Proefschrift Universiteit Maastricht. / Auteursnaam op omslag: Joep Brinkmann. Met bibliogr., lit. opg. - Met samenvatting in het Nederlands.

Gamma-interferon stimulates human macrophages to produce of 7,8-dihydroneopterin (7,8-NP). 7,8-NP and its oxidation product neopterin are excellent inflammatory markers for a variety of chronic conditions, including atherosclerosis. The biological significance of 7,8-NP in atherosclerosis is not fully understood, but 7,8-NP has been shown to protect macrophage cells from oxidised low density lipoprotein (oxLDL). Cellular accumulation of oxLDL-derived lipids and oxLDL-induced cytotoxicity are major drivers of atherosclerotic plaque progression. This thesis investigated the mechanisms of 7,8-NP-mediated protection against oxLDL-induced damage to macrophage cells. The research assessed the relative contribution of the previously identifyed antioxidant capacity of 7,8-NP and its ability to down-regulate oxLDL uptake. OxLDL cytotoxicity was characterised by high intracellular oxidative stress within the first 12 hours of exposure, which was critical to oxLDL toxicity. Exogenously added 7,8-NP effectively scavenged the intracellular oxidants generated in response to oxLDL, shown by the oxidation of 7,8-NP to neopterin. The ability of 7,8-NP to alleviate oxidative stress during the critical time-frame of acute toxicity was the primary mechanism of protection. 7,8-NP was also found to down-regulate the levels of intracellular oxysterol esters in oxLDL-treated macrophages. This decrease was associated with the reduction of CD36 scavenger receptor protein and mRNA expression. The late onset of these processes in the second half of the 24 hour incubation highlighted their potential role in foam cell formation. Research indicated that 7,8-NP may play a role in the reverse cholesterol transport in these cholesterol ester-loaded cells. The CD36 down-regulation by 7,8-NP did not protect macrophages from acute oxLDL cytotoxicity. This research reveals novel detail about the mechanism of 7,8-NP protection of macrophages from cytotoxic effects of oxLDL. It is suggested that 7,8-NP may protect macrophage cells in the atherosclerotic plaques by scavenging ROS produced during acute cytotoxicity and alleviate oxysterol ester accumulation, thus stabilising macrophage cells during chronic oxLDL exposure.

Assembly of intestinal chylomicron particles (lipid-protein complexes) is the fundamental mechanism by which we absorb dietary fat. Two intestinal lipid transporters, Cluster of Differentiation 36 (CD36) and fatty acid-binding protein 1 (FABP1), have been shown to play a role in lipid absorption, however, it remains unclear how knockdown of these proteins bleads to aberrant intestinal chylomicron secretion. In an enterocyte-like cell culture model, Caco-2 cells, we hypothesized that knockdown of CD36 or FABP1 using short-hairpin RNA interference techniques would impair triacylglycerol (TG) and apolipoprotein B (apoB) secretion. Surprisingly, knockdown of these lipid transporters lead to an increase in TG and apoB secretion that was associated with an increase in fatty acid synthase and fatty acid transport protein 4 (FATP4) protein levels. De novo fatty acid synthesis was slightly increased in CD36-, but not FABP1-knockdown Caco-2 cells. This study highlights the importance of fatty acid targeting in regulating chylomicron production.

Assembly of intestinal chylomicron particles (lipid-protein complexes) is the fundamental mechanism by which we absorb dietary fat. Two intestinal lipid transporters, Cluster of Differentiation 36 (CD36) and fatty acid-binding protein 1 (FABP1), have been shown to play a role in lipid absorption, however, it remains unclear how knockdown of these proteins bleads to aberrant intestinal chylomicron secretion. In an enterocyte-like cell culture model, Caco-2 cells, we hypothesized that knockdown of CD36 or FABP1 using short-hairpin RNA interference techniques would impair triacylglycerol (TG) and apolipoprotein B (apoB) secretion. Surprisingly, knockdown of these lipid transporters lead to an increase in TG and apoB secretion that was associated with an increase in fatty acid synthase and fatty acid transport protein 4 (FATP4) protein levels. De novo fatty acid synthesis was slightly increased in CD36-, but not FABP1-knockdown Caco-2 cells. This study highlights the importance of fatty acid targeting in regulating chylomicron production.

Thesis (Ph. D.)--Cornell University, May, 1998. / Vita. Includes bibliographical references (leaves 146-154).

