Conclusions/interpretation Taken together, circulating MBL levels are associated with diabetic nephropathy and are dependent on glycaemic control, possibly in an MBL2-genotype-dependent manner.
The transforming growth factor (TGF)-_ signalling pathway plays a major role in angiogenesis. Aberration of the TGF-_ signalling cascade leads to abnormal remodelling and maturation of the... Show moreThe transforming growth factor (TGF)-_ signalling pathway plays a major role in angiogenesis. Aberration of the TGF-_ signalling cascade leads to abnormal remodelling and maturation of the primitive vascular plexus and decreased vessel wall integrity in adults. Targeted deletion of TGF-_ signalling receptors in mice, such as ALK1, ALK5, T_RII or endoglin, results in embryonic lethality due to impaired vascular development. In humans, mutations in ALK1, ALK5, T_RII or endoglin are associated with human vascular diseases such as HHT and pulmonary hypertension (PAH). Vascular endothelial growth factor (VEGF) is a multifunctional molecule that is involved in vascular growth and remodeling. Perturbation in VEGF signalling also contributes to the pathology of tumor angiogenesis and cardiovascular diseases in humans. This thesis is focused on the characterization of the crosstalk between the TGF-_ and VEGF signalling pathways, on EC function, the effect of bone morphogenetic protein (BMP)9 on EC function and the role of endoglin in VEGF-induced angiogenesis. The results of these studies may give us insights into the impacts/effects of these two angiogenic signalling cascades on EC function. This can be beneficial for the understanding of the etiology of certain vascular diseases and the development of new treatment modalities in the future Show less
Uveal melanoma (UM) is a disease with many faces: ophthalmologists treat the primary tumor, but the patient faces the problem of developing metastases, which are often deadly after a short period.... Show moreUveal melanoma (UM) is a disease with many faces: ophthalmologists treat the primary tumor, but the patient faces the problem of developing metastases, which are often deadly after a short period. Recent insight, indicates the need for knowledge-based treatment of UM. The __pseudohypoxic__ and tumor promoting effects of bevacizumab as described in this thesis is especially relevant. Bevacizumab is frequently used off-label to treat macular edema in UM patients suffering of radiation retinopathy, without the knowledge of possible effect on still viable UM cells. We further observed that specific peptides, such as UMAP1, which can successfully be internalized by targeted UM cells, have demonstrated potential for UM-targeted treatment. These peptides have to be investigated in vivo, to ascertain whether they are a viable clinical tool. Labeling the peptides with radionuclides, and demonstrating specificity for UM cells are some of the challenges which have to be overcome. Another aspect in the patient-specific treatment of UM is the in vitro analysis of primary UM samples to predict treatment responses. In case of Dasatinib, we describe treatment responses associated with monosomy 3 and __kinase__ activity in different primary UM samples. Show less
Estrogen is known to play an important role in longitudinal bone growth and growth plate maturation, but the mechanism by which estrogens exert their effect is not fully understood. In this thesis... Show moreEstrogen is known to play an important role in longitudinal bone growth and growth plate maturation, but the mechanism by which estrogens exert their effect is not fully understood. In this thesis this role is further explored. Chapter 1 contains a general introduction to longitudinal bone growth and the regulation of the growth plate in respect to relevant topics further studied in this thesis. Estrogen can act through a genomic or a nongenomic pathway. Both pathways are explored in rats at the onset of maturation in chapter 2. Estrogen stimulates VEGF expression in uterus and bone, which is an important growth factor for chondrocyte differentiation and chondrocytes survival in the growth plate. In chapter 3 the effect of estrogen on VEGF expression in the growth plate was studied in the rat and human growth plate. Another effect of estrogen is that it accelerates growth plate senescence. Senescence is one of the postulated intrinsic mechanisms by which the growth plate matures and finally fuses. In chapter 4 we investigated senescence in relation to proliferation, by investigating a cell cycle inhibitor p27Kip1. In animal models, catch-up growth is suggested to be caused by delayed growth plate senescence. In chapter 5 this hypothesis was further tested in humans. With puberty estrogen levels increase, the growth plate matures and at the end growth ceases with epiphyseal fusion through mechanisms not yet completely understood. In order to further explore growth plate maturation we subjected two growth plate tissues of the same patient, but with one year and one pubertal Tanner stage in between, to microarray analyses. Gene expression patterns and transcription factor binding sides in relation to pubertal maturation were studied in a longitudinal study within this single patient in chapter 6. In addition, we collected extra prepubertal