Chronic energy surplus causes obesity and promotes insulin resistance and type 2 diabetes (T2D). A major contributor to insulin resistance is chronic, low-grade inflammation in metabolic tissues,... Show moreChronic energy surplus causes obesity and promotes insulin resistance and type 2 diabetes (T2D). A major contributor to insulin resistance is chronic, low-grade inflammation in metabolic tissues, also coined metaflammation. In this context, white adipose tissue and liver-resident innate and adaptive immune cells produce proinflammatory cytokines that exacerbate inflammation and inhibit canonical insulin signaling. Among them, macrophages and dendritic cells were shown to play central roles in metaflammation, although the environmental and cellular changes dictating proinflammatory activation in the context of obesity are not fully understood. This thesis describes novel mechanisms by which macrophages and dendritic cells control metabolic homeostasis in obese mice. In addition, we show that immunomodulatory molecules derived from parasitic worm eggs promote an immune response in metabolic tissues that maintains insulin sensitivity. Finally, we describe the pleiotropic beneficial effects of a novel plant-derived nutritional supplement on metaflammation and metabolic homeostasis in obese mice. Altogether, this work may provide new leads for interventions aimed at improving immunological control of metabolic dysfunctions. Show less
Cardiovascular disease and diabetes are one of the leading causes of death worldwide. Multiple genetic and non-genetic factors play a role in this process. This dissertation aims to study the... Show moreCardiovascular disease and diabetes are one of the leading causes of death worldwide. Multiple genetic and non-genetic factors play a role in this process. This dissertation aims to study the interplay between genetic factors and lifestyle factors (eg sleep, nutrition, physical activity) with diseases such as cardiovascular disease and risk factors for cardiovascular disease (diabetes). For example, 12 blood biomarkers associated with insulin resistance have been identified, 5 of which are specifically much higher in subjects with diabetes. In addition, it appeared that a short sleep duration and poor sleep quality are associated with poorer lipids in the blood (eg cholesterol and LDL) and more insulin resistance. With regard to sleep, 59 new genetic variants have also been identified with regard to blood lipids (HDL, LDL, triglycerides). In addition, the results indicate that a better lifestyle can also help reduce the development of new cardiovascular diseases in people with an increased genetic risk. This is particularly interesting to prevent diseases in persons at high risk. All in all, this thesis has provided new insights into the various factors that are potentially important in the development of cardiovascular disease and diabetes. Show less
Obesity has a great societal impact as it contributes to the development of type 2 diabetes and cardiovascular diseases. Activation of brown adipose tissue (BAT) is seen as a strategy to combat... Show moreObesity has a great societal impact as it contributes to the development of type 2 diabetes and cardiovascular diseases. Activation of brown adipose tissue (BAT) is seen as a strategy to combat adiposity and related disorders, because of its capacity to combust nutrients and increase energy expenditure. To develop novel BAT activating methods, a better understanding of the pathophysiology of diet-induced obesity on BAT function and whole-body metabolism is required. Studies described in this thesis have increased our understanding of nutrient handling by brown adipocytes. We also generated immortalized brown adipocytes which can be used for future research. Furthermore, we gained more insight into the development of diet-induced obesity; feeding a high fat diet (HFD) rapidly made BAT insulin resistant and less active. In addition, HFD feeding increased synthesis of so-called endocannabinoids in both white and brown adipose tissue. Because endocannabinoids regulate both energy intake and expenditure, future research should determine whether inhibiting endocannabinoid signaling specifically in adipose tissue is a worthwhile strategy to pursue in combating obesity. Finally, quercetin, which naturally occurs in fruits and vegetables, induced ‘browning’ of white adipose tissue and thereby improved blood lipid levels. These studies pave the road for further development of BAT-activating strategies! Show less
