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Disorders of Hemostasis |
From the Department of Cardiology and Pneumology, Charité-Universitätsmedizin Berlin, Campus Benjamin Franklin, Berlin, Germany (PG-L, KP, Q-VT, BS, FW, SA, TW, WP, H-PS, UR); Center for Cardiovascular Research, Charité-Universitätsmedizin Berlin, Campus Mitte, Berlin, Germany (HW); Department of Pathology, Charité-Universitätsmedizin Berlin, Campus Benjamin Franklin, Berlin, Germany (MH, DL)
Correspondence: Ursula Rauch, MD, Medical Clinic II, Charité-Universitätsmedizin Berlin Campus Benjamin Franklin, Hindenburgdamm 30, 12200 Berlin, Germany. E-mail: ursula.rauch{at}charite.de
| ABSTRACT |
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Design and Methods: TF expression was determined by quantitative Reverse Transcriptase (TaqMan®) PCR, TF ELISA and TF activity by a two stage chromogenic assay in the time course of days 1, 3, 7, 10, and 17 post IR. To detect IR-induced alterations in gene expression, Affymetrix HG U133 Plus 2.0 microarrays were used.
Results: IR induced a significant increase in TF/GAPDH mRNA ratios and cellular TF protein on days 3 and 7 post IR (20 Gy [p
0.01] and 40 Gy [p
0.01 vs. control]), suggesting a late and persistent induction of TF. An increase in cellular TF activity was already found 1 day post IR (20 Gy and 40 Gy [p
0.001] vs. control respectively), suggesting IR immediately alters the cellular thrombogenicity. TF upregulation post IR was confirmed in PBMNCs. Gene expression profiling showed IR increased the expression of inflammatory and apoptosis-related pathways known to be involved in the regulation of TF expression.
Interpretation and Conclusions: TF upregulation together with inflammation and apoptosis may increase the thrombogenicity of tissues. The demonstrated upregulation of TF might play a pivotal role in radiation associated thrombosis.
Key words: gene expression profiles, ionizing radiation, myelomonocytic cell line THP-1, procoagulability, tissue factor.
Ionizing radiation (IR) is associated with an increased risk of thrombotic occlusion of vessels and organ fibrosis.1 Thrombotic events have been described as a major complication after IR.2 Cells surviving acute genotoxic stress post IR have been shown to display delayed responses that can result in persistent effects such as apoptosis and late thrombosis.3,4 Over-expression and increased activity5 of tissue factor (TF) have been shown to be involved in radiation-induced changes.6 Furthermore, cultures of human arterial endothelial cells expressed TF mRNA after irradiation in combination with mechanical denudation.7
Alterations in transcriptional factor activity may contribute to the increased thrombogenicity present post IR.1 Sreekumar et al.8 found TF protein to be upregulated in response to radiation treatment as shown by application of microarrays in LoVo colon carcinoma cells. TF, the initiator of the extrinsic coagulation system, induces thrombus formation by activation of Factor VII resulting in activation of Factors IX and X. TF is widely thought to play a leading role in thrombus formation during thrombotic disorders.9–13 Besides its role in hemostasis,13,14 upregulation of TF expression appears to be characteristic of tumor tissue. There, TF is expressed in malignant cells as well as in tumor-infiltrating macrophages and endothelial cells.15,16,17 The procoagulant activity of TF appears to play an important role in the development of disseminated intravascular disease (DIC).18 It has been shown that platelet activation and fibrin deposition is an essential part of TF-dependent metastasis.19 In addition, blood clotting abnormalities are detected in up to 90% of patients with metastatic disease, and thrombosis represents the most frequent cause of cancer mortality.20,21
Pathologic activation of the coagulation cascades by aberrant expression of TF on the surface of monocytes has been implicated in life-threatening thrombosis.22 TF is expressed on the surface of human leukocytes and leukemic myelomonocytic cells23,24 where it has been reported to increase cellular thrombogenicity. In this study, THP-1 cells were used as a model because of their cytologic, histochemical, and functional properties which resemble human monocytes.
