The Heterogeneity of White Adipose Tissue

The increasing prevalence of obesity is a major factor driving the worldwide epidemic of type 2 diabetes and metabolic syndrome. Adipose tissue not only stores energy, but also controls metabolism through secretion of hormones, cytokines, proteins, and microRNAs that affect the function of cells and tissues throughout the body. Accumulation of visceral white adipose tissue (WAT) leads to central obesity and is associated with insulin resistance and increased risk of metabolic disease, whereas accumulation of subcutaneous WAT leads to peripheral obesity and may be protective of metabolic syndrome. While much attention has been paid to identifying differences between white, brown and brite/beige adipocytes, there is growing evidence that there is functional heterogeneity among white adipocytes themselves. This heterogeneity, includes depot-specific differences in development, inflammation, and endocrine properties. In addition to the depot-specific differences, even within a single fat depot, WAT is composed of developmentally and phenotypically distinct subpopulations of adipocytes. The following chapter will introduce this concept of white adipocyte heterogeneity

The Role of Cardiotrophin-Like Cytokine Factor 1 on the Development of Atherosclerosis

Le syndrome métabolique représente un problème majeur de la santé publique mondiale ; le taux augmente constamment en dépit de la technologie médicale innovante et des avancées thérapeutiques. Les maladies cardiovasculaires associées à la dyslipidémie demeurent la principale cause de décès et de morbidité à l'échelle mondiale en dépit d'une vaste recherche médicale et d'un large éventail de médicaments ciblant l'athérosclérose, l'obésité, le diabète, et autres. Des recherches récentes suggèrent l'existence et la persistance d'une inflammation de faible intensité dans la pathogenèse des pathologies comme l'athérosclérose et l'obésité. La « symbiose » entre le système métabolique et le système immunitaire est substantielle et toute perturbation contribue au développement des conditions métaboliques altérées qui aboutissent finalement à des troubles tels que l'obésité et l'athérosclérose. L'objectif général de ma maîtrise était de caractériser l'effet de la cardiotrophin-like cytokine factor 1 sur le développement de l'athérosclérose et de valider le dérivé de cardiotrophin-like cytokine factor 1 couplé avec le fragment Fc de l’immunoglobuline G qui possède une longue durée de vie. Cardiotrophin-like cytokine factor 1 est une cytokine du système immunitaire avec activité immunorégulatrice. Cardiotrophin-like cytokine factor 1 appartient à la famille d’interleukine 6. Cardiotrophin-like cytokine factor 1 est efficacement sécrétée en présence de cytokine receptor like factor 1, un récepteur soluble de la cytokine. Cardiotrophin-like cytokine factor 1 possède des activités neurotrophiques médiées par le récepteur du ciliary neurotrophic factor. Cardiotrophin-like cytokine factor 1 est également un ligand à haute affinité pour la sortiline. Des variantes du gène Sort1 codant pour ce récepteur ont été associés à l’hyperlipidémie et au risque d’infarctus du myocarde dans plusieurs études d’associations génomiques. Il a été observé que la cardiotrophin-like cytokine factor 1 lie et active les transfectants co-expriment de la sortiline et récepteur du leukemia inhibitory factor. Les deux récepteurs sont exprimés par les cellules myéloïdes et le récepteur du leukemia inhibitory factor est un puissant inducteur de la polarisation des macrophages de type M2 (anti-inflammatoire). L'objectif général du projet était d'étudier si la cardiotrophin-like cytokine factor 1 ou la cardiotrophin-like cytokine factor 1 couplée avec le fragment Fc interagiraient avec des macrophages des plaques d’athéroscléroses et réduirait la formation de cellules spumeuses et le développement de la plaque. Nos travaux montrent que l'expression de cardiotrophin-like cytokine factor 1 dans le modèle murin d’athérosclérose LDLR-/- ne diminue pas le développement de la plaque. Cependant, certains résultats ont révélé une contribution significative de la cardiotrophin-like cytokine factor 1 dans le gain de masse corporelle sans modification de l'apport calorique.Metabolic syndrome represents a major global health problem. Its rate is constantly increasing. Cardiovascular diseases emerging from dyslipidemia conditions are a worldwide leading cause of death and morbidity, despite extensive medical research and wide range of drugs targeting atherosclerosis, obesity, diabetes etc. Recent findings suggest the existence and persistence of low-grade inflammation in pathogenesis atherosclerosis and obesity. The “symbiosis” between metabolic and immune system is substantial and any perturbation contribute to the development of altered metabolic conditions that ultimately culminate in such disorders as obesity and atherosclerosis. The overall goal of my Master internship was to characterise the effect of cardiotrophin-like cytokine factor 1 on development of atherosclerosis and validate a long half-life derivative of cardiotrophin-like cytokine factor 1 coupled with Fc fragment of immunolglobulin G. Cardiotrophin-like cytokine factor 1 is a cytokine of the immune system with immunoregulatory activity. Cardiotrophin-like cytokine factor 1 belongs to the interleukin 6 family of monomeric cytokines. Cardiotrophin-like cytokine factor 1 is efficiently secreted in the presence of cytokine receptor like factor 1, a soluble cytokine receptor. Cardiotrophin-like cytokine 1 possesses neurotrophic activities mediated through the receptor of ciliary neurotrophic factor. Cardiotrophin-like cytokine factor 1 is a high affinity ligand for sortilin. Genome-wide association studies indicated that plasma low-density lipoprotein cholesterol levels and cardiovascular disease are associated with single nucleotide polymorphisms variants regulating sortilin expression. It was observed that cardiotrophin-like cytokine factor 1 binds and activates transfectants co-expressing sortilin and receptor of leukemia inhibitory factor. Both receptors are expressed by myeloid cells and leukemia inhibitory factor is a potent inducer of anti-inflammatory M2 macrophage differentiation. The overall objective was to investigate if the interaction of cardiotrophin-like cytokine factor 1 or cardiotrophin-like cytokine factor 1 coupled with Fc fragment of immunoglobulin G with atherosclerotic plaque macrophages will reduce the foam cell formation and development of plaque. Our work shows that cardiotrophin-like cytokine 1 expression in mice on LDLR-/- atherosclerosis model does not decrease the development of plaque. However, some results revealed a significant contribution of cardiotrophin-like cytokine factor 1 in gain of body mass without changes in food intake

