Metabolomics Approach to Study the Effect of Nutrient Overload on Metabolic Alterations and Insulin Secretion in Β Cells

Type 2 diabetes mellitus (T2DM) is characterized by development of insulin resistance and relative insulin deficiency. Normally, pancreatic β-cells are sensitive to changes in nutrient levels, and increase insulin secretion to meet the metabolic needs. Certain metabolites in β-cells, known as metabolic coupling factors, play essential roles in nutrient-induced insulin secretion. It is not completely understood how different nutrients affect metabolic coupling factors and how these factors interact in response to nutrients. In this proposal, we will apply a metabolomics approach to study the changes in metabolism including metabolic coupling factors of β-cells during nutrient-induced insulin secretion. During the early stage of diabetic progression, β-cells may compensate for insulin resistance through increase in insulin secretion capacity and hyperplasia/hypertrophy. The failure of β-cells to secrete insulin in the milieu of insulin resistance and hyperglycemia, and even the loss of β-cell mass, play important roles in T2DM pathogenesis. The mechanism underlying β-cell adaptation and failure is far from being completely understood. It has been hypothesized that nutrient overload, such as excessive amount of glucose or lipid, may cause glucotoxicity or lipotoxicity to β-cells and consequently their dysfunction. Another goal of our proposal is to study the effect of nutrient overload on metabolism of β-cells and isolated islets. The corresponding changes in physiology of such cells will also be examined. Moreover, we will use animal models of diabetes, and study the changes in metabolome of their islets during the progression of diabetes. Leucine, a branched-chain amino acids (BCAAs), is known to promote insulin secretion but dietary BCAAs are correlated with insulin resistance in several animal studies. The role of leucine in β-cell dysfunction and T2DM development will be examined. The db/db and control mice will be fed a diabetogenic/high fat or diabetogenic/high fat supplemented with leucine and then analyzed for any time-dependent changes in metabolome of islets and physiological parameters. The finding derived from β-cells/isolated islets study and animal models will help us to pinpoint specific changes in metabolic pathways in β-cells in response to excessive nutrients. It has been proposed that glucotoxicity or lipotoxicity may cause β-cell dysfunction via increase in oxidative stress. However, it appears that the role of oxidative stress is more complex than previously thought, reactive oxygen species (ROS) signaling is involved in glucose-stimulated insulin secretion (GSIS). In the present project, we will study the changes in oxidative stress marker in β-cells and islets, using aforementioned in vitro and in vivo models and to delineate whether redox status affect glucotoxicity- or lipotoxicity-induced β-cell dysfunction. Moreover, we will generate β-cell lines that over-express genes involved in antioxidative mechanisms, or express short hairpin RNA against them. These cells will be exposed to different nutrient load, and their metabolome and physiology will be studied. Furthermore, we will exogenously apply small molecular antioxidant(s) to cell culture or isolated islet systems, and examine their effect on metabolome and β-cell physiology. Through the present project, we will gain an insight into the role of β-cell dysfunction in T2DM progression.

Project ID:PC10708-1227
External Project ID:MOST107-2320-B182-030