PLoS one：增加能量的基因突变

xielirong

一个由Mary-Ellen Harper、Robert Dent和Ruth McPherson博士领导的渥太华研究组联合来自美国加州伯克力的研究人员对AMPK（腺苷单磷酸活化蛋白激酶）基因进行了深入研究。这种酶控制着我们细胞中的能量数量。在两个没有亲缘关系的家族中的成员细胞中发现的这种基因的突变导致肌肉中AMPK活性加倍——模拟了运动时的能量状态。

  该研究组还发现，这种突变导致一种肌肉脂肪储存量的减少和肌肉糖原的增加。这一发现可能用于II型糖尿病的治疗，因为肌肉中储存的高水平的脂肪与胰岛素抗性的发生有关。

  另外，常用的糖尿病药物甲福明二甲双胍是通过增加AMPK活性来起作用的。因此，这项发现为制药研究提供了有价值的信息。这项研究的发现还可能引起运动生理学家的极大兴趣。

  这项研究的结果发表在9月19日的在线版的PLoS ONE上，研究获得了Heart & Stroke Foundation of Ontario资助。

  此前，来自哥伦比亚大学医学中心的研究人员确定了一种作为细胞中心能量表的蛋白质的复杂三维结构。这些结果信息将有助于研究人员了解这种重要蛋白分子AMP蛋白激酶（AMPK）的多种关键细节，从而为研发出新型的糖尿病以及肥胖症药物和方法奠定基础。这项研究的结果发表在《科学》杂志上，文章揭示了细胞最基础及关键的能量过程。

  AMP蛋白激酶（AMPK），它主要控制细胞新陈代谢：它会决定身体中的脂肪是储存还是燃烧，这主要取决于细胞中总能量。当细胞能量水平较高时，细胞中存在高浓度的能量分子ATP（三磷酸腺苷），因此AMPK会促使细胞进行“合成代谢”，将多余能量作为脂肪储存下来；当ATP水平较低时，AMPK将关闭合成代谢，反而激发分解代谢，让脂肪燃烧为能量。  

  研究人员表示，AMPK能作为治疗2型糖尿病的一种有效手段。当AMPK探测到细胞中ATP浓度较低时，它们会利用各种机制使细胞中的葡萄糖变为ATP。对于啮齿类动物的实验已经表明，AMPK对于降低血糖是有效的。  

  文章的作者表示，虽然目前他们还不知道如何单独激发AMPK而不带来副作用，但是了解蛋白质的原子水平结构为研究人员提供了一种强大的治疗工具。

  AMP激活的蛋白激酶(AMP-activated protein kinase,AMPK)广泛存在于真核细胞中,一旦被激活,即可磷酸化下游靶蛋白,关闭消耗ATP的合成代谢途径,开启产生ATP的分解代谢途径,被称为\"细胞能量调节器\"

  在调节细胞能量状态的蛋白激酶级联反应中，AMP激活的蛋白激酶(AMPK)是其中枢组成部分。AMPK的活性受AMP/ATP比值的调节.应激反应可通过ATP的产生减少或利用增加，使细胞内AMP/ATP的比值增加，从而激活AMPK.激活的AMPK可激发一系列的反应来恢复细胞内的能量平衡。AMPK可启动分解代谢途径，如脂肪酸氧化和糖酵解，从而增加ATP的产生，同时关闭合成代谢途径，如脂肪酸合成和蛋白合成，减少ATP的消耗。AMPK不仅可以在细胞水平作为能量的感受器，还可以通过激素和细胞因子，如瘦素、脂联素和ghrelin来参与调节机体的能量消耗和能量摄入。

  糖原是动物体内糖的贮存形式,摄入的糖类大部分转变成甘油三酯贮存在脂肪组织中，只有小部分以糖原形式贮存。其意义在于当机体需要葡萄糖时它可以迅速被动用以供急需。糖原合成与分解的生理性调节主要靠胰岛素和胰高血糖素。机体血糖降低可引起胰高血糖素和肾上腺素分泌增加，此时细胞内cAMP含量增加，促使有活性的A激酶增加。A激酶一方面时糖原合酶磷酸化失去活性，一方面通过磷酸化酶b激酶使磷酸化酶变成有活性的磷酸化酶a，最终结果使糖原合成减少，糖原分解增加，使血糖升高。



原始出处:

PLoS ONE

Received: July 16, 2007; Accepted: August 14, 2007; Published: September 19, 2007

Gain-of-Function R225W Mutation in Human AMPKγ3 Causing Increased Glycogen and Decreased Triglyceride in Skeletal Muscle

Sheila R. Costford1#, Nihan Kavaslar2#, Nadav Ahituv4, Shehla N. Chaudhry1, Wendy S. Schackwitz4,5, Robert Dent3, Len A. Pennacchio4, Ruth McPherson2#, Mary-Ellen Harper1*#

1 Department of Biochemistry, Microbiology and Immunology, Faculty of Medicine, University of Ottawa, Ottawa, Ontario, Canada, 2 Division of Cardiology and Lipoprotein and Atherosclerosis Research Group, University of Ottawa Heart Institute, Ottawa, Ontario, Canada, 3 Ottawa Hospital Weight Management Clinic, Ottawa, Ontario, Canada, 4 Genomics Division, Lawrence Berkeley National Laboratory, Berkeley, California, United States of America, 5 United States Department of Energy Joint Genome Institute, Walnut Creek, California, United States of America

Abstract

Background

AMP-activated protein kinase (AMPK) is a heterotrimeric enzyme that is evolutionarily conserved from yeast to mammals and functions to maintain cellular and whole body energy homeostasis. Studies in experimental animals demonstrate that activation of AMPK in skeletal muscle protects against insulin resistance, type 2 diabetes and obesity. The regulatory γ3 subunit of AMPK is expressed exclusively in skeletal muscle; however, its importance in controlling overall AMPK activity is unknown. While evidence is emerging that gamma subunit mutations interfere specifically with AMP activation, there remains some controversy regarding the impact of gamma subunit mutations [1]–[3]. Here we report the first gain-of-function mutation in the muscle-specific regulatory γ3 subunit in humans.

Methods and Findings

We sequenced the exons and splice junctions of the AMPK γ3 gene (PRKAG3) in 761 obese and 759 lean individuals, identifying 87 sequence variants including a novel R225W mutation in subjects from two unrelated families. The γ3 R225W mutation is homologous in location to the γ2R302Q mutation in patients with Wolf-Parkinson-White syndrome and to the γ3R225Q mutation originally linked to an increase in muscle glycogen content in purebred Hampshire Rendement Napole (RN-) pigs. We demonstrate in differentiated muscle satellite cells obtained from the vastus lateralis of R225W carriers that the mutation is associated with an approximate doubling of both basal and AMP-activated AMPK activities. Moreover, subjects bearing the R225W mutation exhibit a ~90% increase of skeletal muscle glycogen content and a ~30% decrease in intramuscular triglyceride (IMTG).

Conclusions

We have identified for the first time a mutation in the skeletal muscle-specific regulatory γ3 subunit of AMPK in humans. The γ3R225W mutation has significant functional effects as demonstrated by increases in basal and AMP-activated AMPK activities, increased muscle glycogen and decreased IMTG. Overall, these findings are consistent with an important regulatory role for AMPK γ3 in human muscle energy metabolism.