A prevalent variant in PPP1R3A impairs glycogen synthesis and reduces muscle glycogen content in humans and mice.
A prevalent variant in PPP1R3A impairs glycogen synthesis and reduces muscle glycogen content in humans and mice.
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DOI：
10.1371/journal.pmed.0050027
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发表时间：
2008-01-29
期刊：
影响因子：
15.8
通讯作者：
DePaoli-Roach AA
中科院分区：
文献类型：
--
作者：
Savage DB;Zhai L;Ravikumar B;Choi CS;Snaar JE;McGuire AC;Wou SE;Medina-Gomez G;Kim S;Bock CB;Segvich DM;Solanky B;Deelchand D;Vidal-Puig A;Wareham NJ;Shulman GI;Karpe F;Taylor R;Pederson BA;Roach PJ;O'Rahilly S;DePaoli-Roach AA
储存的糖原是骨骼肌的重要能量来源。主要影响骨骼肌糖原周转的人类遗传疾病已得到广泛认可，但很少见。我们之前报道称，英国白人群体中 1.36% 的参与者中存在 PPP1R3A 的移码/过早终止突变，PPP1R3A 是编码 RGL 的基因，RGL 是肌肉糖原代谢的关键调节因子。然而，突变的功能影响尚不清楚。这项研究的目的是表征这种遗传变异的分子和生理后果。在这项研究中，我们发现该变异在 744 名独立的英国白人群体 (1.46%) 中也有类似的患病率，并且利用体内 13C 磁共振波谱研究表明，该变异的人类携带者 (n = 6) 的基础肌糖原水平较低（低 65%，p = 0.002）和餐后肌糖原水平。表达同等突变的小鼠也同样降低了肌糖原水平（杂合基因敲入小鼠降低了 40%，p < 0.05）。在这些小鼠的肌肉组织中，截短的突变体无法结合糖原并与糖原合酶 (GS) 共定位，从而降低了 GS 并增加了糖原磷酸化酶活性状态，这是糖原含量降低的原因。因此，据我们所知，PPP1R3A C1984ΔAG（终止密码子 668）是第一个描述的直接损害糖原合成并降低人类骨骼肌糖原水平的普遍突变。事实上，约 70 名英国白人中就有 1 人存在这种病毒，这一事实增加了这些观察结果的潜在生物医学相关性。 Stephen O'Rahilly 及其同事描述了 PPP1R3A 突变的影响，该突变存在于来自英国的 1.36% 的参与者中，该突变直接损害糖原合成并降低人类骨骼肌中的糖原水平。人体通过称为新陈代谢的过程从食物中获取日常生活所需的能量。然而，并不是所有新陈代谢释放的能量都会被立即使用。有些以糖原的形式储存在骨骼肌中，糖原是一种在高强度运动期间使用的葡萄糖聚合物。进食后，消化系统中的化学物质将食物中的葡萄糖（糖的一种）释放到血液中，从而触发胰腺释放胰岛素。胰岛素指示肌肉、肝脏和脂肪细胞从血液中去除葡萄糖，以将血液中的糖含量保持在安全水平。细胞立即使用葡萄糖作为燃料或将其转化为糖原或脂肪进行储存。糖原周转（糖原储备的消耗和替代）受到糖原合成酶和糖原磷酸化酶（分别产生和破坏糖原的酶）的严格控制。第三种酶称为蛋白磷酸酶 1，通过激活糖原合成酶和灭活糖原磷酸化酶来促进净糖原合成。蛋白磷酸酶 1 的活性由“靶向亚基”家族调节。在肌肉中，这些靶向亚基之一称为 RGL，可促进蛋白磷酸酶 1 对糖原合酶和糖原磷酸化酶的作用。几种已知的人类遗传疾病会影响肌糖原的分解，但很少有基因变化（突变）被发现会减少肌糖原的合成。研究人员对发现影响糖原周转和代谢其他方面的突变感兴趣，因为其中一些可能与糖尿病的发展有关，糖尿病是一种以高血糖为特征的重要代谢性疾病。在这项研究中，研究人员研究了最近发现的 PPP1R3A（编码 RGL 的基因）中的突变如何影响糖原合成。这种突变——PPP1R3A FS——之前在 1.36% 的英国白人中被发现。它会产生短版本的 RGL，该版本缺少将 RGL 与称为肌浆网的细胞结构结合在一起的分子部分，但其糖原结合域保持完整。为了证实 PPP1R3A FS 是英国白人中的常见突变，研究人员对牛津生物银行 (Oxford Biobank) 登记的 744 名健康成年人的基因进行了测序（该银行希望通过监测大量 30 至 50 岁人群的健康状况来收集 DNA，以揭示代谢上重要的遗传变异）。其中 1.46% 的人患有 PPP1R3A FS 突变。为了检查突变载体中糖原的储存情况，研究人员使用了一种称为体内 13C 磁共振波谱的技术。这些个体的基础肌糖原水平和餐后达到的水平低于没有突变的人，但他们的血糖和胰岛素水平正常。最后，为了研究突变如何减少肌糖原，研究人员制作了携带 PPP1R3A FS 突变的小鼠。与人类携带者一样，这些小鼠肌肉中的糖原含量低于正常水平。出乎意料的是，在生化实验中，突变小鼠产生的截短的 RGL 蛋白没有与糖原结合或与糖原合酶共定位。这种结合的缺乏降低了糖原合成酶的活性并增加了糖原磷酸化酶的活性，从而减少了肌糖原。这些发现将 PPP1R3A FS 突变确定为已知的第一个损害糖原合成并降低人类骨骼肌糖原水平的普遍突变。他们还证实这种突变在英国白人中很常见。尽管这些人类携带者没有报告任何运动不耐受，但仍需要进行详细研究来测试该突变是否对骨骼肌性能有任何影响。此外，研究人员表示，该突变可能与 2 型糖尿病的发生有关。胰岛素刺激的糖原合成受损是胰岛素抵抗肌肉和肝细胞的一个特征，被认为是 2 型糖尿病发展的关键事件。尽管之前的一些结果表明PPP1R3A FS突变有时会使人们容易出现胰岛素抵抗，但只有在多个种族群体中进行的大规模人群研究才能揭示PPP1R3A FS突变是否对2型糖尿病的发展具有重要影响。请通过此摘要的在线版本访问这些网站：http://dx.doi.org/10.1371/journal.pmed.0050027。维基百科有关于代谢和糖原的页面（请注意，维基百科是任何人都可以编辑的免费在线百科全书；有多种语言版本） MedlinePlus 百科全书提供有关糖尿病的信息（英语和西班牙语） 英国生物银行正在寻找与代谢和其他疾病相关的人群中的遗传变异 网站上有 Stephen O'Rahily 和 Anna DePaoli-Roach 的研究项目的简要描述
