Chloroplaste | EPFL Graph Search

thumb|300px|right|Schéma d'un chloroplaste d'une plante. thumb|300px|right|Chloroplastes dans des cellules végétales de Plagiomnium observées au microscope optique vignette|Photographie d'une feuille d'élodée du Canada au microscope optique après une coloration au lugol (coloration des grains d'amidon bien visibles dans les chloroplastes). Les chloroplastes sont des organites présents dans le cytoplasme des cellules eucaryotes photosynthétiques (plantes, algues). Ils sont sensibles aux expositions des différentes ondes du spectre lumineux. Ils jouent un rôle essentiel dans le fonctionnement d'une cellule végétale étant donné qu'ils permettent de capter la lumière à l'origine de la photosynthèse. Par l'intermédiaire de la chlorophylle qu'ils possèdent et de leurs ultrastructures, ces organites sont capables de transférer l'énergie véhiculée par les photons à des molécules d'eau. Les chloroplastes jouent un rôle important dans le cycle du carbone, par la transformation du carbone atmosph

The role of recruited bone-marrow derived mesenchymal stem cells in the establishment of the tumor stroma and a growth-supportive environment

Jean-Paul Abbühl

The Mesenchymal Stem Cell (MSC) is a self-renewing multipotent progenitor originally found in the bone marrow. It has drawn strong interest from translational research because of the multipotency of MSCs, their immunosuppression, their intrinsic homing and their promotion of wound healing in human patients. Currently available methods rely on in vitro culture for the isolation and expansion of MSCs and most studies used these cells for their investigation. Fibroblasts constitute the connective tissue and support epithelial or hematopoietic cells. Although they have already been extensively investigated, it is not clear whether stem cells exist in vivo which specifically regenerate fibroblasts. MSCs are a potential candidate, because of their fibroblastic shape in vitro, their differentiation towards several mesodermal lineages and their supportive function. We aim to characterize the in vivo differentiation potential of MSCs toward fibroblasts in normal and tumor tissues. A new transplantation approach was developed in order to transfer labeled MSCs in the bone marrow and assess their recruitment and lineage contribution in vivo. Long-term engraftment was accomplished by isolating and transplanting these cells within one day. To this end, strategies for their purification, preconditioning of the host and transplantation methodologies were established during this thesis. We were able to enrich MSCs over 1000 fold by combining a new extraction protocol, a negative selection by MACS and a positive selection by FACS. Cloning of sorted MSCs was performed to confirm their multipotency at single cell level. GFP-expressing MSCs were able to engraft in host mice tolerant for GFP and their expansion in vivo was stimulated by block of GSK3 activity. Altogether, the chimeric MSC model was used to track the recruitment of bone-marrow derived MSCs into spontaneous breast tumors. The tumor microenvironment encompasses several non-tumorigenic cells interacting with cancer cells. Among them, cancer-associated fibroblasts are known to participate in carcinogenesis. Whilst this heterogeneous stromal population has been extensively investigated, their source(s) remain elusive. I now propose tumoral MSCs as one source of cancer-associated fibroblast, based on their ability to self-renew and reconstitute stromal heterogeneity upon serial transplantation. Finally, I introduced the new concept that the multipotency of MSCs is subjugated by cancer cells to meet their requirements for enhanced tumor progression and prepare for metastasis. I found MSCs present in the tumor microenvironment to differentiate into cancer-associated osteoblasts and produce hydroxyapatite-mineralization in vivo. Microcalcification is an accepted poor prognostic feature in breast cancer patients but its function and origin is not documented. I showed that hydroxyapatite was able to promote proliferation of tumor cells and increased intracellular calcium concentration. Lastly, cancer-associated osteoblast and hydroxyapatite were able to promote tumor growth and metastasis in vivo. To conclude, bone marrow derived MSCs are circulating stem cells that participate in the establishment of the pathogenic stroma in breast cancer. Owing to their multipotency, MSCs give rise to cancer-associated osteoblasts that induce pro-malignant mineralization in situ. Subsequently, cancer cells harbor increased intracellular calcium concentration, enhanced proliferation and metastasis. We foresee the development of new stroma-targeted therapies that prevent the mineralization of tumor tissue and reduce metastasis in breast cancer patients.

