Energy sensing in skeletal muscle: focus on mitochondrial metabolic adaptation

背景资料：线粒体通常被称为“细胞的发电站”，长期以来一直被认为是ATP的主要生产者，ATP是细胞代谢的货币。然而，近几十年来，线粒体越来越多地参与许多其他细胞过程，从细胞钙稳态到甚至细胞死亡。在骨骼肌中，当生物体在休息和运动之间转换时，对细胞的能量需求会迅速波动。已知在运动时肌肉中发生的细胞氧化还原状态的一些扰动构成对线粒体功能以及线粒体周转和生物发生的急性改变的刺激。** 目标：这项研究计划的目的是确定与体育锻炼相关的能量需求增加对骨骼肌线粒体功能的影响，重点是氧化还原生物学和线粒体能量学。有人提出，醌还原酶2（QR 2）在由氧化还原敏感性转录因子Nrf 2介导的反馈回路中起作用，以响应身体活动，从而提高骨骼肌中的线粒体含量和活性。该调节回路的净结果是更稳健的线粒体，能够减轻氧化应激和细胞死亡，此外还增加ATP再合成。为了达到目标，该计划将解决以下问题：1）运动训练如何改变骨骼肌中特定底物/化合物的线粒体代谢？2)除了增加ATP的产生外，运动相关的骨骼肌线粒体功能改变对减轻氧化应激和细胞死亡产生影响的机制是什么？**方法学：为了实现研究计划的目标，我们将使用方法学方法的组合，从标准的分子生物学技术，到最先进的功能测量，对大鼠（运动训练与未训练）和小鼠（Nrf 2和QR 2无效转基因模型）的小骨骼肌样本进行测量。在这样做时，Nrf 2和QR 2两者的细胞定位和表达水平将在不同骨骼肌类型（即，氧化与糖酵解）。将确定运动后骨骼肌中Nrf 2和QR 2含量和活性改变的功能后果。** 影响：本研究的预期短期影响包括更好地了解特定监管机构（例如，QR 2）的线粒体氧化还原生物学的过程中，以前被忽视的基本维持细胞能量和氧化还原稳态。从长远来看，该计划将揭示线粒体生物能量学的关键调节因子，这些调节因子在调节细胞功能的基本模型中一直缺失。

Background: Often referred to as the "powerhouses of the cell," mitochondria have long been recognized as key producers of ATP, the cellular metabolic currency. In recent decades, however, mitochondria have increasingly been implicated in many additional cell processes, ranging from cellular calcium homeostasis to even cell death. In skeletal muscle, the energetic demands placed on the cell can fluctuate rapidly as an organism transitions between rest and exercise. Some of the purturbations in cellular redox state that occur in muscle with exercise are known to constitute a stimulus for acute alterations in mitochondrial function, as well as mitochondrial turnover and biogenesis. ******Objectives: The purpose of this research program is to determine the effects of increased energy demand associated with physical exercise on skeletal muscle mitochondrial function, with a focus on redox biology and mitochondrial energetics. It is proposed that the enzyme quinone reductase 2 (QR2) acts in a feedback loop mediated by the redox-sensitive transcription factor Nrf2, in response to physical activity, to boost mitochondrial content and activity in skeletal muscle The net result of this regulatory loop is more robust mitochondria, capable of mitigating oxidative stress and cell death, in addition to increased ATP resynthesis. In order to meet objectives, the program will address the following questions: 1) How does exercise training alter mitochondrial metabolism of specific substrates/compounds in skeletal muscle? 2) What are the mechanisms by which exercise-associated alterations in skeletal muscle mitochondrial function exert their effects on mitigating oxidative stress and cell death, in addition to increased ATP production?******Methodology: To achieve the research program objectives, we will use a combination of methodological approaches, ranging from standard molecular biology techniques, to state-of-the-art functional measurements on small skeletal muscle samples from rats (exercise-trained versus untrained) and mice (Nrf2 and QR2 null transgenic models). In so doing, the cellular localization and expression levels of both Nrf2 and QR2 will be determined in different skeletal muscle types (i.e., oxidative versus glycolytic) following exercise. The functional consequences of altered Nrf2 and QR2 content and activity in skeletal muscle following exercise will be determined. ******Impact: The expected short-term impact of this research include a better understanding of the mechanisms by which specific regulators (e.g., QR2) of mitochondrial redox biology in processes previously ignored as being fundamental to maintaining cellular energy and redox homeostasis. In the long-term, this program will expose critical regulators of mitochondrial bioenergetics which have been missing from fundamental models of regulating cell function.******