Adiponectin is an abundant hormone secreted by adipocytes that exhibits anti-diabetic, anti-inflammatory and anti-atherogenic properties. However, in obesity, as adipocytes enlarge, adiponectin secretion declines. A sex dimorphism is observed in adiponectin levels with women having higher levels than men. We hypothesized that a lack of adiponectin negatively affects both insulin sensitivity and adipose physiology in a sex-dependent manner. In this study, male and female adiponectin knockout or wild-type mice were fed with either a low fat or high fat diet. Male knockout animals were more glucose intolerant and had elevated fasting glucose levels. In contrast, both adiponectin knockout and wild-type females showed decreased hepatic lipid accumulation on a high fat diet. In both sexes, lean adiponectin knockout mice had significantly smaller fat depot weights and lesser hepatic lipid accumulation than the lean wild-type mice. However, on high fat diet, only male adiponectin knockout mice had fat depot weights that were comparable to wild-type mice, which indicate a novel sex-specific role of adiponectin in determining adiposity. / October 2016

Obesity and its associated metabolic complications are major burdens upon health systems globally highlighting the need for basic research into therapeutic targets to treat such disorders. The circulating hormone adiponectin has protective effects against several obesity-associated metabolic complications including insulin-resistance, hypertension and cardiovascular disease. Recent studies have elucidated the beneficial metabolic effects of adiponectin yet the molecular mechanisms behind its actions remain poorly characterised. The recent discovery of two receptors of adiponectin in 2003, AdipoR1 and AdipoR2, promises to further our understanding of how adiponectin mediates such effects. AdipoR1 and AdipoR2 are predicted to be seven transmembrane domain proteins (7TMs), however, they are considered unique to other 7TMs such as G-protein coupled receptors (GPCRs) since they have been shown to exhibit a reversed topology and also activate a distinct set of signalling molecules. Owing to their recent discovery and a lack of essential tools to permit basic research into adiponectin receptor (AdipoR) biology, our knowledge of these receptors remains extremely limited. The aim of this thesis was to generate tools and further characterise AdipoR structure and function in order to advance our understanding of how adiponectin’s effects are mediated. Early chapters in this thesis focus upon the generation and characterisation of fundamental molecular tools such as AdipoR mammalian expression plasmids and cell lines. Using these tools, we confirm that each AdipoR localises to the plasma membrane (PM) and does indeed possess a reversed topology to GPCRs; having an intracellular amino terminus and an extracellular carboxyl terminus. AdipoR1 and AdipoR2 are able to form both homo and hetero-multimers, as shown for numerous GPCR proteins, but neither receptor appears to be modified by N-linked glycosylation, a common modification of GPCRs. AdipoR-specific polyclonal antibodies were also generated and characterised in early chapters which allowed detection of endogenous AdipoR1 and AdipoR2 protein in multiple cell lines as well as primary human adipocytes. These studies revealed that AdipoRs are not only expressed in a variety of cell lines but also exhibit differential expression profiles suggesting AdipoR1 and AdipoR2 may mediate distinct functions of adiponectin. A major finding of this thesis was the discovery of a novel AdipoR1-interacting protein, ERp46. This is the first AdipoR1-specific interacting protein identified and only the second AdipoR-interacting protein described to date. ERp46 (also known as EndoPDI and pcTRP) has been previously described although knowledge of its function and cell biology is very limited. ERp46 co-immunoprecipitated with AdipoR1 in several different cell lines and showed no evidence of interaction with AdipoR2. Via immunofluorescence microscopy, ectopically expressed ERp46 localised to both the PM and intracellular structures, likely to be the endoplasmic reticulum (ER) whilst subcellular fractionation revealed that endogenous ERp46 localised to the ER-containing and PM-containing fractions in both HeLa and HEK cell lines. In silico analyses predict that ERp46 has a transmembrane domain and exhibits an extracellular / luminal carboxyl terminus, the latter of which was confirmed by immunofluorescence microscopy studies using epitope-tagged ERp46 constructs. Given that ERp46 primarily localises to the ER, we assessed whether ERp46 was involved in regulation of AdipoR trafficking. ShRNA knockdown of ERp46 resulted in increased AdipoR1 and AdipoR2 expression at the PM providing evidence to support a functional role in AdipoR biology. The presence of ERp46 at the PM, together with the data suggesting ERp46 regulates AdipoR subcellular localisation, led to studies investigating whether ERp46 contributes to adiponectin signalling. We demonstrate that adiponectin treatment results in the phosphorylation of key adiponectin targets (such as AMPK and p38MAPK) in HeLa cells and present data to support the requirement of ERp46 for specific adiponectin-induced signalling events. Furthermore, our studies show that ERp46 is not only involved in adiponectin-induced signalling but also in specific signalling events induced by insulin and epidermal growth factor (EGF) treatment. In summary, the work presented in this thesis confirms the findings of the initial publication in which the receptors were described and also identifies several novel features of the adiponectin receptors previously not reported. The identification of an AdipoR1-specific interacting protein that modulates both the localisation and signalling events of adiponectin is of particular interest. The data described in this thesis supports emerging evidence which suggests that AdipoR1 and AdipoR2 have distinct roles in adiponectin signalling and as such, this work has provided further insights into the mechanisms behind adiponectin action and provides a basis for future studies.

