Biochemical Mechanisms of In Vivo Insulin Resistance

描述(申请人提供)：在这个项目中，我们建议继续我们对获得胰岛素抵抗的生化机制(S)的研究。我们的长期重点一直是营养素供应和胰岛素作用之间的联系。在这一点上，瘦素在调节肝脏和外周胰岛素的作用中发挥作用。然而，调节这些效应的生化和神经回路仍有待阐明。在这里，我们希望验证瘦素通过两个主要的中枢成分对肝脏葡萄糖通量发挥快速作用的假设： A)STAT3依赖效应(主要导致糖异生和脂质氧化的快速刺激)； B)非STAT3效应(主要导致糖原分解和葡萄糖的快速抑制 输出)。 此外，下丘脑瘦素信号的激活时间更长，通过限制摄食行为、增加能量消耗和脂肪氧化以及改善胰岛素作用，来协调对营养过剩的生物反应。基于初步结果和这一总体目标，我们希望追求以下具体目标：1.瘦素是否通过激活下丘脑中的STAT3非依赖性通路来敏锐地调节肝脏的葡萄糖流量？我们将研究通过STAT3非依赖通路阻断下丘脑瘦素信号是否改变瘦素对肝脏营养通量的作用。2.瘦素是否通过激活下丘脑中STAT3依赖的通路来敏锐地调节肝脏的葡萄糖流量？我们将研究下丘脑STAT3或黑素皮质素途径中的快速“功能丧失”是否改变瘦素对肝脏营养流动的作用。3.当阻止下丘脑STAT3依赖途径的激活时，瘦素是否通过STAT3非依赖途径强烈抑制肝脏葡萄糖的产生？我们将研究依赖STAT3的下丘脑靶标瘦素的快速“功能丧失”是否揭示了瘦素对肝脏营养流动的“胰岛素样”作用。4.瘦素是否通过激活下丘脑STAT3依赖和/或非STAT3信号调节能量平衡和胰岛素作用？我们将研究通过选择性下游靶点对下丘脑瘦素信号进行长达一周的操作是否调节摄食行为、能量代谢和胰岛素敏感性。5.短期过量喂养如何改变下丘脑瘦素信号对肝脏葡萄糖流量的影响？我们将研究短期刺激下丘脑瘦素的选择性成分是否‘拯救’瘦素对过度喂养大鼠肝脏营养流动的作用。

DESCRIPTION (provided by applicant): In this project, we propose to continue our investigation of the biochemical mechanism(s) by which insulin resistance is acquired. Our long-term focus has been on the link between nutrient availability and insulin action. In this regard, the leptin plays in the regulation of hepatic and peripheral insulin action. However, the biochemical and neural circuitries mediating these effects remain to be elucidated. Here we wish to test the hypothesis that leptin exerts its rapid effects on hepatic glucose fluxes via 2 major central components: a) STAT3-dependent effects (mostly leading to rapid stimulation of gluconeogenesis and lipid oxidation); b) STAT3-independent effects (mostly leading to rapid inhibition of glycogenolysis and glucose output). Additionally, more prolonged activation of hypothalamic leptin signaling orchestrates the biological response to nutrient excess by limiting feeding behavior, by increasing energy expenditure and lipid oxidation, and by improving insulin action. Based on preliminary results and on this overall objective we wish to pursue the following specific aims: 1. Does leptin acutely regulate hepatic glucose fluxes via activation of STAT3-independent pathways in the hypothalamus? We will examine whether blocking hypothalamic leptin signaling via STAT3-independent pathways alters leptin action on hepatic nutrient fluxes. 2. Does leptin acutely regulate hepatic glucose fluxes via activation of STAT3-dependent pathways in the hypothalamus? We will examine whether rapid 'loss-of-function' within the hypothalamic STAT3 or melanocortin pathways alters leptin action on hepatic nutrient fluxes. 3. Does leptin acutely inhibit hepatic glucose production via STAT3-independent pathways when its activation of hypothalamic STAT3-dependent pathways is prevented? We will examine whether rapid 'loss-of-function' of STAT3-dependent hypothalamic targets of leptin unveils 'insulin-like' leptin actions on hepatic nutrient fluxes. 4. Does leptin regulate energy balance and insulin action via activation of hypothalamic STAT3-dependent and/or STAT3-independent signaling? We will examine whether week-long manipulations of hypothalamic leptin signaling via selective downstream targets regulate feeding behavior, energy metabolism, and insulin sensitivity. 5. How does short-term over-feeding modify the effects of hypothalamic leptin signaling on hepatic glucose fluxes? We will examine whether short-term stimulation of selective components of hypothalamic leptin signaling 'rescues' the action of leptin on hepatic nutrient fluxes in over-fed rats.