Effect of oxygen concentration, culture format and donor variability on in vitro chondrogenesis of human adipose tissue-derived stem cells

BACKGROUND

The chondrogenic differentiation potential of the easily accessible adipose tissue-derived stem cells (ASCs) is of particular interest within the field of tissue engineering for treating cartilage defects. However, no consensus has been reached as to which oxygen tension is more beneficial for the differentiation process.

MATERIALS & METHODS

In this investigation, the impact of available oxygen was investigated to identify optimal conditions for human ASC chondrogenesis in vitro. Four physiologically relevant oxygen concentrations of 15, 10, 5 and 1% were compared with ambient air condition, and the ASCs originating from six unrelated donors were subjected to chondrogenic induction in high-density pellet cultures.

RESULTS

The qualitative and quantitative assessment of accumulated extracellular matrix and the gene-expression analysis revealed marked interindividual differences, nevertheless the chondrogenic process was optimally supported in high-density pellet setup at ambient or 15% oxygen concentrations, irrespective of the origin of cells. The histochemical analysis based on alcian blue staining demonstrated that the differentiation took place in a gradient-like fashion, displaying highest levels in restricted regions, most often adjacent to the periphery. The two lowest hypoxic conditions, at 5 and 1% oxygen, seemed to have an inhibitory effect.

CONCLUSION

The micropellet cultures at ambient or 15% oxygen concentration provided the most suitable environment for inducing chondrogenesis in ASCs. Furthermore, in light of the fact that the induction appeared in a zone-dependent manner, this format lends itself as a suitable model for further analysis of the relationship between chondrogenic differentiation and the gradient of nutrients.

Responses of fibroblasts and glial cells to nanostructured platinum surfaces

The chronic performance of implantable neural prostheses is affected by the growth of encapsulation tissue onto the stimulation electrodes. Encapsulation is associated with activation of connective tissue cells at the electrode's metallic contacts, usually made of platinum. Since surface nanotopography can modulate the cellular responses to materials, the aim of the present work was to evaluate the 'in vitro' responses of connective tissue cells to platinum strictly by modulating its surface nanoroughness. Using molecular beam epitaxy combined with sputtering, we produced platinum nanostructured substrates consisting of irregularly distributed nanopyramids and investigated their effect on the proliferation, cytoskeletal organization and cellular morphology of primary fibroblasts and transformed glial cells. Cells were cultured on these substrates and their responses to surface roughness were studied. After one day in culture, the fibroblasts were more elongated and their cytoskeleton less mature when cultured on rough substrates. This effect increased as the roughness of the surface increased and was associated with reduced cell proliferation throughout the observation period (4 days). Morphological changes also occurred in glial cells, but they were triggered by a different roughness scale and did not affect cellular proliferation. In conclusion, surface nanotopography modulates the responses of fibroblasts and glial cells to platinum, which may be an important factor in optimizing the tissue response to implanted neural electrodes.

Response of chronic hypoxic cells to low dose-rate irradiation

PURPOSE

Compare the sensitivity of human cells in vitro to low dose-rate irradiation in air and in moderate hypoxia (4% O2).

MATERIALS AND METHODS

Continuous low dose-rate beta-irradiation at a dose rate of 0.015 or 0.062 Gy/h was given to human T-47D breast cancer cells by incorporation of [3H] -labelled valine into cellular protein. Acute irradiation at a dose rate of 0.4 Gy/min was performed using [137Cs]gamma-irradiation. Cells were cultivated in an atmosphere with 4% O2 using an INVIVO2 hypoxia cabinet.

RESULTS

When grown in ambient air with continuous irradiation, T-47D cells were able to continue growth for at least 23 weeks at a dose-rate of 0.015 Gy/h with a surviving fraction stabilized at around 60%. When the dose rate was increased to 0.062 Gy/h the cell culture died out after about 23 days (corresponding to about 22 Gy). When grown in an atmosphere with 4% O2 we surprisingly found that the continuously irradiated T-47D cells (0.015 Gy/h) were severely inhibited in their growth, and cell death became extensive after about 3 weeks while un-irradiated cells continued growth seemingly unaffected by this low oxygenation. Peri cellular oxygenation varied between 4% and below 0.1% over an ordinary passage due to diffusion-limitations through the 2 mm deep medium. Online O2-recordings over a whole passage showed that oxygen was more depleted in the irradiated compared to the un-irradiated cultures indicating increased respiration during irradiation. While cells growing attached to the bottom were inhibited and inactivated during irradiation it was found that cells attached high up in the neck region, i.e., having only a shallow layer of medium above them, survived and formed colonies. When cells cultivated in 4% O2 for 7 weeks were irradiated with acute doses of 137Cs gamma-rays, the radiosensitivity was the same as for cells cultivated in ambient air.

CONCLUSION

Continuous irradiation with 0.015 Gy/h for several weeks results in a stronger inhibition for T-47D cells grown in an atmosphere with 4% as compared to 20% O2. The data indicate that this may be due to increased oxygen consumption resulting in more severe hypoxia in [3H]-incorporating compared to control (un-irradiated) cells.

The influence of glancing angle deposited nano-rough platinum surfaces on the adsorption of fibrinogen and the proliferation of primary human fibroblasts

We have used the glancing angle deposition (GLAD) method as a simple and fast method to generate nano-rough surfaces for protein adsorption experiments and cell assays. The surface roughness and the detailed geometrical surface morphology of the thin films were characterized by atomic force microscopy (AFM) and scanning electron microscopy (SEM). As the GLAD deposition angle approaches grazing incidence, sharp and whisker-like columnar protrusions are formed. Smaller and less sharp surface features appear for the thin films synthesized at higher deposition angles. By changing the GLAD deposition angle together with the total amount of mass deposited per area on the respective surfaces, the size of the surface features can be varied on the nanoscale. Using the GLAD topographies as model surfaces, we have investigated the influence of the nano-roughness on fibrinogen adsorption and on the proliferation of primary human fibroblasts. It is found that fibrinogen, an important blood protein, preferentially adheres on the whisker-like nano-rough substrates in comparison to a flat surface. Furthermore, the proliferation of the human fibroblasts is significantly reduced on the nano-rough substrates. These results demonstrate that the GLAD technique can be used to fabricate nano-rough surface morphologies that significantly influence both protein and cellular adhesion to surfaces and are therefore well suited for biological assays.

