UMR9187 / U1196 – Chemistry, Modelling and Imaging for Biology (CMIB)

Unit publications

Year of publication 2018

Annalisa Patriarca, Charles Fouillade, Michel Auger, Frédéric Martin, Frédéric Pouzoulet, Catherine Nauraye, Sophie Heinrich, Vincent Favaudon, Samuel Meyroneinc, Rémi Dendale, Alejandro Mazal, Philip Poortmans, Pierre Verrelle, Ludovic De Marzi (2018 Nov 1)

Experimental set-up for FLASH proton irradiation of small animals using a clinical system

International Journal of Radiation Oncology • Biology • Physics : 102 : 619-626 : DOI : 10.1016/j.ijrobp.2018.06.403 Learn more
Summary

Purpose

Recent in vivo investigations have shown that short pulses (FLASH) of electrons are less harmful to healthy tissues, but just as efficient as conventional dose-rate radiation to inhibit tumor growth. In view of the potential clinical value of FLASH and the availability of modern proton therapy infrastructures to achieve this goal, we herein describe a series of technological developments required to investigate the biology of FLASH irradiation, using a commercially available clinical proton therapy system.

Methods and materials

Numerical simulations and experimental dosimetric characterization of a modified clinical proton beamline, upstream from the isocenter were performed with Monte Carlo toolkit and different detectors. A single scattering system was optimized together with a ridge filter and a high current monitoring system. In addition, a submillimetric set-up protocol based on image-guidance using a digital camera and an animal positioning system was also developed.

Results

The dosimetric properties of the resulting beam and monitoring system were characterized: linearity with dose rate and homogeneity for a 12×12 mm2 field size were assessed. Dose rates exceeding 40 Gy/s at energies between 138 and 198 MeV were obtained, enabling uniform irradiation for radiobiology investigations on small animals in a modified clinical proton beam line.

Conclusion

This approach will enable us to conduct FLASH proton therapy experiments on small animals, specifically for mouse lung irradiation. Dose rates exceeding 40 Gy/s were achieved, which was not possible with the conventional clinical mode of the existing beamline.

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Tom Baladi, Jessy Aziz, Florent Dufour, Valentina Abet, Véronique Stoven, François Radvanyi, Florent Poyer, Ting-Di Wu, Jean-Luc Guerquin-Kern, Isabelle Bernard-Pierrot, Sergio Marco Garrido, Sandrine Piguel (2018 Nov 1)

Design, synthesis, biological evaluation and cellular imaging of imidazo[4,5-b]pyridine derivatives as potent and selective TAM inhibitors.

Bioorganic & medicinal chemistry : 26 : 5510-5530 : DOI : 10.1016/j.bmc.2018.09.031 Learn more
Summary

The TAM kinase family arises as a new effective and attractive therapeutic target for cancer therapy, autoimmune and viral diseases. A series of 2,6-disubstituted imidazo[4,5-b]pyridines were designed, synthesized and identified as highly potent TAM inhibitors. Despite remarkable structural similarities within the TAM family, compounds 28 and 25 demonstrated high activity and selectivity in vitro against AXL and MER, with IC value of 0.77 nM and 9 nM respectively and a 120- to 900-fold selectivity. We also observed an unexpected nuclear localization for compound 10Bb, thanks to nanoSIMS technology, which could be correlated to the absence of cytotoxicity on three different cancer cell lines being sensitive to TAM inhibition.

design,synthesis

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M Lupu, Ph Maillard, J Mispelter, F Poyer, C D Thomas (2018 Nov 1)

A glycoporphyrin story: from chemistry to PDT treatment of cancer mouse models.