High Density Lipoproteins: From Biological Understanding to Clinical Exploitation

Pharmacology/Toxicology; Molecular Medicine; Human Physiology; Immunology; Cell Biolog

The biochemical basis of disease

Understanding Biochemistry is an essential online resource for post-16 students, teachers and undergraduates, providing up-to-date overviews of key concepts in biochemistry and molecular biosciences. The Understanding Biochemistry issues of Essays in Biochemistry are Open Access publications, meaning that these issues are freely available online to readers This article gives the reader an insight into the role of biochemistry in some of the current global health and disease problems. It surveys the biochemical causes of disease in an accessible and succinct form while also bringing in aspects of pharmacology, cell biology, pathology and physiology which are closely aligned with biochemistry. The discussion of the selected diseases highlights exciting new developments and illuminates key biochemical pathways and commonalities. The article includes coverage of diabetes, atherosclerosis, cancer, microorganisms and disease, nutrition, liver disease and Alzheimer’s disease, but does not attempt to be comprehensive in its coverage of disease, since this is beyond its remit and scope. Consequently there are many fascinating biochemical aspects of diseases, both common and rare, that are not addressed here that can be explored in the further reading cited. Techniques and biochemical procedures for studying disease are not covered in detail here, but these can be found readily in a range of biochemical methods sources

Beyond the CNS: The many peripheral roles of APOE

Apolipoprotein E (APOE) is a multifunctional protein synthesized and secreted by multiple mammalian tissues. Although hepatocytes contribute about 75% of the peripheral pool, APOE can also be expressed in adipose tissue, the kidney, and the adrenal glands, among other tissues. High levels of APOE production also occur in the brain, where it is primarily synthesized by glia, and peripheral and brain APOE pools are thought to be distinct. In humans, APOE is polymorphic, with three major alleles (e2, e3, and e4). These allelic forms dramatically alter APOE structure and function. Historically, the vast majority of research on APOE has centered on the important role it plays in modulating risk for cardiovascular disease and Alzheimer's disease. However, the established effects of this pleiotropic protein extend well beyond these two critical health challenges, with a demonstrated roles for APOE across a wide spectrum of biological conditions, including adipose tissue function and obesity, metabolic syndrome and diabetes, fertility and longevity, and immune function. While the spectrum of biological systems in which APOE plays a role seems implausibly wide at first glance, there are some potential unifying mechanisms that could tie these seemingly disparate disorders together. In the current review, we aim to concisely summarize a wide breadth of APOE-associated pathologies and to analyze the influence of APOE in the development of several distinct disorders in order to provide insight into potential shared mechanisms implied in these various pathophysiological processes

