Successful immortalization of mesenchymal progenitor cells derived from human placenta and the differentiation abilities of immortalized cells

We reported previously that mesenchymal progenitor cells derived from chorionic villi of the human placenta could differentiate into osteoblasts, adipocytes, and chondrocytes under proper induction conditions and that these cells should be useful for allogeneic regenerative medicine, including cartilage tissue engineering. However, similar to human mesenchymal stem cells (hMSCs), though these placental cells can be isolated easily, they are difficult to study in detail because of their limited life span in vitro. To overcome this problem, we attempted to prolong the life span of human placenta-derived mesenchymal cells (hPDMCs) by modifying hTERT and Bmi-1, and investigated whether these modified hPDMCs retained their differentiation capability and multipotency. Our results indicated that the combination of hTERT and Bmi-1 was highly efficient in prolonging the life span of hPDMCs with differentiation capability to osteogenic, adipogenic, and chondrogenic cells in vitro. Clonal cell lines with directional differentiation ability were established from the immortalized parental hPDMC/hTERT+Bmi-1. Interestingly, hPDMC/Bmi-1 showed extended proliferation after long-term growth arrest and telomerase was activated in the immortal hPDMC/Bmi-1 cells. However, the differentiation potential was lost in these cells. This study reports a method to extend the life span of hPDMCs with hTERT and Bmi-1 that should become a useful tool for the study of mesenchymal stem cells.     

Glioma-associated endothelial cells show evidence of replicative senescence

The innately programmed process of replicative senescence has been studied extensively with respect to cancer, but primarily from the perspective of tumor cells overcoming this stringent innate barrier and acquiring the capacity for unlimited proliferation. In this study, we focus on the potential role of replicative senescence affecting the non-transformed endothelial cells of the blood vessels within the tumor microenvironment. Based on the well-documented aberrant structural and functional features of blood vessels within solid tumors, we hypothesized that tumor-derived factors may lead to premature replicative senescence in tumor-associated brain endothelial cells (TuBEC). We show here that glioma tissue, but not normal brain tissue, contains cells that express the signature of replicative senescence, senescence-associated beta-galactosidase (SA-beta-gal), on CD31-positive endothelial cells. Primary cultures of human TuBEC stain for SA-beta-gal and exhibit characteristics of replicative senescence, including increased levels of the cell cycle inhibitors p21 and p27, increased resistance to cytotoxic drugs, increased growth factor production, and inability to proliferate. These data provide the first demonstration that tumor-derived brain endothelial cells may have reached an end-stage of differentiation known as replicative senescence and underscore the need for anti-angiogenic therapies to target this unique tumor-associated endothelial cell population.     

Immortalization of bovine germ line stem cells by c-myc and hTERT

The limited life span of bovine germ line stem cells in vitro is one of the obstacles to spermatogenesis analysis, genetic manipulation and generating transgenic animal. The aim of this study is to establish immortalized bovine germ line stem cells by c-myc or hTERT. We constructed pEMY and pETE expression vectors and transfected germ line cells from 5-month-old bovine. After G418 screening, four types of positive clones were obtained. The results showed that they expressed exogenous genes c-myc or hTERT at mRNA and protein level by RT-PCR and Western blotting detection. Presumable cell lines GM7, GT3, GMT5 all expressed germ-line-stem-cell-specific makers by immunocytochemical analysis, such as c-kit, Oct-4 and GFR-1. The putative cell lines also had higher capacity of proliferation than freshly isolated bovine spermatogonial stem cells. So we can conclude that exogenous genes c-myc or hTERT have integrated into the genome of bovine germ cells and upregulated the expression of telomerase.     

Telomeres,senescence, and hematopoietic stem cells

The replicative lifespan of normal somatic cells is restricted by the erosion of telomeres, which are protective caps at the ends of linear chromosomes. The loss of telomeres induces antiproliferative signals that eventually lead to cellular senescence. The enzyme complex telomerase can maintain telomeres, but its expression is confined to highly proliferative cells such as stem cells and tumor cells. The immense regenerative capacity of the hematopoietic system is provided by a distinct type of adult stem cell: hematopoietic stem cells (HSCs). Although blood cells have to be produced continuously throughout life, the HSC pool seems not to be spared by aging processes. Indeed, limited expression of telomerase is not sufficient to prevent telomere shortening in these cells, which is thought ultimately to limit their proliferative capacity. In this review, we discuss the relevance of telomere maintenance for the hematopoietic stem cell compartment and consider potential functions of telomerase in this context. We also present possible clinical applications of telomere manipulation in HSCs and new insights affecting the aging of the hematopoietic stem cell pool and replicative exhaustion. This work was supported by European Community Grant LSHC-CT-2004-502943 (MOL CANCER MED).     

