Mechanisms of human skeletal muscle protein turnover

骨骼肌是人体内最大的蛋白质储存库。骨骼肌(和其他组织)中的蛋白质不断地同时合成和降解。这种持续的蛋白质周转为去除受损蛋白质和用新蛋白质替代提供了一种有效的机制。在成熟、生长后期的骨骼肌中，许多激素、营养和机械刺激被整合到肌肉蛋白质合成(MPS)和肌肉蛋白质分解(MPB)的调节过程中。MPS和MPB之间的平衡是肌肉蛋白质净增加的一个重要决定因素，因此，肌肉纤维增大(肥大)或减少(萎缩)。 我的研究计划广泛使用稳定同位素代谢示踪剂来研究骨骼肌蛋白质周转的急性调节，MPS和MPB。我们将这些高度复杂的措施与信号蛋白激活、基因表达和组织化学的措施结合起来，创建了一幅有助于人类骨骼肌蛋白质质量急性调节的因素的综合图景。这些急性蛋白质周转研究也让我们对骨骼肌的长期表型变化有了一些了解。我们还广泛使用加载和卸载，使用自愿阻力运动或肢体固定(即铸型)的范例，试图确定骨骼肌感觉负荷和改变的急性和慢性负荷如何影响MPS和MPB。然而，我们仍然缺乏关于装卸如何影响MPS和MPB变化的基本机械性监管知识。此外，从监管的角度来看，与刺激MPS和抑制MPB相关的营养触发因素研究相对较少。我提出的研究计划旨在试图了解控制急性和慢性MPS和MPB的复杂机制，最终决定骨骼肌蛋白质质量和代谢活动的得失。虽然我们已经成功地解开了其中一些机制并挑战了某些根深蒂固的模式，但更先进和更全面的知识要求建立、验证新的方法，并将其应用于不同的模式。为了解决这些问题，我们将利用质谱学的最新进展、新的同位素示踪剂模型和“组学”技术来了解响应变化，我们将继续使用各种急性和慢性加载和卸载范例来尝试确定骨骼肌如何根据蛋白质周转来感知和响应负载状态。在拟议的项目中，我们还计划通过研究细胞外基质、整合素受体和肌丝之间的这些分子桥梁来扩展我们之前的工作。

Skeletal muscle represents the largest protein reservoir in the human body. The proteins within skeletal muscle (and other tissues) are constantly and simultaneously being synthesized and degraded. This constant protein turnover provides for an efficient mechanism for removal of damaged proteins and replacement with new proteins. In mature, post-growth, skeletal muscle a number of hormonal, nutritional, and mechanical stimuli are integrated in their regulation of the processes of muscle protein synthesis (MPS) and muscle protein breakdown (MPB). The balance between MPS and MPB is a large determinant of net muscle protein gain and thus, muscle fibre enlargement (hypertrophy) or reduction (atrophy). My research program has made extensive use of stable isotope metabolic tracers to study the acute regulation of skeletal muscle protein turnover MPS and MPB. We have combined these highly complex measures with measures of signalling protein activation, gene expression, and histochemistry to create an integrated picture of the factors that contribute to the acute regulation of skeletal muscle protein mass in humans. These acute protein turnover studies have also given us some insight into longer-term phenotypic changes in skeletal muscle. We have also made extensive use of loading and unloading, using voluntary resistance exercise or limb immobilization (i.e., casting), paradigms to try and ascertain how skeletal muscles senses load and altered acute and chronic loading affects both MPS and MPB. However, we still lack basic mechanistic regulatory knowledge as to how loading and unloading work to affect changes in MPS and MPB. As well, from a regulatory standpoint, the nutritional triggers associated with stimulating MPS and supressing MPB are relatively understudied. My proposed program of study is aimed at trying to understand the complex mechanisms that are governing both acute and chronic MPS and MPB, ultimately determining gains or losses in skeletal muscle protein mass and metabolic activity. While we have been successful in unravelling some of these mechanisms and in challenging certain entrenched paradigms, a more advanced and integrated knowledge requires that new methods be established, validated and applied to different models. To address these issues, we will make use of recent advances in mass spectrometry, new models of isotopic tracers, ‘omic’ technologies to understand response variation, and we will continue to use various acute and chronic loading and unloading paradigms to try and ascertain how skeletal muscle senses, and responds to, loading states in terms of protein turnover. In the proposed projects we also plan to extend our previous work by studying these molecular bridges between the extracellular matrix, integrin receptors, and myofilaments.