EPFL2014

Nanoscale Characterization of Amyloid Fibrils and Biomacromolecules by Atomic Force Microscopy Approaches

Jiangtao Zhou

This thesis focuses on the interdisciplinary biophysical research field, in which physical approaches are applied to study the biological phenomena. Specifically, the main object of the research in this thesis is to target biological species,especially the amyloid fibrils by using Atomic Force Microscope (AFM) and several relevant technologies. In the main section, we firstly present the high-resolution AFM and AFM-IR measurement on the LHCII on the chloroplast lipid membrane, and investigation on the regulation of the xanthophyll pigments, including violaxanthin and zeaxanthin, on the supramolecular organization and structural conformation of LHCIIs on the chloroplast lipid. Then, the novel vis-PTIR technique shows it capability for ultra-sensitive nanoscale imaging and chemical analysis.This AFM-based approach is enhanced by both the gap plasmon and the instrumentation resonance that shows a high-spatial resolution and single-molecule layer sensitivity. Then, my following researches are focused on the protein aggregation and amyloid fibrils that are associated with various neurodegenerative diseases. The first research target is to investigate the environmental factors on protein aggregation kinetics and amyloid formation. We designed the experimental setup to highlight the influence of sedimentation, microgravity, hydrodynamic flow,air-water interface on the protein aggregation kinetics and distinct microscopic steps of aggregation.The results show that the interface promotes the primary nucleation and hydrodynamics enhances the secondary nucleation, whereas the sedimentation and microgravity contribute no significant impact on the aggregation kinetics. Similarly, to understand the polymorphism phenomenon encountered in the preceding research, we performed an additional experiment with well-controlled environmental kinetics. This environmental kinetics originated from the different combinations of hydrodynamics and interface. This experiment proves that the amyloid polymorphism is under the control of environmental kinetics, as well as the order-order transition among the polymorphs. This conclusion is expected to expand our understanding on fibrillization mechanism and also to show its significance in the biomaterial applications. Last, but not the least, we propose another possible mechanism of amyloid aggregation, hierarchically assembly model(HAM), that enables the protofilament intertwining to form higher-ordered mature fibrils. In this experiment, this novel intertwining model based on statistical result of AFM images, is verified with the modelling and multiple experimental evidences, that may enrich our current knowledge of fibrillization mechanism and mature fibril formation.In the end of this thesis, we briefly summarize the presented scientific works and their potential in the applications. In addition, we developed the perspective of these research in the future with several examples of the interesting topics.

EPFL2020

Interactions of silver and polystyrene nanoparticles with algae

Xiaomei Li

Nanoparticles have various physicochemical properties attributed by their small dimensions. The global production of nanoparticles lead to a raised concern for their environmental impacts. Algae are of highly ecological importance functioning as primary producers for almost all aquatic life. In the present thesis, interactions of nanoparticles with different fresh water algal strains were examined. First, the toxicity and uptake of citrate-coated silver nanoparticles (AgNP) and AgNO3 were examined in the alga Euglena gracilis, which has no cell wall but a pellicle. Secondly, to examine the role of algal cell wall in determining the particles interactions with algae, four strains were selected, including Euglena gracilis, Haematococcus pluvialis, and Chlamydomonas reinhardtii wild type and a cell wall free mutant. Their interactions with polystyrene nanoparticles (PSNP) of two sizes, 50 nm (PSNP50) and 500 nm (PSNP500), were investigated. Third, interactions of three differently coated AgNP with alkaline phosphatase (AP), an extracellular enzyme used for phosphorus acquisition, were assessed. The selected coatings were citrate (CIT), polyvinylpyrrolidone (PVP) and gelatin (GEL). Exposure to AgNP and AgNO3 for 1-2 hours led to decrease in photosynthetic yield, in a concentration-dependent manner, and changes in cell morphology in E. gracilis. Based on total silver added, AgNP were less toxic than AgNO3. Concentrations causing a 50% reduction in photosynthetic yield were 1.9 µM and 85 for AgNP and AgNO3, respectively. Damaging effects of AgNP were completely prevented by cysteine, suggesting that the toxicity of AgNP was mediated by Ag+ ions. Uptake studies showed that the maximal cell-associated silver was higher in AgNP compared to AgNO3, and the higher silver level was shown to correspond to particles adsorbed to the pellicle. By examining four algal stains, it was found that no strain internalized PSNP, emphasizing the role of algal cell walls as barrier for nanoparticle uptake. Interactions of PSNP with algae were found to be unique for each strain, and depend on particle size. PSNP50 were associated with E. gracilis cells displaying a non-homogenous distribution on pellicle. In H. pluvialis, PSNP50 distributed homogenously around the cells. The wild type and cell wall free mutant of C. reinhardtii cells exposed to PSNP50 were found to clump together packed in the extracellular polymeric substances (EPS). The particles were associated with the EPS. The larger PSNP500 were observed to interact only with the two C. reinhardtii strains. Taken together, these results indicate that the algal cell walls hinder the crossing of nanoparticles. Assessing the sorption of AP to AgNPCIT, AgNPPVP, and AgNPGEL showed that the physiochemical properties of both the particle coatings and the enzyme were determinant for the binding. The enzyme adsorbed to AgNPCIT and AgNPPVP, leading to a 10% and 70% coverage of the particle surface area, respectively. No adsorption was found in the case of AgNPGEL. The three types of AgNP decreased AP activity, however, the inhibitory effects only occurred when the AgNP were added after addition of the substrate to the enzyme, not vice versa. AgNO3 did not affect the AP activity. Thus, the results of this study indicate particle-specific effects due to interactions with the AP-substrate intermediate.

EPFL2015