Continuous hypoxic culturing maintains activation of Notch and allows long-term propagation of human embryonic stem cells without spontaneous differentiation

OBJECTIVE

The maintenance of pluripotency of human embryonic stem cells (hESCs) requires a high efficiency of self-renewal. During in vitro propagation, however, hESCs have a propensity to differentiate spontaneously. In this study, we assessed the nature of hESC responses to hypoxic conditions.

MATERIALS AND METHODS

Human embryonic stem cells were grown in normoxic and hypoxic conditions, and the cells expressing Oct4 and stage-specific embryonic antigen-1 were identified by indirect immunofluorescence. The transcriptional expression of Nanog, Notch1, and Oct4 was determined by a real-time reverse transcription-polymerase chain reaction, and the inhibition of Notch-mediated signalling was achieved with a gamma-secretase inhibitor.

RESULTS

In contrast to culture at 21% oxygen, where the colonies displayed a marked degree of differentiation, we found that during exposure to 5% oxygen, the hESC colonies displayed a homogenous and flat morphology that was consistent with the presence of Oct4-positive phenotype, indicating no spontaneous differentiation. When cultured at 5% oxygen for either 4 weeks or up to 18 months, high levels of Nanog and Notch1 transcriptional expression were detected, albeit the expression was significantly lower during longer exposure. The suppression of differentiation was rapidly reversed on transfer of the hypoxic cultures to normoxic conditions. Looking into the molecular mechanisms of the maintenance of self-renewal at low oxygen tensions, we found that inhibition of Notch signalling fully abrogated the hypoxic induction of undifferentiated phenotype.

CONCLUSION

Our data, thus, indicate that hypoxic exposure has the capacity to sustain long-term self-renewal of hESCs and that this effect is mediated through activation of Notch.

Transcriptional signature of human adipose tissue-derived stem cells (hASCs) preconditioned for chondrogenesis in hypoxic conditions

Hypoxia is an important factor involved in the control of stem cells. To obtain a better insight into the phenotypical changes brought about by hypoxic preconditioning prior to chondrogenic differentiation; we have investigated growth, colony-forming and chondrogenic capacity, and global transcriptional responses of six adipose tissue-derived stem cell lines expanded at oxygen concentrations ranging from ambient to 1%. The assessment of cell proliferation and colony-forming potential revealed that the hypoxic conditions corresponding to 1% oxygen played a major role. The chondrogenic inducibility, examined by high-density pellet model, however, did not improve on hypoxic preconditioning. While the microarray analysis revealed a distinctive inter-donor variability, the exposure to 1% hypoxia superseded the biological variability and produced a specific expression profile with 2581 significantly regulated genes and substantial functional enrichment in the pathways of cell proliferation and apoptosis. Additionally, exposure to 1% oxygen resulted in upregulation of factors related to angiogenesis and cell growth. In particular, leptin (LEP), the key regulator of body weight and food intake was found to be highly upregulated. In conclusion, the results of this investigation demonstrate the significance of donor demographics and the importance of further studies into the use of regulated oxygen tension as a tool for preparation of ASCs in order to exploit their full potential.

Natural killer cell-mediated basal and interferon-enhanced cytotoxicity against liver cancer cells is significantly impaired under in vivo oxygen conditions

Current immunostimulatory treatment protocols of cancer are often met with little success. Several lines of evidence indicate that the tumour microenvironment may impair the cytotoxic activity of natural killer (NK) cells. In this study, the NK cell-mediated killing of liver-derived cells was investigated at oxygen concentrations conform to those present in the human body at physiological and pathological conditions. The in vivo-relevant oxygen concentrations corresponding to 1, 2 and 6% were compared to those of the ambient air (21%) for their effect on the lysis of four liver-derived cell lines and the highly susceptible K562 cells. Exposure to each of the hypoxic conditions had a significantly inhibitory effect on NK cytotoxicity. Treatment with interferon-alpha (IFN-alpha) in hypoxia enhanced the cytotoxic potential of the NK cells less than it enhanced the cytotoxicity at ambient oxygen conditions. In summary, the oxygen tension profoundly affects both the cytoxic activity of NK cells and their activation by IFN-alpha.

Expression of butyrate response factor 1 in HTLV-1-transformed cells and its transactivation by tax protein

Tax oncoprotein of Human T-lymphotropic virus 1 (HTLV-1) has been proposed to dysregulate the expression of a number of cellular genes, many of which play a critical role for cell proliferation. Our initial data demonstrated that the immediate-early gene butyrate response factor 1 ( BRF1) was upregulated in HTLV-1-infected cells. The ensuing studies revealed that the effect of Tax was mediated through two transcription elements. The more proximal element, located in the vicinity of TATA box, accounted for the main Tax transactivating effect, and it appeared to be a novel transcription factor-binding site. It involved the CCTCCTC sequence (nt -59/-53, relative to transcription start site) and was dubbed BRF1 Tax-responsive site (BTRS). The cellular protein(s) recruited into the formation of DNA-protein complex at this binding site were not identified. The other element, located further upstream, was a consensus cAMP-responsive site (CRE) TGACGTCA, spanning positions -400 to -393. CRE-binding protein (CREB) was found to mediate the transactivating effect of Tax at this site. Our results present the first evidence that the Tax transactivator has a capability to modulate the expression of BRF1 and that this effect is mediated by CRE and a novel BTRS motifs.

