Department of Physiology and Pharmacology, Molecular Muscle Physiology and Pathophysiology, Karolinska Institutet, Stockholm, Sweden.
Department of Physiology and Pharmacology, Molecular and Cellular Exercise Physiology, Karolinska Institutet, Stockholm, Sweden.
FASEB J. 2021 Dec;35(12):e22010. doi: 10.1096/fj.202100066R.
The hypoxia-inducible nuclear-encoded mitochondrial protein NADH dehydrogenase (ubiquinone) 1 alpha subcomplex, 4-like 2 (NDUFA4L2) has been demonstrated to decrease oxidative phosphorylation and production of reactive oxygen species in neonatal cardiomyocytes, brain tissue and hypoxic domains of cancer cells. Prolonged local hypoxia can negatively affect skeletal muscle size and tissue oxidative capacity. Although skeletal muscle is a mitochondrial rich, oxygen sensitive tissue, the role of NDUFA4L2 in skeletal muscle has not previously been investigated. Here we ectopically expressed NDUFA4L2 in mouse skeletal muscles using adenovirus-mediated expression and in vivo electroporation. Moreover, femoral artery ligation (FAL) was used as a model of peripheral vascular disease to induce hind limb ischemia and muscle damage. Ectopic NDUFA4L2 expression resulted in reduced mitochondrial respiration and reactive oxygen species followed by lowered AMP, ADP, ATP, and NAD levels without affecting the overall protein content of the mitochondrial electron transport chain. Furthermore, ectopically expressed NDUFA4L2 caused a ~20% reduction in muscle mass that resulted in weaker muscles. The loss of muscle mass was associated with increased gene expression of atrogenes MurF1 and Mul1, and apoptotic genes caspase 3 and Bax. Finally, we showed that NDUFA4L2 was induced by FAL and that the Ndufa4l2 mRNA expression correlated with the reduced capacity of the muscle to generate force after the ischemic insult. These results show, for the first time, that mitochondrial NDUFA4L2 is a novel regulator of skeletal muscle mass and force. Specifically, induced NDUFA4L2 reduces mitochondrial activity leading to lower levels of important intramuscular metabolites, including adenine nucleotides and NAD , which are hallmarks of mitochondrial dysfunction and hence shows that dysfunctional mitochondrial activity may drive muscle wasting.
缺氧诱导核编码的线粒体蛋白 NADH 脱氢酶（泛醌）1 亚基，α 亚单位辅因子 4 样 2（NDUFA4L2）已被证明可降低新生心肌细胞、脑组织和癌细胞缺氧区域的氧化磷酸化和活性氧的产生。长时间的局部缺氧会对骨骼肌的大小和组织的氧化能力产生负面影响。虽然骨骼肌是富含线粒体、对氧气敏感的组织，但 NDUFA4L2 在骨骼肌中的作用尚未被研究过。在这里，我们使用腺病毒介导的表达和体内电穿孔在小鼠骨骼肌中异位表达 NDUFA4L2。此外，股动脉结扎（FAL）被用作外周血管疾病模型，以诱导后肢缺血和肌肉损伤。异位 NDUFA4L2 的表达导致线粒体呼吸和活性氧减少，随后 AMP、ADP、ATP 和 NAD 水平降低，而不影响线粒体电子传递链的整体蛋白含量。此外，异位表达的 NDUFA4L2 导致肌肉质量减少约 20%，导致肌肉力量减弱。肌肉质量的减少与肌肉萎缩基因 MurF1 和 Mul1 以及凋亡基因 caspase 3 和 Bax 的表达增加有关。最后，我们表明 FAL 诱导了 NDUFA4L2 的表达，并且 Ndufa4l2 mRNA 的表达与缺血损伤后肌肉产生力量的能力降低相关。这些结果首次表明，线粒体 NDUFA4L2 是调节骨骼肌质量和力量的新调节因子。具体来说，诱导的 NDUFA4L2 降低了线粒体的活性，导致包括腺嘌呤核苷酸和 NAD 在内的重要肌内代谢物水平降低，这些都是线粒体功能障碍的标志，这表明功能失调的线粒体活性可能导致肌肉减少。