Proefschrift Universiteit Maastricht. / Met bibliogr., lit. opg. - Met samenvatting in het Nederlands.

No description available.

Taste is a major driving force that influences food choice and dietary intake. Animals' taste abilities vary due to genetics, sex, age, and hormonal status. There is evidence that several appetite-regulating hormones can modulate gustatory detection of fat, and this hormonal modulation of fat taste likely influences food palatability and selection, thereby altering fat intake. Adiponectin is a key metabolic hormone predominantly released from adipose tissue, which enhances insulin sensitivity and stimulates glucose and fatty acid metabolism. Adiponectin receptors are highly expressed in the taste system, indicating that adiponectin signaling may play an important role in the modulation of gustatory function. The goal of this dissertation was to explore how adiponectin signaling affects fatty acid detection in the gustatory system, thereby potentially altering dietary fat intake. We investigated the effect of AdipoRon, an adiponectin receptor agonist, on taste cell responses to fatty acids, the prototypical stimuli for fat taste. The findings suggest that AdipoRon selectively enhances cellular responses to fatty acids but not to a mixture of sweet, bitter, and umami tastants by mediating the activation of AMPK and translocation of CD36 in immortalized human fungiform taste cells. Additionally, we examined the molecular mechanism underlying the physiological effects of adiponectin on fat taste in mice. Our results indicate that adiponectin/AdipoRon increases cellular responses to fatty acids by mediating the activation of AMPK and translocation of CD36 in isolated mouse taste bud cells via its receptor AdipoR1. Lastly, we evaluated how fat taste responses and dietary fat intake are altered when AdipoR1 is disrupted. We observed that disruption of AdipoR1 in mice altered the animals’ cellular and behavioral taste responsiveness to fatty acids in a sex-dependent manner; however, little or no effect on dietary fat intake was found. Together, these studies demonstrate that adiponectin/AdipoR1 signaling plays crucial sex-specific roles in the modulation of fat taste and the maintenance of healthy body weight, primarily by regulating energy expenditure rather than dietary intake in mice.

