞免疫荧光检测骨髓间充质干细胞CXCR4受体表达情况;体外迁移体系(Transwell)检测基质细胞衍生因子1对骨髓间充质干细胞迁移的影响。 结果与结论：骨髓间充质干细胞在体外长期增殖后生长逐渐缓慢,在第6,7代衰老细胞增多,其CXCR4受体表达减少。基质细胞衍生因子1对骨髓间充质干细胞的趋化作用呈剂量依赖性。 关键词：趋化作用;骨髓间充质干细胞;细胞衰老;基质细胞衍生因子1;CXCR4受体 doi:10.3969/j.issn.1673-8225.2012.01.013      

SDF-1/CXCR4增强骨髓间质干细胞的造血支持作用

目的探讨基质细胞衍生因子-1(SDF-1)/CXCR4在骨髓间质干细胞(MSCs)支持CD34 造血干/祖细胞(HSPCs)扩增中的作用。方法在长期培养基(LTC)中,以大鼠骨髓MSCs作为饲养层体外扩增骨髓CD34 细胞,每周分别加入SDF-1、SDF-1抗体或CXCR4抗体至5周。计算CD34 细胞数和集落形成细胞(CFC)数,以评价造血支持功能。为评估SDF-1/CXCR4对CD34 细胞增殖周期的影响,进行了杀伤试验以计算增殖指数。流式细胞术检测MSCs和CD34 细胞中SDF-1与CXCR4的表达;ELISA检测MSCs和CD34 细胞培养基中SDF-1的含量。结果CD34 细胞数、CFC数和增殖指数在加入SDF-1后明显增加(P<0.01),加入SDF-1抗体或CXCR4抗体后明显减少(分别为P<0.05,P<0.01)。CD34 细胞表面表达CXCR4,MSCs则不表达;MSCs细胞内表达SDF-1,而CD34 细胞不表达。在MSCs培养基中检测到SDF-1,在CD34 细胞培养基中未发现。结论SDF-1/CXCR4在骨髓MSCs支持HSPCs扩增中起重要作用。     

软骨损伤后基质细胞衍生因子1的表达

背景：研究表明基质细胞衍生因子1对骨髓间充质干细胞的迁移、聚集有影响。 目的：观察软骨损伤后不同时间损伤修复区组织基质细胞衍生因子1的表达以及与骨髓间充质干细胞迁移的关系。 方法：建立兔软骨损伤模型,分别于建模后2,5,7,10,14,28 d取损伤灶及边缘区组织,检测基质细胞衍生因子1表达和体外细胞迁移实验,观察基质细胞衍生因子1对骨髓间充质干细胞、软骨细胞的迁移影响。 结果与结论：基质细胞衍生因子1的表达呈现出时间变化的趋势,软骨损伤后第7天达到高峰(P < 0.05)。体内移植的骨髓间充质干细胞主要聚集在软骨损伤灶周围,但在封闭CXC趋化因子受体4后,此聚集现象逐渐减弱(P < 0.05)。结果证实,局部组织中基质细胞衍生因子1的表达在软骨损伤早期明显升高,对骨髓间充质干细胞向软骨损伤修复区迁移有重要作用。     

Proteoglycans guide SDF-1-induced migration of hematopoietic progenitor cells

Stromal cell-derived factor-1 (SDF-1) is a chemoattractant involved in hematopoietic progenitor cell (HPC) trafficking to the bone marrow. We studied the role of bone marrow endothelial proteoglycans (PGs) in SDF-1-mediated migration of HPC using a transwell assay. A subclone of progenitor cell line KG-1 (KG-1v) was used, displaying CXCR4-dependent transmigration. Cell surface PGs on bone marrow endothelial cell line 4LHBMEC did not mediate SDF-1-induced transendothelial migration. In contrast, transwell filters precoated with various glycosaminoglycans (GAGs) enhanced migration toward SDF-1. SDF-1-induced migration was reduced by degradation of heparan sulfate in subendothelial matrix produced by 4LHBMEC. The stimulating effect of GAGs was caused by the formation of a stable haptotactic SDF-1 gradient, as SDF-1 bound to immobilized GAGs and triggered migration. Soluble heparan sulfate enhanced SDF-1-induced migration dose-dependently, suggesting that SDF-1-heparan sulfate complexes optimized SDF-1 presentation. In conclusion, we provide evidence that PGs in the subendothelial matrix establish an SDF-1 gradient guiding migrating HPC into the bone marrow.     

