Discovery of A Novel Class of Naturally Occurring Lipids with Anti Diabetic and Anti inflammatory Effects
KEYNOTE ADDRESS Diabetes, Obesity and the Central Role of the Adipocyte in Maintaining Systemic Homeostasis Philipp E. Scherer, PhD Gifford O. Touchstone, Jr. and Randolph G. Touchstone Distinguished Chair in Diabetes Research University of Texas Southwestern Medical Center Epidemiologically, obesity is frequently associated with the metabolic syndrome and poses an increased risk for the development of type 2 diabetes and cardiovascular disease. However, the molecular links that connect the phenomenon of obesity per se with insulin resistance are not known. Uncontrolled expansion of adipose tissue, through an increase in both adipocyte size and number, is a hallmark of obesity. Over the past decade, a number of mechanisms have been proposed to explain the phenotypic changes associated with obesity related metabolic disorders. Among them, inflammation, lipotoxicity, fibrosis and the unfolded protein response (UPR) have attracted significant attention. Dysfunctional adipose tissue during states of nutrient excess can promote systemic insulin resistance. Under conditions of obesity, the ability of adipose to buffer excess nutrients is reduced and the secretion of inflammatory cytokines is increased. Importantly, secretion of the anti lipotoxic hormone adiponectin is lowered. Our work has further demonstrated that an enhanced capacity for lipid storage in adipocytes protects against metabolic disturbances, even in the context of massive nutrient excess, by over expressing adiponectin constitutively. We recently published an additional model in which we demonstrated that "the world's most obese mouse" can preserve perfect metabolic health, provided the fat expansion occurs in a "healthy" fashion, i.e. as a combination of enhanced adipogenesis, appropriate vascularization and reduced fibrosis and inflammation. This mouse also achieved its protective high level obesity through massive induction of adiponectin, downstream of altered mitochondrial function. An opposite phenotype can be observed in models of lipodystrophy, whereby the storage capacity of adipose is limited and adiponectin expression is completely ablated. Elevation of ceramide levels is believed to be central to the pathogenesis of diabetic complications. De novo ceramide synthesis begins with the condensation of palmitoyl CoA and serine, catalyzed by serine palmitoyltransferase (SPT) the rate limiting enzyme in ceramide production. Saturated long chain free fatty acids stimulate de novo ceramide synthesis by fueling the pathway with substrate and inducing expression of at least one biosynthetic enzyme (for instance, SPT) Numerous inflammatory agents increase ceramide accumulation, including LPS, and cytokines (TNFa, IL 1, and PAI 1) (reviewed in (32) Ceramidases catalyze the reversible deacylation of ceramide to generate sphingosine and free fatty acids. Recent data from the Lyons group, in addition to our own data, suggest that adiponectin receptors function to activate a neutral ceramidase activity. The sphingosine and sphinganine produced via ceramidase serve as substrates for sphingosine kinases, which produce the potently bioactive sphingolipid Sphingosine 1 phosphate (S 1 P) Ceramide has emerged as a key regulator of numerous cellular events, including the initiation of apoptosis and the inhibition of insulin action. We have demonstrated an essential role of adiponectin on cardioprotective actions in the context of caspase 8 induced cardiac myocyte cell death. Sphingolipid measurements are therefore an integral part of all the genetic manipulations that we perform, in order to gain a better understanding of the role of adiponectin on this important class of lipid effectors which play a central role in cellular homeostasis. Combined, it is apparent that adipocytes in whole, through their function as nutrient storage cells and as key endocrine cells, play a role in the pathogenesis of the metabolic syndrome, and moreover, have the capability to exert profound effects on whole body metabolism. Adiponectin is a central player in this process. ABSTRACTS SESSION IS SESSION I Adipose Tissue MicroRNAs Constitute a Major Fraction of Circulating Exosomal microRNAs and Modulate Hepatic mRNA Expression C. Ronald Kahn, Thomas Thomou, and Marcelo A. Mori C. Ronald Kahn, MD Mark K. Iacocca Professor of Medicine Harvard Medical School MicroRNAs (miRNAs) i.e. small non coding RNAs, are differentially expressed in different fat depots, regulated in obesity, and undergo a broad down regulation in adipose tissue with aging in a Dicer dependent manner. To better understand the role of altered miRNAs in fat we generated mice with a fat specific knockout of Dicer. ADicerKO mice developed a form of partial lipodystrophy with loss of intra abdominal and subcutaneous fat, increase and whitening of brown fat, insulin resistance and dyslipidemia. miRNAs are also found in the circulation, primarily in exosomes. To