Bovine microvascular endothelial cells immortalized with human telomerase

Immortalization of American miniature horse-derived fibroblast by cell cycle regulator with normal karyotype

Immortalized cells serve as a crucial research tool that capitalizes on their robust proliferative properties for functional investigations of an organism. Establishing an immortalized American miniature horse cell line could yield valuable insights into these animals' genetic and physiological characteristics and susceptibility to health issues. To date, immortalized small horse cells with normal karyotypes have not been established. In this study, we successfully established primary and immortalized fibroblast cell lines through the combined expression of human-derived mutant cyclin-dependent kinase 4 (CDK4R24C), cyclin D1, and Telomerase Reverse Transcriptase (TERT), although CDK4R24C and cyclin D1, SV40T and TERT did not result in successful immortalization. Our comparison of the properties of these immortalized cells demonstrated that K4DT immortalized cells maintain a normal karyotype. Ultimately, our findings could pave the way for the development of targeted interventions to enhance the health and well-being of American miniature horses.

Establishment methods and research progress of livestock and poultry immortalized cell lines: A review

An infinite cell line is one of the most favored experimental tools and plays an irreplaceable role in cell-based biological research. Primary cells from normal animal tissues undergo a limited number of divisions and subcultures in vitro before they enter senescence and die. On the contrary, an infinite cell line is a population of non-senescent cells that could proliferate indefinitely in vitro under the stimulation of external factors such as physicochemical stimulation, virus infection, or transfer of immortality genes. Cell immortalization is the basis for establishing an infinite cell line, and previous studies have found that methods to obtain immortalized cells mainly included physical and chemical stimulations, heterologous expression of viral oncogenes, increased telomerase activity, and spontaneous formation. However, some immortalized cells do not necessarily proliferate permanently even though they can extend their lifespan compared with primary cells. An infinite cell line not only avoids the complicated process of collecting primary cell, it also provides a convenient and reliable tool for studying scientific problems in biology. At present, how to establish a stable infinite cell line to maximize the proliferation of cells while maintaining the normal function of cells is a hot issue in the biological community. This review briefly introduces the methods of cell immortalization, discusses the related progress of establishing immortalized cell lines in livestock and poultry, and compares the characteristics of several methods, hoping to provide some ideas for generating new immortalized cell lines.

Bovine Organospecific Microvascular Endothelial Cell Lines as New and Relevant In Vitro Models to Study Viral Infections

Microvascular endothelial cells constitute potential targets for exogenous microorganisms, in particular for vector-borne pathogens. Their phenotypic and functional variations according to the organs they are coming from provide an explanation of the organ selectivity expressed in vivo by pathogens. In order to make available relevant tools for in vitro studies of infection mechanisms, our aim was to immortalize bovine organospecific endothelial cells but also to assess their permissivity to viral infection. Using transfection with SV40 large T antigen, six bovine microvascular endothelial cell lines from various organs and one macrovascular cell line from an umbilical cord were established. They display their own panel of endothelial progenitor/mature markers, as assessed by flow cytometry and RT-qPCR, as well as the typical angiogenesis capacity. Using both Bluetongue and foot-and-mouth disease viruses, we demonstrate that some cell lines are preferentially infected. In addition, they can be transfected and are able to express viral proteins such as BTV8-NS3. Such microvascular endothelial cell lines bring innovative tools for in vitro studies of infection by viruses or bacteria, allowing for the study of host-pathogen interaction mechanisms with the actual in vivo target cells. They are also suitable for applications linked to microvascularization, such as anti-angiogenic and anti-tumor research, growing fields in veterinary medicine.

The catalytic and the RNA subunits of human telomerase are required to immortalize equid primary fibroblasts

Many human primary somatic cells can be immortalized by inducing telomerase activity through the exogenous expression of the human telomerase catalytic subunit (hTERT). This approach has been extended to the immortalization of cell lines from several mammals. Here, we show that hTERT expression is not sufficient to immortalize primary fibroblasts from three equid species, namely donkey, Burchelli’s zebra and Grevy’s zebra. In vitro analysis of a reconstituted telomerase composed by hTERT and an equid RNA component of telomerase (TERC) revealed a low activity of this enzyme compared to human telomerase, suggesting a low compatibility of equid and human telomerase subunits. This conclusion was also strengthened by comparison of human and equid TERC sequences, which revealed nucleotide differences in key regions for TERC and TERT interaction. We then succeeded in immortalizing equid fibroblasts by expressing hTERT and hTERC concomitantly. Expression of both human telomerase subunits led to telomerase activity and telomere elongation, indicating that human telomerase is compatible with the other equid telomerase subunits and proteins involved in telomere metabolism. The immortalization procedure described herein could be extended to primary cells from other mammals. The availability of immortal cells from endangered species could be particularly useful for obtaining new information on the organization and function of their genomes, which is relevant for their preservation.

