Imagerie intégrative : de la molécule à l'organisme

Objective  To examine the retinal histopathologic manifestation of aceruloplasminemia, an autosomal recessive disease caused by mutation of the ferroxidase ceruloplasmin, resulting in tissue iron overload.

Methods  The morphologic features of the human aceruloplasminemic retina were studied with light and electron microscopy. Retinal iron accumulation was assessed with Perls Prussian blue staining, immunohistochemistry, and secondary ion mass spectrometry.

Several genes in human cells are activated by physical genotoxic agents in order to regenerate cell homeostasis. Among the pathways contributing to this response, nucleotide excision repair (NER) is unique in restoring the nucleotide sequence of the DNA molecule without generating mutations. The first step of NER is mediated by a protein complex composed of XPC, RAD23B, an ubiquitin receptor and CENTRIN 2, an EF-hand calcium binding protein. These three proteins are multifunctional and participate in other important biochemical pathways.

In this paper, we report the synthesis of a series of porphyrins, designed as photodynamic therapy (PDT) agents, substituted by three glycosyl units linked by a triazole group to chromophore in the aim to target tumor cells overexpressing lectin-type membrane receptors, by 'click-chemistry' under microwave heating.

We assessed the regional brain atrophy in mouse lemur primates from 4.7 T T2-weighted magnetic resonance images. Thirty animals aged from 1.9 to 11.3 years were imaged. Sixty-one percent of the 23 animals older than 3 years involved in the study displayed an atrophy process. Cross-sectional analysis suggests that the atrophy follows a gradual pathway, starting in the frontal region then involving the temporal and/or the parietal part of the brain and finally the occipital region.

Original palladium complexes involving (-)-ephedrine, (-)-norephedrine, L-prolinol, L-valinol and L-isoleucinol have been rapidly prepared in neutral or basic medium and simply purified. They have been fully characterized by classical analytical methods and four of them were characterized by X-Ray analysis. In parallel with the experimental work, HF-DFT(B3LYP/PCM) computations were performed to obtain additional structural information. Their antiproliferative properties have been evaluated and some complexes showed small activities especially towards HT29 human cancer cells.

A series of 8-arylated purine derivatives bearing either an aniline or an alkyl amide at position 6 were found to inhibit glycogen synthase kinase-3, with good selectivity over ten kinases. Molecular modeling studies indicated that the most active compounds (8a and 8e), adopt a planar conformation, close to the shape of AMPPNP in the crystal structure of GSK-3.

Small and large scale proteomic technologies are providing a wealth of potential interactions between proteins bearing phospho-recognition modules and their substrates. Resulting interaction maps reveal such a dense network of interactions that the functional dissection and understanding of these networks often require to break specific interactions while keeping the rest intact. Here, we developed a computational strategy, called STRIP, to predict the precise interaction site involved in an interaction with a phospho-recognition module.

Membrane proteins are often present in low amounts in cells. Their function can be modulated by interactions with other proteins. Moreover, these complexes can be transiently formed, thus making them difficult to be isolated and to be purified. One way to overcome these difficulties is to visualize these complexes in situ in the cells. For such purpose, electron microscopy coupled to tomography is a promising approach that has been developed over the last decades.

Dynamic contrast-enhanced MRI is extensively studied to define and evaluate biomarkers for early assessment of vasculature-targeting therapies. In this study, two-dimensional and three-dimensional radial multi-gradient-echo techniques for dynamic R*₂-corrected R₁ mapping based on the spoiled gradient recalled signal equation were implemented and validated at 4.7 T. The techniques were evaluated on phantoms and on a respiratory motion animated tumor model.

Centrosomes are cellular organelles that have a major role in the spatial organisation of the microtubule network. The centrosome is comprised of two centrioles that duplicate only once during the cell cycle, generating a procentriole from each mature centriole. Despite the essential roles of centrosomes, the detailed structural mechanisms involved in centriole duplication remain largely unknown. Here, we describe human procentriole assembly using cryo-electron tomography.

Résumé

La photothérapie dynamique (PDT) est une approche récente du traitement de petites tumeurs cancéreuses de surface ou accessibles par endoscopie, associant l’action d’un photosensibilisateur, non toxique à l’obscurité, concentré dans la tumeur et d’une lumière focalisée sur celle-ci, de longueur d’onde appropriée. Le rétinoblastome (Rb) est une tumeur maligne intraoculaire rare de l’enfant. Toutes les formes multifocales sont héréditaires et constituent un syndrome de prédisposition génétique au cancer.

