O'Reilly Colleen L, Davidyan Arik, Cizio Katarzyna, Doidge Stephen M, Bubak Matthew P, Borowik Agnieszka K, Lewis Tommy L, Miller Benjamin F
Aging and Metabolism Research Program, Oklahoma Medical Research Foundation, Oklahoma City, OK.
Med Sci Sports Exerc. 2025 May 1. doi: 10.1249/MSS.0000000000003748.
Mitochondrial dynamics involve two distinct and opposing processes, fusion and fission. Traditionally we assess fusion and fission by snapshots of protein markers at distinct time points or in vitro models to infer outcomes in vivo. Recent technological advancements enable visualization of mitochondrial dynamics in vivo using fluorescent microscopy.
Our study modified this technique to evaluate mitochondrial dynamics in skeletal muscle, comparing young (6mo) and old (24mo) mice in vivo and contrasting this to ex vivo and in vitro models. We hypothesized that in vitro and ex vivo models would have higher rates of dynamics than in vivo models and that young animals would have higher rates than old animals. We electroporated mitochondrial matrix-targeted photo-activatable GFP into the tibialis anterior (TA) of young and old C57Bl6 mice and imaged using multiphoton microscopy. We also measured rates of mitochondrial dynamics using single fibers isolated from the TA of the electroporated mice, as well as C2C12 myotubes transfected with the same plasmids.
We found that the rates of dynamic events in vivo are slower than previously indicated, with the C2C12 myoblasts having the fastest rates of dynamic events across all models. We also observed that dynamic rates are slower in old animals compared to young animals. Finally, we found that rates of dynamic events were higher in old animals after an acute bout of exercise.
Our data demonstrate it is possible to directly measure rates of mitochondrial dynamics in vivo. This technique provides a powerful tool to answer experimental questions about mitochondrial dynamics of skeletal muscle.
线粒体动力学涉及两个截然不同且相互对立的过程，即融合与裂变。传统上，我们通过在不同时间点的蛋白质标记物快照或体外模型来评估融合和裂变，以推断体内的结果。最近的技术进步使得使用荧光显微镜在体内可视化线粒体动力学成为可能。
我们的研究改进了这项技术，以评估骨骼肌中的线粒体动力学，比较了年轻（6个月）和年老（24个月）小鼠在体内的情况，并将其与离体和体外模型进行对比。我们假设体外和离体模型的动力学速率将高于体内模型，并且年轻动物的速率将高于年老动物。我们将线粒体基质靶向的光激活绿色荧光蛋白电穿孔到年轻和年老的C57Bl6小鼠的胫前肌（TA）中，并使用多光子显微镜进行成像。我们还使用从电穿孔小鼠的TA中分离出的单根纤维以及转染了相同质粒的C2C12肌管来测量线粒体动力学速率。
我们发现体内动态事件的速率比先前指出的要慢，在所有模型中C2C12成肌细胞的动态事件速率最快。我们还观察到，与年轻动物相比，年老动物的动态速率较慢。最后，我们发现急性运动后年老动物的动态事件速率更高。
我们的数据表明，有可能直接测量体内线粒体动力学的速率。这项技术为回答有关骨骼肌线粒体动力学的实验问题提供了一个强大的工具。