Telomerase Reverse Transcriptase Upregulation Attenuates Astrocyte Proliferation and Promotes Neuronal Survival in the Hypoxic–Ischemic Rat Brain

Background and Purpose—

Telomerase reverse transcriptase (TERT) is tightly related to the resistance of cells to stress and injury. However, little is known about the roles of TERT in the nervous system. We try to investigate the effects of TERT on the function of astrocytes in developing rat brains subjected to hypoxia–ischemia.

Methods—

TERT expression was detected in rat brains with hypoxia–ischemia. In in vitro study, the function of astrocytes with TERT overexpression was measured, and the effects of astrocyte on neuronal apoptosis were examined. Moreover, overexpression or inhibition of TERT was conducted in vivo by gene transduction. Astrocyte proliferation was examined through Ki67 staining. Terminal deoxynucleotidyltransferase-mediated dUTP nick end labeling staining and brain infarct volume calculation were used to detect neuronal injury.

Results—

Both TERT mRNA and protein were upregulated in neurons within 2 days but shifted to astrocytes at Day 3 after hypoxia–ischemia. Astrocyte proliferation was inhibited with TERT overexpression due to the upregulation of cell-cycle regulatory protein p15. Meanwhile, the apoptosis of neurons increased, whereas neurons were cocultured with conditioned media from astrocytes with TERT inhibition compared with TERT overexpression due to the decrease of neurotrophin-3 expression in astrocytes. Furthermore, Ki67-positive astrocytes and neuronal injury were found to be inhibited in TERT-overexpressing rat brains with hypoxia–ischemia.

Conclusions—

TERT attenuates astrocyte proliferation and promotes neuronal survival in the developing rat brain after hypoxia–ischemia, partly through its enhancement of p15 and neurotrophin-3 expression in astrocytes.

Baculoviral expression of telomerase in primary human fibroblasts to rejuvenate cells for tissue engineering

Tissue engineering involves the use of synthetic or natural materials as a scaffold to support the growth of replacement tissue or organs. The use of autologous cells to populate the scaffold avoids problems associated with rejection; however, a major limitation of this approach is the finite lifespan of primary cells in culture. This finite lifespan is due to the shortening of telomeres, short repetitive sequences of DNA located at the ends of eukaryotic chromosomes. Ectopic expression of telomerase reverse transcriptase (hTERT) is able to reconstitute telomerase activity and maintain the length of telomeres. This study investigated an alternative gene delivery vector, baculovirus, for the expression of hTERT in primary human cells. A recombinant baculovirus was used to efficiently deliver the hTERT gene to primary fibroblasts and the telomerase enzyme was found to be active. Although no increase in telomere length was detected, expression of hTERT in primary fibroblasts resulted in a significant extension of replicative lifespan. To our knowledge this is a novel attempt to use a recombinant baculovirus for the extension of cellular lifespan by exogenous expression of telomerase.

Telomerase-based immortalization modifies the angiogenic/inflammatory responses of human coronary artery endothelial cells

Telomerase reverse transcriptase (TERT) is fundamental in determining the life span by regulating telomere length of chromosomes. To address the question whether the enhancement of the proliferative potential hampers cell differentiation, we generated TERT-over-expressing endothelial cells (ECs) and analyzed in vitro their (1) barrier function; (2) low-density lipoprotein uptake; (3) expression pattern of six selected marker proteins; (4) angiogenic potential in four assays; and (5) inflammatory responses. In contrast to investigations with focus on other cell parameters, we demonstrate that immortalization of ECs by over-expression of TERT resulted in different angiogenic and inflammatory behavior in comparison to cells with low native telomerase levels.

Curcumin regulates low-linear energy transfer γ-radiation-induced NFκB-dependent telomerase activity in human neuroblastoma cells

PURPOSE

We recently reported that curcumin attenuates ionizing radiation (IR)-induced survival signaling and proliferation in human neuroblastoma cells. Also, in the endothelial system, we have demonstrated that NFκB regulates IR-induced telomerase activity (TA). Accordingly, we investigated the effect of curcumin in inhibiting IR-induced NFκB-dependent hTERT transcription, TA, and cell survival in neuroblastoma cells.