Cell surface engineering to enhance mesenchymal stem cell migration toward an SDF-1 gradient

Mesenchymal stem cell (MSC) therapy for the treatment of myocardial infarction (MI) has shown considerable promise in clinical trials. A billion MSCs need to be administered for therapeutic efficacy, however, because only ∼1% of the cells reach the ischemic myocardium after systemic infusion. This is due to the loss of the homing signal on the surface of the MSCs during their expansion in culture. Stromal-derived factor-1 (SDF-1) is up-regulated immediately after infarction and is released into the peripheral blood. This SDF-1 reaches the bone marrow and recruits CXC chemokine receptor 4 (CXCR4)-positive stem cells. The CXCR4/SDF-1 axis plays an important role in MSC homing to the ischemic myocardium. Since SDF-1 is highly expressed for only 48 h after infarction, the current approaches requiring long-term culture of MSCs to induce CXCR4 expression are not clinically useful. To provide a clinically viable means to improve the homing of MSCs, we have developed a surface modification method to incorporate recombinant CXCR4 protein on the membrane of MSCs within 10 min. Using this method, we have confirmed the improved migration of MSCs toward an SDF-1 gradient.     

The in vitro migration capacity of human bone marrow mesenchymal stem cells: comparison of chemokine and growth factor chemotactic activities

Adult bone marrow (BM)-derived stem cells, including hematopoietic stem cells (HSCs) and MSCs, represent an important source of cells for the repair of a number of damaged tissues. In contrast to HSCs, the soluble factors able to induce MSC migration have not been extensively studied. In the present work, we compared the in vitro migration capacity of human BM-derived MSCs, preincubated or not with the inflammatory cytokines interleukin 1beta (IL1beta) and tumor necrosis factor alpha (TNFalpha), in response to 16 growth factors (GFs) and chemokines. We show that BM MSCs migrate in response to many chemotactic factors. The GFs platelet-derived growth factor-AB (PDGF-AB) and insulin-like growth factor 1 (IGF-1) are the most potent, whereas the chemokines RANTES, macrophage-derived chemokine (MDC), and stromal-derived factor-1 (SDF-1) have limited effect. Remarkably, preincubation with TNFalpha leads to increased MSC migration toward chemokines, whereas migration toward most GFs is unchanged. Consistent with these results, BM MSCs express the tyrosine kinase receptors PDGF-receptor (R) alpha, PDGF-Rbeta, and IGF-R, as well as the RANTES and MDC receptors CCR2, CCR3, and CCR4 and the SDF-1 receptor CXCR4. TNFalpha increases CCR2, CCR3, and CCR4 expression (as opposed to that of CXCR4), together with RANTES membrane binding. These data indicate that the migration capacity of BM MSCs is under the control of a large range of receptor tyrosine kinase GFs and CC and CXC chemokines. Most chemokines are more effective on TNFalpha-primed cells. Our results suggest that the mobilization of MSCs and their subsequent homing to injured tissues may depend on the systemic and local inflammatory state. Disclosure of potential conflicts of interest is found at the end of this article.     

皮肤来源间充质干细胞对内皮祖细胞募集效应的体外观察

目的细胞的募集趋化与归巢被认为是间充质干细胞（MSCs）修复重建受损组织的重要机制,本研究拟通过体外实验观察皮肤来源间充质干细胞对在血管化中发挥重要作用的内皮祖细胞（EPCs）的募集效应。方法分离与培养胎鼠皮肤MSCs和大鼠EPCs,利用免疫组织化学法,分别检测二者的SDF-1与CXCR4表达;并利用体外迁移实验,观察MSCs是否影响EPCs的迁移。结果利用免疫组织化学检测,MSCs和EPCs可以分别表达SDF-1与CXCR4;利用双室培养系统发现,MSCs可明显促进EPCs的迁移,且阻断SDF-1表达后,这种促进效应得到抑制（P〈0.05）。结论体外实验证实了MSCs可以促进EPCs的募集趋化。     

The effect of simvastatin on chemotactic capability of SDF-1α and the promotion of bone regeneration

The purpose of this study was to investigate the cooperative effects of simvastatin (SIM) and stromal cell-derived factor-1α (SDF-1α) on the osteogenic and migration capabilities of mesenchymal stem cells (MSCs), and construct a cell-free bone tissue engineering system comprising SIM, SDF-1α and scaffold. We found that 0.2 μm SIM significantly increased alkaline phosphatase activity (P < 0.05) of mouse bone marrow MSCs with no inhibition of cell proliferation, and enhanced the chemotactic capability of SDF-1α (P < 0.05). Next, we constructed a novel cell-free bone tissue engineering system using PLGA loaded with SIM and SDF-1α, and applied it in critical-sized calvarial defects in mice. New bone formation in the defect was evaluated by micro-CT, HE staining and immunohistochemistry. The results showed that PLGA loaded with SIM and SDF-1α promoted bone regeneration significantly more than controls. We investigated possible mechanisms, and showed that SDF-1α combined with SIM increased MSC migration and homing in vivo, promoted angiogenesis and enhanced the expression of BMP-2 in newly-formed bone tissue. In conclusion, SIM enhanced the chemotactic capability of SDF-1α and the cell-free bone tissue engineering system composed of SIM, SDF-1α and scaffold promoted bone regeneration in mouse critical-sized calvarial defects.     

