Mechanisms of human skeletal muscle protein turnover

骨骼肌是人体内最大的蛋白质储存库。骨骼肌的维持是人类运动和代谢健康的关键。骨骼肌中的蛋白质不断地同时合成和降解。这种不断的蛋白质周转提供了一种有效的机制来去除受损的蛋白质，并用新的蛋白质来替代，以维持蛋白质的稳定。在成人骨骼肌中，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主要决定因素，因此，肌肉纤维增大(肥大)，或肌肉蛋白质净损失和肌肉纤维尺寸缩小(萎缩)。拟议的研究计划是对骨骼肌在增加负荷和卸载状态下的综合和系统研究，以揭示肌肉质量增减的调节机制。我们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调节。我们结合了这些世界上只有少数几个实验室才能进行的复杂测量，以及信号转导蛋白激活、转录基因表达和组织化学的测量。因此，我们获得了导致MPS和MPB急剧调节的因素的综合图景。这些尖锐的调节研究也给了我们对骨骼肌长期表型变化的机械性洞察，我们也将对此进行研究。我们开发了一种新的方法，结合动态蛋白质组分析，对调节肌肉蛋白质周转的机制产生了无与伦比的见解。我们广泛使用负荷和卸载模型，使用自愿阻力练习或肢体固定范例，试图确定骨骼肌如何感知负荷和改变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。拟议的研究计划旨在试图了解控制急性和慢性MPS和MPB的复杂分子机制，最终决定骨骼肌蛋白质质量的得失。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，我们将利用最近在质谱学方面的尖端进展、新的同位素示踪剂模型和“基因组”技术来了解对加载和卸载刺激的反应变化。我们的持续研究将鼓励下一代加拿大科学家在公平、多样化和包容性的环境中发展和培训。

Skeletal muscle represents the largest protein reservoir in the human body. Maintenance of skeletal muscle is key for human locomotion and metabolic health. The proteins within skeletal muscle 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 to maintain proteostasis. In adult 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 primary determinant of net muscle protein gain and thus, muscle fibre enlargement (hypertrophy), or net muscle protein loss and a reduction in muscle fibre size (atrophy). The proposed research program is an integrated and systematic study of skeletal muscle in states of increased loading and unloading, to uncover mechanisms regulating muscle mass gain and loss. We make extensive use of stable isotope metabolic tracers to study the regulation of skeletal muscle protein turnover. We combine these complex measures, which only a handful of labs worldwide can make, with measures of signalling protein activation, transcriptomic gene expression, and histochemistry. Thus, we obtain an integrated picture of the factors that contribute to the acute regulation of MPS and MPB. These acute regulatory studies have also given us mechanistic insight into longer-term phenotypic changes in skeletal muscle, which we will also study. We have developed a new method that, combined with dynamic proteomic analysis, yields unparalleled insight into mechanisms regulating muscle protein turnover. We make extensive use of loading and unloading models, using voluntary resistance exercise or limb immobilization paradigms, to try and ascertain how skeletal muscles sense load and alter 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. The proposed program of study is aimed at trying to understand the complex molecular mechanisms that are governing both acute and chronic MPS and MPB, ultimately determining gains or losses in skeletal muscle protein mass. 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 cutting-edge advances in mass spectrometry, new models of isotopic tracers and `omic' technologies to understand response variation to loading an unloading stimuli. Our continuing studies will encourage the development and training of the next generation of Canadian scientists in an equitable, diverse and inclusive environment.