METHODS AND MATERIALS

SK-N-MC or SH-SY5Y cells exposed to IR and treated with curcumin (10-100 nM) with or without IR were harvested after 1 h through 24 h. NFκB-dependent regulation was investigated either by luciferase reporter assays using pNFκB-, pGL3-354-, pGL3-347-, or pUSE-IκBα-Luc, p50/p65, or RelA siRNA-transfected cells. NFκB activity was analyzed using an electrophoretic mobility shift assay and hTERT expression using the quantitative polymerase chain reaction. TA was determined using the telomerase repeat amplification protocol assay and cell survival using the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltertrazolium bromide and clonogenic assay.

RESULTS

Curcumin profoundly inhibited IR-induced NFκB. Consequently, curcumin significantly inhibited IR-induced TA and hTERT mRNA at all points investigated. Furthermore, IR-induced TA is regulated at the transcriptional level by triggering telomerase reverse transcriptase (TERT) promoter activation. Moreover, NFκB becomes functionally activated after IR and mediates TA upregulation by binding to the κB-binding region in the promoter region of the TERT gene. Consistently, elimination of the NFκB-recognition site on the telomerase promoter or inhibition of NFκB by the IκBα mutant compromises IR-induced telomerase promoter activation. Significantly, curcumin inhibited IR-induced TERT transcription. Consequently, curcumin inhibited hTERT mRNA and TA in NFκB overexpressed cells. Furthermore, curcumin enhanced the IR-induced inhibition of cell survival.

CONCLUSIONS

These results strongly suggest that curcumin inhibits IR-induced TA in an NFκB dependent manner in human neuroblastoma cells.

Does telomerase reverse transcriptase induce functional de-differentiation of human endothelial cells?

By counteracting the shortening of chromosome telomeres, telomerase reverse transcriptase (hTERT) prevents senescence and age-related cell death. Embryonic cells display a high telomerase activity that declines rapidly with cell differentiation. Conversely, de-differentiated tumor cells tend to re-express telomerase. In view of the controversial data on the reciprocal correlation between cell proliferation and differentiation, we questioned whether telomerase overexpression and the resulting immortalization would affect the functional phenotype of human endothelial cells. Our comparative analysis addressed (1) distinct cell adhesion to different ECM-proteins analyzed on miniaturized multisubstrate arrays (MSA), (2) protein expression of diverse markers, (3) the uptake of DiI-Ac-LDL, (4) the inflammatory response based on upregulation of ICAM-1, (5) tube formation, and (6) the barrier properties of cell monolayers in transfilter cultures. Our results, based on some 40 data sets, demonstrate that immortalization of primary endothelial cells by hTERT maintains the typical endothelial characteristics without any sign of functional de-differentiation.

Association of growth factors with arterial recanalization and clinical outcome in patients with ischemic stroke treated with tPA

SUMMARY BACKGROUND

Growth factors (GF) such as vascular endothelial growth factor (VEGF), angiopoietin-1 (Ang-1) and granulocyte-colony stimulating factor (G-CSF) have been associated with greater efficacy of tissue plasminogen activator (tPA) in experimental studies.

OBJECTIVES

To study the association of these GF with arterial recanalization and clinical outcome in patients with acute ischemic stroke treated with tPA.

METHODS

We prospectively studied 79 patients with ischemic stroke attributable to MCA occlusion treated with i.v. tPA within the first 3 h from onset of symptoms. Continuous transcranial color-coded sonography (TCCS) was performed during the first 2 h after tPA bolus to assess early MCA recanalization. Hemorrhagic transformation (HT) was classified according to ECASS II definitions. Good functional outcome was defined as a Rankin scale score of 0-2 at 90 days. GF levels were determined by ELISA.

RESULTS

Mean serum levels of VEGF, G-CSF and Ang-1 at baseline were significantly higher in patients with early MCA recanalization (n = 30) (all P < 0.0001). In the multivariate analysis, serum levels of VEGF (OR, 1.03), G-CSF (OR, 1.02) and Ang-1 (OR, 1.07) were independently associated with early MCA recanalization (all P < 0.0001). On the other hand, patients with parenchymal hematoma (PH) (n = 20) showed higher levels of Ang-1 (P < 0.0001). Ang-1 (OR, 1.12; P < 0.0001) was independently associated with PH, whereas patients with good outcome (n = 38) had higher levels of G-CSF (P < 0.0001). G-CSF was independently associated with good outcome (OR, 1.12; P = 0.036).

CONCLUSIONS

These findings suggest that GF may enhance arterial recanalization in patients with ischemic stroke treated with t-PA, although they might increase the HT.