In response to IR, monocytes have been reported to produce inflammatory cytokines such as TNF-
. NF
B, one of the main mediators of cellular responses involved in inflammation, apoptosis and regulation of TF expression, was documented to be activated by IR through a cascade requiring endogenous TNF-
production. 25
The aim of our study was to clarify whether IR induces the expression of procoagulant proteins such as TF in the THP-1 model over a time period of 17 days. In a second step, we examined coordinated gene alterations associated with IR-induced thrombogenicity and increased TF procoagulability on day 7 post IR.
| Design and Methods |
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Isolation of human peripheral blood mononuclear cells (PBMNCs) and human PBMNC culture
Human mononuclear cells were separated from blood samples as follows: 18 mL of EDTA treated human peripheral blood was diluted (1:2) in warm (37°C) phosphate-buffered saline (PBS, without Ca2+ and Mg2+ ) and purified by the Ficoll-Paque Plus. Then 7 mL of Ficoll-Paque were overlayed with 7 mL of the PBS-blood mixture and centrifuged (610xg, 25 mins., room temperature, without brake). The cell layer over the Ficoll-Paque was collected and washed two times in 10 mL PBS and centrifuged (610xg, 10 mins., room temperature). After the last wash, the cell pellet was resuspended in 500 µL RPMI 1640 supplemented with 10% Fetal Calf Serum (FCS), 1mM L-glutamine, and 1% penicillin/streptomycin. It was tested and found to be mycoplasma and endotoxin free. Cell viability was assessed by trypan blue dye exclusion prior to all treatments. For downstream applications, cells were counted in a hematocytometer (MICROS®60-OT System, Axonlab, Stuttgart).
Irradiation of THP-1 cells
THP-1 cells (106/mL) were irradiated with a single IR dose of either 20 or 40 Gray. IR was generated by a linear accelerator (Varian Clinac 600 CD) with a maximum photon energy of 6 MeV. Cell cultures were irradiated in a water-equivalent-environment by a 25x25 cm3 photon field. With this set-up, the dose homogeneity in the cell culture media is in a range of 100–105%. Following irradiation, cells were maintained in growth medium and afterwards subjected to further analysis. To evaluate the effect of the NF
B-pathway, inhibition experiments with BAY 11-7082 were performed with 4x105 THP-1 cells/mL. These were incubated 1h pre IR and daily up to 3 days post IR with 5 µM BAY 11-7082. Furthermore, THP-1 cells pre and post IR were subjected to RNA extraction and QRTPCR analysis.
Tissue factor ELISA
To quantify the total TF protein content in irradiated and control cells, THP-1 cells were subjected to ELISA according to the manufacturers instructions (Imubind Tissue Factor ELISA Kit, American Diagnostica, Pfungstadt, Germany).
Two stage chromogenic tissue factor activity assay
Measurement of TF activity was performed as previously described.14 Briefly, THP-1 cells were washed twice with phosphate buffered saline (PBS), incubated in HEPES buffer containing 0.1 M n-octyl-ß-D-glycopyranosid. After addition of Factor VIIa, Factor X and Ca2+ TF-dependent Factor Xa generation was measured at 405 nm using a chromogenic substrate for Factor Xa. TF activity units were assessed by a standard curve. The standard curve is constructed by plotting the mean slope absorbance value measured for each lipidated TF standard against its corresponding concentration [pg/mL] according to the manufacturers Actichrome® TF instruction sheet (American Diagnostica, Pfungstadt, Germany). The activity (generation of Factor Xa) exhibited by 1 pg of lipidated TF corresponds to 1 arbitrary TF-activity unit.
RNA extraction, reverse transcription
Total RNA of THP-1 cells or PBMNCs (106) was isolated by RNeasy Mini Kit including Qiashredder columns (Qiagen, Hilden, Germany). DNase I (Fermentas, St. Leon-Rot, Germany) digested, reverse transcription of RNA was performed with a First strand cDNA synthesis kit for RTPCR (AMV; Roche Applied Sciences) according to manufacturers instructions.
Quantitative real-time PCR (QRTPCR)
PCR conditions for the TaqMan® (ABI Prism7000 Sequence Detection System, Applied Biosystems, Darmstadt, Germany) are summarized in Table 1. Primers and probes were purchased from TIB Molbiol (Berlin, Germany). Data were analyzed using SDS 7000 software.
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Analysis of GeneChip data
Scanned output files were analyzed with GeneChip Operating Software 1.2 (GCOS; Affymetrix, Santa Clara, CA, USA). Fluorescence intensity was measured for each chip and normalized to the average fluorescence intensity for the entire chip. The normalized data set from three independent replicates (day 7 post IR; untreated controls versus irradiated THP-1 cells with a 20 Gy dose) was used for the Significance Analysis of Microarrays (SAM).26 The SAM statistic identifies significant changes in gene expression by performing a set of gene-specific t-tests. A score is calculated for each gene on the basis of changes in its expression relative to the standard of repeated measurements for that gene. Genes with scores greater than a threshold
are defined as significantly deregulated. A false discovery rate can be estimated from random permutations of all measurements. A cut-off of 1.8-fold expression (q-value
5%, only for TF gene: q-value >5%) was set to identify genes whose expression was significantly differentially regulated.
