Iva Falková

Two New Faces of Amifostine: Protector from DNA Damage in Normal Cells and Inhibitor of DNA Repair in Cancer Cells

Amifostine protects normal cells from DNA damage induction by ionizing radiation or chemotherapeutics, whereas cancer cells typically remain uninfluenced. While confirming this phenomenon, we have revealed by comet assay and currently the most sensitive method of DNA double strand break (DSB) quantification (based on γH2AX/53BP1 high-resolution immunofluorescence microscopy) that amifostine treatment supports DSB repair in γ-irradiated normal NHDF fibroblasts but alters it in MCF7 carcinoma cells. These effects follow from the significantly lower activity of alkaline phosphatase measured in MCF7 cells and their supernatants as compared with NHDF fibroblasts. Liquid chromatography-mass spectrometry confirmed that the amifostine conversion to WR-1065 was significantly more intensive in normal NHDF cells than in tumor MCF cells. In conclusion, due to common differences between normal and cancer cells in their abilities to convert amifostine to its active metabolite WR-1065, amifostine may not only protect in multiple ways normal cells from radiation-induced DNA damage but also make cancer cells suffer from DSB repair alteration.

Heterochromatinization associated with cell differentiation as a model to study DNA double strand break induction and repair in the context of higher-order chromatin structure

Cell differentiation is associated with extensive gene silencing, heterochromatinization and potentially decreasing need for repairing DNA double-strand breaks (DSBs). Differentiation stages of blood cells thus represent an excellent model to study DSB induction, repair and misrepair in the context of changing higher-order chromatin structure. We show that immature granulocytes form γH2AX and 53BP1 foci, contrary to the mature cells; however, these foci colocalize only rarely and DSB repair is inefficient. Moreover, specific chromatin structure of granulocytes probably influences DSB induction.

Function of chromatin structure and dynamics in DNA damage, repair and misrepair: γ-rays and protons in action.

According to their physical characteristics, protons and ion beams promise a revolution in cancer radiotherapy. Curing protocols however reflect rather the empirical knowledge than experimental data on DNA repair. This especially holds for the spatio-temporal organization of repair processes in the context of higher-order chromatin structure-the problematics addressed in this work. The consequences for the mechanism of chromosomal translocations are compared for gamma rays and proton beams.

Sequestration of MBNL1 in tissues of patients with myotonic dystrophy type 2

The pathogenesis of myotonic dystrophy type 2 includes the sequestration of MBNL proteins by expanded CCUG transcripts, which leads to an abnormal splicing of their target pre-mRNAs. We have found CCUG(exp) RNA transcripts of the ZNF9 gene associated with the formation of ribonuclear foci in human skeletal muscle and some non-muscle tissues present in muscle biopsies and skin excisions from myotonic dystrophy type 2 patients. Using RNA-FISH and immunofluorescence-FISH methods in combination with a high-resolution confocal microscopy, we demonstrate a different frequency of nuclei containing the CCUG(exp) foci, a different expression pattern of MBNL1 protein and a different sequestration of MBNL1 by CCUG(exp) repeats in skeletal muscle, vascular smooth muscle and endothelia, Schwann cells, adipocytes, and ectodermal derivatives. The level of CCUG(exp) transcription in epidermal and hair sheath cells is lower compared with that in other tissues examined. We suppose that non-muscle tissues of myotonic dystrophy type 2 patients might be affected by a similar molecular mechanism as the skeletal muscle, as suggested by our observation of an aberrant insulin receptor splicing in myotonic dystrophy type 2 adipocytes.

Theoretical and experimental study of the antifreeze protein AFP752, trehalose and dimethyl sulfoxide cryoprotection mechanism: correlation with cryopreserved cell viability

In this work the physico-chemical properties of selected cryoprotectants (antifreeze protein TrxA-AFP752, trehalose and dimethyl sulfoxide) were correlated with their impact on the constitution of ice and influence on frozen/thawed cell viability. The freezing processes and states of investigated materials solutions were described and explained from a fundamental point of view using ab-initio modelling (molecular dynamics, DFT), Raman spectroscopy, Differential Scanning Calorimetry and X-Ray Diffraction. For the first time, in this work we correlated the microscopic view (modelling) with the description of the frozen solution states and put these results in the context of human skin fibroblast viability after freezing and thawing. DMSO and AFP had different impacts on their solutions freezing process but in both cases the ice crystallinity size was considerably reduced. DMSO and AFP treatment in different ways improved the viability of frozen/thawed cells.