Instructive role of the vascular niche in promoting tumour growth and tissue repair by angiocrine factors

The precise mechanisms whereby anti-angiogenesis therapy blocks tumour growth or causes vascular toxicity are unknown. We propose that endothelial cells establish a vascular niche that promotes tumour growth and tissue repair not only by delivering nutrients and O2 but also through an 'angiocrine' mechanism by producing stem and progenitor cell-active trophogens. Identification of endothelial-derived instructive angiocrine factors will allow direct tumour targeting, while diminishing the unwanted side effects associated with the use of anti-angiogenic agents.

Establishment, immortalisation and characterisation of pteropid bat cell lines

Background

Bats are the suspected natural reservoir hosts for a number of new and emerging zoonotic viruses including Nipah virus, Hendra virus, severe acute respiratory syndrome coronavirus and Ebola virus. Since the discovery of SARS-like coronaviruses in Chinese horseshoe bats, attempts to isolate a SL-CoV from bats have failed and attempts to isolate other bat-borne viruses in various mammalian cell lines have been similarly unsuccessful. New stable bat cell lines are needed to help with these investigations and as tools to assist in the study of bat immunology and virus-host interactions.

Methodology/Findings

Black flying foxes (Pteropus alecto) were captured from the wild and transported live to the laboratory for primary cell culture preparation using a variety of different methods and culture media. Primary cells were successfully cultured from 20 different organs. Cell immortalisation can occur spontaneously, however we used a retroviral system to immortalise cells via the transfer and stable production of the Simian virus 40 Large T antigen and the human telomerase reverse transcriptase protein. Initial infection experiments with both cloned and uncloned cell lines using Hendra and Nipah viruses demonstrated varying degrees of infection efficiency between the different cell lines, although it was possible to infect cells in all tissue types.

Conclusions/Significance

The approaches developed and optimised in this study should be applicable to bats of other species. We are in the process of generating further cell lines from a number of different bat species using the methodology established in this study.

Induced telomerase activity in primary aortic endothelial cells by low-LET gamma-radiation is mediated through NF-kappaB activation

Our objective was to understand the mechanism through which cells that initially survive irradiation could acquire survival advantage. In this study, we show evidence that low-linear energy transfer gamma-radiation can induce telomerase enzyme activity in primary aortic endothelial cells, and that an upstream regulator, nuclear factor kappa B (NF-kappaB), controls this activation. Telomeric repeat amplification protocol (TRAP) assay showed that cells exposed to a dose of 2 Gy induce telomerase activity. Subsequent analysis revealed that radiation-induced telomeric activity is regulated at the transcriptional level by triggering activation of the promoter of the telomerase catalytic subunit, telomerase reverse transcriptase (TERT). A mechanistic study revealed that NF-kappaB becomes functionally activated upon radiation exposure and mediates the upregulation of telomerase activity by binding to the kappaB-binding region in the promoter region of the TERT gene. More significantly, elimination of the NF-small ka, CyrillicB recognition site on the telomerase promoter or inhibition of NF-small ka, CyrillicB by ectopically expressing the inhibitor protein IkappaBalpha mutant (Ismall ka, CyrillicBalpha(S32A/S36A))) compromises radiation-induced telomerase promoter activation. Consistent with the notion that NF-kappaB mediates gamma-ray-induced telomerase responses, TRAP assay revealed that ectopically expressed IkappaBalpha(S32A/S36A)) also attenuated telomerase enzyme activity. These findings indicate that NF-kappaB activation following ionizing radiation exposure may elicit a survival advantage by upregulating and maintaining telomerase activity.

Alkylphospholipids inhibit capillary-like endothelial tube formation in vitro: antiangiogenic properties of a new class of antitumor agents

Synthetic alkylphospholipids (APLs), such as edelfosine, miltefosine and perifosine, constitute a new class of antineoplastic compounds with various clinical applications. Here we have evaluated the antiangiogenic properties of APLs. The sensitivity of three types of vascular endothelial cells (ECs) (bovine aortic ECs, human umbilical vein ECs and human microvascular ECs) to APL-induced apoptosis was dependent on the proliferative status of these cells and correlated with the cellular drug incorporation. Although confluent, nondividing ECs failed to undergo apoptosis, proliferating ECs showed a 3-4-fold higher uptake and significant levels of apoptosis after APL treatment. These findings raised the question of whether APLs interfere with new blood vessel formation. To test the antiangiogenic properties in vitro, we studied the effect of APLs using two different experimental models. The first one tested the ability of human microvascular ECs to invade a three-dimensional human fibrin matrix and form capillary-like tubular networks. In the second model, bovine aortic ECs were grown in a collagen gel sandwich to allow tube formation. We found that all three APLs interfered with endothelial tube formation in a dose-dependent manner, with a more than 50% reduction at 25 micromol/l. Interference with the angiogenic process represents a novel mode of action of APLs and might significantly contribute to the antitumor effect of these compounds.

