Stockebrand Malte, Nejad Ali Sasani, Neu Axel, Kharbanda Kusum K, Sauter Kathrin, Schillemeit Stefan, Isbrandt Dirk, Choe Chi-Un
Institute for Molecular and Behavioral Neuroscience, University of Cologne, Cologne, Germany.
German Center for Neurodegenerative Diseases (DZNE), Bonn, Germany.
Amino Acids. 2016 Aug;48(8):2025-39. doi: 10.1007/s00726-016-2202-7. Epub 2016 Mar 3.
Skeletal muscles require energy either at constant low (e.g., standing and posture) or immediate high rates (e.g., exercise). To fulfill these requirements, myocytes utilize the phosphocreatine (PCr)/creatine (Cr) system as a fast energy buffer and shuttle. We have generated mice lacking L-arginine:glycine amidino transferase (AGAT), the first enzyme of creatine biosynthesis. These AGAT(-/-) (d/d) mice are devoid of the PCr/Cr system and reveal severely altered oxidative phosphorylation. In addition, they exhibit complete resistance to diet-induced obesity, which is associated with a chronic activation of AMP-activated protein kinase in muscle and white adipose tissue. The underlying metabolic rearrangements have not yet been further analyzed. Here, we performed gene expression analysis in skeletal muscle and a serum amino acid profile of d/d mice revealing transcriptomic and metabolic alterations in pyruvate and glucose pathways. Differential pyruvate tolerance tests demonstrated preferential conversion of pyruvate to alanine, which was supported by increased protein levels of enzymes involved in pyruvate and alanine metabolism. Pyruvate tolerance tests suggested severely impaired hepatic gluconeogenesis despite increased availability of pyruvate and alanine. Furthermore, enzymes of serine production and one-carbon metabolism were significantly up-regulated in d/d mice, indicating increased de novo formation of one-carbon units from carbohydrate metabolism linked to NAD(P)H production. Besides the well-established function of the PCr/Cr system in energy metabolism, our transcriptomic and metabolic analyses suggest that it plays a pivotal role in systemic one-carbon metabolism, oxidation/reduction, and biosynthetic processes. Therefore, the PCr/Cr system is not only an energy buffer and shuttle, but also a crucial component involved in numerous systemic metabolic processes.
骨骼肌在持续低能量需求（如站立和维持姿势）或即时高能量需求（如运动）时都需要能量。为满足这些需求，肌细胞利用磷酸肌酸（PCr）/肌酸（Cr）系统作为快速能量缓冲器和穿梭体。我们培育出了缺乏L-精氨酸：甘氨酸脒基转移酶（AGAT）的小鼠，AGAT是肌酸生物合成的首个酶。这些AGAT(-/-)（d/d）小鼠缺乏PCr/Cr系统，并显示出氧化磷酸化严重改变。此外，它们对饮食诱导的肥胖具有完全抗性，这与肌肉和白色脂肪组织中AMP激活的蛋白激酶的慢性激活有关。潜在的代谢重排尚未进一步分析。在此，我们对d/d小鼠的骨骼肌进行了基因表达分析，并检测了血清氨基酸谱，揭示了丙酮酸和葡萄糖途径中的转录组和代谢改变。差异丙酮酸耐量试验表明丙酮酸优先转化为丙氨酸，这得到了参与丙酮酸和丙氨酸代谢的酶蛋白水平升高的支持。丙酮酸耐量试验表明，尽管丙酮酸和丙氨酸的可用性增加，但肝糖异生严重受损。此外，d/d小鼠中丝氨酸生成和一碳代谢的酶显著上调，表明与NAD(P)H生成相关的碳水化合物代谢中一碳单位的从头合成增加。除了PCr/Cr系统在能量代谢中已确立的功能外，我们的转录组和代谢分析表明，它在全身一碳代谢、氧化/还原和生物合成过程中起关键作用。因此，PCr/Cr系统不仅是一种能量缓冲器和穿梭体，也是参与众多全身代谢过程的关键组成部分。
