Adipose tissue derived factors in obesity, inflammation & energy homeostasis

Obesity is the foremost contributory factor in the progression to type 2 diabetes mellitus (T2DM). Moreover, chronic inflammation, through activation of innate immunity is proposed to link obesity, insulin resistance and T2DM. Adipose tissue, traditionally considered a storage compartment for triglycerides, also functions as an active endocrine organ. Adipocyte-secreted products, termed adipokines, may link obesity-associated inflammation and insulin resistance. Adipokines exert multiple effects on insulin sensitisation, glucose homeostasis, inflammatory processes or central systems mediating energy expenditure. This thesis principally examined two adipokines; resistin and adiponectin. Resistin and components of innate immunity were assessed in human obesity. In-vitro analysis established that resistin was expressed and secreted by human adipocytes. Furthermore, key factors in the innate immune pathway were highly expressed in obese and T2DM adipose tissue. This thesis further explored the pro-inflammatory actions of resistin in adipocytes. Resistin stimulated the secretion of inflammatory cytokines from adipocytes and, the expression of key intermediates of the innate immune and insulin signalling pathways. Clinical studies entailed examination of resistin as a marker of inflammation in childhood obesity. Serum analysis revealed gender-differences in resistin levels in obese children. Furthermore, bacterial endotoxin correlated with several markers of inflammation and cardiovascular disease; suggesting endotoxin as a contributor to inflammation in childhood obesity. This thesis subsequently examined another adipokine, adiponectin; considered to have a `ying-and-yang' relationship with resistin. Studies explored a central role for adiponectin in energy homeostasis. Gelfiltration liquid chromatography established that the adiponectin trimer was predominant in human cerebrospinal fluid. Such identification of trimeric adiponectin in vivo implicates the pharmacologically generated globular adiponectin in central regulation of energy expenditure. In conclusion, resistin may serve as a pathogenic pro-inflammatory factor, exacerbating inflammation within adipose tissue; potentially contributing to the progression of obesity-driven T2DM. Alternatively, adiponectin may have favourable central actions, influencing energy expenditure through its basic trimeric form. Collectively, this thesis suggests that resistin and adiponectin, with a range of opposing properties, may substantially affect whole-body metabolism.EThOS - Electronic Theses Online ServiceGBUnited Kingdo

Cyclin D1 Restrains Oncogene-Induced Autophagy by Regulating the AMPK-LKB1 Signaling Axis.

Autophagy activated after DNA damage or other stresses mitigates cellular damage by removing damaged proteins, lipids, and organelles. Activation of the master metabolic kinase AMPK enhances autophagy. Here we report that cyclin D1 restrains autophagy by modulating the activation of AMPK. In cell models of human breast cancer or in a cyclin D1-deficient model, we observed a cyclin D1-mediated reduction in AMPK activation. Mechanistic investigations showed that cyclin D1 inhibited mitochondrial function, promoted glycolysis, and reduced activation of AMPK (pT172), possibly through a mechanism that involves cyclin D1-Cdk4/Cdk6 phosphorylation of LKB1. Our findings suggest how AMPK activation by cyclin D1 may couple cell proliferation to energy homeostasis

Plasma Metabolomic Profiles Reflective of Glucose Homeostasis in Non-Diabetic and Type 2 Diabetic Obese African-American Women

Insulin resistance progressing to type 2 diabetes mellitus (T2DM) is marked by a broad perturbation of macronutrient intermediary metabolism. Understanding the biochemical networks that underlie metabolic homeostasis and how they associate with insulin action will help unravel diabetes etiology and should foster discovery of new biomarkers of disease risk and severity. We examined differences in plasma concentrations of >350 metabolites in fasted obese T2DM vs. obese non-diabetic African-American women, and utilized principal components analysis to identify 158 metabolite components that strongly correlated with fasting HbA1c over a broad range of the latter (r = −0.631; p<0.0001). In addition to many unidentified small molecules, specific metabolites that were increased significantly in T2DM subjects included certain amino acids and their derivatives (i.e., leucine, 2-ketoisocaproate, valine, cystine, histidine), 2-hydroxybutanoate, long-chain fatty acids, and carbohydrate derivatives. Leucine and valine concentrations rose with increasing HbA1c, and significantly correlated with plasma acetylcarnitine concentrations. It is hypothesized that this reflects a close link between abnormalities in glucose homeostasis, amino acid catabolism, and efficiency of fuel combustion in the tricarboxylic acid (TCA) cycle. It is speculated that a mechanism for potential TCA cycle inefficiency concurrent with insulin resistance is “anaplerotic stress” emanating from reduced amino acid-derived carbon flux to TCA cycle intermediates, which if coupled to perturbation in cataplerosis would lead to net reduction in TCA cycle capacity relative to fuel delivery