Object  

The brain of patients with Alzheimer’s disease (AD) is characterized by the presence of amyloid plaques and neurofibrillary tangles. Vascular alterations such as amyloid angiopathy are also commonly reported in patients with AD and participate in mechanisms involved in disease onset and progression. Transgenic mouse models of AD have been engineered to evaluate the pathophysiology and new treatments of the disease.

Lactobacillus sakei is a lactic acid bacterium naturally found on meat. Although it is generally acknowledged that lactic acid bacteria are rare species in the microbial world which do not have iron requirements, the genome sequence of L. sakei 23K has revealed quite complete genetic equipment dedicated to transport and use of this metal. Here, we aimed to investigate which iron sources could be used by this species as well as their role in the bacterium's physiology.

Uranium is an ubiquitous pollutant with known chemical and radiological toxicity, which is naturally present in the plant environment. Due to its high affinity for phosphate, insoluble uranium-phosphate precipitates are formed in soils as well as in contaminated plant cells. To date, consequences of such interactions on uranium toxicity and on phosphate availability and metabolism in plants are unknown.

The aim of this study was to propose and evaluate a methodology to analyze simultaneously acquired T-weighted dynamic susceptibility contrast (DSC) MRI and T₁-weighted dynamic contrast enhanced (DCE) MRI data. Two generalized models of T-relaxation are proposed to account for tracer leakage, and a two-compartment exchange model is used to separate tracer in intra- and extravascular spaces. The methods are evaluated using data extracted from ROIs in three mice with subcutaneously implanted human colorectal tumors.

In recent years, there has been dramatic worldwide increase in incidence of malignant melanoma. Although localised disease is often curable by surgical excision, metastatic melanoma is inherently resistant to most treatments. In this context, targeted radionuclide therapy could be an efficient alternative. After pharmacomodulation study, we selected a quinoxaline derivative molecule (ICF01012) for its high, specific and long-lasting uptake in melanoma with rapid clearance from nontarget organs providing suitable dosimetry parameters for targeted radiotherapy.

Iodine-enhanced synchrotron stereotactic radiotherapy takes advantage of the radiation dose-enhancement produced by high-Z elements when irradiated with mono-energetic beams of synchrotron X-rays. In this study it has been investigated whether therapeutic efficacy could be improved using a thymidine analogue, 5-iodo-2'-deoxyuridine (IUdR), as a radiosentizing agent. IUdR was administered intracerebrally over six days to F98 glioma-bearing rats using Alzet osmotic pumps, beginning seven days after tumor implantation.

¹³C spectroscopy combined with the injection of ¹³C-labeled substrates is a powerful method for the study of brain metabolism in vivo. Since highly localized measurements are required in a heterogeneous organ such as the brain, it is of interest to augment the sensitivity of ¹³C spectroscopy by proton acquisition.

In this paper, we analyze the scaling properties of both the radius of gyration and the surface area for EF-hand calcium binding proteins. These properties are different for two conformational subfamilies: proteins with extended and compact structures, respectively. The radius of gyration is a measure of the shape of protein, whereas its surface fractal dimension is a measure of its interatomic packing.

Identification of proteins in 3D maps of cells is a main challenge in structural cell biology. For light microscopy (LM) clonable reagents such as green fluorescent protein represented a real revolution and equivalent reagents for transmission electron microscopy (TEM) have been pursued for a long time.

An experimental setup consisting of a hollow fiber module (HFM) was developed for the in vitro study of contrast agent (CA) permeability. Controllable flow and known fiber characteristics allowed permeability studies under well-defined conditions with CAs of different molecular weight (MW). In the MRI experiments performed at 4.7 T, the system was perfused at a constant flow rate (5 ml/min) with water and four CA of different MW: Gd-DOTA (MW=0.6 kDa), P846 (3.5 kDa), P792 (6.5 kDa) and P717 (50.5 kDa).

Amyloid deposits are one of the hallmarks of Alzheimer's disease. Recent studies, in transgenic mice modeling Alzheimer's disease showed that, using in vivo, contrast agent-free, MRI, thalamic amyloid plaques are more easily detected than other plaques of the brain. Our study evaluated the characteristics of these thalamic plaques in a large population of APP/PS1, PS1 and C57BL/6 mice. Thalamic spots were detected in all mice but with different frequency and magnitude. Hence, the prevalence and size of the lesions were higher in APP/PS1 mice.

