Nutritional Effects on Insulin Signaling and Action

描述(由申请人提供)：本提案旨在阐明人类胰岛素抵抗的机制，特别是关于营养(过量和喂养不足)对胰岛素作用的影响。特别是，我们认为磷脂酰肌醇(PI)3-激酶亚单位表达的失衡是导致胰岛素抵抗的最早的生化变化。PI-3-激酶由一个调节亚基p85和一个催化亚基p110组成。正常情况下，调节亚基的存在多于催化亚基的存在。因此，在游离P85单体和P85-P110异源二聚体之间存在平衡，后者负责PI3-K的活性。P85表达的增加或减少使这种平衡向游离P85或P85-P100复合体倾斜。由于单体和异源二聚体竞争IRS蛋白上的同一结合部位，不平衡可能导致PI 3-激酶活性增加或降低。如果p85的表达能够在营养上得到增强，由此导致的p85/p110比率的变化可能是随后发生的胰岛素抵抗的最早表现。这也可以解释过度进食和体重增加如何引发胰岛素抵抗。我们推测，正常个体胰岛素靶组织中P85的表达可能受到营养因素的影响(过量喂养)，从而改变P85和P110之间的平衡，导致PI3-K活性降低，从而引发胰岛素抵抗。此外，改善胰岛素敏感性的营养干预(热量限制)应导致P85表达减少，P85/P110比率降低，PI 3-Kinase活性增强，胰岛素敏感性改善。为了探索这些假说，我们将解决以下特定目标：特定目标1：确定短期过量喂养和常量营养素组成对正常个体PI 3-激酶亚基表达、化学计量、PI 3-K活性和胰岛素作用的影响。具体目的2：确定急性热量限制和常量营养素组成对肥胖胰岛素抵抗个体PI 3-K亚单位表达、化学计量、PI 3-K活性和胰岛素作用的影响。具体目标3：确定长期低热量摄入、大量营养素组成和体重减轻对肥胖胰岛素抵抗个体PI 3-K亚单位表达、化学计量、PI 3-K活性和胰岛素作用的影响。最后，我们还将检查正常体重、胰岛素敏感者和肥胖、胰岛素抵抗者之间PI3-激酶亚单位表达和化学计量的基线差异。尽管胰岛素抵抗是一种明确的临床疾病，但其主要原因仍不清楚。在临床上，胰岛素抵抗是肥胖、2型糖尿病、高血压和代谢综合征的一种普遍状况和基本特征。胰岛素抵抗最严重的公共健康后果之一是它经常与心血管问题有关。我们认为，关于胰岛素抵抗是如何诱导的，我们可能有一些初步的线索。揭示胰岛素抵抗的机制将对糖尿病、肥胖症和代谢综合征领域产生巨大影响。

DESCRIPTION (provided by applicant): This proposal seeks to elucidate the mechnaism of insulin resistance in humans, specificially with regard to nutritional (over- and underfeeding) effects on insulin action. In particular, we believe that an imbalance in the expression of the subunits of phosphatidylinositol (PI) 3-kinase represents the earliest biochemical change leading to insulin resistance. PI 3-kinase consists of a regulatory subunit, p85, and a catalytic subunit, p110. Normally, the regulatory subunit exists in excess to the catalytic one. Thus, there exists a balance between the free p85 monomer and the p85-p110 heterodimer with the latter being responsible for PI 3-kinase activity. Increases or decreases in expression of p85 shift this balance in favor of either free p85 or p85-p100 complexes. Because the monomer and the heterodimer compete for the same binding site on the IRS proteins, an imbalance could cause either increased or decreased PI 3-kinase activity. If the expression of p85 can be enhanced nutritionally, the resultant changes in the ratio of p85 to p110 may be the earliest manifestation of ensuing insulin resistance. This can also explain how overfeeding and weight gain trigger insulin resistance. We hypothesize that the expression of p85 in the insulin target tissues of normal individuals can be influenced nutritionally (overfeeding), thus altering the balance between p85 and p110 and leading to reduced PI 3-kinase activity and triggering insulin resistance. Furthermore, nutritional interventions that improve insulin sensitivity (caloric restriction) should lead to a reduction in p85 expression, to a decrease in the ratio of p85 to p110, enhanced PI 3-kinse activity, and improved insulin sensitivity. To explore these hypotheses we will address the following specific aims: Specific Aim 1: To determine the impact of short-term overfeeding and macronutrient composition on expression of PI 3-kinase subunits, their stoichiometry, PI 3-kinase activity, and insulin action in normal individuals. Specific Aim 2: To determine the impact of acute caloric restriction and macronutrient composition on expression of PI 3-kinase subunits, their stoichiometry, PI 3-kinase activity, and insulin action in obese insulin resistant individuals. Specific Aim 3: To determine the impact of long-term hypocaloric intake, macronutrient composition, and weight loss on expression of PI 3-kinase subunits, their stoichiometry, PI 3-kinase activity, and insulin action in obese insulin resistant individuals. Finally, we will also examine the baseline differences in PI3-kinase subunit expression and stoichiometry between normal weight, insulin-sensitive individuals and obese, insulin-resistant individuals. Even though insulin resistance is a well-defined clinical condition, its primary cause remains unknown. Clinically, insulin resistance is a prevalent condition and a cardinal feature of obesity, type 2 diabetes mellitus, hypertension, and the metabolic syndrome. One of the most significant public health consequences of insulin resistance is its frequent association with cardiovascular problems. We believe that we might have some initial clues as to how insulin resistance is being induced. Unraveling the mechanism of insulin resistance would have an enormous impact on the field of diabetes, obesity and metabolic syndrome.