Endoplasmic reticulum (ER) stress has recently been implicated as a cause for obesity associated insulin resistance and inflammation based on the observation that ER stress can be demonstrated in liver and adipose tissue of rodent models of genetic and diet induced obesity and in subcutaneous (sc) fat of obese human subjects. The cause for this obesity associated ER stress, however, is not known. We have found in preliminary studies, that IV infused macronutrients (glucose and lipid) produced ER stress in human subcutaneous (sc) adipose tissue. This suggested that the ER stress in human adipose tissue can be acutely induced by macronutrients.
The specific aims of this proposal are to test the hypotheses 1) that the 3 macronutrients, carbohydrates, lipid and amino acids can produce ER stress in human sc adipose tissue, 2) that the macronutrient induced ER stress is calorie/energy dependent;and 3) that larger macronutrient loads (>3,000 Kcal/10 h) will activate IRE-1, the proximal ER stress sensor, which is connected to activation of stress kinases (including JNK and p38 MAPK) which are known to inhibit insulin signaling and stimulate synthesis and release of proinflammatory cytokines. We will test these hypotheses by assessing the effects of glucose, lipids and amino acids infused IV at increasing rates (ranging from 900-3,600 Kcal over 10 h) and of mixed meals ingested orally, on protein transcription, translation and post-translational modification of ER stress related proteins and on stress kinases and proinflammatory cytokines in sc adipose tissue biopsy samples obtained before and after these studies. Collectively, these studies will enhance our understanding of the effects of excessive nutrient intake, and specifically of differences in excessive intake of different macronutrients, on ER stress, insulin resistance and inflammation which are important contributors to the development of heart attacks, strokes and peripheral vascular disease.
Obesity is tightly linked to insulin resistance (IR) and inflammation (IF). Both contribute to the development of type 2 diabetes, hypertension, dyslipidemia and disorders of coagulation and fibrinolysis, all of which are independent risk factors for heart attacks, strokes and peripheral arterial disease. Therefore, it is important to understand how obesity is linked with IR and IF. In the proposed studies we will examine how excess nutrient intake, the major cause for obesity, can acutely produce IR and IF.
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