Photochemical & photobiological sciences : Official journal of the European Photochemistry Association and the European Society for Photobiology : 17 : 1599-1611 : DOI : 10.1039/c8pp00123e Learn more
Summary

Photodynamic therapy (PDT) represents a non-toxic and non-mutagenic antitumor therapy. The photosensitizer’s (PS) chemo-physical properties are essential for the therapy, being responsible for the biological effects induced in the targeted tissues. In this study, we present the synthesis and development of some glycoconjugated porphyrins based on lectin-type receptor interaction. They were tested in vitro for finally choosing the most effective chemical structure for an optimum antitumor outcome. The most effective photosensitizer is substituted by three diethylene glycol α-D-mannosyl groups. In vivo studies allow firstly the determination of some characteristics of the biological processes triggered by the initial photochemical activation. Secondly, they make it possible to improve the therapeutic protocol in the function of the structural architecture of the targeted tumor tissue.

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Abhijit Saha, Sophie Bombard, Anton Granzhan, Marie-Paule Teulade-Fichou (2018 Oct 27)

Probing of G-Quadruplex Structures via Ligand-Sensitized Photochemical Reactions in BrU-Substituted DNA.

Scientific Reports : 8 : 15814 : DOI : 10.1038/s41598-018-34141-z Learn more
Summary

We studied photochemical reactions of BrU-substituted G-quadruplex (G4) DNA substrates with two pyrene-substituted polyazamacrocyclic ligands, M-1PY and M-2PY. Both ligands bind to and stabilize G4-DNA structures without altering their folding topology, as demonstrated by FRET-melting experiments, fluorimetric titrations and CD spectroscopy. Notably, the bis-pyrene derivative (M-2PY) behaves as a significantly more affine and selective G4 ligand, compared with its mono-pyrene counterpart (M-1PY) and control compounds. Upon short UVA irradiation (365 nm) both ligands, in particular M-2PY, efficiently sensitize photoreactions at BrU residues incorporated in G4 structures and give rise to two kinds of photoproducts, namely DNA strand cleavage and covalent ligand-DNA photoadducts. Remarkably, the photoinduced strand cleavage is observed exclusively with G4 structures presenting BrU residues in lateral or diagonal loops, but not with parallel G4-DNA structures presenting only propeller loops. In contrast, the formation of fluorescent photoadducts is observed with all BrU-substituted G4-DNA substrates, with M-2PY giving significantly higher yields (up to 27%) than M-1PY. Both ligand-sensitized photoreactions are specific to BrU-modified G4-DNA structures with respect to double-stranded or stem-loop substrates. Thus, ligand-sensitized photoreactions with BrU-substituted G4-DNA may be exploited (i) as a photochemical probe, allowing “photofootprinting” of G4 folding topologies in vitro and (ii) for covalent trapping of G4 structures as photoadducts with pyrene-substituted ligands.

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Eloïse Bertiaux, Adeline Mallet, Cécile Fort, Thierry Blisnick, Serge Bonnefoy, Jamin Jung, Moara Lemos, Sergio Marco, Sue Vaughan, Sylvain Trépout, Jean-Yves Tinevez, Philippe Bastin (2018 Oct 3)

Bidirectional intraflagellar transport is restricted to two sets of microtubule doublets in the trypanosome flagellum.

The Journal of cell biology : 217 : 4284 : DOI : 10.1083/jcb.201805030 Learn more
Summary

Intraflagellar transport (IFT) is the rapid bidirectional movement of large protein complexes driven by kinesin and dynein motors along microtubule doublets of cilia and flagella. In this study, we used a combination of high-resolution electron and light microscopy to investigate how and where these IFT trains move within the flagellum of the protist Focused ion beam scanning electron microscopy (FIB-SEM) analysis of trypanosomes showed that trains are found almost exclusively along two sets of doublets (3-4 and 7-8) and distribute in two categories according to their length. High-resolution live imaging of cells expressing mNeonGreen::IFT81 or GFP::IFT52 revealed for the first time IFT trafficking on two parallel lines within the flagellum. Anterograde and retrograde IFT occurs on each of these lines. At the distal end, a large individual anterograde IFT train is converted in several smaller retrograde trains in the space of 3-4 s while remaining on the same side of the axoneme.