Genomic and Epigenomic Responses to Chronic Stress Involve miRNA-Mediated Programming

Stress represents a critical influence on motor system function and has been shown to impair movement performance. We hypothesized that stress-induced motor impairments are due to brain-specific changes in miRNA and protein-encoding gene expression. Here we show a causal link between stress-induced motor impairment and associated genetic and epigenetic responses in relevant central motor areas in a rat model. Exposure to two weeks of mild restraint stress altered the expression of 39 genes and nine miRNAs in the cerebellum. In line with persistent behavioural impairments, some changes in gene and miRNA expression were resistant to recovery from stress. Interestingly, stress up-regulated the expression of Adipoq and prolactin receptor mRNAs in the cerebellum. Stress also altered the expression of Prlr, miR-186, and miR-709 in hippocampus and prefrontal cortex. In addition, our findings demonstrate that miR-186 targets the gene Eps15. Furthermore, we found an age-dependent increase in EphrinB3 and GabaA4 receptors. These data show that even mild stress results in substantial genomic and epigenomic changes involving miRNA expression and associated gene targets in the motor system. These findings suggest a central role of miRNA-regulated gene expression in the stress response and in associated neurological function

Subcellular trafficking of the substrate transporters GLUT4 and CD36 in cardiomyocytes

Cardiomyocytes use glucose as well as fatty acids for ATP production. These substrates are transported into the cell by glucose transporter 4 (GLUT4) and the fatty acid transporter CD36. Besides being located at the sarcolemma, GLUT4 and CD36 are stored in intracellular compartments. Raised plasma insulin concentrations and increased cardiac work will stimulate GLUT4 as well as CD36 to translocate to the sarcolemma. As so far studied, signaling pathways that regulate GLUT4 translocation similarly affect CD36 translocation. During the development of insulin resistance and type 2 diabetes, CD36 becomes permanently localized at the sarcolemma, whereas GLUT4 internalizes. This juxtaposed positioning of GLUT4 and CD36 is important for aberrant substrate uptake in the diabetic heart: chronically increased fatty acid uptake at the expense of glucose. To explain the differences in subcellular localization of GLUT4 and CD36 in type 2 diabetes, recent research has focused on the role of proteins involved in trafficking of cargo between subcellular compartments. Several of these proteins appear to be similarly involved in both GLUT4 and CD36 translocation. Others, however, have different roles in either GLUT4 or CD36 translocation. These trafficking components, which are differently involved in GLUT4 or CD36 translocation, may be considered novel targets for the development of therapies to restore the imbalanced substrate utilization that occurs in obesity, insulin resistance and diabetic cardiomyopathy

Pathogens and host immunity in the ancient human oral cavity.

Calcified dental plaque (dental calculus) preserves for millennia and entraps biomolecules from all domains of life and viruses. We report the first, to our knowledge, high-resolution taxonomic and protein functional characterization of the ancient oral microbiome and demonstrate that the oral cavity has long served as a reservoir for bacteria implicated in both local and systemic disease. We characterize (i) the ancient oral microbiome in a diseased state, (ii) 40 opportunistic pathogens, (iii) ancient human-associated putative antibiotic resistance genes, (iv) a genome reconstruction of the periodontal pathogen Tannerella forsythia, (v) 239 bacterial and 43 human proteins, allowing confirmation of a long-term association between host immune factors, 'red complex' pathogens and periodontal disease, and (vi) DNA sequences matching dietary sources. Directly datable and nearly ubiquitous, dental calculus permits the simultaneous investigation of pathogen activity, host immunity and diet, thereby extending direct investigation of common diseases into the human evolutionary past