The main objective of this thesis is to improve the understanding of the role of helminth infections in the development of insulin resistance, hence type 2 diabetes, and to gain insight into the... Show moreThe main objective of this thesis is to improve the understanding of the role of helminth infections in the development of insulin resistance, hence type 2 diabetes, and to gain insight into the immunological mechanisms underlying this possible interaction. To this end, we initiated a large scale cluster randomized controlled trial, assessing the effect of anthelmintic treatment on insulin resistance and other metabolic, as well as immunological parameters, in a rural area of Indonesia. Deworming significantly reduced the prevalence of helminths, as well as infection intensity. Although treatment did not lead to an increase of whole-body insulin resistance at the community level, a significant increase in insulin resistance was observed among helminth-infected subjects. Furthermore, by comparing immune cells of helminth-infected Indonesians before and after treatment, we gained insight into the specific cell populations that participate in the type 2 and regulatory networks, and show that treatment affects specific cell subsets in these networks. Altogether, the studies described in this thesis show that helminth infections in humans, as well as the administration of helminth molecules in obese mice, have a beneficial effect on the insulin sensitivity, and have shed light on the immunomodulatory effects of helminths. Show less
Metabolic disease has become pandemic in the developed world. Given our lack of understanding of its molecular pathology, we are often unable to diagnose patients before they reach an... Show moreMetabolic disease has become pandemic in the developed world. Given our lack of understanding of its molecular pathology, we are often unable to diagnose patients before they reach an irreversible state of diabetes or cardiovascular disease. Much research has been done on the role of insulin signaling in metabolic disease, as well as the resultant disturbed lipid homeostasis present in cardiovascular disease and atherosclerosis. Here we add to existing work by developing new tools and sketching out the pathology of dysregulated adipose insulin signaling. We discuss the mechanism of lipodystrophy by using adipocytes differentiated from patient-derived iPSCs. These cells mimic the clinical phenotype and hint at mechanism that reduced patients’ adipose tissue mass. In mice we find that if we knock out the adipose insulin receptor, there is disrupted adipose and liver metabolism. There is a protection from diet-induced obesity, but a dramatically reduced lifespan. We also establish a relationship between obesity and inflammation by transcriptomically assessing obese human adipocytes. We find that an immune factor is responsible for lipid droplet formation and content. Lastly, we develop a new differentiation and purification strategy for iPSC-derived hepatocytes, which we employ to in vitro model a SNP that protects against cardiovascular disease. Show less
The main objective of this thesis is to improve understanding of the role of helminth infections in the development of insulin resistance (IR), hence Type 2 Diabetes (T2D), in the light of... Show moreThe main objective of this thesis is to improve understanding of the role of helminth infections in the development of insulin resistance (IR), hence Type 2 Diabetes (T2D), in the light of increasing urbanization in Indonesia. Our large-scale cluster-randomized controlled trial was performed in a rural area of Indonesia, which is endemic for soil-transmitted helminth (STH), and has been previously reported to have a low prevalence of IR and T2D. In STH-infected subjects, as assessed by microscopy, 12-month anthelmintic treatment increased IR, which was mediated by an increase in BMI and leptin to adiponectin ratio, as well as reduction in eosinophil count. Next, we also aimed to assess the different metabolic profile between populations living in rural and urban area, and to study the relative protective effect of rural environment to high-fat diet (HFD). In comparison to those living in rural area, individuals living in urban area had higher whole body IR, which was mainly mediated by the higher adiposity and leptin level, which were progressively increased with increased duration of time spent in urban area. Different environmental factors (including past or current exposure to STH) did not seem to affect the metabolic response to HFD intervention, independent from adiposity. Show less
Overload of nutrients can lead to diet-induced inflammation, also called metabolic inflammation, which is thought to play an important role in many metabolic diseases, including the development of... Show moreOverload of nutrients can lead to diet-induced inflammation, also called metabolic inflammation, which is thought to play an important role in many metabolic diseases, including the development of nonalcoholic fatty liver disease (NAFLD). NAFLD encompasses a spectrum of pathologies that range from simple hepatic steatosis to nonalcoholic steatohepatitis (NASH) and fibrosis. The pathogenesis of NAFLD, including the sequence of events in time and the underlying mechanisms that initiate the transition from a fatty liver to NASH and fibrosis, remain poorly understood. Effective and reliable therapeutic approaches that are based on the understanding of the pathogenesis of NASH are therefore still lacking. In order to gain more insight into the mechanisms of NASH pathogenesis, we started with comparison of human NASH and experimental NASH. Subsequently, we provided evidence that activation of AP-1 and associated neutrophil infiltration is important for NAFL progression towards NASH and this can be induced experimentally by __metabolic__ dietary triggers of inflammation.Furthermore, we explored novel nutritional and pharmacological agents as potential strategies to combat NASH. Finally, we investigated the effects of high fat diet-induced metabolic overload on the liver in relation to inflammation in white adipose tissue and kidney, and the dysfunction of these tissues. Show less
