Séparation des oligomères du chitosane par chromatographie d'affinité sur ions métalliques immobilisés

Depuis les années 1990, les oligomères du chitosane (COS) suscitent un intérêt croissant pour certaines applications biomédicales et alimentaires. Il est possible d'obtenir différents ratios d'oligomères à des degrés de polymérisation (DP) variant de 2 à 8 unités, selon le procédé d'hydrolyse du chitosane employé (chimique ou enzymatique). Il est difficile d'étudier leurs effets tant physiques que biochimiques de façon individuelle car ces oligomères sont difficiles à séparer et jusqu'à maintenant, leur commercialisation est limitée. Tout comme le chitosane, les oligomères possèdent des propriétés de complexation avec des ions métalliques de transition. Plusieurs facteurs interviennent lors de la formation de complexes avec le chitosane, notamment le pH, le degré de polymérisation (DP) ainsi que l'ion métallique. Le travail élaboré dans ce mémoire s'est basé sur l'hypothèse d'une séparation possible d'un mélange de COS (dimère, trimère, tétramère) en faisant intervenir l'affinité avec des ions métalliques en fonction du DP. Nous proposons ainsi une méthode chromatographique basée sur l'affinité entre les ions métalliques cuivre (II) et les groupements amine des oligomères de chitosane. La chromatographie d'affinité sur des ions métalliques immobilisés (IMAC) est déjà appliquée à la purification de biomacromolécules (protéines, ADN). L'adaptation de ce type chromatographique à notre problématique montre un réel intérêt car le développement du système est économique et simple d'utilisation. Des matériaux polyhydroxyliques (Agarose et silice) ont été fonctionnalisés par des groupements de type IMAC. Différentes fonctions chélatantes ont été greffés sur la Sepharose CL-6B (agarose réticulé): l'acide iminodiacétique (IDA), l'acide aspartique carboxyméthylé (CM-Asp) et le tris(carboxymethyl)diamine (TED). Ces matrices ont été caractérisées par FTIR et leurs capacités de rétention de Cu2+ par spectrophotométrie d'adsorption atomique (AAS). Un mélange commercial de COS (dimère, trimère, tétramère) fourni par ISM Biopolymer inc, a été utilisé pour l'étude sur les capacités de rétention. Les différents supports IMAC à base d'agarose (ACL6B) ont montré des quantités de rétention en COS respectivement de 6 mg/cm³, 4 mg/cm³ et 2 mg/cm³ sur les matrices modifiées (ACL6B-IDA, ACL6B-CM-Asp, ACL6B-TED). Les matériaux chromatographiques IMAC ont été employés en mode FPLC (à pression moyenne). Les fractions obtenues ont été analysées par une technique colorimétrique à base d'acide bicinconinique (BCA) et par chromatographie en couche mince avec la détection des oligomères à la ninhydrine. Les résultats sont corrélés avec l'analyse de la population retrouvée des différentes fractions par spectrométrie de masse quadripôle simple. Les oligomères de chitosane ont été partiellement séparés et/ou enrichis (selon la méthode employée) à 95 % pour le dimère, 70 % pour le trimère et 90 % pour le tétramère, avec nos matériaux chélatants obtenus au laboratoire, à base d'agarose réticulée. Ces résultats sont nettement supérieurs à ceux obtenus avec des matériaux chromatographiques commerciaux (Profinity, Chelex-100). Cette nouvelle méthode originale, à base de chromatographie d'affinité IMAC, offre des possibilités de diversification d'applications des COS et pourrait permettre de diminuer les coûts de revient lors de leur préparation à l'échelle industrielle. ______________________________________________________________________________ MOTS-CLÉS DE L’AUTEUR : Chitosane, Chitooligosaccharide (COS), Chromatographie d'affinité sur ions métalliques immobilisés (IMAC)

Hypocholesterolemic phospholipid transfer protein knockout mice exhibit a normal glucocorticoid response to food deprivation

