The regulation of fasting glucose metabolism in people with and without prediabetes

The overall aim of this application is to better understand the pathogenesis of fasting hyperglycemia and its contribution to the development of type 2 diabetes. Insulin and glucagon are the most important glucoregulatory hormones. There is evidence that both α-cells and β-cells (which secrete glucagon and insulin, respectively) can directly regulate (stimulate or inhibit) each other. In addition, both hormone systems alter glucose concentrations through effects on endogenous glucose production (EGP). Through these actions, insulin can indirectly affect glucagon secretion and vice versa. Dysfunction of these regulatory networks leads to prediabetes and, subsequently, to type 2 diabetes. However, the relative importance of these abnormalities, and how they interact to differentially affect fasting vs. postprandial glucose tolerance remains unknown. There is also controversy as to whether minute to minute variation in insulin secretion can control glucagon secretion and whether these pulse characteristics can serve as biomarkers of islet function. In this series of experiments, we will examine how glucagon directly, and indirectly through insulin, affects glucose metabolism. Conversely, we will examine how insulin directly, and indirectly through glucagon, alters glucose metabolism. Subsequently, we will use our novel methodology to measure islet hormone pulse characteristics to identify early defects in islet cell function. The proposed experiments will help elucidate the mechanisms by which fasting hyperglycemia develops in different subtypes of prediabetes thereby providing opportunities to individualize intervention. In addition, we will develop new methods to quantify fasting islet function and identify new biomarkers allowing early prevention and treatment of type 2 diabetes.