Telomerase activation induces elongation of the telomeric single-stranded overhang, but does not prevent chromosome aberrations in human vascular endothelial cells

Chromosome aberrations such as loss of chromosome 13 were frequently observed in human endothelial cells from umbilical cord veins (HUVEC). A recent study showed that the length of telomeric single-stranded 3'-overhangs (G-tails) is more important as an essential structure for chromosome maintenance than the net telomere length in telomere t-loop formation. Here, we have examined G-tail length using G-tail telomere HPA in normal and hTERT-transduced HUVECs. We found that forced expression of hTERT in HUVEC induced G-tail as well as total telomere length elongation. G-tail length was well correlated with total telomere length. However, hTERT introduction did not prevent chromosome aberrations such as loss of chromosome 13. Normal characteristics such as morphology, up-regulation of vWF, and tube formation were observed in hTERT-HUVEC as in young normal HUVEC. These results show that chromosome aberrations in HUVEC are independent of telomere G-tail and total telomere attrition.     

Combined transgene immortalized urothelial cells capable of reprogramming and hepatic differentiation

Human primary cells, including urine-derived cells (UCs), are an excellent source for generation of pluripotent stem cells (iPSCs) to model disease. However, replicative senescence starts early and shortens the time window for generation of iPSCs. We addressed the question whether combinations of transgenes allows efficient immortalization of UCs, iPSC generation, and differentiation into hepatocyte-like cells (HLCs). Retroviral transfer of three gene cassettes HPVE6E7 (H), hTERT/p53DD (T), cyclinD1/CDK4R24C (C) encoding five genes was established in primary UCs. Long-term cell proliferation was observed in cells carrying transgenes H, HT, HC, and HCT, whereas cells carrying transgenes C, T and CT showed early senescence similar to UCs. iPSCs could be exclusively generated from immortalized UCs transduced with transgenes HCT and HC. iPSC colonies appeared however later and in smaller number as compared to UCs. Using an established hepatic differentiation protocol, HLCs were obtained with high efficacy. Of note, a high expression of individual transgenes was observed in immortalized UCs, which was down-regulated after reprogramming in four out of five genes. One transgene was re-expressed in HLCs as compared to iPSCs. Our data suggest that individual transgene combinations result in advanced growth rates of immortalized cells and do not prevent iPSC formation and HLC differentiation. Retroviral transgene expression is mostly silenced in iPSCs but can be rarely re-expressed after hepatic differentiation. An extended time window for iPSC establishment can be proposed that allows straightforward functional analyses of differentiated cells.     

NADPH oxidases 1 and 4 mediate cellular senescence induced by resveratrol in human endothelial cells

Resveratrol is believed to be partially responsible for the French paradox—the low risk of cardiovascular disease despite a high-fat diet in the French population. Recently, resveratrol has also been discussed as a life-span booster in several organisms. Age-related diseases are associated on the cellular level with senescence. We, therefore, hypothesized that resveratrol is vasoprotective by counteracting endothelial cell senescence. Surprisingly, we observed that chronic treatment with resveratrol (10 μM) was prosenescent in primary human endothelial cells. Resveratrol induced elevated reactive oxygen species (ROS) levels that were associated with and causally linked to an accumulation of cells in the S phase of the cell cycle, as measured by flow cytometry. We further show that cell accumulation in S phase leads to increased ROS and finally senescence. Using an siRNA approach, we clearly identified two NADPH oxidases, Nox1 and Nox4, as major targets of resveratrol and primary sources of ROS that act upstream of the observed S-phase accumulation.     

ALK2使内皮细胞转化为类干细胞的机制

内皮细胞向间充质细胞转分化（endothelial-to-mesenchymal transition,EndMT）过程是血管内皮细胞转化为类干细胞的基础,持续激活状态的ALK2在EndMT过程起到关键的促进作用,EndMT发生后内皮细胞能获得类干细胞的表现型.TGF-β2和BMP4作为特异性配体激活ALK2,下调某些内皮细胞标志物并上调某些间质细胞标志物,促进EndMT过程.此外,编码ALK2的基因序列在206号氨基酸上突变形成R206H ALK2后作用类似持续激活状态ALK2,同样也能达到促进内皮细胞向间充质细胞转分化的目的.     