基质细胞衍生因子1α预处理大鼠骨髓间充质干细胞的迁移

背景：骨髓间充质干细胞移植过程中只有少量细胞能定向迁移到损伤组织,因此如何提高细胞定向迁移的数量是干细胞移植的关键因素。 目的：观察基质细胞衍生因子1α预处理对大鼠骨髓间充质干细胞定向迁移的影响。 方法：体外分离培养骨髓间充质干细胞,予以传代。使用Transwell体外迁移体系,观察不同浓度的基质细胞衍生因子1α趋化骨髓间充质干细胞定向迁移,选取最佳浓度值趋化细胞。在基质细胞衍生因子1α预处理、CXCR 4型受体阻断剂AMD3100和Akt通路阻断剂LY294002的干预下观察骨髓间充质干细胞的趋化迁移情况,检测基质细胞衍生因子1α预处理对骨髓间充质干细胞中CXCR 4型受体 mRNA、蛋白水平及AKT磷酸化的影响。 结果与结论：0.2 mg/L的基质细胞衍生因子1α孵育细胞10 h具有最佳趋化细胞迁移效应。骨髓间充质干细胞的定向趋化迁移作用随着基质细胞衍生因子1α预处理细胞浓度的增加而增强,预处理时间为6 h;而AMD3100和LY294002可阻断基质细胞衍生因子1α预处理的促迁移作用;基质细胞衍生因子1α预处理可上调骨髓间充质干细胞CXCR 4型受体的表达并促进Akt蛋白磷酸化。提示基质细胞衍生因子1α预处理可通过增加骨髓间充质干细胞表面的CXCR 4型受体数量,从而增强基质细胞衍生因子1α/CXCR4型受体介导的骨髓间充质干细胞定向迁移,该预处理效应可能与Akt信号途径有关。     

基质细胞衍生因子1预处理抑制大鼠骨髓间充质干细胞的凋亡

背景：研究发现基质细胞衍生因子1除参与趋化干细胞定向迁移途径,还具有抗凋亡作用。 目的：观察基质细胞衍生因子1预处理后对骨髓间充质干细胞凋亡的影响。 方法：以不同浓度H₂O₂诱导大鼠骨髓间充质干细胞凋亡,取最适宜浓度100 μmol/L用于实验。不同质量浓度基质细胞衍生因子1干预100 μmol/L H₂O₂诱导后的大鼠骨髓间充质干细胞,选择0.2 mg/L最佳保护质量浓度用于实验。取第3代大鼠骨髓间充质干细胞,随机分组：正常对照组不进行任何处理;损伤组在培养液中加入H₂O₂作用24 h;基质细胞衍生因子1预处理组于H₂O₂损伤细胞前6 h加入基质细胞衍生因子1;基质细胞衍生因子1+AMD3100(基质细胞衍生因子1受体CXCR4的阻断剂)组于H₂O₂细胞损伤前6 h加入基质细胞衍生因子1与AMD3100共孵。 结果与结论：H2O2能体外模拟缺血缺氧环境诱导骨髓间充质干细胞凋亡,且作用呈剂量依赖性。与损伤组比较,加入基质细胞衍生因子1预处理后细胞凋亡明显减轻(P < 0.01),细胞E2F6基因表达增强(P < 0.05),E2F1基因表达减少(P < 0.05),线粒体细胞色素C转位减少(P < 0.05),Caspase-3活性降低(P < 0.05),AMD3100可阻断基质细胞衍生因子1对骨髓间充质干细胞的保护作用。提示基质细胞衍生因子1可能通过增强E2F6基因,负性调控E2F1基因抑制线粒体损伤导致的骨髓间充质干细胞凋亡。     