Insulin-producing pancreatic _-cells are essential to maintain blood glucose levels within a narrow range. _-cells can adapt to an increased insulin demand by enhancing insulin secretion via... Show moreInsulin-producing pancreatic _-cells are essential to maintain blood glucose levels within a narrow range. _-cells can adapt to an increased insulin demand by enhancing insulin secretion via increased _-cell function and/or increased _-cell mass. Inadequate _-cell adaptation leads to hyperglycemia and eventually diabetes mellitus. Therefore, it is critical to understand how the _-cell mass is regulated. We investigated _- and _-cell adaptation in response to different metabolic changes. We found that _-cell adaptation in response to insulin resistance in mice, rats, and deceased organ donors was regionally heterogeneous throughout the pancreas. We also observed that the glucagon-producing _-cell mass adapts to metabolic changes, resulting in the maintenance of the _- to _-cell ratio. Furthermore, we show that treatment of normoglycemic mice with a glucagon-like-peptide-1 receptor agonist improved _-cell function and that this is associated with a decrease in _-cell mass in order to maintain normoglycemia. In mice fed a high-fat, low-carbohydrate ketogenic diet beta-cell adaptation failed, resulting in symptoms that are associated with diabetes in humans. Finally, we developed three high-throughput culture platforms for human islets to assess _-cell function that can be used in future studies to identify novel mechanisms involved in _- and _-cell adaptation. Show less
People of South Asian origin have an increased risk of developing type 2 diabetes (T2D) and cardiovascular disease (CVD) compared to people of Western European descent. Not only is the prevalence... Show morePeople of South Asian origin have an increased risk of developing type 2 diabetes (T2D) and cardiovascular disease (CVD) compared to people of Western European descent. Not only is the prevalence of these diseases higher in South Asians, they also occur at a younger age and lower BMI, and have a more severe course. The high prevalence of T2D and CVD in South Asians, who comprise one fifth of the total world__s population, poses a major health and socioeconomic burden worldwide. The underlying cause of this excess risk is, however, still poorly understood. The studies described in this thesis were performed to gain more insight in the pathogenesis of T2D and CVD in South Asians and to provide new leads for preventive strategies and treatment options. For this purpose sophisticated techniques were used such as hyperinsulinemic-euglycemic clamp with stable isotopes, indirect calorimetry, skeletal muscle biopsies, MRI and spectroscopy, and brown fat quantification using PET-CT-imaging, combined with short-term dietary interventions, in healthy lean young adult men and overweight adult men. These studies have led to a number of promising areas for further research. It seems that not one, but multiple metabolic mechanisms have been affected, most likely due to gene-environment interactions. Show less
The studies performed in this thesis show that type 1 diabetes mellitus is characterized not only by insulin deficiency, but also by insulin resistance. Both hepatic and peripheral insulin... Show moreThe studies performed in this thesis show that type 1 diabetes mellitus is characterized not only by insulin deficiency, but also by insulin resistance. Both hepatic and peripheral insulin sensitivity were decreased in patients with type 1 diabetes mellitus, as well as inhibition of lipolysis. However, insulin resistance is not a fixed pathophysiological condition in type 1 diabetes. We demonstrated that a single night of partial sleep deprivation decreased insulin sensitivity by 14-20% in patients with type 1 diabetes and by 20-25% in healthy controls. These effects of partial sleep restriction could not be explained by a reduction of total slow wave sleep in patients with type 1 diabetes. Sleep duration is a determinant of insulin sensitivity, also in patients with diabetes. In addition, various aspects of diabetes could be linked to increased prevalence of sleep disturbances. Impaired sleep and type 1 diabetes might potentiate each other in some patients, thereby creating a negative vicious circle. Optimizing sleep duration and sleep quality could therefore be considered as a potential therapeutic target to improve metabolic control in patients with type 1 diabetes. Show less
