1a. Objectives (from AD-416):
1. Define the role and mechanisms of adipocyte death in obesity-associated inflammation and metabolic disorders using genetic and nutritional models of adipocyte growth and death. 2. Determine the role of the macrophage in modulating adipocyte death and associated adipose tissue inflammation using genetically altered animal models. 3. Determine the mechanisms by which alterations in Lipid Droplet (LD) proteins modulate lipolysis and risk of developing metabolic disorders. 4. To determine the role of acyl CoA-synthetase 5 in systemic metabolism.
1b. Approach (from AD-416):
The role of adipocyte death in obesity will be investigated using a combination of transgenic and knockout mouse models and bone-marrow transplantation in mice fed different diets to understand the influence of obesity. In vivo and in vitro studies will investigate glucose and insulin homeostasis complemented by histological, immunohistological, electron microscopic, gene expression, FACS analysis, adipocyte lipolysis and Akt signaling studies. For studies investigating lipid droplet proteins, we will use both adenovirus expression vectors and possibly transgenic animals to determine how alterations in expression and intracellular signaling regulate protein expression, metabolic pathways, and lipolysis in cultured cells and animals. Depending upon which tissue is studied, we will examine lipolysis and protein expression, alterations in cytokine, lipid accumulation, signal transduction pathways, and oxidative gene expression.
3. Progress Report:
This year our laboratory began to investigate the role of the protein, acyl CoA synthetase 5 (ACSL5) in whole body metabolism by beginning to characterize a line of ACSL5 knockout mice that we recently generated. Studies demonstrate that ACSL5 null mice are protected against diet-induced obesity. We have also demonstrated that these mice are protected against the development of insulin resistance and hepatic steatosis. We have begun to investigate the expression of genes in intestine, liver, and white and brown adipose tissue as one important approach to determining how ablation of acyl CoA synthetase 5 protects the development of diet-induced obesity and its metabolic consequences. We have continued to investigate the role of the proteins, fat specific 27 and perilipin 1 in adipose tissue lipid metabolism. To investigate how perilipin protein regulates adipose tissue metabolism we have performed proteomic studies. We have identified over 100 proteins that bind to perilipin 1 in the absence and presence of catecholamine stimulation of cyclic AMP dependent protein kinase A and lipolysis. We have found that perilipin1 binds to fat specific protein 1. Importantly we have detected differences in the proteins bound to perilipin1 depending upon catecholamine stimulation. We predict that proteins binding to perilipin1 with catecholamine stimulation will provide insights in pathways that promote breakdown of fat stored in adipocytes. In summary, our studies will provide important insights into regulation of storage of fat in adipocytes and delineate the mechanisms by which acyl CoA synthetase 5 protects against diet-induced obesity. These insights will lead to the development of nutritional and other therapeutic approaches to protect against the development of obesity and associated metabolic complications.
1. Loss of expression of the protein, perilipin 2 protects against diet-induced obesity. At the present time we do not fully understand the roles of various proteins in regulating obesity that occurs with high caloric diets. ARS funded researchers at JMUSDA-HNRCA at Tufts University at Boston, Massachusetts and colleagues in Denver, Colorado demonstrated that mice in which the protein, perilipin 2, is no longer expressed when provided with a high caloric diet eat significantly less food and are protected against the development of diet-induced obesity. These studies point to the expression of perilipin 2 as an important protein involved in the regulation of food intake that promotes obesity. By defining the actions of perilipin 2 on food intake we will be able to develop new dietary and therapeutic strategies to protect against diet-induced obesity and its complications.