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Biomedical subjects

P Dvorak

Publications and source records attributed to P Dvorak.

15 recordsLinked to original sources
PubMed2006

Embryonic stem cell-derived microvesicles reprogram hematopoietic progenitors: evidence for horizontal transfer of mRNA and protein delivery.

Membrane-derived vesicles (MV) are released from the surface of activated eucaryotic cells and exert pleiotropic effects on surrounding cells. Since the maintenance of pluripotency and undifferentiated propagation of embryonic stem (ES) cells in vitro requires tight cell to cell contacts and effective intercellular signaling, we hypothesize that MV derived from ES cells (ES-MV) express stem cell-specific molecules that may also support self-renewal and expansion of adult stem cells. To address this hypothesis, we employed expansion of hematopoietic progenitor cells (HPC) as a model. We found that ES-MV (10 microg/ml) isolated from murine ES cells (ES-D3) in serum-free cultures significantly (i) enhanced survival and improved expansion of murine HPC, (ii) upregulated the expression of early pluripotent (Oct-4, Nanog and Rex-1) and early hematopoietic stem cells (Scl, HoxB4 and GATA 2) markers in these cells, and (iii) induced phosphorylation of MAPK p42/44 and serine-threonine kinase AKT. Furthermore, molecular analysis revealed that ES-MV express Wnt-3 protein and are selectively highly enriched in mRNA for several pluripotent transcription factors as compared to parental ES cells. More important, this mRNA could be delivered by ES-MV to target cells and translated into the corresponding proteins. The biological effects of ES-MV were inhibited after heat inactivation or pretreatment with RNAse, indicating a major involvement of protein and mRNA components of ES-MV in the observed phenomena. We postulate that ES-MV may efficiently expand HPC by stimulating them with ES-MV expressed ligands (e.g., Wnt-3) as well as increase their pluripotency after horizontal transfer of ES-derived mRNA.

Animals↗
PubMed2003

Increased expression of fibroblast growth factor receptor 3 in CD34+ BCR-ABL+ cells from patients with chronic myeloid leukemia.

Previously, we showed that expression of myeloma-associated (proto)oncogene fibroblast growth factor receptor 3 (FGFR-3) is increased in white blood cells from patients with chronic myeloid leukemia (CML). The abnormal expression was returned back to the normal levels as soon as these patients reconstituted their hematopoiesis following transplantation of allogeneic peripheral blood stem cells. The aims of this study were: (1) to define population(s) of cells overexpressing FGFR-3, and (2) to determine the expression of FGFR-3 during the clinical course of the disease. We show that the vast majority of FGFR-3 transcripts as well as FGFR-3 protein arise from CD34+ BCR-ABL+ cells. Although increased levels of FGFR-3 were found in majority of late chronic phase patients treated with interferon alpha or hydroxyurea, the expression of FGFR-3 was always lowered following treatment with BCR-ABL tyrosine kinase inhibitor STI571. Compared to unstimulated cells, high levels of FGFR-3 were also identified in CD34+ cells from granulocyte colony-stimulating factor-mobilized blood stem cell harvests from healthy donors, suggesting a potential growth factor-dependent basis for elevated expression of FGFR-3 in CML. These findings have implications for the involvement of FGFR-3 in malignant hematopoiesis and depict FGFR-3 tyrosine kinase in CD34+ leukemic cells as a possible target for tyrosine kinase inhibitors.

Antigens, CD34↗
PubMed2001

Changes in the expression of FGFR3 in patients with chronic myeloid leukaemia receiving transplants of allogeneic peripheral blood stem cells.

Fibroblast growth factor receptors (FGFR1-4) are implicated in various cellular events, including cell growth and transformation. Here, we showed that patients suffering from chronic myeloid leukaemia (CML) express high levels of FGFR3 mRNA in white blood cells (WBCs). After stem cell transplantation and reconstitution of haematopoiesis, the expression of FGFR3 decreased and was maintained at low levels that are typical of healthy individuals. However, FGFR3 expression became upregulated again in those patients that had accelerated BCR/ABL rearrangement and underwent relapse of leukaemia. Our findings suggest that, in CML, the changing levels of FGFR3 transcripts in WBCs may have prognostic significance.

Gene Expression↗
PubMed2001

Temperature dependence of polymer-gel dosimeter nuclear magnetic resonance response.

The purpose of this study was to find a physical-mathematical description capable to correct a polymer-gel dosimeter relaxation rate R2-dose response for different temperatures. Four different modifications of polymer-gel dosimeters were used in this study. Samples with polymer-gel dosimeter in glass test vessels were homogeneously irradiated by 60Co gamma photons. A multi-echo sequence with 16 equidistant echoes was used for evaluation of irradiated polymer-gel dosimeters. The sequence parameters were as follows: TR 2000 ms, TE 22.5-360.0 ms, slice thickness 5 mm, FOV 255 mm, one acquisition. The proposed description recommends to subtract R2 response of the nonirradiated dosimeter from the total R2-dose response. The relaxation rate for the irradiated dosimeter can be expressed as a function of temperature and dose. The temperature dependence has an exponential behavior in the measured range. The proposed description allows to correct the measured NMR R2-dose responses for different temperatures.