The suitability and consequence of renal tubule specific adipose triglyceride lipase ablation for the study of targeted lipid accumulation in the kidney

Circulating non-esterified fatty acids (NEFA) rise during fasting and are taken up by the kidneys, either directly from the plasma or during re-uptake of albumin from glomerular filtrate, and are stored as triacylglycerol (TAG). Subsequent utilization of stored fatty acids requires their hydrolytic release from cellular lipid droplets, but relatively little is known about renal lipolysis.We found that total [3H]triolein hydrolase activity of kidney lysates was significantly increased by 15% in the fasted state. Adipose triglyceride lipase (Atgl) and hormone-sensitive lipase (Hsl) mRNA expression was time-dependently increased by fasting, along with other fatty acid metabolism genes (Ppar_, Cd36, and Aox). ATGL and HSL protein levels were also significantly induced (by 239 ± 7% and 322 ± 8%, respectively). Concomitant with changes in total protein levels, there was an increase in ATGL phosphorylation at the AMPK regulated serine 406 site in the 14-3-3 binding motif, and an increase in HSL phosphorylation at serines 565 and 660 that are regulated by AMPK and PKA, respectively. Using immunofluorescence, we further demonstrate nearly ubiquitous expression of ATGL in the renal cortex with a concentration on the apical/lumenal surface of some cortical tubules. Our findings suggest a role for ATGL and HSL in kidney lipolysis.3 year

Dyslipidemia

Dyslipidemia has a complex pathophysiology consisting of various genetic, lifestyle, and environmental factors. It has many adverse health impacts, notably in the development of chronic non-communicable diseases. Significant ethnic differences exist due to the prevalence and types of lipid disorders. While elevated serum total- and LDL-cholesterol are the main concern in Western populations, in other countries hypertriglyceridemia and low HDL-cholesterol are more prevalent. The latter types of lipid disorders are considered as components of the metabolic syndrome. The escalating trend of obesity, as well as changes in lifestyle and environmental factors will make dyslipidemia a global medical and public health threat, not only for adults but for the pediatric age group as well. Several experimental and clinical studies are still being conducted regarding the underlying mechanisms and treatment of dyslipidemia. The current book is providing a general overview of dyslipidemia from diverse aspects of pathophysiology, ethnic differences, prevention, health hazards, and treatment

The Role of Repin1 in Adipose Tissue

Since 1980 worldwide obesity has doubled in incidence to 52 % of people being overweight or obese. Obesity causes various comorbidities such as cardiovascular diseases, type II diabetes, dyslipidemia and several cancer types, making it one of the biggest challenges in worldwide health care systems. It is well known that obesity is highly heritable by either monogenetic causes or multifactorial interactions of different genes that superimpose on environmental factors and behavior. To answer questions in understanding mechanisms of obesity and/or associated metabolic pathways, mouse models have been a powerful tool. Several approaches in characterizing genes involved in obesity development through mouse engineering have been implemented, with the Cre/loxP system emerging as one of the most informative and widespread techniques. Using this approach, promoter-dependent temporal and tissue-specific regulated recombination can be achieved by Tamoxifen administration. To investigate effects of Tamoxifen on adipocyte biology in vivo, we characterized 12 weeks old male C57BL/6NTac mice after Tamoxifen treatment. We found that Tamoxifen treatment caused transient body composition changes, increased HbA1c, triglyceride and free fatty acid serum concentrations as well as smaller adipocytes in combination with browning of subcutaneous adipose tissue. Therefore, we suggest considering these effects when using Tamoxifen as a tool to induce conditional transgenic mouse models and to treat control mice in parallel. Another methodology used to identify genes involved in obesity related traits is QTL mapping in combination with congenic and subcongenic strains of mice or rats. One candidate gene that was previously identified on rat chromosome 4 is replication initiator 1 (Repin1 ). This gene was first described as a 60 kDa zinc finger protein involved in replication activation of the Chinese hamster dihydrofolate reductase (dhfr ) gene. Moreover, a triplet repeat (TTT) in the 3’UTR is associated with facets of the metabolic syndrome, including body weight, serum insulin, cholesterol and triglyceride levels. In vitro studies in 3T3-L1 cells revealed that Repin1 regulates adipocyte size, glucose transport and lipid metabolism. In this thesis functional analyses of Repin1 were performed using different Repin1 deficient mouse models. In the first study we generated a whole body Repin1 deficient db/db double knockout mouse (Rep1−/−x db/db) and systematically characterized the consequences of Repin1 deficiency. Our study provided evidence that loss of Repin1 in db/db mice improves insulin sensitivity and reduces chronic hyperglycemia most likely by reducing fat mass and adipose tissue inflammation. We next generated a liver-specific Repin1 knockout mouse (LRep1−/−) and could show that loss of Repin1 in liver leads to reduced body weight gain in combination with lower fat mass. Liver specific Repin1 deficient mice also show lower triglyceride content in the liver, improved insulin sensitivity and altered gene expression of genes involved in lipid and glucose metabolism. Finally, we inactivated the Repin1 gene in adipose tissue (iARep−/−) at an age of four weeks using Tamoxifen-inducible gene targeting strategies on a background of C57BL/6NTac mice. Mice lacking Repin1 in adipose tissue showed reduced body weight gain, decreased fat mass with smaller adipocytes, improved insulin sensitivity, lower LDL-, HDL- and total cholesterol serum concentrations and reduced expression of genes involved in lipid metabolism (Cd36 and Lcn2 ). In conclusion, the thesis presented here provides novel insights into Repin1 function. Moreover, the data clearly indicate that Repin1 plays a role in insulin sensitivity and lipid metabolism by regulating key genes involved in those pathways