determine if adipose tissue contributes to the circulating miRNA pool and if changes in circulating miRNAs originating from fat tissue might have systemic effects by altering mRNA translation in distant cells and tissues, we isolated circulating exosomal miRNAs from serum of ADicerKO and control mice by differential ultra centrifugation. Profiling of exosomal miRNAs content by qPCR of all known miRNAs revealed a marked reduction in circulating miRNAs in the serum of ADicerKO mice. A subset of exosomal miRNAs was also reduced in human serum from HIV lipodystrophy patients (low Dicer expression) and from generalized lipodystrophy patients (very little fat tissue) when compared to healthy subjects. In addition, when ADicerKO mice received either a subcutaneous, brown or epididymal fat transplant from control mice, exosomal miRNAs were restored in the circulation of brown and subcutaneous transplanted ADicerKO mice suggesting that adipose tissue is a major source of exosomal circulating miRNAs. To test if these exosomal miRNAs could influence gene expression in secondary target cells, when we introduced miRNAs into adipocyte exosomes and co cultured those with hepatic cells, we observed miRNAdependent regulation of key hepatic metabolic regulators such as FGF 21. This could also be demonstrated in vivo using a FGF21 3'UTR reporter. Taken together these findings support the notion that adipose tissue constitutes a major contributor of circulating miRNAs, and that these miRNAs may exhibit specific mRNA regulatory effects on other cells and organs. Physiological Signaling by Adipose Tissue in Hunger and Energy Homeostasis Sadaf Farooqi, PhD, FRCP Professor of Metabolism and Medicine University of Cambridge The rising prevalence of obesity is driven by environmental factors such as changes in diet and levels of physical activity. However, within a given environment, some people develop severe obesity which is strongly influenced by inherited factors. To try to identify the genes and therefore the mechanisms involved in regulating weight, we have studied a cohort of individuals with severe, early onset severe obesity (n=6000) called the Genetics of Obesity Study (GOOS) Candidate gene studies in this cohort have led to the identification of patients with mutations in multiple genes involved in leptinmelanocortin signalling. Whole exome sequencing is proving to be an increasingly important tool in understanding the genetic heterogeneity associated with obesity leading to the discovery of multiple new genes. The discovery of how genetic variation at an individual and at a population level contributes to weight gain can drive further understanding of the molecular and physiological pathways involved in weight regulation and suggest targets for drug discovery and for therapeutic intervention. Discovery of A Novel Class of Naturally Occurring Lipids with Anti Diabetic and Antiinflammatory Effects MM Yorea, I Syeda, PM Moraes Vieirab, T Zhangb, MA Hermanc, E Homanc, J Lee, S Chen, OD Peroni, A Hammarstedt, R Patel, TE McGraw, U Smith, A Saghateliand and BB Kahnd (Same letter denotes shared authorship position. Barbara B. Kahn, MD George R. Minot Professor of Medicine Harvard Medical School and Beth Israel Deaconess Medical Center Increased adipose tissue (AT) lipogenesis is associated with enhanced insulin sensitivity. Mice overexpressing Glut4 in AT (AG4OX) have elevated AT lipogenesis and increased glucose tolerance in spite of obesity and elevated circulating fatty acids. To determine if the lipid profile contributes to improved glucose homeostasis in AG4OX, we performed untargeted lipidomic analysis of AT. This revealed a 16 18 fold increase in a novel class of lipids in AG4OX AT vs wildtype mice. Using a targeted Mass Spec approach, we identified 16 novel lipid family members with multiple isomers based on structural variations. These lipids are branched fatty acid esters of hydroxy fatty acids or FAHFAs. We studied the biologic effects of the isomers of palmitic acid hydroxy stearic acid or PAHSAs. PAHSAs are present at highest levels in brown and white adipose tissue with lower levels in many other tissues. PAHSA levels are acutely regulated by fasting. Most isomers are reduced 50 65% in serum and subcutaneous AT of insulin resistant vs insulin sensitive people. Nearly all isomers in humans correlate remarkably strongly with insulin sensitivity determined by euglycemic clamp. PAHSAs are also reduced in subcutaneous white AT in mice fed a High Fat Diet. A single oral dose of PAHSAs lowers ambient glycemia and enhances glucose tolerance in insulin resistant obese mice while stimulating GLP1 and insulin secretion. PAHSAs also augment insulin stimulated glucose uptake and Glut4 translocation to the plasma membrane in adipocytes. PAHSAs suppress inflammatory processes in immune cells in vitro and decrease proinflammatory cytokines in adipose tissue macrophages in vivo. Biological effects of PAHSAs are mediated through lipid responsive GPCRs. We have identified seve