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Philippe Robert, Thomas Frenzel, Cécile Factor, Gregor Jost, Marlène Rasschaert, Gunnar Schuetz, Nathalie Fretellier, Janina Boyken, Jean-Marc Idée, Hubertus Pietsch (2018 Sep 1)

Methodological Aspects for Preclinical Evaluation of Gadolinium Presence in Brain Tissue: Critical Appraisal and Suggestions for Harmonization-A Joint Initiative.

Investigative radiology : 53 : 499-517 : DOI : 10.1097/RLI.0000000000000467 Learn more
Summary

Gadolinium (Gd)-based contrast agents (GBCAs) are pharmaceuticals that have been approved for 30 years and used daily in millions of patients worldwide. Their clinical benefits are indisputable. Recently, unexpected long-term presence of Gd in the brain has been reported by numerous retrospective clinical studies and confirmed in preclinical models particularly after linear GBCA (L-GBCA) compared with macrocyclic GBCA (M-GBCA). Even if no clinical consequences of Gd presence in brain tissue has been demonstrated so far, in-depth investigations on potential toxicological consequences and the fate of Gd in the body remain crucial to potentially adapt the clinical use of GBCAs, as done during the nephrogenic systemic fibrosis crisis. Preclinical models are instrumental in the understanding of the mechanism of action as well as the potential safety consequences. However, such models may be associated with risks of biases, often related to the protocol design. Selection of adequate terminology is also crucial. This review of the literature intends to summarize and critically discuss the main methodological aspects for accurate design and translational character of preclinical studies.

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Filippo Doria, Valentina Pirota, Michele Petenzi, Marie-Paule Teulade-Fichou, Daniela Verga, Mauro Freccero (2018 Aug 30)

Oxadiazole/Pyridine-Based Ligands: A Structural Tuning for Enhancing G-Quadruplex Binding.

Molecules (Basel, Switzerland) : 23 : 2162 : DOI : 10.3390/molecules23092162 Learn more
Summary

Non-macrocyclic heteroaryls represent a valuable class of ligands for nucleic acid recognition. In this regard, non-macrocyclic pyridyl polyoxazoles and polyoxadiazoles were recently identified as selective G-quadruplex stabilizing compounds with high cytotoxicity and promising anticancer activity. Herein, we describe the synthesis of a new family of heteroaryls containing oxadiazole and pyridine moieties targeting DNA G-quadruplexes. To perform a structure⁻activity analysis identifying determinants of activity and selectivity, we followed a convergent synthetic pathway to modulate the nature and number of the heterocycles (1,3-oxazole vs. 1,2,4-oxadiazole and pyridine vs. benzene). Each ligand was evaluated towards secondary nucleic acid structures, which have been chosen as a prototype to mimic cancer-associated G-quadruplex structures (e.g., the human telomeric sequence, c-myc and c-kit promoters). Interestingly, heptapyridyl-oxadiazole compounds showed preferential binding towards the telomeric sequence (22AG) in competitive conditions vs. duplex DNA. In addition, G4-FID assays suggest a different binding mode from the classical stacking on the external G-quartet. Additionally, CD titrations in the presence of the two most promising compounds for affinity, TOxAzaPy and TOxAzaPhen, display a structural transition of 22AG in K-rich buffer. This investigation suggests that the pyridyl-oxadiazole motif is a promising recognition element for G-quadruplexes, combining seven heteroaryls in a single binding unit.

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Xiao Xie, Oksana Reznichenko, Ludovic Chaput, Pascal Martin, Marie-Paule Teulade-Fichou, Anton Granzhan (2018 Aug 27)

Topology-Selective Fluorescent “Light-Up” Probes for G-Quadruplex DNA Based on Photoinduced Electron Transfer.