Objectives: Glucocorticoids, adrenal-derived steroid hormones, facilitate the physiological response to stress. High-density lipoproteins (HDL) are considered the primary source of cholesterol used for glucocorticoid synthesis in mice. Phospholipid transfer protein (PLTP) is a key player in HDL formation. In the current study we tested the hypothesis that HDL deficiency associated with genetic lack of PLTP negatively impacts the adrenal steroid function. Methods: We determined the glucocorticoid response to overnight food deprivation stress and the adrenal lipid and genetic phenotype of wild-type and PLTP knockout mice. Results: Basal plasma corticosterone levels, adrenal weights, and adrenocortical neutral lipid stores were not different between wild-type and PLTP knockout mice. Strikingly, plasma corticosterone levels were also equally high in the two groups of mice under fasting conditions (twoway ANOVA genotype effect: P>0.05). However, compensatory mechanisms were active to overcome adrenal lipid depletion, since gene expression levels of cholesterol synthesis, acquisition and mobilization proteins were similar to 2-fold higher in PLTP knockout adrenals versus wild-type adrenals. In support of an overall similar glucocorticoid stress response, hepatic relative mRNA expression levels of the glucocorticoid receptor target/glucocorticoid-sensitive genes PEPCK, ANGPTL4, FGF21, TDO2 and HMGCS2 were also not different. Conclusions: We have shown that hypocholesterolemic PLTP knockout mice exhibit a normal glucocorticoid response to food deprivation. These novel data (1) highlight that the effect of HDL deficiency on adrenal glucocorticoid output in mice is model dependent and (2) imply that other (lipoprotein) cholesterol sources than HDL can also generate the pool utilized by adrenocortical cells to synthesize glucocorticoids.Toxicolog

Phenotype-based cell-specific metabolic modeling reveals metabolic liabilities of cancer

Utilizing molecular data to derive functional physiological models tailored for specific cancer cells can facilitate the use of individually tailored therapies. To this end we present an approach termed PRIME for generating cell-specific genome-scale metabolic models (GSMMs) based on molecular and phenotypic data. We build > 280 models of normal and cancer cell-lines that successfully predict metabolic phenotypes in an individual manner. We utilize this set of cell-specific models to predict drug targets that selectively inhibit cancerous but not normal cell proliferation. The top predicted target, MLYCD, is experimentally validated and the metabolic effects of MLYCD depletion investigated. Furthermore, we tested cell-specific predicted responses to the inhibition of metabolic enzymes, and successfully inferred the prognosis of cancer patients based on their PRIME-derived individual GSMMs. These results lay a computational basis and a counterpart experimental proof of concept for future personalized metabolic modeling applications, enhancing the search for novel selective anticancer therapies.Toxicolog

Splicing factors control triple-negative breast cancer cell mitosis through SUN2 interaction and sororin intron retention

BackgroundTriple negative breast cancer (TNBC) is an aggressive subtype of breast cancer with limited therapeutic opportunities. Recently, splicing factors have gained attention as potential targets for cancer treatment. Here we systematically evaluated the role of RNA splicing factors in TNBC cell proliferation.MethodsIn this study, we performed an RNAi screen targeting 244 individual splicing factors to systematically evaluate their role in TNBC cell proliferation. For top candidates, mechanistic insight was gained using amongst others western blot, PCR, FACS, molecular imaging and cloning. Pulldown followed by mass spectrometry were used to determine protein-protein interactions and patient-derived RNA sequencing data was used relate splicing factor expression levels to proliferation markers.ResultsWe identified nine splicing factors, including SNRPD2, SNRPD3 and NHP2L1, of which depletion inhibited proliferation in two TNBC cell lines by deregulation of sister chromatid cohesion (SCC) via increased sororin intron 1 retention and down-regulation of SMC1, MAU2 and ESPL1. Protein-protein interaction analysis of SNRPD2, SNRPD3 and NHP2L1 identified that seven out of the nine identified splicing factors belong to the same spliceosome complex including novel component SUN2 that was also critical for efficient sororin splicing. Finally, sororin transcript levels are highly correlated to various proliferation markers in BC patients.ConclusionWe systematically determined splicing factors that control proliferation of breast cancer cells through a mechanism that involves effective sororin splicing and thereby appropriate sister chromatid cohesion. Moreover, we identified SUN2 as an important new spliceosome complex interacting protein that is critical in this process. We anticipate that deregulating sororin levels through targeting of the relevant splicing factors might be a potential strategy to treat TNBC.Cancer Signaling networks and Molecular Therapeutic