Chromatin differentiation of white blood cells decreases DSB damage induction, prevents functional assembly of repair foci, but has no influence on protrusion of heterochromatic DSBs into the low-dense chromatin

Purpose: Higher order chromatin structure progressively changes with cell differentiation and seems to play an important role in DNA double-strand break (DSB) induction and repair (reviewed in [1]). We compared DNA damage in heterochromatin (Hc) upon the action of qualitatively different radiations. We also studied, how is the sensitivity to DSB induction, assembly of repair foci and processing of DSBs influenced by the differentiation-induced changes in chromatin structure and composition. Materials and methods: Formation, localization (relative to higher-order chromatin domains) and mutual colocalization of γH2AX and p53BP1 repair foci have been studied together with DSB repair kinetics in spatially fixed human skin fibroblast and differently differentiated white blood cells (WBC) irradiated with gamma rays, protons of different energies [2, 3], and 20Ne ions (submitted). Immunostaining and ImmunoFISH were used in combination with high-resolution confocal microscopy [2, 3] and living cell imaging [4]. Results: We found that less DSBs appear in Hc after irradiating cells with gamma rays and protons but not 20Ne ions (preliminary results). In addition, contrary to γ-irradiated human skin fibroblasts and lymphocytes, mature granulocytes neither express DSB repair proteins nor form functional repair foci [5]. At least some DSB repair proteins (e.g. 53BP1) are expressed and γH2AX foci still occur in immature granulocytes and monocytes [2, 5]; however, the colocalization of γH2AX with 53BP1 is low and the majority of DSBs are not repaired. Despite this fact, γH2AX foci protrude from Hc into nuclear subcompartments with low chromatin density. Our living cell observations suggest that 53BP1 can penetrate into the interior of dense Hc domains only after their decondensation [2]. Conclusions: We show that Hc is less sensitive to DSB induction by gamma rays but not heavy ions; lower Hc hydratation and higher protein density (when compared with euchromatin) probably reduce formation of free radicals and increase their sequestration, respectively. This mechanism can protect cells against the indirect effect of ionizing radiation (marked for gamma rays and protons but not heavy ions). Hc features, however, preclude DSB repair, which is best illustrated by its absence in differentiated WBC but not their immature precursors. The protrusion of Hc-DSBs into low-density chromatin nuclear subdomains, however, appears also in differentiated WBC, so the process might simply follow physical forces (e.g. as suggested by M Durantes group). There is no Clinical Trial Registration number.

Chromatin architecture changes and DNA replication fork collapse are critical features in cryopreserved cells that are differentially controlled by cryoprotectants

In this work, we shed new light on the highly debated issue of chromatin fragmentation in cryopreserved cells. Moreover, for the first time, we describe replicating cell-specific DNA damage and higher-order chromatin alterations after freezing and thawing. We identified DNA structural changes associated with the freeze-thaw process and correlated them with the viability of frozen and thawed cells. We simultaneously evaluated DNA defects and the higher-order chromatin structure of frozen and thawed cells with and without cryoprotectant treatment. We found that in replicating (S phase) cells, DNA was preferentially damaged by replication fork collapse, potentially leading to DNA double strand breaks (DSBs), which represent an important source of both genome instability and defects in epigenome maintenance. This induction of DNA defects by the freeze-thaw process was not prevented by any cryoprotectant studied. Both in replicating and non-replicating cells, freezing and thawing altered the chromatin structure in a cryoprotectant-dependent manner. Interestingly, cells with condensed chromatin, which was strongly stimulated by dimethyl sulfoxide (DMSO) prior to freezing had the highest rate of survival after thawing. Our results will facilitate the design of compounds and procedures to decrease injury to cryopreserved cells.