Biological characterization of three novel variants of IFN-alpha 13 produced by human placental trophoblast

Interferon (IFN)-alpha from the human placenta was cloned and expressed with the aim to study the antiviral, antiproliferative, and immunostimulatory activities. In the present study, we describe three previously unknown sequence variants of IFN-alpha 13 originating from the villous trophoblast. The first variant differed from IFN-alpha 13 by a Cys99Arg substitution and a 10-amino acid C-terminal deletion, which led to a severe reduction of the antiviral and antiproliferative potential. The second variant with a Glu32Tyr substitution also displayed diminished antiviral and antiproliferative properties, but to a lesser extent than the first clone. For the third variant, a Ser25Pro substitution in the N-terminal part of the protein and two substitutions in the C-terminal part of the protein, Arg126Gly and Ala140Gly, resulted in diminished antiviral but not antiproliferative properties. Regardless of the altered antiviral and antiproliferative properties, all sequence variants demonstrated natural killer (NK) cell stimulatory potentials paralleling that of prototype IFN-alpha 13. Further studies are needed to gain a better understanding of the functional significance of different IFN-alpha subtypes at the maternal-fetal interface, in particular in light of the controversial role the NK cells play in the positive outcome of pregnancy.

Quantitative gene expression profiles of human liver-derived cell lines exposed to moderate hypoxia

AIMS

To obtain better understanding of molecular events following critical oxygen shortage in liver tissue, we performed a large-scale comparison of gene expression profiles in four human liver cell lines, Chang, Hep3B, HuH7, and HepG2.

METHODS

We used Atlas cDNA expression arrays from Clontech for initial screening, and quantitative real-time RT-PCR to assess the statistical significance of observed changes.

RESULTS

RT-PCR analysis confirmed significantly changed levels of 24 transcripts after 24 hours incubation in 1% O(2). Among the genes most robustly up-regulated were plasminogen activator inhibitor-1 (PAI-1), insulin-like growth factor binding protein-3, and glyceraldehyde-3-phosphate dehydrogenase. Only PAI-1 was concordantly up-regulated in all four cell lines. Conversely, most down-regulated were the stress response genes, including several heat shock proteins, yet only the expression of flap endonuclease-1 was significantly decreased in all cell lines. When comparing individual cell lines, the HepG2 cells displayed a pattern of general down-regulation (83%), followed by Hep3B with 58% of genes down-regulated. In the Chang and HuH7 cells, however, the expression of most genes, 50% and 67%, respectively, remained unchanged.

CONCLUSION

These studies provide information that is of importance for improved insight into the responses of not only liver tumor cells but also normal liver tissue in the conditions where physiological oxygenation is severely impaired.

[Free nerve transplants in the reconstruction of secondary defects of the peripheral nerves of the hand]

BACKGROUND

Peripheral nerve of the hand significantly participate ub the physiological functions of the hand. A defect in the area of the peripheral nerve therefore represents a problem, the solution of which is in the field of microsurgical reconstruction. The study deals with the possibility of microsurgical reconstruction by use of free nerve draft.

SUBJECTIVE

Clinical observation of patients after microsurgical reconstruction of the hand peripheral nerve defect.

MATERIAL AND METHODS

34 patients after lesions of the median nerve, ulnar nerve and mutual impairment of both nerves. The evaluation according the known and spread system system of Medical Research Council, Seddon 1954.

RESULTS

We have achieved very good results after isolated lesions of the median nerve, while the results in this, as well a in other groups are better in younger patients and in patients, in whom the devastation of tissue was not too great. Standard results were achieved in the group with isolated injury of the ulnar nerve and the worst results in a small group of concommitant impairment of both median and ulnar nerves.

CONCLUSIONS

The results indicate that this method is unambiquously appropriate in such a complicated clinical picture. Our results are in accord with the data from other literature sources. MEANING FOR PRACTICE: Inevitability of specialized centres which would deal with this problem thus reducing the necessity of secondary reconstruction operations and naturally the reduction of financial expenditure or social support provision.

Lack of protection against vertical transmission of HIV-1 by interferons produced during pregnancy in a cohort from East African republic of Malawi

Interferons (IFNs) associated with pregnancy were studied for their possible role in inhibition of vertical transmission of the human immunodeficiency virus type 1 (HIV-1). A study group was composed of 43 HIV-1-positive mothers, of whom 15 transmitted the virus to the offspring and 28 did not. The control group included 48 HIV-1-negative mother-infant pairs. The IFN-alpha was detected only sporadically in the maternal sera from the groups of transmitters (27%), nontransmitters (21%), and controls (19%). The average levels of IFN-alpha were low, 16.3 +/- 2.5 pg/ml, 21.4 +/- 9.9 pg/ml, and 21.3 +/- 9.4 pg/ml among the transmitters, nontransmitters, and control subjects, respectively. In the cord blood, IFN-alpha was detected only on two occasions among transmitters, and on a single occasion in the control group. IFN-beta was absent from both maternal and cord blood in the study group, and found to be present in one case in the control group simultaneously in the maternal and fetal sera. In the placentas, on the other hand, both type I and II IFNs were expressed universally in the villous trophoblast, and IFN-alpha and -beta in the stromal macrophages as well. In one case among transmitters, no IFNs were detected; nevertheless, no significant difference with respect to nontransmitters could be confirmed. Our data suggest that although the placental IFNs have an antiviral potential, they are not sufficient to suppress transmission of HIV from mother to infant.

