Biochemical Mechanisms of In Vivo Insulin Resistance

描述（由申请人提供）：在本项目中，我们建议继续研究胰岛素抵抗的生化机制。我们的长期重点一直是营养素的可用性和胰岛素作用之间的联系。在这方面，瘦素在肝脏和外周胰岛素作用的调节中起作用。然而，介导这些影响的生物化学和神经回路仍有待阐明。在这里，我们希望检验瘦素通过2个主要的中心成分对肝脏葡萄糖通量发挥快速作用的假设： a）STAT 3依赖性作用（主要导致快速刺激脂质生成和脂质氧化）; B）STAT 3非依赖性作用（主要导致糖原分解和葡萄糖代谢的快速抑制 输出）。 此外，下丘脑瘦素信号传导的更长时间的激活通过限制进食行为、通过增加能量消耗和脂质氧化以及通过改善胰岛素作用来协调对营养过剩的生物反应。根据初步结果和这一总体目标，我们希望实现以下具体目标：1.瘦素是否通过激活下丘脑中的STAT 3非依赖性通路来急性调节肝脏葡萄糖通量？我们将研究通过STAT 3非依赖性途径阻断下丘脑瘦素信号传导是否会改变瘦素对肝脏营养流的作用。2.瘦素是否通过激活下丘脑中的STAT 3依赖性通路来急性调节肝脏葡萄糖通量？我们将研究下丘脑STAT 3或黑皮质素途径内的快速“功能丧失”是否会改变瘦素对肝脏营养流的作用。3.当下丘脑STAT 3依赖性途径的激活被阻止时，瘦素是否通过STAT 3非依赖性途径急性抑制肝脏葡萄糖的产生？我们将研究是否快速的“功能丧失”的STAT 3依赖性下丘脑瘦素的目标揭示“胰岛素样”瘦素对肝脏营养流的作用。4.瘦素是否通过激活下丘脑STAT 3依赖和/或非依赖信号调节能量平衡和胰岛素作用？我们将研究是否通过选择性下游靶点对下丘脑瘦素信号进行为期一周的操纵，从而调节摄食行为、能量代谢和胰岛素敏感性。5.短期过度喂养如何改变下丘脑瘦素信号对肝脏葡萄糖通量的影响？我们将研究是否短期刺激下丘脑瘦素信号的选择性成分“拯救”瘦素对过度喂养大鼠肝脏营养流的作用。

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.