Getting ‘Smad' about obesity and diabetes

Recent findings on the role of transforming growth factor (TGF)-β/Smad3 signaling in the pathogenesis of obesity and type 2 diabetes have underscored its importance in metabolism and adiposity. Indeed, elevated TGF-β has been previously reported in human adipose tissue during morbid obesity and diabetic neuropathy. In this review, we discuss the pleiotropic effects of TGF-β/Smad3 signaling on metabolism and energy homeostasis, all of which has an important part in the etiology and progression of obesity-linked diabetes; these include adipocyte differentiation, white to brown fat phenotypic transition, glucose and lipid metabolism, pancreatic function, insulin signaling, adipocytokine secretion, inflammation and reactive oxygen species production. We summarize the recent in vivo findings on the role of TGF-β/Smad3 signaling in metabolism based on the studies using Smad3−/− mice. Based on the presence of a dual regulatory effect of Smad3 on peroxisome proliferator-activated receptor (PPAR)β/δ and PPARγ2 promoters, we propose a unifying mechanism by which this signaling pathway contributes to obesity and its associated diabetes. We also discuss how the inhibition of this signaling pathway has been implicated in the amelioration of many facets of metabolic syndromes, thereby offering novel therapeutic avenues for these metabolic conditions

Adipose tissue derived factors in obesity, inflammation & energy homeostasis

Obesity is the foremost contributory factor in the progression to type 2 diabetes mellitus (T2DM). Moreover, chronic inflammation, through activation of innate immunity is proposed to link obesity, insulin resistance and T2DM. Adipose tissue, traditionally considered a storage compartment for triglycerides, also functions as an active endocrine organ. Adipocyte-secreted products, termed adipokines, may link obesity-associated inflammation and insulin resistance. Adipokines exert multiple effects on insulin sensitisation, glucose homeostasis, inflammatory processes or central systems mediating energy expenditure. This thesis principally examined two adipokines; resistin and adiponectin. Resistin and components of innate immunity were assessed in human obesity. In-vitro analysis established that resistin was expressed and secreted by human adipocytes. Furthermore, key factors in the innate immune pathway were highly expressed in obese and T2DM adipose tissue. This thesis further explored the pro-inflammatory actions of resistin in adipocytes. Resistin stimulated the secretion of inflammatory cytokines from adipocytes and, the expression of key intermediates of the innate immune and insulin signalling pathways. Clinical studies entailed examination of resistin as a marker of inflammation in childhood obesity. Serum analysis revealed gender-differences in resistin levels in obese children. Furthermore, bacterial endotoxin correlated with several markers of inflammation and cardiovascular disease; suggesting endotoxin as a contributor to inflammation in childhood obesity. This thesis subsequently examined another adipokine, adiponectin; considered to have a `ying-and-yang' relationship with resistin. Studies explored a central role for adiponectin in energy homeostasis. Gelfiltration liquid chromatography established that the adiponectin trimer was predominant in human cerebrospinal fluid. Such identification of trimeric adiponectin in vivo implicates the pharmacologically generated globular adiponectin in central regulation of energy expenditure. In conclusion, resistin may serve as a pathogenic pro-inflammatory factor, exacerbating inflammation within adipose tissue; potentially contributing to the progression of obesity-driven T2DM. Alternatively, adiponectin may have favourable central actions, influencing energy expenditure through its basic trimeric form. Collectively, this thesis suggests that resistin and adiponectin, with a range of opposing properties, may substantially affect whole-body metabolism

MitoNEET- Parkin Effects in Pancreatic α- and β-Cells, Cellular Survival, and Intrainsular Cross Talk

Mitochondrial metabolism plays an integral role in glucose-stimulated insulin secretion (GSIS) in β-cells. In addition, the diabetogenic role of glucagon released from α-cells plays a major role in the etiology of both type 1 and type 2 diabetes because unopposed hyperglucagonemia is a pertinent contributor to diabetic hyperglycemia. Titrating expression levels of the mitochondrial protein mitoNEET is a powerful approach to fine-tune mitochondrial capacity of cells. Mechanistically, β-cell–specific mitoNEET induction causes hyperglycemia and glucose intolerance due to activation of a Parkin-dependent mitophagic pathway, leading to the formation of vacuoles and uniquely structured mitophagosomes. Induction of mitoNEET in α-cells leads to fasting-induced hypoglycemia and hypersecretion of insulin during GSIS. MitoNEET-challenged α-cells exert potent antiapoptotic effects on β-cells and prevent cellular dysfunction associated with mitoNEET overexpression in β-cells. These observations identify that reduced mitochondrial function in α-cells exerts potently protective effects on β-cells, preserving β-cell viability and mass