Melanosomes are lysosome-related organelles (LROs) in which melanins are synthesized and stored. Early stage melanosomes are characterized morphologically by intralumenal fibrils upon which melanins are deposited in later stages. The integral membrane protein Pmel17 is a component of the fibrils, can nucleate fibril formation in the absence of other pigment cell-specific proteins, and forms amyloid-like fibrils in vitro.

We report the discovery of exceptionally large biogenic magnetite crystals in clay-rich sediments spanning the Paleocene–Eocene Thermal Maximum (PETM) in a borehole at Ancora, NJ. Aside from previously described abundant bacterial magnetofossils, electron microscopy reveals novel spearhead-like and spindle-like magnetite up to 4 μm long and hexaoctahedral prisms up to 1.4 μm long. Similar to magnetite produced by magnetotactic bacteria, these single-crystal particles exhibit chemical composition, lattice perfection, and oxygen isotopes consistent with an aquatic origin.

The increasing incidence of melanoma and the lack of effective therapy have prompted the development of new vectors, more specific to the pigmented tumor, for early detection and treatment. Targeted agents have to exhibit a rapid, high tumor uptake, long tumor retention and rapid clearance from nontarget organs. This joint work presents results obtained with a new melanoma targeting agent, [¹²⁵I]-N-(4-dipropylaminobutyl)-4-iodobenzamide or [¹²⁵I]BZ18.

PURPOSE:

This work investigates whether a synergy in cell death induction exists in combining atomic ions irradiation and addition of platinum salts. Such a synergy could be of interest in view of new cancer therapy protocol based on atomic ions--hadrontherapy--with the addition of radiosensitizing agents containing high-Z atoms. The experiment consists in irradiating by fast ions cultured cells previously exposed to dichloroterpyridine Platinum (PtTC) and analyzing cell survival by a colony-forming assay.

In contrast to physiologic biomineralization occurring in bones, teeth and otoconia in vertebrates, calcification of soft tissues occurs in many pathologic conditions. Although similarities have been noted between the two processes, and despite the important clinical consequences of ectopic calcification, the molecular mechanisms regulating ectopic calcification are poorly understood. Although calcification is mainly extracellular, intracellular calcification has been reported and might indeed contribute to pathologic calcification of soft tissues.

Sodium is the second best nucleus in living systems MRI after proton, but it is the first one concerning its sensitivity to the electrical configuration of the environment, due to its quadrupolar relaxation properties. Retrieving accurate relaxation data from low signal-to-noise ratio (SNR) experiments implies using post-processing procedures in order to fit correctly the decaying relaxation curves. The conventional image reconstruction method is introducing a positive bias due to the rician noise contribution. Phasing the images restores its initial Gaussian characteristic.

Binding human serum albumin (HSA) of three polyoxometalates (POMs) with the Wells−Dawson structure, α₂-[P₂W₁₇O₆₁]¹⁰⁻ (abbreviated as α₂-P₂W₁₇) and two of its metal-substituted derivatives, α₂-[NiP₂W₁₇O₆₁]⁸⁻ and α₂-[CuP₂W₁₇O₆₁]⁸⁻ (α₂-P₂W₁₇Ni and α₂-P₂W₁₇Cu, respectively) was studied in an aqueous medium at pH 7.5.

Identifying the function of uncultured microbes in their environments today remains one of the main challenges for microbial ecologists. In this article, we describe a new method allowing simultaneous analysis of microbial identity and function. This method is based on the visualization of oligonucleotide probe-conferred hybridization signal in single microbial cells and isotopic measurement using high-resolution ion microprobe (NanoSIMS).

Brown algal kelp species are the most efficient iodine accumulators among all living systems, with an average content of 1.0% of dry weight in Laminaria digitata. The iodine distributions in stipe and blade sections from L. digitata were investigated at tissue and subcellular levels. The quantitative tissue mapping of iodine and other trace elements (Cl, K, Ca, Fe, Zn, As and Br) was provided by the proton microprobe with spatial resolutions down to 2 μm.

Xeroderma pigmentousum group C protein (XPC) is involved in the first step of nucleotide excision repair, with multiple functional roles including DNA damage recognition and recruitment of the repair machinery. This human protein of 940 residues forms a strong heterotrimeric complex with Rad23B and centrin 2. The structure of XPC is actually not known, and lack of significant sequence homology with proteins from structural data bases precludes any relevant prediction.