Genetic analysis reveals ongoing HIV type 1 evolution in infected human placental trophoblast

To provide a better understanding of the role of placenta in vertical human immunodeficiency virus (HIV) transmission, we have studied the infection of placental trophoblast in a group of 15 mother-neonate pairs. By nested PCR amplification of the C2V3 env gene region, HIV-1 has been found to infect the placenta in five cases (33%). Phylogenetic analysis of the cloned sequences showed that all recovered maternal variants were of the B subtype. Further investigation into the ancestral relationships at the nucleotide level revealed that the trophoblast sequences evolved into a quasispecies population clearly distant from that observed in the mother. As expected, the populations transmitted to the trophoblast were also found to be more homogeneous than those in the mothers when characterized on the basis of pairwise nucleotide sequence distances. With regard to the predicted biological properties, the primary amino acid structure of the V3 loop domain was consistent, with a macrophage-tropic, non-syncytium-inducing phenotype in all patients. We also attempted to determine if any of a number of selected maternal or viral factors was associated with trophoblast infection. However, none of the followed parameters, including maternal age, disease stage, antiretroviral therapy, CCR5delta32 deletion status of the infant, and viral genotype, could be associated with viral transmission. Moreover, in one pair with proven trophoblast infection, HIV was also detected in the cord blood. Taken together, our data suggest that the productive trophoblast infection by HIV-1 in vivo is a relatively frequent event that may bear direct implications for a further transplacental propagation of the virus.

Oxygen tension and virus replication

An evidence is accumulating that the oxygen tension exerts significant effect on the virus replication in vitro. When the in vitro oxygen tension is maintained at an in vivo physiological level, as a rule higher yields of human viruses are seen that at conventional culturing with access of an unphysiologically high oxygen concentration in ambient air. Although not fully understood, possible explanation for this phenomenon may be provided by a lowered interferon (IFN) output and increased cell replication which is often optimal at physiological oxygen tension. Furthermore, an indirect evidence suggests that the expression of some virus receptors is affected by oxygen tension. Also, the antiviral cell-mediated immunity is likely to be found oxygen tension-dependent as both the NK and cytotoxic T cell activities towards uninfected target cells are oxygen tension-sensitive. At present, the in vitro work with viruses at physiological oxygen tensions is hampered by the fact that cells adapt in the course of several weeks to the new oxygen tension. Whether viruses may adapt to different oxygen tensions is not clear. Workbenches combining safety in manipulation with hazardous viruses and the convenience of controlled gas atmosphere during both manipulation and long-term incubation have been developed. It is suggested that the in vitro virology should ensure that the physiological oxygen tension is better mimicked in the in vivo processes. Much work is to be done to determine the molecular interactions between oxygen tension-sensitive elements of the cell and infecting viruses. Of no lesser importance are the questions regarding the role of oxygen in virus tissue tropism, the cost-benefit of virus production at different oxygen tension levels, and the potential significance of oxygen tension for delivering gene effects to the selected target tissues.

Differential expression of Nur77 family members in human T-lymphotropic virus type 1-infected cells: transactivation of the TR3/nur77 gene by Tax protein

We analyzed the differential expression and regulation of three members of the Nur77 transcription factor family by the human T-lymphotropic virus type 1 (HTLV-1) Tax protein. We have demonstrated that in both HTLV-1-infected cells and Tax-expressing JPX-9 cells, TR3/nur77 is highly expressed, whereas neither NOR-1 nor NOT expression is detectable. Transient transfection analysis further confirmed the Tax transactivation of the TR3/nur77 promoter but not the NOR-1 promoter in different cell types. Furthermore, expression of a luciferase reporter gene driven by the NGFI-B (rat homolog of TR3/Nur77) response element (NBRE) provided evidence that Tax-mediated transactivation resulted in the induction of a functional protein. Cotransfection assays with the TR3/nur77 promoter sequence or the NBRE binding motif together with a series of Tax mutants have shown that Tax-induced TR3/nur77 expression is mediated by CREB/ATF-related transcription factors.

Role of the Fas/Fas ligand pathway in apoptotic cell death induced by the human T cell lymphotropic virus type I Tax transactivator

Two distinct human diseases have been described in association with human T cell lymphotropic virus type I (HTLV-I) infection: adult T cell leukaemia and tropical spastic paraparesis/HTLV-I-associated myelopathy. Although comprehensive understanding of specific mechanisms underlying pathogenesis of either disease has not yet been achieved, the viral regulatory protein Tax is believed to play a significant role. Previous studies demonstrated the potential of Tax to transform host cells. Here, it is shown that the Tax transactivator has in addition the potential to induce T cell death by apoptosis. Using an inducible system (Jurkat cell line JPX-9), significant apoptotic cell death upon Tax expression was observed. In an attempt to detect the cellular genes mediating this effect, it was found that induction of Tax was associated with marked upregulation of the Fas ligand (FasL) gene. Tax-induced apoptosis was inhibited when the Fas/FasL pathway was interrupted by YVAD-cmk, the inhibitor of ICE-like proteases. Transient expression experiments provided additional support for the putative role of endogenous FasL in Tax-induced apoptosis. Upon cotransfection with Tax-expressing plasmid, the transcriptional activity of the FasL promoter was found to be significantly upregulated in Jurkat cells and several other cell lines, as measured by reporter gene expression. Furthermore, cotransfection using different Tax mutants demonstrated that both CREB and NF-kappaB activation domains of Tax protein were required for the transactivation to take effect.