Dose-Response Relationship, Radiation↗
PubMed2001

Energy and dose rate dependence of BANG-2 polymer-gel dosimeter.

The purpose of this study was to evaluate dependence of BANG-2 polymer-gel dosimeter sensitivity on different photon and electron energies as well as on different mean dose rates expressed as repetition rates for a standard clinically used linear accelerator. The sensitivity of the dosimeter was represented by the slope of calibration curve in the linear region measured for each modality. A calibration curve (in the linear region) based on five dosimeters (four irradiated and one background) was obtained for each photon and electron energy and different repetition rates. Dosimeter sensitivity dependence on energy was studied for 4, 6, and 18 MV x-ray photons and for nominal electron energies 9, 12, 16, and 20 MeV. Dosimeter sensitivity dependence on mean dose rate was separately studied for electron and photon beams with the use of repetition rates 80, 160, 240, 320, and 400 MU min(-1). Evaluation of dosimeters was performed on Siemens MAGNETOM EXPERT 1T scanner in the head coil. A multiecho sequence with 16 equidistant echoes was used for the evaluation of irradiated polymer-gel dosimeters. The parameters of the sequence were as follows: TR 2000 ms, TE 22.5-360.0 ms, slice thickness 5 mm, FOV 255 mm, one acquisition. There was observed a trend in polymer-gel dosimeter sensitivity dependence on the quality index of high energy x-ray beams used and on mean electron energy absorbed in the center of the dosimeter. Polymer-gel dosimeter sensitivity was decreasing with increasing photon or electron energy. There was observed no trend in polymer-gel dosimeter sensitivity dependence on mean dose rate expressed as a repetition rate for both photon and electron beams.

Calibration↗
PubMed1999

O-linked carbohydrates are required for FGF-2-mediated proliferation of mouse embryonic cells.

During development, fibroblast growth factors (FGFs) serve highly specific functions that are mediated through high-affinity transmembrane receptors and modulated by membrane-bound proteoglycans. Proteoglycans, in an embryonic environment called embryoglycans, contain numerous carbohydrate ectodomains, the structure of which undergoes rearrangement. Since they can be lost from the cell surface, they are sometimes found in extracellular space where they may also serve some regulatory function. Here we address the potential roles of three naturally occurring isoforms of Lewis X (LeX) in FGF-2-mediated proliferation of embryonic stem (ES) cells. We have found that the addition of sulfated LeX to ES cells at a concentration of 17 nM promotes FGF-2 mitogenic activity while a 10-fold higher concentration leads to a reduction of FGF-2-mediated proliferation. Notably, this dose-dependent modulation operated only for sulfated LeX. Other fucosylated motifs, basic LeX trisaccharide and sialylated LeX, also affected ES cell proliferation but the mechanism cannot be clearly correlated with the presence or absence of FGF-2. The suppression of biosynthesis of O-linked carbohydrates including LeX reduced basal proliferation of ES cells and interfered with the mitogenic effect of FGF-2. However, in inhibitor-treated cells, the stimulatory activity of FGF-2 can be reestablished to its original level by exogenous LeX oligosaccharides. Our results show that (A) O-linked LeX oligosaccharides can regulate mitogenic activity of FGF-2 in embryonic cells, (B) and this ability varies with subtle modifications in their structure. Importantly, our data represent the first insight into the mechanism of how growth factor activities might be modulated by shedded embryoglycan ectodomains.

Animals↗
PubMed1998

Management of health services in the Czech Republic.

During the 1990s, following political transformation, the Czech Republic's health care system has been experiencing profound changes. This article examines how health care institutions, hospitals, in particular, have found themselves having to undergo a transformation from budgetary organizations to free market enterprises. In addition to their daily professional tasks, medical institutions are being forced to adjust to a new environment, to work actively on solutions to their numerous economic problems, and, above all, to generate adequate financial means to support themselves. This article focuses on the challenges faced by public hospitals in the Czech Republic, including an excess of acute beds, financing system and pharmaceutical costs, and the need for effective health management to deal with these challenges.

Czech Republic↗
PubMed1995

Expression of paternal and maternal mitochondrial HSP70 family, hsc74, in preimplantation mouse embryos.

