School of Anatomy, Physiology and Human Biology, the University of Western Australia, Crawley, Western Australia, Australia.
Am J Physiol Cell Physiol. 2013 Jul 1;305(1):C26-35. doi: 10.1152/ajpcell.00027.2013. Epub 2013 Apr 17.
Circadian rhythms and metabolism are tightly integrated, and rhythmic expression of metabolic factors is common in homeostatic processes. We measured the temporal changes in the expression of myogenic regulatory factors and expression and activity level of molecules involved in protein metabolism in skeletal muscles and livers in mice and examined the impact of fasting. Tissues were collected over 24 h (at zeitgeber times ZT1, ZT5, ZT9, ZT13, ZT17, ZT21, and ZT1 the following day) from adult male C57Bl/6J mice that had been either freely fed or fasted for 24 h. In skeletal muscle, there was a robust rise in the mRNA expression of the myogenic regulatory factors MyoD and myogenin during dark hours which was strongly suppressed by fasting. Circadian pattern was observed for mRNA of MuRF1, Akt1, and ribosomal protein S6 in muscles in fed and fasted mice and for Fbxo32 in fed mice. Activity (phosphorylation) levels of Akt(Ser473) displayed temporal regulation in fasted (but not fed) mice and were high at ZT9. Fasting caused significant reductions in phosphorylation for both Akt and S6 in muscles, indicative of inactivation. Hepatic phosphorylated Akt(Ser473) and S6(Ser235/236) proteins did not exhibit daily rhythms. Fasting significantly reduced hepatic Akt(473) phosphorylation compared with fed levels, although (unlike in muscle) it did not affect S6(Ser235/236) phosphorylation. This in vivo circadian study addresses for the first time the signaling activities of key molecules related to protein turnover and their possible cross-regulation of expression of genes related to protein degradation.
昼夜节律和代谢紧密结合，代谢因子的节律表达在稳态过程中很常见。我们测量了小鼠骨骼肌和肝脏中肌生成调节因子的表达以及参与蛋白质代谢的分子的表达和活性水平随时间的变化，并研究了禁食的影响。组织取自成年雄性 C57Bl/6J 小鼠，这些小鼠要么自由进食，要么禁食 24 小时。在自由进食的小鼠中，肌生成调节因子 MyoD 和 myogenin 的 mRNA 表达在黑暗时间内有明显增加，而禁食则强烈抑制了这种增加。在 fed 和 fasted 小鼠的肌肉中，MuRF1、Akt1 和核糖体蛋白 S6 的 mRNA 观察到昼夜节律模式，而在 fed 小鼠中观察到 Fbxo32 的昼夜节律模式。Akt(Ser473)的活性（磷酸化）水平在禁食（而非 fed）小鼠中显示出时间调节，在 ZT9 时水平较高。禁食导致肌肉中 Akt 和 S6 的磷酸化显著减少，表明失活。肝磷酸化 Akt(Ser473)和 S6(Ser235/236)蛋白没有表现出每日节律。与 fed 水平相比，禁食显著降低了肝 Akt(473)的磷酸化水平，尽管（与肌肉不同）它并不影响 S6(Ser235/236)的磷酸化。这项体内昼夜节律研究首次解决了与蛋白质周转相关的关键分子的信号活性及其对与蛋白质降解相关的基因表达的可能交叉调节问题。
