Micro-environnement tumoral | EPFL Graph Search

lien=//upload.wikimedia.org/wikipedia/commons/thumb/0/04/Tumor_microenvironment.jpg/220px-Tumor_microenvironment.jpg|vignette| Plusieurs facteurs déterminent si les cellules tumorales sont éliminées par le système immunitaire ou échappent à sa détection. Le microenvironnement tumoral (TME, pour tumor microenvironment) est l'environnement autour des cellules tumorales qui comprend des vaisseaux sanguins des cellules immunitaires, des fibroblastes, des molécules de signalisation et la matrice extracellulaire (MEC). Les tumeurs se définissent par la somme d'un microenvironnement tumoral et de cellules tumorales. Les cellules tumorales et le microenvironnement tumoral sont étroitement liés et interagissent en permanence. Les cellules tumorales peuvent influencer le microenvironnement en libérant des signaux extracellulaires, en favorisant l'angiogenèse tumorale et en induisant une tolérance immunitaire périphérique, tandis que les cellules

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

Molecular and Functional Characterization of Clonogenic Human Thymic Epithelial Cells

Melissa Maggioni

The thymus is a primary lymphoid organ where bone marrow derived T-cell progenitors come in contact with a unique microenvironment able to sustain their maturation into functional T-cells. This fundamental immunological function of the thymus is supported by thymic epithelial cells, which represent the main component of the thymic stroma. The thymic stroma is organized in a characteristic tridimensional structure that can be distinguished into two main regions, namely, the cortex and medulla. These two regions are responsible for two fundamental processes in the thymus: the positive- and negative- selection of T-cells. The first one involves the selection of T-cells able to react with antigens presented mainly on the surface of cortical cells. T-cell negative selection, meanwhile, is responsible for the elimination of self-reactive T-cells and it is mainly carried out by medullary thymic epithelial cells. The thymic epithelium derives from the primitive endoderm and cortical and medullary thymic epithelial cells have been demonstrated to originate from a common embryonic progenitor population. Currently, the presence of such population has not been described in adult animals and the mechanisms responsible for the maintenance of the post-natal thymus have yet to be clarified. Recently, Bonfanti and colleagues demonstrated that the rat thymus contains a population of clonogenic epithelial cells (rTECs), able to self-renew in the culture system developed in 1975 for epidermal stem cells [Bonfanti et al., 2010, Rheinwald and Green, 1975]. As clonogenicity is a property of skin and other stratified epithelia stem cells, the clonogenic capacity of TECs suggests them as potential thymic epithelial stem cells. Bonfanti and colleagues also demonstrated that rTECs displayed the capacity to integrate into a thymic microenvironment and to express thymic functional markers. The work described in this thesis aims to investigate the stem cell potency and the regenerative capacity of the human thymus. We demonstrated that the human thymus also contains a population of clonogenic thymic epithelial cells (hTECs) able to self-renew and to maintain a general thymic phenotype in the culture system used for skin stem cells and for rTECs. By clonal analysis, we showed that hTECs can be distinguished in three sub-populations, which displayed different molecular phenotypes and different growth and differentiation potentials in vitro. We then investigated the role of Foxn1 transcription factor in hTECs, as Foxn1 is know to be involved in thymic epithelial cells differentiation during development and also in the maintenance of the adult thymus in mice. By experimentally down-regulating Foxn1, we demonstrated that Foxn1 expression is required to sustain the growth of one of the described hTEC sub-populations. We next investigated the differentiation capacity of clonogenic hTECs. Currently, additional experiments are still required to assess hTECs ability to integrate and differentiate in a functional thymic environment. Bonfanti and colleagues also demonstrated that rTECs, if challenged in a hair follicle morphogenetic assay, can be reprogrammed into skin stem cells. Therefore, we decided to investigate the potential of hTECs in an epidermal differentiation assay. In these conditions, hTECs did not show the ability to differentiate into epidermis, probably due to the absence in this assay of the strong morphogenetic signals responsible for the reprogramming process of rTECs into skin stem cells.

EPFL2012