Sarcopenia in old age has been associated with a higher mortality, poor physical functioning, poor outcome of surgery and higher drug toxicity. There is no general consensus on the definition of... Show moreSarcopenia in old age has been associated with a higher mortality, poor physical functioning, poor outcome of surgery and higher drug toxicity. There is no general consensus on the definition of sarcopenia. The aim of the research presented in this thesis was to assess the implications of the use of different diagnostic criteria for sarcopenia, and to define the most accurate criteria for sarcopenia. Currently used diagnostic criteria for sarcopenia can be divided into criteria based on (1) low muscle mass, (2) low muscle strength, and (3) low walking speed. This thesis describes how muscle mass can be further divided into relative muscle mass and absolute muscle mass. A higher body or fat mass is associated with a lower relative muscle mass and with a higher absolute muscle mass. Higher relative muscle mass at old age is associated with better physical performance and with less insulin resistance. It is suggested to reserve the term sarcopenia to describe a low muscle mass and dynapenia to describe a low muscle strength. Most importantly, this research illustrates that it is impossible to compare studies about sarcopenia in scientific literature due to the use of different diagnostic criteria for sarcopenia. Show less
The metabolic syndrome is a multi-component condition that includes obesity hypertriglyceridemia and insulin resistance. The prevalence of the metabolic syndrome is rising world-wide and is... Show moreThe metabolic syndrome is a multi-component condition that includes obesity hypertriglyceridemia and insulin resistance. The prevalence of the metabolic syndrome is rising world-wide and is associated with an increased risk for the development of cardiovascular diseases and type 2 diabetes. In the past decades it has been discovered that obese persons have slightly elevated markers of inflammation in their plasma. This low-grade chronic inflammation, also called metabolic inflammation, is hypothesized to function as the link between the various components of the metabolic syndrome. In this thesis, it is evaluated how alterations in triglyceride (TG) and fatty acid (FA) metabolism and inflammatory pathways interact in the development of obesity and insulin resistance, which are both primary risk factors for the development of type 2 diabetes Show less
Extensive literature links the dopamine receptor D2 to insulin resistance and diabetes mellitus type 2. However, many aspects of the functional relationship remain unclear. In this thesis we... Show moreExtensive literature links the dopamine receptor D2 to insulin resistance and diabetes mellitus type 2. However, many aspects of the functional relationship remain unclear. In this thesis we focused on unraveling the characteristics of the interplay between dopamine D2 receptors and glucose metabolism as well as understanding the underlying mechanism(s). We evaluated the impact of DRD2 agonistic and antagonistic drugs on glucose and insulin metabolism in healthy volunteers, mice and INS-1E cells and we assessed dopaminergic parameters under different metabolic conditions. Our results show that altered dopaminergic parameters associated with obesity are due to mechanisms other than diet composition. But, changes in dopaminergic signaling may set the stage for metabolic corollaries of high fat feeding and may be involved in the beneficial impact of calorie restriction. We also demonstrate that inhibiting DRD2 activation may affect glucose homeostasis independent of body weight alterations. The underlying mechanisms include a reduction in physical activity and a direct effect on insulin sensitivity. In addition we provide evidence that inhibition of insulin secretion may, paradoxically, underlie the beneficial impact of DRD2 activation on glucose metabolism. We believe these findings may offer new ideas for strategies to prevent of treat diabetes mellitus type 2. Show less
This thesis shows the results of a 16-week very low calorie diet on insulin resistance, Quality of Life, low-grade inflammation and ectopic fat depositions
Type 2 diabetes mellitus has now become a global epidemic. The past decade hormones from the gastrointestinal tract have gained much interest as potential new therapeutic drugs in the battle... Show moreType 2 diabetes mellitus has now become a global epidemic. The past decade hormones from the gastrointestinal tract have gained much interest as potential new therapeutic drugs in the battle against this disease. Gut peptides play an important role in regulating food intake and energy homeostasis. In addition, they are able to impact on insulin sensitivity. In the present thesis we focused on modulation of insulin sensitivity by different gut hormones or their analogues. By means of the hyperinsulinemic euglycemic clamp technique we show that these gut hormones beneficially impact on insulin resistance. In addition, we show that these gut hormones can decrease body weight and inhibit lipid production, which are promising results since insulin resistance is a complex disease and is associated with obesity and cardiac disease. Also, we show that the hormone GLP-1 reduces endogenous insulin resistance via the brain. Over the past decade a growing amount of evidence indicates that the gut-brain axis is a key player in the control of glucose homeostasis. Elucidating more precisely the molecular events in the brain that underlie the effects of these hormones could lead to the identification of new (or improved) therapeutic agents. Show less