Preclinical models versus clinical renal ischemia reperfusion injury: a systematic review based on metabolic signatures

Despite decennia of research and numerous successful interventions in the preclinical setting, renal ischemia reperfusion (IR) injury remains a major problem in clinical practice, pointing toward a translational gap. Recently, two clinical studies on renal IR injury (manifested either as acute kidney injury or as delayed graft function) identified metabolic derailment as a key driver of renal IR injury. It was reasoned that these unambiguous metabolic findings enable direct alignment of clinical with preclinical data, thereby providing the opportunity to elaborate potential translational hurdles between preclinical research and the clinical context. A systematic review of studies that reported metabolic data in the context of renal IR was performed according to the PRISMA guidelines. The search (December 2020) identified 35 heterogeneous preclinical studies. The applied methodologies were compared, and metabolic outcomes were semi-quantified and aligned with the clinical data. This review identifies profound methodological challenges, such as the definition of IR injury, the follow-up time, and sampling techniques, as well as shortcomings in the reported metabolic information. In light of these findings, recommendations are provided in order to improve the translatability of preclinical models of renal IR injury.Transplant surger

The direct oral anticoagulants rivaroxaban and dabigatran do not inhibit orthotopic growth and metastasis of human breast cancer in mice

Factor Xa‐targeting DOACs were recently found to reduce recurrentVTE efficiently in cancer patients when compared to the standard treatment withlow‐molecular‐weight heparins (LMWHs). While the anticancer effects of LMWHshave been extensively studied in preclinical cancer models, the effects of FXa‐targetingDOACs on cancer progression remain to be studied.We investigated whether the FXa‐targeting DOAC rivaroxaban and thethrombin‐targeting DOAC dabigatran etexilate (DE) affected human breast cancergrowth and metastasis in orthotopic xenograft models.Mice that were put on a custom‐made chow diet supplementedwith rivaroxaban (0.4 or 1.0 mg/g diet) or dabigatran etexilate (DE) (10 mg/g diet)showed prolonged ex vivo coagulation times (prothrombin time [PT] and activatedpartial thromboplastin time [aPTT] assay, respectively). However, rivaroxabanand DE did not inhibit MDA‐MB‐231 tumor growth and metastasis formationin lungs or livers of 7‐week‐old fully immunodeficient NOD/SCID/ƴC−/− (NSG) mice.Comparable data were obtained for rivaroxaban‐treated mice when using NOD‐SCIDmice. Rivaroxaban and DE treatment also did not significantly inhibit tumor growthand metastasis formation when using another human triple negative breast cancer(TNBC) cell line (HCC1806) in NOD‐SCID mice. The FXa and thrombin‐induced geneexpression of the downstream target CXCL8 in both cell lines, but FXa and thrombin,did not significantly stimulate migration, proliferation, or stemness in vitro.Although effectively inhibiting coagulation, the DOACs rivaroxaban andDE did not inhibit orthotopic growth and metastasis of human TNBC. It remains to beinvestigated whether DOACs exert antitumorigenic effects in other types of cancer.Toxicolog

p140Cap suppresses the invasive properties of highly metastatic MTLn3-EGFR cells via impaired cortactin phosphorylation

ToxicologyComputer Systems, Imagery and Medi

Multiorgan Metastasis of Human HER-2+ Breast Cancer in Rag2−/−;Il2rg−/− Mice and Treatment with PI3K Inhibitor