Efficient in vitro inhibition of HIV-1 gag reverse transcription by peptide nucleic acid (PNA) at minimal ratios of PNA/RNA

We have tested the inhibitory potential of peptide nucleic acid (PNA) on in vitro reverse transcription of the HIV-1 gag gene. PNA was designed to target different regions of the HIV-1 gag gene and the effect on reverse transcription by HIV-1, MMLV and AMV reverse transcriptases (RTs) was investigated. We found that a bis-PNA (parallel antisense 10mer linked to antiparallel antisense 10mer) was superior to both the parallel antisense 10mer and antiparallel antisense 10mer in inhibiting reverse transcription of the gene, thus indicating triplex formation at the target sequence. A complete arrest of reverse transcription was obtained at approximately 6-fold molar excess of the bis-PNA with respect to the gag RNA. At this molar ratio we found no effect on in vitro translation of gag RNA. A 15mer duplex-forming PNA was also found to inhibit reverse transcription at very low molar ratios of PNA/ gag RNA. Specificity of the inhibition of reverse transcription by PNA was confirmed by RNA sequencing, which revealed that all tested RTs were stopped by the PNA/RNA complex at the predicted site. We propose that the effect of PNA is exclusively due to steric hindrance, as we found no signs of RNA degradation that would indicate PNA-mediated RNase H activation of the tested RTs. In conclusion, PNA appears to have a potential to become a specific and efficient inhibitor of reverse transcription in vivo , provided sufficient intracellular levels are achievable.

High interferon alpha levels in placenta, maternal, and cord blood suggest a protective effect against intrauterine herpes simplex virus infection

Interferons (IFN) are produced by the placenta during pregnancy, and they can be detected in the maternal and fetal blood. Although the antiviral potential of IFNs is well established, it remains unclear whether the IFNs associated with pregnancy can prevent transplacental spread of viral infection. The present study was undertaken in order to determine the possible protective effect of placentally produced IFN-alpha on fetal acquisition of herpes simplex virus (HSV). Nine mothers with a known history of genital HSV infection were studied. In five cases IFN-alpha was detected in the placenta, maternal, and fetal blood, whereas in three cases IFN-alpha could not be detected. in the remaining case, IFN-alpha was found only in the maternal blood. As corroborated by the serological evidence of early HSV infection in the cord blood, the single case of vertical HSV transmission was observed in the group of IFN nonproducers. Furthermore, virus transmission did not occur in cases where IFN-alpha was present in the placenta and simultaneously in the maternal and fetal circulations. Thus, the present data indicate that high levels of IFN during pregnancy may protect the fetus from acquiring a possibly fatal intrauterine HSV infection.

Transfer of human T cell lymphotropic virus type I to human term trophoblast cells in vitro

We studied the susceptibility of term placental trophoblast cells to in vitro infection with human T cell leukaemia/lymphotropic virus type I in order to provide further insight into the role of syncytiotrophoblast in transplacental passage of the virus. Pure villous trophoblast cultures were exposed to cell-free virus and the extent of infection was analysed by semiquantitative PCR assay to detect integrated proviral DNA. Four different primer pairs targeting the gag, pol, env and pX regions invariably revealed that virus sequences were present in amounts 10(2)-10(3) times less than in the reference cell line MT-2. Virus expression was studied at both the transcriptional and translational levels. Whereas doubly spliced mRNAs coding for the Tax and Rex regulatory proteins could be detected by RT-PCR no virus-specific proteins were found in the cells by immunoperoxidase staining. The present data lend support to the notion that the placental trophoblast may represent a barrier effectively protecting the fetal compartment from exposure to the virus.

Clonal analysis suggests provirus expression in a subpopulation of human malignant trophoblast cells harbouring the human T cell lymphotropic virus type-I genome

Previous studies have indicated that the villous trophoblast may be involved in intrauterine HTLV-I infection. Although the data furnished by our group (Liu et al., 1995) have demonstrated that the human trophoblast-derived malignant cell lines JAR and JEG-3 are susceptible to HTLV-I, the infection, even after thorough analysis, appeared to be limited to expression at the transcriptional level. In the present report, we sought to explore virus expression at the single cell level using eight clonally selected cell lines which were derived by limiting dilution from the previously infected parental cultures. Of the three cell lines JAR-H2, JAR-H3, and JEG-H3, all of which harboured full-length provirus, only in two (JAR-H2 and JEG-H3) were the virus-specific tax/rex and env transcripts demonstrated using RT-PCR. When compared with MT-2 cells, the detected steady-state levels of HTLV-I mRNA appeared to be lower by three orders of magnitude. Viral Tax protein displaying a typical intranuclear localization was found in 1-2% of JAR-H2 and JEG-H3 cells. Moreover, an altered phenotype characterized by multinucleated syncytia was observed in these cell cultures with the same frequency as Tax transactivator, implying a fusogenic activity of env protein. Infectious virus, however, could not be rescued from JAR-H2 or JEG-H3 clones by coculture with cord blood mononuclear cells. Our data suggest that trophoblast represents a susceptible, albeit a slightly permissive, host system for HTLV-I.

Cell-mediated transmission of human T cell lymphotropic virus type I to human malignant trophoblastic cells results in long-term persistent infection

We investigated permissiveness of the malignantly transformed trophoblast (choriocarcinoma) cell lines JAR, BeWo and JEG-3 to the human T cell lymphotropic virus type I (HTLV-I). After co-culture with the productively infected cell line MT-2 the choriocarcinoma cell lines were analysed for infection over a period of three months. The presence of HTLV-I viral DNA was examined by PCR using primers targeting the gag, pol, env and pX specific sequences. All amplified segments were found consistently in the cell cultures throughout the period of study. Further analysis that aimed to characterize the size variation of the integrated proviral DNA by Southern blotting revealed the presence of integrated proviral sequences which consisted, for the most part, of incomplete genomes. The presence of the full-length HTLV-I genome, however, was unequivocally confirmed in clonally expanded cell cultures derived from the originally infected parental cells. In order to analyse virus expression at the transcriptional level, we used reverse transcriptase (RT)-mediated PCR that was targeted at intra-exon regions (gag, pol, env and pX), and the splicing sites of the env and pX-tax/rex mRNAs. When compared with MT-2 cells, substantially lower levels of all transcripts were found in all the cell lines analysed. We were unsuccessful in attempts to detect viral protein expression using polyvalent or Tax- and Gag-specific monoclonal antibodies by Western blot analysis or immunoprecipitation, and we could not detect any RT activity released into the supernatant of the infected cells either. Collectively, these data suggest that the trophoblastic cells may become persistently but essentially non-productively infected with HTLV-I.