Superfect 高效介导PDX-1基因在骨髓间质干细胞表达

目的：构建含有胰腺十二指肠同源框1(PDX-1)基因的真核表达载体，并提高重组载体在骨髓间质干细胞(MSCs)的表达效率，为骨髓MSCs作为糖尿病基因治疗的靶细胞奠定基础。 方法：RT-PCR体外扩增PDX-1 基因，双酶切后整合入相同双酶切的真核表达载体构建重组载体，对重组载体进行酶切分析和序列测定进行鉴定；利用Percoll 细胞分离液体外培养大鼠骨髓MSCs，流式细胞仪检测细胞周期后，Superfect 介导正确重组的载体转染骨髓 MSCs，检测转染效率和细胞存活率从而对转染条件进行优化；G418筛选阳性细胞后，RT-PCR 和Western blotting 检测PDX-1 基因在骨髓 MSCs 中的表达。 结果：重组载体双酶切分析和序列测定证实重组载体构建成功。流式细胞仪显示 85.9%的MSCs处于G₀/G₁期，提示骨髓MSCs具有强大的分化潜能；荧光显微镜下成功转染的细胞呈现全细胞绿色荧光，Superfect 介导的转染效率和细胞存活率与其绝对用量和孵育细胞的时间有关；RT-PCR显示转染后PDX-1基因在骨髓 MSCs表达，随转染时间延长，表达逐渐增强，与Western blotting结果一致。结论：成功构建了含有PDX-1 基因的真核表达载体；Superfect 能高效介导外源性基因在骨髓MSCs 中表达；转染外源性基因的MSCs可望成为一种理想的基因治疗的载体细胞。     

Repair of rabbit osteochondral defects by an acellular technique with an ultrapurified alginate gel containing stromal cell-derived factor-1

The objective of this study was to determine whether the local administration of stromal cell-derived factor-1 (SDF-1) using ultrapurified alginate gel (UPAL gel) could improve reparative tissues of osteochondral defects compared with those without treatment. For the investigation, a full-thickness osteochondral defect 4.5 mm in diameter and 3 mm in depth was created in the patella groove of the distal femur in rabbits. Local expression of SDF-1 protein was temporarily upregulated at 1 week after creating the osteochondral defect. The local administration of SDF-1 enhanced the migration of host cells, mainly bone marrow stromal cells (BMSCs), to the site of the osteochondral defect. In vitro cell migration assay supported this result. In the SDF-1 (UPAL gel containing SDF-1) treatment group, the histological scores and the compressive modulus of reparative tissues were significantly improved compared with the no-treatment and vehicle (UPAL gel without SDF-1) groups. On the other hand, SDF-1 did not influence the cellular proliferation and chondrogenesis of BMSCs. Based on the results obtained here, we speculate that SDF-1 enhances the reparative process of osteochondral injuries not through direct effects on the behavior of host cells, but through increased migration of host cells to the injured site. UPAL gel, as a vehicle material, may play an important role in chondrogenesis of recruited cells, mainly BMSCs. The cell-free approach with local administration of SDF-1 may be an effective strategy for developing a minimally invasive technique for cartilage tissue regeneration.     

基质细胞衍生因子对骨髓干细胞迁移分化的影响

骨髓干细胞具有很强的可塑性，可向多种组织细胞横向分化，是细胞移植的最好种子之一。体内外许多试验证实，某些细胞因子可以影响移植细胞的微环境，进而影响骨髓干细胞的动员、迁移及分化。基质细胞衍生因子属于趋化因子中CXC亚家族，特异性引起表达CXCR4的骨髓干细胞趋化反应，就基质细胞衍生因子对骨髓干细胞动员、迁移及分化的影响作一综述。     

Differential effects of culture conditions on the migration pattern of stromal cell-derived factor-stimulated hematopoietic stem cells

Evidence is mounting that hematopoietic stem cells (HSCs) play a critical role in bone marrow regeneration and tissue renewal, for which migration is an obvious prerequisite. Computer-aided analysis and a three-dimensional collagen matrix assay enabled us to analyze single-cell migratory characteristics of stromal cell-derived factor-1 alpha (SDF-1 alpha)-stimulated cord blood-derived HSCs. We defined and resolved specific migratory parameters in spontaneous and SDF-1 alpha-induced migration of these cells. The addition of interleukin 6 to the culture medium led to differential SDF-1 alpha-stimulated migratory response, which comprised a recruitment of nonmoving cells and an increase in speed and frequency of pauses but a decrease in pause duration. We were thus able to decipher the exact parameters that result in an increase in the migration of HSCs and demonstrate that extensive analysis of single-cell behavior is elementary in the study of stem cell migration.     

