Polycomb repressor complex protein EZH2 regulation of muscle stem cell migration and differentiation

由于运动、年龄、疾病或不良的生活方式，肌肉在一生中不断受到损伤。但与成人身体的许多组织不同，肌肉能够通过位于肌肉纤维边缘的专门肌肉干细胞的作用进行自我修复。当他们检测到受损的肌肉干细胞移动到受损的部位，然后在一个被称为分化的过程中融入受损的纤维中。肌肉无力，例如随着年龄的增长或在癌症等疾病期间，被认为是由于肌肉干细胞无法修复受损肌肉，而结缔组织和脂肪细胞取代了肌肉纤维。更好地了解肌肉干细胞移动到损伤部位和分化的方式，最终将有助于开发预防或治疗肌肉无力的疗法。为了应对损伤，肌肉干细胞还会利用DNA中被称为“表观遗传”开关的控制区开启或关闭特定基因。这项研究的目的是研究一种酶EZH2，它可以改变DNA中的这些表观遗传开关。因此，EZH2可以潜在地开启或关闭正确的基因来应对肌肉损伤，从而导致肌肉的修复。事实上，我们知道EZH2可以影响肌肉修复，因为当这种酶在老鼠的肌肉中不起作用时，肌肉就不能正常修复。但是当肌肉干细胞修复受损的肌肉时，我们并不确切地知道哪些开关以及基因是由EZH2控制的。这项研究的目的之一是识别这些基因。我们现在有了令人兴奋的初步结果，表明EZH2不仅影响分化，而且还影响肌肉干细胞向损伤部位的运动。我们现在希望了解EZH2如何控制肌肉干细胞向损伤的迁移及其在损伤部位的分化。为了做到这一点，我们将使用斑马鱼的幼虫，因为斑马鱼的肌肉再生很快，而且幼虫是透明的，所以我们可以很容易地看到肌肉干细胞的运动用显微镜。我们将测量肌肉干细胞如何移动到损伤通过斑马鱼幼虫荧光标记的肌肉干细胞。鱼体内的荧光细胞将通过强大的显微镜来观察，制作4D电影，并使用专门开发的计算机软件来跟踪细胞。这在哺乳动物等其他不透明的动物身上是不容易做到的。斑马鱼的肌肉修复过程与人类非常相似，类似的基因在受到损伤时也会开启或关闭，这使得斑马鱼成为研究肌肉修复过程的一个很好的系统。我们将测量当EZH2被阻止工作时，肌肉干细胞在损伤后的表现。然后，我们将询问在修复过程中的哪一点EZH2是重要的，因为我们可以可视化哪些基因在肌肉干细胞受伤之前，期间和之后被打开或关闭。为了证明EZH2是否通过表观遗传开关控制基因，我们将提取迁移肌肉干细胞并测量DNA上的开关。对癌细胞的研究表明，EZH2除了调节基因的开启或关闭之外，还可以单独控制细胞的运动。我们还将研究EZH2是否在肌肉干细胞中也有这种活性，方法是使用癌细胞中发现的EZH2突变版本，并询问它们是否改变了肌肉干细胞的运动方式。我们的研究结果对于理解“表观遗传”开关如何与肌肉干细胞向损伤部位的运动协调以确保肌肉修复成功非常重要。我们还将能够识别在肌肉修复过程中由EZH2控制的基因，因此可能能够针对这些基因作为改善肌肉力量的治疗方法。

Muscle is constantly damaged throughout life, due to exercise, age, sickness or poor lifestyle. But unlike many tissues in the adult body, muscle is able to repair itself through the action of specialised muscle stem cells which lie at the edges of muscle fibres. When they detect damage muscle stem cells move to the site of damage and then integrate into the damaged fibres, in a process called differentiation. Muscle weakness, for instance as we age or during disease such as cancer, is thought to occur due to an inability of muscle stem cells to repair damaged muscle, and instead connective and fat cells take the place of muscle fibres. A better understanding of the ways muscle stem cells move to the site of damage and differentiate will ultimately allow the development of therapies to prevent or treat muscle weakness.In response to damage, muscle stem cells also turn specific genes on or off, using control regions in the DNA called 'epigenetic' switches. This study aims to investigate an enzyme, EZH2, that makes changes to these epigenetic switches in the DNA. EZH2 can therefore potentially turn the correct genes on or off in response to muscle damage and so lead to repair of the muscle. Indeed we know that EZH2 can influence muscle repair, because when this enzyme does not work in the muscle of mice, the muscle is not repaired properly. But we do not know exactly which switches, and therefore genes, are controlled by EZH2 when muscle stem cells repair damaged muscle. One aim of this study is to identify those genes. We now have exciting preliminary results that reveal EZH2 not only influences differentiation, but also influences muscle stem cell movement towards sites of damage. We now wish to understand how EZH2 can control both migration of muscle stem cells towards damage and their differentiation at the site of damage. To do this we will use zebrafish larvae, because the muscle of zebrafish regenerates quickly, and the larvae are transparent so that we can easily see the movement of muscle stem cells using a microscope. We will measure how muscle stem cells move towards injury by using zebrafish larvae that have fluorescently labelled muscle stem cells. Fluorescent cells in the fish will be observed by powerful microscopes to make 4D movies and an especially developed computer software will be used to track cells. This is not something that can easily be done in other, non-transparent, animals such as mammals. Muscle repair in zebrafish also occurs in much the same way as in humans and similar genes are turned on and off in response to damage, making this a good system to study muscle repair processes.We will measure how muscle stem cells behave after injury when EZH2 is prevented from working. We will then ask at which point in the repair process EZH2 is important, as we can visualise which genes are turned on or off in muscle stem cells before, during and after injury. To show if EZH2 controls genes by epigenetic switches we will extract migrating muscle stem cells and measure the switches on the DNA. Studies of cancer cells suggest that EZH2 can also control the movement of cells separately from regulating how genes are turned on or off. We will also investigate whether EZH2 has this activity in muscle stem cells as well, by using mutated versions of EZH2 found in cancer cells and asking if they change the way that the muscle stem cells move. Our results will be important for understanding how the 'epigenetic' switches are coordinated with the movement of muscle stem cells to sites of damage to ensure that muscle repair is successful. We will also be able to identify genes that are controlled by EZH2 as muscle is repaired, and so may be able target these genes as therapies for improving muscle strength.