Nutrient intake in excess of energy expenditure is a major contributing factor to the world-wide epidemic of obesity and type 2 diabetes. Traditionally nutrients have been considered to be precursors for the biosynthesis of macromolecules and as substrates for the production of molecules involved in energy metabolism. However, they are now understood to act through signal transduction cascades to regulate various cellular processes including protein synthesis. The nutrient-sensing pathways are not only interconnected at multiple levels but are tightly coupled to the insulin receptor signaling pathway. Thus, nutrient-sensing and insulin receptor signaling pathways do not function in isolation, but rather as components of a larger, integrated system of intracellular communication. The project proposed herein focuses on the liver, which is an especially important organ in regards to the body's response to nutrient intake because of its position in relation to the gastrointestinal tract, affording it immediate access to the products of digestion appearing in the portal vein. The project also focuses on protein synthesis because the liver, in combination with the gastrointestinal tract, accounts for 25% of the whole body protein synthetic response to a mixed meal. Finally, the project focuses on translational control mechanisms, an area of research for which the expertise of the PI's laboratory is well recognized and one becoming increasingly recognized as playing a prominent role in the regulation of gene expression. The project will employ non-diabetic and diabetic mice maintained on four different diets designed to increase both the fat and caloric intake. The hypothesis to be tested is that chronic nutrient excess and diabetes, alone and in combination, acting through translational control mechanisms, cause both global and specific changes in hepatic protein expression patterns that contribute to pathologies associated with maladapted metabolism. The hypothesis will be tested by pursuing the three following specific aims: (1) define the effects of different dietary regimens and diabetes, alone and in combination, on global and specific changes in protein expression patterns, the translational control mechanisms mediated by eIF2 and eIF4F, and the activation state of nutrient- sensing and insulin receptor signaling pathways in the liver of nondiabetic and diabetic mice;(2) quantitate expression of the mTORC1 repressor REDD1 in the liver of nondiabetic and diabetic mice in response to nutrient excess, define regulatory mechanisms contributing to its upregulated expression, and define its mechanisms of action;and (3) elucidate the signaling pathways and molecular mechanisms through which diabetes-induced hyperglycemia and nutrient excess mediate increased hepatic expression of the translational repressor 4E-BP1. Overall, the project is expected to produce new knowledge that will provide insight into designing strategies for the treatment of pathologies resulting from the maladapted whole body metabolism associated with obesity and diabetes.
Chronic intake of excess nutrients leads to accumulation of lipid in tissues, resulting in the development of insulin resistance and the pathological progression to type 2 diabetes and other metabolic diseases. The project proposed herein will employ a number of novel experimental models and specialized techniques to define effects of nutrient excess and diabetes, alone and in combination, on molecular events that modulate the pattern of protein expression in the liver. Knowledge gained from the project will provide insight into designing strategies for treatment of pathologies resulting from the maladapted whole body metabolism associated with obesity and diabetes.
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