Anti-apoptotic and anti-senescence effects of Klotho on vascular endothelial cells

Klotho-mutated mice manifest multiple age-related disorders that are observed in humans. A recent study suggested that Klotho protein might function as an anti-aging hormone in mammals. Because it has been reported that apoptosis and senescence in vascular endothelial cells are closely related to the progression of atherosclerosis, we investigated Klotho's ability to interfere with apoptosis and cellular senescence in human umbilical vascular endothelial cells (HUVEC). Klotho overexpression decreased H(2)O(2)-induced apoptosis in COS-1 cells and Jurkat cells. Klotho protein also reduced H(2)O(2)- and etoposide-induced apoptosis in HUVEC. Caspase-3 and caspase-9 activity was lower in Klotho-treated HUVEC than in control cells. Senescence-associated beta-gal staining showed that Klotho protein interferes with H(2)O(2)-induced premature cellular senescence. The expression of p53 and p21 was lower in Klotho-treated cells. Our study suggests that Klotho acts as a humoral factor to reduce H(2)O(2)-induced apoptosis and cellular senescence in vascular cells.     

Detection of tyrosine phosphorylated proteins by combination of immunoaffinity enrichment, two-dimensional difference gel electrophoresis and fluorescent Western blotting

We describe fluorescence-based 2-D gel electrophoresis methods for visualization of low abundant, cancer relevant tyrosine phosphorylated (pTyr) proteins. The methods investigated were fluorescent Western blotting and two-dimensional difference gel electrophoresis (2-D DIGE) for detection of non-enriched and immunoaffinity enriched pTyr protein patterns. The same anti-phosphotyrosine specific antibody, 4G10, was used for both approaches. The results from fluorescent Western blotting of total proteins and from enriched CyDye DIGE pre-labeled pTyr proteins showed similar down regulation of phosphorylation upon treating of cells from a cancer model system (K562 chronic myeloid leukemia cells) with imatinib. This treatment introduced a known perturbation of phosphorylation that enabled testing of these new approaches to analyze variations in tyrosine phosphorylation levels. Enrichment of pTyr proteins was found highly advantageous for the outcome. Out of a simplified 2-D DIGE experiment of immunoaffinity enriched control and treated pTyr proteins, differential analysis as well as protein identification by mass spectrometry (MS) was possible.     

eNOS, COX-2, and prostacyclin production are impaired in endothelial cells from diabetics

The vascular endothelium is a well-recognized target of damage for factors leading to increased cardiovascular risk. Among the agents playing an important role in cardiovascular homeostasis, nitric oxide and prostacyclin represent key markers of endothelial integrity. In the present work, we report for the first time the reduced expression of both endothelial nitric oxide synthase and cyclooxygenase-2 (COX-2) proteins, as well as decreased prostacyclin production, in unstimulated human endothelial cells from insulin-dependent diabetic mothers when compared to cells from non-diabetic, control subjects. According to a major role of COX-2 as a source of prostacyclin production even in unstimulated endothelial cells, prostacyclin production was concentration-dependently inhibited by the selective COX-2 inhibitor SC236. Overall, our results suggest a possible link between reduced endothelial COX-2 and NO-synthase expression and the increased risk of cardiovascular diseases affecting diabetic patients, and point to the use of endothelial cells from diabetic patients as a tool for investigating early dysfunction in pathological endothelium.     

Human microvascular endothelial cells immortalized with human telomerase catalytic protein: a model for the study of in vitro angiogenesis

Human microvascular endothelial cell-1 (HMEC-1) generated by transfection with SV40 large T antigen has been the prevailing model for in vitro studies on endothelium. However, the transduction of SV40 may lead to unwanted cell behaviors which are absent in primary cells. Thus, establishing a new microvascular endothelial cell line, which is capable of maintaining inherent features of primary endothelial cells, appears to be extremely important. Here, we immortalized primary human microvascular endothelial cells (pHMECs) by engineering the human telomerase catalytic protein (hTERT) into the cells. Endothelial cell-specific markers were examined and the angiogenic responses were characterized in these cells (termed as HMVECs, for human microvascular endothelial cells). We found that VEGF receptor 2 (Flk-1/KDR), tie1, and tie2 expression is preserved in HMVEC, whereas Flk-1/KDR is absent in HMEC-1. In addition, HMVEC showed similar angiogenic responses to VEGF as HMEC-1. Furthermore, the HMVEC line was found to generate a prominent angiogenic response to periostin, a potent angiogenic factor identified recently. The data indicate that HMVEC may serve as a suitable in vitro endothelium model.     