We have identified ATF2 as a component of the cellular and in vivo insulin signaling systems. Insulin induced ATF2-phosphorylation in A14 fibroblasts, 3T3L1-adipocytes and several mouse tissues in... Show moreWe have identified ATF2 as a component of the cellular and in vivo insulin signaling systems. Insulin induced ATF2-phosphorylation in A14 fibroblasts, 3T3L1-adipocytes and several mouse tissues in vivo. In cell lines, the insulin-induced ATF2-phosphorylation was dependent on cooperation between two Ras-dependent MAPK-pathways: ERK and p38/JNK. Analysis of several described ATF2-target genes identified insulin-induced expression of Egr1, ATF3, c-jun and SREBP1c as being ATF2-dependent in cell lines. These genes encode transcription factors whose targets have been postulated to be involved in several aspects of normal insulin action, like control of hepatic fat and glucose metabolism and proliferation and differentiation of beta-cells. Quantitative PCR analysis showed increased mRNA expression of these genes in mouse livers correlating with hepatic ATF2-phosphorylation induced by insulin, but also in response to HFD-induced insulin resistance. In addition, the known ATF2 target genes, the inflammatory cytokines IL1-beta and TNF-alpha were also significantly induced by the HFD in liver. Although the elucidation of the exact role of ATF2 activation under these conditions needs further experimentation, the data presented in this thesis suggest a potential dual function for ATF2 as a mediator of insulin action on the one hand and a putative regulator of the development or maintenance of insulin resistance and/or diabetes-associated complications on the other. Show less
Children born small-for-gestational-age (SGA) are at risk for short stature, and cardiovascular disease and type 2 diabetes in later life. There is some preliminary evidence for a similar phenotype... Show moreChildren born small-for-gestational-age (SGA) are at risk for short stature, and cardiovascular disease and type 2 diabetes in later life. There is some preliminary evidence for a similar phenotype in survivors of preterm birth. In contrast to children born SGA, preterm infants born appropriate-for-gestational-age who experienced neonatal growth retardation, resulting in a small size at term, are excluded from growth hormone therapy if they fail to catch up in height subsequently. We tested in 19-year-olds born before 32 gestational weeks from the Project On Preterm and Small-for-gestational-age infants cohort the effect of early growth on the growth pattern and adult metabolic health. Childhood growth and adult height were similar in preterm infants born SGA and those with neonatal growth retardation (weight and/or length at 3 months <-2 SD score). Young adults born preterm had a waist circumference and a waist-to-hip ratio much greater than the population reference mean, especially women. In addition, they showed a tendency towards insulin resistance and a high prevalence of hypertension. These findings were not explained by antenatal glucocorticoid treatment. Carriers of the 23K variant of the R23K polymorphism in the glucocorticoid receptor, associated with a mild glucocorticoid resistance, were less insulin-resistant and showed complete catch-up growth early in infancy and attained height was similar to the population reference mean, whereas stature in non-carriers was on average 0.5 SD below this mean Show less
In this thesis we focused on the causes and consequences of hepatic steatosis. Epidemiological studies in humans, as well as experimental studies in animal models, have shown an association between... Show moreIn this thesis we focused on the causes and consequences of hepatic steatosis. Epidemiological studies in humans, as well as experimental studies in animal models, have shown an association between visceral obesity and dyslipidemia, insulin resistance and type 2 diabetes mellitus. The mechanism underlying this association remains unclear. Recently, attention has focused on the role of excessive accumulation of triglycerides (TG) in the liver (hepatic steatosis) in this association. Hepatic steatosis was considered a benign condition until it was discovered that a nonalcoholic fatty liver is associated with many cardiovascular risk factors. Subsequently, many studies have shown a strong association between hepatic TG content and hepatic insulin resistance. The studies in this thesis show that hepatic steatosis is actively and passively involved in the metabolic disturbances in the glucose and lipid metabolism. The prevalence of hepatic steatosis in western countries is high and will certainly increase with the epidemics of obesity and diabetes. This will put an increasing number of subjects at risk for disturbances in the glucose and lipid metabolism and concomitantly for cardiovascular disease. Show less