Chemistry - A European Journal : 24 : 12638-12651 : DOI : 10.1002/chem.201801701 Learn more
Summary

GA-ChemEurJ-2018-1Six novel probes were prepared by covalent attachment of a G4-DNA ligand (PDC) to various coumarin or pyrene fluorophores. In the absence of DNA, the fluorescence of all probes is quenched due to intramolecular photoinduced electron transfer (PET) evidenced by photophysical and electrochemical studies, molecular modeling and DFT calculations. All probes demonstrate similarly high thermal stabilization of various G4-DNA substrates belonging to different folding topologies, as assessed by fluorescence melting experiments; however, their fluorimetric response is strongly heterogeneous with respect to structures of the probes and G4-DNA targets. Thus, the probes containing the 7-diethylaminocoumarin fluorophore demonstrate significant fluorescence enhancement in the presence of G4-DNA, with the strongest “light-up” response (20- to 180-fold) observed for antiparallel G4 structures as well as for hybrid G4 structures, formed by the variants of human telomeric sequence and capable of a conformation change to the antiparallel isoform. These results shed light on the influence of the linker and electronic properties of fluorophores on the efficiency of G4-DNA “light-up” probes operating via PET.

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Donia Essaid, Ali Tfayli, Philippe Maillard, Christophe Sandt, Véronique Rosilio, Arlette Baillet-Guffroy, Athena Kasselouri (2018 Jul 21)

Retinoblastoma membrane models and their interactions with porphyrin photosensitisers: An infrared microspectroscopy study.

Chemistry and physics of lipids : 215 : 34-45 : DOI : 10.1016/j.chemphyslip.2018.07.003 Learn more
Summary

Fourier Transform Infrared (FTIR) microspectroscopy was used to highlight the interactions between two photosensitisers (PS) of different geometries, TPPmOH4 and a glycoconjugated analogous, TPPDegMan, and lipid bilayers modelling retinoblastoma cell membranes. Retinoblastoma is a rare disease occurring in young infants, for whom conservative treatments may present harmful side-effects. Photodynamic therapy (PDT) is expected to induce less side-effects, as the photosensitiser is only activated when the tumour is illuminated.

Since efficiency of the treatment relies on photosensitiser penetration in cancer cells, bilayers with three lipid compositions – pure SOPC, SOPC/SOPE/SOPS/Chol (56:23:11:10) and SOPC/SOPE/SOPS/Chol/CL (42:32:9:8:6) – were used as plasma and mitochondria model membranes. FTIR spectra showed that the interaction of the PSs with the lipid bilayers impacted the lipid organization of the latter, causing significant spectral variations. Both studied photosensitisers inserted at the level of lipid hydrophobic chains, increasing chain fluidity and disorder. This was confirmed by surface pressure measurements. Photosensitisers – TPPmOH4 more than TPPDegMan – also interacted with the polar region of the bilayer, forming hydrogen bonds with phosphate groups that induced major shifts of phosphate absorption bands. This difference in PS interaction with moieties in the polar region was more pronounced with the models with complex lipid composition.

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Marlène Rasschaert, Josef A Schroeder, Ting-Di Wu, Sergio Marco, Andréa Emerit, Heiko Siegmund, Claudia Fischer, Nathalie Fretellier, Jean-Marc Idée, Claire Corot, Christoph Brochhausen, Jean-Luc Guerquin-Kern (2018 Jul 10)

Multimodal Imaging Study of Gadolinium Presence in Rat Cerebellum: Differences Between Gd Chelates, Presence in the Virchow-Robin Space, Association With Lipofuscin, and Hypotheses About Distribution Pathway.

Investigative radiology : 53 : 518-528 : DOI : 10.1097/RLI.0000000000000490 Learn more
Summary

Purpose The aim of this study was to investigate, based on in-depth multimodal imaging, the presence of Gd deposits, their ultrastructure, location, and co-location with endogenous elements, in the cerebellum, after repeated administrations of gadolinium-based contrast agents (GBCAs).

Methods Rats sensitized by subtotal nephrectomy received 20 daily intravenous injections of 0.6 mmol Gd/kg for 5 weeks of commercial forms of either gadoterate, gadobenate or gadodiamide, or saline (n = 2/group). The study was randomized and blinded. Magnetic resonance imaging examination was performed weekly. One month after the last injection, electron microscopy analysis of the deep cerebellar nuclei, the granular layer of cerebellar cortex, and the choroid plexus was performed. Elemental analysis of deposits was carried out by electron energy loss spectroscopy. Secondary ion mass spectroscopy was used for complementary chemical mapping.