In vivo studies of the metastatic process are severely hampered by the fact that most human tumor cell lines derived from highly metastatic tumors fail to consistently metastasize in immunodeficient mice like nude mice. We describe a model system based on a highly immunodeficient double knockout mouse, Rag2−/−;Il2rg−/−, which lacks T, B and NK cell activity. In this model human metastatic HER-2+ breast cancer cells displayed their full multiorgan metastatic potential, without the need for selections or additional manipulations of the system. Human HER-2+ breast cancer cell lines MDA-MB-453 and BT-474 injected into Rag2−/−;Il2rg−/− mice faithfully reproduced human cancer dissemination, with multiple metastatic sites that included lungs, bones, brain, liver, ovaries, and others. Multiorgan metastatic spread was obtained both from local tumors, growing orthotopically or subcutaneously, and from cells injected intravenously. The problem of brain recurrencies is acutely felt in HER-2+ breast cancer, because monoclonal antibodies against HER-2 penetrate poorly the blood-brain barrier. We studied whether a novel oral small molecule inhibitor of downstream PI3K, selected for its penetration of the blood-brain barrier, could affect multiorgan metastatic spread in Rag2−/−; Il2rg−/− mice. NVP-BKM120 effectively controlled metastatic growth in multiple organs, and resulted in a significant proportion of mice free from brain and bone metastases. Human HER-2+ human breast cancer cells in Rag2−/−;Il2rg−/− mice faithfully reproduced the multiorgan metastatic pattern observed in patients, thus allowing the investigation of metastatic mechanisms and the preclinical study of novel antimetastatic agents

Systems microscopy approaches to understand cancer cell migration and metastasis

Cell migration is essential in a number of processes, including wound healing, angiogenesis and cancer metastasis. Especially, invasion of cancer cells in the surrounding tissue is a crucial step that requires increased cell motility. Cell migration is a well-orchestrated process that involves the continuous formation and disassembly of matrix adhesions. Those structural anchor points interact with the extra-cellular matrix and also participate in adhesion-dependent signalling. Although these processes are essential for cancer metastasis, little is known about the molecular mechanisms that regulate adhesion dynamics during tumour cell migration. In this review, we provide an overview of recent advanced imaging strategies together with quantitative image analysis that can be implemented to understand the dynamics of matrix adhesions and its molecular components in relation to tumour cell migration. This dynamic cell imaging together with multiparametric image analysis will help in understanding the molecular mechanisms that define cancer cell migration