We have investigated the regulation of gene expression of a novel mitochondrial HSP70 family, hsc74 in preimplantation mouse embryos. We used a monoclonal antibody, anti-CSA, which reacts with only one of strain variants of the hsc74. By immunostaining with anti-CSA antibody, the hsc74 protein was constitutively detected in C3H embryos from 1-cell to blastocyst stage, but no signals were detectable in C57BL/6 embryos. To know the timing of paternal genome expression, we examined the expression of hsc74 in (C57BL/6 x C3H)F1 embryos. No positive signals were detectable in embryos before 8-cell stage. In early 8-cell stage weakly positive signals appeared in the peripheral region of the blastomeres. From late 8-cell stage, the protein was intensively detectable and was persistently expressed in all types of cells. We have also applied a sensitive methodology to distinguish genetic variants of hsc74 from C3H and C57BL/6 by reverse transcription polymerase chain reaction followed by single strand conformation polymorphism analysis. In (C57BL/6 x C3H)F1 embryos, the paternal transcripts were first detected in 4-cell embryos, while the maternal transcripts were constantly detectable. These results indicate that the transcripts and proteins of hsc74 were derived only from the maternal gene from 1-cell to 4-cell stages, and that from 4-cell stage the paternal gene is also transcribed, and the significant increase of the paternally derived protein occurred around late 8-cell stage.

Animals↗
PubMed1995

Cell mixing during the early development of mouse aggregation chimera.

Two different inbred strain combinations of mouse aggregation chimeras - C3H/HeN (H-2k) x C57BL/6N (H-2b) and C3H/HeN x BALB/cA (H-2d) were used for cell mixing analysis at two points in time - 24 h after aggregation (just prior to transplantation into foster mothers) and 7.5 days post coitum (p.c.). The cell proportion of two H-2 haplotypes at the blastocyst stage was studied using a fluorescence-labeled monoclonal antibody recognizing a C3H-specific alloantigen - CSA (C3H strain-specific antigen) and laser scanning confocal microscopy. The 7.5-day-old chimeras were sectioned and subsequently processed by sensitive biotinylated antibody - avidin peroxidase immunohistochemical technique. Our results showed that 24 h after aggregation (blastocyst stage), there was equal cell mixing and no mouse strain used in the present study was dominant at this time. In 7.5-day-old C3H/HeN x BALB/cA chimeras, cells of both genotypes were intermingled, but the C3H/HeN strain was dominant in all cases. In contrast, the combination C3H/HeN x C57BL/6N clearly showed reduced numbers of C3H/HeN cells (CSA-positive) in 83% of the chimeras evaluated. Generally, CSA positive cells were found only in randomly distributed small distinct areas representing less than 20% of embryonal cells. Surprisingly, the extraembryonal ectoplacental cone was uniformly CSA positive in some C3H/HeN x C57BL/6N chimeras. Furthermore, in 36% of normally implanted chimeras of both strain combinations progressive degeneration was observed. We suggest that the cell mixing pattern as well as the absolute number of cells derived from each strain in the aggregation chimera can be affected by specific immune interactions involving H-2 haplotype combinations of the allogeneic fetus and the fully immunocompetent host organism, at later points in development.

Animals↗
PubMed1985

Experimental elimination of various intestinal segments by means of devascularization (devitalization).

Segments of the small and large intestine, of varying lengths (10-180 cm), were devascularized by simultaneously ligating the mesenteric arteries and veins. When the circulation had been cut off, the ends of the devascularized segment were both ligated, continuity of intestinal passage was renewed by forming an anastomosis and the isolated segment was left in situ, together with its contents. Contrary to accepted views, no changes leading to death (necrosis and peritonitis) occurred, but the devascularized tissue was progressively destroyed and reconstructed until, after four weeks, all that was left was a minute fibrous residue. None of 41 pigs died as a result of devascularization, including those in which large doses of pathogenic microorganisms were injected into the isolated segment. The possibility of employing this technique in the surgical treatment of inoperable tumours is discussed.

Animals↗
PubMedDate not supplied

Modulation of protein synthesis in rabbit inner cell mass-derived cells by FGF-2.

Gastrulation is a critical step in vertebrate development, that depends on synergistic effects of several signalling molecules, including fibroblast growth factor-2 (FGF-2). To follow this phenomenon in vitro we isolated rabbit inner cell masses (ICMs) at embryonic day 4 and we exposed ICM-derived cells to FGF-2. Then, we analysed the quantitative differences in rates of protein synthesis from day 3 to day 5 of culture by two-dimensional (2D) gel electrophoresis. Here we show that both up- and down-regulation of protein synthesis took place in ICM-derived cells upon their exposure to FGF-2. The effect of FGF-2 was most pronounced at day 4 of culture, when the changes were very much in favour of a set of down-regulated proteins. To test the significance of this period of time for FGF-2-mediated regulation of protein synthesis, cells were grown without FGF-2 and then they were pulse-treated with FGF-2 at the end of day 4. When compared to the continuous culture with FGF-2, the FGF-2 pulse resulted in a quite indistinguishable pattern of up- and down-regulated proteins. Thus, the readiness of ICM-derived cells to accept and respond to the FGF-2 signals may be of limited duration.

Animals↗