LKB1- AMPK pathway regulation of glucose metabolism and metformin action in liver

描述(由申请人提供)：外周组织中葡萄糖和脂肪代谢的失调是2型糖尿病的一个标志。AMP激活的蛋白激酶(AMPK)是细胞和机体代谢的主要调节者，是细胞能量状态的感受器，在代谢组织的糖脂平衡中起着关键作用。AMPK被低营养、运动、脂联素等脂肪因子激活，以及被广泛使用的糖尿病治疗药物二甲双胍激活。AMPK在肝脏中被激活后，通过不完全了解的机制来减少糖异生和脂肪生成。此前，丝氨酸/苏氨酸激酶LKB1被认为是大多数哺乳动物组织中介导AMPK激活的关键上游激酶。成年小鼠肝脏中LKB1基因缺失导致肝脏AMPK活性完全丧失，糖异生和肝脏脂肪堆积显著增加，同时减弱了二甲双胍的降血糖能力。该领域的一个主要挑战仍然是解码LKB1-AMPK信号控制新陈代谢的分子机制。在过去的4年里，我的实验室对AMPK的直接底物进行了多管齐下的筛选，这导致了一些新的AMPK底物的鉴定和研究，包括Raptor、ULK1、Cry1、Srebp1和HDACs4、5和7。在第一次更新中，我们建议进一步剖析AMPK及其相关激酶在控制糖代谢中的作用和二甲双胍的治疗作用。鉴于最近在解码LKB1/AMPK信号通路的分子效应器方面的进展，不同的AMPK底物对代谢控制和二甲双胍的治疗作用的相对贡献现在可以开始描述。在目标1，AMPKalpha1、AMPKalpha2和相关的SUK激酶在控制肝脏葡萄糖代谢中的作用将使用新的时间控制的遗传小鼠模型进行比较。在目标2中，我们将利用这些模型来确定肝脏中二甲双胍治疗作用中对LKB1和AMPK亚型的相对需求。这一目标的一个关键方面是与范德比尔特大学的Davi Wasserman博士合作，以确定LKB1和AMPK在这些模型中对代谢流量的影响。最后，在目标3中，我们将通过直接研究IIa类HDAC-FOXO轴和CRTC辅活化子-CREB轴在控制肝脏葡萄糖稳态中的相对作用来扩展我们的最新发现。这些研究排除了LKB1-AMPK通路在肝脏中的作用，将增加对现有广泛使用的糖尿病治疗方法如何工作的理解，并为未来的2型糖尿病治疗确定关键的新靶点。

DESCRIPTION (provided by applicant): Deregulation of glucose and lipid metabolism in peripheral tissues is a hallmark of type 2 diabetes. AMP- activated protein kinase (AMPK) is a master regulator of cellular and organismal metabolism which acts as sensor of cellular energy status and plays key roles in glucose and lipid homeostasis in metabolic tissues. AMPK is activated by low nutrients, exercise, adipokines such adiponectin, and by the widely used diabetes therapeutic metformin. Upon activation in liver, AMPK functions to reduce gluconeogenesis and lipogenesis through incompletely understood mechanisms. Previously, the serine/threonine kinase LKB1 was identified as the critical upstream kinase mediating AMPK activation in most mammalian tissues. Genetic deletion of LKB1 in the liver of adult mice resulted in complete loss of hepatic AMPK activity and significant increases in gluconeogenesis and hepatic lipid accumulation, while attenuating the ability of metformin to lower blood glucose. A major challenge in the field remained in decoding the molecular mechanisms through which LKB1-AMPK signaling controls metabolism. Over the past 4 years of this funding, my laboratory performed a multi-pronged screen for direct substrates of AMPK, which led to the identification and study of a number of novel AMPK substrates critical in metabolism, including Raptor, ULK1, Cry1, Srebp1, and HDACs4, 5, and 7. In this first renewal, it is proposed to further dissect the role of AMPK and related kinases in control of glucose metabolism and the therapeutic action of metformin. Given the recent advances in decoding the molecular effectors of the LKB1/AMPK signaling pathway, the relative contributions of different AMPK substrates to metabolic control and metformin's therapeutic action can now begin to be delineated. In Aim 1, the role of AMPKalpha1, AMPKalpha2, and the related SIK kinases will be compared in control of hepatic glucose metabolism using novel temporally controlled genetic mouse models. In Aim 2, we will utilize these models to define the relative requirement for LKB1 and AMPK isoforms in the therapeutic action of metformin in liver. A key aspect of this aim is a collaboration with Dr. Davi Wasserman at Vanderbilt University to define the effect of LKB1 and AMPK on metabolic flux in these models. Finally, in the Aim 3, we will expand on our recent discoveries by directly examining the relative roles of Class IIa HDAC-FOXO axis versus CRTC coactivators-CREB axis in the control of glucose homeostasis in liver. These studies disecting the role of the LKB1- AMPK pathway in liver will increase the understanding of how existing widely used diabetes modalities work, and identify critical new targets for future type 2 diabetes therapeutics.