Scott Graham R, Guo Kevin H, Dawson Neal J
Department of Biology, McMaster University, 1280 Main Street West, Hamilton, Ontario, Canada L8S 4K1.
Integr Comp Biol. 2018 Sep 1;58(3):506-518. doi: 10.1093/icb/icy056.
Mitochondria play a central role in aerobic performance. Studies aimed at elucidating how evolved variation in mitochondrial physiology contributes to adaptive variation in aerobic performance can therefore provide a unique and powerful lens to understanding the evolution of complex physiological traits. Here, we review our ongoing work on the importance of changes in mitochondrial quantity and quality to adaptive variation in aerobic performance in high-altitude deer mice. Whole-organism aerobic capacity in hypoxia (VO2max) increases in response to hypoxia acclimation in this species, but high-altitude populations have evolved consistently greater VO2max than populations from low altitude. The evolved increase in VO2max in highlanders is associated with an evolved increase in the respiratory capacity of the gastrocnemius muscle. This appears to result from highlanders having more mitochondria in this tissue, attributed to a higher proportional abundance of oxidative fiber-types and a greater mitochondrial volume density within oxidative fibers. The latter is primarily caused by an over-abundance of subsarcolemmal mitochondria in high-altitude mice, which is likely advantageous for mitochondrial O2 supply because more mitochondria are situated adjacent to the cell membrane and close to capillaries. Evolved changes in gastrocnemius phenotype appear to be underpinned by population differences in the expression of genes involved in energy metabolism, muscle development, and vascular development. Hypoxia acclimation has relatively little effect on respiratory capacity of the gastrocnemius, but it increases respiratory capacity of the diaphragm. However, the mechanisms responsible for this increase differ between populations: lowlanders appear to adjust mitochondrial quantity and quality (i.e., increases in citrate synthase [CS] activity, and mitochondrial respiration relative to CS activity) and they exhibit higher rates of mitochondrial release of reactive oxygen species, whereas highlanders only increase mitochondrial quantity in response to hypoxia acclimation. In contrast to the variation in skeletal muscles, the respiratory capacity of cardiac muscle does not appear to be affected by hypoxia acclimation and varies little between populations. Therefore, evolved changes in mitochondrial quantity and quality make important tissue-specific contributions to adaptive variation in aerobic performance in high-altitude deer mice.
线粒体在有氧代谢能力中起着核心作用。因此，旨在阐明线粒体生理学的进化变异如何导致有氧代谢能力适应性变异的研究，能够为理解复杂生理特征的进化提供一个独特而有力的视角。在此，我们回顾了我们正在进行的关于线粒体数量和质量变化对高海拔鹿鼠有氧代谢能力适应性变异重要性的研究工作。在该物种中，低氧环境下的全身体有氧能力（最大摄氧量）会随着低氧适应而增加，但高海拔种群进化出的最大摄氧量始终高于低海拔种群。高海拔地区居民最大摄氧量的进化增加与腓肠肌呼吸能力的进化增加有关。这似乎是由于高海拔地区居民该组织中的线粒体更多，这归因于氧化纤维类型的比例更高以及氧化纤维内的线粒体体积密度更大。后者主要是由高海拔小鼠肌膜下线粒体过多导致的，这可能有利于线粒体的氧气供应，因为更多的线粒体位于细胞膜附近且靠近毛细血管。腓肠肌表型的进化变化似乎是由参与能量代谢、肌肉发育和血管发育的基因表达的种群差异所支撑的。低氧适应对腓肠肌的呼吸能力影响相对较小，但会增加膈肌的呼吸能力。然而，导致这种增加的机制在不同种群之间有所不同：低海拔地区居民似乎会调整线粒体的数量和质量（即柠檬酸合酶[CS]活性增加以及相对于CS活性的线粒体呼吸增加），并且它们表现出更高的线粒体活性氧释放速率；而高海拔地区居民仅在低氧适应时增加线粒体数量。与骨骼肌的变异不同，心肌的呼吸能力似乎不受低氧适应的影响，且种群之间变化不大。因此，线粒体数量和质量的进化变化对高海拔鹿鼠有氧代谢能力的适应性变异做出了重要的组织特异性贡献。
