Irina S. Smirnova

Reactive Oxygen Species Are Required for Human Mesenchymal Stem Cells to Initiate Proliferation after the Quiescence Exit.

The present study focuses on the involvement of reactive oxygen species (ROS) in the process of mesenchymal stem cells “waking up” and entering the cell cycle after the quiescence. Using human endometrial mesenchymal stem cells (eMSCs), we showed that intracellular basal ROS level is positively correlated with the proliferative status of the cell cultures. Our experiments with the eMSCs synchronized in the G0 phase of the cell cycle revealed a transient increase in the ROS level upon the quiescence exit after stimulation of the cell proliferation. This increase was registered before the eMSC entry to the S-phase of the cell cycle, and elimination of this increase by antioxidants (N-acetyl-L-cysteine, Tempol, and Resveratrol) blocked G1–S-phase transition. Similarly, a cell cycle arrest which resulted from the antioxidant treatment was observed in the experiments with synchronized human mesenchymal stem cells derived from the adipose tissue. Thus, we showed that physiologically relevant level of ROS is required for the initiation of human mesenchymal stem cell proliferation and that low levels of ROS due to the antioxidant treatment can block the stem cell self-renewal.

Hepatitis C virus core protein transforms murine fibroblasts by promoting genomic instability

The oncogenic potential of hepatitis C virus (HCV) core protein has been demonstrated, but the precise mechanism of cell transformation triggered by HCV core is still unclear. This study shows that constitutive expression of HCV core protein (core) in NIH 3T3 murine fibroblasts triggers malignant transformation. At the preneoplastic stage, clones that expressed HCV core constitutively demonstrated genomic instability seen as disruption of the mitotic spindle cell checkpoint leading to increased ploidy. Transformation was completed by the loss of DNA and resistance to apoptosis induced by serum starvation. Simultaneously, cells acquired a capacity for anchorage independent growth and absence of contact inhibition. Inoculation of these transformed cells into severe combined immune deficiency (SCID) mice led to formation of solid core-expressing tumors. Transformation and tumorigenicity of core-expressing cell lines coincided with a 5- to 10-fold repression of endogenous p53 transactivation. Thus, long-term HCV core expression alone is sufficient for complete transformation of immortal fibroblasts that can then induce tumors in a susceptible host. This data suggests that malignant transformation by HCV core may occur through primary stress, induction of genomic instability, and further HCV core-induced rescue of surviving mutated cells.

Effect of Nb doping on properties of Y-Ba-Cu ceramics

The properties of Nb-doped YBa2Cu3Oy ceramics obtained by thermolysis of the oxide or nitrate (Y, Ba, Cu) solution in ammonium nitrate melt were studied. For the composition YBa2Cu3-xNb0.05O6.6, Tc = 92 K and the transport critical current Jc = 1000-4000 A cm-2 were obtained. The magnetic flux profile was studied by a magneto-optic method at B = 290 G. Domains of size 200-600 mu m were found with magnetic critical current Jcm = 2 * 104 A cm-2 at 77 K and 105 A cm-2 at 11 K.

Mössbauer study of single crystal Bi2Sr3Fe2Ox isostructural with Bi2Sr2CaCu2O8+x

Single and polycrystalline samples of Bi2Sr2SrFe2Ox (232Fe) are synthesized and studied by Mossbauer spectroscopy. The structure of 232Fe is similar to that of 2212Cu except for a commensurate structure modulation arising from the replacements of the latters Cu and Ca atoms by Fe and Sr. The Mossbauer spectra of the single crystals show two doublets with different parameters. Calculation of electric field gradient based upon the structure data confirms that the two doublets arise from two different Fe environments induced by the modulation wave: at the antinodes of the wave the oxygen coordination octahedrons are largely distorted and at the nodes far less. The experimental data are well explained accordingly. The Fe valence, isomer shift values, line widths and other Mossbauer data in comparison with the 2212Cu compound are also discussed.

Different transformation pathways of murine fibroblast NIH 3T3 cells by hepatitis C virus core and NS3 proteins

The oncogenic potential of both Hepatitis C virus (HCV) core and HCV NS3 proteins has been demonstrated, but these proteins induce transformation of immortal murine fibroblasts NIH 3T3 via different pathways. As long‐term expression (50–100 passages) of HCV core triggers neoplastic transformation of NIH 3T3 through crisis of growth, HCV NS3 induces transformation shortly after transfection. We explain this distinction by different effects of core and NS3 on p53‐mediated transactivation: inhibition by NS3 and activation by core protein.