Statistical analysis
Data analysis was performed using SPSS 12.0. The Kolmogorov-Smirnov-Test was performed to test data distribution. Values are presented as mean ± standard error of mean (SEM) or median and interquartile range for non-parametric data. For parametric data, statistical significance of differences between groups was determined by applying the unpaired Student t-test or one-way analysis of variance (ANOVA) for multiple comparisons. The Mann-Whitney U-test was performed for non-parametric data: p<0.05 was considered significant. All experiments were performed at least five times.
| Results |
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0.05] and vs. 40 Gy [p
0.01]) and on day 7 post IR, TF/GAPDH mRNA ratios gave the highest mRNA expression levels (control vs. 20 Gy [p
0.01] and vs. 40 Gy [p
0.01], repectively) indicating a late induction of TF. PBMNCs were isolated from human peripheral blood to analyze the TF mRNA expression of mononuclear cells compared with the THP-1 cell model. A significant increase in TF/GAPDH mRNA ratios was found 1 day post IR (0.00041±0.00006 vs. 0.0022±0.0006, baseline vs. 20 Gy, p=0.008) and 3 days post IR of PBMNCs (0.00041±0.00006 vs. 0.006±0.002, baseline vs. 20 Gy, p=0.0016).
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B-pathway related TF expression post IR, we performed mRNA expression studies by using the NF
B inhibitor BAY 11-7082. This inhibits I
B
phosphorylation. An inhibitor concentration of 5 µM had almost no effect on the growth of THP-1 cells. A significant inhibition of TF mRNA expression in irradiated cells pretreated with BAY 11-7082 was seen 3 days post IR compared to irradiated cells cultured without NF
B inhibitor (ratio HTF/HGAPDH 0.010±0.001 vs. 0.066±0.018; p
0.0001). At day 3, when THP-1 cells were pretreated with NF
B inhibitor without application of IR, the TF mRNA expression of the NF
B inhibitor-pretreated cells was significantly downregulated compared to untreated control cells (ratio HTF/HGAPDH 0.009±0.001 vs. 0.012±0.001; p
0.05). However, the application of IR without pretreatment with BAY11-7082 was associated with an increased TF mRNA expression compared to non-irradiated and untreated control cells 3 days post IR (ratio HTF/HGAPDH 0.066±0.018 vs. 0.012±0.001; p
0.001). To confirm the data obtained on mRNA level, IR-induced expression of TF protein in THP-1 cells was quantified by ELISA recognizing human TF. A significant increase in cellular TF protein became prominent 3 days post IR with 20 Gy and with 40 Gy and persisted throughout the period of study (Figure 2A). A significant increase in cellular TF activity was already found 1 day post IR with 20 Gy and with 40 Gy, indicating IR alters cellular thrombogenicity (Figure 2B). A 12-fold increase was seen 7 days post IR with a dose of 20 Gy (Figure 2B, p
0.001) and 40 Gy (p
0.001) compared with untreated THP-1 control cells. Increased cellular prothrombogenicity was persistently measurable throughout the period of study (day 0-day 17) (Figure 2B).
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The data discussed in this publication have been deposited in NCBIs Gene Expression Omnibus (GEO, http://www.ncbi.nlm.nih.gov/geo/) and are accessible through GEO Series access number GSE4110. We found a panel of candidate genes to be upregulated on day 3 and day 7 post IR. We performed only one pair of microarray analysis with day 3 post IR and the untreated control. On day 3 post IR, a generally weaker expression pattern of differentially expressed genes in irradiated THP-1 cells was detected. Therefore, 3 further replicate pairs (treated vs. untreated state) were chosen for the SAM statistics (Table 2). The number of genes with elevated expression increased in relation to an increased duration of culture time post IR. All detected 422 gene transcripts with known functions and significant upregulation (>1.8-fold, q
5%) on day 7 post IR compared to non-irradiated controls are available in the online supplement. Altered transcription patterns post IR revealed genes belonging to the following groups: inflammation/cell defense, cell cycle arrest/apoptosis, regulation of transcription, nucleic acid metabolism, protein modification, cell structure/motility, and signaling/communication (Table 2).
