Myosin-linked mechanisms for the regulation of muscle contraction

肌肉使我们活动自如，而活动自如是决定我们生活质量的一个主要因素。不幸的是，随着年龄的增长，我们的肌肉会变得越来越弱，像走路、爬楼梯甚至从椅子上站起来这样的日常活动都会变得越来越困难。许多疾病还会导致严重形式的肌肉无力，其中一些会影响幼儿。一般来说，没有有效的治疗肌肉无力的方法。使用肌肉——锻炼肌肉——确实能让它们变得更强壮，但这并不总是可行的，尤其是对那些患有影响肌肉疾病的人来说。这项提议旨在发现是什么控制着健康肌肉的力量，因为如果我们了解了这一点，我们就可以设计出一种药物来增强虚弱肌肉的力量。肌肉是由一种叫做肌节的基本微观构件的长串构成的。每个肌节包含两种类型的纤维，一种比另一种宽，这两种被称为粗纤维和细纤维。这两组纤维的相对滑动是导致肌肉缩短的原因。当来自大脑的信号沿着神经到达肌肉时，它会触发肌肉细胞内储存的钙的释放。钙与细丝结合，导致细丝的结构发生变化，从而使细丝滑动，肌肉收缩。细丝结构的这种变化是很容易理解的，但它的工作原理就像一个开关——它控制肌肉收缩的时间，而不是收缩的强度。最近很明显，有另一种肌肉控制通过改变粗纤维的结构起作用，这可以改变开和关状态。换句话说，这些粗纤维结构的变化可以控制肌肉的力量，也可以控制肌肉在休息时消耗的能量。由于我们身体重量的三分之一是肌肉，了解如何控制肌肉的OFF状态可能对对抗一个非常不同的健康问题很有用，让我们利用肌肉燃烧掉一些不需要的卡路里。目前我们还不知道肌肉的开关状态是如何被控制的——我们不知道粗纤维的结构是如何变化的，以及是什么控制了这些变化。不过，我们确实知道哪些蛋白质参与其中，以及它们在肌节中的大致位置。在这个项目中，我们将应用我们开发的一种新方法，用小荧光分子标记粗丝蛋白，从肌肉细胞内部报告蛋白质结构的变化。我们对这种方法的初步测试表明，它能够回答一些关于粗丝结构变化如何控制肌肉性能的关键问题：粗丝的OFF和ON结构在分子水平上有什么区别？粗纤维的这些结构变化是如何控制肌肉力量的呢？粗丝结构本身是如何控制的？这种控制与细纤维中的钙开关有什么关系？这些问题的答案将使我们能够详细了解健康肌肉中粗丝结构的变化如何控制OFF和ON状态。反过来，这将使我们能够提出这些状态可能被药物控制的方法，并开发评估潜在新药价值的方法。最后，由于心肌中使用相同的蛋白质成分也会发生非常相似的粗丝结构变化，我们期望这个项目的结果也将有助于指导类似的方法来控制心肌的力量，从而开发潜在的心脏病新疗法。

Muscles make us mobile, and mobility is a major factor determining our quality of life. Unfortunately our muscles get weaker as we get older, and everyday tasks like walking, climbing stairs or even getting up out of a chair get more difficult. Many diseases also lead to severe forms of muscle weakness, and some of these affect young children. In general there is no effective treatment for muscle weakness. Using muscles- exercising them- does make them stronger, but this is not always possible, particularly for those suffering from diseases that affect the muscles. This proposal seeks to discover what controls the strength of healthy muscles because, if we understood that, we might be able to design a drug to boost the strength of weak muscles. Muscles are built from long strings of a basic microscopic building block called a sarcomere. Each sarcomere contains an array of two types of filament, one wider than the other, and these are called thick and thin filaments. The relative sliding of these two sets of filaments is responsible for muscle shortening. When a signal from the brain travels along a nerve and reaches a muscle, it triggers release of calcium from stores inside the muscle cell. The calcium binds to the thin filaments, causing a change in their structure that allows the filaments to slide, and the muscle contracts. This change in thin filament structure is quite well understood, but it works like an OFF/ON switch- it controls when the muscle contracts, but not how strongly. Recently it has become apparent that there is another type of muscle control that works by changing the structure of the thick filaments, and this can alter both the ON and the OFF states. In other words, these changes in thick filament structure can control the strength of a muscle, but also how much energy a muscle uses when it is resting. Since about a third of the weight of our bodies is muscle, understanding how to control the OFF state of muscle might be useful in combatting a very different health problem, allowing us to use muscles to burn off some unwanted calories. At present we don't know how these OFF and ON states of muscle are controlled- we don't know exactly how the structure of the thick filament changes, and what controls those changes. We do know which proteins are involved, though, and roughly where they are in the sarcomere. In this project we will apply a new method that we developed to tag the thick filament proteins with small fluorescent molecules that report changes in protein structure from inside muscle cells. Our preliminary tests with this method shows that it is capable of answering some key questions about how changes in in thick filament structure control muscle performance: What is the difference between the OFF and ON structures of the thick filaments at the molecular level? How do these structural changes in the thick filament control the muscle strength? How is thick filament structure itself controlled? How is that control related to the calcium switch in the thin filaments? The answers to these questions will allow us to develop a detailed picture of how the OFF and ON states are controlled by changes in thick filament structure in healthy muscle. This in turn will enable us to suggest ways in which these states might be controlled by drugs, and to develop ways to assess the value of potential new drugs. Finally, since very similar changes in thick filament structure occur in heart muscle using the same protein components, we expect that the results of this project will also be useful in guiding an analogous approach to controlling the strength of heart muscle, and therefore in developing potential new treatments for heart disease.