Dissertation (Ph.D.)--Auburn University, 2007. / Abstract. Vita. Includes bibliographic references.

No description available.

京都大学 / 0048 / 新制・課程博士 / 博士(社会健康医学) / 甲第22386号 / 社医博第108号 / 新制||社||医11(附属図書館) / 京都大学大学院医学研究科社会健康医学系専攻 / (主査)教授 中山 健夫, 教授 佐藤 俊哉, 教授 川口 義弥 / 学位規則第4条第1項該当 / Doctor of Public Health / Kyoto University / DFAM

Insulin resistance, the cause of type 2 diabetes mellitus, is intimately linked to the dysregulation of adipose tissue. Recent decades have witnessed the discovery and characterization of numerous hormones produced by adipocytes, including leptin, adiponectin and resistin, underscoring the endocrine functions of adipose tissue. To better understand the role of the adipocyte in the mediation of obesity-related insulin resistance and inflammation, this study has optimized the primary adipocyte isolation technique to minimize inflammation inherent to the isolation procedure and has analyzed adiponectin levels and insulin sensitivities of various adipocyte size populations both in vitro and ex vivo.The data described herein suggest that cell size plays an important, but not solitary, role in the regulation of insulin action and adiponectin production. It is possible that obesity-related insulin resistance is associated with the failure of a population of small adipocytes to expand and produce the insulin sensitizing protein hormone, adiponectin.

Thesis--Auburn University, 2005. / Abstract. Vita. Includes bibliographical references (leaves 76-90).

There is an ongoing worldwide obesity epidemic. As a consequence, prevalence of obesity- related diseases and conditions are rapidly increasing. One of these related conditions is type 2 diabetes (T2D), which alone caused 1.5 million deaths in 2012. Thus, it is of upmost importance to develop a more complete understanding of these interrelated diseases. At the heart of all these diseases lies the adipose tissue. This tissue is a major endocrine organ, and one of the key secreted cytokines is adiponectin. Adiponectin interplays with the complex insulin signaling network, and adiponectin levels are inversely related with increased adiposity. The presence of these complex dependencies argues for the usage of mathematical modelling. In the work of Brännmark et al, a model of short-term adiponectin release has been validated. However, this model did not include adrenergic signaling, which is the canonical pathway for in situ regulation of adiponectin secretion. To fill this gap, herein, a mechanistic model describing adrenaline-induced short-term adiponectin exocytosis in white adipocytes has been constructed. The newly constructed model is capable of describing experimental data depicting adiponectin release due to adrenergic stimulation as well as data for different mediator combinations. By implementing adrenergic receptor components, the transition to a more physiological model has been initiated. By finding the smallest possible model capable of describing data, one can argue that the model depicts, to some degree, the fundamental mechanisms for short-term adiponectin secretion. Thus, this work has contributed to solidifying the framework of the mechanisms behind short-term adiponectin secretion from white adipocytes. The result of the model work upholds the role of adrenergic signaling as a central regulatory mechanism for adiponectin release. The constructed model could be used as a fundament for creating a model describing adiponectin release under diabetic conditions.

No description available.

Endothelial dysfunction, or the inability of an artery to dilate sufficiently when subjected to excessive shear stress, serves both as a predictor of future cardiovascular events as well as an early indication of atherosclerosis. Several chronic disease states, including obesity, have been shown to alter endothelial function, which may be mediated through circulating pro- and anti-inflammatory adipokines. Still, the mechanisms by which obesity-related low-grade inflammation alters endothelial function are not fully elucidated. Acute and chronic endurance exercise training has previously been shown to be effective in improving endothelial function; however, chronic resistance exercise training is not universally regarded as beneficial to vascular functioning. Far fewer studies have examined the effect of acute resistance exercise on vascular function and adipokine release. To further understand the effects of resistance exercise training on vascular function, a meta-analysis was completed to examine the effects of resistance training on brachial artery flow mediated dilation (FMD), a common measure of endothelial function. The results of the meta-analysis indicate that resistance training has a small positive effect on FMD. Additionally, the effects of an acute bout of lower body resistance exercise on forearm blood flow (FBF) and two inflammatory cytokines were evaluated in obese (>30% body fat) and non-obese (≤30% body fat) subjects. It was hypothesized that the resistance exercise bout would increase FBF, that those changes would be greater in obese versus non-obese subjects, and that the changes in circulating cytokines (adiponectin and tumor necrosis factor-α) would be related to changes in FBF. The results indicate that FBF measures in obese and non-obese subjects react in a divergent pattern immediately following resistance exercise but return to baseline within 24 hours. These changes were not related to changes in adiponectin or TNF-α although changes in adiponectin were related to changes in TNF-α. In conclusion, resistance exercise training programs may have a small positive effect on vascular function which may reduce overall cardiovascular disease risk. Additionally, obese and non-obese subjects display differing patterns of vascular responses to an acute bout of resistance exercise, supporting the view that obesity, and its associated low-grade inflammatory response, may negatively alter vascular homeostasis.