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Since TF is upregulated in monocytes under inflammatory conditions, especially by stimulation with TNF-
, we further verified the upregulation of TNFRSF10B (TRAIL R2/APO2LR/Killer/DR5). This is a gene for TNFrelated apoptosis-inducing ligand receptor 2 belonging to the cell signaling/communication group, known to be caspase-dependent and associated with apoptotic pathways (Table 3). QRTPCR showed IR clearly increased production of TNF (ligand) superfamily, member 13B (TNFSF13B) gene, a TNF-and APOL-related leukocyte expressed ligand 1, which is a TNF homolog activating the NF
B-, the JNK pathway and inducing apoptosis (Table 3). IFN-
inducible protein 27 (IFI27) gene was also seen to be highly upregulated post IR (Table 3).
We found three genes (TNFRSF10B, TNFSF13B and IFN-
inducible protein 27) whose regulation according to QRTPCR was considerably greater. This was also true of the TF gene, which was 1.8-fold (q-value > 5%) upregulated in the microarray experiment compared to a 3-fold upregulation measured by SYBR Green QRTPCR.
| Discussion |
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Several transcripts for interferon-inducible proteins along with those for IFN-
(IFN-
inducible protein 27; IFI27) and IFN-
showed elevated expression levels on day 3 and on day 7 post IR. IFN-
was reported to increase TNF-
induced apoptosis and, therefore, monocytes have been shown to rapidly undergo apoptosis in cultures. By contrast, endogenously produced TNF-
after
-irradiation was reported to result in enhanced monocyte survival by reducing induction of apoptosis.31 Many downstream targets of interferon were gradually induced following IR treatment. It is known that interferon operates through the JAK-STAT pathway in response to viral infections to mediate transcriptional changes in target genes. This results in antiproliferative effects, involved in suppressing viral replication. In case of IR stress, interferon activity may promote the same effects to prevent propagation of DNA damage.32 TNFRSF10B (TRAILR2) was found to be upregulated post IR. This TNF-
receptor is a potential activator of the NF
B pathway. 33 It is known that increased expression of the TF gene resulting in increased procoagulability is regulated via NF
B by various transcription factors, including NF
B/Rel proteins and Egr-1.34 Hachiya and co-workers25 ahowed that irradiation increased the NF
B binding activity and increased the production of TNF-
in THP-1 cells. Endogenous production of TNF-
is known to be required for NF
B activation post IR.35 Treatment of these cells with anti-TNF-
antibodies blocked the activation of NF
B induced by irradiation and exogenously added TNF-
stimulated NF
B activation. This is in line with the inhibition of TF mRNA expression in THP-1 cells using the NF
B pathway inhibitor BAY 11-7082 as shown here.
In conclusion, irradiation of human monocytic cells induced the upregulation of TF expression and procoagulant activity. The findings on upregulated TF mRNA expression in PBMNCs post IR are in line with our data obtained from irradiated THP-1 cells. We conclude that the THP-1 cells are a suitable model for studying the effect of various agonists on TF expression levels in human mononuclear cells. The demonstrated upregulation of TF and other regulatory pathways might play a pivotal role in radiation associated thrombosis and further studies are warranted to investigate this hypothesis.
| Acknowledgments |
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| Footnotes |
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PG-L: writing the manuscript, interpretation of data, radiation experiments, TF TaqMan® PCR, microarray experiments; KP: contributed equally to the 1 st authors work; Q-VT: radiation experiments, TF ELISA, TF activity assay; BS: critical revision of the manuscript and interpretation of data, discussion; FW: SAM statistics of microarray experiments; SA: validation experiments (SYBR Green TaqMan® PCR); TW: statistical analyses of TF mRNA-, TF ELISA-, and TF activity data; HW: critical revising microarray data and SAM statistics, online submission of microarray data into GEO; MH: providing of the Affymetrix working station, support in microarray experiments; DL: providing of the Affymetrix working station, support in microarray experiments; WP: critical revision of the manuscript, discussion, partly writing the manuscript, final approval of the manuscript; H-PS: critical revision of the manuscript, partly writing the manuscript, final approval of the manuscript; UR: main study concept, methods and design, critical revision and interpretation of data, partly writing the manuscript, final approval of the manuscript.
The authors reported no potential conflicts of interest.
Received for publication August 25, 2006. Accepted for publication May 16, 2007.
| References |
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ia a potent trigger of NF
B activation by irradiation in human monocytic cells THP-1. Cytokine 2004;25:147-54.[CrossRef][ISI][Medline]
expression by inducing Elk-1 phosphorylation and Egr-1 expression. Blood 2001;98:1429-39.
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