Background

Retinoblastoma is the most common malignant intraocular tumor in children. The current treatment gives a good vital prognostic but there are several drawbacks to the arsenal of “classical antitumoral” therapies. Photodynamic therapy (PDT) could be an exciting non-toxic and non-mutagenic alternative protocol.

Transmission electron microscopy is a powerful technique for studying the three-dimensional (3D) structure of a wide range of biological specimens. Knowledge of this structure is crucial for fully understanding complex relationships among macromolecular complexes and organelles in living cells. In this paper, we present the principles and main application domains of 3D transmission electron microscopy in structural biology.

A double-delay SR-MGE-SNAP sequence allowing simultaneous T ₁ and T ₂^* measurement was developed for integrating arterial input function (AIF) measurement into DCE MRI. Implemented on a 4.7-T animal MR system, this technique was applied to mice with colorectal tumor xenografts.

DNA damage checkpoints are signal transduction pathways that are activated after genotoxic insults to protect genomic integrity. At the site of DNA damage, ‘mediator’ proteins are in charge of recruiting ‘signal transducers’ to molecules ‘sensing’ the damage. Budding yeast Rad9, fission yeast Crb2 and metazoan 53BP1 are presented as mediators involved in the activation of checkpoint kinases.

Background

Centrins are calcium-binding proteins that play a significant role in the maintenance of the centrosomal organization, mainly in the continuity between centrosome and microtubular network. Recent data showed that centrosome duplication abnormalities, like overduplication for example, could be due to hydrogen peroxide, suggesting an important impact of oxidative stress. To challenge this hypothesis, we performed one-electron oxidation experiments with human centrin 2, starting from azide radicals.

In Saccharomyces cerevisiae, double-strand breaks (DSBs) activate DNA checkpoint pathways that trigger several responses including a strong G₂/M arrest. We have previously provided evidence that the phosphatases Ptc2 and Ptc3 of the protein phosphatase 2C type are required for DNA checkpoint inactivation after a DSB and probably dephosphorylate the checkpoint kinase Rad53. In this article we have investigated further the interactions between Ptc2 and Rad53.

The purpose of this study was to evidence the tumors by changes in sodium intensity and/or relaxation parameters. In vivo, 23Na spin-echo relaxation study,
performed on mice liver showed that changes in signal intensity, associated with changes in T2 sodium relaxation, occurred in areas detected as tumor
regions, as compared to control. The study suggests that tumor region is distinguishable from haemorragic areas via relaxation. Homogeneous relaxation

Neurodegenerative diseases induce morphological and chemical alterations in well-characterized regions of the brain. Understanding their pathological processes requires the use of methods that assess both morphological and chemical alterations in the tissues. In the past, microprobe approaches such as scanning electron microscopy combined with an X-ray spectrometer, Proton induced X-ray emission, secondary ion mass spectrometry (SIMS), and laser microprobe mass analysis have been used for the study of pathological human brain with limited success.

The paper reports the results of numerical calculations of the pKa’s of the ionizable groups and the electrostatic interactions between calmodulin lobes in three different states of calmodulin: calcium-free, peptide-free; calcium-loaded, peptide-free; and calcium-loaded, peptide-bound. NMR and X-ray studies revealed that in these states the overall structure of calmodulin adopts various conformations referred as: disordered semi-compact, extended and compact conformations, respectively.

Regulatory 14-3-3 proteins activate the plant plasma membrane H⁺-ATPase by binding to its C-terminal autoinhibitory domain. This interaction requires phosphorylation of a C-terminal, mode III, recognition motif as well as an adjacent span of approximately 50 amino acids. Here we report the X-ray crystal structure of 14-3-3 in complex with the entire binding motif, revealing a previously unidentified mode of interaction.

Electron microscopy allows the analysis of synaptic ultrastructure and its modifications during learning or in pathological conditions. However, conventional electron microscopy uses aldehyde fixatives that alter the morphology of the synapse by changing osmolarity and collapsing its molecular components. We have used high-pressure freezing (HPF) to capture within a few milliseconds structural features without aldehyde fixative, and thus to provide a snapshot of living synapses.

A series of amino- and glycoconjugates of pyrido[4,3,2-kl]acridine and pyrido[4,3,2-kl]acridin-4-one have been prepared. The most active molecules, the amino conjugates 7 and 11, display a cytostatic activity against HT-29 cancer cells at micromolar concentration. This activity correlates well with a strong DNA binding. The molecules, amino or glycoconjugates, bind DNA by intercalation, the amino or glyco substituent being located in one groove. None of the molecules inhibits topoisomerase activity.