La thrombospondine-1 (TSP-1) est une glycoprotéine multi-modulaire exprimée de façon ubiquitaire qui régule de nombreux processus pathophysiologiques tels que l'adhérence cellulaire, la prolifération, l'apoptose, l'inflammation et les réponses cardiovasculaires. La TSP-1 est reconnue comme un acteur moléculaire majeur au sein du microenvironnement tumoral et constitue une cible de choix pour le développement d'agents thérapeutiques anti- cancéreux. L'interaction de la TSP-1 avec le récepteur membranaire CD47 est largement rapportée comme étant impliquée dans la progression tumorale et la mise en place d'une résistance aux traitements chiomiothérapeutiques. De ce fait, nous avons cherché à identifier et à caractériser un agent moléculaire novateur se comportant comme antagoniste sélectif de l'interaction TSP-1:CD47. Des expériences de docking protéine-protéine et de simulation moléculaire ont été réalisées afin de concevoir un nouveau peptide dérivé du CD47, nommé TAX2. Le peptide TAX2 empêche l'interaction de la TSP-1 avec le CD47, comme cela a été confirmé par co-immunoprécipitation et test ELISA. De manière intéressante, le peptide TAX2 inhibe la migration des cellules endothéliales, la formation de structures multi- cellulaires de type capillaire ainsi que le développement de micro-vaisseaux à partir d'explants aortiques. De façon cohérente avec ces observations, nos résultats mettent en évidence que le peptide TAX2 promeut la liaison de la TSP-1 au sein de complexes moléculaires comprenant le récepteur CD36, et inhibe en conséquence la voie de signalisation associée au VEGF et au VEGFR2. Enfin, une approche d'imagerie multi-modale et multi-échelles combinant des marquages histologiques, l'analyse de la densité micro-vasculaire, des analyses d'imagerie de résonance magnétique et d'imagerie infra-rouge à transformée de Fourier, ainsi qu'un suivi longitudinal par micro-tomographie à rayons X a été conduite afin de quantifier l'angiographie tumorale in vivo. Les résultats obtenus chez la souris C57Bl/6 révèlent que des administrations intra-péritonéales du peptide TAX2 perturbent fortement le réseau vasculaire associé à la tumeur de mélanome et induisent une importante nécrose tumorale entrainant l'effondrement de la tumeur. De plus, nous avons démontré que le peptide TAX2 inhibe considérablement la dissémination métastatique sans affecter les organes sains. Nous avons donc identifié le premier antagoniste sélectif de l'interaction TSP-1:CD47 qui, en contournant le problème des molécules existantes ciblant aveuglément le CD47, présente des activités anti-angiogéniques, anti-tumorales et anti-métastatiques in vivo qui pourraient à terme fournir de nouvelles approches thérapeutiques en pathologie tumorale. / Thrombospondin-1 (TSP-1) is a ubiquitously expressed multi-modular glycoprotein involved in many pathophysiological processes including regulation of cell adhesion, proliferation, apoptosis, inflammation and cardiovascular response. TSP-1 is recognized as a major molecular actor within tumor microenvironment and constitutes an exciting target for the development of useful therapeutic agents against tumorigenesis. TSP-1 binding to CD47 membrane receptors is widely reported to support tumor progression and may drive chemotherapeutic drug resistance. Thus, we sought to identify and characterize an innovative molecular agent acting as selective antagonist for TSP-1:CD47 interaction. Protein-protein docking and molecular dynamics simulations were conducted to design a novel CD47-derived peptide, called TAX2. TAX2 prevents TSP-1 binding to CD47, as revealed by ELISA binding assays and co-immunoprecipitation experiments. Interestingly, TAX2 inhibits endothelial cell migration, formation of multi-cellular capillary-like structures and sprouting of microvessels from aortic explants. Consistently, our data highlighted that TAX2 peptide promotes TSP-1 binding to CD36-containing complexes, leading to disruption of VEGF/VEGFR2 signaling. Furthermore, a multi-modal and multi-scale imaging approach was conducted combining histopathological staining, tumor-associated microvessel density, magnetic resonance imaging analysis, Fourier transform infrared imaging and micro-computed tomography monitoring for 3D quantification and longitudinal follow-up of tumor angiography in vivo. The results obtained from C57Bl/6 mice revealed that intraperitoneal administration of TAX2 highly disturbs melanoma tumor vascularization network, inducing an extensive tumor necrosis and subsequent tumor collapse. Furthermore, we demonstrated that TAX2 drastically inhibits the melanoma lung metastases dissemination without affecting healthy organs. Overall, we designed the first selective antagonist for TSP-1:CD47 interaction. By bypassing the problem of existing molecules blindly targeting CD47, we revealed that TAX2 exhibits anti- angiogenic, anti-tumor and anti-metastatic activities in vivo that could supply new innovative therapeutic approaches against malignant diseases.

L'obésité est devenue l'un des problèmes de santé publique les plus importants de ce siècle. Un certain nombre de facteurs génétiques et environnementaux contribuent au développement de cette pathologie. L'apport alimentaire quotidien est également l'un des facteurs cruciaux. Une consommation excessive de graisse alimentaire a été jugée essentielle dans le développement de l'obésité. Au cours des deux dernières décennies, plusieurs études ont montré que la détection de graisse orale joue un rôle important dans le développement de l'obésité. Pour prouver une relation entre l'obésité, la détection de graisse orale et les polymorphismes génétiques, nous avons recruté des enfants, des adolescents et des sujets adultes de trois populations différentes. À ce jour, le gène CD36 code le récepteur du goût gras le plus prometteur. De plus, nous avons étudié une relation possible entre le goût gras et le goût amer. Les résultats globaux montrent que les goûts amers et gras sont modifiés chez les personnes obèses. De plus, les polymorphismes CD36 ont une influence significative à la fois, la détection orale et l'obésité. Nos résultats pourraient aider à mieux comprendre une relation entre l'obésité, le goût et les polymorphismes génétiques. / Obesity has become one of most important public health issue in this century. A number of genetic and environmental factors contribute to development of this pathology. Daily dietary intake is also one of the crucial factors. Excessive dietary fat intake has been shown to be critical in the development of obesity. In the last two decades, several studies have shown that oral fat sensing plays an important role in the development of obesity. To prove a relationship between obesity, oral fat sensing and genetic polymorphisms, we recruited children, adolescents and adult subjects from three different populations. To date, CD36 gene encodes the most promising fat taste receptor. Furthermore, we studied a possible relationship between fat taste and bitter taste. Overall results show that bitter and fat tastes are altered in obese individuals. Moreover, CD36 polymorphisms have a significant influence in both, oral sensing and obesity. Our results might help better understand a relationship between obesity, taste and genetic polymorphisms.