Conversion of kynurenine (KYN) to kynurenic acid (KYNA) is the main pathway for free tryptophan degradation in skeletal muscle and has emerged as an important mechanism of how exercise is linked to promotion of mental health. Metabolism of KYN to KYNA mainly depends on the expression of kynurenine aminotransferases (KATs) that is under control of the mitochondria biogenesis regulator PGC-1α. We therefore hypothesized that expression of KATs would vary between muscle fibers that differ in mitochondrial content, i.e. oxidative type I vs more glycolytic type II muscle fibers. Moreover, we tested the hypothesis that KAT expression differs with age. Single muscle fibers were isolated from biopsies taken from the vastus lateralis muscle in young and old healthy subjects. In young and old subjects the abundance of KAT I, KAT III and KAT IV was greater in Type I than Type II fibers without age-dependent difference in the KAT isoform expressions. The link to mitochondrial content was further seen as the expression of KAT IV correlated to mitochondrial cytochrome c oxidase IV (COX IV) abundance in both fiber types. In conclusion, we describe for the first time the expression pattern of KAT isoforms with respect to specific fiber types and age in human skeletal muscle.

中文翻译：

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Kynurenine氨基转移酶同工型在年轻人和老年人的骨骼肌中显示纤维类型的特异性表达。

犬尿氨酸（KYN）向犬尿酸（KYNA）的转化是骨骼肌中游离色氨酸降解的主要途径，并且已成为锻炼与促进心理健康的重要机制。KYN向KYNA的代谢主要取决于在线粒体生物发生调节剂PGC-1α的控制下的犬尿氨酸转氨酶（KAT）的表达。因此，我们假设线粒体含量不同的肌肉纤维之间，即氧化性I型与糖酵解性II型肌肉纤维之间，KAT的表达会有所不同。此外，我们检验了KAT表达随年龄而异的假设。从年轻和老年健康受试者的股外侧肌活检中分离出单条肌纤维。在年轻人和老年人中，KAT I丰富，I型纤维的KAT III和KAT IV大于II型纤维，而KAT亚型的表达没有年龄依赖性。与线粒体含量的联系还被视为两种纤维类型中与线粒体细胞色素C氧化酶IV（COX IV）丰度相关的KAT IV的表达。总之，我们首次描述了关于人骨骼肌中特定纤维类型和年龄的KAT同工型的表达模式。