Immunosuppressive effects of human placental trophoblast interferon-beta on lymphocytes in vitro

Human placental trophoblast cells produce predominantly interferon-beta-type (IFN-beta) when stimulated with viral inducers. The aim of the present study was to determine the in vitro antiproliferative effect of the trophoblast interferon-beta (tro-IFN-beta) on mitogen-stimulated and resting lymphocytes. The antiproliferative effect of the tro-IFN-beta was compared to human recombinant IFN-beta. All activities of tro-IFN-beta and human recombinant IFN-beta ranging between 10-1000 IU/ml showed suppression of proliferative responses on mitogen-stimulated and resting lymphocytes compared to cultures without IFN treatment. The inhibitory level of both tro-IFN-beta and recombinant IFN-beta was significantly higher on the stimulated than on the resting lymphocytes. Although there was a variation in the inhibition of lymphocyte proliferation by both IFNs with respect to time, there was no statistically significant difference in the antiproliferative effect of the IFNs on both resting and mitogen-stimulated lymphocytes. Since IFNs are produced locally by the placenta during pregnancy, our data suggest that in addition to the antiviral activity, the human tro-IFN-beta may participate in the local control of the maternal immune response during pregnancy at the fetomaternal interface.

Basal and Tat-transactivated expression from the human immunodeficiency virus type 1 long terminal repeat in human placental trophoblast rules out promoter-enhancer activation as the partial block to viral replication

We have analysed the capacity of the trophoblast-derived malignant cell lines BeWo, JAR and JEG-3, and primary cultures of highly purified trophoblast cells to support the basal and Tat-mediated trans-activation-enhanced transcriptional activity of two distinct human immunodeficiency virus type 1 (HIV-1) isolates. Kinetic studies based on expression of long terminal repeat (LTR)-chloramphenicol acetyltransferase (CAT) constructs revealed that LTRs of both the prototype strain 3B and the highly cytopathic Zairean variant NDK were activated significantly in all target cells. Overall, the strongest activation was observed in primary trophoblasts. A novel modification of quantitative PCR was used to normalize LTR expression for transfection efficiency, enabling the calculation of specific expression rates in terms of muU CAT enzyme per fmol of transfected DNA. Using the latter criterion we determined that LTRs of both viruses were activated in decreasing order from trophoblasts to JAR, JEG-3 and BeWo cells; furthermore, the expression of HIV-1 3B LTR always significantly surpassed that of HIV-1 NDK. The effects of trans-activation on either of the LTRs, when assayed in cotransfection assays with various amounts of HIV-1 NDK-Tat expression vector, increased in a dose-dependent fashion and were comparable in a particular neoplastic cell line. Furthermore, the cell-specific LTR activity patterns did not correspond to the abundance of transcription factors binding specifically to the viral NF kappa B and SP1 motifs. Unlike SP1-binding proteins which were relatively abundant, substantially smaller amounts of proteins with NF kappa B specificity were found in all cells. Despite this apparent deficit in NF kappa B activity, trophoblasts supported a high basal activity of both LTRs. These data indicate that an insufficiency of basal or Tat-trans-activated LTR activity cannot account for the low level of HIV-1 replication in this important cell type.

In vitro cytotoxic activity of cord blood NK cells against herpes simplex virus type-1 infected purified human term villous cytotrophoblast

Transplacental infection of the fetus with herpes simplex virus (HSV) is associated with high morbidity. The present study was undertaken to shed light on the possible participation of the fetal immune system in the elimination of HSV from placental unit. In a chromium release assay cultured term villous trophoblast cells, regardless of infection with HSV-1, were found resistant to lysis by cord blood natural killer (CBNK) cells. In contrast to this, CBNK cells exhibited a basal level of cytotoxic activity against placental fibroblasts, which was significantly increased by preceding infection of the target cells with HSV-1. Stimulation of CBNK cells with interferon-beta purified from trophoblast (tro-IFN-beta) increased the killing of both HSV-1 infected and uninfected fibroblast, while HSV-1-infected and uninfected term villous trophoblast cells remained resistant to lysis. IL-2-stimulated CBNK cells were able to lyse villous trophoblast cells at a low level, but no significant difference in the susceptibility of the HSV-1-infected and uninfected trophoblast cell was detected.

Physiological oxygen tension is relevant to MHC-1 expression, spontaneous transformation, and interferon response of in vitro aging murine fibroblasts

Working from the hypothesis that modest deviations from physiological oxygen tension will influence cell characteristics important for infections/immunity and tumor development, cells were studied at three oxygen tensions during in vitro aging. Primary mouse embryo fibroblasts were established and subsequently passaged at 3, 6, and 18 kPa oxygen tension (6 representing normal tissue tension and 18 being the conventionally tension at in vitro cultures). The growth rate was slightly higher at 6 than 3 and 18 kPa. All cultures eventually stopped growing and subsequently transformed to nonmalignant cells with unlimited growth capacity. Cells kept at 3 kPa reached the highest number of cell doublings before crisis. Stimulation with PolyI:C resulted in detectable interferon response only at the high oxygen tension, and after transformation none of the cultures responded with interferon production. Expression of the major histocompatibility complex H-2K was elevated above and below physiological oxygen tension, indicating regulatory processes optimizing MHC expression at about physiological oxygen tension.