DFT calculations are carried out on computational models of the active center of the α and β subunits of hemoglobin in both its oxygenated (R) and deoxygenated (T) states. The computational models are defined by the full heme group, including all porphyrin substituents, and the four amino acids closer to it. The role of the protein environment is introduced by freezing the position of the α carbon atom of each of the four amino acids to the positions they have in the available PDB structures.

A series of [1,3]oxazino fused acridines has been prepared as precursors of cytotoxic 3-amino-4-hydroxymethylacridine 2. Their cytotoxic activity has been evaluated against HT29 colon carcinoma cell line and was shown to be dependent on the nature of the substituent located on position 2 of the oxazine ring. Additionally, the nitrophenyl derivative 3f is activated by nitroreductase, indicating its potency as prodrug for either gene-directed or antibody-directed enzyme prodrug therapies.

Dynamic SIMS imaging is proposed to map sub-cellular distributions of isotopically labelled, exogenous compounds. NanoSIMS imaging allows the characterisation of the intracellular transport pathways of exogenous molecules, including peptide vectors employed in innovative therapies, using stable isotopes as molecular markers to detect the compound of interest. Shiga toxin B-subunit (STxB) was chosen as a representative peptide vector.

Background information. Transmission electron tomography is becoming a powerful tool for studying subcellular components of cells. Classical approaches for electron tomography consist of recording images along a single-tilt axis. This approach is being improved by dual-axis reconstructions and/or high-tilt devices (tilt angle>±60°) on microscopes to compensate part of the information loss due to the ‘missing wedge’ phenomena.

bIL41 and bIL170, virulent phages of Lactococcus lactis belonging to the 936 group, possess a late gene named l12, coding a putative fiber sharing partial similarity to diverse gene products of dairy phages, including host-range determinants, but whose function is unknown in this group. We observed that the full-size gpl12 gene product is a minor protein constitutive of both phage particles. A derivative of bIL41 deleted for part of this gene was constructed by homologous recombination.

Objectives: We sought to compare pharmacokinetic modeling of dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI) data by assuming a linear and nonlinear relationship between signal intensity (SI) and contrast agent (CA) concentration.

NMR Probeheads for Biophysical and Biomedical Experiments is essential reading for anyone in the field of NMR or MRI, from students to medical or biological scientists performing experiments under certain physical and/or geometrical conditions, unattainable by conventional or available probes. The material guides the reader through the most basic and comprehensive stages in accomplishing a correct probe design, from a very basic oscillating circuit to much more elaborate designs.

T1 and T2 magnetic resonance relaxation times have the potential to provide biomarkers of amyloid-β deposition that could be helpful to the development of new therapies for Alzheimer's disease. Here, we measured T1 and T2 times as well as plaques and iron loads in APP/PS1 mice, which model brain amyloidosis, and control PS1 mice. Iron was mostly associated with amyloid deposits in APP/PS1 animals, while it was diffuse in the PS1 mice. T1 was negatively correlated with age in most structures in APP/PS1 animals.

Amyloid plaques are one of the hallmarks of Alzheimer's disease (AD). This study evaluated a novel μMRI strategy based on “passive staining” of brain samples by gadoteric acid. The protocol was tested at 4.7T on control animals and APP/PS1 mice modeling AD lesions. T₁ was strongly decreased in passively stained brains. On high-resolution 3D gradient echo images, the contrast between the cortex and subcortical structures was highly improved due to a T₂^* effect. The brains of APP/PS1 mice revealed plaques as hypointense spots.

Centrins are well-conserved calcium binding proteins from the EF-hand superfamily implicated in various cellular functions, such as centrosome duplication, DNA repair, and nuclear mRNA export. The intrinsic molecular flexibility and the self-association tendency make difficult the structural characterization of the integral protein. In this paper we report the solution structure, the Ca²⁺ binding properties, and the intermolecular interactions of the N-terminal domain of two human centrin isoforms, HsCen1 and HsCen2.

Previous studies of the structure of core nanocrystals of ferritin (Ft) in the brains of patients with Alzheimer’s disease (AD) have shown differences in the mineral compound in comparison with physiological Ft. Both Ft cores have a polyphasic composition but whereas the major phase in physiological Ft is hexagonal ferric iron oxide (ferrihydrite), the major phases in brain AD Ft are two cubic mixed ferric–ferrous iron oxides (magnetite and wüstite).