Potential molecular mechanisms underlying muscle fatigue mediated by reactive oxygen and nitrogen species

Abstract

Intense contractile activity causes a dramatic decline in the force and velocity generating capacity of skeletal muscle within a few minutes, a phenomenon that characterizes fatigue. Much of the research effort has focused on how elevated levels of the metabolites of ATP hydrolysis might inhibit the function of the contractile proteins. However, there is now growing evidence that elevated levels of reactive oxygen and nitrogen species (ROS/RNS), which also accumulate in the myoplasm during fatigue, also play a causative role in this type of fatigue. The most compelling evidence comes from observations demonstrating that pre-treatment of intact muscle with a ROS scavenger can significantly attenuate the development of fatigue. A clear advantage of this line of inquiry is that the molecular targets and protein modifications of some of the ROS scavengers are well-characterized enabling researchers to begin to identify potential regions and even specific amino acid residues modified during fatigue. Combining this knowledge with assessments of contractile properties from the whole muscle level down to the dynamic motions within specific contractile proteins enable the linking of the structural modifications to the functional impacts, using advanced chemical and biophysical techniques. Based on this approach at least two areas are beginning emerge as potentially important sites, the regulatory protein troponin and the actin binding region of myosin. This review highlights some of these recent efforts which have the potential to offer uniquely precise information on the underlying molecular basis of fatigue. This work may also have implications beyond muscle fatigue as ROS/RNS mediated protein modifications are also thought to play a role in the loss of muscle function with aging and in some acute pathologies like cardiac arrest and ischemia.

Keywords: fatigue; muscle; myosin; reactive oxygen species; tropomyosin; troponin.

Figure 1

Effect of reactive oxygen species scavengers on fatigue. (A) Effect of pretreatment with ROS scavenger, N-acetylcysteine (circles) vs. control (squares) on the fatigue profile of the tibialis anterior muscle in humans stimulated at 10 Hz with a surface electrode. The drop in force was significant under both conditions but the force was greater with N-acetylcysteine treatment. Reprinted from Reid et al. (1994) with rights and permission from American Society for Clinical Investigation. (B) Effect of the N-acetylcysteine on the development of diaphragm fatigue in an anesthetized intact rabbit preparation. Reprinted from Shindoh et al. (1990) with permission. (C) Effect of N-acetylcysteine on the development of fatigue in isolated mouse extensor digitorum longus muscle. Reprinted from Katz et al. (2014) with permission. ^*, ^** and ^*** indicate significantly different from corresponding control value (open circles) at p < 0.05, p < 0.01, and p < 0.001 respectively.

Figure 2

ROS mediated fatigue and Ca⁺⁺-sensitivity. Force-calcium relation plotted during fatigue of intact mouse flexor brevis muscle fibers stimulated at 100 Hz, at 37°C. Force expressed relative to rested value under control conditions. Fatigue under control conditions produced a strong rightward shift in the relation and depressed maximal force. Maximal force but not Ca⁺⁺-sensitivity was restored with caffeine. Treatment with dithiothreitol (DTT) restored Ca⁺⁺-sensitivity. Reprinted from Moopanar and Allen (2006) with permission from John Wiley and Sons publishing company.