Human trophoblast interferons

The human placental trophoblasts which constitute the first fetal cells and form the major cell layer of the feto-maternal interface are potent producers of interferons (IFNs). The IFN production is dependent on the gestational age of the trophoblast, type of inducer and the stage of differentiation of the trophoblasts. First trimester trophoblast populations produce higher levels (5-6 times) of IFN than the third trimester trophoblasts when stimulated with viruses. Non-viral inducers, such as poly(rl).poly(rC), induce exclusively IFN-beta whereas viruses such as Sendai and Newcastle Disease Virus (NDV) induce mixtures of IFN-alpha subtypes and IFN-beta. Differentiation of mononuclear cytotrophoblasts into syncytiotrophoblasts in vitro increase the IFN production. High-performance and immunoaffinity chromatography of the virus-induced trophoblast IFN preparations resulted in the isolation of three antigenically distinct IFNs, namely, alpha I, alpha II1 (omega 1), and beta with molecular masses of 16, 22 and 24 kDa, respectively, on SDS-PAGE. The human trophoblast IFNs have physical and antiviral activities characteristic of the Type 1 IFNs. The possible roles of the trophoblast IFNs in human placental and fetal development are also discussed in this review.

Absolute quantification of target DNA: a simple competitive PCR for efficient analysis of multiple samples

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Differential interferon production in human first and third trimester trophoblast cultures stimulated with viruses

Stimulation of human placental first and third trimester trophoblast and syncytiotrophoblast cultures with viruses [Newcastle Disease Virus (NDV) and Sendai virus] led to a high interferon (IFN) production. The magnitude of the production was dependent on the gestational age of the trophoblast, type of inducer and the stage of differentiation of the trophoblast. The data obtained indicated that the first trimester trophoblast cultures produced five to sixfold more IFN than the third trimester trophoblast on per cell basis whereas syncytiotrophoblast at term produced twice as much IFN than the mononuclear term trophoblast when stimulated with the viruses. NDV and Sendai virus produced different levels and composition of IFN-alpha and -beta in both first and third trimester trophoblast and syncytiotrophoblast cultures. Purification of the virus-induced trophoblast interferons (tro-IFNs) by tandem high-performance affinity chromatography resulted in specific activities between 0.7 and 2.7 x 10(8) IU/mg of protein when assayed on human amniotic WISH cells. The tro-IFN-alpha protected both human and bovine MDBK cells from virus infection whereas the tro-IFN-beta protected only the human cell lines tested. The possible roles of the tro-IFNs are discussed in light of the observed differences in trophoblast IFN response.

In vitro infection of human placental trophoblast by wild-type vaccinia virus and recombinant virus expressing HIV envelope glycoprotein

Short-time (< or = 7 days) cultures of trophoblast mononuclear cells isolated from term placentae were challenged with vaccinia virus. Cytopathic effects were induced in crude placental cell preparations as well as in cultures established after negative immunosorting of major histocompatibility complex class I epitope-expressing cells, i.e. cultures exclusively derived from villous cytotrophoblast according to our present state of knowledge. The trophoblast in vitro supported a full replicative cycle of both wild-type viruses and a recombinant clone serving as a vector for the human immunodeficiency virus type 1 envelope gene. Results may shed light on mechanisms involved in the rarely observed foetal damage caused by smallpox vaccination during pregnancy.

Bacterially expressed core and envelope proteins of human immunodeficiency virus type-1 (HIV-1): comparative evaluation in detection of type-specific antibodies

Recombinant proteins derived from immunodominant conserved domains of HIV-1 env and gag genes were synthesized in E. coli. An immunoblot system using total cell lysates was employed for the analysis of recombinant bacterial clones. Together 427 serum samples obtained from asymptomatic anti-HIV seropositive individuals, AIDS patients, healthy donors and persons suffering from various conditions were comparatively evaluated for the presence of HIV-1 antibodies using recombinant peptides and commercially available western blot (WB) and ELISA assays. The recombinant antigen product of plasmid pEX41 was found to be superior, with respect to sensitivity and specificity, to the viral gp41 which represents a diagnostically important constituent of the WB.

Isolation, purification and biochemical characterization of human placental interferons by tandem high-performance affinity chromatography

Human placental trophoblasts, fibroblasts and the trophoblast-derived malignant cell JAR are potent producers of interferons (IFNs) when stimulated with Sendai virus. The three cell lines produced different levels and compositions of IFN-alpha subtypes and IFN-beta. Anti-IFN globulins, Cibacron Blue F3GA and Concanavalin A were covalently immobilized on pressure-stable, macroporous polymeric matrices derivatized with vinyl sulphone (HEMA-BIO 1000 VS and HEMA 1000 VS). These supports were packed in biocompatible PEEK columns and were coupled with switching valves, to develop a tandem high-performance affinity chromatographic (HPAC) method for the isolation, purification and biochemical characterization of the IFNs produced in Sendai virus-stimulated human placental trophoblasts, fibroblasts and trophoblast-derived malignant cell, JAR, cultures. Silver-stained SDS-PAGE and gel densitometric analysis revealed the purity of the purified proteins to be between 94 and 98%. Specific activities of the purified IFNs ranged between 0.37-2.76 x 10(8) IU/mg of protein with cumulative recoveries between 90 and 92.2%. The purified IFN components exhibited quantitatively different antiviral activities in human and bovine cell lines. The utility of the tandem method for the purification and characterization of human type 1 IFNs produced from other cell lines are also discussed.

Herpes simplex virus infection of cultured human term trophoblast

Mononuclear trophoblast cells were isolated from term placentas of uncomplicated pregnancies, purified to homogeneity by negative immunomagnetic separation using monoclonal antibodies to the major histocompatibility complex, and challenged with herpes simplex virus (HSV). The cultures were highly susceptible to virus-induced cytopathic effect as evidenced by cytopathic alteration and inhibition of human chorionic gonadotropin (hCG) secretion. Both HSV I and II underwent a full replicative cycle in the trophoblast, although the production of progeny virus was 10-100 times less than that obtained with placental fibroblasts or choriocarcinoma cells. The permissiveness was independent of in vitro syncytial differentiation of the trophoblast. The results suggest that the trophoblast layer may be involved in intrauterine HSV infection.