Changes in cryopreserved cell nuclei serve as indicators of processes during freezing and thawing

The mechanisms underlying cell protection from cryoinjury are not yet fully understood. Recent biological studies have addressed cryopreserved cell survival but have not correlated the cryoprotection effectiveness with the impact of cryoprotectants on the most important cell structure, the nucleus, and the freeze/thaw process. We identified changes of cell nuclei states caused by different types of cryoprotectants and associate them with alterations of the freeze/thaw process in cells. Namely, we investigated both higher-order chromatin structure and nuclear envelope integrity as possible markers of freezing and thawing processes. Moreover, we analyzed in detail the relationship between nuclear envelope integrity, chromatin condensation, freeze/thaw processes in cells, and cryopreservation efficiency for dimethyl sulfoxide, glycerol, trehalose, and antifreeze protein. Our interdisciplinary study reveals how changes in cell nuclei induced by cryoprotectants affect the ability of cells to withstand freezing and thawing and how nuclei changes correlate with processes during freezing and thawing. Our results contribute to the deeper fundamental understanding of the freezing processes, notably in the cell nucleus, which will expand the applications and lead to the rational design of cryoprotective materials and protocols.

Primary and secondary clustering of DSB repair foci and repair kinetics compared for γ-rays, protons of different energies and high-LET 20Ne ions

Purpose: Ionizing radiations of different qualities (e.g. high-LET and low-LET) might differently interact with structurally and functionally distinct higher order chromatin domains (discussed in [ 1] and citations therein); this might be reflected by DNA double strand break (DSB) repair efficiency and the mechanism of how cancerogenous chromosomal translocations (CHT) form. Therefore, we compared the DSB repair kinetics and formation of γH2AX/p53BP1 repair clusters upon the action of γ-rays [ 2, 3], protons (15 and 30 MeV) [ 4], and 20Ne ions (preliminary data). Consequently, we discuss biological impacts of these clusters. Material and methods: Immunostaining methods in combination with high-resolution confocal microscopy, performed on 3D-fixed normal human skin fibroblasts [ 2– 4], were used to study initial distributions of γH2AX and p53BP1 repair foci and their changes during the post-irradiation (PI) time, with a special concern on foci clustering. Irradiations with γ-rays, protons of different energies (15 and 30 MeV), and high-LET 20Ne ions was performed in IBP ASCR Brno (CR), NPI AVCR Řež (CR) and JINR Dubna (Russia), respectively. Results: Upon irradiating cells with 20Ne ions, tracks of multiple clustered γH2AX and p53BP1 repair foci appeared immediately after the irradiation; these clusters, called here as the ‘primary clusters’, were rare in cells irradiated with γ-rays or protons (submitted). Though γH2AX/p53BP1 foci were positionally quite stable [ 2], ‘secondary clusters’ occasionally appeared after all kinds of irradiation during about 30 min PI. The formation of secondary clusters usually appeared due to the heterochromatin decondensation at the sites of heterochromatic DNA double-strand breaks (hcDSBs), followed by their protrusion into a limited space of nuclear subdomains of low density-chromatin (discussed in [ 1, 2, 5]). Conclusions: Primary clusters appear in cell nuclei immediately PI as the consequence of highly localized energy deposition, while secondary clusters develop during (and because of) DSB repair. Primary DSB clusters probably represent the main cause of chromosomal translocations induced with high-LET radiations while secondary clusters seem to be more important for low-LET γ-rays and protons. Secondary clusters of primary clusters (higher-order clusters) observed for 20Ne ions might explain frequent formation of complex translocations upon the action of high-LET radiations. Finally, we suggest [ 1, 2, 4] a model that describes the relationship between the higher order chromatin structure, DSB formation, repair and misrepair.

P5.6 Insulin receptor splicing in human adipose tissue of patients with DM2

called Photovoice will be tested to explore the experience of individuals with DM1. To describe the experiences of individuals with DM1, to identify barriers and facilitators to their health, to assess the feasibility of using Photovoice with this population, and to develop a list of themes and health concerns that may be used to generate future research questions. Photovoice is a qualitative research method that gives participants cameras to document their experiences. Photovoice was developed based on concepts from feminist theory, documentary photography, and the work of educator Paulo Freire. The goal of Photovoice is to give those outside of the traditional power structure the ability to capture their experiences and share them with policy makers. Participants will be given cameras and asked to “take pictures of what it is like to live with DM1”. They will also be asked to take pictures of barriers and facilitators to their health. Their photographs will guide individual interviews and a focus group. There is a need to add patient-centered research to the DM1 literature while exploring new methods for data collection. In this study, we assume that those living with DM1 are experts about their condition, and that Photovoice may be an appropriate research method to use to capture their experiences.