2012 Annual Report
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.
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.
We had originally proposed to study a published mouse model, line of aP2-alpha2-AR transbeta3 AR-/- mice, which was reported to become obese due to increased numbers of small fat cells. In two separate studies, we were not able to replicate the results of the published study. In the meantime we have generated preliminary data in another line of mice, for which we have ablated the gene, acyl CoA synthetase 5 in all tissues in the mouse. Preliminary studies have shown that these mice are protected against the development of obesity and insulin resistance when fed a high fat, high sucrose diet.
Had proposed that Akt modifies perilipin at amino acid 385 (a serine) to regulate its expression. We continue to study the role of serine 385 in perilipin’s action to regulate fat cell metabolism, however we have been unable to demonstrate that serine 385 is important for perilipin protein expression. Over the course of the last year we have found that the protein, cavin1 regulates perilipin phosphorylation in response to catecholamines. Catecholamine mediated phosphorylation of perilipin is critical for its ability to regulate stimulated lipolysis.
Completed studies in mice, in which we have investigated the consequences of fat cell death on metabolic profiles and macrophage subtypes and are now analyzing the data. We have also found that obese individuals with increased accumulation of macrophages and inflammatory markers in subcutaneous fat also have increased abdominal and liver fat and alterations in insulin glucose homeostasis. Our observation suggests that increased inflammation in subcutaneous adipose tissue of obese people may contribute to the development of increased abdominal and liver fat and derangements in glucose-insulin homeostasis.
Additionally, we have completed studies where male and female mice were exposed prenatally to Bisphenol A, an environmental contaminant that can be consumed because of certain packaging of foods. In these studies we investigated the effects of low caloric and high caloric diets on body weight, body fat accumulation, accumulation of fat in the liver, and insulin glucose homeostasis. The results of these studies are presently being analyzed. Preliminary data suggests that perinatal exposure to BPA in male mice promotes insulin resistance, increased adiposity, and accumulation of triglyceride in the liver.
Further, we have been investigating the lipid droplet associated protein FSP27, developing tools to increase its expression or reduce its expression, and a protein that breaks down fat in hepatocytes called adipose tissue triglyceride lipase. As we noted last year, we completed studies on another protein, the ADRP protein, which like FSP27, is associated with lipid droplets and is thought to promote triglyceride accumulation. As a result of these ADRP studies we now understand the role of proteins such as ADRP and FSP7 in liver metabolism. We are currently investigating whether perilipin binds to FSP27 in adipocytes. We have found that the two proteins do bind to each other and importantly the presence of the two proteins results in a remarkable increase in the size of droplets that store fat. We are presently studying the interactions between these two proteins.
Immune cells in human fat predict increased fat in liver, abdomen, and altered blood glucose regulation. At the present time we do not understand why some obese people, but not others, have increased abdominal and liver fat and lose the ability to regulate blood glucose. ARS-funded researchers at JMUSDA-HNRCA at Tufts University, Boston, Massachusetts, in collaboration with University of Southern California Medical School performed fat biopsies on African-American and Hispanic obese young adults and correlated this to other measurements. We found that in both Hispanic and African-American males and females, the presence of specialized cells in fat tissue was associated with accumulation of fat in the liver as well as increased fat tissue within the abdomen. Additionally, we observed that the increase in immune cells in fat tissue correlated with decreased ability to regulate blood glucose. These outcomes provide us with a goal for future nutritional studies to identify food and diets that protect against the increase in immune cells in fat tissue protecting against the development of diabetes and increased fat accumulation in liver and fat.