成年和老年小鼠脑蛋白质组双向电泳图谱比较

使用双向电泳(2-DE)比较成年和老年小鼠脑蛋白质差异,从分子水平初步探索老年脑蛋白整体变化规律.以固相pH梯度等电聚焦为第一向,SDS-聚丙烯酰胺凝胶水平电泳(PAGE)为第二向进行2-DE.图象分析软件Imagemaster^® 2D Elite分析电泳图谱.重复性实验结果显示,同组样品在三次不同实验中所得蛋白质斑点数目的相对标准差（变异系数）为4.43%±0.25%;同一蛋白质斑点在三次实验中等电点、分子质量和蛋白质量的相对标准差分别为8.76%±5.14%, 13.00%±4.22%和10.84%±9.16%.成年和老年小鼠脑组织2-DE图谱分别获得996和1256个蛋白质斑点,其中8个蛋白质在老年脑组织中含量降低,20个蛋白质斑点含量增加.另至少有4个蛋白质斑点在老年脑组织中缺失,14个蛋白质点为老年脑特有. 以上差异点的发现为研究脑老化和退行性疾病机理提供了有益的线索.     

A comparison of the tube forming potentials of early and late endothelial progenitor cells

The identification of circulating endothelial progenitor cells (EPCs) has revolutionized approaches to cell-based therapy for injured and ischemic tissues. However, the mechanisms by which EPCs promote the formation of new vessels remain unclear. In this study, we obtained early EPCs from human peripheral blood and late EPCs from umbilical cord blood. Human umbilical vascular endothelial cells (HUVECs) were also used. Cells were evaluated for their tube-forming potential using our novel in vitro assay system. Cells were seeded linearly along a 60 μm wide path generated by photolithographic methods. After cells had established a linear pattern on the substrate, they were transferred onto Matrigel. Late EPCs formed tubular structures similar to those of HUVECs, whereas early EPCs randomly migrated and failed to form tubular structures. Moreover, late EPCs participate in tubule formation with HUVECs. Interestingly, late EPCs in Matrigel migrated toward pre-existing tubular structures constructed by HUVECs, after which they were incorporated into the tubules. In contrast, early EPCs promote sprouting of HUVECs from tubular structures. The phenomena were also observed in the in vivo model. These observations suggest that early EPCs cause the disorganization of pre-existing vessels, whereas late EPCs constitute and orchestrate vascular tube formation.     

Angiogenic profiling and comparison of immortalized endothelial cells for functional genomics

Genomics efforts of the past decade have resulted in the identification of numerous genes with putative roles in disease processes, including tumor angiogenesis. To functionally validate these genes, cultured endothelial cells are indispensable tools, though these may not completely mimic the phenotype of tissue endothelial cells as the proper microenvironment is lacking. To obtain experimental data representative of normal physiology, the use of primary endothelial cells is preferred. However, these cells are usually limited in passage number, can be difficult to obtain and show great interindividual variety. Furthermore, transfection efficiency is very limited in primary cells, hampering applications in functional genomics and gene function analysis. The use of properly characterized alternative endothelial cell sources is therefore warranted. Here, we compared immortalized endothelial cells - HMEC, RF24 and EVLC2 - with primary HUVEC. We show that RF24, and to a slightly lesser extent HMEC, resembles primary HUVEC most on all facets examined. RF24, in contrast to EVLC2, express the endothelial markers CD31, CD34, CD105, vWF and VE-cadherin, and are capable of migration and tube formation in vitro. Furthermore, the expression levels of angiogenic growth factors and their receptors are comparable to that of primary EC. In addition, whereas primary HUVEC are resistant to transfection using common lipophilic transfection reagents, HMEC and RF24 could be readily transfected. Hence, these cells pose a valuable tool for functional genomics in angiogenesis research.     

Effects of fibulin-5 on attachment, adhesion, and proliferation of primary human endothelial cells

BACKGROUND: Fibulin-5 is a novel extracellular protein that is thought to act as a bridging peptide between elastin fibers and cell surface integrins in blood vessel wall. Fibulin-5 binding to endothelial cell (EC) surface integrins may effect cell proliferation and cell attachment to extracellular matrix (ECM) or to artificial surfaces. In this paper, we describe the effects of fibulin-5 on attachment, adhesion, and proliferation of primary human EC. After demonstrating that fibulin-5 over-expression inhibited EC proliferation, we tested the hypothesis that co-expression of fibulin-5 and VEGF165 will lead to unique EC phenotype that will exhibit increased adherence properties and retain its proliferation capacity. METHODS AND RESULTS: Fibulin-5 and VEGF165 gene transfer to primary human saphenous vein endothelial cells was accomplished using retroviral vectors encoding the two genes. Transgene expression was verified using immunohistochemistry, Western blotting, and ELISA. Fibulin 5 over-expression tended to improve immediate EC attachment (30 min after seeding) and improved significantly adhesion (>40%) under shear stress tested 24h after EC seeding. The effects of fibulin-5 and VEGF165 on EC proliferation in the presence or absence of basic FGF were also tested. EC expressing fibulin-5 had reduced proliferation while VEGF165 co-expression ameliorated this effect. CONCLUSION: Fibulin-5 improved EC attachment to artificial surfaces. Dual transfer of fibulin-5 and VEGF165 resulted in EC phenotype with increased adhesion and improved proliferation. This unique EC phenotype can be useful for tissue engineering on endovascular prostheses.     