Metabolic syndrome, the leptin gene and kidney disease in non-diabetic black South Africans

Includes abstract.Includes bibliographical references (leaves 226-256).Obesity is a worldwide problem and is a factor in the pathogenesis of the metabolic syndrome and kidney disease through the development of obesity-related hypertension and neurohormonal mechanisms that include the action of leptin. As there appear to be no focussed studies that have looked at the association of the LEP gene with kidney disease phenotypes or cardiovascular disease markers like hypertension, the metabolic syndrome and obesity, and especially so in native black Africans, this study sought to establish an association between the obesity gene (LEP) and kidney disease phenotypes (independent of diabetes and hypertension) in a homogenous black African population

Local Macrophage Proliferation in Adipose Tissue Is a Characteristic of Obesity-Associated Inflammation: A Dissertation

Obesity and diabetes are major public health problems facing the world today. Extending our understanding of adipose tissue biology, and how it changes in obesity, will hopefully better equip our society in dealing with the obesity epidemic. Macrophages and other immune cells accumulate in the adipose tissue in obesity and secrete cytokines that can promote insulin resistance. Adipose tissue macrophages (ATMs) are thought to originate from bone marrow-derived monocytes, which infiltrate the tissue from the circulation. Much work has been done to demonstrate that inhibition of monocyte recruitment to the adipose tissue can ameliorate insulin resistance. While monocytes can enter the adipose tissue, we have shown here that local macrophage proliferation may be the predominant mechanism by which macrophages self-renew in the adipose tissue. We demonstrated that two cell proliferation markers, Ki67 and EdU, can be readily detected in macrophages isolated from adipose tissue of both lean and obese mice. These analyses revealed that 2-4% of ATMs in lean and 10-20% of ATMs in obese mice express the proliferation marker Ki67. Importantly, Ki67+ macrophages were identified within the adipose tissue in crown-like structures. Similarly, a 3-hour in vivo pulse with the thymidine analog EdU showed that nearly 5% of macrophages in epididymal adipose tissue of ob/ob mice were in the S-phase of cell division. Interestingly, obesity increased the rate of macrophage proliferation in adipose tissue but did not affect macrophage proliferation in other tissues. We also used clodronate liposomes to deplete circulating monocytes in obese mice. Surprisingly, monocyte depletion for a total of at least 80 hours did not cause a decrease in ATM content in adipose tissue. Prolonged exposure of mice to EdU in drinking water revealed that approximately half of the ATMs in the epididymal fat pads of ob/ob mice had proliferated locally within 80 hours. Amazingly, these rates were the same with or without monocyte depletion, meaning that the proliferating cells were not freshly recruited monocytes. Overall, these results suggest that local proliferation unexpectedly makes a major contribution to maintaining the large population of macrophages present in the obese adipose tissue in the steady state. This suggests that increased rates of local macrophage proliferation may also be partly responsible for the massive increase in ATM content that occurs in obesity. This information could have implications for future therapeutic strategies in the management of diabetes