Results A T1 hypersignal was evidenced in the deep cerebellar nuclei of rats treated with linear GBCAs, and Gd deposits were identified in all the studied cerebellar structures with gadobenate and gadodiamide (except in the granular layer in gadobenate-treated rats). No such effect was found with the macrocyclic GBCA gadoterate. Most of the Gd deposits revealed a characteristic spheroid “sea urchin-like” morphology, rich in phosphorus, and were localized in the basal lamina of microvessels, in the perivascular Virchow-Robin space, and in the interstitium. Gd was also identified in the glial cells, associated with lipofuscin pigments, for these same groups.

Conclusions Transmission electron microscopy analysis of cerebellums of renally impaired rats repeatedly injected with gadobenate and gadodiamide revealed the presence of Gd. Spheroid Gd depositions consisting of a filamentous meshwork were observed in the wall of microvessels, in perivascular Virchow-Robin space, and in the interstitium. Gd was also found in choroid plexus and was associated with pigments (likely lipofuscin) in glial cells. This is consistent with the involvement of the glymphatic distribution pathway for GBCAs. No insoluble Gd deposits were detected in rats injected with the macrocyclic GBCA gadoterate and controls.

 

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Lina Saker, Samar Ali, Caroline Masserot, Guillaume Kellermann, Joel Poupon, Marie-Paule Teulade-Fichou, Evelyne Ségal-Bendirdjian, Sophie Bombard (2018 Jul 3)

Platinum Complexes Can Bind to Telomeres by Coordination.

International journal of molecular sciences : 19 : 1951 : DOI : 10.3390/ijms19071951 Learn more
Summary

It is suggested that several compounds, including G-quadruplex ligands, can target telomeres, inducing their uncapping and, ultimately, cell death. However, it has never been demonstrated whether such ligands can bind directly and quantitatively to telomeres. Here, we employed the property of platinum and platinum-G-quadruplex complexes to target G-rich sequences to investigate and quantify their covalent binding to telomeres. Using inductively coupled plasma mass spectrometry, surprisingly, we found that, in cellulo, in the presence of cisplatin, a di-functional platinum complex, telomeric DNA was platinated 13-times less than genomic DNA in cellulo, as compared to in vitro data. On the contrary, the amount of mono-functional platinum complexes (Pt-ttpy and Pt-tpy) bound either to telomeric or to genomic DNA was similar and occurred in a G-quadruplex independent-manner. Importantly, the quantification revealed that the low level of cisplatin bound to telomeric DNA could not be the direct physical cause of TRF2 displacement from telomeres. Altogether, our data suggest that platinum complexes can affect telomeres both directly and indirectly.img_1

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Marlène Rasschaert, Andréa Emerit, Nathalie Fretellier, Cécile Factor, Philippe Robert, Jean-Marc Idée, Claire Corot (2018 Jun 1)

Gadolinium Retention, Brain T1 Hyperintensity, and Endogenous Metals: A Comparative Study of Macrocyclic Versus Linear Gadolinium Chelates in Renally Sensitized Rats.

Investigative radiology : 53 : 328-337 : DOI : 10.1097/RLI.0000000000000447 Learn more
Summary

Objectives: This preclinical study was designed to compare gadolinium (Gd) brain uptake after repeated injections of a macrocyclic Gd-based contrast agent (GBCA) (gadoterate meglumine) or 2 linear GBCAs (L-GBCAs) (gadobenate dimeglumine or gadodiamide) on a translational model of moderate renal impairment in rats.