绿色荧光蛋白标记的骨髓间充质干细胞在脑缺血大鼠体内迁移的实验研究

目的:探讨基质细胞衍生因子-1α（SDF-1α）对骨髓间充质干细胞(BMSCs)在SD大鼠脑缺血后迁移至脑损伤区的影响。方法:构建大脑中动脉阻塞的脑缺血模型;50只大鼠随机分为脑缺血PBS对照组、脑缺血MSCs治疗组。将腺病毒携带的增强型绿色荧光蛋白(EGFP）标记的MSCs,在脑缺血1d后经尾静脉注射入大鼠体内;用实时定量PCR检测缺血半暗带区基质细胞衍生因子-1α（SDF-1α）的分泌;用流式细胞仪检测骨髓间充质干细胞上CXCR4的表达率;用荧光共聚焦显微镜扫描显示骨髓间充质干细胞的迁移。结果:GFP转染率大约87%转染骨髓间充质干细胞;实时定量PCR显示大鼠海马分泌的SDF-1α在1 d时达到峰值,1-14 d一直维持在较高的水平,14 d后开始缓慢下降,而皮质分泌的SDF-1α在第3 d开始缓慢上升,14 d才达到峰值;流式细胞仪检测BMSCs表面的CXCR4有14%;GFP标记的BMSCs移植后6 h发现聚集在大脑中动脉起始处（嗅球）,在第3 d后在丘脑等缺血半暗带区,在14 d后皮质处的GFP+BMSCs已有明显的增加。结论:损伤组织SDF-1α浓度的升高与骨髓间充质干细胞迁移的增加可能存在一定的关系。     

Bone marrow-derived mesenchymal stromal cells are attracted by multiple myeloma cell-produced chemokine CCL25 and favor myeloma cell growth in vitro and in vivo

Multiple myeloma (MM) is a malignancy of terminally differentiated plasma cells that are predominantly localized in the bone marrow (BM). Mesenchymal stromal cells (MSCs) give rise to most BM stromal cells that interact with MM cells. However, the direct involvement of MSCs in the pathophysiology of MM has not been well addressed. In this study, in vitro and in vivo migration assays revealed that MSCs have tropism toward MM cells, and CCL25 was identified as a major MM cell-produced chemoattractant for MSCs. By coculture experiments, we found that MSCs favor the proliferation of stroma-dependent MM cells through soluble factors and cell to cell contact, which was confirmed by intrafemoral coengraftment experiments. We also demonstrated that MSCs protected MM cells against spontaneous and Bortezomib-induced apoptosis. The tumor-promoting effect of MSCs correlated with their capacity to enhance AKT and ERK activities in MM cells, accompanied with increased expression of CyclinD2, CDK4, and Bcl-XL and decreased cleaved caspase-3 and poly(ADP-ribose) polymerase expression. In turn, MM cells upregulated interleukin-6 (IL-6), IL-10, insulin growth factor-1, vascular endothelial growth factor, and dickkopf homolog 1 expression in MSCs. Finally, infusion of in vitro-expanded murine MSCs in 5T33MM mice resulted in a significantly shorter survival. MSC infusion is a promising way to support hematopoietic recovery and to control graft versus host disease in patients after allogeneic hematopoietic stem cell transplantation. However, our data suggest that MSC-based cytotherapy has a potential risk for MM disease progression or relapse and should be considered with caution in MM patients.     

Functional characterization of podia formation in normal and malignant hematopoietic cells

Hematopoietic cells extend multiple podia of yet unknown function. Our morphological studies using scanning electron microscopy and functional studies using time-lapse video microscopy suggest that podia formed by CD34+ hematopoietic stem cells (HSC) on the bone marrow stroma component fibronectin are characteristic of lamellipodia at the leading edge and uropodia at the trailing edge, cytoskeletal structures that have previously been shown to be responsible for cell locomotion of lymphocytes. In the leukemic cells studied here, stroma-derived factor-1alpha (SDF-1alpha) led to a significant eightfold increase in transmigration (BCR-ABL-positive BV173 leukemia cell line; P<0.05) and podia formation in all BCR-ABL-positive leukemic cell lines studied (BV173, K562, 32Dp210) and in two of three BCR-ABL-negative lines (HL60, 32D, not KG1a). We could show that SDF-1alpha exposure led to a down-regulation of the gene expression of the chemokine receptors CCR4, CXCR4, and CXCR5, which are associated with cell motility and podia formation, indicating a negative feedback control. In BCR-ABL-positive leukemic cells, the effects of SDF-1alpha on podia formation and cell migration were independent of BCR-ABL-tyrosine kinase activity. Our data are compatible with the hypothesis that formation of specific podia by hematopoietic cells is associated with egression of these cells from the bone marrow.