Stored glycogen is an important source of energy for skeletal muscle. Human genetic disorders primarily affecting skeletal muscle glycogen turnover are well-recognised, but rare. We previously reported that a frameshift/premature stop mutation in PPP1R3A, the gene encoding RGL, a key regulator of muscle glycogen metabolism, was present in 1.36% of participants from a population of white individuals in the UK. However, the functional implications of the mutation were not known. The objective of this study was to characterise the molecular and physiological consequences of this genetic variant. In this study we found a similar prevalence of the variant in an independent UK white population of 744 participants (1.46%) and, using in vivo 13C magnetic resonance spectroscopy studies, demonstrate that human carriers (n = 6) of the variant have low basal (65% lower, p = 0.002) and postprandial muscle glycogen levels. Mice engineered to express the equivalent mutation had similarly decreased muscle glycogen levels (40% lower in heterozygous knock-in mice, p < 0.05). In muscle tissue from these mice, failure of the truncated mutant to bind glycogen and colocalize with glycogen synthase (GS) decreased GS and increased glycogen phosphorylase activity states, which account for the decreased glycogen content. Thus, PPP1R3A C1984ΔAG (stop codon 668) is, to our knowledge, the first prevalent mutation described that directly impairs glycogen synthesis and decreases glycogen levels in human skeletal muscle. The fact that it is present in ∼1 in 70 UK whites increases the potential biomedical relevance of these observations. Stephen O'Rahilly and colleagues describe the effect of a mutation inPPP1R3A, present in 1.36% of participants from one UK population, that directly impairs glycogen synthesis and decreases glycogen levels in human skeletal muscle. The human body gets the energy it needs for day-to-day living from food in a process called metabolism. However, not all the energy released by metabolism is used immediately. Some is stored in skeletal muscles as glycogen, a glucose polymer that is used during high intensity exercise. After eating, chemicals in the digestive system release glucose (a type of sugar) from food into the bloodstream where it triggers insulin release from the pancreas. Insulin instructs muscle, liver and fat cells to remove glucose from the bloodstream to keep the amount of sugar in the blood at a safe level. The cells use the glucose immediately as fuel or convert it into glycogen or fat for storage. Glycogen turnover (the depletion and replacement of glycogen stores) is tightly controlled by glycogen synthase and glycogen phosphorylase, enzymes that make and destroy glycogen, respectively. A third enzyme called protein phosphatase 1 promotes net glycogen synthesis by activating glycogen synthase and inactivating glycogen phosphorylase. The activity of protein phosphatase 1 is regulated by a family of “targeting subunits.” In muscle, one of these targeting subunits, called RGL, facilitates protein phosphatase 1 action on glycogen synthase and glycogen phosphorylase. Several known human genetic disorders affect the breakdown of muscle glycogen but few genetic changes (mutations) have been found that decrease the synthesis of muscle glycogen. Researchers are interested in discovering mutations that affect glycogen turnover and other aspects of metabolism because some of these may be involved in the development of diabetes, an important metabolic disorder characterized by high blood sugar levels. In this study, the researchers have