Methods: The study was carried out in subtotally nephrectomized rats. Animals received 4 intravenous injections per week of GBCA (gadoterate meglumine, gadobenate dimeglumine, or gadodiamide) for 5 weeks, resulting in a cumulative dose of 12 mmol/kg, followed by a 1-month injection-free period. T1 hyperintensity in the deep cerebellar nuclei (DCNs) was investigated, and brain structures were carefully dissected to determine elemental Gd, iron (Fe), copper (Cu), and zinc (Zn) distribution by mass spectrometry. Urinary excretion of endogenous metals was also investigated soon after GBCA administration and several days later in order to assess a potential transmetalation phenomenon.

Results: Unlike gadoterate, repeated injections of L-GBCAs gadobenate and gadodiamide both induced T1 hyperintensity in the DCNs. Fine dissection of cerebral and cerebellar structures demonstrated very low levels or absence of Gd after repeated injections of gadoterate, in contrast to the two L-GBCAs, for which the highest total Gd concentration was demonstrated in the DCNs (Gd concentration in DCNs after 4.5 weeks of injection-free period: 27.1 6.5 nmol/g for gadodiamide [P < 0.01 vs saline and P < 0.05 vs gadoterate]; 12.0 +/- 2.6 nmol/g for gadobenate [P < 0.09 vs saline]; compared with 1.4 +/- 0.2 nmol/g for gadoterate [ns vs saline]). The distribution of Gd concentration among the various brain structures dissected was also well correlated with the Fe distribution in these structures. No difference in endogenous metal levels in brain structures was observed. However, injection of gadobenate or gadodiamide resulted in an increase in urinary Zn excretion (urinary Zn concentrations: 57.9 +/- 20.5 nmol/mL with gadobenate [P < 0.01 vs gadoterate and saline] and 221.6 +/- 83.3 nmol/L with gadodiamide [P < 0.0001 vs all other treatments] vs 8.1 +/- 2.3 nmol/L with saline and 10.6 +/- 4.8 nmol/L with gadoterate]).

Conclusions: In a model of renally impaired rats, only traces of gadoterate meglumine were detected in the brain with no T1 hyperintensity of the DCNs, whereas marked Gd retention was observed in almost all brain areas after injections of the L-GBCAs, gadobenate dimeglumine and gadodiamide. Brain structures with higher Gd uptake corresponded to those structures containing more Fe. Urinary Zn excretion was significantly increased after a single injection of L-GBCAs.

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Philippe Robert, Stefanie Fingerhut, Cécile Factor, Véronique Vives, Justine Letien, Michael Sperling, Marlène Rasschaert, Robin Santus, Sébastien Ballet, Jean-Marc Idée, Claire Corot, Uwe Karst (2018 May 23)

One-year Retention of Gadolinium in the Brain: Comparison of Gadodiamide and Gadoterate Meglumine in a Rodent Model.

Radiology : 288 : 424-433 : DOI : 10.1148/radiol.2018172746 Learn more
Summary

Purpose: To compare the long-term brain elimination kinetics and gadolinium species in healthy rats after repeated injections of the contrast agents gadodiamide (a linear contrast agent) or gadoterate (a macrocyclic contrast agent).

Materials and Methods: Nine-week-old rats received five doses of 2.4 mmol gadolinium per kilogram of body weight over 5 weeks and were followed for 12 months with T1-weighted MRI (n = 140 rats, corresponding to seven time points, two contrast agents, and 10 rats per group). Animals were sacrificed at 1 week, 1 month, and 2, 3, 4, 5, and 12 months after the last injection. Brain and plasma were sampled to determine the total gadolinium concentration by using inductively coupled plasma mass spectrometry (ICP-MS). For the cerebellum, gadolinium speciation analysis was performed after mild extraction at four time points (1 month and 3, 5, and 12 months after the last injection) by using size exclusion chromatography and hydrophilic interaction liquid chromatography, both coupled to ICP-MS. Tissue gadolinium kinetics were fitted to estimate the area under the curves and tissue elimination half-lives over the 12-month injection-free period.