A cubic phase in ceramic YBaCuO doped with Nb

Abstract The almost-single-phase ceramic c-YBa 2 Cu 3− x (Nb x )O y ( x = 0.05−0.20) with cubic symmetry has been synthesized by thermolysis of an ammonium nitrate melt containing Y, Ba, Cu and Nb components. XRD patterns, thermogravimetric curves, far-infrared reflection spectra, and the temperature dependence of resistivity have been studied in the samples c-YBa 2 Cu 2.86 (Nb 0.14 )O y and YBa 4 Cu 2.86 (Nb 0.14 )O y prepared by this method. On this basis, the conclusion is made that c-YBa 2 Cu 3− x (Nb x )O y is the well known cubic phase YBa 4 Cu 3 O y containing about 50% Ba vacancies and with the same lattice parameter a = 8.11 A .

Mössbauer study of modulated structure of Bi2Sr2CaFe2Oy phase

Abstract 57 Fe Mossbauer studies of the single crystals of the Bi 2 Sr 2 CaFe 2 O y compound with modulated structure show two quadruopole-splitting doublets (QS(1) = 1.03 mm/s and QS(2) = 0.45 mm/s). The compound is weak paramagnet in the temperature range 330 K−4.2 K. Analysis of the obtained data shows that the Fe atoms in this structure are separated into two groups, which can be attributed to small and strong distorted environments of the Fe atoms. They are in the Fe 3+ valence state. An attempt is made to relate the feature of the results with the structure modulation. From the full profile analysis of the X-ray diffraction data it follows that the modulation wave can be described by a spectral profile close to a “rectangular” one. In the obtained domain-like system the Fe atoms can be divided into two unequal groups having opposite directions of displacements in good agreement with Mossbauer data.

Lattice dynamics of the La2CuO4 Cmca orthorhombic phase at κ = 0

Abstract Lattice dynamics has been employed in the approximation of the rigid-ion model for the orthorhombic Cmca phase of La2CuO4 single crystal at the Γ-point of the Brillouin zone. Satisfactory agreement was achieved between calculated and experimental frequencies and oscillator strengths of dipole-active optical phonons, as well as at the Γ-point frequencies of known modes active in Raman scattering.

X-ray diffraction analysis of the modulated structure of Bi2Sr2CaFe2Oy

The modulated structure of the Bi2Sr2CaFe2Oy compound isomorphous with the Bi2Sr2CaCu2Oy phase was refined by the method of the full profile analysis on the basis of the powder X-ray diffraction data. The analysis was carried out in the superspace group ofN:Abmm: 1 – 11 using the parameters of the unit cell of the basic structurea = 5.466(3),b = 5.446(5) andc = 31.25(9) Å and the modulation vectorq = 0.220(5)b* +c*. The model of excess oxygen interstitials into the BiO plane was used by applying a saw-tooth-type function of the form:U = 2U0 [(X4 -X40/Δ)] [1]. The results point to a strong displacement of the atoms from their positions in the basic structure. An essential improvement of theR factors was obtained by taking into account the modulation waves of the higher harmonics.

Study of the modulated structure of Bi2Sr2CaFe2Ox

The ceramics and single crystals of the Bi2Sr2CaFe2Ox compound were synthesized. The X-ray diffraction data showed orthorhombic symmetry. The lattice parameters are equal toa=5.464 Å,b=5.453 Å,c=31.313 Å. The crystal structure is described by the primitive Bravais lattice with the possible space groups Pbmm. Pbm2 and Pb21m. The obtained X-ray patterns show the presence the incommensurate structural modulation with the following parameters: the modulation vector lies in the (100)-plane, the value of the wave-vector componentqb=0.22(3). The comparison of the obtained results with data for Fe-doped Bi2Sr2CaCu2Ox and Bi2Sr3Fe2Ox are presented. No magnetic peculiarities of the compound were found. Mőssbauer measurements of the ceramic samples indicate the presence mainly of Fe3+ oxidation state and Fe4+ (about 20%). The decrease of the quadrupole-splitting values for 2212Fe in comparison with Fe-doped 2212Cu was revealed that may be connected with higher symmetry of the local environment of Fe atoms in 2212Fe.