Biomarker protein expression in primary cultures of salmon (Salmo salar L.) hepatocytes exposed to environmental pollutants

Primary cultures of salmon (Salmo salar L.) hepatocytes were analysed using ³⁵s-methionine/cysteine incorporation and SDS-PAGE gel electrophoresis (1 and 2-D) and Western blotting after treatment with representative environmental pollutants (benzo(a)pyrene (BaP), 2,3,3', 4,4'-pentachlorobiphenyl (PCB-105)₁ arsenite (AsO₂-) and cadmium (Cd)). The results demonstrated striking similarities in changes in protein expression after treatment with the different pollutants. Hsp70 (Hsp72/73) proteins were induced after treatment with all the compounds as shown by ³⁵S-methionine/cysteine labelling. However, high background levels of these proteins were shown with Western blotting and an anti-Hsp70 antibody, indicating a slow turnover of these proteins. The Hsp70s in salmon hepatocytes were extremely susceptible to degradation in urea used in 2-D electrophoresis, resulting in peptide fragments of 45-46 kDa. In addition to these Hsp70 fragments, arsenite induced several proteins of 42,38, and in the 30-32 kDa range. CYPlA (58 kDa) and an unidentified protein of 16 kDa were furthermore induced after treatment with the organic xenobiotics (BaP, PCB and the model compound β-naphthoflavone, BNF). CYPlA was expressed in a dose-dependent manner, and was resolved into several protein spots in 2-D Western blotting. Elevated levels of metallothionein and haem oxygenase (HO) were indicated in Western blots after treatment with cadmium or arsenite (only HO). The hepatocytes showed cytoplasmic protrusions after treatment with 35 μM arsenite and 100 μM Cd, indicative of cells entering apoptosis.     

Testicular Sertoli cells influence the proliferation and immunogenicity of co-cultured endothelial cells

The major problem of the application of endothelial cells (ECs) in transplantation is the lack of proliferation and their immunogenicity. In this study, we co-cultured ECs with Sertoli cells to monitor whether Sertoli cells can influence the proliferation and immunogenicity of co-cultured ECs. Sertoli cells were isolated from adult testicular tissue. ECs were divided into the control group and the experimental group, which included three sub-groups co-cultured with 1 × 10³, 1 × 10⁴ or 1 × 10⁵ cell/ml of Sertoli cells. The growth and proliferation of ECs were observed microscopically, and the expression of vascular endothelial growth factor (VEGF) receptor-2 (KDR) was examined by Western blotting. In another experiment, ECs were divided into the control group, the single culture group and the co-culture group with the optimal concentration of Sertoli cells. After INF-γ and TNF-α were added to the culture medium, MHC II antigen expression was detected by immunofluorescence staining and western blotting; interleukin (IL)-6, IL-8 and soluble intercellular adhesion molecule (sICAM) were measured in the culture medium by ELISA. We demonstrated that 1 × 10⁴ cell/ml Sertoli cells promoted the proliferation of co-cultured ECs more dramatically than that in other groups (P < 0.05). Western blotting showed that 1 × 10⁴ cell/ml of the Sertoli cells was most effective in the up-regulation of KDR expression in the co-cultured ECs (P < 0.05). Sertoli cells can effectively suppress INF-γ-induced MHC II antigen expression in co-cultured ECs compared with single culture group (P < 0.05). TNF-α induced the expression of IL-6, IL-8 and sICAM in ECs. When co-cultured with Sertoli cells, their expressions were significantly lower than in the EC single culture group (P < 0.05). ECs co-cultured with Sertoli cells also did not significantly increase the stimulation index of spleen lymphocytes compared to the single culture group (P < 0.05). Our results suggested that co-culturing with Sertoli cells can significantly promote the proliferation of ECs, accelerate post-transplant angiogenesis, while reduce EC immunogenicity and stimulus to lymphocytes.