Characteristics of primary and immortalized fibroblast cells derived from the miniature and domestic pigs

Background

The pig, Sus scrofa domestica includes both the miniature and commercial domestic breed. These animals have influenced the human life and economies and have been studied throughout history. Although the miniature breeds are more recent and have increasingly been used in a variety of biomedical studies, their cell lines have rarely been established. Therefore, we sought to establish primary and immortal cell lines derived from both the miniature and domestic pig to better enable insight into possible in vivo growth differences.

Results

The in vitro lifespan of primary domestic pig fibroblast (PF) and miniature pig fibroblast (MPF) cells using a standard 3T3 protocol was determined. Both of the primary PF and MPF cells were shown to have a two-step replicative senescence barrier. Primary MPF cells exhibited a relatively shorter lifespan and slower proliferation rate compared to those of primary PF cells. Beyond senescence barriers, lifespan-extended PF and MPF cells were eventually established and indicated spontaneous cellular immortalization. In contrast to the immortalized PF cells, immortal MPF cells showed a transformed phenotype and possessed more frequent chromosomal abnormalities and loss of p53 regulatory function. The lifespan of primary MPF and PF cells was extended by inactivation of the p53 function using transduction by SV40LT without any detectable senescent phenotype.

Conclusion

These results suggest that p53 signaling might be a major determinant for the replicative senescence in the MPF cells that have the shorter lifespan and slower growth rate compared to PF cells in vitro.

VEGF increases the fibrinolytic activity of endothelial cells within fibrin matrices: involvement of VEGFR-2, tissue type plasminogen activator and matrix metalloproteinases

Proteolysis of fibrin matrices by endothelial cells plays essential roles in the migratory and morphogenic differentiation processes underlying angiogenesis. Using an in vitro fibrinolysis model consisting of human umbilical vein endothelial cells (HUVECs) embedded in a three dimensional fibrin matrix, we show that VEGF, an angiogenic cytokine that plays a crucial role in the onset of angiogenesis, is a potent activator of HUVEC-mediated fibrinolysis. This VEGF-dependent fibrin degradation was completely abrogated by inhibitors of either the plasminogen activator/plasmin or matrix metalloproteinases (MMP) proteolytic systems, suggesting the involvement of both classes of proteases in fibrin degradation. Accordingly, VEGF-induced fibrinolysis correlated with an increase in the expression of tPA and of some MMPs, such as MT2-MMP and was completely blocked by a neutralizing antibody against tPA. Overall, these results indicate that efficient proteolysis of three dimensional fibrin matrices during VEGF-mediated angiogenesis involves a complex interplay between the MMP and plasmin-mediated proteolytic systems.

Morphological Observation and In Vitro Angiogenesis Assay of Endothelial Cells Isolated From Human Cerebral Cavernous Malformations

BACKGROUND AND PURPOSE

Little is known about the role of endothelial cells (ECs) in the pathogenesis of cerebral cavernous malformation because of the difficulties to obtain highly pure ECs. Thus, this study attempted to establish a reliable procedure to isolate and culture ECs from human cerebral cavernous malformation lesions. The biological features and the angiogenic potential of the cultured ECs were also investigated.

METHODS

A modified protocol was developed to isolate and culture cerebral cavernous malformation endothelial cells (CECs)from surgically resected human specimens. The biological features of CECs were investigated by electron microscope, immunostaining, real-time polymerase chain reaction, fluorescence-activated cell sorter, and Western blotting. The tube formation by CECs was examined in an in vitro angiogenesis model with or without the addition of vascular endothelial growth factor.

RESULTS

CECs from the specimens unaffected by the intraoperative bipolar coagulation were cultivated successfully with higher than 95% purity. Comparing to the ECs from control brain tissue, CECs presented primitive nucleus in ultrathin section, expressed higher levels of vascular endothelial growth factor receptor-1 and vascular endothelial growth factor receptor-2, and spontaneously formed tube structures in a 3-dimensional collagen matrix. The tube formation by CECs was significantly promoted by vascular endothelial growth factor treatment.

CONCLUSIONS

A modified protocol for the attainment of purified CECs and the first in vitro angiogenesis model of CECs were successfully established. We provided initial evidence that CECs had enhanced angiogenic potential and showed increased responsiveness to vascular endothelial growth factor.