investigated how a recently identified mutation in PPP1R3A, the gene that encodes RGL, affects glycogen synthesis. This mutation—PPP1R3A FS—was previously found in 1.36% of a UK white population. It causes the production of a short version of RGL that lacks the part of the molecule that tethers RGL to a cellular structure called the sarcoplasmic reticulum but leaves its glycogen binding domain intact. To confirm that PPP1R3A FS is a common mutation in the UK white population, the researchers sequenced the gene in 744 healthy adults enrolled in the Oxford Biobank (which hopes to uncover metabolically important genetic variations by monitoring the health of a large number of 30- to 50-year-old people from whom DNA has been collected). 1.46% of these people had the PPP1R3A FS mutation. To examine glycogen storage in carriers of the mutation, the researchers used a technique called in vivo 13C magnetic resonance spectroscopy. Basal muscle glycogen levels and those reached after a meal were lower in these individuals than in people without the mutation but their blood sugar and insulin levels were normal. Finally, to examine how the mutation reduces muscle glycogen, the researchers made mice carrying the PPP1R3A FS mutation. Like the human carriers, these mice had less glycogen than normal in their muscles. Unexpectedly, in biochemical experiments the truncated RGL protein made by the mutant mice did not bind to glycogen or co-localize with glycogen synthase. This lack of binding decreased the activity of glycogen synthase and increased the activity of glycogen phosphorylase, thus decreasing muscle glycogen. These findings identify the PPP1R3A FS mutation as the first prevalent mutation known to impair glycogen synthesis and to decrease glycogen levels in human skeletal muscles. They also confirm that this mutation is very common in UK whites. Although these human carriers do not report any exercise intolerance, detailed studies are needed to test whether the mutation has any effect on skeletal muscle performance. In addition, suggest the researchers, the mutation might be involved in the development of type 2 diabetes. Impaired insulin-stimulated glycogen synthesis, which is a feature of insulin-resistant muscle and liver cells, is thought to be a key event in the development of type 2 diabetes. Although some previous results indicate that the PPP1R3A FS mutations can sometimes predispose people to develop insulin resistance, only a large population-based study in multiple ethnic groups will reveal whether the PPP1R3A FS mutation has an important impact on the development of type 2 diabetes. Please access these Web sites via the online version of this summary at http://dx.doi.org/10.1371/journal.pmed.0050027. Wikipedia has pages on metabolism and on glycogen (note that Wikipedia is a free online encyclopedia that anyone can edit; available in several languages) The MedlinePlus encyclopedia provides information about diabetes (in English and Spanish) The UK Biobank is looking for genetic variations among human populations that are associated with metabolic and other disorders Web sites are available with brief descriptions of the research programs of Stephen O'Rahilly and Anna DePaoli-Roach