Role du confinement sur l'endocytose dépendante de la clathrine

Clathrin-mediated endocytosis (CME) is the major route of endocytosis for many cargos in eukaryotic cells. Endocytosis takes place at clathrin-coated pits (CCPs), small assemblies of clathrin and clathrin adaptors randomly distributed at the plasma membrane. Clathrin polymerization induces the progressive bending of the plasma membrane resulting in the formation of a vesicle budding off into the cytosol. CME is a highly dynamic process with an average lifetime of CCPs in the order of 30 seconds. In this manner, CME fulfills a range of different functions and enables cells to regulate the surface expression of proteins, to sample the cell’s environment for growth and guidance cues, to control the activation of signaling pathways and to turn over membrane components by sending these components for degradation in the endo-lysosomal pathway. A deregulation of the endocytic pathways was previously shown to be involve in cancer. These modifications can affect CME directly by modifying its actors, or indirectly with mutations on receptors or cargoes undertaken by CME. Tumor progression is dependent of several factors, the first one involving the accumulation of mutations which results in modifications in the cells themselves or on their surrounding environment by changing its biochemical and physical properties, leading to the formation of the tumor niche. These changes reciprocally foster cancer progression. During tumor growth, fibroblasts will be recruited around tumor cells, leading to the remodeling of the microenvironment and to an increase of rigidity nearby the tumor. This stiffness is sensed by the cells and send signals for proliferation and migration as a result. Stiffness sensing engages mainly integrins at the cell surface which will aggregate and initiate signaling cascades accountable for these responses. Integrins are capable of clustering into two types of structures: focal adhesions and clathrin-coated structures (CCSs). Regarding CCSs, it was shown previously that high stiffness strengthen the interaction between integrins and the substrate, hence preventing the budding off of the vesicle, and this is referred to as “frustrated endocytosis”. This holding of CCSs at the cell surface promotes a sustained signaling at the plasma membrane instead of a signal termination after internalization and further degradation in lysosomes. My PhD project relied on these previous findings, with a particular focus on another mechanical alteration observed in tumors, the confinement. Indeed, during the uncontrolled proliferation of cancer cells in a spatially restricted area, cells become subjected to compressive forces. The results I obtained indicate that confinement leads to frustrated endocytosis and hence to sustained signaling from the plasma membrane. In addition, compression also leads to HB-EGF shedding at the cell surface, and the resulting EGF product activate the EGFR in a paracrine manner, thus leading to the activation of the MAP kinase Erk signaling pathway. Indeed, both the absence of EGFR ligands in the medium and the inhibition of the shedding demonstrate the necessity of this mechanism in EGFR activation. To sum up, confinement induces the shedding of the EGFR pro-ligand HB-EGF necessary to EGFR activation in these conditions. Simultaneously, endocytosis is delayed and frustrated endocytosis leads to sustained signaling at the cell surface. Together, these events cooperate to strongly activate the Erk pathway. These findings highlight the interplay between the physical feature of the tumor environment and signaling pathways known to govern tumor growth.L’endocytose dépendante de la clathrine (EDC) est la principale voie d’internalisation des récepteurs de surface et de leurs ligands. L’internalisation se fait suite à l’invagination de la membrane plasmique vers l’intérieur de la cellule suite à la formation, dans un premier temps, de puits recouverts de clathrine (PRCs) qui bourgeonnent ensuite en vésicules recouvertes de clathrine dans le cytosol. L’EDC est un processus très dynamique qui a lieu en l’espace de 30 sec-1mn. Elle est impliquée dans de multiples fonctions et permet ainsi à la cellule de réguler l’expression de ses protéines en surface, de répondre aux signaux de prolifération ou migration envoyés par l’environnement immédiat via l’activation de voies de signalisation spécifiques ou encore de réguler le renouvellement des composants de la membrane plasmique. De par son importance, des dérégulations de l’endocytose dépendante de la clathrine ont déjà été observées dans les cancers. Ces modifications peuvent impliquer directement l’EDC en modifiant ses composants ou indirectement lors d’altérations de récepteurs régulés par celle-ci. La progression tumorale est elle-même régulée par de multiples facteurs, notamment l’accumulation de mutations qui ont des conséquences sur les cellules cancéreuses elle-même ou bien sur l’environnement immédiat, formant ainsi la « niche tumorale ». Ces changements agissent réciproquement sur la progression tumorale afin de l’amplifier. Lors de la croissance tumorale, les cellules cancéreuses recrutent des fibroblastes qui vont participer au remodelage et à l’augmentation de la rigidité autour de la tumeur. La rigidité de la matrice extracellulaire est détectée par les cellules ce qui envoie des signaux déclencheurs de prolifération et de migration en conséquence. Cette détection passe essentiellement par les intégrines à la surface membranaire qui vont s’agréger et induire des cascades de signalisation impliquées dans ces réponses. Ces intégrines peuvent se regrouper dans deux types de structures, les adhésions focales et les structures recouvertes de clathrine. En ce qui concerne ces dernières, il a été démontré précédemment que la rigidité du substrat augmente sa force d’interaction avec les intégrines, et empêche ainsi l’internalisation des vésicules recouvertes de clathrine, on parle alors d’ « endocytose frustrée ». Cette rétention des structures recouvertes de clathrine à la surface provoque une signalisation soutenue à la surface au lieu de l’arrêter par dégradation ultérieure des récepteurs dans les lysosomes. Le laboratoire a démontré que les structures de clathrine frustrées capturent ainsi différent récepteurs conduisant à une signalisation accrue dans la voie de la MAP Kinase Erk. Mon projet de thèse repose sur ces observations en s’intéressant plus particulièrement au rôle d’une autre modification induite par la croissance tumorale, le confinement. En effet, en se multipliant de manière incontrôlée dans un environnement spatialement restreint, les cellules tumorales se retrouvent soumises à des forces de compression. Les résultats mis en évidence au cours de ma thèse ont montré que le confinement provoque, comme la rigidité, une frustration des structures de clathrine qui ne sont donc plus capables de soutenir l’endocytose des récepteurs. De plus, la compression cellulaire induit le clivage d’un pro-ligand de l’EGFR, le HB-EGF, ce qui conduit à l’activation paracrine de l’EGFR et à l’activation de la voie Erk. En effet, l’absence de facteurs de croissance dans le milieu ainsi que l’inhibition de ce clivage démontrent la nécessité de la mise en place de ce mécanisme. En résumé, le confinement induit le clivage du pro-ligand HB-EGF, qui à son tour va activer le récepteur à l’EGF. En parallèle, l’endocytose est ralentie et provoque une signalisation accrue à la membrane. Ces deux évènements coopèrent pour mener à une très forte activation de la voie Erk