and pubertal growth plate tissues and studied these samples with microarray techniques as well in chapter 7. In chapter 8 the process of epiphyseal fusion and apoptosis was studied in human growth plates. Animal models are frequently used but not fully representative for the human growth plate. Therefore we investigated a promising human in vitro model with multipotent mesenchymal stem cells (MSCs) that can differentiate into chondrocytes. MSCs can be isolated from various tissues. In chapter 9 we investigated the chondrogenic potential of MSCs from different origins and in chapter 10 we compared this model with the epiphyseal growth plate by analyzing gene expression patterns and pathways with micro-array analyses. Chapter 11 contains general conclusions and a discussion regarding the results. Show less
The tumour-microenvironment consists of malignant epithelial cells, surrounding cancer associated (myo-)fibroblasts, endothelial cells creating the tumours__ vasculature system and infiltrating... Show moreThe tumour-microenvironment consists of malignant epithelial cells, surrounding cancer associated (myo-)fibroblasts, endothelial cells creating the tumours__ vasculature system and infiltrating inflammatory cells. In this thesis we have studied how interactions between these cell types contribute to the initiation, progression and metastasis formation in gastrointestinal cancers. We have focused on how the availability of two important growth factors (Transforming Growth Factor-_ and Vascular Endothelial Growth Factor) in tumour angiogenesis and myofibroblasts differentiation is regulated by interactions between different cell types. First we revealed that active TGF-_1 levels are strongly increased in gastric and colorectal carcinomas and that they are indicative for the survival of these patients. In premalignant lesions increased activation is not yet observed. In addition we show that active TGF-_ levels are correlated with the number of myofibroblasts in colorectal carcinomas. Furthermore we reveal that interaction between colon cancer cells and cancer associated fibroblasts leads to increased TGF-_ activation, subsequent myofibroblast trans-differentiation accompanied by upregulation of TGF-_ expression and increased matrix metalloproteinase (MMP) secretion. To further evaluate how MMPs regulate tumour progression we have investigated their role in tumour-angiogenesis. We show that MMP-9, derived from tumour-infiltrating neutrophils, contributes to the angiogenic switch, by releasing tumour cell derived VEGF from the extracellular matrix. Finally, we show that tumour-angiogenesis requires endothelial MMP-7 expression and is regulated by MMP-14 dependent cleavage of the TGF-_ co-receptor endoglin on angiogenic endothelial cells. In conclusion, these studies show that interaction between tumour cells, fibroblasts and endothelial cells are important for the generation of myofibroblasts by TGF-_ activation and for the initiation of angiogenesis by regulating VEGF release. These data further validate the tumour-microenvironment as an important therapeutic target. Show less
Vascular maladaptation prior and during implantation may lead to serious complications during pregnancy, perinatally, but also later in life (Barker hypothesis). The consequences later in life... Show moreVascular maladaptation prior and during implantation may lead to serious complications during pregnancy, perinatally, but also later in life (Barker hypothesis). The consequences later in life often appear to be related to endothelial dysfunction. Angiogenesis, the formation of new blood vessels from pre-existing ones, is an important endothelial function and plays a key role in the process of implantation and placentation. Two epidemiological studies described here, show that myocardial infarction is related to low birth weight and that assisted procreation adversely affects birth weight. An optimal intra-uterine environment forms the basis for a good perinatal outcome and is created by a receptive endometrium in which angiogenesis is crucial. To study endometrial angiogenesis, human endometrial endothelial cells were isolated. The high expression of u-PA by these cells was found to contribute to their high angiogenic properties. Furthermore, these cells depend on MT3-MMP to form tubes. The ovarian steroids overall regulate endometrial angiogenesis indirectly via the endometrial stromal cells. During implantation, the embryo takes over as the main (local) regulator by inducing angiogenesis at its implantation site through the expression of VEGF. These results provide more insight in the (patho-)physiology of endometrial angiogenesis and in the role of the embryo in this. Show less
This thesis describes several topics on angiogenesis and screening in uveal melanoma, the most frequent eye tumour in adults. The expression of vascular endothelial growth factor and other... Show moreThis thesis describes several topics on angiogenesis and screening in uveal melanoma, the most frequent eye tumour in adults. The expression of vascular endothelial growth factor and other angiostimulating factors in this tumour are described. In a second part, the use of different screening tests in screening for metastases of uveal melanoma is investigated. Show less