In vitro productive infection of human malignant trophoblastic cell line JAR with human immunodeficiency virus type 1 (HIV-1)

Human choriocarcinoma cells of the JAR line, with no demonstrable surface CD4 receptor were infected with human immunodeficiency virus type 1 (HIV-1), strain RF. Primer-directed enzymatic DNA amplification (polymerase chain reaction, PCR) detected the presence of viral DNA when the cultures were investigated at day 5 post-infection (p.i.). The absence of cytopathic changes attributable to virus replication suggested silent infection of these malignant trophoblastic cells. Neither reverse transcriptase (RT) activity nor HIV-specific antigens were found in the culture nutrient medium during JAR cell propagation. However, when the HIV-carrier JAR cells were continuously cultured and the cocultivation was initiated with CEM-SS lymphoblastoid cells after two subsequent passages, rescue of infectious virus was observed.

Differential HIV replication and HIV-induced interferon production in mononuclear phagocytes: relationship to cell maturation

We have investigated the replication of human immunodeficiency virus (HIV) and HIV-induced interferon (IFN) production in human mononuclear phagocytes at 2 different stages of in vitro maturation. Blood monocytes and monocyte-derived macrophages from 6 healthy, HIV-seronegative donors were challenged with HIV1IIIB and HIV2ROD. Freshly separated monocytes produced IFN when inoculated with both HIV types. In these cultures, an inverse correlation was observed between the amount of IFN production and the rate of HIV replication. In contrast to the monocytes, 5-day-old monocyte-derived macrophages did not produce IFN when challenged with HIV, but a significant replication of HIV1IIIB and HIV2ROD was found in all cultures.

Enhanced chemiluminescence-based hybridization analysis for PCR-mediated HIV-1 DNA detection offers an alternative to 32P-labelled probes

The efficiency of enhanced chemiluminescence based on a novel generation substrate for alkaline phosphatase, adamantyl-1,2-dioxetane phosphate, was compared with that of 32P-labelled probe for visualization of human immunodeficiency virus type 1 (HTV-1)-specific DNA-DNA hybrids. The probe used for nonisotopic detection was digoxigenin labelled and targeted by anti-digoxigenin antibody Fab-fragments conjugated to alkaline phosphatase. The dot-blot hybridization analysis performed on a dilution series of HIV-1 proviral DNA demonstrated a lower sensitivity limit of 0.5 pg with the nonisotopic method. However, one order of magnitude less DNA could still be detected by a random-primed 32P-labelled probe. The ability of nonradioactive and radioactive probes to detect 590-bp gag gene-specific target sequences generated by the polymerase chain reaction (PCR)-mediated amplification of HIV-1 DNA was also compared. Analysis of 20 samples from individuals at increased risk for HIV infection by using the two assayed systems produced virtually equivalent signal images on corresponding specimens. Furthermore, complete concordance in the performance was found when HIV-1 proviral DNA was investigated by PCR in additional 50 samples of human blood mononuclear cells.

Characterization of Sendai virus-induced human placental trophoblast interferons

Human placental trophoblast cultures produce a mixture of interferons (IFNs) when challenged with Sendai virus. High-performance dye-ligand and immunoaffinity chromatography of a trophoblast IFN (tro-IFN) preparation enabled the isolation of three antigenically distinct IFNs, alpha I, alpha II 1 and beta, with Mrs of 16K, 22K and 24K respectively, by reducing and non-reducing SDS-PAGE. The major IFN, responsible for 75% of the total antiviral activity, was tro-IFN-beta, with the remaining activity being due to tro-IFN-alpha I and tro-IFN-alpha II 1, as determined by an antiviral neutralization test using specific anti-human IFN antibodies. The antiviral activities of the tro-IFNs were stable at pH 2.0 for 24 h and tro-IFN-alpha II 1 and -beta were shown to be glycoproteins. The three tro-IFNs showed different antiviral activities when assayed on human and bovine cell species; tro-IFN-alpha I and alpha II 1 protected both human and bovine (MDBK) cells from virus infection, whereas tro-IFN-beta showed a high degree of species specificity, protecting only the human cell types tested.

Susceptibility of cultured human trophoblasts to infection with human immunodeficiency virus type 1

Primary cultures of essentially pure human term trophoblasts were studied to determine their ability to support the expression of complete proviral clones of human immunodeficiency virus (HIV) and their permissiveness to this virus. Transient expression of molecular clones derived from two biologically distinct strains, BRU and NDK, resulted in the release of comparable amounts of infectious virions, which were rescued by cocultivation with permissive CEM-SS cells. Trophoblasts were inoculated with three HIV-1 isolates, RF, 3B and NDK, which differ in their cytopathogenicity on T lymphoblastoid cells. Infection of cells by all three strains was demonstrated by the presence of virus-specific proteins in the trophoblasts and the detection of virus gag gene-related DNA sequences by the polymerase chain reaction (PCR), but cells were more susceptible to infection with the RF and NDK strains than with the 3B strain. The virus was readily transmitted to the CEM-SS cells with simultaneous formation of syncytia between the two cell types. Flow cytometry and direct radioimmunoassay revealed no trace of the CD4 receptor on the surface of the cultured trophoblasts and CD4 mRNA could not be detected by Northern blot hybridization, although a minimal amount of CD4-associated mRNA was detected by PCR. Our data suggest that infection of trophoblasts occurs independently of the pathway mediated by CD4.