Results: T1 hyperintensity of the deep cerebellar nuclei was observed only in gadodiamide-treated rats and remained stable from the 1st month after the last injection (the ratio of the signal intensity of the deep cerebellar nuclei to the signal intensity of the brain stem at 1 year: 1.101 ± 0.023 vs 1.037 ± 0.022 before injection, P < .001). Seventy-five percent of the total gadolinium detected after the last injection of gadodiamide (3.25 nmol/g ± 0.30) was retained in the cerebellum at 1 year (2.45 nmol/g ± 0.35), with binding of soluble gadolinium to macromolecules. No T1 hyperintensity was observed with gadoterate, consistent with a rapid, time-dependent washout of the intact gadolinium chelate down to background levels (0.07 nmol/g ± 0.03).

Conclusion: After repeated administration of gadodiamide, a large portion of gadolinium was retained in the brain, with binding of soluble gadolinium to macromolecules. After repeated injection of gadoterate, only traces of the intact chelated gadolinium were observed with time-dependent clearance.

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Aaron Mendez-Bermudez, Liudmyla Lototska, Serge Bauwens, Marie-Josèphe Giraud-Panis, Olivier Croce, Karine Jamet, Agurtzane Irizar, Macarena Mowinckel, Stephane Koundrioukoff, Nicolas Nottet, Genevieve Almouzni, Mare-Paule Teulade-Fichou, Michael Schertzer, Mylène Perderiset, Arturo Londoño-Vallejo, Michelle Debatisse, Eric Gilson, Jing Ye (2018 May 3)

Genome-wide Control of Heterochromatin Replication by the Telomere Capping Protein TRF2

Molecular cell : 70 : 449-461.e5 : DOI : 10.1016/j.molcel.2018.03.036 Learn more
Summary

Hard-to-replicate regions of chromosomes (e.g., pericentromeres, centromeres, and telomeres) impede replication fork progression, eventually leading, in the event of replication stress, to chromosome fragility, aging, and cancer. Our knowledge of the mechanisms controlling the stability of these regions is essentially limited to telomeres, where fragility is counteracted by the shelterin proteins. Here we show that the shelterin subunit TRF2 ensures progression of the replication fork through pericentromeric heterochromatin, but not centromeric chromatin. In a process involving its N-terminal basic domain, TRF2 binds to pericentromeric Satellite III sequences during S phase, allowing the recruitment of the G-quadruplex-resolving helicase RTEL1 to facilitate fork progression. We also show that TRF2 is required for the stability of other heterochromatic regions localized throughout the genome, paving the way for future research on heterochromatic replication and its relationship with aging and cancer.

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Ana Vujic, Carolin Lerchenmüller, Ting-Di Wu, Christelle Guillermier, Charles P Rabolli, Emilia Gonzalez, Samuel E Senyo, Xiaojun Liu, Jean-Luc Guerquin-Kern, Matthew L Steinhauser, Richard T Lee, Anthony Rosenzweig (2018 Apr 27)

Exercise induces new cardiomyocyte generation in the adult mammalian heart.

Nature communications : 9 : 1659 : DOI : 10.1038/s41467-018-04083-1 Learn more
Summary

Loss of cardiomyocytes is a major cause of heart failure, and while the adult heart has a limited capacity for cardiomyogenesis, little is known about what regulates this ability or whether it can be effectively harnessed. Here we show that 8 weeks of running exercise increase birth of new cardiomyocytes in adult mice (~4.6-fold). New cardiomyocytes are identified based on incorporation of N-thymidine by multi-isotope imaging mass spectrometry (MIMS) and on being mononucleate/diploid. Furthermore, we demonstrate that exercise after myocardial infarction induces a robust cardiomyogenic response in an extended border zone of the infarcted area. Inhibition of miR-222, a microRNA increased by exercise in both animal models and humans, completely blocks the cardiomyogenic exercise response. These findings demonstrate that cardiomyogenesis can be activated by exercise in the normal and injured adult mouse heart and suggest that stimulation of endogenous cardiomyocyte generation could contribute to the benefits of exercise.

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